
==== Front
Acta Pharm Sin B
Acta Pharm Sin B
Acta Pharmaceutica Sinica. B
2211-3835
2211-3843
Elsevier

S2211-3835(24)00246-6
10.1016/j.apsb.2024.06.015
Review
Transepithelial transport of nanoparticles in oral drug delivery: From the perspective of surface and holistic property modulation
Zheng Yaxian a†
Luo Shiqin a†
Xu Min a
He Qin a
Xie Jiang a
Wu Jiawei wujw1993@163.com
b⁎
Huang Yuan huangyuan0@163.com
c⁎
a Department of Pharmacy, the Third People's Hospital of Chengdu, the Affiliated Hospital of Southwest Jiaotong University, College of Medicine, Southwest Jiaotong University, Chengdu 610031, China
b Department of Pharmacy, Personalized Drug Therapy Key Laboratory of Sichuan Province, Sichuan Academy of Medical Sciences & Sichuan Provincial People's Hospital, School of Medicine, University of Electronic Science and Technology of China, Chengdu 610072, China
c Key Laboratory of Drug-Targeting and Drug Delivery System of the Education Ministry and Sichuan Province, Sichuan Engineering Laboratory for Plant-Sourced Drug and Sichuan Research Center for Drug Precision Industrial Technology, West China School of Pharmacy, Sichuan University, Chengdu 610041, China
⁎ Corresponding authors. wujw1993@163.comhuangyuan0@163.com
† These authors made equal contributions to this work.

22 6 2024
9 2024
22 6 2024
14 9 38763900
18 2 2024
23 4 2024
25 5 2024
© 2024 The Authors
2024
https://creativecommons.org/licenses/by-nc-nd/4.0/ This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Despite the promising prospects of nanoparticles in oral drug delivery, the process of oral administration involves a complex transportation pathway that includes cellular uptake, intracellular trafficking, and exocytosis by intestinal epithelial cells, which are necessary steps for nanoparticles to enter the bloodstream and exert therapeutic effects. Current researchers have identified several crucial factors that regulate the interaction between nanoparticles and intestinal epithelial cells, including surface properties such as ligand modification, surface charge, hydrophilicity/hydrophobicity, intestinal protein corona formation, as well as holistic properties like particle size, shape, and rigidity. Understanding these properties is essential for enhancing transepithelial transport efficiency and designing effective oral drug delivery systems. Therefore, this review provides a comprehensive overview of the surface and holistic properties that influence the transepithelial transport of nanoparticles, elucidating the underlying principles governing their impact on transepithelial transport. The review also outlines the chosen of parameters to be considered for the subsequent design of oral drug delivery systems.

Graphical abstract

This review summarizes the crucial factors that influence the transepithelial transport of nanoparticles from the perspective of surface and holistic property modulation.Image 1

Key words

Oral delivery
Nanoparticles
Intestinal epithelial cells
Surface property
Holistic property
Transepithelial transport
==== Body
pmc1 Introduction

With the rapid advancement of nanotechnology, nanoparticles have been extensively utilized as carriers for oral drug delivery in the treatment of various diseases1, 2, 3, 4. These nano-delivery systems can mitigate drug degradation in the gastric acid and enzymatic environment while enhancing their stability within the gastrointestinal tract5,6. However, augmenting the oral bioavailability of drugs remains challenging due to limitations imposed by both the intestinal mucous barrier and epithelial cell barrier7,8. The mucus is a hydrophilic gel layer secreted by intestinal goblet cells, which intercepts foreign substances through electrostatic and hydrophobic interactions, as well as its dense mesh-like structure9. Orally administered nanoparticles are easily entrapped within the mucus, preventing them from effectively reaching the intestinal epithelial cells10, 11, 12. The intestinal epithelial cell layer mainly consists of epithelial cells, goblet cells, and M cells, providing a pathway for water, nutrients, and other exogenous substances to enter the systemic circulation or lymphatic circulation from the intestinal lumen13,14. Meanwhile, the intestinal epithelial cells form a barrier that maintains segregation between luminal microbial communities and the mucosal immune system15,16. Orally administered nanoparticles are insufficient to traverse the intestinal epithelial cell layer via simple diffusion, necessitating a transepithelial transport process encompassing cellular uptake, intracellular trafficking, and basolateral exocytosis in order to access the bloodstream and elicit their pharmacological effects17, 18, 19 (Fig. 1). Therefore, the promotion and enhancement of transepithelial transport of nanoparticles represent pivotal and formidable challenges in the realm of oral drug delivery.Figure 1 Schematic diagram of the physiological barriers in the gastrointestinal tract of nanoparticles for oral administration. Made using BioRender.

Figure 1

The surface properties of nanoparticles, including their hydrophilicity/hydrophobicity, charge, and surface ligands, play a crucial role in determining their interactions with tissues, cells, and organelles. These factors ultimately dictate the fate of the payloads20, 21, 22. For instance, appropriate modification of surface ligands can enhance the affinity of nanoparticles and intestinal epithelial cells, improve cellular uptake efficiency, modulate intracellular trafficking pathways, and ultimately impact the stability and transepithelial transport efficiency of nanoparticles23, 24, 25. In addition to surface properties, the holistic properties of nanoparticles, such as particle size, shape, and elasticity, are also closely related to their transepithelial transport26, 27, 28, 29. Therefore, this article provides a comprehensive review of the research progress on the impact of surface and holistic properties of nanoparticles on transepithelial transport and summarizes the strategies and future exploitation for the design of oral drug delivery systems.

2 The transepithelial transport of nanoparticles

2.1 Paracellular transport

Paracellular transport refers to the translocation of drugs into the bloodstream through the space between intestinal epithelial cells, instead of directly transport across the epithelial monolayers30. The tight junctions between intestinal epithelial cells serve as a barrier against the invasion of exogenous substances and pathogens31,32, but also present a challenge for paracellular drug delivery to cargos with a radius greater than 6 nm33. However, absorption enhancers such as chitosan can effectively increase the paracellular permeability of drugs by reversibly opening the tight junctions34. It is worth noting that even when the tight junctions are fully opened, the intercellular gaps measure only approximately 20 nm, posing a significant challenge for most nanoparticles to traverse35. When the intestinal mucosa is intact, the translocation of nanoparticles through this pathway is generally limited to less than 10%, depending on factors such as particle size and the integrity of epithelial junction14,36. Consequently, achieving effective paracellular transport remains an ongoing hurdle for nano-drug delivery systems.

2.2 M cell-associated pathway

M cells are primarily located in Peyer's patches and are a type of specialized type of cell with invaginations in their cell membranes or basement membranes37,38. The unique structure of M cells facilitates the selective entry of specific substances into the lymphatic tissue beneath the intestinal mucosa through active–transport pathways, offering a potential strategy to enhance drug bioavailability by bypassing first-pass metabolism and reducing toxicity39,40. Despite constituting less than 1% of the absorptive intestinal epithelium's total surface area, the absorption capabilities of M cells primarily rely on the specific types of nanoparticles involved. M cells have a preference for internalizing particles with diameters below 10 μm41. Nanoparticles ranging from 550 to 1100 nm demonstrate improved retention within Peyer's patches compared to nanoparticles measuring at 280 nm. Particles smaller than 1 μm can be taken up by M cells before being transported into lymphatic vessels and entering systemic circulation42, 43, 44. However, comparing findings across various studies proves challenging due to differences in animal models used as well as variations in materials employed and measurement techniques45. It is estimated that this pathway accounts for approximately 0.2%–70% of nanoparticle delivery efficiency range-wise depending on the factors such as particle size and surface modifications. For example, polystyrene particle (PS, 2 μm) exhibited 0.2% of uptake through the M cell-associated pathway, while PS (60 nm) exhibited 60% uptake in the M cell-associated pathway46,47. The improvement of nanoparticle targeting to M cells can also be enhanced by identifying appropriate strategies. He et al.48 designed aptamer-modified liposomes (Apt-Lip) targeted to M-cells for the oral delivery of exenatide. The Apt-Lip was found to increase the transport efficiency of exenatide by 2-fold in M cells and showed better absorption in Peyer's patches. The Ulex europaeus agglutinin 1 (UEA-1, a representative lectin) was modified as ligands targeted to the fucose residues on the apical surface of M cells. The UEA-1 modified nanoparticles enhanced insulin uptake by 4.1-fold in the Peyer's patches and 2.6-fold in intestinal epithelium49. Oral delivery of ovalbumin could also be improved using the nanocapsules with higher binding ability and transport efficiency to M cells50. However, the limited receptor expression poses a formidable challenge for the internalization of most nanoparticles by M cells44,45,51. Furthermore, nanoparticles within the M cell-associated pathway have the potential to be delivered and intercepted by immune cells such as dendritic cells and macrophages, thereby impeding their eventual absorption into the systemic circulation1. Therefore, the M cell-mediated transport is well-suited for oral vaccine delivery as this route promotes mucosal immunity activation52. Although some nanoparticles in this pathway may ultimately undergo phagocytosis by immune cells, leading to restricted systemic absorption45,53.

2.3 Transcytosis pathway

Transcytosis serves as the principal pathway for nanoparticles to access the systemic circulation14. Most nanoparticles undergo a series of processes, including apical endocytosis, intracellular trafficking, and basolateral exocytosis, within the transcytosis pathway to traverse the intestinal epithelial cell layer54. Initially, nanoparticles can enter epithelial cells through macropinocytosis, caveolae-mediated endocytosis, or clathrin-mediated endocytosis from the apical surface of these cells55, 56, 57. Subsequently, they undergo intricate intracellular trafficking within transport vesicles or endosomes7,58,59. The intracellular trafficking of nanoparticles typically involves the degradation pathway, secretion pathway, and recycling pathway60,61. The degradation pathway refers to the transportation of nanoparticles through the endosome–lysosome route after endocytosis. Nanoparticles enter lysosomes via clathrin-mediated endocytosis through the endosome–lysosome pathway58,62. The acidic environment (pH 4.5–5.5) and enzymes in lysosomes can degrade lipid and protein components of nanoparticles as well as encapsulated drugs, significantly reducing transcytosis efficiency63. In contrast, transport through the secretion and recycling pathways can bypass lysosomal degradation, thereby maintaining structural integrity and facilitating nanoparticle transcytosis64,65. Functionalized nanoparticles are transported through early endosomes to the endoplasmic reticulum or Golgi apparatus, and subsequently delivered to the extracellular space via secretory pathways such as the endoplasmic reticulum-Golgi pathway and Golgi-to-cell membrane pathway66. Moreover, recycling pathways like caveolae and recycling endosomes enable the direct transportation of nanoparticles to the cell membrane for release into the extracellular space64. It is important to note that intestinal epithelial cells exhibit polarity, with differential expression of receptors/transporters on their apical and basolateral membranes38,67. The nanoparticles are internalized into cells and subsequently excreted from the apical membrane into the intestinal lumen, resulting in a reduction in oral absorption64,68,69. While some nanoparticles could be transported from the basolateral membrane to enter into blood circulation to exert therapeutic effects62,70,71. Therefore, developing suitable strategies to bypass lysosomes, and achieve unidirectional transport from the apical to the basolateral side is a prospective strategy for effective transcytosis (Fig. 2). The absorption efficiency of diverse nanoparticles exhibits significant variations when undergoing transcytosis to traverse the intestinal epithelial cell layer. Hodges et al.47 found that 73.7% of PS (2 um) particles were transported through the transcytosis pathway. However, The transcytosis pathway exhibited a limited transport efficiency of 5%–10% for PLGA nanoparticles64,72. It was estimated that approximately 5%–70% of nanoparticles were transported across the intestinal epithelium in the transcytosis pathway.Figure 2 Schematic diagram of the potential endocytic pathway for nanoparticle transportation across intestinal epithelial cells. Made using BioRender.

Figure 2

2.4 The pathway to reach the systemic circulation

After transport across the intestinal mucosa, nanoparticles may take different routes until they reach the systemic circulation. For transepithelial transport and paracellular pathway, most nanoparticles are usually absorbed into blood capillaries. Subsequently, they are transported to the liver via hepatic portal veins where they undergo hepatic first-pass metabolism1. The metabolic enzymes in the liver can lead to drug wastage and reduce the amount of intact drugs entering the systemic circulation for therapeutic effect.

Alternatively, some nanoparticles can be absorbed into lacteals after crossing epithelial monolayers16,73. Nanoparticles in the M cell-associated pathway were generally transported into the lymphatic tissue beneath the intestinal mucosa. In addition to reaching lymphatic vessels through the M cell-related pathway, nanoparticles can also be absorbed by lymphocytes through transcytosis across epithelial cells. These nanoparticles then travel with lymph fluids to lymphatic capillaries that converge into collecting vessels before finally entering systemic circulation at thoracic ducts via mesenteric lymph nodes1,74. A representative pathway of intestinal lymphatic transport is the uptake and transport using chylomicrons. The efficiency of nanoparticle routes, however, depends on various factors16. One crucial factor influencing the transport of nanoparticles is the lipid type employed, including its chain length and degree of saturation. The lipophilicity of fatty acids (FAs) correlates with their chain length, which also determines their binding capacity to nanoparticles75,76. Supporting this observation is the discovery that a self-nano emulsifying drug delivery system composed of long chain FAs exhibited higher recovery in the lymph compared to those containing medium-chain FAs77. Moreover, the internalization of nanoparticles via specific transporter-mediated pathways and chylomicron transport pathways can facilitate their transportation into the lymphatic vessel. Bae's group78 found that approximately 47% of bile acid-conjugated particles are transported to the systemic circulation through the gut lymphatic system. Intestinal lymphatic transport may be an obvious route to overcome the first-pass metabolism. The lymphatic capillaries serve as an optimal conduit for the targeted delivery of nanoparticles to the lymph node, while concurrently mitigating the potential diminishment in pharmaceutical bioavailability resulting from first-pass metabolism following nanoparticle absorption within the body.

3 Impact of surface properties on oral drug delivery systems

The surface properties of oral delivery nanoparticles play a pivotal role in governing the interactions of nanoparticles within the intricate physiological environment of the gastrointestinal tract79. These surface properties primarily encompass ligand modification, hydrophilicity/hydrophobicity, and charge, etc., all of which significantly determine the in vivo fate of nanoparticles. Furthermore, it is essential to consider the impact of protein corona formation on nanoparticle surfaces80. This section provides an overview of the surface properties that influence the transepithelial transport of nanoparticles while elucidating the key parameters to be considered for oral drug delivery systems.

3.1 Ligand modification

Receptors located on the membrane surface of intestinal epithelial cells could interact with signaling molecules and nutrients, facilitating signal transmission and substance transport81. Previous studies have demonstrated that ligand modification can activate the specific transport pathways via facilitating the specific interaction between nanoparticles and cell surface receptors, thereby mediating the endocytosis and transepithelial transport of nanoparticles across intestinal epithelial cells70,82,83. The type of ligands and density of ligand modification are both the key factors influencing the transepithelial transport84,85. Therefore, rational ligand modification is essential for achieving the high-efficient transepithelial transport and intestinal absorption of nanoparticles. The orally administered nanoparticles modified by different types of ligands were summarized in Table 118,61,64,72,78,86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99.Table 1 Intracellular transport pathways and advantages of nanoparticles targeting different targets.

Table 1Target	Ligand	Intracellular transport pathway	Advantage	Ref.	
Goblet cell	CSK peptide	The cellular transport of CSK-NPs occurred through clathrin and caveolae dependent endocytosis	Increased the relative bioavailability of insulin to 7.05%	86	
Transferrin receptors	Transferrin	Transferrin NPs were transported in endoplasmic reticulum, Golgi apparatus and lysosome during their intracellular transport	Increased insulin bioavailability by 6.14 times compared to BSA-coated NPs	61,87	
N-Acetyl-d-glucosamine and sialic acid	Wheat germ agglutinin (WGA)	WGA-NPs were absorbed via clathrin and caveolae dependent endocytosis pathways, and Golgi apparatus and lysosome were involved in intracellular transport	Improved the oral bioavailability of drugs by 17.5-fold	88,89	
Neonatal Fc receptor (FcRn)	Fc fragment of IgG	FcRn can then guide bound NP-Fc through a transcytosis pathway, avoiding lysosomal degradation	Enhanced the transport efficiency of NPs through intestinal epithelium	18,90	
Albumin	Increased the amount of insulin penetrating the epithelium by about 5-fold compared to free insulin	91	
Heparan sulfate proteoglycans (HSPGs)	EGP peptide	EGP NPs were transported via caveolae-mediated mechanisms, enabling evasion of lysosomal entrapment, and facilitating direct apical-to-basolateral transcytosis	Increased the cellular uptake by 4.5-fold and transcytosis by 4.2-fold	64	
Monocarboxylate transporter-1 (MCT-1)	Butyric acid (Bu)	Bu-NPs were absorbed via clathrin, caveolae-dependent endocytosis and macropinocytosis. endoplasmic reticulum, Golgi apparatus, microtubule and lysosome were involved in intracellular transport	Increased the oral bioavailability of insulin-loaded Bu-PEG NPs by 2.87-fold compared to bare PEG NPs	92	
Transporters NPC1L1 and ABCA1	2,5-Hydroxycholesterol (25HC)	The 25HC NPs achieved unidirectional transport across the intestinal epithelium with NPC1L1-mediated uptake on the apical side and ABCA1-mediated basolateral exocytosis	Long-term administration of oral liraglutide loaded 25HC NPs could elevate glucose metabolism and relieve the diabetic symptom of db/db mice, with a similar degree achieved by s.c. free liraglutide	93	
Glucose transporter type 2	Fructose (Fru)	Fru-PEG NPs underwent internalization and basolateral exocytosis via GLUT2-dependent process, an important fructose assimilation pathway	Increased epithelial transport efficiency by 8.8-fold and bioavailability by 3.2-fold compared with PEG NPs	72	
Folic acid receptor	Folic acid	/	Increased the bioavailability of DTX by approximately 6.8-fold	94	
VB12 receptor	VB12	/	Enhanced oral relative bioavailability of curcumin	95	
Sodium-dependent bile acid transporter	Bile acids and their derivatives	The NPs entered cells via the ASBT pathway and were transported within the endoplasmic reticulum-Golgi apparatus network	Enhanced the transport efficiency of NPs through intestinal epithelium by ASBT-mediated cell uptake and chylomicron transport pathways	78,93,96, 97, 98, 99	

3.1.1 Peptide and protein ligands

The incorporation of ligands on the drug delivery platforms enables targeted drug delivery to specific cells and tissues, thereby reducing the required dosage and minimizing potential side effects. Some peptides and proteins can specifically bind to receptor proteins highly expressed on the surface of intestinal epithelial cells, thereby serving as ligands for nanoparticles to achieve targeted effects.

3.1.1.1 Goblet cells-targeting

The peptide CSKSSDYQC (CSK) was previously identified from a random phage-peptide library using an in vivo phage display technique. It was found to exhibit affinity for goblet cells while evading mucus blockage. The specific targeting ability of CSK towards goblet cells facilitated the transport of M13 bacteriophage across the intestinal epithelium, suggesting that the CSK holds potential as a ligand for targeted delivery of nanocarriers via oral administration100. Jin et al.86 found that nanoparticles functionalized with a CSKSSDYQC (CSK) targeting peptide exhibited a specific affinity towards goblet cells and facilitated insulin uptake in the villi. The results of the uptake inhibition assay demonstrated that the internalization of CSK-NPs was facilitated by clathrin-dependent and caveolin-dependent endocytosis pathways. Despite potential mucus interference with ligand-receptor recognition, CSK-modified nanoparticles further increase the cellular internalization and cross-cell penetration, and finally exhibit a higher relative oral bioavailability of drugs compared to unmodified one10,86,101.

3.1.1.2 Transferrin receptor-targeting

Transferrin, a protein molecule exhibiting high specificity and affinity, plays a crucial biological role in the transportation, release, and protection of iron elements within living organisms102, 103, 104. Zhu et al.87 discovered that transferrin-coated polyacrylamide nanoparticles (Tf-coated NPs) can be effectively absorbed through transferrin receptor-mediated transepithelial transport. In comparison to bovine serum albumin-coated nanoparticles (BSA-coated NPs), Tf-coated NPs exhibited a remarkable 6.14-fold increase in oral pharmacological bioavailability of insulin. Further investigation conducted by Yang et al.61 revealed that Tf-modified NPs were found to be involved in intracellular transport through the endoplasmic reticulum, Golgi apparatus, and lysosomal pathways. The utilization of transferrin receptor-mediated transport and multiple intracellular pathways significantly augmented the transcytosis efficiency of Tf-modified NPs.

3.1.1.3 N-Acetyl-d-glucosamine and sialic acid-targeting

Wheat germ agglutinin (WGA) is a widely studied lectin for oral delivery, specially targeting N-acetyl-d-glucosamine and sialic acid on the surface of intestinal epithelial cells. WGA has been used for modification of oral nanoparticles, significantly increasing the oral absorption of drugs through specific interaction with intestinal cells, thereby improving the oral bioavailability of drugs by 17.5-fold88. Gao et al.89 demonstrated that WGA-NPs could be absorbed via clathrin and caveolae-dependent endocytosis pathways. Meanwhile, Golgi apparatus and lysosome were involved in their intracellular transport during the transcytosis. Despite the mucus adhesion property of WGA, the modification of hydrophilic materials such as polyethylene glycol (PEG) can potentially enhance the ability of WGA-NPs to traverse the mucus layer and facilitate their internalization.

3.1.1.4 Fc receptor (FcRn)-targeting

Proper modification with peptide and protein ligands can allow nanoparticles to bypass lysosomes and transport from the apical to the basolateral side of cells, overcoming the challenge of “hard in, harder out”. Immunoglobulin G (IgG) has been found to bind to the neonatal Fc receptor (FcRn) on intestinal epithelial cells under lower pH conditions in the intestinal lumen (pH 6.0–6.5), thereby avoiding the lysosomal degradation through FcRn-mediated transport. However, the pH-sensitive binding between FcRn and IgG occurs at pH < 6.5 rather than at physiological pH 7.4. After reaching the basolateral side of cells, IgG is released into the bloodstream under higher pH conditions (pH 7.4)18,38,105,106. Exploiting this phenomenon, nanoparticles were modified with fragments of IgG (IgG Fc) to obtain active-targeted nanoparticles (NP-Fc), which exhibited an approximately 11.4-fold increase in transepithelial transport efficiency compared to unmodified nanoparticles. Approximately 13.7% of NP-Fc successfully crossed the intestinal epithelial cell layer18. Albumin-decorated nanoparticles were also engineered for improved pH-dependent binding to the FcRn, and the functional nanoparticles showed improved transepithelial transport. The albumin-modified nanoparticles loaded with insulin exerted a hypoglycemic effect of around 40% reduction after oral administration for 1 h (Fig. 3A)38.Figure 3 (A) Albumin modified nanoparticles target to the neonatal Fc receptor (FcRn) for oral insulin delivery. Reprinted with permission from Ref. 41. Copyright © Elsevier. (B) EGP peptide modified nanoparticles target to heparan sulfate proteoglycans (HSPGs) for caveolae-mediated transepithelial transport. Reprinted with permission from Ref. 64. Copyright © 2018 American Chemical Society. (C) Fructose-modified nanoparticles transport via glucose transporter type 2 (GLUT2), and administrated with acesulfame potassium (AceK). Reprinted with permission from Ref. 97. Copyright © Elsevier. (D) Glycocholic acid-modified nanoparticles transport via the sodium-dependent bile acid transporter (ASBT) and chylomicron pathway. Reprinted with permission from Ref. 81. Copyright © 2018 American Chemical Society.

Figure 3

3.1.1.5 Heparan sulfate proteoglycans (HSPGs)-targeting

Membrane heparan sulfate proteoglycans (HSPG) are found at the cell surface and act as endocytic receptors107. Zheng et al.64 developed a nano-drug delivery system with targeting characteristics towards HSPGs known as EGP NPs (Fig. 3B). The researchers demonstrated that EGP NPs undergo transepithelial transport via the caveolae-mediated pathway, wherein Caveolin-1, the primary protein component in caveolae, specifically inhibits the activity of protein phosphatase 2A (PP2A), which regulates endosome–lysosome fusion108, 109, 110, 111. Nanoparticles in caveolae could dominantly bypass lysosomes without disruption of endosomal integrity, thereby preserving the bioactivity of biotherapeutics. Compared to unmodified nanoparticles (C NPs), EGP NPs exhibited significantly enhanced retention of loaded insulin's bioactivity while C NP-delivered insulin experienced substantial degradation. Further mechanistic investigations revealed that unlike C NPs delivered through the endo/lysosomal pathway, EGP NPs were transported via caveolae-mediated mechanisms, enabling efficient evasion of lysosomal entrapment and facilitating direct apical-to-basolateral transcytosis. Therefore, rational ligand modification could effectively prevent lysosomal degradation, improve drug stability, and increase cellular uptake by 4.5-fold and transcytosis by 4.2-fold while partially overcoming the challenge of “hard in, harder out” 64.

3.1.2 Small molecule ligands

Virtually nutrients from the diet are absorbed into the bloodstream through the highly polarized epithelial cell layer112,113. Certain small molecules, such as short-chain fatty acids, carbohydrates, cholesterol, bile acids, and their derivatives can specifically interact with receptors or transporters expressed on the surface of intestinal epithelial cells114, 115, 116, 117, 118. Inspired by this phenomenon, the physiological absorption pathways have been explored for nanoparticles to promote oral absorption3.

3.1.2.1 Monocarboxylate transporter-1 (MCT-1)-targeting

The monocarboxylate transporter 1 (MCT1) is a proton-dependent transporter which is located on the apical membrane of intestinal epithelial cells. MCT1 can transport substrates like short-chain, unbranched, aliphatic carboxylates, like C2- or C3-substituted monocarboxylates. Huang et al.92,119 developed butyric acid-modified PEG NPs (Bu-PEG NPs). Compared with PEG NPs, Bu-PEG NPs specifically targeted the MCT-1 expressed on epithelial cells, resulting in a remarkable 3-fold increase in oral bioavailability of the nanoparticles. Mechanism studies confirmed that Bu-PEG NPs and PEG NPs were both internalized via clathrin-dependent, caveolae-dependent endocytosis and macropinocytosis and then transported in endoplasmic reticulum, Golgi apparatus, microtubule and lysosome related pathway. Thereby, the modification of some ligands may enhance the transcytosis of nanoparticles without affecting their intracellular trafficking.

3.1.2.2 Niemann-Pick C1 like 1 (NPC1L1)-targeting

Cholesterol plays a pivotal role in the nutritional metabolism. Within the intestinal tract, there exists an inherent pathway for cholesterol absorption: initially, ingested cholesterol binds to Niemann-Pick C1 Like 1 (NPC1L1) located on the apical membrane of intestinal epithelial cells, facilitating its cellular entry. Subsequently, it is transported towards the basolateral membrane of cells via ATP binding cassette transporter A1 (ABCA1), thereby establishing an efficient and unidirectional “top-down” route for cholesterol absorption. By utilizing this cholesterol absorption pathway, Wu et al.93 designed nanoparticles modified with 2,5-hydroxycholesterol (25HC), which could cross the intestinal epithelial cell barrier in a unidirectional manner by interacting with transporters NPC1L1 and ABCA1. Moreover, long-term administration of oral liraglutide-loaded 25HC NPs could elevate glucose metabolism and relieve the diabetic symptoms of db/db mice, with a similar degree achieved by subcutaneous injection of free liraglutide.

3.1.2.3 Glucose transporter type 2 (GLUT2)-targeting

Glucose transporters, serving as a crucial transporter for glucose and its analogues transportation, exhibit extensive expression on the surface of intestinal epithelial cells. Wu et al.72 designed fructose-modified nanoparticles to specially target glucose transporter type 2 (GLUT2). To further promote the absorption of fructose-modified nanoparticles, the absorption promoters were used in combination. A self-amplifying nanoplatform composed of fructose-modified polyethylene glycol-coated nanoparticles (Fru-PEG NPs) and acesulfame potassium (AceK) was utilized to facilitate the absorption (Fig. 3C). Fru-PEG NPs were internalized and exocytosed basolaterally via a glucose transporter type 2 (GLUT2)-dependent process, while co-administration of AceK primed epithelial cells for increased apical distribution of GLUT2, thereby amplifying the unidirectional transcytosis of nanoparticles.

3.1.2.4 Sodium-dependent bile acid transporter-targeting

Bile acids are regulatory molecules which are derived from cholesterol in the hepatocytes and transported to the intestine for the ingestion of food120. Sodium-dependent bile acid transporter (ASBT), located on the surface of intestinal epithelial cells, acts as a transporter for bile acids and their derivatives, facilitating the active transportation of bile acid-modified nanoparticles across the epithelial barrier96,97. Gan et al.59 found that deoxycholic acid-modified nanoparticles (DNP) could specifically target to ASBT, thus avoiding lysosomal degradation. Subsequently, these nanoparticles undergo apical-to-basolateral exocytosis through intracellular bile acid binding protein (IBABP), ultimately leading to a significant improvement in oral bioavailability compared to unmodified nanoparticles.

The study by Bae et al.78 demonstrated that surface-conjugated solid nanoparticles of glycocholic acid (GCA) could significantly enhance oral bioavailability by utilizing both the ASBT-mediated cellular uptake and chylomicron transport pathways (Fig. 3D). These nanoparticles were able to enter cells through the ASBT pathway, bypassing the endosome–lysosome pathway, and trafficking within the endoplasmic reticulum-Golgi apparatus network. Once inside the cytosol, these nanoparticles appeared to share the chylomicron transport pathways in the enterocytes, following a route involving mesenteric lymph nodes, and finally entering systemic circulation via the left subclavian vein. The same research group also discovered that the conjugation of bile acids onto solid nanoparticles significantly enhanced ASBT-mediated endocytosis and the chylomicron pathway. Detailed mechanistic studies revealed that GCA conjugation altered the mechanisms of endocytosis and downregulated cellular responses to transport at the gene level, establishing a negative feedback loop that induced higher cellular retention of nanoparticles98. The metabolic and immunomodulatory functions of bile acid-derived nanoparticles were observed, presenting potential translational opportunities for the prevention and treatment of type 1 diabetes. Polymerized ursodeoxycholic acid, derived from bile acid polymers, was formulated into nanoparticles for oral insulin delivery. These nanoparticles served as protective carriers for insulin while also acting as high-avidity agonists for bile acid receptors. This dual functionality enhanced intestinal absorption of insulin, induced polarization of intestinal macrophages towards the M2 phenotype, and exhibited preferential accumulation in the pancreas of mice. Furthermore, these nanoparticles demonstrated a strong binding affinity to the islet-cell membrane receptor TGR5 and effectively activated the secretion of glucagon-like peptide and endogenous insulin99.

3.1.3 Ligand modification density

The density of ligand modification is a crucial factor that influences the efficiency of nanoparticle transport121,122. Previous studies have demonstrated a close relationship between ligand density and cellular uptake as well as transepithelial transport of nanoparticles. Song et al.84 investigated the impact of modification density for three different ligands targeting neonatal Fc receptor (FcBP), transferrin receptor (7pep), and αvβ3 integrin receptor (c(RGDfK)) on the cellular uptake and transepithelial transport of nanoparticles. They observed that ligand density could influence the distribution of nanoparticles in the degradation pathway, recycling pathway, and secretion pathway, thereby affecting transepithelial transport efficiency. Furthermore, the effect of ligand density on transepithelial transport was found to be closely associated with the type of ligand used. Cellular uptake and transepithelial transport were positively correlated with ligand density for nanoparticles modified with 7pep and c(RGDfK). Conversely, nanoparticles modified with moderate density of FcBP exhibited the highest levels of cellular uptake and transepithelial transport. Therefore, the optimization of ligand density is advantageous for enhancing the transport of nanoparticles across intestinal epithelial cell barriers.

3.2 Surface charge

The surface charge of nanoparticles is mainly determined by the surface materials with cationic or anionic groups. The surface charge is an important parameter to effect the absorption of nanoparticles123. Due to the negative charge of intestinal mucus and intestinal epithelial cell membranes, usually, a contradictory requirement exists for the surface charge of nanoparticles. On one hand, nanoparticles with strong positive or negative charge are prone to be trapped in mucus or are totally repelled by the mucus, while electrically neutral nanoparticles are more likely to overcome the mucus barrier124,125. On the other hand, positively charged nanoparticles can improve their affinity with cell membranes through electrostatic interaction, thus enhancing the epithelial cell uptake12,126. Wu et al.127 designed nanoparticles with equal amounts of a positive and negative charge, as well as intestinal alkaline phosphatase (IAP) responsive charge-reversal ability (P–R8-Pho NPs). Following traversal through the mucus layer, the outermost surface of nanoparticles undergoes deshielding of its negatively charged group facilitated by IAP activity on the membrane. This timely exposure of the positively charged group enhances cellular uptake and transepithelial transport of nanoparticles. Compared with electrically neutral nanoparticles that cannot undergo charge reversal (P NPs), the oral bioavailability was improved by 2.3 times.

In some studies, compared with negatively charged nanoparticles, positively charged nanoparticles exhibit higher cellular uptake but show reduced transepithelial transport efficiency. For example, the proportion of negatively charged (carboxyl-modified) nanoparticles transported across intestinal epithelial cells is three times that of positively charged (amino-modified) nanoparticles. Mechanism studies revealed that the positively charged nanoparticles are mainly transported through the clathrin-mediated endocytosis pathway, while negatively charged nanoparticles are mainly the caveolin-mediated pathway128. In addition, Lin et al.128 found that the cellular uptake of nearly neutral or negatively charged gold nanoparticles is only 50% of positively charged nanoparticles, but the transepithelial transport efficiency is 10–20 times that of positively charged nanoparticles. Some studies revealed that positively charged NPs cause more pronounced disruption of plasma-membrane integrity, and stronger mitochondrial and lysosomal damage than anionic NPs, indicating that the positively charged NPs would be more prone to bypass the endo-lysosomal pathway129,130. The influence of the surface charge on the transepithelial transport of nanoparticles may be a comprehensive reflection of its effect on endocytosis, intracellular transport, and exocytosis. Therefore, in the design of orally administered nanoparticles, it is necessary to choose the appropriate surface charge based on the specific transport requirement.

3.3 Hydrophilicity/hydrophobicity

The surface hydrophilicity/hydrophobicity is an important parameter that affects the absorption and final fate of nanoparticles. Since the cell membrane is composed of a lipid bilayer and owns a certain degree of lipophilicity, nanoparticles with stronger hydrophobicity are more easily internalized by cells131,132. Qiao et al.133 demonstrated the penetration of hydrophobic fullerene nanoparticles through the lipid bilayer membrane upon their embedding in the inner phase. A distinct response mechanism was elucidated for the hydrophilic derivatives, which exclusively underwent adsorption onto the bilayer. This phenomenon was corroborated by Li et al.134, who computationally simulated and demonstrated that hydrophilic nanoparticles exhibit a preference for surface adsorption rather than incorporation into the bilayer.

Huang et al.119 prepared a series of butyrate-modified nanoparticles with different hydrophobicity by controlling the ratio of hydrophilic polyethylene glycol (PEG) and hydrophobic poly(lactic-co-glycolic acid) (PLGA). The studies demonstrated that while hydrophobicity did not influence the transport pathway of butyrate-modified nanoparticles within intestinal epithelial cells, it did impact the efficiency of exocytosis from either the apical or basolateral side. Specifically, PLGA nanoparticles with higher hydrophobicity exhibited a greater tendency for exocytosis from the basolateral side. Rieux et al.135,136 found that nanoparticles with stronger hydrophobicity were more easily taken up by M cells and could achieve more efficient oral absorption through transepithelial transport by M cells. Additionally, hydrophobic polymers such as polystyrene, polymethyl methacrylate, polyhydroxybutyrate, and glycolic acid polymer nanoparticles demonstrate enhanced absorption in the intestinal Peyer's patches compared to the less hydrophobic lactic acid. The absorption capacity of hydrophobic particles is approximately 100 times greater than that of the hydrophilic cellulose polymer137.

However, though higher hydrophobicity is beneficial to transport across the epithelial cell layer, it goes against the penetration of the mucus layer because surface hydrophilicity is necessary for mucus permeation126. For this dilemma, Cui et al.132 developed nanoparticles with surface “hydrophilicity/hydrophobicity balance” by modulating the ratio of hydrophilic N-(2-hydroxypropyl) methacrylamide (HPMA) and hydrophobic methacrylamido fatty acid ester (FA) analogues. They found that nanoparticles coated with 20% amount of HPMA–cetyl methacrylate copolymer (NPs-C16 (20%)) showed the best hypoglycemic effect in vivo. Therefore, finding an appropriate balance is important for the hydrophilicity/hydrophobicity modulation.

3.4 Intestinal protein corona

When nanoparticles are exposed to the physiological fluids, several thousand proteins would interact with these colloidal nanoparticles and then form the protein adsorption layer on the surface, also known as the “protein corona”138. The protein corona on nanoparticles can modify the diverse physicochemical properties of nanoparticles such as size, surface charge, and surface composition, thereby imparting a novel biological identity to the nanoparticles. The protein corona has been reported to effect the biological destiny of nanoparticles, such as cellular uptake, blood circulation time, biodistribution, and even toxicity139,140.

Upon oral administration, nanoparticles interact with substances in the gastrointestinal tract, forming a protein corona on the surface, which is called the intestinal protein corona80,141. Zhang et al.142 discovered that incubating gold nanoparticles with mucin resulted in the formation of a mucin-protein corona on their surface (Fig. 4A). Although this mucin-protein corona significantly enhanced epithelial cell uptake of gold nanoparticles, it did not effectively improve their transepithelial transport. Further investigations revealed that under the influence of the mucin-protein corona, gold nanoparticles were more readily transported to exocytosis-related organelles like the Golgi apparatus and subsequently exocytosed from the apical side of cells back into the intestinal lumen (Fig. 4B and C). This hindered their exocytosis from the basolateral side and entry into the bloodstream. Therefore, the mucin-protein corona may hinder the transepithelial transport of nanoparticles143. Additionally, proteins in the gastrointestinal tract can adsorb onto the surface of nanoparticles to form an intestinal protein corona. Wu et al.144 discovered significant alterations in the protein corona under different physiological conditions within the body. Distinctions were observed in the intestinal protein corona (IPC) formed in healthy rats compared to those with diabetes or colitis. In cases of diabetes or colitis, disease-specific IPCs can enhance oral nanoparticle absorption (Fig. 4D) by modulating intracellular transport through early endosome, recycling endosome, and endoplasmic reticulum-Golgi apparatus pathways while significantly increasing basolateral exocytosis, ultimately facilitating transepithelial transport (Fig. 4E and F). Thus, disease-specific IPCs have a “positive effect” on intestinal absorption and may benefit systemic drug delivery for diabetes treatment. Conversely, for colitis requiring local treatment in the colon, reducing the formation of disease-specific IPCs can weaken this “positive effect” on intestinal absorption and allow more nanoparticles to reach their intended site. Timely modulation of disease-specific intestinal protein corona formation on nanoparticle surfaces is imperative for effective oral treatment across various diseases.Figure 4 Mucin protein corona for transepithelial transport of nanoparticles. (A) Mucin protein corona adsorbed on PEG-modified gold nanoparticles (PGNPs@mucin). (B) Intracellular distribution of nanoparticles with Golgi apparatus. (C) Transcytosis and exocytosis of nanoparticles, and the schematic diagram for the influence of mucin on the transepithelial transport of nanoparticles. Reprinted with permission from Ref. 147. Copyright © 2018 American Chemical Society. Disease-specific intestinal protein corona (IPC) for transepithelial transport of nanoparticles. (D) The oral absorption of nanoparticles on healthy, diabetic and colitis rats. (E) The bidirectional exocytosis of nanoparticles adsorbed diabetic-IPC (D-IPC@PS) and colitis-IPC (C-IPC@PS). (F) Proteomic analysis for biological functions of D-IPC and C-IPC on the transepithelial transport and intracellular transport of nanoparticles. Reprinted with permission from Ref. 154. Copyright © Elsevier.

Figure 4

The presence of adsorbed protein corona can impact the surface properties of nanoparticles, particularly those have been modified with targeted ligands. Previous studies on nanoparticles via parenteral administration have demonstrated that the coated protein corona in the blood circulation can mask the target ligand on the surface of nanoparticles, thereby diminishing the targeting efficiency in vivo145, 146, 147, 148. As for oral administration, how intestinal protein corona formed in the gastrointestinal tract influences the transepithelial transport of ligand-modified nanoparticles remains to be elucidated. A recent study found that for transferrin-modified nanoparticles (Tf-NPs) adsorbed protein corona from the mucus layers, which masked, displaced, and dampened the active targeting effects of Tf-NPs, thus reducing the transepithelial transport. However, precoated Tf-NPs with mucin as “active protein corona” could weaken the negative effect of “passive protein corona” from the mucus layers, for improving the transepithelial transport. Based on this, the active target ligands coated with protein corona may also lose or weaken their target ability for orally delivered nanoparticles, which was unfavorable for the transepithelial transport143.

An alternative possibility that warrants consideration has recently been proposed. Besides the mucin, proteins in the gastrointestinal tract can also be absorbed to form the intestinal protein corona, potentially exerting diverse impacts on the target ligands. According to recent research by Huang's group, the occurrence of diseases could also influence the composition of the intestinal protein corona (such as diabetic-intestinal protein corona), which demonstrated an enhanced effect on the transepithelial transport and oral absorption of nanoparticles144. These disease-specific protein coronas can be considered as “special ligand” on nanoparticles, thereby potentially displacing the original target ligand and facilitating the transepithelial transport of nanoparticles even when the modified target ligand is masked. Although intestinal protein coronas may not necessarily compromise the targeting efficiency of ligand-modified nanoparticles, empirical investigations are still required to ascertain whether the protein corona masks or inhibits the role of targeted ligands to what extent. Moreover, it is essential to explore how orally formed protein coronas influence the transepithelial transport of nanoparticles modified with other ligands besides transferrin.

3.5 Perspective of surface properties

While numerous studies primarily focus on the impact of an individual property on traversing a specific barrier, it is important to acknowledge that the prerequisites for nanoparticles to cross multiple barriers may exhibit variations and even contradictions. In general, hydrophilic and electrically neutral nanoparticles are more likely to penetrate the intestinal mucus barrier, while hydrophobic and positively charged nanoparticles are more likely to overcome the intestinal epithelial cell absorption barrier. In addition to the studies discussed above, some researchers have developed some nanoparticles with adjustable surface properties. For example, Le et al.149 developed a charge-transfer surface based on a phosphate portion that is cleaved by membrane-bound phosphatase, thereby converting its charge from anion to neutral or cation. Shan et al.11 encapsulated insulin-transmembrane peptide complexes in hydrophilic N-(2-hydroxypropyl) methacrylamide copolymer (pHPMA), which can be stripped off during mucosal penetration, exposing the transmembrane peptide for easier cellular entry. Wang et al.150 formed a protein corona by adsorbing BSA onto the surface of cationic liposomes, which can be enzymatically hydrolyzed during mucosal penetration, exposing the positive charge on the liposome surface to enhance intestinal epithelial cell absorption. Ongoing research is currently underway to develop streamlined strategies for the successful traversal of nanoparticles across both the mucus layer and epithelial cells.

4 Impact of holistic properties on oral drug delivery systems

In addition to surface properties, the holistic properties of nanoparticles, such as particle size, shape, and elasticity, are also closely related to their transepithelial transport151. For example, nanoparticles with different shapes have different surface areas and flow characteristics, which affect their absorption and transport in intestinal epithelial cells152,153. The size of nanoparticles will have a greater impact on their movement in the mucus layer and adhesion in the gastrointestinal tract, and their absorption pathway and absorption efficiency are also affected by their particle size26. Rigidity is also one of the key physicochemical properties of nanoparticles. Nanoparticles with moderate rigidity are more likely to change shape as needed during in vivo movement, which plays a positive role in transepithelial transport29. Moreover, as a crucial part of the nano-drug delivery system, carrier materials play an important role in drug encapsulation, shielding environmental factors, increasing stability, and achieving targeted and controlled release, which is a significant property affecting transepithelial transport154. This section provides an overview of the holistic properties including size, shape, rigidity, and material et al. that influence the transepithelial transport of nanoparticles, elucidating the underlying principles governing their impact on transepithelial transport.

4.1 Particle size

The particle size of nanoparticles is one of the holistic properties that affect their transepithelial transport, as it plays a regulatory role in the transport processes such as cellular uptake, intracellular transport, and exocytosis26,151,155, 156, 157, 158, 159. The transport efficiency of vitamin B12-loaded soy protein (SPI) nanoparticles across the Caco-2 cell monolayers was dependent on particle size, with increasing order observed in the transport of 30 nm  >  100 nm > 180 nm. Among the varied nanoparticles, those with a size of 100 nm showed the highest cellular uptake160. Furthermore, nanoparticle size can modulate intracellular distribution. Schubbe et al.161 demonstrated that 32 nm SiO2 nanoparticles were rapidly internalized by intestinal epithelial cells and prominently localized within the nucleus, whereas 83 nm SiO2 nanoparticles did not penetrate the nucleus. It is worth noting that the impact of particle size on cellular uptake can vary and even exhibit contradictory outcomes. Desai et al.162 synthesized a range of PLGA nanoparticles with varying sizes (100 nm, 500 nm, 1 μm, and 10 μm) and observed that the smallest particles (100 nm) demonstrated the highest level of intestinal absorption. Conversely, research conducted by Mitragotri's group26 revealed that smaller nanoparticles (50 and 200 nm) exhibited significantly greater efficiency in transepithelial transport compared to larger nanoparticles (500 and 1000 nm), with an inverse relationship between particle size reduction and enhanced transepithelial transport. However, no significant difference was observed in transepithelial transport efficiency between nanoparticles sized at 50 and 100 nm. Therefore, selecting nanoparticles within the smaller size range (50–200 nm) may be more advantageous for enhancing their cellular uptake and transepithelial transport.

4.2 Shape

The shape of nanoparticles also exerts a significant influence on the cellular uptake and transepithelial transport behavior of epithelial cells163. Yu et al.164 conducted a comparative study between spherical and rod-shaped nanoparticles in terms of their interaction with the intestinal mucosa, revealing that rod-shaped nanoparticles possess superior mucus penetration ability by employing a “rotation-jump” mechanism. Additionally, these rod-shaped nanoparticles exhibit prolonged mucosal retention time and enhanced absorption within the intestinal mucosa. Banerjee et al.26 conducted a comparison of the cellular uptake, intracellular transport, and transepithelial transport of rod-shaped, disc-shaped, and spherical nanoparticles. Their findings indicate that the efficiency of cellular uptake for nanoparticles is in the order of rod-shaped > disc-shaped > spherical. Upon surface modification with biotin ligands, all groups of nanoparticles showed significant improvement in both cellular uptake and transepithelial transport efficiency; however, the highest enhancement was observed in rod-shaped nanoparticles. Furthermore, nanoparticle shape can significantly influence their intracellular distribution. Compared to spherical and disc-shaped counterparts, rod-shaped nanoparticles are more easily taken up by cells through preferential transportation via the endoplasmic reticulum-Golgi apparatus pathway; thus they are more likely to be transported across intestinal epithelial cell layers165. The cellular uptake of rod-shaped nanoparticles is higher, and they exhibit ideal intracellular transport pathways and enhanced transepithelial transport efficiency, which can be attributed to their contact area and mode with the cell membrane. However, currently, inorganic materials are predominantly employed for the synthesis of non-spherical nanoparticles to investigate the impact of shape on oral nanoparticle absorption. Challenges still exist in utilizing biodegradable organic materials for the preparation of non-spherical nanoparticles. Therefore, it is worth considering the utilization of 3D printing, microfluidics, and other technologies for designing and fabricating degradable non-spherical oral drug delivery systems166.

4.3 Rigidity

In recent years, rigidity has garnered increasing attention as one of the crucial physicochemical parameters of nanoparticles2,29,167,168. Rigidity is commonly characterized by Young's modulus and is closely associated with the material composition169,170. In nature, viruses, cells, and certain entities can adapt their rigidity to different stages of physiological activity171,172. Previous studies have revealed that rigidity significantly impacts the diffusion of nanoparticles across the mucus layer. Yu et al.29 designed PLGA core-lipid shell NPs with Young's modulus values ranging from 7 Mpa to approximately 106 Mpa (Fig. 5A). It found that the semi-elastic NPs (50 Mpa) achieved superior mucus-penetrating ability among all, due to the deformation into ellipsoids and displayed rotational motion in mucus (Fig. 5A and B). In contrast, the soft NPs (7 Mpa) deformed excessively and irregularly, while the hard NPs (106 Mpa) almost completely retained their spherical shape (Fig. 5A–B). In another study by Yu et al.173, a similar phenomenon was observed for liposomes with different rigidity (Fig. 5C). Liposomes with moderate rigidity (Lip4) deformed into the ellipsoidal shape for superior diffusivity compared with soft (Lip1) and hard (Lip6) liposomes (Fig. 5C and D). Therefore, keeping moderate rigidity was ideal for lipid-polymer nanoparticles as well as liposomes to diffuse across the mucus layers and also exhibit superior oral absorption. To further investigate the impact of nanoparticle rigidity on transepithelial transport. Zheng et al.174 constructed a series of amphiphilic gel nanoparticles with different degrees of crosslinking and explored the cellular uptake, intracellular transport, and transepithelial transport of the nanoparticles. It was interesting to find that nanoparticles with higher elasticity had better cellular uptake and transepithelial transport capabilities. Mechanistic studies revealed that nanoparticles with higher rigidity tended to be transported through exocytosis-related pathways such as the endoplasmic reticulum, Golgi apparatus, microtubules, and caveolae, thus showing higher exocytosis efficiency. On the other hand, nanoparticles with lower rigidity were more likely to be trapped in lysosomes, leading to lower exocytosis efficiency. Furthermore, Yu et al.25 investigated the strategy of modulating rigidity in ligand-modified nanoparticles and observed that this modulation had a similar impact on the transepithelial transport of both neonatal Fc receptor domain-binding peptide (FcBP) modified nanoparticles and pristine nanoparticles. They found that increasing rigidity was advantageous for enhancing transepithelial transport. It is important to note that the rigidity of nanoparticles primarily relies on the types and proportions of different materials composing them, leading to compositional variations among different nanoparticles. Therefore, further research is needed to explore the relationship and pattern between nanoparticle rigidity and transepithelial transport to broaden its applicability.Figure 5 PLGA core-lipid shell NPs with different rigidity. (A) Cryo-TEM images, Young's modulus and atomic force microscopy (AFM) images of NPs. (B) 3D mobility and morphology of NPs in rat intestinal mucus imaged by Airyscan microscopy. Reprinted with permission from Ref. 29. Copyright © 2018, Miaorong Yu et al. Liposomes with different rigidity. (C) Young's modulus and AFM images of Liposomes. (D) Representative snapshots of liposomal structures from the simulation, and trajectory analysis of liposomal formulations in mucus. Reprinted with permission from Ref. 181., this material published after 2008, a copyright note is not needed.

Figure 5

4.4 Materials

The carrier material of the nano delivery system plays a crucial role in achieving multiple functions, including encapsulating drugs, shielding them from environmental factors and systemic metabolism, prolonging their residence time in the intestines, providing targeted receptors, and controlling drug release175, 176, 177, 178. These effects significantly enhance the gastrointestinal stability and oral absorption of nanoparticles. The materials can be classified as either inorganic or organic based on their chemical composition154. Organic nanoparticles consist of biological macromolecules (e.g., phospholipids, albumin, chitosan, etc.) and polymeric materials (e.g., PLGA and PEG, etc.)179, 180, 181, 182. Inorganic nanoparticles encompass metallic nanoparticles such as iron, gold, and silver, as well as non-metallic nanoparticles like titanium dioxide, mesoporous silicon, and mesoporous carbon183, 184, 185, 186.

4.4.1 Lipid-based nanoparticles

Lipid molecules can self-assemble in aqueous environments to form liposomes that resemble cell membranes. These miniature vesicles possess both hydrophobic and hydrophilic regions, allowing for the encapsulation of various drugs187. Due to their excellent biocompatibility and biodegradability, liposomes are considered ideal materials for nano-delivery systems188. Conventional liposomes are susceptible to degradation by gastric acid, lipase, and bile salts in the gastrointestinal tract, resulting in drug leakage and limitations in oral delivery189. However, scientists have devised several strategies to address this issue. Hu et al.190 pre-injected bile salts into liposomes to prevent the destruction of physiological bile salts. Hosny et al.191 coated the surface of liposomes with an enteric polymer layer to prevent disintegration in the stomach and increase intestinal absorption. The protective coatings formed by polysaccharides, proteins, and silica have also been shown to enhance the gastrointestinal stability of liposomes192, 193, 194, 195. Additionally, liposomes modified with chitosan, mucin, and other substances have demonstrated stronger mucosal adhesion, prolonged their gastrointestinal retention time, and thus enhanced absorption150,196,197. Ezzat et al.198 found that chitosan-modified liposomes exhibited 1.37 times higher oral bioavailability compared to traditional liposomes and 2.12 times higher than free catechins. Furthermore, liposomes can facilitate oral drug absorption through the M cell-lymphatic pathway74,199. By incorporating specific ligands, liposomes can also improve uptake by intestinal epithelial cells through receptor-mediated endocytosis200,201. The presence of long-chain fatty acids like oleic acid and surfactants such as Tween-80 in liposomes inhibits P-glycoprotein (P-gp) efflux, thereby increasing cross-cell transport efficiency202, 203, 204. Solid lipid nanoparticles (SLN) and nanostructured lipid carriers (NLC) consisting of a phospholipid layer and a solid lipid core demonstrate enhanced gastrointestinal stability and can effectively improve the oral bioavailability of drugs with limited solubility and permeability such as amphotericin B and saquinavir205, 206, 207.

Exosomes are special lipid-based nanoparticles that naturally secrete from cells, featuring a lipid bilayer structure and carrying bioactive substances such as proteins, nucleic acids, miRNA, etc., for intercellular communication208,209. In comparison to regular liposomes, exosomes have higher circulatory stability and biocompatibility, lower immunogenicity, and toxicity, as well as the ability to cross the gastrointestinal barrier, making them naturally advantageous vehicles for oral drug delivery210,211. Umezu et al.212 discovered that Acerola-derived exosomes can protect miRNA from degradation by RNase, strong acid, and base in vitro, demonstrating their feasibility for oral nucleic acid drug deliver. Zhong et al.213 reported that intact milk exosomes can be transported from the intestine into the bloodstream via FcRn receptor-mediated endocytosis. Wu et al.214 employed milk-derived exosomes as vehicles for biomacromolecule drug insulin delivery. Their research demonstrated that milk exosomes exhibited high resistance against the harsh environment of the gastrointestinal tract and can be effectively transported from the apical side of the intestinal epithelium to the basal side, significantly improving the bioavailability of insulin. Munagala et al.215 used milk exosomes for oral delivery of anthocyanins to treat pulmonary tumors in mice and found that it significantly improved the oral bioavailability of anthocyanins and reduced the toxicity of anthocyanins.

4.4.2 Polymer-based nanoparticles

Polymer nanoparticles prepared from various polymer materials have shown potential as carriers for drug and gene delivery, leading to enhanced drug delivery efficiency82,216. Polymer-based nanoparticles have been extensively studied for oral delivery and possess several advantages over other types of materials. First, there is a wide range of polymer materials available with diverse applications, including synthetic polymers such as PLGA, PEG, and polylactic acid, as well as natural polymers such as chitosan, sodium alginate, and proteins217,218. Although non-biodegradable types are unsuitable for therapeutic purposes, they can be utilized as model particles to investigate the effects of nanoparticle surface and holistic properties on their ability to cross the physiological barrier of the gastrointestinal tract26,219. Biodegradable polymers exhibit excellent biocompatibility, high safety, and great encapsulation efficiency, which are well-suited for drug delivery, but their gastrointestinal stability is relatively limited220. Conversely, enteric-soluble polymers have the natural advantage of not being disrupted by gastric acid for oral administration. Singh G et al.221 prepared polymer nanoparticles loaded with atazanavir using enteric-soluble Eudragit RL 100, which enhanced the absorption and permeability of the drug for transfer through intestinal Peyer's patches collection lymph nodes and significantly improved the bioavailability. Reboredo et al.222 employed zein nanoparticles to protect insulin from degradation by gastric juice. Moreover, enteric-coated polymers can also serve as surface coatings for other nanoparticles to assist them in conquering the gastric acid barrier223,224. Second, polymer nanoparticles exhibit significant design flexibility and controllability. By manipulating the structure, composition, and surface modification of materials, polymer nanoparticles can be designed with different particle sizes and surface charges to perform functions such as controlled release, gastrointestinal stabilization, mucosal penetration, or specific targeting, making them more suitable for oral drug delivery225, 226, 227, 228. Xie et al.229 developed PLGA NPs that significantly improved the oral bioavailability of curcumin―a hydrophobic drug―by 5.6 times by enhancing its solubility and permeability while also increasing its retention time within the intestine and inhibiting P-gp-mediated efflux. Inchaurraga et al.230 used PEG to modify the surface of the poly(anhydride) nanoparticle, which reduces the interactions between the NPs and mucus and allows them to rapidly pass through the intestinal mucus barrier.

Hydrophilic polymers are unique polymer materials that can be physically or chemically crosslinked to form hydrogels with a porous three-dimensional network structure231. These hydrogels can rapidly absorb and expand in water and biological fluids without dissolution232,233. In terms of oral administration, hydrogels protect against degradation in harsh gastrointestinal environments and enhance drug stability234. Additionally, their adhesive properties enable prolonged retention in the intestine, thereby improving oral drug absorption and facilitating controlled release235,236. Due to the adjustable physical properties of hydrogels, researchers have invented a variety of intelligent response hydrogels to adapt to various environmental factors in the body, such as pH, temperature, and enzymes237, 238, 239. Among these responsive hydrogels, pH-sensitive ones exhibit shrinkage in acidic conditions (gastric fluid) for drug protection while swelling occurs in weakly alkaline environments (small intestine) to promote drug release and absorption240. Chen et al.241 successfully fabricated pH-sensitive nanohydrogels with particle sizes ranging from 200 to 300 nm through electrostatic interactions and applied them to oral insulin delivery. The resulting cross-linked structure is dense in gastric fluid and loose in the intestine, which can effectively inhibit the rapid release and degradation of insulin in gastric fluid and control its release in the intestine, thus benefiting the absorption and sustained release of insulin after oral administration.

4.4.3 Inorganic materials-based nanoparticles

Based on inorganic materials, inorganic nanoparticles with various morphologies and particle sizes ranging from 1 to 1000 nm could be synthesized through physical or chemical methods242,243. Compared with the above-mentioned nanoparticles based on organic materials, they possess the advantages of facile preparation and storage, controllable size and shape, easy surface modification, and excellent physical and chemical stability244, 245, 246, 247. However, the range of suitable inorganic materials for oral delivery is limited, and their biocompatibility and safety are far inferior to those of certain biological organic materials. Some inorganic nanoparticles such as iron oxide or gold nanoparticles are difficult to degrade and excrete after entering the body which may lead to toxicity and adverse reactions that limit their practical medical applications248,249. Nevertheless, inorganic nanoparticles can achieve rapid degradation under specific physiological conditions by changing the particle size and morphology of the nanoparticles and adjusting the surface properties and doping strategies250, 251, 252. Some inorganic nanoparticles prepared from highly biocompatible inorganic materials such as calcium phosphate and silica are also biodegradable253,254.

Inorganic nanoparticles can be divided into two major categories: metal and non-metal. Among them, metal nanoparticles are often utilized for molecular imaging and targeted photothermal therapy due to their magnetic and photothermal propertie255,256. Gold nanoparticles (GNP) exhibit good physiological stability and can resist hydrolysis by gastric acid and enzymes, therefore, they can be employed for oral administration257. Wang et al.258 discovered that Au25 nanoparticles with a diameter of 25 nm could easily reach the intestine intact after oral administration, effectively clearing ROS from inflammatory sites and exerting antioxidant effects. Another study revealed that GNP synthesized in vivo after oral administration could be completely absorbed into the blood circulation by the gastrointestinal tract of mice and reach distal sites such as bacterial peritonitis259. Kumari et al.260 developed an apple polysaccharide (MAP) modified AuNPs for oral delivery of insulin, which played a dual role in protecting insulin from being destroyed. Compared with direct oral administration, insulin loaded by AuNPs could significantly reduce blood glucose in the short term and demonstrated an effect of improving blood biochemical indicators in long-term studies. However, due to unclear metabolic mechanisms and potential toxicity in vivo, the application of metal nanoparticles in oral drug delivery is currently limited261,262.

Based on non-metallic materials such as silica, porous silicon nanoparticles possess abundant pores, providing a spacious capacity for drug loading and high specific surface area, facilitating sufficient contact between the drug and the dissolving media to promote their efficient dissolution and release. At the same time, the nanoparticles can adhere to the intestinal mucosa, prolonging drug residence time and enhancing oral absorption efficiency263. Additionally, the hydroxyl-abundant surface of porous silicon nanoparticles is easily modifiable to adapt to various physiological environments264. Araújo et al.265 designed diverse nanosystems for oral delivery of inorganic glucagon-like peptide-1 (GLP-1) to treat diabetes. In comparison, porous silicon nanoparticles exhibited higher association efficiency and drug loading capacity than PLGA NPs and solid lipid nanoparticles and showed the best intestinal permeability of GLP-1 after chitosan surface modification. Another inorganic non-metallic material suitable for oral delivery is mesoporous carbon. Compared with mesoporous silicon, mesoporous carbon exhibits superior safety and structural robustness, and excellent physical and chemical stability266, 267, 268, 269. Wang et al.270 investigated the adhesion and absorption between intestinal epithelial cells and mesoporous carbon nanoparticles (UMCS) and found that UMCS could significantly increase cell permeability and uptake, inhibit drug efflux rate, and exhibit remarkable oral bioavailability compared to commercially available capsules.

4.4.4 In vivo stability of nanoparticles

Drug-loaded nanoparticles may encounter various harsh physiological environments during oral delivery, resulting in aggregation, precipitation, or degradation. These factors can significantly impact their in vivo stability and hinder the successful delivery of drugs to the target site. Firstly, nanoparticles encounter amylase and lipase in the oral cavity and then enter the stomach filled with strong acidic liquid, pepsin, and cathepsin. They reach the intestine where various digestive enzymes pose a threat to their stability. Each component of the gastrointestinal tract possesses distinct anatomical and physiological properties that influence the stability of nanoparticles to varying degrees7,271. It is evident that maintaining a certain in vivo stability after oral administration is crucial for effective transepithelial transport of nanoparticles. The key factor determining the in vivo stability of nanoparticles is the nature of their carrier materials. Stable materials help maintain the integrity and functionality of the drug delivery system over an extended period. For example, enteric-soluble polymer materials have a natural advantage in gastric stability224,272. Most inorganic materials are inert and exhibit good physiological stability which can resist the hydrolysis of gastric acid and enzymes244,257. Although biodegradable materials derived from natural polymers like proteins and chitosan offer excellent biocompatibility and safety, they are susceptible to hydrolysis by digestive enzymes which limits their gastrointestinal stability220. In the above paragraph on carrier materials, we have introduced in detail the in vivo stability of nanoparticles formed by various types of carrier materials and the research made by scientists in recent years to improve the oral stability of nanoparticles. Additionally, there is an abundance of proteins present within the gastrointestinal tract that can interact with nanoparticles and form protein corona on their surfaces, thereby modulating the in vivo stability of nanoparticles80,138,273. Some studies have proposed that protein corona can increase the colloidal stability of nanoparticles274,275. When an ample number of proteins form this crown, they can fully encapsulate an individual nanoparticle, thus providing spatial stability between adjacent nanoparticles and reducing their aggregation275. However, the interaction between proteins and nanoparticles is highly complex, and there is no unified conclusion on the effect of protein corona on the stability of nanoparticles. This is determined by the combination of protein binding types and proportions, human-specific physiological environment, and the properties of nanoparticle carrier materials80,144,276,277. The oral nanoparticles prepared using different types of carrier materials, along with their advantages were shown in Table 2124,187,188,199,205, 206, 207, 208, 209,229,234, 235, 236,240,255,256,259,263,265,266,268,278, 279, 280, 281, 282, 283.Table 2 Nanoparticles prepared using different types of carrier materials and their advantages.

Table 2Material type	Nanoparticle type	Advantage	Ref.	
Lipid	Liposome	Wide drug loading range
Good biocompatibility and biodegradability
Lymphatic absorption	187,188,199	
Solid lipid nanoparticles (SLN)
Nanostructured lipid carriers (NLC)	High drug loading capacity
Enhanced gastrointestinal tract stability and permeability of intestinal mucus barriers
Ease of large-scale manufacture	205, 206, 207	
Exosome	Good biocompatibility and permeability
Minimal immunogenicity
Enhanced gastrointestinal tract stability
Intestinal cell-targeted	208,209	
Polymer	PLGA NPs	Increased drug solubility
Enhanced gastrointestinal tract stability and permeability of intestinal mucus barriers
Facile surface modification	124,229,278	
Nanohydrogels	Excellent gastrointestinal stability and intestinal adhesion
Intelligent response to physiological environment
Controlled drug release	234, 235, 236,240	
Polymeric micelles	Increased drug solubility
Enhanced gastrointestinal tract stability and permeability of intestinal mucus barriers	279,280	
Metallic	Gold nanoparticles
CeO2 nanoparticles	Facile preparation and storage
Controlled size, shape, and surface functionalization
Resistant against acids and enzymes
Available for molecular imaging and GI disease diagnosis	255,256,259,281	
Metalloid	Mesoporous silicon nanoparticles
Mesoporous carbon nanoparticles	Large drug-loading space and high surface modifiability
Increased drug solubility and release
Excellent gastrointestinal stability and intestinal adhesion	263,265,266,268	
Hybrid	Metal-organic framework	Controlled size, structure and surface functionalization
Enhanced gastrointestinal tract stability and permeability of intestinal mucus barriers	282,283	

4.5 The perspective of holistic properties

The holistic properties of nanoparticles significantly impact oral transepithelial transport efficiency. However, researchers should prioritize factors based on actual situations and specific needs. Nanoparticle size could be regulated for optimal effect by adjusting parameters like the preparation process or carrier material26, while the customization of nanoparticle shapes still presents challenges. Although the rod-shaped nanoparticles offer advantages in oral transepithelial transport, the creation of non-spherical organic-based particles is generally limited by the lack of universal technical conditions and methods26,166. In addition to the above essential factors, various nanoparticle carrier materials with different performances and advantages must be considered when designing drug delivery systems. These materials may include polymer nanoparticles, liposomes, metal nanoparticles, etc. They have different biocompatibility, stability and drug release characteristics, and the most suitable carrier material needs to be selected according to the specific application. Some researchers have developed aspheric organic nanoparticles using PLGA or liposomes, but their post-administration shape requires further study due to potential expansion or deformation29,284,285. The safety of non-spherical nanoparticles in drug delivery systems still requires further observation and investigation, despite the gradual application of 3D printing technology. Moreover, nanoparticles should possess the ability to facilitate efficient drug release. This can be accomplished by employing materials with appropriate holistic properties, including particle size and shape, which enable the controlled release of the drug at the desired rate and location. The development of nanoparticles with distinct characteristics and advantages should be based on the clinical requirements.

5 Summaries and perspectives

Intestinal epithelial cells, as the primary constituent of the intestinal mucosa, possess a substantial theoretical absorption surface area. However, achieving effective transportation of particles across these cells remains challenging, resulting in limited absorption of conventional oral nanoparticles. Various strategies have been explored to enhance transepithelial transport of nanoparticles in intestinal epithelial cells while considering safety concerns. For instance, the material of nanoparticles is generally selected based on their biocompatibility and biodegradability to mitigate potential toxicity risks. Additionally, ligand modification and property modulation can be utilized to enhance transepithelial transport through specific pathways without interfering with the normal function of epithelial cells. Compared to the paracellular pathway that facilitates opening tight junctions but lacks selectivity in promoting substance absorption, we believe that the trans-epithelial pathway holds greater significance as a transport route for enhancing oral delivery of nanoparticles. Thereby, finding appropriate strategies to enhance the transepithelial transport efficiency of drug delivery systems holds potential for clinical translation of oral nanoparticles in the future.

Research has demonstrated that manipulating the surface properties of nanoparticles, such as ligand modification, surface charge, hydrophilicity/hydrophobicity, and regulating holistic properties including size, shape, and rigidity can facilitate the transepithelial transport of nanoparticles (Table 312,26,29,41,42,125,126,128, 129, 130,134, 135, 136,142,144,162,164,165,174). Based on studies on oral nanoparticles and their properties (Fig. 6), we have summarized some common conclusions. For example, small molecule ligands seem to be better suitable for oral drug delivery systems than peptide and protein ligands, due to the potential disruptions caused by the harsh pH environment and digestive enzymes in the gastrointestinal tract. Moreover, small molecular ligands such as fatty acids, glucose, and bile acids are more cost-effective and easily obtainable while aligning with the natural absorption pathway of nutrient molecules for mediating transepithelial transport, thus having better in vivo safety. The particle size of nanoparticles has been previously confirmed to have an inverse relationship with mucus entrapment, as smaller particles exhibit enhanced cellular uptake and transepithelial transport efficiency. While the choice of nanocarrier materials may vary, maintaining a particle size within the range of 50–200 nm is advantageous for oral delivery. Moreover, the impact of nanoparticle shape on oral delivery is also summarized. In comparison to conventional spherical nanoparticles, non-spherical rod-shaped nanoparticles demonstrate simultaneous enhancements in mucus penetration, cellular uptake, and transepithelial transport. However, the preparation of non-spherical nanoparticles often entails greater complexity than their spherical counterparts.Table 3 Properties that influence the transepithelial transport of nanoparticles.

Table 3Property	Classification	Effect	Ref.	
Ligands	The information can be found in Table 1	
Surface charge	Positive charge	The positively charged nanoparticles are mainly transported through the clathrin-mediated endocytosis pathway and are more prone to bypass the endo-lysosomal pathway	12,128, 129, 130	
Negative charge	The negatively charged nanoparticles are mainly the caveolin-mediated pathway and show enhanced transepithelial transport efficiency	128	
Electric neutrality	The electrically neutral nanoparticles are more proper to overcome the mucus barrier	125	
Hydrophilicity
/hydrophobicity	Hydrophilicity	The hydrophilic nanoparticles were more easily penetrated the mucus layer	126	
Hydrophobicity	The hydrophobic nanoparticles were more efficiently exocytosis from the basolateral side and were more likely to transport by the M cell-associated pathway	134, 135, 136	
Protein corona	Mucin-protein corona	The mucin-protein corona facilitated the exocytosis of nanoparticles from the apical side of cells into the intestinal lumen, while impeding their exocytosis from the basolateral side and subsequent entry into the bloodstream	142	
Intestinal protein corona	The disease-specific IPCs can modulate intracellular transport of NPs through early endosome, recycling endosome, and endoplasmic reticulum-Golgi apparatus pathways while increasing basolateral exocytosis and facilitating transepithelial transport	144	
Size	<50 nm	The nanoparticles within the size range of 50–200 nm may be more advantageous for enhancing their cellular uptake and transepithelial transport
Nanoparticles ranging from 55 to 1100 nm showed improved retention within Peyer's patches compared to nanoparticles with smaller size	26,41,42,162	
50–200 nm	
200–1100 nm	
Shape	Rod-shaped	The efficiency of cellular uptake for nanoparticles is in the order of rod-shaped > disc-shaped > spherical
The rod-shaped nanoparticles are more easily taken up by cells through preferential transportation via the endoplasmic reticulum-Golgi apparatus pathway, thus they are more likely to be transported across intestinal epithelial cell layers	26,164,165	
Disc-shaped	
Spherical	
Rigidity	Soft	The soft NPs with lower rigidity were more likely to be trapped in lysosomes, leading to lower exocytosis efficiency	174	
Moderate	The nanoparticles with moderate rigidity exhibit enhanced deformability and possess superior mucosal penetration capability	29	
Hard	The hard NPs with higher rigidity tended to be transported through exocytosis-related pathways such as the endoplasmic reticulum, Golgi apparatus, microtubules, and caveolae, thus showing higher exocytosis efficiency	174	
Materials	The information can be found in Table 2	

Figure 6 Overview of the surface and holistic properties that influence the transepithelial transport of nanoparticles. Made using BioRender.

Figure 6

When selecting materials for oral nanoparticles, it is crucial to consider the specific drugs being delivered. Lipid-based materials are biocompatible and possess the ability to enhance oral absorption, rendering them suitable for delivering a wide range of drugs orally. In cases where controlled drug release is required, polymer-based materials such as PLGA and chitosan can be considered to modulate the release behavior of drug-loaded nanoparticles by adjusting the composition or proportion of polymers accordingly. Furthermore, if there is a need for enhanced drug loading capacity within the delivery systems, biodegradable inorganic materials like mesoporous silicon and mesoporous carbon can be employed due to their porous structure.

Although numerous studies have explored strategies to improve the transepithelial transport of nano-drug delivery systems from the perspective of surface and holistic properties, they are almost limited to achieving certain improvements in animal models (mostly rodent models)16. However, the translation of oral nano-formulation from basic research to clinical practice remains challenging. Recently registered clinical trials involving orally administrated nanoparticles showed that the lipid-based nanoparticles account for a large proportion, such as liposomes (NCT03530436, NCT02278822, NCT03719326), nanolipospheres (NCT03877991, NCT01893424), lipid crystal nanoparticles (NCT02971007, NCT02629419), and phospholipid nanoemulsions (NCT05742022). Other types of nanoparticles include polymer-based nanoparticles for ethylcellulose-based polymeric nanoparticles (NCT03774680), protein-based nanoparticles for albumin-stabilized nanoparticles (NCT00313599), and inorganic nanoparticles for silica nanoparticles (NCT01772251), silver nanoparticles (NCT04978025) as well as gold nanoparticles (NCT05347602)1. When selecting nanocarriers for drug delivery systems, organic materials with good biocompatibility are preferred. Among them, lipid-based materials are particularly favored due to their advantages of easy availability, large-scale production capability, and good safety profile. Additionally, the clinical translation of nanoparticles will be greatly limited by the requirement for excessive additional materials or more complex manufacturing processes to achieve the ideal surface and holistic properties (such as charge, hydrophilicity, particle size, and rigidity). Therefore, it is crucial to take into account the design of oral drug delivery systems from an economic and production perspective right from the beginning.

Furthermore, it is evident that the ligand-modified nanoparticles for oral delivery have hardly progressed to the clinical trial stage. We speculate that this may be attributed to species variations between animals and humans including differences in the small intestinal absorption area, the length and proportion of small intestinal segments (duodenum, jejunum and ileum), and the expressions of intestinal receptors and transporters286,287. Among these factors, discrepancies in receptor and transporter expressions of intestinal mucosa may play a more crucial role in the clinical translation of ligand-modified nanoparticles. For instance, for intestine peptide transporters and glucose transporters, human HPET1 and SGLT1 expression is higher than that of mice, but PEPT1, GLUT1 and GLUT5 expression is lower than that of rat287. The activity of human apical sodium-dependent bile acid transporter (ASBT) is higher than that of rat159. Consequently, for targeting receptors or transporters with lower expression in humans, ligand modification may not achieve the desired effect in humans. Therefore, in the development of ligands for oral delivery, it is crucial to consider specific subtypes of intestinal receptors or transporters and prioritize targets with higher expression levels in humans. At the same time, employing more animal models that are closer to human beings, rather than just rodent models, can more accurately evaluate the effectiveness of the nanoparticles and their potential for clinical translation.

Due to variations in preparation processes, material compositions, and therapeutic drugs employed, these approaches for property modulation may not be universally applicable. Therefore, it is imperative to select suitable strategies based on nanoparticle characteristics and the intended destination for drug delivery. Additionally, several unresolved issues persist: (1) Does a synergistic promotion or mutual inhibition effect exist between surface properties and holistic properties on nanoparticle transepithelial transport? (2) Which specific nanoparticle properties are considered significant contributors? (3) Are there any other influential factors governing nanoparticle transepithelial transport? Furthermore, in addition to commonly used in vitro models like epithelial cell monolayers, it is crucial to employ multiple appropriate in vivo models collectively to investigate the process, effectiveness, and mechanisms underlying oral drug delivery.

Author contributions

Yaxian Zheng: Conceptualization, Funding acquisition, Project administration, Resources, Validation, Visualization, Writing – original draft, Writing – review & editing, Data curation. Shiqin Luo: Conceptualization, Resources, Validation, Visualization, Writing – original draft, Writing – review & editing, Data curation. Min Xu: Validation, Visualization, Writing – original draft, Writing – review & editing. Qin He: Validation, Visualization, Writing – original draft, Writing – review & editing. Jiang Xie: Validation, Visualization, Writing – original draft, Writing – review & editing. Jiawei Wu: Conceptualization, Data curation, Project administration, Validation, Visualization, Writing – original draft, Writing – review & editing. Yuan Huang: Conceptualization, Funding acquisition, Investigation, Project administration, Validation, Writing – original draft, Writing – review & editing.

Conflicts of interest

The authors declare no conflict of interest.

Acknowledgments

The authors acknowledge financial support from the 10.13039/501100001809 National Natural Science Foundation of China (82104069 ), the Regional Innovation and Development Joint Fund of the 10.13039/501100001809 National Natural Science Foundation of China (U22A20356 ), the Japan–China Sasakawa Medical Fellowship, Sichuan Science and Technology Department Project (2022089 ), Sichuan Medical Association Youth Innovation Research Project (Q20019 ), the Third People's Hospital of Chengdu Scientific Research Project (2023PI16) and Clinical Research Program (CSY-YN-01-2023-015).

Peer review under the responsibility of Chinese Pharmaceutical Association and Institute of Materia Medica, Chinese Academy of Medical Sciences.
==== Refs
References

1 Ejazi S.A. Louisthelmy R. Maisel K. Mechanisms of nanoparticle transport across intestinal tissue: an oral delivery perspective ACS Nano 17 2023 13044 13061 37410891
2 Zhang T. Li L. Chunta S. Wu W. Chen Z. Lu Y. Enhanced oral bioavailability from food protein nanoparticles: a mini review J Control Release 354 2023 146 154 36566844
3 Lei T. Yang Z. Jiang C. Wang X. Yang W. Yang X. Mannose-integrated nanoparticle hitchhike glucose transporter 1 recycling to overcome various barriers of oral delivery for alzheimer's disease therapy ACS Nano 18 2024 3234 3250 38214975
4 Chen C. Beloqui A. Xu Y. Oral nanomedicine biointeractions in the gastrointestinal tract in health and disease Adv Drug Deliv Rev 203 2023 115117
5 Niu Z. Conejos-Sánchez I. Griffin B.T. O'Driscoll C.M. Alonso M.J. Lipid-based nanocarriers for oral peptide delivery Adv Drug Deliv Rev 106 2016 337 354 27080735
6 Drucker D.J. Advances in oral peptide therapeutics Nat Rev Drug Discov 19 2020 277 289 31848464
7 Lundquist P. Artursson P. Oral absorption of peptides and nanoparticles across the human intestine: opportunities, limitations and studies in human tissues Adv Drug Deliv Rev 106 2016 256 276 27496705
8 Abramson A. Caffarel-Salvador E. Khang M. Dellal D. Silverstein D. Gao Y. An ingestible self-orienting system for oral delivery of macromolecules Science 363 2019 611 615 30733413
9 Murgia X. Loretz B. Hartwig O. Hittinger M. Lehr C.M. The role of mucus on drug transport and its potential to affect therapeutic outcomes Adv Drug Deliv Rev 124 2018 82 97 29106910
10 Jin Y. Song Y. Zhu X. Zhou D. Chen C. Zhang Z. Goblet cell-targeting nanoparticles for oral insulin delivery and the influence of mucus on insulin transport Biomaterials 33 2012 1573 1582 22093292
11 Shan W. Zhu X. Liu M. Li L. Zhong J. Sun W. Overcoming the diffusion barrier of mucus and absorption barrier of epithelium by self-assembled nanoparticles for oral delivery of insulin ACS nano 9 2015 2345 2356 25658958
12 Liu M. Zhang J. Zhu X. Shan W. Li L. Zhong J. Efficient mucus permeation and tight junction opening by dissociable “mucus-inert” agent coated trimethyl chitosan nanoparticles for oral insulin delivery J Control Release 222 2016 67 77 26686663
13 Van Der Flier L.G. Clevers H. Stem cells, self-renewal, and differentiation in the intestinal epithelium Annu Rev Physiol 71 2009 241 260 18808327
14 Yu M. Yang Y. Zhu C. Guo S. Gan Y. Advances in the transepithelial transport of nanoparticles Drug Discov Today 21 2016 1155 1161 27196527
15 Peterson L.W. Artis D. Intestinal epithelial cells: regulators of barrier function and immune homeostasis Nat Rev Immunol 14 2014 141 153 24566914
16 Kim K.S. Na K. Bae Y.H. Nanoparticle oral absorption and its clinical translational potential J Control Release 360 2023 149 162 37348679
17 Fan W. Xia D. Zhu Q. Hu L. Gan Y. Intracellular transport of nanocarriers across the intestinal epithelium Drug Discov Today 21 2016 856 863 27094490
18 Pridgen E.M. Alexis F. Kuo T.T. Levy-Nissenbaum E. Karnik R. Blumberg R.S. Transepithelial transport of Fc-targeted nanoparticles by the neonatal fc receptor for oral delivery Sci Transl Med 5 2013 213ra167-213ra167
19 Wang D. Jiang Q. Dong Z. Meng T. Hu F. Wang J. Nanocarriers transport across the gastrointestinal barriers: the contribution to oral bioavailability via blood circulation and lymphatic pathway Adv Drug Deliv Rev 203 2023 115130
20 Shi L. Zhang J. Zhao M. Tang S. Cheng X. Zhang W. Effects of polyethylene glycol on the surface of nanoparticles for targeted drug delivery Nanoscale 13 2021 10748 10764 34132312
21 Li S. Wang S. Yan B. Yue T. Surface properties of nanoparticles dictate their toxicity by regulating adsorption of humic acid molecules ACS Sustainable Chem Eng 9 2021 13705 13716
22 Xiao K. Li Y. Luo J. Lee J.S. Xiao W. Gonik A.M. The effect of surface charge on in vivo biodistribution of PEG-oligocholic acid based micellar nanoparticles Biomaterials 32 2011 3435 3446 21295849
23 Yun Y. Cho Y.W. Park K. Nanoparticles for oral delivery: targeted nanoparticles with peptidic ligands for oral protein delivery Adv Drug Deliv Rev 65 2013 822 832 23123292
24 Zhang Y. Wang Y. Li X. Nie D. Liu C. Gan Y. Ligand-modified nanocarriers for oral drug delivery: challenges, rational design, and applications J Control Release 352 2022 813 832 36368493
25 Yu Y. Xing L. Li L. Wu J. He J. Huang Y. Coordination of rigidity modulation and targeting ligand modification on orally-delivered nanoparticles for the treatment of liver fibrosis J Control Release 341 2022 215 226 34822908
26 Banerjee A. Qi J. Gogoi R. Wong J. Mitragotri S. Role of nanoparticle size, shape and surface chemistry in oral drug delivery J Control Release 238 2016 176 185 27480450
27 Gupta R. Badhe Y. Mitragotri S. Rai B. Permeation of nanoparticles across the intestinal lipid membrane: dependence on shape and surface chemistry studied through molecular simulations Nanoscale 12 2020 6318 6333 32133467
28 Iriarte-Mesa C. Jobst M. Bergen J. Kiss E. Ryoo R. Kim J.C. Morphology-dependent interaction of silica nanoparticles with intestinal cells: connecting shape to barrier function Nano Lett 23 2023 7758 7766 37433061
29 Yu M. Xu L. Tian F. Su Q. Zheng N. Yang Y. Rapid transport of deformation-tuned nanoparticles across biological hydrogels and cellular barriers Nat Commun 9 2018 2607 29973592
30 Taverner A. Dondi R. Almansour K. Laurent F. Owens S.-E. Eggleston I.M. Enhanced paracellular transport of insulin can be achieved via transient induction of myosin light chain phosphorylation J Control Release 210 2015 189 197 25980620
31 Suzuki T. Regulation of intestinal epithelial permeability by tight junctions Cell Mol Life Sci 70 2013 631 659 22782113
32 Acosta E. Bioavailability of nanoparticles in nutrient and nutraceutical delivery Curr Opin Colloid Interf Sci 14 2009 3 15
33 Teshima C.W. Meddings J.B. The measurement and clinical significance of intestinal permeability Curr Gastroenterol Rep 10 2008 443 449 18799118
34 Sonaje K. Chuang E.Y. Lin K.J. Yen T.C. Su F.Y. Tseng M.T. Opening of epithelial tight junctions and enhancement of paracellular permeation by chitosan: microscopic, ultrastructural, and computed-tomographic observations Mol Pharmaceutics 9 2012 1271 1279
35 Yu S.H. Tang D.W. Hsieh H.Y. Wu W.S. Lin B.X. Chuang E.Y. Nanoparticle-induced tight-junction opening for the transport of an anti-angiogenic sulfated polysaccharide across Caco-2 cell monolayers Acta Biomater 9 2013 7449 7459 23583645
36 Lee M. Ni N. Tang H. Li Y. Wei W. Kakinen A. A framework of paracellular transport via nanoparticles-induced endothelial leakiness Adv Sci 8 2021 e2102519
37 Brayden D.J. Jepson M.A. Baird A.W. Keynote review: intestinal Peyer's patch M cells and oral vaccine targeting Drug Discov Today 10 2005 1145 1157 16182207
38 Azevedo C. Nilsen J. Grevys A. Nunes R. Andersen J.T. Sarmento B. Engineered albumin-functionalized nanoparticles for improved FcRn binding enhance oral delivery of insulin J Control Release 327 2020 161 173 32771477
39 Zhu Q. Chen Z. Paul P.K. Lu Y. Wu W. Qi J. Oral delivery of proteins and peptides: challenges, status quo and future perspectives Acta Pharm Sin B 11 2021 2416 2448 34522593
40 Lopes M.A. Abrahim B.A. Cabral L.M. Rodrigues C.R. Seiça R.M.F. de Baptista Veiga F.J. Intestinal absorption of insulin nanoparticles: contribution of M cells Nanomed Nanotechnol Biol Med 10 2014 1139 1151
41 Brayden D.J. Baird A.W. Microparticle vaccine approaches to stimulate mucosal immunisation Microbes Infect 3 2001 867 876 11580982
42 Shen C. Yang Y. Shen B. Xie Y. Qi J. Dong X. Self-discriminating fluorescent hybrid nanocrystals: efficient and accurate tracking of translocation via oral delivery Nanoscale 10 2017 436 450 29227499
43 Xie Y. Shi B. Xia F. Qi J. Dong X. Zhao W. Epithelia transmembrane transport of orally administered ultrafine drug particles evidenced by environment sensitive fluorophores in cellular and animal studies J Control Release 270 2018 65 75 29196044
44 Islam M.A. Firdous J. Badruddoza A.Z.M. Reesor E. Azad M. Hasan A. M cell targeting engineered biomaterials for effective vaccination Biomaterials 192 2019 75 94 30439573
45 Delon L. Gibson R.J. Prestidge C.A. Thierry B. Mechanisms of uptake and transport of particulate formulations in the small intestine J Control Release 343 2022 584 599 35149142
46 Hillery A.M. Jani P.U. Florence A.T. Comparative, quantitative study of lymphoid and non-lymphoid uptake of 60 nm polystyrene particles J Drug Target 2 1994 151 156 8069593
47 Hodges G.M. Carr E.A. Hazzard R.A. O'Reilly C. Carr K.E. A commentary on morphological and quantitative aspects of microparticle translocation across the gastrointestinal mucosa J Drug Target 3 1995 57 60 7655821
48 He Y. Huang Y. Xu H. Yang X. Liu N. Xu Y. Aptamer-modified M cell targeting liposomes for oral delivery of macromolecules Colloids Surf B Biointerfaces 222 2023 113109
49 Nosrati H. Aramideh Khouy R. Nosrati A. Khodaei M. Banitalebi-Dehkordi M. Ashrafi-Dehkordi K. Nanocomposite scaffolds for accelerating chronic wound healing by enhancing angiogenesis J Nanobiotechnology 19 2021 1 33397416
50 Luo H. Zhang Y. Chi C. Wang T. Chen L. Li X. Starch nanocarriers for enhanced M-cell transport and oral delivery of bioactive proteins ACS Appl Nano Mater 6 2023 4793 4802
51 Pandya P. Giram P. Bhole R.P. Chang H.I. Raut S.Y. Nanocarriers based oral lymphatic drug targeting: strategic bioavailability enhancement approaches J Drug Deliv Sci Technol 64 2021 102585
52 Amin M.K. Boateng J. Surface functionalization of PLGA nanoparticles for potential oral vaccine delivery targeting intestinal immune cells Colloids Surf B Biointerfaces 222 2023 113121
53 Hirai T. Ikeda K. Tsushima H. Fujishiro M. Hayakawa K. Yoshida Y. Circulating plasma microRNA profiling in patients with polymyositis/dermatomyositis before and after treatment: miRNA may be associated with polymyositis/dermatomyositis Inflamm Regen 38 2018 1 29321815
54 Tuma P. Hubbard A.L. Transcytosis: crossing cellular barriers Physiol Rev 83 2003 871 932 12843411
55 Foroozandeh P. Aziz A.A. Insight into cellular uptake and intracellular trafficking of nanoparticles Nanoscale Res Lett 13 2018 339 30361809
56 Neves A.R. Queiroz J.F. Costa Lima S.A. Figueiredo F. Fernandes R. Reis S. Cellular uptake and transcytosis of lipid-based nanoparticles across the intestinal barrier: relevance for oral drug delivery J Colloid Interf Sci 463 2016 258 265
57 Du X.J. Wang J.L. Iqbal S. Li H.J. Cao Z.T. Wang Y.C. The effect of surface charge on oral absorption of polymeric nanoparticles Biomater Sci 6 2018 642 650 29412203
58 Xu Y. Zheng Y. Wu L. Zhu X. Zhang Z. Huang Y. Novel solid lipid nanoparticle with endosomal escape function for oral delivery of insulin ACS Appl Mater Inter 10 2018 9315 9324
59 Fan W. Xia D. Zhu Q. Li X. He S. Zhu C. Functional nanoparticles exploit the bile acid pathway to overcome multiple barriers of the intestinal epithelium for oral insulin delivery Biomaterials 151 2018 13 23 29055774
60 Grant B.D. Donaldson J.G. Pathways and mechanisms of endocytic recycling Nat Rev Mol Cel Biol 10 2009 597 608
61 Yang D. Liu D. Deng H. Zhang J. Qin M. Yuan L. Transferrin functionization elevates transcytosis of nanogranules across epithelium by triggering polarity-associated transport flow and positive cellular feedback loop ACS Nano 13 2019 5058 5076 31034211
62 Cui Y. Shan W. Zhou R. Liu M. Wu L. Guo Q. The combination of endolysosomal escape and basolateral stimulation to overcome the difficulties of "easy uptake hard transcytosis" of ligand-modified nanoparticles in oral drug delivery Nanoscale 10 2018 1494 1507 29303184
63 Qi J. Zhuang J. Lu Y. Dong X. Zhao W. Wu W. In vivo fate of lipid-based nanoparticles Drug Discov Today 22 2017 166 172 27713035
64 Zheng Y. Wu J. Shan W. Wu L. Zhou R. Liu M. Multifunctional nanoparticles enable efficient oral delivery of biomacromolecules via improving payload stability and regulating the transcytosis pathway ACS Appl Mater Inter 10 2018 34039 34049
65 Patel S. Ashwanikumar N. Robinson E. DuRoss A. Sun C. Murphy-Benenato K.E. Boosting intracellular delivery of lipid nanoparticle-encapsulated mRNA Nano Lett 17 2017 5711 5718 28836442
66 Zhang M. Xu N. Xu W. Ling G. Zhang P. Potential therapies and diagnosis based on Golgi-targeted nano drug delivery systems Pharmacol Res 175 2022 105861
67 Kristensen M. Nielsen H.M. Cell-penetrating peptides as carriers for oral delivery of biopharmaceuticals Basic Clin Pharmacol Toxicol 118 2016 99 106 26525297
68 Liu X. Wu R. Li Y. Wang L. Zhou R. Li L. Angiopep-2-functionalized nanoparticles enhance transport of protein drugs across intestinal epithelia by self-regulation of targeted receptors Biomater Sci 9 2021 2903 2916 33599658
69 Wong C.Y. Al-Salami H. Dass C.R. Cellular assays and applied technologies for characterisation of orally administered protein nanoparticles: a systematic review J Drug Target 28 2020 585 599 32013626
70 Yu Y. Wu Z. Wu J. Shen X. Wu R. Zhou M. Investigation of FcRn-mediated transepithelial mechanisms for oral nanoparticle delivery systems Adv Ther 4 2021 2100145
71 Li J. Zhang Y. Yu M. Wang A. Qiu Y. Fan W. The upregulated intestinal folate transporters direct the uptake of ligand-modified nanoparticles for enhanced oral insulin delivery Acta Pharm Sin B 12 2022 1460 1472 35530154
72 Wu L. Bai Y. Wang L. Liu X. Zhou R. Li L. Promoting apical-to-basolateral unidirectional transport of nanoformulations by manipulating the nutrient-absorption pathway J Control Release 323 2020 151 160 32277961
73 Beilstein F. Carrière V. Leturque A. Demignot S. Characteristics and functions of lipid droplets and associated proteins in enterocytes Exp Cel Res 340 2016 172 179
74 Zhang Z. Lu Y. Qi J. Wu W. An update on oral drug delivery via intestinal lymphatic transport Acta Pharm Sin B 11 2021 2449 2468 34522594
75 Mu H. Høy C.E. The digestion of dietary triacylglycerols Prog Lipid Res 43 2004 105 133 14654090
76 Imada C. Takahashi T. Kuramoto M. Masuda K. Ogawara K. Sato A. Improvement of oral bioavailability of n-251, a novel antimalarial drug, by increasing lymphatic transport with long-chain fatty acid-based self-nanoemulsifying drug delivery system Pharm Res (N Y) 32 2015 2595 2608
77 Caliph S.M. Charman W.N. Porter C.J. Effect of short-, medium-, and long-chain fatty acid-based vehicles on the absolute oral bioavailability and intestinal lymphatic transport of halofantrine and assessment of mass balance in lymph-cannulated and non-cannulated rats J Pharm Sci 89 2000 1073 1084 10906731
78 Kim K.S. Suzuki K. Cho H. Youn Y.S. Bae Y.H. Oral nanoparticles exhibit specific high-efficiency intestinal uptake and lymphatic transport ACS Nano 12 2018 8893 8900 30088412
79 Spleis H. Sandmeier M. Claus V. Bernkop-Schnürch A. Surface design of nanocarriers: key to more efficient oral drug delivery systems Adv Colloid Interf Sci 313 2023 102848
80 Zhang T. Zhu G. Lu B. Qian Z. Peng Q. Protein corona formed in the gastrointestinal tract and its impacts on oral delivery of nanoparticles Med Res Rev 41 2021 1835 1850
81 Ezpeleta I. Arangoa M.A. Irache J.M. Stainmesse S. Chabenat C. Popineau Y. Preparation of Ulex europaeus lectin-gliadin nanoparticle conjugates and their interaction with gastrointestinal mucus Int J Pharm 191 1999 25 32 10556737
82 Pridgen E.M. Alexis F. Farokhzad O.C. Polymeric nanoparticle technologies for oral drug delivery Clin Gastroenterol Hepatol 12 2014 1605 1610 24981782
83 Du W. Fan Y. Zheng N. He B. Yuan L. Zhang H. Transferrin receptor specific nanocarriers conjugated with functional 7peptide for oral drug delivery Biomaterials 34 2013 794 806 23103156
84 Song X. Li R. Deng H. Li Y. Cui Y. Zhang H. Receptor mediated transcytosis in biological barrier: the influence of receptor character and their ligand density on the transmembrane pathway of active-targeting nanocarriers Biomaterials 180 2018 78 90 30025247
85 Yang T. Wang A. Nie D. Fan W. Jiang X. Yu M. Ligand-switchable nanoparticles resembling viral surface for sequential drug delivery and improved oral insulin therapy Nat Commun 13 2022 6649 36333321
86 Zhang P. Xu Y. Zhu X. Huang Y. Goblet cell targeting nanoparticle containing drug-loaded micelle cores for oral delivery of insulin Int J Pharm 496 2015 993 1005 26541299
87 Zhu X. Wu J. Shan W. Tao W. Zhao L. Lim J.M. Polymeric nanoparticles amenable to simultaneous installation of exterior targeting and interior therapeutic proteins Angew Chem 128 2016 3370 3373
88 Xia D. Tao J. He Y. Zhu Q. Chen D. Yu M. Enhanced transport of nanocage stabilized pure nanodrug across intestinal epithelial barrier mimicking Listeria monocytogenes Biomaterials 37 2015 320 332 25453961
89 Gao X. Wang T. Wu B. Chen J. Chen J. Yue Y. Quantum dots for tracking cellular transport of lectin-functionalized nanoparticles Biochem Biophys Res Commun 377 2008 35 40 18823949
90 Martins J.P. Liu D. Fontana F. Ferreira M.P.A. Correia A. Valentino S. Microfluidic nanoassembly of bioengineered chitosan-modified Fcrn-targeted porous silicon nanoparticles @ hypromellose acetate succinate for oral delivery of antidiabetic peptides ACS Appl Mater Inter 10 2018 44354 44367
91 Martins J.P. D'Auria R. Liu D. Fontana F. Ferreira M.P.A. Correia A. Engineered multifunctional albumin-decorated porous silicon nanoparticles for fcrn translocation of insulin Small 14 2018 e1800462
92 Wu L. Liu M. Shan W. Zhu X. Li L. Zhang Z. Bioinspired butyrate-functionalized nanovehicles for targeted oral delivery of biomacromolecular drugs J Control Release 262 2017 273 283 28774842
93 Wu R. Wu Z. Xing L. Liu X. Wu L. Zhou Z. Mimicking natural cholesterol assimilation to elevate the oral delivery of liraglutide for type II diabetes therapy Asian J Pharm Sci 17 2022 653 665 36382301
94 Sajjad M. Khan M.I. Naveed S. Ijaz S. Qureshi O.S. Raza S.A. Folate-functionalized thiomeric nanoparticles for enhanced docetaxel cytotoxicity and improved oral bioavailability AAPS PharmSciTech 20 2019 81 30645705
95 Liu Y. Jiang Z. Hou X. Xie X. Shi J. Shen J. Functional lipid polymeric nanoparticles for oral drug delivery: rapid mucus penetration and improved cell entry and cellular transport Nanomedicine 21 2019 102075
96 Roberts M.S. Magnusson B.M. Burczynski F.J. Weiss M. Enterohepatic circulation: physiological, pharmacokinetic and clinical implications Clin Pharmacokinet 41 2002 751 790 12162761
97 Deng F. Bae Y.H. Bile acid transporter-mediated oral drug delivery J Control Release 327 2020 100 116 32711025
98 Deng F. Kim K.S. Moon J. Bae Y.H. Bile acid conjugation on solid nanoparticles enhances asbt-mediated endocytosis and chylomicron pathway but weakens the transcytosis by inducing transport flow in a cellular negative feedback loop Adv Sci 9 2022 2201414
99 Lee J.S. Han P. Chaudhury R. Khan S. Bickerton S. McHugh M.D. Metabolic and immunomodulatory control of type 1 diabetes via orally delivered bile-acid-polymer nanocarriers of insulin or rapamycin Nat Biomed Eng 5 2021 983 997 34616050
100 Kang S.K. Woo J.H. Kim M.K. Woo S.S. Choi J.H. Lee H.G. Identification of a peptide sequence that improves transport of macromolecules across the intestinal mucosal barrier targeting goblet cells J Biotechnol 135 2008 210 216 18440083
101 Chen G. Svirskis D. Lu W. Ying M. Huang Y. Wen J. N-trimethyl chitosan nanoparticles and CSKSSDYQC peptide: N-trimethyl chitosan conjugates enhance the oral bioavailability of gemcitabine to treat breast cancer J Control Release 277 2018 142 153 29548985
102 Choi C.H.J. Alabi C.A. Webster P. Davis M.E. Mechanism of active targeting in solid tumors with transferrin-containing gold nanoparticles Proc Natl Acad Sci U S A 107 2010 1235 1240 20080552
103 Clark A.J. Davis M.E. Increased brain uptake of targeted nanoparticles by adding an acid-cleavable linkage between transferrin and the nanoparticle core Proc Natl Acad Sci U S A 112 2015 12486 12491 26392563
104 Ulbrich K. Hekmatara T. Herbert E. Kreuter J. Transferrin-and transferrin-receptor-antibody-modified nanoparticles enable drug delivery across the blood–brain barrier (BBB) Eur J Pharm Biopharm 71 2009 251 256 18805484
105 Hameedat F. Pizarroso N.A. Teixeira N. Pinto S. Sarmento B. Functionalized FcRn-targeted nanosystems for oral drug delivery: a new approach to colorectal cancer treatment Eur J Pharm Sci 2022 106259
106 Hashem L. Swedrowska M. Vllasaliu D. Intestinal uptake and transport of albumin nanoparticles: potential for oral delivery Nanomedicine 13 2018 1255 1265 29949465
107 Sarrazin S. Lamanna W.C. Esko J.D. Heparan sulfate proteoglycans Cold Spring Harb Perspect Biol 3 2011 a004952 21690215
108 Pelkmans L. Bürli T. Zerial M. Helenius A. Caveolin-stabilized membrane domains as multifunctional transport and sorting devices in endocytic membrane traffic Cell 118 2004 767 780 15369675
109 Pelkmans L. Secrets of caveolae-and lipid raft-mediated endocytosis revealed by mammalian viruses Biochim Biophys Acta 1746 2005 295 304 16126288
110 Li L. Ren C.H. Tahir S.A. Ren C. Thompson T.C. Caveolin-1 maintains activated akt in prostate cancer cells through scaffolding domain binding site interactions with andinhibition of serine/threonine protein phosphatases PP1 and PP2A Mol Cel Biol 23 2003 9389 9404
111 Wang Z. Tiruppathi C. Cho J. Minshall R.D. Malik A.B. Delivery of nanoparticle-complexed drugs across the vascular endothelial barrier via caveolae IUBMB life 63 2011 659 667 21766412
112 Kiela P.R. Ghishan F.K. Physiology of intestinal absorption and secretion Best Pract Res Clin Gastroenterol 30 2016 145 159 27086882
113 Caspary W.F. Physiology and pathophysiology of intestinal absorption Am J Clin Nutr 55 1992 299S 308S 1728844
114 Dyer J. Hosie K.B. Shirazi-Beechey S.P. Nutrient regulation of human intestinal sugar transporter (SGLT1) expression Gut 41 1997 56 59 9274472
115 Ferraris R.P. Diamond J.M. Specific regulation of intestinal nutrient transporters by their dietary substrates Annu Rev Physiol 51 1989 125 141 2653177
116 Hadjiagapiou C. Schmidt L. Dudeja P.K. Layden T.J. Ramaswamy K. Mechanism (s) of butyrate transport in Caco-2 cells: role of monocarboxylate transporter 1 Am J Physiol Gastrointest Liver Physiol 279 2000 G775 G780 11005765
117 Hui D.Y. Howles P.N. Molecular mechanisms of cholesterol absorption and transport in the intestine Semin Cel Dev Biol 16 2005 182 192
118 Dawson P.A. Role of the intestinal bile acid transporters in bile acid and drug disposition Handb Exp Pharmacol 201 2011 169 203
119 Wu L. Bai Y. Liu M. Li L. Shan W. Zhang Z. Transport mechanisms of butyrate modified nanoparticles: insight into “easy entry, hard transcytosis” of active targeting system in oral administration Mol Pharmaceutics 15 2018 4273 4283
120 Zwicker B.L. Agellon L.B. Transport and biological activities of bile acids Int J Biochem Cel Biol 45 2013 1389 1398
121 Abstiens K. Gregoritza M. Goepferich A.M. Ligand density and linker length are critical factors for multivalent nanoparticle–receptor interactions ACS Appl Mater Inter 11 2018 1311 1320
122 Elias D.R. Poloukhtine A. Popik V. Tsourkas A. Effect of ligand density, receptor density, and nanoparticle size on cell targeting Nanomedicine 9 2013 194 201 22687896
123 Honary S. Zahir F. Effect of zeta potential on the properties of nano-drug delivery systems-a review (Part 1) Trop J Pharm Res 12 2013 255 264
124 Tang B.C. Dawson M. Lai S.K. Wang Y.Y. Suk J.S. Yang M. Biodegradable polymer nanoparticles that rapidly penetrate the human mucus barrier Proc Natl Acad Sci U S A 106 2009 19268 19273 19901335
125 Wang Y.Y. Lai S.K. Suk J.S. Pace A. Cone R. Hanes J. Addressing the PEG mucoadhesivity paradox to engineer nanoparticles that “slip” through the human mucus barrier Angew Chem 120 2008 9872 9875
126 Lai S.K. Wang Y.Y. Hanes J. Mucus-penetrating nanoparticles for drug and gene delivery to mucosal tissues Adv Drug Deliv Rev 61 2009 158 171 19133304
127 Wu J. Zheng Y. Liu M. Shan W. Zhang Z. Huang Y. Biomimetic viruslike and charge reversible nanoparticles to sequentially overcome mucus and epithelial barriers for oral insulin delivery ACS Appl Mater Inter 10 2018 9916 9928
128 Bannunah A.M. Vllasaliu D. Lord J. Stolnik S. Mechanisms of nanoparticle internalization and transport across an intestinal epithelial cell model: effect of size and surface charge Mol Pharmaceutics 11 2014 4363 4373
129 Fröhlich E. The role of surface charge in cellular uptake and cytotoxicity of medical nanoparticles Int J Nanomed 2012 5577 5591
130 Harush-Frenkel O. Rozentur E. Benita S. Altschuler Y. Surface charge of nanoparticles determines their endocytic and transcytotic pathway in polarized MDCK cells Biomacromolecules 9 2008 435 443 18189360
131 Florence A.T. Hillery A.M. Hussain N. Jani P.U. Nanoparticles as carriers for oral peptide absorption: studies on particle uptake and fate J Control Release 36 1995 39 46
132 Cui Y. Shan W. Liu M. Wu L. Huang Y. A strategy for developing effective orally-delivered nanoparticles through modulation of the surface "hydrophilicity/hydrophobicity balance" J Mater Chem B 5 2017 1302 1314 32263598
133 Qiao R. Roberts A.P. Mount A.S. Klaine S.J. Ke P.C. Translocation of C60 and its derivatives across a lipid bilayer Nano Lett 7 2007 614 619 17316055
134 Li Y. Chen X. Gu N. Computational investigation of interaction between nanoparticles and membranes: hydrophobic/hydrophilic effect J Phys Chem B 112 2008 16647 16653 19032046
135 Garinot M. Fiévez V. Pourcelle V. Stoffelbach F. des Rieux A. Plapied L. PEGylated PLGA-based nanoparticles targeting M cells for oral vaccination J Control Release 120 2007 195 204 17586081
136 des Rieux A. Fievez V. Garinot M. Schneider Y.-J. Préat V. Nanoparticles as potential oral delivery systems of proteins and vaccines: a mechanistic approach J Control Release 116 2006 1 27 17050027
137 Cao S.J. Xu S. Wang H.M. Ling Y. Dong J. Xia R.D. Nanoparticles: oral delivery for protein and peptide drugs AAPS PharmSciTech 20 2019 190 31111296
138 Docter D. Westmeier D. Markiewicz M. Stolte S. Knauer S.K. Stauber R.H. The nanoparticle biomolecule corona: lessons learned‒challenge accepted? Chem Soc Rev 44 2015 6094 6121 26065524
139 Nguyen V.H. Lee B.-J. Protein corona: a new approach for nanomedicine design Int J Nanomed 2017 3137 3151
140 Ke P.C. Lin S. Parak W.J. Davis T.P. Caruso F. A decade of the protein corona ACS nano 11 2017 11773 11776 29206030
141 Cao X. Han Y. Li F. Li Z. McClements D.J. He L. Impact of protein-nanoparticle interactions on gastrointestinal fate of ingested nanoparticles: not just simple protein corona effects NanoImpact 13 2019 37 43
142 Yang D. Liu D. Qin M. Chen B. Song S. Dai W. Intestinal mucin induces more endocytosis but less transcytosis of nanoparticles across enterocytes by triggering nanoclustering and strengthening the retrograde pathway ACS Appl Mater Inter 10 2018 11443 11456
143 Yang D. Feng Y. Yuan Y. Zhang L. Zhou Y. Midgley A.C. Protein coronas derived from mucus act as both spear and shield to regulate transferrin functionalized nanoparticle transcellular transport in enterocytes ACS Nano 18 2024 7455 7472 38417159
144 Wu J. Xing L. Zheng Y. Yu Y. Wu R. Liu X. Disease-specific protein corona formed in pathological intestine enhances the oral absorption of nanoparticles Acta Pharm Sin B 13 2023 3876 3891 37719377
145 Salvati A. Pitek A.S. Monopoli M.P. Prapainop K. Bombelli F.B. Hristov D.R. Transferrin-functionalized nanoparticles lose their targeting capabilities when a biomolecule corona adsorbs on the surface Nat Nanotechnol 8 2013 137 143 23334168
146 Xiao W. Wang Y. Zhang H. Liu Y. Xie R. He X. The protein corona hampers the transcytosis of transferrin-modified nanoparticles through blood-brain barrier and attenuates their targeting ability to brain tumor Biomaterials 274 2021 120888
147 Oh J.Y. Kim H.S. Palanikumar L. Go E.M. Jana B. Park S.A. Cloaking nanoparticles with protein corona shield for targeted drug delivery Nat Commun 9 2018 4548 30382085
148 Naidu P.S.R. Gavriel N. Gray C.G.G. Bartlett C.A. Toomey L.M. Kretzmann J.A. Elucidating the inability of functionalized nanoparticles to cross the blood‒brain barrier and target specific cells in vivo ACS Appl Mater Inter 11 2019 22085 22095
149 Le N.N. Steinbring C. Le-Vinh B. Jalil A. Matuszczak B. Bernkop-Schnürch A. Polyphosphate coatings: a promising strategy to overcome the polycation dilemma J Colloid Interf Sci 587 2021 279 289
150 Wang A. Yang T. Fan W. Yang Y. Zhu Q. Guo S. Protein corona liposomes achieve efficient oral insulin delivery by overcoming mucus and epithelial barriers Adv Healthc Mater 8 2019 e1801123
151 Wang Y. Pi C. Feng X. Hou Y. Zhao L. Wei Y. The influence of nanoparticle properties on oral bioavailability of drugs Int J Nanomedicine 15 2020 6295 6310 32943863
152 Zhao Z. Ukidve A. Krishnan V. Mitragotri S. Effect of physicochemical and surface properties on in vivo fate of drug nanocarriers Adv Drug Deliv Rev 143 2019 3 21 30639257
153 Toy R. Peiris P.M. Ghaghada K.B. Karathanasis E. Shaping cancer nanomedicine: the effect of particle shape on the in vivo journey of nanoparticles Nanomedicine 9 2014 121 134 24354814
154 Joudeh N. Linke D. Nanoparticle classification, physicochemical properties, characterization, and applications: a comprehensive review for biologists J Nanobiotechnology 20 2022 262 35672712
155 Yu Y. Tian Y. Zhang H. Jia Q. Chen X. Kang D. The evaluation of meloxicam nanocrystals by oral administration with different particle sizes Molecules 27 2022 421 35056734
156 Zhou X. Liu Y. Wang X. Li X. Xiao B. Effect of particle size on the cellular uptake and anti-inflammatory activity of oral nanotherapeutics Colloids Surf, B 187 2020 110880
157 Yao S. Chen N. Li M. Wang Q. Sun X. Feng X. Elucidating the particle size effect of andrographolide suspensions on their IVIVC performance in oral absorption Eur J Pharm Biopharm 179 2022 65 73 36058447
158 Jiang W. Kim B.Y. Rutka J.T. Chan W.C. Nanoparticle-mediated cellular response is size-dependent Nat Nanotechnol 3 2008 145 150 18654486
159 Li M. Vokral I. Evers B. de Graaf I.A.M. de Jager M.H. Groothuis G.M.M. Human and rat precision-cut intestinal slices as ex vivo models to study bile acid uptake by the apical sodium-dependent bile acid transporter Eur J Pharm Sci 121 2018 65 73 29751102
160 Zhang J. Field C.J. Vine D. Chen L. Intestinal uptake and transport of vitamin B12-loaded soy protein nanoparticles Pharm Res (N Y) 32 2015 1288 1303
161 Schübbe S. Schumann C. Cavelius C. Koch M. Müller T. Kraegeloh A. Size-dependent localization and quantitative evaluation of the intracellular migration of silica nanoparticles in Caco-2 cells Chem Mater 24 2012 914 923
162 Desai M.P. Labhasetwar V. Amidon G.L. Levy R.J. Gastrointestinal uptake of biodegradable microparticles: effect of particle size Pharm Res (N Y) 13 1996 1838 1845
163 Zhuang J. Wang D. Li D. Yang Y. Lu Y. Wu W. The influence of nanoparticle shape on bilateral exocytosis from Caco-2 cells Chin Chem Lett 29 2018 1815 1818
164 Yu M. Wang J. Yang Y. Zhu C. Su Q. Guo S. Rotation-facilitated rapid transport of nanorods in mucosal tissues Nano Lett 16 2016 7176 7182 27700115
165 Guo M. Wei M. Li W. Guo M. Guo C. Ma M. Impacts of particle shapes on the oral delivery of drug nanocrystals: mucus permeation, transepithelial transport and bioavailability J Control Release 307 2019 64 75 31207275
166 Yang Y. Nie D. Liu Y. Yu M. Gan Y. Advances in particle shape engineering for improved drug delivery Drug Discov Today 24 2019 575 583 30342244
167 Sun J. Zhang L. Wang J. Feng Q. Liu D. Yin Q. Tunable rigidity of (polymeric core)-(lipid shell) nanoparticles for regulated cellular uptake Adv Mater 27 2015 1402 1407 25529120
168 Gurnani P. Sanchez-Cano C. Probing the effect of rigidity on the cellular uptake of core‒shell nanoparticles: stiffness effects are size dependent Small 18 2022 e2203070
169 Hui Y. Yi X. Role of nanoparticle mechanical properties in cancer drug delivery ACS nano 13 2019 7410 7424 31287659
170 Anselmo A.C. Mitragotri S. Impact of particle elasticity on particle-based drug delivery systems Adv Drug Deliv Rev 108 2017 51 67 26806856
171 Yi X. Shi X. Gao H. Cellular uptake of elastic nanoparticles Phys Rev Lett 107 2011 098101
172 Mebius R.E. Kraal G. Structure and function of the spleen Nat Rev Immunol 5 2005 606 616 16056254
173 Yu M. Song W. Tian F. Dai Z. Zhu Q. Ahmad E. Temperature- and rigidity-mediated rapid transport of lipid nanovesicles in hydrogels Proc Natl Acad Sci U S A 116 2019 5362 5369 30837316
174 Zheng Y. Xing L. Chen L. Zhou R. Wu J. Zhu X. Tailored elasticity combined with biomimetic surface promotes nanoparticle transcytosis to overcome mucosal epithelial barrier Biomaterials 262 2020 120323
175 Daeihamed M. Dadashzadeh S. Haeri A. Akhlaghi M.F. Potential of liposomes for enhancement of oral drug absorption Curr Drug Deliv 14 2017 289 303 26768542
176 Roger E. Lagarce F. Garcion E. Benoit J.P. Biopharmaceutical parameters to consider in order to alter the fate of nanocarriers after oral delivery Nanomedicine 5 2010 287 306 20148639
177 Zhang L. Wang S. Zhang M. Sun J. Nanocarriers for oral drug delivery J Drug Target 21 2013 515 527 23621127
178 Deng B. Liu S. Wang Y. Ali B. Kong N. Xie T. Oral nanomedicine: challenges and opportunities Adv Mater 2023 e2306081
179 Cui J. Wen Z. Zhang W. Wu W. Recent advances in oral peptide or protein-based drug liposomes Pharmaceuticals 15 2022 1072 36145293
180 Beloqui A. des Rieux A. Preat V. Mechanisms of transport of polymeric and lipidic nanoparticles across the intestinal barrier Adv Drug Deliv Rev 106 2016 242 255 27117710
181 Chaves L.L. Costa Lima S.A. Vieira A.C.C. Barreiros L. Segundo M.A. Ferreira D. Development of PLGA nanoparticles loaded with clofazimine for oral delivery: assessment of formulation variables and intestinal permeability Eur J Pharm Sci 112 2018 28 37 29122712
182 Chen M.C. Mi F.L. Liao Z.X. Hsiao C.W. Sonaje K. Chung M.F. Recent advances in chitosan-based nanoparticles for oral delivery of macromolecules Adv Drug Deliv Rev 65 2013 865 879 23159541
183 Dreaden E.C. Alkilany A.M. Huang X. Murphy C.J. El-Sayed M.A. The golden age: gold nanoparticles for biomedicine Chem Soc Rev 41 2012 2740 2779 22109657
184 Kawish M. Elhissi A. Jabri T. Iqbal K.M. Zahid H. Shah M.R. Enhancement in oral absorption of ceftriaxone by highly functionalized magnetic iron oxide nanoparticles Pharmaceutics 12 2020 492 32481715
185 Wang T. Zhao P. Zhao Q. Wang B. Wang S. The mechanism for increasing the oral bioavailability of poorly water-soluble drugs using uniform mesoporous carbon spheres as a carrier Drug Deliv 23 2016 420 428 24870199
186 Han C. Huang H. Dong Y. Sui X. Jian B. Zhu W. A comparative study of the use of mesoporous carbon and mesoporous silica as drug carriers for oral delivery of the water-insoluble drug carvedilol Molecules 24 2019 1770 31067732
187 Gregoriadis G. Florence A.T. Liposomes in drug delivery. Clinical, diagnostic and ophthalmic potential Drugs 45 1993 15 28
188 Mallick S. Choi J.S. Liposomes: versatile and biocompatible nanovesicles for efficient biomolecules delivery J Nanosci Nanotechnol 14 2014 755 765 24730295
189 Kokkona M. Kallinteri P. Fatouros D. Antimisiaris S.G. Stability of SUV liposomes in the presence of cholate salts and pancreatic lipases: effect of lipid composition Eur J Pharm Sci 9 2000 245 252 10594380
190 Hu S. Niu M. Hu F. Lu Y. Qi J. Yin Z. Integrity and stability of oral liposomes containing bile salts studied in simulated and ex vivo gastrointestinal media Int J Pharm 441 2013 693 700 23089580
191 Hosny K.M. Ahmed O.A. Al-Abdali R.T. Enteric-coated alendronate sodium nanoliposomes: a novel formula to overcome barriers for the treatment of osteoporosis Expert Opin Drug Deliv 10 2013 741 746 23656470
192 Nguyen T.X. Huang L. Liu L. Elamin Abdalla A.M. Gauthier M. Yang G. Chitosan-coated nano-liposomes for the oral delivery of berberine hydrochloride J Mater Chem B 2 2014 7149 7159 32261793
193 Gradauer K. Dunnhaupt S. Vonach C. Szollosi H. Pali-Scholl I. Mangge H. Thiomer-coated liposomes harbor permeation enhancing and efflux pump inhibitory properties J Control Release 165 2013 207 215 23228848
194 Li C. Zhang Y. Su T. Feng L. Long Y. Chen Z. Silica-coated flexible liposomes as a nanohybrid delivery system for enhanced oral bioavailability of curcumin Int J Nanomedicine 7 2012 5995 6002 23233804
195 Liu W. Ye A. Liu W. Liu C. Han J. Singh H. Behaviour of liposomes loaded with bovine serum albumin during in vitro digestion Food Chem 175 2015 16 24 25577045
196 Klemetsrud T. Jonassen H. Hiorth M. Kjoniksen A.L. Smistad G. Studies on pectin-coated liposomes and their interaction with mucin Colloids Surf B Biointerfaces 103 2013 158 165 23201733
197 Barea M.J. Jenkins M.J. Gaber M.H. Bridson R.H. Evaluation of liposomes coated with a pH responsive polymer Int J Pharm 402 2010 89 94 20888403
198 Ezzat H.M. Elnaggar Y.S.R. Abdallah O.Y. Improved oral bioavailability of the anticancer drug catechin using chitosomes: design, in-vitro appraisal and in-vivo studies Int J Pharm 565 2019 488 498 31100382
199 Ling S.S. Magosso E. Khan N.A. Yuen K.H. Barker S.A. Enhanced oral bioavailability and intestinal lymphatic transport of a hydrophilic drug using liposomes Drug Dev Ind Pharm 32 2006 335 345 16556538
200 Roger E. Kalscheuer S. Kirtane A. Guru B.R. Grill A.E. Whittum-Hudson J. Folic acid functionalized nanoparticles for enhanced oral drug delivery Mol Pharm 9 2012 2103 2110 22670575
201 Zhu S. Chen S. Gao Y. Guo F. Li F. Xie B. Enhanced oral bioavailability of insulin using PLGA nanoparticles co-modified with cell-penetrating peptides and engrailed secretion peptide (Sec) Drug Deliv 23 2016 1980 1991 26181841
202 Rathod S. Desai H. Patil R. Sarolia J. Non-ionic surfactants as a P-glycoprotein(P-gp) efflux inhibitor for optimal drug delivery—a concise outlook AAPS PharmSciTech 23 2022 55 35043278
203 Houshaymi B. Nasreddine N. Kedees M. Soayfane Z. Oleic acid increases uptake and decreases the P-gp-mediated efflux of the veterinary anthelmintic Ivermectin Drug Res 69 2019 173 180
204 Weinheimer M. Fricker G. Burhenne J. Mylius P. Schubert R. The application of P-gp inhibiting phospholipids as novel oral bioavailability enhancers—an in vitro and in vivo comparison Eur J Pharm Sci 108 2017 13 22 27590127
205 Talegaonkar S. Bhattacharyya A. Potential of lipid nanoparticles (SLNs and NLCs) in enhancing oral bioavailability of drugs with poor intestinal permeability AAPS PharmSciTech 20 2019 121 30805893
206 Chaudhari M.B. Desai P.P. Patel P.A. Patravale V.B. Solid lipid nanoparticles of amphotericin B (AmbiOnp): in vitro and in vivo assessment towards safe and effective oral treatment module Drug Deliv Transl Res 6 2016 354 364 26712123
207 Beloqui A. Solinis M.A. Gascon A.R. del Pozo-Rodriguez A. des Rieux A. Preat V. Mechanism of transport of saquinavir-loaded nanostructured lipid carriers across the intestinal barrier J Control Release 166 2013 115 123 23266764
208 Théry C. Zitvogel L. Amigorena S. Exosomes: composition, biogenesis and function Nat Rev Immunol 2 2002 569 579 12154376
209 Lindenbergh M.F.S. Stoorvogel W. Antigen presentation by extracellular vesicles from professional antigen-presenting cells Annu Rev Immunol 36 2018 435 459 29400984
210 Aqil F. Munagala R. Jeyabalan J. Agrawal A.K. Kyakulaga A.H. Wilcher S.A. Milk exosomes—natural nanoparticles for siRNA delivery Cancer Lett 449 2019 186 195 30771430
211 Cheng L. Hill A.F. Therapeutically harnessing extracellular vesicles Nat Rev Drug Discov 21 2022 379 399 35236964
212 Umezu T. Takanashi M. Murakami Y. Ohno S.I. Kanekura K. Sudo K. Acerola exosome-like nanovesicles to systemically deliver nucleic acid medicine via oral administration Mol Ther Methods Clin Dev 21 2021 199 208 33850951
213 Zhong J. Xia B. Shan S. Zheng A. Zhang S. Chen J. High-quality milk exosomes as oral drug delivery system Biomaterials 277 2021 121126
214 Wu L. Wang L. Liu X. Bai Y. Wu R. Li X. Milk-derived exosomes exhibit versatile effects for improved oral drug delivery Acta Pharm Sin B 12 2022 2029 2042 35847507
215 Munagala R. Aqil F. Jeyabalan J. Agrawal A.K. Mudd A.M. Kyakulaga A.H. Exosomal formulation of anthocyanidins against multiple cancer types Cancer Lett 393 2017 94 102 28202351
216 Zielinska A. Carreiro F. Oliveira A.M. Neves A. Pires B. Venkatesh D.N. Polymeric nanoparticles: production, characterization, toxicology and ecotoxicology Molecules 25 2020 3731 32824172
217 Kamaly N. Yameen B. Wu J. Farokhzad O.C. Degradable controlled-release polymers and polymeric nanoparticles: mechanisms of controlling drug release Chem Rev 116 2016 2602 2663 26854975
218 Hunter A.C. Elsom J. Wibroe P.P. Moghimi S.M. Polymeric particulate technologies for oral drug delivery and targeting: a pathophysiological perspective Maturitas 73 2012 5 18 22709523
219 Sinnecker H. Ramaker K. Frey A. Coating with luminal gut-constituents alters adherence of nanoparticles to intestinal epithelial cells Beilstein J Nanotechnol 5 2014 2308 2315 25551058
220 Bakhru S.H. Furtado S. Morello A.P. Mathiowitz E. Oral delivery of proteins by biodegradable nanoparticles Adv Drug Deliv Rev 65 2013 811 821 23608641
221 Singh G. Pai R.S. Atazanavir-loaded Eudragit RL 100 nanoparticles to improve oral bioavailability: optimization and in vitro/in vivo appraisal Drug Deliv 23 2016 532 539 24963752
222 Reboredo C. Gonzalez-Navarro C.J. Martinez-Lopez A.L. Martinez-Oharriz C. Sarmento B. Irache J.M. Zein-based nanoparticles as oral carriers for insulin delivery Pharmaceutics 14 2021 39 35056935
223 Sun H. Liu D. Li Y. Tang X. Cong Y. Preparation and in vitro/in vivo characterization of enteric-coated nanoparticles loaded with the antihypertensive peptide VLPVPR Int J Nanomedicine 9 2014 1709 1716 24729706
224 El-Maghawry E. Tadros M.I. Elkheshen S.A. Abd-Elbary A. Eudragit((R))-S100 coated PLGA nanoparticles for colon targeting of etoricoxib: optimization and pharmacokinetic assessments in healthy human volunteers Int J Nanomedicine 15 2020 3965 3980 32606658
225 Alexis F. Pridgen E. Molnar L.K. Farokhzad O.C. Factors affecting the clearance and biodistribution of polymeric nanoparticles Mol Pharm 5 2008 505 515 18672949
226 Valencia P.M. Pridgen E.M. Rhee M. Langer R. Farokhzad O.C. Karnik R. Microfluidic platform for combinatorial synthesis and optimization of targeted nanoparticles for cancer therapy ACS Nano 7 2013 10671 10680 24215426
227 Deirram N. Zhang C. Kermaniyan S.S. Johnston A.P.R. Such G.K. PH-responsive polymer nanoparticles for drug delivery Macromol Rapid Commun 40 2019 e1800917
228 Fievez V. Plapied L. des Rieux A. Pourcelle V. Freichels H. Wascotte V. Targeting nanoparticles to M cells with non-peptidic ligands for oral vaccination Eur J Pharm Biopharm 73 2009 16 24 19409989
229 Xie X. Tao Q. Zou Y. Zhang F. Guo M. Wang Y. PLGA nanoparticles improve the oral bioavailability of curcumin in rats: characterizations and mechanisms J Agric Food Chem 59 2011 9280 9289 21797282
230 Inchaurraga L. Martín-Arbella N. Zabaleta V. Quincoces G. Peñuelas I. Irache J.M. In vivo study of the mucus-permeating properties of PEG-coated nanoparticles following oral administration Eur J Pharm Biopharm 97 2015 280 289 25541441
231 Chander S. Kulkarni G.T. Dhiman N. Kharkwal H. Protein-based nanohydrogels for bioactive delivery Front Chem 9 2021 573748
232 Schoener C.A. Hutson H.N. Peppas N.A. pH-responsive hydrogels with dispersed hydrophobic nanoparticles for the oral delivery of chemotherapeutics J Biomed Mater Res 101 2013 2229 2236
233 Buwalda S.J. Boere K.W. Dijkstra P.J. Feijen J. Vermonden T. Hennink W.E. Hydrogels in a historical perspective: from simple networks to smart materials J Control Release 190 2014 254 273 24746623
234 Narayanaswamy R. Torchilin V.P. Hydrogels and their applications in targeted drug delivery Molecules 24 2019 603 30744011
235 Sharpe L.A. Daily A.M. Horava S.D. Peppas N.A. Therapeutic applications of hydrogels in oral drug delivery Expert Opin Drug Deliv 11 2014 901 915 24848309
236 Wang D. Wang W. Wang P. Wang C. Niu J. Liu Y. Research progress of colon-targeted oral hydrogel system based on natural polysaccharides Int J Pharm 643 2023 123222
237 Kasinski A. Zielinska-Pisklak M. Oledzka E. Sobczak M. Smart hydrogels - synthetic stimuli-responsive antitumor drug release systems Int J Nanomedicine 15 2020 4541 4572 32617004
238 Zheng Y. Wang W. Zhao J. Wu C. Ye C. Huang M. Preparation of injectable temperature-sensitive chitosan-based hydrogel for combined hyperthermia and chemotherapy of colon cancer Carbohydr Polym 222 2019 115039
239 Skaalure S.C. Chu S. Bryant S.J. An enzyme-sensitive PEG hydrogel based on aggrecan catabolism for cartilage tissue engineering Adv Healthc Mater 4 2015 420 431 25296398
240 Puranik A.S. Pao L.P. White V.M. Peppas N.A. Synthesis and characterization of pH-responsive nanoscale hydrogels for oral delivery of hydrophobic therapeutics Eur J Pharm Biopharm 108 2016 196 213 27634646
241 Chen T. Li S. Zhu W. Liang Z. Zeng Q. Self-assembly pH-sensitive chitosan/alginate coated polyelectrolyte complexes for oral delivery of insulin J Microencapsul 36 2019 96 107 30958080
242 Murakami T. Tsuchida K. Recent advances in inorganic nanoparticle-based drug delivery systems Mini Rev Med Chem 8 2008 175 183 18289101
243 Wang F. Li C. Cheng J. Yuan Z. Recent advances on inorganic nanoparticle-based cancer therapeutic agents Int J Environ Res Public Health 13 2016 1182 27898016
244 Slowing I.I. Vivero-Escoto J.L. Wu C.W. Lin V.S. Mesoporous silica nanoparticles as controlled release drug delivery and gene transfection carriers Adv Drug Deliv Rev 60 2008 1278 1288 18514969
245 Karakoti A.S. Das S. Thevuthasan S. Seal S. PEGylated inorganic nanoparticles Angew Chem Int Ed Engl 50 2011 1980 1994 21275011
246 Sperling R.A. Parak W.J. Surface modification, functionalization and bioconjugation of colloidal inorganic nanoparticles Philos Trans A Math Phys Eng Sci 368 2010 1333 1383 20156828
247 Mitchell M.J. Billingsley M.M. Haley R.M. Wechsler M.E. Peppas N.A. Langer R. Engineering precision nanoparticles for drug delivery Nat Rev Drug Discov 20 2021 101 124 33277608
248 Levy M. Luciani N. Alloyeau D. Elgrabli D. Deveaux V. Pechoux C. Long term in vivo biotransformation of iron oxide nanoparticles Biomaterials 32 2011 3988 3999 21392823
249 Kolosnjaj-Tabi J. Javed Y. Lartigue L. Volatron J. Elgrabli D. Marangon I. The one year fate of iron oxide coated gold nanoparticles in mice ACS Nano 9 2015 7925 7939 26168364
250 Xia Q. Li H. Xiao K. Factors affecting the pharmacokinetics, biodistribution and toxicity of gold nanoparticles in drug delivery Curr Drug Metab 17 2016 849 861 27364829
251 Lartigue L. Alloyeau D. Kolosnjaj-Tabi J. Javed Y. Guardia P. Riedinger A. Biodegradation of iron oxide nanocubes: high-resolution in situ monitoring ACS Nano 7 2013 3939 3952 23634880
252 Yang G. Phua S.Z.F. Bindra A.K. Zhao Y. Degradability and clearance of inorganic nanoparticles for biomedical applications Adv Mater 31 2019 e1805730
253 Khalifehzadeh R. Arami H. Biodegradable calcium phosphate nanoparticles for cancer therapy Adv Colloid Interf Sci 279 2020 102157
254 Qiu M. AjayWang DouQu JunleSwihart MarkZhang HanPrasad Paras N. Biocompatible and biodegradable inorganic nanostructures for nanomedicine: silicon and black phosphorus Nano Today 25 2019 135 155
255 Miao Z. Gao Z. Chen R. Yu X. Su Z. Wei G. Surface-bioengineered gold nanoparticles for biomedical applications Curr Med Chem 25 2018 1920 1944 29345568
256 Milan J. Niemczyk K. Kus-Liskiewicz M. Treasure on the earth-gold nanoparticles and their biomedical applications Materials 15 2022 3355 35591689
257 Guo X. Li C. Zhang J. Sun M. Xu J. Xu C. Chiral nanoparticle-remodeled gut microbiota alleviates neurodegeneration via the gut‒brain axis Nat Aging 3 2023 1415 1429 37946041
258 Wang F. Li Q. Xu T. Li Z. Jiang Y. Ma Y. An orally administered gold nanocluster with ROS scavenging for inflammatory bowel disease treatment Fundam Res 2022
259 Wang L. Yang J. Li S. Li Q. Liu S. Zheng W. Oral administration of starting materials for in vivo synthesis of antibacterial gold nanoparticles for curing remote infections Nano Lett 21 2021 1124 1131 33459020
260 Kumari Y. Singh S.K. Kumar R. Kumar B. Kaur G. Gulati M. Modified apple polysaccharide capped gold nanoparticles for oral delivery of insulin Int J Biol Macromol 149 2020 976 988 32018009
261 Zhang X. Wu H. Wu D. Wang Y. Chang J. Zhai Z. Toxicologic effects of gold nanoparticles in vivo by different administration routes Int J Nanomed 49 2010 771 781
262 Ren Q. Ma J. Li X. Meng Q. Wu S. Xie Y. Intestinal toxicity of metal nanoparticles: silver nanoparticles disorder the intestinal immune microenvironment ACS Appl Mater Inter 15 2023 27774 27788
263 Florek J. Caillard R. Kleitz F. Evaluation of mesoporous silica nanoparticles for oral drug delivery—current status and perspective of MSNs drug carriers Nanoscale 9 2017 15252 15277 28984885
264 Bremmell K.E. Prestidge C.A. Enhancing oral bioavailability of poorly soluble drugs with mesoporous silica based systems: opportunities and challenges Drug Dev Ind Pharm 45 2019 349 358 30411991
265 Araújo F. Shrestha N. Shahbazi M.A. Fonte P. Mäkilä E.M. Salonen J.J. The impact of nanoparticles on the mucosal translocation and transport of GLP-1 across the intestinal epithelium Biomaterials 35 2014 9199 9207 25109441
266 Rahman M.M. Ara M.G. Alim M.A. Uddin M.S. Najda A. Albadrani G.M. Mesoporous carbon: a versatile material for scientific applications Int J Mol Sci 22 2021 4498 33925852
267 Kim T.W. Chung P.W. Slowing I.I. Tsunoda M. Yeung E.S. Lin V.S. Structurally ordered mesoporous carbon nanoparticles as transmembrane delivery vehicle in human cancer cells Nano Lett 8 2008 3724 3727 18954128
268 Zhao Q. Lin Y. Han N. Li X. Geng H. Wang X. Mesoporous carbon nanomaterials in drug delivery and biomedical application Drug Deliv 24 2017 94 107 29124979
269 Mamai M. Giasafaki D. Salvanou E.A. Charalambopoulou G. Steriotis T. Bouziotis P. Biodistribution of mesoporous carbon nanoparticles via Technetium-99m radiolabelling after oral administration to mice Nanomaterials 11 2021 3260 34947611
270 Xin W. Song Y. Mesoporous carbons: recent advances in synthesis and typical applications RSC Adv 5 2015 83239 83285
271 Dos Santos A.M. Carvalho S.G. Meneguin A.B. Sábio R.M. Gremião M.P.D. Chorilli M. Oral delivery of micro/nanoparticulate systems based on natural polysaccharides for intestinal diseases therapy: challenges, advances and future perspectives J Control Release 334 2021 353 366 33901582
272 Thiyagarajan V. Lin S.X. Lee C.H. Weng C.F. A focal adhesion kinase inhibitor 16-hydroxy-cleroda-3,13-dien-16,15-olide incorporated into enteric-coated nanoparticles for controlled anti-glioma drug delivery Colloids Surf B Biointerfaces 141 2016 120 131 26851441
273 Bing J. Xiao X. McClements D.J. Biao Y. Chongjiang C. Protein corona formation around inorganic nanoparticles: food plant proteins-TiO2 nanoparticle interactions Food Hydrocolloids 115 2021 106594
274 Xiao W. Gao H. The impact of protein corona on the behavior and targeting capability of nanoparticle-based delivery system Int J Pharm 552 2018 328 339 30308270
275 Li H. Wang Y. Tang Q. Yin D. Tang C. He E. The protein corona and its effects on nanoparticle-based drug delivery systems Acta Biomater 129 2021 57 72 34048973
276 Bashiri G. Padilla M.S. Swingle K.L. Shepherd S.J. Mitchell M.J. Wang K. Nanoparticle protein corona: from structure and function to therapeutic targeting Lab Chip 23 2023 1432 1466 36655824
277 Falahati M. Attar F. Sharifi M. Haertlé T. Berret J.F. Khan R.H. A health concern regarding the protein corona, aggregation and disaggregation Biochim Biophys Acta Gen Subj 1863 2019 971 991 30802594
278 Pang H. Huang X. Xu Z.P. Chen C. Han F.Y. Progress in oral insulin delivery by PLGA nanoparticles for the management of diabetes Drug Discov Today 28 2023 103393
279 Simões S.M. Figueiras A.R. Veiga F. Concheiro A. Alvarez-Lorenzo C. Polymeric micelles for oral drug administration enabling locoregional and systemic treatments Expert Opin Drug Deliv 12 2015 297 318 25227130
280 Yu H. Xia D. Zhu Q. Zhu C. Chen D. Gan Y. Supersaturated polymeric micelles for oral cyclosporine A delivery Eur J Pharm Biopharm 85 2013 1325 1336 23954511
281 Naha P.C. Hsu J.C. Kim J. Shah S. Bouché M. Si-Mohamed S. Dextran-coated cerium oxide nanoparticles: a computed tomography contrast agent for imaging the gastrointestinal tract and inflammatory bowel disease ACS Nano 14 2020 10187 10197 32692538
282 Li L. Qi Z. Han S. Li X. Liu B. Liu Y. Advances and applications of metal-organic framework nanomaterials as oral delivery carriers: a review Mini Rev Med Chem 22 2022 2564 2580 35362373
283 Zou J.J. Wei G. Xiong C. Yu Y. Li S. Hu L. Efficient oral insulin delivery enabled by transferrin-coated acid-resistant metal-organic framework nanoparticles Sci Adv 8 2022 eabm4677
284 Enlow E.M. Luft J.C. Napier M.E. DeSimone J.M. Potent engineered PLGA nanoparticles by virtue of exceptionally high chemotherapeutic loadings Nano Lett 11 2011 808 813 21265552
285 Gupta P.N. Pattani A. Malcolm R.K. Curran R.M. Andrews G. Development of liposome-based freeze-dried rods for vaginal vaccine delivery against HIV-1 J Control Release 148 2010 e108 e110 21529580
286 DeSesso J.M. Jacobson C.F. Anatomical and physiological parameters affecting gastrointestinal absorption in humans and rats Food Chem Toxicol 39 2001 209 228 11278053
287 Kim H.R. Park S.W. Cho H.J. Chae K.A. Sung J.M. Kim J.S. Comparative gene expression profiles of intestinal transporters in mice, rats and humans Pharmacol Res 56 2007 224 236 17681807
