Abstract
BACKGROUND: Nano-formulations show significant promise for oral administration, but their absorption mechanisms-including how nanoparticles traverse intestinal epithelium, whether enhanced absorption stems from solubilization or intact particle uptake, and the fraction of intact nanoparticles entering the bloodstream-remain poorly understood. This hinders their development and clinical application. Research methods are crucial for studying oral absorption mechanisms; however, systematic reviews addressing the research techniques and methods of these mechanisms are still scarce. Consequently, this review was compiled to provide practical methodological guidance for in-depth research on their absorption mechanisms. METHODOLOGY: The literature published from 2018 to 2024 was searched in the Web of Science and PubMed databases using the topic 'oral absorption mechanism'. A subset of significant reviews and articles pertaining to the oral absorption mechanism of nano-formulations was chosen from the vast collection of retrieved articles. This review was compiled through a systematic categorization and comparative analysis of the diverse research methods employed to investigate these mechanisms. RESULTS: This review systematically compared the advantages, disadvantages, and rational applications of various experimental models and summarized current methods/techniques for investigating the oral absorption mechanisms of nano-formulations, including mucus layer penetration, endocytosis, intracellular transport and exocytosis pathways, paracellular transport, and lymphatic transport. Careful analysis showed that commonly used cell and tissue models are inadequate to fully simulate the complex gastrointestinal absorption environment; current detection techniques fail to capture the actual in vivo changes and absorption mechanisms of nano-formulations; existing research methods often dissect oral absorption processes in isolation, leading to fragmented results. Finally, the review anticipated new promising experimental models and cutting-edge technologies (e.g., organoid models, microphysiological systems, gene editing, and in vivo sub-cellular high-resolution imaging techniques) with potential to address these limitations. CONCLUSIONS: The limitations of existing models, techniques, and research approaches underscore the need for innovative methods to advance understanding of oral nano-formulation absorption. Emerging technologies, despite being in the infant stage and facing many bottlenecks, offer transformative potential to overcome these challenges. They are expected to revolutionize research on oral absorption mechanisms of nano-formulations, thus ushering in a new era of comprehensive exploration.