Introduction
In the recent decade, researchers have continuously developed many in vitro models, from 2D to 3D, and particularly, organ chips have evolved from conceptual to powerful tools that hold the potential to partially replace traditional in vitro models and animal models.[1-3] Nevertheless, the widespread adoption of organ chip systems currently faces certain challenges, including the reliance on labor-intensive external pumps and limited throughput.[4-6] In addition, although microfluidic systems reduce the use of cells and drugs, they also increase the difficulty of characterization and detection. For example, more precise manual operations or complex sensors are often required when measuring TEER, which can be challenging to achieve in small chips.[7, 8]Overcoming these challenges necessitates addressing both biological and engineering obstacles. This endeavor entails developing innovative microfluidic designs or platforms capable of precisely controlling the flow of fluids, as well as establishing reproducible and physiologically relevant cell culture microenvironment.[9-11]
Currently, a variety of organ chips, such as intestine-on-a-chip,[12]liver-on-a-chip,[13]brain-on-a-chip,[14] have been developed. Of the various organ-on-chip devices, the intestine-on-a-chip are one of the most widely used models. A traditional intestine-on-a-chip is typically composed of two channels separated by a porous membrane lined with intestinal epithelial cells.[15-17] To replicate the dynamic in vivo microenvironment, the medium is commonly circulated through the channels using either syringes or peristaltic pumps. Intestine-on-a-chip systems allow for the analysis of drug absorption, toxicity, and efficacy, as well as the simulation of intricate host-microbe interactions.[18-21]
As we all know, the Caco-2 monolayer cultured on a transwell insert is widely recognized as one of the most commonly utilized models for studying human intestinal barrier absorption due to its simplicity and cost-effectiveness.[22]However, despite the widespread use of the transwell model in research, the cell culture process involved a prolonged time period, and the two-dimensional growth of cells in static culture does not entirely replicate the in vivo environment.[23, 24] Due to the effectiveness of organ chips in advancing the development of novel drugs and therapies, it offers a more physiologically relevant and reproducible alternative to traditional in vitro models.[25] On the other hand, existing chips used for drug evaluation often require high-precision instruments for detection due to low drug volume, which potentially increases the cost of application. Therefore, developing a high-throughput organ chip system that eliminates the need for complex pumps and valves has the potential to revolutionize drug discovery and toxicity testing.
In this study, we present a generic, pump-free and high-throughput 3D organ-on-a-chip platform that enables dynamic cell culture in vitro similar to traditional chip system. A rocker was utilized to generate periodic fluid force in our system which replaces the pump and intertwined pipelines. Using our platform, we established a gut-on-a-chip system that simulates human intestine. 3D stereoscopic structure and enhanced expression of intestinal barrier-associated proteins (ZO-1) was observed in our platform, which was deficient in static cultures. We also observed the spatial distribution of differentiated (Villin, MUC-2) and proliferative cells (Ki67) markers, suggesting that cell differentiation on the chip occurs similarly to that in vivo. RNA sequencing analysis demonstrated that cells showed significantly enriched pathways and up-regulated genes associated with drug metabolism function compared to those in static cultures. Based on these findings, we evaluated the drug bioavailability using our platform and achieved reliable and predictive simulation results, thus providing a promising tool for predicting the intestinal drug absorption of new drugs and a valuable asset for drug development and personalized medicine.