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.