Organ-level physiology is recapitulated in vitro by culturing cells in perfused, microfluidic devices.

Microfluidic organs-on-chips

From 3D cell culture to organs-on-chips.

Development of an in vitro living cell-based model of the intestine that mimics the mechanical, structural, absorptive, transport and pathophysiological properties of the human gut along with its crucial microbial symbionts could accelerate pharmaceutical development, and potentially replace animal testing. Here, we describe a biomimetic ‘human gut-on-a-chip’ microdevice composed of two microfluidic channels separated by a porous flexible membrane coated with extracellular matrix (ECM) and lined by human intestinal epithelial (Caco-2) cells that mimics the complex structure and physiology of living intestine. The gut microenvironment is recreated by flowing fluid at a low rate (30 μL h−1) producing low shear stress (0.02 dyne cm−2) over the microchannels, and by exerting cyclic strain (10%; 0.15 Hz) that mimics physiological peristaltic motions. Under these conditions, a columnar epithelium develops that polarizes rapidly, spontaneously grows into folds that recapitulate the structure of intestinal villi, and forms a high integrity barrier to small molecules that better mimics whole intestine than cells in cultured in static Transwell models. In addition, a normal intestinal microbe (Lactobacillus rhamnosus GG) can be successfully co-cultured for extended periods (>1 week) on the luminal surface of the cultured epithelium without compromising epithelial cell viability, and this actually improves barrier function as previously observed in humans. Thus, this gut-on-a-chip recapitulates multiple dynamic physical and functional features of human intestine that are critical for its function within a controlled microfluidic environment that is amenable for transport, absorption, and toxicity studies, and hence it should have great value for drug testing as well as development of novel intestinal disease models.

Human gut-on-a-chip inhabited by microbial flora that experiences intestinal peristalsis-like motions and flow

Hydrogels are hydrophilic polymer-based materials with high water content and physical characteristics that resemble the native extracellular matrix. Because of their remarkable properties, hydrogel systems are used for a wide range of biomedical applications, such as three-dimensional (3D) matrices for tissue engineering, drug-delivery vehicles, composite biomaterials, and as injectable fillers in minimally invasive surgeries. In addition, the rational design of hydrogels with controlled physical and biological properties can be used to modulate cellular functionality and tissue morphogenesis. Here, the development of advanced hydrogels with tunable physiochemical properties is highlighted, with particular emphasis on elastomeric, light-sensitive, composite, and shape-memory hydrogels. Emerging technologies developed over the past decade to control hydrogel architecture are also discussed and a number of potential applications and challenges in the utilization of hydrogels in regenerative medicine are reviewed. It is anticipated that the continued development of sophisticated hydrogels will result in clinical applications that will improve patient care and quality of life.

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25th Anniversary Article: Rational Design and Applications of Hydrogels in Regenerative Medicine

Microengineered cell culture systems are becoming sufficiently sophisticated that they can recapitulate many of the phenomena observed in tissues and organisms. Here, Huh and colleagues discuss the advances made in these 'organs-on-chips' and how they could be used in drug development, including target identification and validation, toxicity screening and stratified medicine.

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Organs-on-chips at the frontiers of drug discovery

Drug discovery is often impeded by the poor predictability of in vitro assays for drug toxicity. One primary reason for this observation is the inability to reproduce the pharmacokinetics (PK) of drugs in vitro. Mathematical models to predict the pharmacokinetics-pharmacodynamics (PK-PD) of drugs are available, but have several limitations, preventing broader application. A microscale cell culture analog (microCCA) is a microfluidic device based on a PK-PD model, where multiple cell culture chambers are connected with fluidic channels to mimic multi-organ interactions and test drug toxicity in a pharmacokinetic-based manner. One critical issue with microfluidics, including the microCCA, is that specialized techniques are required for assembly and operation, limiting its usability to non-experts. Here, we describe a novel design, with enhanced usability while allowing hydrogel-cell cultures of multiple types. Gravity-induced flow enables pumpless operation and prevents bubble formation. Three cell lines representing the liver, tumor and marrow were cultured in the three-chamber microCCA to test the toxicity of an anticancer drug, 5-fluorouracil. The result was analyzed with a PK-PD model of the device, and compared with the result in static conditions. Each cell type exhibited differential responses to 5-FU, and the responses in the microfluidic environment were different from those in static environment. Combination of a mathematical modeling approach (PK-PD modeling) and an in vitro experimental approach (microCCA) provides a novel platform with improved predictability for testing drug toxicity and can help researchers gain a better insight into the drug's mechanism of action.

Carrie Kam

Papers

A microfluidic device for a pharmacokinetic–pharmacodynamic (PK–PD) model on a chip