(670h) Simulating Intestinal Molecular Transport Using Tissue Engineered in Vitro Models

Introduction: The intestinal mucosal barrier lining the gastrointestinal tract â?? composed of an epithelial cell monolayer and the mucins they secrete â?? plays a critical role in maintaining metabolic and immunological homeostasis. Recently developed microfluidic gut-on-a-chip devices have significantly advanced the capability of in vitro models in recapitulating in vivo intestinal tissue physiology (1). However, remaining key challenges for such devices include (i) supporting both anaerobic and aerobic intestinal milieu, (ii) simultaneous human cell co-culture, and (iii) real-time in situ observation of their dynamic crosstalk. Here, we introduce a new bioengineered platform technology with high analytical power that can potentially allow for anaerobic and aerobic culture by creating a transverse compartmentalized device that retains previously identified anatomical and mechanical tissue complexities. Peristaltic motion that is critical in promoting gut epithelial cell growth and function was further simulated via pneumatic actuation.

Materials and Methods: Type I collagen infused polyacrylamide hydrogel precursor solution was casted in a 500µm thick PDMS sheet having pre-cut villous mimicking micropatterns on a silanized glass slide. (2) An actuating layer made with Ecoflex that has been used in soft-robotics (3) was attached outside of a hydrogel layer and sealed with another glass slide. We then increased the cellular and extracellular complexity by sequentially introducing (i) HT-29 intestinal epithelial cells, (ii) mucin extract from pig intestines, (iii) bacteria, and (iv) human peripheral blood-derived mononuclear cells (PBMC). By using a solenoid valve in tandem with a microcontroller (µC), the chamber was expanded and contracted at controlled pressures and frequencies using in house vacuum and air.

Results and Discussion: Covalent attachment of polyacrylamide hydrogels to silanized glass slides was achieved in a sealed, compartmentalized microfluidic device. Molecular diffusion tests using rhodamine dye showed that the hydrogels are permeable to gas and allow for small molecular diffusion. Different spatially patterned hydrogels can be microfabricated with villous-like structures that recapitulate the physiology of the gastrointestinal tract. The luminal compartment of the microfluidic was seeded with HT-29 colorectal cancer cells that preferentially adhered to the hydrogel, forming an epithelial barrier while the tissue compartment was filled with PBMCs derived from blood donors. Additionally, mucin and bacteria were introduced in the luminal compartment and continuously perfused in order to reduce bacterial density while cell-to-cell interactions were imaged in real-time. Actuation was controlled by an Arduino-based µC that can have very diverse control of operations.

Conclusions: We have developed a new type of microfluidic device that integrates soft biomaterials. We envision that such a modular in vitro microphysiological intestinal tissue model can serve as a translational platform to discover the biophysical etiology of disruption of the mucosal barrier.