(128b) Straightforward Incorporation of Tailorable Stromal Compartments into Microfluidic Microphysiological Systems

The extracellular matrix (ECM) is well appreciated to impact cellular function, morphology, and phenotype. In recent years advances in in vitro models have included the incorporation of spatial and temporal control of the biochemical and biophysical properties of 3D hydrogels to recapitulate the native microenvironment of a tissue. However, these methods are difficult to incorporate into microfluidic fabrication techniques for organ-on-a-chip microphysiological systems. These microfluidic models of organs and tissues allow for the incorporation of dynamic fluid forces and relevant transport kinetics and length scales which are also well appreciated to impact cellular function. To merge these two powerful approaches, we have developed simple, cleanroom-free methods to incorporate microfluidic fabrication with a tailorable stromal compartment into microphysiological systems.

For this work, we created a placenta-on-a-chip as an exemplar microphysiological model for the validation of transplacental drug transport kinetics. Fibroblasts were embedded within a thin collagen-I hydrogel fabricated on a silicon support. Placental epithelial cells (BeWo) and endothelial cells (HUVECs) were seeded on either side of the collagen-I hydrogel and cultured for at least four days to ensure monolayer formation. The seeded gel and support were incorporated into a microfluidic device by clamping the support between two laser-etched, acrylic sheets containing microfluidic channels. The resulting construct creates a maternal fluid channel lined with BeWo cells and a fetal fluid channel lined with HUVECs on either side of a hydrogel stromal compartment with embedded fibroblasts.

To test the function or this assembled system, we used immunostaining and fluorescent microscopy to observe confluent epithelial and endothelial cell layers were formed on the obverse and reverse of the collagen gel. Fibroblasts were successfully cultured within the hydrated stromal layer as validated with live-dead staining over the week-long culture period. Barrier formation was confirmed with transepithelial electrical resistance (TEER). Following seven days of culture, antipyrine, sodium-fluorescein, and glucose were used to validate transport dynamics in static and dynamic conditions. In addition to the functional tests for this placenta-on-a-chip model, we validated that these fabrication methods are compatible with a range of native and synthetic hydrogels as well as reconstituted decellularized ECM scaffolds.

In this work we have developed methods to generate microphysiological systems with tailorable stromal compartments using a placenta-on-a-chip as a model. These methods integrate an extensive biomaterials toolbox into these fluidic 3D multicell in vitro models, significantly expanding the ability to investigate how cell-ECM interactions regulate disease processes and homeostasis. Our simple fabrication approach, with the ability to include stromal cells, such as fibroblasts and tissue-resident immune cells, will enable more complex in vitro models of complex organs such as the small intestine, kidney, lung, or placenta.