Here we present a novel approach to evaluate peripheral blood mononuclear cell vascular adhesion using a microfluidic model designed to approximate the complexity of a human arteriole. While EC monolayer assays are commonly used to investigate leukocyte-EC interactions, we hypothesized that our single channel arteriole (SCA) on a chip would recapitulate the microvasculature more accurately and provide additional insight into the initial stages of atherogenesis.

This model is comprised of stromal cells embedded in a hydrogel surrounding a channel lined by endothelial cells (EC) that has an inner diameter approximating a small arteriole. Under physiologic shear conditions, the EC take on a phenotype distinct from monolayer cultures, including alignment with the direction of flow.

Significant differences were found between the SCA and monolayer cultures in the expression of key EC and stromal cell markers, including ICAM-1, VCAM-1, PDGFB, aSMA, and KLF2. Indeed, flow-induced PDGFB expression likely mediated the recruitment and differentiation of αSMA-positive cells to the vessel wall. Importantly, the vessels were responsive to stimulation by inflammatory mediators, showing both increased leukocyte adhesion and increased permeability. Finally, mechanically mediated protrusion of the vessel wall into the lumen disrupted flow, producing increased shear over the vessel wall.

In summary, our studies demonstrate the utility of the SCA model for studies of small vessel physiology under both normal and disrupted flow and to lay the groundwork for further development into a model for atherosclerosis. Additionally, our data emphasize the advantages of complex 3D assays over more traditional 2D cultures.