Endothelial cell monolayer-based microfluidic systems mimicking complex in vivo microenvironments for the study of leukocyte dynamics in inflamed blood vessels.

In response to inflammatory signals, leukocytes circulating in blood vessels undergo dynamic interaction with endothelium lining blood vessel walls, known as leukocyte adhesion cascade, to leave the blood vessels, and infiltrate the inflamed tissue. During leukocyte extravasation, leukocytes recognize and respond to various biophysical and biochemical cues present in the complex microenvironments of inflamed blood vessels to find optimal pathways. Although advances in intravital imaging of live animals have enabled us to observe leukocyte dynamics during extravasation, in vitro model systems mimicking complex in vivo microenvironments are still needed for mechanistic studies. A parallel-plate flow chamber assembled by placing a fluidic chamber on an endothelial cell (EC) monolayer has been widely used as an in vitro model to study leukocyte dynamics in inflamed blood vessels. Although this is a simple yet powerful model providing well-defined flow conditions, a parallel-plate flow chamber lacks the complex microenvironments of inflamed blood vessels. In this article, we first describe the basic design, assembly, and operation principles of a parallel-plate flow chamber. Then, we present methods of incorporating various features of in vivo microenvironments into parallel-plate flow chambers, including EC alignment using nanogrooved surfaces, insertion of a stenotic structure for complex flow generation, and extension to 3D blood vessel/inflamed tissue models.