Characterization of in vitro endothelial linings grown within microfluidic channels.

In vivo, endothelial cells grow on the inner surface of blood vessels and are shaped to conform to the vessel's geometry. In the smallest vessels this shape entails substantial bending within each cell. Microfabricated channels can replicate these small-scale geometries, but endothelial cells grown within them have not been fully characterized. In particular, the presence of focal adhesions and adherens junctions in endothelial cells grown in microchannels with corners has not been confirmed. We have fabricated square microfluidic channels (50 μm wide, 50 μm deep) and semicircular microfluidic channels (60 μm wide, 45 μm deep) in polydimethylsiloxane and cultured human umbilical vein endothelial cells (HUVEC) within them. Immunofluorescent staining and three-dimensional reconstruction of image stacks taken with confocal microscopy confirmed that HUVEC are capable of forming adherens junctions on all channel walls in both channel geometries, including the sidewalls of square profile channels. The presence of shear stress is critical for the cells to form focal adhesions within both channel geometries. Shear stress is also responsible for the conforming of HUVEC to the channel walls and produces a square cross-sectional geometry of in vitro endothelial linings within square profile channels. Thus, geometry and applied shear stress are important design criteria for the development of in vitro endothelial linings of microvessels.