MTL Annual Research Report 2004-2005

Mechanical forces are important regulators of cell biology in health and disease. Cells in the vascular system are subjected to fluid shear stress, cyclic stretch, and differential pressure [1]. Numerous investigations have revealed the vast pathological and physical responses of endothelial cells to fluid shear stress by culturing the cells on the rigid surfaces of a flow chamber. This approach, however, fails to mimic the true environment of cells in vivo that grow on flexible, porous basement membranes with a defined microstructure [1-4]. In order to create an improved model for this in vivo condition, we developed a new microfluidic bioreactor system that enables us to study cell-matrix interactions on soft substrates made of gel under conditions of controlled shear stress and pressure difference. A gel cage consisting of three thin layers (Figure 1) is constructed from PDMS using a silicon master made by the deep RIE process. Flow chambers, also made of PDMS, are cured on an SU-8 patterned master. Separate channels are included that allow for filling this central chamber with a gel that mimics the extracellular matrix and also allows for independent control over the flows in the upper and lower channels. The assembled bioreactor is shown in Figure 2. To conduct experiments, we introduce a peptide solution into the gel cage, allow it to gel, and then seed cells on the gel surface exposed through the holes of gel cage. After cell adhesion, the flow chambers are sealed by the application of a vacuum to the top and bottom sides of the gel cage. Flows are then applied to each chamber with controlled pressures and flow rates. With this system, we will apply controlled shear stress and pressure on the cell layers. We plan to study the process of angiogenesis that entails the growth of vascular sprouts emanating from one endothelial surface and connecting with the other.