Core B (the Microfluidics Core) will design and build microfluidic devices and flow control systems, develop advanced substrate-coating techniques, and work with the laboratories participating in the Program to apply them to studies of surface adhesion of platelet and leukocytes. Core B will set up, upgrade, conjugate with microscopy, and maintain microfluidic systems in the laboratories of the Program, will train the personnel of the laboratories and take part in pilot experiments with the systems. Core B will fabricate microfluidic devices, supply them to the Program laboratories, and modify the devices and techniques based on the feedback from the laboratories. For experiments on substrate adhesion and aggregation of platelets (Projects 1 - 3), Core B will build microfluidic devices subjecting blood to two to three orders-of-magnitude ranges of shear stress in each assay, with shear stress reaching >1000 dynes/cm^2 for experiments with von Willebrand factor, VWF, (Project 3) and with small amounts of blood (<100 uL for Projects 1 and 2 and <400 uL for Project 3) required for an assay. Platelet adhesion from two different blood samples to identical substrates will be tested in parallel. Substrate coating techniques will be developed to control the site densities of adhesion molecules (collagen, fibrinogen, and VWF) and to test the adhesion to substrates with a range of site densities in a single assay. Micro-channels with constrictions will be fabricated to study the effect of extensional vs. shear flow on the activity of VWF and on VWF-mediated adhesion and aggregation of platelets (Project 3). For experiments on rolling and arrest of leukocytes (Projects 1), Core B will build microfluidic devices with a range of shear stresses and customized substrate coatings. Mixed substrate coatings will be created with site densities of different adhesion molecules (e.g., P-selectin and VCAM-1) independently varied and controlled. Substrates with sharp boundaries between differently coated areas will be produced to test for possible integrin activation by adhesion molecules and to study the dynamics of neutrophil arrest (Project 1). Micro-patterned substrates with ~1um-wide differently coated strips will be made to emulate non-uniform distributions of adhesion molecules expressed on endothelium.

Adhesion of platelets and leukocyte to endothelium and extracellular matrix from flowing blood plays a crucial role in vascular injury and in the initiation of thrombosis. Microfluidics Core Unit B will provide Projects 1 - 3 with the capability to analyze the adhesion in broad ranges of shear stress in microfluidic perfusion chambers using small blood samples. The perfusion chambers will be coated with adhesion molecules, emulating their site densities and spatial distributions in vivo.