Design considerations for a microfluidic device to quantify the platelet adhesion to collagen at physiological shear rates.

Accurate assessment of blood platelet function is essential in understanding thrombus formation which plays a central role in cardiovascular disease. Parallel plate flow chambers have been widely used as they allow for platelet adhesion on a collagen surface at physiologically relevant fluid mechanical forces. Standard parallel plate flow chambers typically need several milliliters of blood, which is substantially more than can be obtained from small animals. We designed, fabricated, and assessed the functionality of a microfluidic channel with a width of 500 microm and a height of 50 microm in which a wall shear rate of 1000 s(-1) can be achieved with a flow rate of 15 microL/min. The velocity distribution in the microchannel predicted from the equations of motion was compared to experimentally measured velocities of fluorescent beads. This analysis showed that the motion of beads was quite similar to the predicted motion. Adhesion of platelets from whole blood at a shear rate of 1000 s(-1) onto a collagen surface using the microfluidic flow channel was qualitatively similar to platelet adhesion observed with a standard sized parallel plate flow chamber. After 5 min flow the surface coverage of platelets in the microfluidic device was about 55% while in a traditional size flow chamber the surface coverage was about 75%. This suggests that the microfluidic flow chamber can be used to quantify platelet adhesion for system where only very small amounts of blood are available.