A High Spatial Method to Determine Three-Dimensional Velocity Gradient Tensor using Micro Particle Image Velocimetry

Micro Particle Image Velocimetry (μPIV) is a non-invasive flow field measurement technique, which is becoming the method of choice for the investigation of micro-flows. Measurements of flows which occur within the human body represent one of the most important applications of μPIV. A three-component two-dimensional scanning micro-Particle Image Velocimetry (μPIV) technique is presented in this paper. This technique yields high spatial resolution of the wall normal velocity gradient, γz, which relates directly to the shear stress experienced by adhering cells. The flow characteristics around a fixed thrombus in a rectangular glass micro-slide are examined in order to understand the role of flow mechanics in platelet aggregation and thrombus formation. Close to the wall regions of low normal velocity gradient occur around the fixed thrombus. Additionally, the in plane velocity gradient, γxy, is high around the sides of the thrombus but low at the front and rear. Accordingly a platelet moving from a relatively low shear environment at the front of the thrombus experiences increased shear at the thrombus sides followed by low shear at the rear. In-vitro observations indicate that this pattern of shear history provides favourable conditions for platelet recruitment at the rear of the thrombus.