05. Micro- and Nano-Scale Transport, MEMS

Blood is a complex non-Newtonian fluid comprising red blood cells (RBCs), white blood cells (WBCs), platelets, plasma, etc… In microfluidic device separation, it often incorporate micropillar structures for cell separation, crucial for applications such as detecting circulating tumor cells (CTCs) and other biomarkers. However, a significant issue arises from the deposition of blood cells (mainly RBCs and WBCs), behind micropillars, leading to clogging and microdevice failure. This study investigates the dynamics of blood flow and clogging phenomena in microchannels with micropillars by both numerical simulations and experimental methods. Numerical simulations were conducted to analyze the effects of micropillar diameter, shape, and gap on blood flow characteristics, employing ANSYS Fluent for modeling. Various shapes, including circular, elliptical, and airfoil, were examined to understand their influence on flow separation and recirculation zones. Results indicated that larger diameters and smaller gaps increased drag coefficients and enhanced recirculation regions, promoting cell deposition and clogging. Experimental studies were performed using microfluidic devices fabricated via photolithography and CNC milling, testing blood flow at different parameters. Observations confirmed that cell deposition occurred predominantly behind micropillars, irrespective of their size or arrangement, leading to microchannel blockage over time. Additionally, the potential of CNC milling for micropillar fabrication was evaluated, highlighting its advantages in rapid prototyping and cost-effectiveness compared to photolithography. Despite limitations in achieving smaller diameters, CNC-milled devices successfully facilitated the separation of HT-29 (human colorectal aancer cell line) cancer cells from whole blood. This study highlights the importance of optimizing micropillar designs to reduce clogging and enhance the performance of microfluidic devices in biomedical applications.