Abstract:
This study is divided into two phases. The first phase is about the investigation of cell viability and damage of white blood cells after sorting in both a spiral microchannel and contraction and expansion array (CEA) at appropriate flow rates for cell separation. Three techniques such as Trypan Blue staining, Scanning Electron Microscopy (SEM) and Wright-Giemsa staining are employed in the experiments. After flowing the sample through a whole setup of spiral microchannel at 2 ml/min, 85% of cells are viable while 30% of cells are significantly deformed and 2% of cells are seriously damaged in their intracellular structures. In CEA experiments, they are 89, 12 and 14%, respectively, at 0.3 ml/min. Considering computational results of flow dynamics at the same conditions, shear stress dominates over extensional stress in the spiral microchannel covering the entire length of the channel close to the walls with long exposure time. This may cause cell death and significant deformation. On the other hand, extensional stress dominates in the CEA and occurs at the corner where the cross-section of the flow channel changes. Despite of short exposure time due to high flow rate, the extensional stress with extremely high magnitude covers almost entire the cross-section of the flow channel. It potentially causes intracellular damage to the cells, and cell death. Therefore, the spiral microchannel and CEA cause cell damage in different ways due to the different types of stresses. The second phase demonstrates the integrated microfluidic device combining with the spiral microchannel and triangular wells together. The system is tested with microbeads and mast-cell-tumor (MCT) cells. When the flow rate increases in the range of 0.2, 0.5, 1 and 2 ml/min, the 10, 15 and 20 µm microbeads gradually move towards the inner wall at the outlet of the spiral channel, and comes in the 3rd, 2nd and 1st chamber of microwells. At the flow rate of 0.5 ml/min, the maximal percentage of the trapping for 15 µm microbeads is found at 80% in the 3rd chamber. Regarding this reason, this flow rate is used in the cell experiments since the size of MCT cells is about 15 µm. When sorting the MCT cells at this flow rate, cell viability is 74%. After culturing in the microwells for three days, cell viability is 68% when the continuous flow of nutrient is fed at 10 µl/hr. The results show the feasibility of the developed system in biological applications.
