Study In Microfluidic Technology For Cell Manipulation

Cell capture and sorting is the technology to fix or separate target cells from the non-homogeneous population of cells, for example, separating tumor cells from peripheral blood. Nowadays capturing and separating cells from different kinds of biological fluids is an important engineering methods for future analysis and is quite significant no matter in the field of scientific research or in the actual clinical application. At present, the traditional ways of cell manipulation, such as optical tweezers and microscopy, can control a single cell accurately, even the tiny organelles, but the strong dependence on equipment, low operating efficiency, invasive operation and so on make these technologies difficult to apply to high-throughput and high-efficiency occasion. Compared with the traditional ways of cell manipulation, microfluidic technology is famous for its low cost, low sample consumption, fast analysis speed, high sensitivity, high throughput and other advantages, which can make up for the inadequacy of traditional way of cell manipulation. However, many existing microfluidic chip-based cell capturing and sorting schemes are deficient, such as complex processing and low separation efficiency.To solve the shortage of the existing methods, we design four cell capture and sorting structures based on the principle of dam. The four structures are straight structure, triangular structure, circular structure and interdigitated structure. We use FLUENT software to simulate the four dam-based structures and the existing u-shaped structure, comparing the flow field distribution and analyzing the cell capture process. We also validate the theoretical analysis result through the experiment and evaluate the capture efficiency of the five structures. The result indicates that the interdigital structure has an advantage considering cells capture capacity or storage stability. The main advantage of the interdigitated structure is that it makes full use of the length of the chip to increase the cell capture capacity without increasing the chip width and can also solve the problem of clogging which may appear in the array structure like the U-shaped structure. Meanwhile, we can use it for cell sorting through multi chip cascade. In detail, researching work in this paper includes:① Chip structure design and computer simulationWe design four dam-based structures to study cell capture and sorting, and use FLUENT to simulate the four structures as well as the existing u-shaped structure. According to the pressure and velocity distribution of the chip, we adjust structure design parameters to seek for the optimal structure and analyze the cell manipulation process. The result demonstrates that there is a blind area in the depths of blind folded of interdigitated structure with slow flow rate, which will help cell capture and storage.② Microfluidic chip processingThis thesis analyzes the advantages and disadvantages of the existing several common processing technology, and then selects a proper solution which is suitable for processing chip. Chip manufacturing process includes mold making, PDMS molding and chip bonding. We make mold on silicon substrate coated SU-8 negative glue using photolithography method. Due to the existence of two kinds of height in the structure, the mold making process is different from the single height chips, and it requires twice mask, double exposure and one development. Because of the alignment problem, the mold made by conventional processing method is ineffective. We improve the mold making craft and propose an efficient scheme to solve the alignment problem. Then we coat PDMS on the mold to prepare chip and bond with the glass through oxygen plasma treatment. Finally, we verify the effectiveness of the chip.③ Cell manipulationWe use five structures to study cell manipulation including cell capture and sorting, and compare the result. We find the interdigitated structure has the largest capacity and the lowest rate of leakage catch.In order to simulate the situation where the peripheral circulating blood has tumor cells, we mix up the K562 cells and the red blood cells, which is future applied into the interdigitated structure to study cell sorting and K562 cells capturing. Cell separation experiments mainly include the separation of red and white cells from normal blood and K562 cells from the mixture of red blood cells and K562 cells. After 50ul diluted whole blood passes through with red blood cell density to be 2×105 cells per milliliter, we capture eight leukocytes. The proportion of red and white cells is 1250:1, within the range of normal adult red and white cells proportion (380:1-1375:1). After 50ul the mixture of red blood cells and K562 cells passes through with K562 cell density to be 2×103 cells per milliliter and red blood cell density to be 2×105 cells per milliliter, we capture 96 K562 cells. The experimental results show that the interdigitated structure has a strong ability to capture and is of high trapping efficiency.