Microfluidic-based Magnetic Separation Of Tumor Cells

Based on traditional micro-processing technology, microfluidics miniaturizes the fundamental manipulations of physics, material science, chemistry and biomedical engineering on a chip, which only has the size of a single coin, through structure design and function integration. Compared with traditional techniques, microfluidic chip has a brighter future for applications because its less sample consumption, faster processing speed, high throughput and low cost.By utilizing those advantages of microfluidics, which is mentioned above, traditional method of magnetic separation is integrated in microfluidics for the capture and isolation of tumor cells. Compared with the existing and reported works, our microfluidic chip can realize efficient capture and controllable release, and further the detachment of tumor cells and magnetic beads, providing new opportunities for the research and analysis of circulating tumor cells in biomedical applications.The main content of my thesis is briefly summarized here:Firstly, the common background of the research field and significant techniques as well as the state-of-art are demonstrated. Specifically, the origin and development of microfluidics is introduced at the beginning, then the microprocessing technology and fundamental theories are elaborated. Next, the micro-mixing and micro-isolating methods are critically discussed and related examples are also provided. The motivation and topic of my thesis are given at last.Then, the experimental details of the fabrication and surface modification are demonstrated. Various methods of synthesizing magnetic particles are compared before presenting our hydrothermal method. Then the as-prepared magnetic particles, or magnetic beads are functionalized for further biomedical assays. And next, the experimental method for the fabrication of microfluidic chip is given and finite element analysis is used to confirm and validated the function of our microchips. Specifically, our microchip consists two parts:the PDMS herringbone structure and nickel micropillar arrays. The PDMS polymer chip is fabricated by soft-lithography and the nickel micropillars in the microchannel is electroplated on the glass substrate. To validate the function of our microfluidic chip, we turn to numerical simulation to analyze the distribution of magnetic field and velocity field in the microchannel.Furthermore, our prepared microfluidic chip was utilized to capture tumor cells in blood samples. For the proof-of-concept study, a HCT116 colorectal cancer cell line is employed to exam the capture efficiency. The flow rate and the micropillar geometry are optimized by studying their effects on capture efficiency. Then different number of HCT116 cells spiked in two kinds of cell suspension were investigated, yielding capture efficiency >70% in culture medium and >40% in blood sample, respectively. Moreover, the captured HCT116 cells are able to be released from the micropillars with a saturated efficiency of 92.9% upon the removal of applied magnetic field and we found that 78% of the released cancer cells are viable, making them suitable for subsequent biological analysis.Based on the work mentioned above, by combining on-chip purification and off-chip enzymatic treatment, we demonstrate a two-stage strategy to enhance the purity of captured cancer cells from blood samples. The on-chip purification introduces stirring flow to increase the capture sensitivity and decrease non-specifically bounded cells. The off-chip enzymatic treatment enables the cancer cells to be released from the attached magnetic beads, further improving the purity and enabling next re-culture. For the proof-of-concept study, spiked cancer cells are successfully obtained from unprocessed whole blood with high recovery rate (-68%) and purity (～61%), facilitating next RNA expression analysis.Finally, I will give a brief summary of my work during my Ph.D. time, from the fabrication of magnetic beads and microchips to the capture and release of tumor cells; And a perspective of the future work, which can extend my present research, is also provide.