Microfluidic Devices with Engineered Micro-/Nanostructures for Cell Isolation

Abstract

Isolation of cells from blood is critical for vast biomedical applications. The focus of this dissertation is on the isolation of circulating tumor cells (CTCs) from patient blood, which contains important prognostic and diagnostic information. Challenges in this field originates from the striking contrast between the rare amount of CTCs (1-10 per mL) and vast other normal cells (millions of white blood cells (WBCs) and billions of red blood cells per mL). Various techniques have been developed to isolate CTCs in the recent decades, while the most demanding clinical requirements lie in two aspects: higher capture efficiency meaning the strong ability to isolate the rare CTCs and higher purity meaning the strong ability to repel all other normal cells. In order to better serve clinical practice, we developed four microfluidic platforms aiming at high capture efficiency and high purity, thus advancing the cancer patient care. By extending the concept of the hallmark immunoaffinity based grooved-herringbone (HB) chip, we first developed a wavy-HB chip by smoothing the grooved patterns to wavy patterns. The wavy-HB chip was demonstrated to not only achieve high capture efficiency (up to 85.0%) by micro-vortexes induced by HB structures, but achieve high purity (up to 39.4%) due to the smooth wavy microstructures. The HB structures were then further optimized through a refined computational model implemented with cell adhesion probability. The particulate cell transport dynamics was shown to be crucial in determining the optimized geometry for CTC capture. To further enhance the CTC capture, integration of nanostructures was examined due to their intrinsic large surface area-to-volume ratio. By exploring the geometric effects of nanopillars on CTC capture, we unraveled an interesting linear relationship between CTC capture efficiency and effective nanopillar contact area. We then developed a fabrication approach to deposit nanoparticles on the wavy-HB patterns to form hierarchical micro/nanostructures. The hierarchical wavy-HB chip was demonstrated to achieve a capture efficiency up to ~98% and a high purity performance (only ~680 WBCs per 1 mL blood). Over the course of the above-mentioned work, there emerges another clinical need which requires captured CTCs to be released and re-cultured for post-analysis such as drug screening. We thus developed two microfluidic chips attempting to achieve this goal. The first platform is an integration of immunomagnetic particles on the developed wavy-HB chip. In addition to the good device performance brought by the wavy-HB patterns, CTCs were able to be released from the capture bed by removing the magnetic field. The collected CTCs labeled with magnetic particles were able to be re-cultured and it was found that these magnetic particles were subject to self-removal during cell proliferations. The second platform was an inclined wavy patterns coated with E-selectin, which was able to form weak adhesion forces with WBCs and CTCs. A proof-of-concept work was performed to demonstrate that WBCs and CTCs were able to be separated along different pathways due to the different adhesion forces and the inclined direction guidance. With all these developed cancer cell isolation microfluidic chips, we showed our contributions toward effective cancer cell isolation and eventually cancer treatment