Blood rheology and biomimetic rare cell segregation on microfluidic platforms
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Microtechnology has provided a new set of tools for studying fluid dynamics of blood at the scale of real microvessels. It has great potential for enrichment of specific cell populations such as leukocytes and circulating cancer cells from a sample of whole blood, which is the required first step of many clinical and basic research assays. Microfluidic devices are ideally suited for live cell separations because the sizes of blood cells lie in the range of channel sizes easily produced with polydimethylsiloxane (PDMS) soft lithography. However, standard molding methodologies produce channels with rectangular cross sections rather than tubes. To determine the applicability of such rectangular microchannels for blood flow analysis, I studied white blood cell (WBC) margination in channels of various geometries and blood compositions, focusing on rheological properties of blood well described in tubes and real blood vessels. I found that WBCs marginate in rectangular channels, and that the margination is enhanced downstream of sudden expansions; this behavior is similar to that seen in real blood vessels. Furthermore, the margination was dramatically affected by channel design. Based on this discovery, I have developed and optimized micro fluidic devices that take advantage of the natural flow properties of blood to separate nucleated cells (NCs) and circulating tumor cells (CTCs) from whole blood. The biomimetic nucleated cell extraction device consists of rectangular microchannels that are 20-400μ wide, 11μ deep and up to 2cm long. This invention requires only positive fluid pressure delivered by a syringe pump to operate. I have optimized the device design using experiments and computational predictions. This device is the first lab-on-a-chip device that operates on whole blood with no preprocessing or dilution and is able to extract 99% of NCs with 97.5% purity. The device is ready to be implemented as the initial stage of lab-on-a- chip devices. The potential applications are numerous, encompassing all preclinical and clinical assays that require blood cell separation (e.g. centrifugation or RBC lysis) as a preliminary step. Many such assays have already been migrated to lab-on-a-chip devices, but the nucleated cells still have to be separated off-chip using traditional, labor-intensive methods. Example down-stream analysis units which can be merged with my separation device include on-chip flow cytometry, genetic analyses, and leukoreduction of blood with sickle cell traits. I have further shown that a biomimetic CTC separation device can be developed based on blood rheology (plasma skimming and margination) coupled with immunohistochemistry.
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