Biomimetic postcapillary expansions for enhancing rare blood cell separation on a microfluidic chip

Abstract

Blood cells naturally auto-segregate in postcapillary venules, with the erythrocytes (red blood cells, RBCs) aggregating near the axis of flow and the nucleated cells (NCs)—which include leukocytes, progenitor cells and, in cancer patients, circulating tumor cells—marginating toward the vessel wall. We have used this principle to design a microfluidic device that extracts nucleated cells (NCs) from whole blood. Fabricated using polydimethylsiloxane (PDMS) soft lithography, the biomimetic cell extraction device consists of rectangular microchannels that are 20–400 μm wide, 11 μm deep and up to 2 cm long. The key design feature is the use of repeated expansions/contractions of triangular geometry mimicking postcapillary venules, which enhance margination and optimize the extraction. The device operates on unprocessed whole blood and is able to extract 94 ± 4.5% of NCs with 45.75 ± 2.5-fold enrichment in concentration at a rate of 5 nl s⁻¹. The device eliminates the need to preprocess blood viacentrifugation or RBC lysis, and is ready to be implemented as the initial stage of lab-on-a-chip devices that require enriched nucleated cells. The potential downstream applications are numerous, encompassing all preclinical and clinical assays that operate on enriched NC populations and include on-chip flow cytometry (A. Y. Fu et al., Anal. Chem., 2002, 74, 2451–2457; A. Y. Fu et al., Nat. Biotechnol., 1999, 17, 1109–1111), genetic analyses (M. M. Wang et al., Nat. Biotechnol., 2005, 23, 83–87; L. C. Waters et al., Anal. Chem., 1998, 70, 5172–5176) and circulating tumor cell extraction (S. Nagrath et al., Nature, 2007, 450, 1235–1241; S. L. Stott et al., Proc. Natl. Acad. Sci. U. S. A., 2010, 18392–18397; H. K. Lin et al., Clin. Cancer Res., 2010, 16, 5011–5018).