Adhesion assays of endothelial cells on nanopatterned surfaces within a microfluidic channel.

We present a simple analytical method to measure adhesion of human umbilical vein endothelial cells (HUVECs) and calf pulmonary artery endothelial cells (CPAEs) using nanopatterned, biodegradable poly(lactic-co-glycolic acid) (PLGA) surfaces for potential applications to artificial tissue-engineered blood vessel. Various nanostructured PLGA surfaces (350 nm wide ridges/350 nm grooves, 350 nm ridges/700 nm grooves, 350 nm ridges/1750 nm grooves, 700 nm ridges/350 nm grooves, 1050 nm ridges/350 nm grooves, 1750 nm ridges/350 nm grooves) and flat (unpatterned) surfaces were fabricated on the bottom of polydimethylsiloxane (PDMS) microfluidic channel of 2 mm width and 60 microm height by using thermal imprinting and irreversible channel bonding. To measure adhesion strength of HUVECs and CPAEs, the cells were exposed to a range of shear stress (12, 40, and 80 dyn/cm(2)) within the channels for 20 min after a preculture for 3 days and the remaining cells were counted under each condition. The highest adhesion strength was found on the surface of 700 nm wide ridges, 350 nm wide grooves for both cell types. The enhanced adhesion on nanopatterned surfaces can be attributed to two aspects: (i) contact guidance along the line direction and (ii) clustered focal adhesions. In particular, the contact guidance induced cell alignment along the line directions, which in turn lowers wall shear stress applied to the cell surface, as supported by a simple hydrodynamic model based on cell morphology.

Label-free, microfluidic separation and enrichment of human breast cancer cells by adhesion difference.

A label-free microfluidic method for separation and enrichment of human breast cancer cells is presented using cell adhesion as a physical marker. To maximize the adhesion difference between normal epithelial and cancer cells, flat or nanostructured polymer surfaces (400 nm pillars, 400 nm perpendicular, or 400 nm parallel lines) were constructed on the bottom of polydimethylsiloxane (PDMS) microfluidic channels in a parallel fashion using a UV-assisted capillary moulding technique. The adhesion of human breast epithelial cells (MCF10A) and cancer cells (MCF7) on each channel was independently measured based on detachment assays where the adherent cells were counted with increasing flow rate after a pre-culture for a period of time (e.g., one, two, and four hours). It was found that MCF10A cells showed higher adhesion than MCF7 cells regardless of culture time and surface nanotopography at all flow rates, resulting in label-free separation and enrichment of cancer cells. For the cell types used in our study, an optimum separation was found for 2 hours pre-culture on the 400 nm perpendicular line pattern followed by flow-induced detachment at a flow rate of 200 microl min(-1). The fraction of MCF7 cells was increased from 0.36 +/- 0.04 to 0.83 +/- 0.04 under these optimized conditions.