Control of cell detachment in a microfluidic device using a thermo-responsive copolymer on a gold substrate

The control of cell adhesion is crucial in many procedures in cellular biotechnology. A thermo-responsive poly(N-isopropylacrylamide)-poly(ethylene glycol)-thiol (PNIPAAm-PEG-thiol) copolymer was synthesized for the formation of self-assembled monolayers (SAM) that allow the control of adhesion of cells on gold substrates. The contact angle of water on these layers varies between 65 degrees at a temperature of 45 degrees C and 54 degrees at 25 degrees C. This behaviour is consistent with a transition of the polymer chains from an extended and highly hydrated to a collapsed coil-like state. At 37 degrees C, cultivated fibroblasts adhere and spread normally on this surface and detach by reducing the temperature below the lower critical solution temperature (LCST). Layers can repeatedly be used without loss of their functionality. In order to quantify the capability of the copolymer layer to induce cell detachment, defined shear forces are applied to the cells. For this purpose, the laminar flow in a microfluidic device is used. Our approach provides a strategy for the optimization of layer properties that is based on establishing a correlation between a functional parameter and molecular details of the layers.