Ultrathin Poly(N-isopropylacrylamide) Grafted Layer on Polystyrene Surfaces for Cell Adhesion/Detachment Control

We investigated physicochemical properties of two types of poly(N-isopropylacrylamide) (PIPAAm)-grafted tissue culture polystyrene (TCPS) surfaces, to elucidate the influential factors for thermally regulated cell adhesion and detachment to PIPAAm-grafted surfaces. The two types of PIPAAm-grafted surfaces were prepared by the electron beam polymerization method. Attenuated total reflection Fourier transform infrared spectroscopy revealed that amounts of the grafted polymers were 1.4 +/- 0.1 microg/cm2 for PIPAAm-1.4 and 2.9 +/- 0.1 microg/cm2 for PIPAAm-2.9. Both PIPAAm-grafted surfaces showed hydrophobic/hydrophilic property alterations in response to temperature. However, PIPAAm-1.4 surfaces were more hydrophobic (cos theta = 0.21 at 37 degrees C and cos theta = 0.35 at 20 degrees C) than PIPAAm-2.9 (cos theta = 0.42 at 37 degrees C and cos theta = 0.50 at 20 degrees C) both above and below the PIPAAm's transition temperature. Thicknesses of the grafted PIPAAm layers were estimated to be 15.5 +/- 7.2 nm for PIPAAm-1.4 and 29.5 +/- 8.4 nm for PIPAAm-2.9, by the use of UV excimer laser and atomic force microscope. Bovine carotid artery endothelial cells (ECs) adhere to the surfaces of PIPAAm-1.4 and proliferate to form confluent cell monolayers. The cell monolayers were harvested as single cell sheets by temperature decrease from 37 to 20 degrees C. On the contrary, ECs did not adhere to the surfaces of PIPAAm-2.9. This phenomenon was correlated with an adsorption of cell adhesion protein, fibronectin, onto surfaces ofPIPAAm-1.4 and -2.9. In the case of nano-ordered thin grafted surfaces, the surface chain mobility is strongly influenced by the thickness of PIPAAm grafted layers because dehydration of PIPAAm chains should be enhanced by the hydrophobic TCPS surfaces. PIPAAm graft amounts, that is, thickness of the PIPAAm grafted layers, play a crucial role in temperature-induced hydrophilic/hydrophobic property alterations and cell adhesion/detachment behavior.