Nanometric grafting of poly (N-isopropylacrylamide) onto polystyrene film by different doses of gamma radiation

Poly N-isopropylacrylamide was successfully grafted onto a polystyrene cell culture dish by gamma ray. In this study, the effect of a radiation dose (radiation absorbed dosages of 10, 20, 30, 40 KGy) under appropriate temperature and grafting conditions was investigated. The FTIR analysis showed the existence of the graft PNIPAAm on the substrate. The optimal value of the dose for grafting was 40 KGy at 50°C. The SEM and AFM images clearly showed that increasing the absorbed dose of radiation would increase the amount of grafting. Surface topography and graft thickness in AFM images of the radiated samples showed that the PNIPAAm at the absorbed dose of radiation was properly grafted. The thickness of these grafts was about 50–100 nm. The drop water contact angles of the best grafted sample at 37°C and 10°C were 55.3 ± 1.2o and 61.2 ± 0.9o respectively, which showed the hydrophilicity and hydrophobicity of the grafted surfaces. DSC analysis also revealed the LCST of the grafted sample to be 32°C. Thermo-responsive polymers were grafted to dishes covalently which allowed fibroblast cells to attach and proliferate at 37°C; the cells also detached spontaneously without using enzymes when the temperature dropped below 32°C. This characteristic proves that this type of grafted material has potential as a biomaterial for cell sheet engineering.