We developed a new biomaterial for use in cell culture. The biomaterial enabled protein-free cell culture and the recovery of viable cells by lowering the temperature without the aid of supplements. insulin was immobilized and a thermoresponsive polymer was grafted onto a substrate. We investigated the effect of insulin coupling on the lower critical solution temperature (LCST) of the thermoresponsive polymer, poly(N-isopropylacrylamide-co-acrylic acid), using polymers that were ungrafted, or coupled with insulin. The insulin conjugates were precipitated from an aqueous solution at high temperatures, but they were soluble at low temperatures. The LCST was not significantly affected by the insulin coupling. The thermoresponsive polymer was grafted to glow-discharged polystyrene film and covalently conjugated with insulin. The surface wettability of the conjugate film was high at low temperatures and low at high temperatures. The amounts of immobilized insulin required to stimulate cell growth were 1-10% of the amount of free insulin required to produce the same effect. The maximal mitogenic effect of immobilized insulin was greater than that of free insulin. About half of the viable cells was detached from the film only by lowering the temperature. The recovered cells proliferated normally on new culture dishes.