To obtain a hydrogel-like elastic membrane, we prepared semi-interpenetrating polymer networks (IPNs) by the radical polymerization of methacrylates such as 2-methacryloyloxyethyl phosphorylcholine (MPC), 2-hydroxyethylmethacrylate, and triethyleneglycol dimethacrylate diffused into segmented polyurethane (SPU) membranes swollen with a monomer mixture. The values of Young's modulus for the hydrated semi-IPN membranes were less than that for an SPU membrane because of higher hydration, but they were much higher than that for a hydrated MPC polymer gel (non-SPU). According to a thermal analysis, the MPC polymer influenced the segment association of SPU. The diffusion coefficient of 8-anilino-2-naphthalenesulfonic acid sodium salt from the semi-IPN membrane could be controlled with different MPC unit concentrations in the membrane, and it was about 7 x 10(2) times higher than that of the SPU membrane. Fibroblast cell adhesion on the semi-IPN membrane was effectively reduced by the MPC units. We concluded that semi-IPNs composed of the MPC polymer and SPU may be novel polymer materials possessing attractive mechanical, diffusive-release, and nonbiofouling properties.