Selectively permeable membranes for biosensors are provided. In one embodiment, the membrane includes a polymer mixture that includes a polyurethane component, a siloxane component, and a hydrogel component, the components in the mixture in amounts of about 60 to about 80 wt % polyurethane, about 10 to about 20 wt % siloxane, and about 10 to about 20 wt % hydrogel. The membrane has a surface restructured to be hydrophilic, with the restructured surface being crosslinked ed via reactive end groups on at least one of the polyurethane, the siloxane, and the hydrogel components. In another embodiment, the membrane includes a solvent cast film which includes a mixture of a first polyether-based thermoplastic polyurethane copolymer, a polyether-based polyurethane copolymer, and, optionally, a second polyether-based thermoplastic polyurethane copolymer.