Biocompatible zwitterionic copolymer networks with controllable swelling and mechanical characteristics of their hydrogels.

The equilibrium swelling ratio in both water and physiological solution of the biocompatible copolymer networks of 3-dimethyl(methacryloyloxyethyl)ammonium propane sulfonate (DMAPS) and N-vinyl-2-pyrrolidone (NVP) is determined as a function of copolymer composition. It is established that equilibrium swelling ratio of the polymer networks in physiological solution increase with raise of zwitterionic monomer unit fraction. A sharp decrease of this ratio in water with increase of zwitterionic monomer unit fraction is related to the formation of thermolabile physical junctions produced by dipole-dipole interactions between the zwitterionic side groups. The same fact affects considerably the storage and loss moduli of the copolymer hydrogels as well as the morphology of the dried networks. Scanning electron microscopy images provided evidence of the occurrence of a lamellar structure forming the morphology of the polymers. This was corroborated by differential scanning calorimetry experiments. In this way a possibility for effective control on swelling ratio in different solutions and the mechanical properties of these novel biocompatible networks are established.