Temperature modulated protein release from pH/temperature-sensitive hydrogels.

A hydrogel which exhibits a volume phase transition in response to pH as well as temperature has been synthesized and utilized as a matrix for the controlled release of insulin. Insulin crystals have been entrapped into the hydrogel matrix during the copolymerization process of N-isopropylacrylamide and the cationic monomer, N,N'-dimethylaminopropylmethacrylamide. The former allows the gel to exhibit a temperature sensitivity, and the latter gives the gel a pH-sensitivity. Insulin release profiles from the gel matrix have been investigated as functions of pH, temperature, and thermal cycling operation. Temperature and thermal cycling operations largely affected the insulin release rate while pH variation did not significantly influence the release profiles.