Design and synthesis of dual-responsive hydrogels based on N,N-dimethylaminoethyl methacrylate by copolymerization with N-isopropylacrylamide

Copolymeric hydrogels of N,N-dimethylaminoethyl methacrylate (DMAEMA) and N-isopropylacrylamide (NIPA) of various monomer ratios were evaluated as thermo-responsive and pH-responsive systems for the development of controlled-release and targeted-delivery devices. The swelling properties were investigated with different temperature, pH, and monomer feed ratios. The results show that the temperature-dependent and pH-dependent phase transition of poly(N,N-dimethylaminoethyl methacrylate-N-isopropylacrylamide) (P(DMAEMA-NIPA)) copolymeric hydrogels can be controlled by changing the amount of NIPA units in the network chains. In experiments to determine the temperature-dependent swelling of copolymeric hydrogels in water, it was found that the swelling ratio rapidly decreases as the temperature increases between 35 and 70 C. To characterize the network structure of the copolymeric hydrogels corresponding to effective cross-linking density and average network chain length, uniaxial compressive mechanical testing was carried both after the preparation of hydrogels and after their equilibrium swelling in water. The data obtained demonstrates that the resulting copolymeric hydrogels are promising as materials with tunable hydrophilicity-hydrophobicity and swelling behavior responsive to temperature and pH. [Figure not available: see fulltext.]