Poly(maleic anhydride-co-acrylic acid)/poly(ethylene glycol) hydrogels with pH- and ionic-strength-responses

 Poly(maleic anhydride-co-acrylic acid), P(MA-AA), was synthesized by the free-radical copolymerization of maleic anhydride with acrylic acid, and fast responsive pH-sensitive poly(maleic anhydride-co-acrylic acid)/polyethylene glycol, P(MA-AA)/PEG, hydrogels were prepared using PEG as macromolecular cross-linking agent. FT-IR and 1H-NMR spectrometry were applied to characterize the structure of P(MA-AA). The influences of pH and ionic strength on the swelling behavior of P(MA-AA)/PEG hydrogels and the swelling-deswelling changes along with the repeated changes between acid and alkali conditions were studied. The results showed that there was a hundredfold difference in the swelling ratios between the conditions of acid and alkali, and the swelling capability could not be weakened after multiple swelling-deswelling cycles. The results of swelling kinetics demonstrated that the response rate of P(MA-AA)/PEG hydrogels was very fast, because the swelling transition points always occurred at 10 min. The pH-responsive hydrogels reported here might be a smart material for potentially applications in many areas, including biosensors, drug-delivery devices and tissue engineering.