Thermo-responsive hydrogels with N-isopropylacrylamide/acrylamide interpenetrating networks for controlled drug release.

Series of thermo-sensitive hydrogels (PNAs) based on N-isopropylacrylamide/acrylamide interpenetrating polymer networks were synthesized via in situ free-radical polymerization. Poly (ethylene glycol diacrylate) and poly (ε-caprolactone diacrylate) were synthesized as macro-cross-linkers due to their excellent biocompatibilities. The macro-cross-linkers and hydrogels were characterized by (1)H NMR and FT-IR, respectively. The interior morphology of the hydrogels was observed by scanning electron microscopy. The swelling ratios at different temperatures and the swelling/deswelling kinetics of the hydrogels were studied. Their volume phase transition temperatures were also measured by differential scanning calorimetry characterization. The results indicated that the PNA hydrogels had uniform macroporous structures, and they not only had considerable swelling ratios, but also exhibited rapid swelling/deswelling kinetics and response sensitivities. In addition, the weight ratio of AAm/NIPAAm also affected the swelling performance and phase transition temperature of hydrogels, and its value less than 5% was the optimal proportion to achieve excellent comprehensive properties. Levofloxacin lactate and Naproxen were selected as drugs and simulated in vitro condition release, and the drug release results showed that the PNA hydrogels behaved fast release performance.