Biobased thermo/pH sensitive poly(N-isopropylacrylamide-co-crotonic acid) hydrogels for targeted drug delivery

Materials sensitive to external stimuli are recognized as safe and effective tool able to respond to specific demands in the therapy of various diseases. Thermo sensitive hydrogels based on poly(N-isopropylacrylamide) (P(NIPAAM)) are widely investigated for targeted drug delivery. Still, the abundance of the stimuli in the human body often requires more than one responsive group able to act simultaneously to achieve optimal therapeutic effects. Due to its pH sensitivity and bio-based production, crotonic acid (CA) was a monomer of choice for preparation of eco-friendly copolymer hydrogels based on NIPAAM and CA (P(NIPAAMcoCA)), which turned to be thermo and pH sensitive at the same time. The potential of the P(NIPAAMcoCA) system for encapsulation and controlled release of drugs with different solubility was investigated engaging water-soluble lidocaine hydrochloride and poorly water-soluble ibuprofen as model drugs. The hydrogels were characterized by various technics: FTIR, DSC, SEM and single compressive tests, while swelling behavior and controlled release of the drugs were analyzed with respect to the CA amount in two environments with different pH values at 25 °C and 37 °C. It was demonstrated that due to their dual responsiveness the P(NIPAAMcoCA) hydrogels have potential for controlled release of drugs with different solubility.