Swelling and hydrolytic degradation behaviour of pH-responsive hydrogels of poly[(N-isopropylacrylamide)-co-(methacrylic acid)] crosslinked by biodegradable polycaprolactone chains

BACKGROUND: Stimuli-responsive hydrogels are typically obtained from non-biodegradable monomers. The use of biodegradable crosslinkers can overcome this limitation. In this context, the main aim of this work was to use modified polycaprolactone as a crosslinker in the preparation of pH-responsive hydrogels based on N-isopropylacrylamide and methacrylic acid to give poly[ (N-isopropylacrylamide)-co-(methacrylic acid)] (P(N-iPAAm-co-MAA)). RESULTS: Poly(caprolactone) dimethacrylate macromonomer was synthesized and successfully employed as crosslinker with various ratios in the synthesis of well-known pH-responsive hydrogels of P(N-iPAAm-co-MAA). The swelling properties of these degradable hydrogels were investigated. They practically do not swell at pH = 2, but exhibit a very high swelling capacity in distilled water and in solutions of pH = 7. In addition, degradation studies at pH = 12 showed that the hydrolysis of the ester groups in the polycaprolactone chains produces, after a relatively short time, the total solubilization of the polymer chains. CONCLUSION: The hydrogels under study have certain characteristics that could make them good candidates for use as matrices in controlled drug delivery. On the one hand, they do not swell in acid pH solution (stomach conditions) but they swell extensively at neutral pH. On the other hand, they became rapidly water soluble following degradation. (C) 2009 Society of Chemical Industry