Synthesis and Properties of Photopolymerized pH-Sensitive Hydrogels of Methacrylic Acid and Biodegradable PEG-b-PCL Macromer

The pH-sensitive hydrogels were synthesized via in situ copolymerization ofmethacrylic acid (MAA) with poly(ethylene glycol)-b-poly(ε-caprolactone) (PEGb-PCL) macromer as a biodegradable cross-linker in aqueous solutions underUV irradiation. The swelling measurement results indicated that pH sensitivity of thehydrogels was highly dependent on the MAA content in the hydrogels as well as the pHof the surrounding medium. The pH-sensitive hydrogels displayed faster deswellingrates and lower water retentions at high MAA content. In vitro hydrolytic degradationinvestigation showed that the introduction of MAA component could improve thedegradation rate of the hydrogels, and an increase in its content could induceaccelerated degradation of the hydrogel at pH 7.4 of PBS solutions at 37°C. Thepotential of the hydrogels as vehicles for delivering BSA was examined. Theaccumulative release percentage of BSA (Fraction V) as a model protein drug could betuned by changing the compositions of the hydrogels and pH of the local medium. Therelease mechanism of BSA based on the Peppas equation followed the non-Fickiandiffusion at pH 7.4 of PBS solutions at 37°C. The interior morphology of the hydrogelswas also observed by scanning electron microscopy (SEM) after freeze drying at theirequilibrium states of pH 7.4 of PBS solutions. The results revealed that the pore size ofthe hydrogels became larger when introducing the MAA moieties and increased withthe increase of the MAA content of the hydrogels. These biodegradable pH-sensitivesynthetic hydrogels could be potentially used as smart drug delivery systems