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 of methacrylic acid (MAA) with poly(ethylene glycol)-b-poly(ε-caprolactone) (PEGb- PCL) macromer as a biodegradable cross-linker in aqueous solutions under UV irradiation. The swelling measurement results indicated that pH sensitivity of the hydrogels was highly dependent on the MAA content in the hydrogels as well as the pH of the surrounding medium. The pH-sensitive hydrogels displayed faster deswelling rates and lower water retentions at high MAA content. In vitro hydrolytic degradation investigation showed that the introduction of MAA component could improve the degradation rate of the hydrogels, and an increase in its content could induce accelerated degradation of the hydrogel at pH 7.4 of PBS solutions at 37°C. The potential of the hydrogels as vehicles for delivering BSA was examined. The accumulative release percentage of BSA (Fraction V) as a model protein drug could be tuned by changing the compositions of the hydrogels and pH of the local medium. The release mechanism of BSA based on the Peppas equation followed the non-Fickian diffusion at pH 7.4 of PBS solutions at 37°C. The interior morphology of the hydrogels was also observed by scanning electron microscopy (SEM) after freeze drying at their equilibrium states of pH 7.4 of PBS solutions. The results revealed that the pore size of the hydrogels became larger when introducing the MAA moieties and increased with the increase of the MAA content of the hydrogels. These biodegradable pH-sensitive synthetic hydrogels could be potentially used as smart drug delivery systems.