Composite poly(DL-lactide-co-glycolide)/poly(acrylic acid) hydrogels synthesized using UV and gamma irradiation: comparison of material properties

Composite hydrogels capable of controlled drug delivery via ion exchange are an interesting group of materials for the construction of implantable drug reservoirs for electrically charged drugs. In this study, we synthesized composite poly(DL-lactide-co-glycolide)/poly(acrylic acid) (PLGA-PAA) hydrogels by sequential application of UV or gamma irradiation and traditional phase inversion. Physicochemical properties of the composite PLGAPAA hydrogels were investigated using Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). We examined the ion exchange capacity (IEC) and swelling behavior of these materials to determine their potential as drug reservoirs. Composite PLGA-PAA hydrogel synthesized using UV irradiation (UV-PLGA-PAA) exhibited a porous microstructure with submicron-sized hydrogel-rich aggregates and homogeneous chemical composition. Swelling behavior and IEC of this material were highly reproducible. Composite PLGA-PAA hydrogels synthesized using gamma irradiation (G-PLGA-PAAs) had a less uniform microstructure with larger pores and micron-sized hydrogel-rich aggregates while exhibiting rather inhomogeneous chemical composition. These materials showed superior swelling properties, but a more variable IEC, compared to the material fabricated using UV irradiation. Results of DSC analysis showed a dose-dependent decrease in glass transition temperature for G-PLGA-PAAs indicating the effects of PLGA chain scission. Our findings indicate that gamma irradiation is a possible alternative to UV irradiation in the synthesis of composite PLGA-PAA hydrogels which can modify or control important material properties. However, the synthesis protocol using gamma irradiation should be further optimized to improve the IEC reproducibility. In our future research, we will investigate the in vitro release of charged drugs from synthesized composite PLGA-PAA hydr