Injectable and thermosensitive PLGA-g-PEG hydrogels containing hydroxyapatite: preparation, characterization and in vitro release behavior.

Here we report the design and characterization of injectable and thermosensitive hydrogel composites comprised of poly(lactic acid-co-glycolic acid)-g-poly(ethylene glycol)(PLGA-g-PEG) containing hydroxyapatite (HA) for potential application in bone tissue engineering. Inclusion of HA into the hydrogels would provide both enhanced mechanical properties and bioactivity to the composites. The effects of HA on the properties of the hydrogels were investigated in terms of storage modulus, sol-gel transition properties, pH and in vitro dye release behavior. The hydrogel composites were also studied by scanning electron microscopy (SEM), x-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The results revealed that hydrogel composites preserved their sol-gel transition properties in the presence of HA. The storage modulus of the hydrogels was enhanced in a HA-content dependent manner, and the acidic pH environment of the hydrogel was neutralized by HA, both representing great advantages over the hydrogel alone. SEM images showed that HA particles were well dispersed and distributed within the hydrogel matrix. The composites showed a sustained release of a small molecule model dye for up to two weeks with slight increase of release with addition of HA. This work demonstrates the formation of novel thermogelling composites of PLGA-g-PEG and HA that are injectable and promote controlled release.