Injectable in Situ Shape-Forming Osteogenic Nanocomposite Hydrogel for Regenerating Irregular Bone Defects.

The in situ forming injectable hydrogels are appealing for irregular bone defects because of the ease of administration and the addition of ceramics, molecules, and proteins into the hydrogel. We have developed in situ shape-forming hydrogel using oxidized alginate and gelatin as the hydrogel matrix. Whitlockite bioceramic nanoparticles (WH NPs) were incorporated, as they provide enhanced osteogenic stimulation compared to hydroxyapatite via providing higher local ion concentration. The drug simvastatin was also incorporated into the hydrogel system, as it increases the expression of BMP-2 thereby provide environment for bone regeneration. The presence of both WH nanoparticles and simvastatin would enhance bone regeneration potential. The whitlockite nanoparticles (80 ± 8 nm) were synthesized by precipitation method and were characterized. The nanocomposite hydrogel system was characterized by SEM, FTIR and rheologically. The gelation time of the in situ nanocomposite hydrogel was determined by rheological analysis as 28 s, whereas hydrogel alone showed 132 s. Addition of WH NPs not only shortened the gelation time but also increased the gel strength. The in vitro release of simvastatin from the nanocomposite hydrogel showed a release over a period of 28 days. The alkaline phosphatase (ALP) level also showed a significant increase. RUNX2 and BMP2 expressions showed that nanocomposite hydrogel enhanced the osteogenic differentiation. In vivo bone regeneration studies in mice cranial defect studies showed nanocomposite hydrogel was effective in regenerating the bone compared to controls. Thus, the simvastatin-incorporated oxidized alginate-gelatin/WH NPs hydrogel system has the potential to be used as a repairing and regenerative system in cranial bone defects.