Tissue response to composite hydrogels for vertical bone augmentation in the rat

The objective of the present study was to develop a preclinical animal model for evaluating bone augmentation and to examine the level of bone augmentation induced by hydrogel composites. Design criteria outlined for the development of the animal model included rigid immobilization of bilateral implants apposed to the parietal bone of the rat, while avoiding the calvarial sutures. The animal model was evaluated through the implantation of hydrogel composites of oligo(poly(ethylene glycol) fumarate) (OPF) and gelatin microparticles releasing bone morphogenetic protein-2 (BMP-2). The BMP-2 release profile was varied and compared to the implantation of a material control without BMP-2. Each hydrogel composite was implanted within a polypropylene cassette, which was immobilized to the calvarial bone using screws, and empty cassettes were implanted as a control. The design criteria for the animal model were realized; however, the level of bone augmentation did not vary between any of the groups after 4 weeks. Osteoclastic bone resorption occurred to a higher extent in groups releasing BMP-2, but the cause could not be elucidated. In conclusion, a promising bone augmentation model was established in the rat; however, refinement of the hydrogel composites was suggested to optimize the constructs for bone augmentation applications.