Improved osteoconduction of cortical bone grafts by biodegradable foam coating

Alteration of the geometrical surface configuration of cortical bone allografts may improve incorporation into host bone. A porous biodegradable coating that would maintain immediate structural recovery and subsequently allow normal graft healing and remodeling by promoting bony ingrowth could provide an osteoconductive surface scaffold. We investigated the feasibility of augmenting cortical bone grafts with osteoconductive biodegradable polymeric scaffold coatings. Three types of bone grafts were prepared: Type I--cortical bone without coating (control), Type II--cortical bone coated with PLGA-foam, Type III--cortical bone coated with PPF-foam. The grafts were implanted into the rat tibial metaphysis (16 animals for each type of bone graft). Post-operatively the animals were sacrificed at 2 weeks and 4 weeks (8 animals for each type of bone graft at each time point). Histologic and histomorphometric analysis of grafts showed that the amount of new bone forming around the foam-coated grafts was significantly higher than in the control group (uncoated; p < 0.02). Although both foam formulations were initially equally osteoconductive, PLGA-based foam coatings appeared to have degraded at two weeks postoperatively, whereas PPF-based foam coatings were still present at 4 weeks postoperatively. While significant resorption was present in control allografts with little accompanying reactive new bone formation, PLGA-coated bone grafts showed evidence of bone resorption and subsequent bony ingrowth earlier than those coated with PPF-based foams suggesting that PPF-coated cortical bone grafts were longer protected against host reactions resulting in bone resorption.