Evaluation of a novel malleable, biodegradable osteoconductive composite in a rabbit cranial defect model

The ceramic form of calcium phosphate osteoconductive material such as hydroxyapatite is brittle, non-malleable and non-degradable, and these mechanical properties limit its clinical application in calvarium reconstruction. To improve these properties, we developed a malleable, biodegradable osteoconductive composite composed of tricalcium phosphate particles bound by a gelatin which is set by glutaraldehyde mediated cross-linking. The composite was implanted into a 15 X 15 mm full-thickness, calvarial defect in 20 rabbits for up to 3 months. Twelve rabbits were left unreconstructed as controls. Specimens were retrieved at 2 weeks, 1, 2 and 3 months. Five reconstructed and 3 unreconstructed rabbits were examined for each time period. The assessment included a series of post operative gross examinations, radiographs and histologic evaluations. We are able to demonstrate that this composite is (1) biocompatible, with little tissue reaction; (2) osteoconductive, with progressive growth of new bone into the calvarial defect; (3) biodegradable, with progressive replacement of the composite by new bone, acellular matrix and bone-like material. Replacement of this composite by new bone is postulated to occur by a combination of osteoconduction and biodegradation. These results indicate that further experimental research to combine this malleable, biodegradable, osteoconductive composite with an osteoinductive agent such as bone morphogenetic protein may generate new biomaterial for full-thickness calvarial defect reconstruction.