Plain and drug loaded polyphosphazene membranes and microspheres in the treatment of rabbit bone defects

The healing of periodontal surgical defects was studied in rabbits, using p olyphosphazenes (POP) membranes and microspheres, both plain or drug-enrich ed. POP polymers having amino acid ester as backbone substituents, are used sin ce they resorb and undergo hydrolytic degradation to ammonia, phosphate and amino acids. Fourteen animal were operated in tibia, and other fourteen at angle of the mandible, that was reached by extraoral access. Bone defects were performed in tibiae, and covered either with POP or with poly-tetrafluoroethylene (P TFE) membranes, while other rabbits served as controls. The animals were sa crificed after one and two months, and the tibiae taken and processed for o ptical microscopy. Similar surgical defects were made in mandible, and POP membranes were plac ed over the breaches, some of which were filled with POP microspheres, both alone or mixed with granular hydroxyapatite. For comparison, two rabbits w ere treated with PTFE membranes, while other two served as controls. The an imals operated at the mandible were all sacrificed after one month, and the operated bones taken and processed for histology. It was found that POP membranes were very effective in promoting the healin g in tibiae, while less satisfactory results were found in the animals trea ted with PTFE membranes and in controls. In mandible, the healing occurred without a clear relationship with the grafted microgranular material or the membrane, since repairing bone was found also in controls. In any case, bo th POP membranes and microspheres showed excellent biocompatibility, as no inflammatory cells or macrophages were found in the surrounding tissue. Thi s property was completely independent from the presence of drug, since the matrix-entrapped drugs, released in the tissue, did not hamper the bone hea ling. It was also found that POP, by itself, has a positive effect in stimu lating the bone repair. (C) 2000 Kluwer Academic Publishers.