In order to develop a biodegradable pin for diaphyseal femoral fracture fixation, polylactide acid (PLA) pins were implanted in the femoral bone of rats. A distal diaphyseal fracture was performed. Union and tissue reaction to PLA pins versus stainless steel pins was studied after 15 days, and 1, 2 and 6 months of implantation. PLA and stainless steel pins induced the same union and a similar tissue reaction during the 6-month period. Biocompatibility of material was satisfactory.

In order to develop a biodegradable interlocking nail for fracture fixation, hydoxylapatite pins and paste were implanted in the femoral bone of rats. A distal fracture was performed. The union and the tissue reaction to hydroxylapatite versus stainless-steel rods were studied after 15 days, 1, 2 and 6 months implantation. Metal pins induced a union. Hydroxylapatite pins (Ossatite®) did not prevent callus formation, but did not lead to consolidation in all cases due to weakness of gelatin matrix binding the apatite particles together. The biocompatility of material is satisfactory and the osteo-inductive properties of hydroxylapatite was confirmed. With injectable Ossatite®, we could not obtain rat femoral fracture consolidation. We can confirm good biomaterial tolerance in bone which contrasts with important soft tissue reactions. Use of such material should be carefully limited to filling intra-osseous cavities.

Hydroxyapatite (HAp) coatings were deposited onto substrates of metal biomaterials (Ti, Ti6Al4V, and 316L stainless steel) by electrophoretic deposition (EPD). Only ultra-high surface area HAp powder, prepared by the metathesis method 10Ca(NO3)2 + 6(NH4)2HPO4 + 8NH4OH), could produce dense coatings when sintered at 875–1000°C. Single EPD coatings cracked during sintering owing to the 15–18% sintering shrinkage, but the HAp did not decompose. The use of dual coatings (coat, sinter, coat, sinter) resolved the cracking problem. Scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) inspection revealed that the second coating filled in the “valleys” in the cracks of the first coating. The interfacial shear strength of the dual coatings was found, by ASTM F1044-87, to be ∼12 MPa on a titanium substrate and ∼22 MPa on 316L stainless steel, comparing quite favorably with the 34 MPa benchmark (the shear strength of bovine cortical bone was found to be 34 MPa). Stainless steel gave the better result since α-316L (20.5 μm mK-1) > α-HAp (∼14 μm mK-1), resulting in residual compressive stresses in the coating, whereas α-titanium (∼10.3 μm mK-1) < α-HAp, resulting in residual tensile stresses in the coating. © 1999 Kluwer Academic Publishers