Ultrastructural features of the bone response to a plasma-sprayed hydroxyapatite coating in sheep

The intentions of this study were to characterize the macrosopic, microscopic, and structural aspects of a plasma‐sprayed implant and to thoroughly investigate bone tissue response after its implantation in sheep. Therefore, we used scanning electron microscopy, transmission electron microscopy (TEM), high‐resolution TEM, X‐ray diffraction, and energy‐dispersive X‐ray analyses. Assessment of the biomaterial prior to implantation showed a coating with irregular outlines and varying thickness, mainly consisting of hydroxyapatite (HA) covering a rough metallic implant core. Six months after insertion of the HA‐coated Ti‐6Al‐4V implant, neither mechanical failure of the coating‐substrate interface nor a significant loss of coating thickness was evident. However, an occasional lack of HA coating and phagocytosis of HA particles were noted. More generally, the implant was surrounded by well‐mineralized bone investing the smallest cavities of the plasma‐sprayed layer. Newly formed microcrystals with size, shape, and structure similar to those of bone apatite crystals were growing directly at the coating surface. These results suggest that the bone‐bonding behavior of the considered grooved implant should provide satisfactory osseointegration and be suitable for fixed prostheses. © 1997 John Wiley & Sons, Inc. J Biomed Mater Res, 36, 418–425, 1997.