J. L. Morenza

The improvement of the reliability of the contact between the osseous tissues and the implant materials has been tested by recovering the metallic implants with ceramic materials, usually calcium phosphates. In our study, the calcium phosphate recovering layers were deposited by means of a pulsed-laser deposition technique. Our aim was to to evaluate the tissue interactions established between cortical bone and titanium implants covered by five different layers, ranging from amorphous calcium phosphate to crystalline hydroxyapatite, obtained by altering the parameters of the laser ablation process. The surgical protocol of the study consisted in the simultaneous implantation of the five types of implants in both the tibial dyaphisis of three Beagle dogs, sacrificed respectively one, two and three months after the last surgical procedures. After the sacrifice, the samples were submitted to a scheduled procedure of embedding in plastic polymers without prior decalcification, in order to perform the ultrastructural studies: scanning microscopy with secondary and backscattered electrons (BS-SEM). Our observations show that both in terms of the calcified tissues appearing as a response to the presence of the different coatings and of time of recovering, the implants coated with crystalline calcium phosphate layers by laser ablation present a better result than the amorphous-calcium-phosphate-coated implants. Moreover, the constant presence of chondroid tissue, related with the mechanical induction by forces applied on the recovering area, strongly suggests that the mechanisms implied in osteointegration are related to endomembranous, rather than endochondral ossification processes.

Ceramic-metal Cr3C2-NiCr composite coatings obtained by high velocity oxy fuel thermal spraying (HVOF) lack of wear and corrosion resistance due to their high porosity. One solution to this problem can be achieved through the irradiation of the coating by means of a high power laser in order to melt a thin superficial layer and seal the coating. A Nd:YAG laser has been used to irradiate samples under those conditions where the best sealing results are obtained. The properties of either untreated and laser treated coatings have been investigated through scanning electron microscopy, x-ray diffractometry and profilometry. These analyses have revealed that the laser treatment induces important changes in the surface of the irradiated samples leading to a decrease in roughness, the elimination of porosity and an increase in hardness. Unfortunately, the treatment also promotes the presence of cracks.