HYDROXYAPATITE COATINGS ON TI BASED IMPLANTS

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Surgical and dental implants represent one of the fastest growing sectors in the health care industry. As many as 40 biomaterials are used for the 50 prosthetic devices used in medical and dental surgery. The proposed research program seeks to develop strongly adherent bioactive hydroxapatite (A) coatings on Titanium alloy implants. The program aims to develop a basic understanding of adherence (bonding), internal stresses and interfacial fracture resistance for HA coatings on Ti alloys. The program has three main goals: 1) to develop strongly adherent bioactive coatings on Ti alloys, 2) to elucidate a detailed understanding of the coating/Ti adherence, and 3) to provide fundamental understanding of the mechanical degradation of protective commercial and experimental HA coating layers through the measurement of internal stresses and interfacial fracture resistance for the HA/Ti coating systems. Several glasses in the system P2O5-MgO-CaO-SiO2-Na2-O-K2O system will be prepared. These glasses are adapted based on bioactive glass originally developed by Hench. Coatings will be made to study wetting and prepare specimens for interfacial reaction studies. Coated specimens will be analyzed by SEM, microprobe and thin film x-ray diffraction (TF-XRD) to identify the redox reactions that take place at the interface and with the glasses, and analysis of the interface itself by Auger and XPS with slow sputtering of surfaced parallel to the interface. Stability of the glasses will be determined in simulated body fluid (SBF) experiments. Glass surfaces after immersion experiments in SBF will be analyzed by SEM, TF-XRD, AAS, ICP and FTIS in order to determine the extent of HA formation on glass surfaces. Internal stresses and thermal expansion mismatch stresses will be analyzed by refined methods for performing in situ deflection measurements for determination of the residual stresses and stress gradients within the coating system. The objective will be to develop methods with sufficient precision to characterize both stresses at the interface and thermal stresses and to provide an adequate description of the driving forces for coating delamination and cracking. The fracture resistance of the coatings and the coating Ti/interface will be studied at room temperature by fracture mechanics testing and tensile testing of coated specimens. Indentation tests will also be used to measure the resistance to crack propagation (i.e., "toughness") of the interface, and thereby provide a quantitative measure of the bond strength.