DEGRADATION POTENTIAL OF PLASMA-SPRAYED HYDROXYAPATITE-COATED TITANIUM IMPLANTS

The purpose of this study was to develop an analytical method for eval uating the dissolution behavior of plasma-sprayed hydroxyapatite (HAP) coatings. Six commercially available and clinically used coatings app lied to nonporous titanium coupons according to their respective speci fications for orthopedic devices were used in this study. Dissolution behavior was monitored by first preconditioning the implant in 0.15 mo l L(-1) sodium chloride solution at 37 degrees C until either equilibr ium or the desired change in solution hydrogen and calcium ion concent rations had been reached. In the second step, the implants were subjec ted to dual constant composition (DCC) dissolution under conditions of controlled undersaturation. Results indicate that the dissolution rat es of the HAP coatings may differ by as much as a factor of 5 despite the fact that analytical techniques, including X-ray diffraction and F TIR, indicate no change in crystallinity or composition of the coating s before and after the solution treatment. These results indicate that HAP coatings from different sources react very differently when place d in the same local aqueous environment. However, more work will be ne cessary before these in vitro results can be used to predict in vivo b ehavior. (C) 1995 John Wiley & Sons, Inc.