EVALUATION OF DIFFERENT PREPARATIONS OF PLASMA-SPRAY HYDROXYAPATITE COATING ON TITANIUM-ALLOY AND DUPLEX STAINLESS-STEEL IN THE RABBIT

Many variables are involved in hydroxyapatite coating of metals by pla sma-spray techniques. The authors have investigated the biological res ponse to some of the most relevant variables in a controlled in vivo t rial. The bone response in the rabbit towards hydroxyapatite coated cy linders was studied keeping the following variables fixed: (a) crystal linity of coating (greater than 90% and between 70% and 60%); (b) thic kness of coating (50 and 100 mu m); (c) metallic substrate (titanium a lloy and duplex stainless steel). Analysis of the results highlights t he importance of defining the crystallinity of the coating to forecast its in vivo behaviour: highly crystalline coating is more stable in t ime but can give rise to fragmented bulky particles; a less crystallin e coating is subject to slow degradation in the long term but facilita tes its substitution by newly formed bone. Furthermore, it has been fo und that no relevant differences can be ascribed to a variation in coa ting thickness between 50 and 100 mu m. It has, also, been observed th at there are no differences when duplex stainless steel is used instea d of titanium alloy as metallic substrate, confirming that bone respon ds primarily to the coating.