Análise do substrato e revestimento de próteses de quadril fabricadas em titânio puro e liga Ti-6Al-4V.

Abstract

Metallic porous coatings have been used on hip orthopedic prostheses to promote ingrowth of bone into the porous coating prostheses. Among different materials used to manufacture hip prostheses and coatings are titanium materials. Mostly used and available are commercially pure titanium and Ti-6Al4V alloy. Titanium and its alloys are allotrope. Its characteristics are influenced by two principal factors: chemical composition and microstructure. Thickness, porosity, pore size e interconnectivity between pores and coating are important for the bone growth and prosthesis fixation. Different mechanism of hip prosthesis failures in result of the coating placed on the prosthesis have been reported in the literature. In this thesis various technical standards for Titanium commercially pure and Ti-6Al-4V were identified. They are related to the material, the forging and metallic powders for coatings, Furthermore, evaluation methods for coating and industry guidelines, some with acceptance criteria, some without, were found. Within the standard ABNT NBR 15628-4 inconsistencies regarding the required microstructures were found. Technical standards were compared and linked to data from the literature. Critical points related to porous metallic coating, production methods, its effects on Ti-6Al-4V substrate and characteristics of porous coatings. 8 in Brazil commercially available products were evaluated considering their registration at ANVISA and analysis of their coatings in a lab. The chemical composition of the substrate was determined by optical emission spectroscopy. Optical microscopy was used to evaluate the microstructure of the substrate and for stereological analysis of the coating. Chemical composition analyses of the substrate pointed 2 components made of Titanium commercially pure and 6 made of Ti-6Al-4V. One sample had results of substrate according Ti-6Al-4V alloy besides registration information at ANVISA described substrate made of Ti commercially pure. Regarding the microstructural analysis of the substrate, the majority of problems occurred with products made by sintering and by foreign producers. 50% of products made by Ti-6Al-4V presented microstructures with continuous alpha phase on the beta grain boundaries. Therefore it can be concluded that they were processed at temperatures higher than beta transus temperatures. Analyzing the thickness of the coating, all samples from foreign producers had a bigger thickness than any national product. No national product had a thickness bigger than 500µm. Therefore it is possible to conclude that the microstructure was affected by the thermic processes and that those need better controls, regulation and surveillance in order to supply more secure and effective products.