When AISI 316L stainless steels are submitted to the nitriding process at temperatures lower than 450 °C, a high nitrogen content expanded austenite phase is formed, which shows higher hardness and higher pitting corrosion resistance compared to the untreated material. As a result, this material becomes adequate for biomedical application. The conditions of the nitriding technique, such as gas mixture, pressure, time and temperature, play an important role in some properties of the modified layer, including: thickness, hardness and N concentration along the layer. This paper explores a set of six samples of AISI 316L, nitrided at different times and temperatures, whose properties show important differences. The aim of this research is to investigate the correlation between the nitrided layer thickness (in the range of 0.77 to 11 µm) with both X-ray patterns characteristics and hardness measurements, which used two distinct loads. The results of this study show that: whereas the 3.6 gf load was suitable to measure the real hardness for four of the nitrided layers showing thickness ≥ 2.9 µm, the 50 gf load measured a substrate contribution, probably even for the highest thickness, 11 µm. Moreover, analyzing different reflections of the X-ray patterns showed evidence of the clear consistency between the X-Ray depths and the nitrided layer thicknesses: if the layer thickness is lower than the penetration depth of X-rays, two phases (austenite and expanded substrate) are present. If the layer thickness is higher, only the austenite is observed. Finally, concerning the citotoxicity property, all the samples, nitrided or not, were approved in the test for biocompatibility, indicating their potential use for biomedical applications.

Hidroxiapatita porosa foi produzida por meio de uma nova técnica de processamento, visando aplicações na área de implantes ósseos. A produção do material poroso é feita através da produção de espumas pela agitação de suspensões cerâmicas aquosas contendo tensoativos adequados. A solidificação que segue é obtida pela adição de reagentes iniciadores da polimerização in situ de monômeros orgânicos, inicialmente incluídos nas composições, formando um gel. Este método permite a produção de corpos com formatos de alta complexidade e elevada resistência mecânica com níveis de porosidade próximos de 90%vol, que suportam corte e torneamento no estado a verde. Os aditivos orgânicos são eliminados a 300 °C e sinterização a 1350 °C é efetuada para consolidação da matriz. A otimização da resistência mecânica decorre da combinação entre uma matriz cerâmica de alta densidade a uma estrutura de poros esféricos com diâmetros que variam de 20-1000 <FONT FACE="Symbol">m</font>m possuindo inter-conecções de aproximadamente 10-100 <FONT FACE="Symbol">m</font>m, dependendo da densidade. O material sinterizado foi avaliado quanto a sua citoxicidade, utilizando-se o método quantitativo de formação de colônias que calcula o índice de citotoxicidade IC50(%) após contato do extrato do material com células de mamíferos. Os resultados mostraram que o processo de fabricação e os reagentes utilizados não afetaram os baixos níveis de toxicidade do pó de hidroxiapatita que era originalmente de pureza biomédica.

A novel technique has been applied to manufacture porous hydroxyapatite for implant applications. The process involved generation of foam from an aqueous suspension of the powder followed by in situ polymerisation of organic monomers, which had been previously added to the compositions. This method produces strong gelled and complex-shaped bodies with up to 90% porosity that can withstand machining in the green state. The organic additives are eliminated at temperatures above 300 °C and sintering is carried out for consolidation of the ceramic matrix. An optimized mechanical strength results from a highly densified matrix combined with spherical inter-connected cells of diameter ranging from 20 to 1000 <FONT FACE="Symbol">m</font>m and channels of 10-100 <FONT FACE="Symbol">m</font>m, depending on the specimen density. Cytotoxicity test was conducted with sintered HA extracts in contact with mammalian cells, based on a quantitative method of colonies formation suppression. The in vitro test revealed that the original purity of the biomedical-grade hydroxyapatite powder was neither affected through processing nor by the employed reagents.