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Manufacture and viability assessment of a composite Ti/HAp coating for replacement of single HAp layers on stain-less steel type 316 medical implant spinal screws
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Current medical implant spinal screws rely on a thin Hydroxyapatite layer to im-prove bone-implant fixation, however this coating presents weak mechanical strength performance.
Recent advances in materials science research have explored the production of composite coating for the use in medical implant coatings industry. This new field of composite engineering approaches, enabled a promising cheaper and improved alter-native to current production methods using solely Hydroxyapatite. CERAMED S.A. in-terest on developing new upgraded and cheaper Atmospheric Plasma Spray coatings culminated on this work where it was manufactured by Turbula mixing a composite pow-der for J3 at 101 RPM, using known at the time of this study available commercial pow-ders of Titanium and Hydroxyapatite of size range [5-200] and [15-200] μm respectively and density 4,522 and 3,148 g/cm3 respectively. This composite powder is used trough an Atmospheric Plasma Spray system to transform it into a coating hard coating for spe-cific use in stainless steel type 316 implant spinal screws. Based on previous literature and available equipment and materials at CERAMED S.A. facilities, an Atmospheric Plasma Spray program 1 was created. A preliminary study using, pre-selected primary parameters was made to understand the direct influence of Atmospheric Plasma spray system parameters, on coating properties like thickness, pull-out strength, coating crys-tallinity and roughness. The coating showed good results on pull out strength on trough a wide set of ranges showing an improved adhesion strength compared to Hydroxyap-atite, however crystallinity presented results under the required for commercial usage. Using 4 main primary Plasma Spray system factors (Nozzle Distance, Plasma Power, Primary Gas Flow and Secondary Gas Flow), a Design of experiments using 2 best lev-els within the range. By using a full factorial study design of experiences an analysis of variance was performed and the best set of levels for each factor was calculated. Pre-dicted range of results showed to be close to standard requirements but not in compli-ance, between [34,16- 39,66] % of crystallinity. A confirmation experience was per-formed using the best levels for crystallinity with a value of 34,31% and adhesion strength of the coating showed a value of 18,89 ± 3,76 MPa, considerably above the values for single HAp.