Structural and mechanical characterizations of nano calcium phosphate coatings prepared by induction suspension plasma spray (rf-SPS)

Abstract

Event Abstract Back to Event Structural and mechanical characterizations of nano calcium phosphate coatings prepared by induction suspension plasma spray (rf-SPS) Frédéric Faivre1, 2, Max Loszach2, Ghislaine Bertrand1, François Gitzhofer2, Joel Alexis3, Jade Pecune3, David Grossin1 and Christian Rey1 1 CIRIMAT, Université de Toulouse, France 2 Université de Sherbrooke, Département de génie chimique et génie biotechnologique, Canada 3 LGP, Université de Toulouse, France Introduction: Among the variety of coating technologies developed to deposit stoichiometric hydroxyapatite, plasma spraying is the most widely used technique implemented by industry to treat prosthetic devices.[1] The good biocompatibility and osteoconductivity of this material have been found to enhance bone healing at early implantation time but long-term stability is still controversial. The mechanisms which are responsible for this change can be related to instability of the coating/bone tissue interface (dissolution at neutral pH, resorption by osteoclasts) or of the coating/implant interface (delamination due to stress, preferential dissolution of amorphous phase, poor initial adhesion).[2] To find an optimal and sustainable integration, a nanostructured substituted hydroxyapatite coating mimicking the complex surface topography (roughness, grain size, porosity) and structure (Ca/P ratio, stoichiometry, crystallinity) of the mineral part of the natural bone was produced implementing the suspension/solution inductively rf coupled plasma spray system.[3] The objective of the present study is to assess the influence of operating conditions (suspension composition, power, pressure, gas composition, spraying distance) on coating/TA6V substrate adherence and coating physical and structural characteristics. Materials and Methods: Hydroxyapatite and substituted hydroxyapatite (Mg,Na,K)xCa10-x(PO4)6(F,Cl)y(OH)2-y coatings have been produced using a 50 kW inductively coupled RF plasma spray system operating at 3 MHz and equipped with a suspension feeder nozzle (Tekna Plasma System Inc.). The structural characteristics were determined by XRD, FTIR and Raman spectroscopies, the chemical compositions by ICP or SAAF and the morphology by SEM. Qualitative and quantitative determination of the phases, including the crystallinity of the coatings has been carried using Rietveld refinement. Micro and nano hardness tests were performed to evaluate the Young modulus and coating cohesion. 3-points bending tests with stiffener were applied to determine the coating adhesion. Results and Discussion: The spraying chamber pressure, the power, the liquid/solid phase ratio in the suspension and the spraying distance have a strong influence on the CaP phases. It was demonstrated that the optimized coating was mainly constituted of HA (91 vol.%) with nanometric sizes (below 100 nm). The secondary phases were (a-TCP, β-TCP, CaO and TTCP) as usually in plasma sprayed calcium phosphate coatings. Furthermore, it was showed that multisubstituted hydroxyapatite coating is achievable by suspension plasma spray. Coating roughness was around 5 µm and could be adapted thanks to substrate surface treatment. Finally mechanical properties of optimized coatings exhibited similar values (bending test Fc=140N, hardness test E=7±2 GPa, H=2.5±1 GPa) to the ones of a commercial HA coating (Fc=100 to 160 N, E=10 GPa, H=1.5 to 3 GPa). Conclusion: Both physical and structural characteristics can be tuned by adjusting the operating plasma spray parameters in order to favor the nanometric grain size, crystallinity (targeted phase HA), adhesion and cohesion as well as complex compositions. We would like to thank the CPCFQ-biennum 2013-2014 for providing financial support to this project during two years.