The aim of this study was to create a nano-structured coating using Plasma Thermal Spraying (PTS). This process consists in introducing pre-agglomerated nanosized particles in a high-temperature and high-velocity gas jet and projected them onto the substrate to form, layer by layer, a nanostructured coating. In order to retain nanometer grain sizes in the deposited coating through specific PTS technologies, a thermal field and velocity distribution in the plasma jet are analytically calculated. A finite element analysis is employed to calculate the thermal field evolution inside the agglomerated particles and the thermal induced internal stress distribution is determined. The parameters determined by the theoretical analysis are used for experimental coatings. The average crystallite size of nano-hydroxyapatite powder was 90nm. After deposit via Plasma Thermal Spraying (PTS) process and followed by a 2 hours heat treatment to reduce amorphous fraction, the experimental deposited coating shows that it retains the nanometer crystallite sizes. The substructure of nanocrystals was evaluated at about 120nm in size. Such a nanocoating may play the role of nucleation site to bone, allowing a faster stabilization of the implant.
Technology developments of implant composition and manufacture have been used in the medical field. Several different implants have been developed with varying degrees of commercial success. As a long-term establishment is a measure of the therapeutic success, it is necessary to use biocompatible implants in order to have good mechanical and fracture resistance of new bone reconstructed at the interface with the implant. Titanium (Ti-Al-4V) implants coated with hydroxyapatite (HAp), Ca10 (PO4)6 (OH)2 are widely used in orthopedic applications in order to obtain a stable and functional direct connection between the bone and the implant. At the implant-bone interface the new bone reconstituted after implantation must have the same orientation as the natural bone in order to accept the implant. Therefore we studied the texture and the crystallinity of the new bone crystals reconstituted at the interface applying by high-energy synchrotron radiation on beamline ID15 at ESRF in Grenoble, France.
In recent years, nanostructured coatings by Plasma Thermal Spraying (PTS) attracted intense interest due to their enhanced mechanical properties as hardness, strength and ductility. The aim of this study was to evaluate the influence of coating the implant by nanohydroxyaptite, n-HAp, Ca10 (PO4)6(OH)2. The results obtained with n-HAp will also compared with the implant coated with HAp. Bone is a composite material in which are associated a mineral phase in the form of crystals of HAp and an organic matrix constituted by collagen. The c-axes of HAp and the collagen fibers are preferentially oriented in the direction of the stresses that the bones need to withstand. At the interface implant-bone, the new bone reconstituted after implantation must have the same proprieties of the original bone in order to have good fixation with the implant. Therefore, it is necessary to study the mechanical properties of this new bone crystals reconstituted at the interface with the implants coated with n-HAp and HAp by neutrons diffraction on D20 at ILL.
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