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Développement de Revêtements Radiopaques Biohydroxyapatite / Bioglass Déposés par Projection Thermique pour des Applications Biomédicales

Abstract : Hydroxyapatite (HAp) and bioactive glass (BG45S5) are widely employed as precursors of thermally sprayed coatings to enhance the biocompatibility of biomedical implants. This, due to the similar structure of HAp with the bone tissue and the high reactivity of BG with biological media allowing the rapid bone tissue ingrowth on its surface. The combined deposition of both materials leads to build-up highly bioactive coatings with proper stability in comparison with single coatings. Furthermore, the HAp bioactivity and the BG45S5 radiopacity can be improved by obtaining the first from natural sources, as bovine-derived HAp (BHAp), and the second through the addition of radio-opacifiers as Bi2O3 to the BG structure. Consequently, coatings with augmented both, biocompatibility and x-rays opacity that allow improving the bioactivity and facilitate the use of non-invasive diagnostic methods, can be achieved. This research presents the development of biocompatible and opacified thick coatings deposited by High-Velocity Oxygen Fuel (HVOF) and Atmospheric Plasma Spray (APS) techniques. The chemical composition, structure, and microstructure of radiopaque BHAp/BG45S5+Bi2O3 coatings were studied, as well as the properties of raw materials were also analyzed. Afterward, the bioactivity of several coatings’ architecture, i.e., monolayers, graded, and multilayers, were assessed. The experimental results show that BHAp feedstock powder is mainly carbonated B-type apatite with a high purity HAp phase. The lab-made BG45S5 powders exhibit the chemical composition and physical properties with a substantial similarity compared to commercial BG45S5. The weight percent of 1 up to 20 of Bi2O3 was added to the bioactive glass to modify its radiopacity. Radiographic images of BG45S5+Bi2O3 show that 10 wt.% of the opacified material allows increasing the opacity of the BG mixture homogeneously by 3.6 times with no considerable effects on its structural and thermal properties. Regarding the thermally sprayed coatings, CO32- and the Mg contents on BHAp lead to the formation of dolomite in the crystalline phase of the surface of single HVOF BHAp coating. Single BHAp APS coating does not exhibit any secondary phases in its surface crystalline content. A typical apatite layer is evidenced after 3 days of immersion in simulated body fluid (SBF) in the surface of both coatings and single BHAp HVOF coating show delamination after 5 days of immersion. Thus, APS was chosen to spray and analyze single BG45S5, BG45S5+10 wt.% Bi2O3 and gradual BHAp/BG45S5+10 wt.% Bi2O3 coatings. Single BG45S5+10 wt.% Bi2O3 coating shows similar microstructure and amorphous structure in comparison with the plasma-sprayed single coating using commercial BG45S5 feedstock powder without Bi2O3. However, delamination and a reduced rate of apatite layer formation are observed. Graded BHAp/BG45S5+10 wt. % Bi2O3 coating shows a similar rate of apatite layer growth compared to single BG45S5+10 wt. % Bi2O3 coating. Nevertheless, the apatite formation after 10 days of immersion in SBF and no delamination are observed on the surface of the coating due to the graded deposition of BG45S5+10 wt. % Bi2O3 combined with BHAp.
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Germán Andrés Clavijo Mejía. Développement de Revêtements Radiopaques Biohydroxyapatite / Bioglass Déposés par Projection Thermique pour des Applications Biomédicales. Matériaux. Université de Limoges; El Centro de Investigacion y de Estudios Avanzados del Insituto Politécnico National. Cinvestav (Méxique), 2019. Français. ⟨NNT : 2019LIMO0099⟩. ⟨tel-02477546⟩

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