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Contribution à la compréhension de la formation de la porosité dans des revêtements et des particules de verre bioactif élaborés par projection thermique pour des applications biomédicales

Abstract : This PhD work was focused on the strategies developed to achieve a mechano-biological performance in bioactive glasses, which contribute to archive the requirements of the biomedical industry and, more recently, of the pharmaceutical industry. One part of the studies highlighted the effect of the thermokinetic treatment of the 45S5 Bioglass® microparticles on the formation of globular porosity in the coatings manufactured by Atmospheric Plasma Spraying (APS). The understanding of the behaviour of 45S5 Bioglass® particles in the plasma jet made it possible to identify the chemical composition changes undergone by the sprayed powder due to the volatilization of Na+ and P+ species, as well as to establish strategies to reduce the structural defects in the coatings and Glass/yttria-stabilized zirconia (YSZ) composite coatings manufactured by co-spraying using APS and suspension plasma spraying (SPS) were also studied. Their structures consisted of 45S5 Bioglass® microparticle splats/lamellae surrounded by YSZ nanoparticles. The double approach of reducing globular porosity and adding nanoparticle reinforcement improved the Vickers microhardness of 45S5 Bioglass® glass-based coatings. Furthermore, YSZ nanoparticles exhibited a catalytic effect on apatite formation upon exposure of these coatings to Simulated Physiological Fluid (SBF). The porosity formation in glass particles atomized by Flame Spraying (FS) has also been studied. This study led to identifying the phenomena occurring in in-flight particles and to establishing the appropriate atomization parameters. The formation of interconnected porosity in atomized particles is limited by the excessive decrease in their viscosity in-flight and the heterogeneous heat flow in irregular morphology particles. The retention of this porosity, in highly amorphous materials with significant species volatilization during atomization, is promoted using an external agent (AE, e.g., CaCO3). The AE limits the thermal energy exchanged by in-flight glass particles, such that viscosity can also be controlled by the glass/AE mass ratio, in addition to atomization conditions. This external agent on the surface of atomized glass particles acts as a crater-forming agent while facilitating the conduction of thermal energy towards the centre of the atomized particles if their thermal conductivity (λp) is higher. The use of porous particles in hierarchical porosity architectures (scaffolds) constitutes the final part of this PhD work. Scaffolds exhibited bacterial inhibition by releasing gentamicin sulphate (SG) molecules stored in their structure. The inhibitory effect of the scaffolds is prolonged to ~ 72 and 120 hours, respectively, for the Gram-positive and Gram-negative strains. The osteoblast cells demonstrated moderate viability in contact with these scaffolds given the changes in the chemical composition of the particles from 43S2.5 to 51S9.0 glass (according to Hench’s nomenclature) during oxy-acetylene flame atomization. Cell viability decreases with the increasing mass content of YSZ nanoparticles infiltrated into 51S9.0 porous glass particles due to cell apoptosis caused by the leaching of Y+ ions. However, the catalytic effect of YSZ in the apatite formation promotes the adhesion, proliferation, and reproduction of surviving osteoblast cells in those scaffolds having 10% by weight of YSZ.
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Submitted on : Friday, February 11, 2022 - 3:08:08 PM
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Óscar Iván Rojas Giraldo. Contribution à la compréhension de la formation de la porosité dans des revêtements et des particules de verre bioactif élaborés par projection thermique pour des applications biomédicales. Matériaux. Université de Limoges; Universidad de Antioquia (Medellin), 2021. Français. ⟨NNT : 2021LIMO0105⟩. ⟨tel-03566421⟩

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