Nicolas Somers

Ce travail de thèse porte sur l’élaboration de phosphate β-tricalcique (β-TCP, β-Ca3(PO4)2) dopé à l’aide de quatre cations (Mg2+, Sr2+, Ag+ et Cu2+) par la méthode de co-précipitation et la fabrication de macroporeux par robocasting. Le β-TCP est l'un des biomatériaux les plus étudiés dans le domaine de la réparation osseuse car il présente une excellente biocompatibilité ainsi qu’un caractère ostéoconductif et résorbable dans le corps humain. Différentes compositions de β-TCP dopé et co-dopé sont synthétisées et l’effet de la présence des dopants sur la stabilité thermique, la densification, les propriétés mécaniques et la biocompatibilité est évalué. Ensuite, l’impression de macroporeux de β-TCP à partir des poudres synthétisées est optimisée en développant une pâte de robocasting et en adaptant la méthode de séchage ainsi que les paramètres d’impression. Le procédé développé a permis de produire des macroporeux relativement denses caractérisés toutefois par une porosité interne résiduelle et des microfissures. Des essais biologiques préliminaires ont montré une certaine cytotoxicité des poudres produites, probablement due à une libération d’ions néfastes pour les cellules dans les premiers jours de contact. Un potentiel comportement antibactérien a été observé sur une composition co-dopée à base d’Ag+ et de Cu2+, laissant supposer une synergie des deux cations sur le comportement antibactérien.

High-silicon steels, specifically Fe–6.5 wt% Si (Fe6.5Si), are essential for high-efficiency electrical machines due to their high magnetic permeability and near-zero magnetostriction. However, their extreme brittleness makes conventional processing difficult, driving the need for high-quality powders for additive manufacturing (AM) and powder injection molding (PIM). This study proposes a novel, sustainable synthesis route for Fe6.5Si powders by combining ATEX-compliant spray drying with reductive calcination, utilizing recycled silicon sourced from end-of-life photovoltaic cells. The research systematically compares three iron precursors, iron nitrate (Fe(NO3)3.9H2O), iron hydroxide (Fe(OH)3) and iron oxide (Fe2O3) to determine their impact on powder morphology and yield. Spray drying parameters were optimized to produce spherical particles. Subsequent reductive calcination at 700°C for 6 hours under Ar/H2 was found to be the critical threshold to achieve phase-pure Fe6.5Si. Fe(OH)3 emerged as the superior precursor, providing the highest calcination yield (81%), the most robust spherical morphology and high chemical homogeneity, as confirmed by EDX mapping and Mössbauer spectroscopy. The successful incorporation of recycled PV-silicon establishes a lower-temperature, sustainable alternative to traditional gas atomization. These results demonstrate a versatile framework for producing high-performance soft magnetic alloy powders with the flowability and structural integrity required for advanced manufacturing of electrical components.

β‐tricalcium phosphate (β‐TCP, β‐Ca₃(PO₄)₂) is an attractive biomaterial for bone repair applications. However, its sintering and mechanical properties are limited by a problematic phase transition to α‐TCP. Cationic doping of β‐TCP is able to postpone the formation of α‐TCP allowing higher sintering temperatures and better mechanical properties. The co‐doping of β‐TCP with Mg²⁺ and Sr²⁺ has already been studied in detail, but the addition of antibacterial cations (Ag⁺ and Cu²⁺) on the Mg–Sr β‐TCP co‐doped composition remains unexplored. Thus, two co‐doped β‐TCP compositions were realized by aqueous precipitation technique without any secondary phase and compared with undoped β‐TCP: Mg–Sr (2.0–2.0 mol%) and Mg–Sr–Ag–Cu (2.0–2.0–0.1–0.1 mol%). Differential thermal analysis and dilatometry analyses showed a slight decrease of the β‐TCP → α‐TCP phase transition temperature for the Mg–Sr–Ag–Cu (2.0–2.0–0.1–0.1% mol) composition as compared to the Mg–Sr (2.0–2.0 mol%). However, both exhibited much higher transition temperatures than undoped β‐TCP. The addition of Ag⁺ and Cu²⁺ slightly reduces the grain size after sintering compared to the Mg–Sr (2.0–2.0 mol%) and the undoped compositions. The co‐doped compositions also exhibited improved mechanical properties, specifically a higher Vickers hardness and elastic modulus. Finally, cell proliferation assays showed that the presence of dopants, even Ag⁺ and Cu²⁺, does not affect the survival and proliferation of cells. Thus, the use of Mg²⁺, Sr²⁺, Ag⁺, and Cu²⁺ co‐doped β‐TCP could be very promising for biomedical applications due to the improvements of these dopants on the thermal stability and mechanical and biological properties.

To assess the application potential of novel biomaterials, their behaviour in model media and upon sterilization should be investigated, as well as the stability related to their storage conditions. Such data are lacking for Mg-substituted HAP (Mg-HAP). Therefore, the changes in the local structure of non-substituted and Mg-HAP after irradiation and immersion in corrected simulated fluid and saline solution for 28 days were followed by electron paramagnetic resonance (EPR) spectroscopy for the first time. To better understand the stability of radical species induced by sterilization, EPR spectra of samples kept for 2 h at temperatures up to 373 K were recorded to provide an insight into the stability of the sample storage conditions by the accelerated aging method. Samples were characterized by PXRD, FTIR, SEM, EDS, AAS and TGA. Results confirmed that irradiation does not induce changes in the composition or the structure of any of the investigated materials. Fading or the complete disappearance of radical signals in the EPR spectra after immersion in both media was accompanied by the disappearance of other phases formed as a minor byproduct in the synthesis of substituted HAP, as confirmed by PXRD and FTIR analysis. Obtained results confirm the great potential of Mg-HAPs for biomedical applications, although closer attention should be given to the processes related to sample storage stability at different temperatures.