Tailoring calcium phosphate powder properties for additive manufacturing

Calcium phosphates ceramics (stoichiometric hydroxyapatite (HA), β-TCP, substituted calcium phosphates, and biphasic compounds) are privileged biomaterials as orthopaedic implants or dental restorations in medical or aesthetics applications. In combination with additive manufacturing technologies, bioceramic parts can be designed with complex shapes with better biocompatibility and bioactivity than metals improving the osseointegration/osseoincorporation of the implant. Powder bed fusion (PBF) and VAT photopolymerization are promising additive manufacturing (AM) groups of techniques allowing the production of functional complex net-shaped or fully dense parts. However, specific tailored ceramic powders for these 3D printing techniques need to be produced. In this context, the challenge here is the evaluation of the characteristics of a suitable feedstock depending of the additive manufacturing technique. HA was chosen as starting material for the production of scaffolds for bone tissue regeneration. In the course of tailoring the AM feedstock properties, depending on the additive manufacturing technique different processes can be necessary. In the case of the PBF techniques, the processability of the powder feedstock is better achieved when using laser-reactive and flowable dry microspheres. In this regard, this thesis deals with the tailoring of the HA particles morphology through a combination of processes such as, synthesis, wet milling, spray drying, and mixing of the powder with absorption additives. For a second AM group of technologies, like VAT photopolymerization, different characteristics are required for the material feedstock. In this case, the production of slurries composed of stable and low viscosity HA powder-filled photosensitive resins was essential. Their preparation was achieved by a milling step of the powder and a proper homogenization of the different components (photoinitiator, monomers, and diluent). Thus, as part of this PhD work the understanding of the relationships between the powder properties and the processing parameters was of special importance. For this reason, a wide variety of powder and suspension characterization methods was employed to assess the effect of the formulation and the operating parameters on the final product properties. It included the analysis of the chemical composition and structure of the compounds, as well as the physical properties of the particles dispersed in a liquid or in a dry state (morphology, flowability, stability, and rheology of suspensions). Finally, the suitability of the feedstock produced was examined through direct testing on the AM technologies and the quality of the printed parts was evaluated in terms of relative density, porosity, and mechanical properties

A review of additive manufacturing of ceramics by powder bed selective laser processing (sintering / melting): Calcium phosphate, silicon carbide, zirconia, alumina, and their composites

This review offers an overview on the latest advances in the powder bed selective laser processing, known as selective laser sintering/melting, of calcium phosphate, silicon carbide, zirconia, alumina, and some of their composites. A number of published studies between 1991 and August 2020 was collected, analyzed and an inclusive state of the art was created for this review. The paper focuses on the process description, feedstock criteria and process parameters and strategy. A comparison is made between direct and indirect powder bed selective laser processing of each ceramic, regarding the present achievements, limitations and solutions. In addition, technical aspects and challenges about how to address these issues are presented

Adapter les propriétés de la poudre de phosphate de calcium à la fabrication additive

Calcium phosphates ceramics (stoichiometric hydroxyapatite (HA), -TCP, substituted calcium phosphates, and biphasic compounds) are privileged biomaterials as orthopaedic implants or dental restorations in medical or aesthetics applications. In combination with additive manufacturing technologies, bioceramic parts can be designed with complex shapes with better biocompatibility and bioactivity than metals improving the osseointegration/osseoincorporation of the implant. Powder bed fusion (PBF) and VAT photopolymerization are promising additive manufacturing (AM) groups of techniques allowing the production of functional complex net- shaped or fully dense parts. However, specific tailored ceramic powders for these 3D printing techniques need to be produced. In this context, the challenge here is the evaluation of the characteristics of a suitable feedstock depending of the additive manufacturing technique. HA was chosen as starting material for the production of scaffolds for bone tissue regeneration. In the course of tailoring the AM feedstock properties, depending on the additive manufacturing technique different processes can be necessary. In the case of the PBF techniques, the processability of the powder feedstock is better achieved when using laser-reactive and flowable dry microspheres. In this regard, this thesis deals with the tailoring of the HA particles morphology through a combination of processes such as, synthesis, wet milling, spray drying, and mixing of the powder with absorption additives. For a second AM group of technologies, like VAT photopolymerization, different characteristics are required for the material feedstock. In this case, the production of slurries composed of stable and low viscosity HA powder-filled photosensitive resins was essential. Their preparation was achieved by a milling step of the powder and a proper homogenization of the different components (photoinitiator, monomers, and diluent). Thus, as part of this PhD work the understanding of the relationships between the powder properties and the processing parameters was of special importance. For this reason, a wide variety of powder and suspension characterization methods was employed to assess the effect of the formulation and the operating parameters on the final product properties. It included the analysis of the chemical composition and structure of the compounds, as well as the physical properties of the particles dispersed in a liquid or in a dry state (morphology, flowability, stability, and rheology of suspensions). Finally, the suitability of the feedstock produced was examined through direct testing on the AM technologies and the quality of the printed parts was evaluated in terms of relative density, porosity, and mechanical properties.Les céramiques de phosphates de calcium (hydroxyapatite stoechiométrique (HA), -TCP, phosphates de calcium substitués et composés biphasiques) sont des biomatériaux privilégiés comme implants orthopédiques ou pour réaliser des restaurations dentaires dans des applications médicales ou esthétiques. En association avec les technologies de fabrication additive (FA), les pièces biocéramiques peuvent être conçues avec des formes complexes tout en ayant une meilleure biocompatibilité et bioactivité que les métaux améliorant l'ostéointégration/ostéoincorporation de l'implant. La fusion sur lit de poudre (FLP) et la photopolymérisation (VAT) sont des familles de techniques de fabrication additive prometteuses permettant la production de pièces complexes fonctionnelles sous forme de réseaux poreux ou entièrement denses. Cependant, un défi est de produire une poudre céramique ayant des propriétés spécifiques pour ces techniques d'impression 3D. Dans ce contexte, l'enjeu dans cette thèse est l'évaluation des caractéristiques de la matière première adaptée à chaque technique de fabrication additive. HA a été choisie comme matériau de départ pour la production de pièces pour la régénération du tissu osseux. En fonction de la technique de fabrication additive utilisée, différents procédés peuvent être nécessaires pour l'optimisation des propriétés de la matière première à imprimer. Dans le cas des techniques FLP, de meilleurs résultats sont obtenus lors de l'utilisation d’une poudre constituée de microsphères réactives au laser et présentant de bonnes propriétés d’écoulement. Dans cette thèse l’optimisation de la morphologie des particules de HA a été étudiée grâce à une combinaison de procédés tels que la synthèse, le broyage en voie humide, le séchage par atomisation et le mélange de la poudre avec des additifs d'absorption. Pour les technologies de FA telles que la photopolymérisation VAT, des caractéristiques différentes sont requises pour la matière première. Dans ce cas, il est essentiel de produire des suspensions composées de résines photosensibles chargées de poudre d’HA, stables et de faible viscosité. Leur préparation a été réalisée par une étape de broyage de la poudre suivi d’une bonne homogénéisation des différents composants (photoinitiateur, monomère, et diluant). Dans le cadre de cette thèse, la compréhension des relations entre les propriétés de la poudre et les paramètres des procédés sont d'une grande importance. Une large gamme de techniques de caractérisation des poudres et des suspensions a été utilisée pour évaluer l'effet de la formulation et des paramètres opératoires sur les propriétés du produit final à chaque étape. Ces techniques ont permis l'analyse de la composition chimique et de la structure des composés, ainsi que la détermination des propriétés physiques des particules dispersées dans un liquide ou à l'état sec (morphologie, coulabilité, stabilité, et rhéologie des suspensions). Enfin, l'adéquation de la poudre produite a été évaluée directement par des expériences réalisées avec les technologies de FA, et la qualité des pièces imprimées a été analysée en termes de densité relative, de porosité et de propriétés mécaniques

Preparation and characterization of nanostructures based on bent-core molecules onto graphene

Máster en Materiales Nanoestructurados para Aplicaciones Nanotecnológicas (Nanostructured Materials for Nanotechnology Applications).[ES]: Este proyecto presenta la preparación y caracterización de diferentes materiales supramoleculares basados en moléculas bent-core con unidades pireno (cristales líquidos, geles físicos y SAMs), centrando el interés principal en la interacción que tiene lugar entre las unidades pireno y el óxido de grafeno reducido (rGO). A través de una ruta de síntesis orgánica de los compuestos bent-core funcionalizados con unidades pireno fue posible su preparación y caracterización por técnicas espectroscópicas y analíticas (NMR, FTIR, EA, MS). La formación de los cristales líquidos ha sido estudiada por microscopia óptica (POM) y técnicas calorimétricas (DSC) mientras que los geles han sido caracterizados por microscopia electrónica de barrido (SEM). Los compuestos sintetizados y otros proporcionados por el grupo de investigación de Cristales Líquidos y Polímeros fueron ensamblados al grafeno usando la técnica de auto-ensamblado y las películas formadas fueron caracterizadas usando técnicas espectroscópicas (XPS, Raman) y de microscopia de sonda local (AFM) para estudiar tanto la organización como la interacción molécula-grafeno. Los parámetros estructurales tales como el número de unidades pireno (una o dos) en la molécula como la longitud del espaciador que conecta el bent-core y la unidad de pireno fueron analizados con el objetivo de estudiar su influencia en la formación de los cristales líquidos y los geles además de las geometrías formadas en las películas SAM. En cuanto a la formación de los SAMs, los resultados mostraron que es posible obtener películas SAMs a través de la interacción pireno-grafeno y que el número de unidades pireno y la longitud del espaciador afectan a la formación de estas películas. Se observó que cuando solo hay presente una unidad de pireno en la estructura de la molécula un mayor porcentaje de moléculas interaccionan con la superficie de rGO; siendo aún mayor con un espaciador largo entre el bent-core y la unidad pireno. Aunque la presencia de dos unidades pireno en una molécula lleva a unas interacciones mas fuertes con la superficie de rGO.[EN]: This project presents the preparation and characterization of different supramolecular materials based on pyrene-containing bent-core molecules (liquid crystals, physical gels and SAMs), focusing the main interest on the results of the interaction that take place between the pyrene moieties and reduced graphene oxide (rGO). Through organic synthetic routes bent-core organic compounds functionalized with pyrene units were prepared and characterized by spectroscopic and analytical techniques (NMR, FTIR, EA, MS). Liquid crystal formation have ben studied by optical microspic (POM) and calorimetric techniques (DSC) while the gels have been characterized by scanning electron microscopy (SEM). The synthetised compounds and others provided by the Liquid Crystals and Polymer research group were assembled into graphene using self-assembly technique and the formed films were characterized by using spectroscopic (XPS, Raman) and scanning probes microscopy (AFM) techniques to study both the molecular oganization and the interaction molecule-graphene. Structural parameters such as the number of pyrene units (one or two) in the molecule as well as the spacer length connecting the bent-core and the pyrene unit were checked in order to study their influcence on the formation of liquid crystals and gels as well as in the nanostructure geometry of the SAM films. Concerning SAM formation, the results showed that through pyrene-graphene interactions it is possible to obtain SAM films and both, the number of pyrene moieties and spacer length affect the film formation. Thus, a higher percentages of molecules interact with rGO surface when just one pyrene unit is present; better with a longer spacer between the bent-core and the pyrene moiety. Although the presence of two pyrene units in a molecule seems to lead to stronger interactions with the rGO surface.Peer reviewe