ESR01 - Nicolas Somers

Background:

Nicolas obtained a Bachelor degree in chemistry and realised a Master in chemical sciences at the University of Liège (Belgium).

The objective of his master thesis was to synthesize hydroxyapatite powders by different methods and incorporate them into stereolithography resins in order to print ceramic parts by additive manufacturing. Powders characteristics (crystallite size, granulometry, composition, reactivity,…) were studied in order to optimize the dispersion in resin, the printing process and the properties of the final ceramic piece. The thermal decomposition of hydroxyapatite was also studied to attempt making biphasic calcium phosphate.

During his studies, he had the opportunity to make some traineeships:

• He worked at the GreenMat laboratory of the University of Liège on the synthesis and the shaping of ceramic powders (CaMnO3 and hydroxyapatite) for different applications (thermoelectric and biocompatible materials). He made some research there about the synthesis and shaping of hydroxyapatite powders for 3D printing of biocompatible ceramic parts by stereolithography.
• Moreover, he spent 10 weeks working for a start-up named Cerhum SA in Liège. I was trained in 3D printing and worked with Cerhum employees to optimize the 3D printing of ceramics by stereolithography. The main aim of this work was to develop an optimized debinding cycle for printed parts of hydroxyapatite and zirconia with the help of thermogravimetric analysis.

Since October 2018, he's working as a PhD student at the Laboratory of Ceramic Materials and Associated Processes (LMPCA) from the Polytechnic University of Hauts-De-France (UPHF). He is part of DOC-3D-Printing project as an Early-stage researcher (ESR01) and his work is about the synthesis of biocompatible doped calcium phosphate powder.

Presentation of the individual project:

β-tricalcium phosphate (β-TCP, β-Ca3(PO4)2) is one of the most attractive biomaterials for bone repair since it shows an excellent biological compatibility, osteoconductivity, and resorbability. Owing to its high resorption properties in human body, it is foreseen to be used as temporary support for natural tissue colonization for specific applications like complex shaped posterior spinal fusion and cranio-maxillofacial parts. Indeed, the new formed bone could gradually replace these temporary resorbable supports.

However, when heating, β-TCP presents a phase transition to α-TCP at 1150°C which occurs with a large lattice expansion (~7%) causing microcracks and reducing shrinkage during sintering with, as a consequence, a sintering temperature limitation. Possible solutions is to dope the TCP with additives able to increase the β thermal stability region like Na+; K+, Mg2+, Sr2+, Zn2+ or Ag+ that replace Ca2+ within the phosphate lattice.

The aim of this work will be to increase the sintering temperature of β-TCP above the typical allotrotropic transformation temperature by dopant addition in order to reach higher relative density value and thus higher mechanical properties. In addition, cationic dopants will be also used to improve the biological properties of β-TCP in order to optimize the bone regeneration ability of implants. Moreover, the use of these doped powders would permit to use original sintering methods like flash sintering, Spark Plasma Sintering, microwave sintering.These processes present a difficult control of the temperature but also advantages as very short thermal treatment durations and close control of the grain growth.

Besides the doped powders synthesis and characterization (this part will be realized in LMCPA-Maubeuge), the thesis topic will include the study of adequate formulations to shape the complex shape and macroporous scaffolds by the robocasting technique (this part will be realized in BCRC-Mons). The as-prepared green scaffolds will be densified by conventional and microwave sintering with comparison of microstructural and mechanical properties.