Analysis of selective laser melting of resorbable bioceramics

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Since few years, an intense research activity has been undertaken on obtaining orthopedic implants by direct laser manufacturing. Metallic (titanium alloys) heap implants have been the first parts obtained by laser cladding, with dental implants (chromium cobalt alloys) obtained by selective laser melting. In parallel, different studies have been initiated on direct manufacturing of bioceramics. These materials have the main advantage to be completely or partly replaced by real bone after colonization by bone cells. From that family, Hydroxyapatite (HAP) and Tri Calcium Phosphate (TCP) material are the best candidates because their compositions are close the real bone.This article presents the experiments we have conducted to generate TCP structure by selective laser melting. These are part of a French research project ORTHOFLASE related to this topic. First, powder provision and quality has been identity as a critical point for the success of the project. Ultrapure TCP with very low metallic pollutant content has been manufactured.As the TCP powder produced is very pure, it has been necessary to control its absorptivity for existing laser sources. Very low absorptivity of the powder has been evidenced at continuous laser at near infrared wavelength (YAG, fiber or near infrared diode lasers). However, the powder has exhibited a very good absorptivity for far infrared CO2 laser.Then, a parameter study has been undertaken on an existing selective laser melting device with CO2 laser. The main parameters are the powder layer thickness, the laser power, and the travel speed. The process parameter window is determined and results of the experiments are presented.Finally, from considerations of the material structure required for a good colonization by the bone cells, simple 3D geometries are manufactured presented in the article.