Processing of hydroxyapatite and its composites using ceramic fused filament fabrication (CF³)

In this article, we report the fabrication of hydroxyapatite (HAp) and its composites with 7.75 vol% Si3N4 (HAp10SN) using ceramic fused filament fabrication (CF3). Homogeneous feedstock with 40 vol% ceramic powder was prepared and used to extrude filaments for further printing using a desktop printer. Our results showed that the addition of Si3N4 to HAp increases the feedstock viscosity. However, the filaments and CF3 parts made using HAp and HAp10SN feedstocks exhibited comparable densities without gross defects. We have obtained relatively smoother CF3 parts with HAp10SN than pure HAp, which is attributed to their high feedstock viscosity and formation of liquid phase during sintering. Sintering at 1250 degrees C for 4 h in air, after thermal debinding, resulted in a relative density of-85% with HAp and tricalcium phosphate (TCP) as major constituents. Sintered HAp10SN samples also revealed almost 70% reduction in the grain size and 4-fold increase in the hardness compared to pure HAp. Our results indicate that the CF3 processed HAp10SN samples containing-15% porosity, Si3N4 particles and Si-substituted HAp/TCP have strong potential as bone replacements.