Influence of raw powder preparation routes on properties of hydroxyapatite fabricated by 3D printing technique

A comparison between two routes of raw powder preparation, namely spray drying and grinding, for 3D printing of hydroxyapatite was carried out. Hydroxyapatite particles prepared by the spray drying technique were spherical in shape whereas the grinding route gave irregular-shaped agglomerates. Spray-dried powders had higher tap density than milled powders, however milled powders yielded 3DP specimens with greater green density and strength. After sintering at 1300 °C for 1 and 5 h, samples fabricated from milled powders showed a 32% higher in sintered density, a 20% lower in porosity and approximately two times higher flexural modulus and strength than samples fabricated from spray-dried powders. This difference was related to the better packing characteristics of milled powders which promoted improved inter- and intra-particle densification during high temperature sintering compared to the spray-dried powders which yielded only high intra-particle densification, but lower inter-particle densification.