Preparation of porous apatite granules from calcium phosphate cement

A versatile method for preparing spherical, micro- and macroporous (micro: 2–10 and macro: 150–550 μm pores), carbonated apatitic calcium phosphate (Ap-CaP) granules (2–4 mm in size) was developed by using NaCl crystals as the porogen. The entire granule production was performed between 21 and 37 °C. A CaP cement powder, comprising α-Ca₃(PO₄)₂ (61 wt.%), CaHPO₄ (26%), CaCO₃ (10%) and precipitated hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂ (3%), was dry mixed with NaCl crystals varying in size from 420 μm to 1 mm. Cement powder (35 wt.%) and NaCl (65 wt.%) mixture was kneaded with an ethanol–Na₂HPO₄ initiator solution, and the formed dough was immediately agitated on an automatic sieve shaker for a few minutes to produce the spherical granules. Embedded NaCl crystals were then leached out of the granules by soaking them in deionized water. CaP granules were micro- and macroporous with a total porosity of 50% or more. Granules were composed of carbonated, poorly crystallized, apatitic CaP phase. These were the first spherical and porous CaP granules ever produced from a self-setting calcium phosphate cement. The granules reached their final handling strength at the ambient temperature through the cement setting reaction, without having a need for sintering. Certain commercial equipment, instruments or materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement by the author, nor does it imply that the equipment or materials identified are necessarily the best available for the purpose.