Densification of calcium phosphates (CaP) is usually achieved by pressureless sintering technique at high temperatures. Unfortunately, this approach increase crystallinity and change chemical composition of CaP’s, negatively affecting their biological properties. Low-crystalline CaP phases cannot be sintered by pressureless sintering technique without transformation to other less biologically active CaP phases. Here we show that low-crystalline CaP phases – amorphous calcium phosphate (ACP), low-crystalline apatite (LowAp) and octa-calcium phosphate (OCP) can be densified to near full density by simple uniaxial die pressing at moderate pressure at room temperature. ACP and LowAp were synthesized by a dissolution-precipitation method while the OCP via a hydrolysis of α-tricalcium phosphate route. Specific surface area of the synthesized CaP’s was in the range of 60-120 m2/g. The synthesized CaP’s were sintered by uniaxial die pressing at 1250-1500 MPa at room temperature. After sintering the samples retained ACP, LowAp, and OCP structure. Relative density of all sintered samples exceeded 90% and their specific surface area were several hundred times smaller than that of the starting powders. The conditions used for the sintering of the low-crystalline CaP’s allowed to co-sinter them with certain drugs and polymers thus widening their potential application area.

ACKNOWLEDGMENT

The authors acknowledge financial support from the Baltic Research Programme project No. EEA-RESEARCH-85 “Waste-to-resource: eggshells as a source for next generation biomaterials for bone regeneration (EGGSHELL)” under the EEA Grant of Iceland, Liechtenstein and Norway No. EEZ/BPP/VIAA/2021/1.