Mechanical and Biological properties of Sodium, Potassium, and Carbonate-containing Strontium Hydroxyfluorapatite Bioceramics

Hydroxyfluorapatites are particularly requested in dentistry and orthopedics because they are very similar to bone and dentine in terms of structure and composition. To improve their ability in defects repair, it is important to incorporate certain trace ions to better mimic the natural mineral phase of biological tissues. This study examines Hydroxyfluorapatites bioceramics doped with sodium (Na + ), potassium (K + ), and carbonate (CO 3 ²⁻ ), focusing on their mechanical and biological properties. The studied formulations were Sr 9.5-x (Na,K) x (PO 4 ) 5 (CO 3 )OH 1.5 F 0.5 with (0.25 ≤ x ≤ 1) and Sr 9.75-(y/2) (K,Na) 0.25 (PO 4 ) 6-y (CO 3 ) y OHF with 0 ≤ y ≤ 1. In the range 0-1; x and y were varied by 0.25. Samples synthesized via precipitation method and then sintered at the temperatures range 1000-1250°C for one hour under oxygen atmosphere. Maximum densification reached 94% at 1200°C and the observed morphology indicates that the hydroxyfluorapatite particles are characterized by a nanoscale grain size. Consistently with other sintered carbonated apatite systems, X-ray diffraction revealed a minor decomposition of the apatite into a secondary β-Sr 3 (PO 4 ) 3 phase specifically when carbonate doping levels y equal or exceed 0.25. The densest materials showed a Young’s modulus of 93 GPa, flexural strength of 42 GPa, and fracture toughness of 1.07 MPa·m 1/2 . When immersed in simulated body fluid, an amorphous strontium phosphate apatite layer formed after 14 days, indicating bone-bonding potential. Biocompatibility tests with MG-63 and Saos-2 cells confirmed good cell adhesion and proliferation. Overall, doping Hydroxyfluorapatites with K + , Na + , and CO 3 ²⁻ ions significantly improves mechanical strength and biological performance, highlighting their potential for clinical use in bone repair and dental treatments particularly spacing or filling bone defects or prosthesis coating.