Structural and biological properties of hydroxyfluorapatite containing sodium and potassium and substituted with carbonates bioceramics for bone tissue engineering

Calcium phosphates are extensively utilized in the biomedical domain, specifically in dentistry and orthopedics, owing to their chemical resemblance to the mineral constituent of hard tissue. Ions substitutions within the apatite lattice play a vital role in cell-biological interaction and organ metabolism. Here, a serial of hydroxyapatite bioceramics has been ions-substituted with sodium (Na⁺), potassium (K⁺), carbonate (CO₃²⁻), and fluoride (F⁻). The general formula for the compounds is Ca_(9.75−y/2)(Na, K)_0.25(PO₄)_6−y(CO₃)_yOHF (HFAp) with (0 ≤ y ≤ 1). After undergoing analysis and characterization using numerous methods and techniques, the obtained samples were confirmed to be pure apatite. The HFAp structure was found to contain the necessary amounts of introduced substituted ions. The thermal analysis of the samples revealed that the apatite phase was the primary component from room temperature to 1000 °C, whereas the formation of β-Ca₃(PO₄)₂ occurred at a temperature of 750 °C. The pressureless sintering process resulted in achieving a densification ratio of 93% for the samples. The biocompatibility of the samples was studied in-vitro. The interaction between cells and materials was studied using the methyl thiazolyl tetrazolium (MTT) assay with human osteosarcoma cells MG-63 and Saos-2. The biological response resulted in cell proliferation on the materials’ surface. The in vitro bioactivity investigations conducted on materials submerged in Simulated Body Fluid (SBF) demonstrated a remarkably bioactive nature, as indicated by the enhanced mineralization of a new apatite layer. The synthesized biomaterial shows potential for repairing and reconstructing sick body components.