New Na⁺,Mg^2+,Zn²⁺ -containing hydroxyapatite/ZrO₂ composites: preparation, mechanic properties and cytotoxicity

Firstly apatite-type carbonated calcium phosphate and biphasic calcium phosphates (mixture of phases based on Ca₁₀(PO₄)₆(OH)₂ and β-Ca₃(PO₄)₂ with weight ratio 60 : 40%) which contained the trace elements complex (Na⁺, Mg²⁺, Zn²⁺) were obtained from aqueous solutions and heated to 600 °C. Composites based on apatite-related calcium phosphates with 5, 10, 25wt% of ZrO₂ were also prepared used one-stage method. In vitro testing of new prepared samples in phosphate-buffered solution (at 37 °C and pH = 7.45) showed increasing of pH value to 10 during 96 h in the presence of apatite-related Na⁺ (0.6wt%), Mg²⁺ (0.6wt%), Zn²⁺ (1.7wt%), CO₃^2- (3wt%)-containing calcium phosphate. At the same time, increasing of pH only to 8.78 during 48 h was found for the biphasic calcium phosphate with the similar amount of doping cations. This result indicates that carbonated modified hydroxyapatites can be more appropriate for bone tissue engineering than biphasic calcium phosphates with similar amount of trace elements. An increase in the ZrO₂ amount from 10 to 25 wt% in the composite with apatite-related Na⁺ (0.6wt%), Mg²⁺ (0.6wt%), Zn²⁺ (1.7wt%), CO₃^2- (3wt%)-containing calcium phosphate led to an increase of its hardness in 1.4 times. The results of in vitro investigation using both the MTT and resazurin assays demonstrate that the prepared apatite-related Na⁺ (0.6wt%), Mg²⁺ (0.6wt%), Zn²⁺ (1.7wt%), CO₃^2-(3wt%)-containing calcium phosphate and its composite with 25 wt% ZrO₂ have a dose-dependent effect on the metabolic and proliferation activity (viability) of the mouse monocyte-macrophage RAW264.7 and J774A.1 cell lines. The stimulation of RAW264.7 macrophages growth within 100-155% compared with the control was found at samples concentration 0.1 and 0.01 mg/ml in the cell cultivation medium. Obtained results are important at creation of bioactive materials with special microhardness for the medical application.