Diffusion of Copper Ions in the Lattice of Substituted Hydroxyapatite during Heat Treatment

The doping of hydroxyapatite with various substituent ions can give this material new and useful properties. Nonetheless, local distortions of structure after doping can change the properties of the material. In this work, the thermal stability of copper-substituted hydroxyapatite synthesized by the mechanochemical method was investigated. In situ diffraction analyses showed that copper ion diffusion during the heating of Cu-substituted hydroxyapatite promotes phase transformations in the substituted hydroxyapatite. The behavior of copper ions was studied in samples with ratios (Ca + Cu)/P = 1.75 and 1.67. It was found that in both cases, single-phase Cu-substituted hydroxyapatite with the general formula Ca_10-xCu_x(PO₄)_6-y(CO₃)_y(OH)_2-yO_y is formed by the mechanochemical synthesis. When heated at approximately 600-700 °C, the lattice loses copper cations, but at higher temperatures, CuO diffusion into the hydroxyl channel takes place. Cuprate-substituted hydroxyapatite with the general formula Ca₁₀(PO₄)₆(OH)_2-2x(CuO₂)_x forms in this context. At 1200 °C, the sample is single-phase at (Ca + Cu)/P = 1.75. Nonetheless, slow cooling of the material leads to the emergence of a CuO phase, as in the case of (Ca + Cu)/P = 1.67, where the material contains not only CuO but also Cu-substituted tricalcium phosphate. In the manufacture of ceramic products from Cu-substituted hydroxyapatite, these structural transformations must be taken into account, as they alter not only thermal but also biological properties of such materials.

Lanthanum-silicate-substituted apatite synthesized by fast mechanochemical method: Characterization of powders and biocoatings produced by micro-arc oxidation

Lanthanum-silicate substituted apatite with equal concentrations of the substituents in the range of 0.2-6.0 mol were produced by a fast method - mechanochemical synthesis. This method makes it possible to synthesize a nanosized single-phase product by activating reaction mixtures containing CaHPO₄, CaO, La(OH)₃ and SiO₂·H₂O for 25-30 min in AGO-2 and AGO-3 planetary mills. The structure of the apatites was investigated by the FTIR and XRD methods. It was found that the synthesized samples with substituent concentrations up to 2 mol are substituted oxy-hydroxyapatites, at higher concentrations, they are substituted oxyapatites. The mechanochemically synthesized apatite with a substituent concentration of 0.5 mol was used for depositing biocoatings on titanium substrates by the micro-arc oxidation method. The structure of the coatings is mainly amorphous. In vitro biological tests demonstrated high biocompatibility of the coatings and the absence of cytotoxic action on mesenchymal stem cells.

Solid-state NMR and computational insights into the crystal structure of silicocarnotite-based bioceramic materials synthesized mechanochemically

In this work, we report the results of a detailed structural study of a promising bioceramic material silicocarnotite Ca₅(PO₄)₂SiO₄ (SC) synthesized from mechanochemically treated nanosized silicon-substituted hydroxyapatite by annealing at 1000°C. This novel synthetic approach represents an attractive and efficient route towards large-scale manufacturing of the silicocarnotite-based bioceramics. A combination of solid-state nuclear magnetic resonance (NMR), powder X-ray crystallography and density function theory (DFT) calculations has been implemented to characterize the phase composition of the prepared composite materials and to gain insight into the crystal structure of silicocarnotite. The phase composition analysis based on the multinuclear solid-state NMR has been found in agreement with X-ray powder diffraction indicating the minority phases of CaO (5-6wt%) and residual silicon-apatite (7-8wt%), while the rest of the material being a fairly crystalline silicocarnotite phase (86-88wt%). A combination of computational (CASTEP) and experimental methods was used to address the anionic site disorder in the silicocarnotite crystal structure. Distorted [OPO₃] pyramids have appeared as an important structural motif in the SC crystal structure. The ratio between regular [PO₄] and distorted [OPO₃] tetrahedra is found between 2:1 and 3:1 based on XRD experiments and CASTEP calculations. The natural abundance ⁴³Ca magic angle spinning NMR spectra of silicocarnotite are reported for the first time.

In vitro regulation of cell behavior by calcium phosphates synthesized by the mechanochemical method

Biological activity of eight hydroxyapatite powders synthesized by the mechanochemical method was studied in vitro. Introduction of copper and zinc atoms into synthetic hydroxyapatite structure promotes cell adhesion. Hydroxyapatites obtained by the mechanochemical method are promising base for a new class of materials and coatings with regulated bioactivity for orthopedics and traumatology.