IMET RAS in cooperation with Lomonosov Moscow State University and Belgorod State University have investigated the thermal stability of the synthetic hydroxyapatite (HA) - the analogs material of human bone tissue. The obtained results have demonstrated that Al3+ doping of the HA structure in the tiny amounts enhanced its thermal stability and biocompatibility. This lead to apply this material as a coating for implants and for high-temperature bioceramics creation. In the cooperation with Kazan Federal University and Kazan Institute of Biochemistry and Biophysics of Kazan Science Centre of the Russian Academy of Sciences, the scientists described the HA structure properties and predicted the model of the Al incorporation in the HA crystal lattice. Scientists from the Federal State Budgetary Institution National Medical Research Radiological Center of the Ministry of Health of the Russian Federation carried out the certification of sintered materials in vitro, which showed an improvement in the biological characteristics of aluminum-containing materials. The results were published in Journal of Materials Research and Technology and the Journal of Physical Chemistry B.
HA is the main mineral of the native bone tissue. Scientists have been studied the synthesis and properties of HA in IMET RAS since 1990. HA powder was synthesized and heat-treated at high temperature for bone tissue implants engineering. It decomposes at the temperature higher than 1100 °C losing OH-groups which follows by phase transformation and formation of undesirable phases.
Scientists from IMET RAS have been investigated the influence of different cations on the thermal stability of HA. Increasing the thermal stability of HA will allow it to be applied as a coating for Al2O3 or Ti6Al14V implants and to obtain dense and porous high-temperature bioceramics. In the first article, it was found that the introduction of aluminum up to 1 mol % can ensure the preservation of the pure HA phase at 1200 °C, as well as provide the predominant formation of HA (up to 88 wt.%) at 1400 °C. A further increase of Al concentration in the HA leads to destabilization of the crystal lattice and the decrease of thermal stability, up to a complete transformation from HA to tricalcium phosphate at 900 °? in the case of substitution of 20 mol. % Al. To identify this effect a wide range of material studies was carried out together with scientists from Lomonosov Moscow State University and Belgorod State University. The effect of aluminum on the parameters of the crystal lattice, the intensity of vibrations of functional groups in the molecules were studied and the mass loss during heating was found. The obtained results became the basis for the diagram of the thermal stability of HA, which can help engineers and technologists in the determination of the temperature conditions of sintering or coating in order to preserve the single-phase state of the substance.
In the second article, the influence of aluminum on electron paramagnetic resonance and electron-nuclear paramagnetic resonance was studied. Together with colleagues from Kazan Federal University and Kazan Institute of Biochemistry and Biophysics of Kazan Science Centre of the Russian Academy of Sciences a model of the introduction of aluminum cations into the HA lattice was predicted using the theory of functional density. Scientists from the Federal State Budgetary Institution National Medical Research Radiological Center of the Ministry of Health of the Russian Federation carried out the certification of sintered materials in vitro, which showed an improvement in the biological characteristics of aluminum-containing materials compared to pure HA. Thus, the effect of aluminum on the crystalline structure, thermal and biological behavior of HA was experimentally studied.
Scientific researcher Margarita Goldberg, PhD said: "In spite of the fact that the information about the effect of aluminum in the form of compounds on the human body is controversial nowadays, Al is using as a basis for injections, a drug carrier, a doping cation for creating implants. Recent investigations have shown that the introduction of small doses of aluminum into the HA lattice in the form of a cation, rather than in a metallic state, contributed to the improvement of biocompatibility and the growth of the matrix properties of the implant surface".