Investigation of tricalcium phosphate with gadolinium ions by electron paramagnetic resonance

In this article, the tricalcium phosphate (TCP) material doped with gadolinium Gd3+ ions, which is extremely promising in orthopedics and dentistry due to its high biocompatibility with human bone tissue and the presence of such important properties as osteoconductivity and bioresorption, has been studied by electron paramagnetic resonance (EPR). To control each stage of healing and the degree of regeneration of hard tissues, it is necessary to use physical imaging methods (radiography, computed tomography (CT) and magnetic resonance imaging (MRI)) by introducing contrast agents (Gd3+) to the bone substitute TCP. In this study, it was unequivocally established that gadolinium with a valence of 3+ is embedded in the TCP crystal lattice without damaging it and without changing the local environment. Simulation of EPR spectra by different sets of fine structure parameters (crystal field) indicates the presence of two nonequivalent Gd3+ positions (at extremely low concentrations x = 0.001) with axial and lower symmetry. Low-field resonant absorptions with effective g-factors 5.9, 2.8 and 2 related to high-spin S = 7/2 centers in orientationally disordered samples were observed and identified.