A Comparative EPR Study of Non-Substituted and Mg-Substituted Hydroxyapatite Behaviour in Model Media and during Accelerated Ageing

Abstract

To assess the application potential of novel biomaterials, their behaviour in model media and upon sterilization should be investigated, as well as the stability related to their storage conditions. Such data are lacking for Mg-substituted HAP (Mg-HAP). Therefore, the changes in the local structure of non-substituted and Mg-HAP after irradiation and immersion in corrected simulated fluid and saline solution for 28 days were followed by electron paramagnetic resonance (EPR) spectroscopy for the first time. To better understand the stability of radical species induced by sterilization, EPR spectra of samples kept for 2 h at temperatures up to 373 K were recorded to provide an insight into the stability of the sample storage conditions by the accelerated aging method. Samples were characterized by PXRD, FTIR, SEM, EDS, AAS and TGA. Results confirmed that irradiation does not induce changes in the composition or the structure of any of the investigated materials. Fading or the complete disappearance of radical signals in the EPR spectra after immersion in both media was accompanied by the disappearance of other phases formed as a minor byproduct in the synthesis of substituted HAP, as confirmed by PXRD and FTIR analysis. Obtained results confirm the great potential of Mg-HAPs for biomedical applications, although closer attention should be given to the processes related to sample storage stability at different temperatures.

Calcium Phosphate Loaded Biopolymer Composites—A Comprehensive Review on the Most Recent Progress and Promising Trends

“…Generally, the ionic substitutions can be rendered cationic by replacing the Ca 2+ with Mg 2+ , Zn 2+ , Sr 2+ , Si 4+ ions, or anionic when the PO 4 3− groups are substituted by CO 3 2− or fluoride anions. The preparations, thorough characterizations, and properties of these materials have been exhaustively studied and reported in numerous papers and summarized in reviews [34][35][36][37][38][39][40]. A further purpose of ionic substitution is to achieve antibacterial properties, using silver or other specific additives [41,42].…”

Investigation in Hydroxyapatite After Cationic Substitution with Neodymium and Magnesium

“…The hexagonal unit cell of hydroxyapatite contains ten Ca2+ ions, six (PO43-) ions, and two (OH-) ions. Ca(I) and Ca(II) are two distinct cation sites, where the big cations can be hosted at the Ca(II) site, while small cations and limited amounts of bigger cations can be hosted at the Ca(I) site [11]. The solubility of substituted HA is typically enhanced by replacing certain Ca2+ ions with other cations.…”