Influence of manganese on stability and particle growth of hydroxyapatite in simulated body fluid

The Mn substituted hydroxyapatites (HAPMn) were prepared by coprecipitation of manganese and calcium with PO43− ions (the content of Mn up to 0.25 wt.%) or by ion-exchange with 14% exchange of Ca2+ ions in hydroxyapatites (HAP). The partially dissolution of hydroxyapatite particles with simultaneously change of their morphology was confirmed during ion exchange. All HAPMn had the hydroxyapatite structure without the presence of any secondary phases. The decomposition of the hydroxyapatite structure in manganese substituted HAP to tricalcium phosphate begins above the temperature of 800 °C. Origin HAP particles (before ion-exchange) and HAPMn prepared by precipitation had globular morphology but the stick shape of individual particles of HAPMn was found after ion-exchange. High concentration of manganese at the surface of hydroxyapatite particles after ion-exchange causes rapid decrease in growth rate of hydroxyapatite in simulated body fluid (SBF) solutions. The particle aggregates of pure HAP and HAPMn prepared by coprecipitation have globular morphology. Aggregates of ion-exchange prepared HAPMn are represented by the mixture of spherical and plate-like shapes. The shape of aggregates was not changed after treatment of hydroxyapatite in SBF solutions but rise of the Ca2+ and PO43− concentrations in SBF causes the separation of individual aggregates.