O papel do nitrato de cálcio na mineralização precoce de hidroxiapatita durante a síntese sol-gel de vidros do tipo 58S e seus efeitos sobre bioatividade e adsorção de proteínas

Abstract

The early mineralization of hydroxyapatite during the synthesis of bioactive glasses derived from sol-gel synthesis has been frequently reported in the literature. To date, there is no consensus on how this early mineralization occurs and whether it can affect the subsequent biological behavior of the glass. In this work, we explored the time effect of the calcium precursor addition and alkoxide hydrolysis on this early mineralization process, and the consequent bioactivity and protein adsorption capacity of a 58S glass (58SiO2-33CaO-9P2O5, wt. %). It was demonstrated that the addition of calcium nitrate after the alkoxide hydrolyses produced a heterogeneous microstructure in which Ca2+-rich regions promoted the formation of nanocrystalline hydroxyapatite domains during heat treatment in a devitrification-like process. This microstructure resulted in an increased albumin adsorption capacity. Conversely, bioactivity was not significantly affected by this early mineralization process. Thus, it is concluded that, although bioactivity cannot be affected by this early hydroxyapatite mineralization, the microstructure of the glass and its protein adsorption capacity can be modulated by the moment at which calcium nitrate is added to the sol-gel synthesis.