Silver Doping Mechanism in Bioceramics—From Ag+: Doped HAp to Ag°/BCP Nanocomposite

Abstract

The results presented in this paper, based on the powder X-ray diffraction technique followed by Rietveld analyses, are devoted to the mechanism of silver incorporation in biphasic calcium phosphates. Results were confirmed by SEM observation. Samples were synthesized via the sol-gel route, followed by heat treatments. Two incorporation sites were highlighted: Ca2+ replacement by Ag+ into the calcium phosphates (HAp: hydroxyapatite and β-TCP: tricalcium phosphate), and the other as metallic silver Ag° nanoparticles (formed by autogenous reduction). The samples obtained were thus nanocomposites, written Ag°/BCP, composed of closely-mixed Ag° particles of about 100 nm at 400 °C (which became micrometric upon heating) and calcium phosphates, themselves substituted by Ag+ cations. Between 400 °C and 700 °C the cationic silver part was mainly located in the HAp phase of the composition Ca10-xAgx(PO4)6(OH)2-x (written Ag+: HAp). From 600 °C silver cations migrated to β-TCP to form the definite compound Ca10Ag(PO4)7 (written Ag+: TCP). Due to the melting point of Ag°, the doping element completely left our sample at temperatures above 1000 °C. In order to correctly understand the biological behavior of such material, which is potentially interesting for biomaterial applications, its complex doping mechanism should be taken into consideration for subsequent cytotoxic and bacteriologic studies.