Thermoluminescence in silicon substituted apatite and silicon stabilized tricalcium phosphate bioceramic

Abstract

Silicon stabilized tricalcium phosphate (Si-TCP), with a crystal structure similar to a-TCP (Ca3(PO4)2) is formed when a stoichiometric calcium hydroxyapatite (HA or Ca5(PO4)3OH) precipitate is sintered in the presence of added silica (SiO2) at temperatures between 850 and 1,000 C [1–3]. A change in the lattice constants with silicon content of both the P21/a Si-TCP and the P63/m HA crystallographic unit cell suggests that Si is incorporated into both of these phases [3]. In the absence of silicon, an a-TCP phase is expected to be present only after sintering at temperatures greater than 1,200 C [4]. Unlike undoped counterparts, Si-TCP based materials prepared by adding SiO2 to HA are resorbable by osteoclast cells and exhibit good osteoconductive properties [2]. As Si is implicated in the biological performance of these materials, it is of the utmost importance to determine the changes induced by Si in this calcium phosphate system. IR and NMR measurements indicate a significant loss of OH from the starting HA composition as a function of silica doping [3]. It has been suggested that when HA is sintered in the presence of SiO2, species such as SiO4 4) substitute for PO4 3) with the creation of VOH AE for charge compensation [5, 6]. Recently it has been proposed that SiO2 substitution in HA without removal of phosphate from the HA mix to ensure stoichiometric production of Si-HA, results in the formation of a-TCP, according to the reaction [7]: