Altair Contreras Jaimes is a Post-Doctoral Researcher at the Otto Schott Institute of Materials Research (Structure-Property Relationships in Glasses) working with bioactive glasses and glass ionomer cements. Her PhD was carried at The University of Sheffield, and she has a background in biomaterials with a MSc. in Bioengineering from The University of Nottingham and an MEng. Degree in Metallurgical Engineering from Universidad Central de Venezuela.
Apatite-containing glass-ceramics based on bioactive glasses
1Altair T. Contreras Jaimes, 1Gloria Kirste, 2Jonathan Massera, 2Delia S. Brauer
1Otto-Schott-Institut für Materialforschung, Friedrich-Schiller-Universität Jena
2Faculty of Biomedical Sciences and Engineering, Tampere University of Technology, Tampere, Finland
Bioactive glass powders or granules are used clinically as bone grafts. While the use of porous, three-dimensional scaffolds would be a desired alternative here, their preparation is limited by the pronounced tendency of bioactive glasses to undergo crystallisation during sintering. Moreover, it has been reported that full or partial crystallisation of the glass negatively affects the release of ions required for apatite formation. Therefore, the aim of this study was to characterise the crystallisation and dissolution behaviour of a SiO2-P2O5-CaO-CaF2 glass system, in which the network connectivity was kept at 2.1. Increasing amounts of P2O5 were added together with CaO to charge balance PO43– groups in the glass structure. In addition, CaF2 was included in the glass to allow crystallisation of apatite. These glasses were melted and fritted in water and powdered to obtain a particle size between 125-250 µm; their thermal properties were analysed by DSC. Crystallisation was achieved via heat treatment at the crystallisation peak temperature for one hour. The glasses and corresponding glass-ceramics were characterised by XRD, ATR-FTIR and in vitro solubility testing in Tris buffer solution.
XRD results showed diffraction peaks associated with (fluoride-substituted) apatite for P2O5 contents above 3 mol%. Characterisation by ATR-FTIR showed the characteristic Si-O-Si and Si-O-NBO bands for the glasses, while for the glass-ceramics narrow bands in the same regions suggest crystallisation of silicate phases. Bands at 560-550 cm-1 confirm the presence of apatite phases. Interestingly, the Si4+ and Ca2+ concentrations in Tris buffer solution after immersion tests did not show significant differences in ion release between the glasses and corresponding glass-ceramics. Regarding the in vitro study in Tris-buffer, it was confirmed that increasing P2O5 content accelerated the apatite formation for both glasses and glass-ceramics, with the band at ~1050 cm-1 appearing more readily on the glasses, and the split bands between 550 and 600 cm-1 appearing more readily for the glass-ceramics.
In summary, this study showed that fluoride-containing phosphosilicate glasses may form glass-ceramics containing (fluoro) apatite as a crystal phase. This partial crystallisation did not inhibit degradation as ion release in vitro apatite precipitation remained comparable for the amorphous glasses and their corresponding glass-ceramics.