Strontium‐releasing fluorapatite glass‐ceramics: Crystallization behavior, microstructure, and solubility

Abstract

The purpose of this work was to investigate the effect of strontium partial replacement for calcium on the crystallization behavior, microstructure and solubility of fluorapatite glass-ceramics. Four glass compositions were prepared with increasing amounts of strontium partially replacing calcium. The crystallization behavior was analyzed by differential scanning calorimetry and X-ray diffraction (XRD). The microstructure was investigated by scanning electron microscopy. The chemical solubility was quantified according to ISO standard 10993-14. The amount of strontium released in solution after incubation in TRIS-HCl or citric acid buffer was measured by atomic absorption spectroscopy. XRD analyses revealed that partially substituted strontium-fluorapatite and strontium-åkermanite crystallized after strontium additions. The lattice cell volume of both phases increased linearly with the amount of strontium in the composition. Strontium additions led to a reduction in crystal size and an increase in crystal number density. The chemical solubility and amount of strontium released in solution increased linearly with the amount of strontium present in the composition in both TRIS-HCl and citric acid buffers. Total amounts of strontium released reached a maximum of 547 ± 80 ppm in TRIS-HCl and 1252 ± 290 ppm in citric acid buffer for the glass composition with the highest amount of strontium. For all strontium-containing compositions, the amount released in TRIS-HCl continued to increase between 70 and 120 h, indicating sustained release rather than burst release. © 2017 Wiley Periodicals, Inc. J Biomater Res Part B: 106B: 1421-1430, 2018.

Strontium-releasing fluorapatite glass-ceramic scaffolds: Structural characterization and in vivo performance

“…Traces of fluorapatite (PDF 15-876) were found in the as-sintered strontium-free scaffolds (GSr-0), while fully crystallized fluorapatite was present after crystallization heat treatment (GCSr-0). Strontium-substituted fluorapatite crystallized in the strontium-containing glasses, in agreement with our previous work [ 23 ]. The extent of strontium substitution in the fluorapatite structure was in line with the amount of strontium in the glass composition [ 23 , 30 – 32 ].…”

“…This zone is tentatively identified as a reaction zone indicative of scaffold biodegradation and interaction with surrounding cells and nutrients. This finding was expected, as we already reported the bioactivity of these compositions, and their solubility in TRIS-HCl at pH 7.4, together with sustained strontium release for relevant compositions [23]. The release of strontium from the scaffolds for groups GCSr-12 and GCSr-24 was indirectly confirmed by its identification by x-ray fluorescence spectrometry within newly formed bone for these compositions (Fig.…”

“…As mentioned earlier, the crystallization behavior, density and solubility of these glass compositions were recently reported [ 23 ]. The focus of the present manuscript was to assess the suitability of strontium-releasing compositions for producing synthetic scaffolds for bone graft substitutes.…”

“…Fluorapatite-based glasses in the SiO 2 –Al 2 O 3 –P 2 O 5 –MgO–Na 2 O–K 2 O–(Ca (1-x) Sr x )O–CaF 2 system, with increasing amounts of strontium from 0 to 24 mol% were prepared by mixing adequate amounts of reagent grade oxides and carbonates, as previously described [ 23 ]. Glasses were labeled GSr-0, GSr-12 and GSr-24 to reflect the amount of strontium in the composition ( Table 1 ).…”

“…Our recent work investigated the thermal behavior and microstructure of fluorapatite glass-ceramics and the effect of strontium additions on their bioactivity and strontium-release ability [ 21 , 22 ]. It was shown that strontium additions in this glass system led to a finer microstructure, increased solubility and promoted sustained strontium release [ 23 ].…”