Abstract
This study investigated the impact of different calcium reagents on the morphology, composition, bioactivity and biocompatibility of two-component (CaO-SiO2) glasses produced by the Stöber process with respect to their potential application in guided tissue regeneration (GTR) membranes for periodontal repair. The properties of the binary glasses were compared with those of pure silica Stöber particles. The direct addition of calcium chloride (CC), calcium nitrate (CN), calcium methoxide (CM) or calcium ethoxide (CE) at 5 mol % with respect to tetraethyl orthosilicate in the reagent mixture gave rise to textured, micron-sized aggregates rather than monodispersed ~500 nm spheres obtained from the pure silica Stöber synthesis. The broadening of the Si-O-Si band at ~1100 cm−1 in the infrared spectra of the calcium-doped glasses indicated that the silicate network was depolymerised by the incorporation of Ca2+ ions and energy dispersive X-ray analysis revealed that, in all cases, the Ca:Si ratios were significantly lower than the nominal value of 0.05. The distribution of Ca2+ ions was also found to be highly inhomogeneous in the methoxide-derived glass. All samples released soluble silica species on exposure to simulated body fluid, although only calcium-doped glasses exhibited in vitro bioactivity via the formation of hydroxyapatite. The biocompatibilities of model chitosan-glass GTR membranes were assessed using human MG63 osteosarcoma cells and were found to be of the order: CN < pure silica ≈ CC << CM ≈ CE. Calcium nitrate is the most commonly reported precursor for the sol-gel synthesis of bioactive glasses; however, the incomplete removal of nitrate ions during washing compromised the cytocompatibility of the resulting glass. The superior bioactivity and biocompatibility of the alkoxide-derived glasses is attributed to their ease of dissolution and lack of residual toxic anions. Overall, calcium ethoxide was found to be the preferred precursor with respect to extent of calcium-incorporation, homogeneity, bioactivity and biocompatibility.
Highlights
Periodontitis is a widespread infectious disease characterised by inflammation and progressive destruction of the tooth attachment apparatus [1,2,3]
Binary and multicomponent sol-gel-derived calcium silicate glasses are most commonly produced by the acid-catalysed condensation of tetraethyl orthosilicate (TEOS) in the presence of calcium nitrate
Temperatures in excess of 600 ◦C are required to integrate calcium ions into the silicate network if calcium hydroxide reagent is used, and chloride-derived calcium ions fail to enter the silicate network below the point of crystallisation at ~700 ◦C
Summary
Periodontitis is a widespread infectious disease characterised by inflammation and progressive destruction of the tooth attachment apparatus [1,2,3]. Guided tissue regeneration (GTR) of damaged periodontal structures involves the placement of a barrier membrane to exclude the fast-growing epithelial tissues from the exposed root surface in order to enable the more slow-growing ligament and hard tissues to regenerate [1,2,3]. Various silica-based phases, such as multi-component glasses [2], Stöber particles [5], minerals [6] and diatomite [7] have been incorporated into the polymer matrices in order to enhance the mechanical and/or osteogenic properties of the GTR membranes. The Stöber process is a simple, ambient-temperature, one-pot, sol-gel processing route for the synthesis of spherical monodispersed silica (SiO2) particles (between 0.05 and 2 μm in diameter) [8]. The original Stöber process has been widely modified to functionalise the resulting particles with fluorescent labels, therapeutic ions and a range of active pharmaceutical ingredients [9,10,11,12,13,14]
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