Lithium-silicate sol-gel bioactive glass and the effect of lithium precursor on structure-property relationships

This work reports the synthesis of lithium-silicate glass, containing 10 mol% of Li2O by the sol-gel process, intended for the regeneration of cartilage. Lithium citrate and lithium nitrate were selected as lithium precursors. The effects of the lithium precursor on the sol-gel process, and the resulting glass structure, morphology, dissolution behaviour, chondrocyte viability and proliferation, were investigated. When lithium citrate was used, mesoporous glass containing lithium as a network modifier was obtained, whereas the use of lithium nitrate produced relatively dense glass-ceramic with the presence of lithium metasilicate, as shown by X-ray diffraction, Si-29 and Li-7 MAS NMR and nitrogen sorption data. Nitrate has a better affinity for lithium than citrate, leading to heterogeneous crystallisation from the mesopores, where lithium salts precipitated during drying. Citrate decomposed at a lower temperature, where the crystallisation of lithium-silicate crystal is not thermodynamically favourable. Upon decomposition of the citrate, a solid-state salt metathesis reaction between citrate and silanol occurred, followed by the diffusion of lithium within the structure of the glass. Both glass and glass-ceramic released silica and lithium ions in culture media, but release rate was lower for the glass-ceramic. Both samples did not affect chondrocyte viability and proliferation.