Influence of strontium for calcium substitution in bioactive glasses on degradation, ion release and apatite formation

TLDR

Bioactive glasses bond to bone by forming hydroxy‑carbonate apatite, and Sr‑releasing variants are attractive for osteoporosis because Sr promotes bone formation in vitro and in vivo. This study aims to elucidate the composition–structure–property relationships in Sr‑substituted bioactive glasses to design next‑generation biomaterials that combine bone regeneration with therapeutic Sr release. The authors prepared a melt‑derived glass series with 0–100 % Ca replaced by Sr and examined its dissolution, ion release, and apatite formation in simulated body fluid and Tris buffer at 37 °C for up to 8 h, finding that Sr substitution increased dissolution and ion release due to the larger Sr ionic radius expanding the glass network. Sr release increased linearly with Sr content, and the fully Sr‑substituted glass showed markedly enhanced apatite formation, leading to improved osteoblast attachment, proliferation, and regulation of osteoblast/osteoclast activity.

Abstract

Bioactive glasses are able to bond to bone through the formation of hydroxy-carbonate apatite in body fluids while strontium (Sr)-releasing bioactive glasses are of interest for patients suffering from osteoporosis, as Sr was shown to increase bone formation both in vitro and in vivo . A melt-derived glass series (SiO 2 –P 2 O 5 –CaO–Na 2 O) with 0–100% of calcium (Ca) replaced by Sr on a molar base was prepared. pH change, ion release and apatite formation during immersion of glass powder in simulated body fluid and Tris buffer at 37°C over up to 8 h were investigated and showed that substituting Sr for Ca increased glass dissolution and ion release, an effect owing to an expansion of the glass network caused by the larger ionic radius of Sr ions compared with Ca. Sr release increased linearly with Sr substitution, and apatite formation was enhanced significantly in the fully Sr-substituted glass, which allowed for enhanced osteoblast attachment as well as proliferation and control of osteoblast and osteoclast activity as shown previously. Studying the composition–structure–property relationship in bioactive glasses enables us to successfully design next-generation biomaterials that combine the bone regenerative properties of bioactive glasses with the release of therapeutically active Sr ions.