Advances in strontium-releasing biomaterials for bone repair.

Strontium-containing biomaterials offer promising avenues for enhancing bone repair by leveraging the ion's reported dual anabolic and anti-catabolic effects on bone cells. These biomaterials aim to encourage site-specific bone growth, heal fractures, and improve metallic implant fixation through controlled release of strontium ions. Here, we provide an overview of strontium's use as a treatment for osteoporosis, and report current advances in biomaterials designed to deliver strontium locally to the skeleton from bioactive glasses, calcium phosphates, bone cements, polymers, and implant coatings. Strontium's putative mechanisms of action on bone, including by directly stimulating osteoblasts and osteoclasts and through physicochemical interactions with the bone mineral are discussed. We also appraise dosing, noting discrepancies between in vitro stimulatory ranges and concentrations likely to be achieved in vivo. Strontium-releasing materials are widely reported to be efficacious in preclinical models, but there is very limited human experience. Thus, we also focus on translational issues, including dose and release quantification, safety and systemic exposure monitoring, regulatory pathways, and manufacturing constraints. The review concludes with recommendations for future studies to elucidate strontium's biological and physicochemical mechanisms of action, guidance to refine delivery strategies, and a call to standardise the reporting of dosing. Together, these changes should advance these promising materials toward early clinical testing and improved outcomes in bone repair applications.