  The osteoinductive property of strontium was repeatedly proven in the last
decades. Compelling $\textit{in vitro}$ data demonstrated that strontium
hydroxyapatite nanoparticles exert a dual action, by promoting
osteoblasts-driven matrix secretion and inhibiting osteoclasts-driven matrix
resorption. Recombinant human bone morphogenetic protein 2 (rhBMP2) is a
powerful osteoinductive biologic, used for the treatment of vertebral fractures
and critically-sized bone defects. Although effective, the use of rhBMP2 has
limitations due its recombinant morphogen nature. In this study, we examined
the comparison between two osteoinductive agents: rhBMP2 and the innovative
strontium-substituted hydroxyapatite nanoparticles. To test their
effectiveness, we independently loaded Gelfoam sponges with the two
osteoinductive agents and used the sponges as agent-carriers. Gelfoam are
FDA-approved biodegradable medical devices used as delivery system for
musculoskeletal defects. Their porous structure and spongy morphology make them
attractive in orthopedic field. The abiotic characterization of the loaded
sponges, involving ion release pattern and structure investigation, was
followed by $\textit{in vivo}$ implantation onto the periosteum of healthy mice
and comparison of the effects induced by each implant was performed. The
results demonstrated the use of sponges loaded with strontium nanoparticles as
potential bone grafts might provide better outcomes for complex fractures.
Strontium nanoparticles are a novel and effective non-biologic treatment for
bone injuries and can be used as novel powerful therapeutics for bone
regeneration.
