Facile synthesis, microstructure and BMP-2 delivery of novel silica hollow flowers for enhanced osteoblast differentiation

•Silica hollow flowers were synthesized via novel apatite template sol–gel route.•Their shells were constructed by numerous silica hollow nanosheets.•They can serve as sustained release system for BMP-2.•The released BMP-2 was biologically active to stimulate cell differentiation.

Novel silica hollow flowers (1–5 μm) were synthesized using globular apatite flowers as sacrificed template via a sol–gel route and then employed as biocompatible carrier of bone morphogenetic protein-2 (BMP-2) to stimulate osteoblast differentiation. Apatite was bio-mimetically synthesized from a well-known Kokubo’s simulated body fluid (SBF), then coated with silica in a Stöber-type silica sol–gel system, and finally dissolved in an acetic solution to yield silica hollow flowers. Analyses of SEM and TEM images show that the resultant silica flowers had a porous and hollow structure due to removal of apatite template by acetic treatment and their shell was constructed by numerous silica nanosheets (∼10 nm in silica shell). A larger specific surface of 890 m2/g was obtained for silica hollow flowers compared to silica-coated apatite due to the presence of porous and hollow structure. Silica hollow flowers had no significant toxicity after incubation with osteoblast MC3T3-E1 cells, indicating a good biocompatibility. They favored adsorption and supported a sustained release behavior of BMP-2. The released BMP-2 was biological active and enhanced osteoblast differentiation with higher ALP activity and larger amount of osteocalcin. The present silica hollow flowers are thus applicable to delivery system in tissue generation.