Hydroxyapatite mineral tubes developed for the loading and release of biological proteins

• Hydroxyapatite mineral tubes developed through the replication of polymer nanofiber mesh.
• Heat-treatment temperature tailored the crystallinity, crystalline size and surface area of tubes.
• Biological protein adsorption and release dependent on the properties of tubes.

Hydroxyapatite (HA) mineral tubes developed through the replication of polymer nanofiber mesh were studied for loading and delivery of biological proteins. With varying heat-treatment temperature (500, 800 and 1100 °C), the physicochemical properties of the HA mineral tubes differed substantially, i.e., while crystallinity and crystallite size increased the surface area decreased with increase in the temperature. All mineral tubes retained negative surface charges (around −10 mV) at physiological conditions. Cytochrome C (cyt C), used as a model protein of being positively-charged, was adsorbed well onto the HA mineral tubes, with adsorption being saturated within a few hours. The adsorption amount was significantly higher in the case treated at lower temperature. The cyt C showed a similar release pattern from the HA mineral tubes, with an initial rapid release for a few hours followed by a reduced rate over ∼24 h. Results indicated the HA mineral tubes might be tailored to properly load and delivery biological molecules for bone repair.