Preparation and characterization of hydroxyapatite reinforced with hardystonite as a novel bio-nanocomposite for tissue engineering

Objecttive(s): Despite the poor mechanical properties of hydroxyapatite, its unique biological properties leads we think about study on improving its properties rather than completely replacing it with other biomaterials. Accordingly, in this study we introduced hydroxyapatite reinforced with hardystonite as a novel bio-nanocompositeand evaluate its in-vitro bioactivity with the aim of developing a mechanically strong and highly porous scaffold for bone tissue engineering applications.Materials and Methods: Natural Hydroxyapatite (NHA)-Hardystonite (HT) nanocomposite with different percentage of HT was synthesized by mechanical activation method and subsequent heating annealing process. This study showed that the addition of HT to HA not only increases the mechanical properties of HA but also improves its bioactivity. Dissolution curves presented in this study indicated that the pH value of SBF solution in the vicinity of HA-HT nanocomposite increases during the first week of experiment and decreases to blood pH at the second weekend. Hardystonite was composed of nano-crystalline structure with approximately diameter 40 nm. Specimens were composed of a blend of pure calcite (CaCO3) (98% purity, Merck), silica amorphous (SiO2) (98% purity, Merck) powder and pure zinc oxide (ZnO) with 50 % wt., 30 %wt and 20 %wt., respectively. These powders were milled by high energy ball mill using ball-to- powder ratio 10:1 and rotation speed of 600 rpm for 5 and 10 h. Then, the mixture mechanical activated has been pressed under 20 MPa. The samples pressed have been heated at 1100 ºC for 3 h in muffle furnace at air atmosphere. X-ray diffraction (XRD), scanning electron microscopy (SEM) and BET performed on the samples to characterize. Results: According to XRD results, the sample milled for 10 h just indicated the hardystonite phase, while the sample milled for 5 h illustrate hardystonite phase along with several phases. Conclusion: In fact, our study indicated that hardystonite powder was composed of nano-crystalline structure, about 40 nm, can be prepared by mechanical activation to use as a new biomaterials for orthopedic applications.