Preparation Of Apatite Nanocomposites Based On Biomimetic Mineralization Regulated By Templates

The natural bone is formed with the regulation of template molecules. The hierarchical structure of bone has been intensively studied, but the biomineralization mechanism of the bone has not been completely revealed yet. The synthesis of apatite nanocomposite via the biomimetic approaches of template regulation can not only demonstrate the assembly mechanism of natural bone tissues, but also produce new materials similar to natural bone structures in vitro. In this study, two types of template systems, including silk fibroin(SF)/sodium alginate(ALG) composite and chitosan/polyacrylic acid(CS-PAA) nanogel, were used in biomimetic mineralization. Furthermore, XRD, FTIR, SEM, TEM and TG-DTA were applied to investigate the influence of template on hydroxyapatite crystals formation. The results showed that hydroxyapatite was the main inorganic phase. When SF was used as template alone, the additional zinc ions influenced the crystal formation of hydroxyapatite significantly. With the synergy of Zn2+ and alginate ions, the preferred orientations of(002)and(211)were obvious. Finally, small crystallites of several nanometers were assembled into large size sheets, whose thickness was 3 nm and size was more than 100 nm. For the other system, the morphology of hybrid nanogel-HA nanoparticles changed with using different concentrations of CS-PAA nanogel, which indicated that some strong interactions existed between the nanogel and HA crystals. It was indicated that the template played a regulatory role in the formation of HA crystals.Specific template systems could be designed to controll the process of biomimetic mineralization and the resultant apatite composite materials have shown a great potential in the practical applications, which have attracted great attentions in the the field of biomedical applications. In this study, bovine serum albumin(BSA) was used as a model protein drug to study the loading and release behaviors of the hybrid nanogel-HA nanoparticles. The loading amount of BSA reached 67.6 mg/g for the hybrid nanoparticles when the mineral content was 90.4%, which decreased when the nanogel concentration increased. The release profile of BSA was sustained in neutral buffer. Meanwhile, an initial burst release was found at pH4.5, followed by a slow release. These hybrid nanoparticles could be novel artificial bone repair materials loaded protein growth factor. Cytotoxicity was evaluated by co-cultivation of BMSCs and extracts of nanocomposites after mineralization. The nanocomposites were not toxic to BMSCs proliferation. In addition, the hybrid nanogel-HA nanoparticles had good blood compatibility according to the tests. The above composite mineralized materials have shown potential as a biomaterial in the medical applications.