Study On Preparation Of Zinc Substituted Hydroxyapatite Nanocomposites Based On Biomimetic Mineralization Regulated By Silk Fibroin Template And Their Coatings Produced By Electrophoretic Deposition

As the main inorganic component of natural bone tissues,hydroxyapatite?HA?is always focus of studies in the field of bone-like materials.However,it is a difficult problem of fabricating a material in vitro whose mechanical properties could match the natural bone.It is well known that biomineralization of bone is a complicated process regulated by various template molecules and substituted ions.Through mimicking the process of biomineralization,HA nanocomposites with high bioactivity can be prepared by the combination of template regulation and ionic subsitutions.Herein,we synthesized bone-like hydroxyapatite by using silk fibroin?SF?as template and zinc?Zn?as doping ions.The obtained products were characterized by XRD,FTIR,FESEM,TEM and TG-DTA.It was found that SF could regulate the nucleation and growth of HA crystals,thus HA nano-sheet crystals with the length of about 100 nm were obtained.After adding zinc ions,the morphology of HA crystals changed into large and wide sheets with folds,indicating that zinc ions influenced the combination of SF with HA.In addition,the formation of B-type carbonate substitution in HA was observed.In the experiments,the more Zn²⁺ions doped,the more SF remained in the final products,and the lower crystallinity HA exhibited.It was concluded that both zinc substitution and silk fibroin played an important role during the formation of HA.Metal and its alloys are widely used as implant materials in the applications of bone repair,especially for the load bearing sites,because of their excellent mechanical properties,for example titanium?Ti?.It is a good choice to improve the surface properties of Ti implants with HA coatings,which can not only improve the corrosion resistance of metals,but also promote the interfacial bonding between Ti and natural bone.In this study,we prepared HA coatings(with and without Zn²⁺)contained SF by electrophoretic deposition?EPD?at room temperature.The results showed that the SF-HA coatings prepared by EPD not only had excellent adhesion strength on Ti substrates,but also promoted the production of new apatite layer in simulated body fluid?SBF?.The doped Zn²⁺ions didn't affect the morphology of newly formed apatite.Furthermore it could increase the crystallinity of apatite.Compared with pure Ti,the substrates modified with SF-HA coatings(with or without Zn²⁺)could promote the MC3T3-E1 cells adhesion and had a positive effect on cell proliferation and osteogenic differentiation.The Ti-based SF-HA coatings with high concentration of doped Zn²⁺ions had a positive influence on osteogenic differentiation of MC3T3-E1 cells after a21-day-culture.It was demonstrated that the SF-HA coatings on Ti prepared by EPD have potential applications in clinic.There were often a few cracks occurred on the SF-HA coatings prepared by EPD.We took the advantages of multi-wall carbon nanotubes?MWCNT?,which had high strength and high toughness,to enhance performances of Ti-based SF-HA coatings.The results showed that MWCNT-SF-HA could improve the corrosion resistance and maintain the advantages of SF-HA coatings such as good adhesion strength on Ti and apatite formation ability in SBF.In addition,the process of high concentration doped with Zn²⁺?5%,mole ratio?could further enhanced the corrosion resistance of Ti-based SF-HA coatings.In summary,the obtained SF-HA,SF-ZnHA and their nanocomposite coatings are promising candidates in the applications of bone grafts and Ti-based implants.