Composition Of Nano-Hydroxyapatite Composited With Modified Silk Fibroin

Fibroin fibers from well-defined silkworm silk, which have unique mechanical properties and excellent biocompatibility in vitro and in vivo, have been used as biomedical suture material for centuries. The nano-hydroxyapatite/silk fibroin (n-HA/SF) composite is supposed to be a novel biomaterial that is fit for hard tissues even as load-bearing bone implants. However, the regenerated fibroin contains generally lots of molecule inner links, which extremely decreases the tenacity of solid silk fibroin materials. Therefore, the composite n- HA/SF without interface bonding is restricted on mechanical property and hard to meet the requirement of load-bearing application.In order to improve the weakness, the research is concentrated to reduce the molecule inner links in regenerated fibroin and construct a web structure to guide n-HA formation in the composite. Firstly, a series of composites were prepared under different reaction conditions in order to search optimal technical parameters for synthesizing of HA/SF composite. Secondly, a crosslinking agent named polyethylene glycol diglycidyl ether (PGDE) was adopted to improve the interface between n-HA and SF in the composite. By the connecting reaction between PGDE and SF molecules, the molecule inner links were expected to be reduced. Finally, the microstructure, phase composition and conformation of in-site synthesized composite were determined by Transmission Electron Microscope (TEM), X-Ray Diffraction (XRD), Fourier Transform Infra Red (FTIR) and so on.Nano-HA/SF composites with the particle size of 100¹50nm were prepared by an in situ co-precipitation method, with CaCl₂ and (NH₄)₂HPO₄ as reaction agents for HA. The XRD test showed HA phase was successfully synthesized with the existence of SF. FTIR results validated that the random coil SF has strong chemical interactions with HA in the composites, while the part without bonding with HA is easy to dissolve in water and gets lost. The pH value in the reaction had significant effect on morphologies, components and conformations of HA/SF. At high pH value, nano-HA/SF crystallites formed in high length/diameter ratio and the random coil SF easily convert to 6 sheet structure, while at low pH value additional phase than HA may appear.The regenerated fibroin is too frangible to test mechanical property. With the adopting of PGDE, its flexility is obviously improved, but superfluous coupling agent will decrease the tensile strength.PGDE was introduced to the HA/SF composite by in situ co-precipitation method, in order to obtain cross-linked structure by reacting with SF and enhance the interface bonding between n- HA particles and SF matrix. The coupling agent can strengthen the directional growth of HA particles in the composite and decrease the brittleness of solid SF. Various tests have proved that PGDE can improve the crystallization of SF in the composite, simultaneously the mechanical properties of HA/SF was significantly enhanced by 100%. The fracture surface of PGDE coupled composite took on traces of plastic deformation. This reveals the bonds between SF molecules by PGDE can reduce the inner molecule links, which is the main cause of SF's brittleness. And the results of SBF soaking and Cell culture experiments showed PGDE haven't decreased the biocompatibility of composite. So the cross-linked HA/SF by PGDE can meet the requirement of load-bearing application.