Fiberacating Of Fibroin-Mediated Nano-Hydroxyapatite/Silk Composites

Bone tissue is a particularly complex composite because it contains multiple levels of hierarchical organization. At the lowest level of this hierarchy is the organization of collagen fibrils with respect to hydroxyapatite (HA) crystals. Fabrication of resemble bone, even at lowest level of hierarchical organization, is very difficult because it involves two dissimilar organic and inorganic nanophases that have a specific spatial relation with respect to one another. One way to mimic this combination in an artificial system is to prepare an organic nanophase designed to exert control over crystal nucleation and growth of the inorganic component. Silks are generally defined as protein polymers that are spun into fibers by some Lepidoptera larva such as silkworms, spiders, scorpions, mites and flies. Silk from the silkworm has been used as biomedical suture for centuries. It is shown that silk sericin may induce the extrinsic reaction of organism while silk fibroin (SF) protein shows a better biological compatibility. Recently, lots of studies exhibit SF has a comparable biocompatibility similar to polylactic acid and collagen that is main organic component of natural bone.The present study is aimed to develop a novel biomimetic approach by which the HA/SF nanocomposites are fabricated to mimic the process and component of natural bone. During the experimental procedure, raw silk fibers were degummed twice in 0.5 wt % Na₂CO₃ boiling solution and then rinsed with distilled water. Degummed silk was dissolved in a ternary solvent system of CaCl₂/C₂H₅OH /H₂O at 80℃. After dialyzed with dialysis membrane for 3 days, the pure solution of SF was obtained. Two hundred milliliter 0.09M (NH₄)₂HPO₄ aqueous solution was added dropwise into 200mL SF calcium chloride (0.15M) solution containing 10.0g SF at pH 8. The molar ratio of Ca/P was 1.67. The mixture solution was stirred softly at 50℃to concentrate to 100mL so that a phase transformation happened to obtain the recrystallized SF with theβ-sheet secondary structure. Subsequently, the mixture was vacuum-dried at 60℃to obtain biomimetic nanocomposite containing 40wt % of SF. Pure HA and SF were prepared as control samples by the same process. The influence of SF on the nucleation, microstructure and physico-chemical properties of the product was analyzed by XRD, SEM and FTIR. The nanocomposite with nano HA crystallites dispersed homogeneously in SF matrix possesses a compression strength of 97.6 MPa higher than that of woven bone. The biocompatibility of material was studied using cell culture analysis. The results indicate that it shows better biomcompatilbility. The results demonstrated that HA/SF crosslinked together by hydrogen bonds and HA fabricated by this system showed the growth with a preferred orientation and stable to 1200℃. In addition, nano-HA crystallites dispersed homogeneously in SF matrix. The methodology has a great potential for designing and engineering special functionalities biomaterials with. The novel nano-composite may be used as bone substitutes and tissue engineering scaffolds.