Silk Fibroin/Hydroxyapatite Composite Prepared By Silk Fibroin Blend Films Through A Biomimetic Method

Silk fibers from Bombyx mori fibroin have been used as biomedical material for a long time, because of their outstanding mechanical properties, environmental stability and biocompatibility. SF plays an important role for the mineralization, its molecular structure contains a large number of active groups, such as-COOH group, which is easy to induce inorganic mineral phase deposited, such as calcium carbonate and calcium phosphate deposition. Silk fibroin provides a lot of nucleation sites for inorganic mineral deposited. In recent years, silk fibroin was widely used as organic template for the preparation of organic/inorganic composites. Meanwhile, many studies have shown that non-collagen macromolecular polymers can significantly affect the nucleation and growth of inorganic mineral phase.In the study, in order to enhance the deposition of inorganic mineral, blend membranes consist of silk fibroin (SF) and different polymers were prepared. Silk fibroin was mixed with polymers to prepared different blend ratio membranes. After ethanol treatment and premineralization process, the films were immersed into a simulated body fluid with the ion concentration 1.5 times higher than that of the standard one. This process was to induce nucleation and growth of calcium and phosphorus ions on the membrane surface, and after 24h the hydroxyapatite-deposited SF films were got. We have investigated the influence of the blend ratio of polymers/SF and pre-mineralization temperature on the content of the precipitation, calcium/phosphorus ratio and morphology.For the first content of the thesis, the polyacrylic acid/silk fibroin/hyaroxyapatite (PAA/SF/HA) composite materials were synthesized. PAA/SF blend membranes were prepared by mixing SF and PAA together. Two different methods were used for the films treatment. The first one, the films were treated with 60%(v/v) ethanol, through a treatment with the use of Ca(OH)2 and K2HPO4 solution, the films were then immersed into SBF to induce apatite deposition. As contract, another film was untreated with ethanol, then dealed with the same method in the next process. This study investigated effect of ethanol treatment on the composite material. The results from the tests of SEM, XRD, EDX and FTIR showed that the hydroxyapatite crystals in the composite had low crystallinity, which was close to that in the natural bone. Furthermore, ethanol treatment significantly enhanced the HA deposition on the blend films.The second part, polyaspartic acid/silk fibroin/hyaroxyapatite (PASP/SF/HA) composite materials were synthesized. PASP/SF blend membranes were prepared by mixing different content SF and PASP together. These films were treated with 60% (v/v) ethanol, through a treatment with the use of Ca(OH)2 and K2HPO4 solution, the films were then immersed into SBF to induce apatite deposition. This study investigated the effect of the PASP/SF blend ratio and temperature of premineralization on the amount of HA deposition and its morphology. The results from the tests of SEM, XRD, ICP and FTIR showed that the amount of crystals increased with the PASP/SF ratio increasing. Meanwhile, a gradual increase of Ca/P ratio was also appeared through PASP/SF enhanced. Furthermore, the amount of apatite deposition and its Ca/P ratio were increased as the temperature of precalcification increased. A change of morphology was found as the PASP/SF blend ratio and precalcification temperature changed.At the third part of this thesis, the effect of aspartic acid on the SF/HA deposition was also studied. We prepared four kinds of precalcification solution by adding different volume of ASP into SF solution. After treated with 60%(v/v) ethanol solution, SF films were pretreated with the four kinds precalcification solution. The pretreatment films were then then immersed into SBF 24h to induce apatite deposition. The SEM, XRD, ICP and FTIR results showed that the amount of ASP in the precalcification can significantly influence the morphology of composite. The amount of deposition and its Ca/P ratio were also influenced by the ASP content.In summary, silk fibroin was used as organic template to control the nucleation and growth of calcium and phosphorous on its surface. On the regulation of silk fibroin, the apatite crystals can successfully deposited on SF surface. The composition and structure of SF/HA composite were similar to the natural bone.