Regulation Of Silk Fibroin On Biomineralization And Preparation Of Silk Fibroin/Mineral Hybrid Materials

Biological organisms regularly produce bimolecular-inorganic hybrid materials such as bone,teeth,diatoms and shells,which all tend to have much superior mechanical properties over synthetic material hybrids.During the past few decades, Studies on biomineralization,as well as the organic/inorganic composite materials based on the principles of biomineralization,have attracted considerable interest of researchers.Natural animal silks,mainly from silkworms,have been in practically used by man for centuries mainly because of its unique luster,fineness,and mechanical properties.In recent years,extensive studies have been carried on the application of silk fibroin(SF) for non-textile uses.Although not chosen by the nature to involve into the biominerals as collagen,silk fibroin has surprisingly comparability with the silk-like protein in the organic template of nacre.That is why silk fibroin is considered as potential template in biomineralization.In addition,the biomedical application of silk as well as the regenerated silk fibroin materials made it important to control the mineral-regulating ability of silk fibroin.In the present work,we examined the morphology and crystallographic polymorph formation process of calcium carbonate and calcium phosphate in the presence of dissolved silk fibroin;note that the conformation of regenerated silk fibroin(RSF) can be controlled via the solvent environment.Based on the interaction of SF and minerals,SF/silica composite material and SF/calcium carbonate hybrid scaffold were prepared and characterized.Moreover,template effect of degummed silk and uniaxially deformed SF film and chitosan form on the deposition of calcium carbonate was deeply investigated.At first,In order to probe if there is interaction between silk protein and silica, and further more,whether the interaction can improve the mechanical properties of composite materials,the structure and property of the silk fibroin/silica composite material were studied.The results revealed the good compatibility of silk fibroin and silica in the composite system.Comparing to the pure silk fibroin material,the composite material showed better dynamic mechanical property in the range of 15℃to 55℃.Due to both the hydrogen bond and electrostatic interaction between SiO₂ and silk fibroin,the silica particles' interfusion among the chains of protein had a motive-impeding influence on the protein chains.This influence together with the stableβ-sheet conformation of silk fibroin matrices led the avoidance of modulus dissipation of the material.Mollusk shell is one of the best studied of all calcium carbonate biominerals.Its silk-like binder-matrix protein plays pivotal role during the formation of aragonite crystals in the nacre sheets.In the second part of our work,we provide novel experimental insights into the interaction of mineral and protein using a model system of reconstituted Bombyx mori silk fibroin solutions as templates for the crystallization of calcium carbonate(CaCO₃).We observed that inherent(self-assembling) aggregation process of silk fibroin molecules affected both of the morphology and crystallographic polymorph of CaCO₃ aggregates.This combination fostered the growth of a novel,rice-grain shaped protein/mineral hybrid with hollow structure with an aragonite polymorph formed after ripening.These observations suggest new hypotheses about the role of silk-like protein in the natural biomineralization process, but it also may serve to shed light on the formation process of those ersatz hybrids regulated by artificially selected structural proteins.Based on the SF solution-mediate mineralization,we investigated the crystallization of calcium carbonate on degummed silks and RSF films which were used as the solid substrate.By dipping in the supersaturated solution of calcium carbonate containing silk fibroin,clusters of parallel arranged calcium carbonatecrystals with obvious orientation were obtained on the surface of silk fibre after degumming.Silk samples completely covered by calcium carbonate deposition were prepared,and the amount and speed of the deposition can be controlled by the time of mineralization and the pH value of the solution.Influence of the oriented structures of the silk surface on the tropism of the mineral growth was studied by treating the silk fibre after degumming with lithium bromide solution to destroy the surface structure.No obvious orientation was found in the obtained calcium carbonate crystals on the treated silks.The results inspired the strong interaction between the oriented silk surface and the dissociative fibroin chains in the solution,which arose from the similar structure and the nucleation induced byβ-sheet structure.Afterwards, oriented deposition of calcium carbonate was obtained while calcium carbonate particles absorbed on the dissociative fibroin moulding by the oriented silk substrate. This mechanism can also be strongly supported by the similar oriented calcium carbonate crystals obtained on the surface of uniaxial deformed regenerated silk fibroin film in present of RSF solution.Moreover,silk fibroin/calcium carbonate composite scaffold was synthesized assisted by the strong combination between silk fibroin and mineral.After the characterization of the morphology,polymorph and component of the porous composites,the mechanisms of the different appearance and crystallization of the calcium carbonate were further discussed and some of the mechanical properties of the products we obtained were investigated.At last,we did some pilot research about the mechanism of crystallization of the calcium carbonate in chitosan/silk fibroin bionic system.Our work mainly focused on the influence of oriented chitosan structure on the crystallization of calcium carbonate and the effects of silk fibroin as intermediate in the system.We found that the growth of calcium carbonate layer with regular structure could be controlled by silk fibroin and the selective adsorption of calcium carbonate(104) crystal plane could be induced by oriented chitosan film.