Preparation And Characterization Of Wool Keratin/Silk Fibroin Composite Films

As natural protein fibers,wool and silk develop their unique structural fetures and mechanical properties.Inside the nanofibrils,a large number of ?-crystallites are connected by molecular chains.Within the nanofibrils,?-crystallites are formed jointly by different intra ?-sheets of silk protein molecules,forming the ?-crystalline molecular networks.Unlike silk fibroin materials,wool fibers and keratin materials are mainly dominated by the ?-helical structures,which force the polypeptide backbone to coil in a right-handed helix.Within such a structure,hydrogen bonds between amino acids at different locations in polypeptide contribute to the flexible and tenacious property of keratinous fibers.In this thesis,wool keratin and SF composites are prepared and characterized to obtain the ideal tunable GTR membrane materials.We focus on the forming and hierarchical structures of keratin/SF films,and try to clarify the relationship between structure and macroscopic performance such as mechanical and biodegradable properties.Wool keratin based membranes with dense structure are prepared via solution casting method in this thesis and then reinforced by HA particles.Thickness uniformity,crystallinity,biodegradability,thermostability and mechanical properties of composte films are all improved with the increasing HA content,moreover,the introduction of HA particles will not alter the conformation of keratin in composites.However,when the HA content occupies more than 5wt%,the distinct modulus of wool keratin and HA results in interfacial defects,weakening the reinforcement of HA particles.In this work,we attempt to explore the protein with good mechanical properties and similar amino acids to instead the inorganic reinforcement.Therefore,a series of wool keratin/silk fibroin(SF)composite films are prepared and compared with keratin/HA membranes.It can be confirmed that formibility and flexibility of keratin/SF membranes are better than keratin/HA composites and the synergy effects of these two proteins improve and control the macroperformance to obtain the GTR membranes suitable for clinical application.Simultaneously,we discuss the secondary structure,crystallite structure and molecular network of keratin/SF composites,to establish the correlation between above structures and macro-properties,confirming that the strength of composite films is determined by the ?-crystallinity,on the other hand,the ?-helices from keratin components can transit to ?-sheets under stress,which give rise to the strain-hardening and better elasticity,which lay the theoretical and practical basis for the tunable structure and properties of composite films.In consideration of complexity of dissolution process of wool fibers,we obtain a new keratin solution via excessive reducing agent,which can accelerate the process of SF solution transfers to gel,thereby composite hydrogel will be obtained in a very short time without external stimuli.With the addition of keratin containing a large amount of sulfhydryls,an increasing number of hydrophobic group are exposed and the SF chains are liable to unfold and self-assemble upon hydrophobic interaction,leading to ?-sheet conformation.Subsequently,taking the initial ?-sheets as template,another SF chain starts to form a ?-sheet on it and becomes a new layer continually,leading to the formation of ?-crystallite by folding and packing of following ?-sheets.This process can be regarded as the nucleation of ?-crystallites,therefore,the increasing keratin content with sulfhydryls creates more possibilities for the ?-sheet template,leading to higher nucleation density,consequently,resulting in the different mechanical/rheological properties of keratin/SF hydrogels.Furthermore we explore the keratin/SF porous films with freeze-dried keratin/SF gels and discuss the correlation between pore structures and macroscopic properties,consequently acquire the tunable porous films.In addition,considering the special structures of GTR membranes,we also prepare the bilayer film on the optimal ratio of dense and porous layer and take the characterization on the morphology,structure and mechanical properties,which is intended to provide theoretical foundation for the application of GTR membranes.