Oriented Epitaxy Growth Kinetics Of Regenerated Silk Fibroin

In recent years,silk materials have made great progress in tissue engineering,flexible electronics and biomedicine due to their excellent mechanical properties,biocompatibility and biodegradability.Due to silk fibroin composites has many advantages such as controllable properties and excellent performance,for example,graphene and carbon nanotubes can regulate the mechanical properties of silk fibroin materials,and wool keratin can regulate the biodegradation rate of silk fibroin materials,which becomes a hot research field now.At present,studies on silk fibroin composite materials are mainly focused on the functional diversification and performance optimization of the materials,and the research on the nucleation growth mechanism under the influence of doped materials(heterogeneous substrates and additive molecules)is still insufficient.In silk fibroin composites,the macroscopic function and properties depend on the correlation length,binding strength,topological structure and ordering of mesoscopic structure.Therefore,the kinetics of silk fibroin nucleation determines the microstructure and macroscopic properties of silk fibroin composites.In this thesis,we use multilayer graphite(heterogeneous substrate)and bovine serum albumin(additive)system as an example,using atomic force microscope liquid in situ test,studied the nucleation growth mechanism of silk fibroin fibers on heterogeneous substrate,and the influence of additive molecular to silk fibroin fiber nucleating growth,the results are as follows:(1)Silk fibroin solution can be assembled and grown on multilayer graphite,so as to obtain ordered silk fibroin fiber structure.As a contrast experiment,we also studied the in-situ nucleation and growth process of fibroin fibers on glass and mica substrates.The results showed that the graphite substrates had a directional induction effect on the growth of fibroin fibers.(2)Exogenous additive molecules such as Bovine Serum Albumin(BSA)and Bovine Serum Albumin Albumin-Templated Gold Nanocluster(BSA@AuNCs)can affect the growth rate and structure orientation of silk fibroin fibers in multilayer graphite.A small amount of BSA can delay the formation of fibroin crystal network structure and slow the growth rate of fiber.With the addition of a large amount of BSA,the content of total protein in the whole system increased,which reduced the distribution range of fibroin protein,and the existence of restriction farther promoted the hydrophilic and hydrophobic effect of fibroin molecules,improved the formation efficiency of fibroin crystal network,and promoted the growth of fibroin fiber.In addition,the growth rate of fibroin fibers increased after adding the BSA@AuNCs solution to the fibroin solution.According to the nucleation theory,it was equivalent to introducing the foreign crystal nucleus as the inducing condition to promote the growth of fibroin on the surface of the crystal nucleus.In summary,the above studies revealed the mechanism of fibroin fiber epitaxial nucleation on multilayer graphite substrate and the effect of additive molecules on fibroin protein epitaxial growth on graphite surface.Due to the fact that the nucleation mechanism turns out to be very important in the development of key fabrication technologies for the high performance soft materials(strong fibers)and flexible devices,and the templated nucleation mechanism have never been reported yet.Therefore,our work will not only guide the way to apply doping materials as a modulator in controlling the gelation process of silk protein,but also lay down the foundation for future research in soft materials functionalization and flexible devices.