The Studies Of The Interaction And Spinning Of Silk Fibroin Molecules And Silk Fibroin Nanoribbons Based On Microfluidic Technology

As the most widely used animal fiber,silk possesses good biocompatibility,degradability,low cytotoxicity,and excellent mechanical properties.In order to further expand its application,researchers use regenerated silk fibroin(RSF)solution for artificial spinning,but the mechanical properties of pure RSF fibers still need be improved furtherly.As the basic construct element,silk fibroin nanoribbons(SNR)or silk fibroin nanofibers(SNF)can assemble in complicated hierarchical structure which is the important reason for the excellent properties of natural silk.At present,pure SNR-based fibers with excellent mechanical properties can be obtained by artificial spinning.However,the SNR-based spinning solution is based on the large amount of organic solvents,and the charge characteristics of the SNR were not fully used during the spinning process.Hence,the SNR-based fiber has only single morphology,which limits its widely application.Microfluidic chip spinning is a spinning method that can effectively induce orderly arrangement and assembly of nanofibers or molecular chains.In addition,multi-channel spinning can be realized,therefore,crosslinking agent which has a physical/chemical effect on SNR can be added in the middle or outer channels,resulting in the obtained fibers with special morphology.In order to obtain the fibroin-based RSF/SNR spinning solution with excellent spinnability,we first use atomic force microscope(AFM),transmission electron microscope(TEM),optical microscope,nanoparticle size and Zeta potentiometer,Haake rheometer,optical micro-rheometer to study the interaction between SNR and RSF,and adopt small-angle X-ray scattering(SAXS)to study the orientation structure of RSF/SNR spinning solution in the microfluidic chip in situ.The results of AFM and TEM show that the SNR is lamellar with uniform size,with a length of 200-500 nm,a width of 50-100 nm,and a thickness of 2-8 nm.The results of optical microscope and Zeta potential show that SNR and RSF have positive and negative charges interaction with each other,and SNR can induce RSF to grow into micron fibers on the surface of SNR.At the same time,the results of the Haake rheometer and the optical micro-rheometer show that the RSF/SNR mixture with a mass fraction of 33%has better spinnability,and SNR can reduce the sensitivity of the mixture at high shear rates.The RSF/SNR mixture can form a weak gel structure.In addition,with the increase of SNR content,the number of internal gel grids increases,but the grid size decreases.The in-situ study of the structural changes of the RSF/SNR mixture in the microchannel shows that compared with the pure RSF aqueous solution,the addition of SNR can increase the orientation of the spinning solution.Based on the above results,this thesis adopted a single-channel microfluidic chip to wet-spin the RSF/SNR spinning solution with ethanol solution as the coagulation bath.The SNR content and post-stretching treatment on the morphology of the obtained fiber,structure and mechanical properties were studied.The results show that with the increase of SNR content,the surface roughness of RSF/SNR fiber decreases,the fiber breaking energy and the resistance to external force damage increases.The reason is that SNR induces the increase of the content of?-sheet and?-turn structure,resulting in the increase of crystallinity of fiber.With the increase of the post-stretching ratio of the fiber,both the?-sheet content and crystallinity increase.As a result,the strength,modulus,elongation and breaking energy of the obtained fiber are improved simultaneously.When the mass ratio of RSF/SNR is 500/1 and the post-treatment stretching ratio is 4 times,the strength of the obtained fiber is 227.9±27.5 MPa,which is nearly 40%higher than that of RSF fiber.When the mass ratio is increased to 300/1,the strength and breaking energy of the obtained fiber are 195.1±16.6 MPa and 25.2±5.2 k J/kg,which increased by 19%and 200%,respectively.When the mass ratio of RSF to SNR is 500/1 and the post-drawing ratio is 6 times,the strength and elongation at break reaches reach up to 405.6 MPa and the 25.1%,respectively.In order to prepare RSF/SNR fibers with unique morphology,good mechanical properties to expand its applications,this thesis explored the microgel structure of the RSF/SNR mixture.Subsequently,RSF/SNR fibers with unique morphology were fabricated through a three-channel microfluidic wet-spinning chip with RSF/SNR mixture as the sheath fluid,while the polyethylene glycol solution containing Fe³⁺as the core fluid.SEM results show that the core layer of the obtained fiber is mostly porous network,while the skin layer is a regular structure.With the increase of Fe³⁺concentration,the porous network structure is closer to the outer surface of the fiber,and its thickness in the fiber increases.The reason for the above mentioned unique morphology is that under the shearing of the microfluidic chip,the SNR aggregates are oriented and arranged,and Fe³⁺crosslinks SNR to form a porous network structure in the middle of the fibers.When the mass ratio of RSF/SNR in the sheath fluid is 1000/1,the resultant fiber shows the best mechanical properties,with a breaking strength of 60.2±6.6 MPa.