| Biocompatible silks,such as spider dragline silk,are ideal optical biomaterial because their excellent mechanical properties compared to other commercial fibers.Since spider dragline silk cannot be obtained in large scale through raising,the preparation of strong artificial animal silk with regenerated silk fibroin(RSF)has become one of the focuses in the field of biomimetic spinning.However,there is still a gap between the mechanical properties of natural spider silk and artificial animal silk fiber,which is difficult to achieve mass production.Microfluidic spinning can integrate the shearing,stretching,concentration,ion regulation and spinning of silk fibroin,and to realize the bionic simulation of the spinning process of spider and silkworm.However,there are still some problems,for example the low degree of bionics,and the insufficient research on the mechanism of fiber formation during microfluidic spinning.Cellulose nanofiber(CNF)with high aspect ratio is an ideal reinforcing material.In this study,RSF containing CNF was prepared as mixtures.Firstly,the structure and property of high concentration RSF/CNF mixtures were studied.The interaction between RSF and CNF was investigated.Secondly,flow analysis of the bioinspired microfluidic chip mimicked the shape of spider's major ampullate gland and spinning duct were characterized by in-situ Synchrotron Radiation Small Angle X-ray Scattering(SR-SAXS)and Finite Element Method Simulation(FEMs),which provides theoretical support for biomimetic microfluidic technology.Then the influence of microchannel on the orientation structure and order parameter of RSF/CNF mixture was investigated for guiding the preparation of high-performance artificial animal silk.Thirdly,high performance RSF/CNF composite dry spun fibers were fabricated and used as a research model to investigate the reinforce mechanism of CNF.Finally,low-loss light guiding,weavable and strong RSF/CNF composite wet spun fibers with high sound velocity,good biocompatibility and biodegradability were generated by a microfluidic chip and applied in photodynamic therapy for tumor tissues.A large amount of CNF was mixed into highly concentrated RSF spinning dope to further reinforce the hybrid fibers using dry-spinning method.The application of photodynamic therapy was investigated successfully.Firstly,based on RSF solution and CNF suspension,high concentration RSF/CNF mixture was constructed,and the rheological properties and aggregation structure evolution of the mixture were studied.Results from the structure of the concentrated RSF/CNF mixtures show that RSF/CNF mixtures(45 wt%)has good spinnability.The addition of CNF increases the viscosity of mixtures and improves the phenomenon of shear thinning,as CNF delays the process of solution/gel transformation.Results of SR-SAXS show that the shear process causes the aggregation structure transition of RSF molecules.The increase of shear rate could reduce the occurrence time of large aggregates,maximum mean square radius of rotation(Rg)and maximum viscosity point,which indicates that there are intermolecular forces such as hydrogen bond and electrostatic force between RSF and CNF.Moreover,results of multiple light scattering experiments show that CNF has good dispersion and stability in RSF/CNF mixtures.Microfluidic spinning has been used to mimic and discover the natural spinning process of silk.However,understanding the orientation and alignment of silk spinning through the microfluidic chips is still challenging.In this thesis,we reported flow analysis of a bioinspired microfluidic chip which mimicked the shape of spider's major ampullate gland and spinning duct by in-situ SR-SAXS and FEMs.Order parameter of RSF/CNF mixture increased from 0.1 to 0.36 implying higher orientation and alignment after flowing through the microfluidic chip.This confinement is attributed to the extrusion pressure drops of the silk proteins and the shear and elongation forces from the anisotropic microchannel.In addition,the order parameters increased with the increase of CNF content.However,when the CNF content is increased from 5 wt%to 7 wt%,the order parameter decreased slightly,probably resulted from the aggregation of the charged CNF.Furthermore,the order parameters increased from 0.23 to 0.7 along with the flow velocity ranging from 10?L/min to 25?L/min.However,higher flow velocity of 30?L/min did not further enhance the orientation but decreased slightly.Additionnaly,in the stretching segment of the microfluidic chip,RSF molecules change from isotropic to anisotropic,and birefringence occurs.It provides theoretical support for further development of microfluidic spinning.High performance RSF/CNF composite dry spun fibers were prepared through a microfluidic chip,which mimicked the shape of spider's major ampullate gland.The breaking stress and modulus of RSF/CNF fibers were much larger than those of De-silk(degummed silk)and RSF fibers.This indicated that the addition of CNF notably improved the mechanical properties of regenerated silk.RSF/CNF-1-df(the weight ratio of CNF/RSF=1%)exhibited the largest average tensile strength of487 MPa and a maximum breaking stress of 686 MPa,which was 2.5 times of that of De-silk(265MPa),and 2.2 times of RSF fibers(307 MPa).Moreover,the breaking elongation,Young's modulus and breaking energy were increased.To further verify the enhencement schematic of CNF,the structure of RSF/CNF fibers was characterized by FTIR,Wide Angle X-ray Diffraction(WAXD)and SAXS.Results show that the?-sheet content increased with the increase of CNF content,which means the addition of CNF was favorable to the conformational of RSF molecules transformed from random coil or helix to?-sheet.WAXD results show that CNF was favorable to the increase of crystallinity,mesophase content and decrease of crystallite size.SAXS show that CNF prefered to increase the thickness of the interface zone(?R),decrease the average fibril length(L),and increase the orientation of fibers.To further reinforce RSF fiber,a large amount of CNF was mixed into highly concentrated RSF spinning dope for wet-spinning via the bioinspired microfluidic chip.We found that the breaking strength of the RSF/CNF-5-wf(the weight ratio of CNF/RSF=7%)was 710±33 MPa with a maximum value of 785 MPa,which is 2.5 times higher than that of the neat RSF fiber(310.3 MPa),and 3 times higher than that of the De-silk(265.2 MPa).Moreover,the addition of CNF was favorable causing light to dramatically attenuate from 5.1 to 1.0 dB/cm.Additionally,the light loss of RSF/CNF-7-wf(the weight ratio of CNF/RSF=7%)was much lower than that of De-silk optical waveguides(3.8 dB/cm).We also found that an appropriate addition of CNF could increase the sound velocity of RSF/CNF composite wet spun fibers,especially for that of the RSF/CNF-5-wf(3.0 km·s-1,the weight ratio of CNF/RSF=5%),which was 2 folds higher than that of the polyamide-6 fiber(PA-6,1.5 km·s-1).The prepared RSF/CNF composite wet spun fibers had excellent mechanical strength and elasticity.Thus,they were employed to prepare a weaved fabric with a plain pattern using flat knitting.The structure of RSF/CNF composite wet spun fibers were characterized by FTIR,Raman,WAXD and SAXS.Results show that the addition of CNF was favorable to the crystallinity and orientation of RSF/CNF composite wet spun fibers,which was consistent with the dry spun fibers.Due to the excellent mechanical properties and low light-loss of RSF/CNF composite wet spun fiber,the biocompatibility and potential application in photodynamic therapy were further investigated.The RSF/CNF composite wet spun fibers were weaved into a scaffold for L929 cell culture.The number and morphology of cells on the scaffold were characterized.Results show that L929 cells well proliferate,adhere,and spread on the scaffold,which indicates the good biocompatibility of RSF/CNF composite wet spun fibers.Then,the RSF/CNF composite wet spun fibers were soaked in PBS solution with XIV(1 U/m L)to characterize the morphology of the fiber.Results show that the diameter of the fiber decreased significantly after 4 weeks soaked in PBS solution,which indicated the good biodegradability of RSF/CNF composite wet spun fibers.Subsequently,in order to further study the optical loss of RSF/CNF optical waveguide in animal tissues,the RSF/CNF composite wet spun fibers were placed in pork tissue(2 mm)to test the light loss.Results show that light could propagate along RSF/CNF fiber about 10 cm in pork tissue with the lowest light loss of 4.7 dB/cm,indicating that RSF/CNF composite wet spun fibers have the advantage of low light-loss and long transmission distance in pork tissue.Finally,the RSF/CNF composite wet spun fibers were implanted into tumor site of mice.Results show that the tumor site gradually changed from bright red to pink after photodynamic therapy.The weight of tumor site was only 0.094 g,which was 85%less than that in control group(0.61 g).At the same time,there was no significant change in the weight of the mice(15-20 g),indicating that the RSF/CNF composite wet spun fibers almost have no toxicity and played an important role in photodynamic therapy of tumor.Therefore,the high-performance RSF/CNF composite fiber showed great potential in biomedical field due to its excellent biocompatibility,biodegradability,and good photodynamic therapy performance. |
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