Silk Fibroin Based Functional Materials:Preparation,Structure And Properties

Due to the excellent mechanical properties and excellent biocompatibility,Silk fibroin(SF)is one of the widely used natural fibers in textile and biomedical applications.In addition to directly utilizing the structure and performance of natural SF,the introduction of more new functions while maintaining the superior intrinsic properties of SF has become a research hotspot for SF-based materials.At present,natural SF can be reconstituted into different forms of materials through a variety of treatment technologies,but the mechanical properties of the SF-based materials prepared from regenerated SF(RSF)will be significantly reduced.Many methods have been used for the modification of SF materials.The modified materials have improved mechanical properties,but the function is limited and usually has no stimulation response.Therefore,It is of great significance to further expand the application of SF based materials in biomedical field by studying the regulation of mechanical properties and versatility(including stimulus response)of SF based materials.This work aims at enhancing the mechanical properties of RSF-based materials and introducting stimulus response as the research goal,and SF was the main raw material to prepare RSF-based functional composite materials.The main research work is as follows:Traditional "regeneration" treatment will dissolve natural SF to a single chian,resulting in significant decrease in the mechanical properties of the prepared RSF nanofibers.To enhance the mechanical properties of electrospinning RSF-based nanofibers and introduce more functions.SF/lithium niobate(LN/SF)multifunctional composite nanofibers were prepared by electrospinning.The physical and chemical properties of the LN/SF nanofibers were systematically characterized by scanning electron microscopy,infrared,transmission electron microscopy and X-ray diffraction.First,by dissolving the degummed SF in calcium chloride/formic acid to preserve the nanofibril structure of natural SF,and improve mechanical properties of electrospun RSF nanofibers.Then the LN nanoparticles are added to further improve the mechanical properties of the RSF nanofiber membrane(By regulating the secondary structure of RSF)and introduce piezoelectric functions.The LN/SF composite nanofiber membrane can generate charges under external forces,and improve the filtration efficiency of pollutants through electrostatic interaction.In addition,carbon nitride could be introduced into the LN/SF nanofiber membrane,so that it has good antibacterial ability while filterting bacteria.Cytotoxicity test showed that LN/SF nanofiber membrane had good biocompatibility.Simulated degradation experiments showed that the LN/SF nanofiber membrane has good degradability.The constructed LN/SF multifunctional composite nanofiber membrane has broad application prospects in air purification.Compared with inorganic materials,synthetic degradable polymers have better biocompatibility and degradation performance.The composite of RSF and synthetic degradable polymer polycaprolactone(PCL)can combine their respective advantages to prepare material with better mechanical properties and biocompatibility.The functional core-shell nanofiber with PCL as the shell and SF heavy chain(H-fibroin)as the core was prepared through the non-aqueous phase emulsion electrospinning.The physical and chemical properties of the core-shell nanofiber were systematically characterized using scanning electron microscopy,transmission electron microscopy,infrared and mechanical measurements.The results indicated that ethanol treatment could induce the formation of ?-sheet structure in the composite nanofiber,and enhance the mechanical properties of PCL/H-fibroin nanofiber membrane.PCL/H-fibroin 50:50 nanofiber membrane has better breaking strength and elongation at break(6.89 MPa and 38.6 %).The contact angle indicated that the surface water contact angle of PCL/H-fibroin decreases with the increase of H-fibroi.In vitro cell experiments show that PCL/H-fibroin nanofiber membranes have good biocompatibility,and PCL/H-fibroin 50:50 nanofiber membrane was more conducive to cell adhesion.In vitro drug release results showed that,PCL/H-fibroin core-shell nanofibers could effectively reduce the early burst of drug molecules and significantly extend the drug release time compared to pure PCL nanofibers.PCL/H-fibroin core-shell nanofiber membrane has potential application in the fields of tissue engineering,drug carriers and wound dressings.Stimulus-responsive materials have attractive application potential in the fields of controlled drug release and cancer therapy.To further study the application form of SF-based stimulusresponsive materials and expand its application range,we grafted SF light chain(L-fibroin)with polyisopropylacrylamide(PNIPAm)to prepare a temperature-sensitive RSF-based composite film(L-SF-g-PNIPAm).The material was systematically characterize using nuclear magnetic,infrared,contact angle and other technologies.Isocyanoethyl methacrylate(MOI)was introduced into Lfibroin to prepare reactive L-fibroin.Then,PNIPAm was prepared by RAFT polymerization,and the trithiocarbonate in the RAFT chain reagent was ammonolyzed using n-butylamine to prepare PNIPAm-SH.The structure and molecular weight of PNIPAm-SH were characterized by nuclear magnetism,infrared.Its low critical phase transition temperature was about 36 ?,and the PNIPAm-SH aqueous solution has good temperature stimulus response and temperature sensitivity reversibility.The PNIPAm-SH was successfully graft into L-fibroin using sulfhydryl-ene reaction.It was proved that L-SF-g-PNIPAm film has a temperature stimulus response through measuring the change of the contact angle of the L-SF-g-PNIPAm film surface at different temperatures.In vitro cell experiments proved that L-SF-g-PNIPAm film has good biocompatibility.The prepared L-SF-g-PNIPAm has potential biomedical applications,such as temperature-controlled drug release,heat-sensitive filters and functional textiles.Micro/nanoparticles are widely used in drug carriers.The research on the preparation and drug loading properties of RSF micro/nano particles can be the basis for the preparation of stimulation responsive RSF based micro/nano particle drug carriers.We studied the effect of RSF molecular weight on the morphology,particle size,drug loading and release kinetics of RSF micro and nanospheres prepared under different preparation methods.The RSF micro/nanoparticles were prepared by using different RSF with molecular weight.The loading and release of RSF micro/nanoparticles on three model drug molecules with different properties were studied.It was found that the RSF particles prepared from the high MW RSF could load large molecular weight and negatively charged drugs(bovine serum albumin)compared to the intermediate and low molecular weight RSF,while RSF particles prepared from low MW RSF have a higher encapsulation efficiency for small molecular weight and positively charged drugs(Rh B)(74.58%)and a slower release(240 h).Therefore,it is necessary to select appropriate molecular weight SF as carrier according to the physical and chemical properties of drug molecules and the use environment to achieve the optimal therapeutic effect.This result provided certain guidance for the selection of SF drug matrix and process optimization when SF was used as a drug carrier.