| Silk fibroin(SF)is an important part of silk.Because of its good biocompatibility,biodegradability and physical and mechanical properties,silk fibroin has become an important raw material for the development of biomedical materials and bio-photoelectric materials.Silk fibroin can be prepared into multi-dimensional biomaterials such as microspheres,fibers,films,sponges and hydrogels.It can be applied to many fields such as tissue engineering,wound dressing,bioactive interface and transparent conductive substrate.Among them,silk fibroin membrane has been widely studied.The traditional method of preparing silk fibroin membrane usually takes the solid as the mold and forms the membrane by tape casting or drying.The silk fibroin membrane is often brittle and the thickness is difficult to control.In this study,we prepared silk fibroin membrane on the air-liquid interface using ammonium sulfate solution and PEG 200 solution as the mold,respectively.This method has the advantages of fast membrane forming speed,controllable protein membrane thickness,and porous and non porous structure by adjusting the subphase solution.This rapid interfacial membranes-forming method creates conditions for the large-scale preparation of silk fibroin membranes,and the diversity of structure and properties also lays a foundation for the multifunctional application of silk fibroin membranes.The specific research contents of this paper are as follows:(1)Preparation of silk fibroin membrane by air-liquid interface and its mechanismUsing methanol/lithium bromide to dissolve the degummed silk fibroin,the pale yellow gel fibroin is obtained.The initial concentration is 30%,and the fibrin structure of the silk fibroin is retained.The size is about 330 nm.The soluble silk fibroin is diluted to 25wt% with water,and the membrane is formed on the surface of different concentrations of PEG 200 and pure water.The results show that the membrane could not be formed on the surface of pure water.With the decrease of PEG 200 concentration,the curing time of the membrane is prolonged and the diffusion area is increased.In addition,25wt% silk fibroin and 20wt% gelatin are mixed according to different mass ratios,and the membrane is formed on the surface of 95% PEG 200.With 30% ammonium sulfate as the control group,pure gelatin could not form the membrane at the interface.The addition of a small number of gelatin do not affect the film formation at the interface of the solution,and the curing time is within 1min,while the curing time of pure silk fibroin solution on the surface of ammonium sulfate is 35 min.The process of silk fibroin film formation can be divided into three stages: solution diffusion,protein self-assembly and membrane curing.In the diffusion stage,silk fibroin solution diffuses rapidly at the air-liquid interface driven by the surface tension difference between the subphase and silk fibroin solution.Silk fibroin solution can diffuse on the surface of PEG 200 in 10 s and ammonium sulfate in 1s.In the self-assembly stage,the subphase causes the phase separation and phase transformation of silk fibroin to form protein oligomer.In the curing stage,silk fibroin continued to form insoluble ?-sheet crystal structure,and finally form a solid membrane.(2)Study on the structure and properties of silk fibroin membraneSilk fibroin membranes prepared by interfacial membrane forming has the characteristics of ultra thin,transparent and flexible.The structure and properties of silk fibroin / gelatin solution with different mixing ratio were studied by using PEG 200 as the subphase.The surface of PSF100 is smooth,compact and nonporous,and the thickness decreases with the decrease of PEG 200 concentration,which can be reduced to about 600 nm.The results of X-ray diffraction show that the structure of silk fibroin molecules,silk I and silk II,coexist in the membranes.The silk fibroin membrane(NSF100)prepared on the surface of 30% ammonium sulfate solution has porous structure,with an average pore diameter of 315 nm and a porosity of 15.42%.The rapid diffusion of silk fibroin solution and the volatilization of small molecular solvents lead to phase separation behavior.The two silk fibroin membranes have good hydrophilicity.The water contact angle of PSF100 is about 50 ° and that of NSF100 is about 40 ° and the better hydrophilicity of NSF100 is due to its porous structure.The two membranes have good light transmittance,the light transmittance of PSF100 is 93% and NSF100 is less than 85%.These are related to the microstructure of the two membranes.In PSF100,silk fibroin molecules can be arranged orderly by surface tension,forming a smaller ?-sheet structure with smaller grain boundaries,which does not affect light transmission;while on the surface of ammonium sulfate solution,silk fibroin molecules are severely denatured,hydrophobic groups are exposed,and larger oligomers are formed by hydrophobic action,which hinders the transmission of light.The mechanical properties of silk fibroin membranes are good,and the tensile strength and elongation at break can reach 30 MPa and20% respectively.The in-vitro degradation test showed that silk fibroin membrane had good biodegradability.(3)Preparation of multifunctional silk fibroin membraneStarting from the application field of silk fibroin membrane,antibacterial silk fibroin membrane and conductive silk fibroin membrane are designed and manufactured.The antibacterial silk fibroin membrane takes advantage of the characteristics of porous silk fibroin membrane and non porous silk fibroin membrane.The two kinds of silk fibroin membrane sandwich a layer of chitosan quaternary ammonium salt membrane to form a "sandwich" structure of antibacterial composite membrane.The cell survival rate is 97.8%,and the cytotoxicity was grade 0,which meet the requirements of general wound excipients.The antibacterial membrane have good inhibition on Escherichia coli and Staphylococcus aureus,and the inhibition rate is up to 91.1% and 94.3%,respectively.Conductive silk fibroin membrane is a layer of copper deposited on the surface of pure silk fibroin membrane.The results show that the conductive membrane still have good conductivity in the state of straightening,bending and twisting.Moreover,the conductive membrane have good sensing properties,and can sensitively form stable periodic electrical signals for various strain responses,including finger bending,wrist bending,knee bending,finger pressing,balloon pressing and vocal cord vibration testing.These functional application studies show that the prepared silk fibroin membrane can be applied to biomedical materials,such as wound dressing,postoperative anti adhesion membrane,flexible bioelectrode,biosensor and so on.In conclusion,silk fibroin membrane is prepared by air-liquid interface method with silk fibroin as raw material,which is simple and efficient.By adjusting the subphase solution,the structure of silk fibroin membrane can be adjusted,and two kinds of structure,non porous and microporous,can be obtained.It can be used to develop multifunctional silk fibroin composite membrane,and is expected to be applied in the field of biomedical materials and biological flexible electronic devices. |
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