| In tissue engineering,it is very important to design fibrous scaffolds that can simulate the multiple functions of the extracellular matrix(ECM)to accelerate cell adhesion,proliferation,differentiation,and histogenesis.Electrospun conductive polymer composite nanofibers based on conductive polymers and biocompatible polymers(natural or synthetic)have attracted extensive attention due to their high specific surface area and porosity as well as high electrical conductivity,which can enhance cell function.Exploring the mechanical and electrical properties of single nanofibers is beneficial to optimize the application of conductive scaffolds in tissue engineering.The well-arranged fibers have been paid more attention because of their ability to promote cell growth.Magnetic-field-assisted electrospinning can control the diameter and uniformity of fibers and facilitate the transfer of fibers,which is of great significance.The mechanical and electrical properties of polyaniline(PANi)/gelatin composite electrospun nanofibers was mainly studied and the effect of magnetic field intensity on electrospun polyvinylidene fluoride(PVDF)nanofibers was also studied in this thesis.The PANi/gelatin composite nanofibers were prepared by electrospinning.It was found that the optimal parameters of solution concentration,voltage,flow rate and receiving distance were45%,12 k V,0.8 m L/h and 14 cm,respectively.The Young's modulus of single PANi/gelatin composite fiber was measured by three-point bending test.The results show that the size effect exists in the Young's modulus of single fiber,and the Young's modulus increases with the increase of PANi proportion.It was found that the PAGE-3 fiber with 45%PANi reached the maximum value of 5.75 GPa in the diameter range of 100?250nm.The tensile modulus of the cast films with different PANi proportion was measured by uniaxial tensile test.The results of Raman characterization showed that the gelatin molecules were partially transformed from disordered structure to ordered?-structure due to the tensile action of electrospinning,which made the Young's modulus of a single electrospun nanofiber one order of magnitude higher than the tensile modulus of the cast film.The electrical conductivity of PANi/gelatin fiber mat,cast film and single fiber with different PANi proportion was measured,and it was found that the increase of PANi concentration could improve their electrical conductivity,because the conformation of PANi chain was influenced by the interaction between dopant and solvent and became conductive.The electrical conductivity of composite fiber mat,cast film and single fiber with the highest PANi content reached the maximum value of 3.08×10-3 S/cm,3.37×10-2 S/cm and 4.85×10-2 S/cm,respectively.The conductivity of the fiber mat is about 0.1 times that of the cast film due to the consideration of the air between the fibers,while the electrical conductivity of a single nanofiber is about 15 times that of the fiber mat due to the elimination of the influence of air conductivity.Compared with cast films,single nanofibers have higher electrical conductivity due to the stretching of polymer chains during electrospinning,which allows electrons to be transferred along the ordered molecular chains.The oriented PVDF nanofibers were prepared by magnetic-field-assisted electrospinning.It was found that with the increase of magnetic field strength,the diameter of the nanofibers decreased,the degree of arrangement increased,the tensile force of the nanofibers increased,the degree of orientation of the fiber molecular chain along the axial direction of the fiber increased,and the Young's modulus of a single fiber increased.The Young's modulus of a single PVDF nanofiber increases to a maximum of 10 GPa in the 50?100 nm diameter range when the magnetic field strength is increased to 0.5 T.The study on the mechanical and electrical properties of single polymer nanofibers can provide a design basis for the application of nanofibers in tissue engineering scaffolds. |
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