Preparation And Properties Of Polypyrrole-coated Keratin Composite Nanofiber Membranes

Keratin is an important structural protein in nature.It is widely found in the hair,skin,horns,claws,hooves,and nails of dairy animals,birds and reptiles.Because of its good biocompatibility and biodegradability,it is widely used in the area of tissue engineering and wound dressing.As a conductive high molecular polymer,polypyrrole has excellent electrical conductivity and good stability,meanwhile it is easy to synthesize and is non-toxic in the environment.It is widely used in the fields of biosensors and tissue engineering.In this study,we extracted keratin from waste wool using reduction method,and then obtained water-insoluble keratin nanofibers using electrospinning and cross-linking modification methods.After this,polypyrrole was uniformly coated on keratin nanofibers by chemical in-situ polymerization to obtain polypyrrole-coated keratin conductive nanofibers.In this paper,three different secondary cross-linking methods of hot air,oxygen,and ultraviolet light were used to improve the mechanical properties and water resistance of the keratin nanofibers.The microscopic morphology,chemical structure,hydrophilicity,water absorption,swelling,mechanical properties and biocompatibility of these crosslinked nanofibers were tested.The results showed that the secondary crosslinking had no effect on the microscopic morphology and the structure of keratin macromolecules.These nanofibers were still arranged in disorder with high porosity.There was no difference among these nanofibers in the obvious characteristic infrared bands of amide bands.The oxygen secondary crosslinked nanofiber owned smallest contact angle and excellent hydrophilicity,while the hot air secondary crosslinked nanofiber had the best mechanical property.Biocompatibility studies showed that cells can proliferate and grow well on different secondary cross-linked nanofibers,indicating that various nanofibers had no inhibitory effect on cell growth.In addition,this study employed chemical in-situ polymerization to successfully coat polypyrrole particles on keratin nanofibers.By changing the oxidant concentration and dopant type,the main conductive factors of the polypyrrole/keratin conductive nanofibers were discussed.The microscopic morphology,chemical structure,mechanical properties and biocompatibility of nanofibers were tested.Discussing the effect of applying a certain intensity of direct current on cell growth,and then the cell growth under electrical stimulation was measured by cell morphology.The results showed that after coating polypyrrole particles,the fiber diameters increased significantly,the pore structure remained intact,and the fiber surface became rough with some obvious graininess,while the nanofibers turned to black.When ptoluenesulfonic acid was selected as the dopant and the oxidant concentration was 0.6mol/L,polypyrrole/keratin conductive nanofibers showed the best conductivity of 1.46S/cm.The addition of polypyrrole significantly improved the mechanical properties and thermal stability of the keratin nanofibers,but there was no effect on the biocompatibility of the nanofiber.In other words,the conductive nanofiber had good biocompatibility and no cytotoxicity.The constant stimulation time was 5 min/d,and when the current was 160 ?A,the cell growth was best after 3 days of continuous stimulation,and the cell proliferation was good.Constant current was 80 ?A,when the stimulation time was 10 min/d,the cell growth is the best after 3 days of continuous stimulation,and the cell proliferation was good.