Green Extraction Of Keratin And Preparation And Evaluation Of Keratin Hydrogel

At present,a lot of feathers abandoned in the world,which was a serious waste of resources and environmental pollution.The green economy will attract attention in the current and future social economy,therefore,the recycling of resources and environmental protection will become more and more popular.Keratin is a kind of fibrous protein which exists widely in human and animals’skin,hair,and claw.The cysteine of keratin content is 7-20%,and exits in the form of disulfide bonds.It has been proved that the keratin has no immunogenicity,good biocompatibility,biodegradability,and can be applied in drug carriers,tissue engineering scaffold materials.However,keratin has low solubility in water because of the existence of a large number of disulfide bonds,and is difficult to be extracted from the feather by the ordinary chemical or physical methods.At present,some extraction methods have been reported,such as reductive method,enzymatic hydrolysis,oxidative method and mechanical method.The method was widely used becaues of its’simple processing and good maintance of the original thiol groups.The current study generally focused on the improvement of production yield of keratin,but little on the influences of the extraction methods on the protein structure and properties.This thesis first examined the effects of the reductant,i.e.,the traditional Na₂S₂O₅ and green harmless cysteine,on the secondary structure,molecular weight,production yield of keratins.The results showed that the keratin prepared by cysteine method had better water-solublility,liquid viscosity.In addition,the influences of the dialysis methods and dry methods on protein properties were also investgated.It was found that dialysis had little impact on,and freeze drying method was better than the vacuum drying and the oven drying method.Using the keratin produced by the cysteine reduction method,pure keratin hydrogel was fabricated through the disulfide bond rearrangement method and solvent evaporation method.The result found that the hydrogel obtained by the disulfide bond rearrangement method had a short gel-forming time,compact pore structure,high mechanical strength,slow degradation rate.The reasons were that the disulfide bonds in the original keratin were opened by adding cysteine,and new disulfide bonds were generated after oxygen oxidation.Then the effect of protein concentration was investigated on the gel properties,and it was found that the increase of the concentration could improve the hydrogel’s mechanical strength.In addition,considering the long drying time and high equipment cost of the freeze drying method,the keratin powder by vacuum drying method was prepared and utilized to form hydrogel.The results showed that the keratin by vacuum drying method had better dissolution in alkaline condition.The disulfide bond rearrangement method could effectively reduce the required p H to prepare the hydrogel.Finally,this thesis evaluated the cellular compatibility of keratin hydrogel and their applications as drug carriers.The results showed that the keratin hydrogel improved the growth of newborn mice skull osteoblast cells by CCK-8 kit.Using the ciprofloxacin as drug model,the keratin hydrogel prepared by disulfide bond rearrangement method exhibited a slow release action of drug,with 60%released after 20 days,and a good antibacterial effect.