| Silk,a natural protein fiber,except as textile fibers,has been developed into a variety of forms to applied to biomedical,electronic information and other fields,which due to its excellent mechanical properties,good biocompatibility,large-scale acquisition and sustainable development etc.The development and application of silk materials can further realize the value of silk,which is an important direction to solve the problem of silk expansion application,and is also an important means to enhance the sustainable development of silk industry.Presently,preparation of functional silk materials with high-performance nanomaterials has become a trend.Among them,feeding method is a novel modification technology to prepare high-performance,multi-functional silk and has the advantage of convenient large-scale production.The post-finishing of silk fabric is a simple and universal way to expand the application of silk fabric.Electro-spinning is a good technology to prepare silk fibroin into composite microfiber material which possess high surface area,high porosity,size effect and have a wide range of applications in various fields.Therefore,the graphene oxide/silk composite materials were prepared by the above three methods.The effects on the growth,the spinning of cocoon,the activity of partial silkworm enzyme and the properties of silk were studied.The modification mechanism of silk by feeding graphene oxide was analyzed.In addition,the conductive silk fabrics were prepared by post-finishing method.Its properties were investigated.And the potential application of conductive silk fabrics was explored.At the same time,the silk microfiber membrane was prepared by electro-spinning.The properties of microfiber membrane were studied.And the possibility of it as a disposable protective mask was evaluated.The main research content and obtained results are as follows:1.Preparation of modified silk by feeding graphene oxide and its propertiesThe larvae were fed with different concentrations of graphene oxide?0%,0.05%,0.10%,0.50%,1.00%?from the second day of fifth instar.The growth of larvae every day were recorded and the situation of cocoon were investigated.The influence of feeding on the appearance and diameter of silk was analyzed.The mechanical properties of silk were carried out.And the mechanical properties of silk were compared with other research.At the same time,the thermal stability of the silk was analyzed by thermal gravimetric analysis,differential scanning calorimeter etc.The degummed silk was prepared into silk scaffolds to culture the fibroblasts of mice to study the biocompatibility of silk.The results showed that the weight growth rate of larvae with feeding graphene oxide was similar to that of control group and there has been no disadvantage effect on the growth of larvae.And there has a positive effect on cocooning by feeding graphene oxide.For the control group,the average major axis of cocoons was 30.53 mm and the average minor axis was 18.45 mm.The average weight of fresh cocoon was 1.296 g,and the average weight of dry cocoon was 0.527 g.The cocoon is the largest,with average major axis of 31.50 mm,average minor axis of 19.05 mm,and an increase of7.63%in the average weight of fresh cocoon,an increase of 5.12%in the average weight of dry cocoon when feeding concentration was 0.1%.The mechanical properties of silk were improved,with increase of 91%,92%of silk toughness when the feeding concentration was 0.1%,0.5%respectively.And the feeding concentration of 0.1%was suitable.In addition,the thermal stability of silk was improved via feeding graphene oxide.With the increase in the concentration of feeding,the amount of residual carbon gradually increased,which indirectly proved that graphene oxide can combine with silk.After feeding graphene oxide,the biocompatibility of silk was excellent.2.The modification mechanism of silk feeding with graphene oxideThe mulberries are digested and absorbed by midgut.Then the amino acids and other nutrients were transported through hemolymph.Finally,the amino acids and nutrients transported into the glands to synthesis silk protein.Several enzymes represented by alkaline phosphatase are involved in the absorption and transport of substances in larvae.Thus the activity of alkaline phosphatase and reductive glutathione content in midgut in larvae were measured by alkaline phosphatase and reductive glutathione kit.The effect of graphene oxide on the activity of enzymes in larvae were analyzied.The free amino acids content in the hemolymph of larvae was tested to analyze the the effects of graphene oxide on the absorption and transport of amino acids by larvae.Organic element analysis of midgut,silkworms'excrement and silk were carried out to obtain the ingestion and digestion of graphene oxide in the larvae.Last but not the least,the amino acids composition and secondary structure of silk were analyzied by amino acid analyzer,infrared spectrometer,X-ray diffraction instrument,to explore the modification mechanism of graphene oxide on the structure and properties of silk.It suggested that the activity of alkaline phosphatase was improved and the intake of nutrients was promoted by feeding graphene oxide.And the reductive glutathione content in the silkworm were increased.In addition,the content of amino acids in the larval hemolymph was also positively affected by feeding graphene oxide.After the feeding,the main four amino acid content to synthesis silk were increased.Therefore,the size and weight of cocoon were increased.The rheological measurements of the native silk gland showed that the silk gland became more unstable and susceptible to shear forces after feeding graphene oxide.The content of the?-sheet structure of silk decreased after feeding graphene oxide.And the content of random coils structure and the?-turn structure were increased.With the increasing of graphene oxide concentration,the crystallinity of silk gradually decreased.When feeding concentration was 0.1%,the silk crystal size was the smallest and the orientation factor was 0.926,which was higher than the control group.After feeding graphene oxide,the content of polar amino acids in silk were increased.And the increase of polar amino acid content will increase the force between the molecules in the crystalline region of silk.Overall,the ingestion of larvae was improved by feeding graphene.And has positive effect on the size and weight of the cocoon.The secondary structure of silk was influenced.The?-sheet structure,crystallinity and crystallite sizes of silk were reduced.The orientation factor and polar amino acid content were increased.The mechanical properties of silk were improved eventually.3.Preparation of reduce graphene oxide coating conductive silk fabric by in-situ thermal reduction and its propertiesThe reduced graphene oxide coating silk fabric was prepared by in situ thermal reduction,with silk fibroin or bovine serum albumin?BSA?as crosslinking agent.The conductivity of silk fabrics was investigated with different silk fibroin concentration and different graphene oxide concentration?2 mg/mL,5 mg/mL?.The properties of silk fabrics were tested by scanning electron microscope,infrared spectrometer,Raman spectrometer,thermal gravimetric analyzer and four-probe test system,as well as universal testing machine.The effect of heat reduction treatment on the properties of silk fabric was investigated.The conductive stability and deformation responsiveness of reduced graphene oxide coating silk fabric were analyzed.The results showed that the conductivity of the reduced graphene oxide coating silk fabric using silk fibroin as cross-linking agent was the highest,which resistivity can lower to 3.28 K?·cm-1 and conductivity can reach 3.06×10-4 S·cm-1.The silk fabrics possessed excellent conductivity via simple heat treatment to remove the oxygen-containing groups of graphene oxide.The secondary structure and crystallinity of silk fabric have not been broken.And the mechanical properties of silk fabric were maintained.The reduce graphene oxide coating silk fabric possessed good thermal stability,good conductive stability and deformation responsiveness,which can be applied to sensors,flexible electrodes,wearable electronic equipment etc.4.Preparation of silk fibroin/poly?lactic-co-glycolic acid?/graphene oxide microfiber mat via electrospinning and its propertiesThe silk fibroin/poly?lactic-co-glycolic acid??SF/PLGA?and silk fibroin/poly?lactic-co-glycolic acid?/graphene oxide?SF/PLGA/GO?microfiber mat were prepared by electrospinning.The silk fibroin/poly?lactic-co-glycolic acid??SF/PLGA?and silk fibroin/poly?lactic-co-glycolic acid?/graphene oxide?SF/PLGA/GO?microfiber mat were tested by scanning electron microscopes,contact angle meters,infrared spectrometers,Raman spectrometers,thermal gravimetric analyzer,surface area&pore size analyzer,universal tensile tester.The properties of these mats with or without graphene oxide were analyzed.The pore-size of silk fibroin/poly?lactic-co-glycolic acid?/graphene oxide?SF/PLGA/GO?microfiber mat was compared with the size of common pathogenic particles,to explore the possibilities of microfiber mats in the use of disposable protective masks.The results showed that the silk fibroin/poly?lactic-co-glycolic acid?/graphene oxide?SF/PLGA/GO?microfiber mat has higher ultimate tensile stress,Young's modulus and thermal stability.The ultimate tensile strain of the silk fibroin/poly?lactic-co-glycolic acid?/graphene oxide?SF/PLGA/GO?microfiber mat was 3.71 MPa,which was 53%higher than the silk fibroin/poly(lactic-co-glycolic acid?SF/PLGA?microfiber mat.Silk fibroin/poly?lactic-co-glycolic acid?/graphene oxide?SF/PLGA/GO?microfiber mat has good physical properties.The surface area and pore volume of silk fibroin/poly?lactic-co-glycolic acid?/graphene oxide?SF/PLGA/GO?microfiber mat were 2.63 m2·?g-1,7.09×10-3cm3·g-11 respectively,possessing good breathability.The most importantly,its pore size was 4 to 10 nm,which is much smaller than the size of common pathogenic particles,resulting in effectively preventing these pollutants.In addition,the silk fibroin/poly?lactic-co-glycolic acid?/graphene oxide?SF/PLGA/GO?microfiber possessed hydrophobic characteristics and contained graphene oxide which can inhibit the growth of microorganisms.Thus the mats inhibited the reproduction and growth of microorganisms effectively.The biocompatibility test suggested that the biocompatibility of microfiber mats was good with introduction of graphene oxide.Comparing with the disposable masks for sale,prepared silk fibroin/poly?lactic-co-glycolic acid?/graphene oxide?SF/PLGA/GO?here possessed better filtration and inhibition of microbial reproduction,and can be degraded after discarding,which has great application potential in protective textiles.In conclusion,the silk/graphene oxide composite materials were prepared via three different ways.The properties and application possibilities of silk/graphene oxide composite materials were investigated from the perspectives of multidisciplinary such as material,chemical and biological system.From the macro appearance to the mechanism analysis,the results of the research provided a theoretical basis for the development and application of silk materials.This research is of positive significance for further realizing the value of silk and maintaining the sustainable development of silk industry. |
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