Effect Of Cu Nanoparticles With Different Sizes On Mechanical Properties And Structure Of Regenerated Silk

The regenerated silk materials are widely used in biopharmaceutical,medical and health,tissue engineering and other fields with its unique molecular structure,non-toxicity,non-irritating,degradable and excellent biocompatibility.However,after a series of studies on the spinning conditions such as dissolution of silk,the types and concentrations of regenerated silk fibroin solution and coagulation bath,the mechanical properties of silk fibroin fibers still show poorer breaking strength and a certain degree of brittleness compared to natural silk.Thus,the improvement of mechanical properties of regenerated silk has attracted wide attention.In some researches,the mechanical properties of regenerated silk fibroin can be improved by adding suitable blend material to the regenerated silk fibroin solution.Meanwhile,the size and dosage of nanoparticles affect the strength of binding to proteins and the agglomeration behavior of nanoparticles.Our research group found that mechanical properties of silk can be significantly improved by feeding copper nanoparticles(Cu NPs)to silkworms.In this paper,to find the optimal condition of the mechanical properties of the regenerated silk,the spinning speed,the concentration of formic acid-calcium chloride solution and the draw ratio in the wet spinning process were firstly optimized.Then,the effect of blending copper nanoparticles of different sizes and different qualities on the morphology,mechanical properties and structure of the regenerated silk were studied,the research contents and results are as follows:1.In this paper,the breaking strength and breaking elongation were taken as indexes,and the effects of different spinning speed,calcium chloride-formic acid solution concentration and draw ratios on the mechanical properties of regenerated silk fiber were studied.Compared with mechanical properties of regenerated silk under different conditions,the suitable spinning speed,the concentration of calcium chloride-formic acid solution and the drawing ratio were obtained as the spinning parameters for the following research.2.The mechanical properties of regenerated silk under different technological conditions were compared.It was found that spinning speed,concentration of calcium chloride-formic acid solution and tensile ratio all have great influence on the mechanical properties of regenerated silk The optimal spinning conditions for the regenerated silk were calcium chloride-formic acid solution concentration of 5%,spinning speed of 300,and draw ratio of 2.3.Effects of blending Cu NPs with different particle sizes and qualities on the mechanical properties of regenerated silk prepared by wet spinning were investigated.The results showed that the breaking strength and elongation at break of regenerated silks made from different copper nanoparticles sizes were higher than that of the control group(breaking strength 168.80 ± 1.16 MPa,breaking elongation 22.48 ± 4.42%).Meanwhile,with the increase of Cu NPs concentration,the mechanical properties of regenerated silk increased first and then decreased.When the blend ratio of 20 nm Cu NPs,40 nm Cu NPs,70 nm Cu NPs and 100 nm Cu NPs was 4 mg / g,the mechanical properties of the regenerated silk were the better,and the breaking strength and breaking elongation strength were 307.49 ± 13.74 MPa,38.34 ± 4.40%;291.60 ± 14.74 MPa,37.39 ± 4.50%;286.71 ±13.84 MPa,36.13 ± 2.58%;263.87 ± 20.49 MPa,35.63 ± 5.07%,respectively.Moreover,as the copper nanoparticle size increased,the mechanical properties of the regenerated silk show the gradually decrease trend.When the copper nanoparticle size was 20 nm and the blending ratio was 4 mg/g,the mechanical properties of the regenerated silk were the best,and the breaking strength and breaking elongation were 307.49 ± 13.74 MPa and 38.34 ±4.40 %,respectively,which was 82.16 % and 70.54 % higher than the control group(breaking strength 168.80 ± 1.16 MPa,breaking elongation 22.48 ± 4.42%),that is,the mechanical properties of regenerated silk made without blending nano copper.The effects of Cu NPs sizes on the mechanical properties of regenerated silk fibers were: 20 nm>40 nm> 70 nm> 100 nm.4.In this paper,the effects of copper nanoparticle of different sizes on the morphology and secondary structure of the regenerated silk under different blending ratios were determined by scanning electron microscope,Fourier infrared spectroscopy and X-ray diffractometer.SEM results showed that the blend of Cu NPs had little effect on the morphology of regenerated silk.The results of FTIR showed that the secondary structure of the regenerated silk prepared by blending Cu NPs did not change significantly compared to the regenerated silk protein prepared without blending.However,the peak fitting of the regenerated silk amide III region revealed that the conformational content of the secondary structure had changed.The ?-sheet content of the regenerated silk blended with Cu NPs increased to varying degrees compared with the control group,and the ?-sheet content increased first and then decreased with the increase of the blending ratio.Moreover as the Cu NPs particle size increased,the ?-sheet content gradually decreased,showing a certain size effect.The XRD results showed that the secondary structure of the regenerated silk did not change significantly.This result was consistent with the results of infrared spectroscopy,but the crystallinity of the regenerated silk blended with Cu NPs was higher than that of the unblended regenerated silk,and the crystallinity of the regenerated silk decreased with the increased of Cu NPs particle size.