Preparation And Study Of AgNPs-modified Antibacterial Silk

Silk is an attractive natural fiber due to its excellent biocompatibility and good mechanical properties,therefore it has been widely used in textiles,biomedical materials,flexible electronic-materials,etc.However,silk still suffers from several drawbacks,for example,it is susceptible to wrinkle,photo-induced yellowing,and bacterial contamination in some applications.In order to improve silk performance and thus increase its practical value,xenobiotic modification of pristine silk is gaining significant attentions.Recently,modification methods,such as nanoparticle feeding or injection into silkworms,allow the xenobiotic material to directly enter silkworms and in situ modify silk by inherently combining with silk protein.Silver nanoparticles(AgNPs),as one of the most widely used nanomaterials with broad-spectrum and highefficiency antibacterial effects,have been widely used to modify silk.Here in this paper,the effects of AgNPs with different contents or particle sizes on the silkworm growth and silk performance were studied by nanoparticle feeding or injection into silkworms,their distributions and biotoxicity in silkworm were also investigated.Firstly,silk modification by direct AgNPs injection into silkworm was studied.The results showed that the toxicity of AgNPs increased with the increase of AgNPs content(500-2000 ?g per silkworm)or particle size(20-100 nm).The particle size of AgNPs will affect the entry efficiency into the silkworm tissues,thus affecting the content of AgNPs in silk.50 nm AgNPs are more likely to accumulate in the silk gland tissues and eventually bind to the silk fibers.However,this method has a limitation that only a trace amount of Agwas detected in produced silks,and has no obvious influence on the structure and performance of silk fibers.Secondly,silk modification by silkworm feeding diets with AgNPs was studied.It was found that AgNPs-modified antibacterial silk with good thermal stability and biocompatibility could be obtained by feeding silkworms with mulberry leaves coated AgNPs.When the additive amount of AgNPs was 1%,AgNPs showed no obvious toxicity.With the increase of AgNPs content,the AgNPs in silk increased,whereas the biotoxicity increased and silk yield decreased.Fourier Transform Infrared Spectroscopy(FTIR)spectra indicated that AgNPs confined the conformation transition of silk fibers from ?-helix to ?-sheet.Further studies found that the particle size of AgNPs affected the biological distribution and the silk payload of AgNPs.AgNPs with a particle size of50 nm were prone to enter the silk glands and eventually appear in the silk fibers.They showed the highest silver content in silk fibers(147.5 mg/kg)compared with 20,80,or100 nm AgNPs and were successfully qualified with antibacterial activity against both E.coli and S.aureus.These results indicated that the thermal stability and antibacterial performance of modified silks could be significantly improved by optimizing AgNPs particle size in feeding diets.These findings are useful to better understand the interactions between nanoparticles and the silkworm physiological system,and can help optimize the design of silk-based materials.This flexible feeding method is promising to combine functional materials with silks at a low cost and effectively improve their performance.