Mys­ter­ies of Spider Silk Strength Unraveled

“Spider silk has a unique com­bin­a­tion of mech­an­ic­al strength and elasti­city that make it one of the toughest mater­i­als we know,” said Jef­fery Yar­ger, a pro­fess­or in ASU’s Depart­ment of Chem­istry and Bio­chem­istry and lead research­er of the study. ​“This work rep­res­ents the most com­plete under­stand­ing we have of the under­ly­ing mech­an­ic­al prop­er­ties of spider silks.” Spider silk is an excep­tion­al bio­lo­gic­al poly­mer, related to col­la­gen (the stuff of skin and bones) but much more com­plex in its struc­ture. The ASU team of chem­ists is study­ing its molecu­lar struc­ture in an effort to pro­duce mater­i­als ran­ging from bul­let­proof vests to arti­fi­cial ten­dons. The extens­ive array of elast­ic and mech­an­ic­al prop­er­ties of spider silks in situ, obtained by the ASU team, is the first of its kind and will greatly facil­it­ate future mod­el­ing efforts aimed at under­stand­ing the inter­play of the mech­an­ic­al prop­er­ties and the molecu­lar struc­ture of silk used to pro­duce spider webs. The team pub­lished their res­ults on Janu­ary 27^th online issue of Nature mater­i­als and their paper is titled ​“Non-invas­ive determ­in­a­tion of the com­plete elast­ic mod­uli of spider silks.” ​“This inform­a­tion should help provide a blue­print for struc­tur­al engin­eer­ing of an abund­ant array of bio-inspired mater­i­als, such as pre­cise mater­i­als engin­eer­ing of syn­thet­ic fibers to cre­ate stronger, stretch­i­er and more elast­ic mater­i­als,” explained Yar­ger. The Bril­louin light scat­ter­ing tech­nique used an extremely low power laser, less than 3.5 mil­li­watts, which is sig­ni­fic­antly less than the aver­age laser point­er. Record­ing what happened to this laser beam as it passed through the intact spider webs enabled the research­ers to spa­tially map the elast­ic stiff­nesses of each web without deform­ing or dis­rupt­ing it. This non-invas­ive, non-con­tact meas­ure­ment pro­duced find­ings show­ing vari­ations among dis­crete fibers, junc­tions and glue spots. Four dif­fer­ent types of spider webs were stud­ied. They included Nephila cla­vi­pes (pic­tured), A. aur­antia (“gil­ded sil­ver face”-common to the con­tigu­ous United States), L. Hes­per­us, the west­ern black wid­ow and P. virid­ans, the green lynx spider, the only spider included that does not build a web for catch­ing prey but has major silk elast­ic prop­er­ties sim­il­ar to those of the oth­er spe­cies stud­ied. The group also invest­ig­ated one of the most stud­ied aspects of orb-weav­ing dragline spider silk, namely super­con­trac­tion, a prop­erty unique to silk. Spider silk takes up water when exposed to high humid­ity. Absorbed water leads to shrink­age in an unres­trained fiber up to 50 per­cent shrink­age with 100 per­cent humid­ity in N. cla­vi­pes silk. Their res­ults are con­sist­ent with the hypo­thes­is that super­con­trac­tion helps the spider tail­or the prop­er­ties of the silk dur­ing spin­ning. This type of beha­vi­or, spe­cific­ally adjust­ing mech­an­ic­al prop­er­ties by simply adjust­ing water con­tent, is inspir­a­tion­al from a bio-inspired mech­an­ic­al struc­ture per­spect­ive. ​“This study is unique in that we can extract all the elast­ic prop­er­ties of spider silk that can­not and have not been meas­ured with con­ven­tion­al test­ing,” con­cluded Yar­ger. The Depart­ment of Defense and the Nation­al Sci­ence Found­a­tion sup­por­ted this research. Source: Ari­zona State University