A new study finds the amount of stretching determines the fibres’ properties. When spiders weave their webs, each spider pulls at the silk threads, from its spinneret, using its hind legs. This pulling action not only aids with the release of the silk, it also helps with the strengthening of the silk fibres to create a more durable web.
There are over 41,000 described species of spiders, most spinning multiple types of silk. This leads to an estimate of over 200,000 types of unique silks, covering a range of material properties.
Once a fibre is extruded, its mechanical properties are relatively weak (formed of spherical globs of proteins). However, when it is stretch up to six times its initial length, it becomes very strong (stretching turns the protein globs into an interconnected network. The protein chains stack on top of one another, and the network becomes more and more interconnected).
Spider silk is shown to possess strength as high as 1.75 GPa at a breaking elongation of over 26 percent.
New simulations, using a computational model, conducted at Northwestern University reveal that stretching during spinning causes the protein chains within the fibres to align and the number of hydrogen bonds between those chains to increase. Specifically, stretching changes the order of proteins, the connection of proteins to one another and the movement of molecules within the fibres.
These insights were made possible by the researchers being able to probe activity at the nanoscale, using spectroscopy techniques. The researchers next validated these computational predictions through laboratory experiments using engineered spider silk. The scientists found it is possible to modify a fibre’s mechanical properties simply through modifying the amount of stretching.
These factors in combination increase the silk fibres’ overall strength and toughness. These findings are not only of general research interest for the insights could be applied to designing stronger, tougher synthetic materials. For example, for creating strong, biodegradable sutures and tough, high-performance, blast-proof body armour.
Stronger than steel, tougher than Kevlar
Spider silk has remarkable properties. It is stronger than steel, tougher than Kevlar and stretchy like rubber making it the strongest organic fibre. It also has the advantage of being biodegradable.
Based on the research, the scientists have been engineering microbes to produce spider-silk materials. By extruding engineered spider silk proteins and then stretching them by hand, the researchers have developed artificial fibres similar to threads from the golden silk orb weaver, a large spider with a spectacularly strong web.
The study appears in the journal Science Advances and it is titled “Charting the envelope of mechanical properties of synthetic silk fibers through predictive modeling of the drawing process.”
