For something that seems so delicate, spider silk is an extraordinary substance. At a sixth of the density of steel, the tensile strength of spider silk is comparable to that of high-grade steel alloy, and its ability to absorb energy without fracturing is greater than that of Kevlar.
This combination of low density and light weight, toughness and tensile strength makes it a material of much interest. But it's only really a viable material if spiders can be removed from the equation.
This is not because spiders are ooky. (.) It's because extracting the silk from spiders is an extraordinarily inefficient means of producing the volumes of silk that would be required for commercial applications.
Several companies have made attempts at creating spider silk, but the conditions under which spider silk is created in spiders are complicated. First, the silk material needs to be synthesised, using the unique proteins. The molecular structure of unspun spider silk is unusually complex.
Then the spinnerets, through which the silk is spun, need to be replicated.
The bacterial approach has also been taken by researchers at MIT, who believe that spider silk would make the ideal material for biomedical applications, such as suturing and scaffolding for organ replacements. Spider silks are bio-compatible with humans and don't cause adverse reactions. They don't need to be removed either, since they are eventually absorbed by the body.
Before working with the proteins extracted from genetically modified bacteria, the team created simulations using scalable computational modelling tools. These simulations allowed the researchers to determine the best composition for the unspun silk material, as well as the best "spinning" conditions, to make what they call "outstanding silk fibre formation" in the abstract of their paper, published this week in the journal Nature Communications.
The proteins themselves are dissolved in water, then extruded through a tiny opening. This causes the molecules, created from blend of hydrophobic and hydrophilic compounds to line up, bonding together to form a material much stronger than their constituent parts. The ratio of molecules was key. Too many hydrophobic proteins, and the web emerged as an ugly mess.
Synthesising the proteins takes several months. If the proportions are wrong, the process needs to be started again from the beginning. The solution was simulation. It was the first time simulations had been used to understand spider silk production at the molecular level.
The simulations allowed the team to scan a large range of proteins, locating the compounds that create the ideal fibre. This could also allow modifications to the end fibre. For example, silk for sutures doesn't need to be as stretchy as spider web, so the compounds could be modified for that purpose.
The next step in the research is fine-tuning the process. The lab-produced silk isn't as strong as spider-produced silk, but achieving the right balance to increase the strength of the material should simply be a matter of tweaking the materials. And, because the material can be processed at room temperature using water-based solutions, scaling it up for larger volumes should be an easy process.
"Our goal is to improve the strength, elasticity, and toughness of artificially spun fibres by borrowing bright ideas from nature," Shangchao Lin, who worked on the project as a postdoc at MIT, said in a statement.