Montreal team exploits complex behaviour of viscous liquids to copy the sacrificial-coil structure that gives spider-silk its strength
Mimicking the properties of spider-silk has long been a goal of materials scientists. Exceptionally lightweight yet ten times stronger than steel, materials with spider-silk properties would have applications in bullet-proof materials with better characteristic than Kevlar and tyres that could resist highly abrasive and aggressive surfaces.
A team at Polytechnique Montreal is now claiming to have found a way to mimic spider-silk’s strength. “The silk protein coils upon itself like a spring. Each loop of the spring is attached to its neighbours with sacrificial bonds, chemical connections that break before the main molecular structural chain tears,” explained Prof Frederick Gosselin, who is supervising research by Renaud Passieux into the problem. “To break the protein by stretching it, you need to uncoil the spring and break each of the sacrificial bonds one by one, which takes a lot of energy. This is the mechanism we’re seeking to reproduce in laboratory.”
Passieux is working on a method for forming a polymer strand on a moving surface. “The method consists in pouring a filament of viscous polymeric solution toward a sub-layer that moves at a certain speed. So we create an instability,” said Passieux. “The filament forms a series of loops or coils, kind of like when you pour a thread of honey onto a piece of toast. Depending on the instability determined by the way the fluid runs, the fibre presents a particular geometry. It forms regular periodic patterns, which we call instability patterns.”
When the solvent of the solution evaporates, some of the loops bind to themselves, forming a sacrificial bond like the ones in spider-silk. The problem is that the process, though seeming simple, is in fact very complex. “This project aims to understand how the instability used in making the substance influences the loops’ geometry and, as a result, the mechanical properties of the fibres we obtain,” explained Prof Therriault. “Our challenge is that the manufacturing process is multiphysical. It draws on concepts from numerous fields: fluid mechanics, microfabrication, strength of materials, polymer rheology and more.”
The Montreal team explain their research in the journal Advanced Materials. Other applications could include explosion-containing aircraft engine casings and surgical devices, they say.