New polymers – as strong as silk
People have been producing and using silk for more than 5 000 years, but now – thanks to an ERC Advanced Grant – Professor Fritz Vollrath is increasing our understanding of this material. His research could help to improve existing industrial polymers and develop new silk industries, adapted to the local conditions and resources in Asia, Africa and South America.
Portrait copyright © F Vollrath,
Image (silk worm) © Vollrath/OxfordSilkGroup
Silk worms, which were first domesticated in China as early as 3500 BC, have played a significant role throughout history – from the prestigious fabrics created from silk to the resulting boom in trade and cultural exchange along the Silk Road. Today, the global market for silk products is worth more than € 100 billion. The ‘Silks as Biomimetic Ideals for Polymers’ (SABIP) project is studying this naturally occurring thread. The aim of the research is to improve silk production and widen knowledge of silk's properties, to the extent that we can develop better industrial polymers.
“There are different kinds of silk, produced by several animal species such as silk worms, moth and spiders" explains Prof Vollrath from Oxford University, who heads the project. “Spider silks have evolved to absorb impact energy, whereas cocoon silks have developed to be integrated into a composite.”
The project is looking at the chemical make-up and genetic basis of different silks through ‘biomining’ and studying the correlations with their mechanical properties. “Biomining will help us to discover novel silks with interesting material properties and gene sequences, while studying them will allow us to discover novel principles of bio-polymer design,” says Prof Vollrath. “We are already beginning to understand what makes a good silk and the chemical signals that correlate to the quality of the silk,” he continues. “Silks are a type of protein called amyloid fibril. Inside the animal, water keeps the molecule in a temporarily stable condition, preventing the proteins from cross-linking. When the liquid silk is extruded, the water is eliminated and the mobile protein molecules link and fold more or less tightly, making the silk thread both tough and indigestible by fungi and bacteria. Silk needs the right combination of order and disorder: too much order and it is brittle, too little and it is weak. Spiders use the extrusion process to control the mechanical properties of the silk, which in turn allows them to tune their webs to the ambient conditions and types of prey available.”
These mechanisms have evolved independently in several different animals: some silk moths even have comparable silk DNA sequences to spiders. An understanding of these processes should enable the development of artificial polymers that replicate silk's properties of great strength and durability.
“It seems that silk production is about one thousand times more energy efficient than the production of synthetic plastics," says Prof Vollrath, “and we are beginning to understand how to learn from silks to create new, more effective artificial polymers.”
The project is also using molecular models in an effort to improve the researchers' understanding of the collected data. “We’re modelling from first principles,” explains Prof David Porter, who also works on SABIP. This approach allows the team to optimise test conditions to produce deeper insights. Previously, researchers have concentrated on silk worms, but worms spin their silk – making the process hard to study. Spiders, on the other hand, produce straight silk which can be spun in controlled conditions, collected and studied.
Prof Vollrath acknowledges that “The ERC Advanced Grant allowed us to tie these different project elements together and its generous funding made our team possible.” The team are also working on commercialising their technology and results. “We are talking to European companies using silk in textiles, bio-tech and medical implants – as silk is bio-compatible and can even be made biodegradable.” Other potential applications include establishing silk producing industries in new regions, such as Africa, adapted to the local moth species and native trees.