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| CSIRO | SOLVE | Issue 8 | Aug 06 | |
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ARTICLE
 REPLACING RUBBER: Natural Bounce By Gio Braidotti
CSIRO scientists have borrowed from the insect world to develop a blueprint for a versatile new ‘rubber’Hailing a new material as possessing unmatched physical performance would be tantamount to unleashing a ‘patent genie from the R&D bottle’ – which explains the fanfare when in October 2005 CSIRO introduced resilin to the world. This natural substance, which gives insects their flying and leaping capabilities, is tipped to deliver a monumental upgrade to the whole class of rubber materials. The commercial implications span numerous industries including medicine, sport, leisure and defence. The anticipated rubber makeover arises from the work of a molecular biologist from CSIRO Livestock Industries, Dr Chris Elvin, that makes use of a discovery route that is unique to biology. “For hundreds of millions of years, nature has been trying out new materials, performing a mass screening exercise for us,” Dr Elvin says. “Nature isn’t intelligent about the way it designs materials – it just tries a whole bunch of different options. The resultant biodiversity resembles a big database of chemical structures with tried and tested activities.”
Called resilin, the material is built from a protein encoded by a single gene – surprising given that proteins are not known for their elasticity. Nonetheless, when the instructions for making the resilin protein were identified in the fruit fly genome in 2001, it was Dr Elvin who grasped the importance of the gene to materials science. “We used a portion of the fruit fly gene to transform bacterial cells into resilin factories, using them as a cheap and easy way to produce the protein,” Dr Elvin says. “However, what we extracted from the bacteria was a liquid form of the rubber – the resilin units dissolved as free-floating molecules.” Over a single year, Dr Elvin and his research collaborators first discovered and then patented a way to artificially mesh the resilin molecules so that the liquid sets into an easily moulded and rubbery solid. “To make resilin synthetically, we needed to learn how to cross-link the molecules so that about 20 per cent of the tyrosine residues on each protein form covalent bonds with other molecules,” Dr Elvin says. The method proved so effective that the team stunned the scientific world in 2005 when they announced in Nature that the synthetic form of resilin replicates the near-ideal properties of the biological material. “In resilin, we have a rubber with two extremely unusual properties,” says Dr Anita Hill of CSIRO Manufacturing and Materials Technology (CMMT), who is helping Dr Elvin with the analysis of resilin’s molecular structure. “Its extremely long fatigue life means you can load and unload the material, stressing it for hundreds of millions of cycles, and it continues to give you perfect performance. “In contrast, synthetic rubber polymers degrade a little bit with every cycle and eventually fail, sometimes catastrophically.” The other property – resilience – is a measure of the amount of energy a material returns as elasticity rather than dissipating it as heat, noise or internal molecular friction. It can be visualised as the bounce of a superball dropped from a metre above the ground. “A superball will return to about 80 per cent of its original height and the material in rubber bands manages a 50 per cent return,” Dr Hill says. “But resilin returns 99 per cent of the energy put into it – the only known rubber to have near-perfect resilience.” With the development of synthetic resilin, the researchers effectively own the worldwide patents for resilin’s advanced performance traits – lock, stock and barrel. This lands Australian research organisations with the task of articulating and developing resilin’s commercial possibilities. “We are at the point where we want to take resilin’s superior properties and transfer them into manufactured products,” Dr Hill says. “There are so many applications. Products made from resilin can be helpful in the engineering environment, as implants for the human body, as sensors and, of course, in consumer products like high-performance athletic shoes. Initially we are thinking about products with the quickest route to market.” In the longer term, Dr Elvin is enthusiastic about the prospect of developing a resilin-based implant to replace crushed or damaged spinal discs: “We move our backs about a hundred million times in a lifetime and attempts to use metals, ceramics and polyethylene as implants do not seem to deliver the required lifetime. I’d like to incorporate the long fatigue life of resilin into a new material that might be useful for spinal discs.” Faith in resilin’s potential has attracted $1.5 million in R&D funds, with CMMT’s science director, Dr Terry Turney, promoting the project internally as a CSIRO Emerging Science Initiative. Given the scope of possibilities, Dr Turney has encouraged a network of collaborators to work on different pieces of the commercialisation puzzle, an operating style that resembles a gigantic parallel processor. “It’s a real team effort,” says Dr Elvin, whose collaborators have included his wife, Dr Nancy Liyou. “Besides CSIRO Livestock Industries and CMMT, two other divisions are involved – Molecular and Health Technologies, and Textiles and Fibre Technologies. On board, we also have the University of Queensland, University of South Australia, Australian National University and Monash University.” As the scientists prepare business plans and talk to potential industry partners, there is an ongoing push throughout the collaborative network to better understand the physical mechanisms that give resilin its unique properties. “Resilin is revealing a new side to protein chemistry, that has previously slipped under the radar,” Dr Hill says. “There is potential here to open up a new domain in materials science.” Dr Elvin agrees: “The more you understand resilin’s structure the easier it is to manufacture new materials. Additionally, that knowledge is like a ‘chemical code’ for engineering very specific effects into manufactured products based on nature’s own perfect rubber. The opportunities are limited only by the level of investment in the development of this material.” APPLICATION Resilin – a substance that gives insects their flying and leaping capabilities – has been successfully synthesised into the ‘perfect’ rubber BENEFIT With its extremely high resilience and long fatigue life, resilin has potential in engineering, medicine, sport and leisure, and defence For further information contact: |
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Just as spider silk is renowned for its enormous strength, entomologists have known since the early 1960s that to perfect their flying and leaping skills, insects evolved an elastic material that amounts to the perfect rubber. 
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