Researchers at Tufts University in the US have developed a method to make silk-based materials that refuse to stick to water, or almost anything else containing water for that matter.
- The modified silk, which can be moulded into forms like plastic, or coated onto surfaces as a film, has nonstick properties that surpass those of nonstick surfaces typically used on cookware, and it could see applications that extend into a wide range of consumer products, as well as medicine.
- The development has been reported in the journal ChemBioChem.
The fibre: Silk is a natural fibre spun by moths and has been used for thousands of years to make durable and fine fabrics—and surgical sutures to close wounds.
- More recently, scientists have learned to break down the fibres to their basic protein element—silk fibroin—and reconstitute it into gels, films, sponges, and other forms to create everything from implantable orthopaedic screws to textile inks that change colour in response to body chemistry.
Modifying the fibre: Silk is a unique material since not only can it take on a wide range of forms and shapes, but one can easily change its properties by chemically modifying the silk fibroin.
- To make orthopaedic screws that are absorbed by the body at different rates using silk fibroin, only the chemistry has to be modified.
- Turning silk into a water repellent material involved covering the surface of the silk fibroin with short chemical chains containing carbon and fluorine, called perfluorocarbons.
- These chains are very stable and do not react with other chemicals, nor do they interact with proteins and other biological chemicals in the body.
- While the natural surface of the silk protein acts like a magnet to water, with negatively and positively charged branches on the silk attracting water, a silk protein covered with perfluorocarbons leaves little for the water to grab on to.
- Perfluorocarbons even resist attraction caused by other forces that typically bring molecules together. Changing the number and length of perfluorocarbon chains on the silk protein can adjust how 'unsticky' it behaves.
- Luke Davis, Assistant Professor of Chemistry, established the level of fluorine required on the surface of silk to exhibit nonstick behaviour.
- The chemical synthesis is done under mild conditions, so unlike the production of other nonstick substances, the manufacturing process could be safer, both for workers and the environment.
- The researchers measured the nonstick property by observing how water beads up on the surface of the material—like how water rolls off a waxed car. On nonstick silk moulded into bars using the highest level of perfluorocarbons, the water rolled up into drops that are rounded even tighter than they do on Teflon.
What they said:
The success we had with modifying silk to repel water extends our successes with chemically modifying silk for other functionalities—such as the ability to change color, conduct electrical charge, or persist or degrade in a biological environment. As a protein, silk lends itself well to modular chemistry—the ability to 'plug in' different functional components on a natural scaffold.
— David Kaplan
Stern Family Professor of Engineering
Tufts University
