Scientists break down silk to invent extremely efficient non-stick material
Researchers at Tufts University have developed a method for developing silk-based materials that refuse to stick to water and exhibit non-stick properties that surpass those of current non-stick surfaces, according to a press release by the institution published on Friday.
Breaking down silk fibroin
It all has to do with breaking down the fibers to their basic protein element: silk fibroin.
“What makes silk such a unique material is that 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,” said Krishna Kumar, Robinson Professor of Chemistry at Tufts.
“If we want to make orthopedic screws that are absorbed by the body at different rates using silk fibroin, we modify the chemistry,” he said. “If we want to create a blood sensor that detects oxygen, or glucose, or other blood components, we modify the chemistry. In this study, we modified silk fibroin to repel water, and we can do it in a way that can ‘tune’ the material to be more or less water repellant.”
The researchers managed to achieve this high level of non-stickiness by covering the surface of the silk fibroin with short chemical chains containing carbon and fluorine, called perfluorocarbons. These chains do not react with other chemicals, nor do they interact with proteins and other biological chemicals in the body.
The scientists then measured the non-stick property by observing how water beads up on the surface of the new material. They found that on non-stick silk molded into bars using the highest level of perfluorocarbons, the water was rejected and proceeded to simply roll up into drops.
Better yet, it’s not just water that rolled off the non-stick silk, but any substance that had water as a major component.
Silk-based non-stick surfaces could now offer a safer alternative to commercially available non-stick coatings that carry the risk of chemicals being absorbed by the body. The researchers further state that their invention could have countless applications.
“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,” said David Kaplan, Stern Family Professor of Engineering at Tufts.
“As a protein, silk lends itself well to modular chemistry – the ability to ‘plug in’ different functional components on a natural scaffold.”
In addition to being implemented in medical devices, the new material could have uses as automotive windshields where rainwater just rolls off without using wipers, coatings on metals that help prevent rust, or on fabrics to make them easier to clean.
“Modifying medical devices to prevent detrimental interactions with water and other biologics has the potential to preserve strength and integrity for as long as they are needed,” explained Julia Fountain, a graduate student in Kumar’s lab and co-author of the paper.
“Silk is already relatively inert to the immune system, so tuning its ability to repel cells or other substances could make it even more useful.”
The study was published in the journal ChemBioChem.
Silk fibroin protein is a biomaterial with excellent biocompatibility and low immunogenicity. These properties have catapulted the material as a leader for extensive use in stents, catheters, and wound dressings. Modulation of hydrophobicity of silk fibroin protein to further expand the scope and utility however has been elusive. We report that installing perfluorocarbon chains on the surface of silk fibroin transforms this water-soluble protein into a remarkably hydrophobic polymer that can be solvent-cast. A clear relationship emerged between fluorine content of the modified silk and film hydrophobicity. Water contact angles of the most decorated silk fibroin protein exceeded that of Teflon®. We further show that water uptake in prefabricated silk bars is dramatically reduced, extending their lifetimes, and maintaining mechanical integrity. These results highlight the power of chemistry under moderate conditions to install unnatural groups onto the silk fibroin surface and will enable further exploration into applications of this versatile biomaterial.
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