Mussels are remarkable creatures, not only in how good they taste steamed and buttered, but also in their ability to cling to rocks that are pounded by ocean waves. Their tenacious grip comes courtesy of byssal holdfast fibers that are secreted by the mussels themselves. Last year, scientists from Germany’s Max Planck Institute for Colloids and Interfaces analyzed these fibers in an effort to determine how they were able to maintain their brute strength, while also giving slightly to avoid snapping. This week, scientists from the University of Chicago announced that they have been able to replicate the fibers, producing an adhesive that could be used on underwater machinery, as a surgical adhesive, or as a bonding agent for implants.
Conventional adhesives typically involve a trade-off between strength and brittleness – they give, but can be ripped, or are hard, but can be snapped. Such substances are linked by covalent bonds, which are held together by two atoms sharing two or more electrons. U Chicago’s synthetic mussel adhesive, however, is linked by metals. This allows it to exhibit both strength and flexibility, as the bonds automatically self-heal if broken, without adding any energy to the system.
One of the keys to the material is a long-chain polymer, developed at Northwestern University. It takes the form of a green solution when combined with metal salts at low pH, but becomes a sticky red gel when mixed with sodium hydroxide to change its pH from high acidity to high alkalinity. This gel can repair tears to itself within minutes. Its stiffness and strength can be tweaked both by altering its pH, or by using different types of metal ions when creating it. The scientists are now trying to determine what other factors might affect its properties.
Besides offering an optimum combination of strength and give, the adhesive should also be environmentally-friendly, as it’s made from natural ingredients. A patent is currently pending.
“Our aspiration is to learn some new design principles from nature that we haven’t yet actually been using in man-made materials that we can then apply to make man-made materials even better,” said Chicago postdoctoral scholar Niels Holten-Andersen.
The research was published this week in the Proceedings of the National Academy of Sciences Early Edition.