WHEN it comes to hanging on tight, the lowly mussel has few rivals in nature. Researchers have sought the secrets behind the bivalve's steadfast grip on wet, slippery rock. Now they have used the mollusc's tricks to develop medical applications. These include a biocompatible glue that could one day seal foetal membranes, allowing prenatal surgeons to repair birth defects without triggering dangerous premature labour.
To hold fast beneath the surging waves, mussels secrete liquid proteins that harden into a solid, water-resistant glue. What's easy for the animals, however, has been hard for human engineers. Not even Super Glue will stick in a fish aquarium because a layer of water forms that keeps the two surfaces from bonding. But mussels somehow elbow the water aside, Herbert Waite, a biologist at University of California, Santa Barbara, says.
Over 30 years, Waite's team has uncovered the basis of this remarkable ability. Each of the 15 proteins that make up the molluscs' holdfasts - thread-like structures that help attach the mussel to a hard substrate - contains an abundance of an amino acid called dihydroxyphenylalanine, or DOPA. This is particularly abundant in parts of the proteins that face out towards the hard surface. It enables liquid holdfast proteins to solidify rapidly and stick flawlessly to wet and salty surfaces.
"If I were to list the desired properties for medical adhesives, they would look exactly the same," Phillip Messersmith, a materials scientist at Northwestern University in Illinois, says. He and his colleagues have created a synthetic, thread-like polymer called polyethylene glycol that mimics the mussel protein, and they have attached a synthetic form of DOPA to the thread's tips.
To see if the compound worked in live animals, a veterinary surgeon collaborating with Messersmith's team made a 2.5-centimetre incision in the carotid artery of a dog and placed four stitches along the length of that incision to hold it in place. With the stitches alone, the incision bled when the surgeon pressed it. But just 20 seconds after the mussel-based glue was applied, the artery was sealed and did not bleed.
More recently, Messersmith's team began testing its glue on foetal membranes. For the past few decades, surgeons have begun surgically repairing birth defects such as spina bifida while a foetus is still in the uterus. But the process is risky because the surgery risks rupturing the foetal membrane prematurely, sending the mother into premature labour.
There are no good adhesives on the market for surgeons to repair such foetal-membrane tears. But in recent, unpublished experiments in rabbits, Messersmith's team found that after a veterinary surgeon poked a 3.5-millimetre hole in the foetal membrane, the new, mussel-inspired glue readily sealed up the puncture.