Medical technology: the common mussel gives us the bio-adhesive of the future
Medical technology: the common mussel gives us the bio-adhesive of the future
Fraunhofer scientists reproduce a synthetic version of the secretion that mussel glands produce great demand in the medical industry.
Mussels supply the perfect adhesive: it keeps them stuck fast even to surfaces that are as smooth as glass. Even in a damp environment, where other adhesives fail, the mussel secretion can be relied on to stay put. That is why it is ideal for medical applications like the dressing of wounds and fixing of broken bones. Scientists at the Fraunhofer Institute for Manufacturing and Advanced Materials (IFAM) in Bremen are working on a way to produce this natural product in the laboratory and so to pave the way for its industrial production. The IFAM is Europe's largest independent research and further education facility in the field of adhesive bonding technology. It offers engineers and technicians from all over Europe a groundbreaking adhesive technology qualification programme with internationally recognised diplomas.
The common mussel is a true master of adhesive bonding. Mussels stick fast not only to iron, wood and stone, but also to panes of glass, painted surfaces and teflon coatings. Neither brute force nor wind and weather can break this bond. These molluscs can hold onto walls and posts by their adhesive threads for years, even when pounded by mighty salt-water waves and surf. Biologists and chemists have now largely deciphered the composition of this adhesive and shipping lines and port authorities are hoping for an antidote that will keep mussels from populating ships' hulls, navigation marks and wharfage.
Exceptional medical properties
The scientists at the Fraunhofer IFAM are going the other way and reverse engineering the adhesive in order to be able to make industrial use of its exceptional properties. “Adhesives normally lose their grip on surfaces in salt water or in a humid environment. By contrast, these are the conditions in which the secretion of the common mussel achieves top form,” Dr Ingo Grunwald, a Biologist at the Fraunhofer IFAM, explains. This is what makes mussel adhesive particularly interesting for medical applications. The scientists envisage it one day replacing stitches in the treatment of cuts and gashes, joining broken bones or serving as a fixative aid for ligaments.
Other potential areas of applications are, for example, in retina repair, as a fixative for dental prostheses or for anchoring tissue samples on slides for microscopic examination. Although adhesives are already used in medicine today,their applications are limited as they can release toxins, such as formaldehyde. The mussel adhesive, on the other hand, is relatively well tolerated by the body. Until now, it has had to be extracted naturally and is therefore barely affordable. Since, some 10,000 molluscs are needed to produce one gram of the material, the price is approximately e200,000.
Small wonder that the costly substance has only been used in minimal amounts for selected scientific applications to date and that doctors and medical technology companies are extremely interested in the prospect of a low-cost method of synthetic production.
Mussel adhesive from the test tube
Special proteins are the basic element of the adhesive secreted by the common mussel's glands. These proteins can react chemically with almost any surface so that the animals stick fast everywhere. One protein building block in particular is responsible for this flexibility: the amino acid DOPA, which is also well known as an active agent in the treatment of Parkinson's disease. The glands of the common mussel can also produce adhesive threads that contain both elastic and also rigid fibres. This enables the animals to bond flexibly with hard and soft materials and to withstand different traction forces. The scientists of the Fraunhofer IFAM are now busy reproducing the mussel's adhesive proteins in the laboratory.
“Here we apply nature's structural elements to a technically made product,” IFAM researcher Dr Klaus Rischka explains. This is done with the aid of a solid-phase peptide synthesiser, which automatically attaches the amino acids that make up the proteins to plastic globules and then links them up chemically in a specific order. Each adhesive protein produced by the common mussel consists of around 800 amino acids, whereas the solid-phase synthesiser can only produce chains of 50 amino acids at most. However, the Fraunhofer scientists are taking advantage of the proteins' special structure. The proteins' basic component, namely, is a chain of just ten different amino acids that repeats itself up to 80 times. These chains of ten can be reproduced and then linked to form larger structures. Initial tests are currently under way and the adhesive should be produced as a two-component bonding agent. One of the two substances provides the adhesive effect, while the other accelerates curing. The benefits of synthetic production as compared with collecting the natural mussel secretion are self-evident as the adhesive can be produced by the kilogram in large chemical reactors a significantly cheaper proposition. An added advantage is that mussel populations are preserved.
IFAM is Europe's largest independent research institute in the field of industrial adhesive bonding technology. The Fraunhofer IFAM Department of Adhesive Bonding Technology and Surfaces focuses on the development and characterization of adhesives, stress-related design and simulation of adhesive and hybrid compounds as well as their testing, and qualification. Planning and automation of industrial production processes complete the work done here. Another core competency of the department are process reviews and diploma further training courses in adhesive bonding technology. Industrial fields of application include the motor industry and mechanical engineering, power engineering with the focus on wind and solar power microproduction and the packaging and electrical industry.
