Volume 18 | Issue 4 | Year 2015

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An adhesive that is safe enough that doctors can use in place of sutures and holds promise to be less toxic than traditional materials. A material that is strong enough to hold together aluminum or carbon fibers used by automotive and aeronautical manufacturers. A glue that is gentle enough to attach synthetic eyelashes or fingernails and works in wet conditions. These are three possible applications of an adhesive that effectively can be used in wet or moist areas.

This innovation is the result of 16 years of research by Jonathan Wilker, Ph.D., a Professor of Chemistry and Materials Engineering at Purdue University in West Lafayette, Ind. “Adhesives are all around us. They’re almost everywhere that you look from glue under a carpet to the glue that holds together our shoes,” Wilker said. “Adhesives that we have right now are great in many regards but there are some difficulties with them including not being able to work well in wet environments.”

Generating Synthetic Adhesives from Marine Sources
Wilker set out to develop an adhesive that could work well in wet environments.

He began his research by observing an unlikely source – shellfish that live in the sea, like oysters, mussels and barnacles. Wilker is working to determine what material enables them to stick to rocks in the water, and then he and his team are working to make that material synthetic so it could be used in a product.

“A lot of the chemistry involved in the animals’ adhesive is protein-based, but making a complicated protein for large-scale applications is not practical,” he said. “We are substituting simple polymers for the proteins while maintaining other aspects of the adhesive chemistry.”

Wilker and his team determined that their innovation needs to meet three requirements: to set wet, to be non-toxic and to make a strong bond.

“Right now there is nothing on the market that meets all three of these requirements,” he said. “By learning about mussel and oyster adhesives, we can gain strategies for developing synthetic materials that mimic the shellfish’s ability to set and hold in wet environments. We have looked at the design and synthesis changes that we can make and compared our adhesive to what the shellfish are making.”

Wilker said that his adhesive can be generated on larger scales yet maintain the functions that are compatible for industry. This synthetic mimic approach allows the team to tailor the material for specific bonding situations and applications.

Marine, Medical Applications for Adhesives
Wilker has found that the adhesive could be useful for industries such as fisheries, boating and medicine.

“Hundreds of different marine species attach themselves to ships, increasing drag and reducing sailing speeds. Preventing and controlling their accumulation, called fouling, is a major expense for the world’s shipping fleet,” he said. “Finding common threads in the sticky substances produced by marine organisms is key to the development of both synthetic adhesives and treatments to prevent the accumulation of these animals on ships.

“Current antifouling methods rely on toxicity, and ship bottoms are often coated with a copper-based paint that kills marine organisms in their larval states. If we can figure out a non-toxic way to defeat the adhesives, we could keep them off ships without harming the environment.”

Wilker said dentistry and medicine also may benefit from this material.

“In the case of sutures, you are poking holes in healthy tissue and you can get mechanical stress concentrated in those areas. Sutures also facilitate the formation of infections,” Wilker said. “Patients could heal better with an effective and safe adhesive, rather than sutures.”

The Problem with Conventional Adhesives
Many adhesives that currently are on the market are made from petroleum feedstocks and can emit toxic substances, according to Wilker. So, in addition to creating an adhesive that can be adapted by several industrial markets, Wilker and his team are developing it from sustainable, non-toxic ingredients.

“There is a need for a non-toxic adhesive that can effectively bond tissue and materials for the automotive, construction, airplane manufacturing and even cosmetic industries,” he said. Wilker said the process is not as simple as licensing the materials to an established company for marketing, or developing a startup to market it. In this case, they probably will have to be adapted to the particular industry for which they are being used, which may result in multiple products of the new adhesive on the market.

For example, in the automotive industry the traditional material used to make cars and trucks is steel, but that is changing, Wilker said. Because of this, the materials used to make the parts hold together will change too. To get better fuel mileage and be gentler on the environment, there is a shift happening, replacing steel parts with aluminum to make automobiles lighter.

“So far what we’ve done is develop what I think is a very exciting series of new materials. We have adhesives that can bond more strongly than established commercial glues you find in the store and that also can set in a wet environment,” he said. “It will have to be developed into different directions to address specific markets. So if we want to go in a biomedical direction we might be partnering with one group, if we want to talk about construction of cars it would be with another group, airplanes in another group and maybe even cosmetics would be in a unique direction with different people.”

Wilker said it is possible that the adhesive could also be used by aeronautical companies.

“Several industries are using carbon fibers instead of aluminum, including the aerospace and astronautics fields,” he said. “Carbon fiber can’t be held together well by welding or rivets, and must use adhesives, so there is a growing need for an adhesive that provides the strength and flexibility for these changing industries.”

Impacting the Ecosystem
Wilker hopes his work also could add to the overall understanding of shellfish and their importance for a healthy ecosystem.

“Overfishing, pollution and disease have reduced the oyster population by 98 percent or more since the mid-1800s,” he said. “Many people are now trying to reintroduce the animals to their prior habitats. Perhaps our work will add to the understanding of this shellfish and what is needed for oysters and the larger coastal ecosystem to thrive.”

Wilker’s technology was patented in 2014 by the U.S. Patent and Trademark Office. The Purdue Research Foundation Office of Technology Commercialization received that patent. For more information, visit www.chem.purdue.edu/wilker/Home/Research.html or http://otc-prf.org. Wilker can be contacted at wilker@purdue.edu.

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