Making things stick: Nature schools engineers in adhesion
Adhesives are all around us, holding together our walls, furniture, cars, electronics and packaging. In nature, adhesives are used by shellfish for sticking themselves to rocks, by algae and bacteria for making slimes on outside surfaces, and by insects and geckos when they crawl up walls.
We are learning how nature makes adhesives in order to develop new technologies for benefiting society. Currently, the great majority of adhesives are synthetic and derived from petroleum. Epoxies; acrylates (e.g., Super Glue); and urethanes (like Gorilla Glue) all get their start from oil.
But petroleum-based adhesives create all sorts of environmental problems. Amongst these issues are that adhesives can be toxic. Current adhesives do not function well in wet environments. Plus bonds are usually permanent, which makes separating products for recycling difficult. Glues also gum up recycling machinery — consequently, a lot of the products and packaging that we put into the recycling bin just end up in landfills.
We are looking to nature for new ideas. Our research group starts by working to characterize the chemistry and properties of different natural adhesives. Mussels and oysters are the animals that we examine most often. Then we use this knowledge gained to create new biomimetic materials. The idea is to incorporate biological adhesive chemistry into materials for access to properties that we have not seen before. Many of these bio-inspired materials are synthetic, but we also are developing bio-based systems that do not require specialized synthesis — particularly helpful when pursuing sustainability goals.
Given how prevalent adhesives are in our lives, there are nearly limitless opportunities to develop many kinds of new products. Applications like industrial bonding in wet environments; biomedical adhesives for joining tissues; and replacement of petroleum-based glues with sustainably sourced, degradable alternatives are all part of our ongoing work.
Our lab has everything from live shellfish in tanks to advanced chemical instrumentation, full synthesis facilities, and materials engineering testing systems. We quite like having the ability to start with marine biology; work through to biochemistry, chemistry, and materials engineering; and even touch upon product design.
The chemistries of epoxies, acrylates and urethanes have been around for generations. No substantially new adhesive chemistry has been brought to market since before most of us were born. We are hoping that biomimetic systems will become the future of adhesives by enabling wet bonding and sustainability in the marketplace.
Two startups have been spun out using our biomimetic adhesive technologies, with the Purdue Office of Technology Commercialization helping us secure patents and build bridges to industrial partners. One of the companies, Mussel Polymers, Inc. in Bethlehem, Pennsylvania, is using a system that mimics mussel adhesives for sticking to underwater substrates. The company has shown an ability to generate bonds in wet environments, and its first product is now on the market. Potential applications are in the dental, defense and electronics fields, as well as in coral reef restoration. GluECO Adhesives, in Ashburnham, Massachusetts, works with a protein-based adhesive for sustainability needs. Having such bio-based glues may mean that more of our electronics, furniture and packaging can be recycled instead of landfilled or actually degrade when discarded.
We are continually developing new adhesive systems, each with unique attributes. While these technologies become more advanced, we are looking for partners to help bring bio-inspired materials to market. Sustainable systems, biomedical bonding, tunable degradation, bio-based materials, and adhering in challenging environments each can present appealing commercial opportunities. Nature still holds a great many secrets. As these biological design strategies are revealed, we see great excitement in both new knowledge and societal impacts.
Jonathan J. Wilker
Professor, Department of Chemistry, College of Science, and School of Materials Engineering, College of Engineering (by courtesy)
Purdue University
