An adhesive being peeled off a surface with tweezers.
Credit: George Degen
Mucin proteins give this hydrogel adhesive natural antibacterial properties.
Jonathan Wilker swivels in his chair and sweeps his hand around the room. “There’s the computer, the book bindings, the furniture, shoes, the carpet, all the packaging and boxes, plywood, the walls,” he says.
Wilker, a chemist and materials engineer, is sitting in his office in the Herbert C. Brown chemistry building at Purdue University. He is talking about all the things in the room that contain adhesives. In a laboratory down the hall, his group is at work creating the next generation of adhesives and coatings, inspired by sticky substances found in nature. Glues are everywhere, hiding in plain sight, Wilker says. “You don’t really see them, so people don’t think about them that much, [but] adhesives are in almost everything.”
Adhesives hold the world together. In 2024, the world consumed over 19 million metric tons of adhesives—equivalent to the weight of water needed to fill 7,600 Olympic-sized swimming pools, according to the market intelligence firm Research and Markets. The growth in markets such as construction, packaging, vehicles, electronics, and medical devices is driving the need for more sealants.
Nearly all glues today are based on chemical compounds derived from petroleum. Exceptions are terpene and rosin resins recovered during the pulping of pine trees and often combined with synthetic polymers to make adhesives. Glue production emits carbon dioxide, and adhesives can release harmful volatile organic compounds and solvents into the air and soil over their life cycle. Synthetic adhesives also persist in the environment for decades and hinder the recycling of materials that they bind.
Wilker is part of a small group of chemists and engineers trying to shift the world away from petroleum-based adhesives toward those made from biological, renewable materials. Compounds such as carbohydrates, proteins, lipids, and plant-derived polymers and chemicals provide perfect starting materials to develop biobased glues.
Biobased formulations hold the potential of being degradable, which would make all sorts of food and consumer product packaging easier to recycle. Components of today’s packaging— including adhesives in laminated plastic materials, labels, and various kinds of tape—often make recycling a challenge. “If you could fix the packaging adhesion problem, it would enormously decrease the amount of waste we create,” Wilker says.
From sap to superglue
What connects all adhesives on a molecular level is their ability to bond to stuff, a property fittingly known in technical circles as adhesion. Adhesives also need internal strength, or cohesion, to hold stuff together, which is why they are almost always polymers. A material with adhesion but not cohesion is merely a coating, whereas one with cohesion but not adhesion is just a solid piece of material, Wilker says.
The chemistry of adhesives is as varied as their applications. They can grip surfaces through intermolecular forces, hydrogen bonds, or in some cases, chemical bonds. Some, such as epoxies, undergo chemical reactions during the curing process to increase their cohesive strength.
Generally, Wilker says, adhesive polymers have to be a bit amorphous because they have to be able to flow around the surface they are adhering to and then grab onto its microscopic defects.
Humans have been using natural materials as adhesives for thousands of years. Synthetic glues have existed for only about a century. As far back as the Stone Age, people used twine reinforced with plant sap to secure their spearheads. The ancient Egyptians, Greeks, and Romans used animal collagen to bond pieces of wood to make weapons, furniture, boats, and more.
Until around the turn of the 20th century, animal proteins such as collagen and casein remained the state of the art for adhesion—that’s where the old joke about horses going to the glue factory comes from, Wilker explains. The shift toward synthetics started in the late 1800s, when chemists figured out how to modify natural polymers such as cellulose and rubber. That led to the invention of products like masking tape and rubber cement in the 1920s and ’30s.
But it wasn’t until World War II that the petroleum-based polymer infrastructure we know today took off in a big way and spawned a new generation of all-synthetic adhesives. For example, epoxies were invented for aircraft construction, and Eastman Kodak chemist Harry Coover stumbled on cyanoacrylate superglue while working on polymers for gunsights.
Biobased polymers still do a few things better than synthetics. Adhering to wet surfaces is one of them. But for many applications, petroleum-based adhesives perform better than their predecessors, Wilker says. They’re also much cheaper, because nowadays “almost our entire materials economy is based on petroleum.” Competing with petrochemicals is a tall order. But researchers are eager to challenge that paradigm.
Putting lipids to work
Wilker’s lab holds half a dozen glass tanks teeming with live mussels and oysters. The soft-spoken chemist has spent more than 2 decades studying the shellfish’s waterproof superglues. “They have remarkable performance, and the chemistries they use are very different from industrial adhesives,” he says. “It gives you ideas of different directions you can take for making new materials.”
Four metal strips immersed in a beaker of clear liquid.
Credit: Jonathan Wilker/Purdue University
Strips of metal bonded with a soy-based adhesive are immersed in boiling water to test the glue’s strength in a simulation of real-world exposure to moisture.
Two years ago, inspiration struck from the vast soybean fields that surround Purdue. For biobased glues to compete with petroleum-based adhesives, large scale and low cost are key. So Wilker’s group turned to epoxidized soy oil—made by heating soy oil with an acid and an oxidant—a common plasticizer used in the flexible insulating sheaths on electrical wires. “It has reactive epoxy groups that you can do chemistry with, and it’s available on train-car scales,” Wilker says.
In epoxidized soy oil, the researchers had found an ideal plant-based alternative to the superstrong epoxy resin that holds together airplane fuselages and wind turbine blades. Conventional epoxy resins made from bisphenol A are cured with amine hardeners. Nitrogen atoms in the amine groups bond with carbon in the epoxy rings, creating 3D-cross-linked networks. To mimic conventional epoxies, the team also needed a biobased curing agent.
After screening several biobased amines, including those found in spider venom (“not really a scalable source,” Wilker admits) the group tested acids and alcohols as cross-linkers. They settled on malic acid, which gives apples their tart flavor, and tannic acid, found in wine and tea. Mussel chemistry provided guidance. The secret behind the mollusks’ powerful underwater glues are proteins with catechol groups that provide cross-linking for robust adhesion and cohesion. Tannic acid contains similar catechol groups.
The Purdue researchers found that heating a mix of epoxidized oil, malic acid, and tannic acid yielded a sticky goo that bonded plastic, metal, and wood as tightly as, if not more tightly than, conventional epoxy (Nature 2023, DOI: 10.1038/s41586-023-06335-7).
The raw materials are low cost and plentiful, Wilker says, and “our calculations show that the adhesive is carbon-negative.” Growing soy and other plants the raw materials are sourced from absorbs more carbon dioxide than the process of making the adhesive releases. The team is now looking for a partner to commercialize the system.
Other researchers are also using lipids and acids to make glues. Bioengineer Phillip Messersmith’s team at the University of California, Berkeley, starts with lipoic acid, a fatty acid found in mammalian cells. The researchers modify it with an electrophilic ester to impart stability when the acid polymerizes in the presence of water. By tweaking the monomer ratio and salt content, the researchers can produce a flexible glue or a rigid structural resin.
It turns out that the glue is easy to break down into reusable lipoic acid monomers using a water and sodium hydroxide–based treatment. This degradability could limit some applications but be beneficial for others. AsparaGlue, a start-up cofounded by Messersmith, is developing superglues for surgery, where slow degradation would be advantageous. The researchers have also developed prototype pressure-sensitive glues for fully degradable sticky notes and tape.
Lipoic acid costs 10–15 times as much as most commodity monomers, and Messersmith acknowledges that presents a challenge for commercialization. But costs could come down with economies of scale. “New polymer systems are always expensive,” he says. “Polystyrene was an exotic polymer when it was first introduced. Now it costs pennies.”
Sticky saccharides
The wood composite industry is one of the largest users of adhesives. Europe alone produces about 25 million metric tons per year of particleboard, and formaldehyde binders make up about 10% of that weight, says Hendrikus van Herwijnen, a chemist at the Austrian research institute Wood K Plus. The institute was part of the Susbind project, a consortium of 11 research and industry partners, including Ikea and Cargill, formed to develop sustainable glues for wood panel boards.
Formaldehyde adhesives have a big carbon footprint and release the carcinogenic gas over time, albeit within standard exposure limits. But these glues are cheap, strong, and colorless, and they cure quickly. They rely on reactions between formaldehyde and urea to form methylol groups that cross-link with other molecules to form a strong 3D network. “Particleboards are produced at extremely high speed, which means you have to have very reactive adhesives,” van Herwijnen says.
You don’t really see them, so people don’t think about them that much, [but] adhesives are in almost everything.
Jonathan Wilker, professor of chemistry and materials engineering, Purdue University
Aiming to make a sustainable alternative, Catherine Rosenfeld, then a PhD student at the University of Natural Resources and Life Sciences working on the Susbind project, started with 5-hydroxymethylfurfural (5-HMF), which is made by heating and reducing sugar. Because pure 5-HMF is so reactive that it is susceptible to unwanted polymerization and decomposition, Rosenfeld made a 5-HMF-rich sugar solution instead. By adding 15% polyamine to the solution, she formed a sprayable liquid that cures as fast and at the same temperature as industrial binders.
Ikea turned particleboard made with the new glue into prototype furniture pieces. But the research formulation used fossil-based polyamines, and the researchers are looking for a biobased version that works just as well. A follow-up project will fine-tune the technology to further reduce the carbon footprint and cost “to deliver a solution applicable at industrial scale,” says Massimo Bregola, global R&D director at Cargill.
Ikea, which declined an interview for this story, has announced that it plans by 2030 to replace 40% of the fossil-based glues in its particleboard with biobased glues. It’s unclear whether the company is currently using the 5-HMF adhesive on a large scale. But it says in a press release that it is now using a glue that combines a starch-based component made from non-food-grade corn with a synthetic cross-linker.
A key advantage of using plant-sourced raw materials for adhesives is that they can be locally obtained, says Asmare Tezera, a chemical engineer at Bahir Dar University. His group makes hot-melt adhesives from starches found in cassava root, mango seeds, and corn kernels. The researchers are targeting applications in fabric bonding and biodegradable packaging.
“The use of locally sourced materials not only reinforces economic sustainability by supporting local agricultural practice but also reduces transportation costs, fostering a more efficient and eco-friendly production paradigm,” Tezera says.
Protein power
Glues made from animal proteins are still used in niche applications such as bookbinding and construction of musical instruments, much as they have for hundreds of years. But protein-based glues have come a long way since the days of sending horses to the glue factory.
Proteins’ strength comes from their complexity. Proteins have intricate 3D structures and a wide variety of chemistries available to them through the side chains of their amino acid building blocks, which can confer properties beyond the capability of synthetic polymers. And by using synthetic biology techniques, it’s possible for scientists to program a protein sequence to fine-tune its adhesion properties.
An orange weight hanging from a black metal panel.
Credit: Jonathan Wilker/Purdue University
Pieces of a truck’s metal frame (silver) and side panel (black) glued with a soy-based adhesive undergo mechanical testing using a weight (orange).
George Degen, a postdoctoral researcher at the Massachusetts Institute of Technology studying adhesive biomaterials, says mucins are a prime example of natural proteins’ advantages. These slimy, cysteine-rich proteins are also decorated with sugars that give them antimicrobial properties. “The gold standard is the natural material,” Degen says. No synthetic material has yet come close to matching mucin.
Natural proteins are also the reigning champions of sticking to wet surfaces, though researchers have made significant advances in synthetic glues inspired by mussels in the past decade or so. In fact, the Bethlehem, Pennsylvania–based start-up Mussel Polymers is commercializing the mussel-inspired glues that Wilker’s group at Purdue has developed.
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Degen sought to take the mussel chemistry he picked up in his PhD studies and apply it to mucins to make sticky antimicrobial hydrogels that could pave the way for new medical glues (Proc. Nat. Acad. Sci. 2025, DOI: 10.1073/pnas.2415927122).
He combined mucins extracted from pig intestines with a synthetic polymer decorated with catechols, the functional groups responsible for mussel adhesion. The catechols react with thiols on the protein to form a cross-linked gel network that combines the waterproof stickiness of mussel glues with the antibacterial properties of mucus.
The reaction between thiols and catechols is found in plenty of places in nature, but Degen says that it has been “relatively overlooked” when it comes to adhesives. He saw that gap as an opportunity to make his mark as a postdoc.
Degen’s mucus glue is not optimized yet—he says that it’s still largely a proof of concept but that he’s “really excited about this as a platform for future development.” Degen envisions that a similar approach would work with other cysteine-rich proteins such as keratin, which he plans to investigate when he starts his own lab in a couple of years.
Meanwhile, Wilker’s group has crafted glues from zein proteins found in corn—which, like soy, is a crop of the US heartland, available at commodity scale. The team mixes the protein, which is a by-product of making corn ethanol, with tannic acid to make a superglue that binds to a variety of surfaces underwater. The Lafayette, Indiana–based start-up BioBond licensed the technology in February to develop biodegradable adhesives for packaging.
Engineering from micro to macro
Eugene Chen of Colorado State University got into adhesives as part of a larger effort to engineer a single bioderived polymer to express the properties of various petroleum-based materials.
Poly(3-hydroxybutyrate), or P3HB, is part of the polyhydroxyalkanoate (PHA) family. PHAs are polyesters that certain species of bacteria produce as a carbon-storage material; they’ve gained a fair amount of attention in recent years as a renewable and biodegradable alternative to polypropylene and similar commodity plastics.
Chemical structure of a poly(3-hydroxybutyrate) adhesive with an illustration of the polymer network showing rigid and flexible segments.
Credit: Adapted from Science
Eugene Chen and his group showed that poly(3-hydroxybutyrate) can be engineered with a wide range of properties, including adhesion, by controlling the proportion of rigid (green) and flexible (blue) segments in the polymer backbone.
Chen’s group uses biobased dimethyl diolide and β-butyrolactone monomers as starting materials and polymerizes them using chiral metal catalysts. This approach enables the team to alter the stereochemistry of the polymer backbone to adjust the material’s overall properties—essentially creating multiple polymers for the price of one.
“Tunability without changing chemical composition, to us, is incredibly powerful,” Chen says.
The polar ester groups in P3HB’s backbone have the potential to form adhesive interactions, though the polymer’s natural form is too crystalline to take advantage of that potential. Chen and his team found that by dialing in some microstructural disorder to soften the material, they could unlock adhesive capabilities on par with commercial hot glues (Science 2025, DOI: 10.1126/science.adr7175).
Eleftheria Roumeli at the University of Washington, on the other hand, explicitly does not strive for precise control over the biomaterials she works with. In fact, she and her team have demonstrated that unpurified seaweed works surprisingly well as a replacement for formaldehyde-based glues in particleboard (MRS Bulletin 2024, DOI: 10.1557/s43577-024-00734-5). “It’s the whole seaweed just cleaned and ground up,” with nothing chemically added or removed, she says.
The researchers use algae cultivated by collaborators at Pacific Northwest National Laboratory or collected from beaches in Washington and Hawaii. “We have annual harvest days in the lab, where we go and pick up the seaweed,” Roumeli says.
The powdered seaweed contains proteins and carbohydrates that, with a bit of heat and pressure, bond wood bits (sourced from a local carpentry shop) just as well as a synthetic resin. The biobonded boards aren’t quite as water resistant as control boards made with formaldehyde, but they’re naturally more fire resistant, Roumeli says.
Roumeli and her group are working on understanding how their algae adhesives work on a molecular level so they can fine-tune the composition and re-create it with other biomaterials. “The whole goal is getting the design rules” so that the formula doesn’t depend on sourcing specific algae, she says.
Whether the aim is to hold wood together or seal surgical wounds, Roumeli says, adhesives researchers should be considering environmental impact from the start. Her vision of a sustainable future is one in which people use natural biomaterials in harmony with high-tech synthetic or bioengineered polymers to overcome sticky sustainability problems: “I really think that hybrid approach is where the solution will be.”
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