KAIST Engineers Microbes to Produce Biodegradable Hot-Melt Adhesives from Glucose

Hot-melt adhesives hold together the world's packaging, furniture, electronics, and cars. They are solid until heated, then flow to bond surfaces, then harden as they cool—a simple, effective process that has made them indispensable across industries. The catch is that nearly all of them are made from petroleum. They stick well and last a long time, which is precisely the problem: they do not break down in nature, and when they are bonded into supposedly biodegradable products, they undermine the entire premise of degradation and recyclability.

A team at KAIST, South Korea's premier science and engineering university, has engineered a way around this. Led by Distinguished Professor Sang Yup Lee from the Department of Chemical and Biomolecular Engineering, researchers reprogrammed the bacterium Escherichia coli to manufacture adhesives from glucose instead of crude oil. The work, published in July in Nature Communications, demonstrates that microorganisms can be redesigned to produce functional materials with tunable properties—and that those materials can match or exceed the performance of their petroleum-derived counterparts.

The approach hinges on a class of polymers called polyhydroxyalkanoates, or PHAs, which microorganisms naturally produce and which biodegrade readily. The KAIST team used systems metabolic engineering—a technique that rewires an organism's entire metabolic network—to coax E. coli into producing two new aromatic PHAs from glucose: poly(4HB-co-PhLA) and poly(3HB-co-4HB-co-PhLA). The names are technical, but the principle is elegant. The researchers incorporated two different molecular building blocks into a single polymer. One component, 4-hydroxybutyrate, contributes softness and adhesion. The other, phenyllactate, adds rigidity and heat resistance. By varying the proportions of these components, the team could tune the material's properties to suit different applications.

The engineering work was substantial. The researchers had to design intracellular pathways so that E. coli would consume glucose, manufacture both monomers simultaneously, and link them into long polymer chains. When multiple monomers are produced at once, metabolic imbalances arise—the cell cannot keep pace with demand for certain precursors, or bottlenecks form in the production pipeline. The team addressed this by adjusting the strength and timing of gene expression, adding an enzyme to facilitate reactions, and using computational models to identify and optimize the pathways that were slowing production. Through fed-batch fermentation, in which nutrients are continuously supplied during cultivation, they produced 10.2 grams of poly(4HB-co-PhLA) per liter of culture medium. When they added a third component to the mix, they achieved yields of up to 52.8 grams per liter.

The adhesives had to work. In a lap shear adhesion test using stainless steel, poly(4HB-co-PhLA) recorded a lap-shear strength of 4.58 megapascals—higher than the 4.20 megapascals achieved by a commercial ethylene-vinyl acetate adhesive, the petroleum-based standard. The bio-based polymer also retained substantial adhesive strength even after repeated melting and rebonding, and it showed comparable performance to EVA in wood adhesion tests. The incorporation of phenyllactate improved heat resistance, a critical property for adhesives that must withstand thermal cycling in real-world applications.

Perhaps most importantly, the new polymers actually degrade. When the researchers treated the materials with lipase, an enzyme that breaks down fats, they observed surface damage and measurable decreases in molecular weight and overall mass. This is not a theoretical advantage—it is a functional one. A biodegradable adhesive means that a biodegradable package can actually biodegrade. The entire product becomes circular rather than remaining tethered to a petroleum-derived component that will persist for decades.

The significance extends beyond adhesives. The work demonstrates that metabolic engineering can produce not just bulk chemicals but functional materials with properties tailored to specific needs. Sang Yup Lee noted that the approach could be expanded to manufacture a wide range of functional polymers—materials that have traditionally required petrochemical synthesis—from renewable feedstocks like glucose. The implications are substantial: a biomanufacturing technology that replaces petroleum-derived polymers across multiple industries, reduces plastic waste, and enables genuinely circular production systems. The bacteria do the work; glucose is the feedstock; the output is a material that can be engineered to specification and will eventually return to the environment. What remains to be seen is whether this laboratory success can scale to the volumes and costs required to compete with established petrochemical processes.