Inspired by the modest mussel, scientists discover a naturally derived flame retardant

Flame retardants aren’t just found in your furniture. It’s likely you also have detectable amounts of the chemical in your body too, which is pretty worrisome considering the growing amount of research connecting flame retardants to serious health risks. Researchers have linked to the chemicals to reproductive health problems, adverse neurobehavioral development in kids, and endocrine and thyroid disruption. And so the question arises: Do the risks of today’s flame retardants outweigh the benefits?

Chemical engineer Christopher Ellison, an associate professor in the University of Texas-Austin McKetta Department of Chemical Engineering, doesn’t know the answer to this question in particular. However, he and his colleagues might have just discovered a naturally derived flame retardant that contains the same organic chemicals already found in our bodies. Plus, according to preliminary findings recently published in the journal Chemistry of Materials, this new alternative seems to work even better at slowing down fires than the flame retardants in use today. And at the center of the discovery is a creature we’re all familiar with: the modest mussel.

This is where it gets really interesting. Ellison explains to me that about eight years ago, researchers at Northwestern University found that the adhesive mucus that mussels use to stick to just about any surface contains a large amount of dopamine-like units. (Dopamine is an organic compound in our brains and bodies that enables all kinds of important functions, such as acting as a neurotransmitter that sends information from one neuron to the next.) The stickiness of this mucus is key because flame retardants need to be able to easily adhere to a surface. However, the adhesive characteristic of the dopamine units are just one piece of the puzzle, Ellison tells me.

The other piece is a molecule known as a catechol (for you chemistry aficionados, that’s a benzene ring with two hydroxyls hanging off it). For years, Ellison had been studying catechols and had observed that one of the molecule’s purposes was to scavenge free radicals. Catechols also naturally occur in the human body — in fact, dopamine is a catechol. And here’s where Ellison and his colleagues make the big and pretty amazing connection.

You see, he tells me, when materials burn, the carbon bonds break and the chemical makeup of an object begins to degrade, generating a ton of radicals. These radicals are highly reactive, and eventually so much degradation takes place that the radicals become a volatile flammable fuel that feeds a fire. This is why we use flame retardants in the first place — to slow the spread of a fire and reduce the risk of fire-related death and injury as well as property damage. But knowing that these catechol molecules can sequester free radicals, Ellison and his colleagues had a hunch they could also act as flame retardants.

Now, back to the mussel. The mucus in the mussel can stick to just about anything and contains dopamine-like units, which contain the catechols that can inactivate the free radicals that fuel a fire. (Light bulb clicks on overhead! Ding!) So, Ellison and his colleagues developed a synthetic coating of polydopamine, which is dopamine turned into polymeric form. Next, they began dipping polyurethane foams, which are found in all kinds of typical household items, into the new coating to test its effectiveness as a flame retardant. They found that the polydopamine coating on foams led to a 67 percent reduction in the peak heat release rate, which measures fire intensity and imminent danger to people and first responders. In fact, their new, naturally derived flame retardant reduced the fire’s intensity about 20 percent better than common flame retardants on the market today.

In the Chemistry of Materials study, Ellison and co-authors Joon Hee Cho, Vivek Vasagar, Kadhiravan Shanmuganathan, Amanda Jones and Sergei Nazarenko write:

The radical scavenging capability of (polydopamine) along with its universal adhesive nature strongly suggests that (polydopamine) could be useful for a flame retardant surface coating system, which is exceptionally suitable for highly flammable foamed materials with low densities, complicated geometries, and large surface areas. Moreover, given its biological origin (in living animals), (polydopamine) is intrinsically nontoxic and biocompatible. This biomimetic coating could serve as an effective and environmentally friendly flame retardant system for flexible (polyurethane) foams.

Ellison also noted that one of the biggest drawbacks and risks of traditional flame retardants is that the chemicals can leech out of materials over time. In contrast, the mussel-inspired polydopamine flame retardant is in the form of a polymer, so it’s too big to cross over and penetrate a person’s skin. Plus, the polydopamine flame retardant is physically and covalently attached to the foam, not just mixed in like traditional flame retardants, Ellison tells me. In addition, Ellison said when he and his colleagues conducted the fire test, not only did the experimental flame retardant slow down the burn, the fire actually self-extinguished.

As to the toxicity for human health, Ellison’s research doesn’t answer this question. But he did say that “given that the subunits that make up the coating are already present in our bodies, I have to believe it’s going to be better than something completely synthetic and manmade.”

Ellison said the next steps in this research are to determine whether polydopamine is the ideal structure to slow a fire or whether some variant would work even better as well as how the new flame retardant works on other types of fabrics and materials.

“This is only our first paper,” Ellison told me. “But it’s really opened up a new realm of investigation and right now, we don’t know if polydopamine is even the best alternative. We just tried it because we knew it would stick really well. But this is a promising first step — there might be a lot of potential here.”

To request a full copy of the study, visit Chemistry of Materials. To see the experimental flame retardant in action, check out this video from UT-Austin.

Kim Krisberg is a freelance public health writer living in Austin, Texas, and has been writing about public health for more than a decade.