Bug-hunting worm provides template for polymeric materials
A worm that spits on its prey to immobilize it could inspire new biodegradable polymeric materials. Researchers from AMI’s BioNanomaterials group have been investigating the unique properties of the slime projected by the carnivorous velvet worm.
Small bugs in the rainforest are exposed to many dangers. One of the more surprising threats they face is barely bigger than the insects themselves: onychophorans, typically known as velvet worms, are voracious and active carnivores whose most remarkable feature is a pair of slime glands located on both sides of its head. When hunting, velvet worms use their antennae and chemosensory organs close to their mouths to identify their prey. Once it has found its target, the tiny predator shoots sticky white slime onto its prey to pin it down. This “glue” is ejected quickly at a rate of five meters per second, and as it immobilizes its prey, the worm is then able to inject digestive saliva before consuming the insect. The more the prey tries to disentangle itself from the slime, the stiffer this becomes, as it hardens quickly when mechanically stimulated. The slime is originally viscous like egg yolk, and turns into a solid high-strength polymer comparable to nylon in just mere seconds. This material, however, is biodegradable, as it is composed of water, proteins, lipids, and carbohydrates.
The BioNanomaterials researchers chose to investigate the micro- and nanostructures of the slime of Epiperipatus biolleyi, a Costa Rican velvet worm species. “I had learned about this rare and unique mechanoresponsive slime, and one day, I was lucky enough to collect a sample, which I submitted to a microscope analysis,” explains Dr. Yendry Corrales, who has been leading the project. “What I observed was a natural material formed by micro- and nanostructures that had not been previously reported in scientific literature.” Corrales, who arrived at AMI after receiving the NCCR Bio-Inspired Materials Women in Science postdoctoral fellowship, had worked on protein-based nanomaterials during her PhD studies. For her next career step, she wanted to investigate novel bio-inspired materials using the biodiversity of her native Costa Rica as inspiration.
Further investigations carried out at AMI have now revealed that the slime is a composite material formed by a protein matrix and vesicles containing inorganic salts, requiring two important processes to occur to complete the transition from liquid to solid. In a first step, the proteins contained in the matrix are stretched when force is applied, and water is eliminated. The proteins shift from a ball-like conformation to a fiber-like one. In a second step, the disruption of the vesicles triggers the release of its components, leading to a chemical reaction that catalyzes the gelation and hardening of the slime. “It has the strength of petroleum-derived polymers such as nylon, but it has the added advantages of being protein-based and biodegradable,” adds Corrales.
The velvet worm slime composition could be used as a model to formulate bio-inspired biodegradable materials to replace petroleum-derived plastics such as polyester or acrylics, according to Corrales. This could lead to engineering new and efficient processes for drying and molding biopolymeric materials, making them much more attractive for applications and commercialization. The first steps are already underway: “We are now working on the development of bio-inspired mechano-responsive vesicles that could be added to biopolymer solutions used in bio-printing,” says Corrales. “We aim to improve the precision of bio-printing processes without degrading the bio-polymers.”