Imagine a caterpillar with soft, fancy, velvety skin; that’s what a velvet worm looks like. However, unlike most caterpillars, these worms are fierce carnivores. They hunt by shooting sticky slime to trap their prey. A new study reveals something remarkable about this velvet worm slime.

Scientists have discovered novel proteins in velvet worm slime that could lead to strong, recyclable bioplastics. These proteins have a history dating back 380 million years and work like cell receptors in the immune system.

“The structures of proteins are highly conserved evolutionarily in the two distantly related velvet worm subgroups, indicating pervasive presence of this mechanism across species that has been maintained for ~380 MY,” the study authors note.

The uncanny slime action

The slime is stored inside a special gland in the velvet worm’s body and released through oral papillae, small openings located near the mouth. It is initially in a liquid state, but as soon as it is shot, it turns into glassy fiber.

“This liquid-to-solid transformation is very unusual and faster than the better-known silk spinning by spiders,” Ali Miserez, one of the study authors and a professor at Singapore-based Nanyang Technological Institute (NTU), told IFL Science.

However, the slime’s unique molecular action doesn’t end here. Within seconds, the glassy fiber solidifies and becomes as strong as nylon. What’s interesting here is that if you dissolve these fibers in water, they turn back to their original liquid form. 

“From this solution, fibers can be re-drawn. So, the entire process is repeatable, and the fibers are fully recyclable. This provides a great biomimicry example to produce the next generation of non-toxic, fully biodegradable bioplastics,” Miserez added.

Decoding its intriguing chemistry

To examine the slime in detail, the study authors employed protein sequencing with AlphaFold, a state-of-the-art AI tool that allows scientists to predict the 3D structure of molecules accurately. 

They discovered that the unique action of velvet worm slime is driven by leucine-rich repeat (LPR) proteins. These proteins share similarities with toll-like receptors (TLRs), another class of proteins that are found on the surface and inside immune cells. 

TLRs act as sensors that detect harmful microbes like bacteria and viruses by recognizing their unique molecular patterns. They are essential for innate immunity and are crucial for fighting infections. Their dysfunction is linked to autoimmune diseases and inflammatory disorders.

However, LPRs in velvet worms, despite being similar to TLRs in many ways, aren’t involved in immune signaling. Instead, they play a completely different role—they act like molecular glue to form strong, reversible fibers, which is completely unexpected.

Understanding how LRR proteins interact to form fibers may allow scientists to engineer similar proteins that could lead to the creation of strong, reusable bioplastics that self-assemble and disassemble like velvet worm slime. 

Such bioplastics could replace traditional petroleum-based precursors and help us reduce the ever-growing plastic waste problem.

Not everything that dissolves is good

The velvet worm slime could inspire new types of strong, durable, and renewable plastic-like materials. However, it still doesn’t answer many questions.

For instance, the LPR can be reused by dissolving it in water, but a bioplastic that dissolves in water may not be practical in every situation. Obviously, you won’t be able to use this type of plastic for a beverage bottle.

The researchers are aware of such limitations, and they are hopeful that further research will reveal practical ways to create and realize the true potential of slime-inspired biomaterials.

“By adjusting the chemistry of this binding mechanism, we can get around this issue,” Matthew Harrington, one of the study authors and a chemistry professor at McGill University, said.

The study is published in the journal PNAS.