Nature’s Armor: A Lobster Tale

| August 25, 2017

Biological structures may provide insight to prevent and treat sports-related injuries.

Lobsters and other crustaceans have exoskeletons with extraordinarily high impact resistance that has been studied for manufacturing stronger materials. Photo courtesy of Wikimedia Commons.

According to a study published this July in the Journal of the American Medical Association, chronic traumatic encephalopathy (CTE) was found in 99% of deceased NFL players’ brains donated to scientific research.

CTE results from taking repeated blows to the head, par for the course in contact sports like football and boxing, and is associated with memory disturbance, behavioral and personality changes, Parkinson’s Disease, and speech and gait abnormalities.

The good news: a team of USC Viterbi engineers might aid in future CTE prevention and treat other sports injuries with 3-D printed body armor like helmets, other protective devices and prosthetics – all by learning from nature’s toughest structures.

Learning From Lobsters

USC Viterbi post-doctoral scholar Yang Yang first came to the idea while eating lobster in a restaurant and having difficulty breaking the lobster’s claws to get to the meat.

“I thought maybe there was some special structure involved that brings the lobster claws very high impact resistance,” Yang said.

I thought maybe there was some special structure involved that brings the lobster claws very high impact resistance.Yang Yang

Indeed there was.

As it turns out, former research has found that lobsters as well as fellow sea-dwellers, mantis shrimps, have an especially strong design to their outer shells made up of chitin, a fibrous material. This design, called Bouligand-type fiber alignment, means that structural fibers align in a spiral and are constantly rotating, making it difficult for small cracks to expand into larger cracks.

“The crack has to rotate with the fibers, so you get a much longer cracking propagation path,” said Yong Chen, a USC associate professor of Industrial and Systems Engineering. “You may have a micro-crack, but it doesn’t break the shell.”

Brilliant By Design

Chen, an expert in 3-D printing, also supervises Yang and together they have developed an electric-assisted 3-D printing process that aligns layers of material in bio-inspired and physically resilient ways like Bouligand-type alignment. They are the first to integrate an electrical field into 3-D printing.

Electrically-assisted 3-D printing can create materials with stronger high-impact resistance. Photo courtesy of Yong Chen.

Their study involved 3-D printing small prototypes of the human meniscus in the knee, essentially cartilage that acts as a shock absorber between the thighbone and shinbone and is vulnerable to sports-related injury. This year, the research team made the cover of the March 2017 issue of Advanced Materials for their innovation.

In the experiment, the team tested the impact resistance of a plastic model, a model made of plastic and carbon nanotubes – a type of fiber, and one made of plastic and carbon nanotubes with an electric field applied during the printing process to align the fibers within.

“The carbon nanotube is a microscale fiber, so basically when you try to pull it, you have a lot of fiber inside, so it’s reinforced, over a thousand times stronger than plastic,” said Chen. “When you just add nanofibers to plastic, overall you get 4x improvement in strength. And if we add and then align the same nanofibers with a 1000-volt electric field, you get 8x improvement in strength.”

Brave New Armor

Next steps for the research include building bigger prototypes and making them biocompatible.

“For clinical applications like a prosthetic meniscus, the material needs to be biocompatible, so we need to find the perfect material, perhaps hydrogel,” Yang said.

“Right now, we’re trying to improve this electric-assisted 3-D printing process with the help of an NSF grant started April 1, 2017,” Chen said. “The electrically assisted 3-D printing provides a new tool to fabricate arbitrary 3-D geometries with any nanofiber orientations. In addition to the reinforced structures, we believe this manufacturing capability offers tremendous possibilities for applications in aerospace, mechanical, and tissue engineering.”

In the future, this could mean that a football player has their head scanned, and using a digital design of their own unique head shape, a customized, super-strength helmet is 3-D printed on the spot. For a prosthetic meniscus, a person’s knee could be scanned to print a replacement with the appropriate dimensions.

In other words, we could be looking toward a brave new world of personalized protection. Thanks, in part, to lobsters.

For their research paper, Chen and Yang worked with co-authors Kirk Shung and Qifa Zhou, both professors in the USC Viterbi Department of Biomedical Engineering. To learn more, read the research paper published in Advanced Materials.