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.
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.
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. Their research was featured in Advanced Materials.
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,” 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.
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