Engineers from the University of Southern California Viterbi School of Engineering say they could prevent future sports trauma and injuries with body armour and protective devices inspired by the lobster.
Chronic traumatic encephalopathy (CTE) results from taking repeated blows to the head - a common issue in contact sports like football and boxing. It is associated with serious consequences such as memory disturbance, behavioural and personality changes, Parkinson's Disease, and speech and gait abnormalities.
According to the engineers, 3D printed body armour like helmets and prosthetics based on the tough structures of a lobster's shell could help prevent CTE and treat other sports injuries.
The research was initiated by USC Viterbi post-doctoral scholar Yang Yang, who hit on the idea while eating lobster in a restaurant and had 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.
The team leveraged previous research into the shells of lobsters and mantis shrimps, which found that the chitin-based outer shells have an especially strong design. This design, called Bouligand-type fibre alignment, means that structural fibres align in a spiral and are constantly rotating, making it difficult for small cracks to expand into larger cracks.
According to Yong Chen, a USC associated professor of Industrial and Systems Engineering, because the crack has to rotate with the fibres, there is a much longer cracking propagation path. As a result, while micro-cracks are still possible, the shell does not break.
Chen is an expert in 3D printing, and together with Yang, developed an electric-assisted 3D printing process that aligns layers of material in bio-inspired and physically resilient ways like Bouligand-type alignment. The team is also the first to integrate an electrical field into 3D printing.
The team 3D printed small prototypes of the human meniscus in the knee, which is cartilage that acts as a shock absorber between the thighbone and shinbone, and is particularly vulnerable to sports-related injury.
In the experiment, the team tested the impact resistance of a model made of plastic and carbon nanotubes, 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 fibre, so basically when you try to pull it, you have a lot of fibre inside, so it’s reinforced, over a thousand times stronger than plastic,” said Chen. “When you just add nanofibres to plastic, overall you get 4x improvement in strength. And if we add and then align the same nanofibres with a 1000-volt electric field, you get 8x improvement in strength.”
The next steps for the engineers is to build bigger prototypes, and make them biocompatible. They are exploring hydrogel as an alternative material.
In the future, a football player could have their head scanned, and, using a digital design of their unique head shape, engineers could 3D print a customised, super-strength helmet.
But the applications are not just limited to sports.
“The electrically assisted 3D printing provides a new tool to fabricate arbitrary 3D geometries with any nanofiber orientations," Chen explained. "In addition to the reinforced structures, we believe this manufacturing capability offers tremendous possibilities for applications in aerospace, mechanical, and tissue engineering.”
[Caption: Lobsters and other crustaceans have exoskeletons with extraordinarily high impact resistance that has been studied for manufacturing stronger materials. Courtesy: Wikimedia Commons.]