Strong as a snail

Extremely resilient and as thin as a cloth jacket, the high-tech, bullet-stopping armor of the future could have its origins in insights gained from a lowly seaweed-eating snail—the abalone.
Impressed by snails’ ability to construct helmet-like shells capable of withstanding incredibly heavy blows, a research team at the University of California, San Diego (UCSD) headed by Professor Marc Meyers, is studying the mollusk in order to develop a new generation of lightweight materials that could toughen everything from tanks to body armor. In their efforts to aid law enforcement officers and military personnel, many scientists are increasingly researching biological systems with the purpose of extracting their unique capabilities and transitioning them into effective personal safety and security solutions.
And the need for really lightweight, extremely tough body armor is great. Rated and tested by the Office of Law Enforcement Standards (OLES), body-armor design is classified into seven categories, with Category I body armor offering the lowest level of protection, and Category VII offering the highest. While hard body armor made of thick ceramic or metal plates belongs to the higher categories and offers more protection, the average police officer is usually equipped with Category I body armor, the lowest-level design that stops only relatively small-caliber bullets that have less force on impact. The reason? Higher-ranked armor is heavier and more cumbersome to maneuver around in, impeding police work.
“The only limitation of body armor is the fact that many law enforcement professionals still choose not to wear armor due to the “discomfort” caused by wearing it,” said Alex Cejas, the director of operations at Protective Product International, a company that makes body armor based in Sunrise, Fla. “While developments have been made in the industry to make armor lighter and more comfortable, we are still talking about a life-saving device that must not only stop a bullet but also dissipate the trauma caused by the bullet, so as to not cause any significant internal bruising or damage.”
Further progress in making highly effective body armor using hard ceramics has mostly resulted in heavier armor designs that only increase the discomfort factor, reducing mobility and making its adoption by law enforcement personnel even more unlikely, in spite of the growing prevalence of increasingly lethal bullets.
“Conventional ceramic armor, backed by composites and Kevlar, can stop an armor-piercing bullet from an AK47 rifle at muzzle velocity,” said Meyers. “These armor-piercing bullets have a steel core and can go through conventional (soft) armor like a knife through butter. The problem is that the armor needed is too heavy. It takes about 15 pounds of armor per square foot of protection. If an officer needs four square feet of armor, it translates into 60 pounds. That’s a little less than the weight of armor worn in the Middle Ages, and modern soldiers cannot ride into battle on horseback. If we can decrease this weight to 30 pounds, we have something feasible.”
Learning from nature
This is where biomimetics plays a role. While biology-inspired structures have been mimicked to create many commercial applications, Meyer’s research into the abalone shell could have a great impact on the body armor industry, helping scientists to create similarly lightweight, sturdy shields.
Abalones use chalk, the same brittle material that teachers use on boards, to create a shell that’s immensely stronger than the calcium carbonate of which it’s made. By using thousands of layers of calcium carbonate as “tiles” held together by an organic glue, the abalone can disperse the force of a blow in such a way that the shell remains intact. The key lies in the glue; strong enough to hold the layers of tiles firmly together, but weak enough to permit them to slip apart, it absorbs the energy of a heavy blow so that the shell “gives” a little but doesn’t break
“We now understand how the animal takes weak components and makes a strong composite,” said Meyers. “The snail fabricates tiny tiles shaped as hexagon-like tiles in the floor. Made of chalk, these tiles are so small that it would literarily take hundreds of them to fill the space equivalent to the cross-section of a human hair. Since each tile is so tiny, even small cracks are arrested by the organic glue between them. So, the abalone shell is incredibly stronger than chalk. However, it is weaker than our man-made ceramics. The beauty of our study is that we are showing how the animal fabricates these tiny tiles and how it assembles them in intricate ensembles.”
While an abalone shell can’t stop an AK47 bullet, Meyers believes that similar construction techniques could be used to fabricate a new class of extra-strong materials by employing existing strong ceramics as building blocks. The team plans to take hard ceramics such as alumina, silicon carbide, boron carbide and even diamonds and make tiny tiles, assembling them all with a special glue to form an extremely strong lightweight structure. The research team also is analyzing the strong, but extremely lightweight beak of the Toco toucan—a Central and South American bird that squashes fruit and berries with its beak—trying to discover what makes it so strong.
“Will the toucan beak and abalone ever be used to make armor?” asks Meyers. “No and no. However, the lessons learned will guide future designs, new materials with structures inspired by these systems. In the case of abalone, the shell was especially designed to resist predators just like a tank or body armor.”
With biomimetic researchers delving deeply into the properties of naturally occurring tough materials, experts hope they will discover and develop more convenient safety solutions.
“We have law enforcement professionals and military personnel all over the world in need of armor for protection, but there is only so much traditional fiber available to fill the demand,” said Cejas. “If new materials can be found to perform just as well, if not better, then that just improves the chances of getting the armor to those who need it most as soon as possible. We are still a long way from developing armor that is as thin and comfortable as everyday clothing, but a piece of soft armor that is flexible, less than quarter of an inch thick, and less than 5 pounds, doesn’t seem to be asking too much in the grand scheme of things.” HST

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