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  National Geographic 17 Jul 06
Animals Inspire Next Generation of Body Armor
John Roach for National Geographic News

Animals' natural defenses are providing inspiration for researchers developing the next generation of lighter, tougher body armor.

Benjamin Bruet, a graduate student in engineering at the Massachusetts Institute of Technology in Cambridge, is part of a team funded by the U.S. military to create new materials to protect soldiers in the field.

Bruet and his colleagues have tested horns, antlers, fish scales, and other natural materials to study how animals shield themselves in the wild. These insights could be used to design new, better materials for equipment such as helmets and bulletproof vests.

"Real soldiers will start to benefit from our research as early as the coming years," Bruet said in an email interview. "And within ten years, drastic improvements will have already been implemented that will revolutionize the battle suit."

Mother of Pearl

The team has become particularly interested in the soft-bodied snail Trochus niloticus and the inner layer of the shell that protects it.

The inside of the snail's shell is made of nacre, also known as mother of pearl. Nacre is composed of about 95 percent calcium carbonate, a relatively weak ceramic. The other 5 percent is a soft, pliable material called biopolymer.

Bruet calls biopolymer "organic glue." "At the microscale, nacre looks like a brick-and-mortar type of material with tiny tablets about 10 microns (a hundred-thousandth of a meter) in diameter and 1 micron (a millionth of a meter) thick," Bruet said. The tiny tablets are stacked on top of each other like rolls of coins held together by the organic glue.

Bruet said the structure of nacre is fairly well known. But scientists are still trying to understand what makes it so strong. It takes twice as much energy to break a piece of nacre than what nacre's structure should be able to withstand, Bruet explains.

"Hence there has to be additional mechanisms [at work] at smaller length scales making nacre even more efficient at resisting cracking," he said.

Nano Studies

To find out what makes nacre so strong, Bruet and his colleagues are studying how the material is structured at the nanometer scale. A nanometer is a billionth of a meter. A human hair is about 80,000 nanometers wide. The researchers used an atomic force microscope to scan individual plates of nacre. The microscope uses a laser beam to map the surface of the plates.

The secret of nacre's strength, Bruet says, is in exactly how the gluelike biopolymers stick to the plates. The key, he said, "lies in the complex interaction between the organic glue and the nanoscopic crystalline grains of calcium carbonate that make up nacre at the nanoscale, as well as the intrinsic properties of these components."

The team found that each individual plate is divided like a pie into separate sections, and the surface of each plate is covered in groups of nano-size bumps. The organic glue molecules are bound to the bumps. The team is currently studying the forces between the ceramic plates and the glue, Bruet says.

Ultimately, researchers hope to copy the nanostructure of nacre to create stronger, lighter helmets, bulletproof vests, and automobile panels.

Body Amor's Future

Nick Taylor is the manager of ArmorUP, an Austin, Texas-based retailer of body armor. He said today's armor is "very good" but added that "anything you can do to make it lighter is better."

Weight, he says, is a major limitation of body armor. "For military use, your basic [body armor] setup is 15 to 20 pounds [7 to 9 kilograms]. The average soldier also wears about 40 pounds [18 kilograms] of gear on top of that, plus a helmet is 3 pounds [1.4 kilograms]," he said. "Ultimately what becomes prohibitive is the weight."

Taylor cautions that any new body armor must be thoroughly tested before it is used on the battlefield or worn by police officers on city streets. He says the body-armor industry learned a lesson with Zylon, a trademarked armor that gained wide use in 1998. The material was marketed as lighter, thinner, and more flexible than other body armors. However, in 2003, police officers in California and Pennsylvania were killed while wearing Zylon vests. Research showed that the material may degrade quickly, rendering it ineffective after a few years.

"There are bigger issues than just lighter, thinner, and more flexible," Taylor said. "You also have to have good long-term tests in the harsh environment of an end user."
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