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October 4, 2007
University researcher Jonghwan Suhr says a recent study could lead to new materials that will mimic biological tissues and artificial muscles.
The assistant professor of mechanical engineering has been working on the ability of carbon nanotubes to withstand repeated stress and still be able to retain their structural and mechanical integrity, similar to the behavior of soft tissue. While extensive research has been done over the past decade into the mechanical properties of carbon nanotube structures, this study is the first to explore and document their fatigue behavior.
"If you can smartly control properties and materials, you can more efficiently control the whole structure," Suhr said. "If these nanotubes can mimic artificial muscles, then some day they might be utilized as the soft tissue of the stomach wall or even as tendons throughout the body."
Many researchers believe carbon nanotubes are the future of electronic circuitry and the successors of silicon, which, according to scientists, has nearly reached the limit of its applications. Suhr and a team of national engineers tested the nanotubes' ability to resist fatigue by building a two-millimeter-square block in which millions of nanotubes were aligned vertically. Then, they repeatedly compressed it between two steel plates once every 0.75 seconds for more than 100 hours.
After 500,000 compressions in which the tubes were repeatedly squashed to 75 per cent of their original length, the block kept springing back almost to its original shape. The springiness is similar to real muscles' ability to return to their original shapes over a lifetime of perpetual extension and contraction.
But it's not only artificial muscles that interest Suhr. Because real muscles create a smoother motion than jerky electric motors or pneumatic devices, some of the new materials would be used to power robots and prosthetic limbs, as well as artificial tissue for implantation. Suhr is now combining nanotubes with different polymers, which control when an artificial muscle gets stretched, to improve their resistance to fatigue.
"I want to focus on new materials and other applications," Suhr said. "We need to discern which of these polymers will work best, and then we can fabricate the new material ourselves."
Although carbon nanotubes are not currently used in commercial applications, they are being studied intensely by researchers. The miniscule tubes, some of which are only one nanometer wide (a human hair is 50,000 nanometers wide), may one day have uses in computer-chip technology as transistors.