Originally Published MPMN March 2002

SPECIAL

Electroactive polymers flex their muscles

Imagine an artificial muscle made of plastic that could defeat its human counterpart in an arm-wrestling match by flexing and stretching in response to an electrical stimulus. It might seem like an unusual application for a new kind of intelligent plastics called electroactive polymers (EAPs), but it is just one of many being developed at NASA's Jet Propulsion Laboratory (Pasadena, CA; www.jpl.nasa.gov). Based on work dating back to an 1880 experiment performed by Wilhelm Roentgen, EAPs may help designers simplify a range of mechanical tasks by emulating the qualities of biological muscles. "With these materials, it will someday be possible to produce biologically inspired robotic systems that are agile, resilient, damage tolerant, noiseless, and lightweight," says senior research scientist and group leader Yoseph Bar-Cohen.

EAPs are generally classified into two types by the movement they offer: bending or stretching. Bending plastics are constructed of flexible ribbons of carbon, fluorine, and oxygen molecules. When electricity is applied to the ribbon, charged particles in the polymer are pushed or pulled to either side depending on polarity, causing the material to bend. Stretching EAPs consist of thin plastic sheets that are wrapped into cigarlike cylinders. When a positive charge is applied to one end of the cylinder and a negative charge to the other, the sheets contract toward the center of the tube, forcing a lengthwise expansion of as much as 380%. Activation charges for these plastics range from one to several thousand volts.

With high actuation displacement and force, EAP materials should have many applications in the medical field in years to come. One of the most interesting is the replacement or augmentation of damaged human muscles. Other possible uses include catheter-steering mechanisms, miniature in vivo diagnostic and microsurgery robots, and interface devices used to connect neurons and electronic devices. And while many of these materials are not yet robust enough for commercial use, Bar-Cohen remains confident about their potential. "My hope is someday to see a handicapped person jogging to the grocery store using this technology," he says.

Benjamin Lichtman, Norbert Sparrow, Katherine Sweeny, Zachary Turke, and Susan Wallace

Copyright ©2002 Medical Product Manufacturing News