Moving toward more lifelike artificial limbs

Bryn Nelson Columnist

The need for better prosthetics, driven in part by the hundreds of amputees returning from Iraq and Afghanistan, has spurred a host of innovations enabling unprecedented control over artificial arms and legs. Already, researchers have begun unveiling sensor and microprocessor-packed “intelligent” knees, thought-controlled mechanical arms, and artificial hands with fingers able to pinch and grab.

But what about prosthetics for coming generations? Inspiration has to begin somewhere, after all, and a robot-steering “robo-moth,” a newly discovered phenomenon related to vibrating cell phones and a squid’s unusual beak are hinting at what might be on the horizon — and what hurdles must still be overcome to get from here to there.

If the observations eventually pan out, lifelike replacement limbs of the future could be formed from body-friendly composites that prevent injury, boast strong and flexible materials that generate electricity needed to transmit signals, and possibly even integrate directly with neural implants to produce more natural movements.

The 'robo-moth'
In November, researchers at the University of Arizona turned heads when they unveiled a six-inch-tall robot propelled by the eyes and brain of a hawk moth at the annual Society of Neuroscience meeting. Beyond the gee-whiz factor, scientists say the “robo-moth” hybrid could have intriguing implications for neural implants, yielding better control over limbs immobilized by paralysis or replaced by prosthetics.

By implanting an electrode in a single neuron that stabilizes moth vision during flight, researchers found that the moth could effectively steer the wheeled robot in a left-right direction for about a minute and a half, via electrical signals amplified in the robot, and by a translation of those signals into action through a computer attached to the robot.

Charles M. Higgins, an associate professor of electrical engineering and neurobiology at the university, warns that plenty of pitfalls remain. Even so, working out the neural signals needed for locomotion could hold promise for future applications using brain implants to steer robotic arms or legs.

Other researchers have experimented with more advanced brain implants in primates, with non-invasive devices and with electrode bypasses that send brain signals to nearby muscles that can be used to control artificial limbs.

Higgins expects such systems to increase in sophistication, but concedes that keeping a working electrode in the human brain without harming the individual remains a major obstacle. The challenge is heightened by the brain’s tendency to surround and inactivate an electrode with insulating tissue in a process called gliosis. “It’s not quite ready for prime-time because you don’t want to replace it every three months,” he said.

A neural implant also must evade rejection by the brain while remaining precisely located, he said. Plus, researchers would have to figure out how to process the outgoing information so a signal to move a finger doesn’t move a leg instead. “These are all problems that will have to be solved before we see the ‘Six Million Dollar Man’ of 1975,” Higgins said.

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