Gerald Loeb Discusses Future of Prosthetics

Sunday, March 8th, 2009

“Clever engineers try to emulate nature,” said Gerald Loeb, professor of biomedical engineering at the University of Southern California (Los Angeles). Loeb was the featured speaker last night at Stuart Karten Design (Marina del Rey, CA) where he discussed the future of prosthetics. The event was part of a salon-style series called “Conversations” hosted by the design firm, which has worked on several medical devices.

One of the original developers of the cochlear implant, which restores hearing to the profoundly deaf, Loeb has spent decades working to advance biomimetic microelectronic systems to restore lost function in complex neural systems. Currently, he’s in the final development stages of technology that enables the human brain to experience sensory input from mechanical limbs.

The big three goals that scientists have been in pursuit of, he said, are how to make the deaf hear, the blind see, and the lame walk. He already has helped to accomplish the first goal with the cochlear implant. Efforts to help the blind see are in various stages of progression and show promise, he said. Making the lame walk, however, may be the wrong goal, he suggested. Problems such as urinary and respiratory complications, as well as bed sores, are more of a priority for paraplegics. There’s also the small market, hazards, and liability for control failure to consider. “And the most able-bodies athlete still can’t beat the wheelchair in a race,” he added.

Focusing efforts on understanding the body’s own signal processing may be the better goal. “We’ve got to get over the notion that electricity in the body is magical,” said Loeb. He and his research teams have devoted much of their time to studying movement and how to coordinate a signal interface with what a patient wants his or her prosthetic limb to do. Using a needle made of nonconductive material, Loeb can inject leadless microstimulators into the body. “The central nervous system doesn’t regenerate but peripheral nerves can, so we direct them into the muscle,” he explained. “It is possible to make a person feel a prosthesis as their own limb through tactors on the skin.”

Using a biomimetic tactile sensing array, Loeb says it is possible to convert deformation of skin into easily measured electrode impedances. “Fingerprints are not just there for the FBI,” he joked. “The ridges of fingerprints feel patterns of vibrations to detect texture discrimination.”

Recognizing nature’s own tools, such as fingerprint ridges, to communicate with other parts of the body is key to Loeb’s research. In creating a prosthetic fingertip, he said that the farther along they got in the research, the more they realized the benefits of the finger’s natural shape and construction. Like natural fingerprint ridges, electrodes are embedded in the prosthesis finger pad to distinguish texture and pressure. The skin-like material effectively holds the electrodes, sensors, and salt water inside the device, or fingertip, and the nail on top secures everything together.

But such developments can be slowed when the right components are not available. There have been several times when Loeb has designed a component himself because what he needed for his device design simply didn’t exist. One big problem that persists is with custom integrated circuit designs, which remain arcane and cumbersome, usually a mix of analog and digital as well as a mix of voltages, he said. As the demands of the industry change, different companies, such as chip suppliers, seem to “suddenly” discover medical applications for their products, he said. Part and equipment suppliers are in the unique position of potentially making the lives of device manufacturers easier. The real issue is making devices–and their components manufacturable. “We need the ability to transform designs into chips without spending millions of dollars and years to do it,” Loeb said.

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