Neural Prosthetics

It was mid-July 2004 when Christa Wheeler (pictured left) walked "with anticipation and a few butterflies" through the doors of the Cleveland, Ohio, MetroHealth Medical Center to begin her career as a Case Western Reserve University graduate student in biomedical engineering. "I was excited on that first day to finally begin research in neural prosthetics that seemed to be a perfect fit for my biomedical interests. I had found a field to bridge my technological and clinical interests," says Wheeler.

Neural prosthetics, one of the newest faces of biomedical engineering, involves a wide variety of prosthetic implants that interface with the nervous system to replace the body's damaged circuitry. Such devices include cochlear implants that have enabled thousands of previously deaf people to hear again and, more recently, retinal implants that return sight to the blind. Functional electrical stimulation (FES), the area Wheeler is specializing in, involves returning movement to paralyzed people using implanted electrodes to animate muscles in a controlled manner. She chose this field because it allows her to combine her love of technology with her desire to work with patients and improve their lives.

Wheeler seriously considered medical school, but during her undergraduate days she developed an affinity for electronic engineering, which she felt she would have to give up if she became a physician. "I wanted to use electronic design to help people. With biomedical engineering, I figured I could have the best of both worlds," she says. Wheeler is now developing a wrist-activated controller for a system that enables quadriplegics to use a hand to accomplish everyday tasks.

Wheeler's dual interests in biology and technology date to her high school days in Westlake, Ohio, near Cleveland, where, she says, she had an abundance of good teachers and mentors. While a high school junior, for example, she had an outstanding biology teacher who focused on anatomy and physiology. "After that class, I was certain I wanted to be a doctor," says Wheeler.

Her interest in medicine and the mechanics of the body was also the result of her early childhood years as a serious gymnast. She started as a 3-year-old, and by the time she was 9, she was working out 3 hours a day, 5 days a week. This intense regimen led to numerous injuries, some of which she learned to tape on her own. She was convinced that she wanted to be an orthopedist so she could help athletes like herself.

During her senior year in high school, Wheeler had another excellent teacher, this time in physics, and her certainty about medicine wavered. Uncertain about her career direction, she applied to several colleges and narrowed her choice to two, about 11 kilometers apart: Duke and the University of North Carolina (UNC), Chapel Hill.

It was while visiting Duke that she first learned about biomedical engineering, which piqued her interest because it encompasses both biology and engineering. But instead of entering the biomedical program at Duke, she opted for a premed program at UNC, which appealed to her more. She would, she decided, take a lot of science courses, which she would need for either discipline, and leave her final decision to the future. Then, during her sophomore year, she learned that UNC had a program in applied science that would allow her to follow a biomedical-engineering track. "I was still thinking premed and trying to decide if I wanted to do med school or not," says Wheeler, but she declared a major in applied sciences.

Designing for the Disabled

An "Enabling Technologies" course Wheeler took during her junior year solidified her decision. In that course, she and the other students designed devices to help people with physical disabilities. With some other students, Wheeler designed an orientation game for visually impaired toddlers. Visually impaired children often don't explore their environment because when they do they hurt themselves by bumping into things. Wheeler's team modified commercially available toys and connected them via an electronic control box. The toys are placed in different parts of the room, and music emanates from one of them, inviting the child to move toward it. When the child reaches the toy and pushes a button, another toy begins to play music, encouraging the child to explore another part of the room.

During this project, Wheeler realized that biomedical engineering was the best field for her. "What was driving me was that I was helping people," she says. "While I was working in the lab for hours trying to get the circuits to work, I felt good knowing this was going to help someone who isn't as fortunate as I am."

Grad School at Case

The next stop, Wheeler decided, was graduate school. "With there being so many different areas of biomedical engineering one can get into, it would be really hard to make a decision as to what to do for a substantial part of your life if you didn't go to grad school first," she says.

With a 3.97 grade point average in her major (3.9 overall), Wheeler had her pick of graduate schools. She chose Case Western Reserve University's Ph.D. program in biomedical engineering because it meshed well with her growing interest in designing prosthetic devices. Case is affiliated with the Cleveland FES Center, which is known worldwide for creating implantable systems to return movement to people who are paralyzed. The center was founded by P. Hunter Peckham, a biomedical engineering professor and Wheeler's graduate adviser.

Case offered a smorgasbord of scientific opportunities. "We have several different foci in biomedical engineering, one of which is neural engineering/neural prosthetics," says Peckham. "Students have the opportunity to do things from the very fundamental cellular and molecular level all the way through to clinical applications. They realize they can't do all that, but many times they don't know which component they want to do early on. They realize if they come here, they will have that opportunity to learn what best suits them."

Wheeler's Research

The first day that Wheeler entered the MetroHealth Medical Center, she met patients implanted with a hand-control device, known as the Freehand, invented by Peckham. By using eight implanted electrodes that snake through the patient's arm, stimulating muscles in the hand, the Freehand allows quadriplegics to groom and feed themselves and in some cases even to operate a computer. It is now being used by hundreds of quadriplegics.

The system is controlled by a joystick-like device taped to the user's shoulder, where many quadriplegics retain some movement; the device is activated by moving the shoulder. When activated, a wheelchair-mounted computer causes jolts of electricity to be sent to those electrodes in the hand, causing the muscles to contract.

The FES Center, in collaboration with NDI Medical, a medical device development company, was interested in developing a completely implantable stimulator for a newer version of the hand system, dubbed Micropulse II, that would include its own battery power and microprocessor, eliminating the need for any external equipment except for a controller. Peckham suggested to Wheeler that she develop the controller for her Ph.D. research. With fresh memories of how much she enjoyed designing the control system for the toy for visually impaired toddlers, Wheeler accepted the challenge.

After determining that, for those who retained wrist movement, the flexing of a wrist would be the best way to activate the controller, she settled on a wristwatch-like configuration made possible by the advent of a new kind of sensor called, despite its small size, the gigantic magnetoresistive sensor. These sensors can measure very small magnetic fields, enabling Wheeler to place the magnet and sensor farther from each other than was previously possible. Hence, the sensor can be located in a device worn on the wrist, and the magnet, about the size of a dime, can be attached to the back of the hand, or, eventually, implanted under the skin in a minimally invasive procedure.

Wheeler plans to have a prototype controller ready for testing on a neural-prosthesis user by May 2006. In the meantime, she is working on the myriad challenges of designing a complex electronic device, such as programming a small chip to be placed in the wrist apparatus to enable it to transmit joint-angle information to the implanted stimulator.

A Super Volunteer

Wheeler's eagerness to help others doesn't end with her research in the lab. In her spare time she is, as she puts it, "a super volunteer." This includes being the social chair of the Case Graduate Student Association (GSA), which involves planning parties and outings, and cooking dinners for the Ronald McDonald House, among other activities. As a member of the GSA executive board, she hosts prospective students, works on open houses, and organizes lab tours. She is also a distance runner and is planning her first half-marathon (21 km) in May.

Wheeler wants to go into industry when she finishes her doctorate. "I would like to stay in this field and work on the clinical side," she says. "I like the research, but I don't want to be stuck in a lab by myself not interacting with people. I still want to interact with patients."

This material is based upon work supported by the National Science Foundation Grant No. SES-0549096. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

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Victor D. Chase is a Yorktown Heights, New York-based writer. He has written a book about neural prosthetics entitled Shattered Nerves: How Science Is Solving Modern Medicine's Most Perplexing Problem, to be published by Johns Hopkins University Press this fall. He can be contacted at .

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