Designing and building better prosthetic limbs is a subject that has fascinated him since he was a young boy, and one that his career has put him in a unique position to achieve.

Growing up in the Atlanta area, Goldfarb exhibited his mechanical aptitude at an early age. "As far back as I can remember, I would take things apart and put them together. Anything like toy blocks, erector sets, Legos and so on. Those were the kinds of things I liked to do."

Even household appliances weren't safe. "According to my parents, I took the vacuum cleaner apart when I was two. To this day, I don't know if that is true-or whether I got it back together or not."

In high school, Goldfarb found that he was good at math and science. He also found a unique way to use his mechanical talents to promote school spirit. "Like most high schools, we built floats for homecoming. The rest of my class let me build mechanisms to move things on our floats. It became something of a tradition."

His grandmother provided Goldfarb with another early outlet for his abilities. She volunteered full time at the local Veteran's Administration (VA) hospital. Aware of his interest in prosthetics, she talked with the director, who arranged a job for him in the hospital's prosthetics lab. "They were very grateful for her service and did what they could to accommodate her, so they gave me the job," he says.

Although his parents divorced, Goldfarb's father - a heart surgeon living in Phoenix - kept track of his academic performance. When he was a junior in high school, his father called with an unusual proposition. "He asked if I wanted to skip my senior year and go to the University of Arizona in Tucson," Goldfarb says. "So I did. I ended up dropping out of high school and going to this school that I'd never heard of."

To this day, Goldfarb doesn't know how he did it, but his father not only got him admitted but also arranged for a full scholarship. He also enrolled the younger Goldfarb in some classes, but that was about all the preparation he made. "He basically drove me down there, stopped at a Target to buy me a pillow and some sheets, and dropped me off. That's just the way he is," says Goldfarb matter-of-factly.

Looking back at this sink-or-swim beginning, Goldfarb says, "It was kind of fun because it was very much having to navigate my own way."

The young scholar found his way from arts and sciences, where his father had enrolled him, to engineering. He also got a job in the Tucson VA hospital and built an artificial arm for his senior design project.

Prosthetic limbs continued to be his focus in graduate study at the Massachusetts Institute of Technology. His master's work was to design a robotic artificial leg, and his doctoral work was developing a computer-controlled brace that paraplegics could wear in conjunction with electrical stimulation of their muscles to help them walk.

"Occasionally I'm asked why I'm so interested [in artificial limbs], and I don't have a good answer for that. I think that it has something to do with the fact that building an artificial limb is like trying to imitate the ultimate machine," he says.

When Goldfarb joined the faculty at Vanderbilt in 1994, however, he was diverted into robotics because the government was aggressively funding research in this area. He teamed up with another Vanderbilt professor, Ephrahim Garcia, to develop a robot bug capable of covering a significant distance using only the energy it can carry.

The project led him to concentrate on the power issue and to identify the Achilles heel of the current generation of mobile robots. "Did you know that today's androids are something of a fraud? The best of them can run for less than a half hour before exhausting their battery packs. To operate longer they must be plugged into an outlet," he says.

Goldfarb determined that the conventional approach of using batteries and electric motors simply would not work for insect-sized robots: They are too heavy for the amount of energy they can store. In order to meet the goal of the project, he replaced the electric motor with rods made from a special material that expands and contracts when exposed to varying electric voltage.

In 2000, Goldfarb found an opportunity to move back in the direction of his first love. He joined researchers at the University of California, Berkeley on a Defense Advanced Research Project Agency (DARPA) project to develop an exoskeleton designed to help foot soldiers carry heavy loads on the battle field. Goldfarb's job was to design the power source. As was the case with the robotic bugs, he quickly rejected the conventional combo of batteries and electric motors. Instead, he came up with an elegant alternative system fueled by hydrogen peroxide, which you can buy in a diluted form in any drug store but which can also be used as rocket fuel at higher concentrations.

The Berkeley project failed to achieve its ambitious goals, but other researchers were impressed by Goldfarb's contribution. As a result, in 2005 a group of researchers at Johns Hopkins University invited him to join them in another major multi-university project to develop an advanced prosthetic arm also funded by DARPA.

Government interest in developing better prosthetic limbs has grown as a result of the Iraq war. Improvements in body armor and in battlefield medical practices have lowered the number of casualties from that conflict, but with the side effect of significantly increasing the number of amputees. "It's one of those ironic lessons of history that wartime is the only time that advances in prosthetics are made," says Goldfarb. "Because of recent advances in materials and electronics, there is a tremendous opportunity right now to make major improvements in artificial limbs."

The $30 million DARPA project is intended to develop an advanced prosthetic arm that can be produced commercially within two years. Goldfarb and his team at the Center for Intelligent Mechatronics have the job of producing the most advanced of the three mechanical arms being developed by the program.

The radical design, which has a surprising number of similarities to the arm he designed in college looks and performs very much like the real thing. The arm has greater dexterity and freedom of movement than any other prosthetic to date, and its unique liquid-fuel power system is compact and lightweight yet has the capability to deliver near human strength. After a year and half, Goldfarb's group has met all its design goals and has produced a working arm.

In the same DARPA program, neurobiologists at the California Institute of Technology and the University of Utah have been making progress in developing advanced methods for controlling the three prototype arms. Instead of the current, often clumsy system of straps and shoulder movements, they are looking at several approaches for implanting electrodes into the nervous system to enable an amputee to control the arm directly.

Despite all of the advances in the technologies in biomimetic devices, however, Goldfarb notes that there will always be fundamental differences between biological and mechanical systems.

"We just can't do things the way biological systems can," Goldfarb says. "Animals do things in a totally different way [than machines]. There is no machine that has the maneuverability of a hummingbird. At the same time, there are some things that man-made systems can do better. There is no animal that can fly as high or as fast as a 747.

"Biology and man-made systems are at opposite ends of the spectrum. That is one reason prosthetics are such a challenge. Functionally, we can try to provide the same function as an arm, but we have to do it in a very different way. From the outside, the arms might look the same, but from the inside - the fundamental way in which they operate - they are going to be very different. I, and I think a lot of engineers, would love to be able to develop things very close to a biomimetic route, but our work is just fundamentally different," he says.

Goldfarb plans to continue his work on the arm as well as a parallel project on an artificial leg of similar design, funded by the National Institutes of Health.

Just as his professional life has involved finding the balance between mechanical form and function, Goldfarb's personal life is centered around the balance of career, home and family. His wife Sally is a former Vanderbilt Spanish professor who now trains horses. The two met while in Arizona, and together the couple has three daughters aged five, seven, and nine. Asked if any of the girls is a potential engineer, Goldfarb is inclined to believe that they will probably be something else. "We'll see. Let them be what they want to be," he says.

So far, all the household appliances remain intact.

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