April 04, 2008 –
It’s a far cry from the claw-like apparatus dangling from Capt. Hook’s arm. Today’s technology is making possible innovative aesthetic and functional improvements in prosthetic limbs.
A sophisticated prosthetic hand is under development at UCI, part of a nationwide effort funded by DARPA to construct a bionic arm that is wired directly into the nervous system. This neural wiring will allow amputees degrees of motor control and feeling that were previously unattainable.
UCI is one of 30 organizations, including 10 universities in Canada, Europe and the United States working on phase two of “The Revolutionizing Prosthetics Program,” which intends to make these advanced devices available by 2009.
Existing prosthetics are either purely cosmetic or somewhat functional, but not both, according to Bill Tang, professor of biomedical engineering. Tang and his group participated in phase one of the project, investigating artificial muscles that could power the prosthesis and allow it to move with the ease of a natural hand.
They experimented with a pressurized-gas hydraulic system that could better mimic muscle function than motors, pulleys and gears. Energy from highly compressed air is controlled to inflate balloon-type artificial muscles, eliminating the need for a battery. This system is also quieter, smoother and more flexible than a motor-and-gear system, Tang says.
When completed, the prosthetic device will imitate the force, agility and multiple degrees-of-freedom of a natural hand. It also will interface directly with the user’s nervous system. A team led by James Fallon, professor emeritus of psychiatry and human behavior, also participated in the first phase of the project, securing the neural probes onto the user’s peripheral nerves in such a way that a signal from the nerve could control the hand’s movement.
Infusing Tactile Sensitivity
Remarkably, the hand will also possess a tactile sensing system that will allow it to discern temperature, texture, pressure and degrees of hardness, as well as perform social functions like shaking hands or gesturing. “Human touch is very sensitive and a lot of that has to do with multi-modal sensing,” says Abraham Lee, biomedical engineering professor and leader of the tactile research component. “Our ultimate goal is to get to that level, where we give the user the overall sense of the human hand.”
Three different types of sensors are being fabricated on a common platform and integrated into a skin-like covering. One measures pressure, another vibration – both by way of microfluidics, the movement of fluid through tiny channels – and the third senses proximity of objects to the limb by detecting the electric field around it.
A human hand uses multiple types of receptors simultaneously when performing functions like using a tool or holding a hot cup of coffee. Doctoral candidate Jeff Fisher assembled a behavioral chart that spells out which senses and what combination of sensor functionalities are required to perform specific tasks.
Tool manipulation, for example, requires the ability to sense graduated pressure, slippage, position, location, orientation, movement and curvature. Each of these senses requires a combination of sensors – those that can detect low frequency vibration, high frequency vibration, shear forces, local tissue stress and others.
IT is the messenger that keeps the components communicating. “We not only need to send information to the robotic hand to control it, but we also need to get information back from it,” says Tang. “Think about picking up an egg. A human can sense how much force he is exerting on the egg. But for the robotic arm, we need to have that tactile information sent back to the controller so it can manage the amount of force the robotic fingers are exerting.”
Adds Lee: “What we are ultimately trying to do is connect the brain to the senses, to the nerves, to the neuron firing and then connect those to our sensors so the user will have the same sensation as with a human hand. That’s where IT really comes in.”
— Anna Lynn Spitzer