Most actuators that are used in orthotic and prosthetic devices are electrical motors or electrical wires that shrink when current is passed through them. While these devices can provide contractile force, they do not come close to mimicking the dynamic flexibility of living muscle tissue. But what if you could make real muscle actuators? In Hugh Herr's laboratory at MIT, they have made a robotic fish that propelled by living muscle tissue taken from frog legs. The robotic fish had the following components:
- A styrofoam float allows the fish to float
- Electrical wires make the connections
- A silicone tail provides the swimming force
- Lithium batteries provide power
- A microcontroller control the robot's movement
- An infrared sensor enables the microcontroller to communicate with a handheld device
- A stimulator unit electrically stimulates the muscles
The frog muscles were attached to either side of the tail and to the plastic spine of the robot and electrodes from the stimulator were attached to them. The muscles on either side were alternately stimulated to produce a swimming motion. The robotic fish was placed in a tank of salt solution designed to keep the muscles alive. The fish swam for 4 hours out of 42 with a velocity greater than 75 percent of its maximum. The robot could swim forward, backward, turn, and stop. This was a prototype of a biomechatronic device with a living actuator.
While advancements in body armor technology can help soldiers in the Iraq War survive explosions, many of these survivors suffer damaged limbs (hands, arms, feet, legs) that require amputation. This situation has spurred research into advanced orthotic/prosthetic devices such as the ones developed in Hugh Herr's lab at MIT. The Department of Veterans Affairs and the Dept. of Defense are funding several biomechatronics groups to meet the needs of veterans and soldiers in the field.
Recently, Claudia Mitchell, a former Marine and amputee, has tested a prosthetic arm developed by Dr. Todd Kuiken at the Rehabilitation Institute of Chicago. A plastic surgeon, Dr. Gregory Dumainian at Northwestern Memorial Hospital in Chicago re-directed the nerves that control her missing arm to her chest. The nerves re-grew close to the skin of her chest. Tiny electrodes on her skin pick up the electrical activity of these nerves and send signals to the motors in the arm. She is able to control the arm's movements by thinking about it. As of now, the prosthetic arm is not truly biomechatronic in that signals only go one way, from Claudia to the arm. Dr. Kuiken is working on the next step of having the arm provide feedback to her, including sensations such as pain and pressure.
Until now, we have primarily addressed how biomechatronic devices can help people with impaired motor function. But what could these devices do to a normal person? Could they give him/her superhuman strength like Steve Austin, the "Six Million Dollar Man"? To this effect, investigators at the University of California at Berkeley have developed a machine or exoskeleton to enhance the walking ability of a normal human. The Berkeley Lower Extremity Exoskeleton (BLEEX) uses metal leg braces that powered by motors to make it easier for the wearer to walk. Sensors and actuators in the device provide feedback information to adjust the movements and the load while walking. The device's controller and engine are located in avest attached to a backpack frame. While the device itself weighs 100 pounds, it enables a person to haul a 70-pound backpack, while feeling as if he/she is merely carrying 5 pounds.
BLEEX could have many uses for the military as well as civilians. With BLEEX, soldiers could carry heavy loads across rugged terrain without fatigue. Similarly, military medics could carry injured victims off the battlefield. Fire and rescue workers could carry heavy gear or supplies great distances where vehicles could not travel.
When fully developed, biomechatronic devices will be useful in many ways:
- They can provide improved motor function that better mimics normal biological function to impaired individuals
- They can be used to train individuals with impaired motor function (physical therapy uses)
- They can adjust to each person without requiring a third party
- They can enhance performance of normal individuals
The major drawbacks to biomechatronics devices are the possibility of infection (as non-biological parts are implanted into living tissue) pain and discomfort. However, the promises of this new technology provide hope that those individuals with impaired motor function will be able to have restored functions that mimic normal human movements and, perhaps, make them better, stronger or faster than before.
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