How Things Work: Bionic arm

When science fiction starts to resemble present-day reality, it does not take long to realize how advanced modern technology has become. Medical technology is now starting to enable people who have lost limbs to wear functional prosthetic ones.
Jesse Sullivan, a man from Tennessee, is much like any other active grandfather. He is able to perform typical daily tasks like shaving, dressing, and eating by himself. Every now and then, he plays catch with his young grandson.

However, Sullivan’s story, reported on, is not as ordinary as it seems. Both of Sullivan’s arms are prostheses, which are substitutes for missing body parts.

After having his arms amputated because of an enormous electric shock, doctors at the Rehabilitation Institute of Chicago fitted him with bionic arms controlled by nerves in his chest. Moments after thinking about closing his hand, his prosthetic hand closes.
Medical technology like this is part of a field of study called biomechatronics, which studies the integration of mechanics, electronics, and biology.

Most of the research is geared toward inserting mechanical devices into humans in order to facilitate actions or provide therapeutic relief.

A familiar application of this science would be the artificial heart, which was first successfully used in 1952.
Bionic arms are more complex than artificial hearts, as their motion is not constant and is based on conscious commands from the user.
When humans move a limb to perform an action, many things happen in quick succession. The brain sends signals to appropriate muscles in the limb, which send feedback information to the brain in order to constantly adjust the amount of force that needs to be applied. Nerves also send information to the brain to detect the position of the limb. In order for limbs to be functional, three major components must be present: biosensors, controllers, and actuators. Biosensors are the nerve cells and muscle cells, controllers are the brain and anything related to nerve signaling, like the spinal cord, and actuators are the muscles that actively move the limbs. Biomechatronic limbs have the same components. Mechanical biosensors detect electrical activity through many devices, including special kinds of wires placed on the skin or electrodes directly implanted into the muscles themselves.

They detect the intention of the wearer and send this information to the controller. Mechanical sensors, like force meters or accelerometers, relay information such as limb position and force.

The controller connects the wearer’s muscles or nerves to the electronic arm and interprets and controls the signals from the biosensors as movement, which it relays to the actuator. The actuator, usually a motor, controls the physical movements of the device, moving the limb or providing force. The concept is very simple, but currently, bionic limbs do not provide much feedback and cannot truly adapt to a varied number of scenarios as a real limb can. Researchers around the world are working to make prosthetic limbs more accurately mimic the complex motions of real limbs.

At the University of Twente in the Netherlands, researchers are using cameras and various sensors to analyze walking versus standing in healthy people. Researchers at MIT are also studying walking and running motions, and have developed a lower leg called the “Rheo-Knee,” which moves based on the viscosity of an iron-oil fluid, making a nearly realistic-looking walking motion. In the future, researchers hope to create biomechatronic limbs based on living tissue. Research is being done at MIT using living frog muscle tissue to power a robotic fish. Two sets of muscles were alternately stimulated by electrodes, creating a swimming motion. This is the first example of a device created using living material.

Current applications are very important in the military. Many soldiers suffer from damaged or removed limbs because of explosions or other wounds. Using prosthetics would make life easier for many war veterans.

Claudia Mitchell, a former Marine who lost her arm in a motorcycle accident, was the first woman to be fitted with a prosthetic arm with the ability to “feel” through the hand. Nerves above her breast were rewired to send signals to the region of the brain that usually detects sensations in the hand. The same was done with Sullivan, who can feel his hands through nerves in his chest. Current problems with biomechatronics are infection and pain for the user. However, modern technology has advanced greatly and will only improve.
In the future, biomechatronics might be applied to people not affected by limb loss to make them stronger or faster.