In the TV series "The Six Million Dollar Man," scientists restore a crippled test pilot, who lost legs, one arm and an eye. They have the technology, so they rebuild Steve Austin and give him superhuman qualities. While this is total science fiction, modern robotics is inching ever closer to this vision in a field known as biomechatronics.

Biomechatronics is the merging of man with machine -- like the cyborg of science fiction. It is an interdisciplinary field encompassing biology, neurosciences, mechanics, electronics and robotics. Biomechatronic scientists attempt to make devices that interact with human muscle, skeleton, and nervous systems with the goals of assisting or enhancing human motor control that can be lost or impaired by trauma, disease or birth defects.

a soldier using prosthetics to play foosball
Photo courtesy U.S. Army
A Soldier with prosthetic arms plays foosball.
In this article, we will find out how biomechatronic devices work, explore the current progress of biomechatronics research and learn about the benefits of such devices.

Consider what happens when you lift your foot to walk:

  1. The motor center of your brain sends impulses to the muscles in your foot and leg. The appropriate muscles contract in the appropriate sequence to move and lift your foot.
  2. Nerve cells in your foot sense the ground and feedback information to your brain to adjust the force, or the number of muscle groups required to walk across the surface. You don't apply the same force to walk on a wooden floor as you do to walk through snow or mud, for example.
  3. Nerve cells in your leg muscle spindles sense the position of the floor and feedback information to the brain. You do not have to look at the floor to know where it is.
  4. Once you raise your foot to take a step, your brain sends appropriate signals to the leg and foot muscles to set it down
This system has sensors (nerve cells, muscle spindles), actuators (muscles) and a controller (brain/spinal cord).

Any biomechatronic system must have the same types of components.:

Biosensors
Biosensors detect the user's "intentions." Depending upon the impairment and type of device, this information can come from the user's nervous and/or muscle system. The biosensor relates this information to a controller located either externally or inside the device itself, in the case of a prosthetic. Biosensors also feedback from the limb and actuator (such as the limb position and applied force) and relate this information to the controller or the user's nervous/muscle system.

Biosensors may be wires that detect electrical activity such as galvanic detectors (which detect an electric current produced by chemical means) on the skin, needle electrodes implanted in muscle, and/or solid-state electrode arrays with nerves growing through them.

Thank You
Thanks to Dr. Scott Bernstein for his assistance with this article.
Mechanical Sensors
Mechanical sensors measure information about the device (such as limb position, applied force and load) and relate to the biosensor and/or the controller. These are mechanical devices such as force meters and accelerometers.

Controller
The controller is interfaces the user's nerve or muscle system and the device. It relays and/or interprets intention commands from the user to the actuators of the device . It also relays and/or interprets feedback information from the mechanical and biosensors to the user. The controller also monitors and controls the movements of the biomechatronic device.

Actuator
The actuator is an artificial muscle that produces force or movement. The actuator can be a motor that aids or replaces the user's native muscle depending upon whether the device is orthotic or prosthetic.

We'll look at the progress made in the field of biomechatronics next.

Orthotics vs. Prosthetics
Orthotic devices artificially assist human movement without replacing the impaired limb. In contrast, prosthetic devices replace the lost or injured limb to restore movement.

Why use biomechatronics rather than conventional orthotic/prosthetic devices? While many new orthotic/prosthetic devices use microelectronics and robotic components, they cannot accurately emulate the complex motions of human limbs. Current orthotic/prosthetic devices do not feedback to people or adjust to variable loads or complex terrains. They do not adjust on a moment-to-moment basis to the individual wearer. Biomechatronic devices promise to overcome these limitations by interfacing directly with the wearer's muscle and nervous systems to assist/restore motor control.