Robotic Fish May Hold Key to Better Artificial Limbs

Scientists at Massachusetts Institute of Technology (Cambridge, MA; web.mit.edu) have developed a robotic fish incorporating whole frog-muscle explants that may be the first step toward building better prosthetic devices for humans. Based on Luigi Galvani's 1786 discovery that an electrical current makes a dissected frog's legs twitch, this new research explores the issue of tissue to replace the inefficient synthetic means of momentum currently used in artificial limbs. The first successful example of this technology is a 120-mm biomechatronic "fish" that combines an electronics package with a 50-mm section of frog muscle. Buoyed by a Styrofoam block in a glucose solution that serves as a source of energy, the unit uses a microprocessor to send variable electrical signals to the muscle tissue. The resulting contractions enable the fish to start, stop, and turn with a maximum speed of 60 mm/sec.

Using real muscle in prosthetic devices will yield many benefits, according to researchers. Muscle has the ability to adapt to its environment, healing and changing structure as required. It is also very efficient, generating as much as 4000 kJ from 1 kg of glucose under aerobic conditions. This energy is generated silently, eliminating many of the noise concerns associated with traditional devices. Because it delivers great isometric force, hybrid technology would also allow prosthetics to have extremities that are light but still very strong.

MIT scientists are presently working on developing muscle cultures that can survive outside their source body for several months. The tissues currently used remain effective for only a few hours. Other goals include creating the technology necessary to engineer muscle tissues directly from small tissue samples taken from the device user. Native sampling would allow the prosthesis to be fully compatible with its beneficiary. Among the many parties that have shown interest in this hybrid technology are the Pentagon's Defense Advanced Research Projects Agency, which may focus on developing hybrid suits to increase the physical capabilities of U.S. soldiers.

Zachary Turke