WHEN Hugh Herr put his robotic fish into its tank, it swam off looking
surprisingly lifelike. But a few minutes later, it was flagging鈥攁nd
eventually came to a complete stop. It wasn鈥檛 faulty: it just needed a break.
The reason? Herr鈥檚 robot is the first one to be powered by real muscles.
Researchers have known for centuries that they can make muscles contract in
the lab: in 1786, Luigi Galvani discovered that electricity made a dissected
frog鈥檚 leg twitch. But until now, no one has ever tried to harness the
phenomenon to power a machine.
So Herr and his colleagues at the Massachusetts Institute of Technology鈥檚
Biomechatronics group built themselves a robotic fish. Inside it, a
microprocessor sends electric signals to frog muscles on either side of the
fish, making them contract. Tendons on the muscles are sewn to the nose and tail
so the 鈥渇ish鈥� wiggles and swims in response to the signals. The muscles get
their energy from the glucose solution the fish is swimming in (see video at
www-personal.umich.edu/ ~bobden/biomechatronic_devices.html).
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One of Herr鈥檚 aims is to power prosthetic limbs with real muscles. Artificial
limbs tend to be much stiffer than real ones and can鈥檛 adapt to different
surfaces, so they behave the same way whether you are walking on cement or sand.
Even a top-of-the-range prosthetic ankle won鈥檛 provide active thrust, which
makes walking tiring. Prototype limbs that can thrust contain noisy joint
motors. 鈥淚f all our muscles were motors, we couldn鈥檛 hear ourselves talking,鈥�
says Herr, who lost his own legs below the knee to frostbite.
Other researchers are attempting to make better prosthetics using artificial
muscles made from polymer fibres. These muscles are strong and silent, and
contract when a voltage is applied. But 鈥渢here are issues of robustness. They
oxidise easily,鈥� admits Yoseph Bar-Cohen, who heads NASA鈥檚 advanced actuators
laboratory in Pasadena, California.
鈥淲hy would anyone want to build artificial muscle?鈥� asks Bob Dennis, a
colleague of Herr. 鈥淩eal muscle can adapt to its environment, it can heal
itself, it can self-regulate.鈥� But live muscle has serious drawbacks. 鈥淧eople
ask: how are you going to sustain a muscle and activate it?鈥� says Zeynep Erim of
the Neuromuscular Research Center at Boston University. So although many
researchers had tested muscle performance in the lab, nobody had ever put them
to use in a robot.
Herr wants to improve his prototype by giving it a small stomach to supply
the tiny muscles with glucose. And for bigger muscles, he needs to add a
circulatory system that pumps the glucose to the muscles.
The robot has since expired, because its muscles only keep for a few hours
outside the body. But Dennis is now growing muscle cultures that live for
several months. He has fine-tuned a muscle-culturing technology
(see 鈥淢uscles to order鈥�) and aims to create muscle on demand.
MIT鈥檚 project is funded by the Pentagon鈥檚 Defense Advanced Research Projects
Agency, which wants to know if real muscle can be used as a silent actuator in
robotic systems. The military鈥檚 interest could revolve around
鈥渆xoskeletons鈥濃�攑rosthetic suits that will one day let soldiers run faster,
jump higher or carry more weapons. Such systems might employ real muscle.
FOR the first time, researchers have managed to grow human muscle
artificially. The technique might make some animal tests redundant, say Bob
Dennis at the University of Michigan and Paul Kosnik of Cell Based Delivery, a
Rhode Island biotech start-up.
Dennis and Kosnik have persuaded muscle fibres to grow by stimulating them
electrically. Normally, muscle cells get strain signals from their neighbours
which tell the fibres how to align and grow. Dennis and Kosnik鈥檚 signals mimic
those caused by the stresses and strains of growing muscles cells. The
researchers are patenting a 鈥渂ioreactor鈥� in which different signals organise the
fibres into muscles of various shapes. Their grown muscles are hardy, surviving
three to five months, compared with only several hours outside a body for fresh
adult muscle, but they are currently only one-tenth as strong.
They believe their muscle could replace animal tissue in some lab tests,
because Kosnik has already tested the effect of chemicals on his muscle
cultures. 鈥淎t a conservative estimate, I would have used fifty times as many
rats [in such tests],鈥� he says.