A team of bioengineers has genetically engineered skeletal muscle tissue to produce a protein that reacts to light, and plans to use it to build a robot with realistic manoeuvrability.
The MIT and University of Pennsylvania team decided that mimicking animal behaviour in robotics was not enough -- by mimicking the genetic materials that allow those behaviours, they could make a giant leap towards feasible biorobots. It is the first time skeletal muscle has ever been manipulated to react to light, with past studies focusing only on cardiac muscle cells.
"With bio-inspired designs, biology is a metaphor, and robotics is the tool to make it happen," said MIT engineering professor Harry Asada, who has co-authored a paper on the study, due to appear in the journal Lab on a Chip. "With bio-integrated designs, biology provides the materials, not just the metaphor. This is a new direction we're pushing in biorobotics."
Skeletal muscle, which needs external stimuli to flex, was chosen as the ideal basis for the future biorobot because it is stronger than the two other major muscle groups, cardiac and smooth -- examples of skeletal muscles in humans include those used during vigorous exercise, including the biceps and the sartorius (which runs down the thigh to help it bend and turn). The team considered stimulating the muscle with electrodes, but wanted a less invasive approach that would not call for adding too much apparatus to a robot. Taking inspiration from optogenetics, which uses light to stimulate neural activity, the team set about investigating how they could manipulate the skeletal tissue -- repeated experiments had already shown that the cells in cardiac muscles will respond to light, but trials had not been successfully carried out on other tissue.
After genetically modifying skeletal muscle cell cultures to produce light-activated proteins, the team introduced them to muscle fibres. They found that once the fusion was complete, 20-millisecond bursts of blue light could be focused to stimulate just one fibre, or a group of fibres, demonstrating the type of exacting control someone could one day exert on a biorobot covered in the light-stimulated tissue.
The group then grew the genetically-altered muscle fibres with a hydrogel solution to create fully-formed muscle tissue, which performed in the same manner when light was administered.
In what surely looked like the most gruesome gym workout ever devised, the team secured strips of muscle to the two flexible posts of a micromechanical chip and watched as it bent the posts inwards when stimulated with light. This method, Asada says, will strengthen the muscle tissue even further in the lab, before it is then fused to a robot in the future.
"Like bedridden people, its muscle tone goes down very quickly without exercise," he said.
Though the movement the tissue is exhibiting is in a very small range, under one millimetre, Asada points out "there's no actuator that can do that kind of job right now."
Before they start on building a menagerie of lifelike robot animals, the team has suggested it will focus on manipulating the muscle to create an endoscopic device that can effectively travel through the body, lighting the way. It could also be used to help investigate the effectiveness of drugs for motor-related diseases.