Cambridge, MA--Scientists at the Massachusetts Institute of Technology (MIT) and the University of Pennsylvania (Philadelphia, PA) are not only being inspired by nature through biomimetics, but are also now taking ingredients from nature. The researchers have genetically engineered muscle cells that flex in response to light, and are planning to use the light-sensitive tissue to build highly articulated robots. This approach is inspired by optogenetics—a form of phototherapy where materials/tissues are controlled by light and—says the research team—may one day enable robotic animals that move with the strength and flexibility of their living counterparts.
The research will appear in the journal Lab on a Chip and the technique is demonstrated in the following video (Courtesy MIT):
Harry Asada, the Ford Professor of Engineering in MIT's Department of Mechanical Engineering, says the group’s design effectively blurs the boundary between nature and machines. "With bio-inspired designs, biology is a metaphor, and robotics is the tool to make it happen," says Asada, who is a co-author on the paper. "With bio-integrated designs, biology provides the materials, not just the metaphor. This is a new direction we're pushing in biorobotics."
In deciding which bodily tissue to use in their robotic design, the researchers set upon skeletal muscle—a stronger, more powerful tissue than cardiac or smooth muscle. But unlike cardiac tissue, which beats involuntarily, skeletal muscles--those involved in running, walking and other physical motions--need external stimuli to flex. Normally, neurons act to excite muscles, sending electrical impulses that cause a muscle to contract. In the lab, researchers have employed electrodes to stimulate muscle fibers with small amounts of current. But Asada says such a technique, while effective, is unwieldy. Moreover, he says, electrodes, along with their power supply, would likely bog down a small robot.
Instead, the team looked to a relatively new field called optogenetics, invented in 2005 by MIT's Ed Boyden and Karl Deisseroth from Stanford University, who genetically modified neurons to respond to short laser pulses. Since then, researchers have used the technique to stimulate cardiac cells to twitch. The researchers cultured such cells, or myoblasts, genetically modifying them to express a light-activated protein. The group fused myoblasts into long muscle fibers, then shone 20-millisecond pulses of blue light into the dish. They found that the genetically altered fibers responded in spatially specific ways: Small beams of light shone on just one fiber caused only that fiber to contract, while larger beams covering multiple fibers stimulated all those fibers to contract.
The researchers tested the strength of the engineered tissue using a small micromechanical chip—designed by Christopher Chen at Penn—that contains multiple wells, each housing two flexible posts. The group attached muscle strips to each post, then stimulated the tissue with light. As the muscle contracts, it pulls the posts inward; because the stiffness of each post is known, the group can calculate the muscle’s force using each post's bent angle. The light-sensitive muscle tissue exhibits a wide range of motions, which may enable highly articulated, flexible robots–a goal the group is now working toward.
Rashid Bashir, a professor of electrical and computer engineering and bioengineering at the University of Illinois at Urbana-Champaign, says the group’s light-activated muscle may have multiple applications in robotics, medical devices, navigation and locomotion, and adds, "Development of ways to increase the forces of contraction and being able to scale up the size of the muscle fibers would be very useful for future applications."
In the meantime, there may be a more immediate application for both the engineered muscles and the microchip: screening drugs for motor-related diseases. Scientists could grow light-sensitive muscle strips in multiple wells, and monitor their reaction—and the force of their contractions—in response to various drugs.
This research was supported by the National Science Foundation, the National Institutes of Health, the RESBIO Technology Resource for Polymeric Biomaterials, the Center for Engineering Cells and Regeneration of the University of Pennsylvania, and the Singapore-MIT Alliance for Research and Technology.