Genetically engineered muscle tissue that flexes in response to light could one day be incorporated into robots, giving them the strength and flexibility of their living counterparts. “With bio-inspired designs, biology is a metaphor, and robotics is the tool to make it happen,” said MIT engineering professor Harry Asada, who co-authored a paper about the work along with colleagues at MIT and the University of Pennsylvania. “With bio-integrated designs, biology provides the materials, not just the metaphor. This is a new direction we’re pushing in biorobotics.” Asada and his team developed the approach using skeletal muscle, a stronger, more powerful tissue than cardiac or smooth muscle, but which needs external stimuli to flex. Current lab techniques that excite muscles with electrodes are unwieldy and could bog down a small robot. Instead, Asada’s team turned to the field of optogenetics, which uses short laser pulses to stimulate genetically modified neurons. The researchers wanted to be the first to do the same – use light as a stimulus – with skeletal muscle cells. They genetically modified myoblasts, or muscle cell, to express a light-activated protein, then fused the cells into long muscle fibers. Under 20-ms pulses of blue light, myoblasts in a dish responded in spatially specific ways. Light shone in large swaths affected all fibers in those areas, while light trained on specific fibers caused only those fibers to contract. Going a step further, Asada grew muscle fibers with a hydrogel mixture to form a 3-D muscle tissue and restimulated it with light. The muscle responded in much the same way as individual muscle fibers, bending and twisting in areas exposed to beams of light. The findings appeared in Lab on a Chip (doi: 10.1039/C2LC40338B). The strength of the engineered tissue was tested using a small micromechanical chip – designed by Christopher Chen at Penn – that contained multiple wells, each housing two flexible posts. Muscle strips were attached to each post, and the tissue was stimulated with light. As the muscle contracted, it pulled the posts inward; from each post’s bent angle, the muscle’s force could be calculated. Because the tissue exhibits a wide range of motion, the group is working toward using it in highly articulated, flexible robots. One potential robotic device may involve endoscopy. Asada said a robot made of light-sensitive muscle may be small and nimble enough to navigate tight spaces – even within the body’s vasculature. Although it will be some time before such a device can be engineered, the results are promising. “We can put 10 degrees of freedom in a limited space, less than one millimeter,” Asada said. “There’s no actuator that can do that kind of job right now.” The light-activated muscle may have applications in robotics, medical devices, drug screening and more.