Roboticists have for the first time built an automated computational system for controlling the movements of a living multicellular organism—a genetically engineered worm (Caenorhabditis elegans) whose muscles contract in response to blue light. The laser-guided nematode, described last week (June 30) in Science Robotics, is called RoboWorm.
“Most of the biohybrid microrobots [in development] are mainly based on bacteria,” says Li Zhang, a nanomaterials and microrobotics researcher at the Chinese University of Hong Kong who was not involved in the research. But in this study, “they propose the use of C. elegans, a worm, as a robotic agent . . . [in a] very interesting and smart way.”
The natural world is an endless source of inspiration for human feats of engineering, and nowhere is that more apparent than in the field of robotics. Animals have inspired the way large robots walk, fly, and swim, while at the microrobotic scale, roboticists are employing actual living cells and microorganisms to perform computer-controlled tasks such as magnetized bacteria that can ferry drugs or neutrophils that can be directed into tumors. Now, engineer Xinyu Liu of the University of Toronto and colleagues have gone a step further by converting an entire living multicellular organism into a controllable biological microrobot.
That organism, C. elegans, is a free-living nematode worm approximately 1 mm in length that resides in soil and is an extensively studied model organism in laboratories around the world. Liu says he does not have a particular application in mind for RoboWorm; rather, its creation was a “conceptual demonstration.” But it may inspire further microrobotic developments. Indeed, says Zhang, while C. elegans does not live in humans, it has close parasitic relatives that do, and perhaps future versions of RoboWorm could have biomedical uses.
To generate RoboWorm, Liu’s team used a genetically engineered strain of C. elegans in which the muscle cells produce a light-responsive ion channel called channelrhodopsin. When the worm’s muscles are illuminated with a blue laser, the channels open, calcium ions flood into the cells, and the contraction machinery is activated. The worm’s own neuromuscular signals were first deactivated with an antiparasitic drug called ivermectin that paralyzes the animal. Essentially, they disconnected the worm’s internal controls to stop them from interfering, explains engineer Sylvain Martel of the Polytechnique Montréal who did not participate in the study.
To direct locomotion as opposed to random muscle contractions, the team first analyzed natural worm movements and muscle activity under a microscope. Based on these studies, they determined how to target the worm’s body—using a specialized microscope that could deliver precisely patterned laser beams—so as to activate specific muscles in specific patterns. Scanning this laser pattern down the length of the worm led to a wave of muscle contractions that drove the worm forward in its characteristic S-shape, or sinusoidal, movement.
The team then fully automated the RoboWorm guidance system. Image processing algorithms tracked the animals’ movements in real time and fed the data back to the algorithms that controlled the laser position and beam patterns. In this way they could drive the worms forward, backward, and—by altering the intensity of certain laser beams and therefore the strength of particular muscle contractions—steer the animals through gradual or sharp curves and even make them double back. As an ultimate test of the automated system and the worms, the team programmed the computer to guide the worms through a maze.
While biomedical applications may be “too far away to envision” right now, Liu says he thinks that the system will be useful for studying the natural biology of locomotion in nematodes, as well as for aiding the design of future microrobots.
RoboWorm “provides a new avenue, a new possibility for researchers to advance the field of microrobotics,” says Martel. “This is very welcome . . . [and has] very exciting potential.”