Canadian scientists have built a computer system that can specifically control the movements of a genetically modified nematode (Caenorhabditis elegans) with laser pulses. The – living – worm becomes a kind of zombie biorobot. With the one in the journal Science Robotics featured work Xianke Dong and colleagues say that they are not targeting “any particular application”. However, the work enables progress in the study of the motion control of living beings on the one hand and further progress in the development of micro-robots for medical applications on the other.
The nematode Caenorhabditis elegans is mainly used in developmental biology and genetics because it has a simply structured, well-documented nervous system. The worm, which grows to around a millimeter long and around 65 micrometers thick, usually lives in the soil and feeds on bacteria. To create the RoboWorm, Dong and colleagues used a genetically modified strain of C. elegans in which the muscle cells have ion channels that respond to light. When the worm’s muscles are illuminated with a blue laser, the channels open, calcium ions flow into the cells, and the muscles contract. At the same time, the researchers paralyzed the worm’s neuromuscular signals with an anti-parasitic drug.
To control the worm’s locomotion, the researchers then illuminated the worm’s sides in sections so that the animal curved in a characteristic S-shaped manner. If you let the contractions run over the side at different times, the worm snakes forward.
Laser through the labyrinth
However, because the movement of the animals is too irregular, the necessary phase shift between the contractions cannot simply be modeled with a mathematical function. The researchers therefore built feedback into their system: software with image processing tracks the animals’ movements and controls the laser position and the light pattern.
In this way, the researchers were able to drive the worms forwards and backwards and – by changing the intensity of certain laser beams and thus the strength of certain muscle contractions – also around tight curves. To demonstrate the capabilities of their system, the researchers even steered worms through a simple plastic maze that was placed on an agar substrate.
In fact, Dong and his colleagues weren’t the first to use optogenetics to control worms. Back in 2011, a team from Harvard University showed one very similar work. However, at the time, the researchers working with Aravinthan DT Samuel concentrated on activating certain nerve cells in the nematode using laser light in order to trigger the desired behavior. For example, a neuron at the worm’s head reacts to touch – if the researchers activated this neuron with light, the worm began to crawl backwards. Another activated neuron even stimulated the worms to produce an egg.