Scientists at Tampere University in Finland have trained a strip of plastic to move on its own by responding to light. This is the first time that thermoplastic, a synthetic actuator, has learned how to walk without computer programming. The team published their findings on December 4, 2019, in the journal Matter.
Exposing the plastic strip to light causes it to move. The team had to condition it so that it would be able to respond the same way as it does from heat. (Image Credit: Aalto University, Tampere University, Cell Press)
The plastics used in this project are made from thermo-responsive liquid crystal polymer networks that have been coated with dye and can convert energy into mechanical motion. At first, the soft actuators were only able to respond to heat, but it can now respond to light since it’s associated with heat. The actuator is flexible and can bend itself easily. When light is beamed onto the actuator and heats up, it “walks” similarly to a worm, moving at a speed of 1mm/s.
The project was inspired by Pavlov’s experiments on his dogs. During his experiments, Pavlov’s dogs would start salivating whenever they saw food. For those who don’t know - Pavlov then rang the bell before giving the dog food, which was repeated numerous times until the dogs salivated at the sound of the bell. This was caused from associating the sound of the bell with food. By using this analogy, the team conditioned the plastic strip to associate light with heat.
Professor Arri Priimägi exposed the plastic strip to heat and light at the same time to condition the plastic. Afterward, the strip was only exposed to light, which caused it to respond the same way as it would when exposed to heat. The conditioned strip then curled up whenever light was directly beamed on it and uncurled when the light was removed. The shape of the plastic allows it to move forward instead of staying in one place.
The team will be looking to make the system more complex and functional, which will help them to discover limits of analogies that can be used in a biological system. The current system is capable of doing more than just walking. The team has taught the strips to grab onto objects and in the future, it will be able to respond to different wavelengths of light that correspond to the coating of its dye. This allows the plastic strip to be turned into a lightweight robot that won’t need to carry a power supply and can be controlled from a distance by using light. This could be very useful in biomedical applications.
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