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Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →In a 2017 laboratory demonstration, ultraviolet light made a polymer gel contract, while visible light released stored tension and let it expand again. The system linked light-responsive molecular machinery to polymer chains, so motion at the molecular scale could move a centimeter-sized piece of gel. Its “reverse gear” was not a motor simply spinning backward: the second light stimulus unlocked the material and let elastic energy drive the return.
How the gel changes shape
The system reported by Nicolas Giuseppone and colleagues at the University of Strasbourg used two molecular components attached to polymer chains embedded in a gel. One component drove contraction; the other held the strained chains in place and later released them.
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Ultraviolet light winds the chains
A sterically crowded alkene acts as a molecular ratchet. Under ultraviolet (UV) light, it turns and winds the attached polymer chains around one another. The chains shorten, pulling the polymer network into a contracted state.
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Visible light unlocks the strained material
A second component, a dithienylethene photoswitch, helps sustain the tension created by the winding. In its cyclized, locked form, it holds the strained configuration. Visible light changes it to an open-chain form, unlocking the system. The stored elastic energy then drives the chains to unwind, allowing the gel to expand.
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That is why “reverse gear” is a convenient shorthand rather than a literal description of the motor reversing direction. UV light drives the winding and contraction; visible light switches the lock and releases energy for unwinding and expansion.
How molecular motion moves a visible-sized material
A molecular motor rotating on its own would not necessarily move a useful object. Here, the machinery was coupled to polymer chains, and those chains were part of a gel. Their collective shortening and relaxation translated molecular-scale changes into a macroscopic shape change. Chemistry World described movement in a centimeter-sized gel sample.
The report also said that modulators took several hours to unwind a fully contracted piece of gel. That is the response time described in the 2017 account, not a current performance specification or a general figure for other light-responsive materials.
What the demonstration does—and does not—show
The reported result was light-controlled contraction and expansion of a polymer gel. Chemistry World presented artificial muscles and macroscopic machines that move using light as possible future applications, not as devices demonstrated or commercially available in that report.
Rank #2
- Demonstrated: UV-driven gel contraction and visible-light-triggered release and expansion.
- Not established by the report: a finished artificial muscle, a deployed machine, or a product available to buy.
- Important distinction: the return motion uses stored elastic energy released by switching; it is not described as the motor actively turning in reverse.
Why reversibility matters
For a molecular actuator to do useful work repeatedly, it needs a way to return to a starting state, not just produce one-way movement. Nathalie Katsonis, a researcher at the University of Twente who was not involved in the work, emphasized this broader challenge in Chemistry World: “If we want to go towards mechanised molecular matter we need to be able bring machines back to their initial state so they can produce work again and again.”
The report’s account establishes a light-triggered contraction-and-release cycle, but it does not provide a detailed cycle-life result or evidence of a finished working machine. Reversibility in this demonstration should not be taken as proof of long-term durability or practical performance.
Source and evidence limits
Chemistry World reported the work on 20 March 2017 and cited J. T. Foy et al., Nature Nanotechnology (2017), DOI 10.1038/nnano.2017.28. Its account also cites Q. Li et al., Nature Nanotechnology (2015), 10, 161, DOI 10.1038/nnano.2014.315, as related background on the motor component. The mechanism, scale, and response-time descriptions here reflect the Chemistry World report; they are not independent measurements from the primary papers.
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