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Ultraviolet light makes a molecular ratchet wind polymer chains together, shrinking a gel; visible light switches a separate molecular component, releasing stored elastic energy so the chains unwind and the gel expands. The 2017 demonstration connected motion at the molecular scale to a centimeter-sized gel sample. Its “reverse gear” is shorthand: visible light triggers release and unwinding, not a motor simply turning backward.
What the nanomachines are—and what they do
The term “nanomachines” here refers to synthetic molecular machinery, not autonomous miniature robots. Nicolas Giuseppone and colleagues at the University of Strasbourg reported attaching light-responsive components to polymer chains and embedding those chains in a gel. The arrangement links molecular-scale changes to a visible change in the bulk material.
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The system has two functional components: a molecular ratchet that winds the chains, and a photoswitch that can hold or release the resulting tension.
The UV-driven ratchet contracts the gel
The ratchet is a sterically crowded alkene. UV light drives it to turn, winding the attached polymer chains around one another. The chains shorten as they wind, pulling the polymer network into a contracted state.
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A visible-light switch releases the tension
A second component, a dithienylethene photoswitch, has a cyclized, locked form that sustains tension created by the motor. Visible light changes it to an open-chain form. That unlocks the system, allowing elastic energy stored in the braided chains to drive their unwinding and the gel’s expansion.
Why “reverse gear” is not quite literal
The two light conditions do not operate as a conventional motor turning first one way and then backward. UV light powers the winding and contraction stage; visible light changes the modulator so stored elastic energy can be released. The expansion is therefore driven by the material’s stored energy after unlocking, rather than by a described reverse rotation of the ratchet.
The distinction matters when assessing what the system demonstrates: light controls both the loading of the polymer and the release of that load, but through different mechanisms.
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How large and fast was the reported movement?
Chemistry World’s 20 March 2017 report describes movement in a centimeter-sized gel sample, making the material-level change macroscopic even though the active components are molecular. It says the modulators took several hours to unwind a fully contracted piece of gel. These are descriptions reported in 2017, not a current performance specification or independently verified measurements of the primary study.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the demonstration does—and does not—establish
The reported result is light-controlled shrinking and expansion of a polymer gel. Chemistry World cited artificial muscles and incorporation into larger machines that move using light as possible future applications. Those are prospects, not devices shown in the report to have been built or made commercially available.
The report cites J. T. Foy et al., Nature Nanotechnology (2017), DOI 10.1038/nnano.2017.28. Its account also cites earlier related work on the motor component by Q. Li et al., Nature Nanotechnology (2015), 10, 161, DOI 10.1038/nnano.2014.315. The mechanism and performance details described here are limited to the Chemistry World report.
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