Caitlin Stier, video intern
A colour-changing gel driven by a classic chemical reaction can now be resuscitated by adding pressure after the reaction has stabilised. Developed by Irene Chou Chen, a graduate student at the Massachusetts Institute of Technology, it's the first time oscillations in a responsive gel have been revived by a mechanical trigger.
When the metal-containing gel interacts with the solution around it, it flips between an orange and more positively charged green state in a Belousov-Zhabotinsky (BZ) reaction. By adding bromide, the self-oscillating system stabilises. But the video above shows how the trippy colours can be revived by adding pressure. Like wringing out a sponge, the compression depletes the solution sopped up in the gel, offsetting the balance between the reactants and restarting the reaction.
The video also shows how the gel can communicate pressure points, allowing the reaction to spread to neighbouring areas. In the first clip, compressing the smile also causes the eyes to change colour. However, this only works if the gel segments are close enough together. In the second clip, the reaction is limited to the smile because the eyes are too far away.
Smart gels usually employ acidity levels or chemical changes to incite a reaction but this work shows that a mechanical trigger can do the trick as well. The group, led by materials scientist Krystyn Van Vliet in collaboration with colleagues at the University of Pittsburgh in Pennsylvania, is looking into using these gels as pressure sensors that could mimic wound healing. A synthetic self-healing system would detect an injury and initiate a chemical response to repair it. The gel could also be used to fashion muscles for robots.
The research, funded by the National Science Foundation, will be published in an upcoming issue of Advanced Functional Materials.
If you enjoyed this video, check out a magnetic gel that can swim and walk or see a creeping gel powered and controlled by an oscillating chemical reaction.
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