Chemical reactions used to create self-folding microscale origami machines

A team led by Nicholas Abbott, a Tisch University Professor in the Robert F. Smith School of Chemical and Biomolecular Engineering at Cornell, along with Itai Cohen, Paul McEuen, and David Muller, has developed a method to create self-folding microscale origami machines using chemical reactions. This allows the machines to operate in dry environments and at room temperature, freeing them from the liquids they typically require.

The team’s research, “Gas-Phase Microactuation Using Kinetically Controlled Surface States of Ultrathin Catalytic Sheets,” was published in Proceedings of the National Academy of Sciences. The goal is to use this approach to develop tiny, autonomous devices that can quickly respond to changes in their chemical environment. While electric motors can effectively transduce electrical to mechanical energy, options for direct chemical to mechanical transduction are limited. The paper’s co-lead authors are Nanqi Bao and Qingkun Liu.

Reversible actuation of a SCA during cycles of exposure to a O2-H2 mixture (10:1) and H2 at room temperature (real time). Credit: Proceedings of the National Academy of Sciences (2023). DOI: 10.1073/pnas.2221740120

Previous attempts to use chemical reactions for microscale machines relied on extreme conditions like high temperatures exceeding several hundred degrees Celsius. Additionally, the reactions were often slow, sometimes taking up to 10 minutes, which made them impractical for everyday use. However, Abbott’s group discovered a solution by analyzing data from a catalysis experiment. They found that a small portion of the chemical reaction pathway contained both slow and fast steps. By focusing on the rapid steps, they could operate the chemical actuator and ignore the slower ones. This allowed the microscale machines to fold autonomously in a bent state, which was more extreme than either of the two end states. The new method offers a promising avenue for the creation of autonomous devices that can quickly respond to their environment. The paper’s lead authors are Nanqi Bao and Qingkun Liu.

To leverage the rapid kinetic moment in their chemical actuator, the researchers employed ultrathin platinum sheets coated with titanium, a material platform developed by McEuen, Cohen, and Muller. The team collaborated with theorists from the University of Wisconsin, led by Professor Manos Mavrikakis, who used electronic structure calculations to understand the chemical reaction that occurs when hydrogen reacts with oxygen on the material. By exploiting the moment when oxygen strips hydrogen, the material deforms and bends like a hinge. The actuator cycles every 600 milliseconds and can function at room temperature and in dry environments. This technique is generalizable to other catalytic metals like palladium and palladium-gold alloys. The researchers anticipate developing autonomous material systems, where onboard computation and controlling circuitry are integrated into the material’s response. This breakthrough opens the door to creating microscale origami machines that operate in gaseous environments, exciting Cohen and the team.

Source: Cornell University

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