The gear is one of the oldest mechanical tools and led to machines ranging from early irrigation systems and clocks, to modern engines and robotics. Anna C. Balazs — Distinguished Professor of Chemical and Petroleum Engineering and the John A. Swanson Chair of Engineering — and her researchers have utilized a catalytic reaction that causes a two-dimensional, chemically coated sheet to spontaneously “morph” into a three-dimensional gear that performs sustained work.
The findings indicate the potential to develop chemically driven machines that do not rely on external power but simply require the addition of reactants to the surrounding solution. Computational modeling has shown that chemo-mechanical transduction (conversion of chemical energy into motion) at active sheets presents a novel way to replicate the behavior of gears in environments without access to traditional power sources.
In the simulations, catalysts are placed at various points on a two-dimensional sheet resembling a wheel with spokes, with heavier nodes on the sheet’s circumference. The flexible sheet, approximately a millimeter in length, is then placed in a fluid-filled microchamber. A reactant is added to the chamber that activates the catalysts on the flat “wheel,” thereby causing the fluid to spontaneously flow. The inward fluid flow drives the lighter sections of the sheet to pop up, forming an active rotor that catches the flow and rotates.
In nature, organisms use chemical energy to change their shape and move. For the new chemical sheet to move, it also has to spontaneously morph into a new shape, which allows it to catch the fluid flow and perform its function.
The team found that not all the gear parts needed to be chemically active for motion to occur; in fact, asymmetry is crucial to create movement. By determining the design rules for the placement, the researchers could direct the rotation to be clockwise or counterclockwise. This added “program” enabled the control of independent rotors to move sequentially or in a cascade effect, with active and passive gear systems. This more complex action is controlled by the internal structure of the spokes and the placement within the fluid domain.
In the future, the researchers will investigate how the relative spatial organization of multiple gears can lead to greater functionality, potentially designing a system that appears to act as if it were making decisions.