Engineers build chemically driven wheels that “turn” into gears to perform mechanical work

2A₂ in solution at y = 3 mm for side view and at z = 0.4 mm for top view. The introduction of D-glucose into the solution activates the GOx-coated rotor, which transforms into a 3D structure and begins to rotate spontaneously. The CAT-coated rotor remains flat and stationary. H₂A₂ it is produced by the first reaction, constituting the first step of the cascade reaction. In the presence of H₂A₂, The CAT-coated rotor becomes active and begins to rotate, while the GOx-coated rotor becomes flat and stationary as the glucose in the solution is depleted. In time, H₂A₂ the solution is depleted and therefore the movement of the CAT-coated rotor stops and the sheet becomes flat. Credit: A. Laskar “width =” 600 “height =” 480″/>

The gear is one of the oldest mechanical tools in human history and has led to machines ranging from early irrigation systems and clocks to modern and robotic engines. For the first time, researchers at Swanson School of Engineering at the University of Pittsburgh used a catalytic reaction that causes a two-dimensional, chemically coated sheet to spontaneously “transform” into a three-dimensional gear that does 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. Published today in the journal Cell Press Material, the research was developed by Anna C. Balazs, Distinguished Professor of Chemical and Petroleum Engineering and John A. Swanson Department of Engineering. The lead author is Abhrajit Laskar and the co-author is Oleg E. Shklyaev, both postdoctoral fellows.

“Gears provide a mechanical life for machines; however, they require some kind of external energy, such as steam or electricity, to perform a task. This limits the potential of future machines to operate in low-resource or remote environments.” Balazs explains. “Abhrajit’s computer modeling has shown that chemical-mechanical transduction (conversion of chemical energy into motion) to active sheets presents a new way of reproducing the behavior of tools in environments without access to traditional energy sources.”

2A₂ solution. CAT immobilized on sheet decomposes H₂A₂ in the host solution to lighter products (water and oxygen), thus producing spontaneous flows of liquids. These fluid flows at the bottom of the fluid domain lead the 2D flexible sheet to appear in the center (lighter than the edge nodes), forming an ideal 3D structure (see side view), which catches the flow and rotates clockwise. . Credit: A. Laskar”/>

In the simulations, the catalysts are placed at different points on a two-dimensional sheet similar to a spoke wheel, with heavier knots on the circumference of the sheet. The flexible sheet, about one millimeter long, is then placed in a microcamera filled with liquid. A reactant is added to the chamber which activates the catalysts on the flat “wheel”, thus causing the fluid to flow spontaneously. The internal flow of fluid leads to lighter sections of the sheet to appear, forming an active rotor that catches the flow and rotates.

“What is really distinctive about this research is the coupling of deformation and propulsion to change the shape of the object to create motion,” says Laskar. “Deformation of the object is essential; we see in nature that organisms use chemical energy to change their shape and move. In order for our chemical sheet to move, it must spontaneously transform into a new shape, which allows it to catch fluid flow and perform its function. “

In addition, Laskar and Shklyaev found that not all gear components need to be chemically active for movement to occur; in fact, asymmetry is crucial to creating movement. By determining the design rules for placement, Laskar and Shklyaev could direct the rotation clockwise or counterclockwise. This added “program” allowed the control of independent rotors to move sequentially or in cascade, with active and passive transmission systems. This more complex action is controlled by the internal structure of the spokes and the placement in the fluid domain.

“Because a gear is a central component of any machine, you have to start with the basics, and what Abhrajit created is like a millimeter-scale internal combustion engine,” says Shklyaev. “While this will not power your car, it has the potential to build the basic mechanisms for driving small-scale chemical machines and soft robots.”

In the future, Balazs will investigate how the relative spatial organization of multiple gears can lead to greater functionality and potentially the design of a system that appears to act as if it were making decisions.

“The further away a car is from human control, the more you need the car itself to provide control to perform a given task,” Balazs said. “The chemical-mechanical nature of our devices allows this to happen without any external source of energy.

These self-transformation tools are the latest evolution of the chemical-mechanical processes developed by Balazs, Laskar and Shklyaev. Other advances include the creation of crab-type sheets that mimic feeding, flying, and fighting responses; and “flying carpet” -like sheets that wrap, flap, and strain.