Engineers Build Chemically Driven Wheels That “Morph” Into Gears To Carry Out Mechanical Work

Switching Gears Into Chemical Machines

Teeth are one of the oldest mechanical devices in human history1 leading to machines ranging from irrigation systems and clocks, to modern machines and robotics. For the first time, researchers at the University of Pittsburgh Swanson School of Engineering have taken advantage of a catalytic reaction that results in a two-dimensional, chemically-coated sheet “morph” into a three-dimensional device that performs a robust task.

The findings suggest the possibility of developing chemically driven machines that do not rely on external forces, but simply need to add reactants to the surrounding solution. Published on December 18, 2020, in the journal Cell Press case, research developed by Anna C. Balazs, Distinguished Professor of Chemical and Petroleum Engineering and John A. Swanson Head of Engineering. The lead author is Abhrajit Laskar and the author’s friend is Oleg E. Shklyaev, both doctoral candidates.

Spectra-temporal control of Rotors

Animation of simulation shows control of spatio-temporal rotors by cascade reaction. The GOx (magenta) coated rotor is on the left side of the room, while the CAT (green) coated rotor is on the right side. The background color map shows the spatial distribution of H2O2 in solution at y = 3mm for side view and at z = 0.4 mm for top view. The introduction of D-glucose in solution activates the coated-GOx rotor, which morphs into a 3D structure and begins to rotate spontaneously. CAT-coated rotors remain flat and stationary. H2O2 is produced by the first reaction, which is the first step of the cascade reaction. In the presence of H2O2, the CAT-coated rotor becomes active and begins to rotate, while the coated-GOx rotor becomes flat and stays like glucose in its solution. Over time, the H2O2 in the solution is also depleted and as a result, the rotor movement coated with CAT stops and the sheet becomes flat. Credit: A. Laskar

“Gears help give machines mechanical life; however, they require some type of external power, such as steam or electricity, to perform a task. This limits the potential for future engines to operate in poorly resourced or remote environments,” Balazs explained. “Abhrajit’s computational model has shown that chemo-mechanical transmission (conversion of chemical energy into motion) in an active sheet presents a novel way of mimicking dental behavior in the environment without access to traditional power sources.”

In the simulation, the catalyst is placed at several points on a two-dimensional sheet that resembles a wheel with a fingertip, with heavier points around the sheet. Flexible sheets, about a millimeter long, are then stored in a liquid-filled micro-space. The reactants are inserted into a space that activates the catalyst on a flat “wheel”, causing the liquid to flow spontaneously. The flow of inner fluid pushes the lighter part of the sheet to appear, forming an active rotor that captures the flow and rotation.

Gearing Up Chemical Machinery

The animation of the simulation shows the dynamics of CAT-coated flexible sheets in H2O2 solution. CAT does not move the sheets degrading H2O2 in the host solution for lighter products (water and oxygen), resulting in spontaneous fluid flow. This fluid flows under the fluidic domain running a 2D flexible sheet to appear in the center (lighter than the edge node), forming an ideal 3D structure (see side view), which captures its flow and rotates clockwise. Credit: A. Laskar

“What is really typical of this research is the coupling of deformation and propulsion to change the shape of the object to create movement,” said Laskar. “Object deformation is key; we see naturally the organism uses chemical energy to change its shape and motion. For a chemical sheet we can move, it must also spontaneously morph into a new shape, which allows it to capture fluid flow and perform its functions.”

In addition, Laskar and Shklyaev found that not all parts of the equipment needed to be chemically active for movement; in fact, asymmetry is essential for creating motion. By judging the placement design rules, Laskar and Shklyaev can direct the rotation to be clockwise or clockwise. This added “program” allows the operator of independent rotors to move sequentially or under the influence of cascade, with an active and passive gear system. This more complex action is controlled by the internal structure of the spokesperson, and its placement within the fluid domain.

Motion Gear some

Transmission of rotational motion from active gear to two passive gears. In fluidic space, the active device can rotate several passive gears, which are stored to disrupt the symmetry of the flow field. Credit: A. Laskar

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

In the future, Balazs will examine how the relative spatial organization of multiple gears can lead to greater functionality and potentially design a system that seems to act as a decision maker.

“The farther the machine is out of human control, the more you need the machine alone to give control to complete the task that has been assigned,” said Balazs. “The chemo-mechanical nature of our equipment allows that to happen without an external power source.”

This standalone tool is the latest evolution of the chemo-mechanical process developed by Balazs, Laskar, and Shklyaev. Other advances include creating sheets such as crabs that mimic feed, flight, and combat responses; and sheets like “flying carpets” that wrap, cover, and creep.

References: “Self-Morphing, Gears Driven and Chemical Machines” by Abhrajit Laskar, Oleg E. Shklyaev and Anna C. Balazs, December 18, 2020, case,
DOI: 10.1016 / j.matt.2020.11.04

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