Chemical reactions set soft materials in motion

Before life evolved nerves and humans built electric circuits, motion arose with chemistry. In the earliest organisms, waves of reacting molecules rippled through soft tissues and coordinated movement without any central control. Researchers at the University of Pittsburgh have now captured that process in synthetic form, modeling a soft material that moves and organizes itself through chemical reactions alone (PNAS Nexus 2025, DOI: 10.1093/pnasnexus/pgaf330).

Chemical engineer Anna C. Balazs and research assistant Oleg E. Shklyaev designed a computer model of a soft, continuous network of enzyme-coated microscopic beads linked by flexible connectors and immersed in a chemical fluid that transforms chemical energy directly into motion.

Each bead acts as a tiny chemical oscillator where enzymes drive a reaction network called a repressilator, a three-component feedback loop in which one chemical suppresses the next in sequence. This cycle generates rhythmic waves of chemical concentration that travel through the fluid and produce small-scale density gradients that stimulate motion. The motion leads to fluid flows that tug on the elastic links and make the structure bend and move—a direct conversion of chemistry to mechanics.

Balazs says that the result is “a material that can take in a chemical and turn it into mechanical work, like eating a hamburger and raising your hand.” Once the reaction starts, the motion is entirely self-contained. Balazs compares it to a beating heart—driven by chemical cycles that continuously turn fuel into motion.

In the computer model, waves of chemical reactions ripple through the network, creating coordinated motion like the rhythmic pulses that enable a jellyfish to swim. Guided by a nerve net rather than a brain, jellyfish move through distributed control—the same principle this chemical system captures. “But jellyfish are still way too evolved,” Shklyaev says. “This is a much simpler system, using chemical reactions instead of nerves.”

“The real importance of the work lies in its significance to living systems,” says Ayushman Sen, a chemist at Penn State not involved in the research. The work could shed light on the process that lets living systems turn chemical reactions into movement, known as chemo-mechanical transduction, that governs effects such as muscle contractions and cell motion. “Living systems involve chemo-mechanical transduction at all levels,” Sen adds. Balazs says the process is not well understood. In the future, the team wants to create more-sophisticated systems that may help reveal how such processes really work.

Long term, chemo-mechanical materials could inspire soft robots or biocompatible devices that operate without electronics. Because enzymes are naturally occurring and nontoxic, similar systems could in principle function inside the body: drawing power from ambient chemicals instead of batteries. Balazs also envisions chemical computer networks performing simple logic operations the way neurons or electronic gates do, but with molecular signals instead of electric ones.

“Right now, the reactions are slow,” Shklyaev says. “But we’re not competing with electronic computers.” Still, Balazs adds, systems like these [chemical computers] may one day find uses scientists can’t yet imagine: “When you invent a new kind of machine, its most interesting applications often come later.”