Scientists have built microscopic, light-powered robots that can think, swim, and operate independently at the scale of living cells.

Researchers at the University of Pennsylvania and the University of Michigan have developed the smallest fully programmable autonomous robots ever made. These tiny machines can swim through liquid, sense and respond to their surroundings on their own, operate continuously for months, and cost roughly one penny apiece.

Each robot is nearly invisible without magnification. Measuring about 200 by 300 by 50 micrometers, they are smaller than a grain of salt. Because they function at the same scale as many microorganisms, the robots could eventually support new medical tools for monitoring individual cells and enable new manufacturing techniques for building extremely small devices.

The robots are powered by light and contain microscopic computers. They can be programmed to follow intricate movement patterns, detect temperature changes in their immediate environment, and alter their direction based on those readings.

Details of the work were published in Science Robotics and Proceedings of the National Academy of Sciences (PNAS). Unlike earlier small-scale machines, these robots do not rely on wires, magnetic guidance, or external joystick-style control. That independence makes them the first programmable robots at this size that can truly operate on their own.

“We’ve made autonomous robots 10,000 times smaller,” says Marc Miskin, Assistant Professor in Electrical and Systems Engineering at Penn Engineering and the papers’ senior author. “That opens up an entirely new scale for programmable robots.”

Why building tiny robots has taken so long
Over the years, electronic components have steadily shrunk, but autonomous robots have not followed the same trend. According to Miskin, shrinking robots below one millimeter while keeping them independent has remained an unsolved challenge. “Building robots that operate independently at sizes below one millimeter is incredibly difficult,” he says. “The field has essentially been stuck on this problem for 40 years.”

The difficulty lies in how physics changes at small scales. In everyday life, motion is shaped by forces like gravity and inertia, which depend on an object’s volume. At the size of a cell, surface-related forces such as drag and viscosity dominate instead. “If you’re small enough, pushing on water is like pushing through tar,” Miskin explains.

Because of this, traditional robot designs fail when scaled down. Limbs and joints that work for larger machines become fragile and impractical. “Very tiny legs and arms are easy to break,” says Miskin. “They’re also very hard to build.”

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