These Robots Are the Size of Single Cells and Cost Just a Penny Apiece

The robots, each the size of a single cell, casually turn circles in a bath of water. Suddenly, their sensors detect a change: Parts of the bath are heating up. The microrobots halt their twirls and head for warmer waters, where they once again settle into lounge-mode—all without human interference.

For 40 years, scientists have tried to engineer ‘smart’ microrobots. But building microscopic machines that sense, learn, and act based on their programming has eluded researchers. Today’s most sophisticated robots, such as Boston Dynamics’ Atlas, already embody these functions using computer chips, algorithms, and actuators. The seemingly simple solution would be to simply shrink down larger systems, and voila, mission accomplished.

It's not so easy. The physical laws governing semiconductors and other aspects of robotics go sideways at the microscopic scale. “Fundamentally different approaches are required for truly microscopic robots,” wrote Marc Miskin and team at the University of Pennsylvania.

Their study, published last week in Science Robotics, packed the autonomous abilities of full-sized robots into microrobots 10,000 times smaller—each one roughly the size of a single-celled paramecium. Costing just a penny per unit to manufacture, the bots are loaded with sensors, processors, communications modules, and actuators to propel them.

In tests, the microrobots responded to a variety of instructions transmitted from a computer workstation helmed by a person. After receiving the code, however, the bots functioned autonomously with energy consumption near that of single cells.

While just prototypes, similar designs could one day roam the body to deposit medications, monitor the environment, or make nanomanufacturing more adjustable.

Spooky Physics

Intelligent living “microrobots” surround us. Despite their miniature size and lack of a central brain, single-celled creatures are quick to sense, learn, and adapt to shifting surroundings. If evolution can craft these resilient microorganisms, why can’t we?

So far, the smallest robots that can sense, be reprogrammed, and move on command are at least bigger than a millimeter, or roughly the size of a grain of sand. Further shrinking runs into roadblocks based on fundamental physical principles.

Just as quantum computing departs from everyday physics—with one computational quirk famously called “spooky action at a distance” by Albert Einstein—the rules that guide computer chip and robotic performance also begin to behave differently at the microscopic scale.

For example, forces on a robot’s surface become disproportionately large, so the devices stick to everything, including themselves. This means motors have to ramp up their power, which swiftly exhausts scarce energy resources. Drag also limits mobility, like trying to move with a parachute in strong winds. Processors suffer too—shrinking down computer chips causes noise to skyrocket—while sensors rapidly lose sensitivity.

You can get around all this by controlling a bot’s movement externally with light or magnets, which offloads multiple hardware components. But this sacrifices “programmability, sensing, and/or autonomy in the process,” wrote the team. Such microrobots struggle in changing environments and can only switch between a limited number of coded behaviors.

Alternatively, you can weave functions directly into the materials so microrobots change their properties as the environment shifts. This also switches their computation. Most examples are soft and biocompatible, but they’re harder to manufacture at scale and often require expensive hardware to control, crippling real-world practicality.