“It all started with a challenge that had languished in the robotics community for four decades: how to create a fully autonomous system that was smaller than a millimeter. The team at the University of Pennsylvania and the University of Michigan have now shattered this challenge by revealing the world’s smallest fully programmable and autonomous robots, microscopic swimmers that can sense, decide, and act independently.”
1. Breaking the Sub-Millimeter Barrier
Each robot is about 200 × 300 × 50 micrometers in size smaller than a grain of salt and scales down with microorganisms. “We have created robots 10,000 times smaller than ones that are autonomous,” declared Marc Miskin, the Penn Integrates Career Faculty in Electrical and Systems Engineering. In this size regime, the effects of friction and viscosity are most pronounced: “The viscosity of water approaches the viscosity of tar.” “The limbs would not work. Propellers wouldn’t work,” Miskin continued.
2. Electrokinetic Propulsion Without Moving Components
“The propulsion system developed by Penn’s team uses an electric field to gently push ions in the surrounding liquid,” she said. “These ions in turn push water molecules near them, propelling the robot.” “In essence, the robot appears to swim in a ‘moving river’, but the robot itself ‘makes the river move,” she added. The system has no moving components, so the robots are very robust, allowing them to be transported from sample to sample easily using a micropipette, with the ability to swim for months using light.”
3. Ultra-Low-Power Computing at Microscopic
“Autonomy requires onboard processing.”David Blaauw’s group at Michigan, world record-holding builders of the world’s smallest computer, modified their microprocessor to be no larger than this nanorobot’s fractional millimeter footprint. The solar cells that energize it now pump only 75 nanowatts, 100,000 times less than a smartwatch’s energy budget; that’s a 1,000-fold reduction in usage. The memory issues were overcome by breaking down complex propulsion algorithms into a series of individual instructions that are only a few cycles long.
4. Sensing and Environmental Response
The robots also incorporate temperature sensors with a resolution of 0.3°C, allowing them to migrate to warmer areas or provide temperature information as an indirect measure of cell activity. Information transfer between robots uses a “waggle dance” conveyed through their patterns of movement, which scientists unscramble through a microscope.
5. Light-Based Programming and Unique Addresses
Power and programming rely on the same medium, which is light. The bursts of light from both the LEDs are necessary for powering the robots and carrying out instructions. They both have a special identifier, which makes it possible to program them individually, and this is essential when the robots are supposed to work together. It is possible to set up the programming system for as low as $100, using standard LEDs, a raspberry Pi, and a smartphone camera equipped with a macro lens.
6. Medical and Industrial Applications
Scales at the cell level provide opportunities for cell health monitoring, targeted drug delivery, and device fabrication. Similar works carried out by the Chinese Academy of Sciences have shown the ability of multi-material microrobots to grasp or transport single cells, showing the possibility of manipulation integrated with autonomous navigation.
7. Overcoming Current Limitations
The current prototypes work in a hydrogen peroxide solution, which is cytotoxic, and they lose memory when the light is turned off. Improvements include the development of biocompatible actuators and energy sources for in vivo applications. As Miskin pointed out, the actuators can be changed arbitrarily when the voltage and current ratings are the same, somedical-grade actuators could be developed.
8. Physics of Micro-Scale Locomotion
In these regards, propulsion efficiency depends upon the handling of ion currents and friction. For electrokinetic designs, there is compatibility with onboard technology, the use at low voltages, and the ability to function over periods of months. There is propulsion at speeds no greater than one body length per second, and when grouped, the action is akin to fish school behavior.
9. Future Development Pathways
The platform’s current use is general-purpose: “scalable fabrication,” “low-cost electronics,” and “adaptable propulsion.” Future designs may offer increased sensors beyond the camera, higher capacity to store complex programs, faster speed, and operation under more extreme conditions. Onboard memory capacity will expand proportionally to more advanced process generations and may offer thousands of lines of code. Such robots, which cost only a penny each when produced in large quantities, are a revolution in and of itself in the realm of micro-scale robots. “This is very much the first chapter,” said Miskin. “Once you have this foundation established, you can build all sorts of intelligence and functionality right on top.”