Researchers Develop World's First Microscopic Autonomous Robot, Smaller Than A Grain Of Salt

Hyderabad: Researchers at the University of Pennsylvania and the University of Michigan have created microscopic swimming robots, measuring smaller than a grain of salt at 200 x 300 x 50 micrometres, capable of monitoring the health of individual cells. Almost visible to the naked eye, these robots are powered by light and can be programmed to move in complex patterns by sensing local temperatures, making them the world's smallest fully programmable autonomous robots that can not only operate at the scale of many biological microorganisms but can also help construct microscale devices.

The way these microscopic robots move is akin to swimming. However, unlike aquatic creatures like fish that move by pushing the water behind them, these robots don't flex their bodies but generate an electrical field that nudges ions in the surrounding solution, which in turn push on nearby water molecules and pushing them forward, based on Newton's Third Law of Motion, where the water exerts an equal and opposite force on the robot.

Electrokinetic propulsion for microrobots. (A) Schematic of the electrokinetic mechanism. (B) Optical image of a silicon chip with hundreds of robots on it. (C) Micrograph of a 4 PV design with Ti/Pt electrodes at both ends of the device’s SiO2 body. (D) Montage of a device moving under global microscope illumination in solution. (Lucas C Hanson, William H Reinhardt, Scott Shrager, Tarunyaa Sivakumar, Marc Z Miskin via PNAS)

Since the robots can adjust the electrical field causing the effect, they can move in complex patterns and even travel in coordinated groups at a speed of up to one body length per second, which comes down to 300 micrometres per second based on their size. The electronic sensors allow the robots to detect the temperature within a third of a degree Celsius, enabling them to monitor the health of individual cells and move towards areas of increasing temperature.

According to the research paper, titled Electrokinetic propulsion for electronically integrated microscopic robots, the robots are extremely durable since they don't have any moving parts. Also, they aren't very expensive as they can keep swimming for months on end, charged by the glow of an LED.

Addressability and swarming behavior enabled by circuits. (A and B) The control program can be given a list of target positions in order to guide each robot to its nearest waypoint. (C) Robots can be assigned individual lists of waypoints in order to trace out separate paths in unison. (D) Waypoints can also be dynamic and change at each timestep. Shown in blue, “follower” robots are assigned the location of another robot in the system as a waypoint. This rule results in chain-like structures following the “leader,” shown in red. (Lucas C Hanson, William H Reinhardt, Scott Shrager, Tarunyaa Sivakumar, Marc Z Miskin via PNAS)

To make the robots truly autonomous, it required a computer to make decisions, electronics to sense its surroundings and control its propulsion, and tiny solar panels to power everything. This is where the University of Michigan's tiny electronic computers came into play. They developed special circuits that operate at extremely low voltages, bringing down the computer's power consumption by more than 1000 times. Working together with the University of Pennsylvania, they crammed the processor and memory to store a program in the little space that remained after installing the solar panel that occupied the majority of the space on the robot.

The end result became the first microscopic robot that can sense and act for itself, powered by a true computer.

These robots are programmed by pulses of light that also power them. Individual robots hold a unique address, allowing researchers to load different programmes on each robot.

Researchers explain that the future versions of the robots could store more complex programmes, move faster, integrate new sensors, and may even operate in more challenging environments. This opens doors for the robot to be customised for different applications.