Penn and UMich create world’s smallest programmable, autonomous robots
Smaller than a grain of salt, the light-powered bots can think, sense and act on their own, opening up new possibilities in manufacturing and medicine
University of Pennsylvania School of Engineering and Applied Science
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A microrobot, fully integrated with sensors and a computer, small enough to balance on the ridge of a fingerprint.view more Credit: Marc Miskin, University of Pennsylvania
Researchers at the University of Pennsylvania and University of Michigan have created the world’s smallest fully programmable, autonomous robots: microscopic swimming machines that can independently sense and respond to their surroundings, operate for months and cost just a penny each.
Barely visible to the naked eye, each robot measures about 200 by 300 by 50 micrometers, smaller than a grain of salt. Operating at the scale of many biological microorganisms, the robots could advance medicine by monitoring the health of individual cells and manufacturing by helping construct microscale devices.
Powered by light, the robots carry microscopic computers and can be programmed to move in complex patterns, sense local temperatures and adjust their paths accordingly.
Described in Science Robotics and Proceedings of the National Academy of Sciences (PNAS), the robots operate without tethers, magnetic fields or joystick-like control from the outside, making them the first truly autonomous, programmable robots at this scale.
“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.”
Breaking the Sub-Millimeter Barrier
For decades, electronics have gotten smaller and smaller, but robots have struggled to keep pace. “Building robots that operate independently at sizes below one millimeter is incredibly difficult,” says Miskin. “The field has essentially been stuck on this problem for 40 years.”
The forces that dominate the human world, like gravity and inertia, depend on volume. Shrink down to the size of a cell, however, and forces tied to surface area, like drag and viscosity, take over. “If you’re small enough, pushing on water is like pushing through tar,” says Miskin.
In other words, at the microscale, strategies that move larger robots, like limbs, rarely succeed. “Very tiny legs and arms are easy to break,” says Miskin. “They’re also very hard to build.”
So the team had to design an entirely new propulsion system, one that worked with — rather than against — the unique physics of locomotion in the microscopic realm.
Making the Robots Swim
Large aquatic creatures, like fish, move by pushing the water behind them. Thanks to Newton’s Third Law, the water exerts an equal and opposite force on the fish, propelling it forward.
The new robots, by contrast, don’t flex their bodies at all. Rather, they generate an electrical field that nudges ions in the surrounding solution. Those ions, in turn, push on nearby water molecules, animating the water around the robot’s body. “It’s as if the robot is in a moving river,” says Miskin, “but the robot is also causing the river to move.”
The robots can adjust the electrical field that causes the effect, allowing them to move in complex patterns and even travel in coordinated groups, much like a school of fish, at speeds of up to one body length per second.
And because the electrodes that generate the field have no moving parts, the robots are extremely durable. “You can repeatedly transfer these robots from one sample to another using a micropipette without damaging them,” says Miskin. Charged by the glow of an LED, the robots can keep swimming for months on end.
Giving the Robots Brains
To be truly autonomous, a robot needs a computer to make decisions, electronics to sense its surroundings and control its propulsion, and tiny solar panels to power everything, and all that needs to fit on a chip that is a fraction of a millimeter in size. This is where David Blaauw’s team at the University of Michigan came into action.
Blaauw’s lab holds the record for the world’s smallest computer. When Miskin and Blaauw first met at a presentation hosted by the Defense Advanced Research Projects Agency (DARPA) five years ago, the pair immediately realized that their technologies were a perfect match. “We saw that Penn Engineering’s propulsion system and our tiny electronic computers were just made for each other,” says Blaauw. Still, it took five years of hard work on both sides to deliver their first working robot.
“The key challenge for the electronics,” says Blaauw, “is that the solar panels are tiny and produce only 75 nanowatts of power. That is over 100,000 times less power than what a smart watch consumes.” To run the robot’s computer on such little power, the Michigan team developed special circuits that operate at extremely low voltages and bring down the computer’s power consumption by more than 1000 times.
Still, the solar panels occupy the majority of the space on the robot. Therefore, the second challenge was to cram the processor and memory to store a program in the little space that remained. “We had to totally rethink the computer program instructions,” says Blaauw, “condensing what conventionally would require many instructions for propulsion control into a single, special instruction to shrink the program’s length to fit in the robot’s tiny memory space.”
Robots that Sense, Remember and React
What these innovations made possible is the first sub-millimeter robot that can actually think. To the researchers’ knowledge, no one has previously put a true computer — processor, memory and sensors — into a robot this small. That breakthrough makes these devices the first microscopic robots that can sense and act for themselves.
The robots have electronic sensors that can detect the temperature to within a third of a degree Celsius. This lets robots move towards areas of increasing temperature, or report the temperature — a proxy for cellular activity — allowing them to monitor the health of individual cells.
“To report out their temperature measurements, we designed a special computer instruction that encodes a value, such as the measured temperature, in the wiggles of a little dance the robot performs,” says Blaauw. “We then look at this dance through a microscope with a camera and decode from the wiggles what the robots are saying to us. It’s very similar to how honey bees communicate with each other.”
The robots are programmed by pulses of light that also power them. Each robot has a unique address that allows the researchers to load different programs on each robot. “This opens up a host of possibilities,” adds Blaauw, “with each robot potentially performing a different role in a larger, joint task.”
Only the Beginning
Future versions of the robots could store more complex programs, move faster, integrate new sensors or operate in more challenging environments. In essence, the current design is a general platform: its propulsion system works seamlessly with electronics, its circuits can be fabricated cheaply at scale and its design allows for adding new capabilities.
“This is really just the first chapter,” says Miskin. “We’ve shown that you can put a brain, a sensor and a motor into something almost too small to see, and have it survive and work for months. Once you have that foundation, you can layer on all kinds of intelligence and functionality. It opens the door to a whole new future for robotics at the microscale.”
These studies were conducted at the University of Pennsylvania (Penn) School of Engineering and Applied Science, Penn School of Arts & Sciences, and the University of Michigan, Department of Electrical Engineering and Computer Science and supported by the National Science Foundation (NSF 2221576), the University of Pennsylvania Office of the President, the Air Force Office of Scientific Research (AFOSR FA9550-21-1-0313) the Army Research Office (ARO YIP W911NF-17-S-0002), the Packard Foundation, the Sloan Foundation and the NSF National Nanotechnology Coordinated Infrastructure Program (NNCI-2025608), which supports the Singh Center for Nanotechnology, and Fujitsu Semiconductors.
Additional co-authors include Maya M. Lassiter, Kyle Skelil, Lucas C. Hanson, Scott Shrager, William H. Reinhardt, Tarunyaa Sivakumar and Mark Yim of the University of Pennsylvania, and Dennis Sylvester, Li Xu, and Jungho Lee of the University of Michigan.
Journal
Science Robotics
Method of Research
Experimental study
Subject of Research
Not applicable
Article Title
Microscopic Robots That Sense, Think, Act, and Compute
Article Publication Date
10-Dec-2025
A microrobot on a US penny, showing scale.
Credit
Michael Simari, University of Michigan
A projected timelapse of tracer particle trajectories near a robot consisting of three motors tied together.
Credit
Lucas Hanson and William Reinhardt, University of Pennsylvania
The final stages of microrobot fabrication deploy hundreds of robots all at once. The tiny machines can then be programmed individually or en masse to carry out experiments.
Credit
Maya Lassiter, University of Pennsylvania
The robot has a complete onboard computer, which allows it to receive and follow instructions autonomously.
Credit
Miskin Lab, Penn Engineering; Blaauw Lab, University of Michigan
The robots, each smaller than a grain of salt, move by using an electrical field to manipulate the ions around them. They can sense temperatures, and could potentially advance medicine by monitoring the health of individual cells.
Credit
Bella Ciervo, Penn Engineering
Advanced microrobots driven by acoustic and magnetic fields for biomedical applications
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(A) Illustration of the soft microswimmer with a single microbubble. (B) Illustration of CeFlowBots with bubble arrays. (C) Illustration of the microbubble-aided microrobots. (D) Illustration of the Janus micromotors. (E) The starfish-inspired microrobot with an asymmetric cilia array.
view moreCredit: Xiaoming Liu, Beijing Institute of Technology.
Microrobots span dimensions from nanometers to sub-millimeters, can navigate biological fluids/tissues and localize to specific targets, and—owing to their miniaturization, untethered actuation, and multimodal locomotion—can access deep, narrow, and complex regions (e.g., vasculature and brain tissue) with minimal invasiveness, enabling broad prospects in targeted drug delivery, minimally invasive surgery, cell manipulation, and imaging. Yet propulsion and motion control at low Reynolds number remain fundamental challenges, motivating diverse external-field actuation schemes; while electric and optical approaches are constrained by potential cellular damage and limited tissue penetration, magnetic and acoustic actuation have attracted particular attention due to favorable biocompatibility and tissue penetration for in vivo use. Importantly, single-field paradigms exhibit intrinsic trade-offs: magnetic actuation offers precise controllability but suffers from limited propulsive force due to spatial field decay and increased system/fabrication complexity, whereas acoustic actuation provides strong propulsion and functional effects (e.g., cavitation and sonochemistry) but still struggles with accurate directional and 3D control and with the resolution–penetration trade-off. Accordingly, hybrid magneto-acoustic actuation—combining magnetic steering with acoustic propulsion/activation—has emerged as a systematic solution and a growing research focus. “In this article, we provide a comprehensive overview of hybrid magneto-acoustic microrobots, covering their actuation mechanisms, representative structural designs, biomedical applications, and key challenges and future directions.” said the author Xiaoming Liu, a researcher at Beijing Institute of Technology.
The working mechanisms of hybrid magneto-acoustic microrobots can be broadly divided into two categories: (i) magnetic steering with acoustic propulsion, where magnetic responsiveness (e.g., via embedded magnetic nanoparticles) enables programmable orientation/trajectory control through alignment of induced dipoles or intrinsic magnetic moments, while ultrasound-induced acoustic streaming supplies efficient thrust—often generated by microbubbles, asymmetric Janus geometries, or cilia arrays—thereby combining precise navigation with powerful locomotion in complex environments. From a field-property perspective, magnetic fields are typically anisotropic and well suited for accurate directional control but less effective for uniform velocity regulation, whereas acoustic fields elicit more isotropic responses that provide strong energy input yet limited directionality; accordingly, this scheme assigns the main propulsion energy cost to the acoustic field and uses the magnetic field primarily for directional adjustment to improve energy efficiency and mitigate the force limitation caused by rapid magnetic-field decay. (ii) magnetic propulsion with acoustic manipulation, in which magnetic actuation ensures targeted locomotion and precise positioning, and ultrasound is applied on demand to trigger functional operations (e.g., mixing or drug release) via acoustic streaming, cavitation, and sonochemical effects, effectively decoupling locomotion from manipulation and reducing mutual interference.
Magneto-acoustic microrobots have advanced rapidly thanks to robust propulsion, precise positioning, multifunctionality, biocompatibility, and remote controllability. Authors highlights three application domains: targeted drug delivery, minimally invasive surgery, and medical imaging. Targeted delivery improves efficacy and reduces systemic side effects, yet passive transport is hindered by drug instability, poor localization, and biological barriers; magneto-acoustic microrobots can navigate complex environments and enable precise guidance/control using external magnetic and acoustic fields. Typical work involves using ultrasound induced local effects for targeted release/enhanced therapy, such as using magnetic controlled sonodynamic nanorobots to precisely deliver sonosensitizers to tumors and enhance ROS generation, thereby improving tumor cell killing. Alternatively, magnetic microbubbles can be used to load drugs, with magnetic targeting first to enrich the lesion, and then focused ultrasound to rupture the microbubbles and trigger drug release. In terms of minimally invasive surgery, these microrobots can act as microsurgical tools for tissue puncture, biofilm degradation, and thrombus removal; their size and maneuverability enable access beyond conventional instruments, while acoustic stimulation at the target enhances local penetration/effects—potentially reducing incision size, tissue damage, infection risk, and recovery time. In a study on thrombolysis, magnetic microbubbles undergo cavitation and rotation under ultrasound to form microfluidics, mechanically disrupting the fibrin network and forming microchannels, promoting the infiltration of drug loaded nanodroplets, ultimately leading to thrombus rupture due to cavitation within the fibrous network. In the field of medical imaging, clinical use requires real-time imaging to track individual or collective microrobots for accurate navigation; designs using gas-filled microbubbles or MNP coatings enhance acoustic contrast for deep-tissue ultrasound guidance, enabling high spatiotemporal tracking of motion and localization. Microrobot accumulation (e.g., magnetic microbubbles) at lesions under magnetic targeting amplifies local contrast; they can be monitored by ultrasound and collapsed under focused ultrasound for on-demand release; the authors note potential integration with fluorescence or X-ray for multimodal imaging.
Overall, microrobots driven by magnetic and acoustic fields are well suited for in vivo operation due to favorable biocompatibility and tissue penetration; however, single-field actuation is constrained by limited magnetic propulsion and the difficulty of precise steering under acoustic actuation. Consequently, hybrid magneto-acoustic systems exploit complementary coupling—magnetic precision control combined with acoustically enabled strong propulsion/functional activation—to improve locomotion efficiency and functional capability without sacrificing directionality. Recent magneto-acoustic microrobots have demonstrated advantages in high thrust, accurate positioning, low energy consumption, and decoupled locomotion–manipulation control, supporting targeted drug transport, tissue puncture/biofilm degradation, and multimodal imaging, with additional potential in microgravity and space life science contexts. Nevertheless, clinical translation is still limited by major safety and control challenges, including long-term risks from residual magnetic nanoparticles after degradation, insufficient adaptability of control strategies in dynamic physiological environments, and the lack of selective individual control in swarms. “Future research should focus on three priorities: (i) developing low-toxicity, controllably biodegradable magnetic materials together with feasible in vivo clearance strategies for residual particles; (ii) tightly integrating magneto-acoustic control with real-time, high-resolution medical imaging to enable image-feedback intelligent control (e.g., MPC and reinforcement learning) under dynamic disturbances such as blood flow; and (iii) designing swarms with differentiated physical properties to flexibly switch between collective control and selective individual control.” said Xiaoming Liu.
Authors of the paper include Tingting Wang, Zhuo Chen, Qiang Huang, Tatsuo Arai, and Xiaoming Liu.
This research was supported in part by the National Natural Science Foundation of China (grant 62273052 to X.L. and grant W2431050 to T.A.), the Beijing Natural Science Foundation (grant L248102 to X.L. and grant IS23062 to T.A.), and the Grant-in-Aid for Scientific Research (23K22712 to T.A.) from the Ministry of Education, Culture, Sports, Science and Technology of Japan.
The paper, “Advanced Microrobots Driven by Acoustic and Magnetic Fields for Biomedical Applications” was published in the journal Cyborg and Bionic Systems on Nov. 10, 2025, at DOI: 10.34133/cbsystems.0386.
