Miniaturizing robots is a complex and costly process. As an alternative, researchers are exploring the use of stimuli-responsive actuators, which can eliminate the need for control circuitry and batteries. One promising approach is using light to control micro- and nanoscale robots with high precision.
Other techniques, such as magnetic fields and acoustic waves, have also been studied. But light stands out for its versatility. Its properties can be precisely tuned for specific applications, and it offers exceptional spatial resolution.
A wide range of tools can be used to direct and modulate light, making it a powerful option for wireless robotic control.
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Photomechanical and Photothermal Mechanisms in Soft Robotics
Photomobile Light Controlled Liquid-Crystal Soft Robots
Photomobile soft robots use light as their sole energy source, eliminating the need for batteries or wired power. These systems rely on liquid-crystal polymers (LCPs), organic materials that respond to light-induced heat. When exposed to light, the LCPs undergo a phase change from anisotropic to isotropic, causing a shift in their molecular structure.
This shift generates internal elastic stress, allowing the robot to deform and move. The resulting motion resembles how biological organisms use body deformation to interact with surfaces and overcome resistance.1
In 2018, researchers demonstrated a millimeter-scale walking robot powered by light. It was built from a monolithic liquid-crystal polymer, carefully aligned using patterning techniques. A modulated LED light source controlled its movement with precision.2
Photo-Thermal Driven Soft Robot
Designing soft robots that operate wirelessly, without bulky 3D structures or restrictive environments, remains challenging. One recent approach uses a photothermal-responsive LCP actuator paired with bristle-like structures that mimic biological friction mechanisms.
These bristles, created through UV curing, allow directional sliding by reducing resistance in the forward direction. The actuator consists of an LCP film laminated with polyimide (PI), which bends and straightens in response to near-infrared (NIR) light.
The angled bristle design reduces resistance when sliding forward and increases it when sliding backward. This directional friction grows as the bristle inclination increases. By flexibly connecting the actuator and bristles, the system can balance driving force and resistance by adjusting the number of LCP films. The robot’s crawling speed is tunable by changing the actuator’s length or the distance from the NIR light source.3
Photothermal effects like these offer promising methods for controlling motion in soft nanorobots.#
Caterpillar Soft Robot Powered by Light
Light-Controlled Phagocytic Robot for Treating Biological Threats
Using soft micro- and nanorobots in biomedical applications is a growing but challenging field. Many of these robots are made from synthetic materials, which can be difficult to integrate with living systems.
Macrophages—key immune cells in the body—have attracted interest for their natural ability to target and eliminate threats. Researchers have repurposed them as drug carriers for targeted cancer therapies. Light, as a noninvasive control method, offers a precise way to influence biological cells remotely.
Building on this idea, scientists developed a light-powered microrobot known as a “phagobot.” This system is based on living macrophages with tunable phagocytic activity. Using localized optothermal stimulation with NIR light, they converted a resting macrophage into an active robotic unit capable of controlled movement.
The activation of the phagobot by light waves allows the user to perform a range of motion tasks like directional navigation, and follow complex paths with adjustable speed. By integrating precise spatiotemporal control via light with the strong phagocytic function of macrophages, the phagobot is capable of targeting and eliminating diverse biological threats of varying sizes.
The research team demonstrated its capabilities in both in vitro and in vivo settings, including successful operation inside a living zebrafish.4 This work suggests that integrating optical biomodulation into living cells could lead to AI-enhanced, next-generation microrobots capable of fine-tuned biological control.
Battery-Free Optical Actuation: The MilliMobile
In a recent development, researchers created the MilliMobile—the first battery-free robot powered by harvested solar energy and radio waves. The prototype weighed less than 1.1 grams, with a chassis measuring approximately 10 × 10 mm.
Despite its small size, the MilliMobile could carry up to three times its own weight. During testing, it experienced only a 25 % drop in speed when transporting a 1-gram payload.
The robot used a programmable nRF52 series Bluetooth system-on-chip (SoC) to enable low-power processing and wireless communication. Its circuit board included four photodiodes to detect light levels, along with sensors for temperature and humidity.
Achieving precise motion control is typically difficult in battery-free systems. However, the MilliMobile managed this using very low power. It operated untethered and autonomously under typical lighting and RF power conditions, consuming as little as 57 µW through intermittent motion.5
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Challenges and Future Outlook
Light-powered microrobots face two main challenges: fabrication and optical control. A key fabrication issue is scalability. Reducing the size of components—particularly electronic circuits—to the nanoscale is technically complex. In soft microrobots, the limited resolution of 3D printing adds further constraints. As size decreases, smaller structural features are needed, which increases design and manufacturing complexity.
Producing consistent, high-resolution structures at these scales also requires careful optimization of materials and printing conditions. These demands contribute to higher costs and slower development.
Controlling these robots with light becomes more difficult in complex environments. Modulating light intensity and waveform in heterogeneous or opaque materials remains a challenge. In dense media—such as turbid liquids—light penetration is limited, making optical actuation less effective.
To address these issues, researchers are exploring hybrid approaches that combine light with other forms of actuation, such as magnetic, acoustic, or chemical methods. These combinations may improve performance in settings where light alone is insufficient.6
Light-controlled microrobots may find applications in fields like targeted drug delivery, environmental sensing, or microscale assembly. Integration with AI could improve motion control and responsiveness. While the technology is still in development, research is continuing to evaluate its practical potential.
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References and Further Reading
- Zeng, H., et al. (2018). Light robots: bridging the gap between microrobotics and photomechanics in soft materials. Advanced Materials. Available at: https://doi.org/10.1002/adma.201703554
- Zeng, H., et al. (2018). Light‐driven, caterpillar‐inspired miniature inching robot. Macromolecular rapid communications. https://doi.org/10.1002/marc.201700224
- Lou, P., et. al. (2024). Photothermal‐Driven Crawlable Soft Robot with Bionic Earthworm‐Like Bristle Structure. Advanced Intelligent Systems, 6(1), 2300540. Available at: https://doi.org/10.1002/aisy.202300540
- Li, X., et al. (2025). Light-powered phagocytic macrophage microrobot (phagobot): both in vitro and in vivo. Light Sci Appl. https://doi.org/10.1038/s41377-025-01881-3
- Johnson, K., et al. (2023). Millimobile: An autonomous battery-free wireless microrobot. Proceedings of the 29th Annual International Conference on Mobile Computing and Networking. https://doi.org/10.1145/3570361.3613304
- Bunea, A., et al. (2021). Light‐powered microrobots: challenges and opportunities for hard and soft responsive microswimmers. Advanced Intelligent Systems. https://doi.org/10.1002/aisy.202000256
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