Background
Microrobots have long drawn inspiration from microorganisms, especially their ability to adapt and communicate within dynamic environments. While materials that respond to stimuli have enabled advances in navigation and collective behavior, real-time communication has remained a challenge, particularly without relying on rigid components or power-hungry systems.
Efforts to miniaturize wireless communication often hit a wall: rigid chips don’t scale down well, and tethered designs limit movement. This study tackles that issue head-on by integrating a flexible antenna into a shape-changing robot. As the robot morphs in response to temperature, the antenna’s RF signal shifts accordingly. That signal serves as both a temperature readout and a real-time indicator of the robot’s physical state.
With this approach, the team unifies navigation, sensing, and wireless communication in a fully soft and scalable microrobotic system. Even when hidden behind barriers or submerged in biological fluids, these robots can be tracked and monitored without the need for a camera.
Fabrication and Design
The robot’s construction began with a silicon wafer layered with a dissolvable PMMA base. On top, a flexible gold dipole antenna was patterned using electron beam deposition, photolithography, and wet etching. Additional SU-8 layers were added to form the scaffold and spacer structure that supported shape change.
The active layer was a thermoresponsive, magnetic hydrogel made from N-isopropylacrylamide (NIPAM), cross-linkers, acrylic acid, and iron oxide nanoparticles (IONPs). To impart directional magnetic properties, the hydrogel was cured under a 10 millitesla magnetic field, aligning the IONPs. After the sacrificial layers were removed, the final microrobot was free-standing and fully soft.
The robot’s function depended on its temperature-driven shape shift: it coiled into a helix at 20?°C and flattened at 40?°C. Magnetic actuation was achieved using 3D Helmholtz coils, allowing for precise remote control. Simultaneously, the antenna’s signal that was measured via transmission coefficient changes using RF coils and a vector network analyzer shifted as the robot changed shape. These changes provided a wireless, binary indicator of temperature.
COMSOL Multiphysics simulations confirmed the antenna's performance, and the fabrication process consistently produced stable, repeatable results. When multiple robots were used together, their combined signals enhanced detection, enabling reliable group-based sensing.
Results and Performance Evaluation
Tests confirmed that the robot’s three-layer design delivered on both mobility and communication. At cooler temperatures, the swollen hydrogel interacted with the support structure to create a helical shape. This configuration supported corkscrew-style propulsion at speeds of up to 0.6 mm/second. As the temperature rose past 40?°C, the hydrogel contracted, and the robot flattened into a planar state.
This shape transformation drove a clear shift in the robot’s electromagnetic profile. Specifically, the antenna’s RF signature changed in both amplitude and frequency. Using external coils and a network analyzer, researchers were able to remotely distinguish between the helical and flat states, enabling real-time monitoring.
Size optimization revealed that a 2 mm × 15 mm form factor offered a good balance of maneuverability and signal clarity. Larger designs produced stronger signal changes due to their broader effective aperture. Most notably, when several microrobots were used together, the RF signal shift increased significantly from ~1.3 dB with one robot to ~4.1 dB with seven robots at ~12.06 GHz.
These results held up in biological environments as well. In phosphate-buffered saline (PBS), for instance, the resonance frequency shifted from ~12 GHz (in air) to ~1.5 GHz, yet the system still performed reliably. In a complete demonstration, the robots were magnetically guided to a heated zone, changed shape, and successfully broadcasted their new state, validating the system’s full sensing and signaling cycle.
Discussion and Future Directions
What sets this system apart is how the robot’s temperature-induced shape shift directly alters its antenna, enabling wireless sensing without relying on rigid parts or external power.
The fabrication process, based on photolithography, is compatible with existing semiconductor workflows, which means that there is a lot of potential for integrating additional sensors or control circuits. The antenna’s nanometer-scale thickness allows it to bend and stretch with the robot while maintaining signal performance.
Group behavior was also found to enhance functionality. Clusters of microrobots amplified signal strength, improving detection and reliability. The team also demonstrated a simple method for wireless localization by scanning across a grid with an RF probe. Signal dips corresponded to robot presence and shape.
Initial biocompatibility results were also encouraging. Cytotoxicity tests using HUVEC cells showed over 80 % viability after 72 hours, suggesting the system could be suitable for biomedical applications like localized temperature sensing inside tissues.
While current sensing is limited to binary states (helical or flat), future work may involve hydrogels with varied transition temperatures to enable more nuanced detection. With only ~1 mW of power needed, far below RF ablation systems (~1–10 W) and well under the SAR safety threshold of 2 W/kg, this approach is promising for safe use in vivo.
Conclusion
This research bridges a long-standing gap in soft microrobotics by delivering a fully untethered, shape-morphing robot that can sense and communicate wirelessly. By merging a flexible antenna with a thermoresponsive hydrogel body, the team created a system where physical state changes produce readable RF signals - no rigid chips, no external power, no tether.
With scalable fabrication, group-enhanced signal strength, and reliable function in biological environments, this microrobot platform offers a new path forward for intelligent, autonomous systems at small scales. Its ability to operate behind barriers and in ionic media further expands its potential applications.
Journal Reference
Gao et al.(2025). Soft magnetic microrobots with remote sensing and communication capabilities. Nature Communications, 16(1). DOI:10.1038/s41467-025-65459-8. https://www.nature.com/articles/s41467-025-65459-8
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