Wing-Like Fans in Ripple Bugs Inspire Miniature Robots

Ripple bugs (Rhagovelia) live in fast-flowing streams, where turbulent waters would overwhelm most insects. Their survival depends on a remarkable adaptation: collapsible, wing-like fans on their feet. These fans spread instantly when submerged to generate thrust but collapse the moment they leave the water, minimizing drag.

Scientists studying these insects have not only uncovered how these fans work but have also engineered artificial versions to test in robotic systems. The result is a new propulsion concept—elastocapillary fans—that could transform small-scale robotics, biomedical applications, and other fields where smart materials and thin-film fabrication intersect.

Nature’s Blueprint: Ripple Bugs’ Collapsible Fans

In their natural environment, ripple bugs face strong currents and unpredictable turbulence. High-speed imaging revealed that their foot fans spread when submerged to push against water and fold tightly when lifted, avoiding resistance. This dynamic system enables ripple bugs to row continuously, perform rapid turns of nearly 13,000° per second, and survive in conditions that reach turbulence levels of 65%.

Perhaps most striking is their endurance. In controlled lab settings, ripple bugs rowed almost continuously for months, pausing only during molting or feeding. This nonstop propulsion highlights the efficiency of their collapsible fan design and parallels principles studied in vibration damping, damping capacity, and adaptive micro-scale structures.

Engineering the Artificial Fan

To understand and replicate these natural fans, researchers dissected ripple bug appendages, analyzed them with high-speed cameras, and measured their stiffness with atomic force microscopy. The natural barbs showed a modulus of around 15 MPa, flexible enough to bend but strong enough to recover.

The artificial fans were constructed from thin layers of polyimide films, each 16 micrometers thick, bonded with a one-micrometer PET adhesive. Layers were heat-pressed under controlled pressure, cut into fan shapes using UV laser machining, and thermally set at 300°C to fix their curvature. When submerged, these synthetic fans spread like their biological counterparts; when lifted, they collapsed under surface tension, dramatically reducing the energy required for movement. Such thin-film fabrication methods echo approaches used for NiTi thin films, wafer-based monolithic fabrication, and even magnetron sputtering processes in advanced electronic materials.

Emma Perry/Univ. of Maine and Victor Ortega-Jimenez/UC Berkeley

At left is a photo of the fan and claw at the end of Rhagovelia’s two oaring legs. At right, a colorized scanning electron microscope image of the fan shows the flat, ribbon-like microstructure of the barbs and the smaller barbules (green) that comprise the fan. The structure allows the flexible fan to morph into a rigid oar underwater (Sanders, 2025).

Building the Rhagobot

The research team then integrated these fans into a miniature robot, dubbed the “Rhagobot.” Its structure combined shape memory alloy wires for actuation, glass-reinforced epoxy laminates for the frame, and copper legs coated with hydrophobic material to minimize drag. Shape-memory alloys rely on phase transformation and thermoelastic martensite to convert heat into motion, making them a cornerstone of smart materials research.

Tests revealed that rigid paddles required nearly 18 microjoules to lift from water, while collapsible fans needed only 1.4 microjoules. The difference was decisive: robots with rigid paddles failed to move efficiently, but those equipped with collapsible fans maneuvered forward, turned, and even braked with agility. This efficiency reflects the promise of electromechanical coupling, grain refinement in metallic films, and twinning microstructures that underpin the design of high-performance actuators.

Insights and Applications Beyond the Lab

The study demonstrates how elastocapillarity can be harnessed for energy-efficient locomotion at small scales. Ripple bugs show that agility comes from balancing thrust generation with drag reduction, a principle that robotics can now adopt.

Potential applications are wide-ranging. Microrobots could be designed for environmental monitoring, skimming water surfaces to collect data. Biomedical applications are particularly compelling: concepts such as self-propelling stents, artificial clots for vascular occlusion, and medical implants designed for blood vessels could integrate collapsible or origami structures inspired by ripple bugs. Coupled with advances in rotating magnetic fields and Helmholtz coils, microrobots may also leverage magnetic torque or optothermal phoretic force for steering. Parallel innovations include helical microrobots optimized by helix angle and diameter evolution, guided by vision-based feedback control systems.

Beyond medicine, elastocapillary strategies could extend to lab-on-chip devices, plastic capillaries for vessel expansion, and adaptive actuators for soft robotics. Related work in Advanced Robotics Research, Advanced Intelligent Systems, and Advanced Optical Materials highlights how smart materials and origami-inspired self-folding mechanisms can expand capabilities across industries.

Clip from Victor Ortega-Jimenez/UC Berkeley about Rhagovelia insects on how they maneuver thier fans in turbulent waters.

Final Thoughts: Materials Make Innovation Possible

Behind every breakthrough in biomimicry is a foundation of materials and methods. Thin polymer films, PET adhesives, shape memory alloys, hydrophobic coatings, and analytical systems like AFM and SEM were all critical in translating ripple bug biology into functional robotics. These materials sit within a larger context of advanced research.

MSE Supplies supports these efforts by providing not only access to advanced materials and instruments but also the flexibility to source hard-to-find items or deliver customized solutions when off-the-shelf options fall short. Whether the goal is to study natural phenomena or engineer the next generation of robotics, we ensure that researchers have what they need to make discovery possible.

Nature continues to inspire engineering breakthroughs, but turning those ideas into reality requires the right materials and tools. Partner with MSE Supplies to accelerate your research, from polymers and alloys to advanced coatings and analytical systems. Contact our team, connect with us on LinkedIn, or join our newsletter to explore how we can support your next discovery.

Sources:

1. Ortega-Jimenez, V. M., Kim, D., Kumar, S., Kim, C., Koh, J., & Bhamla, S. (2025). Ultrafast elastocapillary fans control agile maneuvering in ripple bugs and robots. Science, 389(6762), 811–817. https://doi.org/10.1126/science.adv2792

2. Sanders, R. (2025, August 21). Wing-like fans on the feet of ripple bugs inspire a novel propulsion system for miniature robots - Berkeley News. Berkeley News. Retrieved September 8, 2025, from https://news.berkeley.edu/2025/08/21/wing-like-fans-on-the-feet-of-ripple-bugs-inspire-a-novel-propulsion-system-for-miniature-robots/