Tiny knot robots leap to plant seeds without power or electronics

Friday 24 April 2026 - 10:00

Engineers at the University of Pennsylvania have developed millimeter scale soft robots made from knotted fibers that can jump nearly two meters, flip, spin, and even return to their starting point without electronics, batteries, or external control. The study, published in Science, demonstrates how these devices could be used to plant seeds autonomously, offering a new approach to reforestation.

The system relies on a dual material fiber less than one millimeter thick. A rigid Kevlar core provides strength, while an outer layer of liquid crystal elastomer responds to heat. When twisted and tied into a knot, the fiber stores elastic energy like a compressed spring. As temperature rises between 60 and 90 degrees Celsius, the outer layer contracts and loosens the knot, triggering a rapid release of stored energy that converts into motion.

The structure of the knot determines how the robot moves. A simple knot produces a flipping motion, while a figure eight knot generates rotation. More complex configurations can release energy in stages, creating controlled sequences of movement in midair. Researchers say this design turns the knot itself into an active mechanical system, capable of producing diverse motion without motors or circuits.

The team demonstrated a practical use by attaching seed carrying structures inspired by maple seeds. These wing like additions allow the robots to travel in curved paths or return like a boomerang. In tests, pine and rocket seeds attached to the devices were driven into the soil upon landing. The impact generated pressures about 30 times higher than earlier moisture driven planting systems, enabling successful germination.

The concept could be especially useful in regions where rainfall is limited. Heat from sunlight alone can activate the fibers, allowing the robots to function in dry environments where traditional planting methods struggle. The researchers are now working to lower the activation temperature and develop more environmentally friendly materials for outdoor deployment, aiming to scale the technology for real world applications.