We are all familiar with the satisfying click of a pen or the snap of a hair clip.
Behind these simple motions lies a powerful mechanical phenomenon called “snap-through.”
It is also used in nature—tiny insects and plants like the Venus flytrap harness it to unleash quick, powerful movements far beyond what their small bodies should allow.
Now, inspired by this natural trick, researchers at Hanyang University in South Korea have created a soft polymer jumper that can leap high into the air or spin off in a chosen direction—all powered by the snap-through effect and activated simply with ultraviolet (UV) light.
Their study, published in Science Advances, offers a fresh way to solve a long-standing engineering challenge: how to make soft materials move both quickly and forcefully.
The problem lies in balance. To store enough energy for a strong motion, a material must be stiff. But if it is too stiff, it cannot bend and store that energy in the first place.
Too soft, and the stored energy is too weak to produce a powerful leap.
The Hanyang team, led by Professor Jeong Jae (JJ) Wie, overcame this trade-off by embedding regions of different stiffness within one sheet of polymer.
The result was a material that bends easily where it is soft but stores and releases elastic energy efficiently where it is stiff.
When enough force builds up, the material suddenly “snaps” from one curved shape to another. This rapid flip converts stored elastic energy into motion, propelling the material off the ground. It’s the same principle you feel when bending a ruler until it suddenly flicks.
By carefully controlling where the stiff areas were placed, the team could program the jumper’s movements.
With a stiff region at one corner, the material spun and leapt sideways with remarkable precision.
This level of directional control is usually difficult in soft robots, which often need angled light sources or external cues. But here, the built-in asymmetry did all the work under uniform UV light.
Placing a stiff region in the center, meanwhile, enabled powerful vertical jumps. The polymer sheet launched itself nearly 50 millimeters into the air—about 25 times its own length. That’s a record-setting leap for this kind of material.
The researchers also designed a “dual-mode” jumper by alternating stiff and soft regions along the body. Depending on its shape before release, the same piece of polymer could switch between high vertical leaps and directional jumps in rapid sequence. This versatility is rarely seen in soft robotic systems, which are usually specialized for one type of motion.
Looking forward, this approach could inspire a new generation of soft actuators and robots that are not only flexible and adaptable but also powerful.
By borrowing the snap-through trick from nature, engineers are learning how to make soft machines move with strength, speed, and precision.
