This photo taken on Jan. 2, 2025 shows untethered terrestrial-aerial micro-robots developed by a research team from Tsinghua University, in Beijing, capital of China. [Photo/Tsinghua University handout via Xinhua]

Enabling robots to walk, run, jump, fly, climb and "lock" into arbitrary shapes in real-time is crucial for expanding their application scenarios.

A research team from Tsinghua University in Beijing has developed a thin-film-shaped small-scale actuator which enables micro-robots to continuously transform their shapes and "lock" into specific configurations, much like the "Transformers" seen in a famous cinema attraction, and thereby significantly enhancing their environmental adaptability. This breakthrough has been published online in Nature Machine Intelligence, a leading international journal.

"By integrating this actuator with our Lego-inspired design strategy, we created the world's smallest and lightest untethered terrestrial-aerial micro-robot known in the relevant literature, measuring just 9 centimeters in length and weighing 25 grams," said Zhang Yihui from Tsinghua University's School of Aerospace Engineering and the State Key Laboratory of Flexible Electronics Technology.

Actuators, the "heart" of micro-robots, are devices with controllable shape-morphing capability.

"Developing untethered, ultra-compact micro-robots with complex shape-morphing capabilities is extremely challenging," Zhang explained.

Existing actuators measuring under five centimeters in size typically face challenges in achieving continuous shape morphing and locking, severely limiting miniaturization and untethered control of multimodal robots.

Through innovative synergistic material-structure design, Zhang's team developed a miniature actuator as small as a few millimeters in size. Serving as a "morphable exoskeleton," it can integrate functional components like sensors and motors to build complex robotic systems.

Notably, this actuator can be electrically controlled to continuously morph into any desired shape and then "lock" the deformed configuration, which was difficult to achieve with previous small-scale actuators.

"Using the Lego-inspired design strategy, we constructed an untethered terrestrial-aerial micro-robot capable of agile aerial flight and land movement, and with a speed of up to 1.6 meters per second on the ground," Zhang said.

In addition, the team also developed a 4.5-centimeter-high, 0.8-gram mini-"Transformer" actuator employing more than ten actuator units, as well as a multi-functional wheeled robot that can morph into "sports car," "winged car," and "van" modes.

Inspired by grasshoppers and other insects, researchers incorporated biological morphologies and locomotion capabilities into their designs.

This work offers new ideas and routes for the development of micro-robots. "Future applications include equipment diagnostics, geological surveys, and hazardous environment operations," Zhang said. "The actuator can also be used in bio-electronic devices, enabling the development of deployable implantable medical devices and VR/AR haptic interfaces."