Mechanical engineers at Duke University have developed a new class of programmable materials that blur the line between passive structures and living systems. The work, which was published in Science Advances, demonstrates solid building blocks whose mechanical behavior can be rewritten on demand – allowing the same structure to behave like soft rubber, rigid plastic, or something in between without being rebuilt or reshaped.
At the center of the research are Lego-like cubes, each composed of 27 internal cells. Every cell contains a gallium-iron composite that can switch between solid and liquid states at room temperature. By selectively heating individual cells with small electrical currents, researchers can liquify precise regions inside the block, effectively encoding stiffness, damping, and movement into an otherwise rigid object.
The geometry never changes. Only the internal state does.
In early demonstrations, the team assembled multiple cubes into beams and columns. Simply altering which internal cells were liquified caused the same structure to bend, vibrate, or resist motion in dramatically different ways. Mechanical behavior was no longer fixed at the time of manufacture but became a variable that could be adjusted repeatedly after assembly.
One of the most striking experiments took place underwater. Researchers connected ten cubes into a straight column and attached it to a motor, forming a programmable tail for a robotic fish. With the same motor input, different internal configurations caused the fish to swim along sharply different paths. Motion was altered not by changing motors or control software, but by reprogramming the material itself.
“We want to make materials that are alive,” said Yun Bai, the study’s first author and a PhD student at Duke. “Traditional manufacturing lets you print a material with a certain stiffness, but to change it you have to start over. We wanted something closer to human muscle – a material that can adjust its mechanical response in real time.”
Unlike shape-shifting systems, the Duke approach does not rely on changing form. Instead, it rewrites how forces propagate through a structure. In two-dimensional tests, thin sheets made from the same composite demonstrated a wide range of stiffness and damping behaviors while maintaining identical shapes. In performance tests, the sheets rivaled or exceeded commercially available materials across multiple mechanical metrics.
The modular design adds another layer of flexibility. Each cube can be attached or removed like a building block, allowing engineers to assemble larger systems with highly customized mechanical behavior. Once a configuration has been tested, freezing the structure at zero degrees Celsius returns all internal cells to a solid state, effectively resetting the system for reprogramming.
“This gives us a way to build three-dimensional structures whose mechanical properties are not fixed,” Bai said. “You can test one configuration, reset it, and try another – again and again.”
The researchers see applications far beyond robotics. By adjusting the metal composition, the freezing and melting points could be tuned for environments such as the human body. Miniaturized versions could one day navigate blood vessels, form adaptive medical implants, or create electronics that physically respond to changing conditions.
“Our long-term goal is to construct larger systems using these composite materials,” said Xiaoyue Ni, an assistant professor of mechanical engineering and materials science at Duke. “We want to enable robots and machines to adapt mechanically to different tasks and environments without redesigning the entire system.”
The work suggests a future where materials are no longer passive components, but active participants – structures that can be programmed, reset, and adapted as easily as software.
