Durham, North Carolina – Engineers at Duke University have created a proof-of-concept system of Lego-like building blocks that can change their stiffness and mechanical properties on demand. Using a special metal mixture of gallium and iron, individual cells within each block can shift between solid and liquid states when heated electrically, allowing structures to bend, flex, and reconfigure without changing shape.

In demonstrations, the team assembled ten of these cubes into a programmable tail attached to a simple motor within a robotic fish. By changing which cells were solid or liquid, the tail produced very different swimming paths using the same motor activity, showing how reconfigurable stiffness can control motion.

“This gives us the flexibility to create 3D structures with different mechanical properties,” said Yun Bai, first author of the study. “Freezing the blocks at zero degrees resets all the cells to solid, so the configuration can be reprogrammed again and again.”

The material acts like a thin sheet in two dimensions, capable of mimicking a wide range of soft commercial materials from plastics to rubbers, while the three-dimensional cubes can be combined, detached, and recombined like Lego bricks. The team envisions miniaturized versions capable of maneuvering in tight spaces, such as inside human blood vessels, or forming adaptive medical devices like stents.

“Our goal is to eventually construct larger systems using the composite materials,” said Xiaoyue Ni, assistant professor of mechanical engineering and materials science. “We want to build flexible, programmable materials for robotics that can perform a wide variety of tasks in many environments.”

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