Programmable Lego-Like Material Emulates Life’s Flexibility

Mechanical engineers at Duke University have demonstrated a proof-of-concept method for programming mechanical properties into solid Lego-like building blocks. By controlling the solidity of hundreds of individual cells in specific patterns, the approach could allow futuristic robotics to alter their mechanical properties and functionalities on the fly.

In their initial tests, the researchers show how a tail-like 3D beam with various configurations can move a robotic fish through water along different paths with the same motor activity. The team envisions miniaturized versions of the technology that could, for example, maneuver through blood vessels to survey their health or even reconfigure to form an adaptive stent.

The research appeared online in the journal Science Advances.

“We want to make materials that are alive,” explained Yun Bai, first author on the paper and a PhD student in the laboratory of Xiaoyue Ni, assistant professor of mechanical engineering and materials science at Duke. “3D printers can create materials with specific mechanical properties, but you have to repeat the print to change them. We wanted to create something like human muscles that can change their stiffness in real time.”

To make that happen, the researchers filled individual cells with a recipe of gallium and iron. At room temperature, this metal composite can be either a solid or a liquid. Starting as a complete solid, researchers can apply heat with an electrical current to liquify any pattern of cells, almost like writing and storing 1s and 0s into a hard drive.

In two dimensions, the resulting material is essentially a thin sheet that can be programmed to precisely change stiffness and damping without altering its shape or geometry. The material was heavily tested, showing vast flexibility to mimic a range of commercially available soft materials from plastics to rubbers. 

The concept, however, gets even more interesting in three dimensions. In their demonstration, the researchers created Lego-like building blocks that can be stuck and unstuck together in any configuration. Each block resembles a Rubik’s cube containing 27 individual cells, each of which can be liquified through localized heat from an electrical signal.

“This gives us the flexibility to create 3D structures with different mechanical properties,” said Bai. “And freezing the blocks at zero degrees resets all the cells to their solid state so that their configuration can be reprogrammed again and again.”

In the paper, the researchers stuck 10 of these cubes together into a straight column to create a sort of programmable tail, attached it to a simple motor within a robotic fish and tested the swimming abilities of various configurations. The same robotic fish with different arrangements of solid cells in the tail showcased very different swimming trajectories.

Building from this platform, the researchers envision using different metals to create different freezing and melting points that could enable these materials to, for example, be used within a human body. They also believe the setup could be miniaturized to work within tiny confines such as human blood vessels or delicate electronic systems.

“Our goal is to eventually construct larger systems using the composite materials,” said Ni. “We want to build flexible, programmable materials for robotics that can enable them to perform a wide variety of tasks in a wide variety of environments.”

This work was supported by the Duke University Shared Materials Instrumentation Facility, a member of the North Carolina Research Triangle Nanotechnology Network, which is supported by the National Science Foundation (ECCS-2025064) and the Beyond the Horizon Initiative of the Pratt School of Engineering at Duke University.