Robots are usually built from materials with fixed properties.
Once a robot is assembled, its stiffness, flexibility and movement patterns are largely locked in.
Engineers at Duke University are now challenging that limitation by developing a programmable, Lego-like material that can change its mechanical behavior in real time, much like living tissue.
The new approach allows researchers to control how stiff or flexible different parts of a solid structure are by switching individual internal cells between solid and liquid states.
By carefully choosing which cells are solid and which are softened, the material can take on very different behaviors without changing its overall shape. The research was published in the journal Science Advances.
The idea was inspired by biology. Human muscles, for example, can stiffen or relax instantly to support movement, balance or strength.
Traditional 3D-printed materials cannot do this. To change their mechanical properties, they usually need to be reprinted from scratch. The Duke team wanted to create a material that could adapt on the fly.
To make this possible, the researchers filled small internal cells with a special mixture of gallium and iron. At room temperature, this metal blend can exist as either a solid or a liquid.
By sending a small electrical current through selected cells, the researchers can heat them up and melt the metal inside. This process allows them to “write” patterns into the material, similar to storing digital information as ones and zeros.
In flat, two-dimensional sheets, the material can be programmed to precisely adjust stiffness and energy absorption without bending or changing shape. Tests showed that it can mimic a wide range of common materials, from stiff plastics to soft rubber.
The concept becomes even more powerful in three dimensions. The team created small cube-shaped blocks that resemble Lego bricks. Each cube contains 27 internal cells, and multiple cubes can be attached together in different arrangements. Once assembled, the entire structure can be reprogrammed by melting selected cells. Cooling the material freezes everything back into place, allowing the process to be repeated again and again.
To demonstrate the idea, the researchers connected 10 cubes into a flexible tail and attached it to a simple robotic fish. By changing which cells in the tail were solid, the same motor produced very different swimming motions. With no mechanical redesign, the fish could follow multiple paths through water.
Looking ahead, the team believes the technology could be miniaturized and adapted for medical and engineering applications. Future versions might move through blood vessels to inspect health or reconfigure themselves as temporary medical supports.
Ultimately, the researchers hope this programmable material will help robots become more adaptable, resilient and lifelike as they take on tasks in complex and changing environments.
