Engineers have created a soft material that reacts to magnets at a very small scale. The gel can form intricate three-dimensional shapes smaller than a millimeter. These shapes can move and grip objects when guided by an external magnet. Researchers see potential for soft microscopic robots that could deliver drugs or take tissue samples inside the body.
The material is a type of hydrogel that gains magnetic properties through a special process. At the macro scale, people already use magnets to move objects like paper clips. At the micro scale, scientists have made magnetic micro-swimmers, tiny components less than a millimeter wide that can travel through narrow spaces. Most earlier designs mix magnetic particles into a resin before printing, which limits complexity.
In contrast, the new approach allows more flexible and detailed structures based on metamaterials engineered with microscopic patterns that give them unusual abilities, such as extra strength or responsiveness to stimuli. Magnetic control offers instant, contact-free movement without waiting for chemical reactions.
A two-step printing and infusion process
The fabrication begins with standard three-dimensional printing using laser light to solidify a plain polymer gel layer by layer. This technique, known as two-photon lithography, creates fine details down to the micron level. After printing, the gel is dipped first into a solution with iron ions that soak into it, then into a second solution with hydroxide ions. The iron and hydroxide combine to form tiny magnetic iron-oxide particles inside the gel.
By adjusting the laser power during printing, engineers can control how tightly the gel forms in different parts. Tighter areas absorb fewer magnetic particles, allowing different sections of one structure to respond with varying strength to the same magnet. This gives precise local control within a single tiny object.
Demonstrations include lollipop-shaped structures whose heads bend differently toward a magnet, mimicking a gripping hand. Another example is a small switch with oar-like parts that flip direction when the magnet moves, acting like a valve to control fluid flow. These advances could lead to programmable miniature devices for medicine and other fields.
This research is published in Matter.