'4-D Printing' Technique Creates Objects That Change Over Time

A hydrogel flower curls up after being immersed in water. Wyss Institute at Harvard University

While 3-D printers are versatile tools, the objects they create are largely static — but a new technique from Harvard's Wyss Institute, inspired by structures in plants, allows for creations that change their shape over time.

Instead of pushing out heated plastic, the printer head lays down hydrogel, a material that absorbs water, mixed with cellulose fibers harvested from plants. When the resulting structure is immersed in water, it swells — but by carefully controlling the alignment of the fibers in the gel lattice forming the object, the researchers can control how that happens.

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The result: objects that bend and move just as their creators intend, like these flowers that curl or close up like the real thing.

"It is wonderful to be able to design and realize, in an engineered structure, some of nature's solutions," said L. Mahadevan, who worked on the Nature Materials paper describing the technique, in a news release.

By integrating other materials into these designs — like ones activated by heat or electricity — even more complex structures may be planned out.

"It enables the design of almost any arbitrary, transformable shape from a wide range of available materials with different properties and potential applications," said Donald Ingber, the Wyss Institute's founder.