Image of 4D-printed metamaterials.
4D-printed metamaterials can be temporarily transformed into any deformed shape and then returned to their original shape on demand when heated. Scale bar: 2 mm. (Credit: Chen Yang/Rutgers University-New Brunswick)

Engineers have created flexible, lightweight materials with 4D printing that could lead to better soft robotics and tiny implantable biomedical devices. The stiffness can be adjusted more than 100-fold and can be reshaped on demand when heated.

3D printing, also known as additive manufacturing, turns digital blueprints to physical objects by building them layer by layer. 4D printing is based on this technology, with one big difference: it uses special materials and sophisticated designs to print objects that change shape with environmental conditions such as temperature acting as a trigger.

The engineers created a new class of “metamaterials” — materials engineered to have unusual and counterintuitive properties that are not found in nature. Previously, the shape and properties of metamaterials were irreversible once they were manufactured. But the engineers can tune their plastic-like materials with heat, so they stay rigid when struck or become soft as a sponge to absorb shock.

The stiffness can be adjusted more than 100-fold in temperatures between room temperature (73°) and 194 °F, allowing great control of shock absorption. The materials can be reshaped for a wide variety of purposes. They can be temporarily transformed into any deformed shape and then returned to their original shape on demand when heated.

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