'4D printing' creates shape-changing objects

MIT researchers have used 4D printing to create shape-changing three-dimensional structures that may be used in a range of applications from medical implants to home appliances.
Lead study author Dan Raviv, a mathematician at Massachusetts Institute of Technology, and colleagues are working on 4D printing, which involves 3D printing items that are designed to change shape after they are printed.
The researchers printed 3D structures using two materials with different properties. One material was a stiff plastic, and stayed rigid, while the other was water absorbent, and could double in volume when submerged in water.
The formula of this water-absorbent material, developed by 3D-printing company Stratasys in Eden Prairie, Minnesota, has not been revealed, 'Live Science' reported.

In the study, researchers printed up a square grid, measuring about 15 inches (38 centimetres) on each side.
When they placed the grid in water, they found that the water-absorbent material could act like joints that stretch and fold, producing a broad range of shapes with complex geometries.

The researchers created a 3D-printed shape that resembled the initials "MIT" that could transform into another shape resembling the initials "SAL."
"In the future, we imagine a wide range of applications," Raviv said.
These could include appliances that can adapt to heat and improve functionality or comfort, childcare products that can react to humidity or temperature, and clothing and footwear that will perform better by sensing the environment, he said.

One key health-care application might be cardiac stents, tubes placed inside the heart to aid healing, researchers said.