Three-dimensional printing, the process of manufacturing physical objects from digital files, has made huge advances: Printed prosthetics are becoming an affordable option for kids who quickly outgrow them; a usable wrench was printed in the International Space Station.

Scientists, meanwhile, have already skipped ahead to the future. Researchers at Harvard recently unveiled their latest advances in 4-D printing.

In this case, the fourth dimension refers to time. The objects begin as a gel composite drawn onto a flat surface, then expand into a three-dimensional shape when submerged in water. The gel contains tiny fibers of cellulose, an organic compound found in plants. How these fibers are aligned determines their stiffness and the degree to which they'll swell when placed in water. 

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The team at Harvard, led by Jennifer Lewis at the university's Wyss Institute, was inspired by the way plants change their shape over time based on outside stimuli like sunlight, temperature, or humidity. A demonstration released by the school shows a 4-D printed flower-shaped object fluttering under water. 

The concept of 4-D printing isn't new: MIT professor Skylar Tibbits introduced the phrase at a TED conference in 2013. But while Tibbits's process required two materials, one soft and one hard, the Harvard team's uses one: the fiber-infused gel, which it refers to as a "hydrogel composite ink."

What remains to be seen is exactly what problems 4-D printing is capable of solving. The hope is that 3-D printing could someday create new tissue or fully functional replacement organs. The added dimension of time means, in theory, that printed objects could adapt and alter their shape as a human body changes. But the MIT Technology Review contends that this is still a long way off--mostly because even the less complex 3-D printing isn't close to being perfected yet.

Regardless, creating a movable three-dimensional object from something two-dimensional is pretty impressive. Check out the Harvard team's 60-second video below for a demonstration.