We were all impressed by 3D printing for a hot minute, but that's all over now. Enter "4D printing," the printing which also involves the fourth dimension: time. Applause, applause, applause.

Scientists at the Wyss Institute for Biologically Inspired Engineering at Harvard have developed hydrogel structures which change their shape when placed in water. In other words, they are able to respond to their environment (in this case, the water) the same way a plant does to its own environment: a sunflower bends toward the light, a vine climbs up a building for support, a pinecone spreads open, and so on.

The researchers didn't have to look far for inspiration, but they did have to leave the lab. Using flowers, leaves and tendrils as their muses, the engineers took cellulose fibrils (very small fibers) from wood, in order to work with the same sort of matter that gives plants their unique properties. They then manipulated that cellulose to form hydrogel structures. Hydrogel is especially well-regarded for its ability to absorb water.

Once the material was designed, the engineers used a mathematical model to print the material in a specific manner so that it would transform its shape in whatever way they desired. Check out the cool video at bottom to see what this looks like.

As the senior author of the study, Jennifer Lewis, put it, "We have now gone beyond integrating form and function to create transformable architectures."

The team effort was truly interdisciplinary, comprised of experts from the fields of engineering, mathematics, chemistry and, of course, plant biology. They foresee it having countless applications, including industrial machinery, robotics, administration of medicine, and engineering tissues for medical patients. It could also lead to objects that can self-regulate and even take over the task of building themselves.

The study was published Jan. 25 in the journal Nature Materials.

Check out this video from Harvard where the printer uses hydrogel composite ink containing aligned cellulose fibrils to outline the orchid-shaped structure.