We’ve written many, many times before about the promising uses of 3D printing when it comes to medicine — doctors are already using for everything from crafting low-cost prosthetics, to mending or even replacing broken bones, and even creating new drugs. But when it comes to replacing organs, there’s one major problem 3D printed materials face — they just can’t move or change shape over time in a way that mimics natural processes. That’s why researchers at Harvard are beginning to test out “4D printing,” a method of 3D printing objects that can be designed to shift and flex over time.

Jennifer Lewis and her team of researchers at the Wyss Institute for Biologically Inspired Engineering at Harvard have been using cellulose fibers from wood pulp to create glowing 3D printed flowers that bend and twist when placed in water. The secret to the flowers’ shape? The fibers are mixed with a jelly-like substance called acrylamide hydrogel, which expands when wet. Because the fibers can be printed to line up in a specific direction, the gel expands lengthwise, but not sideways. Using mathematical models, the team is able to create crisscross designs, aligning the fibers so that the flowers bend in specific, predetermined shapes.

Related: MIT Unveils 4D-Printed Objects that ‘Make Themselves’

This new printing method has some interesting implications for medical technology if it could be replicated with tissue cultures. This would make it easier to create, say, a 3D printed heart, because instead of having to print the entire structure in layers, the tissue could be printed in a flat sheet which would simply transform itself into the required shape. You can find more details of the Harvard study in the journal Nature Materials.

+ The Wyss Institute

Via New Scientist

Images via The Wyss Institute