Scientists are borrowing from nature to print objects that can move independently when submerged in water. Harvard University researchers recently used hygroscopic ink, which absorbs water, to push 3D printing into the 4D realm. The resulting shapes mimic the movement of leaves and petals as they react to stimuli.

The use of hygroscopic ink was critical to the study’s success, says A. Sydney Gladman, a research assistant who works for Professor Jennifer A. Lewis at Harvard University’s Wyss Institute for Biologically Inspired Engineering.

Previous researchers achieved simple shape changes using multiple materials or induced movement through forces such as magnetic fields. The Harvard team’s method, however, allowed them to align cellulose fibrils in the ink “on the fly,” Gladman says.

Their latest project involves printing transformable tissue engineering scaffolds that can support cell growth. At this stage, water immersion is the best medium because biomedical and tissue engineering applications also use hydration. The next challenge, however, is to experiment with a shape that changes outside a water bath.

Researchers Follow Nature’s Lead

Next steps include working on a suite of inks capable of responsive shape change and able to react to stimulants such as heat, light and pH. Researchers will also study materials with biocompatibility or electrical conductivity.

Professor Lewis’s lab set up its 3D printer to use an extrusion-based process, using traditional G-code programming to print architectures in about 10 minutes. “By simply changing the print path, we were able to create a variety of shape-changing architectures,” Gladman says.

The printed ink is a hydrogel embedded with stiff cellulose fibrils. Researchers place tiny cellulose fibrils on a flat print bed with room to expand and immerse them in water.

Similar research is underway at the Massachusetts Institute of Technology’s Self-Assembly Lab, led by Skylar Tibbits, who spearheaded 4D printing with Autodesk and Stratasys. Their collaboration led to the first 4D-printed objects capable of self-adapting shapes and geometries that can change form. During his February 2013 TED Talk, Tibbits described smart material that can self-assemble and even “think” if scientists embed that ability in its DNA.

The newest frontier of 4D printing is growing tissues and organs in a lab setting. That’s happening at the Wake Forest Institute for Regenerative Medicine, where researchers recently 3D-printed structures made of living cells that could replace human tissues.

Before 4D printing goes mainstream, researchers must develop standards, certifications and regulatory policies, says Vinod Baya, director of PwC’s Center for Technology & Innovation.

Even so, Baya acknowledges that the technology is a game changer: “It’s like giving nonliving matter the characteristics of living matter, where stimulus-response is natively programmed into the DNA of the organic matter.”