Engineers from Rutgers have developed a “4D printing” method using a smart gel that could be used to produce living structures within the human body, soft robotics and targeted drug delivery. Findings were published in Scientific Reports.

The so-called 4D-printing process involves printing a 3D object with hydrogel that allows it to change shape with the temperature. The 3D-printed hydrogel could provide the structure in human organs and can contain small molecules like water or drugs. Additionally, the gel could enable new applications of soft robotics like flexible sensors, actuators, biomedical devices and scaffolding for cell growth.

"The full potential of this smart hydrogel has not been unleashed until now," said Howon Lee, senior author of a new study and assistant professor at Rutgers University-New Brunswick. "We added another dimension to it, and this is the first time anybody has done it on this scale. They're flexible, shape-morphing materials. I like to call them smart materials."

In the study, researchers outlined how they used a lithography-based technique to print different materials into 3D shapes with layers of resin. The resin contains the hydrogel, a chemical binder, a chemical that facilitates binding and a dye to control light penetration.

The hydrogel expands and contract depending on the temperature of its environment. For example, the gel expands in temperatures above 32 degrees Celsius and contracts in temperatures lower than that. Researchers noted the hydrogel had a range from being as wide as a human hair to several millimeters.

"If you have full control of the shape, then you can program its function," Lee said. "I think that's the power of 3D printing of shape-shifting material. You can apply this principle almost everywhere."