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Watch: Temp grows and shrinks ‘4D-printed’ objects

(Credit: Daehoon Han/Rutgers University–New Brunswick)

A new “4D printing” method for a smart gel could lead to the development of “living” structures in human organs and tissues, soft robots, and targeted drug delivery.

The 4D printing approach involves printing a 3D object with a hydrogel (water-containing gel) that changes shape over time when temperatures change, says Howon Lee, senior author of a new study and assistant professor in the department of mechanical and aerospace engineering at Rutgers University–New Brunswick.

“If you have full control of the shape, then you can program its function.”

The study, published in Scientific Reports, demonstrates fast, scalable, high-resolution 3D printing of hydrogels, which remain solid and retain their shape despite containing water. Hydrogels are everywhere in our lives, including in Jell-O, contact lenses, diapers, and the human body.

The smart gel could provide structural rigidity in organs such as the lungs, and can contain small molecules like water or drugs to be transported in the body and released. It could also create a new area of soft robotics, and enable new applications in flexible sensors and actuators, biomedical devices, and platforms or scaffolds for cells to grow, Lee says.

“The full potential of this smart hydrogel has not been unleashed until now,” says Lee, who works in the School of Engineering. “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 their study, the engineers used a lithography-based technique that’s fast, inexpensive, and can print a wide range of materials into a 3D shape. It involves printing layers of a special resin to build a 3D object. The resin consists of the hydrogel, a chemical that acts as a binder, another chemical that facilitates bonding when light hits it and a dye that controls light penetration.

Heat makes 3D-printed box fold itself up

The engineers learned how to precisely control hydrogel growth and shrinkage. In temperatures below 32 degrees Celsius (about 90 degrees Fahrenheit), the hydrogel absorbs more water and swells in size. When temperatures exceed 32 degrees Celsius, the hydrogel begins to expel water and shrinks. The objects they can create with the hydrogel range from the width of a human hair to several millimeters long. The engineers also found that they can grow one area of a 3D-printed object—creating and programming motion—by changing temperatures.

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

Additional coauthors are from Rutgers and the New Jersey Institute of Technology.

Source: Rutgers University