The approach builds on an innovation known as rotational multimaterial 3D printing, in which a single nozzle can print more than one material at the same time. As the printer rotates and reorients, it extrudes ink in patterns that can be customized to create complex internal geometries.

Using the technique, the researchers printed filaments with a polyurethane outer shell and an inner channel made from a poloxamer — a polymer commonly used in hair gels. By controlling nozzle design, rotation speed and material flow, the researchers programmed the size, shape and orientation of each inner channel.

After the outer shell solidified, the team washed away the inner material, leaving behind tubular structures with hollow channels. Those channels can be pressurized with air to bend in different directions, creating building blocks for soft devices that can expand, contract and grasp.

The work was led by graduate student Jackson Wilt and former postdoctoral researcher Natalie Larson in the lab of Jennifer Lewis, the Hansjorg Wyss Professor of Biologically Inspired Engineering at Harvard’s John A. Paulson School of Engineering and Applied Sciences.

“In this work, we don’t have a mold. We print the structures, we program them rapidly, and we’re able to quickly customize actuation,” Wilt said.

To demonstrate the technique, the team printed a spiral flower pattern in a single continuous path and created a five-digit handle with knuckle-like joints that bend.

Wilt said the work could support applications ranging from surgical robotics to assistive devices.