Home Research & Education 3D-printed mini actuators can move small soft robots and shape them into...

3D-printed mini actuators can move small soft robots and shape them into new forms

Researchers at North Carolina State University have presented miniature soft hydraulic actuators that can be used to control the deformation and movement of soft robots that are less than a millimeter thick.

The new technology is based on the production of soft robots consisting of two layers. The first layer is a flexible polymer produced using 3D printing technologies and contains a pattern of microfluidic channels. The second layer is a flexible shape memory polymer. Together, the soft robot is only 0.8 millimeters thick.

“Soft robotics holds promise for many applications, but it is challenging to design the actuators that drive the motion of soft robots on a small scale,” says Jie Yin, corresponding author of a paper on the work and an associate professor of mechanical and aerospace engineering at NC State. “Our approach makes use of commercially available multi-material 3D printing technologies and shape memory polymers to create soft actuators on a microscale that allow us to control very small soft robots, which allows for exceptional control and delicacy.”

Pumping fluid into the microfluid channels creates hydraulic pressure that moves the soft robot and changes its shape. The pattern of the microfluid channels controls the movement and shape changes of the soft robot – whether it bends, turns or moves in other ways. In addition, the speed of movement and the force of the robot is regulated by the amount and speed of the fluid introduced.

If users want to “freeze” the shape of the soft robot, they can apply moderate heat (64°C) and allow the robot to cool briefly. This prevents the soft robot from returning to its original shape even if the liquid is removed from the microfluid channels. To return the robot to its original shape, the heat is applied again after the liquid has been pumped out.

“A key factor here is fine-tuning the thickness of the shape memory layer relative to the layer that contains the microfluidic channels,” says Yinding Chi, co-lead author of the paper and a former Ph.D. student at NC State. “You need the shape memory layer to be thin enough to bend when the actuator’s pressure is applied, but thick enough to get the soft robot to retain its shape even after the pressure is removed.”

To demonstrate the technology, the researchers developed a soft robotic gripper that can pick up small objects. Hydraulic pressure was used to close the gripper around an object. The researchers used heat to fix the gripper in its closed position, even after the pressure was removed. The gripper was able to transport the object and release it by heating it up again.

“Because these soft robots are so thin, we can heat them up to 64C quickly and easily using a small infrared light source – and they also cool very quickly,” says Haitao Qing, co-lead author of the paper and a Ph.D. student at NC State. “So this entire series of operations only takes about two minutes. And the movement does not have to be a gripper that pinches. We’ve also demonstrated a gripper that was inspired by vines in nature. These grippers quickly wrap around an object and clasp it tightly, allowing for a secure grip. This paper serves as a proof-of-concept for this new technique, and we’re excited about potential applications for this class of miniature soft actuators in small-scale soft robots, shape-shifting machines, and biomedical engineering.”

The research paper, “Fully 3D-Printed Miniature Soft Hydraulic Actuators with Shape Memory Effect for Morphing and Manipulation,” was published in the journal Advanced Materials. The work was supported by the National Science Foundation.

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