Penn State University develops 3D printable material for wearables

Researchers at Penn State University have developed a new, soft and stretchable material that can be 3D printed. The material can be used to make wearable devices.

Liquid metal-based stretchable conductors have inherent complexities and challenges due to the activation process after fabrication. These secondary activation methods include stretching, compression, shear friction, mechanical sintering and laser activation, all of which can lead to manufacturing issues and cause leakage of the liquid metal, which in turn leads to device failure.

“Our method does not require any secondary activation to make the material conductive,” said corresponding author Tao Zhou, Penn State assistant professor of engineering science and mechanics and of biomedical engineering in the College of Engineering and of materials science and engineering in the College of Earth and Mineral Sciences. “The material can self-assemble to make its bottom surface be very conductive and its top surface self-insulated.”

In the new method, the researchers combine liquid metal, a conductive polymer mixture called PEDOT and hydrophilic polyurethane, which converts the liquid metal into particles. When the soft composite material is printed and heated, the liquid metal particles on the bottom self-assemble into a conductive path. The particles in the top layer are exposed to an oxygen-rich environment and oxidize, creating an insulated top layer. The conductive layer is crucial for transmitting information to the sensor, such as muscle activity recordings and strain measurements on the body, while the insulated layer prevents signal leakage, resulting in more accurate data collections.

The material can also be 3D printed, making it easier to manufacture wearable devices. The researchers are continuing to explore potential applications, particularly in the field of assistive technology for people with disabilities.

“Our innovation here is a materials one,” said Zhou, who also has affiliations with the Huck Institutes of the Life Sciences and the Materials Research Institute.. “Normally, when liquid metal mixes with polymers, they are not conductive and require secondary activation to achieve conductivity. But these three components allow for the self-assembly that produces the high conductivity of soft and stretchable material without a secondary activation method.”

Other authors include graduate students Salahuddin Ahmed, Marzia Momin and Jiashu Ren from the Department of Engineering Science and Mechanics and Hyunjin Lee from the Department of Biomedical Engineering at Penn State.

The work, published in the journal Advanced Materials, was supported by the National Taipei University of Technology-Penn State Collaborative Seed Grant Program and by the Department of Engineering and Mechanics, the Materials Research Institute and the Huck Institutes of the Life Sciences at Penn State.