New self-folding, highly conductive sensors could improve wearable devices

To advance soft robotics, skin-integrated electronics and biomedical devices, Penn State researchers have developed a 3D-printed material that is soft and stretchable — characteristics essential for matching the properties of tissues and organs — and that self-assembles. Their approach uses a process that overcomes many of the drawbacks of previous manufacturing methods, such as lower conductivity or device failure, the team said.

They published their results in Advanced materials.

“People have been developing soft and stretchable conductors for almost a decade, but their conductivity is usually not very high,” said corresponding author Tao Zhou, assistant professor of engineering science and mechanical and biomedical engineering in the Penn State College of Engineering and of materials science and engineering in the College of Earth and Mineral Sciences. “Researchers realized they could achieve high conductivity using liquid metal-based conductors, but a significant limitation is that it requires a secondary method to activate the material before it can achieve high conductivity.”

Stretchable liquid metal-based conductors suffer from inherent complexity and challenges posed by the post-fabrication activation process, the researchers said. Secondary activation methods include stretching, compression, shear friction, mechanical sintering and laser activation, which can lead to challenges in fabrication and can cause liquid metal leakage, resulting in device failure.

“Our method does not require any secondary activation to make the material conductive,” said Zhou, who is also affiliated with the Huck Institutes of the Life Sciences and the Materials Research Institute. “The material can self-assemble so that its bottom surface is highly conductive and its top surface is self-insulating.”

In the new method, the researchers combine liquid metal, a conductive polymer blend called PEDOT:PSS, and a hydrophilic polyurethane that allows the liquid metal to transform into molecules. When the composite soft material is printed and heated, the liquid metal molecules on its bottom surface self-organize into a conductive path. The molecules in the top layer are exposed to an oxygen-rich environment and oxidize, creating an insulated top layer. The conductive layer is critical for transmitting information to the sensor—such as recording muscle activity and detecting body stress—while the insulating layer helps prevent signal leakage that could lead to less accurate data collection.

“Our innovation is in the materials,” Zhou said. “Usually, when liquid metal is mixed with polymers, they are not conductive and require secondary activation to become conductive. However, these three components enable self-assembly, which provides high conductivity in a soft and stretchable material without a secondary activation method.”

The material can also be 3D printed, Zhou said, making it easier to produce wearable devices. The researchers are still investigating potential applications, with a focus on assistive technology for people with disabilities.

Reference: Ahmed S, Momin M, Ren J, Lee H, Zhou T. Self-assembled, printed, asymmetric, self-insulating, stretchable conductor for human interface. Advanced materials. 2024;36(25):2400082. doi: 10.1002/adma.202400082

This article has been republished from the following materials. Please note that the material may have been edited for length and content. For more information, please contact the source listed. Our press release policy is available Here.