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Flexible circuits

Chinese Researchers Develop Non-Toxic, Flexible Material for Circuits

A hybrid material developed by Chinese researchers can be used to develop flexible, biocompatible electronic circuits.

Researchers have developed a hybrid material of polymer and liquid metal that can be used to develop non-toxic, stretchable circuits for next-generation flexible electronics and medical devices.

A team at the National Center for Nanoscience and Technology created the material. Called a metal-polymer conductor (MPC), it is composed of elastic polymer and liquid metal. It can be bent and stretched at will, meaning that circuits made with it can take most two-dimensional shapes.

LED circuits interconnected by a new hybrid material developed by researchers in China can undergo repeated bending, twisting, and stretching. (Image source: Tang et al., National Center for Nanoscience and Technology)

The material also is biocompatible, making the components made with it non-toxic, said Xingyu Jiang, a professor at the center who worked on the project. This is well-suited to one of the goal applications for the team: the development of new biomedical devices.

"These are the first flexible electronics that are at once highly conductive and stretchable, fully biocompatible, and able to be fabricated conveniently across size scales with micro-feature precision," he said. "We believe that they will have broad applications for both wearable electronics and implantable devices."

The components comprising the MPC are at the same time very different, yet have properties that are equally needed for the material to function, researchers said. The metals in the material are gallium and indium rather than the usual conductive solids, such as copper, silver, or gold. In this case, the metals exist as thick, syrupy liquids that still permit electricity to flow.  

Support Structure 

In fact, as researchers discovered, embedding masses of this liquid-metal mixture within a supporting network of silicone-based polymer created mechanically resilient materials with sufficient connectivity to support functioning circuits, Jiang said. Researchers published a paper on their work in the journal iScience.

When examined closely, the MPC’s structure appears like round liquid-metal islands floating in a sea of polymer, with a liquid-metal mantle underneath to ensure full conductivity.

Researchers used both screen printing and microfluidic patterning in their process to fabricate the material. They said this is well-suited to scaling up for industry, as it can accommodate any two-dimensional geometry or different thicknesses and electrical properties, depending on the concentrations of the liquid-metal inks to be sprayed.

Variety of Uses

The team experimented with different MPC formulations in a variety of applications with reported success. These tests included using the material to develop sensors for wearable-keyboard gloves and as electrodes for stimulating the passage of DNA through the membranes of live cells, they said.

During their tests, researchers found that the applications of the MPC depended on the polymers. For example, super-elastic polymers made the MPCs viable for the development of stretchable circuits. To design implantable devices, researchers used biocompatible and biodegradable polymers.

Indeed, biomedical applications are one of the key reasons for the design of the material, Jiang said. "We wanted to develop biocompatible materials that could be used to build wearable or implantable devices for diagnosing and treating disease without compromising quality of life, and we believe that this is a first step toward changing the way that cardiovascular diseases and other afflictions are managed," he said. Researchers even anticipate using the material to build soft robots in the future by combining electro-active polymers, he added.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for 20 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time, she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.

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