Scientists in China have developed stretchy circuits that are highly conductive, flexible and biocompatible, according to a new study. A new hybrid conductive material was produced that is part elastic polymer and part liquid metal, and which can be bent and stretched easily, and also fabricated conveniently across size scales with micro-feature precision.
The research, which is featured in the journal iScience [Tang et al. iSci. (2018) DOI: 10.1016/j.isci.2018.05.013], showed that circuits made with the material, known as a metal–polymer conductor (MPC), can take most 2D shapes and are also non-toxic. The metals used are not the usual conductive solids, such as copper, silver or gold, but rather gallium and indium, which are thick liquids that still allow electricity to flow.
In their paper, “Printable metal-polymer conductors for highly stretchable bio-devices”, it was shown that integrating some of this liquid metal mixture within a supporting network of silicone-based polymer provided mechanically resilient materials with sufficient conductivity to support functioning circuits. Such circuitry could have a wide range of potential applications in the next generation of both wearable electronics and implantable devices.
“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.”Xingyu Jiang
The structure of the MPC is similar to round pieces of liquid metal surrounded by polymer, with a liquid metal mantle below to offer complete conductivity. The team successfully tested a range of MPC formulations in many applications, such as in sensors for wearable keyboard gloves and as electrodes for stimulating the passage of DNA through the membranes of live cells.
Its flexibility could also help produce biomedical applications, such as flexible patches for identifying and mitigating heart disease. As senior author Xingyu 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.”
It is hoped the method for producing MPCs – which involves screen printing and microfluidic patterning – could accommodate any 2D geometry, and also different thicknesses and electrical properties, depending on the concentrations of the liquid metal inks to be sprayed. How the MPC is applied is dependent on the polymers, and here they cast super-elastic polymers to make MPCs for stretchable circuits, while biocompatible and biodegradable polymers can be used for MPCs for implantable devices. It might also be possible to one day create soft robots based on a combination of electroactive polymers.