Gallium is a key ingredient of this self-healing and pliable circuit for next-generation wearables, other smart devices.

Flexibility, durability, and efficiency are some of the key functions scientists are trying to narrow down for wearable tech, soft robotics, or smart devices. In comparison, there have been numerous advances in this field, but the recipe for something as pervasive as the cellphone has yet to meet the mark. That may change with a novel liquid metal circuit developed by National University of Singapore scientists that is pliable, self-healing, and highly conductive.

For years, imaginations have conceived a stretchable and durable sensor for monitoring patients that seems almost a part of one's skin or perhaps a cellphone embedded directly into the palm of one's hand. This dream of seamless and convenient connectivity has long held a place in the annals of science fiction; however, the primary limiting factor has been the rigidity of today's circuits.

Named the Bilayer Liquid-Solid Conductor (BiLiSC), this newly engineered material can reportedly stretch up to 22 times its original length without sustaining a significant drop in its electrical conductivity – a property that has not been previously achieved.

Due to this capability, the researchers say this stretchiness enhances the effectiveness as well as comfort of potential human-device interfaces, opening up a wide array of opportunities for its use in healthcare wearables.

"We have developed this technology in response to the need for circuitry with robust performance, functionality and yet 'unbreakable' for next-generation wearable, robotic and smart devices," said the Director of the NUS Institute of Health and Technology and research team leader, Professor Lim Chwee Teck. "The liquid metal circuitry using BiLiSC allows these devices to withstand large deformation and even self-heal to ensure electronic and functional integrity."

What makes BiLiSC?

Reported late last year in the journal Advanced Materials, BiLiSC is an exciting technology that is ideal for use in wearable devices, according to the NUS team, as it is able to account for the shape and various movements of the body.

Consisting of two layers, the first layer is a self-assembled pure liquid metal, which can provide high conductivity, even under high strain, and ultimately reduces energy loss during power transmission or signal output.

In the supplemental information under their published work, a nonconductive gallium oxide shell is mentioned once, and eutectic gallium-indium particle (eGaInP)s was specified frequently.

As it appears a unique and possibly proprietary technology, the exact material composition is purely conjecture but can be reasonably presumed contains gallium and indium for their structure and conductivity.

The second layer is a composite material containing liquid metal particles, which is where its self-healing properties come into play. Were a crack or tear to occur, the liquid metal that escapes would fill in the gap, allowing the material to repair itself almost instantaneously to retain its conductivity.

To highlight the potential of this technology making its way to consumers, the NUS team made sure to fabricate BiLiSC in a highly scalable and cost-efficient manner, with the highest expectations of making sure the innovation is commercially viable.

Functionality and future

The NUS team demonstrated that their BiLiSC can be made into numerous electrical components for wearable electronics, such as pressure sensors, interconnections, wearable heaters, and wearable antennas for wireless communication.

In laboratory experiments, a robotic arm using interconnections was quicker in detecting and responding to minute changes in pressure. Additionally, the bending and twisting motion of the robotic arm did not impede the transmission of signals from the sensor to the signal processing unit, compared to another interconnection made with a non-BiLiSC material.

Following the successful demonstration of BiLiSC, the NUS team is now working on material innovation and process fabrication.

Looking to engineer an improved version of its material that can be printed without the need for a template, this goal aims to reduce costs further and improve the precision in future fabrication of BiLiSC.