Highly Stretchable and Strain‐Insensitive Liquid Metal based Elastic Kirigami Electrodes (LM‐eKE)

Abstract

Kirigami, a traditional paper‐cutting art, is a promising method for creating mechanically robust circuitry for unconventional devices capable of extreme stretchability through structural deformation. In this study, this design approach is expanded upon by introducing Liquid Metal based Elastic Kirigami Electrodes (LM‐eKE) in which kirigami‐patterned soft elastomers are coated with eutectic gallium‐indium (EGaIn) alloy. Overcoming the mechanical and electrical limitations of previous efforts with paper‐like kirigami, the all soft LM‐eKE can be stretched to 820% strain while the electrical resistance only increases by 33%. This is enabled by the fluidic properties of the EGaIn coating, which maintains high electrical conductivity even as the elastic substrate undergoes extreme deformation. Applying the LM‐eKE to human knee joints and fingers, the resistance change during physical activities is under 1.7%, thereby allowing for stable electrical operation of wearable health monitoring devices for tracking electroencephalogram (EEG) signals and other physiological activity.

Materials-Driven Soft Wearable Bioelectronics for Connected Healthcare

“…Nevertheless, it is critically important to establish a conformal contact of bioelectrodes with the scalp for reliable EEG measurement with a high SNR value. 575 A self-supporting kirigami-structured LM paper (KLP) was fabricated with uniaxial, biaxial, and square spiral structures, showing considerable stretchability, ultrathin thickness, and conductor-exposing feature for a multifunctional E-skin. 576 The biaxial KLP could obtain precise real-time EEG recording for a subject engaged in three mental states including deep-thinking, closed eyes, and sleeping, showing distinct frequencies and intensities.…”

“…Another obstacle for long-term reliable EEG recording lies in the fact that the dense hairs of the head would cause interference to the effective contact of electrodes with the scalp. Nevertheless, it is critically important to establish a conformal contact of bioelectrodes with the scalp for reliable EEG measurement with a high SNR value . A self-supporting kirigami-structured LM paper (KLP) was fabricated with uniaxial, biaxial, and square spiral structures, showing considerable stretchability, ultrathin thickness, and conductor-exposing feature for a multifunctional E-skin .…”

Liquid Metal–Polymer Conductor-Based Conformal Cyborg Devices

“…134 The biphasic Au-EGaIn film has little mechanical stiffness and allows LM-eKE to maintain a low elastic modulus (∼kPa scale) and high deformability. 134 Researchers also report a wafer-scale patternable strategy for the high-resolution fabrication of super soft, stretchable, and permeable liquid metal microelectrodes, by utilizing the selectivity wetting of EGaIn between Ag (the pattern) and SBS fiber mat (the substrate). 135 his method can also be used to fabricate composite materials.…”

Omnidirectional Configuration of Stretchable Strain Sensor Enabled by the Strain Engineering with Chiral Auxetic Metamaterial

“…The change of strain distribution leads to the different response of the electric signal, and thus the performance of the stretchable strain sensor is regulated. Since this paradigm merely relies on engineering the mechanical properties of the sensor, it works with various types of active materials and can be used to enhance the performance of existing stretchable strain sensors or stretchable electrodes. − …”