Surface-Embedded Liquid Metal Electrodes with Abrasion Resistance via Direct Magnetic Printing

Abstract

Gallium-based liquid metals (LMs) featuring both high conductivity and fluidity are ideal conductors for soft and stretchable electronics. However, their liquid nature is a doubleedged sword in many key applications since LMs are inherently prone to mechanical damage. Although additional encapsulation is frequently used for the protection of delicate LM electrodes, it hinders the electrical interfacing with other objects for interconnection, sensing, and stimulation. Here, different from conventional patterning methods that deposit LM on or inside substrates, we for the first time report a simple strategy to create surface-embedded LM of eutectic gallium-indium (EGaIn) circuits with mechanical damage endurance. This was achieved by using direct magnetic printing to overcome the high surface tension of LM, allowing it to be passively filled into the laser-patterned microgrooves on soft substrates. We show that the surface-embedded LM circuits are resistant to mechanical erasure, washing, and peeling. We also show the applications of our surface-embedded LM electrodes in respiration monitoring and electrical stimulation of nerves. This work provides a simple and efficient way to create mechanically reliable LM microelectrodes, holding great promise for wearable and implantable bioelectronics.

Liquid Metal-Based Electronics for On-Skin Healthcare

“…The encapsulation layers serve in the form of a condensed elastomer film [95], electrospun mat [124], and sheath for the core conductive fibers [78]. Second, other nanomaterials and novel structures have been introduced to LM conductive networks, such as the carbon nanofiber protection layer on LM particles in [125] and the microgrooves design for the abrasion resistance of LM in [126]. In addition, the size effect of LM was developed very recently, and the LM leakage issue can be addressed in an LM-elastomer mixture with the LM sized <5 µm [127].…”

Research Progress in Stretchable Circuits: Materials, Methods, and Applications

“…Recent methods of preparing liquid metal for stretchable circuits include direct-write extrusion, [29] micro-contact printing, [30] inkjet printing, [31] selective wetting, [32,33] and masked deposition. [34,35] Among these methods, inkjet printing technology is extensively used in the research of stretchable circuits due to its high degree of automation, fast preparation speed, and the advantages of high resolution.…”

“…Recent methods of preparing liquid metal for stretchable circuits include direct‐write extrusion, [ 29 ] micro‐contact printing, [ 30 ] inkjet printing, [ 31 ] selective wetting, [ 32,33 ] and masked deposition. [ 34,35 ]…”

Highly Stable Liquid Metal Conductors with Superior Electrical Stability and Tough Interface Bonding for Stretchable Electronics

“…10,28 Embedding the LM into the surface microstructure effectively improves the mechanical reliability, making it resistant to mechanical erasure and washing. 29,30 Unfortunately, the rheological properties of LM such as low viscosity, high surface tension, and spontaneous formation of oxide skins hinder the spread of LM into the embedded structure. 17 The interface contact area between LM and elastomer cannot be further increased to strengthen adhesive bonding.…”

“…Another method is to utilize physical methods to construct LM–polymer composite materials, including dispersing liquid metal particles (LMPs) or LMPs with a solid conductive filler in an elastomer, , doping LMPs in a polymer substrate, and forming a biphasic LM alloy. , These methods enable a favorable interaction with the substrate, while low conductivity or deteriorating stretchability are still issues. Moreover, coating LM on a fibrous or porous structure allows us to attain excellent interface interaction by mechanical interlocking. , Embedding the LM into the surface microstructure effectively improves the mechanical reliability, making it resistant to mechanical erasure and washing. , Unfortunately, the rheological properties of LM such as low viscosity, high surface tension, and spontaneous formation of oxide skins hinder the spread of LM into the embedded structure . The interface contact area between LM and elastomer cannot be further increased to strengthen adhesive bonding.…”