Highly Conductive and Ultra-Thin Elastic Silver-Nanosheet Membrane for Neural Recording

Nanocomposites are gaining prominence as suitable materials for skin wearable and implantable electronics due to their tissue-like mechanical properties and adequate electrical properties. However, achieving both conformal adhesion and excellent electrical and mechanical properties is challenging, as thickness and conductivity are often in a trade-off relationship for most of the materials. To overcome the challenge, highly elastic and conductive nanomembranes have been developed by leveraging 1-dimensional nanowires to form a nanocomposite with enhanced percolation networks between conducting nanofillers. However, owing to the geometrical anisotropy of the nanowire, nanomembrane exhibited different properties depending on the directions. Here, we present a stretchable and laser-patternable nanomembrane using 2-dimensional(2D) silver nanosheets with isotropic and high electromechanical properties. The single layer of nanomembrane is ultrathin (~ 250 nm) and highly conductive (> 80,000 S/cm) yet remains stretchable since the elastomer layer separated from the nanosheets dissipates the stress induced to the membrane. Furthermore, 2-dimensional nanosheets endow the membrane with isotropic mechanical and electrical performances in every direction. Based on float assembly fabrication, silver nanosheets were tightly gathered and partially embedded into the elastomer on the larger surface area of the silver nanosheet and constructed partial face-to-face contact. This face-to-face junction decreases the contact resistance of the nanomaterials, contributing to the high conductivity of the membrane. In addition, the silver nanosheet membrane was able to be manufactured with different dimensions and thicknesses by controlling fabrication variables, displaying distinct characteristics in electrical conductivity, stretchability, impedance, and modulus in each variable-controlled membrane. Moreover, through the bilayer stacking process, the contacts between silver nanosheets created extra percolation networks, resulting in a significant enhancement of conductivity, reaching up to 125,000 S/cm. By patterning the encapsulated nanomembrane with laser, we fabricated a stretchable electrode array making a conformal adhesion to the skin and nerves, demonstrating the future potential of the membrane for broad application both in wearable and implantable approaches.