2D and 3D Structuring of Freestanding Metallic Wires Enabled by Room-Temperature Welding for Soft and Stretchable Electronics

In
this work, a facile and cost-effective approach to assemble
metallic wires into two-dimensional (2D) and three-dimensional (3D)
freestanding geometries by room-temperature welding is demonstrated.
The low melting point of gallium (29.8 °C) enables the welding
at room temperature without the aid of high-energy sources required
for high-melting-point metals and alloys. The welding enables assembly
of solid gallium wires into 2D and 3D geometries that could create
freestanding architectures with multiple junctions along any inclined
direction. These 2D and 3D freestanding metallic structures are freeze-cast
in soft elastomers to obtain stretchable and soft devices: a 2D stretchable
resistive and capacitive sensor patterned with parallel metal lines,
a 2D stretchable capacitive sensor patterned with an interdigitated
metal structure with capacitive changes on stretching in both x- and y-axes, and a 3D compressive sensor
by assembly of liquid metal helices, which could sense foot pressure
compression. We also developed a facile method to interconnect between
soft circuits and external electronics, suppressing stress during
mechanical deformation.