Soft, Stretchable and Wireless Sensor Patch with Digitally Printed Liquid Metal Alloy Interconnects

Characteristics of high electrical conductivity, high strain tolerance and resistance to fatigue are vital for electronic circuits of on-skin wearable systems. Gallium-based liquid metals offer a unique combination of these characteristics making them excellent alternatives to conventional conductive stretchable inks. In order to obtain better wearing experience, it is advantageous to fabricate devices using breathable materials. However, effective automation solutions for the production of high-resolution digitally patterned circuits for soft and stretchable devices remain a challenge. The presented manufacturing strategy involves adopting a needle dispensing technique for the precise patterning of liquid metal conductors. The circuitry is deposited onto a soft, thin and highly breathable polyurethane medical film. Further, we investigate and map conditions of reliable printing of liquid metal on the polyurethane film for two sizes of dispensing needles with inner diameters of
$150\ \mu \mathrm{m}$
and
$360\ \mu \mathrm{m}$
. Despite the increased porosity and surface roughness associated with the high breathability of the film, it is possible to reliably deposit liquid metal interconnects with a line width and height below
$100\ \mu \mathrm{m}$
. The technological solution results in a first demonstrator presented: an electrophysiological patch.