EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The conversion of commercial polymers into conductive porous graphene by direct laser scribing with a CO2 infrared laser, creating the Laser Induced Graphene (LIG), is an easy and highly scalable production method for conductive track patterning. LIG is a 3D porous material exhibiting very high surface area, excellent conductivity and high thermal stability.
While polyimide and other rigid commercially available polymer sheets represent excellent LIG precursors, their unfitting mechanical properties and poor gas permeability are limiting their use in epidermal applications, especially over long-term and in real-life scenarios. A seamless interfacing with skin is indeed sought after in epidermal electronics applications.
In this study we present a strategy to overcome these issues by transferring LIG onto substrates which provide excellent conformal adhesion on skin, stretchability, high breathability and waterproof stability. All of these features are combined in a commercially available medical grade polyurethane (MPU). MPU allows for the transfer and embedding of LIG resulting in a composite with excellent electro-mechanical characteristics and long term stability. Fabricated LIG/MPU composites show high stretchability over 100%, as well as long-term durability in electromechanical tensile tests up to 200 cycles. Thin (30 µm) and soft (E ~15 MPa) epidermal devices with high wearing comfort and tunable electro-mechanical properties are realized, which can be worn on skin for several days retaining full stability and functionality, even after showering.

By tuning the laser scribing parameters, the LIG morphology (“flat” porous vs. fibrous) and therefore the resulting sheet resistance and stretching behaviour can be controlled.
LIG/MPU composites were implemented as minimally invasive epidermal sensing devices including skin-contact dry electrode for electromyographic (EMG) recording on limb and as piezoresistive sensors for pressure/touch and respiration detection.