Nanocellulose–polyurethane substrate material with tunable mechanical properties for wearable electronics

Wearable electronics require thin and flexible substrate materials for user comfort. We propose a substrate material based on a nanocellulose–polyurethane matrix. The stretchability, i.e. Young's modulus and breaking strain, of the material can be tuned by nanocellulose concentration. We describe the fabrication process and demonstrate the modulation of the mechanical properties. Further, we present oxygen and water vapour permeability, as well as dielectric properties' measurements. Effects of substrate properties on printing of metallic conductors are considered. Laser cutting of the substrate and lamination of several layers of substrate material together are demonstrated, as well as hybrid integration of discrete components on the substrate. As an integrated demonstrator, a patch for local skin surface temperature measurement is presented. The patch thickness is 50 μm, and it consists of two layers of the substrate material, printed metallic conductors and hybrid integrated temperature sensors.