High stretchability and conductive stability of flexible hybrid electronic materials for smart clothing

In this study, a flexible hybrid electronic (FHE) material with enhanced conductivity was developed and successfully applied to electromyograms (EMG) and electrocardiograms (ECG) of smart clothing. The FHE material comprises a highly stretchable patterned circuit with dry flexible electrodes. The pre-stretched circuit was obtained by mixing three-dimensional (3D) dendritic silver nanoparticles (AgNPs) with two-dimensional (2D) reduced graphene oxide (rGO) in a thermoplastic elastomer and patterning the resultant as wires using steel plate stencil printing. Based on the nano-dispersion principle, the geometrical differences of nanomaterials could be exploited to form a 3D continuous phase conductive network with improved tensile properties. A highly stretchable and bendable conductive film with a resistance of 1.4 × 10−2 ohm/sq was obtained by mixing 80 wt% of 3D dendritic AgNPs and 1 wt% of rGO to produce pre-strained nanowires with a horseshoe pattern. Furthermore, the conductive film could be coated with a polyurethane (PU) layer to achieve good stability in the washing test. In the tensile fatigue test, the resistance variation ΔR of horseshoe patterned nanowire was only 1.9 ohm under 500 stretches. Additionally, a low-resistance film (∼103 ohm.cm) was fabricated by adding 7 wt% of carbon black and 2D graphene nanoplatelets (CB/GNPs, 4:1) and styrene maleic anhydride-amide (SMA-amide, 10:1 ratio with carbon material), yielding superior fatigue resistance. Finally, a design combining the pre-stretched circuit pattern with dry sensing flexible conductive electrodes was developed and successfully applied for EMG and ECG of smart clothes.