Ultra stable and stretchable liquid-metal precisely patterned circuits for integrated wearable devices under heat-pressed

Abstract

Liquid metal (LM) has widespread applications in flexible wearable electronic devices. Despite this, challenges persist with LM and thermoplastic polyurethane (TPU) composite materials in creating flexible electronic circuits, including complex processes, limited pattern precision and material inefficiencies. This study introduced a LM composite material, TPU@LM ink, suitable for dispensing printing. By fine-tuning the ratio of LM to TPU, this ink enabled the production of micron-scale ultrastable flexible circuits. The patterned TPU@LM circuit achieved a minimum line width of 239.01 μm and conductivity of 7.5 × 10³ S/cm, exhibiting stretchable conductivity stability (1000 cycles), thermal stability (25°C-100 °C) and repairability. The hysteresis error of the sensing performance was only ±3.18 % upon stretching to 400 %. The circuit could be repeated 2000 times and could detect a tensile strain of 0.5 %. The temperature of the TPU@LM circuit could be increased to 70.51 °C, the temperature only decreased by 0.4 °C after stretching 2000 times and the heating-cooling process could be cycled. Additionally, the recovery rate of TPU@LM ink was 93.8 % and it could be reused. Additionally, motion monitoring and thermal therapy experiments confirmed that the TPU@LM circuit maintains stable conductivity under high temperature and pressure conditions (100 °C and 20 kPa), facilitating seamless integration between the TPU@LM circuit and clothing and accessories.