Iron-On Wearable Electronics through Liquid Metal Adhesive Composites

E-textiles and wearable electronics can enable diverse applications from health care and environmental monitoring to robotics and human-machine interfaces. These technologies demand circuity that is flexible and stretchable while being able to integrate with functional components and deformable substrates like fabrics. Therefore, stretchable conductors and processing techniques that tightly integrate these diverse components both electronically and mechanically are important for these emerging devices. Here, we create composites of liquid metal (LM) microdroplets within a thermoplastic polyurethane (TPU) matrix that is stretchable (greater than 600% strain at break), adhesive to various common fabrics via heat transfer (toughness up to 6400 J m^-2), and electrically conductive as prepared (up to 8.0 × 10⁵ S m^-1). By using a thermoplastic matrix, the LM-TPU composites can be reprocessed, making them applicable to hot melt adhesion while the LM droplets enable electrical conductivity. The LM-TPU composites create soft conductors that electrically and mechanically integrate via heat transfer with rigid components and fabrics to create functional soft circuits. This enables flexible, electrically conductive composites that can be readily integrated for applications in wearable circuits and e-textiles.