# Iron-On Wearable Electronics through Liquid Metal Adhesive Composites

## TL;DR

This paper introduces a new type of stretchable and adhesive composite material for wearable electronics that can be easily integrated with fabrics and other components.

## Contribution

The novel contribution is a stretchable, conductive, and reprocessable composite of liquid metal microdroplets in a thermoplastic matrix suitable for wearable electronics.

## Key findings

- The LM-TPU composites exhibit high stretchability (over 600% strain at break) and strong adhesion to fabrics.
- The composites maintain electrical conductivity (up to 8.0 × 10⁵ S m⁻¹) and can be reprocessed for hot melt adhesion.
- The material enables the integration of soft conductors with rigid components and fabrics for functional soft circuits.

## Abstract

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.