Liquid metal flexible electronics: Past, present, and future

Flexible electronics is one of the most overwhelming and promising technologies available today, receiving widespread attention from both academia and industry. As it continues to evolve, demands on flexible conductive materials are becoming increasingly prominent. Liquid metals (LMs), which combine the compliance of fluids with the electrical conductivity of metals, are excellent candidates among various material options for fabricating flexible electronics. Following more than a decade of development, LM flexible electronics has become a rather promising research field. This review aims to provide a comprehensive summary and interpretation of the typical progress in LM flexible electronics so as to promote further advancement in the area. First, modification strategies of LMs, such as oxidation and composite approaches (doped particles or mixed polymers), are systematically digested to improve their performances and increase the formability involved. Furthermore, we divide the LM flexible electronics into three major architectures (LM flexible electronics with channels, LM printed electronics, and LM/polymer flexible electronics) and introduce the core patterning methods for each type. In addition, we provide an overview of the representative applications of LM flexible electronics in the categories of soft sensors, biomedicine, flexible energy, electronic fabrics, etc. Finally, the current challenges and potential directions of LM flexible electronics are discussed. Overall, the past progress, current situation, and future outlook as outlined in full view in the present article is expected to inspire tremendous new opportunities for further fundamental research or practical explorations of LM flexible electronics in the coming time.