Directly Printable and Adhesive Liquid Metal Ink for Wearable Devices

Leveraging the fluidity and excellent conductivity of liquid metal (gallium-indium alloy), liquid metal (LM) can be utilized to manufacture flexible and stretchable electronic products for applications in soft robotics, wearable devices, and human–machine interaction. However, the high surface tension and low surface adhesion of LM hinder its patterning and high-resolution fabrication of soft electronics. Here a recyclable LM-silicon dioxide (LMS) ink is proposed. Under stirring, silicon dioxide (SiO₂) particles are encapsulated by the oxide layer of the LM, consuming the oxide layer. Meanwhile, gallium in the LM reacts with oxygen from the air to form a new oxide layer, enhancing the adhesion of the LM to the substrate while maintaining its conductivity. The in-situ printing of LMS ink is verified on various materials (e.g., paper, polymer, and glass) with a resolution of up to 165 µm and an exceptional conductivity of ≈6.53 × 10⁶ S m⁻¹. The printed patterns can be erased with an anhydrous ethanol solution, allowing the recovered LMS ink to be reused for multiple writing cycles. The general method for direct LM circuits printing can fabricate various wearable sensors for soft electronic devices and human–machine interaction.