Low-Temperature-Printed Liquid Metal-Based 3-D Circuits Applied for Stretchable Biomedical Electronics

The integrated development of stretchable electronics is inevitably led to an increase in the density of electronic components, which substantially increase the complexity of conductive pathways. This complexity causes substantial challenges in circuit design. Therefore, the formation of a three-dimensional (3-D) cross-bridge wire interconnection structure is of vital significance for the high-density integrated development of stretchable electronic devices. To fulfill this requirement, this study introduces a low-temperature liquid metal (LM)-based 3-D printing technology, which can print LM-based 3-D circuits. First, the influence of cooling temperature, nozzle diameter, printing speed, and the distance between nozzle and substrate on the accuracy of LM-based circuits is characterized. After characterization, various complex LM-based 3-D structures are successfully generated. To verify its reliability, LM-based 3-D circuits and LED lights are integrated, which exhibited stable mechanical and electrical properties under various deformations. These included bending, twisting, and stretching. Finally, based on the low-temperature LM-based 3-D printing technology, a portable noninvasive stretchable biomedical electronic device is developed that is composed of LM-based 3-D circuits, a heart rate, and a blood oxygen sensor. The results revealed that the stretchable biomedical sensor has the potential to help patients improve their lives in the future.