Printable Liquid-Metal@PDMS Stretchable Heater with High Stretchability and Dynamic Stability for Wearable Thermotherapy

As a type of flexible electronics, wearable heaters have attracted broad attention because of their giant potential market value, such as for use in wearable thermotherapy. Wearable heaters are required to simultaneously possess high stretchability and dynamic stability, in order to realize joints or muscles thermotherapy during exercising. Here, a high-performance electrically driven heater using the conductive composite of liquid-metal (LM) and polydimethylsiloxane (PDMS) is reported, which is patterned as sinusoidal structure by the printing technology of direct ink writing. Because high conductive LM is chosen as the active material, the LM@PDMS stretchable heater possesses high stretchability (>100% strain) and good conductivity (1.81 x 10(3) S cm(-1)). It also exhibits superb dynamic stability, due to the 3D conductive network of LM in matrix and the sinusoidal structure of the composite. While being stretched to the strain level of 100%, the heating temperature variation of LM@PDMS stretchable heater is less than 8%. This relatively low temperature variation is several times smaller than that of existing heaters at the same large strain levels. It is demonstrated that the LM@PDMS stretchable heater worn on the knee joint works well during strenuous exercise, thus proving great potential in wearable thermotherapy.