Laser-assisted direct three-dimensional printing of free-standing thermoset devices

The three-dimensional printing of thermoset materials is of use in the development of flexible electronics and soft robotics. However, the process typically involves the deposition and removal of supporting materials that require extensive cycles of pre- and post-processing. Here we describe a three-dimensional printing method for constructing functional and arbitrary free-standing thermoset structures without using supporting materials. The approach integrates in situ laser-induced solidification with direct ink writing. During printing, the integrated laser is focused on a micro-sized polymer jet, leading to thermoset crosslinking in less than 0.25 s through a strong photothermal effect. The process offers a resolution as fine as 50 μm, with mechanical properties tunable by up to tenfold and electrical properties by up to 20-fold. We used this approach to print stretchable electronics with stiffness gradients for strain inhibition, flexible sensors with high sensitivity and three-dimensional soft magnetic robots for actuation functions.