Multi-Material 3D Printing of Highly Stretchable Silicone Elastomer.

3D printing of silicone elastomers with direct ink writing (DIW) process has demonstrated great potential in areas as diverse as flexible electronics, medical devices and soft robotics. However, most of current silicones are not printable due to their low viscosity and long curing time. The lack of systematic research on materials, devices and processes during printing makes it a huge challenge to apply DIW process more deeply and widely. In this report, aiming at the dilemmas in materials, devices and processes, we proposed a comprehensive guide for printing highly stretchable silicone. Specifically, to improve the printability of silicone elastomer, nano silica was added as rheology modifier without sacrificing any stretch ability. To effectively control print speed and accuracy, a theoretical model was built and verified. With this strategy, silicone elastomers with different mechanical properties can all be printed and can realize infinite time and high speed printing (>25 mm/s) while maintaining accuracy. Here, super-stretchable silicone that can be stretched to 2000% was printed for the first time and complex structures can be printed with high quality. For further demonstration, prosthetic nose, data glove capable of detecting fingers' movement and artificial muscle that can lift objects were printed directly. We believe this work could provide a guide for further work using DIW process to print soft matters in a wide range of application scenarios.