Digital light processing 3D printing of stretchable and compressible porous polymers for soft robotics

This study introduces an approach for developing highly stretchable and compressible porous materials for soft robotics applications using vat photopolymerization 3D-printing technology. The materials are developed by a stable photopolymerizable water-in-oil (W/O) emulsion, where water droplets function as pore templates, and a polyurethane diacrylate forms the surrounding stretchable matrix. The emulsion is created by mixing the dispersed aqueous phase with the continuous phase containing photoinitiators and emulsifiers, resulting in a stable emulsion suitable for 3D printing. Finally, after photopolymerization and subsequent removal of the internal water droplets, an open-cell structure is achieved, exhibiting a remarkable elongation-at-break of 450% and excellent reversible compressibility at 80%. These properties endow the material with both high compliance and strength, essential for actuator performance. Furthermore, this method allows the fabrication of high-resolution complex objects with customized porosity, incorporating both macro-pores by design and inherent micro-pores. The potential of these materials is demonstrated through the creation of novel actuators for soft robotics, showcasing unique actuation performance, shape adaptability, and high holding force. The high compliance of this material is particularly relevant for actuators as it enables efficient deformation under low energy inputs, enhancing the performance and energy efficiency of soft robotic systems.