Underwater 3D Printing Using Dual‐Photoresponsive Droplets

ABSTRACT Droplet‐based 3D printing, particularly drop‐on‐demand (DOD) printing, has attracted considerable interest due to its wide range of applications in tissue engineering and biomedical research. However, challenges remain in reported DOD printing systems, such as the elimination of satellite droplets, the accurate control of droplet size, and the precise placement of droplets after generation. To address these issues, we have developed a photocontrolled underwater DOD printing system based on dual photo‐responsive droplets. The organic droplets are composed of spiropyran, alkylphosphonic acid, a photoinitiator, and monomers, which act as building blocks. Light controls the entire 3D printing process, including the on‐demand generation, manipulation, and solidification of each droplet underwater. Spiropyran and alkylphosphonic acid are typically used for droplet generation and manipulation under 405 nm light illumination, while the photoinitiator and monomers are used for droplet solidification under 365 nm light. Using this unique DOD technology, we have successfully printed simple 3D models such as line structures, triangle walls, and pillars underwater. We have also printed patches to separate communicating vessels or repair leaks underwater. This technology has great potential for developing the next generation of additive manufacturing technologies, such as underwater 3D printing.