Crystal Growth Inhibition in the Preparation of Water-Dispersible Photoinitiator Particles for High-Precision Three-Dimensional Printing of Double Network Hydrogels

The double network hydrogel (DN gel) is widely used in applications such as soft robotics, artificial muscle, wearable electronics, and biomedical engineering due to its unique combination of softness and toughness. Three-dimensional (3D) printing of the DN gel provides a rapid and cost-effective approach for producing shapes desired in these applications, making it an ideal solution for customization and performance enhancement. However, 3D printing of water-soluble resins such as DN gels remains challenging due to the high cost and the complexity of the synthesis or preparation processes of water-soluble or water-dispersible photoinitiators. In this study, we present a cost-effective method for preparing water-dispersible photoinitiator particles and demonstrate 3D dynamic light processing (DLP) 3D printing. By optimizing the ratio of cophotoinitiators and cosurfactants in the manufacturing process, the growth of photoinitiator crystals was effectively suppressed, and the manufacturing process was greatly simplified compared to previous methods. The introduction of water-dispersible photoinitiator particles facilitated the rapid conversion of acrylate functional groups, achieving over 95% conversion within 10 s. This fast curing rate allowed successful printing even with a low-cost DLP 3D printer (∼$500) utilizing a typical light-emitting diode (LED) light source. As a result, we achieved high-precision printing of the DN gel using water-dispersible photoinitiator particles and confirmed that the printed structures exhibited outstanding mechanical properties, including elongation exceeding 1700% and tensile strength greater than 220 kPa. In addition, it was confirmed that cytocompatibility was enhanced through the postprocess of removing residual photoinitiator particles. We expect that the facile and cost-effective production of water-dispersible photoinitiator particles will accelerate research in the 3D printing of water-based resins, particularly hydrogel-based 3D printing.