Surface modification of 3D printed microfluidic devices by photochemical grafting.

Three-dimensional (3D) printing has emerged as a promising method for fabricating microfluidic devices due to its rapid prototyping, adaptability, and cost-effectiveness. However, the intrinsic hydrophobicity of commercial photocurable resins limits their ability to generate stable oil-in-water (O/W) emulsion droplets. In this study, we addressed this limitation by introducing a simple yet effective surface modification technique, photochemical grafting, which covalently attaches hydrophilic methacrylic acid groups onto the surfaces of 3D-printed channels, enabling reliable monodisperse O/W droplet formation. Integrating two modules with contrasting wettabilities yields a modular platform for single-step production of double emulsions (W/O/W and O/W/O). The result is a versatile system with precise control over droplet formation and exceptional monodispersity with tunable shell-to-core ratios. The grafted surfaces retained wettability and droplet-generation performance after three months of storage and 25 hours of continuous shear. Collectively, this work presents a robust and scalable strategy to bridge rapid 3D printing with durable surface functionalization, expanding the potential of customizable emulsion generation in lab-on-a-chip applications.