Three-dimensional Manipulation of Hydrogel Microparticles by Positional Change of Light Focus in Stop Flow Lithography

Hydrogel microparticles have garnered substantial attention in the fields of drug delivery, tissue engineering, and biosensing due to their properties of high biocompatibility, hydrophilicity, and tunability. Stop Flow Lithography (SFL), a microfluidic-based photopolymerization technique, has emerged as one of the leading methods by which these particles are synthesized due to its high throughput of controlled geometrically defined particles and ease of use. Previous research assumes that light distributes evenly throughout the SFL flow channel due to the almost instantaneous speed of light (3*108 m/s), synthesizing uniformly shaped hydrogels. In this study, the position of UV-light focus in SFL was manipulated using microscope focus, to which three-dimensional differences in hydrogel shapes were observed, disproving this presumption and ultimately suggesting that light intensity is not uniformly distributed. In observing these three-dimensional differences, we also discovered a technique by which SFL, normally confined to two-dimensional control, can be used to manipulate three-dimensional hydrogel shape. Furthermore, we explored potential applications of this technique in the fields of multiplex immunoassays, tissue engineering, and drug delivery. Our results indicate that the ability to manipulate hydrogels in a three-dimensional manner significantly enhanced all three fields, demonstrating promising application of this technique in biomedical and clinical fields.