Oxygen-free discontinuous dewetting in a degassed mold for anisotropic colloidal hydrogel microparticle synthesis

Anisotropic colloidal hydrogel microparticles offer unique advantages owing to their shape-dependent interactions, and enhanced diffusion and reaction kinetics, which is favorable in solution-based processes. However, their fabrication remains difficult, mainly due to limitations of surface energy and oxygen inhibition. In this study, we present a versatile synthesis platform for anisotropic colloidal hydrogel microparticles using oxygen-free discontinuous dewetting in a degassed mold. By a simple substitution of ambient air to inert gas, oxygen inhibition is effectively suppressed, achieving fabrication of particles with feature sizes as small as 600 nm. The colloidal nature of the synthesized hydrogel particles was verified by observing Brownian motion, and the resolution improvement was quantitatively confirmed by comparing the feature fidelity under atmospheric and oxygen-free conditions. Computational analysis revealed a sharp decrease in oxygen concentration near the mold surface under inert conditions, supporting the experimental findings. To demonstrate the applicability of the hydrogel particles, we analyzed the residual acrylate double bonds, which can act as functional moieties for straightforward post-synthetic modification. Finally, as an application of enhanced resolution of the particles, we conduct imaging flow cytometry using particles with few-micrometer dimensions and achieved an analytical throughput surpassing those of previous studies employing hundred-micrometer-scale hydrogel particles without compromising the decoding accuracy. This is made possible by the oxygen-free discontinuous dewetting in a degassed mold, which enabled the fabrication of colloidal hydrogel particles. This work provides a robust and scalable method for producing anisotropic colloidal hydrogel microparticles, enabling broader applications in microscale material systems and high-throughput analytical technologies.