Microfluidic production of cyclodextrin/alginate microcapsules with controlled morphology based on dimensionless analysis

We report an approach to produce microcapsules templated with cyclodextrin (CD) -stabilized droplets by integrating microfluidic generation with gelation in calcium chloride solution. An emulsion droplet is formed in the microchannel using essential oil as the inner phase, CD as the middle phase and sodium alginate (SA) as the outer phase. We identify three distinct flow regimes: stratified flow, dripping and jetting as a function of the flow rate ratio of the liquid phases, and unravel how the process variables during the droplet gelation govern the morphology of the microcapsule. The microcapsule formation process includes impact-driven deformation, diffusion-controlled permeation and gravitational settling. Moreover, dimensionless analysis using Ohnesorge (Oh) and Reynolds (Re) numbers quantifies the competing roles of viscous, inertial and interfacial forces in shaping transient droplet behavior. Notably, phosphate ions induce various structured morphologies including teardrop-like, hemispherical, spherical, conical and elliptical shapes by modulating crosslinking kinetics. The microcapsules exhibit exceptional monodispersity, controllable size, high encapsulation efficiency and sustained release behavior. This work establishes a predictive framework for tailoring microcapsule architecture, emphasizing the critical interplay between fluid-structure interactions and process design.