One-Step microfluidic synthesis of spherical and bullet-like alginate microcapsules with a core–shell structure

Abstract This work reports a novel and facile route to generate spherical and bullet-like alginate microcapsules with a core–shell structure based on the deformation of double-emulsion droplets. Here, monodisperse double-emulsion templates are synthesized from a dual-coaxial capillary microfluidic device and solidified via internal gelation in microchannel to achieve one-step preparation of the bullet-like and spherical microcapsules. The deformation degrees and internal structures of droplets and corresponding microcapsules can be flexibly controlled by simply adjusting the fluid flow rates. In addition, the spherical and bullet-like microcapsules can be successfully prepared by varying the concentrations of reactants. And the shell thickness and core diameter of the spherical microcapsules can be precisely tailored by modulation of the flow rate of fluids. The release performance of as-fabricated spherical and bullet-like microcapsules is investigated in detail by using α-tocopherol as a model drug. The results show that the bullet-like microcapsules with one inner core exhibit a faster release rate than that of spherical microcapsules in phosphate buffer solution (PBS, pH 7.4). In addition, one by one release of the inner cores can be observed in bullet-like microcapsules with two inner cores, which is different from spherical microcapsules that the two inner cores are first fused and then released. Our study provides an easy and effective strategy for the one-step synthesis of spherical and non-spherical microcapsules, which can be potentially used for drug delivery, cell encapsulation, microstructure control, and rheology.