Shape-tunable synthesis of alginate particles

Alginate microparticles are extensively used in pharmaceutical, cosmetic, and food industries due to their biocompatibility, biodegradability, and non-toxicity. Non-spherical alginate particles offer several advantageous features important to controlled drug release and cell encapsulation, including higher surface to volume ratio and a shorter diffusion path. Here, we synthesize shape-tunable alginate particles by dripping a sodium alginate solution with various concentrations of a yield-stress fluid, such as Carbopol, into an aqueous CaCl₂ bath where the droplet is subsequently ionically crosslinked. We take advantage of the yield stress property of Carbopol to tune the shape of the resulting particles. We identify several distinct regimes of alginate particle formation, ranging from symmetrical, spherical beads to asymmetric, anisotropic morphologies. Our results suggest that droplet deformation is initially (before bath entry) determined by the relative strength of yield-stress and surface forces. After the bath entry, a competition between the time scales of the yield-stress fluid relaxation and the crosslinking reaction determines the overall shape