Microfluidic Generation of Calcium Alginate Hydrogel Beads using External Gelation for Microalgae Cultivation

Calcium alginate hydrogel beads are spherical polymeric particles with highly crosslinked network structures, known for their excellent monodispersity and retention capabilities. These beads, produced by high-throughput droplet-based microfluidic techniques, are widely used for encapsulating and cultivating various microscopic particles such as cells. While internal gelation has been commonly utilized for crosslinking of calcium alginate hydrogel beads in microalgae encapsulation, the use of external gelation remains underexplored. This study utilized droplet-based microfluidic technology combined with external gelation to produce calcium alginate hydrogel beads for encapsulating the microalgal strain Chlorella vulgaris. Emulsions containing emulsified calcium ions served as the crosslinking phase. Initial geometrical analysis indicated that beads crosslinked with a high concentration of calcium ions (1 g/mL) achieve superior size uniformity and shape consistency. Microalgae cultivation experiments using these beads demonstrated steady growth of Chlorella vulgaris over a 5-day period, with the beads maintaining their geometric stability until the final day when minor cell leakage was observed. These results provide a foundation for future molecular-level studies on microalgae cultivation in hydrogel beads and suggest potential applications in fields requiring precisely controlled microalgae growth.