Fabrication of alginate-based core/shell microgels

Low-viscosity (LV, 250 cPs) and high-viscosity (HV, 20,000–40,000 cPs) sodium alginates (SAs) from brown algae and anhydrous calcium chloride (CaCl₂) were purchased from Sigma Aldrich, Milan, Italy. Deionized water was used for the preparation of the solutions. Sodium alginate (SA) aqueous solutions were prepared at 2% w/v for the HV-SA and 0.5% w/v for the LV-SA solutions. For the fabrication of core/shell microgels, a commercial machine (NF500 MECC, Fukuoka, Japan) was used, equipped with a metal ultra-coaxial needle—inner channel 27 G and outer channel 18 G—and a tailor-made magnetic stirrer working as a collector, as reported in previous studies [31 (link)]. The EFDA parameters were optimized to control the size and shape of microgels. Briefly, the solutions were placed in two different 5 mL syringes, and each one was connected to a syringe pump with an imposed feed rate equal to 0.5 and 2.0 mL/h, respectively. The applied voltage was set at 25 kV, while the tip-to-collector distance was set at 150 mm. Droplets were collected into a CaCl₂ solution at a concentration of 1.1% under magnetic stirring to trigger the ionotropic interaction in the aqueous solution.