Agar is a gelatinous substance mainly composed of agarose and agaropectin, which can be extracted from the cell walls of algae such as Gelidium and Gracilaria (Ogonori) in Rhodophyta. The gel formation and melting process of agar are based on hydrogen bonding and belong to physical gels, so the gelation process is reversible. With its unique physicochemical properties, agar is widely used in food additives, plant tissue culture, microbial medium preparation, fingerprint development, and medical-related fields.

Preparation of Sulfamethizole-loaded Agar Microspheres [3]
(1) Add 1.5 g of agar to 20 mL of water, heat and stir until fully dissolved, then cool the system to approximately 70 °C.
(2) Add 2 g of sulfamethizole to the above agar solution and mix uniformly. Add the mixture dropwise into a 100 mL graduated cylinder containing Burgess’s reagent using a 3 mL plastic syringe; the graduated cylinder is pre-placed in an ice-water bath.
(3) Filter the resulting microspheres, followed by vacuum drying at room temperature (20 °C) for 24 h.