Sodium alginate is a byproduct of extracting iodine and mannitol from brown algae such as kelp or seaweed. Its molecule is composed of β - D-mannuronic acid (M) and α - L-guluronic acid (G) connected by (1 → 4) bonds. Sodium alginate aqueous solution has high viscosity and has been used as a thickener, stabilizer, emulsifier, etc. in food. Sodium alginate is a non-toxic food that was included in the United States Pharmacopeia as early as 1938. Sodium alginate contains a large amount of - COO -, which can exhibit polyanionic behavior in aqueous solution and has a certain degree of adhesion. It can be used as a drug carrier for treating mucosal tissue. Under acidic conditions, - When COO - is transformed into COOH, the ionization degree decreases, the hydrophilicity of sodium alginate decreases, the molecular chain shrinks, and the pH value increases The COOH group continuously dissociates, increasing the hydrophilicity of sodium alginate and stretching the molecular chain. Therefore, sodium alginate has significant pH sensitivity. Sodium alginate can quickly form gel under extremely mild conditions. When cations such as Ca2+and Sr2+exist, the Na+on the G unit will exchange with divalent cations, and the G unit will stack to form a cross-linked network structure, thus forming a hydrogel. The conditions under which sodium alginate forms gel are mild, which can avoid the inactivation of sensitive drugs, proteins, cells, enzymes and other active substances. Due to these excellent properties, sodium alginate has been widely used in the food industry and pharmaceutical fields.