**Abstract**

Seaweeds are one of the rich sources of minerals, protein, vitamins, edible fibers, and also have different functional polysaccharides necessary for human nutrition. Alginates are natural polymers that are part of the polysaccharides group. Alginate is a naturally occurring biopolymer that is found in the cell walls of algae or brown seaweed. Sodium alginate is one of the best-known members of the hydrogel group. The hydrogel is a water-swollen and cross-linked polymeric network produced by the simple reaction of one or more monomers. It has a linear (unbranched) structure based on d-mannuronic and l-guluronic acids. The placement of these monomers depending on the source of its production is alternating, sequential, and random. Sodium alginate is the most commonly used form of alginate used in wide range of applications in various industries including the food industry, medicine, tissue engineering, wastewater treatment, the pharmaceutical industry, and fuel. This review discusses its chemical structure along with its production process and application in various industries.

**Keywords:** alginate, alginic acid, biocompatible, natural polymers, biomaterial-seaweed

## **1. Introduction**

Seaweeds are one of the renewable resources that are obtained from the marine environment and can be used for treatment and food, and they can be divided into two groups: macroalgae and microalgae. Marine macroalgae are photosynthetic plants that are primary biomasses in intertidal areas [1].

There are about 9000 species of macroalgae, which are broadly classified into three main groups, brown, red, and green algae based on pigments, each of which has a type of polysaccharide, so Alginate is the most abundant in brown seaweed and sometimes makes up more than 40% of the dry weight of brown seaweed. These polysaccharides are obtained from both plant and bacterial sources [2–4].

The chemical composition depends on the type of species, the age of algae, the number and sequence of G and M units, the growing season, the biological source, and the conditions of algae growth [5, 6].

Seaweeds make up 85% of the total global production of aquatic plants, therefore, they are considered as one of the biggest producers of the sea [7]. Also, they are one of the rich sources of minerals, protein, vitamins, edible fibers, and also have different

functional polysaccharides necessary for human nutrition [8]. Alginates are natural polymers that are part of the polysaccharides group, which show unique properties. One of these properties is the ability of alginate to store and transport all kinds of drugs and biological molecules as a suitable substrate and place, which has boosted their use as a biomedical polymer. This polysaccharide extracted from brown seaweed is one of the common gelling agents used in the food industry [9].

Due to the presence of alginate, brown seaweeds are used in many fields such as tissue engineering, microencapsulation of food-drug compounds, and the preparation of special drugs in medical science, and they are of great economic importance [10].

Certain biopolymers like collagen and gelatin are employed in cosmetic surgery, tissue scaffolds, and cellophane for packing materials, and cellulose, hemicelluloses, lignin, starch, and alginate-based biopolymers are employed for 3D printing feedstocks [11].

Biodegradable polymers are usually referred to as "biopolymers" because these polymers are mostly derived from various natural sources. Biopolymers that are naturally biodegradable are limited in number and have the least to minimal effect in increasing the environmental carbon footprint. Biodegradable polymers represent a growing field. A large number of biodegradable polymers (e.g., cellulose, chitin, starch, polyhydroxyalkanoate, polylactide, poly(ε-caprolactone), collagen, and other polypeptides) are made during the growth cycle of organisms in the natural environment. Are or are formed some microorganisms and enzymes capable of degrading such polymers have been identified.

Sodium alginate is a linear polysaccharide derived from alginic acid, which is present in the cell wall of brown algae and contains approximately 30–60% alginic acid. In recent decades, alginates have attracted the attention of researchers due to their unique physical and chemical properties and their wide applications as a natural polymer. Sodium alginate is known with the chemical formula (C6H7NaO6)n and is available in the form of white to brown strands or in granular, powder, and granular form. This salt compound is derived from alginic acid. It is a polysaccharide acid that is widely present in the cell walls of brown algae and forms a sticky gum when hydrated.

Alginates are made up of two uronic acids: D-mannuronic acid (M) and L-guluronic acid (G) extracted from brown seaweeds Phaeophyceae and kelp [12, 13]. The alginic acid form of alginate is extracted from the seaweed in alkaline conditions, then precipitated and ion exchanged (e.g., with potassium). Alginates have a wide application in the cosmeceutical industry because of their use as high-stability thickening and gelling agents. The first alginate application in the cosmeceutical field started in 1927. Alginate is applicable in grafting the skin in plastic surgery [14].

Alginate is the common term for alginic acid salts. Alginic acids are polyuronidic, which is to say polysaccharide molecules that are composed of uronic acid residues. The commercial alginates, such as *Laminaria digitata*, *Laminaria hyperborea*, and *Macrocystis pyrifera*, are currently obtained by removing brown algae. However, several bacteria like *Azotobacter vinelandii*, a nitrogen-fixing aerobic, and *Pseudomonas aeruginosa*, an opportunism pathogen, also produce alginates. The alginates are exceptional in their characteristically complex uses for food and pharmaceutical sectors, such as emulators, thickeners, stabilizers, gelling, and film formulation. Biocompatibility, biodegradability, immunogenicity, and non-toxicity of alginate made it an excellent polysaccharide for drug delivery application. Alginate-based bionanocomposites are vital in the biomedical field and are used as instruments

in various applications of human health, such as drug delivery excipients (DDS), wound clothing, dental printing materials, and inter alia, formulations for preventing gastric reflux, etc. [15]. This chapter discusses the origin of alginate and its extraction methods and uses.
