**2. Chitosan**

*Chitin and Chitosan - Physicochemical Properties and Industrial Applications*

and antimicrobial activity have attracted interest in medicine, pharmacy, biomedical and health-related applications [1, 3, 4]. Numerous Cts-based materials were produced such as nano and microparticles, gels, sponges, films and membranes [4]. They have created an efficient field of application for drug delivery, wound healing

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**Figure 2.**

**Figure 1.**

*Field of application of Cts.*

and tissue regeneration applications.

*Biopolymer classification: Animal, agro, and protein origins.*

### **2.1 Sources of chitin and chitosan**

Chitin is usually found in nature in seaweeds, protozoa (flagellates, amoebic ciliates, etc.), selenterals, mollusks, arthropods, bacteria, fungi, insects and some plants. The richest sources of chitin are; crab, shrimp, lobster and crayfish shells. Chitin biopolymers of animal origin are mainly found in animals. Chitin is the most considerable polysaccharide on the planet. Due to its strong hydrogen bonds and high crystal property of its cohesive structure forces, chitin is an insoluble substance in normal solvents, including water and organic matter [5]. Cts is abundant in marine or terrestrial animals such as crustaceans, insects, mollusks and fungi [6] without a backbone, such as various insects and marine diatoms. Commercial production of Cts by alkaline hydrolysis by extracting chitin from shrimp shell waste has been carried out by a group scientist [3, 6].

#### **2.2 Chitosan production**

Cts is obtained from chitin. Rouget became aware of Cts in 1859 while conducting experimental activities on deacetylated forms of chitin [7]. Cts is obtained from waste shrimp and crab shells from the seafood industries by chemical methods in industrial processes around the world [4]. Basic structure properties of Cts are related to its molecular weight and degree of deacetylation. The crystallinity of Cts is important in classifying its particle size, moisture and ash content, which is based on its surface morphology properties. The solubility, antibacterial, polycationic character, biocompatibility and bio adhesiveness of Cts are the basis that define the Cts structure and application areas [8, 9].

Chemical modifications of Cts have been extensively described in recent studies. Cts contains the reactive amino (-NH2) and hydroxyl (-OH) groups in its structure and can very easily be converted into new modified forms. The presence of amino groups in the Cts matrix (deacetylation degree) in macromolecular chains indicates that Cts has a polycationic property in acidic aqueous solutions. The protonation of amino groups in the polymer structure seriously affects the structure of macromolecules in solutions, and it is known that the structure behavior may be managed through changing the pH or ionic strength of the solution it is in.

Cts production is carried out by two basic methods, chemically and biologically. Classically, the chemical method is the method in which physical and chemical methods are used together. Chemical method; the isolation of the chitin is carried out by removing other substances in the shell. The procedures for this can be grouped under four main steps:


3.Deproteinization (removal of proteins).

4.Decoloration (removal of pigments). These stages are given in **Figure 3**.

Biological methods are processes that can be examined under several headings. Cell cultures of various organisms such as Mucor rouxii, Phycomyces blakesleeanus are used in the microbial synthesis of Cts. The product obtained is developed by adding Aspergillus niger to the culture medium. Thus, this production mechanism also leads to the deacetylation of the Cts. Cts is obtained at the end of the 96-hour incubation period [10]. As a biological method, the use of proteolytic enzymes such as pepsin, trypsin, protease, proteinase and papain in protein removal can be counted [11]. Today, many other polymers used in industry are produced synthetically. Synthetic polymers have limited biocompatibility and biodegradability compared to Cts, a natural polymer.
