Physicochemical and Biological Properties of Chitosan

4 as it is a weak base (pATa 6.2-7). Adjusting solution pH to approximately 

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Table 16.1 Physicochemical and biological properties of chitosan as a function of its molecular weight and degree of deacetylation...

The DDA of chitosan is an important parameter that determines many physicochemical and biological properties of the biopolymer such as solubility, biodegradability, and biocompatibility. As mentioned earher in this chapter, the DDA of chitosan can be defined as... 

The physical and mechanical properties of chitosan can be amefiorated by using graft copolymerization and crosslinking. Chitosan forms aldimines and ketimines with aldehydes and ketones, respectively. Upon hydrogenation with simple aldehydes, chitosan produces A-alkyl chitosan [60]. The physicochemical and biological properties [61] as well as conformational structures [62] of chitosan are very effective for biomedical applications. 

The degree of acetylation (or deacetylation) and the molecular mass are undoubtedly the most important parameters to establish the chemical and physical identity of chitin and chitosan. Both parameters vary with the biological source of the raw material and the preparation method. They also dictate the physicochemical, functional and biological properties of these polysaccharides, essential to fit an application or end product. Solubility, pK, viscosity, gelling capacity, among other properties, are all dependent on these parameters. 

Chitosan possesses many functional groups available for chemical derivatization, forming a large number of biofunctional materials with superior properties than chitosan itself, as the fundamental skeleton of chitosan remains unchanged but its physicochemical and biological properties can be selectively modulated. 

Oligomers and polymers of chitin, chitosan, and their derivatives are extensively used in a broad range of fields that include agriculture, food, textile, cosmetics and medicine (Sandford and Hutchings 1987, Sandford 1989, Sandford and Steinnes 1991, Shahidi et al. 1999, Chatelet et al. 2001). They find vast applications because of their numerous interesting biological, physicochemical, and mechanical properties (Domard et al. 

Recent research explored various chemically modified conjugates and derivatives to improve its physico-chemical and biological properties. This modification allows significant applications of chitosan in various disciplines of biomedical research. So far various fabrication methods have been employed for the development of chemically modified chitosan e.g. chitosan-poly(acrylic acid) nanoparticles and acylated chitosan nanoparticles have been recently explored to examine their modifications effect on physicochemical properties and blood compatibility [151, 152], Similarly self-aggregated NPs of cholesterol-modified 0-carboxymethyl chitosan conjugates were fabricated to improve the pharmaceutical and biomedical applications of chitosan [153], Various examples of chitosan and its chemically modified synthetic derivatives are mentioned in Table 3.2. 

The deacetylation process involves the removal of acetyl groups from chltln molecules. The DAC is defined as the average number of glucosamine units per 100 monomers expressed as a percentage. It determines the content of free amino groups [-NH2] in the chitosan and is one of the most important chemical characteristics that influence the physicochemical properties, biological properties, antibacterial activity, and applications of chitosan. In other words, DAC value determines the functionality, reactivity, polarity, and water solubility of the polymer. Chitin does not dissolve in dilute acetic acid. When chitin is deacetylated to a certain degree ( 60% deacetylation] where it becomes soluble in the acid, it is referred to as chitosan [18, 21]. 

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