The complex world of polysaccharides edited by Desiree Nedra Karunaratne

 

The Complex World of Polysaccharides 

 

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11. Parameters influencing the behavior of the biopolymer 

The main parameters influencing the characteristics of chitosan are its degree of 

deacetylation (DD) and molecular weight (Mw), which affect the solubility, rheological and 

physical properties. Various grades of chitosan are available commercially, which differ 

primarily in the degree of deacetylation and molecular weight. Different conditions such as 

type and concentration of reagents, time and temperature employed throughout the 

processing can affect the physical characteristics and performance of the final chitosan 

product [50]. However, both DD and molecular weight can be further modified. For 

example, DD can be lowered by reacetylation [51-55] and molecular weight can be lowered 

by acidic or enzymatic depolymerisation [56-58]. 

12. Degree of Deacetylation (DD) 

Deacetylation describes a reaction that removes an acetyl functional group. When the degree 

of deacetylation of chitin reaches about 50% (depending on the origin of the polymer), it 

becomes soluble in aqueous acidic media and is called chitosan. The solubilization occurs by 

protonation of the –NH

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 function on the C-2 position of the D-glucosamine repeat unit, 

whereby the polysaccharide is converted to a polyelectrolyte in acidic media. Chitosan is the 

only pseudonatural cationic polymer and thus, it finds many applications that follow from 

its unique character (flocculants for protein recovery, depollution, etc.). Being soluble in 

aqueous solutions, it is largely used in different applications as solutions, gels, or films and 

fibers. 

 

Figure 4.

 Chitin deacetylation 

A highly deacetylated polymer has been used to explore methods of characterization [59]. 

The solution properties of a chitosan depend not only on its average DA but also on the 

distribution of the acetyl groups along the main chain in addition of the molecular weight 

[60-62]. Several methods have been proposed for alkaline deacetylation to obtain chitosan 

[6,17]. The conditions used in the deacetylation determines the polymer molecular weight 

and degree of deacetylation (DD).  

Chitosan has been largely employed in many areas, such as photography, biotechnology, 

cosmetics, food processing, biomedical products (artificial skin, wound dressing, contact 

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Is Chitosan a New Panacea? Areas of Application 

 

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lens, etc.), system of controlled liberation of medicines (capsules and microcapsules), 

treatment of industrial effluents for removal of metallic and coloring ions. The amino 

groups are responsible for the distinct characteristics attributed to this basic polymer 

(compared to an acidic biopolymer). Therefore, the characterization of the polymer in 

either chitin or chitosan is extremely important according to the structure-properties 

relationship, defining a possible industrial application. Thus many techniques are available 

to determine the degree of deacetylation. Elson Santiago de Alvarenga (2011) published on 

line describing the most important parameters to be evaluated in chitosan as 

“deacetylation degree” (DD) [63]. 

The methods for carrying out the analysis of the degree of deacetylation are: Elemental 

analysis; Titration; HPLC; Infrared; 

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H nuclear magnetic resonance; CP-MAS 

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C NMR; CP-

MAS 

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N NMR; steric exclusion; nitrous acid deamination; thermal analysis. 

13. Molecular weight  

Another important characteristic to consider for these polymers is the molecular weight and 

its distribution. The first difficulty encountered in this respect concerns the solubility of the 

samples and dissociation of aggregates often present in polysaccharide solutions [16, 57, 64, 

65, 66]. As to choice of a solvent for chitosan characterization, various systems have been 

proposed, including an acid at a given concentration for protonation together with a salt to 

screen the electrostatic interaction. The solvent is important also when molecular weight has 

to be calculated from intrinsic viscosity using the Mark–Houwink relation.  

14. Biological properties of chitosan 

14.1. Biocompatibility 

Biocompatibility of a biomaterial refers to the extent to which the material does not have 

toxic or injurious effects on biological systems [67, 68]. One of the present trends in 

biomedical research requires materials that are derived from nature as natural materials 

have been shown to exhibit better biocompatibility with humans and because chitosan’s 

monomeric unit, N-acetylglucosamine, occurs in hyaluronic acid, an extracellular 

macromolecule that is important in wound repair. Additionally, the N-

acetylglucosamine moiety in chitosan is structurally similar to glycosaminoglycans 

(GAGs), heparin, chondroitin sulphate and hyaluronic acid in which they are 

biocompatible, and hold the specific interactions with various growth factors, receptors 

and adhesion proteins besides being the biologically important mucopolysaccharides 

and in all mammals. Therefore, the analogous structure in chitosan may also exert 

similar bioactivity and biocompatibility [69, 70].  

The potential of chitosan stems from its cationic nature and high charge density in solution. 

An effective approach for developing a clinically applicable chitosan is to modify the surface 

of the material that already has excellent biofunctionality and bulk properties [71]. Altering 

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