The complex world of polysaccharides edited by Desiree Nedra Karunaratne

 

The Complex World of Polysaccharides 

 

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the physical and chemical properties of the chitosan in order to improve its medicinal 

quality will also influence its biocompatibility [69.70]. 

The excellent biological properties of chitosan can be potentially improved with a variety of 

additional chemicals such as polyethylene glycol and carboxymethyl N-acyl groups in order 

to produce biocompatible chitosan derivatives for use as wound dressings [72]. Chitosan’s 

positive surface charge enables it to effectively support cell growth [73]. Chitosan-gelatin 

sponge wound dressing had demonstrated a superior antibacterial effect. Additionally, 

chitosan gelatin sponge allowed the wound site to contract markedly and shortened the 

wound healing time, as compared with sterile Vaseline gauze [74]. Widely used surface 

modification techniques include coating, oxidation by low temperature plasma for better 

printing and adhesion and surfactant addition for antistatic. Blends are often used to 

improve tensile properties and to provide a stronger structural component for separation 

media that supports the active polymer. The physical properties of a polymer can also be 

altered by introducing a second polymer that improves the properties of the original 

polymer in certain aspects, such as hydrophobility, lowered melt temperature, raised glass 

transition temperature, etc [75]. A thorough understanding of cell and proteins interactions 

with artificial surfaces is of importance to design suitable implant surfaces and substrates. 

The surface properties of newly synthesized biomedical grade chitosan derivatives, 

including surface composition, wettability, domain composition, surface oxidation, surface 

charge and morphology, may influence protein adsorption and subsequently, the cellular 

responses to biomaterial implants [76-81]. 

15. Biodegradability 

The claim “biodegradable” is often associated with environmentally friendly products. It is 

defined as being able to be broken down by natural processes, into more basic components. 

Products are usually broken down by bacteria, fungi or other simple organisms [82]. 

An important aspect in the use of polymers as drug delivery systems is their metabolic fate 

in the body or biodegradation. In the case of the systemic absorption of hydrophilic 

polymers such as chitosan, they should have a suitable Mw for renal clearance. If the 

administered polymer's size is larger than this, then the polymer should undergo 

degradation. Biodegradation (chemical or enzymatic) provides fragments suitable for renal 

clearance. Chemical degradation in this case refers to acid catalysed degradation i.e. in the 

stomach. Enzymatically, chitosan can be degraded by enzymes able to hydrolyse 

glucosamine–glucosamine, glucosamine–N- acetyl-glucosamine and N-acetyl-glucosamine–

N-acetyl- glucosamine linkages [83]. Even though depolymerisation through oxidation–

reduction reaction [84] and free radical degradation [85] of chitosan have been reported 

these are unlikely to play a significant role in the in vivo degradation. 

Chitosan is thought to be degraded in vertebrates predominantly by lysozyme and by 

bacterial enzymes in the colon [83, 86]. However, eight human chitinases (in the glycoside 

hydrolase 18 family) have been identified, three of which have shown enzymatic activity 

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Is Chitosan a New Panacea? Areas of Application 

 

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[87]. A variety of microorganisms synthesises and/or degrades chitin, the biological 

precursor of chitosan. In general, chitinases in microorganisms hydrolyze N-acetyl-β-1,4-

glucosaminide linkages randomly i.e. they are endo-chitinases (EC 3.2.1.14). Chitinases are 

also present in higher plants, even though they do not have chitin structural components. 

Chemical characterisation assays determining the degradation of chitosan commonly use 

viscometry and/or gel permeation chromatography to evaluate a decrease in Mw [88]. 

Lysozyme has been found to efficiently degrade chitosan; 50% acetylated chitosan had 66% 

loss in viscosity after a 4 h incubation in vitro at pH 5.5 (0.1 M phosphate buffer, 0.2 M NaCl, 

37 °C) [88]. This degradation appears to be dependent on the degree of acetylation with 

degradation of acetylated chitosan (more chitin like) showing the faster [89,90]. 

 

Figure 5.

 Biodegradation of chitosan thermosensible gel inside the rat´s body after 5 days. 

16. Safe biomaterial 

Chitosan is a potentially biologically compatible material that is chemically versatile (–NH

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groups and various Mw). These two basic properties have been used by drug delivery and tissue 

engineering to create a great amount of formulations and scaffolds that show promise in 

healthcare. It is approved for dietary applications in Japan, Italy and Finland [91] and it has been 

approved by the FDA for use in wound dressings [92] but is not approved for any product in 

drug delivery. The term “Chitosan” represents a large group of structurally different chemical 

entities that may show different biodistribution, biodegradation and toxicological profiles. 

The formulation of chitosan with a drug may alter the pharmacokinetic and biodistribution 

profile.The balancing, or reduction, of the positive charges on the chitosan molecule has 

effects on its interaction with cells and the microenvironment, often leading to decreased 

uptake and a decrease in toxicity. The modifications made to chitosan could make it more or 

less toxic and any residual reactants should be carefully removed. In addition, the route of 

administration determines the uptake, concentration, contact time and cell types affected. 

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