Zargar2015

A Review on Chitin and Chitosan Polymers: Structure,
Chemistry, Solubility, Derivatives, and Applications
Vida Zargar[1]
, Morteza Asghari[1],
*, Amir Dashti[1]
www.ChemBioEngRev.de ª 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ChemBioEng Rev 2015, 2, No. 3, 204–226 204
Abstract
Chitin and chitosan are considerably versatile and
promising biomaterials. The deacetylated chitin de-
rivative chitosan is a useful and interesting bioactive
polymer. Despite its biodegradability, it has many
reactive amino side groups, which offer possibilities
of chemical modifications, formation of a large vari-
ety of beneficial derivatives, which are commercially
available or can be made available via graft reactions
and ionic interactions. This study looks at the con-
temporary research in chitin and chitosan towards
structure, properties, and applications in various in-
dustrial and biomedical fields.
Keywords: Chitin, Chitosan, Deacetylation, Membranes, Organic materials, Polymers
Received: August 21, 2014; revised: December 12, 2014; accepted: December 19, 2014
DOI: 10.1002/cben.201400025
1 Introduction
Chitin, a linear polysaccharide composed of (1-4)-linked
2-acetamido-2-deoxy-b-D-glucopyranose units [1], is the sec-
ond prevalent form of polymerized carbon in nature [2]. It is
categorized as a cellulose derivative, in spite of the fact that it
does not appear in organisms producing cellulose. Its structure
is similar to cellulose, but at the C2 position, it has an acet-
amide group (-NHCOCH3). Every year, molluscs, crustaceans,
insects, fungus, algae, and related organisms approximately
produce 10 billion t of chitin. Chitin is biorenewable, environ-
mentally friendly, biocompatible, biodegradable and biofunc-
tional, and is beneficial as a chelating agent, water treatment
additive, drug carrier, biodegradable pressure-sensitive adhe-
sive tape, wound-healing agents, in membranes and has other
advantages for several important applications. Because of these
advantages, much attention is paid to this characteristic bioma-
terial. However, nowadays, chitin is not vastly employed by the
pharmaceutical industry. Because of its weak solubility, it has
unique applications. Chitin is insoluble in common organic
solvents and diluted aqueous solvents because it is highly hy-
drophobic due to the highly expanded hydrogen-bonded semi-
crystalline structure of chitin. Its derivative, chitosan, is pre-
pared by deacetylation and depolymerization of native chitin,
(partial) deacetylation of chitin in the solid state under alkaline
conditions (concentrated NaOH), or enzymatic hydrolysis in
the presence of a chitin deacetylase [3]. Chitin is a white, in-
elastic, rigid, nitrogenous polysaccharide that is present in the
exoskeleton and internal structure of invertebrates. The wastes
of these natural polymers cause surface pollution in coastal re-
gions. The waste of the food industry, particularly if it contains
the recovery of carotenoids, is a suitable source for production
of chitosan from crustacean shells and economically feasible.
Nowadays, chitin and chitosan are produced commercially in
Norway, India, Japan, Poland, the US, and Australia [4]. Chitin
and chitosan have many applications in waste water treatment
(removal of metal ions [5], dyes [6], and as membrane in puri-
fication processes [7]), food industry (anti-cholesterol and fat
binding [8], packaging material [9], preservative and food addi-
tive [10]), agriculture (seed and fertilizer coating [11], con-
trolled agrochemical release [12]), pulp and paper industry
(surface treatment [13], adhesive paper [14]), cosmetics ( body
creams [15], lotions, etc.), in tissue engineering [16, 17], wound
healing [18], as excipients for drug delivery [17, 19] and gene
delivery [20, 21]. Chitin and chitosan are easily processed into
gels [22], membranes [16, 17, 19, 23, 24], nanofibers [25, 26],
beads [27], microparticles [28], nanoparticles [29], scaffolds
[18, 26, 28, 30–32], and sponges [33].
2 Chitosan Structure and
Characterization
2.1 Structures of Chitin and Chitosan
Similar to cellulose, the natural function of chitin is that of a
structural polysaccharide, but its properties are different from
cellulose. As previously mentioned, Chitin is highly hydropho-
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[1]
Vida Zargar, Dr. Morteza Asghari (corresponding author), Amir Dashti
University of Kashan, Department of Engineering, Energy Re-
search Institute, Separation Processes Research Group (SPRG),
Ghotb-e-Ravandi Ave., Kashan 8731751167, Iran.
E-Mail: asghari@kashanu.ac.ir

bic and insoluble in water and most organic solvents [34, 35]. It
is a structural biopolymer, which has a similar function to that
of collagen in the higher animals and cellulose in plants. Plants
produce cellulose in their cell walls while insects and crusta-
ceans produce chitin in their shells [36] (Tab. 1). Therefore, cel-
lulose and chitin are two influential and structurally related
polysaccharides that cause the uniformity of structure and pro-
tection to plants and animals, respectively [37]. Chitin natu-
rally exists as ordered crystalline microfibrils forming structur-
al components in the exoskeleton of arthropods or in the cell
walls of the kingdom of fungi like yeast [38].
The crystallography of chitin has been investigated for a long
time [39]. Chitin is a homopolymer of 2-acetamido-2-deoxy-b-
D-glucopyranose, although some of the glucopyranose residues
are in the deacetylated form as 2-amino-2-deoxy-b-D-gluco-
pyranose. Chitosan is the polymer with a majority of the gluco-
pyranose residues in the deacetylated form. Chitin is infre-
quently found entirely in the N-acetyl or acetamido form, nor
is chitosan completely deacetylated except under rigorous con-
ditions. Neither is found in the pure state in nature but in con-
junction with other polysaccharides, proteins, and perhaps
minerals [3]. Chitin may be considered as cellulose with the
hydroxyl at position C2 substituted with an acetamido group
[37]. Both are polymers of structural monosaccharides consist-
ing of b-(1-4)-2-acetamido-2-deoxy-b-D-glucose and b-(1-4)-
2-deoxy-b-D-glucopyranose units, respectively (Fig. 1). Thus,
chitin is poly-b-(1-4)-N-acetyl-D-glucosamine [40] (Fig. 2).
Similar to cellulose, chitin can be found in three various
polymorphic forms (a, b and g) [41]. Recent investigations
have declared that the g-form is a different form of the a-fam-
ily [42]. The polymorphic forms of chitin are different in the
packing and polarities of near chains in successive sheets; in
the b-form, all chains are arranged in a parallel mode, which is
not the case in a-chitin. All types of chitin are comprised of
piles of chains attached together by CO-NH bonds originating
from the N-acetyl side groups of glucosamine residues. In a pile
of chains, the chain direction is the same, in other words, a pile
has a clear direction, say C1fiC4. Where these piles come to-
gether in the crystalline structure of a-chitin, neighboring piles
are of opposite chain direction and the system is thus described
as antiparallel, having chains up and down (›fl). By contrast,
in b-chitin, the chain directions of neighboring piles are the
same, meaning all up (››). In g-chitin, the chain directions in
successive piles are thought of as two up and one down (›fl›)
[43]. A simple treatment with 20 % NaOH followed by washing
www.ChemBioEngRev.de ª 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ChemBioEng Rev 2015, 2, No. 3, 204–226 205
Table 1. Sources of chitin and chitosan [22].
Sea animals Insects Microorganisms
Crustaceans
Coelenterata
Annelida
Mollusca
Lobster
Shrimp
Prawn
Krill
Crab
Scorpions
Brachiopods
Cockroaches
Spiders
Beetles
Ants
Green algae
Yeast (b-Type)
Fungi (cell walls)
Mycelia penicillium
Brown algae
Chytridiaceae
Ascomydes
Blastocladiaceae
Spores
Figure 1. Structure of glucosamine (monomer of chitosan) and
glucose (monomer of cellulose).
Figure 2. Structure of chitin and chitosan (reproduced from [40]).

with water is reported to convert a-chitin to b-chitin [44, 45].
Conversion from b- to a-chitin can be accomplished with
steam annealing [46] and irreversibly in the swollen state with-
out a destruction of fibrous orientation, but with longitudinal
shrinkage. The molecular arrangement of chitin depends on
the physiological role and tissue characteristics. The grasping
spines of Sagitta are made of pure a-chitin, because they
should be rigid enough to hold a prey, while the centric diatom
Thalassiosira contains pure b-chitin. In both structures, the
chitin chains are arranged in sheets where they are tightly held
by a number of intra-sheet hydrogen bonds with the a and b-
chains packed in antiparallel arrangements [47, 48].
In chitin, the degree of acetylation (DA; a reaction that inserts
an acetyl functional group into a chemical compound) is typi-
cally 0.90, showing the presence of some amino groups. As some
quantity of deacetylation might occur during extraction, chitin
may include about 5–15 % amino groups [49, 50]. The degree of
N-acetylation, i.e., the ratio of 2-acetamido-2-deoxy-D-gluco-
pyranose to 2-amino-2-deoxy-D-glucopyranose structural units
has a noticeable influence on chitin solubility and solution prop-
erties [34, 50]. Chitosan is usually prepared by deacetylation of
a-chitin by 40–50 % aqueous alkali solution at 100–160 C for a
few hours. The resulting chitosan has a degree of deacetylation
(DD) up to 0.95. The alkaline treatment can be repeated to
acheive complete deacetylation. Chitosan is the N-deacetylated
derivative of chitin with a typical DA of less than 0.35. It is a
copolymer comprised of glucosamine and N-acetylglucosamine.
The physical properties of chitosan depend on parameters such
as the molecular weight (from about 10 000 to 1 million Dalton),
DD (in the range of 50–95 %), purity of the product and sequence
of the amino and the acetamido groups [47, 51]. The waste prod-
ucts of the food industry consisting of crustacean shells (crabs,
etc.) are commercially used for the production of chitin and chi-
tosan [52]. It is reported that at least 1011
t (1013
kg) of chitin are
produced and degraded, but only over 150 000 t of chitin are pre-
pared for commercial use [53].
3 Chitin and Chitosan Processing
Chitin and chitosan are useless products of the crabbing and
shrimp canning industry. The processing of crustacean shells
mainly involves the removal of proteins and the dissolution of
high concentration of calcium carbonate in crab shells. Final
chitosan is deacetylated in 40 % sodium hydroxide for 1–3 h at
120 C (Fig. 3). As a result, 70 % deacetylated chitosan can be
produced [4]. The chitin and chitosan processing includes (1)
crustacean shells, (2) size reduction, (3) protein separation, (4)
NaOH, (5) washing demineralization (HCl), (6) washing and
dewatering, (7) decoloration, (8) chitin, (9) deacetylation
(NaOH), (10) washing and dewatering, (11) chitosan.
3.1 Chemical Properties of Chitosan
The chemical properties of chitosan include [54]:
– linear aminopolysaccharide with too much nitrogen content
– rigid D-glucosamine structure; high hydrophilicity, crystal-
linity
– weak base; deprotonated amino group acts a powerful nu-
cleophile (pKa 6.3)
– enable to form hydrogen bonds intermolecularly; high vis-
cosity
– consisting of great reactive groups for cross-linking and
chemical activation
– insoluble in water and organic solvents; soluble in dilute
aqueous acidic solutions
– forms salts with organic and inorganic acids
– chelating and complexing properties
– ionic conductivity
– polyelectrolytes (at acidic pH)
– cationic biopolymer with high charge density (one positive
charge per glucosamine residue)
www.ChemBioEngRev.de ª 2015 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ChemBioEng Rev 2015, 2, No. 3, 204–226 206
Shrimp Crab Squid
Chitin-Deacetylase
Shellfish from food processing
Decalcification in dilute aqueous HCL Solution
Deproteination in dilute aqueous NaOH Solution
Decolorization
Chitin
Figure 3. Chitin and chitosan processing.

– flocculating agent; interacts with negatively charged molecules
– entrapment and adsorption properties; filtration and separa-
tion
– film-forming ability; adhesivity materials for isolation of bio-
molecules
– biological properties biocompatibility
– bioadhesivity
– bioactivity
– nontoxic
– biodegradable
– adsorbable
– antimicrobial activity (fungi, bacteria, viruses)
– antiacid, antiulcer, and antitumoral properties
– blood anticoagulants
– hypolipidemic activity
3.2 Molecular Weight
The general method of preparing chitosans with various molec-
ular weights is employing nitrous acid in dilute HCl aqueous
solution [55, 56]. Chitosan depolymerization by nitrous acid
(HONO) is beneficial because the reaction between chitosan
and HONO has been examined and the stoichiometry and re-
action products are identified [57, 58]
Chitosan molecular weight distributions have been calcu-
lated by HPLC [59, 60]. The weight-average molecular weight
(Mw) of chitin and chitosan has been obtained by light scatter-
ing [61]. Viscometry is a fast and uncomplicated route for the
determination of the molecular weight; the constants a and K
in the Mark-Houwink equation have been determined in 0.1 M
acetic acid and 0.2 M sodium chloride solution. The intrinsic
viscosity h is expressed as [62]:
[h] = KMa
= 1.81 · 10–3
M0.93
(1)
The charged nature of chitosan in acid solvents and chitosan
propensity to create aggregation complexes need more atten-
tion when these constants are used. Additionally, transforming
chitin into chitosan decreases the molecular weight, changes
the extent of deacetylation, and by means of that the charge
distribution changes, which has an important effects on the ag-
glomeration. The weight-average molecular weight of chitin is
1.03 · 106
to 2.5 · 106
, but the N-deacetylation reaction de-
creases it from 1 · 105
to 5 · 105
[63].
When molecular weight has to be calculated from intrinsic
viscosity using the Mark-Houwink relation, the type of solvent
is crucial. The value of the parameter K depends on the nature
of the solvent and polymer. For instance, one solvent system
suggested for molecular weight characterization (0.1 M
AcOH/0.2 M NaCl) was demonstrated to promote aggregation
and the calculated values of molecular weights were overesti-
mated [64, 65]. In an acid-soluble chitosan solution with dif-
ferent DA, it was concluded that the stiffness of the chain was
almost independent of the DA and it was shown that the dif-
ferent parameters only depended slightly on the DA [66]. But
Kasaai et al. indicated that a and K are inversely related and
that they are affected by DA, pH, and ionic strength of the
solvent [196]. The data of K determined by various authors
[67] can be plotted against DA which shows that there cannot
be any relationship between the DA and the K value (Kasaai
has since modified his work [68]). As the values of K and a
differ, it is suggested that it would always be beneficial to fol-
low the values for which the authors have used a standard
reference for comparing the molecular weights and a standard
method such as gel permeation chromatography or light
scattering [60, 61] to determine the absolute molecular
weights. On the other hand, Varum et al. suggested that
the Mark-Houwink-Sakurada equation can be written as
[h] = 0.10Mw
0.68
(mL g–1
) [69].
3.3 Chitin and Chitosan Solubility
As the cohesive energy, which is related to strong intermolecu-
lar interactions through hydrogen bonds, is high, dissolution of
chitin like cellulose is hard [70]. Chitin is insoluble in many
organic solvents but chitosan is greatly soluble in dilute acidic
solutions below pH 6.0, which is due to it being a strong base
because it has primary amino groups with a pKa value of 6.3.
The existence of the amino groups shows that pH considerably
changes the charged state and properties of chitosan [71]. At
low pH, these amines get protonated and become positively
charged and that causes chitosan to become a water-soluble
cationic polyelectrolyte. On the other hand, as the pH increases
to 6 and above, the amines of chitosan become deprotonated
and the polymer loses its charge and becomes insoluble. The
soluble-insoluble transition occurs at its pKa value around a
pH between 6 and 6.5. As the pKa value is highly dependent on
the degree of N-acetylation, so is the solubility of chitosan. For-
mic acid had been discovered as the best solvent for chitosan
and solutions are acquired in aqueous systems with 0.2–100 %
of formic acid [71]. The most widespread solvent is 1 % acetic
acid (as a reference) at a pH near 4. Also, chitosan is soluble in
1 % hydrochloric acid and dilute nitric acid, but is insoluble in
sulfuric and phosphoric acids. But acetic acid solutions with high
concentration at elevated temperature can provide depolymeri-
zation of chitosan [72, 73]. There are many important factors
that have vital effects on chitosan solubility. These factors can in-
clude temperature, alkali concentration, time of deacetylation,
prior treatments applied to chitin isolation, ratio of chitin to alka-
li solution, particle size, etc. [74]. Therefore, the solution proper-
ties of chitosan not only depend on its average DA, but also on
the distribution of the acetyl groups along the main chain as well
as the molecular weight [75–77]. In addition to DD, the molecu-
lar weight is also a significant parameter that dominates the solu-
bility and other properties of chitosan [78–81]. It was reported
that both DD and the molecular weight had an effect on the
properties of electrospun chitosan nanofibers [82].
3.4 Degree of Acetylation
The degree of acetylation is the ratio of 2-acetamido-2-deoxy-
D-glucopyranose to 2-amino-2-deoxy-D-glucopyranose struc-
tural units. This ratio has a noticeable effect on chitin solubility
and solution properties. Different techniques, in addition to
potentiometric titration [83], have been proposed, such as IR

[83–86] elemental analysis, an enzymatic reaction [87], UV
[87], 1
H liquid-state NMR [88] and solid-state 13
CNMR
[89–91]. The fraction of -NH2 in the polymer (which deter-
mines the DA) can be acquired by stoichiometry dissolution of
neutral chitosan in a small excess of HCl followed by neutrali-
zation of the protonated -NH2 groups by NaOH using pH or
conductivity measurements [83].
3.5 Viscosity
Values of the intrinsic viscosity according to Huggins, [h]Hug,
and Kraemer, [h]kra, for chitosan in buffer aqueous solution
(0.3/0.2 M CH3COOH/CH3COONa) were 637 and 646, respec-
tively [92].
4 Some of Chitosan Derivatives
4.1 O-and N-Carboxymethl Chitosans
Too many studies have been conducted on carboxymethyl chi-
tosan (CM-chitosan), a derivative of chitosan. Carboxymethyl
chitosan, a water soluble derivative of chitosan, has attracted
great interests in many fields such as in vitro diagnostics
[93–95], theranostics [96], bioimaging [97], biosensors [98, 99],
wound healing [100], gene therapy [101–104], and food tech-
nology [105, 106]. It is an amphoteric (a molecule or ion that
can react as an acid as well as a base) polymer and its solubility
is dominated by the pH. Under controlled reaction conditions
with sodium monochloracetate in the presence of NaOH,
O- and N-carboxymethylation take place. The result of substit-
uents on the three positions was determined by NMR
[88, 107, 108]. This reaction increases the range of pH 7, in
which chitosan is water-soluble, but because of the balance be-
tween positive and negative charges on the polymer, a phase
separation occurred at 2.5 pH 6.5. It was demonstrated that
the prevalence of positive or negative charges along the poly-
mer chains at each pH, and then the solubility of the polymer,
is determined by the balance including the protonation of the
amino groups and the dissociation of the carboxymethyl
groups. Therefore, the negative charges predominated if the
medium was moderately acidic to neutral and alkaline while
the positive charges were predominant in acid medium. Appa-
rently, the main factor determining the solubility of the poly-
mer at a given pH is the excess of positive or negative charges,
the insolubility of the polymer resulting of an insufficient ex-
cess of charge. Accordingly, the more substituted carboxymeth-
yl chitosan samples exhibited a wider range of solubility [109].
N-carboxymethylchitosan is prepared by reacting chitosan
with glyoxylic acid with a reducing agent [108]. The distribu-
tion of monosubstituted (-NH-CH2COOH) and disubstituted
(-N(-CH2COOH)2) groups was established by 1
H and
13
C-NMR. Disubstitution was easily acquired, providing an in-
teresting derivative for ion complexation. A specific oxidation
of the C6 position hydroxyl group was discovered by the
TEMPO reactant ((2,2,6,6-Tetramethylpiperidin-1-yl)oxy, or
(2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl is a chemical com-
pound with the formula (CH2)3(CMe2)2NO, which serves in
oxidations as catalyst) on chitin to produce a chitin-based hya-
luronic acid analogue [110]. This derivative was water soluble
in an extended range of pH, but only if it was produced from a
fully acetylated chitin.
In order to enhance antimicrobial activity of chitosan, Sun
et al. [111] reported the preparation of quaternized carboxy-
methyl chitosan (QCMC) in which a carboxymethyl group and
a quaternary ammonium group are simultaneously inserted in-
to the chitosan molecular chain.
Upadhyaya et al. [112] reviewed advances in carboxymethyl
chitosan-based targeted drug delivery and tissue engineering
applications.
4.2 Trimethylchitosan Ammonium
This cationic derivative, which is water soluble in nearly the
whole pH range, was produced by quaternization of chitosan
[113]. It was gained by reaction of a low acetyl content chitosan
with methyl iodide and sodium hydroxide under controlled
conditions, and had been entirely characterized by NMR [114].
Under all tested conditions, a great decrease in molecular
weight occurred during this reaction. For a degree of quaterni-
zation greater than 25 %, these polymers are soluble in water,
whatever the pH. These polymers exhibited suitable flocculat-
ing properties with kaolin dispersions, which make them appli-
cable for paper manufacturing [115]. It was claimed that other
quaternized derivatives had antistatic properties [116].
Xiao et al. [117] prepared N-(2-hydroxy)propyl-3-trimethyl
ammonium chitosan chloride for use in gene delivery.
4.3 N-Methylene Phosphonic Chitosans
Heras et al. [118] synthesized N-methylene phosphonic chito-
san (NMPC) with the improvement of an increased solubility
over an extended pH range. These interesting anionic deriva-
tives, with some amphoteric character were synthesized under
different conditions, and demonstrated acceptable complexing
efficiency for cations such as Ca2+
and many transition metals
(Cu (II), Cd (II), Zn (II), etc.) [119, 120]. The complexation
protected metal surfaces from corrosion [121]. These deriva-
tives were grafted with alkyl chains to have amphiphilic prop-
erties that can be applicable in cosmetics [122].
Ramous et al. [123] modified NMPC with poly(ethylenegly-
col)-aldehyde (PEG-CHO) with different molecular weight
using reductive amination. The crosslinking with PEG-COH
chains in NMPC increased the water swelling and hygroscopic-
ity (humid absorption). The modification with high molecular
weight PEG created swelling in alkaline pH and remains solu-
ble in acidic medium. The ability to form films and swelling
properties made these crosslinked NMPC derivatives a suitable
material for medical items.
4.4 Chitosan 6-O-sulfate
This derivative is an anticoagulant. First it was provided as an
O-sulfated derivative [124, 125] and more recently as N-sul-

fated chitosan [126]. Recently, this derivative has been used in
biomedical applications such as pharmacy [127, 128].
4.5 Lactic-Glycolic Acid-Chitosan Hydrogels
Qu et al. [129] synthesized chitosan hydrogels by direct graft-
ing of D,L-lactic and/or glycolic acid onto chitosan without
catalysts. They showed a stronger interaction between water
and chitosan chains after grafting with lactic and/or glycolic
acid. These hydrogels are pH-sensitive chitosan hydrogels
[130–133] that are potentially beneficial for biomedical [134]
applications such as drug delivery systems and wound dress-
ings, because both polyester side chains and chitosan are bio-
compatible and biodegradable [135].
4.6 Cadmium Sulfide Quantum Dots Chitosan
Biocomposite
A cadmium sulfide (CdS) quantum dots (QDs) chitosan deriva-
tive with a narrow size distribution showed enhanced aqueous
solubility and stability. It also affected the thermal decomposition
of chitosan and altered it to 50C. A suitable and effective proce-
dure for the preparation of CdS QDs chitosan biocomposite was
performed by mixing chitosan with Cd(Ac)2 and then dissolving
in 1 % HAC aqueous solution, followed by the treatment with
CdS, and finally smooth flat, yellow CdS QDs chitosan composite
films were produced [136]. Dilag et al. [137] used highly photolu-
minescent CdS QDs encapsulated in an inexpensive biopolymeric
chitosan matrix for latent fingermark detection. Cadmium ions
were chelated within the chitosan matrix followed by the rapid ad-
dition of sodium sulfide. Yanjun Chen et al. [138] demonstrated a
simple gas-liquid microfluidic approach to create uniform-sized
chitosan microcapsules containing CdS QDs. CdS QDs are encap-
sulated into the liquid-core of the microcapsules. The sizes of the
microcapsules can be easily controlled by gas flow rate. QDs-
chitosan microcapsules exhibited good fluorescent stability in
water and showed fluorescent responses to chemical environmen-
tal stimuli. These stimuli-responsive microcapsules are inexpen-
sive and easy to be prepared by gas-liquid microfluidic technique,
and can be employed as a suitable micro-detector to chemicals,
such as CDs. Lian et al. [139] developed an enhanced imprinted
film-based electrochemical sensor for urea identification by CdS
QDs-doped chitosan as the functional matrix. The developed sen-
sor was employed to determine the urea in human blood serum
samples based on its good reproducibility and stability.
4.7 Carbohydrate-Branched Chitosans
Attachment of carbohydrates to the chitosan converts this
water-insoluble, linear polymer into branched-chain water-sol-
uble derivatives. Grafting carbohydrates can be done on the
chitosan backbone at the C2 position using reductive alkyla-
tion: Disaccharides (cellobiose, lactose, etc.) with a reducing
end group and in the presence of a reductant were inserted to
chitosan in the open chain form [140, 141]. These derivatives
were water soluble. Galactosylated chitosan was mentioned
previously [142]. Carbohydrates can also be inserted on the C6
position without ring opening [143]. These derivatives are vital
because they are identified by the comparable specific lectins
and, thus, could be employed for drug targeting. A special case
is the grafting of a cyclic oligosaccharide, cyclodextrin [144].
Recently, Thaku et al. [54] reviewed progresses in graft copoly-
merization and applications of chitosan.
4.8 Alkylated Chitosans
Alkylated chitosans are very important as amphiphilic poly-
mers based on polysaccharides. The physico-chemical proper-
ties of chitosan can be changed by chemical modification pro-
ducing a lot of materials with a wide range of technological
applications. For example, the introduction of linear or cyclic
carbohydrates onto chitosan makes it water-soluble while its
tunable partial alkylation produces polymers that can be still
soluble in water at acidic pH, but that also efficiently self-aggre-
gate in water, giving rise to hydrophobic pools. This is espe-
cially significant in the drug release field [145] for the possibili-
ty to dissolve both hydrophilic and hydrophobic drugs into the
chitosan matrix. Several papers dealing with the physicochemi-
cal properties of alkylated chitosans are present in the literature
and several experimental approaches, such as rheology [65,
146–148], interfacial tension [146], scattering techniques [65],
and fluorescence [65], have been employed. However, only the
physico-chemical behavior of alkylated chitosans of low alkyla-
tion degree (AD), generally 2–4 % in mole of the cyclic units,
has been considered. The increase of the AD value could be
relevant in order to obtain hydrophobic pools suitable to solu-
bilize hydrophobic guests. Holme et al. [149] chemically modi-
fied chitosan for the purpose of preparing controlled solubility
derivatives of this intractable polymer. Ortona et al. [150] in-
vestigated the physico-chemical behavior of a series of substi-
tuted chitosans with aliphatic chains of different length at 10 %
AD, with the aim to give a quantitative insight about the self-
aggregation behavior of these grafted polymers in solution.
They showed that in dilute solution the grafting of a short
chain of five carbon atoms is not yet able to hydrophobically
promote intra-aggregation of the polymermolecules, but in
contrast, makes the chitosan structure more rigid and improves
the polymer-solvent interaction.
By employing carboxylic anhydrides with various chain
lengths on CM-chitosan, highly substituted derivatives with
low regularity were acquired. They were insoluble in water and
their biodegradability was reduced [151]. Desbieres et al. [152]
prepared chitosans which are substituted with alkyl chains with
various chain lengths (Cn from 3 to 14) and controlled DS
(usually lower than 10 % to maintain water solubility in acidic
conditions), using the reductive amination. The substituted
chitosans with alkyl chains of a sufficient length (a minimum
of six carbon atoms is essential) exhibited hydrophobic charac-
teristics [152]. This approach was also used to introduce
n-lauryl chains [153]. Alkylated chitosans with suitable solubil-
ity in acidic environments (pH 6) had many interesting prop-
erties. In a work of Desbrières et al. [154], chitin was first car-
boxymethylated and then alkylated. Two technics were
employed for that purpose: ionic surfactants playing the role of

counterions form an electrostatic complex, and covalent deri-
vatization. The alkylated carboxymethylchitins present ten-
sioactive properties which may be compared with the complex
formed between the anionic polyelectrolyte and a cationic
surfactant. In another work of Desbrières et al. [154], they
demonstrated the interesting properties of alkylated chitosans
in aqueous solution, in which the viscosity is largely increased
due to interchain hydrophobic interactions; in some condi-
tions, a gel-like behavior is observed.
It should be mentioned that alkyl chitosans were compatible
with cationic and neutral surfactants. It was proven that cati-
onic surfactant adsorbed on the alkyl chain grafted on chitosan,
enhanced its solubility [155].
Chitosan is a weak base with a pKa value of 6.5 [156]. There-
fore, chitosans of high molecular weight are rarely soluble in
aqueous solutions at neutral pH. This clearly limits the bio-
medical applications of this family of polymers. This problem
can be solved somehow by using low molecular weight chito-
sans [157–162] which are water soluble in a wide pH range and
are still able to condense DNA. In order to enhance the
potency of oligochitosan derivatives as nonviral vectors, they
should be bestowed with surfactant-like structures and proper-
ties. This may be obtained by alkylating low molecular weight
chitosans, which due to their small size are expected to com-
pensate the solubility decrease consecutive to alkylation. In this
respect, we have recently prepared [27] a series of hydrophobi-
cally modified oligochitosans with different degrees of covalent
substitution by N-/2(3)-(dodec-2-enyl) succinoyl alkyl chains.
Because of their relatively low molecular weight and the car-
boxyl groups associated with the alkyl chains, these samples
exhibit a good solubility in water at neutral pH. The surface
activity, i.e., the ability to decrease the surface tension, of these
chitosan samples increases with increasing TDC (tetradecenoyl
substitution) values, whereas the critical micelle concentration
(CMC) decreases. Yang et al. [163] investigated antibacterial
activity of the water-soluble N-alkylated disaccharide chitosan
derivatives against Escherichia coli and Staphylococcus aureus.
It was discovered that the antibacterial activity of chitosan de-
rivatives was influenced by the degree of substitution (DS) with
disaccharide and the kind of disaccharide present in the mole-
cule. Among the chitosan derivatives tested, maltose derivative
with a DS of 30–40 % showed the highest antibacterial action
against S. aureus, while E. coli was the pronest to a cellobiose
derivative with DS = 30–40 %. In addition, the N-alkylated dis-
accharide chitosan derivatives tested demonstrated a higher
antibacterial activity than the native chitosan at pH 7.0.
Guo-qing Ying et al. [164] improved water-solubility at neu-
tral or basic pH of chitosan by particular attachment of carbo-
hydrates to the 2-amino functions using the Maillard reaction
or further reductive alkylation of Schiff bases. The results dem-
onstrated that the water-soluble chitosan derivatives produced
through the Maillard reaction may be promising commercial
additives in cosmetics and food.
5 Applications of Chitin and Chitosan
Some chitin and chitosan applications are summerized in
Tab. 2 and investigated in the following.
5.1 Application in Medicine and Pharmacy
Chitosan is a beneficial polymer for biomedical applications
due to biocompatibility, biodegradability, and low toxicity.
Chitin has also been described as biocompatible and biode-
gradable and many of its applications for specific purposes,
such as sponges and bandages for the treatment of wounds and
suture threads have been discovered. However, due to chitins
insolubility in water and low reactivity, less attention has been
paid to it. It is significant to consider that its insolubility in or-
dinary solvents makes chitin characterization and processing
so hard. The biodegradability of chitin and chitosan was princi-
pally attributed to their vulnerability to enzymatic hydrolysis
by lysozyme, a non-specific proteolytic enzyme that exists in all
human body tissues. Lipase, an enzyme which exist in the sali-
va and in human gastric and pancreatic fluids, has the ability to
degrade chitosan [165]. The products of the enzymatic degra-
dation of chitosan were non-toxic. The degree of acetylation,
the molecular weight, the pH and even the method of prepara-
tion of chitosan had an influence on biodegradation. In contact
with blood, due to the interaction of the amino groups with the
acid groups of blood cells, chitosan activates the formation of
clots [166]. Most of the investigations demonstrated that the
interactions of free amino groups of chitosan with plasma pro-
teins or/and blood cells could cause a thrombogenic or/and a
hemolytic response. Many of them reported that chitosan is
highly thrombogenic [167] because it has the ability to activate
both complement [168] and blood coagulation systems [169].
The mechanism of blood-chitosan interaction has been ex-
plained by an initial adsorption of plasma proteins on chito-
san-based systems, followed by adhesion and activation of
platelets that lead to the formation of a thrombus [170, 171].
Thus, it is a suitable haemostatic agent. However, it was found
that water-soluble chitosan and chitosan oligomers did not
present thrombogenic activity, but the sulphated derivatives of
chitosan demonstrated anticoagulant activity [172]. Another
way used to acquire chitosan derivatives with improved hemo-
compatibility was based on the modification with sulfates
[173–177]. Sulphated chitosan, a water-soluble chitosan deriva-
tive with a sulphate substituent on one or both hydroxyl and
amino groups of the biopolymer showed good biocompatibility
and biological activities, such as blood anticoagulant, hemag-
glutination inhibition activity, antimicrobial, and antioxidant
activity [19]. It was claimed that chitosan was hypocholestero-
lemic and hypolipidemic [178]. It had antimicrobial, antiviral
and antitumoral activity. Also, the immune adjuvant activity of
chitosan was identified. Because of these excellent characteris-
tics, there are different applications of chitosan and its deriva-
tives not only in biomedicine, such as surgical sutures,
bandages and biodegradable sponges [166], matrices (in micro-
spheres, microcapsules, membranes and compressed tablets)
for the delivery of drugs [179], as well as orthopedic materials
and dentistry [180].
5.2 Chitosan as Biomaterial
The diversity of applications of chitosan as a biomaterial is re-
lated to its superior properties at a time of interacting with the

human body: bioactivity, antimicrobial activity, immunostimu-
lation, chemotactic action, mucoadhesion, enzymatic bio-
degradability and epithelial permeability, which reinforce the
adhesion and proliferation of different kinds of cells [181].
Chitosan has been tested for applications such as contact
lenses, tissue adhesive, preventing bacterial adhesion, sutures,
etc. However, this biopolymer has been extensively studied
mainly in two biomedical fields. First, it has been employed si-
multaneously with chitin in the treatment of wounds, ulcers
and burns, because of its haemostatic characteristics and its
hastening wound healing effect. Second, because of its cell
affinity and biodegradability, it has been employed in tissue re-
generation and restoration, including its perspective utilization
as a structural material in tissue engineering [182].
5.3 Treatment of Wounds and Burns
Jayakumar et al. [183] reviewed Biomaterials based on chitin
and chitosan in wound dressing applications. Treatment of
Table 2. Some applications of chitin and chitosan.
Application Example Ref.
Chitin
Biomedical and pharmaceutical
materials
Sponges and bandages for the treatment of wounds and suture threats [165]
Agriculture Defensive inducing mechanisms in plants [204]
Water engineering For decontaminated plutonium-containing wastewater and water-containing
methylmercury acetate
[214]
Chitosan
Biomedical and pharmaceutical
materials
Treating major burns, preparation of artificial skin, surgical sutures, contact lenses,
blood dialysis membranes and artificial blood vessels, as antitumor, blood anticoagulant,
antigastritis, haemostatic, hypochlesterolaemic and antithrombogenic agents, in drug- and
gene-delivery systems, and in dental therapy
[215–217]
Cosmetics Skin- and hair-care products [218]
Tissue engineering Cell growth and proliferation in tracheal cartilage, nerve
Bone tissue repair and regeneration materials for cartilage repair
Porous 3D scaffolds of chitosan-calcium phosphate composites for bone regeneration
Chitosan-chondroitin sulphate sponges in bone regeneration
Chitosan-calcium alginate capsules with the aim of developing an artificial pancreas for
the treatment of diabetes mellitus
[180, 189, 191–193]
Agriculture Seed- and fruit-coating fertilizer and fungicide [219]
Chromatographic media and
analytical
Immobilization of enzymes, as a matrix in affinity and gel permeation chromatography
and as enzyme substracts
[215, 218, 220–223]
Food and feed additives Clarification and de-acidification of fruits and beverages, color stabilization, reduction of
lipid adsorption, natural flavor extender
Controlling agent, food preservative and antioxidant, emulsifying, thickening and
stabilizing agent, livestock and fish-feed additive, and preparation of dietary fibers
[215, 218]
Water engineering Wastewater treatment, recovery of metal ions and pesticides, removal of phenol, proteins,
radioistopes, PCBs and dyes, recovery of solid materials from food-processing, wastes, re-
moval of petroleum and petroleum products from waste water, as an adsorbent for remov-
al of color from dyehouse effluents, metal capture from wastewater, color removal from
textile mill effluents.
[210, 218, 224]
Chitin and Chitosan
Medicine and pharmacy Wounds, ulcers and burns treatment, due to its haemostatic properties and its accelerating
wound healing effect
[182]
Agriculture Controlling parasitic nematodes in soils
The antimicrobial properties of chitosan and its excellent film forming aptitude have been
exploited in the post-harvest preservation of fruits and vegetables in soil, enhance plant-
microorganism symbiotic interactions to the benefit of plants, as in the case of micorrizas
chitosan and its derivatives
Induce favorable changes in the metabolism of plants and fruits
[205, 206, 208]

wounds and burns is certainly one of the most promising med-
ical applications for chitin and chitosan. The adhesive proper-
ties of chitosan, in addition to its antifungal and bactericidal
character, and its permeability to oxygen, are significant prop-
erties associated with the treatment of wounds and burns. For
this purpose, various derivatives of chitin and chitosan have
been patented in the form of membranes, woven fibers, hydro-
gels, etc. A number of these formulations has come out to the
market, like Beschitin in Japan (based on chitin) or Hem Con
in USA (based on chitosan).
Both polysaccharides raise granulation (with angiogenesis)
and cell organization during wound healing. The analgesic
effect of both chitin and chitosan has been investigated [184].
Also, water-soluble chitosan (WSC) and heparin have been
investigated as matrices for wound healing, as it was proven
that heparin interacts with and stabilizes growth factors in-
volved in the wound healing procedure [185].
5.4 Tissue Engineering
Tissue engineering techniques commonly need to employ
three-dimensional (3D) supports for initial cell attachment and
subsequent tissue formation. Chitosan has similar structural
characteristics as glycosamino glycans (GAGs) found in the ex-
tracellular matrix of several human tissues. Therefore, it has
been used a lot in tissue engineering, because it makes cell
attachment and the maintenance of differentiating functions
easier. Gelatin-chitosan or collagen-chitosan supports (some of
them crosslinked with glutaraldehyde) have been discovered
with excellent results in cell growth and proliferation in trache-
al [186], cartilage [187], nerve [187], and bone tissue [188] re-
pair and regeneration. In the latter context, a composite with
hydroxyapatite was used. Chitosan-chondroitin sulphate mem-
branes have been proven to support chondrogenesis. Therefore,
they are suitable materials for cartilage repair [189].
Also, platelet-derived growth factor releasing chitosan-chon-
droitin sulphate sponges have been investigated in bone regen-
eration [190]. An equivalent of human skin composed of colla-
gen-GAG-chitosan has been produced [191]. The biological
properties of chitosan-chondroitin sulphate and chitosan-hya-
luronate polyelectrolyte complexes (PEC) have been investi-
gated [192].
These materials were cytocompatible, but with pure chito-
san, better cell attachment and proliferation was obtained.
Chitosan-GAG materials, including chitosan-heparin, have
been discovered as modulators of vascular cells proliferation.
In this same vein, antigenic collagen-hyaluronic acid mixtures
have been found to enhance fibroblasts growth for tissue re-
pairing. Also, porous 3D scaffolds of chitosan-calcium phos-
phate composites have been discovered for bone regeneration
[180]. Calcium phosphate strengthened the chitosan matrix ex-
tremely and adjusted the release burst effect, when loaded with
gentamicin. Moreover, good cellular biocompatibility was ob-
served. Also, the preparation of chitosan-tricalcium phosphate
sponges by mixing and freeze drying, in some cases loaded with
platelet-derived growth factor, has been reported [192]. A stim-
ulating method in tissue engineering is the encapsulation or
immunoisolation of pancreatic and hepatic cells. To make an
artificial pancreas for the treatment of diabetes mellitus, Lan-
gerhans islets have been enclosed in chitosan-calcium alginate
capsules [193].
5.5 Pharmaceutical Applications
Chitosan has been employed extensively as promising vehicles
for oral drug sustained-release formulations and as matrix in
drug-release systems in the form of beads and granules. Chito-
san films showed low swelling in water, but membranes with
different hydrophilic aptitudes can be prepared by the forma-
tion of mixtures or semi-interpenetrated and interpenetrated
networks of chitosan with highly hydrophilic polymers such as
poly(vinyl alcohol), poly(vinylpyrrolidone) and gelatin [62].
PECs of chitosan with polyanions of natural origin like pectin,
alginate, CMC, or with synthetic ones like poly (acrylic acid)
have been discovered as matrices for controlled-release systems
[194]. A pH-sensitive drug delivery system based on a glutaral-
dehyde-crosslinked chitosan-gelatin hybrid network has been
developed. This gel swells at low pH and de-swells at high pH,
demonstrating pH-dependent release of drugs. Intelligent drug
delivery systems (DDS) can release a drug in reaction to
changes in environmental conditions, e.g., temperature, pH,
light, electric field and certain chemicals. DDS are based on
stimulus-sensitive gels as carriers. The results showed that the
drug delivery is controlled by diffusion and relaxation process-
es, while the diffusion coefficient and relaxation time are highly
dependent on the pH of the medium. In addition, the drug sol-
ubility in water clearly has an effect on the release [195].
Chitosan-polyethylene glycol-alginate miscrospheres have
been reported as suitable materials for the delivery of low mo-
lecular weight (LMW) heparin with antithrombotic properties
[196]. Chitosan-CMC microcapsules of various compositions
were tested as a protective matrix against the acid pH of the
stomach for the oral administration of proteins and drugs
[197]. Chitosan-xanthan microspheres are biodegradable and
sensitive to pH and give a protective effect to the drug in the
gastric and intestinal environment. They have also been sug-
gested as a potential drug delivery system in the gastrointesti-
nal tract [198]. Chitosan nanoparticles have been employed for
the nasal dosage of drugs and vaccines because they improve
the penetration of macromolecules through the nasal barrier
[199]. Transdermal-drug delivery (TDD) devices with chitosan
have been developed for the permeation-controlled delivery of
propranolol hydrochloride. These systems consist of chitosan
membranes with different crosslink densities as drug release
controlling tools and chitosan gel as the drug reservoir. Drug
release is widely influenced by the crosslinking density of chito-
san. Chitosan is a good candidate for non-viral gene delivery
systems because cationically charged chitosan can be com-
plexed with negatively charged plasmid DNA. Recently, many
new delivery systems have been developed like the entrapment
of drugs, proteins, antigens or genes in small vesicles or within
polymeric matrices [200]. Due to reduced unwanted toxic side
effect and improved therapeutic effect, the colloidal delivery
system is one of the most promising delivery systems [201].
Colloidal delivery systems include liposomes, microemulsions,
nanoparticles, polymeric self-assemblies, and so on. Among

them, self-assembly of polymeric amphiphiles in aqueous me-
dia such as block copolymer micelles and self-aggregates of hy-
drophobically modified polymers has been widely applied to
the field of biotechnology and pharmaceutics [202]. Self-aggre-
gates of chitosan hydrophobically modified by deoxycholic acid
(mean diameter of ca. 160 nm) can create charged complexes
when mixed with plasmid DNA. These self-aggregate-DNA
complexes are beneficial for gene delivery into mammalian
cells in vitro (Once cells are disrupted and individual parts are
tested or analyzed, this is known as in vitro) and can work as a
good delivery system [203].
5.6 Agricultural Applications
Using chitin and chitosan in agriculture has four main direc-
tions: (a) plant protection against plagues and diseases in pre-
and post-harvest, (b) enhancing antagonist microorganism
action and biological control, (c) support of beneficial plant-
microorganism symbiotic relationships and (d) plant growth
regulation and development. Chitin and its derivatives have
been employed extensively for impeling defensive mechanisms
in plants. Yamaguchi et al. [204] evaluated N-acetylchitooligo-
saccharides (oligochitin, chitin oligosaccharides) of a specific
size as potent elicitor signals in plants to protect them against
many vegetable diseases. Chitin and chitosan have fungicidal
(which destroys fungi) activity against many phytopathogenic
(an organism parasitic on a plant host) fungi. The antiviral and
antibacterial activity of chitosan and its derivatives have also
been identified. These polysaccharides have been used success-
fully to control the parasitic nematodes in soils. The addition
of chitin to the soil raises the population of chitinolytic micro-
organisms (relating to the enzyme converting chitin (a poly-
saccharide) into chitobiose (a disaccharide)) that ruin the eggs
and cuticles of young nematodes which have chitin in their
composition [205]. The chitinase and chitosanase activity in
seeds protected by films of chitin and its derivatives has also
been reported. The antimicrobial properties of chitosan and its
outstanding film-creating aptitude have been exploited in the
post-harvest preservation of fruits and vegetables. Covering
fruits and vegetables with a chitosan film grants them anti-
microbial protection and enhanced shelf life [206].
Chitin and chitosan in soil increase plan-microorganism
symbiotic interactions which is beneficial for plants, as in the
case of micorrizas. They also improve the action of plague-con-
trolling biological organisms such as Tricoderma sp, Bacilus sp
[207], and are suitable for the encapsulation of biocides. There-
fore, their efficiency in the control against pathogenic micro-
organisms and plagues is enhanced.
Chitosan and its derivatives cause desirable changes in the
metabolism of plants and fruits. This brings about improved
germination and higher crop yields [208].
5.7 Food and Nutrition Applications
The N-acetylglucosamine (NAG) moiety existing in human
milk improves the growth of Bifido bacteria, which block other
kinds of microorganisms and produce the needed lactase for
digestion of milk lactose. Cow milk has a limited amount of the
NAG moiety; therefore, some infants fed cow milk may have
indigestion. Some animals and humans (including the elderly)
have similar lactose intolerances.
Investigations on animal nutritional have demonstrated that
the employment of whey may be enhanced if the diet contains
small amounts of chitinous material. This improvement is as-
cribed to the change in the intestinal microflora caused by the
chitinous supplement. Chickens fed a commercial broiler diet
containing 20 % dried whey and 2 or 0.5 % chitin had consider-
ably enhanced weight again compared to controls. The feed
efficiency ratio changed from 2.5 to 2.38 because of incorpora-
tion of chitin in the feed [62]. Other food applications of chitin,
chitosan, and their derivatives are shown in Tab. 3.
5.8 Cosmetics
For cosmetic applications, organic acids are generally suitable
solvents, chitin and chitosan have fungicidal and fungi static
properties. Chitosan is the only natural cationic gum that turns
viscous on being neutralized with acid. These materials are em-
ployed in creams, lotions and permanent waving lotions. Sever-
al derivatives have also been reported as nail lacquers [209].
5.9 Chitosan as an Artificial Skin
Peoples with extensive losses of skin, commonly in fires, are ill
and in danger of succumbing due to massive infection or strict
fluid loss. Patients often need to deal with difficulties of reha-
bilitation of deep, disfiguring scars and crippling contractures.
Malette et al. investigated the effect of treatment with chitosan
and saline solution on curing and fibroplasia of wounds made
by scalpel insertions in skin and subcutaneous tissue in the ab-
dominal surface of dogs.
Yannas et al proposed a design for artificial skin, applicable
for long-term chronic use, focusing on a non-antigenic mem-
brane, which acts as a biodegradable template for the synthesis
of neodermal tissue [211]. It seems that chitosans possessing
structural characteristics similar to glycosamino glycans could
be considered for developing such substratum for skin replace-
ment [212].
5.10 Opthalmology
Chitosan has all the necessary characteristics for fabricating an
ideal contact lens: optical clarity, mechanical stability, gas per-
meability, sufficient optical correction, particularly towards
oxygen, wettability and immunological compatibility. Contact
lenses are made from partially depolymerized and purified
squid pen chitosan by spin casting technology and these con-
tact lenses are clear, tough and have other necessary physical
properties such as modulus, tensile strength, tear strength,
elongation, water content and oxygen permeability. The anti-
microbial and wound healing properties of chitosan as well as a
superior film capability make chitosan appropriate for prepar-
ing ocular bandage lenses [213].

5.11 Water Engineering, Reverse Osmosis
and Heavy Metal Recovery
Because of its polycationic nature, chitosan can be employed as
flocculating agent. It can also work as chelating agent, and
heavy metals trapper. Weltroswki et al. [225] used chitosan
N-benzyl sulphonate derivatives as sorbents for the removal of
metal ions in acidic medium. In 1999, Sridhari and Dutta [226]
used chitosan as an adsorbent for the removal of color from
dyehouse effluents. Substantial amounts of the world produc-
tion of chitin and chitosan and derivatives are used in waste-
water treatment. Chitosan molecules greatly agglomerate an-
ionic wastes in solution to form precipitates and floe; therefore,
they work as a flocculent for recycling of food processing waste.
Chitosan can compete efficiently with synthetic resins in the
capture of heavy metals from processing water.
Chitin has been used to decontaminate plutonium-
containing wastewater, and water-containing me-
thylmercury acetate, a significant pollutant of
wastewater from acetaldehyde production.
The application of a chitosan-chitin mixture was
discovered to remove arsenic from polluted drink-
ing water. Chitosan is effective in the removal of
petroleum and petroleum products from waste-
water [214]. Vakili et al. [227] reviewed the applica-
tion of chitosan and its derivatives as adsorbents
for dye removal from water and wastewater.
Yang et al. [228] prepared alkali-resistant reverse
osmosis membranes by spreading solutions of chito-
san in acetic acid on a glass plate. The membrane had
a flux rate of 1.67 · 10–3
cm3
cm–2
s–1
and a salt rejec-
tion capability of 78.8 % with 0.2 % NaCl at 680 psi.
Rutherford et al. [229] studied the permeability of
chitin films cast from the DMAc-5 % LiCl solvent
system. Solute flux was 100–300 times less than the
water flux. This membrane can be used as reverse
osmosis (RO) membranes or in other applications
requiring the separation of water and solutes.
One of the perpetual areas for chitosan is as an
absorbent of industrial waste, especially on the
interaction of its free amine group with metal ions
in heavy metal pollution control. The application
of chitosan materials for waste dye and heavy metal
adsorption in industry over a 10-year period was
reviewed by Ngah et al. in 2011 [230].
Different combinations of chitosan with clay,
polymers such as PU, PVA, cotton, and cellulose
have been employed with different efficiency.
Clearly, low costs with high removal capacities are
vital factors. Others include scale-up and adsorbent
regeneration studies. The authors suggested that
using such chitosan-based materials is suitable.
In the work of heavy metal recovery by Monier,
he prepared chitosan-thioglyceraldehyde Schiff’s
base cross-linked magnetic resin (CSTG) for com-
parative studies on the removal of toxic metal ions
like Hg2+
, Cu2+
and Zn2+
from aqueous solutions
[231]. The ions were efficiently adsorbed by the
resin at higher pH and low temperatures.
The removal of Cd(II) from industrial waste water was in-
vestigated by Lu et al. [232]. Carboxymethyl chitosan (CMCS)
was employed as an ion-imprinted polymer onto silica. Utiliza-
tion of the chitin sponge from Aplysina aerophoba to recover
uranium from mining wastes in rock and soil was a successful
work [233].
Experiments on uranyl solution studied the interactions be-
tween chitin and uranyl ions, the extraction and desorption
characteristics, as well as the feasibility for reuse of the chitin
sponge. The results showed a high absorption capacity for ura-
nyl ions by the chitin sponges.
Kocak et al. [234] prepared nanochitosan that was derivat-
ized with 2,5-dihydroxybenzaldehyde via a Schiff base reaction.
The derivatized nanochitosan was combined with graphite
powder and fabricated into a carbon paste electrode. The modi-
Table 3. Food applications of chitin, chitosan, and their derivatives [210].
Area of application Examples
Antimicrobial agent Bactericidal
Fungicidal
Measure of mold contamination in agricultural
commodities
Edible film industry Controlled moisture transfer between food and
surrounding environment
Controlled release of antimicrobial substances
Controlled release of antioxidants
Controlled release of nutrients, flavors and drugs
Reduction of oxygen partial pressure
Controlled rate of respiration
Temperature control
Controlled enzymatic browning in fruits
Reverse osmosis membranes
Additive Clarification and deacilification of fruits and beverages
Natural flavor extender
Texture controlling agent
Emulsifying agent
Food mimetic
Thickening and stabilizing agent
Color stabilization
Nutritional quality Dietary fiber
Hypocholesterolemic effect
Livestock and fish feed additive
Reduction of lipid absorption
Production of single cell protein
Antigastritis agent
Infant feed ingredient
Recovery of solid materials From food processing wastes
Affinity flocculation
Fractionation of agar
Purification of water Recovery of metal ions, pesticides, phenols and PCBs
(polychlorinated biphenyl)
Removal of dyes
Other application Enzyme immobilization
Encapsulation of nutraceuticals
Chromatography
Analytical reagents

fied electrode was used in voltammetry to investigate its ca-
pacity to detect trace concentrations of Pb(II) ions.
5.12 Pervaporation
Pervaporation is a separation method in which separation of a
liquid mixture happens during transport through a non-porous
liophilic membrane. The liquid feed is in direct contact with
one membrane surface. The components of the permeate are
removed in a vapor state from the other side of the membrane
into a vacuum or inert carrier gas [235, 236]. One of the com-
ponents of the separated mixture is preferably transported
through the membrane. The separation arises from the differ-
ences of sorption of mixture components and differences of
their diffusivities through the non-porous membrane. The effi-
cient pervaporation membrane should be characterized by a
good chemical resistance, mechanical durability, high selectiv-
ity and high permeate rates. The principle of the pervaporation
process is displayed in Fig. 4 [236].
Chitosan is also a multifunctional polymer with large num-
bers of reactive amine groups together with hydroxyl groups,
which make it a hydrophilic material and capable of reacting
with groups such as the epoxy group [235]. These hydrophilic
groups are considered to play an influential role in preferential
water sorption and diffusion through the chitosan membrane.
Chitosan has been proven to have good film forming proper-
ties, chemical resistance and high water permeability [237].
Many studies have reported that the chitosan membranes were
highly water- permselective for the pervaporation of aqueous
alcoholic solutions. Tab. 4 has summarized the configuration of
chitosan membranes prepared and applied in the pervapora-
tion by the previous researchers.
5.13 Other Applications of Chitin and its
Derivatives
Chitins have been employed as an additive in paper manufac-
ture. The potential application of chitosan as a spermicide is
being investigated as an alternative to chemical spermicides.
Two new chitin derivatives, tosyl-chitins and iodo-chitins, are
characterized by noteworthy solubility in many organic sol-
vents and high reactivity. Therefore, they are used as multipur-
pose precursors that would enable regulated modification of
chitin and other biopolymers [238]. Solid chitin particles have
been used as stabilizers for oil-water emulsions. Very stable
emulsions were acquired at a chitin concentration of 25 kg m–3
and addition of surfactants extremely raised the emulsifying
Figure 4. Principle of pervaporation.
Table 4. Configurations of chitosan membranes produced by previous researchers.
Membrane Application Ref.
Chitosan derivative membranes Separation of ethanol-water mixtures [244]
Chitosan salt membrane Separation of water-ethanol mixtures [245]
Modified chitosan membranes, chitosan-acetic acid and -metal ion complex membranes Separation of water-ethanol mixtures [246]
Poly(vinyl alcohol)-chitosan blend membrane Separation of water-ethanol mixtures [247]
Crosslinked chitosan membranes Separation of water-ethanol vapor mixtures [248]
Chitosan membranes Separation of water from ethylene glycol [249]
Chitosan membrane Separation of ethanol-water mixtures [250]
Chitosan membranes Dehydration of isopropanol-water [251]
Blend membranes of chitosan and polyacrylic acid Separation of ethanol-water mixtures [252]
Crosslinked chitosan composite membranes Separation of water-alcohol mixtures [253]
Chitosan-N-methylol nylon 6 blend membranes Separation of ethanol-water mixtures [254]
Sodium alginate-chitosan polyelectrolyte complex membrane Separation of water-organic liquids mixtures [255]
Chitosan-silk fibroin blend membrane Separation of alcohol-water mixture [256]
Crosslinked chitosan-polysulfone composite membranes Dehydration of alcohol mixturess [257]
Novel two-ply composite membranes of chitosan Dehydration of isopropanol and ethanol [258]
Surface crosslinked chitosan membranes Separation of ethylene glycol-water mixtures [259]
Chitosan-poly (N-vinyl-2-pyrrolidone) blend membranes Separation of MeOH-MTBE [260]
Chitosan composite membrane modified with surfactants Separation of methanol-methyl t-butyl ether [261]
Chitosan-hydroxyethylcellulose blended membranes Dehydration of isopropanol [262]
N-acetylated chitosan membranes Separation of alcohol-toluene mixtures [263]

HY zeolite-filled chitosan membranes Separation of ethanol-water mixtues [264]
N-acetylated chitosan membranes Separation of alcohol-toluene mixtures [263]
Chitosan-anionic surfactant complex membranes Separation of methanol-MTBE mixtures [265]
Chitosan membranes Separation of dimethyl carbonate-methanol-water
mixtures
[266]
Chitosan-hydroxyethylcellulose (CS-HEC) composite membranes Dehydration of ethanol-water mixtures [237]
Crosslinked quaternized chitosan composite membranes Separation ethanol-water vapors [267]
Crosslinked chitosan membranes Separation of isopropanol-water mixtures [268]
Crosslinked chitosan membranes Separation of dimethyl carbonate-methanol-water
mixtures
[269]
Complex crosslinked chitosan composite membranes Dehydration of alcohols [270]
Blend membranes of chitosan and sodium alginate Dehydration of ethanol [271]
Chitosan-cellulose acetate composite hollow-fiber membranes Separation water-alcohol mixtures [272]
Poly(vinyl alcohol)-chitosan blend membranes Separation benzene-cyclohexane mixtures [273]
Crosslinked chitosan membranes Separation of isopropanol-water mixtures [268]
Chitosan membranes cross-linked with toluylene diisocyanate Separation of tertiary butanol-water mixtures [274]
Chitosan and NaY zeolite membranes Separation of water-isopropanol mixtures [275]
Blended chitosan and polyvinyl alcohol membranes Dehydration of isopropanol [276]
Chitosan-silica complex membranes Dehydration of ethanol-water solutions [277]
Novel chitosan-impregnated bacterial cellulose membranes and chitosan-poly
(vinyl alcohol) blends
Separation of ethanol-water mixtures [278]
Chitosan membranes Separation of acetone-butanol-ethanol (ABE) [279]
Novel NH4Y zeolite-filled chitosan membranes Dehydration of water-isopropanol mixture [280]
Modification of tetraethylorthosilicate crosslinked PVA membrane Separation of water-isopropanol mixtures [281]
Blend membranes of chitosan and hydroxyl ethyl cellulose Dehydration of 2-butanol [282]
Novel graphite-filled PVA-CS hybrid membrane Separation of benzene-cyclohexane mixtures [283]
Chitosan-PVA-PAN composite membranes Separation of ethanol-water mixtures [284]
Blend membranes of chitosan and poly(vinyl alcohol) Dehydration of isopropanol and tetrahydrofuran [285]
Hybrid membranes composed of chitosan and g-glycidyloxypropyltrimethoxy-silane Separation of water-acetic acid mixtures [286]
Sodium alginate-chitosan polyelectrolyte complex composite membranes Separation of water-alcohol mixtures [287]
Blend membranes of poly(vinyl alcohol) and chitosan Dehydration of 1,4-dioxane [288]
Modified blend membranes of chitosan and nylon 66 Dehydration of 1,4-dioxane [289]
Chitosan and hydroxypropyl cellulose Dehydration of isopropanol [290]
Chitosan-poly(tetrafluoroethylene) composite membranes Dehydration of isopropanol [291]
Composite hybrid membrane of chitosan-silica membranes Separation of MeOH-DMC mixtures [292]
Chitosan-poly(acrylic acid) polyelectrolyte complex membranes Dehydration of ethylene glycol [293]
Crosslinked carboxymethyl chitosan-PSf hollow-fiber composite membranes Separation of water-isopropanol mixtures [294]
Chitosan membranes cross-linked by 3-aminopropyltriethoxysilane Dehydration of ethanol [295]
Diisocyanate crosslinked chitosan membranes Separation of water-isopropanol mixtures [296]
Trimesoyl chloride crosslinked chitosan membranes Dehydration of isopropanol [297]
Novel ZSM-5 zeolite-filled chitosan membranes Separation of dimethyl carbonate-methanol mixtures [298]
Blend membranes of chitosan and poly(vinyl alcohol) Dehydration of isopropanol and tetrahydration [285]
Chitosan-clay composite membranes Dehydration of ethanol [299]
Chitosan membrane Separation of isopropanol-water mixtures [300]
Silicalite zeolite embedded chitosan mixed matrix membranes Separation of toluene-alcohol mixtures [301]
Table 4. Continued.

Chitosan-polyacrylonitrile hollow fiber membrane Dehydration of isopropanol [302]
Chitosan-polysulfone composite membrane Dehydration of ethylene glycol [303]
Chitosan-polysulfone composite hollow-fiber membranes Dehydration of ethanol [304]
H-ZSM-5 filled chitosan membranes Dehydration of aqueous ethanol solution [305]
Crosslinked calcium alginate-chitosan blend membranes Dehydration of 1,4-dioxane [306]
Surface-modified zeolite-filled chitosan membranes Dehydration ethanol [307]
Chitosan-poly(vinyl pyrrolidone) blend membranes Dehydration of ethyl acetate-ethanol-water
azeotrope
[308]
Development of polyelectrolyte complexes of chitosan and phosphotungstic acid Dehydration of isopropanol [309]
Chitosan-poly(vinyl alcohol) blend membranes Dehydration of ethylene glycol [310]
Chitosan-TiO2 nanocomposite membranes Dehydration of ethanol [311]
Maleic anhydride crosslinked alginate-chitosan blend membranes Separation of ethylene glycol-water mixtures [312]
Chitosan-sodium carboxymethyl cellulose polyelectrolyte complexes Dehydration of ethanol [313]
Chitosan-TEOS hybrid membranes Dehydration of ethanol and lactic acid [314]
Chitosan-poly(vinyl alcohol) blend membranes Dehydration of ethylene glycol [310]
Novel composite chitosan membranes Dehydration of isopropanol [315]
Chitosan-TEOS hybrid membranes Dehydration of ethanol [314]
Chitosan-gelatin blend membranes Dehydration of 1,4-dioxane [316]
Chitosan-polyacrylonitrile composite membrane Dehydration of ethanol [317]
Poly(vinyl alcohol)-chitosan composite membranes Dehydration of organic-water mixtures [318]
Chitosan coated zeolite filled regenerated cellulose membrane Dehydration of ethylene glycol-water mixtures [319]
Chitosan-g-polyaniline membranes Dehydration of isopropanol [320]
Hybrid membranes of chitosan and silica precursors Separation of water+ isopropanol mixtures [321]
Poly(vinyl alcohol)-chitosan composite membranes Dehydration of organic-water mixtures [318]
Crosslinked PVA and chitosan membranes Dehydration of caprolactam [322]
Ceramic-supported poly(vinyl alcohol)-chitosan composite membranes Dehydration of organic-water mixtures [318]
Chitosan hydrogel membranes Dehydration of alcohols [236]
Poly(3-hydroxybutyrate)-functionalised multi-walled carbon nanotubes-chitosan
green nanocomposite membranes
Dehydration of ethanol [323]
Titanate nanotubes-embedded chitosan nanocomposite membranes Dehydration of isopropanol [324]
Phosphorylated chitosan membranes Separation of ethanol-water mixtures [325]
Chitosan-konjac glucomannan blending membrane Dehydration of caprolactam solution [326]
Chitosan-poly (acrylic acid) composite membrane Dehydration of caprolactam solution [327]
New chitosan-konjac glucomannan blending membrane Dehydration of caprolactam solution [327]
Hybrid membranes using chitosan and 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane Dehydration of isopropanol [328]
Functionalized silica-chitosan hybrid membrane Dehydration of ethanol-water azeotrope [329]
Sodium alginate and chitosan-wrapped MWCNT membranes Dehydration of isopropanol [330]
Chitosan-sulfonated polyethersulfone-polyethersulfone (CS-SPES-PES) composite
membranes
Dehydration of ethanol [331]
Chitosan membranes containing iron oxide nanoparticles Dehydration of ethanol [332]
Chitosan and 2-(3,4-epoxycyclohexyl) ethyltrimethoxysilane Dehydration of isopropanol [333]
Poly(3-hydroxybutyrate)-functionalised multi-walled carbon nanotubes-chitosan
green nanocomposite membranes
1,4-dioxane dehydration [334]
Mixed matrix membranes of chitosan and Ag+
-carbon nanotubes Pervaporation of benzene-cyclohexane [335]
Chitosan membrane with functionalized multiwalled carbon nanotubes Dehydration of ethanol [336]
Chitosan and silica hybrid membranes Dehydration of isopropanol [337]
Table 4. Continued.

capacity [239]. Thin films of chitosan acetate + silver nitrate
complex were fabricated by the solution cast method. The elec-
trical conductivity of the films was measured by impedance
spectroscopy. It showed low electrical conductivity of the mate-
rial and its quality as an electrolyte for electrochemical cell fab-
rication [240]. Octacalcium phosphate is one of the important
precursors in bony tissue formation. Addition of chitosan had
strong effects on the crystallisation of octacalcium phosphate
[241]. Oh et al. [242] reviewed the application of chitin and
chitosan in the construction of electrochemical hybrid devices.
Chitosan gels have been used in lasers and LEDs [4]. Also, it
has been reported that it has been used as solid state batteries
[4], in developing photographs [2], chromatographic separa-
tion [243], and food processing [4].
6 Conclusion
Chitin and chitosan are biopolymers of polysaccharide groups
with excellent structural possibilities for chemical and mechan-
ical modifications to create novel properties, functions and ap-
plications especially in the biomedical area. Chitin is the most
widespread aminopolysaccharide and is the second natural
polysaccharide after cellulose. Despite its enormous availability,
the use of chitin has been limited by its intractability and insol-
ubility. Several attempts have been reported on solving these
problems, which have been reviewed here. Their derivatives
that are soluble in aqueous media have the unique properties
of chitin as film-forming polymer, with biodegradable, renew-
able, antibacterial and fungistatic properties. Because of limits
like high cost, hard chemical modification and etc., the applica-
tions of chitin are limited to the biomedical and pharmaceuti-
cal industry, with cosmetics in second place. Chitosan, which is
water soluble in acidic media, or under specified conditions at
neutral pH, is the most important derivative of chitin. The dif-
ficulty to get reproducible initial polymers is the one of the lim-
its of chitosan. The advantage of chitosan over other polysac-
charides is that its chemical modification is feasible. In this
review, applications of chitin and chitosan polymers have been
extensively reviewed.
Vida Zargar received her
M.Sc. degree in Chemical
Engineering from University
of Kashan. She is currently a
Superior Researcher Scholar of
University of Kashan and in-
terested in the synthesis of
mixed matrix membranes for
gas separation and pervapora-
tion.
Morteza Asghari, currently a
candidate for associated pro-
fessor, received his Ph.D. in
chemical engineering from
IUST (1st ranking of graduate
Ph.D. students). He is Superior
Researcher Superior master
of education at the University
of Kashan. He was on rank 3
of inventors in 3rd National
Congress of Young Elites of
Iran, gaining a Ph.D. Scholar-
ship by Iran’s Ministry of
Science, Research and Tech-
nology. He is interested in membrane synthesis and modi-
fication, membrane gas separation, MD, PV and synthesis
of related nanostructured materials. As head of the Separa-
tion Processes Research Group (SPRG), he also attempts to
apply novel methods to enhance membrane specifications
to fit environmental purposes (green technologies).
Amir Dashti received his
M.Sc. degree in Chemical
Engineering from the Univer-
sity of Kashan. He is interested
in membrane science and
modeling and neural network
applications in separation pro-
cesses.
Symbols used
[h] [mL g–1
] intrinsic viscosity
K [–] constant
M [–] molecular weight
MW [g mol–1
] weight-average molecular weight
a [–] constant
Abbreviations
AD alkylation degree
CM carboxymethyl
CMC critical micelle concentration
CMCS carboxymethyl chitosan
CSTG cross-linked magnetic resin
DA degree of acetylation
DDS drug delivery systems
DS degree of substitution
GAGs glycosamino glycans

NAG N-acetylglucosamine
NMPC N-methylene phosphonic chitosan
PEC polyelectrolyte complexes
PEG-CHO poly(ethyleneglycol)-aldehyde
QCMC quaternized carboxymethyl chitosan
RO reverse osmosis
TDC tetradecenoyl substitution
TDD transdermal-drug delivery
TEMPO 2,2,6,6-Tetramethylpiperidin-1-yl)oxy
WSC water-soluble chitosan
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