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References 163
8.5.4 The Antimicrobial Properties of Alginate Wound Dressing
Because of the swelling of alginate bers upon contact with wound exudate, the
capillary space between bers are closed and the bacteria attached on the bers are
trapped, with their ability to grow and cause infection inhibited. Bowler et al. [10]
placed alginate dressing in a test solution containing bacteria and found that the
alginate dressing can suppress bacteria growth. Young [89] used alginate dressing
on infected and highly exuding wounds and achieved good clinical results.
8.5.5 Alginate Wound Dressings as Cavity Filler
Barnett and Varley [3], Dealey [24], and Chaloner [16] applied alginate wound
dressings on cavity wounds. They found that the high absorption and gelling
properties of alginate wound dressings are particularly suited to the management
of cavity wounds, whereby the dressings can eectively ll the cavity and are easy
to remove. Xie et al. [88] used alginate dressing in nasal surgery and compared
its clinical ecacy to three other commonly used materials. The alginate dressing
relieved pain and reduced blood loss and generally outperformed Vaseline gauze
and expansive foam.
8.5.6 Cost-Effectiveness of Alginate Wound Dressings
Although the individual piece of alginate dressing is more expensive than conven-
tional gauze products, the application of alginate wound dressing is cost-ecient
in that the overall cost of material and nursing time is low because of the reduced
dressing change and fast wound healing [27, 50, 75, 77–79].
8.6 Summary
Because of the ionexchangebetweencalcium ions in theberand sodium ions inthe
wound exudate, alginate bers can form gel when applied to exuding wounds. The
gelling process is accompanied by the absorption of wound exudate into the ber
structure and as the bers swell, the capillary structure in the nonwoven wound
dressing is closed, thereby blocking the lateral spreading of liquid. This unique “gel
blocking” property of alginate wound dressings helps to reduce wound maceration.
In addition, since alginatewound dressings have novel hemostatic andantimicrobial
properties, especially with the addition of silver ions, they are ideally suited for the
management of chronic wounds where a high level of exudate is common.
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164 8 Clinical Applications of Alginate Wound Dressings
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168 8 Clinical Applications of Alginate Wound Dressings
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169
9
Functional Modifications of Alginate Fibers and Wound
Dressings
9.1 Introduction
The production of wound dressings from alginate represents a chain of processes
comprising the extraction of sodium alginate from brown seaweeds to wet spinning
of alginate bers, production of nonwoven fabrics, packaging and sterilization,
etc. In each of these many steps, innovative technologies have been applied to
modify the structure and properties so that the end product can better meet clinical
requirements. These improvements aim to increase absorption capacities, enhance
antimicrobial properties, and introduce many other novel features.
In addition to their own unique structures and product performances, alginate
bers and wound dressingscanbe combined with other typesof materials to produce
modied materials with enhanced functionalities. In this respect, the development
in other related elds, such as nano-materials, biomaterials, micro-electronics,
and biotechnology, has made it possible to develop smart materials for medical
and healthcare applications by utilizing functional biomaterials, photochromic
materials, thermochromic materials, conductive polymers, and bers, as well as
phase change materials, light-emitting polymers, optical bers, shape memory
polymers, etc.
As illustrated in Figure 9.1, functional modications can be carried out in the pro-
duction of sodium alginate raw materials, in the alginate ber-making process, in
the development of alginate ber-based textile materials, and with novel applica-
tions of alginate-based wound dressings. The many developments in these areas are
summarized in this chapter.
9.2 Chemical Modification of Alginic Acid
Alginate is a linear anionic polysaccharide consisting of two types of 1,4-linked
hexuronic acid residues, namely, β-
D-mannuronopyranosyl (M) and α-L-gulurono-
pyranosyl (G) residues, arranged in blocks of repeating M residues (MM blocks),
blocks of repeating G residues (GG blocks), and blocks of mixed M and G residues
Alginate Fibers and Wound Dressings: Seaweed Derived Natural Therapy, First Edition. Yimin Qin.
© 2024 WILEY-VCH GmbH. Published 2024 by WILEY-VCH GmbH.
170 9 Functional Modifications of Alginate Fibers and Wound Dressings
Sodium alginate powder
Alginate fiber
Yarn
BraidedKnittedWoven Nonwoven
Alginate-based
fabric
Alginate wound dressing
Packaging and sterilization
Figure 9.1 Structural hierarchy of alginate fiber-based wound dressings.
(MG blocks). Alginate has an abundance of free hydroxyl and carboxyl groups
distributed along the polymer chain backbone, which can be chemically modied
to generate derivatives with new functional characteristics. The chemical reactions
include oxidation, reductive amination, sulfation, copolymerization, coupling of
cyclodextrin units, and many others, which can be applied to the hydroxyl and
carboxylic acid groups [107]. Through functionalizing available hydroxyl and
carboxyl groups, the properties such as solubility, hydrophobicity, physicochemical,
and biological characteristics can be modied to broaden applications [66]. When
used in the ber-making process, these chemically modied alginate derivatives
can generate new properties for the alginate bers and wound dressings.
9.2.1 Chemical Modification of the Hydroxyl Groups
9.2.1.1 Oxidation
Oxidation of alginate can generate more reactive groups and a faster degradation
when used for drug delivery [11, 43]. Oxidation reaction is applied on the –OH
groups at C-2 and C-3 positions of the uronic units of sodium alginate with sodium
periodate, resulting in the rupture of carbon–carbon bond and the formation of two
aldehyde groups in each oxidized monomeric unit, and as a result, larger rotational
freedom and new reactive groups along the backbone are obtained. The degree of
oxidation can be controlled by varyingthe concentration ofthe oxidant. Gomez et al.
[32] synthesized oxidized alginates by using sodium periodate and found that when
the degree of oxidationwas over 10 mol%, no more gels were formed in the presence
of excessive calciumions. Figure 9.2 shows anillustration of theoxidation of sodium
alginate by using sodium periodate.
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9.2 Chemical Modification of Alginic Acid 171
O
OH
OH
OH
OH
HO
HO
O
O
O
O
O
O
−
OOC
−
OOC
−
OOC
O
OH
O
O
OH
HO
HO
O
O
O
O
O
O
−
OOC
−
OOC
−
OOC
O
(c)
OH
OH
OH
HO
O
O
O
O
O
O
O
−
OOC
−
OOC
−
OOC
IO
4
−
(a)
(b)
Figure 9.2 An illustration of the oxidation of sodium alginate by using sodium periodate.
Source: Adapted with permission from He et al. [34].
9.2.1.2 Reductive-Amination of Oxidized Alginate
The aldehyde groups in oxidized alginate can be used to prepare more alginate
derivatives by reductive amination, which can be carried out by using NaCNBH
3
as reducing agent, as it is more reactive and selective than the frequently employed
sodium hydroborate (NaBH
4
). The advantage of NaCNBH
3
is that the reduction
of imine intermediate groups by CNBH
3
−
anion is rapid at pH values of 6–7, and
the reduction of aldehyde or ketone is negligible in this pH range [4, 13, 39]. Kang
et al. [39] used this method to prepare alginate-derived polymeric surfactants
by the addition of long alkyl chains to the alginates, which endowed them with
amphiphilic characteristics, such as lower surface tension, solubilizing of solid
azobenzene, and adsorption of heavy metal ions in practical application. Li et al.
[48] made microsphere beads with the alginate-derived polymeric surfactants in
aqueous solution of sodium chloride and calcium chloride. A hydrophobic drug of
ibuprofen was loaded on the modied alginate for controlling release in vitro.Itwas
found that the loading level of drug was obviously increased and the release rate
was well controlled. Laurienzo et al. [46] synthesized a novel alginate–polyethylene
glycol (PEG) graft copolymer by reacting a mono-carboxyl terminated PEG with
a sodium alginate modied by inserting a given amount of amine functionalities.
The coupling between PEG and alginate was carried out using carbodiimide
172 9 Functional Modifications of Alginate Fibers and Wound Dressings
chemistry in aqueous solutions. The alginate–PEG copolymers retain the gelation
characteristics of alginate since the PEG chemical grafting does not consume the
carboxyl groups. The presence of grafted PEG molecules inside alginate gels can
increase the pore dimensions and induce improved cell anchorage.
9.2.1.3 Sulfation
Sulfated alginate has high blood compatibility because of its structural similarity to
heparin, which has been widely used for anticoagulant therapy [3]. Huang et al. [37]
prepared alginate sulfate through reaction with ClSO
3
H in formamide using the fol-
lowing condition: 10 g sodium alginate is added to the sulfating reagent containing
80 ml formamide and 20 ml ClSO
3
H, and the mixture is preserved at 60
∘
Cforfour
hours to give a brown solution. In total, 200 ml acetone is added to precipitate the
solution, and the precipitate is redissolved in distilled water and its pH is adjusted
to 10–11 by 0.1mol/l NaOH, then the solution is dialyzed for 72 hours and con-
centrated to give alginate sulfates. The in vitro coagulation assay of human plasma
containing the sulfates indicated that alginate sulfates had considerably high anti-
coagulant activity especially in the intrinsic coagulation pathway. Figure 9.3 shows
the preparation and chemical structure of sulfated alginate in the presence of dicy-
clohexylcarbodiimide.
9.2.1.4 Cyclodextrin-Linked Alginate
Cyclodextrin can be covalentlylinkedtoalginate to oer drug-carryingproperties for
controlled release. Pluemsab et al. [68] showed that the inclusion ability of alginate
was introduced by covalently linking cyclodextrin to the hydroxyl groupsof alginate.
Stable and spherical beads were also obtained simply by dropping an aqueous solu-
tion of modied CD–alginate into a calcium chloride solution. Figure 9.4 shows the
chemical structure of cyclodextrin.
9.2.1.5 Acetylation of Alginate
Schweiger [74] reported the synthesis of both partially and fully acetylated alginic
acid derivatives using an acid-catalyzed esterication technique. The reaction was
performed by suspending alginicacidin a mixture of aceticacid and acetic anhydride
containing perchloric acid. ProductswithDS values up to 1.85wereachieved at mod-
erate temperatures without signicant degradation. Chamberlain et al. [15] found
that the presence of water was essential to the availability of hydroxyl groups for
N
C
N
+
+
H
2
SO
4
+
NH
CO
NH
NH
CO O
−
NH
O
S
O
+
OO
Na
O
O
HO
OH
−
+
n
O
Na
−
+
O
O
O
HO
OSO
3
Na
n
Figure 9.3 Preparation and chemical structure of sulfated alginate in the presence of
dicyclohexylcarbodiimide.
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