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B.6 What Are the M ain Applications of Alginate Wound Dressings? 223
B.4 How Can Calcium Alginate Dressing Form Hydrogel
on Contact With Wound Exudate?
When calcium alginate bers in the nonwoven dressing are in contact with wound
exudate, the sodium ions in the exudate exchange with calcium ions in the bers,
resulting in the formation of bers that contain both calcium and sodium alginate.
Since sodium alginate is water soluble, when more and more calcium ions are
replaced by sodium ions, the bers pick up more and more water into the ber
structure, which is accompanied by the swelling of the bers to form a brous
hydrogel. During application on exuding wounds, these dressings are capable of
absorbing a large amount of wound exudate and forming a moist healing environ-
ment due to the conversion of calcium alginate bers to calcium sodium alginate
bers.
B.5 What Role Does Alginate Wound Dressings Play in
“Moist Healing”?
The birth and widespread acceptance of the “moist healing” mechanism in wound
management helped to promote the applications of alginate wound dressings.
In 1962, Dr. George Winter of the University of London published his ndings
in Nature concerning the formation of scab and the rate of epithelialization of
supercial wounds in the skin of the young domestic pig. It was found that wounds
that are kept in a moist condition heal faster than being kept in a dry condition.
Under the guidance of this theory, modern wound dressings such as hydrocolloids,
polyurethanes, and alginate wound dressing are designed to main a moist but not
wet condition on the wounds, resulting in a fundamental change in the research,
development, and applications of modern functional wound dressings. Since the
1980s, many types of alginate wound dressings have been developed and launched
in the world market. Due to their excellent properties, alginate wound dressings
gained widespread acceptance as an excellent product for the management of
wounds with medium to high levels of exudate.
B.6 What Are the Main Applications of Alginate Wound
Dressings?
Alginate wound dressings are by their chemical and physical nature highly
absorbent when in contact with wound exudate, making them suitable for man-
aging exuding wounds. The bers can be processed into dierent forms in order
to meet clinical requirements concerning dierent types of wounds. The main
type of alginate wound dressing is made of nonwoven fabrics which are produced
224 B Appendix B: Answers to Commonly Asked Questions About Alginate Wound Dressings
12
3
Figure B.3 Main varieties of alginate wound dressings, 1. nonwoven fabric; 2. rope;
3. strip.
by rst opening the bers and card them into a thin sheet of loose bers which
are then cross-lapped into a thicker web before being needled to form nonwoven
alginate fabric. This type of at sheet structure as shown in Figure B.3 (1) is suitable
for covering at open wounds. Alternatively, the bers can be carded and then
combined into a rope with a porous loose structure, which is used to ll cavity
wounds. The nonwoven fabric can also be cut into narrow strips which are also
used to ll deep cavities. Table B.1 shows the common sizes for alginate dressings.
Nonwoven alginate fabric can be combined with other types of wound manage-
ment materials tomakeplasters that areeasier to apply. Figure B.4 shows an alginate
plaster with a piece of nonwoven alginate as the core and hydroentangled viscose
nonwoven fabric as the outer layer, which is coated with pressure-sensitive adhe-
sive. The outer layer can also be made of polyurethane lm, membrane, and foam
to oer more functional properties, such as regulating water evaporation, and pre-
venting bacteria invasion. These novel properties are suited for the management of
many types of wounds, as illustrated in Figure B.5.
Tabl e B.1 Common sizes for alginate dressings.
Product Size
Flat dressing 5cm × 5 cm, 5cm × 10 cm, 7.5cm× 12.5 cm, 10cm× 10 cm, 10 cm× 20cm,
20 cm × 20 cm, 20 cm × 30 cm, 30 cm × 30 cm
Cavity ller 1 g/15 cm, 1 g/30 cm, 2g/30cm
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B.6 What Are the M ain Applications of Alginate Wound Dressings? 225
Figure B.4 Alginate plaster.
Figure B.5 Clinical
applications of alginate wound
dressings.
Surgical incision
Burn
Pressure soreDonor site
Leg ulcer
Diabetic foot ulcer
Anal fistula
Nasal packing
226 B Appendix B: Answers to Commonly Asked Questions About Alginate Wound Dressings
B.7 What Is the Absorption Mechanism of Alginate
Wound Dressing?
Commercial alginate wound dressings are mostly made through nonwoven pro-
cesses where the bers are arranged in loose forms. The nonwoven structure is
highly porous and there are a lot of capillary spaces between bers that can hold
water when the dressing is in contact with wound exudate. Once the exudate enters
into the dressing, the bers swell following the exchange between calcium ions in
the ber and sodium ions in the exudate. This swelling causes the closure of the
porous structure, thereby blocking the lateral spreading of liquid, resulting in the
“gel blocking” mechanism of alginate wound dressings which is known to prevent
the maceration of skin on the edge of the wounded area. The vertical rise of wound
exudate is not aected because during the production process, the needling of the
fabric creates vertical channels that can facilitate the diusion of wound exudate.
Figure B.6 oers an illustration of the structure of needled nonwoven fabric.
B.8 What Is t he Reason That Calcium Alginate Fibers Do
Not Gel in Pure Water?
For alginate bers, gelling means the expansion of ber diameter following the dif-
fusion of water into the ber structure. When calcium alginate bers are placed in
plain water, they do not gel because the bers remain in a closely intact structure
as the polymeric molecules are bound by hydrogen bonds through the –OH groups
along the polymer chain. When the contact solution contains sodium ions, as is the
case for wound exudate, the sodium ions would exchange with calcium ions in the
calcium alginate bers, and as a result, part of the bers are converted into sodium
200 μm
Figure B.6 An illustration of the structure of needled nonwoven fabric.
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B.10 What Are the Differences Between High G and High M Alginate Fibers When They Are Applied 227
alginate. Since sodium alginate is water soluble, a large amount of water is drawn
into the bers, turning them into broushydrogelwhich can provide a moist healing
environment when applied on exuding wounds.
B.9 What Are the Differences Between the Absorption
of Wound Exudate by Cotton Gauze and Alginate Wound
Dressings?
Figure B.7 compares the absorption of liquid by alginate wound dressing and cotton
gauze. In the cotton gauze, the liquid is mainly held in the spaces between yarns
by physical force, which can easily spread along the gauze, and the water is also
easy to evaporate. On the other hand, when alginate bers absorb water, the water is
absorbed into thebers where it is combined with the carboxylic acid groups to form
a hydrogel. Since the water is chemically combined with alginate, it is not easy to
evaporate and a moist healing environment can be facilitated on the wound surface.
B.10 What Are the Differences Between High G and
High M Alginate Fibers When They Are Applied on
Exuding Wounds?
As a polymeric acid, alginate has ion-exchange properties and in the case of wound
dressings, the ion-exchangeis mainly concerned with calcium and sodium ions. The
exchange of calcium alginate ber with sodium ions in the contacting solution is
guided by the following equation:
Calcium alginate Ordinary nonwoven Cotton gauze
Front
Back
Figure B.7 An illustration of the absorption of liquid by calcium alginate dressing,
ordinary nonwoven fabric, and cotton gauze.
228 B Appendix B: Answers to Commonly Asked Questions About Alginate Wound Dressings
Tabl e B.2 The ion-exchange coefficient for two types of alginate.
Metal ions M/G ratio
High M, M/G = 1.60 High G, M/G = 0.45
Ca
2+
− Na
+
7.5 20
K =
[Calcium ions in the ber][Sodium ions in the solution]
2
[Sodium ions in the ber]
2
[Calcium ions in the solution]
The ion-exchange coecient K is dependent on the guluronic acid and man-
nuronic acid content of alginate, with high G alginate having relatively high
exchange coecient. As can be seen in Table B.2, the G and M contents of alginate
have a signicant eect on the exchange coecient of alginate. When high M
alginate bers are applied on exuding wounds, the sodium ions in the exudate
can easily replace the calcium ions in the ber, resulting in the rapid formation of
a hydrogel on the wound surface. On the other hand, high G alginate bers are
more dicult to form hydrogel, mainly because of the low ion exchange coecient
between calcium ions in the bers and sodium ions in the wound exudate.
B.11 Can Sodium Alginate Be Absorbed by the Body
When Calcium Alginate Fibers Are Converted Into Sodium
Alginate Upon Contact With Wound Exudate?
Alginate is a marine biopolymer that cannot be digested by the human body since
there is no enzyme in the human system to digest alginate. Inthe food industry, algi-
nate is known as a dietary ber that can benet the digestive system mainly because
it cannot be digested by the digestive system. When applied on the wound surface,
the calcium alginate bers are converted into sodium alginate through ion exchange
and as the wound heals, the alginate bers are detached from the wound surface as
part of the healing process.
B.12 Alginate Wound Dressings Are Divided Into Wet
Integral and Wet Dispersible, What Does These Two Types
Mean?
The wet integrity of alginate wound dressings are mainly caused by the variations
in the chemical structure of alginic acid. Alginate with a high degree of guluronic
acid is capable of strong ionic binding and the resultant bers are stable in solution
A and are integral when applied on exuding wounds. On the other hand, alginate
bers made from alginate with a high content of mannuronic acid are capable of a
high degree of swelling, andas a result, wound dressingsmade from high M alginate
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B.15 Are There Any Differences Between the Alginate Wound Dressings Under Different Brands? 229
bers lose the nonwoven structure easily when in contact with wound exudate. In
the test method of British Pharmacopoeia, wet integrity means that the dressing can
retain its nonwoven structure when shaken in 40 times its own weight of solution
A, while wet dispersible means that the dressingloses its nonwoven structure under
the same circumstances.
B.13 How Can Alginate Wound Dressings Reduce Pain?
Pain is caused by mechanical stimulation such as knife cutting, stick beating, physi-
cal factors such as electrical current, high temperature, and chemical factors such as
strong acid and strong bases. Pain is common in clinical practices. Alginate wound
dressings can relieve pain through its in-situ formation of hydrogel on contact
with exuding wounds to provide a moist hydrogel on the wound which can reduce
friction and oer a protective layer to the nerve endings exposed to the wound.
These dressings can be easily removed, which oers an additional benet to pain
relief.
B.14 Are There Any Inappropriate Consequences for the
Residue Alginate Fibers Left on the Wound Surface?
As a loosely constructed nonwoven fabric, alginate wound dressings have loose
bers on the surface of the dressing, which would shed on the wound surface when
applied on exuding wounds. In addition, when the dressing is peeled o during
removal, some of the bers in the dressing would be left behind. However, these
residue bers are harmless since rst, they are nontoxic to the human body, and
second, as the wound heals, the dead tissue on the wound would be detached
from the body together with the bers as a part of the metabolic process for skin
regeneration. Many clinical applications have proven that the loose bers left on
wound are harmless to the human body.
B.15 Are There Any Differences Between the Alginate
Wound Dressings Under Different Brands?
Yes, the alginate wound dressings under dierent brands dier considerably in their
chemical structures and physical properties, mainly due to the fact that alginates
are dierent in their monomer composition in that the contents of α-
L-guluronic
acid (M) and β-
D-mannuronic acid (M) are considerably dierent depending on the
types of brown seaweeds where they are extracted from. In addition, the ber com-
position and nonwoven construction are also dierent for dierent types of alginate
wound dressings. Table B.3 summarizes the productcharacteristicsof the main types
of alginate wound dressings in the international market.
230 B Appendix B: Answers to Commonly Asked Questions About Alginate Wound Dressings
Tabl e B.3 Product characteristics of the main types of alginate wound dressings in the
international market.
Brand name Distributor Product characteristics
Algisite Smith & Nephew Needle-punched high M calcium alginate
Algosteril Beiersdorf Needle punched high G calcium alginate
Comfeel SeaSorb Coloplast Freeze dried alginate foam
Kaltogel Convatec Needle-punched high M calcium alginate
Kaltostat Convatec Needle punched high G calcium/sodium alginate
Melgisorb Molnlycke Needle-punched high M calcium alginate
Sorbsan Maersk Nip rolled high M calcium alginate
Tegagel 3M Health Care Hydro-entangled high M calcium alginate
B.16 In the Manufacturing Processes, What Do Nip
Rolling, Needle Punching, and Freeze Drying Mean?
During the manufacture of alginate wound dressings, the alginate bers are carded
on a nonwoven processing machine to form a thin web of bers which is then
cross-lapped to form a thick layer of bers. At this stage, the layer of bers is either
pressed to form a loosely connected fabric that is further cut into small pieces of
dressings or it is punched by needles to form an integral nonwoven fabric before
being processed into dressings. In the case of loosely formed fabric, the resultant
wound dressing can be easily washed o the wound at the end of application, while
in the case of integral needle-punched nonwoven dressing, it can be lifted o the
wound as a while piece.
Freeze-dried alginate wound dressing is made by dissolving sodium alginate to
form a viscous liquid and placing the solution in a at-bottomed container before
calcium ions are added to form calcium alginate gel. This gel is then freeze-dried to
form a porous foam material, which is then cut into pieces and sterilized to produce
wound dressings with high absorption capacity.
B.17 Can Alginate Wound Dressings Be Used in
Combination With Topical Medicines Such as
Anti-inflammatory Drugs Like Iodine?
Alginate wound dressings can be used in combination with iodine and any other
anti-inammatory drugs to protect the wound against infection.
B.18 Can Alginate Wound Dressings Be Used on
Infected Wounds?
Alginate wound dressings can be used on infected wounds, especially when they
contain antimicrobial agents such as silver ions.
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B.23 What Are the Clinical Efficacy of Alginate Wound Dressings When Used for Leg Ulcer Wounds? 231
B.19 Can Alginate Wound Dressings Be Cut Into Pieces
Before Being Applied to Wounds?
In order to t into the wound, alginate wound dressings can either be folded or cut
into small pieces that can be applied to wound of various depths and sizes.
B.20 What Should Be Done When Alginate Wound
Dressings Adhere to the Wound Surface?
When alginate dressing adheres to the wound bed, the easy way to remove it is to
apply warm saline on the dressing. Once the bers swell due to the ion exchange
between calcium ions in the dressing and sodium ions in saline, they become soft
and can be easily rinsed o.
B.21 Some Patients Experience Granulation Edema
When Applied With Alginate Wound Dressings, Is This
Related to the Release of Calcium Ions by the Dressing?
Wound healing is a complicated process. Some individual patients may experience
granulation edema because the ionic content in the wound bed is dierent from the
rest of the tissue. The dressings should be frequently changed in order to maintain
a fresh environment at the wound surface. For the calcium ions released during the
ion exchange process, the majority should remain in the dressing structure. Some
may diuse into the tissue uid.
B.22 What Are the Clinical Efficacy of Alginate Wound
Dressings When Used for Pressure Sore Wounds?
Many literature studies haveshown that when alginate wounddressings are used on
pressure sore wounds, they can reduce the number of dressing changes and related
nursing time and direct cost, hence improve overall nursing eciency. Compared to
traditional dressings, the clinical benets include reduction of pain during dressing
change, improvement in healing rate, and reduction in overall nursing time. The
alginate wound dressings are safe, eective, and comfortable to use, they can pro-
mote the healing of phases III–IV pressure sore wounds, especially when they are
used in combination withtransparentsemi-permeablelm dressings, when they can
eectively promote wound tissue granulation and capillary formation. In general,
when used on pressure-sore wounds, the alginate wound dressings cause minimal
wound tissue damage and can improve the quality of wound healing.
B.23 What Are the Clinical Efficacy of Alginate Wound
Dressings When U sed for Leg Ulcer Wounds?
When alginate wound dressings are used on leg ulcer wounds, the clinical bene-
ts include improved reduction in wound surface, pain level, and bleeding during
232 B Appendix B: Answers to Commonly Asked Questions About Alginate Wound Dressings
dressing change as compared to traditional therapy. The dressing does not adhere to
the wound bed and it can be easily removed without causing pain to patients.
B.24 What Are the Clinical Efficacy of Alginate Wound
Dressings When Used for Diabetic Foot Ulcer Wounds?
For diabetic foot ulcer wounds, the application of alginate wound dressings can
help to facilitate a moist healing environment that benets the healing process. The
healing time can be reduced on average by 5–7 days. In addition, alginate wound
dressings can accelerate the migration of immune cells and promote phagocytes to
digest dead tissue, bacteria, and other microorganisms. The high absorption capac-
ity of alginate wound dressings is useful in containing the dead tissue on the wound
surface and also donating moist to the wound to soften hard eschar.
B.25 What Are the Clinical Efficacy of Alginate Wound
Dressings When Used for Burn Wounds?
Alginate wound dressings can be used on burn wounds with many clinical benets.
In general, alginate wound dressings can absorb a large amount of wound exudate
while at the same time forming a soft hydrogel on wound surface in situ. For burn
wounds, frequent dressing change is not desirable since it not only increases pain,
it also introduces exposure to wound infection. Alginate wound dressings can pro-
vide a moist healing environment that reduces pain, minimizes infection, and also
promotes healing.
B.26 What Are the Clinical Efficacy of Alginate Wound
Dressings When Used for Anal Fistula Wounds?
When alginate wound dressings are used for anal stula wounds, they are mainly
used as a cavity ller, which can reduce pain, reduce the level of bleeding, and
improve the absorption of wound exudate. In the area surrounding anal stula
wounds, the gelling properties of alginate wound dressings are particularly useful
in that the nonwoven structure can immobilize the exudate and the microorgan-
isms within the liquid. The hydrophilic nature of the dressing can reduce water
evaporation and help to maintain a moist environment that is highly benecial to
the patient.
B.27 Does Alginate Wound Dressing Possess Hemostatic
Properties?
Calcium alginate dressings have excellent hemostatic properties. Many clinical
studies have conrmed that bleeding stopped within ve minutes of applying the
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