An ‘in-vitro’ comparison of the physical characteristics ofhydrocolloids, hydrogels, foams, and alginate/cmc fibrous
dressings.
SummaryThis document describes the results of a testing programme that was undertaken to compare certain
elements of the performance of dressings produced by one major European manufacturer withsimilar products from other companies that hold a significant market share in each of the categories
examined. Standard test methods were used during the study to eliminate bias and facilitate future
testing by other interested parties.
The publication of test data generated from standard methods by an independent accredited test
laboratory in this way provides both clinicians and manufacturers with a baseline for futurecomparisons, and should also reduce biased or inaccurate product claims resulting from the use ofdata derived from manufacturers’ ‘in-house’ test methods that could favour a particular productdesign.

Introduction to current study
The present study was commissioned and funded by Coloplast Ltd to provide both the company,
and potential users of their products, with independent comparative test data on certain key aspectsof the physical characteristics and performance of the various dressing groups derived using
standard test systems. No attempt was made to identify or predict how the clinical use of thesematerials would impact upon the biochemical or physiological processes involved in woundhealing. Publication of test data was undertaken in accordance with the terms and conditions
identified on http://www.dressings.org/.

Product groups tested
Hydrocolloid dressings
The term ‘hydrocolloid’ was coined in the 1960s during the development of muco-adhesives andoral bandages, and was first referenced in a US patent authored by J.L Chen published in 1967. In
the early 1970s the description was applied to a new family of gel-forming, adhesive sheet
dressings typically containing carboxymethyl-cellulose (CMC) as the principal absorbent dispersed
in a mixture of adhesives and tackifiers.
Recently, however, the term ‘hydrocolloid’ has been used to describe two very different products,
an amorphous hydrogel dressing and a fibrous dressing made from modified
carboxymethylcellulose (CMC), which are totally dissimilar in structure and appearance to theadhesive sheet dressings that were first described in this way.
Whilst it is possible to argue that most hydrogels are in fact true colloidal dispersions and that the
CMC fibres form a colloidal dispersion in the presence of liquid, the same can also be said of othergel-forming fibres made from alginates, hyaluronidase, chitin or chitosan. Extending the use of theterm hydrocolloid in this way to materials with totally different physical characteristics and clinicalindications from the original adhesive gel-forming sheets cuts across existing and well understood,
dressing classification systems.

Page 1 of 24

For the purpose of this investigation, the term hydrocolloid will therefore be applied to theadhesive sheet formulation in which, typically, the gel forming agents are combined withelastomers and adhesives and applied to a carrier – commonly consisting of a sheet of polyurethane
foam or film, to form an absorbent, self adhesive, waterproof dressing.
When applied to a wound the adhesive mass in such dressings absorbs liquid and forms a gel, but
the speed of this process and the properties of the resultant gel are determined by the nature of theformulation.
In the intact state most hydrocolloid sheet dressings are impermeable to water vapour, but as thegelling process takes place, the dressing becomes progressively more permeable. The loss of water
through the dressing in this way enhances the ability of the product to cope with exudate
production.
Hydrocolloid sheets are widely used as primary dressings in the management of many different
types of wounds including leg ulcers, burns, donor sites and pressure ulcers but their relatively
limited fluid handling properties tend to restrict their use to the management of light to moderately
exuding wounds. For more heavily exuding wounds, products made from polyurethane foam areoften preferred.
Thinner versions of the standard hydrocolloid dressings are also available and these may be used asalternatives to vapour permeable film dressings in the management of superficial injuries, or as
secondary dressings over products such as alginates or hydrogels.
The hydrocolloid dressings included in the present study are shown in Table 1.
Table 1: Hydrocolloid dressings tested

Manufacturer
Coloplast A/S
Coloplast A/S

Competitor A

Competitor A

Item
Comfeel Plus
Ulcer Dressing
Comfeel Plus
Transparent
Dressing
A bordered
standardhydrocolloid
An extra thinhydrocolloid

Page 2 of 24

Batch/Lot No
95504.01
95961.20

Fluid Handling Studies
Summary of test method
The fluid handling properties of the dressings were examined using SMTL test method TM-65,
which is based upon that described in BS EN 13726-1:2002. Test methods for primary wounddressings. Part 1: Aspects of Absorbency, section 3.3 Fluid Handling Capacity.
In this test five samples of each dressing of known weight are applied to Paddington cups (modified
Payne cups) to which are added 20 ml of Solution A, a solution of sodium/calcium chloride
containing 142 mmol/litre of sodium ions and 2.5 mmol/litre of calcium ions, concentrations which
are comparable to those present in serum and wound fluid.
The cups are weighed and placed in an incubator at 37+/-2°C, together with a tray containing 1kg
of freshly regenerated self-indicating silica gel for a period of 24 hours. At the end of the test thecups are removed from the incubator, allowed to equilibrate to room temperature and reweighed.
From these weighings the loss in weight due to the passage of moisture vapour through the dressing
is determined.
The base of each cup is then removed, and any remaining fluid allowed to drain for 15 minutes. (Ifthere is an accumulation of test fluid between two components of the dressing, the inner component
must be slit with a scalpel blade to allow free drainage of the entrapped fluid).
Each cup is then reweighed once again and the weight of fluid retained by the dressing calculatedby difference.
From a clinical perspective, this standard test provides valuable information on two importantmechanisms of exudate management.
•

Absorbency, the ability for the dressing to absorb and retain wound fluid•

Moisture vapour loss, the evaporation of a proportion of the aqueous component of wound
fluid through the outer surface of the dressing to the external environment.

The total fluid handling capacity of a dressing is defined as the sum of the values determined
during the course of these tests.
In clinical practice, fluid-handling capacity determines the wear time of a dressing because it
affects both exudate leakage and/or maceration of the peri-wound skin, factors that can adversely
affect a patient’s quality of life.
Fluid Handling Results
The results of the fluid handling tests conducted over 24, 48 and 72 hours are presented in Tables
2-4 and summarised in Figures 1 to 4 which clearly show that although the absorbent capacity of
the four products examined is reached after 24 hours, the dressings continue to permit the passageof moisture vapour throughout the period of the test.

Page 3 of 24

Table 2: Fluid handling properties following 24 hours incubation

Dressing

Moisture
Vapour Loss
(g/10cm2)

Absorbency(g10cm2)

Fluid
Handling
Capacity(g/10cm2)

Comfeel Plus Ulcer Dressing
Comfeel Plus Transparent Dressing
Competitor A Bordered
Competitor A Extra Thin

0.23 (0.062)
2.48 (0.129)
0.36 (0.126)
0.26 (0.009)

3.10 (0.916)
1.79 (0.130)
1.96 (0.456)
1.62 (0.048)

3.32 (0.900)
4.27 (0.217)
2.31 (0.469)
1.88 (0.053)

Table 3: Fluid Handling Properties following 48 hours incubation

Dressing

Moisture
Vapour Loss
(g/10cm2)

Absorbency(g/10cm2)

Fluid Handling
Capacity(g/10cm2)

Comfeel Plus Ulcer Dressing
Comfeel Plus Transparent Dressing
Competitor A Bordered
Competitor A Extra Thin

1.01 (0.260)
5.72 (0.221)
1.31 (0.070)
0.79 (0.163)

4.07 (0.151)
1.83 (0.209)
1.92 (0.087)
2.26 (0.106)

5.08 (0.311)
7.55 (0.287)
3.23 (0.096)
3.05 (0.191)

Table 4: Fluid Handling Properties following 72 hours incubation

Dressing

Moisture
Vapour Loss
(g/10cm2)

Absorbency(g/10cm2)

Fluid Handling
Capacity(g/10cm2)

Comfeel Plus Ulcer Dressing
Comfeel Plus Transparent Dressing
Competitor A Bordered
Competitor A Extra Thin

1.85 (0.330)
10.30 (0.603)
2.39 (0.121)
0.89 (0.035)

3.92 (0.035)
2.00 (0.167)
2.21 (0.008)
2.69 (0.118)

5.77 (0.330)
12.30 (0.579)
4.61 (0.126)
3.57 (0.121)(Note: In all these tables, the results quoted represent the mean of 5 determinations and thefigures in brackets denote standard deviations)Page 4 of 24

Figures 1-4

Page 5 of 24

Permeability: Moisture Vapour Transmission Rate (MVTR)
Test method
The previously described fluid-handling test measures both the absorbency of a dressing and thetotal weight of moisture vapour lost through the outer surface during the period of the test.
It does not, however, provide any indication of time-related changes that may take place in thepermeability of some dressings, such as hydrocolloids, which can increase dramatically as the
product absorbs liquid to form a gel, reaching a steady state after a number of hours.
Time related changes in moisture vapour permeability of the dressings were determined using
SMTL test method TM-8 which is also based on the methods described in BS EN 13726-2:2002.
Test methods for primary wound dressings. Part 2: Moisture vapour transmission rate ofpermeable film dressings.
In this test, a sample of dressing is applied to a Paddington cup to which is added 20 ml of Solution
A. The cup is placed in an inverted position (with the test solution in contact with the dressing in an
incubator set at 37+-2.0°C upon the pan of a top loading balance. The balance is connected to anelectronic data-logging device, which records changes in the weight of the cup resulting from theloss of moisture vapour through the dressing. A tray containing 1 kg of freshly dried silica gel isplaced in the bottom of the incubator to maintain a low relative humidity within the chamber.
At the end of the test the recorded data is downloaded for statistical analysis. For dressings thathave a lag time before the MVTR reaches a steady state, the linear part of the slope is taken for
regression analysis to determine the maximum value for moisture vapour transmission.
Results
The individual results of the MVTR testing are shown in Table 5 are also expressed graphically in
Figures 5 to 9.
Table 5: Change in balance Weight over 72 hours

Maximum MVTR (g/10cm2/24Hrs)

Dressing

Comfeel Plus Ulcer
Dressing
Comfeel Plus
Transparent Dressing
Competitor A
BorderedCompetitor A Extra
Thin

Run 1

Run 2

Run 3

0.516

0.652

0.956

3.704

3.321

3.429

1.049

1.297

1.098

0.375

0.385

0.364

Page 6 of 24

Figures 5-9

Page 7 of 24

Page 8 of 24

Alginate/cmc fibrous dressings
Dressings made from gel-forming polysaccharides have a long history in the management of
exuding wounds. Alginates derived from seaweed have been used in a fibrous form for many years
as haemostats and surgical absorbents.
More recently, dressings have been produced from chemically modified carboxymethylcellulose,
which are similar in appearance and gel forming properties to the alginates, and which are claimed
to offer similar benefits to a healing wound.
The dressings function by absorbing exudate to form a moist gel on the wound surface that isthought to facilitate healing. They are, therefore, best suited for application to exuding wounds as a
primary dressing beneath a more absorbent secondary layer. If a wound is too dry to transform analginate fibre into a hydrogel-like material, then the wound surface remains dry and the undissolved
fibres do not provide a moist healing environment
Gel formation involves an ionic exchange process in the case of alginate dressings as insoluble
calcium alginate is partially converted into the soluble sodium form as it takes up sodium ions fromwound fluid. The process of gel formation with CMC fibre dressings is more of a physical process
due to the uptake of water by the fibres although the presence of sodium and calcium ions still
exerts an effect upon gel formation.
The dressings included in the present study were as shown in Table 6..
Table 6: Fibrous dressings tested

Manufacturer
Coloplast A/S
Competitor A
Competitor B

Item

Batch/Lot
No

SeaSorb Soft Dressing
Carboxymethylcellulose
Dressing
Alginate Dressing

75083.02

Page 9 of 24

Absorbency of alginate/cmc forming fibrous dressings
Test method
The absorbency of the dressings was determined using SMTL test method TM-101 based BS EN
13726-2:2001. Test methods for primary wound dressings. Part 1: Aspects of Absorbency, Section
3.2, Free swell absorptive capacity.
In this test, a 400ml solution of Solution A is brought to 37°C in a water bath. A sample ofdressing measuring 5 x 5 cm of known weight is placed in a Petri dish and a volume of test solution
equal to 40 times the weight of the test sample added to that sample using a pipette. The Petri dishand its contents are incubated at 37+/-2.0\°C for 30 +/- 1 minutes. Using forceps, the sample isremoved from the Petri dish, suspended for 30 seconds and reweighed. This test is repeated until
10 samples have been tested. From these results, the mean weight of solution retained per 100cm2
is calculated.
Results
The results of the absorbency testing are summarised in Table 7 and Figure 10. These predict how
much fluid each dressing may be expected to retain in clinical practice when applied to an exuding
wound.
In this table the absorbency results have been expressed as g/10cm2/24 hours to facilitatecomparisons with the results of the hydrocolloid and foam products.

Table 7: Absorbency of alginate/cmc fibrous dressings
Absorbency grams/10cm2

Dressing

SeaSorb Soft Dressing
2.57 (0.20)
Carboxymethylcellulose Dressing
1.83(0.13)
Alginate Dressing
1.51 (0.10)
Each result is the mean of 10 determinations and figures in brackets are Standard Deviations.

Page 10 of 24

Figure 10: Absorbency of alginate/cmc fibrous dressings

Absorbency
grams/10cm2

3
2.5
2
1.5
1
0.5
0

SeaSorb

CMC

Page 11 of 24

AlginateDispersion Characteristics/Wet Integrity
Test method
The dispersion characteristics/wet integrity of the dressing samples were examined using SMTL
test method TM-112.which is based upon the recommendations contained within BS EN 137262:2001. Test methods for primary wound dressings. Part 1: Aspects of Absorbency, Section 3.6,
Dispersion characteristics,
In this test a 5 x 5 cm sample of the dressing under test is placed into a 250 ml conical flask, towhich is added 50 +/- 1ml of Solution A. The flask is gently swirled for 60 seconds without causing
a vortex, and the integrity of the dressing is visually established. The dressing can then be
categorised in accordance with the descriptions laid down in the standard.
Results
The results of the dispersion characteristics test are summarised inTable 8.
Table 8 Dispersion characteristics

Dressing

Dispersion/Nondispersion

Seasorb Soft Dressing
Carboxymethylcellulose Dressing
Alginate Dressing

No Dispersion
No Dispersion
Dispersion

The results of the wet integrity/dispersion test indicate how the physical characteristics of adressing will change when it interacts with wound fluid. Specifically it will determine whether itwill form an amorphous gel or retain its original structure, factors which will have implications forthe method of removal. Hence, a product with no dispersion will retain its original structure during
removal and therefore be easier to remove.

Page 12 of 24

Hydrogel dressings
Hydrogel dressings in various forms have been used in wound management for over 20 years. They
are available in several forms, based upon a variety of different polymers. Some polymers arecross-linked to impart a degree of structural stability to the final product, which often takes theform of a thin sheet used for application to relatively shallow surface wounds. The absence ofstructural cross-links result in the formation of gels that have no defined structure, and these are
more suitable for introduction into cavity wounds or sinuses. Originally conceived as alternatives toabsorbent dressings in the treatment of chronic wounds such as leg ulcers, most amorphoushydrogels are now used to facilitate wound cleansing and promote autolytic debridement althoughsome products are used for more specialized indications. The high moisture content maintains adesirable moist interface which facilitates cell migration and prevents dressing adherence.
The hydrogel dressings included in the present study are shown in Table 9.
Table 9: Hydrogel products tested

Manufacturer
Coloplast A/S
Competitor C

Item
Purilon Gel
Amorphous Gel

Batch/Lot No
95749.71

Fluid affinity
The fluid affinity of a hydrogel dressing determines the way in which a product might be expected
to influence the moisture content of a wound and the standard test investigates its ability to donate
moisture to, or absorb liquid fluid from standard substrates.
A product that is capable of donating fluid will facilitate the rehydration of dry necrotic tissue or
slough to promote autolytic debridement. A product that has a marked affinity for liquid will
absorb excess wound exudate and liquefied tissue debris once autolytic debridement has takenplace. A product that combines good absorption and moisture donating properties should therefore
be suitable for the treatment of a wider range of wound types.
Test for fluid affinity
The fluid affinities of amorphous hydrogels were determined using the SMTL test method TM-238
based upon BS EN 13726-1:2002 Test methods for primary wound dressings. Part 1 Aspects ofabsorbency, Section 3.4,Fluid affinity of amorphous hydrogel wound dressings.
In this method 10 +/- 0.1gram samples of the test material are placed onto the surface of a series of
10 +/- 0.1gram plugs of gelatine (20 and 35%) or agar (2 and 8%) contained within the barrel of
50/60ml syringes from which the closed (nozzle) ends have been removed to form smooth-sided
cylinders. Once the test materials are in place, the open ends of the cylinders are sealed with animpermeable cover. For the purpose of this test both the gelatine and agar are made up with
Solution A.
Following incubation of the sealed syringes for 48 hours +/-30minutes at 25 +/-2ºC the test material
is gently removed from the plugs, which are then re-weighed. From these results the percentagechange in weight of each hydrogel sample is calculated.
Page 13 of 24

The standard only requires that the gel be tested upon 2% agar and 35% gelatine, but the additional
substrates were included at the request of the client. A dressing that absorbs a large volume of fluid
from 2% agar but does not donate significant amounts of fluid to 35% gelatine may be categorised
as a ‘Type 3a’ hydrogel in accordance with Table 10 below. Conversely, a dressing that donates
fluid well but is less able to absorb liquid could be categorised as a ‘Type 1c’ hydrogel.
Table 10: Classification of hydrogels by fluid affinity

Agar (absorption)
Type

Gelatine (donation)% Increase inhydrogel weightType% Decrease inhydrogel weight

0-10>10-20>20-30>30-40>40-50

a
b
c
d
e

0-5
>5-10
>10-15>15-20>20-251
2
3
4
5

Results
The results of fluid affinity testing of the hydrogels included in this study are presented inTable 11 and Table 12 from which the gels are classified according to the system described
previously. Based upon the test method BS EN 13726 and the definitions contained therein, Purilon
Gel is classified as a Type 3c hydrogel and the competitor product is a Type 2b hydrogel.
Table 11: Fluid uptake by hydrogel dressings

Hydrogel
Purilon Gel
Competitor C

Agarconcentration

Mean % increasein hydrogel weight

2%
8%
2%
8%

21.90 (0.503)
3.66 (0.511)
15.67 (0.884)
1.90 (0.100)

Page 14 of 24

Table 12: Fluid donation by hydrogel dressings

HydrogelGelatine
concentration

Mean % decreasein hydrogel weight

Purilon Gel

20%
4.15 (0.727)
35%
11.87 (0.390)
Competitor C
20%
0.07 (0.311)
35%
7.00 (0.702)(Data in brackets denotes standard deviations, only four samples were tested for 20% gelatine.)

Hydrogel Migration
Test Method
The migration of amorphous hydrogels were determined using the SMTL test method TM-384
The apparatus consists of a hinged stainless plate upon which is securely mounted an angle meter.
Using a clamp stand, boss and clamp, the plate is held horizontally under the crosshead of aconstant rate of traverse machine (Instron tensiometer), with one end able to swivel vertically at thehinge. The movable end of the plate is connected to the clamp in the movable crosshead, whichallows the plate to move at a constant rate.
One ml of the hydrogel under examination is applied to a square box 10 mm x 10mm drawn on theplate, the hydrogel being applied to cover the area of the box in a uniform layer.
Using the attached angle meter, the plate is levelled and the Instron switched on with a constant rateof traverse of 50mm/min to allow the free end of the swivelling plate to move down under its own
weight. A timer is started at the same time as the Instron is set in motion.
As the plate is allowed to move, the angle that the hydrogel starts to migrate is noted, and the plateis allowed to continue to move at the same speed until it reaches an angle of 90 degrees (ie.
vertically straight down). The hydrogel is then observed as it migrates down the plate and the time
is noted that it takes to reach a line drawn across the plate at a distance of 10mm from the lower
edge of the box.
Should the hydrogel reach the line marked at 10mm from the starting point before the angle of theplate reaches 90 degrees, then the time and angle at which it reaches the line is recorded.
This information provides an indication of the viscosity/ cohesive properties of the gel, which, inclinical practice, will determine its ability to stay in place once applied to a wound.

Page 15 of 24

Results
The results of the hydrogel adhesion/migration testing are presented inTable 13. None of the test samples reached the 10 mm mark before the plate reached the 90-degree
position.
Table 13: Adhesion/Migration of hydrogel dressings

Hydrogel
Dressing

Run Number

10mm Migration
time andinclination angle

Purilon Gel

1
2
3
4
5
1
2
3
4
5

20 min 40 s at 90º
13 min 39 s at 90º
8 min 0 s at 90º
6 min 42 s at 90º
6 min 44 s at 90º
4 min 15 s at 90º
5 min 14 s at 90º
4 min 24 s at 90º
5 min 53 s at 90º
4 min 44 s at 90ºCompetitor C

The results show that both gels migrated slowly down the plate in the vertical plane, but the Purilon
Gel due to its higher viscosity took a little longer to move 10 mm.

Page 16 of 24

Foam dressings
Foam dressings are commonly produced from polyurethane and may be used alone or in
combination with an integral backing layer to form a bacterial barrier.
Foam dressings are capable of absorbing significant volumes of exudate and therefore aresometimes regarded as the products of choice for moderate to heavily exuding wounds. As withhydrocolloid dressings, the fluid handling capacity of foam dressing is a function of its absorbency
and moisture vapour permeability but unlike hydrocolloids there is usually no extended lag phaseduring which the product increases its permeability as the hydrocolloid adhesive layer becomessaturated with fluid. The foam products included in the study are shown in Table 14.
Table 14: Foam dressings included in study

Manufacturer
Coloplast A/S
Coloplast A/S
Competitor C
Competitor C
Competitor D
Competitor D

Item

Batch/
Lot NoBiatain Non-Adhesive
Dressing
Biatain Adhesive Dressing
Adhesive foam dressing
Non-adhesive foam dressing
Adhesive bordered dressing
Adhesive dressing

95749.34,
95749.65
95749.66

Page 17 of 24

Fluid Handling Properties
Test method
The fluid handling properties of the dressings were examined using the Paddington Cup techniquepreviously described for the hydrocolloid dressings according to BS EN 13726-1:2002 Part 1.
Fluid handling results
The results of the fluid handling tests are shown in Table 15 and summarised in Figure 11.
Table 15: Fluid handling properties of foam dressings

Dressing

Code

Moisture Vapour
Loss g/10cm2)

Absorbency(g/10cm2)

Fluid
Handling
Capacity(g/10cm2)

Biatain Non-Adhesive
Biatain Adhesive
Competitor C Adhesive
foam dressing
Competitor C
Non-adhesive foam
dressing
Competitor D Adhesivebordered dressing
Competitor D Adhesive
dressing

B NA
BA
CA

9.27 (1.233)
1.48 (0.146)
0.98 (0.051)

4.06 (0.429)
11.97 (0.162)
3.03 (0.406)

13.33 (1.328)
13.44 (0.274)
4.01 (0.404)

C NA

1.80 (0.059)

4.70 (0.276)

6.51 (0.304)

D AB

4.82 (0.241)

5.63 (0.223)

10.45 (0.371)

DA

1.44 (0.075)

6.56 (0.165)

7.99 (0.170)

The results are the mean of 5 determinations and figures in brackets denote standard deviations
As with the hydrocolloid dressings, in clinical practice absorption is important in terms of
preventing leakage and maceration. The fluid handling capacity, the sum of absorbency andmoisture vapour loss, influences not only prevention of maceration and leakage but also dressingchange frequency and can therefore impact upon the total cost of care.

Page 18 of 24

Figure 11: Fluid Handling Properties of Foam Dressings
14

MVL g/10cm2)

12Absorbency (g/10cm2)

10
8
6
4
2
0

B NA

BA

CA

C NA

Page 19 of 24

D AB

DA

Moisture Vapour Transmission Rate (MVTR)
MethodThe moisture vapour permeability of the dressings was determined as previously described for thehydrocolloid dressings.
Results
Results from MVTR tests on foam dressings are presented in Table 16.
Table 16: Change in Balance Weight over 24 hours

Maximum MVTR (g/10cm2/24 hrs)

Dressing

Biatain Non-Adhesive
Biatain Adhesive
Competitor C Non-adhesive foam dressing
Competitor C Adhesive foam dressing
Competitor D Adhesive bordered dressing
Competitor D Adhesive dressing

Page 20 of 24

Run 1

Run 2

Run 3

8.074
2.025
1.898
0.922
4.174
1.706

9.253
2.352
1.895
0.985
6.101
1.657

8.283
2.208
1.752
0.918
4.571
1.656

Thickness and weight per unit area
Determination of weight per unit area
The length, width and weight of ten intact samples is determined and the individual and mean
weight per unit area of the samples is calculated.
Results
The results of the determination of the weight per unit area are presented inTable 17.
Table 17: Weight per unit area

Dressing

Weight per unit area
(g/m2)

Biatain Non-Adhesive
Biatain Adhesive
Competitor C Adhesive foam dressing
Competitor C Non-adhesive foam dressing
Competitor D Adhesive bordered dressing
Competitor D Adhesive dressing

677.06 (18.993)
705.82 (14.800)
549.30 (12.310)
765.52 (35.780)
637.39 (16.82)
815.15 (11.553)

Each result is the mean of 10 determinations; figures in brackets denote standard deviations.

Page 21 of 24

Determination of thickness
The thickness of the dressing was determined using SMTL test method TM-267.
In this test, the thickness of the dressing at 5 different locations is determined using a Wallace
thickness gauge. A total of three dressings are examined and the mean thickness is reported.
Results
The results of the thickness testing are summarised in Table 18
Table 18: Thickness of dressings

Dressing

Mean thickness (mm)sample 1

sample 2

sample 3

Biatain Non-Adhesive
4.3
4.3
Biatain Adhesive
3.6
3.5
Competitor C
6.1
6.4
Non-adhesive foam
dressing
Competitor C
4.0
4.1
Adhesive foam
dressing
Competitor D
3.9
4.0
Adhesive bordered
dressing
Competitor D
6.1
6.0
Adhesive dressing
Each results represents the mean of 5 determinations

4.3
3.3
6.2

4.0

3.7

5.7

The results of these tests indicate that the total fluid handling capacity of the dressings is notdirectly related to the weight or thickness of the foam in the different dressings.

Page 22 of 24

Discussion
The tests undertaken during the course of the current investigation have, in the main, been designed
to address key issues relating to the ability of the various dressings to control the moisture content
or state of hydration of a wound.
The Paddington Cup test, performed on both the hydrocolloid dressings and the foam products,
provides useful data on the ability of the various dressings to absorb liquid and allow evaporation
through the outer surface, although the relative importance of these two parameters varies fromproduct to product.
When interpreting the fluid handling results previously quoted for the various products, it isimportant to remember that once a dressing has become saturated with fluid over perhaps a 24 hour
period, its ability to take up additional exudate will be seriously impaired although the transmissionof moisture vapour will continue at a relatively constant rate over several days which may prolong
the effective life of the dressing.
Information on the volume of exudate produced by chronic wounds is limited, but one publishedstudy has suggested that venous leg ulcers typically produce up to about 0.5 ml/cm2/24 hours[1]although values double this were recorded in some patients. A dressing sample applied to a
Paddington Cup has an area of 10cm2, which means that it would be required to absorb orotherwise cope with between 5-10 ml of fluid in the treatment of a heavily exuding wound.
The results of the present study confirm that, in general terms, the foam dressings have asubstantially higher fluid handling capacity than the hydrocolloids, which makes them better suitedfor the treatment of exuding wounds such as leg ulcers and pressure ulcers. Somewhat surprisingly,
the test results suggest that the fluid handling properties of the foam products examined were notdirectly proportional to the thickness of the dressing.
Although not a major factor in determining clinical acceptability, the thickness of a dressing can, insome circumstances, influence the conformability and therefore the clinical acceptability of the
products concerned but it is also possible that thicker foam may provide enhanced padding orprotection for some indications. The ability of a dressing to retain absorbed fluid undercompression is also important, but this parameter was not requested during the current investigation
because it is not part of the test method.
The results from the dynamic moisture vapour transmission test indicate that some hydrocolloids
initially have limited permeability, which may make them better suited for application to lightly
exuding wounds or dry necrotic tissue. In such situations the relatively impermeable nature ofthese products in the intact state prevents the additional loss of moisture from tissue that is alreadypartially dehydrated and therefore helps to retain moisture and facilitate autolytic debridement
The fluid handling test on the alginate/cmc fibrous dressings also showed significant differences
between the various products, ranging from 0.15 to 0.25 ml/cm2/24 hours. These values aresubstantially lower than the volumes of exudate determined clinically, which indicates that thesematerials should not be regarded as dressings in their own right, but as wound contact layers thatmust be used with more absorbent secondary dressings.
The fluid affinity tests performed on the hydrogel dressings clearly identify differences in the way
the dressings absorb fluid from agar, representing a moist wound, and donate fluid to a gelatine gel
representing a dry wound or area of necrotic tissue.

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The clinical significance of these observations has not been confirmed in vivo but in the absence of
these data it is not unreasonable to assume these differences must have some clinical relevance.
The finding that it is possible for a dressing to both effectively absorb and donate fluid according to
the condition of the test substrate is of interest, and suggests that it might enable the material inquestion to be used upon a wider range of wound types than is normally the case with hydrogel
dressings although this remains to be confirmed clinically.
The migration test was designed to examine the ability of a dressing to stay in place for areasonable length of time. When applied to a patient with a leg ulcer, for example, it is useful if the
dressing can resist the effects of gravity whilst the secondary dressing or retention system is being
prepared or applied.

Conclusions
The results of this laboratory study clearly demonstrate that within each of the categories examined,
although the dressings are similar in appearance, differences exist in the performance of the various
products, which in some instances may have important clinical implications. Considerable variation
exists in the ability of both the foams and hydrocolloids to absorb test solution or transmit moisturevapour, which may have important implications for the ability of the different products to cope withexudate production in vivo. As previously suggested, the introduction of a classification or grading
system for these materials based upon their ability to cope with fluid production would provide
potential users with useful information to facilitate the selection process. Such a classification
system should also take account of the conformability and ease of use of the products concerned.

References
1.
Thomas, S., et al., The effect of dressings on the production of exudate from venous leg
ulcers. Wounds, 1996. 8(5): p. 145-149.

Date of report
Laboratory testing completed January 2004
Expanded report completed May 2005

Report authors
Dr Stephen Thomas Director,
Dr Gavin Hughes Technical Manager,
Paul Fram Laboratory Scientist,
Alex Hallett Laboratory Scientist
Surgical Materials Testing Laboratory,
Princess of Wales Hospital,
Bridgend,
S. Wales.
CF 31 1RQ

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