Performance Characterisation of a
New Foam Cover Dressing
Dave Pritchard , Lewis Jones , Claire Brewer , Steve Bishop , Helen Shaw and Christine Cochrane
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ConvaTec GDC, Deeside, Flintshire CH5 2NU; 2Dept. Veterinary Clinical Science, University of Liverpool
Introduction
• Contouring to an in vitro Simulated Wound Tissue Model
Foam dressings have been used successfully on a wide range of exuding wounds for
many years. A new design of foam cover dressing has now been developed, with unique
performance characteristics. This new foam cover dressing’s performance characteristics
have been measured through the performance of a range of in-vitro laboratory tests, in
order to determine the potential advantages which may be offered by this new design
of dressing.
Methods & Results
The following dressing performance characteristics have been assessed within this
in-vitro study:
A small hole was placed in the wall of a Petri dish. A section of pork belly (approximately
5cm x 1cm x 1cm) was used as a simulated wound bed and placed inside along the wall of
the Petri dish. A section of the dressing was then placed over the pork belly. The dressings
were secured in place with adhesive tape. A 21 gauge syringe needle was then inserted at
a 45° angle through the pork belly and the hole in the Petri dish, until it had been pushed
through to the simulated wound bed surface, just underneath the dressing’s wound
contact surface. A Microjet Micro pump was set to dispense 4.3ml/hour of 0.01% (w/v)
o-Toluidine Blue dye in Solution A (Calcium Chloride & Sodium Chloride Test Solution BP)
through the syringe needle. Images of this set up were captured every 20 seconds during
the test, using a QImaging digital camera, until the sample was fully hydrated.
New Foam
• Fluid Retention Under Compression Force
As the Hydrofiber® layer absorbed fluid
and formed a cohesive gel, intimate
contact with the simulated wound bed was
observed. The fluid was then observed to
wick into the foam layer.
This technique, based on standard Pharmacopoeia method (BP 1993, Volume II,
Appendices, A222, Appendix XX, T. Water-retention Capacity) measures the fluid absorbed
and retained by dressings whilst using different loads to simulate varying levels of
compression. The fluid absorbency and retention under a load equivalent to 40mmHg
pressure was measured for each dressing.
Pre Hydration
Absorbency
(g/g/24hrs)
Retention
(g/g/24hrs)
New Foam
7.30 ± 0.26 [6.96 – 7.85]
6.92 ± 0.23 [6.58 – 7.50]
Foam A
3.50 ± 0.08 [3.43 – 3.59]
3.39 ± 0.08 [3.32 – 3.47]
Foam B
5.19 ± 0.20 [5.06 – 5.41]
4.89 ± 0.21 [4.74 – 5.13]
Post Hydration
Foam A
Foam A dressing was observed to not
completely conform to the simulated
wound bed even when the dressing had
absorbed fluid (see arrows).
Pre Hydration
Post Hydration
Foam B
Table 1.
Foam B dressing was observed to not
completely conform to the simulated
wound bed even when the dressing had
absorbed fluid (see arrows).
Absorbency/Retention Under Compression
8
Absorbency (g/g)
Retention (g/g)
7
6
g/g
5
Pre Hydration
4
3
Post Hydration
Figure 3.
2
• Bioadhesion Studies
1
0
New Foam
Foam A
Foam B
Figure 1.
• Directional Spread of Fluid Across the Wound Contacting Layer
A plastic 50ml Terumo syringe was cut so that the bottom (dispensing end) half of the
syringe was removed to form an open-ended plastic vial of 29.2mm open diameter. This
vial was positioned in the centre of the wound contact layer of the test dressing and held
in place. 20ml of simulated exudate (horse serum) was injected into the vial. Once the
full content of the vial had been expelled, the stopwatch was started. When 60 seconds
had elapsed, any non-absorbed fluid was removed from the vial using an intact syringe.
The plastic vial was then removed. A metal rule was placed underneath the dressing
and a photograph was taken of both dressing and rule using a digital camera. Once all
photographs had been taken, the area of lateral fluid spread was measured using image
analysis software.
The lateral spread, expressed as a % of the original “wound” area was calculated
as follows:
Fibroblasts were cultured from debrided tissue which was immediately transferred into
a sterile dish containing Hank’s balanced salt solution (HBSS). The tissue was washed
and cut into small (3–5mm2) pieces which were then placed into 25cm2 tissue culture
flasks containing media (Dulbecco’s Modified Eagle Medium (DMEM), supplemented with
10% foetal calf serum (FCS) (Sigma, UK), 20 mM Hepes buffer, 100μg/ml gentamicin and
0.5μg/ml amphotericin B). Cell cultures were incubated at 37°C in a 5% CO2/95% air
environment. Readiness for sub-culturing was determined by the extent of fibroblast cell
outgrowth (5–10 days). Cells were farmed successively in a 1:4 split ratio to passage 3–8
before experimental use. Fibroblasts were harvested from stock dishes and plated out
at 2x105 cells/ml in 6 well plates. A 1cm2 piece of each dressing was cut from the central
area and applied either as the dry dressing or a wet dressing following hydration (1ml
of cell culture medium). All cut dressings were placed onto the monolayer of fibroblasts
and pressed gently in place. After 24 hours the dressings were carefully removed from
the surface of the culture, using minimal force to avoid damaging the cells or causing
any additional cells to detach from the dressing. The cell numbers on each dressing were
determined through trypsinisation and counting using a Neubauer cell counting chamber.
Bioadhesion of the Pad Layer of Foam Dressing
90
– 100
Cell Number x1000
Lateral Spread Area x 100
Vial Area
Wet
Dry
80
Where vial area = original “wound” area = 669.7mm
2
% Lateral Spread
70
60
50
40
30
20
10
New Foam
18.8 ± 5.1 [14.4 – 24.3]
0
Foam A
New Foam
Foam A
83.6 ± 8.2 [76.9 – 92.8]
Foam B
140.0 ± 7.7 [131.3 – 146.0]
Lateral Spread (% Area)
140
120
100
% Area
Figure 4.
Conclusion
In-vitro testing shows that the new design of foam cover dressing demonstrates a unique
combination of fluid absorption and fluid retention under a force equivalent to 40mmHg
(representative of the pressure applied with a high compression bandage) [Table 1],
low lateral spread of fluid across the dressing surface [Table 2], intimate contact with a
simulated wound bed [Figure 3] and low fibroblast cellular adhesion in a bioadhesion study
[Figure 4].
Table 2.
160
Foam B
References
80
60
40
20
0
New Foam
Foam A
Foam B
WHRI3524 MS064 In Vitro testing of AQUACEL foam & Competitor Dressings - Intimate Contact.pdf
WHRI3525 MS065 In Vitro testing of AQUACEL foam Competitor Dressings - Lateral spread rev 1.pdf
WHRI3526 MS066 In Vitro testing of AQUACEL foam Competitor Dressings - Fluid Retention rev 1.pdf
CCA084 CVT Trials 17650 & Foam Competitor Products - Evaluation of Cellular Adhesion to Wound Dressings
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Figure 2.
© 2012 ConvaTec Inc.
AP-012539-MM