Technology and product reviews
Dressing
HF-Ag AL-Ag
Foam A Foam B Foam C
Number of cells adhered, average (n=3) Cell adherence expressed as a % of highest result
Dry
27167 46333 75000 69000 79333
Pre-hydrated 17333 21167 69000 55000 68667
Dry 34 58 95 87
100 Table 2 – Adherence of fibroblasts to the silver-containing dressings.
light microscope at low magnification (x15 to x50), and a scanning electron microscope (SEM) for higher magnification. For SEM, samples were gold-coated before examination (approximately 2–3 minutes in the sputter coater).
Image analysis Quantitative measurements of the visible open liquid absorption channels (ie pores) on the wound contact surface of each dressing were made from images produced under the light microscope. Image analysis software (Image-Pro Plus Version 7.0, MediaCybernetics®, UK) was used to measure and calculate the maximum dimensions, surface area and percentage surface area of these channels from images each with a field of view of approximately 2x1cm.
References
8. World Union of Wound Healing Societies [WUWHS], Principles of best practice: Minimising pain at dressing related procedures. A
consensus document. WoundPedia Inc 2007.
9. Woo KY, Harding K, Price P, Sibbald G. Minimising wound-related pain at dressing change: evidence-informed practice. Int Wound J 2008; 5(2): 144–57.
10. Cutting K, Harding K. Criteria
for identifying wound infection. J Wound Care 1994; 3: 198–201.
SEEDED AGAR MICROBIAL MODEL Preparation Two bacterial species (Pseudomonas aeruginosa and Staphylococcus aureus) were studied separately. Overnight-colonies were cultured on TSA plates, from which bacterial suspensions in MRD were prepared, such that they had an optical density equivalent to approximately 1x108cfu/ml. These suspensions were further diluted in MRD to give a population of approximately 1x107cfu/ml. A quantitative count of this solution was performed to accurately confirm the inoculum concentration. Molten TSA (80ml) was dispensed into
140mm Petri-dishes and allowed to solidify. 2ml of the 107 bacterial suspension was inoculated into 200ml of molten TSA (pre- cooled to approximately 45°C) to give a final concentration in the agar of approximately 1x105cfu/ml. A 45ml volume of this bacteria-
39 Wounds International Vol 2 | Issue 4 | ©Wounds International 2011
containing molten TSA was aseptically poured over the solidified 80ml agar layer already in the dish and allowed to cool. The result was a seeded-agar layer, approximately 2–3mm in depth overlaying a 6mm deep sterile agar layer. All seeded agar plates were incubated at 35°C (±3°C) for four hours to initiate growth.
Dressing application Immediately following the four-hour incubation period, a silver-containing dressing (≥10cmx10cm) was aseptically applied to the centre of a seeded-agar plate (n=3 for each challenge organism), and gently pressed down to ensure good contact with the surface. For HF-Ag and AL-Ag dressings, an adhesive absorbent cover dressing (ACD) was applied as a secondary dressing, as indicated in the manufacturers’ instructions for use. A seeded- agar plate without a dressing was also included as a negative control (n=1 for each challenge organism) to confirm the extent of uninhibited bacterial growth. All plates (including negative controls)
were incubated aerobically at 35°C (±3°C) for 48 hours, after which time dressings were aseptically removed and the plate and the wound contact surface of the dressing were photographed. All seeded-agar plates were re-incubated at 35°C (±3°C) for an additional 24 hours to allow any inhibited but still viable bacteria to mature into visible colonies. After incubation the plates were visualised and photographed. To assess whether the silver- containing dressings were bactericidal (ie killed bacteria) or bacteriostatic (ie inhibited bacterial growth), a stab culture (ie a sterile loop inserted into the bacteria seeded agar) was taken from the centre of each seeded-agar plate and sub-cultured onto DEA plates.
Pre-hydrated 25 31
100 80
100
% reduction of cell adherence caused by pre-hydration
36 54 8
20 13
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