Technology update Evaluation of low-adherent antimicrobial dressings
this test was performed. The results indicated that visualisation of bacterial growth was independent of the challenge organism, but may be dependent on a dressing’s ability to make the antimicrobial agent available at the dressing/seeded-agar interface. When the upper surface of the dressing was presented to the seeded-agar surface, there was a strong tendency for foams B and C to curl away from the surface [Figures 15c and 15d]. However, even where it remained in contact, there was no observed inhibition of bacterial growth. The visualised pattern of growth was also different because of the absence of pores [Figures 15c and 15d]. Although foam A remained in contact with the seeded-agar surface it was observed that both the WSCL and the upper surface did not inhibit growth [Figure 14]. When a cut edge of each foam dressing was placed onto the seeded-agar surface, no growth was observed [Figures 14 and 15c and 15d]. For the AL-Ag dressing there is no specific
WSCL and both faces of the dressing could be placed onto the seeded-agar surface. Consequently, both sides were observed to show slight growth. However, when this dressing was placed on its exposed cut edge, no growth was visible [Figure 15b]. For the HF-Ag dressing, no growth was observed regardless of the orientation of the dressing [Figure 15a].
DISCUSSION One of the key issues for patients, regardless of wound aetiology, is the prevention of pain and trauma associated with dressing removal through adherence to the wound bed[7, 8, 9]
.
Equally important to clinicians is the need to limit the risk of infection in wounds due to the presence of invading wound pathogens[8, 10, 11]
.
Both aspects should be considered as part of a protocol of care for ‘at-risk’ wounds. However, wound care product awareness and an ability to select an appropriate wound dressing is still thought to be highly variable[7]
. In an in vitro fibroblast bioadhesion model,
it was observed that all the tested dressings had a higher cellular adhesion when applied in a dry state than when hydrated, and that the two examples of gelling fibre dressings were significantly less adherent than the three examples of adhesive foam dressings tested (p<0.001). Although cellular adhesion was reduced by product hydration, this reduction was only slight for the adhesive foams, suggesting that the presence of fluid may have had little effect on their adhesive properties. For the
gelling dressings, the reduction in adherence was greater and more significant [Figure 1]. This suggests that the fibres’ ability to absorb fluid and swell considerably to form a soft cohesive gelled structure (as discussed for HF-Ag[12]
) may be an
important factor in reducing cell adhesion, and may explain the reported significantly reduced pain levels observed both during wear time
(reduction from baseline at three days [p=0.0006] [13]
[p<0.01]15
and during dressing changes ([p=0.009][14] ; and [p<0.02][16]
). Recent in vitro studies suggest a possible
correlation between achieving close proximity of silver-containing dressings to the wound bacterial bioburden and antimicrobial activity[5,17]
. These studies investigated the
relative abilities of certain adhesive foam dressings and gelling fibre dressings to contour closely to a simulated shallow wound bed[5,17] In these latest in vitro studies, a flat agar surface
.
was used so that close contact between the WSCL of the dressing and the contaminated surface was guaranteed. Under these conditions the ability of each dressing to make available sufficient antimicrobial agent to exert an effect at the wound-dressing interface was investigated. The gelling fibre dressing (HF-Ag) killed bacteria on the flat agar surface. The tested foam dressings with an adhesive WSCL did not appear to prevent the growth of bacteria on the flat agar surface. While AL-Ag showed bacteriostatic activity (ie prevented bacterial proliferation but did not kill all bacteria), HF-Ag produced a bactericidal action (killed all viable bacteria) [Table 3]. The three silver-containing foam dressings tested were neither bacteriostatic nor bactericidal in this in vitro model, and bacterial growth was observed directly beneath these intact foam dressings. However, when a cut edge of each dressing was placed directly onto a bacteria-seeded agar surface (ie exposing the inner foam matrix), greater antimicrobial activity was visually observed. Elemental analysis revealed that the
silver was exclusively contained within the foam structure and was not associated with the adhesive. These observations suggested that the adhesive WSCL of the foam dressings may have been acting as a barrier to the availability of the antimicrobial agent to the underlying bioburden. Similar conclusions were drawn in an independent study, which reported hydrophobicity and antimicrobial activity only from the exposed foam[17]
. HF-Ag was observed to contain only
gelling fibres with silver evenly distributed throughout. Contact with the high water content agar caused the surface to gel, and
www.woundsinternational.com 46 ;
Page points
1. One of the key issues for patients, regardless of wound aetiology, is the prevention of pain and trauma associated with dressing removal through adherence to the wound bed
2. In anin vitro fibroblast bioadhesion model, it was observed that all the tested dressings had a higher cellular adhesion when applied in a dry state than when hydrated
3. Although cellular adhesion was reduced by product hydration, this reduction was only slight for the adhesive foams, suggesting that the presence of fluid may have had little effect on their adhesive properties
Technology and product reviews
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