The Effect of Several Silver-Containing Wound Dressings on Fibroblast Function In Vitro Using the Collagen Lattice Contraction M
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Materials and Methods
Dressings. This study assessed the characteristics of 7 proprietary silver-containing antimicrobial dressings that have all received an appropriate regulatory (eg, US Food and Drug Administration) risk-benefit profile: 3 fibrous dressings—AQUACEL® Ag (ConvaTec, Skillman, NJ, USA; referred to throughout this article as nonwoven A), Acticoat® Absorbent (Smith & Nephew, London, UK; referred to throughout this article as nonwoven B), and SILVERCEL® (Johnson & Johnson Wound Management, Somerville, NJ, USA; referred to throughout this article as nonwoven C); 2 foam dressings—Contreet® Foam (Coloplast, Holtedam, Denmark; referred to throughout this article as foam A) and PolyMem® Silver (Ferris Pharmaceuticals, Burr Ridge, Ill, USA; referred to throughout this article as foam B); a gauze dressing—Urgotul® S.Ag (Laboratoires Urgo, Chenôve, France; referred to throughout this article as gauze); and a nonadhesive polymer hydrogel sheet—SilvaSorb® (AcryMed/Medline, Mundelein, Ill, USA; referred to throughout this paper as hydrogel). The physical and chemical characteristics of these dressings have been previously described.7
Cell culture. Granulation tissue fibroblasts (GTFs) were taken from slow-healing areas of equine wounds, and the fibroblast-seeded collagen gels were prepared as described previously.6 Briefly, tissue samples were immediately transferred to a sterile Petri dish, washed in Hanks’ balanced salt solution (HBSS) (all cell culture materials were supplied by Gibco, UK unless otherwise stated), and cut into 3–5 mm2 pieces before being placed into 25 cm2 tissue culture flasks containing media (prepared by adding 10% fetal calf serum to Dulbecco’s Modified Eagle Medium [DMEM], supplemented with 20 mM Hepes buffer, 100 µg/mL gentamicin, and 0.5 µg/mL amphotericin B) and incubated in a 5% carbon dioxide/95% air environment at 37˚C.
Following incubation, the fibroblasts were harvested from stock dishes and plated in 35 mm 6-well plates at a concentration of 1 x 106 cells/mL in molten type I collagen (Sigma, UK) prior to the application of moistened dressings.
Gel contraction and viability assays. For gel contraction and viability assays, 0.5 g of each silver-containing wound dressing was pre-moistened with sterile saline (0.5 mL) and placed onto the surface of the fibroblast-seeded collagen gel, and 0.5 mL of sterile saline was applied directly to the control gel with no dressing. Gel contraction measurements were made using calipers (mm) at 24-hour intervals over a period of 96 hours. Quantitative evaluation of fibroblast viability was carried out at the end of the experiment (ie, after 96 hours) using the trypan blue exclusion assay. Six replicates were performed for each dressing plus controls.
Statistical analysis. A multivariate analysis of variance (Duncan’s multiple comparison test) was used to analyze the data.
To more accurately measure the individual effect of a dressing on fibroblast contraction, a percentage area of collagen gel contraction relative to the control was calculated for each dressing using the equations outlined as follows. Equation 1 shows the calculation for the absolute area of contraction (AAC) for the control and each individual dressing expressed as a percentage:
AAC= [initial radius of the gel (ie, 35 mm)]2 – (final radius)2 X 100 ÷ (initial radius)2
Equation 2 expresses the AAC of each dressing as a percentage contraction relative to the control:
% contraction relative to control =AAC dressing ÷ AAC control X 100
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