Materials
Silver impregnated dressings such as Medifoam®Silver (Genewel Co., Ltd, South Korea), AAG (Allevyn® AG (Smith & Nephew Co. TX, USA)). MAG (Mepilex® AG (Mölnlycke Health Care Co. Sweden)) and PS (Polymem® Silver (Ferris Manufacturing Co. Illinois, USA)) were obtained or purchased from each respective company. Phosphate-buffered saline (PBS, pH 7.4, 0.01 M, with pigment (SCU656, 0.1 %, DaeBo Co. ltd, Gyeonggi-do, Korea) was purchased from Gibco (NY, USA). All organic solvents were used as HPLC grade without further purification.
Thickness and density measurements
Thickness was measured using MDH micrometer high accuracy sub-micron digimatic micrometer (CD-15CPX, Mitutoyo Co. Ltd., Kawasaki, Japan) repeatedly at least 10 times with different samples. The value of thickness was described in mm as mean ± standard deviation.
Density was calculated from measurement of (weight, width, length and thickness) of the foam dressing materials and described in g/cm3.
$$ Density\ \left(\frac{g}{c{m}^3}\right)=\frac{weight}{width* length* thickness} $$
Density measurement was also repeated at least 10 times with different samples (Mean ± standard deviation).
Morphology assessment
To assess morphology of foam dressing, field-emission scanning electron microscope (FE-SEM, S-4800, Hitachi, Tokyo, Japan) was employed. Each foam dressing was cut into uniform size and then coated by platinum coater. The prepared specimens were assessed at 25 kV. In the morphology analysis, the pore size and pore size uniformity of each dressing were measured and compared. Pore size was measured directly from the photo with a ruler. At least, more than three photos were taken from different positions and used to analyze pore size measurement.
Tensile strength and elongation
Material test machine (3343Q9831, Instron Co., MA, USA) was used for measuring tensile strength. Foam dressings were carefully clipped out of Dog-bone (6 mm × 105 mm) using a wood-molded blade with maintenance of the surface of foam dressing unscathed. Clipped foam dressing was installed into the test machine symmetrically across the cross-section of the grip of the instrument. Foam dressings were pulled out (speed: 300 mm/min) at a snap and the value was calculated in the following equation: [Tensile Strength (kgf/cm2) = MAX Failure Strength (kgf)/Cross-section of Specimen (mm2)]. Elongation was calculated in the following equation:
$$ Elongation\ \left(\%\right)=\left(\frac{D2-D1}{D1}\right)*100 $$
D1: Initial Inter-clip Distance. D2: Inter-clip Distance at Snap.
Absorption rate
Absorption rate was measured as follows: After dressing materials were placed onto flat surfaces, phosphate-buffered saline (PBS, pH 7.4, 0.01 M) solution was pipetted onto the wound contact layer at the height of 1.0 ± 0.5 cm. The absorption rate of PBS was measured using stopwatch, repeatedly, minimum five times. The values were expressed as mean ± standard deviation.
Absorption and retention capacity
Absorption and retention capacity was carried out in accordance with BS EN 13726–1:20022. Five samples of foam dressings measuring 5 × 5 cm were prepared to measure absorption capacity. The baseline weight (W1) and thickness (T) of each sample was recorded. Distilled water (37.0 ± 1 °C) equal to 40 times of the weight of the sample was added to each experimental sample. Temperature of distilled water was constantly controlled with Pyrostat (OF-21E, Jeio Tech, Daejeon, Korea) at 37 °C for 30 min. After 30 min, dressings were suspended and then weighed for 30 s (W2). The absorption rate was calculated with following formula:
$$ Absorption\ \left(\frac{g}{c{m}^2}\right) = \left(\frac{W2-W1}{Initial\ area\ of\ dressing\ \left(c{m}^2\right)}\right) $$
The absorption and retention capacity was measured. Initial weight (A) and thickness (B) of dressings were measured to similar with absorption study. Once absorption rate was measured, each sample was pressed by a 5 kg weight (111209, Jongro industrial Co., Ltd., Seoul, Korea) for 20 s and then weighed again (W3). Then, the retention weight (D) was calculated with following formula: Retention capacity (g/cm2) = W3 – W1/initial specimen area (cm2). The mean absorption and retention of the samples of each product were calculated.
Water-vapor transmission (WVT) measurement
The WVT value of dressing materials was measured as follows: Aluminum cups with diameter of 62 mm and absorptive area of 0.0028 m2 were preheated in a dry oven (100 °C) and placed with CaCl2 (20 g). Each dressing was tied onto the top of the aluminum cup. Ten glass bottles were used for each dressing. The specimen was set to face CaCl2 in the aluminum cup and the dead center of the cup to create a concentric ring. To seal the edges, preheated paraffin solution in a dry oven (100 °C) was poured along the edge of the absorptive cup (beaker) and then paraffin debris was removed thereafter. The joint aluminum cups containing CaCl2 and covering dressing was weighed for baseline (W1) and 24 h after it was placed into the thermo-hygrostat (37 °C, 75 % humidity) (W2). The MVTR of the samples were calculated as follows:
$$ WVT\ \left(\frac{g}{c{m}^2}* day\right) = \left(\frac{W2-W1}{B* day}\right) $$
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W1 : initial weight of the sample before put into the thermo-hygrostat.
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W2 : weight of the sample in thermo-hygrostat after 24 h.
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B : absorptive area (0.0028 m2).
Antibacterial activity
The antimicrobial activity of the foam dressings was compared against Staphylococcus aureus and Pseudomonas aeruginosa obtained from the American Type Culture Collection (ATCC, Manassas, VA, USA); ATCC 6538 and ATCC 10145, respectively. To evaluate antimicrobial activity, the dynamic shake flask test was used. Briefly, 50 ml of culture inoculum containing approximately 1×106 CFU/ml were added to a sterile 250 ml screw-cap Erlenmeyer flask (Triforestlabware, CA, USA). Bacterial concentration of solution was determined at the “0” time by performing serial dilutions and standard plate count techniques from the “inoculum only” sample flask. Each dressing (1 cm × 1 cm) was placed in the individual flask and incubated under dynamic conditions at 32 °C. Following incubation, at different time intervals (1 min, 5 min, 10 min, 20 min, 30 min, and 1 h), the dressings were removed and the resulting suspensions were incubated at 35 °C for 24 h in Petri dishes (BD(Becton Dickinson), CA, USA). The numbers of colonies (CFU/ml) for the dressing-containing flask (A) and for the “inoculum only” flask (B) were counted. The reduction of microorganisms (%) for each dressing was calculated using the following formula;
$$ \mathrm{L}\mathrm{o}{\mathrm{g}}_{10}\kern0.5em \mathrm{reduction}\ \left(\mathrm{L}\mathrm{R}\right) = \mathrm{l}\mathrm{o}{\mathrm{g}}_{10}\left(\mathrm{B}\right)\ \hbox{-}\ \mathrm{l}\mathrm{o}{\mathrm{g}}_{10}\left(\mathrm{A}\right) $$
$$ \mathrm{Percent}\ \mathrm{reduction}\ \left(\%\right) = 100 \times \left(1\ \hbox{-}\ 1{0}^{\hbox{-} \mathrm{L}\mathrm{R}}\right) $$
Statistical analysis
All experimental data were expressed as mean ± standard deviation (S.D.). Statistical alaysis was evaluated by Student’s t test using Sigmaplot program (Sigmaplot version 11.2, Systat software, Inc., CA, USA) and p value < 0.05 was considered as statistically significant.