WOUND DRESSING WITH APERTURED COVER SHEET

Abstract

A wound dressing comprising an antimicrobial absorbent layer containing silver, and an apertured sheet covering the antimicrobial absorbent layer, wherein the apertured sheet is formed from a liquid-impermeable sheet material having an array of apertures therein, said apertures having a mean effective diameter of from about 0.5 mm to about 2 mm, and wherein the percentage open area of the apertured sheet is from about 7% to about 25%. The selection of apertures in this range provides enhanced antimicrobial efficacy.

Claims

1. A wound dressing comprising: an antimicrobial absorbent layer of nonwoven fabric having hydrogel-forming absorbent fibers and non-absorbent textile fibers, wherein at least some of the non-absorbent textile fibers contain silver; and an apertured sheet covering the antimicrobial absorbent layer of nonwoven fabric, wherein the apertured sheet is formed from a liquid-impermeable sheet material having an array of apertures therein, said apertures having a mean effective diameter in a range of 1 mm to 2 mm, and wherein a percentage open area of the apertured sheet is in a range of 17% to 25%.

2. A wound dressing according to claim 1, wherein the antimicrobial absorbent layer of nonwoven fabric comprises at least about 10 wt. % of the hydrogel-forming absorbent fibers based on the dry weight of the fabric.

3. A wound dressing according to claim 1, wherein the silver consist essentially of metallic silver (Ag.sup.0).

4. A wound dressing according to claim 1, wherein the antimicrobial absorbent layer of nonwoven fabric comprises a mixture of from about 10 wt. % to about 90 wt. % of the hydrogel-forming absorbent fibers and from about 90 wt. % to about 10 wt. % of the non-absorbent textile fibers, in which at least some of the non-absorbent textile fibers are coated with metallic silver (Ag.sup.0).

5. A wound dressing according to claim 1, wherein the apertured sheet is melt-bonded directly to a wound facing surface of the antimicrobial absorbent layer of nonwoven fabric.

6. A wound dressing according to claim 1, wherein the silver consists essentially of ionic silver (Ag.sup.+).

7. A wound dressing according to claim 6, wherein the absorbent layer further comprises an anionic polymer having said ionic silver complexed thereto.

8. A wound dressing according to claim 1, wherein the aperture sheet has apertures with mean effective diameter from 1.1 mm to 1.6 mm and percentage open area from 19% to 25%.

9. A wound dressing according to claim 1, wherein the wound dressing is sterile.

10. A wound dressing according to claim 9, wherein the wound dressing is packaged in a microorganism impermeable container.

11. The wound dressing according to claim 1, wherein the apertured sheet is a single sheet, and wherein the apertures are annular openings.

12. The wound dressing according to claim 1, wherein the apertured sheet has apertures with a mean effective diameter of 1.3 mm and an open area of 22%.

13. The wound dressing according to claim 11, wherein the apertured sheet is non-elastomeric and wherein a depth of each aperture corresponds to a thickness of the apertured sheet.

14. A wound dressing comprising: an antimicrobial absorbent layer containing silver; and an apertured sheet covering the antimicrobial absorbent layer, wherein the apertured sheet is formed from a liquid-impermeable textured sheet material having an array of apertures therein, said apertures having a mean effective diameter of from 1 mm to 2 mm, and wherein a percentage open area of the apertured sheet is from 17% to 25%.

15. The wound dressing according to claim 14, wherein the texture is a pattern of ridges protruding from about 0.1 mm to about 1.5 mm above the medium plane of the surface of the apertured sheet.

16. A wound dressing according to claim 1, wherein the silver consists essentially of metallic silver (Ag.sup.0), and wherein the apertured sheet has apertures with mean effective diameter from 1.0 mm to 1.5 mm.

17. A wound dressing according to claim 16, wherein the apertured sheet has a percentage open area from 17% to 19%.

18. (canceled)

19. A wound dressing according to claim 1, wherein the mean effective diameter of the apertures is in a range of 1.3 mm to 1.5 mm, and the percentage open area of the apertured sheet is in a range of 17% to 19%.

20. (canceled)

21. A wound dressing according to claim 14, wherein the mean effective diameter of the apertures is in a range of 1.3 mm to 1.5 mm, and the percentage open area of the apertured sheet is in a range of 17% to 19%.

22. (canceled)

23. A wound dressing according to claim 14, wherein the total amount of silver in the antimicrobial absorbent layer is from 0.5 wt. % to 10 wt. % based on the dry weight of the absorbent layer.

24. A wound dressing according to claim 19, wherein the total amount of silver in the antimicrobial absorbent layer is from 1 wt. % to 5 wt. % based on the dry weight of the absorbent layer.

Description

[0038] Specific embodiments of the present invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

[0039] FIG. 1 shows a perspective view of a dressing according to the invention;

[0040] FIGS. 2A-2E show schematic drawings of the aperture distribution in five different top sheets used for testing;

[0041] FIG. 3 shows a plot of measured silver release after 24 hours versus aperture size and open area of the top sheet for a dressing containing metallic silver;

[0042] FIG. 4 shows a contour plot of measured log 10 bacterial reduction versus aperture size and open area of the top sheet for a dressing containing metallic silver

[0043] FIG. 5 shows a contour plot of swab test results in a three-day zone of inhibition test versus aperture size and open area of the top sheet for a dressing containing metallic silver

[0044] FIG. 6 shows a plot of measured silver release after 24 hours versus aperture size and open area of the top sheet for a dressing containing ionic silver; and

[0045] FIG. 7 shows a contour plot of measured log 10 bacterial reduction versus aperture size and open area of the top sheet for a dressing containing ionic silver

[0046] Referring to FIG. 1, the dressing 1 comprises an absorbent layer 2 containing metallic or ionic silver, having front and back sheets 3,4 of apertured EMA thermoplastic film bonded to the major surfaces thereof by application of heat and pressure.

Example 1

[0047] Wound dressings according to the invention containing metallic silver were made with the structure shown in FIG. 1. The absorbent layer is a calcium alginate needled felt dressing incorporating silver-coated nylon fibers. The composition is as follows, by weight: calcium alginate and carboxymethyl cellulose (CMC) fibers 60% and silver coated nylon 40%. The basis weight of the fabric layer is about 150 g/m.sup.2, and the uncompressed thickness of the fabric layer is about 2 mm. The total silver content of the fabric is about 8 wt. %. The fabric layer is commercially available from Johnson & Johnson under the Registered Trade Mark SILVERCEL.

[0048] Dressings of this type were evaluated having top sheets with a range of hole sizes and percentage open areas, some of which are shown schematically in FIG. 2. Specifically, FIG. 2(a) represents 0.8 mm hole size, 1% open area; FIG. 2(b) represents 2 mm hole size, 1% open area; FIG. 2(c) represents 1.4 mm hole size, 13% open area; FIG. 2(d) represents 0.8 mm hole size, 25% open area; and FIG. 2(e) represents 2 mm hole size, 25% open area.

[0049] A total of 15 dressings of this type having differently perforated top sheets were tested. Hole sizes tested were, 0.8, 1.4 and 2.0 mm diameter, and percent open areas tested were 1%, 7%, 13%, 19% and 25%.

Example 2

[0050] Wound dressings according to the invention containing ionic silver were made with the structure shown in FIG. 1. The absorbent layer is a calcium alginate felt dressing incorporating an ionic silver complex. The composition is as follows, calcium alginate, carboxymethyl cellulose (CMC) fibers and silver sodium hydrogen zirconium phosphate. The total silver content of the fabric is about 0.5 wt. %. The fabric layer is commercially available from Laboratories Urgo, under the Registered Trade Mark Urgosorb Silver.

[0051] A total of 5 dressings of this type having differently perforated top sheets were tested. Hole sizes tested were, 0.8, 1.4 and 2.0 mm diameter, and percent open areas tested were 1%, 13%, and 25%.

Procedure 1Silver Release

[0052] Samples of the dressings of Examples 1 and 2 were immersed into a solution of simulated wound fluid (SWF), 0.013M Calcium Chloride, 0.2M Sodium Chloride and 0.04M Tris containing 2% Bovine Albumin at pH 7.5. Samples were gently agitated in 10 an amount of SWF equivalent to 5 ml/2.52.5 cm.sup.2. At a specific time point, for example 24 hours, a sample of fluid was removed and diluted in SWF and analysed against a silver standard Analysis was performed against a silver standard curve prepared in SWF using the Perkin Elmer Analyst 200 Atomic Absorption Spectrometer. Standards of known concentration were prepared in the same SWF as used for the samples. Specimen data for silver release in ppm are shown in Table 1 and are represented graphically in FIGS. 3 and 6.

TABLE-US-00001 TABLE 1 Silver release - Metallic Silver Dressings Percent open area 1 7 13 19 25 Hole size 0.8 16.3 +/ 2.6 16.2 +/ 1.1 16.7 +/ 0.8 16.7 +/ 0.6 16.4 +/ 1.3 (mm) 1.4 16.4 +/ 1.3 18.0 +/ 1.0 17.7 +/ 1.4 17.4 +/ 1.4 17.4 +/ 1.1 2 15.0 +/ 0.7 15.6 +/ 1.4 16.5 +/ 1.2 17.1 +/ 1.8 15.9 +/ 1.6

TABLE-US-00002 TABLE 2 Silver release - Ionic Silver Dressings Percent open area 1 13 25 Hole size (mm) 0.8 19.6 +/ 0.37 20.41 +/ 0.88 19.21 +/ 0.53 1.4 20.75 +/ 0.33 20.04 +/ 0.18 20.38 +/ 1.38 2 20.00 +/ 0.83 18.73 +/ 0.61 20.5 +/ 0.95

[0053] It can be seen that there is a maximum in the silver release from the metallic silver dressings at a hole size of 1.4 mm and percentage open area 13%. At larger hole sizes and larger percentage open area the silver release is unexpectedly lower. The ionic silver dressings showed a maximum silver release at hole size of 1.4 mm, apparently independent of open area in the samples tested.

Procedure 2Inactivation of Bacteria in Suspension

[0054] Testing was performed using common wound pathogens, Staphylococcus aureus and Pseudomonas aeruginosa. The test dressings were immersed in a quantified bacterial suspension and then sampled to determine the numbers of challenge bacteria killed over a 120 minute test period. The log.sub.10 bacterial inactivation was calculated.

[0055] The results are shown graphically in FIGS. 4 and 7 as contour plots. For the metallic silver dressings of FIG. 4, it can be seen that the log.sub.10 bacterial inactivation increases sharply at hole sizes above about 0.8 mm, and shows two distinct maxima at percentage open areas about 7% and about 20%. For the ionic silver dressings of FIG. 7, it can be seen that the log.sub.10 bacterial inactivation increases sharply at hole sizes above about 1.0 mm, and at open area above about 7%.

Procedure 3Three Day Zone of Inhibition Test and Swab Test

[0056] Testing was performed using agar plates inoculated with Staphylococcus aureus. Silver preferentially acts upon gram-negative bacteria (Pseudomonas aeruginosa) over gram-positive bacteria. (Staphylococcus aureus), and therefore Staphylococcus aureus was considered a more demanding test organism for the dressings of the invention. Dressings were transferred onto freshly inoculated agar plates on a daily basis for three days. The zone of inhibition was calculated by measuring the distance from the edge of the dressing to the edge of the clear zone surrounding the dressing. These measurements 30 were made daily, prior to dressing transfer in order to determine the antimicrobial activity of the wound dressings, and whether this activity was sustained over three days. The meanstandard deviation was calculated for the zone of inhibition.

[0057] In addition, the ability of the dressing to prevent the growth of bacteria beneath the dressing was determined by taking a swab sample from the agar surface in direct contact with the dressing material and testing the swab for the presence of the bacteria.

[0058] The zone of inhibition (in mm) and swab results from dressings tested against Staphylococcus aureus are given in Tables 3 and 4. Positive results indicate growth of bacteria from swabs taken from the agar surface. One positive (1.sup.+) swab result is within the normal range of currently marketed anti-microbial dressings, therefore acceptable. Greater than one positive result upon swabbing is not acceptable for this test method. Ideally, no positive swab results (Negative swab) results should be obtained.

TABLE-US-00003 TABLE 3 Swab results - Metallic Silver Hole Size (mm) Open Area (%) 0.8 1.4 2.0 1 3.13 0.53 3.11 0.44 3 + swab 3 + swab 7 3.21 0.36 1 + swab 13 3.13 0.23 3.61 0.64 Negative swab 1 + swab 19 3.58 0.34 Negative swab 25 2.82 0.71 3.3 0.40 Negative swab Negative swab

TABLE-US-00004 TABLE 4 Swab results - Ionic Silver Hole Size (mm) Open Area (%) 0.8 1.4 2.0 1 2.24 0.71 2.83 0.47 2 + swab 3 + swab 13 4.17 0.45 2 + swab 25 4.89 0.41 4.96 0.56 Negative swab Negative swab

[0059] It can be seen from the data that there is an optimal combination of aperture size and density for silver release and antimicrobial properties of the dressings.

[0060] The above embodiments have been described for the purpose of illustration only. Many other embodiments falling within the scope of the present invention will be apparent to the skilled reader.