Wound dressing materials

Abstract

A wound dressing material comprising: a wound dressing carrier, N-acetyl cysteine or a salt or derivative thereof, and a stabilized ascorbate. Suitably, the stabilized ascorbate comprises an ascorbate-2-polyphosphate. Also provided are wound dressings comprising the materials, methods of treatment with the materials, and methods of making the materials.

Claims

1. A wound dressing, comprising: an active layer comprising a wound-facing side, N-acetyl cysteine or a salt thereof, and a stabilized ascorbate, wherein a weight ratio of N-acetyl cysteine or a salt thereof to the stabilized ascorbate is from about 1:4 to about 4:1; a backing sheet extending over the active layer opposite to the wound facing side; and a moisture-vapor transmitting adhesive layer disposed between the backing sheet and the active layer; wherein the stabilized ascorbate comprises a member selected from the group consisting of ascorbate 2-phosphate or polyphosphate compounds, trisodium L-ascorbyl-2-monophosphate, 2-phospho-L-ascorbic acid trisodium salt, magnesium ascorbyl phosphate (MAP), L-ascorbic acid mono(dihydrogen phosphate) magnesium salt, magnesium L-ascorbic acid-2-phosphate, trisodium L-ascorbyl-2-polyphosphate, and a combination of any two or more thereof.

2. The wound dressing of claim 1, further comprising an absorbent layer positioned between the active layer and the backing sheet.

3. The wound dressing of claim 1, wherein the active layer further comprises a carrier material.

4. The wound dressing of claim 3, wherein the carrier material is bioabsorbable and adapted to provide sustainable release of N-acetyl cysteine or a salt thereof and the stabilized ascorbate.

5. The wound dressing of claim 3, wherein the carrier material consists essentially of a freeze-dried sponge or a solvent-dried sponge.

6. The wound dressing of claim 5, wherein the carrier material comprises oxidized cellulose, in combination with collagen or chitosan.

7. The wound dressing of claim 1, further comprising a liquid-permeable top sheet disposed on the wound facing side of the active layer.

8. The wound dressing of claim 1, wherein the moisture-vapor transmitting adhesive layer is a substantially continuous layer of pressure-sensitive polyurethane adhesive coated on the backing sheet.

9. The wound dressing of claim 1, wherein the backing sheet comprises substantially closed-cell polyurethane foam.

10. The wound dressing of claim 1, wherein the backing sheet is larger than the active layer and extends beyond one or more edges of the active layer to form a marginal region.

11. The wound dressing of claim 1, which is sterile and packaged in a microorganism-impermeable container.

12. The wound dressing of claim 1, wherein the stabilized ascorbate comprises ascorbate-2-triphosphate.

13. The wound dressing of claim 3, wherein the active layer comprises from about 1 wt. % to about 10 wt. % of N-acetyl cysteine or salts thereof, and from about 1 wt. % to about 10 wt. % of the stabilized ascorbate.

Description

(1) Specific embodiments of the invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a wound dressing according to the present invention incorporating a sheet of the material according to the invention.

(3) FIG. 2 shows the percentage stimulation of collagen synthesis in dermal fibroblast cells measured by Procedure 1 for the examples and reference examples.

(4) FIG. 3 shows the observed radius of the collagen sheet in the gel contraction measurement according to Procedure 2 for certain examples and reference examples.

(5) Referring to FIG. 1, a wound dressing 1 according to the present invention is an island-type, self-adhesive wound dressing comprising a backing layer 2 of microporous liquid-impermeable polyurethane foam. The backing layer 2 is permeable to water vapor, but impermeable to wound exudate and microorganisms.

(6) The backing layer is coated with a substantially continuous layer of pressure-sensitive polyurethane adhesive. A rectangular island 3 of a wound dressing material according to the invention in sheet form, made in accordance with Example 1 below, is adhered to a central region of the adhesive-coated backing sheet 2 such that an adhesive-coated margin 4 of the backing sheet extends around the island for attachment of the dressing to the skin around a wound.

(7) The dressing further comprises protective, release-coated cover sheets 5,6. These cover sheets are removed immediately before use of the dressing. The dressing is suitably sterile and packaged in a microorganism-impermeable pouch (not shown) prior to use.

Example 1

(8) A collagen/ORC sponge containing NAC and AZP was prepared by a modification of the method for the preparation of Collagen/ORC sponges described in Example 1 of EP-A-1153622.

(9) Briefly, the collagen component is prepared from bovine corium as follows. Bovine corium is split from cow hide, scraped and soaked in sodium hypochlorite solution (0.03% w/v) to inhibit microbial activity pending further processing. The corium is then washed with water and treated with a solution containing sodium hydroxide (0.2% w/v) and hydrogen peroxide (0.02% w/v) to swell and sterilize the corium at ambient temperature. The corium splits then undergo an alkali treatment step in a solution containing sodium hydroxide, calcium hydroxide and sodium bicarbonate (0.4% w/v, 0.6% w/v and 0.05% w/v, respectively) at pH greater than 12.2, ambient temperature, and for a time of 10-14 days, with tumbling, until an amide nitrogen level less than 0.24 mmol/g is reached. The corium splits then undergo an acid treatment step with 1% hydrochloric acid at ambient temperature and pH 0.8-1.2. The treatment is continued with tumbling until the corium splits have absorbed sufficient acid to reach a pH less than 2.5. The splits are then washed with water until the pH value of corium splits reaches 3.0-3.4. The corium splits are then comminuted with ice in a bowl chopper first with a coarse comminution and then with a fine comminution setting. The resulting paste, which is made up in a ratio of 650 g of the corium splits to 100 g of water, as ice, is frozen and stored before use in the next stage of the process. However, the collagen is not freeze-dried before admixture with the ORC in the next stage.

(10) The ORC component of the freeze-dried pad is prepared as follows. A SURGICEL cloth (Johnson & Johnson Medical, Arlington) is milled using a rotary knife cutter through a screen-plate, maintaining the temperature below 60? C.

(11) The milled ORC powder and the required weight (according to solids content) of frozen collagen paste are then added to a sufficient amount of water acidified with acetic acid to form an aqueous dispersion. NAC and Ascorbate 2-triphosphate (STAY-C, Roche) are each dissolved into the aqueous acetic acid prior to addition of the ORC and collagen, to give a final concentrations of NAC of 4.5 mM and a final concentration of ascorbate 2-triphosphate of 4.5 mM. The resulting aqueous dispersion has pH value of 3.0 and a total solids content of 2.0% (note: the method of Example 1 of EP-A-1153622 uses a 1% solids slurry). The mixture is homogenized through a Fryma MZ130D homogenizer, progressively diminishing the settings to form a homogeneous slurry. The pH of the slurry is maintained at 2.9-3.1. The slurry temperature is maintained below 20? C., and the solids content is maintained at 2%?0.07. Surprisingly, it was found that the slurry having this higher solids content has a sufficiently low viscosity for handling in the subsequent stages of the process.

(12) The resulting slurry is pumped to a degassing vessel. Vacuum is initiated for a minimum of 30 minutes, with intermittent stirring, to degas the slurry. The slurry is then pumped into freeze-drier trays to a depth of 25 mm. The trays are placed onto freezer shelves where the temperature has been preset to ?40? C. The freeze-drier programme is then initiated to dry and dehydrothermally cross-link the collagen and ORC to form thick sponge pads. On completion of the cycle, the vacuum is released, the freeze-dried blocks are removed, and are then split to remove the top and bottom surface layers, and to divide the remainder of the blocks into 3 mm-thick pads. The step of splitting the freeze-dried blocks into pads is carried out with a Fecken Kirfel K1 slitter. Finally, the pads are die-cut to the desired size and shape on a die-cutter, packaged, and sterilized with 18-29 KGy of cobalt 60 gamma-irradiation. Surprisingly, this irradiation does not cause significant denaturation of the collagen, which appears to be stabilized by the presence of ORC. The resulting freeze-dried collagen ORC pads have a uniform, white, velvety appearance. The thickness of the pads is 3.2?0.17 mm (N=8 batches).

Example 2

(13) The procedure of Example 1 was repeated, but with addition of NAC and ascorbate-2-triphosphate in amounts of 2.5 mM and 2.5 mM respectively to the slurry.

Example 3

(14) The procedure of Example 1 was repeated, but with addition of NAC and ascorbate-2-triphosphate in amounts of 0.5 mM and 0.5 mM respectively to the slurry.

Reference Examples 4-9

(15) Reference sponges were prepared by the method of Example 1 with the following actives in the slurry in the following amounts:

(16) Reference Example 4: NAC

(17) Reference Example 5: NAC 5 mM

(18) Reference Example 6: NAC 9 mM

(19) Reference Example 7: ascorbate-2-triphosphate 1 mM

(20) Reference Example 8: ascorbate-2-triphosphate 5 mM

(21) Reference Example 9: ascorbate-2-triphosphate 9 mM

(22) Procedure 1; Measurement of Collagen Synthesis by Dermal Fibroblasts

(23) A collagen synthesis assay with dermal fibroblasts was performed. This is standard assay which shows the amount of collagen synthesised by fibroblasts after stimulation with the active agents.

(24) Briefly, the collagen synthesis assay involved plating 8.4?10.sup.4 human fibroblasts (per well) into 24-well plates, and incubating them at 37? C., 5% CO.sub.2, in 10% FBS-DMEM. Once cells were confluent (within 24 hours of plating), the 10% FBS-DMEM was removed, cells washed 3? with SF-DMEM, before a SF-DMEM extract of the sponge samples of Examples 1-9 was added to the cells. Cells were incubated for 72 hours after which time the media were collected. A commercial immunoassay (Metra-CICP Kit, Quidel, San Diego, USA) was used that measured the level of C-terminal propeptide of Type-1 Collagen (CICP) present in the cell culture media. The level of CICP in the media, which is released by the fibroblasts as a by-product of collagen synthesis, is proportional to the level of collagen synthesis and so its level was used to determine the level of collagen synthesis.

(25) The results are shown graphically in FIG. 2. It can be seen that the combination of ascorbate-2-triphosphate with NAC gives a synergistic improvement in collagen synthesis. This is expected to result in improved wound healing in vivo, in particular for chronic wounds.

(26) Procedure 2: Measurement of Collagen Gel Contraction

(27) The measurement of collagen gel contraction, performed in vitro, gives a good indication of the ability of actives to promote cellular response. The procedure was as follows:

(28) 1. Normal human dermal fibroblasts were maintained in 10% FBS/DMEM (Fetal bovine serum & Dulbecco's minimally modified medium), and grown in a humidified incubator containing 5% CO.sub.2. Cells were split at 95% confluency and were used for experiments when approx. 90% confluent.
2. Cells were harvested using 0.05% trypsin/EDTA (GIBCO BRL), counted using a haemocytometer and centrifuged to obtain cell pellet.
3. Cells were then resuspended at a cell density of 140,000 cells/ml4 times the final cell density in the collagen gel.
4. The following cell/collagen mixture was prepared for each 24-well plate:
14 mls 10% FBS/DMEM
7 mls cells at 140,000 cells/ml
7 mls soluble collagenrat tail type I collagen from Collaborative Biomedical (supplied by Fred Baker Scientific: 356236)final concentration 1 mg/mlit is usually supplied at approx. 4 mg/ml thus 7 mls was taken directly from the bought stock solution. This mixture was then distributed at 1 ml/well into each of a 24-well tissue culture plate, and allowed to gel for 1 hr at 37? C.
5. Once the gels had polymerized they were rimmed with a sterile pipette tip and an additional 0.5 ml of medium added carefully to each well. This additional medium contained the test reagent (at 3 times the final required concentration to account for dilution).

(29) The plates were photographed and then incubated at 37? C. in 5% CO.sub.2 in a humid environment. Photographs were taken at similar times each day until the end of the experimentusually day 14 or 15 after setup. At day four the measurements of each well for each test substance were averaged and were compared to each other and to the control. A faster the rate of contraction was indicated by a reduction in diameter of the gel.

(30) Collagen gel contractions were prepared and incubated over four days with the following solutions. Positive control; 10% FBS DMEMNegative control; Serum Free DMEM. Test Solutions, 9 mM AZP, 9 mM NAC, 9 mM AZP/NAC combination and 4.5 mM NAG/AZP combination.

(31) The results show that a faster rate of contraction is achieved with the 4.5 mM AZP/NAC combination that with any other solution. This is a faster rate than the ascorbate-2-triphosphate or the NAC on their own and is faster than the positive control. This indicates that this level of active is optimal for the contraction of collagen and proliferation of the dermal fibroblasts.

(32) All patent applications referred to herein are expressly incorporated in their entirety.

(33) The above examples have been described for the purpose of illustration only. Many other embodiments falling within the scope of the accompanying claims will be apparent to the skilled reader.