Wound dressing for use in vacuum therapy

Abstract

A wound dressing for use in vacuum wound therapy comprising a wound contact layer which is an open structure comprising a yarn comprising gel-forming filaments or fibres, the structure having a porosity which allows exudate to flow through it.

Claims

1. A wound dressing for use in vacuum wound therapy comprising a wound contact layer comprising an open structure in a form of a net comprising a spun yarn comprising a blend of gel-forming filaments or fibres and textile fibres, the net having a pore or mesh size from 0.5 mm.sup.2 to 5.0 mm.sup.2 that allows exudate to flow through the net, wherein the yarn has a linear density of 20 tex to 40 tex, wherein the yarn has a dry tensile strength of at least 10 cN/tex, wherein the textile fibers have an absorbency of between 5 g/g and 10 g/g as measured by the free swell method, and wherein the blend of gel-forming filaments or fibres and textile fibres includes only one type of gel-forming filaments or fibres.

2. A wound dressing as claimed in claim 1 wherein the net is knitted, woven, or embroidered.

3. A wound dressing as claimed in claim 1 wherein the pore or mesh size of the net is between 3.0 mm.sup.2 to 4.0 mm.sup.2.

4. A wound dressing as claimed in claim 1 wherein the net is knitted.

5. A wound dressing as claimed in claim 1 wherein the net is joined at intervals to form a set of meshes.

6. A wound dressing as claimed in claim 1 wherein the yarn comprises 30% to 100% by weight gel-forming filaments or fibres.

7. A wound dressing as claimed in claim 1 wherein the net comprises 50% to 100% by weight gel-forming filaments or fibres.

8. The wound dressing of claim 1 wherein the yarn has a dry tensile strength from 10 cN/tex to 40 cN/tex.

9. The wound dressing of claim 1 wherein the spun yarn comprises a blend of the gel-forming filaments or fibres and the textile fibres in a ratio of 60:40 to 70:30.

10. The wound dressing of claim 1, wherein the pore or mesh size of the net facilitates application of strain to tissue through pores or mesh of the net to stimulate tissue growth when a vacuum of at least 0.4 atm is applied by a vacuum source to the wound dressing such that a relative vacuum is retained in the wound dressing.

11. A device for vacuum wound therapy comprising: a wound dressing comprising an open structure in a form of a net comprising a spun yarn comprising a blend of gel-forming filaments or fibres and textile fibres, the net having a pore or mesh size from 0.5 mm.sup.2 to 5.0 mm.sup.2 that allows exudate to flow through the net, wherein the yarn has a linear density of 20 tex to 40 tex, wherein the yarn has a dry tensile strength of at least 10 cN/tex, and wherein the blend of gel-forming filaments or fibres and textile fibres includes only one type of gel-forming filaments or fibres; a source of vacuum situated to be separated from a wound bed by the wound dressing; and a vacuum sealing layer separate from the wound dressing that covers the wound dressing and is adapted to retain relative vacuum in the wound dressing, wherein the pore or mesh size of the net facilitates application of strain to tissue through pores or mesh of the net to stimulate tissue growth when a vacuum of at least 0.4 atm is applied by the source of vacuum to the wound dressing such that the relative vacuum is retained in the wound dressing by the vacuum sealing layer.

12. A device as claimed in claim 11 wherein the net is knitted, woven, or embroidered.

13. A device as claimed in claim 11 wherein the yarn comprises 30% to 100% by weight gel-forming filaments or fibres.

14. A device as claimed in claim 11 wherein the net comprises 50% to 100% by weight gel-forming filaments or fibres.

15. The device of claim 11 wherein the yarn has a dry tensile strength from 10 cN/tex to 40 cN/tex.

16. The device of claim 11 wherein the spun yarn comprises a blend of the gel-forming filaments or fibres and the textile fibres in a ratio of 60:40 to 70:30.

17. The device of claim 11, wherein the textile fibers have an absorbency of between 5 g/g and 10 g/g as measured by the free swell method.

18. A wound dressing comprising a wound contact layer comprising an open structure in a form of a net comprising a spun yarn comprising a blend of gel-forming filaments or fibres and textile fibres, the net having a pore or mesh size from 0.5 mm.sup.2 to 5.0 mm.sup.2 that allows exudate to flow through the net, wherein the yarn has a linear density of 20 tex to 40 tex, wherein the yarn has a dry tensile strength of at least 10 cN/tex, and wherein the blend of gel-forming filaments or fibres and textile fibres includes only one type of gel-forming filaments or fibres.

19. The wound dressing of claim 18 wherein the yarn has a dry tensile strength from 10 cN/tex to 40 cN/tex.

20. The wound dressing of claim 18, wherein the pore or mesh size of the net facilitates application of strain to tissue through pores or mesh of the net to stimulate tissue growth when a vacuum of at least 0.4 atm is applied by a vacuum source to the wound dressing such that a relative vacuum is retained in the wound dressing.

Description

(1) Preferred embodiments of the invention are illustrated in the drawings in which:

(2) FIG. 1 is a graph showing tensile strengths for yarns according to the invention;

(3) FIG. 2 shows open structures produced from a yarn comprising gel forming fibres in a relaxed, slightly stretched out and wet and slightly stretched out state;

(4) FIG. 3a shows a fabric knitted using Tencel warps and weft insertion of a yarn according to the invention in both dray and wet states;

(5) FIG. 3b shows the locking in of one yarn by another for the fabrics in FIG. 3a;

(6) FIG. 4 shows an open structure produced by embroidering a textile yarn on a film, (a) showing the embroidered two layered structure on a film, (b) showing the converted dry structure and (c) showing that structure wet;

(7) FIG. 5 shows a locked in a warp knitted structure produced using HF-2011/250;

(8) FIG. 6 shows a microscope image of FIG. 5 showing connecting yarns forming stitches within the pillar stitch;

(9) FIG. 7 shows a converted woven structure in a dry state;

(10) FIG. 8 shows the structure from FIG. 7 but wet.

(11) The invention is illustrated by the following examples.

EXAMPLE 1

(12) Spinning Yarn from Staple Gel-Forming Fibres

(13) Lyocell fibres and carboxymethyl cellulose staple fibres in blends of 50:50, 60:40 and 70:30 CMC:Lyocell were made by carding on a Trutzschler cotton card and spinning the resulting sliver at a twist of 650 turns/meter.

EXAMPLE 2

(14) Converting a Textile Yarn to a Gel-Forming Yarn

(15) Yarns were converted in the laboratory using a mini kier. In both trials, staple and filament lyocell yarns were converted. The yarns used for the conversion were staple 33 Tex Tencel®; HF-2011/090; and 20 Tex filament lyocell batches HF-2011/051 (trial 1) and HF-2011/125 (trial 2). Tencel® is a Lenzing owned, trademarked brand of lyocell and the Tencel® yarn used was a spun staple yarn. The filament lyocell was supplied by Acelon chemicals and Fiber Corporation (Taiwan) via Offtree Ltd.

(16) The advantages of converting a yarn are that complete cones of yarn could potentially be converted in one relatively simple process, and the processing of gelling fibres is avoided, thus reducing the number of processing steps required and damage to the fibres.

(17) Trial 1—Yarn Wrapped Around Kier Core

(18) In this trial, Tencel® yarn was tightly wrapped around the perforated core of the kier using an electric drill to rotate the core and pull the yarn from the packages for speed. This meant that the yarn was wrapped tightly around the core under tension.

(19) The yarn was converted by a process as described in WO 00/01425 in which carboxymethylation was carried out by pumping fluid through the kier and therefore the cellulosic materials at 65 C. for 90 minutes. The reaction fluid was a solution of an alkali (typically sodium hydroxide) and sodium monochloroacetate in industrial denatured alcohol. After the reaction time, the reaction was neutralised with acid and washed before being dried in a laboratory oven for 1 hour at 40 C.

(20) The conversion was successful and both staple and filament gelling yarns were produced; HF-2011/103 and HF-2011/105 respectively. Due to the tight and uneven wrapping of the staple yarn around the core, it had to be removed using a scalpel which left multiple short lengths (approximately 14 cm) of the converted yarn.

(21) Trial 2—Small Yarn Hanks

(22) The aim of the second trial was to produce longer lengths of converted yarns for testing hence a small hank was made of each the staple and filament lyocell yarns by hand and these were placed between layers of fabric for the conversion.

(23) The yarn was converted by placing the hanks in a kier and converting to form a gel-forming fibre yarn as described above for Trial 1.

(24) The conversion was successful and both staple and filament gelling yarns were produced; HF-2011/146 and HF-2011/147 respectively.

(25) Yarn Summary

(26) TABLE-US-00001 Sample HF# Gelling Yarns 50:50 Spun staple gelling yarn HF-2011/001 60:40 Spun staple gelling yarn HF-2011/088 70:30 Spun staple gelling yarn HF-2011/108 Converted staple yarn (trial 1) HF-2011/103 Converted filament yarn (trial 1) HF-2011/105 Converted staple yarn (trial 2) HF-2011/146 Converted filament yarn (trial 2) HF-2011/147 Non-Gelling Yarns Staple Tencel ® HF-2011/090 Filament lyocell (sample) HF-2011/051 Filament lyocell (bulk) HF-2011/125
Results from Examples 1 and 2

(27) With the exception of HF-2011/051, all of the yarns were tested for wet and dry tensile strength. Adaptations were made to the standard method BS EN ISO 2062:2009; “Textiles—Yarns from packages: Determination of single-end breaking force and elongation at break using constant rate of extension (CRE) tester”. A Zwick tensile testing machine was used with a gauge length of 100 mm. The test uses a 100N or 20N liad cell to exert a constant rate of extension on the yarn until the breaking point is reached. Wet tensile testing was measured by wetting the samples with 0.2 ml of solution A in the central 3 to 4 cm of each yarn and leaving for 1 minute. The wetted sample was then placed in the jaws of the Zwick and clamped shut. Tensile strength was tested as the yarns produced need to be strong enough to withstand the tensions and forces applied during knitting, weaving and embroidery.

(28) Tensile Strength

(29) The results showed that all of the yarns were stronger when they were dry than when they were wet, with HF-2011/108, the 70:30 gelling yarn, showing the largest proportional strength decrease.

(30) Of the yarns tested, HF-2011/108 was the weakest yarn both when wet and dry with tensile strengths of 12.4 and 3.4 cN/Tex respectively, despite containing 30% lyocell fibres. As this was the weakest yarn, but it was successfully weft knitted; HF-2011/120 and woven; HF-2011/169 into fabrics, it is believed that all of the other yarns would also be strong enough to be converted into fabrics.

(31) Both approaches successfully produced gelling yarns.

EXAMPLE 3

(32) Producing Open Structures from Gel-Forming Yarn

(33) A yarn was produced with a 2/12 s worsted count consisting of 60% CMC fibres and 40% viscose fibres, each with a staple length of ˜40 mm and the fibres were blended at the fibre stage. The yarn was produced using a worsted system and two 12 count strands were plied together. When dry, the yarn felt soft and the plying was clear as the two strands wrapped around each other. On wetting with Solution A, the yarn gelled and swelled to form a thicker yarn, and the plying became more pronounced.

(34) A sample was made using this yarn on a warp knitting/stitch bonding machine and was hydrated with Solution A.

(35) The sample structure was knitted with Tencel warp yarns and gelling yarn wefts in a net-like arrangement, which is especially visible when the structure is opened by gentle stretching, as shown in FIG. 2. On wetting the structure gels slightly and feels wet but it holds its open shape well.

EXAMPLE 4

(36) A yarn comprising gel forming fibres was produced by the method of example 3. Using this yarn a fabric was knitted using Tencel warps and gelling yarn weft insertion. The weft yarns were inserted in such a way that they became locked in due to the pattern of knitting. This material has the weft yarn path notation of 0-1/1-1/1-2/2-3/3-2/2-1/1-2//. The material felt quite thin and when wet, it gels but seems to hold fluid on its surface.

EXAMPLE 5

(37) Producing Open Structures from a Textile Yarn

(38) Using a Tajima TMEX-C1201 embroidery machine fabrics were produced on a PVA film from lyocell thread (on the bobbin and as the top thread). Thread=Gütermann 120 Tex lyocell thread from Tony Slade (T.S. Sewing Supplies) Software=Wilcom ES Programme name=honeycomb Number of stitches=12,369 per 2 layers Backing film=Soluble PVA film Speed used=1200 rpm

(39) The film was removed by washing in warm tap water in a sink using lots of agitation until the film looked to have been removed. The samples were air dried on the bench The fabrics were converted by a process as described in WO 00/01425 and detailed in Example 2.

EXAMPLE 6

(40) Warp Knitting to Produce a Locked in Structure.

(41) To produce a fully locked in structure, a warp knitted fabric without any weft inlays is preferred. In the following example (FIG. 5) a fabric has been formed from a set of 4 pillar stitches, the yarn then underlaps to the adjacent set of pillar stitches and continues to form pillar stitches on this needle before underlapping back to the initial needle. Eg a typical yarn path notation for the simplest type of this fabric would be 0-2/2-1/2-1/2-0/0-1/0-1//. By using 2 sets of warp ends within one set of chain stitch alternating the yarn used for each stitch stops the structure being able to be unravelled easily. This structure could be complicated by using more needles within the design or using addition warp beams to underlap in opposite directions. The fabric produced is a locked in structure as the each knitted stitch is secured by a knitted stitch of another yarn end stopping the structure from unravelling and the threads going perpendicular to the pillar stitches also form loops within the structure, as shown in FIG. 6, ensuring that these are locked in.

EXAMPLE 7

(42) Weaving

(43) Open plain weave structures have been produced on a Northrop loom, using a gelling yarn previously described, HF-2011/108 to produce fabric HF-2011/169. And by using a Tencel spun yarn HF-2011/090 and converting at the fabric stage, to produce fabric HF-2011/136. The structure uses a warp density of 7.8 ends/cm and a weft density of 5.5 picks/cm.

(44) FIG. 7 shows HF-2011/136, the sample converted at the fabric stage using the lab conversion process as previously described. This produced an open structure that is thin and flexible in its dry form. When wet this structure is less stable and bunches, but forms a gelled structure as shown in FIG. 8.

EXAMPLE 8

(45) To produce a locked in woven sample, leno weaving is used. Leno weaving is a form of weaving in which warp threads are made to cross one another between the picks. As the warp yarns cross one another they are able to hold the weft yarns in place so little movement occurs within the structure. When the sample is cut theoretically the yarns should not be able to be removed as the free end is held in place by multiple warps within the rest of the structure. The leno can be applied to all or some of the yarns within the fabric.