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Title:
VACUUM WOUND DRESSINGS
Document Type and Number:
WIPO Patent Application WO/2006/005939
Kind Code:
A1
Abstract:
A wound dressing for vacuum therapy comprising: a cover configured for placement over the wound to provide a sealed environment around the wound and adapted for communication with a source of vacuum, and a screen structure for placement between the cover and the wound, wherein the screen structure comprises a bundle of strandular material. Also provided are kits and systems for making and using wound dressings according to the invention.

Inventors:
Lowing, Paul Howard (1 Broomfield Street, Keighley, West Yorkshire BD21 2BZ, GB)
Del Bono, Michelle (7 Priory Way, Barnoldswick BB18 5HJ, GB)
Application Number:
PCT/GB2005/002726
Publication Date:
January 19, 2006
Filing Date:
July 11, 2005
Export Citation:
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Assignee:
ETHICON, INC. (US Route 22 West, Somerville, NJ, 08876, US)
Lowing, Paul Howard (1 Broomfield Street, Keighley, West Yorkshire BD21 2BZ, GB)
Del Bono, Michelle (7 Priory Way, Barnoldswick BB18 5HJ, GB)
International Classes:
A61F13/00; A61M1/00; A61M27/00; (IPC1-7): A61F13/00; A61M1/00; A61M27/00
Attorney, Agent or Firm:
James, Anthony Christopher W. P. (Carpmaels & Ransford, 43-45 Bloomsbury Square, London WC1A 2RA, GB)
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Claims:
CLAIMS
1. A wound dressing for vacuum therapy comprising: a cover configured for placement over the wound to provide a sealed environment around the wound and adapted for communication with a source of vacuum, and a screen structure for placement between the cover and the wound, wherein the screen structure comprises a bundle of strandular material.
2. A wound dressing according to claim 1, wherein the cover is semirigid and convex.
3. A wound dressing according to any preceding claim, further comprising tubing for connecting the cover to the vacuum source.
4. A wound dressing according to any preceding claim, wherein the screen structure consists essentially of the bundle of strandular material.
5. A wound dressing according to any preceding claim, wherein the bundle of strandular material can be removed from the wound in one piece.
6. A wound dressing according to any preceding claim, wherein the bundle is formed from a single strand of strandular material.
7. A wound dressing according to any preceding claim, wherein the bundle comprises a randomly entangled bundle of strandular material.
8. A wound dressing according to any preceding claim, wherein the bundle comprises a plurality of mutually entangled strands of strandular material.
9. A wound dressing according to any preceding claim, wherein the bundle comprises a plurality of strands of the strandular material that are joined together.
10. A wound dressing according to any preceding claim, wherein the strandular material is hydrophilic.
11. A wound dressing according to any preceding claim, wherein the strandular material is bioabsorbable.
12. A wound dressing according to any preceding claim, wherein the strandular material has a substantially uniform cross section and composition along its length.
13. A wound dressing according to any preceding claim, wherein the strandular material comprises, or consists essentially of, a polymeric foam material.
14. A wound dressing according to any preceding claim, wherein the strandular material comprises, or consists essentially of, a textile filament, thread or string.
15. A wound dressing according to any preceding claim, wherein the strandular material comprises, or consists essentially of, a plurality of spacefilling bodies linked by one or more flexible linear bodies.
16. A wound dressing according to claim 15, wherein the spacefilling bodies comprise a polymeric foam or a gel.
17. A wound dressing according to claim 15 or 16, wherein the one or more flexible bodies comprise a filament, a thread or a string.
18. A wound dressing according to any preceding claim, wherein the screen comprises, or consists essentially of, a plurality of elongate absorbent flexible filaments radiating from a core region.
19. A wound dressing according to claim 18, wherein at least ten filaments radiate from the core region, more preferably at least 50 such filaments and still more preferably at least 100 such filaments.
20. A kit for assembly into a wound dressing according to claim 1, said kit comprising: a cover configured for placement over the wound to provide a sealed environment around the wound and adapted for communication with a source of vacuum, and a screen structure for placement between the cover and the wound, wherein the screen structure comprises a bundle of strandular material, or a length of strandular material suitable for forming into a bundle.
21. A kit for assembly into a wound dressing according to claim 1, said kit comprising: a cover configured for placement over the wound to provide a sealed environment around the wound and adapted for communication with a source of vacuum, and a pressurized can containing a medically acceptable synthetic resin dissolved in a mixture of a solvent and a pressurized gas propellant, suitably also including a plasticizer for the resin, whereby as the composition is expelled from the can, it forms a thin string of the synthetic resin in expanded form.
22. A wound treatment system comprising a wound dressing according to claim 1 and a vacuum source for providing said vacuum treatment to a wound.
23. The system of claim 21, wherein the vacuum source is programmed to supply vacuum intermittently to the wound treatment space.
24. The system of claim 23, wherein the step of applying a vacuum includes lowering the pressure in the wound treatment space to an absolute value of from about 0.1 bar to about 0.9bar, preferably to an absolute value of from about 0.75bar to about 0.85bar.
25. A method for promoting wound healing comprising the steps of : applying a wound dressing according to claim 1 to a wound in substantially airtight fashion, connecting the cover to a vacuum source, and creating a vacuum within the wound treatment space.
26. The method of claim 25, wherein the vacuum is applied intermittently to the wound treatment space.
27. The method of claim 25, wherein the step of applying a vacuum includes lowering the pressure in the wound treatment space to an absolute value of from about 0.1 bar to about 0.9bar, preferably to an absolute value of from about 0.75bar to about 0.85bar.
Description:
VACUUM WOUND DRESSINGS

The present invention relates to improved wound dressings for use in vacuum therapy of wounds. The invention also relates to wound treatment systems incorporating such dressings, and to kits for the manufacture of such dressings.

EP-A-0620720 and EP-A-0688189 describe vacuum treatment for accelerating wound healing. They describe the use of a cover for sealing about the outer perimeter of the wound and under which a vacuum is established to act on the wound surface. This vacuum applied to the wound surface accelerates healing of chronic wounds. The vacuum is applied for a sufficient duration and magnitude to promote tissue migration in order to facilitate the closure of the wound. Suitable vacuum is between about 0.1 and 0.99 atmospheres. The vacuum can be substantially continuous, wherein the pressure is relieved only to change the dressing on the wound. Alternatively, the patent teaches cyclic application of vacuum in alternating periods of application and nonapplication. In a preferred embodiment, vacuum is applied in 5 minute periods of application and non- application. A screen of open cell foam material is provided under the cover to provide the space in which the vacuum is formed and to reduce tissue ingrowth. The foam-based screen are insufficiently conformable to fit every deep wound, unless they are cut into shape. Furthermore, such structures can be relatively difficult to remove from a deep wound after use without causing further trauma.

WO01/89431 describes vacuum wound dressings further comprising a layer of a collagen scaffold material to promote wound healing. The preferred collagen material is small intestine submucosa (SIS).

WO2004/037334 describes an apparatus for cleansing wounds in which irrigant fluid from a reservoir is supplied to a conformable wound dressing, and wound exudate from the dressing is recirculated through a flow path which passes through the dressing. The apparatus further comprises a means, located outside the dressing, for cleansing the wound fluid before it is recirculated back to the dressing. The cleansing means removes materials deleterious to wound healing. A number of different screen configurations for the vacuum dressing are described. The present invention provides a wound dressing for vacuum therapy comprising: a cover configured for placement over the wound to provide a sealed environment around the wound and adapted for communication with a source of vacuum, and a screen structure for placement between the cover and the wound, wherein the screen structure comprises a bundle of strandular material.

The cover may be any one of the cover types described in the aforementioned patent applications EP-A-0620720, EP-A-0688189, WOO 1/89431, and WO2004/037334 relating to vacuum wound treatment, the entire contents of which are incorporated herein by reference. Briefly, the cover should be formed from substantially gas-impermeable material in order to be able to maintain a reduced pressure in the space over the wound being treated. Thermoplastic sheet materials of various types are suitable. The cover may suitably be substantially convex, and/or it may suitably be made of a semi-rigid material in order to help support the vacuum without collapsing. The cover may be provided with a layer of a medically acceptable pressure-sensitive adhesive on at least the periphery thereof for attachment of the cover to the skin around the wound to be treated. In other embodiments, the adhesive may be omitted and the cover sheet may be attached to the wound by suction.

Suitably, the wound dressing according to the present invention further comprises tubing for connecting the cover to the vacuum source. The connection is usually made through an aperture in the cover. The tubing may extend only outwardly of the cover, or it may extend inwardly through the cover into the vacuum wound treatment space. In these embodiments, the tubing may be connected to a fluid collection manifold located inside the cover sheet. The term "fluid collection manifold" refers to a hollow body having a plurality of apertures for collecting fluid from a plurality of locations under the cover sheet. The manifold may for example comprise an apertured envelope or a perforated spiral-wound tube. Other suitable fluid collection manifolds are described in WO2004/037334. The tubing may further be provided with a valve for controlling the application of vacuum. In certain embodiments the valve may be closed to maintain a desired atmosphere or pressure in the wound treatment space, or it may be a one-way or non-return valve to maintain reduced pressure over the wound after removal of the vacuum source. The tubing and/or the cover sheet may be provided with a suitable coupling for attachment of a vacuum source.

The wound dressing of the present invention makes use of a screen structure that comprises, or in some cases consists essentially of, a bundle of strandular material. The term "strandular material" refers to materials formed in flexible strings or strands that can be linked or entangled to form a resilient, fluid-permeable bundle under the cover to function as the screen means for the vacuum dressing. In certain embodiments, the bundle comprises a randomly entangled bundle of strandular material. The bundle may comprise a plurality of mutually entangled or joined strands of strandular material, or it may comprise only a single strand that has been formed into a bundle. Suitably, at least one of the strands making up the bundle has a length of at least 5cm, for example at least about lOcnij or at least about 20cm. The length of each strand in the bundle is normally at least 10 times its mean width, and more preferably at least 20 times its mean width.

The bundle of strandular material is highly conformable to different wound cavities, and easy to remove from the wound by grasping one strand of the bundle. Preferably, the strands are all entangled or joined together to the extent that the bundle of strandular material can be removed from the wound in one piece. The wound dressing can readily be tailored to different wound cavity sizes by cutting the strands to an appropriate length before forming the bundle.

The strandular material may be made from any medically acceptable substance or substances. Suitably, the strandular material is hydrophilic. In certain embodiments, the strandular material may be bioabsorbable. In certain embodiments the strandular material comprises, or consists essentially of, a polymeric foam material. Suitable materials for the manufacture of the strands include hydrophilic polyurethane foams such as those described in EP-A-0541391. Further details concerning suitable strandular materials are described below.

In certain embodiments the bundle may contain a medicament. Suitable medicaments include antimicrobials, growth factors, steroids, antifungal agents, and pain relieving agents. Suitable antimicrobials include antibiotics, silver salts, povidone iodine and chlorhexidine. Preferred amounts of the antimicrobials are from 0.01 to 100 mg per gram of the strands on a dry weight basis, more preferably from 0.1 to 10 mg/g.

In certain embodiments the strands may comprise a therapeutically active biopolymer such as collagen, an alginate or hyaluronic acid (to promote wound healing), or oxidized regenerated cellulose (a haemostat).

Strine

In the simplest embodiments of the wound dressing according to the present invention, the strandular material has a substantially uniform cross section and composition along its length. In these embodiments, the screen resembles a simple filamentary bundle, preferably formed from a single filament. The strandular material may for example comprise, or consist essentially of, textile filaments, threads or strings, microporous sponge strands, polymer foam strands, hollow polymer tubes, solid polymer strands, elastomer strands, or combinations thereof. Suitable materials include textile threads made up of multiple hydrophilic textile fibers such as viscose, and filaments of insoluble alginates such as calcium alginate. Preferably, short (staple) textile fibers are avoided because they may shed from the bundle into the wound. The textile filaments may be melt bonded to increase their integrity in use. The filaments may be coated with a hydrogel or other hydrophilic and wound-compatible coating.

The filaments should be flexible to provide the article with excellent conformability. The filaments may be absorbent, that is to say they may absorb a substantial amount of physiological saline at ambient temperature. The filaments must be biologically compatible in vivo. That is to say, the filaments should be non-toxic, non-antigenic and preferably not shed particles into the wound. The filaments may be coated with a hydrogel or other hydrophilic and wound-compatible coating.

In certain embodiments, the filaments may be bioabsorbable in vivo. Such filaments include collagen filaments, spun polylactide/polyglycolide filaments, and filaments of oxidised regenerated cellulose (ORC). For example, threads of ORC formed by oxidation of viscose rayon threads with dinitrogen tetroxide may be used. Beads on a String

In certain embodiments, the strandular material forming the screen structure comprises, or may consist essentially of, a plurality of space filling bodies linked by one or more flexible linear bodies.

The use of a plurality of space filling bodies enables wounds to be filled by shorter lengths of strandular material, while maintaining high conformability to any wound cavity shape or size. The flexible linkage enables the dressing to take up any shape, but also enables the dressing to be removed from the cavity easily just by pulling on any part of the dressing.

Preferably, the plurality of space filling bodies comprises at least three space filling bodies, more preferably at least five, and most preferably at least eight space filling bodies. In certain preferred embodiments, the dressing may be manufactured in lengths of 10, 20, 50, 100 or even more space filling bodies, in which case the dressing would normally be cut to size by the care giver before application to the wound. This enables different lengths of the same screen material to be used for a variety of differently sized wounds without wastage.

For optimum comfort and conformability the space filling bodies preferably each have a volume of from 0.001 to 10 cm , more preferably from 0.01 to 1 cm . Preferably, the space filling bodies have an aspect ratio (ratio of the largest dimension to the smallest dimension) no greater than 5, preferably no greater than 3, and more preferably no greater than 2. In certain embodiments the space filling bodies are substantially round.

The space filling bodies may be made of any material that is acceptable for application to a wound, including solid or hollow polymeric bodies, woven and nonwoven textile materials, polymeric foam materials (both open-cell and closed-cell), such as polyurethane or polyester foams, biopolymers such as alginates and cellulose, and materials that are fully absorbable in vivo such as collagen sponges. Preferably, the materials are not fully absorbable in vivo, since it is a particular advantage of the present invention that it allows easy removal of screen after use. It will be appreciated that the space filling bodies may comprise any combination of textile filaments, hydrogel and/or sponge.

The flexible linear bodies that link the space-filling bodies may be in the form of a flexible strip or sheet. However, for maximum conformability of the wound dressing the one or more flexible bodies comprise a filament, a thread or a string. Preferably, the flexible bodies consist of a single linear filament, thread or string. Preferably, the space filling bodies are spaced along the filament, thread or string. Preferably, the space filling bodies are spaced at uniform intervals along the filament, thread or string. Preferably, the mean length of filament, thread or string between the space filling bodies is from 1 to 40 mm, more preferably from 5 to 20 mm. The dressing then preferably takes the form of a string of beads.

Suitable materials for the filament, thread or string are preferably highly flexible, medically acceptable and non-biodegradable. Nylon thread is preferred. Any of the flexible strandular materials described above for use in the dressings of the present invention may be suitable for linking together the space-filling bodies.

The flexible body is suitably attached to the space filling bodies by knotting, adhesion or melt bonding. Preferably, the filament, thread or string extends through the space filling bodies, more preferably near the center of the space filling bodies, in order to provide the most secure attachment of the space filling bodies to the filament, thread or string.

Suitable methods of making strandular materials for use in these embodiments of the invention can be found in WO-A-03000302, the entire content of which is incorporated herein by reference.

Spikev Ball

In certain embodiments, the screen comprises or consists essentially of a plurality of elongate absorbent flexible filaments radiating from a core region. Any of the flexible strandular materials described above for use in the dressings of the present invention may be suitable for use as the elongate absorbent flexible filaments in these embodiments of the invetnion.

Preferably, at least ten filaments radiate from the core region, more preferably at least 50 such filaments and still more preferably at least 100 such filaments. Preferably, the filaments radiate from the core region in plural angularly offset planes. This provides the article with improved space filling properties.

Preferably, the flexible filaments are free to flex outside the core region. That is to say, the filaments are not tied or embedded in a matrix outside the core region. This allows the filaments to bend freely to assume the shape of any cavity into which the article is inserted. It also enables the threads to swell as necessary to absorb wound fluid. It also makes it easy to remove the bundle once it is saturated with wound fluid, by grasping a free end of any thread. Furthermore, the bundle is adapted to any size of wound cavity, since it is straightforward to insert and remove more than one article into larger cavities.

Preferably, the filaments radiate a distance of lmm to 50mm from the core. More preferably, substantially all of the filaments radiate a substantially equal distance from the core, whereby the article has a substantially spherical appearance in the absence of external forces. Preferably, the dry cross-sectional area of said filaments is in the range of from 0.1 to 4mm , and more preferably it is in the range of from 0.2 to 1.00mm . Preferably, the ratio of length to maximum diameter of the filaments outside the core is in the range of from 10:1 to 100:1. Preferably, the filaments have a liquid absorbency for physiological saline of at least 2g/g at 37C, more preferably at least 5g/g.

The bundles for use in these embodiments of the invention may be made by the process described in EP-A-0295114, the entire content of which is incorporated herein by reference. Briefly, three continuous lengths of textile filaments are each wound in a pattern of reverse bend loops, and are then stretched as loops. Three such loops are then stretched orthogonally A nylon tie is used to secure the loops together, and the six ends of the loops are then cut, and the loops released to form the bundle. An alternative method of forming for use in these embodiments of the invention may be found in WO-A-0147459, the entire content of which is incorporated herein by reference.

Kits, Systems, etc.

In another aspect, the present invention provides a kit for assembly into a wound dressing according to the present invention, said kit comprising: a cover configured for placement over the wound to provide a sealed environment around the wound and adapted for communication with a source of vacuum, and a screen for placement between the cover and the wound, wherein the screen comprises a bundle of strandular material, or a length of strandular material suitable for forming into a bundle.

The cover and the screen may be packaged together, or separately. One or both of the cover and the screen may be sterile and packaged in a microorganism-impermeable container.

The kit would comprise the cover sheet, optionally the vacuum tube and adhesive layer (with cover sheet), packaged separately or together, for assembly at the time of use. The kit would also comprise either the screen bundle already formed, or a suitable precursor of the screen bundle. For example, the already-formed screen bundle could be a core having filaments radiating therefrom as described above, for example made as described in WO- A-0147459 or EP-A-0295114.

One suitable precursor of the screen bundle is a roll of the strandular material that could be cut into a suitable length (or lengths) for entanglement to form the bundle. This has the advantage that the size of the bundle can be tailored to the dimensions of the wound cavity.

Another suitable precursor would be a pressurized can containing a medically acceptable synthetic resin dissolved in a mixture of a solvent and a pressurized gas propellant, suitably also including a plasticizer for the resin, for example as described above and in US-A- 3705669, the entire content of which is incorporated herein by reference. Such a composition is preferably in the form of a substantially single phase liquid for best expulsion from a pressurized can. As the composition is expelled, it remains in the form of a thin string because of the structural properties of the plasticized resin. Because of the very high vapour pressure of the solvent and propellant, a somewhat tough skin quickly forms on the string as these materials evaporate. The resin is still, however, plastically deformable and as the propellant and solvent within the skin vaporize, the string foams and expands to a few times its original diameter. The skin formed is also somewhat elastic so that as the solvent and propellant diffuse through the skin it collapses again to a string having less than its maximum diameter. In this way, the bundle of strandular material can simply be sprayed into the wound cavity as necessary.

Yet another suitable precursor of the screen bundle is a length of any one of the strandular materials as hereinbefore described encapsulated between two sheets of microorganism- impermeable polymer film material. This film material functions as the primary packaging for the strandular material, and may remove any need for a secondary outer packaging envelope. It also enables the strandular material screen structure to be made, stored and used in lengths or rolls. The strand (or strands) may be encapsulated between the two sheets of film material by vacuum encapsulation, heat shrinkage, or preferably by forming the strandular structure in situ between the two plastic films as described in more detail below. The plastic films may be opposite sides of a plastics film tube, or they may be a single sheet folded over and bonded along a margin, or they may be two separate sheets bonded along opposed margins. The bonding between the sheets may be melt bonding or permanent adhesive, in which case the screen structure is released from the package by slitting or cutting the plastic films. Alternatively, the plastic films may be bonded together at least in party by means of a releasable adhesive (e.g. a pressure-sensitive adhesive contacting a silicone release layer on the opposite plastics sheet), so that the package can be opened by peeling apart the films. It may also be advantageous to provide the internal surfaces of the polymer films that contact the strands with non-stick or release coatings to assist removal of the strands from the package.

Suitably, the strandular material for forming the screen structure may be encapsulated between two opposed sheets of microorganism-impermeable plastic sheet material wherein the opposed sheets contact the strands to form a microorganism-impermeable barrier around the circumference of the strands in at least a region of the strands. Preferably, the opposed sheets contact the strands to form a microorganism-impermeable barrier around the circumference of the strands substantially along the whole length of the screen structure. In other embodiments the opposed sheets contact the strands to form a microorganism-impermeable barrier around the circumference of the strands at a plurality of intervals along the length of the screen structure.

Preferably, the plastic films are bonded together at least in part by means of a releasable adhesive so that the package can be opened by peeling apart the films. Preferably, an internal surface of the polymer films that contacts the strands comprises a non-stick or release material to assist removal of the screen structure from the package.

In certain of these embodiments of the screen precursor, the strands comprises a plurality of space filling bodies linked by one or more flexible bodies as hereinbefore described. Preferably, the absorbent body has been formed in situ between the two sheets of plastic material, for example by injecting a foamable polyurethane precursor composition into a tubular cavity between the sheets. As already noted, this aspect of the invention provides the advantage that the strandular material can be manufactured in indefinite lengths, for example 50cm or Im or 10m or more, for example in rolls, without any need for sterile secondary packaging. The lengths of rolls are straightforward to use, and lengths are simply cut to provide a sufficient volume of strandular material to pack any given wound. The fact that the packaging sheet contacts the strandular material at least at intervals along the length of the material allows lengths to be cut from the material without the remainder of the material becoming contaminated, and still without the need for secondary packaging.

These precursors of the screen bundle may be made by a method comprising the steps of: providing a two sheets of microorganism impermeable polymer film in face to face relationship with a cavity or cavities therebetween; introducing a fluid precursor of a solid wound dressing material into said cavity or cavities; allowing the fluid precursor to set in the cavity or cavities to provide the packaged strandular material. The cavities may bne linked by a suitable flexible linker, for example a thread, as hereinbefore described. Suitably, the precursor comprises an isocyanate capped polyurethane prepolymer as hereinbefore described. Further details of strandular materials for use as precursors of the bundles in these embodiments of the invention and methods of manufacture thereof can be found in WO-A-03000302, the entire content of which is incorporated herein by reference. The features of the cover and the screen structure in the kits according to the present invention may suitably be any of the features as hereinbefore described in relation to the first aspect of the invention. The use of a kit allows assembly of the wound dressing by the care giver. A given cover may be combined with a screen structure having the most appropriate therapeutic effect at the time of treatment in order to optimize wound healing.

Preferably the screen structure used in the present invention is sterile, and preferably it is packaged in a microorganism-impermeable container. It may be packaged together with the cover sheet, or separately therefrom.

In another aspect, the present invention provides a wound treatment system comprising a wound dressing according to the present invention as hereinbefore defined, and a vacuum source for providing said vacuum treatment to a wound.

In a further aspect, the present invention provides a method for promoting wound healing in a mammal comprising the steps of : applying a wound dressing according to the present invention over a wound in substantially airtight fashion to define a wound treatment space between the cover and a surface of the wound, connecting the cover to a vacuum source, and creating a vacuum within the wound treatment space.

The term "vacuum" here and elsewhere in the present specification refers to any pressure below ambient atmospheric pressure. Suitably, the step of applying a vacuum includes lowering the pressure in the wound treatment space to an absolute value of from about O.lbar to about 0.95bar, suitably from about 0.5 bar to about 0.9 bar and typically to an absolute value of from about 0.75bar to about 0.85bar. The vacuum may be static or dynamic. The vacuum may be applied continuously or intermittently to the wound treatment space, substantially as hereinbefore described.

It will be appreciated that any feature or embodiment of the present invention that is described in relation to any one embodiment is equally applicable to any other embodiment of the invention mutatis mutandis. Specific embodiments of the present invention will now be discussed further, by way of example, with reference to the accompany drawings, in which:

Figure 1 shows a schematic longitudinal cross-section through a wound dressing according to the first embodiment of the present invention; and

Figure 2 shows a schematic longitudinal cross-section through a wound dressing according to a second embodiment of the present invention;

Referring to Figure 1, the wound dressing 1 according to the first embodiment comprises a cover sheet 2 formed of substantially impermeable, thermoformed thermoplastic. A tube 6 passes through the cover sheet 2, for connection to a source of vacuum. A layer of medically acceptable pressure-sensitive adhesive 3 extends around the periphery of the underside of the cover sheet 2, for attachment of the cover sheet to the skin 4 around the wound 5 being treated. The wound dressing further comprises a screen 7, which in this particular embodiment consists of a core having a large number of filaments of nylon thread radiating therefrom.

The cover sheet 2 and screen bundle 7 are usually packaged separately in two microorganism-impermeable containers, and are each sterilised e.g. by gamma-irradiation. It will be appreciated that the embodiment of Figure 1 could be made up from such a kit at the time of use.

Referring to Fig.2, the dressing 10 according to the second embodiment of the invention comprises a cover 11, and adhesive layer 12 and a vacuum tube 15 generally similar to those of the embodiment of Figure 1. The dressing is attached to the skin 13 around wound 14 in the same way. However, the screen 16 in the embodiment of Figure 2 is formed from a single strand of a closed-cell polyurethane foam that has been randomly- entangled into a bundle. The bundle could also be formed of a plurality of randomly entangled strands of the closed-cell polyurethane foam, or of another filamentary material.

The embodiment of Figure 2 could also be made up from a kit according to the present invention. The kit would comprise the cover 11, tube 15 and adhesive layer 12 (with protective cover sheet), packaged separately or together, for assembly at the time of use. The kit would also comprise either the screen bundle 16 already formed, or a suitable precursor of the screen bundle 16. One suitable precursor would be a roll of the polyurethane foam filament that could be cut into a suitable length or lengths for entanglement to form the bundle. This has the advantage that the size of the bundle can be tailored to the dimensions of the wound cavity. The length of polyyurethane foam filament could be packaged or even cast in-situ between peelable sheets of protective microorganism-impermeable sheet material, as described above. Another suitable precursor would be a pressurized can containing a medically acceptable synthetic resin dissolved in a mixture of a solvent and a pressurized gas propellant, suitably also including a plasticizer for the resin, for example as described above and in US-A-3705669, the entire content of which is incorporated herein by reference.

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