Vacuum assisted wound dressing

Abstract

Apparatus for the application of topical negative pressure therapy to a wound site is described, the apparatus comprising: a wound contacting element for retaining wound exudate fluid therein; a wound covering element that provides a substantially airtight seal over the wound contacting element and wound site; a vacuum connection tube connecting a wound cavity to a vacuum source; and a vacuum source connected to a distal end of the vacuum connection tube.

Claims

1. An apparatus for the application of topical negative pressure therapy to a wound, the apparatus comprising: a wound covering element configured to be positioned over a wound; and a self-coalescing liquid blocking material configured to be positioned in a flow-path between the wound and a vacuum source.

2. The apparatus of claim 1, wherein the wound covering element comprises an aperture.

3. The apparatus of claim 2, further comprising a vacuum connection conduit configured to be connected to the wound covering element.

4. The apparatus of claim 1, wherein the liquid blocking material comprises a valve that closes upon contact with wound exudate and blocks all liquid transport beyond itself away from the wound site, the valve being open prior to contact with wound exudate.

5. The apparatus of claim 1, wherein the wound covering element additionally comprises an adhesive configured for adhering to a portion of skin surrounding the wound.

6. The apparatus of claim 1, wherein the liquid blocking material comprises self-coalescing fibers.

7. The apparatus of claim 2, wherein the liquid blocking material is configured to be positioned at the aperture.

8. The apparatus of claim 1, wherein the wound covering element is substantially impermeable to the flow of liquid, but is substantially permeable to the transmission of water vapor.

9. The apparatus of claim 1, wherein the wound covering element is a transparent polyurethane.

10. The apparatus of claim 1, wherein the wound covering element comprises an absorbent foam.

11. The apparatus of claim 1, wherein the vacuum source is electrically powered.

12. The apparatus of claim 1, wherein the wound covering element and the self-coalescing liquid blocking material are combined into a single element.

13. A method for the application of topical negative pressure therapy to a wound, the method comprising: applying a wound covering element over a wound; and delivering negative pressure to the wound from a source of negative pressure; wherein a self-coalescing liquid blocking material is positioned in a flow-path between the wound and the source of negative pressure.

14. The method of claim 13, wherein the wound covering element comprises an aperture.

15. The method of claim 14, wherein negative pressure is delivered through the aperture.

16. The method of claim 15, wherein negative pressure is delivered through a vacuum connection conduit connected to the wound covering element.

17. The method of claim 13, wherein the source of negative pressure is electrically powered.

18. The method of claim 13, wherein the liquid blocking material comprises self-coalescing fibers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In order that the present invention may be more fully understood examples will now be described by way of illustration only with reference to the accompanying drawings, of which:

(2) FIG. 1 shows a schematic cross section of an embodiment of apparatus according to the present invention and a wound being treated by TNP therapy;

(3) FIGS. 2A to 2C which show the arrangement of FIG. 1 simplified and the progression of saturation of a wound contacting element; and

(4) FIG. 3 illustrates a liquid contact triggered valve.

DETAILED DESCRIPTION OF SOME EXEMPLIFYING EMBODIMENTS

(5) Referring now to the drawings and where the same features are denoted by common reference numerals.

(6) FIG. 1 shows a schematic cross section through a wound 10 having an embodiment of apparatus 12 according to the present invention applied to it for the purpose of TNP therapy of the wound. The wound 10 has a wound contacting element 14 placed in the cavity defined by the wound, the wound contacting element being roughly level with surrounding sound skin 16. A wound covering element 18 is applied over the wound to contact and seal with the surrounding sound skin by means of a layer of pressure sensitive adhesive (not shown) coated onto the skin contacting surface of the wound covering element material. The wound covering element 18 has an aperture 20 in the area above a part of the wound and the wound contacting element 14. A one-way valve 22 is positioned in the aperture 20 to permit fluid in the form of air to be extracted from the wound cavity 24 defined by the wound covering element 18 and the wound 10 itself. A vacuum source 26 in the form, in this example, of a battery powered vacuum pump is connected to the wound cavity by a vacuum connection tube 28 and a cup-shaped connection member 30 having an aperture 32 therein to accept the end of the vacuum connection tube 28. The cup-shaped member 30 has a flange portion 34 which seats onto the upper surface 36 of the wound covering element 18 material and seals therewith. The valve 22 has an orifice 40 which is normally closed due to the resilience of the material from which it is moulded, for example, silicone plastics based material. The orifice 40 is in the form of a slit normally closed by two lips 42, 44 (the shape of the valve orifice may be likened to a flat bladed screwdriver and the valve orifice 40 in FIG. 1 runs normal to the plane of the page). The valve 22 is initially held in and sealed to the wound covering element material 18 by a flange portion 46 bearing against the underside of the wound covering element 18 material and a circular shoulder 48 and recess 50 which is held in the aperture 20. To evacuate the wound cavity 24, the vacuum pump 26 is started and the cup-shaped member 30 placed on the wound covering element material above the valve 22 and the reduction in pressure within the wound cavity 24 causes the cup-shaped member 30 to be sealed securely to the dressing by the excess pressure of the surrounding ambient air. As the vacuum in the wound cavity develops, the wound covering element 18 is pushed down against the wound contacting element 14 by ambient air pressure and the wound contacting element 14 compressed against the wound surface to apply TNP therapy thereto.

(7) Whilst it is perfectly feasible for the lower surface of the flange portion 34 of the cup-shaped member 30 to be adhesively coated and to be so retained on the wound covering element material, in this example retention of the vacuum connection tube 28 to the wound dressing is solely by ambient air pressure as described above. In case the patient wishes to detach the vacuum pump 26 and leave it behind this may simply be achieved by turning off the pump 26 and allowing the vacuum to degrade and removing the cup-shaped connection member 30. In this case the valve 22 is self-sealing prevents access of bacteria and the like to the wound cavity 24.

(8) The valve 22 exemplified above is a miniValve (trade mark) supplied by Mini Valve International. However, this valve is merely exemplary and many other types of suitable valves are available commercially.

(9) For example International Patent Application No PCT/EP2008/063046 discloses a composition which coalesces on hydration and which can be used to provide a valve which closes upon contact with liquid. The application is included fully herein by way of reference but briefly discloses a suitable composition that enables a new physical transformation. The physical transformation in question involves the conversion of a first stable physical geometry into a second stable physical geometry upon hydration, wherein hydration enables the self-coalescence (fusion) of spatially separated elements or surfaces of the first stable physical geometry.

(10) Each geometry is physically stable. Thus, immersion of the first stable physical geometry in excess solution results in conversion to the second stable physical geometry without significant loss of the material mass by dissolution. That is, the second stable geometry is insoluble, or has only very limited solubility, in the excess solution. The second stable physical geometry is, at least substantially, self supporting such that it is able to retain its shape when is excess solution, or when removed therefrom. In typical preferred forms in the second stable physical geometry the material of the invention is a gel or gel like material.

(11) A feature of the composition is the physical homogeneity of the object in both the first and second physical geometries.

(12) The novel transformation is enabled by construction of the object, at least in part, from materials that can exist in physically stable forms in the dry state and the hydrated state. Furthermore, the hydrated state of the material must be sufficiently self-cohesive, even when immersed in excess solvent, to enable fusion to occur. This, we believe, is a property unique to a limited range of states of matter, some of which we prepare to exemplify this invention.

(13) In broad terms the composition of matter when formed into an object of suitable geometry, can self-coalesce upon hydration in a suitable solvent.

(14) According to a first aspect of the composition there is provided a high molecular mass cationic polymer material having a first state which includes at least two separate but adjacent surfaces and a second state in which the polymer consists of a homogeneous body, wherein the material transitions from the first state to the second state upon hydration.

(15) Thus, on hydration the material expands and the surfaces merge or coalesce to result in a body of self supporting material, typically a gel or gel-like material, which has uniform properties in any dimension. Surfaces and other boundaries within the body of material are absent. Furthermore the body of material is insoluble, or at least of limited solubility in the hydrating solvent and is able to retain its physical geometry under leading (for example gravity).

(16) The term ‘suitable geometry’ is taken to describe an arrangement where separate (for example spatially separate, but not necessarily physically separate) elements or surfaces of the object are sufficiently proximate to enable coalescence upon hydration-induced expansion.

(17) The term ‘suitable solvent’ is taken to describe a fluid (liquid or gas) that can be absorbed be the object, causing expansion and a change in the physical properties of the object (e.g. surface energy). The suitable solvent is typically and preferably an aqueous medium.

(18) The term ‘self-coalesce’ is taken to describe the transformation of two or more spatially separated physically homogeneous elements into a single physically homogeneous element or of fusion of previously spatially separated surfaces of the same element.

(19) Suitable compositions of matter from which objects can be formed are those comprised, entirely or in part, of high average molecular weight cationic polymers including zwitterionic (carrying both anionic and cationic charge) polymers with a cationic charge bias. The cationic polymer may be, or may be a derivative of, a synthetic or a naturally occurring polymer. Preferably, the cationic polymer is one carrying amine functionality. More preferably, the cationic polymer is a polysaccharide. More preferably still, the cationic polymer is chitosan or a derivative of chitosan. The chitosan may be derived from any source, marine or fungal, and is preferably of a weight average molecular weight (Mw) exceeding 10 kDa (kilodaltons), more preferably exceeding 100 kDa and most preferably exceeding 200 kDa.

(20) Where the polymer is a derivative of chitosan, it is preferably a carboxylated derivative. More preferably, it is a carboxyalkyl derivative of chitosan. More preferably still, it is a carboxymethyl derivative of chitosan. The carboxymethyl derivative of chitosan is preferably of a weight average molecular weight exceeding 50 kDa, more preferably exceeding 100 kDa, especially exceeding 500 kDa, more especially exceeding 600 kDa and especially 700 kDa or more.

(21) Carboxymethylation is preferably achieved using known reagents: a base and chloroacetic acid or preferably a neutral salt of chloroacetic acid such as sodium chloroacetate. Preferably, the reaction is carried out in a single step: chitosan fibres or (less preferably) particles being immersed in a solution of reagents or vice versa. Suitable reaction solvents include mixtures of an alcohol with water. The alcohol may be any known but is preferably a non-solvent for chitosan and carboxymethylchitosan, for example isopropanol. The base may be any known but is preferably a water-soluble inorganic base such as sodium hydroxide or potassium hydroxide, preferably sodium hydroxide.

(22) According to a second aspect of the composition there is provided a method of preparing high molecular mass carboxymethylchitosan comprising the steps: a. mixing chitosan with a solution of a base and chloroacetic acid, or a neutral salt thereof, dissolved in a reaction solvent comprising a mixture of an alcohol and water; b. allowing the reaction to proceed at ambient temperature for at least 8 hours whilst ensuring adequate exposure of the chitosan to the reaction solvent; c. when the reaction is complete, washing the reaction product in excess alcohol-containing solvent;

(23) wherein the volume (in millilitres) of the reaction solvent is at least 20-times the mass (in grams) of chitosan.

(24) A high molecular mass carboxymethyl chitosan preferably comprises a carboxymethyl chitosan having a mass of at least 500 kDa, more especially at least 600 kDa and especially 700 kDa or more.

(25) In one preferred embodiment the volume of reaction solvent (in millilitres) exceeds the mass of chitosan (in grams) by more than 20 but less than 70-times, more preferably by more than 30-times but less than 40-times.

(26) In another preferred embodiment the mass of sodium chloroacetate exceeds the mass of chitosan by not more than 2-times, more preferably by not more that 1.2-times.

(27) In a preferred embodiment, the alcohol of the reaction solvent is isopropanol.

(28) In further preferred embodiments the reaction is carried out at ambient temperature for a period of at least 8 hours, more preferably for at least 15 hours and even more preferably for at least 18 hours.

(29) In a particularly preferred embodiment, the alcohol of the reaction solvent is isopropanol, the mass of sodium chloroacetate is not more than twice (more especially not more than 1.2 times) the mass of the chitosan and the reaction is allowed to proceed for at least 8 hours.

(30) When the chitosan is provided for reaction in powder or fibre form, this material should be adequately exposed to the turbid reaction solvent throughout the duration of the reaction. This process can be facilitated by any means known to the artisan but can be simply achieved by rolling the reaction vessel, for example.

(31) When the reaction is complete, reaction by-products detrimental to the stability of the product, such as sodium chloride or sodium hydroxyacetate, should be removed to the maximum extent feasible. To achieve this, the reaction product is washed, preferably in one or more steps, in excess solvent comprised of at least 60 parts alcohol (such as ethanol) and 40 parts water (60:40).

(32) More than one washing step is preferred and, when this is the case, the first wash step has preferably a higher water content than subsequent steps, with water content decreasing in every wash step. For example, a suitable two-step wash procedure involves a first wash in excess solvent comprised of at least 60 parts ethanol and 40 parts water (60:40) and a second wash in excess solvent comprised of at least 90 parts ethanol and 10 parts water (90:10).

(33) Thus in a preferred embodiment the reaction product is washed in a plurality of washing stages, each employing an excess of a solvent comprising alcohol and water, wherein in each succeeding stage the solvent consists of a higher proportion of alcohol. Preferably the alcohol is ethanol

(34) It is essential that wash solvents always includes some water to avoid excessive dehydration of the product, which can result in brittleness.

(35) The composition of the wash solvent may include any suitable alcohols such as ethanol, isopropanol or methanol. Ethanol is preferred.

(36) The product resulting from washing and solvent removal can be sterilised by methods typical for the sterilisation of medical devices, for example gamma-irradiation, electron-beam irradiation or ethylene oxide treatment.

(37) Prior to radiation-based sterilisation, the washed reaction product should be adequately solvent-free. This can be achieved by any drying process known to the skilled artisan. A preferred drying process is conducted at temperatures not exceeding 40° C., more preferably not exceeding 30° C. Preferably, solvent removal is achieved by placing the material under a sub-atmospheric pressure. The pressure is preferably less than 500 mbar, more preferably less than 1000 mbar. The duration of the drying process, when achieved by vacuum drying, preferably exceeds 8 hours, more preferably exceeding 12 hours.

(38) The weight average molecular weight of the material following washing and radiation sterilisation is preferably greater than 120 kDa, more preferably greater than 130 kDa and after washing and ethylene oxide sterilisation is preferably greater than 400 kDa, more preferably greater than 500 kDa. It is important that these molecular weights are obtained to avoid mechanical integrity problems in the final product and dissolution problems when exposed to fluid.

(39) Additives and co-components can be added at any stage of the above process, prior to terminal sterilisation. These agents may be any suitable for a topical or internal medical application, such as analgesics, anaesthetics, antimicrobial agents, anti-cancer agents, nicotine or nicotine substitutes or other synthetic or naturally-derived pharmaceuticals including peptides, proteins such as growth factors or retardants, enzymes (e.g. those facilitating tissue debridement), DNA or RNA fragments.

(40) When the additive is an antimicrobial agent, it may be for example: silver or silver compounds, iodine or iodine compounds, quaternary amine-based antimicrobials such as polyhexamethylenebiguanide or chlorhexidene, antibiotics such as gentamycin, vancomycin or a peptide-based agent.

(41) When silver is introduced into the formulation, and the formulation is carboxymethylchitosan-based, addition is preferably achieved by immersion in a solvent mixture of a similar composition as that applied during the carboxymethylation process.

(42) In a third aspect, the composition can be used to provide a method of fusing two or more solid surfaces, wherein the surfaces are initially separate (in particular, spatially separated) but adjacent surfaces of one or more object(s) comprising a self-coalescing material as herein described, notably the high molecular mass polymer material of the first aspect of the invention. The method comprises the step of immersing said surfaces in an aqueous medium and thus hydrating and expanding the self-coalescing material. In one embodiment, the surfaces are initially spatially separated surfaces of the same object. Alternatively, the surfaces are initially spatially separated surfaces of different objects. These alternatives are not mutually exclusive. The surfaces may be the surfaces of fibres, for example in a woven or, more especially, a non-woven fibrous material. In such materials, the surfaces may have portions which are spaced apart and portions which, while being separate, are in contact.

(43) Objects fabricated from the compositions defined above, and suitable for the method, need to be suitably designed to enable coalescence upon hydration. For example, an isolated linear object would not have the opportunity to self-coalesce upon hydration. In contrast, a pair of isolated but adjacent linear objects would have the opportunity to swell and coalesce upon hydration. In this context, ‘adjacent’ means located within about 10 mm of one another. Thus, suitable objects can be defined as containing, at least in part, spatially separated elements or surfaces located within about 10 mm of one another. Preferably, the spatially separated elements or surfaces are located within 5 mm of one another. More preferably, the spatially separated elements or surfaces are located within 1 mm of one another. In some cases, for example fibre based materials, at least parts of adjacent surfaces may be in contact.

(44) Preferred physical formats that meet the above description are fibre-based materials such as woven and non-woven materials. Other suitable formats include knits, open-celled foams and laminates including corrugated materials. More complex arrangements can be fabricated by methods known to one skilled in the art, such as lithography, micromachining and electrospinning. The composition and its uses is not restricted to formats of high open area but includes solid monoliths. Fibre based materials are preferred and fibre-based non-woven materials are particularly preferred.

(45) The composition in use is not restricted to objects consisting exclusively of self-coalescent material, but includes composites, for example composites of common medical device formats and self-coalescent material and surface-coatings, for example implantable metal- or biomaterial based devices including soft-tissue substitutes and joint implants. Composites suitable for topical and internal wound management include those combining polyurethane based materials, such as foams, slabs and films with self-coalescent materials, for example in powdered or, more especially, fibrous form.

(46) When devices comprised, at least in part, of the compositions are immersed in a fluid, they absorb fluid, become swollen and self-coalesce across contact points. Use is not restricted to specific compositions or specific fluids, but in preferred forms and for preferred end-sues, the fluid is most preferably water based. For example, in the case of carboxymethylchitosan-based materials, the fluid is preferably water based. Examples of water based fluids include water or a solution of water, such as saline or a biologically-derived fluid such as whole blood, blood plasma, serum, saliva, wound exudate or bone marrow aspirate.

(47) The novel material properties of the described self-coalescing materials can be exploited in a range of applications, for example in irreversible fluid valving systems and moulding materials.

EXAMPLES

Example 1

(48) Generation of Self-Coalescing Carboxymethylchitosan Fibres

(49) A) Synthesis

(50) Immediately prior to reaction, sodium chloroacetate (1.75 g) was dissolved in 4% aqueous sodium hydroxide solution (7 ml). This solution was added to isopropanol (45 ml) and shaken vigorously, resulting in a turbid suspension. This mixture was added to a vessel containing chitosan fibres (1.50 g), the container sealed and rolled at approximately 60 rpm for 18 hours.

(51) B) Washing Steps

(52) B1) After step A, the fibres were removed from the now clear reaction solvent and transferred to a vessel containing 99:1 ethanol:water (200 ml). The material was disturbed every 15 minutes for 1 hour, after which time the material was removed and physically dried by the application of hand pressure between several layers of absorbent material. Following gross drying, the material was vacuum dried at ambient temperature overnight.

(53) B2) After step A, the fibres were removed from the now clear reaction solvent and transferred to a vessel containing 60:40 ethanol:water (200 ml). The material was disturbed every 15 minutes for 1 hour, after which time the material was removed and transferred to a second vessel containing 90:10 ethanol:water (200 ml). The material was disturbed every 15 minutes for 1 hour, after which time the material was removed and physically dried by the application of hand pressure between several layers of absorbent material. Following gross drying, the material was vacuum dried at ambient temperature overnight.

Example 2

(54) Generation of Self-Coalescing Carboxymethylchitosan Fibres (Scale-Up)

(55) Immediately prior to reaction, sodium chloroacetate (96.8 g) was dissolved in 4% aqueous sodium hydroxide solution (387 ml). This solution was added to isopropanol (2490 ml) and shaken vigorously, resulting in a turbid suspension. This mixture was added to a vessel containing chitosan fibres (83.0 g), the container sealed and rolled at approximately 60 rpm for 18 hours. After this time, the fibres were removed from the now clear reaction solvent and transferred to a vessel containing 99:1 ethanol:water (2000 ml). The material was disturbed every 15 minutes for 1 hour, after which time the material was removed and physically dried by the application of hand pressure between several layers of absorbent material. Following gross drying, the material was vacuum dried at ambient temperature overnight.

Example 3

(56) Radiation Sterilisation of Self-Coalescing Carboxymethylchitosan Fibres

(57) The material resulting from Example 1, step B2 was packaged in gas-permeable sterilisation pouches and sterilised by gamma irradiation at 30-40 kGy. The molecular weight of the material pre- and post-sterilisation was determined by gel permeation chromatography. The molecular weight prior to sterilisation was approximately Mw 700 kDa; the molecular weight post-sterilisation was approximately Mw 140 kDa. The molecular weight change in the material, although substantial, was such that the physical properties of the material were not significantly altered by sterilisation.

Example 4

(58) Ethylene Oxide Sterilisation of Self-Coalescing Carboxymethylchitosan Fibres

(59) The material resulting from Example 1, step B2 was packaged in gas-permeable sterilisation pouches and sterilised by ethylene oxide treatment. The molecular weight of the material pre- and post-sterilisation was determined by gel permeation chromatography. The molecular weight prior to sterilisation was approximately Mw 700 kDa; the molecular weight post-sterilisation was approximately Mw 575 kDa. The molecular weight change in the material was such that the physical properties of the material were not significantly altered by sterilisation.

Example 5

(60) Water Absorbency of Self-Coalescing Carboxymethylchitosan Fibres

(61) The material resulting from Example 3 (100 mg) was immersed in water (4 ml) for 1 minute and withdrawn. Excess liquid was allowed to drain and then the hydrated transparent mass was weighed. The material was calculated to absorb approximately 25-times its own mass in water without significant dissolution.

Example 6

(62) Serum Absorbency of Self-Coalescing Carboxymethylchitosan Fibres

(63) The material resulting from Example 3 (100 mg) was immersed in serum (4 ml) for 1 minute and withdrawn. Excess liquid was allowed to drain and then the hydrated transparent mass was weighed. The material was calculated to absorb approximately 13-times its own mass in serum without significant dissolution.

Example 7

(64) Self-Coalescence of Carboxymethylchitosan Fibres in Water

(65) The material resulting from Example 3 (100 mg) was immersed in water (4 ml) for 1 minute and withdrawn. Excess liquid was allowed to drain and then the hydrated transparent mass was allowed to stand for 4 hours. After this time, the individual fibres of the material had self-coalesced and the material was then effectively a homogeneous, elastic hydrogel, able to stably retain its physical geometry under loading (FIG. 2).

Example 8

(66) Self-Coalescence of Carboxymethylchitosan Fibres in Serum

(67) The material resulting from Example 3 (100 mg) was immersed in serum (4 ml) for 1 minute and withdrawn. Excess liquid was allowed to drain and then the hydrated transparent mass was allowed to stand for 4 hours. After this time, the individual fibres of the material have self-coalesced and the material as effectively a homogeneous, elastic hydrogel, able to stably retain its physical geometry under loading.

(68) FIGS. 2A to 2C show stages in the absorption of wound exudate into the wound contacting element 14. The basic arrangement may be the same as that of FIG. 1, however, the drawings of FIG. 2 have been simplified. FIG. 2A shows a clean dressing newly installed in the wound 10 and without any exudate being taken up; FIG. 2B shows the wound contacting element 14 partially full of exudate; and, FIG. 2C shows the wound contacting element 14 saturated with wound exudate. However, the nature of the wound contacting element material 14 is such that no liquid is aspirated by the vacuum connection tube 28 out of the wound cavity 24 or indeed out of the wound contacting element 14 itself.

(69) FIG. 3 shows paradigms of the conversion of a first stable physical geometry into a second stable physical geometry upon hydration, wherein hydration enables the self-coalescence (fusion) of spatially separated elements of the first stable physical geometry. In case A, the self-coalescence comprises the fusion of spatially separated surfaces of a single element; in case B the surfaces are adjacent surfaces of two separate elements.

(70) The Examples described below are based on the use of the apparatus arrangement shown in FIG. 1 and/or FIG. 2 and/or FIG. 3.

Example 1

(71) Application of apparatus of FIG. 1 to ex vivo cavity wound. A 5 cm diameter, 5 cm depth cavity wound was cut by scalpel into a porcine leg joint. The musculature in the area of the wound cavity was injected with saline to ensure that the tissue was adequately hydrated for the duration of the experiment. The wound cavity was packed with two wound contacting elements of non-woven balls of carboxymethylchitosan fibre and the wound cavity and filling was covered over with an adhesive silicone gel sheet CicaCare (trade mark) made by Smith & Nephew Medical Ltd with a central 5 mm diameter aperture 20. A luer loc fitting attached to a coiled vacuum hose was inserted through the aperture and connected to a battery-powered vacuum source Pac-Vac (trade mark) made by Virtual Industries Inc. Immediate contraction of the wound margin was observed and the non-woven balls were compressed down to be flush with the surface of the skin. The system was left in place for 8 hours undisturbed, after which time no fluid had exited the cavity packing but had collected within it.

Example 2

(72) Assembly of apparatus based on FIG. 1 having a wound covering element 14 of Allevyn Adhesive (trade mark) made by Smith & Nephew Medical Ltd. A 3 mm diameter aperture in the top film of Allevyn Adhesive was created using a biopsy punch. Over this aperture was bonded a silicone elastomer dome miniValve (trade mark) made by Mini Valve International B. V., part number DO 072.004. A miniature vacuum source made by Virtual Industries Inc., PAC-VAC V3200 (trade mark) was coupled by vacuum tubing 28 to a hand-made silicone rubber cup 30.

Example 3

(73) Usage of apparatus based on Allevyn Adhesive as in Example 2. A 5 cm diameter, 5 cm depth cavity wound was cut by scalpel into a porcine leg joint. The musculature in the area of the wound cavity was injected with saline to ensure that the tissue was adequately hydrated for the duration of the experiment. The wound cavity was packed with wound contacting element 14 comprising two non-woven balls of carboxymethylchitosan fibre and the wound cavity 24 and filling was covered over with the modified Allevyn Adhesive dressing described in Example 2. The vacuum source, as described in Example 2, was turned on and the vacuum tubing cup placed over the dome valve positioned centrally on the Allevyn Adhesive. Immediate contraction of the Allevyn Adhesive dressing and the wound margin was observed and the non-woven balls were compressed down to be flush with the surface of the skin. The system was left in place for 8 hours undisturbed, after which time no fluid had exited the cavity packing but had collected within it.

Example 4

(74) Usage of apparatus based on Allevyn Adhesive as described in Example 2. A 5 cm diameter, 5 mm depth shallow wound was cut by scalpel into a porcine leg joint. The musculature in the area of the wound was injected with saline to ensure that the tissue was adequately hydrated for the duration of the experiment. The wound was covered with a non-woven sheet of carboxymethylchitosan as the wound contacting element 14 and the wound and non-woven sheet was covered over with the modified Allevyn Adhesive dressing described in Example 2 as the wound covering element 18. The vacuum source, as described in Example 2, was turned on and the vacuum tubing cup placed over the dome valve positioned centrally on the Allevyn Adhesive. Immediate contraction of the Allevyn Adhesive dressing was observed. The system was left in place for 8 hours undisturbed, after which time no fluid had exited the wound dressing but had collected within it.

(75) Throughout the description and claims of this specification, the words “comprise” and “contain” and variations of the words, for example “comprising” and “comprises”, means “including but not limited to”, and is not intended to (and does not) exclude other moieties, additives, components, integers or steps.

(76) Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

(77) Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith.