WO1997046265A1

WO1997046265A1 - Wound dressing

Info

Publication number: WO1997046265A1
Application number: PCT/SE1997/000946
Authority: WO
Inventors: Staffan Bowald; Gudmund Dvärsäter
Original assignee: Astra Aktiebolag (Publ)
Priority date: 1996-06-03
Filing date: 1997-05-30
Publication date: 1997-12-11
Also published as: KR20000016251A; NO985628L; EP0906126A1; HUP0003151A3; CN1226178A; CA2255627A1; ZA974846B; AU3112897A; TW347318B; PL330307A1; ID17733A; AR007386A1; JP2000511446A; AU719419B2; BR9709639A; HUP0003151A2; NO985628D0; NZ332950A; IS4898A; IL127107A0

Abstract

A wound dressing (10; 110; 210) for dressing a wound (2; 102; 202) on a tissue structure of a living human or animal body comprising a lower section (1; 101; 201) which when the wound dressing dresses the wound is disposed adjacent the wound, the lower section being fluid permeable and comprising a bioresorbable material which promotes the healing process in the wound, and an upper section (3; 103; 203) which when the dressing dresses the wound overlies the lower section, the upper section being permeable to vapour and impermeable to bacteria. The wound dressing may be an integrally formed structure, an integrated structure or formed when the wound is dressed.

Description

WOUND DRESSING

The present invention relates to wound dressings for dressing of wounds on internal or external tissue structures of living human or animal bodies.

Existing wound dressings have a number of disadvantages. Conventionally, gauze dressings have been used for the treatment of wounds such as burns, cuts, abrasions and other tissue disorders. Such dressings, however, require to be changed frequently and the application and subsequent removal of a dressing for replacement with a fresh one can be painful for the patient. In fact, some dressings are so inconvenient that they may immobilise the patient

In EP-A-0349505 (Astra Meditec AB) it is taught that the healing of soft tissue in mammals including man can be improved by the use of a porous flexible sheet of a protein-free bioresorbable polymer having a pore size which permits passage of water and salts therethrough but which locks out cells and other tissue particles. The sheet is disclosed as causing a specific stimulating effect on the formation of macrophages in soft tissue, the macrophages releasing a growth factor which stimulates tissue healing. Suitable polymer materials mentioned in EP-A-0349505 for the sheet are those based on polyglycolic acid, copolymers of glycolic acid and lactic acid, copolymers of lactic acid and ε-aminocapronic acid, lactide polymers, polydesoxazon, poIy(3-hydroxybutyrate), copolymers of poly(3- hydroxybutyrate) and 3-hydroxyvalerate, polyesters of succinic acid and cross-linked hyaluronic acid. EP-A-0349505 makes known forming a non-woven sheet of poly(3- hydroxybutyrate) having the requisite properties by pressing together solution-spun fibres of poly(3-hydroxybutyrate) manufactured in accordance with US-A-4603070 (Steel et al).

As the size of the pores in the sheet of EP-A-0349505 are sufficient to allow the passage of water therethrough there is the possibility of bacteria passing through the sheet to the wound. While this might not be so problematic for the case where the sheet is for internal use, that is to say, to be disposed inside a human or animal body to coyer an internal wound, it might be problematical in the case of external wounds such as skin wounds. GB-A-2166354 (Imperial Chemical Industries Pic) discloses a wound dressing comprising a poly(3-hydroxybutyrate) polymer dissolved or swollen with a volatile solvent such as chloroform, preferably co-polymerised with 3-hydroxyvalerate units. The material is painted onto the wound as a solution or gel to give a thin film of polymer in intimate contact with the treated area. The poly(3-hydroxybutyrate) is stated to be hydrophilic, obviating the need for an outer hydrophilic layer. The dressing is stated to be particularly suitable for rapid protection of a wound site with a temporary covering.

The thin layer of hydrophilic poly(3-hydroxybutyrate) disclosed in GB-A-2166354 has a number of disadvantages as a wound dressing. To start with, there is no provision for removal of excess fluid since the layer of poly(3-hydroxybutyrate) is not particularly absorbent and exudate from the wound will not pass through it. Furthermore, it could be difficult to remove the dressing from an open wound and the volatile solvent in it tends to be cell-toxic and could cause irritation of the wound site. Moreover, the pore size distribution created in the poly(3-hydroxybutyrate) layer would be such that the size of the pores closest the wound would be less than the size of the pores remote from the wound. The possibility of infection of the wound through ingress of bacteria to the dressing therefore exists.

In summary, the prior art has not addressed the problem of providing a convenient wound dressing for use during the gradual healing of wounds that may be conveniendy applied and, where needed, removed, which provides thermal insulation to maintain body temperature in the vicinity of the wound surface and keeps the wound moist yet permits removal of excessive fluid from the wound.

The present invention proposes to improve this situation.

According to the present invention there is provided a wound dressing for dressing a wound on a tissue structure of a living human or animal body comprising a lower section which when the wound dressing dresses the wound is disposed adjacent the wound, the lower section being fluid permeable, for example liquid permeable, and comprising a bioresorbable material which promotes the healing process of the wound, and an upper section which when the dressing dresses the wound overlies the lower section, the upper section being permeable to vapour and impermeable to bacteria.

Such a dressing is relatively simple to manufacture. Moreover, the dressing is easy to apply and can be adapted to facilitate easy removal. The dressing furthermore provides thermal insulation to maintain the body temperature in the vicinity of the wound surface and keeps the wound moist while removing excessive fluid from the wound. Ensuring that the upper section is essentially impermeable to bacteria also means that a barrier is presented to prevent infection from occurring.

Transport of exudate away from the wound could be hindered if the exudate has no means of escape after it has accumulated on the upper surface of the lower section remote from the wound. The provision of an upper section which is permeable to vapour, for example by being microporous, alleviates this problem by allowing the exudate to be slowly dispersed by evaporation. In addition, vapour from the tissue surrounding the wound will also be able to pass through the upper section.

The drawing of exudate from the wound into the lower section and subsequent evaporation of excess moisture creates a flux of material in the sense going away from the wound into the atmosphere. This flux further hinders the passing of bacteria in the opposite sense and thus infection from occurring.

The wound dressing of the invention may be left in place for a relatively long period. This means that fewer changes of dressing are needed than were hitherto, thus avoiding disturbing the healing process with less pain for the patient The use of an upper section which is vapour permeable ensures that the wound is kept moist, irrespective of how effective the removal of excessive fluid from the wound may be. Preventing the wound from drying out results in pain being controlled.

In a first form of the invention the wound dressing is an integral structure.

In a second form of the invention the wound dressing is formed as an integrated structure. For example, the upper and lower sections may respectively be presented by upper and lower wound dressing layers which are coupled to one another prior to dressing of the wound.

In a third form of the invention the wound dressing is formed once the wound is dressed, for example the upper and lower sections are respectively presented by upper and lower wound dressing layers which are applied to the wound separately.

Having the lower section of the wound dressing as a lower wound dressing layer, for instance a sheet, means that it can be easily put in position and used as a barrier facilitating the transport of exudate from the wound and retaining it away from the wound.

In an embodiment of the invention according to its various forms the wound dressing further comprises an intermediate section between the upper and lower sections which is adapted to absorb liquid. This is particularly advantageous where a large amount of exudate is encountered. For the second and third forms the intermediate section may be of any suitable material, for example treated cellulose fibres or polyacrylic acids. However, a hydrocoUoid is particularly suitable. A hydrocoUoid is normally able to absorb four to six times its own volume of fluid, and new hydrocoUoids have been reported that absorb twenty times their own volume. HydrocoUoids also are adhesive to the skin, so the hydrocoUoid can perform the dual function of intermediate absorbent layer and adhesive edge for the dressing. The intermediate section of the second and third forms of the invention may be in the form of an intermediate wound dressing layer or instead be part of the upper or lower wound dressing layer of the wound dressing.

In an embodiment of the first form of the invention the wound dressing consists of the upper and lower sections with the lower and upper sections comprising the bioresorbable material. The bioresorbable material may be in particulate or fibre form. For example, the wound dressing may comprise particles or fibres of the bioresorbable material in a matrix material such as a gel matrix of hyaluronic acid or the like. On the other hand, the wound dressing may be a fibre sheet of the bioresorbable material, for instance a non- woven fibre sheet

In an embodiment of the invention according to the second and third forms one or more of the wound dressing layers are in the form of one or more wound dressing sheets.

In an embodiment of the second form of the invention the wound dressing consists of the upper and lower wound dressing layers with the lower dressing layer being adhered to a lower surface of the upper wound dressing layer. Alternatively, where the wound dressing comprises the intermediate wound dressing layer the upper and lower wound dressing layers are respectively adhered to upper and lower surfaces of the intermediate wound dressing layer.

In an embodiment of the second form of the invention the lower wound dressing layer is releasably secured to the balance of the wound dressing. For example, the lower wound dressing layer may be releasably secured to the lower surface of the upper wound dressing layer or the lower surface of the intermediate wound dressing layer.

In a preferred embodiment of the invention according to its various forms the lower section of the wound dressing is substantiaUy free of volatile solvent In an embodiment of the second and third forms of the invention the lower wound dressing layer is presented by a layer of particles of the bioresorbable material. The particles may be supported in a matrix material, for example a gel matrix comprising hyaluronic acid.

In an embodiment of the second form of the invention the bioresorbable particulate material of the lower wound dressing layer is adhered to the lower surface of the upper or intermediate wound dressing layer by mixing the particles in a solvent, coating the mixture to the lower surface and then evaporating the solvent. Chloroform may be mentioned as a suitable solvent

In an embodiment of the invention according to its third form, when the wound dressing dresses the wound the lower section is presented by a layer of loose particles or fibres of the bioresorbable material positioned on the wound. Alternatively, the lower wound dressing layer may be a gel comprising the bioresorbable material coated onto the wound or one or more lower wound dressing sheets laid over the wound.

In an embodiment of the second and third forms of the invention the bioresorbable material of the lower wound dressing layer is in fibre form, for example supported in a matrix such as a gel matrix formed from hyaluronic acid. Alternately, the lower wound dressing layer may take the form of one or more lower wound dressing fibre sheets, for example formed from non- woven fibres in which case the lower surface of the lower wound dressing layer may to advantage be roughened to expose ends of the fibres.

In an embodiment of the various forms of the invention the bioresorbable material of the lower section is a polymer. For example, the polymer is protein-free, examples of which being poly(3-hydroxybutyrate) (PHB), polylactic acids, polyglycoUc acid, copolymers of glycolic acid and lactic acid, copolymers of lactic acid and ε-aminocapronic acid, lactide polymers, polydesoxazon, copolymers of poly(3-hydroxybutyrate) and 3-hydroxyvalerate, polyesters of succinic acid and cross-linked hyaluronic acid. Use of a protein-free bioresorbable polymer in the lower section appears to stimulate healing during degradation by stimulating macrophages, by forming a barrier against the surrounding and working as a scaffold for ceU growth. The macrophage invasion caused by protein-free polymers covers the wound with tissue and controls the wound pain effectively in the first day or two. Vascularization and microcirculation occur, again stimulated by the polymer. Moreover, degradation of certain protein-free polymers such as PHB has a bacteriostatic and fungistatic effect and facUitates the wound heaUng of skin. The invading macrophages also have a bactericidal effect. The wound dressing can be left in place for a longer period owing to the bacteriostatic and fungistatic properties and the wound healing environment created beneath the dressing. Fewer changes of dressing means less disturbance of the healing process and less pain for the patient.

Poly(3-hydroxybutyrate) is the preferred material for the lower section because Applicant has found that PHB has the abUity to attract macrophages to the wound site at a greater rate than other polymers tested. The PHB also appears to lead to an increased vascularization, perhaps through a macrophage effect promoted by the PHB. In addition, the dressing period is further enhanced when PHB is used due to the fact that the bacteriostatic and fungistatic properties increase over time with the degradation of the PHB.

Furthermore, in the case where the lower section is formed as a fibrous PHB sheet, for instance a non-woven sheet, having hydrophobic fibres the nature of the PHB fibres is such that the sheet has a capUlary capacity which aids in the exudate being drawn away from the wound and retained in the region between the sheet and the upper section. Moreover, a non-woven PHB fibre sheet wUl sweU during the first ten days or so by adding blood components and ceUs from the surrounding tissue owing to its construction despite the fibres being hydrophobic. In conclusion, a PHB fibre sheet as the lower section of the wound dressing wiU aUow the wound to "breath" and enable vapour transport thereby leaving the wound surface with an adequate humidity. Where poly(3-hydroxybutyrate) is selected oligo(3-hydroxybutyrate), e.g. having 3 to 10 monomer units, may also be included in the lower section or may constitute the lower section.

A wide range of other materials may be suited for the function of the lower section which would easily be apparent to a skilled reader in the art, non-limiting examples being polysacchandes such as chitosan, collagen and proteins.

In an embodiment of the various forms of the invention the wound dressing is flexible thereby enabUng the dressing to follow the contour of the wound, for example a recessed wound.

In an embodiment of the second and third forms of the invention the lower wound dressing layer is adapted to foUow the contour of the wound, for example by being flexible.

To assist in the wound heakng process the lower section of the various forms of wound dressing according to the invention may support one or more growth factors.

In an embodiment of the second and third forms of the invention the upper wound dressing layer of the wound dressing comprises a polymeric material. The polymeric material may be bioresorbable and may further be protein-free. As an example, the upper section may comprise poly(3-hydroxybutyrate). Alternately, the upper section may comprise a non- bioresorbable non-biodegradable material, non-limiting polymeric examples being polyurethane and polytetrafluoroethylene.

In an embodiment of the invention according to its various forms the upper section of the wound dressing is porous. Where the upper and lower sections are both porous the pore size of the pores of the upper section wiU be less than the pore size of the pores of the lower section. TypicaUy, the pore size of the upper section wiU be less than about 0.25μra In an embodiment of the invention according to its various forms the wound dressing presents an adhesive edge for releasably adhering to a surface of the tissue structure adjacent the wound. This facUitates application and removal of the dressing or the upper part thereof.

In an embodiment of the second and third forms of the invention the upper wound dressing layer presents the adhesive edge in which case the upper wound dressing layer may completely surround the lower wound dressing layer. An ideal overlap margin is approximately 10 to 15 mm. Where the upper wound dressing layer includes the intermedi- ate section, the adhesive edge may be presented by the intermediate section of the upper wound dressing layer.

In an embodiment of the second and third forms of the invention the intermediate wound dressing layer presents the adhesive edge.

According to the invention there is also provided a method of treatment of a wound on a tissue structure of a Uving human or animal body comprising the steps of applying to the wound a fluid permeable lower layer of a bioresorbable material which promotes healing processes in the wound and overlaying the lower layer with a vapour permeable, bacteria impermeable upper layer.

The invention further provides a method for the manufacture of a wound dressing comprising the steps of coupUng a fluid permeable layer of a bioresorbable material which promotes healing processes in a wound to a vapour permeable, bacteria impermeable layer.

According to the invention there is yet further provided the use of poly(3-hydroxybutyrate) in the form of fibres or powder substantiaUy free of volatile solvent in the manufacture of a wound dressing for the skin. Embodiments of the invention wUl now be described by way of example with reference to the accompanying Figures of drawings in which:-

Fig. 1 is a cross-sectional side view of a first wound dressing in accordance with the present invention;

Fig. 2 is a cross-sectional side view of a second wound dressing in accordance with the present invention; and

Fig. 3 is a cross-sectional side view of a third wound dressing in accordance with the present invention.

As can be seen from Fig. 1, a wound dressing 10 in accordance with the present invention comprises a layer 1 of a bioresorbable material which promotes wound healing processes, in this case poly(3-hydroxybutyτate) (hereinafter "PHB"), applied to a skin wound 2 in the form of a fibrous non-woven sheet substantially free of volatile solvent, and an exterior microporous layer 3 of a polyurethane polymer. The pores of the exterior polymer layer 3 have a pore size of less than 0.22 μm. This renders the layer 3 permeable to vapour and gases whUst maintaining the layer 3 essentiaUy impermeable to bacteria.

The dressing 10-may be conveniently applied and removed and further provides thermal insulation to maintain the body temperature in the vicinity of the wound surface by virtue of the exterior polymer layer 3. The dressing 10 also keeps the wound 2 moist yet, by being permeable to moisture vapour, enables removal of excessive fluid from the wound 2. This prevents the nerve endings in the wound from drying out and concomitantly a cause of pain to the patient

To facilitate application and removal of the dressing 10 the exterior polymer layer 3 has an adhesive edge 4. The PHB fibres in the dressing 10 exhibit hydrophobic properties. The nature of the PHB fibres is such that exudate is drawn away from the wound 2 and retained in the PHB layer 1 and space between the PHB layer 1 and the exterior polymer layer 3.

The wound dressing 10 may be left in place for a relatively long period. This means that fewer changes of dressing are needed than with hitherto proposed dressings. This avoids disturbing the healing process with less pain for the patient. One possibUity when changing the dressing 10 would be to remove the exterior layer of polymer 3 and excess exudate only, then put a fresh exterior layer 3 in place without disturbing the PHB layer 1. Alternatively, most of the PHB layer 1 may be removed as weU and replaced by a fresh piece of PHB, with fibres of PHB that are adhering to the wound 2 being left.

In Fig. 2 there is shown a second wound dressing 110 in accordance with the present invention which comprises a layer 101 of PHB applied to a skin wound 102 in the form of a fibrous non-woven sheet substantiaUy free of volatile solvent and an exterior microporous layer 103 of a polyurethane polymer. The PHB layer 101 is in the form of a patch completely surrounded by the exterior polymer layer 103 with a 10 to 15 mm margin (m) of the exterior polymer layer 103 around the PHB patch 101 being left. The size of the PHB patch 101 itself may vary according to the size of the wound 102.

Furthermore, arrintermediate absorbent layer 105 of a hydrocoUoid material is provided. This absorbs exudate that is transported away from the wound 102 by the PHB patch 101 and promotes the transport away of further exudate. The microporosity of the polyurethane exterior layer 103 means that the exudate can be slowly dispersed whUe still keeping the wound 102 moist and at the same time excluding bacteria. Vapour from the skin surrounding the wound 102 will also be able to pass through the exterior polymer layer 103.

The exterior polymer layer 103 has an adhesive edge 104 to faciUtate application and removal of the dressing 110. Turning now to Fig. 3, a third wound dressing 210 in accordance with the present invention comprises a layer 201 of PHB appUed to a skin wound 202 in the form of a fibrous non¬ woven sheet substantially free of volatile solvent and an exterior microporous layer 203 of a polyurethane polymer. The PHB is again in the form of a patch completely surrounded by the exterior polymer layer 203 with a 10 to 15 mm margin (m) of the polymer left around the PHB patch. An intermediate absorbent layer 205 of a hydrocoUoid material is again provided, but in this case the hydrocoUoid layer 205 is made integral with the exterior polymer layer 203. As the hydrocoUoid material is adhesive to the skin, it may be stuck to the skin by its edge 204. Thus the hydrocoUoid performs the dual function of intermediate absorbent layer and adhesive edge to the exterior layer 203.

A skiUed reader in the art wUl readily appreciate that the invention is not restricted to the specific wound dressing examples described hereinabove with reference to the accompanying drawings but that the invention may take many forms or guises within the scope of the claims.

Applicant has observed that wound dressings ought to meet the foUowing objectives: -

• Thermal insulation should maintain body temperature of the wound surface.

• The wound should be kept moist but excess fluid should be removed.

• The dressing should be permeable to vapour but impermeable to bacteria.

• The dressing should be absorbent and breathable.

• Pain should be controlled.

• The dressing should be easy to apply and, where needed, to remove. • The dressing should stimulate healing.

• The dressing should comply with other treatments, for example allowing an outer com¬ pressing bandage to be provided and for effective debridement of dead skin to occur.

• The dressing should be biocompatible and non-toxic.

• The dressing should not immobilise the patient

The wound dressings hereinabove described with reference to the accompanying Figures of drawings satisfy these objectives in a simple and inexpensive manner.

In a comparative test a wound dressing in accordance with the invention and a wound

TM dressing comprising a sheet of polyurethane (Tagerderm ) were used to dress a skin wound of a mammaUan body. The dressing in accordance with the invention consisted of a lower section in the form of a non-woven fibre sheet of PHB and an upper section of a polyurethane sheet The wound dressing of the invention produced an improved healed wound compared to the polyurethane sheet wound dressing. This was characterised by the healed wound covered by the wound dressing of the invention having a thicker and better quality layer of epithelial ceUs in the regenerated tissue than in the healed wound covered by the polyurethane sheet wound dressing.

Claims

Claims:

1. A wound dressing for dressing a wound on a tissue structure of a Uving human or animal body comprising a lower section which when the wound dressing dresses the wound is disposed adjacent the wound, the lower section being fluid permeable and comprising a bioresorbable material which promotes the healing process of the wound, and an upper section which when the dressing dresses the wound overUes the lower section, the upper section being permeable to vapour and impermeable to bacteria.

2. A wound dressing according to claim 1, characterised in that the lower section is kquid permeable

3. A wound dressing according to claim 1 or 2, characterised in that the lower section of the wound dressing is substantiaUy free of volatile solvent

4. A wound dressing according to any one of claims 1 to 3, characterised in that the wound dressing is an integral structure.

5. A wound dressing according to claim 4, characterised in that the wound dressing is in the form of a wound dressing with the upper and lower sections.

6. A wound dressing according to claim 5, characterised in that the wound dressing consists of the upper and lower sections with the lower and upper sections comprising the bioresorbable material.

7. A wound dressing according to claim 5, characterised in that the wound dressing further comprises an intermediate section between the upper and lower sections which is adapted to absorb liquid.

8. A wound dressing according to claim 5, 6 or 7, characterised in that the wound dressing is in the form of a sheet.

9. A wound dressing according to any one of claims 5 to 8, characterised in that the bioresorbable material is in particulate or fibre form.

10. A wound dressing according to any one of claims 5 to 8, characterised in that the wound dressing comprises particles or fibres of the bioresorbable material in a matrix material.

11. A wound dressing according to claim 10 when appendent to any one of claims 5 to 7, characterised in that the matrix is a gel matrix.

12. A wound dressing according to claim 11 , characterised in that the gel matrix is of hyaluronic acid.

13. A wound dressing according to claim 9 when appendent on claim 8, characterised in that the wound dressing is a fibre sheet of the bioresorbable material

14. A wound dressing according to claim 13, characterised in that the wound dressing is a non- woven -fibre sheet

15. A wound dressing according to claim 14, characterised in that the lower surface of the wound dressing is roughened to expose ends of the fibres.

16. A wound dressing according to any one claims 5 to 15, characterised in that the bioresorbable material of the lower section comprises a polymer.

17. A wound dressing according to claim 16, characterised in that the polymer is protein-free.

18. A wound dressing according to claim 17, characterised in that the polymer is poly(3-hydroxybutyrate), a polylactic acid, polyglycoUc acid, a copolymer of glycolic acid and lactic acid, a copolymer of lactic acid and ε-aminocapronic acid, a lactide polymer, polydesoxazon, a copolymer of poly(3-hydroxybutyτate) and 3-hydroxyvalerate, a polyester of succinic acid or cross-linked hyaluronic acid.

19. A wound dressing according to claim 16, characterised in that the lower section comprises poly(3-hydroxybutyrate) and oligo(3-hydroxybutyrate).

20. A wound dressing according to any one of claims 5 to 15, characterised in that the bioresorbable material of the lower section comprises a polysaccharide such as chitosan, collagen or a protein.

21. A wound dressing according to any one of claims 5 to 20, characterised in that the wound dressing is flexible thereby enabUng the dressing to foUow the contour of the wound such as a recessed wound.

22. A wound dressing according to any one of claims 5 to 21 , characterised in that the lower section is porous.

26. A wound dressing according to any one of the claims 5 to 22, characterised in that the upper section of the wound dressing is porous.

24.. A wound dressing according to claim 23 when appendent to claim 22, characterised in that the pore size of the pores of the upper section is less than the pore size of the pores of the lower section.

25. A wound dressing according to claim 23 or 24, characterised in that the pore size of the upper section is less than about 0.25μm.

26. A wound dressing according to claim 1, 2 or 3, characterised in that the wound dressing is formed as an integrated structure.

27. A wound dressing according to claim 26, characterised in that the upper and lower sections are respectively presented by upper and lower wound dressing layers which are coupled to one another prior to dressing of the wound.

28. A wound dressing according to claim 27, characterised in that the lower section is porous.

29. A wound dressing according to claim 27, characterised in that the lower section is perforate.

30. A wound dressing according to any one of claims 27 to 29, characterised in that the wound dressing further comprises an intermediate section between the upper and lower sections which is adapted to absorb tiquid.

31. A wound dressing according to claim 30, characterised in that the intermediate section is in the form of an intermediate wound dressing layer.

3-2. A wound dressing according to claim 30, characterised in that the intermediate section is part of the upper or lower wound dressing layer of the wound dressing.

33. A wound dressing according to any one of claims 27 to 29 and 32, characterised in that the wound dressing consists of the upper and lower wound dressing layers with the lower wound dressing layer being adhered to a lower surface of the upper wound dressing layer.

34. A wound dressing according to claim 31, characterised in that the upper and lower wound dressing layers are respectively adhered to upper and lower surfaces of the intermediate wound dressing layer.

35. A wound dressing according to any one of claims 27 to 34, characterised in that the lower wound dressing layer is releasably secured to the balance of the wound dressing.

36. A wound dressing according to claim 35 when appendent on any one of claims 27 to 29, 32 or 33, characterised in that the lower wound dressing layer is releasably secured to the lower surface of the upper wound dressing layer.

37. A wound dressing according to claim 35 when appendent on claim 31 or claim 34, characterised in that the lower wound dressing layer is releasably secured to the lower surface of the intermediate wound dressing layer.

38. A wound dressing according to any one of claims 27 to 37, characterised in that the lower wound dressing layer is presented by a layer of particles of the bioresorbable material.

39. A wound dressing according to claim 38, characterised in that the particles may be supported in a matrix material.

40. A wound dressing according to claim 39, characterised in that the matrix is a gel matrix.

41. A wound dressing according to claim 40, characterised in that gel matrix comprises hyaluronic acid.

42. A wound dressing according to claim 38, characterised in that the bioresorbable particulate material of the lower wound dressing layer is adhered to the lower surface of the upper or intermediate wound dressing layer by mixing the particles in a solvent, coating the mixture to the lower surface and then evaporating the solvent.

43. A wound dressing according to claim 42, characterised in that chloroform is used as the solvent.

44. A wound dressing according to any one of claims 27 to 43, characterised in that one or more of the wound dressing layers are in the form of one or more wound dressing sheets.

45. A wound dressing according to claim 1, 2 or 3, characterised in that the wound dressing is formed once the wound is dressed.

46. A wound dressing according to claim 45, characterised in that the upper and lower sections are respectively presented by upper and lower wound dressing layers which are applied to the wound separately.

47. A wound dressing according to claim 46, characterised in that the lower section is porous.

48. A wound dressing according to claim 46, characterised in that the lower section is perforate.

49. A wound dressing according to any one of claims 46 to 48, characterised in that the wound dressing further comprises an intermediate section between the upper and lower sections which is adapted to absorb liquid.

50. A wound dressing according to claim 49, characterised in that the intermediate section is in the form of an intermediate wound dressing layer.

51. A wound dressing according to claim 49, characterised in that the intermediate section is part of the upper or lower wound dressing layer of the wound dressing.

52. A wound dressing according to any one of claims 46 to 51 , characterised in that the lower wound dressing layer is presented by a layer of particles of the bioresorbable material.

53. A wound dressing according to claim 52, characterised in that the particles are supported in a matrix material.

54. A wound dressing according to claim 53, characterised in that the matrix is a gel matrix.

55. A wound dressing according to claim 54, characterised in that gel matrix comprises hyaluronic acid.

56. A wound dressing according to any one of claims 46 to 50, characterised in that when the wound dressing dresses the wound the lower section is presented by a layer of loose particles or fibres of the bioresorbable material positioned on the wound.

57. A wound dressing according to any one of claims 46 to 50, characterised in that the lower wound dressing layer is a gel comprising the bioresorbable material coated onto the wound.

58. A wound dressing according to any one of claims 46 to 57, characterised in that one or more of the wound dressing layers are in the form of one or more wound dressing sheets.

59. A wound dressing according to claim 58 when appendent to any one of claims 46 to 51 , characterised in that the lower wound dressing layer is presented by one or more lower wound dressing sheets laid over the wound.

60. A wound dressing according to any one of claims 27 to 37, 44, 46 to 51 , 58 or 59, characterised in that the bioresorbable material of the lower wound dressing layer is in fibre form.

61. A wound dressing according to claim 60, characterised in that the bioresorbable fibre material is supported in a matrix.

62. A wound dressing according to claim 61, characterised in that the bioresorbable fibre material is supported in a gel matrix.

63. A wound dressing according to claim 62, characterised in that the bioresorbable fibre material is supported in a gel matrix formed from hyaluronic acid.

64. A wound dressing according to claim 60, characterised in that the lower wound dressing layer is presented by one or more lower wound dressing fibre sheets

65. A wound dressing according to claim 64, characterised in that the lower wound dressing fibre sheet or sheets are formed from non-woven fibres.

66. A wound dressing according to claim 65, characterised in that the lower surface of the lower wound dressing layer is roughened to expose ends of the fibres.

67. A wound dressing according to any one of claims 26 to 66, characterised in that the bioresorbable material of the lower section comprises a polymer.

68. A wound dressing according to claim 67, characterised in that the polymer is protein-free.

69. A wound dressing according to claim 68, characterised in that the polymer is poly(3-hydroxybutyrate), a polylactic acid, polyglycoUc acid, a copolymer of glycoUc acid and lactic acid, a copolymer of lactic acid and ε-aminocapronic acid, a lactide polymer, polydesoxazon, a copolymer of poly(3-hydroxybutyrate) and 3-hydroxyvalerate, a polyester of succinic acid or cross-linked hyaluronic acid.

70. A wound dressing according to claim 67, characterised in that the lower section comprises poly(3-hydroxybutyrate) and oligo(3-hydroxybutyrate).

71. A wound dressing according to claim 67, characterised in that the bioresorbable material of the lower section comprises a polysacchande such as a lipopolysaccharide or chitosan, collagen or a protein.

72. A wound dressing according to any one of claims 26 to 71, characterised in that the wound dressing is flexible thereby enabling the dressing to follow the contour of the wound such as a recessed wound.

73. A wound dressing according to any one of claims 27 to 44 or 46 to 71, characterised in that the lower wound dressing layer is adapted to follow the contour of the wound.

74. A wound dressing according to claim 73, characterised in that the lower wound dressing layer is flexible.

75. A wound dressing according to any one of the preceding claims, characterised in that the lower section supports one or more growth factors.

76. A wound dressing according to any one of claims 26 to 75, characterised in that the upper wound dressing layer of the wound dressing comprises a polymeric material.

77. A wound dressing according to claim 76, characterised in that the polymeric 5 material is bioresorbable.

78. A wound dressing according to claim 77, characterised in that the polymeric material is protein-free.

o 79. A wound dressing according to claim 78, characterised in that the upper section comprises poly(3-hydroxybutyrate).

80. A wound dressing according to any one of claims 26 to 75, characterised in that the upper section comprises a non-bioresorbable material. 5

81. A wound dressing according to claim 80, characterised in that the upper section comprises a non-bioresorbable polymeric material.

82. A wound dressing according to claim 81, characterised in that the polymeric 0 material is polyurethane or polytetrafluoroethylene.

83. A wound dressing according to any one of claims 26 to 82, characterised in that the upper section of the wound dressing is porous.

5 84. A wound dressing according to claim 83 when appendent to claim 28 or claim 47, characterised in that the pore size of the pores of the upper section is less than the pore size of the pores of the lower section.

85. A wound dressing according to claim 83 or 84, characterised in that the pore size o of the upper section is less than about 0.25μra

86. A wound dressing according to any one of the preceding claims, characterised in that the wound dressing presents an adhesive edge for adhering to a surface of the tissue structure adjacent the wound.

87. A wound dressing according to claim 86 when appendent to any one of claims 27 to 44, 46 to 71, 73 or 74, characterised in that the upper wound dressing layer presents the adhesive edge.

88. A wound dressing according to claim 87, characterised in that the upper wound dressing layer completely surrounds the balance of the wound dressing.

89. A wound dressing according to claim 87 or 88, characterised in that the upper wound dressing layer overlaps the balance of the wound dressing by a margin of approximately 10 to 15 mm.

90. A wound dressing according to claim 86 when appendent to claim 32 or claim 51, characterised in that the upper wound dressing layer includes the intermediate section and that the adhesive edge is presented by the intermediate section of the upper wound dressing layer.

91. A wound dressing according to claim 86 when appendent to claim 31 or 50, characterised in that the intermediate wound dressing layer presents the adhesive edge.

92. A wound dressing according to claim 30, 31 , 32, 34, 37, 49, 50, 51 , 90 or 91 , characterised in that the intermediate section comprises a hydrocoUoid.

93. A method of treatment of a wound on a tissue structure of a Uving human or animal body comprising the steps of applying to the wound a fluid permeable lower layer of a bioresorbable material which promotes heaUng processes in the wound and overlaying the lower layer with a vapour permeable, bacteria impermeable upper layer.

94. A method for the manufacture of a wound dressing comprising the steps of coupling a fluid permeable layer of a bioresorbable material which promotes healing processes in a wound to a vapour permeable, bacteria impermeable layer.

95. A method according to claim 93 or 94, characterised in that the bioresorbable material is a bioresorbable polymer.

96. A method according to claim 95, characterised in that the polymer is protein-free.

97. A method according to claim 96, characterised in that the polymer comprises poly(3-hydroxybutyτate).

98. Use of poly (3 -hydroxybutyrate) in the form of fibres or powder substantiaUy free of volatile solvent in the manufacture of a wound dressing for the skin.

99. Use as claimed in claim 98, characterised in that no solvent is present in the fibres or powder.