HK1021945A - Wound dressing - Google Patents

Description

Wound dressing

The present invention relates to a wound dressing for bandaging a wound in internal or external tissue of a living human or animal body.

Existing wound dressings have a number of disadvantages. Gauze dressings have been commonly used to treat wounds such as burns, incisions, abrasions and other tissue disorders. However, such dressings require frequent changing and it is painful for the patient to apply such dressings and subsequently remove them from the wound by replacing them with fresh dressings. In fact, some dressings are inconvenient in that they immobilize the patient's joint.

In EP- ｃA-0349505(astrｃA Meditec AB) it is taught that healing of the soft tissues of our animals including humans can be improved by using ｃA porous flexible sheet of protein-free bioabsorbable polymer having pore sizes that allow water and salt to permeate, but that the cells and other tissue particles are shielded outside. The disclosed sheet causes a specific stimulation of the formation of macrophages of the soft tissue, which macrophages release growth factors that stimulate tissue healing. Suitable polymeric materials for the preparation of the flakes described in EP-A-0349505 are those based on polyglycolic acid, copolymers of glycolic acid and lactic acid, lactic acid and epsilon-aminocaproic acid, lactide polymers, polydeoxazon, poly (3-hydroxybutyrate), copolymers of poly (3-hydroxybutyrate) and 3-hydroxyvalerate, copolymers of succinic acid and polyesters of crosslinked hyaluronic acid. EP-A-0349505 produces known non-woven sheets of poly (3-hydroxybutyrate) with the requisite properties by extruding together A collapsed-spun fiber of poly (3-hydroxybutyrate) prepared according to US-A-4603070(Steel et al).

Since the pore size of the sheet of EP- ｃA-0349505 is large enough to allow water to pass through, bacteriｃA may pass through the sheet into the wound. Such a sheet may not present a problem for use as an internal application, that is to say for placing the sheet inside a human or animal body to cover an internal wound, but is cumbersome for application to an external wound, such as a skin wound.

GB-A-2166354 (Imperial chemical industries) discloses a wound dressing comprising poly (3-hydroxybutyrate) preferably copolymerized with 3-hydroxyvalerate units dissolved or imbibed with a volatile solvent such as chloroform. The material in solution or gel form is applied to the wound to obtain a thin layer of polymer with maximum contact with the treated area. It is believed that the poly (3-hydroxybutyrate) is hydrophilic, reducing the need for an external hydrophobic layer. The dressing is particularly useful for rapid protection of wound sites requiring temporary coverage.

The thin layer of hydrophilic poly (3-hydroxybutyrate) disclosed in GB-a-2166354 has a number of disadvantages as a wound dressing. First, because the thin layer of poly (3-hydroxybutyrate) is not particularly absorbent, wound exudate cannot penetrate the thin layer, and there is no provision for removing excess fluid. Furthermore, it is difficult to remove the dressing from the incised wound, where the volatile solvents tend to be cytotoxic and cause irritation of the wound site. Furthermore, the pore size of the thin layer of poly (3-hydroxybutyrate) was prepared stepwise so that the pore size closest to the wound was smaller than the pore size further away from the wound. There is a possibility of infection of the wound due to bacteria entering the dressing.

In summary, the prior art does not address the problem of providing a convenient wound dressing for use during the gradual healing of a wound, which may be conveniently applied to or removed from the wound if required, which provides insulation near the wound surface to maintain body temperature and maintain wound moisture, and also allows excess liquid to be removed from the wound.

The object of the invention is to improve this situation.

According to the present invention there is provided a wound dressing for dressing a wound in the internal or external tissue of a living human or animal body, comprising a lower section which is positioned adjacent the wound when the wound dressing dresses the wound, the lower section being permeable to bodily fluids, for example liquids, and comprising a bioabsorbable material which promotes the healing process of the wound, the dressing comprising an upper section which covers the lower section when the dressing dresses the wound, 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 use and may be adapted for convenient removal. Again, the dressing provides insulation to maintain body temperature at the wound surface and to maintain moisture of the wound as excess body fluid is removed from the wound. It is ensured that the upper section is substantially impermeable to bacteria, i.e. a barrier is provided to prevent infection.

This prevents transport of exudate from the wound if it cannot flow after it has accumulated on the upper surface of the lower section remote from the wound. Precautions, for example against the cross-section of the microporous vapour-permeable upper layer, solve this problem by allowing the exudate to slowly diffuse through evaporation. In addition, steam from the tissue surrounding the wound can also penetrate the upper section.

Drainage of exudate from the wound into the underlying section and subsequent evaporation of excess moisture creates a flow of material in the direction from the wound into the atmosphere. This material flow further prevents the bacteria from penetrating in the opposite direction, thus preventing infection from occurring.

The wound dressing of the present invention is allowed to stand for a relatively long time. This means that it requires fewer changes than dressings to date, thus avoiding interference with the healing process and reducing patient pain.

The use of a vapour permeable upper section ensures that the wound remains moist, and that prevention of drying of the wound, despite the effect of removing excess body fluid from the wound, can control patient distress.

For the first form of the invention, the wound dressing is of unitary construction.

For the second form of the invention, the wound dressing is a combined structure. For example, the upper and lower sections may be provided by upper and lower wound dressing layers, respectively, which are bonded to each other before the wound is secured.

With the third form of the invention, once a wound is dressed, the wound dressing is formed, for example with the upper and lower sections being provided by upper and lower wound dressing layers applied separately to the wound.

The wound dressing having a lower section of the lower wound dressing, for example in sheet form, means that it is easily held in place and acts as a barrier to facilitate transport of exudate from the wound and to keep exudate transported away from the wound.

In one embodiment of the invention in each form, the wound dressing further comprises an intermediate section between the upper and lower sections, the sections being adapted to absorb liquid. Such dressings are particularly advantageous when large amounts of exudate are encountered. For the second and third forms of the invention, the intermediate section may be of any suitable material, for example treated cellulose fibres or polyacrylic acid. But hydrocolloids are particularly suitable. Generally, a hydrogenated colloid is capable of absorbing 4 to 6 times its own volume of liquid, and it has been reported that a new hydrogenated colloid is capable of absorbing 20 times its own volume. The hydrocolloid also adsorbs to the skin, so that it performs the dual function of the intermediate absorbent layer and the adhesive edge of the dressing. The intermediate section of the second and third forms of the invention may be the intermediate wound dressing layer or be replaced by a portion of the upper or lower wound dressing layer of the wound dressing.

In a first form of the embodiment of the invention, the wound dressing is made up of upper and lower sections having a lower section comprising a bioabsorbable material and an upper section. The bioabsorbable material can be in particulate or fibrous form. For example, the wound dressing may comprise particles or fibres of a bioabsorbable material in a matrix material such as a gel matrix of hyaluronic acid or the like. Alternatively, the wound dressing may be a fibrous sheet of bioabsorbable material, such as a non-woven fibrous sheet.

In embodiments of the second and third forms of the invention, the one or more wound dressing layers are in the form of one or more wound dressing sheets.

In a second form of embodiment, the wound dressing is made up of an upper layer having a lower wound dressing layer adhered to a lower surface of the upper wound dressing layer and a lower wound dressing layer. Alternatively, where the wound dressing comprises an intermediate wound dressing layer, the upper and lower wound dressing layers may be adhered to the upper and lower surfaces of the intermediate wound dressing layer respectively.

In a second form of embodiment, the underlying wound dressing layer is releasably secured to the remainder of the wound dressing. For example, the bottom wound dressing layer may be releasably secured to the bottom surface of the upper wound dressing layer or the bottom surface of the intermediate wound dressing layer.

In preferred embodiments of various forms of the invention, the lower section of the wound dressing is substantially free of volatile solvents.

In the second and third forms of the invention, the lower wound dressing layer is composed of a layer of particles of a bioabsorbable material. The particles may be supported by a matrix material, such as a gel matrix comprising hyaluronic acid.

In a second form of the invention, the bioabsorbable particulate material of the lower wound dressing layer adheres to the lower surface of the upper or intermediate wound dressing layer by mixing the particles in a solvent, coating the mixture onto the lower surface and then evaporating the solvent. Chloroform, as mentioned above, is a suitable solvent.

In a third form of the invention, the lower section is provided by a layer of loose particles or fibres of bioabsorbable material positioned in the wound when the wound dressing dresses the wound. Alternatively, the lower wound dressing layer may be a gel comprising a bioabsorbable material that is applied to the wound or one or more lower wound dressing sheets that cover the wound.

In embodiments of the second and third inventive forms of the present invention, the bioresorbable material of the lower wound dressing is in the form of a fibre, for example supported by a matrix such as a gel matrix formed from hyaluronic acid. Alternatively, the lower wound dressing layer may be in the form of one or more lower wound dressing fibrous sheets, for example formed from non-woven fibres, in which case it is preferred that the lower surface of the lower wound dressing layer may be in loose fibre end contact.

In various forms of embodiment of the invention, the bioabsorbable material of the lower section is a polymer. For example, the polymer is protein-free, and examples of such polymers are poly (3-hydroxybutyrate) (PHB), polylactic acid, polyglycolic acid, copolymers of glycolic acid and lactic acid, lactic acid and epsilon-aminocaproic acid, lactide polymers, polydesoxazon, copolymers of poly (3-hydroxybutyrate) and 3-hydroxyvalerate, copolymers of succinic acid and a polyester of crosslinked hyaluronic acid.

The use of protein-free bioabsorbable polymers in the underlying fracture seems to promote healing during decay by stimulating macrophages by forming a barrier against the surrounding environment and operations such as cytoskeleton. Invasion of macrophages by the protein-free polymer covered the tissue of the wound and effectively controlled the pain of the wound on the first or second day. Angiogenesis and microcirculation also occur as a result of stimulation by the polymer. Moreover, the degradation of certain protein-free polymers such as PHB has bacteriostatic and fungistatic effects and helps heal skin wounds. Invasive macrophages also have a bactericidal effect. Because of its bacteriostatic and fungistatic properties, the wound dressing may be placed for extended periods of time and create a wound healing environment beneath the dressing. Less dressing changes means less disruption to the healing process and less pain for the patient.

Poly (3-hydroxybutyrate) is the preferred material for use as the base section because applicants have found that PHB has the ability to attract macrophages to the wound site at a greater rate than the other polymers tested. PHB also appears to cause increased angiogenesis, possibly by the action of PHB-initiated macrophages. In addition, when PHB is to be used, the bandaging phase is further enhanced by the fact that the bacteriostatic and fungistatic properties are increased throughout the PHB.

Furthermore, in the case of a PHB sheet with a lower section formed in the form of a fiber, such as a non-woven sheet with hydrophobic fibers, the properties of the PHB fibers are such that the sheet has capillary surface tension capabilities that help to drain exudate from the wound and maintain the area between the sheet and the upper section. Moreover, although the fibers were hydrophobic, the non-woven PHB fiber sheet, due to its construction, swelled or added the blood components and cells of the surrounding tissue on the first 10 days. The result is that the PHB fiber sheet, which is the lower section of the wound dressing, will allow the wound to "breathe" and be able to transport steam, thereby maintaining the proper moisture on the wound surface.

When poly (3-hydroxybutyrate) is chosen, it is also possible to include oligo (3-hydroxybutyrate) with, for example, 3-10 monomer units in the bottom section or to compose the bottom section from this oligo (3-hydroxybutyrate).

A wide variety of other materials are suitable for the function of the lower section, as will be apparent to those skilled in the art, non-limiting examples being polysaccharides such as chitosan, collagen and proteins.

In various forms of embodiments of the invention, the wound dressing is flexible, thereby enabling the dressing to follow the contour of the wound, such as a recessed wound.

In the second and third forms of the invention, the lower wound dressing layer may be modified to be, for example, flexible in the form of a wound.

To assist in the wound healing process, the lower section of the various forms of wound dressings of the present invention may support one or more growth factors.

In embodiments of the second and third inventive forms of the present invention, the upper wound dressing layer of the wound dressing comprises a polymeric material. The polymeric material may be bioabsorbable and further protein-free. By way of example, the upper section comprises poly (3-hydroxybutyrate). Alternatively, the upper section may comprise a non-bioabsorbable, non-biodegradable material, non-limiting examples of polymers being polyurethane and polytetrafluoroethylene.

In various forms of embodiment of the invention, the upper section of the wound dressing is porous. When the upper layer section and the bottom layer section are both provided with holes, the hole diameter of the hole of the upper layer section is smaller than that of the hole of the bottom layer section. Typically, the pore size of the upper section is less than about 0.25 microns.

In various forms of embodiments of the invention, the wound dressing provides an adhesive edge for releasable adherence to the surface of a tissue structure adjacent a wound. This facilitates application and removal of the dressing or an upper portion thereof.

In embodiments of the second and third inventive forms of the present invention, the upper wound dressing layer provides an adhesive edge in which case the upper wound dressing layer may completely surround the lower wound dressing layer. The ideal coverage margin is about 10-15 mm. When the upper wound dressing layer includes a mid-plane discontinuity, the adhesive edge is traversed by the mid-plane of the upper wound dressing layer.

In embodiments of the second and third inventive forms of the present invention, the intermediate wound dressing layer provides an adhesive edge.

According to the present invention there is also provided a method of treating a wound in a tissue structure of a living human or animal body, the method including the steps of applying to the wound a body fluid permeable lower layer of a bioabsorbable material which assists in the healing process of the wound and covering the lower layer with a breathable, bacteria impermeable upper layer.

The present invention further provides a method for preparing a wound dressing comprising the step of coupling a body fluid permeable bottom layer of a bioabsorbable material to a breathable, bacteria impermeable layer, wherein the material initiates the healing process.

According to the present invention there is also provided the use of poly (3-hydroxybutyrate) in fibre or powder form substantially free of volatile solvents in the manufacture of a wound dressing for the skin.

Said solution of the invention is now described by means of an embodiment and with reference to the attached drawings, in which:

FIG. 1 is a cross-sectional side view of a first wound dressing of the invention;

FIG. 2 is a cross-sectional side view of a second wound dressing of the invention;

fig. 3 is a cross-sectional side view of a third wound dressing of the invention.

As can be seen in FIG. 1, a wound dressing 10 according to the present invention includes a layer of absorbable material 1 which initiates the wound healing process, in this case poly (3-hydroxybutyrate) in the form of a finely divided non-woven sheet applied to a skin wound 2 substantially free of volatile solvents, and an outer microporous layer 3 of polyurethane polymer. The pores of the outer polymer layer 3 have a pore size of less than 0.22 microns. This renders layer 3 permeable to vapour and gas while keeping layer 3 substantially impermeable to bacteria.

The dressing 10 may be conveniently applied and removed, further providing a thermal insulating effect to maintain body temperature near the wound surface by means of the outer polymer layer 3. Since its moisture permeable vapour dressing 10 also maintains the moisture of the wound 2, excess body fluid can be removed from the wound 2. It prevents drying of the nerve ends of the wound and the attendant pain of the patient.

To facilitate application and removal of the dressing 10, the outer polymer layer 3 has an adhesive border 4.

The PHB fibers of dressing 10 exhibit hydrophobic characteristics. The properties of the PHB fiber allow exudate to drain from wound 2 and to remain in the PHB layer 1 and the space between the PHB layer 1 and the outer polymer layer 3.

Wound dressing 10 may be maintained for a relatively long period of time. This means that fewer changes of dressing are required than hitherto suggested. This avoids interference with the healing process and reduces pain for the patient. One possibility when changing the dressing 10 is to remove the polymer 3 and the outer layer with only excessive exudate and then place the fresh outer layer 3 in this position without interfering with the PHB layer 1. Alternatively, the majority of the PHB layer 1 was also removed and replaced with fresh PHB sheet, leaving the PHB fibers adhered to the wound 2.

In fig. 2, a second wound dressing 110 of the invention is shown, comprising a PHB layer 101 applied to a skin wound 102 and a microporous outer layer 103 of polyurethane polymer, the layer 101 being a non-woven fibrous sheet, substantially free of volatile solvents. The PHB101 layer is a pad completely surrounded by the outer polymer layer 103, leaving a 10-15 mm edge (m) of the outer polymer layer 103 around the PHB pad 101. The size of the PHB pad 101 varies depending on the size of the wound 102.

Furthermore, an intermediate absorbing layer 105 of a hydrogenated colloidal material is provided. This layer absorbs exudate transported by the PHB pad 101 from the wound 102 and aids in the transport of other exudates. The presence of the microporous polyurethane outer layer 103 means that exudate is slowly dispersed while the wound 102 remains moist and at the same time bacteria are eliminated. Vapor from the skin surrounding the wound 102 is also able to permeate through the outer polymer layer 103.

The outer polymer layer 103 has an adhesive edge to aid in application and removal of the dressing 10.

Turning now to fig. 3, a third wound dressing 210 of the invention includes a PHB layer 201 applied to a skin wound 202 and a microporous outer layer 203 of polyurethane polymer, the layer 201 being a non-woven fibrous sheet, substantially free of volatile solvents. This PHB is also in the form of a pad completely surrounded by an outer polymer layer 203, leaving a 10-15 mm edge (m) of polymer around the PHB pad. An intermediate absorbent layer 205 of hydrocolloidal material is also provided, in this case an inner hydrocolloidal layer 205 is prepared and has an outer polymer composition 03. As the hydrocolloid material adheres to the skin, it adheres to the skin via its rim 204. The hydrocolloids thus have the dual function of an adhesive edge between the middle adsorbent layer and the outer layer 203.

Those skilled in the art will readily appreciate that the present invention is not limited to the particular wound dressing embodiments described above with reference to the drawings, but that the invention may take many forms or be included within the scope of the invention.

The applicant has observed that a wound dressing should fulfil the following objectives:

● the insulating effect maintains the body temperature of the wound surface.

● should keep the wound moist but should remove excess body fluid.

● the dressing should be permeable to vapor but impermeable to bacteria.

● the dressing should be absorbable and breathable

● should be able to control pain.

● the dressing should be easy to use and remove when needed.

● the dressing should promote healing.

● the dressing should be useful for other treatments, for example to allow the provision of external compression bandages and the effective deposition of dead skin.

● the dressing should be biocompatible and non-toxic.

● the dressing should not be patient restraining.

The wound dressing described above with reference to the drawings fulfills these objects in a simple and inexpensive manner.

In a comparative test, a wound dressing of the invention and a wound dressing comprising a layer of polyurethane (Tagerderm) were tested^TM) The sheet wound dressing is used for dressing skin wounds of a mammalian body. The dressing of the invention consists of a lower section in the form of a PHB non-woven fibrous sheet and an upper section of a polyurethane sheet. The wound dressing of the present invention produces improved wound healing compared to polyurethane sheet wound dressings. Characterized in that the healed wound is covered by the wound dressing of the invention, with a thicker and better quality layer of epidermal cells in the form of regenerated tissue than the healed wound covered by the polyurethane sheet wound dressing.

Claims (99)

1. A wound dressing for dressing a wound on internal or external tissue of a living human or animal body, comprising a lower section which is positioned adjacent the wound when the wound dressing dresses the wound, the lower section being permeable to bodily fluids and comprising a bioabsorbable material which promotes the healing process of the wound, the dressing comprising an upper section which covers the lower section when the dressing dresses the wound, the upper section being permeable to gas and impermeable to bacteria.

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

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

4. A wound dressing according to any one of claims 1 to 3, characterised in that the wound dressing is of unitary construction.

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

6. A wound dressing according to claim 5, characterised in that the wound dressing is composed of upper and lower sections having lower and upper sections comprising 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 fibrous 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 dependent on 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 hyaluronic acid.

13. A wound dressing according to claim 9 when dependent on claim 8, characterised in that the wound dressing is a fibrous sheet of bioabsorbable 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 (roughened) to expose the fibre ends.

16. A wound dressing according to any one of 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) (PHB), polylactic acid, polyglycolic acid, copolymers of glycolic and lactic acids, copolymers of lactic acid and epsilon-aminocaproic acid, lactide polymers, polydesoxazon, copolymers of poly (3-hydroxybutyrate) and 3-hydroxyvalerate, succinic acid polyester 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 protein.

21. A wound dressing according to any one of claims 5 to 20, characterised in that the wound dressing is flexible so that the dressing can conform to the contours of a wound, for example a recessed wound.

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

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

24. A wound dressing according to claim 23 when dependent on claim 22, characterised in that the apertures of the upper section are smaller than the apertures of the lower section.

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

26. A wound dressing according to claim 1,2 or 3, characterised in that the wound dressing is in the form of an integral structure.

27. A wound dressing according to claim 26, characterised in that the upper and lower sections are provided by upper and lower wound dressing layers, respectively, which are coupled to each other prior to dressing the wound.

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

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

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

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

32. A wound dressing according to claim 30, characterised in that the intermediate section is 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 upper and lower wound dressing layers with the lower wound dressing layer adhered to the 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 adhered to the upper and lower surfaces, respectively, of the intermediate wound dressing layer.

35. A wound dressing according to claims 27 to 34, characterised in that the lower wound dressing layer releasably shields the remainder of the wound dressing.

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

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

38. A wound dressing according to claims 27 to 37, characterised in that the lower wound dressing layer is provided by a granular layer of bioresorbable material.

39. A wound dressing according to claim 38, characterised in that the particles may be supported by 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 the 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 into a solvent, coating the mixture onto 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 is 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 provided by upper and lower wound section layers applied separately to the wound.

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

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

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 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 provided by a granular layer of bioabsorbable material.

53. A wound dressing according to claim 52, characterised in that the particles are supported by 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 the gel matrix comprises hyaluronic acid.

56. A wound dressing according to any one of claims 46 to 50, characterised in that the lower section is provided by a loose particulate or fibrous layer of bioresorbable material positioned on the wound when the wound dressing dresses 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 a 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 is in the form of one or more wound dressing sheets.

59. A wound dressing according to claim 58 when dependent on claims 46 to 51, characterised in that the lower wound dressing layer is provided by one or more lower wound dressing sheets covering 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 the form of fibres.

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

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

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

64. A wound dressing according to claim 60, characterised in that the lower wound dressing layer is provided 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 the fibre ends.

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) (PHB), polylactic acid, polyglycolic acid, copolymers of glycolic and lactic acids, copolymers of lactic acid and epsilon-aminocaproic acid, lactide polymers, polydesoxazon, copolymers of poly (3-hydroxybutyrate) and 3-hydroxyvalerate, polyesters 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 polysaccharide such as 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 so that the dressing can conform to the contours of a wound, for example 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 modifiable to conform to the wound contour.

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 material is bioabsorbable.

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

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-bioabsorbable material.

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

82. A wound dressing according to claim 81, characterised in that the polymeric 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.

84. A wound dressing according to claim 83, when dependent on claim 28 or claim 47, characterised in that the apertures of the upper section are smaller than the apertures of the lower section.

85. A wound dressing according to claim 83 or 84, characterised in that the pores of the upper section have a pore size of less than about 0.25 microns.

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

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

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

89. A wound dressing according to claim 87 or 88, characterised in that the upper wound dressing layer covers the remainder of the wound dressing with a rim of about 10-15 mm.

90. A wound dressing according to claim 86, when dependent on claim 31 or 51, characterised in that the upper wound dressing layer includes a middle section and the adhesive edge is provided by the middle section of the upper wound dressing layer.

91. A wound dressing according to claim 86, when dependent on claim 31 or claim 50, characterised in that the intermediate wound dressing layer provides an 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 an ionised gel.

93. A method of treating a wound in a tissue structure of a living human or animal body, the method comprising the steps of applying to the wound a body fluid permeable bottom layer of a bioabsorbable material which assists in the healing process of the wound and covering the bottom layer with a breathable, bacteria impermeable upper layer.

94. A method of making a wound dressing comprising the step of coupling a body fluid permeable bottom layer of a bioabsorbable material to a breathable, bacteria impermeable layer, wherein the material initiates the healing process.

95. The method of claim 93 or 94, wherein the bioabsorbable material is a bioabsorbable polymer.

96. The method of claim 95, wherein the polymer is protein-free.

97. The method of claim 96, wherein the polymer comprises poly (3-hydroxybutyrate).

98. Use of poly (3-hydroxybutyrate) in the form of a fibre or powder substantially free of volatile solvents in the manufacture of a wound dressing for the skin.

99. The use according to claim 98, characterized in that no solvent is present in the fiber or powder.