WO2009151380A1

WO2009151380A1 - A wound dressing

Info

Publication number: WO2009151380A1
Application number: PCT/SE2009/050670
Authority: WO
Inventors: Tomas Fabo
Original assignee: Mölnlycke Health Care Ab
Priority date: 2008-06-12
Filing date: 2009-06-04
Publication date: 2009-12-17
Also published as: SE0801375L

Abstract

The present invention relates to a wound dressing (1) including a layer of airimpermeable material (4) and means for attaching the dressing to the skin surrounding a wound. According to the invention a resilient body (2) of foam material having a slow expansion rate is included in the dressing.

Description

A wound dressing.

TECHNICAL FIELD

The present invention relates to wound dressing including a layer of air- impermeable material, means for attaching the dressing to the skin surrounding a wound, and a resilient body of foam material. The invention also relates to the use of such a body in a wound dressing or the like.

BACKGROUND TO THE INVENTION

It has been shown to be beneficial for the healing of a wound if the wound bed is subjected to a sub-atmospheric pressure or sub-pressure. Wound dressings in which a sub-pressure is created in a space surrounding a wound bed are also known in the art, see for example US 4,969,880, US 5,645,081 , US 5,636,643, US 6,855,135, WO2006/025848, US2008/0082059 and US 2008/0004559. Such dressings, so called NPT-dressings (Negative Pressure Therapy), are usually connected to a pump-driven, often external source of sub-pressure by a tubing or the like. The external source of sub-pressure may be a stationary device or a device that the patient can bring with him. Depending on the tightness against leakage of air into the dressing, the external source may be driven continuously or intermittently. Sub-pressure also increases the rate of exudation and thereby improves cleaning of a wound. In addition, wound dressing systems with sub-pressure also effectively take care of the exudate and reduce the risk of leakage from the wound dressing to the wound environment. The wound exudate sucked up from the wound bed can be stored in an external container or a porous body included in the dressing. The application and handling of known sub-pressure dressings and relating devices are thus rather complicated and time-consuming and there is accordingly room for improvement. Furthermore, the tubing used in such dressings must be rigid enough to withstand the pressure difference between the sub-pressure and the atmospheric pressure essentially without change of sectional shape. Such tubing can therefore be irritating or damaging to the skin of a patient if it is pressed against the skin by external forces, such as affixing tape or tight clothing or if the patient is lying thereon. In addition to a complicated waste handling, there are also the above described disadvantages concerning patient comfort and skin damage when instead portable pumps (e.g. mechanical or electrical) are used by the patient. It would therefore be an advantage if such equipment could be avoided.

In US 2008/0103462 Al it is proposed to compress an absorbent body of an expandable material in a wound dressing before this dressing is applied to a wound. In one example shown in figures IA- ID of such a dressing such a compressed body is encased in vapour- impermeable layer including a layer typically in contact with a wound and having openings therein. When compressing the dressing before use, air is expelled from the body and escape out of said openings. The compressed dressing is thereafter applied to a wound. However, there is no information on how the compression of the body is maintained during the application of the dressing, i.e. how air is prevented from entering into the body through said openings. In another example said openings are closed by a dissolvable sealant, thereby preventing air from entering the compressed body.

The objective of the present invention is to solve the problem of maintaining the compressed body of a wound dressing compressed to a high degree during application of a wound dressing having a compressed dressing to a wound. SUMMARY OF THE INVENTION

This objective is accomplished by a wound dressing including a layer of air- impermeable material, means for attaching the dressing to the skin surrounding a wound, and a resilient body of foam material, characterised in that the body consists of a foam material having a slow expansion rate so that the body expands after compression to between 1 and 30% of initial thickness after 30 seconds in room atmosphere and in room temperature. A body of such a foam material rather slowly retain its initial shape after compression and can be compressed manually or by machine before the dressing is attached to a wound. When such a resilient material is used, most of the compression of the material and thereby its ability to create a sub-pressure is maintained after attachment of the dressing. Such a dressing gives the person appropriate time to apply the wound dressing without risk that an overly rapid expansion of compressed body which will significantly reduce its ability to create the desired sub-pressure.

In a preferred embodiment, the foam material of which the body is made expands, after compression, to less than 20% of initial thickness after 30 seconds in room atmosphere and in room temperature. Preferably, the foam material expands, after compression, to between 1 and 50%, preferably to less than 25% of initial thickness, after 60 seconds in room atmosphere and in room temperature.

The body of foam material has the ability to directly or indirectly suck liquid from a wound bed and can constitute the wound pad. The wound pad can instead be constituted of several layers.

The dressing is to advantage stored in a vacuum package. The invention also relates to a combination of a first wound dressing including a wound pad and a cover layer of air-tight material and a second wound dressing according to the dressing described above, which is attached on top of the first wound dressing in a region thereof surrounding a hole in the cover layer of the first wound dressing.

The invention also relates to the use of a body which consists of a foam material having a slow expansion rate so that the body expands after compression to between 1 and 30% of initial thickness after 30 seconds in room atmosphere and in room temperature, in a wound dressing.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described with reference to the enclosed figures, of which;

fig. 1 schematically discloses a cross-sectional view of a wound dressing according to a first preferred embodiment of the invention, and

fig. 2 schematically discloses a cross-sectional view of a wound dressing according to a second preferred embodiment of the invention.

DESCRIPTION OF EMBODIMENTS

In figure 1 a cross-sectional view of a wound dressing 1 according to a first preferred embodiment is schematically disclosed. The dressing 1 includes a body 2 of compressible and resilient material. The body 2 is covered by a layer 3 of an airtight material, preferably a plastic film, which extends laterally beyond the circumference of body 2 in order to enable affixation of the dressing 1 to skin surrounding a wound bed. On the underside of film 3, i.e. the side turned against body 2, a coating of a skin- friendly adhesive is applied at least in the portion of the film extending laterally outside of the circumference of body 2.

Before use of the dressing, the underside thereof is covered with a protection layer (not shown) for protecting the adhesive coating before use as is usual in the art. The protection layer is made of or coated with a substance that adheres poorly to the adhesive. Thus, the material used for the protection layer is depending on the adhesive used and all known material combinations of adhesive and protection layer can be used in the present invention. An example of such a combination is a silicone adhesive covered by a polyethylene layer or a paper layer having a polyethylene coating on the side thereof releasab Iy attached to the silicone adhesive.

Moreover, if the covering plastic film 3 is very thin, e.g. thinner than 50 micrometer, a stiffening layer (not shown) in form of a frame around the edge regions of the portion of film 3 extending laterally outside of body 2 is removably attached to the top side of film 3. i.e. the side distal from the body 2 as also is usual in the art. The stiffening layer can be made of any material known in the art to be used for stiffening layers for film dressings or the like.

In accordance with the present invention, the body 2 of compressible and resilient material is arranged to be in a pre-compressed state when the wound dressing 1 is affixed to skin surrounding a wound bed. Said pre-compressed state is obtained by compressing the body 2 by any suitable means and by maintaining compression of the body 2 at least until the wound dressing has been attached to skin surrounding a wound. According to the invention the body 2 is made of a material with a slow expansion rate, such as visco-elastic foam, sometimes also referred to as a shape memory foam or memory foam. If compressed, such a material will only loose a small portion of the compression during the time it takes to attach the wound dressing 1 to a wound. Most of the initial compression of the pre- compressed body will then be maintained after the dressing has been attached. Examples of methods for manufacturing visco-elastic foams are given in US 4,158,087, WO98/16567 and US 6,946,497. A visco-elastic foam with a glass transition point (Tg) somewhat below the body temperature is preferably used to secure a controlled expansion of the foam (see for instance US 6,583,194, US 5,049,591, US 5,418,261, US 5,032,622).

When the wound dressing 1 has been attached to an exuding wound, the exudate comes into contact with the body 2 which will start to expand due to its resiliency. The expanding body will create an expanding volume under the covering film and thereby create a sub-pressure in the fluidum between the wound surface and the covering film. When more exudate is entering into the wound dressing, the body will continue to expand. When the body has reached its fully expanded shape or is hindered to expand further by external mechanical forcers (such as e.g. from the plastic film or the surrounding atmospheric pressure), no more sub-pressure will be generated by the body.

In order for the wound dressing 1 to function well, it is essential that the compressed body 2 will not loose too much of it compression when the compressed wound dressing is applied to a wound. Most resilient plastic foams have a fast rate of expansion which means that they normally have time to retain their initial shape during the time it takes to apply the wound dressing to a wound in room atmosphere, i.e. under the pressure conditions prevailing in the atmosphere in the room. Resilient foams typically retain their initial shape in less than 15 seconds after release of compression forces.

In contrast thereto, the visco-elastic foam material of which the body is made expands, after compression to between 1 and 30%, preferably to less than 20% of initial thickness, at the most to 33% of initial thickness, preferably to less than 20%, after 30 seconds in room atmosphere and in room temperature. Furthermore, the visco-elastic foam material of which the body is made expands, after compression to between 1 and 30%, preferably to less than 20% of initial thickness, at the most to 50% of initial thickness, preferably to less than 25%, after 60 seconds in room atmosphere and in room temperature. Most wound dressings can be carefully applied to a wound within 30 seconds. With the expansion rates stated above, a body compressed to 17% of initial thickness will after 30 seconds have at least have 65% of its volume left for expansion, preferably at least 80%. In this respect it is pointed out that the wound dressing 1 must be carefully applied so that it is ensured that it is tightly attached to skin surrounding the wound bed so that air is prevented from leaking into the space over the wound bed after application of the dressing 1. However, if the wound dressing is to be attached to a part of a body of a patient having a complicated shape, the application of the dressing might take longer than 30 seconds. In such cases, a body compressed to 17% of initial thickness will at least have 50% of its volume left for expansion after the dressing is applied to a wound, preferably at least 75%. If the body is compressed to less than 17% of its initial thickness, a corresponding increase of volume left for expansion after the dressing had been applied would usually prevail.

The percentages left for expansion mentioned above presuppose that the visco- elastic foams used will expand to 100% of initial thickness. This is not the case for all visco-elastic foams but visco-elastic foams suitable to use in a wound dressing according to the present invention should after compression to less than 20% of initial thickness after 24 hours in room atmosphere and room temperature have expanded to at least 80%, preferably at least 90%, of initial thickness.

The compression of body 2 of the wound dressing 1 shown in figure 1 could be made just before the dressing is applied to a wound. The compression would then usually be made manually with the protection layer attached to the adhesive layer and the protection layer is removed before application of the dressing.

In some cases it might be of interest to compress the body in connection with the manufacture of the dressing. Maintaining of the compression of the body in the dressing during storing and transport to a user can be done in two different ways. A first way would be to compress the body during manufacture and then place it in a so called vacuum package, i.e. a package in which air has been evacuated,

Another way of maintaining pre-compression of the body in such cases involves enclosing the compressed body in an airtight envelope before it is disposed within the dressing. Thereby, the pre-compression is maintained when the wound dressing is attached to a wound. In order to enable such a dressing to absorb exudate from a wound when applied thereto the air-tight envelope should consist entirely or at least on the underside thereof, of a material which dissolves when in contact with liquid, for example a film of polyvinyl alcohol. The upper side of such an envelope may preferably be attached in one or more parts to the underside of the plastic film covering the wound pad. However, even if the pre-compressed body is enclosed in an airtight envelope, a vacuum package or other external mechanical means to keep the dressing compressed is preferably used for the wound dressing.

The adhesive coating on the underside of film 3 should be such that the space delimited by a wound bed and the portion of film 3 covering the top and sides of body 2 is sealed against the environment so that air can not leak into this space. A coating of a silicone adhesive with a softness of at least 10 mm and applied in an amount of at least e.g. 50 g/m is suitable for this purpose as is evident from WO 2006/075950, to which is referred to for further details.

In figure 2, a wound dressing 1 according to figure 1 used in combination with a conventional dressing 4 is schematically shown. The wound dressing 4 differs from the wound dressing 1 described with reference to figure 1 mainly in that it contains a wound pad 5 of conventional design, for example a body made of absorbent foam or absorbent fibre material. Furthermore, a hole 7 through the cover layer 6 of dressing 4 is present therein.

The wound dressing 1 with its body 2 in a compressed state is attached to the dressing 4 after this dressing has been applied to a wound. When the liquid exudate absorbed by the wound pad 5 of dressing 4 comes into contact with the lower side of the compressed body 2, liquid exudate is sucked into this body and this body begin to expand thereby creating a sub-pressure within the space containing the body 2 of dressing 1 and the wound pad 5 of dressing 4, the wound bed thereby be subjected to this sub-pressure. The expansion of the body 2 of dressing 1 will continue until wound pad 5 is emptied of liquid exudate or until body 2 is fully expanded. Body 2 will thus drain the wound pad 5 of dressing 4. When the body of dressing 1 is full or after a predetermined time dressing 1 is removed and substituted by a fresh dressing 1 with its body 2 in a compressed state. This combination of dressings 1,4 has the advantage of enabling change of dressing 1 without disturbance of the wound bed or surrounding skin which promote healing of the wound and at the same time establishing a sub-pressure over the wound which also promotes healing of the wound.

The hole 7 in cover layer can be manually cut just before attaching of dressing 1 to dressing 4. Another possibility is of course to have the hole made during manufacture of the dressing 4 and thereafter covering it with a film of an airtight liquid soluble material.

It is of course also possible to attach the dressing 1 to dressing 4 in connection with the manufacture of the dressings. In such a case, the unit of dressings 1,4 with the body 2 of dressing 1 in a compressed state should be packaged in a vacuum package or the body 2 should be enveloped in an airtight envelope which at least partly is made of a liquid soluble film.

Due to the sub-pressure created when the wound dressing 1 has been attached to dressing 4 and when possible liquid soluble material constituting the seal between body 2 and the environment is broken in the attached wound dressing 1 , the bodies 2,5 will be pressed tightly against each other and body 5 will be pressed tightly to the wound bed mainly by a pressure corresponding to the pressure difference between the atmospheric pressure and the sub-pressure created in the space above the wound bed. Exudate will then be drained from body 5 and sucked into body 2 mainly due to the created sub-pressure but also by capillary forces.

The expansion of the body 2 must develop unobstructed by the film 3. The size of the film 3 is thus preferably such that it allows expansion of the body 2 to a relaxed state. It is of course possible to choose a larger or intermediate size of the film 3 depending on desired properties of the wound dressing. A larger size can be chosen in order to ensure that the ability of the compressed resilient body 2 to expand is used completely. An intermediate size can be used in order to indicate when the wound dressing 1 has to be changed in order to ensure that the wound is continuously subjected to a sub-pressure.

The indication would then be that the wound dressing should be changed when folds or uneven parts no longer are present on the film 3. In this respect, it is pointed out that although the underside of film 3 may have an adhesive coating on parts covering the body 2, the regions of the film which contains folds or the like due to the oversize of film 3 must of course be free of adhesive.

In the embodiment shown in figure 2, the body 5 is constituted by an absorbent material, such as a foam with open cells or a fibrous nonwoven or textile material made of absorbent fibres. However, when dressing 4 is used in combination with dressing 1 it is not necessary that the body 5 is of absorbent material, it is enough that it is permeable for air and liquid. It can thus, for example, be constituted of a net of absorbent or non-absorbent material, a perforated plastic film or a nonwoven or textile material made of non- absorbent fibres.

An absorbent or non-absorbent body similar to body 5 in the second embodiment can of course also be present in the wound dressing 1 according to figure 1 placed between body 2 and the wound bed.

The materials used in a wound dressing according to the present invention are such that the dressing can be sterilized, for example by ethylene oxide. A wound dressing according to the present invention has many advantages compared with conventional island dressings. Firstly, the pressure difference between atmospheric pressure and the sub-pressure created presses the wound pad tightly against the wound bed so that a good contact between wound pad and the wound bed is ensured. As a matter of fact, said pressure difference will assure a better fixation of the wound dressing as a whole. The sub-pressure created above the wound bed will also ensure a better removal of exudates from the wound bed and also improve the healing of the wound.

In comparison with existing NPT-dressings, a wound dressing according to the present invention is less spatious, needs no electric or manual pump, makes no sound and is easier to use. A wound dressing according to the present invention is also of the disposable type and needs no service or cleaning. Moreover, it is a closed system with no external air- flow and consequently no external tubing which makes it very easy to use and to apply and also reduces the risk for cross-infection in comparison with reusables. A wound dressing according to the present invention has fewer parts than existing NPT-dressings and is thus easier to store and handle and can also be manufactured at a lower cost.

Furthermore, the use of a visco-elastic foam will give the person that shall apply a wound dressing according to the present invention a long enough time, after compressing thereof, to remove protective layers, carefully place the dressing over a wound bed and attach it tightly to the skin surrounding the wound bed without too much expansion of the compressed body.

The described embodiments can of course be modified without leaving the scope of invention. The shapes of the wound dressings can for example be different than shown and described with reference to the figures. Other adhesives and materials used for known film dressings than stated above can be used. So called superabsorbent particles can be mixed within the bodies or be present in additional layers on top of the bodies in order to further enlarge the liquid storing capacity of the wound dressings. The wound pad of a dressing 1 according to the invention can consist of several layers, of which a layer of visco-elastic foam is one. The scope of invention shall therefore only be restricted by the content of the enclosed patent claims.

Claims

1. A wound dressing (1) including a layer of air- impermeable material (3), means for attaching the dressing to the skin surrounding a wound, and a resilient body (2) of foam material, characterised in that the body (2) consists of a foam material having a slow expansion rate so that the body (2) expands after compression to between 1 and 30% of initial thickness after 30 seconds in room atmosphere and in room temperature.

2. The dressing according to claim 1, wherein the foam material of which the body (2) is made expands, after compression, to less than 20% of initial thickness after 30 seconds in room atmosphere and in room temperature.

3. The dressing according to claim 2, wherein the visco-elastic foam material of which the body (2) is made expands, after compression, to between 1 and 50%, preferably to less than 25% of initial thickness, after 60 seconds in room atmosphere and in room temperature.

4. The dressing according to claim 1, 2 or 3, wherein the body (2) of visco- eoastic foam material has the ability to directly or indirectly suck liquid from a wound bed.

5. The dressing according to claim 1,2,3 or 4, wherein the body (2) of visco- elastic foam constitutes the wound pad.

6. The dressing according to claim 1, 2,3, or 4, wherein the wound pad (2) is constituted of several layers.

7. The dressing according to any of claims 1-6, wherein the dressing (1) is stored in a vacuum package.

8. A combination of a first wound dressing including a wound pad and a cover layer of air-tight material and a second wound dressing according to claim 1 , which is attached on top of the first wound dressing in a region thereof surrounding a hole in the cover layer of the first wound dressing.

9. Use of a body (2) which consists of a foam material having a slow expansion rate so that the body (2) expands after compression to between 1 and 30% of initial thickness after 30 seconds in room atmosphere and in room temperature, in a wound dressing.