WO2015145117A1

WO2015145117A1 - Wound dressing

Info

Publication number: WO2015145117A1
Application number: PCT/GB2015/050839
Authority: WO
Inventors: Stephen Cotton
Original assignee: Brightwake Limited
Priority date: 2014-03-25
Filing date: 2015-03-20
Publication date: 2015-10-01
Also published as: GB2524510B; GB201405284D0; GB2524510A

Abstract

A wound dressing comprising an absorbent core of foam material having a regular array of perforations formed therein, and a wound-contact layer bonded to a first face of the absorbent core and comprising gelling fibres, wherein at least the absorbent core is impregnated with honey. The perforations in the absorbent core result in increased honey capacity, while the absorbent core absorbs exudate, reducing dilution of the honey.

Description

Wound dressing

This invention relates to wound dressings, in particular, the invention concerns wound dressings that include honey.

Healing properties have long been associated with honey. Honey is a mixture of sugars, water and other active ingredients such as vitamin C, catalase and chrysin, that are thought to act as antioxidants. As such, it has much greater activity than sugar alone.

In particular, certain honeys such as manuka honey, produced from the plant species Leptospermum scoparium., have been shown to have high anti-bacterial, non-peroxide activity which inhibits the growth of various species of bacteria. As such, honey can support wound healing through its anti-inflammatory action, its natural anti-bacterial properties, its debriding action and its stimulatory effect on granulation and epithelialisation. In fact, honey has been shown to have considerable wound- and ulcer-healing capacity and strong anti-microbial capacity even in moist healing environments.

Different types of wound dressing are required to meet different clinical needs. However, there are several desirable characteristics that are common to all wound dressings. Pain-free removal and the ability to remove a dressing without trauma to the wound and the surrounding skin are two of the most important

characteristics. In order to prevent pain and trauma, the wound contact surface of a wound dressing needs to maintain a moist layer over the wound to prevent adherence to the drying wound. It is known that for efficient wound healing the area of the wound should be kept moist, but the surrounding healthy skin should be kept dry to avoid maceration of the healthy skin. If a wound dressing cannot be cleanly removed from a wound, then a patient will suffer additional trauma.

Gelling fibres such as alginate or pectin fibres are known for use in wound dressings. They have a greater capacity for absorbing liquid than standard textile fibres and, on absorbing liquid, they become moist and slippery. This prevents the dressing from adhering to the wound and therefore makes removal of the dressing easier. Dressings comprising honey are also known in the art. However, the honey capacity of the currently available dressings is limited and lower than desired. One reason for this is the fluid nature of honey. The honey incorporated in a dressing is liable to flow away from the site of the wound. In addition, if a wound produces a significant volume of exudate, the exudate may dilute the honey and exacerbate the problems associated with the fluid nature of the honey.

There has now been devised an improved honey-containing dressing, which overcomes or substantially mitigates the above-mentioned and/or other shortcomings or disadvantages of the prior art.

According to the invention there is provided a wound dressing comprising an absorbent core of foam material having a regular array of perforations formed therein, and a wound-contact layer bonded to a first face of the absorbent core and comprising gelling fibres, wherein at least the absorbent core is impregnated with honey.

The wound dressing according to the invention is advantageous primarily in that it enables a larger volume of honey to be held in contact with a wound site. In addition, the presence of the wound-contact layer between the absorbent core and the wound site may reduce the rate at which honey is released from the dressing to the wound site. The dressing according to the invention may therefore increase the amount of honey delivered to the wound site, and/or it may prolong the duration of action of the honey. The perforations in the absorbent core provide pockets for the honey and result in an increased honey capacity. In addition, the absorbent core may absorb exudate from the wound, thereby reducing the rate at which honey is diluted and flushed away from the wound site. Again, this may prolong the action of the dressing. The absorbent core may also provide cushioning and may increase the conformability of the dressing. Furthermore, because the wound-contact layer contains gelling fibres, that layer becomes gelatinous in use, when exposed to wound exudate. This renders the dressing non-adherent and allows for atraumatic removal of the dressing. In preferred embodiments of the invention, one face of the absorbent core is bonded to the wound-contact layer and the other face is bonded to a backing layer. Preferably, the backing layer is identical to the wound-contact layer, ie the dressing may be symmetrical about the absorbent core. This has the advantage that it eliminates the risk of the dressing being placed on the wound in the wrong orientation, and also allows for the possibility of the dressing being used first in one orientation and then being inverted, thus prolonging the useful life of the dressing and leading to cost-savings. In other embodiments, however, the backing layer is different to the wound-contact layer. The backing layer may be a non-gelling fabric layer, or it may be a plastics film, eg a polyurethane film of the general type that is widely used in wound dressings. Such a film is preferably sufficiently porous to permit the transmission of moisture vapour, but not so porous as to prevent the loss of liquid or to permit the ingress of bacteria.

The foam material used in the absorbent core may be any suitable foam known in the art. Usually, the foam is an open-celled foam. Preferably, the foam is a hydrophilic foam. More preferably, the hydrophilic foam is a polyurethane foam. Most preferably, the foam is an open-celled polyurethane foam. The open cellular structure allows exudate from a wound to pass through the foam as well as be absorbed by it. The structure is sufficiently open as to allow exudate to pass through it. The foam typically has a thickness of 0.5mm to 10mm, preferably from 1 mm to 4mm, and the foam most preferably has a thickness of 1 mm to 2mm.

Foams are generally absorbent. If the foam is an open-celled foam it will have a higher absorbent capacity. This is advantageous in that the foam may wick away exudate from the wound. This can prevent the honey from becoming diluted and reduce the likelihood of the honey becoming sufficiently fluid to run away from the wound site. The perforated foam layer has perforations spaced regularly across the extent of the layer. The perforations may be any suitable shape, but are typically circular and have a diameter of from 3mm to 10mm, preferably 4mm to 8mm and most preferably about 5mm to about 7mm, The perforations may be arranged in any suitable pattern across the dressing but are most preferably arranged in a hexagonal array. Depending on the size of the perforations, the centre-to-centre separation of perforations in such an array may be between 7mm and 20mm, or between 10mm and 15mm. It should be understood, however, that any regular array of perforations may be appropriate for use in the invention. The perforations may, for instance, be square or rectangular and arranged in parallel lines, or they may be elongate slots in a herringbone arrangement, or they may be elliptical or triangular or any other suitable shape.

The wound-contact layer has an open structure that allows wound exudate from a wound to pass through it as well as be absorbed by it. It also allows honey to pass from the dressing to the wound site.

The wound-contact layer may be non-woven, knitted or woven. Most preferably, the wound-contact layer is a knitted material. Knitting is a process whereby fabric is formed by the interlocking of loops of yarn. A variety of knitting techniques are known in the art, and are suitable for use in the present invention.

The wound facing layer comprises gelling fibres. Gelling fibres allow the dressing to be non-adherent and enable atraumatic removal of the dressing. Gelling fibres are also absorbent. Gelling fibres can absorb excess wound exudate and reduce the effects of dilution of the honey at the wound site.

By "gelling fibre" is meant in relation to the invention fibres that are capable of absorbing aqueous fluid, such as wound exudate, and which on absorbing liquid become gel-like, moist and slippery. The gelling fibres may have an absorbency of at least 2 grams 0,9% saline solution per gram of fibre, as measured by the free swell absorbency test (ie dispersing a known dry weight of fibre in the test liquid (saline) for sufficient time for the fibre to absorb liquid, removing the excess liquid by vacuum filtration, and measuring the increase in weight of the fibre). The absorbency may be considerably higher, eg at least 5g/g, or at least 10g/g, or at least 15g/g, or at least 25g/g. The gelling fibres may be any suitable gelling fibre known in the art, including pectin fibres, alginate fibres, fibres made from alginate and another

polysaccharide, chitosan fibres, hyaluronic acid fibres, fibres of other

polysaccharides or derived from gums, or chemically-modified cellulosic fibres, eg carboxymethyl cellulose (CMC). The gelling fibres may be a combination or blend of different gelling fibres.

Currently preferred gelling fibres are alginate fibres and pectin fibres.

Alginates are high molecular weight, hydrophilic polymers, which are derived from seaweed and which form a gel on contact with aqueous fluids. Their hydrophilic nature encourages the absorption of liquid such as wound exudate, making them extremely useful in wound dressings.

The alginate polymer is formed of two basic monomeric units, mannuronic acid and guluronic acid. Differing proportions of these units in the polymer alter the properties of the alginate. In addition to this, alginate polymers are associated with cations, and are normally produced in the form of sodium alginate, calcium alginate or a sodium/calcium alginate mix. Other forms, such as potassium alginate, are also known.

The nature of the cation which is associated with the alginate polymer changes the properties of the alginate. For example, sodium alginate is water-soluble, whereas calcium alginate is not. By altering the alginate used in a wound dressing it is therefore possible to ensure that the final dressing displays the desired

characteristics.

Pectins are a family of complex polysaccharides comprising 1 ,4-linked γ-D- galactosyluronic residues, found primarily in the cell walls of terrestrial plants. Pectins can be separated into two main groups which have different gelling properties: low-methoxy and high-methoxy pectins. Low-methoxy pectins are pectins in which less than half the carbonyl groups in the chain of galacturonic residues are esterified with methanol, Low-methoxy pectins can form a gel in the presence of divalent cations (eg calcium), due to non-covalent ionic interactions between blocks of galacturonic acid residues and the divalent ion. High-methoxy pectins are those in which more than half of the carbonyl groups have been esterified with methanol. Such pectins can gel in the presence of sugar and acid, forming two-dimensional networks of pectin molecules in which the solvent (water) is immobilised with the sugar and acid co-solutes.

Another class of gelling fibres that are known to be useful in absorbent wound dressings are those made from chemically-modified cellulose. In particular, carboxymethylated cellulose fibres may be used, eg in the form of sodium carboxymethyl cellulose. Such fibres preferably have a degree of substitution of at least 0.2 carboxymethyl groups per glucose unit, or at least 0.3 or at least 0.5.

The wound-contact layer may comprise only gelling fibres. However, at least where the wound-contact layer is woven or knitted, it is preferred that it comprises a blend of gelling fibres and non-gelling fibres. Preferably the material comprises at least 50% w/w gelling fibres. The material may be formed from a mixture of yarns of gelling fibre and yarns of non-gelling fibre. More preferably, however, the material is formed, most preferably knitted, from a single yarn that is a blend of gelling and non-gelling fibres. Suitable yarns include those disclosed in

Internationa! Patent Application WO2013/064831 .

The combination of gelling fibre and non-gelling fibre in such blended yarns produces a strong, flexible yarn, even where there is a relatively low proportion of non-gelling fibre.

The non-gelling fibres may be any suitable fibres known in the art, or may be a mixture of two or more non-gelling fibres. The non-ge!!ing fibres may be textile fibres, and may be natural, eg cotton, may be natural fibres which have been modified eg cei!u!osic fibres such as viscose or lyocell (sold under the trade name TENCEL®), or they may be synthetic, eg polyester, polypropylene or polyamide. Different fibres have different characteristics in terms of tensile strength and absorbency, and appropriate non-gelling fibres may be chosen according to the desired characteristics of the wound dressing. In addition, a combination of two or more non-gelling fibres may be used in order to achieve the desired

characteristics. Preferably, the non-gelling fibres are natural fibres which have been modified. More preferably, the non-gelling fibres are cellulosic fibres. Thus, in some embodiments of the invention, the wound-contact layer may comprise a combination of alginate fibres and cellulosic fibres. In such cases, the wound-contact layer preferably comprises a combination of calcium alginate fibres and cellulosic fibres. More preferably, the wound-contact layer comprises calcium alginate and viscose, or calcium alginate and lyocell.

In other embodiments of the invention, the wound-contact layer may comprise a combination of pectin fibres and cellulosic fibres. In such cases, the wound- contact layer preferably comprises a combination of pectin fibres and viscose, or pectin fibres and lyocell.

Preferably the wound-contact layer retains its structural integrity after use in the wound dressing. Even when saturated with liquid, the structure retains sufficient integrity that it can be easily removed from the wound with little or no breakage or disintegration,

The wound-contact layer is bonded to the perforated foam layer. The layers may be bonded by any suitable means known in the art. Preferably the layers are heat- bonded. Most preferably, the wound-contact layer is heat-bonded to the foam layer using a heat-fusible polymer layer.

At least the perforated foam absorbent core of the dressing is impregnated with honey. In practice, however, it is preferable for both the absorbent core and the wound-contact layer to be impregnated with honey. Indeed, especially where the dressing is symmetrical, with the absorbent core bonded to a wound-contact layer and a backing layer (which may be identical to the wound-contact layer), the whole dressing may be impregnated with honey. Thus, the absorbent foam core may be impregnated with honey prior to being incorporated into the dressing, or the various layers of the dressing may be bonded together and then impregnated with honey. Impregnation with honey may take place by dipping the component(s) of the dressing that are to be impregnated in honey. For instance, the honey may be contained in a suitable vat through which those component(s) are passed in a continuous process. It should be understood that in practice the dressing of the invention will in most instances be manufactured by bonding the material of the various layers together to form a stock material from which individual dressings are cut or otherwise separated. Thus, it will most commonly be that stock of dressing material that is impregnated with honey, followed by division of the stock material into individual dressings, rather than impregnation of individual pre- formed dressings. When the material is impregnated, the perforations in the foam layer fill with honey, and the wound-contact layer (and, if it is of an appropriate material, the backing layer - which may be identical to the wound-contact layer) is saturated with honey. Excess honey may be removed, for instance by passing the honey-impregnated material through calendaring rollers.

The honey enters the perforations in the foam and impregnates the wound-contact layer. The perforations thus provide pockets for the honey and increase the honey capacity of the dressing. The results in a dressing with a high honey capacity. In use, the honey is in direct contact with the wound. The wound-contact layer, having an open structure, permits honey to be transmitted to the wound site.

However, the wound-contact layer also constrains that flow of honey so that honey is not lost from the dressing excessively quickly. The wound-contact layer also permits wound exudate to be taken up by the absorbent core, thereby reducing dilution of the honey and the tendency for the honey to be washed away from the wound site by the wound exudate.

After the stock material has been impregnated with honey, individual dressings can be formed, eg by cutting out using a suitable punch or other cutter. The dressings may have any desired shape, but are most commonly square or rectangular. The size of the dressing may vary between a few centimetres in one or both of length and width, to a few tens of centimetres in one or both of length and width. Thus, the dressing may be square, with sides of up to 5cm, or up to 10cm, or up to 20cm or more, The dressing may alternatively be rectangular, with a length of up to 5cm, or up to 10cm, or up to 20cm or more, and a width of up to 5cm, or up to 10cm or more,

The honey may be any suitable honey. Preferably the honey is manuka honey or another honey produced by bees that have collected nectar from plants of the genus Leptospermum, eg Leptospermum scoparium (manuka) or Leptospermum poiyga!ifo!ium (jelly bush). As noted above, these honeys are known to exhibit highly beneficial properties in wound healing, Where the perforations in the absorbent foam core are circular and are arranged in a regular hexagonal array, and where the whole dressing is impregnated with honey, the dressing may have an appearance reminiscent of a natural

honeycomb, Whilst that appearance is not in itself of technical significance, it may give the dressing a pleasing aesthetic, natural-looking appearance, which may be reassuring to patients and so may improve patient compliance.

The dressing will generally be supplied with a releasable liner on one or both sides of the dressing. The releasable liner may cover the wound dressing prior to use, and be removed from the dressing immediately before application of the dressing to the wound, This reduces the risk of contamination of the wound dressing and facilitates handling of the dressing.

Such releasable liners are commonly used on wound dressings known in the art, and suitable materials which can be employed in the present invention will be familiar to the skilled worker. For example, the releasable liner may be of a suitable plastics sheet or a siliconised paper or the like. The re!easab!e liner may be a single sheet which covers a side of the wound dressing, or may be formed of two or more sheets. The releasable liner may further comprise a tab to enable the liner to be easily removed from the dressing before use. In particular, where the releasable liner is formed of two or more parts, the parts may either overlap or abut and extend outwards from the wound dressing, thus providing an easy method for removal of the releasable liner.

After individual dressings have been produced, they are preferably individually packaged and sterilised. Sterilisation may be undertaken by conventional means, eg gamma-irradiation.

The invention will now be described in greater detail, by way of example only, with reference to the accompanying drawings, in which Figure 1 is an exploded view of a dressing according to the invention prior to impregnation with honey;

Figure 2 is a perspective view of a dressing according to the invention; and Figure 3 is a schematic representation of the process of manufacturing a dressing according to the invention.

In Figures 1 and 2 there is shown an embodiment of a dressing according to the invention, generally designated 1 . The dressing comprises a perforated polyurethane foam layer 2 and two knitted facing layers 3. The foam layer 2 is bonded to the facing layers 3 by heat-fusable polymer layers 4 which are interposed between the foam layer 2 and each of the facing layers 3. The layers are impregnated with manuka honey such that each of the perforations 5 is filled with honey and the facing layers 3 are saturated with honey.

The foam layer is approximately 1 ,5mm thick. The perforations 5 are arranged across the full extent of the foam layer 2 in a hexagonal array. The perforations 5 have approximate diameter 5mm and are spaced between 10 and 15mm apart. The knitted facing layers 3 are knitted from a blended alginate and tencel yarn in a tricot ground fabric structure, The dressing 1 may be manufactured by the following general method (see Figure 3).

The manufacturing method is a continuous process, in which the component layers of the dressing 1 are brought together to form a stock material that is then impregnated with honey. Individual dressings are then cut from the stock material and packaged.

First a laminate comprising the perforated foam layer 2, the heat-fusable polymer layers 4 and the knitted facing layers 3 is produced. These layers are bonded together by passing the layered sheets through a set of heated rollers 6. The heat-fusable polymer layers 4 melt and bond the perforated foam layer 2 to the two facing layers 3, The heat-fusible layers 4 are of a lightweight, so-called dryweb material that effectively disintegrates on heating and so does not occlude either the perforations 5 in the foam 2 or the gaps in the knitted structure of the facing layers 3. Once the layers are bonded together, the laminate is passed through a dipping tank of manuka honey 7. Excess honey is calendered from the

impregnated laminate by a set of rollers 8 and collected in the dipping tank 7. A release liner 9 is applied to the impregnated laminate, and individual dressings 1 are cut out using a reciprocating punch 10 and packaged. The packages may then be sterilised, eg by gamma-irradiation.

The dressing 1 may be cut to any suitable size or shape.

Claims

1 . A wound dressing comprising an absorbent core of foam material having a regular array of perforations formed therein, and a wound-contact layer bonded to a first face of the absorbent core and comprising gelling fibres, wherein at least the absorbent core is impregnated with honey.

2. A wound dressing according to any preceding claim, wherein the foam material of the absorbent core is a polyurethane foam material.

3. A wound dressing according to any preceding claim, wherein a backing layer is bonded to the opposite face of the absorbent core to the wound-contact layer.

4. A wound dressing according to any preceding claim, wherein the backing layer is identical to the wound-contact layer.

5. A wound dressing according to any preceding claim, wherein the

perforations in the absorbent core are between 3mm and 10mm in diameter.

6. A wound dressing according to any preceding claim, wherein the

perforations in the absorbent core are about 5mm to about 7mm in diameter.

7. A wound dressing according to any preceding claim, wherein the absorbent core is between 0.5mm and 10mm thick.

8. A wound dressing according to any preceding claim, wherein the absorbent core is between 1 mm and 4mm thick.

9. A wound dressing according to any preceding claim, wherein the absorbent core is between 1 mm and 2mm thick.

10. A wound dressing according to any preceding claim, wherein the wound- contact layer is knitted.

1 1 . A wound dressing according to any preceding claim, wherein the gelling fibres are alginate gelling fibres.

12. A wound dressing according to any of Claims 1 to 10, wherein the gelling fibres are pectin gelling fibres.

13. A wound dressing according to any of Claims 1 to 10, wherein the gelling fibres are modified CMC gelling fibres.

14. A wound dressing according to any preceding claim, wherein the wound- contact layer comprises lyocell fibres.

15. A wound dressing according to Claim 10, wherein the wound-contact layer is a knitted fabric of blended yarn comprising gelling and non-gelling fibres.

16. A wound dressin according to Claim 15, wherein the yarn comprises a blend of alginate fibres and cellulosic fibres.

17. A wound dressing according to any preceding claim, wherein the absorbent core is heat bonded to the wound-contact layer.

18. A wound dressing according to any preceding claim, wherein the honey is manuka honey.

19. A dressing according to Claim 1 , wherein

the absorbent core is a polyurethane foam and the perforations are approximately 5mm in diameter and spaced between 10mm and 15mm apart; the wound-contact layer is a knitted alginate and lyocell fabric;

the layers are heat bonded together; and

the honey is manuka honey.

20. A dressing according to Claim 1 , wherein

the absorbent core is a polyurethane foam and the perforations are approximately 5mm in diameter and spaced between 10mm and 15mm apart; the wound-contact layer and the backing layer are a knitted alginate and lyocell fabric;

the layers are heat bonded together; and

the honey is manuka honey.

21 . A dressing substantially as hereinbefore described and as illustrated in the accompanying Figures 1 and 2.