Wound dressings having low adherency

Details Wound dressings having low adherency Wound dressings having low adherency

2002-02-14

2003-05-20

Lucchesi, Nicholas D. (Department: 3764)

Surgery: splint, brace, or bandage

Bandage structure

Skin laceration or wound cover

C602S043000, C604S304000, C604S307000, C604S367000, C604S369000

Reexamination Certificate

active

06566577

ABSTRACT:

The present invention relates to wound dressings, and in particular to such dressings having low adherency for use on low- to non-exuding wounds. The present invention also relates to processes for the preparation of such wound dressings, and to an apparatus specifically adapted for use in such processes.
Wound dressings are known that consist of a layer of absorbent material, such as an absorbent gauze or foam layer, wherein the layer is supported on an adhesive-coated semipermeable backing sheet. An adhesive-coated margin of the backing sheet extends outwardly from the edges of the absorbent layer for attachment of the dressing over a wound by adhesion to the skin surrounding the wound. The absorbent layer serves to absorb wound exudate. Such dressings are commonly known as island wound dressings.
A difficulty that can arise with island wound dressings is that most absorbent layers, such as nonwoven fibrous webs, are somewhat adherent to a wound surface, and is particular tend to dry out and adhere to wounds having a low rate of exudate production, or to non-exuding wounds. Adherence can also be a problem with bleeding wounds because of clot formation in the dressing. Adherence is unfavorable for wound healing, and can result in discomfort when the island wound dressing is changed. There is a further risk that the absorbent island could shed fibers or particles into the wound.
Another drawback of such dressings is that many absorbent island materials, such as nonwoven fibrous webs, show relatively poor attachment to the adhesive coating of the backing sheet. There is therefore a risk that the absorbent island can detach from the backing sheet. The problem of poor attachment of the island to the backing sheet is exacerbated when attempts are made to render the island less adherent to the wound, for example by using a bonded or coated island.
GB-A-2074029 describes island-type wound dressings having a top sheet of perforated polytetrafluoroethylene (PTFE) film covering the absorbent layer. The PTFE film provides a non-adherent wound contacting layer for the dressing.
GB-A-2085305 describes wound dressings in which the absorbent island is entirely embraced by a cellular plastics film having perforations which have been produced by passing electrical discharges therethrough. The film may be provided with a layer of adhesive for attachment around a wound.
GB-A-1526778 describes wound dressings comprising an absorbent layer and a top sheet over the absorbent lays, wherein the top sheet is a textured perforated plastic film that provides improved passage of fluids into the absorbent layer.
It is an object of the present invention to provides improved wound dressings, in particular improved island-type wound dressings, especially suitable for the treatment of wounds that product little or no exudate and for bleeding wounds.
It is a further object of the present invention to provide an improved wound dressing that has low adherency to the wound surface, and preferably substantially no adherency to the wound surface.
Is a further object of the present invention to provide an improved wound dressing that provides improved securement of the absorbent island to the backing sheet.
Is a further object of the present invention to provide as improved wound dressing that has less tendency to cause low- to non-exuding wounds and bleeding wounds to dry out and form scabs, and to optimise wound healing conditions under the wound dressing.
If a further object of the present invention to provides an improved wound dressing that has reduced tendency to shed fibers or particles into the wound during treatment.
The present invention provides a wound dressing comprising:
as absorbent layer;
an envelope formed from thermoplastic film enclosing the absorbent layer, wherein the film has a textured perforated surface on a front side of the envelope and a smoothed perforated surface on a rear side of the envelope;
a semipermeable backing sheet covering the rear side of the envelope and, extending outwardly therefrom; and
a layer of adhesive on the backing sheet adjacent to the rear side of the envelope and bonding the rear side of the envelope to the backing sheet.
The wound dressings according to the present invention are especially suitable as wound dressings for use on low- or non-exuding wounds of bleeding wounds. The area of the absorbent layer is typically in the range of from 1 cm
2
to 200 cm
2
, more preferably from 4 cm
2
to 100 cm
2
.
The absorbent layer may be any of the layers conventionally used for absorbing wound fluids, serum or blood in the wound healing art, including gauzes, nonwoven fabrics, superabsorbents, hydrogels and mixtures thereof. Preferably, the absorbent layer comprises a layer of absorbent foam, such as an open celled hydrophilic polyurethane foam prepared in accordance with EP-A-0541391, the entire content of which is expressly incorporated herein by reference. In other embodiments, the absorbent layer may be a nonwoven fibrous web, for example a carded web of viscose staple fibers. Since the wound dressings according to the present invention are generally only intended for use on low- or non-exuding wounds or bleeding wounds, it follows that the thickness and absorbency of the absorbent layer is preferably not very high. Preferably, the basis weight of the absorbent layer is in the range of 50-500 g/m
2
, more preferably 100-400 g/m
2
. The uncompressed thickness of the absorbent layer is preferably in the range of from 0.5 mm to 5 mm, more preferably 1 mm to 4 mm. The free (uncompressed) liquid absorbency measured for physiological saline is preferably in the range of 5 to 30 g/g at 25° C.
The thermoplastic film enclosing the absorbent layer may be formed from substantially any thermoplastic film-forming polymer. Preferably, the polymer is conformable but not substantially elastomeric. Preferably, the polymer is hydrophilic. Suitable polymers include, but are not limited to, polyethylene, polypropylene, polyester, polyamides such as nylons, fluoropolymers such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE), and mixtures thereof. The currently preferred film forming thermoplastic polymer is ethylene methyl acrylate (EMA).
The thermoplastic film is textured and perforated. The term “textured” indicates that the film is patterned in relief, for example, patterned with protruding ridges or nubbles, for example by embossing. The texturing renders the film less adherent to a wound bed. The ridges island nubbles are preferably rounded, and preferably project by 0.1 to 1.5 mm above the median plane of the film surface. More preferably they project by 0.2 to 1.0 mm above the median plane of the film.
Preferably, the thermoplastic film is both textured and perforated by means of mesh perforation. In this method, the film is supported on a reticulated mesh surface and heated to its softening temperature. Suction is then applied through the mesh, or air is blown onto the film above the mesh, which results in impression of the mesh into the film and the formation of perforations in the film at the interstices of the mesh. Mesh perforation technique are described in more detail in U.S. Pat. No. 3,054,148, the entire content of which is expressly incorporated herein by reference.
Preferably, the thermoplastic film has from 5 to 50 perforations/cm
2
, more preferably from 10 to 30 perforations/cm
2
. Preferably, the perforations have an area of from 0.01 to 2.0 mm
2
. The hole-to-land ratio, defined as the ratio of the total area of the perforations to the total area of the film less the area of the perforations, both areas being viewed in plans projection, is preferably from 0.01 to 1.0, more preferably from 0.05 to 0.5 and most preferably from 0.1 to 0.3.
The thermoplastic film should be as thin as possible consistent with the need for physical integrity during manufacture and use. Typically, the film has a basis weight of from 1 to 500 g/m
2
, preferably island 10 to 200 g/m
2
.
The thermoplastic film is formed into an envelope for the absorbent layer. The term

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