Dressings

Details Dressings Dressings

1999-09-13

2001-02-20

Brown, Michael A. (Department: 3764)

Surgery: splint, brace, or bandage

Bandage structure

C602S042000, C602S043000

Reexamination Certificate

active

06191335

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to wound dressings and to methods of manufacture and the use thereof.
RELATED ART
Recently in wound developments dressings have been aimed at providing dressings which promote moist wound healing. Such dressings include, for example, that are sold by Smith & Nephew under the name ALLEVYN Adhesive (Trade Mark) and are described in European Patent Publication No. 0059049. Existing devices are essentially reservoirs for wound exudate, that is, they absorb exudate by means of an absorbent or hydrophilic material. Once the reservoir is saturated the dressing is generally changed. If such dressings are retained on the wound too long and dry out they are likely to adhere to the healing wound bed causing trauma, pain and delay in the wound healing process when they are removed
There is therefore a need for a wound dressing which promotes moist wound healing but which does not rely solely on the physical process of absorption as a means of controlling exudate and the moist wound healing environment.
SUMMARY OF THE INVENTION
We have now found that such a dressing may be manufactured which employs both processes of absorption and moisture vapour transmission in conjunction. This is achieved by using a highly exudate absorbent reservoir in combination with a backing layer whose water transmission rate (WTR) is not less than its moisture vapour transmission rate (MVTR). The methods for measuring moisture vapour transmission rate (MVTR) and water transmission rate (WTR) which also described as inverted moisture vapour transmission rate are described in our European Patent Publication No. 0091800. As used herein both the WTR and MVTR transmission rates expressed in grams per square meter per 24 hours (gm
−2
24 hr
−1
) at 37° C. and the MVTR is measured at a relative humidity difference of from 10 to 100%.
Thus according to the invention we provide a dressing which comprises a backing layer and a wound facing layer and an absorbent layer intermediate the backing and wound facing layers characterised in that the backing layer has a water transmission rate (WTR) not less than its moisture vapour transmission rate (MVTR) and in that the absorbent layer is a fibrous layer comprising fibrous component which on absorbing moisture undergo a phase change to form a gel and a component which does not undergo a phase change to form a gel in the presence of moisture.
Preferably the WTR of the backing layer is great than its MVTR.
Suitably the backing layer is a thin film and may comprise any of those materials which are conventionally employed to form thin film surgical dressings. Suitable materials include those described in U.S. Pat. Nos. 4,595,001 and 4,747,401. Particularly apt materials are polyurethanes, for example polyester or polyether polyurethanes known as Estanes (Trade Mark). Other apt materials are elastomeric polyether polyesters, for example those known as Hytrels (Trade Mark) and polyether polyamides, for example those known as Pebaxes (Trade Mark). Other favoured materials include hydrophilic polymers such as hydrophilic polyurethanes including those described in UK Patent No.2093190B, especially the polyurethane described in Example 2 therein.
The backing layer may be moisture vapour permeable and may have a moisture vapour transmission rate of at least 500 gm
−2
24 hrs
−1
suitably at least 1000 gm
−2
24 hrs
−1,
more suitably at least 1200 gm
−2
24 hrs
−1
and preferably at least 1600 gm
−2
24 hrs
−1
up to 5000 gm
−2
24 hrs. Most preferably the MVTR should not be more than 3000 gm
−2
24 hrs
−1
.
The WTR of the backing layer may be at least 2000 gm
−2
24 hr
−1
, more suitably at least 3000 gm
−2
24 hr
−1
and preferably at least 6000 gm
−2
24 hr
−1
up to 20,000 gm
−2
24 hr
−1
.
The backing layer may have a thickness of from 15 to 100 &mgr;m, preferably 20 to 80 &mgr;m and more preferably 25 to 50 &mgr;m, for example 27.5 &mgr;m, 30 &mgr;m, 35 &mgr;m, 40 &mgr;m.
The wound facing layer may comprise an apertured film or a net.
A preferred apertured film for use in the invention are those formed by a hot melt perforation process comprising the use of flames or hot gas.
Preferred apertured films for use in the invention are in the form of flexible polymer nets. A polymer net is used herein as a polymer sheet having apertures defined by integral strands and junctures. Such nets may be formed by stretching films or sheets embossed with thinner areas.
Any conventionally known material may be used, but favoured polymer nets comprise an elastomeric polymer and in particular a thermoplastic elastomeric polymer.
Such nets of elastomeric polymer can impart ‘softness’ to the surface of the device of the invention.
Suitable thermoplastic elastomeric polymers include polyether ester and polyether-polyamide block copolymers, polyurethanes, styrene-butadiene and styreneisoprene block copolymers, polyisobutadiene and ethylene-vinyl acetate copolymers.
Nets for use in the invention may comprise a blend of elastomeric polymer such as ethylene vinyl acetate copolymer with a compatible polymer or an incompatible polymer such as polyolefine, for example low density polyethylene or polystyrene.
Suitable nets for use in the invention which comprise a blend of ethylene vinyl acetate and an incompatible polymer are disclosed in European Patent No.141592.
The intermediate absorbent layer may comprise any conventionally known absorbent materials. Preferably, the absorbent layer will provide resistance to, e.g. high molecular weight materials, such as proteins, polysaccharides etc., which might tend to effect the WTR of the backing layer when the wound is highly exuding. Thus the gelling component of the absorbent layer may comprise a superabsorbent material which gels when wet. Suitable superabsorbent hydrogels are described in U.S. Pat. Nos. 3,669,103 and 3,670,737. Within the scope of such hydrogels it is intended to include, e.g. alginate and/or other hydrocolloids. A preferred superabsorber is polyacrylic acid an example of which is that known as OASIS fibres (Technical Absorbents). The gelling component of the absorbent layer will be a fibrous or filamentary material.
The non-gelling component of the absorbent layer may comprise fibrous constituents which are non-absorbent or sparingly absorbent. When the composite comprises two fibrous components then it is preferred that one constituent will be a superabsorber as hereinbefore described and the other will be non-absorbent or sparingly absorbent to exudate.
The fibrous components of the absorbent layer may be present in amount of from 130 gm
−2
to 300 gm
−2
, preferably from 100 to 175 gm
−2
.
The size and shape of the fibres used may vary according to, inter alia, that nature of the fibrous material and the degree of absorption/transmission desired in the article. Nevertheless, fibres which are substantially linear are preferred. The diameter of such fibres would be similar to that conventionally used in absorbent articles and/or dressings. Substantially linear fibres may be of conventional lengths used in the art. Preferred substantially linear fibres are from 5 to 50 mm long, preferably from 10 to 20 mm long.
The non-gelling fibrous components may comprise one or more fibrous materials. The fibrous material in the composite may comprise any conventionally known fibres including natural or synthetic materials. For example, a fibrous component may comprise a cellulosic fibre or a composite of a cellulosic fibre and a thermobonding fibre. Examples of cellulosic fibre include, but are not limited to cotton fibres or wood pulp fibres. Thermobonding fibres include, for example, Danaklon ESC.
The use of non-gelling fibrous components in the composite absorbent layer may be advantageous in that they may provide support for the superabsorber fibres, particularly when the superabsorber becomes a gel as it becomes wet; such non-gelling fibres may provide improved wi

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