Surgery: splint – brace – or bandage – Bandage structure – Skin laceration or wound cover
Reexamination Certificate
2001-10-05
2003-04-22
Lewis, Kim M. (Department: 3761)
Surgery: splint, brace, or bandage
Bandage structure
Skin laceration or wound cover
C602S041000, C602S042000, C602S054000, C602S056000
Reexamination Certificate
active
06552244
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This Application is a U.S. national phase application, filed under 35 U.S.C. §371, of International Patent Application PCT/EP00/00132, which was filed on Jan. 7, 2000; and claims priority to Great Britain Application No. 9900348, filed Jan. 9, 1999.
The present invention relates to a multi layered wound dressing particularly, but not exclusively, for use as a dressing on highly exudating wounds.
BACKGROUND OF THE INVENTION
It is known to make wound dressings for use on heavily exudating wounds from materials with a high moisture vapour transmission rate (MVTR). Such dressings rely on exudate being taken up by the dressing and spread across much of the surface area of the dressing in order to ensure sufficient moisture evaporation. Examples of such dressings are ALLEVYN marketed in adhesive or non-adhesive versions by Smith and Nephew or TIELLE marketed by Johnson and Johnson. Such dressings are not designed to absorb and retain the exudate but manage the exudate by allowing the moisture present in the exudate to evaporate. A dressing said to have a high rate of moisture evaporation is described in EP 304 536A. The dressing disclosed in this document has a flexible hydrophilic layer that absorbs exudate, sandwiched between two layers of adhesive. The absorbent layer additionally contains a fabric layer which is intended to improve the structural integrity of the dressing once it is exposed to exudate. A disadvantage of such dressings is that the lateral wicking of exudate is not contained and can cause normal skin surrounding the wound to macerate. A further disadvantage of such dressings is that the rapid loss of exudate can cause the wound to desiccate.
EP-A 0538917 discloses a vented wound dressing is disclosed comprising a thin conformable sheet material (
12
) at least a portion of the surface area of which it intended for placement as a dressing over a wound, which portion carries a pressure-sensitive adhesive coating (
14
) on one surface thereof for adhering the dressing to skin, the coating being applied to provide repeating areas (
16
) of the sheet material containing no adhesive, at least a portion of the repeating areas of no adhesive having slits (
18
) extending through the thickness thereof to permit transfer or wound fluids through the sheet material unimpeded by presence of adhesive material which can clog the slits and thereby inhibit fluid transfer therethrough.
There is thus a need for a wound dressing which is capable of absorbing exudate at the rate it is produced by a heavily exudating wound and which also does not cause maceration to the skin surrounding the wound thereby increasing the wear time of the dressing.
BRIEF SUMMARY OF THE INVENTION
We have now developed a multi layered wound dressing which alleviates the above problems and there is provided by a first embodiment of the present invention a multi layered wound dressing comprising:
(a) an absorbent layer having high absorbency but low lateral wicking;
(b) a transmission layer having a high MVTR overlying the side of said absorbent layer furthest from the wound.
We have found that wound dressings according to the invention may mitigate the problems associated with the management of high levels of exudate produced by some wounds yet not induce maceration in the skin surrounding the wound. It is thought that this is achieved by the combined use of the absorbent layer with low lateral wicking, which readily absorbs exudate and transmits it to the transmission layer.
In a second embodiment of the invention the dressing further comprises a high lateral wicking layer between the absorbent and transmission layers which aids the spread of exudate across a greater area of the dressing but away from the wound. In this way exudate is spread across a large surface area to provide sufficient moisture vapour transmission but in a location distant from the wound and skin. The passage of exudate through the dressing is therefore in a “T” shape where the lateral spread is limited in the absorbent layer and maximised in the transmission layer. Such a mechanism avoids maceration of the skin surrounding the wound since the exudate is not contained in contact with the skin. As the absorbent layer does however retain exudate in the immediate region of the wound, desiccation of the wound is avoided. This allows longer wear time for the patient and less disturbance of the wound on dressing change.
A second embodiment of the invention of the present invention provides a multi layered wound dressing comprising:
(a) an absorbent layer having high absorbency but low lateral wicking;
(b) a transmission layer having a high MVTR overlying said absorbent layer; and
(c) a spreading layer having high lateral wicking positioned between the transmission and absorbent layers, the spreading layer overlying the side of the absorbent layer furthest from the wound.
The absorbent layer is present to transport wound fluid away from the wound and absorb it while containing lateral spread of exudate. By high absorbency in the context of the present invention is meant an absorbency of at least 10 g/g preferably from 15 g/g to 50 g/g and most preferably an absorbency of from 20 g/g to 50 g/g. By low lateral wicking is meant a lateral wicking rate of less than 20 mm/60 s preferably from 1 mm/60 s to 15 mm/60 s and most preferably a lateral wicking rate of from 1 mm/60 s to 10 mm/60 s. The absorbent layer is preferably fibrous and most preferably comprises gel-forming fibres. We have found that fibrous layers as opposed to polymeric absorbent layers have the advantage that they are especially able to gel block which resists the lateral spread of exudate. In addition exudate is absorbed rapidly and retained under pressure.
The fibres suitable for use in the absorbent layer of the present invention include hydrophilic fibres, which upon the uptake of wound exudate become moist and slippery or gelatinous and thus reduce the tendency for the surrounding fibres to adhere to the wound. The fibres can be of the type, which retain their structural integrity on absorption of exudate or can be of the type, which lose their fibrous form and become a structureless gel or a solution on absorption of exudate.
The gel forming fibres are preferably spun sodium carboxymethylcellulose fibres, chemically modified cellulosic fibres, in particular carboxymethylated cellulose fibres as described in PCT WO/9312275 to Courtaulds Plc or GB93/01258 to Courtaulds Plc, pectin fibres, alginate fibres and particularly those as described in WO94/17227 to E. R. Squibb and Sons or EP 433354 to CV Laboratories Ltd or EP 476756 to CV Laboratories Ltd, or composite fibres of alginate and polysaccharide such as those described in EP 0892863 to Bristol-Myers Squibb Company, chitosan fibres, hyaluronic acid fibres, or other polysaccharide fibres or fibres derived from gums. The cellulosic fibres preferably have a degree of substitution of at least 0.05 carboxymethyl groups per glucose unit. The production of solvent-spun cellulose fibres is described for example in U.S. Pat. Nos. 4,246,221 and 4,196,281 as well as in PCT WO/9312275 mentioned above.
Preferably the gel forming fibres for use in the present invention have an absorbency of either water or saline of at least 15 g/g as measured in the free swell absorbency method, more preferably at least 25 g/g or 50 g/g. The degree of substitution of the gel forming fibre is preferably at least 0.2 carboxymethyl groups per glucose unit, more preferably between 0.3 and 0.5. The tenacity of the fibre is preferably in the range 25-15 cN/tex.
The gel forming fibres are preferably mixed to give a dressing comprising fibres of different absorbencies and also different absorbency rates and profiles. This can improve the strength and integrity of the absorbent layer in a wet or moist state.
The absorbent layer may comprise other fibres such as textile fibres which can be natural or synthetic but are preferably cellulosic fibres for example viscose rayon, multi-limbed viscose, cotton, or regenerated cell
Bishop Steven M.
Griffiths Bryan
Jacques Elizabeth
Lydon Michael J.
Bristol--Myers Squibb Company
Kilcoyne John M.
Lewis Kim M.
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