Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Web – sheet or filament bases; compositions of bandages; or...
Patent
1995-03-02
1997-05-27
Phelan, D. Gabrielle
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Web, sheet or filament bases; compositions of bandages; or...
424448, 602 58, 602 41, A61F 1300
Patent
active
056330073
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to adhesive, moisture vapour permeable surgical dressings for use on human bodies, for example in contact with moist wounds. In particular, this invention relates to a dressing comprising plurality of discrete cells and adapted to transmit water into and through each cell.
It is desirable to allow a wound to heal in its moist state, especially if covered with a layer of wound exudate as this state is believed to be capable of accelerating wound healing. The problems with moist wound healing when the wound is covered with a surgical dressing is that a "blister" of exudate can form under the dressing which is not only unsightly and uncomfortable but may also cause the dressing to leak, thereby defeating the aim of sterility. Such an excess of exudate therefore needs to be removed before a harmful blister forms. Normal methods of aspiration however, may also lead to wound infection. Finally, in order to preserve wound healing in a moist environment, it is desirable not to remove all the exudate as a "dry" wound since a slower healing wound would result.
An attempt to overcome these disadvantages has been proposed in which an adhesive coated moisture vapour permeable, liquid water impervious first layer which contains perforations as a wound contacting layer and an imperforate, moisture vapour permeable, liquid water impermeable film attached to the first layer to form a sealed reservoir into which exudate from a wound may pass. Such dressings suffer from the disadvantage that they are only available in pre-formed sizes. It has also been observed that the performance of such dressings has not been as good as might have been expected in that it has been observed that exudate does not pass through the perforations into the reservoir at a rate which is sufficient to prevent `blister` formation.
We have found that the use of a large number of physically separate small cells of reservoirs results in a dressing having a better performance than dressings comprising a single reservoir. The dressings of the present invention therefore seek to mitigate the disadvantage of blister formation and wound adherence and to offer the additional advantage of being able to cut the dressing to a desired shape or size.
Accordingly the present invention provides an adhesive dressing suitable for moist wounds including a first layer comprising a substrate having a layer of pressure sensitive adhesive on a wound facing surface and a second layer comprising a moisture vapour permeable continuous film, said second layer being attached to the non wound facing surface of the first layer at spaced apart intervals thereby to form a plurality of discrete cellular voids between said first and second layers, wherein the first layer has apertures therein to allow passage of liquids therethrough into the cellular voids and wherein total area of the dressing defined by the cellular voids is from 20% to 80% of the total operable area of the dressing.
Aptly, the adhesive coated first layer has a low uninterrupted moisture vapour permeability. By low moisture vapour permeability is meant an upright (as hereinafter defined) moisture vapour permeability of less than 300 gm.sup.-2 24 hr.sup.-1 preferably less than 200 gm.sup.-2 24 hr.sup.-1 when measured at 37.degree. C. and 100% to 10% relative humidity difference. By an "uninterrupted moisture vapour permeability" is meant the moisture vapour permeability of the material is the absence of holes therethrough i.e. the moisture vapour permeability of the uninterrupted material.
The moisture vapour permeability (MVP) of the materials employed in the present invention may be determined as follows:
Upright MVP Determination
Discs of the material under test are clamped over Payne Permeability Cups (flanged metal cups) using sealing rings and screw clamps. The exposed surface area of the test sample is 10 cm.sup.2. Each cup contains approximately 10 ml. of distilled water.
After weighing the cups are placed in a fan assisted electric oven which is maintained at 37.degree. C.
REFERENCES:
patent: 4499896 (1985-02-01), Heinecke
patent: 4657006 (1987-04-01), Rawlings
patent: 5010883 (1991-04-01), Rawlings
patent: 5244457 (1993-09-01), Karami
patent: 5328450 (1994-07-01), Smith
Blott Patrick L.
Farrar David F.
Houldridge David
MacFarlane Anna F.
Reed Christopher I.
Phelan D. Gabrielle
Smith & Nephew plc
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