Surgery: splint – brace – or bandage – Bandage structure
Reexamination Certificate
1999-04-13
2001-07-31
Brown, Michael A. (Department: 3764)
Surgery: splint, brace, or bandage
Bandage structure
C602S042000, C602S043000, C602S044000, C602S045000, C602S046000, C602S047000
Reexamination Certificate
active
06268544
ABSTRACT:
The invention relates to knitted wound dressings and particularly to wound dressings comprising a mixture of textile fibres and gel-forming fibres and a method for making same.
The invention also relates to a method of treating a wound comprising applying the dressing to a wound.
It is well known that the cleansing and debriding of wounds and the removal of wound exudate is important to the process of healing wounds. Commonly used wound dressings comprise gauze, foams, sponges, cotton wads or other fibrous materials. Gauze and other fibrous materials absorb fluids by capillary action with the disadvantage that when new tissue is formed as part of the healing process, it engulfs the fibres and is torn when the material is removed causing wound injury.
There thus exists a need for a dressing which is non-adherent while being absorbent.
PCT WO 95/91795 to Bristol-Myers Squibb Company describes a wound dressing comprising a mixture of textile fibres and gel-forming fibres to form an inexpensive, non-adherent dressing. The dressings disclosed are non-woven structures, the fibres being carded together to form a felt. Non woven fabrics generally have less tensile strength in both wet and dry states than woven fabrics. It is desirable for wound dressings to have a sufficiently high tensile strength that they may be handled during processing and packaging and be removable from a wound in a wet state, in one piece. For this reason woven fabrics are desirable as wound dressings. In addition a woven structure broadens the type of fibre that can be used in dressings.
In the past it has been difficult to produce knitted fabrics comprising gel-forming fibres because of the brittleness of the fibres. Their brittleness can lead to breakage and shedding of the gel-forming fibres during processing which not only limits machine speeds but is also undesirable in a product that is in direct contact with a wound.
We have now found that it is possible to make knitted wound dressings from a mixture of gel-forming fibres and textile fibres.
Accordingly the present invention provides a wound dressing comprising a mixture of textile fibres and gel-forming fibres wherein the dressing is a knitted fabric comprising support yarn and in-laid yarn, the support yarn being substantially free of gel-forming fibres.
The wound dressing according to the invention may have the advantage that fast knitting speeds are possible in the production of the dressing and the resulting product has better integrity than a dressing where gel-forming fibres are included in the support yarn.
The dressings may also have the advantage that because they are produced by knitting, the final product has good dimensional stability without the choice of fibre being unduly limited.
In the context of the present invention by yarn is meant a continuous strand of textile or staple fibers, filaments or other material in a form suitable for knitting. By staple yarn is meant a yarn composed of staple fibers held together by some binding mechanism such as twisting. By knitting is meant warp, weft or ring knitting.
Preferably the wound dressing is a warp knitted fabric. By warp knitting is meant a knit characterised by the fact that each warp yarn is more or less in line with the direction in which the fabric is produced. The warp yarn forms a support structure of pillars or chains of stitches and for this reason is also known as structural or pillar yarn. The pillars of stitches are held together by a further structural yarn and/or an in-laid yarn which is more or less perpendicular to the direction in which the fabric is produced. Examples of warp knitted fabrics are tricots, raschels, nets and laces such as are described in “Textile Science” by Kathryn L. Hatch, West Publishing Company 1993.
The knitted dressing preferably comprises from 5% to 95% of textile fibres by total weight of the dressing and from 5% to 95% of gel-forming fibres by total weight of the dressing. More preferably the dressing comprises from 15% to 70% by weight of gel-forming fibres and more particularly 20% to 60% by weight.
The textile fibres for use in the present invention can be natural or synthetic but are preferably cellulosic fibres for example viscose rayon, multi-limbed viscose, cotton, or regenerated cellulose or fibres having a higher absorbency than most textile fibres such as the multi-limbed cellulose fibres as described in EP-A-301874. In general textile fibres absorb liquids by capillary action and are not hygroscopic. This means that their absorbancies as measured by the free swell absorbancy test are low such as less than 1 gram of liquid per gram of fibre.
The gel-forming fibres for use in the present invention are hygroscopic fibres which upon the uptake of wound exudate become moist -and slippery or gelatinous and thus reduce the tendancy for the surrounding fibres to adhere to the wound. The gel-forming fibres may also swell and separate the textile fibres from the wound surface. The gel-forming 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 sodium carboxymethylcellulose fibres, chemically modified cellulosic fibres, in particular carboxymethylated cellulose fibres as described in PCT WO/9312275, pectin fibres, alginate fibres, fibres made from a composite of alginate and another polysaccharide, chitosan fibres, hyaluronic acid fibres, or other polysaccharide fibres or fibres derived from gums. In particular the alginate fibres described in EP-A-0721355 to Bristol-Myers Squibb Company are particularly preferred. The cellulosic fibres preferably have a degree of substitution of at least 0.05 carboxymethyl groups per glucose unit. The gel-forming fibres preferably have an absorbency of at least 2 grams 0.9% saline solution per gram of fibre (as measured by the free swell absorbency test) and a tenacity of at least 10 cN/tex. The production of solvent-spun cellulose fibres is described for example in U.S. Pat. No. 4,246,221 and U.S. Pat. No. 4,196,281 as well as in PCT WO/9312275. The gel-forming fibres for use in dressings of the present invention may also be composite or co-spun gel-forming fibres as described in our co-pending applications GB9607600.5 and GB9618658.0 which describe fibres that are composites of alginate and another polysaccharide or those described in PCT WO 96/10106 to Innovative Technologies Limited.
Preferably the gel-forming fibres for use in the present invention have an absorbency of at least 15 g/g as measured in the free swell absorbency method, more preferably between 25 g/g and 50 g/g.
The gel-forming fibres suitable for use in the present invention can be processed using conventional textile machinery, for example by the staple route including cutting, carding and if desired crimping,. drafting and spinning.
The wound dressing of the present invention may be made by spinning or twisting gel-forming fibres and textile fibres together to form the in-laid yarn and then warp knitting using a yarn consisting of textile fibres as the pillar yarn to form a gauze, bandage or stocking. The wound dressing of the present invention may be used as a primary or secondary dressing especially in the treatment of leg ulcers.
The in-laid yarn may be a staple yarn comprising from 0% to 80% by weight of textile fibre and 20% to 100% of gel-forming fibre, more preferably from 0% to 75% by weight of textile fibre and 25% to 100% of gel-forming fibre. Alternatively the in-laid yarn may be a continuous filament yarn comprising from 20% to 100% of gel-forming fibres.
The support yarn is preferably a continuous filament viscose, polypropylene, polyester, polyamide or polythylene yarn or mixture thereof.
The wound dressing of the invention preferably comprises from 5% to 80% by weight of support yarn and from 20% to 95% by weight of in-laid yarn. More preferably from 5% to 60% of support yarn and from 40% to 95% of in-laid yarn.
Various optional
Court Andrew D.
Lydon Michael James
Mahoney Peter M. J.
Bristol--Myers Squibb Company
Brown Michael A.
Furman, Jr. Theodore R.
Hamilton Lalita M.
Kilcoyne John M.
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