Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Having discontinuous gas or vapor phase – e.g. – foam:
Reexamination Certificate
2000-09-21
2003-12-02
Lovering, Richard D. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Having discontinuous gas or vapor phase, e.g., foam:
C424S078060, C428S311510, C514S779000, C514S945000, C516S018000, C516S019000, C516S105000, C516S106000
Reexamination Certificate
active
06656974
ABSTRACT:
This application is a 371 of PCT/GB98/03106 filed Oct. 19, 1998.
The present invention relates to foam materials which are useful particularly but not exclusively as wound dressings.
It is well know that various materials having useful properties (e.g. for the production of wound dressings) may be produced by cross-linking of water soluble anionic polymeric materials (e.g. hydrocolloids).
Thus for example alginate fibres may be produced by spinning an alginate solution into a coagulating bath containing cations (e.g. Ca
2+
) capable of cross-linking the alginate thus resulting in fibre production. Such fibres are highly absorbent and may be used in the form of a tow for packing a wound or may be formed into a mat, felt or the like as an alternative form of wound dressing. Furthermore, it is known to product alginates in the form of a dehydrated hydrogel by a process in which an alginate hydrogel is treated with fibres (e.g. calcium alginate fibres) which provide cations for cross-linking the alginate in the hydrogel followed by removal of water to produce a cross-linked, dehydrated hydrogel containing the fibres as reinforcement (see WO-A-96/13285). Such a hydrogel may also be used as a wound dressing.
In all cases, the alginate provide high absorbency for the wound dressing so that relatively large amounts of wound-exudate may be taken up. This is a valuable property of the alginate for wound management. Furthermore, depending on the actual alginate polymer used, the dressing may be such that, in the wound, it retains its integrity so as to be removable in one-piece, or such that (in the wound) it becomes wet-dispersible so that it can be removed by irrigation. Depending on the nature of the wound, one or other method of removing the alginate may be desirable. Alginates are therefore very versatile materials for use as wound dressings.
In both cases, the alginate absorbs exudate and is converted into a moist gel on the wound. The wound may thus be maintained in a moist environment which is ideal for wound healing to take place.
There are however a number of disadvantages associated with the use of alignates in fibrous form for use as wound dressings. In particular, the process for producing the fibres is relatively lengthy and expensive involving, as it does, producing the dope, extrusion, washing, cutting the tow obtained by extrusion and carding of the staple fibre. Additionally, the carding step may break some of the fibres and those shorter fibres may be left as a residue in the wound. Furthermore, if the dope includes an agent to be incorporated in the fibre for delivery to the wound there is the danger that the agent will be “washed-out” of the fibre during the production process.
Similar disadvantages exist with cross-linked products produced from the types of water soluble anionic polymers (e.g. low-methoxyl pectin).
It is an object of the present invention to obviate or mitigate the abovementioned disadvantage.
According to a first aspect of the present invention there is provided an absorbent foam material which comprises a solid, cross-linked form of an anionic polymer and fibres or other polymeric particulates which have donated cations for effecting cross-linking of the anionic polymer.
Such “other polymeric particulates” may for instance comprise anionic polysaccharide particulates containing appropriate cross-linking ions.
As set out in the preceding paragraph, the anionic polymer is in a solid form which, in the context of the invention, describes the physical state of matter of the polymeric material rather than implying any particular physical property from the foam itself. Thus the foam may have various physical properties and may, for example, be a flexible or drapable material. Alternatively or additionally the foam may be compressible or resilient.
In view of the solid nature of the polymer, the foams may be regarded as self-supporting although we do not preclude the possibility of the foam incorporating or being associated with an additional supporting element as described more fully below.
According to a second aspect of the present invention there is provided a method of producing a foam material comprising generating a precursor foam comprising a solution of an anionic polymer in a solvent therefor and fibres or other polymeric particulates capable of donating cations for effecting cross-linking of said polymer, and converting the dissolved anionic polymer into a solid, form cross-linked by cations from said fibres or other particulates.
Foam materials in accordance with the invention may be produced (e.g. using the procedures described below) as highly conformable, absorbent material e.g. having a thickness of 1 to 5 mm and are eminently suitable for a variety of wound dressing applications, e.g. pressure sores, leg ulcers and other wounds with moderate to heavy exudate. For use as a dressing, the foam material may be used alone or may be juxtaposed (e.g. laminated) to at least one other type of wound dressing material. For example, the foam material may be used in conjunction with an alginate felt and/or a film of the type having a higher Moisture Vapour Transmission Rate (MVTR) capability in the presence of liquid water as compared to moisture vapour alone.
The anionic polymer which is cross-linked to produce the foam of the invention is preferably a water soluble polymer and may for example be a hydrocolloid. It is particularly preferred that the anionic polymer is a polysaccharide.
Examples of anionic polymers which may be used for the invention include alginates, low-methoxyl pectins, carrageenans, chrondoitin sulphate, hyaluronic acid, carboxymethyl cellulose, carboxymethyl starch, carboxymethyl guar, cellulose sulphate, dextran sulphate, gellan, xanthan, polyacrylic acid, a nucleic acid, or anionic derivatives of other hydrocolloids.
It is particularly preferred that the anionic polymer is an alginate.
Any number of a wide range of alginate polymers may be used in the invention. Thus, for example, the alginate may (prior to cross-linking) have a molecular weight of 200,000 to 1,000000 although it is generally preferred to use alginates towards the upper end of this range. More particularly, it is preferred to use an alginate having a viscosity of 600-800 cP for a 1% solution. Furthermore, the alginate used may have a wide range of G (Guluronic acid) and M (Mannuronic acid) values. Thus, for example, alginates which may be used in the present invention may have a G content of 30-70% and a M content of 70−30%. It is particularly preferred that the alginate has a G content of about 40% and an M content of about 60%.
A suitable alginate for use in the invention in Sobalg FD 156 (available from Danisco Ingredients).
In the production of foams of the invention, the anionic polymer is cross-linked by cations (preferably multivalent cations e.g. calcium) donated by fibres or other particulates with which the anionic polymer is admixed during production of the foam. The fibres/particulates may for example be of an insolubilised polysaccharide. Such fibres may be produced by spinning a solution of the polysaccharide into a bath containing cations which result in cross-linking of the polysaccharides to produce an insoluble fibrous form thereof capable of donating cations for effecting cross-linking of the anionic polymer. Alternatively the films may be formed by coagulating the polysaccharide in alcohol or a water miscible solvent. The fibrous structure generated by this latter technique may only be discernible under a microscope and as such are not fibres in the textile sense but nevertheless fall within the term “fibres” as used herein.
The fibres remain in the final foam to act as reinforcement. The fibres may for example be used in the form of a non-woven structure.
Examples of suitable fibres/particulates are calcium/sodium forms for which the calcium ions effect cross-linking. It is particularly preferred to use, as such fibres or particulates, those in which 60-85%, more preferably about 70%, of the alginic acid is in the form of the
Qin Yimin
Renn Donald W.
Rossetto Chiara
Advanced Medical Solutions Limited
Lovering Richard D.
Woodard Emhardt Moriarty McNett & Henry LLP
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