The present invention relates to alginate containing fibres which are useful

particularly, but not exclusively, in the manufacture of wound dressings.

Alginates are a family of polymers which may be obtained from seaweed and

which contain varying proportions of mannuronic and guluronic residues depending on

the source of the polymer.

It is established practice to produce alginate fibres by spinning a solution of a

soluble form of an alginate polymer into a gelation (or coagulation) bath in which an

insoluble form of the alginate precipitates. Typically the soluble form of the polymer is

the sodium salt and the bath contains calcium ions to produce insoluble calcium

alginate. Fibres produced in this way have high absorbency and are used in the

manufacture of wound dressings, e.g. for wet wounds such as pressure sores, leg ulcers,

surgical incisions and donor sites where the primary function of the alginate is to absorb

exudate.

The present invention relates to modified alginate fibres which are useful in

wound dressings.

According to a first aspect of the present invention there is provided fibres

comprising an alginate co-spun with at least one water soluble organic polymeric

species (other than an alginate).

According to a second aspect of the invention there is provided a method of

producing fibres comprising co-spinning a dope which contains dissolved alginate and

at least one dissolved organic polymeric species (other than an alginate) into an aqueous

coagulation bath which causes precipitation of fibres each comprised of the alginate and

said other polymeric species.

The non-alginate polymer is preferably (but not necessarily) one having negative

charges along the polymer chain, i.e. a polyanion. Alternatively the polymer may be

uncharged.

Preferably the fibres comprise 70-95% by weight alginate and 5-30% by weight

of the non-alginate polymer.

The incorporation of the water soluble non-alginate polymeric species into the

fibres with the alginate allows useful fibres of modified properties to be obtained, as

compared to the properties obtained of the alginate is the sole component of the fibres.

The modified properties may, for example, be increased absorbency of the fibres.

Generally the fibres will comprise a major proportion by weight of the alginate,

e.g. 50-95% by weight, and a minor proportion of the non-alginate polymeric species.

The alginate may be one having a G-content of 35-70% and correspondingly an M-

content of 65-30% by weight. Typically the alginate will be such that a 1% solution will

have a viscosity of 30-300 cP, preferably 40-100 cP.

If the non-alginate polymeric species contains negatively charged groups, these

may be provided, for example, by COO ^" or S0 ₄ ^2" groups along the polymer chain.

In one embodiment of the invention, alginates may be co-spun with non-alginate

species containing COO ^' groups along the chain, examples of which include

polysaccharides, polycarboxyamino acids it is also possible t o use acrylic acid and/or

metharcrylic acid, or salts thereof (e.g. the sodium salt). More specific examples include pectin, carboxymethyl cellulose, N-,0-carboxymethyl chitosan (NOCC), carrageenan, xanthan, gellan, polyaspartic acid and polyglutamic acid.

The alginate may be co-spun with a non-alginate polymer containing COO ^' groups which results in a fibre having increased absorbency as compared to one

prepared from the alginate alone. Examples of such non-alginate polymers which result in increased absorbency include carboxymethyl cellulose, carrageenan, polyacrylic acid

and NOCC. Thus fibres of improved absorbency may comprise 70-90% alginate and a total of 5-30% of at least one of CMC, carrageenan, polyacrylic acid and N,0- carboxymethyl chitosan (NOCC) or O-carboxymethyl chitosan (OCC).

If the alginate is co-spun with pectin, fibres are produced which, when made into (and used) as a wound dressing, soften dry wounds, start autolysis procedures, and assist debridement macrophage stimulation. Preferably the pectin comprises 5-30% (more

preferably 10-20%) by weight of the fibres.

The presence of pectin (which consists chiefly of partially methoxylated polygalacturonic acids) does reduce the absorbency of the fibres. Therefore a balance may need to be struck between the absorbency of the fibres (as provided by the alginate) and the wound healing properties thereof (as provided by the pectin). It is possible to co-spin alginate, pectin and at least one non-alginate polymer bearing negative charges which boosts absorbency. Thus fibres may be produced by co-spinning alginate, pectin and either CMC, NOCC or OCC, typically in a ratio of 60%-80% alginate, 10%-20%

pectin and 10%-20% CMC, NOCC or OCC.

Further examples of fibres which may be produced in accordance with the first

embodiment of the invention include a mixture of components producing a product

which is a cross between an alginate and a hydrocolloid. Thus, for example, it is

possible to spin such alginate hydrocolloid products from solutions of alginate, gelatin,

pectin, and CMC, e.g. in the following amounts:

Alginate Gelatin Pectin CMC

45 10 25 20

35 10 35 20

In a second embodiment of the invention, the non-alginate polymeric species is

one corltaining S0 ₄ ^" groups along the polymer chain. Examples include sulphonated

polysaccharides which are naturally occurring elements of tissue (serving to keep water

in the tissue). Co-spinning of alginates with sulphated polysaccharides results in

materials which may be likened to artificial tissue.

Specific examples of sulphated polysaccharides which may be co-spun with

alginate include chondroitin, dermatan, and heparan sulphates as well as heparin. Fibres

comprising alginate co-spun with at least one of these polysaccharides provide an ideal

matrix for growth of tissue (e.g. skin on a burn).

In a further embodiment of the invention, the non-alginate polymer is uncharged.

Examples of such uncharged polymers which may be used include Ace Mannan (e.g. clinical grade material as obtainable from Carrington Laboratories, Dallas, Texas,

U.S.A) or other component of Aloe Vera.

As indicated above, the incorporation of the water soluble non-alginate

polymeric species produces fibres having modified properties compared to those

containing pure alginate. Whilst we do not wish to be bound by any particular theory,

we believe this is because pure alginate fibre has a compact "egg box" structure and the

non-alginate polymer can disrupt the regular packing of the alginate materials therefore

providing increased swelling and absorbancy capability. In the case of fibres

comprising alginate and 15% CMC, we have found that the absorbency of a non-woven

dressing produced therefrom was 19 g/g as compared to 17 g/g for a dressing produced

from fibres of the alginate which had not been co-spun with the CMC.

Apart from absorbency changes, the non-alginate component may introduce

active healing or other medical properties in the dressing. The inclusion of pectin, for

example, increases the debridement properties of the dressing.

Fibres in accordance with the invention may be produced by spinning a dope

comprising a total dissolved solids content of less than 10% (e.g. about 6%) into an

aqueous medium containing cations which will result in the formation of insoluble

fibres. The amount of the cation may, for example, be less than 1% by weight.

In the case of non-alginate polymers containing COO ^" groups it is preferred that

the coagulating cation is calcium. If the non-alginate polymer contains S0 ₄ ^" groups, it

is preferred that the coagulating cation is zinc because of the greater insolubility of the

calcium sulphate bridge which will cause slower ion exchange with ions in wound

fluids. However this type of slower ion exchange can effectively be used to 'fine-tune'

the exudate handling characteristics. This zinc and calcium for instance behave in

opposite ways in sulphated species as compared to carboxylated molecules, i.e. calcium

is a more effective cross-link in sulphated molecules whereas zinc is more effective in

carboxylated species.

The invention will be illustrated by the following non-limiting Examples.

Example 1

This example describes the production of alginate/CMC/pectin fibres.

A spinning dope was prepared by mixing 12 kg of sodium alginate (Protanal

LF 10/60, (available from Pronova Biopolymers), viscosity in 1% solution between 40 to

60 cps), 1.5 kg of sodium carboxymethyl cellulose and 1.5 kg of high methyloxy pectin

in 235 litres of water. After storage at room temperature for two days to remove the

bubbles, fibres were produced by extruding the dope through a 40,000 hole spinneret

(hole diameter 70 um) at 12 m/min. The as-spun fibres were taken up at 7.2 m/min and

then stretched at 80°C to 9 m/min. The fibres were then washed with water before they were dried by first passing the fibres through an acetone bath and then drying with

heated air. Finally, the dry tow was crimped and cut to produce staple fibres. The staple

fibres could be carded and needled to form a non-woven felt which could be cut into

individual dressings.

Example 2

This example describes the production of alginate/CMC fibres.

Example 1 was repeated except that the dope was produced by mixing 13.5 kg

of sodium alginate (Protanal LF 10/60, viscosity in 1% solution between 40 to 60 cps)

and 1.5 kg of sodium carboxymethyl cellulose in 235 litres of water. The fibres could

be spun and carded into a non-woven dressing as in Example 1.

The alginate/CMC dressing as produced in this way had an absorbency of 19 g/g

as compared to 17 g/g for dressings made from fibres without addition of CMC under

exactly the same processing conditions.

Example 3

This Example describes the production of alginate/ Ace Mannan fibres.

Example 1 was repeated except that the dope was produced by mixing 13.5 kg

of sodium alginate (Protanal LF 10/60, viscosity in 1% solution between 40 to 60 cps)

and 1.5 kg of Ace Mannan (ex-Carrington Laboratories) in 235 litres of water. The

fibres could be spun and carded into a non-woven dressing as in Example 1.