GB2401879A

GB2401879A - Absorbent material

Info

Publication number: GB2401879A
Application number: GB0311448A
Authority: GB
Inventors: Richard Freeman; Haydar Jaafar
Original assignee: Advanced Medical Solutions Ltd
Current assignee: Advanced Medical Solutions Ltd
Priority date: 2003-05-19
Filing date: 2003-05-19
Publication date: 2004-11-24
Also published as: GB0311448D0

Abstract

An absorbent material, e.g. for use as a wound dressing, comprises 55% to 95% by weight of gelling fibres and 5% to 45% by weight of non-gelling fibres. Most preferably the material comprises about 60% by weight of gelling fibres and 40% by weight of non-gelling fibres. The gelling fibres may, for example, be an alliginate. The non-gelling fibres may for example be a synthetic polymer.

Description

2401 879

ABSORBENT MATERIAL

The present invention relates to an absorbent material and more particularly to such a material comprised of gelling and non-gelling fibres. The invention relates even more particularly, but not exclusively, to a wound dressing comprised of such a material.

WO-A-9519795 (Bristol-Myers Squibb) discloses a wound dressing in the form of a sheet which is comprised of a mixture of gelling and non- gelling (textile) fibres. Such a dressing is considered to overcome disadvantages associated with dressings comprised solely of either gelling or non-gelling fibres. With regard to dressings comprised of gelling fibres, the incorporation of textile fibres reduces the overall cost of the dressing (since gel forming fibres are relatively expensive). With regard to dressings comprised of textile fibres (e.g. cotton gauze), a dressing comprised of a mixture of textile fibres and gelling fibres may be left in contact with the wound for longer.

The dressing specifically disclosed in WO-A-9519795 comprises from 50 /O to 95% by weight of textile fibres and from 5% to 50% by weight of gel forming fibres.

More preferred embodiments as disclosed in WO-A-9519795 comprise 75% to 90% (e.g. 80%) by weight of textile fibres and from 10% to 25% (e.g. 20%) by weight of gel forming fibres.

Thus the dressings specifically disclosed in WO-A-9519795 comprise a major proportion by weight of the textile (non-gelling) fibres and a minor proportion by weight of the gelling fibres. These relative amounts ensure moist wound healing to achieve an absorbency of at least 16g/g and intact removal of the dressing from the, , Some known dressings suffer from the disadvantage of a wet tensile strength À :.

of less than 1.2 N. À : À À e À en. :- À -

According to the present invention there is provided an absorbent material which comprises 55% to 95% by weight of gel forming fibres and 5% to 45% by weight of non-gelling fibres.

The invention is based on our unexpected finding that an absorbent material comprised of a major proportion by weight of gelling fibres and a minor proportion by weight of non-gelling fibres not only has good absorbency (as provided by the gelling fibres) but also has surprisingly high wet strength, typically greater than 4 N. in spite of the relatively high content of the gelling fibres. In fact, it is possible to achieve wet strengths which are higher than the dry strength values.

The absorbent material is preferably a non-woven material.

The absorbent material of the invention may be provided as a sheet or other physical form.

Absorbent materials in accordance with the invention are particularly useful as wound dressings. Such a dressing may be placed in direct contact with a wound (which may for example be an infected wound or a chronic wound) and are capable of absorbing relatively high levels of exudates. The dressing may be such that its wet integrity is such that the dressing may subsequently be removed in one piece without adhering to the wound. For use as a wound dressing, the absorbent material of the invention may, for example, be provided as a sheet or other form, e.g. a rope.

The invention is not however limited to use of the absorbent material as a À..

wound dressing and other applications are possible. Thus, for example, the material..

will find utility in tissue engineering, e.g. as a scaffold. À:. a.

Preferred materials in accordance with the invention comprise 55% to 65% by À . weight of the gelling fibres and 35% to 45% by weight of the nongelling fibres. A, À - particularly preferred embodiment comprises about 60% by weight of gelling fibres and about 40% by weight of non-gelling fibres.

Materials in accordance with the invention may have an absorbency of at least gig. More particularly, the absorbency may be at least 12 g/g, 14 gig or 16 g/g.

Yet more particularly, the absorbency may be at least 20 g/g or even higher. The absorbency of the higher absorbency materials (for example, those exhibiting an absorbency of greater than 18 g/lOOcm2) is a function of the specific composition of the material used.

Absorbency was measured using the following methods.

7.1 Conventional Absorbency 7.1.1 If felt or foam samples are greater than 5 x 5 cm, accurately cut 10 felt or foam samples using the 5 x 5 cm cutter (being careful not to stretch or distort the felt/foam). If testing rope samples, select and cut 10 rope samples, each approximately 4 cm in length. If testing the Spiral form of Alginate Dressing imagine to draw a line that joins the beginning of the spiral cut with the end point. With the scissors cut along this line the first 2 rings of the spiral dressing. The small spiral left is the sample to test.

7.1.2 Condition the sample in the conditioning chamber for a minimum of 16 hours. The conditioning chamber is kept at room temperature and contains a solution of Sodium Nitrite to maintain a constant humidity (66% humidity at 20 C). À. .

7.1.3 Place the empty petri dish on the balance and tare the balance.

À:::-: À.. . À À e. :* À.

7.1.4 Place one 5 x 5 cm sample of dressing (or one 4 cm rope/small spiral shaped sample) into the petri dish and record the weight to 3 decimal placed (We). Remove the petri dish and sample from the balance.

7.1.5 Either: Add solution A to the petri dish allowing a minimum ratio of solution A/rope weight of 100 and allow to stand for 30 minutes +/-1 minute, at approximately 37 C +/-3OC.

Or: Multiply We by 40 to the nearest 0.50g and add this weight of solution A to the petri dish and allow to stand for 30 minutes +/-1 minute, at approximately 37 C +/-3OC. NB in this latter case, the result will be BP absorption capacity.

7.1.6 Using forceps, suspend the sample by one corner for 30 seconds +/-1 second.

7.1.7 Weigh the sample (W2) 7.1.8 Repeat stages 7.2 - 7.8 above with the other 9 samples.

7.2 Sink Test Method 7.2.1 For the Sink Test method the samples do not need to be conditioned.

7.2.2 For 5 x 5 cm samples, eight samples should be used in each test. For x 10 cm sizes use two dressings, for all larger sizes of felt and all ropes, one piece should be used. For rollstock, cut a 30cm length of rope or two 10 x 10 cm pieces of felt. . a, . ..

7.2.3 Weigh the dry cage and record the weight as We : oe s 7.2.4 Felt samples should be folded if required and then rolled and placed into the testing 'cage' provided. The sample should be allowed to uncoil and fill the 'cage'.

7.2.5 Rope samples should be torn in two from end to end (i.e. forming two thin ropes of the same length as the original). Coil these two thin ropes and place into the sample cage provided, allowing the ropes to uncoil to fill the 'cage'.

7.2.6 Weigh the dry cage and sample W2.

7.2.7 Fill the 2000 ml beaker with solution A to a depth of lOcm.

7.2.8 Hold the 'cage' horizontally 1 cm above the liquid surface.

7.2.9 Drop the cage and wait for it to reach the bottom of the beaker.

7.2.10 Using your fingers, lift the cage out of the solution holding at one end so that it hangs at approximately 45 . Hold it in this way for precisely seconds allowing it to drain back into the beaker.

7.2.11 Weigh the wet sample and cage W3.

7.2.12 Repeat stages 7.2.1 to 7.2.1 1 a further two times.

7.2.13 Dry the cage after each test.

7.3 Results/Calculations.

To calculate absorbency in 'g/lOOcm2' (Not applicable to Spiral Alginate I Foam) : À. i' 1 -

g/100 cm2= (W2 - W') x 100/25, if the size is exactly 5 x 5 cm if not exactly 25 cm2, let area = x g/100 cm2= (W2 - We) x 100/x 7.3.2 Absorbency in g/g (applicable to spiral alginate foam dressing) Both the felt, foam and rope absorbency in gig can be calculated directly as: W2 - Wit Wl Calculate for all samples, then calculate XIO +/- 2SD 7.3.3 Absorbency in g/dressing If 5 x 5 cm dressing is tested, then W2 - We = Absorbency in g/dressing ActualAreacm For all other dressing sizes, (W2 - We) x 25 2 = Absorbency in g/dr Where, 25 = 5 x 5 cm. Calculate for each sample, then calculate XIO +/- 2SD.

The gelling fibres may comprise a water-absorbent natural or synthetic polymer that is capable of forming a gel on contact with water. The gel forming fibres will, for preference, be comprised of at least one polysaccharide which may be selected from the group consisting of alginates, cellulose (e.g. carboxymethyl cellulose, such as sodium carboxymethyl cellulose), chitosan, viscose and/or mixtures thereof. . . It is particularly preferred that the gelling fibres comprise at least a major.

proportion by weight, e.g. at least 80% by weight, of an alginate. The alginate is:.

preferably a calcium alginate. The alginate may comprise calcium alginate and sodium alginate in any ratio to suit a particular application. For example, in one preferred embodiment of the invention the calcium content expressed as a percentage of the total amount of calcium and sodium in the alginate is greater than 60% and may be greater than 90%.

Alginate dope contains only sodium alginate. The alginate dope is past through a spinneret in a coagulation bath containing calcium chloride solution.

Exchange of ions occurs to form calcium alginate. This results in calcium alginate fibre. By adding sodium chloride to the coagulation bath with calcium chloride in certain proportions the result is a mixture of sodium/calcium alginate fibres, comprising, for example, greater than 85% calcium expressed as a percentage of the total amount of calcium and sodium present in the alginate.

It is particularly preferred that the alginate has a G (guluronic) content of 65% to 75% by weight and correspondingly an M (mannuronic) content of 25% to 35% by weight. Preferably the alginate has a viscosity of between 30 to 100 cps in a 1% solution of the alginate in reverse osmosis deionised water.

A particularly suitable alginate may be derived from the seaweed Laminaria- Hyperborea which is harvested along the Norwegian coastline. Protanal LF 10/60 (available from FMC Biopymers, Norway) is an especially appropriate alginate.

It is particularly preferred that the gelling fibres comprised of a major proportion by weight of the alginate also incorporate carboxymethyl cellulose. For preference, such fibres comprise 80% to 90% by weight of the alginate and 10% to 20% by weight of the carboxymethyl cellulose. More preferably, such fibres comprise 84% to 86% (preferably about 85%) by weight of the alginate and 14% to 16% (preferably about 15% by weight of the carboxymethyl cellulose). Such fibres may be produced by the co-spinning technique disclosed in WO-A- 9610106. More particularly, a spinning dope comprised of an aqueous solution of the sodium salt of the alginate and sodium carboxymethyl cellulose may be extruded through a spinneret into a bath containing calcium ions to produce co-spun fibres, e.g. using the technique as described in Example 1 of WO-A-9610106.

The non-gelling fibres may be textile fibres and may for example be a polyamide (such as Nylon), polyester or polyether. Nylon fibres are particularly preferred.

The gelling and non-gelling fibres in the absorbent material may for example have a length of 2 cm to 20 cm and may be of 1 to 1000 denier. More preferably, the gelling and non-gelling fibres may have a length of 3 cm to 8 cm and may be of 1 to denier.

Absorbent materials in accordance with the invention in sheet form may, for example have a basis weight of 50 to 1000 gem, e.g. 100 to 200 gsm.

Preferred absorbent materials in accordance with the invention comprise a single layer, which is a mixture of the gelling and non-gelling fibres. Other constructions are however possible. For example, the absorbent material may comprise two layers, one being of the gelling fibres and the other being of the non- gelling fibres. A further possibility is a 3-layer structure, each of which comprises only one type of fibres. A still further possibility is a two of more layer structure in which one layer comprises one fibres type and a further layer comprises a mixture of fibres. À '

For use as wound dressing, it is preferred that the absorbent material.

incorporates a medicament that is released when in contact with wound exudates. The medicament may for example be selected from anaesthetic, analgesic, non-steroidal À..

anti-inflammatory drug (NSAID), steroid, hormone, antibiotic, antimicrobial, À , antifungal, metal salt, elemental metal, mineral, herbal extract (such as green tea....

extract), honey and combinations thereof. À.

It is particularly preferred that the medicament is an antimicrobial agent and is most preferably silver which is most preferably incorporated in or on the non-gelling fibres. It is particularly preferred that the silver is provided as a coating on the non- gelling fibres. Most preferably, the silver coating provides 20% to 30%, e.g. about 25%, by weight of the non-gelling fibres. The inventive material provides the advantages of not staining tissue with which it is in contact whilst enabling the release of silver ions at bactericidal levels. The specific composition of the inventive material and the manner in which the dressing is applied/removed enables accurate control of the administration of the antimicrobial agent to the wound.

Particularly preferred non-gelling fibres for use in the wound dressing in accordance with the invention comprise Nylon with a silver coating. The gelling fibres may comprise polyglytone or rayon.

A particularly preferred wound dressing in accordance with the invention has antimicrobial properties and comprises: (i) 55% to 65% (most preferably about 60%) by weight of gelling fibres which themselves comprise 80% to 90% by weight of calcium alginate and 10% to 20% by weight of carboxymethyl cellulose; and (ii) 35% to 45% (most preferably about 40%) by weight of silver-coated Nylon fibres. r r I À

The wound dressing preferably comprises a layer of fibres as defined for (i) . and (ii) above. À:e

The alginate fibres (i) are preferably as defined more specifically above. À . The Nylon fibres preferably comprise 20% to 30%, most preferably about ' ' 25%, by weight of silver. À Absorbent materials in accordance with the invention may be produced by conventional operations. Thus, for example, the materials may be produced by a carding operation. The fibres may initially be subjected to an 'opening procedure' to separate the fibres and reduced density and may then be passed to carding rollers to produce a carded web which may then be fed to a cross-lapper. If desired, the web may be subjected to a needling operation to achieve a thin layered, structured material.

The invention will be further illustrated with reference to the following non-

limiting Examples.

Example 1

This Example describes a wound dressing comprised of 40% by weight of nongelling fibres and 60% by weight of gelling fibres.

The gelling fibres were produced by co-spinning carboxymethyl cellulose and calcium alginate using the procedures disclosed in WO-A-9610106. The calcium alginate was Protanal LF 10/60 which has a G content in the range of 65% to 75% by weight. The CMC was Blanose_ (available from Aqualon (a division of Hercules Inc.)). The fibres comprise 15% by weight of the CMC and 85% by weight of the calcium alginate.

The fibres were of 1 to 5 denier and were cut to a length of 5 cm for the.

...DTD: purposes of producing the wound dressing. . The non-gelling fibres comprised 75% by weight of Nylon 6,6 coated with À.

25% by weight of silver. The fibres are commercially available under the brand name. À X-Static (Noble Fiber Technologies). ...

The non-gelling fibres were of 120 to 170 denier and had a length of 5 cm. À The gelling and non-gelling fibres were converted, by means of a carding operation, into a non-woven fibrous web. For this purpose, the gelling and non- gelling fibres were separately subjected to an 'opening procedure' to separate the fibres and reduce density. The 'open' fibres were then mixed together in the required weight ratio and fed to carding rollers operating at a constant speed to form a thin (e.g. greater than 1 mm) carded web. The carded web was fed into a cross- lapper where the mixed fibre web was folded into successive layers at constant speed to form a thicker, cross-laid web of thickness 5 to 15 cm. The web was then fed to a needling loom for packing. The needled web was wound and slit to produce a desired width of roll stock. In the case of 10 x 10 cm squares the machine achieve 5-6 rolls; in the case of rope the machine achieves 2 rolls.

The resulting material had a basis weight of between 100 to 170 gem with a mean basis weight of 135 gem.

Two types of wound dressing were produced using this procedure. For one material, the roll stock web had a width of 10 cm and was cut into 10 x 10 cm squares which were then sterilised and packaged according to standard techniques.

For the other type of wound dressing (the flat rope), the roll stock web had a width of 30.5 cm and was then cut into 2.5 cm sections which were individually wound into a blister pot which were then sterilised and packaged using conventional techniques.

The materials that had been subjected to packaging and sterilization were then.

tested for their properties. À .

Strips of the two types of dressing were tested for their dry-and wetstrength À , properties. Wet-strength was tested using the following procedure: .... À .

(i) For the lOxlO cm dressings, 20 mm strips were cut from a number of À À.

samples in each of the cross-and-machine-directions. For the 2.5 x 30.5 cm rope samples, 20 mm wide strips were cut in the cross and machine directions.

(ii) All strips were conditioned at a temperature of 20 C, 65% Relative I Humidity for 16 hours.

(iii) Each strip was then soaked in 40 times its own weight of Solution A (containing 142 millimoles of sodium ions and 2.5 millimoles calcium ion in distilled water) that had previously been warmed to 37 C and incubated at a temperature of 37 C for 30 minutes).

(iv) The strip was then suspended for 30 seconds.

(v) The wet strength was then measured using a Lloyd Instruments LRX (with 50N load cell and flat grips) and data logging station.

Dry strength was also measured using strips as detailed in (i) above and an apparatus as detailed in (v) above.

The above tests for dry and wet strength were repeated on several different batches of dressings.

The results for the strips cut from the 10 x 10 cm samples were as shown in

Table 1. .... À .

Table 1 À:.

BATCH NO. DRY STRENGTH WET STRENGTH ': 1 5.05 +/- 2.72 9.12 +/- 4.84....

5.83 +/- 4.60 6.88 +/- 3.90 ' ' 6.42 +/-3.59 11.65 +/- 6.16.. :.

Strength measured in N/sample width of 20 mm.

The results for the strips from the 2.5 x 30.5 samples are as shown in Table 2.

Table 2

BATCH NO. DRY STRENGTH WET STRENGTH 4 9.84 +/- 1.98 14.93 +/- 2.98 7.02 +/- 1.43 12.01 +/- 3.16 6 10.07 +/- 4.46 17.42 +/-3.6 Strength measured in N/sample width of 20 mm.

It can be seen from Tables 1 and 2 that, for all batches tested, the wet strength of the dressing was increased as compared to the dry strength. This is a particularly unexpected result in view of the relatively high amount of gelling fibres present in the dressings.

Example 2

A number of absorbent materials having various rations of gelling: nongelling; fibres were produced using the same fibres as described in Example 1. The absorbency of the materials was measured and the results are shown in Table 3.

Table 3

Ratio of gelling: non-gelling fibres Absorbency Absorbency g/g..e g/lOOcm2 À : 55:45 22 18...

60:40 25 20....

70:30 27 19 A:.

The mean basis weight of the samples tested was 135 gem using the Absorbancy test methods 7.1 and 7.2 as described above. À 1 I, À:

7 ' ' 7 À 7 A.

Claims

1. An absorbent material comprising 55% to 95% by weight of gelling fibres and 5% to 45% by weight of non-gelling fibres.

2. A material as claimed in claim 1 comprising 55% to 65% by weight of gelling fibres and 35% to 45% by weight of non-gelling fibres.

3. A material as claimed in claim 2 comprising about 60% by weight of gelling fibres and about 40% by weight of non-gelling fibres.

4. A material as claimed in any one of claims I or 3 wherein the gelling fibres comprises at least one polysaccharide.

5. A material as claimed in claim 4 wherein the polysaccharide is selected from the group consisting of alginates, cellulose, chitosan, viscose and/or mixtures thereof.

6. A material as claimed in claim 5 wherein the polysaccharide comprises an alginate.

7. A material as claimed in claim 5 wherein the alginate has a G content of 65% to 75% by weight.

8. A material as claimed in claim 6 or 7 wherein the alginate comprises calcium alginate. . ..

9. A material as claimed in any one of claims 6 to 8 wherein the gelling fibre À..

comprises the alginate and carboxymethyl cellulose. :.

10. A material as claimed in claim 9 wherein the gelling fibre comprises 80% to À 90% by weight of the alginate and 10% to 20% by weight of the carboxymethyl À.

cellulose.

11. A material as claimed in claim 10 wherein the gelling fibres comprises 84% to 86% by weight of the alginate and 14% to 16% by weight of the carboxymethyl cellulose.

12. A material as claimed in claim 11 wherein the gelling fibres comprise about 85% by weight of the alginate and about 15% by weight of the carboxymethyl cellulose.

13. A material as claimed in any one of claims 9 to 12 wherein the fibres comprised of alginate and carboxymethyl cellulose have been produced by co- spinning the alginate and the carboxymethyl cellulose.

14. A material as claimed in any one of claims 1 to 3 wherein the gelling fibres comprise a synthetic polymer.

15. A material as claimed in claim 14 wherein the gelling fibres comprise polyglytone or rayon.

16. A material as claimed in any one of claims 1 to 15 wherein the nongelling fibres comprise textile fibres.

17. A material as claimed in any one of claims 1 to 16 wherein the nongelling fibres comprise a polyamide, polyester or polyether. . . .

18. A material as claimed in any one of claims 1 to 17 wherein the gelling and non-gelling fibres have a length of 2cm to 20cm. À

19. A material as claimed in any one of claims 1 to 18 wherein the gelling and the, non-gelling fibres are from 1 to 1000 denier. .

20. A material as claimed in any one of claims 1 to 19 in sheet form.

21. A material as claimed in claim 20 having a basis weight of 50 to 1000 gem.

22. A material as claimed in claim 20 or 21 having a thickness of 1 to 20 mm.

23. A material as claimed in any one of claims 1 to 22 which is a nonwoven material.

24. A material as claimed in any one of claims 1 to 23 having an absorbency of at least 10 g/g.

25. A material as claimed in claim 24 having an absorbency of at least 15 gig.

26. A wound dressing comprising a material as claimed in any one of claims 1 to 25.

27. A wound dressing as claimed in claim 26 incorporating a drug or other medically active component.

28. A wound dressing as claimed in claim 27 wherein the medically active component is selected from an anaesthetic, analgesic, non-steroidal antiinflammatory drug (NSAID), steroid, hormone, antibiotic, antimicrobial, antifungal, metal salt, elemental metal, mineral, herbal extract, honey and combinations thereof.

29. A wound dressing as claimed in claim 28 wherein the herbal extract is green; tea extract.

30. A wound dressing as claimed in claim 28 wherein the component is silver. I,, ' .,

31. A wound dressing as claimed in claim 30 wherein the silver is incorporated in the non-gelling fibres. I'

32. A dressing as claimed in claim 31 wherein the silver is provided as a coating on the non-gelling fibres.

33. An antimicrobial wound dressing comprising: (i) 55% to 65% by weight of gelling fibres which themselves comprise 80% to 90% by weight of calcium alginate and 10% to 20% by weight of carboxymethyl cellulose; and (ii) 35% to 45% by weight of silver-coated Nylon fibres.

34. A wound dressing as claimed in claim 31 which comprises: (i) About 60% by weight of said gelling fibres; and (ii) About 40% by weight of said silver-coated Nylon fibres.

35. A dressing as claimed in claim 33 or 34 wherein the alginate fibres have a G- content of 65% to 70% by weight.

36. A dressing as claimed in any one of claims 33 to 35 wherein the alginate fibres comprise 84% to 86% by weight of the alginate and 14% to 16% by weight of the carboxymethyl cellulose.

37. A method of treating a wound comprising applying to the wound a dressing as, ; claimed in any one of claims 26-36.

38. A method as claimed in claim 37 wherein the wound is an infected wound or a e e chronic wound. a a eeae À.a

39. A scaffold for cell growth comprised of a material as claimed in any one of a claims 1 to 24.