Silver containing wound dressing

Abstract

A wound dressing having anti-microbial activity comprises a first fiber capable of bonding with silver (1) cations. The wound dressing comprises a blend of the first fiber to which silver (1) cations are bonded and a second fiber which is substantially free from silver. The wound dressing comprises from 0.01 to 5.0 percent by weight of silver (1) cations, based on the weight of fiber.

Claims

1. A wound dressing comprising gel-forming fibres having anti-microbial activity, comprising a first fibre, which is gel-forming and substantially insoluble in water having silver (I) cations bonded thereto and discoloring on exposure to light, and a second fibre, which is gel-forming and substantially free from silver, wherein the wound dressing comprises a uniform blend of the first fibre and the second fibre, said wound dressing comprising from 0.01 to 5.0 percent by weight of silver (I) cations based on a total weight of first and second fibres, whereby discoloration of the blend on exposure to light is lessened compared with discoloration on exposure to light of a batch of the first fibre having a same average amount of the silver (I) cations present as is present in the blend.

2. A wound dressing according to claim 1, which comprises from 0.01 to 4.0 percent by weight of silver (I) cations based on the total weight of first and second fibres.

3. A wound dressing according to claim 1, which comprises from 0.25 to 3.0 percent by weight of silver (I) cations based on the total weight of the first and second fibres.

4. A wound dressing according to claim 1, wherein the first fibre is selected from a group consisting of a carboxymethylcellulose fibre, an alginate fibre, a chitosan fibre, a chitosan derivative fibre and an acrylic fibre.

5. A wound dressing according to claim 4, wherein the first fibre is the carboxymethylcellulose fibre and the wound dressing contains from 1.0 to 2.0 percent by weight of silver (I) cations, based on the total weight of the first and second fibres.

6. A wound dressing according to claim 4, wherein the first fibre is the alginate fibre and the wound dressing contains from 0.25 to 0.75 percent by weight of silver (I) cations, based on the total weight of the first and second fibres.

7. A wound dressing according to claim 4, wherein the first fibre is the acrylic fibre which incorporates a comonomer to provide dye-sites in the first fibre.

8. A wound dressing according to claim 1, wherein the second fibre contains no silver or low levels of silver such that it discolors to a degree which is not aesthetically objectionable.

9. A wound dressing according to claim 1, wherein the second fibre contains no silver or low levels of silver such that it does not discolor at all.

10. A wound dressing according to claim 1, wherein a ratio of the first fibre to the second fibre is in a range of from 5 to 20% by weight of the total weight of the first and second fibres.

11. A wound dressing according to claim 1, wherein a ratio of the first fibre to the second fibre is in a range of from 0.5 to 25% by weight of the total weight of the first and second fibres.

12. A wound dressing according to claim 1, wherein the first fibre includes at least 8% by weight, based on the total weight of the first and second fibres, of silver (I) cations.

13. A wound dressing according to claim 12, wherein the first fibre is prepared using at least a 4% silver nitrate solution.

14. A wound dressing according to claim 1, wherein the silver (I) cations are chemically bonded to the first fibre.

15. A wound dressing according to claim 1, wherein the silver (I) cations are introduced into the first fibre by ion-exchange.

16. A wound dressing according to claim 1, wherein the first fibre having silver (I) cations bonded thereto is pre-exposed to light prior to blending with the second fibre.

17. A wound dressing according to claim 1, wherein the first fibre is a carboxymethylcellulose fibre and a degree of substitution of the carboxymethylcellulose fibre is less than 0.4.

18. A wound dressing according to claim 1, wherein the second fibre is a carboxymethylcellulose fibre.

19. A wound dressing comprising gel-forming fibres having anti-microbial activity, comprising a first fibre, which is gel-forming and substantially insoluble in water having silver (I) cations bonded thereto and discoloring on exposure to light, and a second fibre, which is gel-forming and substantially free from silver, wherein the wound dressing consisting essentially of a uniform blend of the first fibre and the second fibre, said wound dressing comprising from 0.01 to 5.0 percent by weight of silver (I) cations based on a total weight of first and second fibres, whereby discoloration of the uniform blend on exposure to light is lessened compared with discoloration on exposure to light of a batch of the first fibre having a same average amount of the silver (I) cations present as is present in the uniform blend.

Description

EXAMPLE 1

(1) Manufacture of Master Batch Material

(2) The optimum conditions for manufacture of a master batch material were determined as follows:

(3) Sodium carboxy methyl cellulose fibre (CMC), Hydrocel, available from Acordis Speciality Fibres Limited of Coventry England, was soaked in silver nitrate (AgNO.sub.3) solution in 50 volume % industrial methylated spirit/50 volume % water and the following table shows the percentage silver take-up after soaking, as measured by x-ray fluorescence.

(4) TABLE-US-00001 % AgNO.sub.3 Conditions 4% AgNO.sub.3 8% AgNO.sub.3 15 minutes @ 65 C. 8.1 6.1 15 minutes @ ambient 12.6 11.2 4 hours @ ambient 8.0 9.0

(5) From the above results, it was determined that higher concentrations of silver nitrate did not appear to be beneficial and that the use of a solution having a concentration of approximately 4% silver nitrate to produce a fibre having a silver content of 8% would give the optimum results. It was therefore decided to produce the master batch material using such a solution.

(6) CMC tow or staple (50 g) was added to a solution of 4% silver nitrate (300 g) in industrial methylated spirit/water 50/50 at ambient temperature. The solution was held for convenience in a round screw top bottle so that it could be rolled on a laboratory bottle roller. The bottle was rolled for 15 minutes whereupon an ion exchange mechanism took place which produced silver containing CMCreferred to herein as silver CMC (8% w/w, Ag).

(7) The spent silver nitrate solution was discarded and replaced with 50/50 industrial methylated spirit/water wash liquor (300 g) followed by shaking for five minutes. This washing process was repeated and finally a soft finish was used. This consisted of 0.5% polysorbate 20 (Tween) 20 in 90:10 industrial methylated spirit/water (i.e. 1.5 g in 300 g).

(8) Excess liquor was squeezed out of the fibre, which was then allowed to dry at ambient temperature. The silver CMC tow was then opened out and spread onto an open bench to allow maximum access to light. The discolouring tow was handled periodically to expose new surfaces to the light. This was continued until the majority of the tow assumed a chocolate brown coloration (about two weeks).

(9) The predominantly brown silver CMC tow produced was blended with untreated carboxymethyl cellulose (CMC) fibre at the ratios shown as follows to produce blends having 0.5%, 1.0% and 2.0% silver: 6.25% silver CMC+93.75% CMC fibre=0.5% Ag 12.5% silver CMC+87.50% CMC fibre=1.0% Ag 25.0% silver CMC+75.00% CMC fibre=2.0% Ag

(10) Blending was accomplished by carrying out a carding operation twice to achieve a uniform blend, on hand pre-mixed fibre. The carded web was then cross-folded to give the desired basis weight. The web was then bonded on a needle loom to give a coherent web from which individual dressings were cut. In addition, a conventional carboxymethyl cellulose fibre control sample was manufactured by the same method.

(11) Absorbency Results

(12) The master batch material was produced by the soaking of CMC fibre tow in silver nitrate and the absorbency tests were first of all carried out on tow using a free swell test. It was found that the CMC fibre control had an absorbency of 28 g/g and the silver CMC had an absorbency of 30 g/g. These differences were not considered to be significant.

(13) Absorbency tests were then carried out on fabric produced by needle felting from fibres as above.

(14) Fabric absorbencies as measured by the test identified in the British Pharmacopeia 1993 Addendum 1995 page 1706, Alginate Dressing Absorbency were found to be as shown in the following table, in which gsm=grams per square meter and is a measure of the amount of fabric produced.

(15) TABLE-US-00002 gsm Absorbency g/g Absorbency g/piece CMC control 111 16.0 18.0 0.5% silver CMC 99 20.0 19.5 1.0% silver CMC 91 20.5 18.7 2.0% silver CMC 65 22.3 14.5

(16) As can be seen from the above table, the addition of silver was found to have very little effect on the absorbency, if anything increasing the absorbency on a gram per gram basis, though having less effect on absorbency on a gram per piece basis.

(17) After wetting for 30 minutes in saline, the fabrics which were initially a fairly dark fawn, changed colour and became lighter and more translucent as time passed.

(18) It appeared that there was no difference in the gelling properties between the CMC and the silver CMC, which is an important observation in that the silver addition does not destroy the valuable gelling properties.

(19) Microbial Activity

(20) To measure the efficiency of the silver containing material in reducing microbial activity, 250 g of milk was mixed with 0.2 g of fibre. The results were as follows:

(21) TABLE-US-00003 Control (milk alone) Malodour in 2 days Control (CMC in milk) Malodour in 2 days 0.5% Silver (web) Malodour in 2 weeks 8.0% Silver (tow) No Malodour in 3 weeks

(22) These tests were repeated with 0.9 wt. sodium chloride additions (chosen to be equivalent to the salt level in body fluids) to the milk, and the same results were obtained. This shows that the chloride ions in the salt were not detrimental to the antimicrobial properties of the silver in the silver CMC.

(23) As can be seen from the above results, milk alone and milk containing CMC fibre alone went off in two days, as could be easily determined by the smell. By comparison, where the web contained 0.5% silver, there was a two week period before the milk went off and could be smelt. With unblended tow containing 8% silver, no smell could be detected after a three week period when the test was stopped.

(24) In practice, the wound treatment products utilising the invention are unlikely to be left on a wound for more than a few days, and certainly no more than a week, so that it be seen that a blend containing 0.5% silver retains its efficiency in terms of antimicrobial effect for at least twice the period that would be required in practice.

EXAMPLE 2

(25) A solution of water (33.1 g) and industrial methylated spirit (IMS) (36.0 g) was made up in a black glass bottle suitable for rolling on a bottle roller. To it was added silver nitrate (30.0 g) and the latter was stirred until it dissolved. No heat was required. To this solution was added 12 g of high manuronic calcium alginate tow and the whole was rolled on a bottle roller for four hours. After this period of time the tow was removed and washed in a solution (70 g) containing IMS and water as a 50/50 mixture. Soft finish in the form of polysorbate 20 (0.7 g) was dissolved in (70 g) solution of IMS/water as a 95/5 mixture and the tow was soaked in this medium for approximately 50 minutes. The silver alginate master batch was then dried in a fume cupboard to give a product having 13.7% of silver overall on the fibre.

(26) 5 g of the above silver alginate master batch was weighed and cut into staple and opened by hand. 95 g of standard high manuronic calcium alginate fibre was also cut into staple and opened. The two were blended on the in-put feed belt of a laboratory carding machine.

(27) The diluted silver alginate fibre was then carded, cross-folded and needled into a non-woven web. By calculation the final product would contain silver at an average level of 0.6%. It had a light grey-brown flecked mottled appearance.

(28) In a comparative example, the same level (0.68%) of silver was applied uniformly to a batch of the same calcium alginate fibre, and it was then carded, cross-folded, and needled to form a nonwoven web. The web was exposed to light and developed a uniform darkish brown colour, appearing much darker than the mottled appearance of the blended web having the same average amount of silver present.

(29) The invention also contemplates multiple layer dressings some or all of which layers may comprise blended product incorporated silver additions. For example, a silver containing blended layer of a non-gel forming fibre, such as a silver containing acrylic fibre blended with pure acrylic fibre could be faced with a wound contact layer of a gel forming fibre. An example of the contact layer could be an alginate fibre and the alginate layer could be blended with a silver added fibre or may have no silver at all, being a simple gel forming alginate fibre.