Wound dressing

Abstract

A wound dressing comprising a mat of gel forming fibers comprising silver, the mat having an open structure reinforced with textile fibers or threads, or fibers or threads of limited absorbency for use in the treatment of wounds.

Claims

1. A wound dressing comprising a mat of gel forming fibres comprising between about 0.1% and 20% by weight of silver, the mat having an open structure in which the free internal volume of the mat exceeds the solid fibres volume, and reinforced with fibres or thread of limited absorbency of less than 10 g/g as measured by the free swell method for use in the treatment of wounds, wherein the gel forming fibres and the fibres or thread of limited absorbency are blended during the formation of the mat, wherein the mat has a punch density of from 10 to 50 per cm.sup.2, and wherein the basis weight of the mat is from 50 to 200 grams per square meter.

2. A wound dressing as claimed in claim 1 wherein the mat is further reinforced with stitch-bonding in a thread of textile fibre.

3. A wound dressing as claimed in claim 1 wherein the mat is further reinforced with stitch-bonding in a line of longitudinal stitches.

4. A wound dressing as claimed in claim 1 wherein the gel forming fibres are modified cellulose gel forming fibres.

5. A wound dressing as claimed in claim 1 wherein the dressing has a rate of moisture loss at least 25% lower than a dressing made from a mat with a punch density of 60 per cm.sup.2 or higher.

6. A wound dressing as claimed in claim 1 wherein the dressing maintains the hydration of the wound by having a rate of moisture loss (as measured by the percentage weight loss from the dressing) of less than 75% over the first 48 hours of wear.

7. The wound dressing of claim 1, wherein the punch density is from 10 to 40 per cm.sup.2.

8. A wound dressing comprising two superposed mats of gel forming fibres comprising between about 0.1% and 20% by weight of silver, each mat having an open structure in which the free internal volume of the mat exceeds the solid fibres volume, and reinforced with fibres or threads of limited absorbency of less than 10 g/g as measured by the free swell method for use in the treatment of wounds, wherein each mat has a punch density of from 10 to 50 per cm.sup.2, and wherein the basis weight of the mat is from 50 to 200 grams per square meter.

9. A wound dressing as claimed in claim 8 wherein each mat is reinforced with textile fibres blended with the gel-forming fibres in each mat.

10. A wound dressing as claimed in claim 8 wherein the superposed mats are stich-bonded together with a thread of textile fibre.

11. A wound dressing as claimed in claim 8 wherein the superposed mats are stitch-bonded together with a line of longitudinal stitches.

12. A wound dressing as claimed in claim 8 wherein the gel forming fibres are modified cellulose gel forming fibres.

13. The wound dressing of claim 8, wherein the punch density is from 10 to 40 per cm.sup.2.

14. A mat for treatment of wounds, said mat comprising gel forming fibres, and between about 0.12% and 20% by weight of silver, wherein said mat has an open structure in which the free internal volume of the mat exceeds the solid fibres volume, is reinforced with fibres or thread of limited absorbency of less than 10 g/g as measured by the free swell method, and has a punch density of from 10 to 50 per cm.sup.2, wherein the gel forming fibres and the fibres or thread of limited absorbency are blended during the formation of the mat, and wherein the basis weight of the mat is from 50 to 200 grams per square meter.

15. The mat of claim 14, wherein the punch density is from 10 to 40 per cm.sup.2.

Description

(1) The invention is illustrated by the following figures in which:

(2) FIG. 1 is a table showing results from Example 1 below.

(3) The invention is illustrated by the following examples.

EXAMPLE 1

(4) The dehydration properties of various fibrous mats for use in wound dressings according to the invention were compared.

(5) The fibrous mat samples used are detailed below in Table 1:

(6) TABLE-US-00001 Description Basis weight Needle Punch Density Prototype (g per m.sup.2 or gsm) (punches per cm.sup.2) Dehydration Test HF-2010/200 88 60 HF-2010/209 171 30 HF-2010/211 181 30 HF-2010/214 218 30 HF-2010/216 104 15 HF-2010/218 163 75 HF-2010/219 163 100 HF-2010/223 183 30 HF-2010/225 184 50 HF-2010/226 183 100

(7) In the test, 5 cm?5 cm samples of the prototypes were immersed in an isotonic solution until fully hydrated and then placed on a petri dish. The dehydration rates of the prototypes were assessed gravimetrically as shown in FIG. 1.

(8) FIG. 1 shows how the different degrees of needle punch density affected the hydration performance of the mats. Among the prototype mats that managed to retain the fluid for longer are:

(9) HF-2010/223, HF-2010/29, HF-2010/211, HF-2010/214 and HF-2010/216.

(10) Despite the basis weight differences of the prototypes tested, the best performing prototypes have all been textiled with a low needle punch density, for instance less than 60.

(11) Table 2 shows the needle punch density against the % weight loss on drying for the samples in Table 1.

(12) TABLE-US-00002 24 hrs 48 hrs gsm p/cm.sup.2 batch % loss Rank % loss Rank 171 30 HF-2010/209 36 1 60 2 183 30 HF-2010/223 38 2 59 1 218 30 HF-2010/214 39 3 65 4 104 15 HF-2010/216 41 4 68 6 181 30 HF-2010/211 42 5 64 3 184 50 HF-2010/225 42 6 71 7 104 15 HF-2010/216 43 7 68 5 183 100 HF-2010/226 47 8 75 8 163 100 HF-2010/219 57 9 87 9 88 60 HF-2010/200 62 10 94 11 163 75 HF-2010/218 65 11 90 10

(13) The mats to be used in dressings according to the invention demonstrated that they can maintain a moist wound environment for a sustained period of time. It can be concluded, that a low needle punch density, provides a loftier structure which allows more space between the fibres to expand and gel, thus, increasing the absorption capacity. This structure also contributes to retaining the fluid for a longer time, therefore, drying out at a slower rate.

(14) These results show that a dressing according to the invention maintains a moist wound environment for the wear time of a dressing.

EXAMPLE 2

(15) A wound dressing according to the invention was made by preparing two mats of gel-forming fibres (carboxymethylcellulose) by carding, cross-lapping and needle punching to a needle punch density of 22 to make a mat of 70 gsm. The mats were impregnated with silver ions by the method described in WO/02 43743A to give a total silver content of around 1.18% based on the anhydrous dressing. The mats were placed one on top of the other and stitch-bonded by the method described in PCT/GB2009/001138 so that the weft stitches were in between the mats.

(16) The release of silver from such a wound dressing was measured by silver assay using atomic absorption spectrophotometer (AAS) equipped with a silver hollow cathode lamp. In that method a dialysis membrane was pre-soaked in water for a minimum of 16 hours. Samples of the dressing are cut into 5 cm?5 cm squares and weighed. Each sample is placed into a pouch created from the prehydrated dialysis membrane and placed into 200 ml of isotonic saline at 37? C. contained within a suitable screw topped glass vessel and stirred by magnetic stirrer. A 10.0 ml aliquot from each vessel was taken at the following time-points: 3 h, 6 h, 24 h, 48 h, 72 h and 96 h and replaced with 10.0 ml of fresh saline in order to maintain the dissolution volume of 200 ml. The liquid samples were then assayed by AAS comparing to standard silver solutions of known concentration.

(17) The results were as follows:

(18) TABLE-US-00003 Time point Silver Released (hours) ppm (?g/ml) Std Dev 3 0.36 0.01 6 0.37 0.02 24 0.37 0.00 48 0.37 0.01 72 0.40 0.01 96 0.41 0.01

(19) These results show that dressings according to the invention give a steady release of silver from the dressing.

EXAMPLE 3

(20) This example shows the relationship between the hydration state of the optimized open structure fibrous mat and antimicrobial effectiveness.

(21) An optimized open structure fibrous mat according to the invention consists of two gel forming 77 gsm mats stitch-bonded together following the method described in PCT/GB2009/001138. Each mat being comprised of carded, cross-lapped and needled punched sodium carboxymethylcellulose fibres (at a needle punch density of 22 per cm.sup.2) which have been previously impregnated with silver ions as described in WO02/43743A.

(22) 140 mm diameter pre-dried Tryptone Soy Agar (TSA) test plates were surface-inoculated with Staphylococcus aureus (NCIMB 9518) to create a confluent lawn and incubated for 4 hours at 35? C. to initiate growth. The surface of each plate was then totally covered with sterile prehydrated dialysis membrane. Dry 35 mm diameter optimized open structure fibrous mats, were placed on top of the dialysis membrane at the centre of each plate. In half the tests (n=3) the optimized open structure fibrous mat was saturated with isotonic saline (2 ml), for the other half of the tests the mat was left dry. Plates were incubated at 35? C. for 48 hours. The open structure fibrous mats were then removed and the plates re-incubated for a further 24 hours.

(23) Results were as follows:

(24) TABLE-US-00004 Condition Visual Observation of Agar Plate Dry Growth beneath dressing (n = 3) Hydrated No Growth beneath dressing (n = 3)

(25) These results confirm that hydration is required for an antimicrobial effect to be exerted by the optimized open structure fibrous mat described. It is therefore possible to conclude that maintaining hydration for a longer period of time will extend the effective period of antimicrobial protection and will improve the overall antimicrobial effect.

EXAMPLE 4

(26) This example shows the relationship between the rate of dehydration of optimized open structure fibrous mats and the ease of their removal from a fragile surface.

(27) Fibrous mat 5 cm?5 cm samples of conventional 100 gsm fibre mats with a needle punch density of 60 per cm.sup.2 and optimized open structure mats according to the invention as described in example 3 were fully hydrated by immersion in isotonic saline. Drained samples were placed on agar plates (tryptone 15 g/l, soy peptone 5 g/l, sodium chloride 5 g/l & Agar No. 2 12 g/l). Mats were then left to dehydrate in a forced-air cabinet for 24 hours at ambient room temperature (?22? C.). At this point, sample mats had become adhered to the agar surface and could not be removed without disrupting the agar. 10 ml of isotonic saline was then applied to each fibrous mat to start a rehydration process. Taking hold of the edge of the mat with tweezers, a constant gentle lifting force was applied. The time between application of the rehydrating solution and the successful non-disruptive removal of the mat from the agar surface was recorded.

(28) The following results were obtained (results are expressed in seconds):

(29) TABLE-US-00005 Open structure mat according to the Sample replicate Conventional fibre mat invention 1 290 40 2 255 60 3 347 23 4 241 48 5 331 49 6 280 40 7 (no result - test error) 50 8 274 36 Average 288 43

(30) The conventional fibre mats had a drier appearance after 24 hrs on the agar surface and rehydration was visibly slower when compared to the optimized open structured mats. In clinical practice, dressings are likely to be changed at fixed intervals rather than when absorption capacity is reached or the dressing begins to adhere due to a reduction in the rate of exudation. There may also be limited time available to make dressing changes. Waiting for rehydration may not therefore be an option. Given these circumstances, the invention offers a distinct advantage in that tissue damage caused by dressing change is less likely to occur with the optimized open structure mat according to the invention.