Hydrogel wound dressings exhibiting reduced fiber losses in use

Abstract

A wound dressing comprising: a water-absorbent fabric comprising at least about 10 wt. % of hydrogel-forming absorbent fibers based on the dry weight of the fabric; and an adhesion-resistant, water-permeable wound contacting surface textile layer that is substantially continuously bonded to at least one surface of said fabric. The surface textile layer may be formed by surface treatment of the fabric, or by bonding a suitable textile web to the surface of the fabric.

Claims

1. A wound dressing comprising: a water-absorbent fabric comprising at least 10 wt. % of hydrogel-forming absorbent fibers based on the dry weight of the fabric; and an adhesion-resistant, water-permeable wound contacting surface textile layer that is substantially continuously bonded to at least one surface of said fabric, wherein the fabric comprises at least 10 wt. % based on the dry weight of the fabric of substantially non-water-absorbent textile fibers and wherein the fabric comprises a mixture of the hydrogel-forming fibers and the substantially non-water-absorbent textile fibers, and wherein at least a fraction of the non-water-absorbent fibers are coated with silver.

2. A wound dressing according to claim 1, wherein said adhesion resistant surface textile layer has been formed by treating a surface layer of the fabric with a lubricant.

3. A wound dressing according to claim 2, wherein the lubricant comprises a silicone compound or a fluorocarbon.

4. A wound dressing according to claim 2, wherein the lubricant comprises a substance selected from the group consisting of medically acceptable lipids, mineral oils, mucopolysaccharides, and mixtures thereof.

5. A wound dressing according to claim 1, wherein said adhesion resistant surface layer comprises a nonwoven textile web having a basis weight of from 2 to 100 g/m.sup.2 that is continuously bonded to said surface of the fabric.

6. A wound dressing according to claim 5, wherein said nonwoven textile web comprises thermofusible fibers, and the textile web has been bonded to the water-absorbent textile web by melt bonding.

7. A wound dressing according to claim 1, which is sterile and packaged in a microorganism-impermeable container.

Description

(1) Specific embodiments of the present invention will now be described further, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a schematic cross-section through a wound dressing according to the present invention;

(3) FIG. 2 shows a bar chart of measured peak fibrin clot adhesion force for wound dressings according to the invention and for certain reference dressings; and

(4) FIG. 3 shows a bar chart of measured liquid absorbency for wound dressings according to the invention and for certain reference dressings.

(5) Referring to FIG. 1, the dressing 1 comprises a fabric layer 2 containing hydrogel-forming fibers and non-absorbent textile fibers, some of which are coated with metallic silver. The dressing further comprises adhesion-resistant nonwoven textile webs 3,4 (the thickness of which is exaggerated in the Figure) continuously bonded over the upper and lower surfaces of the fabric layer 2.

EXAMPLE 1

(6) The fabric layer is a calcium alginate needled felt dressing incorporating silver-coated nylon fibers. The composition is as follows: calcium alginate and carboxymethyl cellulose (CMC) fibers 60% and silver coated nylon 40%. The basis weight of the fabric layer is about 150 g/m.sup.2, and the uncompressed thickness of the fabric layer is about 2 mm. The fabric layer is commercially available from Johnson & Johnson under the Registered Trade Mark SILVERCEL.

(7) The adhesion-resistant nonwoven web is formed from a layer of M1590 heat laminating material obtained from Freudenberg Vliesstoffe KG. It comprises 80% of an aliphatic non-cyclic co-polyamide (6/66.6/12-copolyamide, CAS number 26777-62-8), and 20% of polyetherester block copolyamide in which the polyetherester comprises a polyether block of medium molecular weight and the polyamide block is aliphatic and non-cyclic. The basis weight of the web is only about 10 g/m.sup.2. This gives the layer a high porosity for water uptake from the wound.

(8) The nonwoven web 2 was bonded to the fabric layer 1 by heating and compression. Suitable conditions are 116-127 C., press time 10-14 seconds, and pressure 150-300 kPa.

EXAMPLE 2

(9) A dressing according to the invention was prepared as described in Example 1, except that bonding of the textile surface layer to the fabric body was achieved without compression, by placing the laminate in an oven at 150 C. for 10 minutes.

EXAMPLE 3

(10) A dressing according to the invention was prepared as described in Example 2, except that the textile surface layer had a basis weight of 20 g/m.sup.2.

EXAMPLES 4-10

(11) Silicone-coated hydrogel fiber fabrics were prepared from a SILVERCEL fabric containing hydrogel-forming fibers as described in Example 1.

(12) The silicone coating was made by first mixing together the two silicone components (SILOPREN RTV 2K Gel AC3293 components A and B supplied by GE BAYER) and then dissolving the mixture in acetone to assist spraying. Acetone concentration was 20-35% based on the weight of the mixture (hexane can also be used). The silicone coating was applied to both sides of the fabric in the following amounts (total dry weight of siliconei.e. divide by two for the coating density per side of the fabric): Example 4 4 g/m.sup.2 Example 5 8 g/m.sup.2 Example 6 14 g/m.sup.2 Example 7 20 g/m.sup.2 Example 8 21 g/m.sup.2 Example 9 24 g/m.sup.2 Example 10 26 g/m.sup.2

EXAMPLES 11-12

(13) Lubricant-coated hydrogel fiber fabrics were prepared from a SILVERCEL fabric containing hydrogel-forming fibers as described in Example 1 by spraying the surfaces of the fabric with a medically acceptable mineral oil. Two different coating weights were used.

EXAMPLE 13

(14) A lubricant-coated hydrogel fiber fabric was prepared from a SILVERCEL fabric containing hydrogel-forming fibers as described in Example 1 by spraying the surfaces of the fabric with a solution of Hyaluronic acid.

REFERENCE EXAMPLE 1

(15) Measurements of fiber loss, adherency and absorbency as detailed below were also carried out on a reference sample of SILVERCEL fabric as described in Example 1, without any coating.

REFERENCE EXAMPLE 2

(16) Measurements of adherency and absorbency as detailed below were also carried out on a reference sample of AQUACEL Ag fabric supplied by. AQUACEL Ag is a needle-bonded nonwoven fabric formed from carboxymethylcellulose gel-forming fibers and containing silver in ionic form bonded to the CMC. There is no coating on the surfaces of the fabric.

REFERENCE EXAMPLE 3

(17) Measurements of adherency and absorbency as detailed below were also carried out on a reference sample of a wound dressing made by heat-bonding a vacuum-perforated ethylene methyl acrylate (EMA) film onto the surfaces of a fabric layer as described in Example 1. The characteristics of the EMA film were as described in EP-A-1168998, the entire content of which is incorporated herein by reference. The lamination was performed at about 150 C., between sheets of siliconized release paper.

REFERENCE EXAMPLE 4

(18) Measurements of adherency and absorbency as detailed below were also carried out on a reference sample of a wound dressing made by heat-bonding a thermoplastic net of base weight 10-88 g/m2, hole size 100-1400 micrometers and thickness 0.05-0.3 mm obtained from Delstar Technologies Inc. of Bristol, UK onto the surfaces of a fabric layer as described in Example 1. The lamination was performed at about 150 C., between sheets of siliconized release paper.

(19) Procedure 1

(20) A qualitative assessment of fiber loss was performed by applying adhesive tape to the surface of the dressing with the adhesive side down at an applied pressure of about 5 g/cm2, followed by lifting the tape from the dressing and observing the amount of fiber attached to the tape. It was found that fiber shedding onto the tape of the dressing of Example 1 was very much less than that observed with Reference Example 1.

(21) Procedure 2

(22) A Fibrin Clot Adhesion Test used as an in-vitro method to evaluate likely fiber loss to the wound surface. A fibrin clot is formed from bovine plasma fibrinogen, phosphate buffered saline, bovine serum albumin and bovine thrombin. The formed clot is placed between two samples of the dressing, dried and pulled apart in an Instron force measurement device. The force required to pull the dressings apart is measured.

(23) The peak force required to pull the dressings apart is shown graphically in FIG. 2 for the above Examples. It can be seen that all of the examples exhibit a reduced fibrin clot adhesion force. The effect is especially marked for the siliconized samples. The effect is observed down to very low coating weights of the silicone composition.

(24) Procedure 3

(25) The wound fluid absorbency of the example dressings was evaluated as follows. The method was based on the absorbency test on Alginate dressings described in the British Pharmacopoeia 1993, Addendum 1995, Page 1706.

(26) Briefly, a 5 cm5 cm sample was excised form a dressing and weighed. This sample was placed in a Petri dish. The sample is then submerged in a solution of sodium chloride and calcium chloride that had been heated to 37 C. The material was suspended for 30 seconds using a set of forceps before the sample was weighed. This test was repeated on a further 4 samples. The absorbency was then expressed as the average weight of solution retained per 100 cm.sup.2. The results are shown in FIG. 3. It can be seen that the dressings according to the invention all have absorbency similar to that of the unmodified SILVERCEL dressings.

(27) Procedure 4

(28) The silver release into simulated wound fluid at 37 C. over a period of 3 days of the dressings according to the above examples was evaluated as follows.

(29) The simulated wound fluid was a solution containing:

(30) $\begin{array}{c}0.013M{\mathrm{CaCl}}_{2,}\\ 0.2M\mathrm{NaCl}\\ 0.04M\mathrm{Tris},\\ 2\%\mathrm{Bovine}\mathrm{Albumin}\end{array}\}\mathrm{at}\mathrm{pH}7.5$

(31) The wound dressings were tested over 3 days. At each 24 hour time-point, the dressings were re-challenged with a fresh amount of simulated wound fluid equivalent to 5 ml/2.52.5 cm.sup.2. Each batch was analysed in triplicate.

(32) Analysis was performed against a silver standard curve prepared in simulated wound fluid was carried out using the Perkin Elmer A Analyst 200 Atomic Absorption Spectrometer

(33) Standards of known concentration were prepared in the same simulated wound fluid as used for the dressings. Calibration curves were prepared daily.

(34) The results showed that the dressings according to the present invention gave substantially the same rate and amount of silver release as the untreated SILVERCEL dressings.

(35) The above embodiments have been described for the purpose of illustration only. Many other embodiments falling within the scope of the present invention will be apparent to the skilled reader.