Silicone wound dressing laminate and method for making the same

Abstract

A method of making a wound dressing comprising the steps of: providing an apertured substrate layer; coating the substrate layer with a fluid silicone prepolymer composition; thermally partially curing said silicone prepolymer composition to form a partially cured silicone coating on the substrate; laminating the coated substrate layer to a base layer to form a laminate having said partially cured silicone coating in contact with a surface of the base layer; followed by exposing the laminate to ionizing radiation, to further cure the partially cured silicone coating and to bond the silicone coating to said surface of the base layer. The radiation cure results in strong bonding between the siliconized substrate and incompatible base layers such as polyurethane foams. Also provided are wound dressings obtainable by the process of the invention.

Claims

1. A wound dressing comprising: an absorbent polyurethane base layer; an apertured substrate; and a silicone coating on the apertured substrate; wherein the silicone coating on the apertured substrate is covalently bonded to the absorbent polyurethane base layer; and the silicone coating comprises a bis-dimethylvinyl terminated polydimethylsiloxane and a bis-hydride terminated polydimethylsiloxane.

2. The wound dressing according to claim 1, wherein the absorbent polyurethane base layer is further laminated to an adhesive-coated liquid-impermeable backing sheet.

3. The wound dressing according to claim 2, wherein the wound dressing is in the form of an island dressing wherein the adhesive-coated liquid-impermeable backing sheet is larger than the absorbent polyurethane base layer whereby a margin of the backing sheet extends around one or more edges of the absorbent polyurethane base layer.

4. The wound dressing according to claim 1, wherein a peel strength greater than 200 mN/cm is required to separate the silicone coated apertured substrate from the absorbent polyurethane base layer.

5. The wound dressing according to claim 1, wherein the absorbent polyurethane base layer is in the form of a polymeric film sheet, a foam, a sponge, or a film.

6. The wound dressing according to claim 1, wherein the absorbent polyurethane base layer to which the silicone coating is bonded is hydrophilic.

7. The wound dressing according to claim 1, wherein the absorbent polyurethane base layer is a semipermeable polyurethane film or a hydrophilic polyurethane foam sheet.

8. The wound dressing according to claim 1, wherein the apertured substrate is coated on both sides with the silicone coating, and a surface of the silicone coating opposite the absorbent polyurethane base layer is non-adherent or tacky.

9. The wound dressing according to claim 1, wherein the wound dressing is sterile and is packaged in a microorganism-impermeable container.

10. A wound dressing of claim 1 obtainable by a method comprising the steps of: providing the apertured substrate layer; coating the substrate layer with a fluid silicone prepolymer composition; thermally partially curing said silicone prepolymer composition to form a partially cured silicone coating on the substrate; laminating the coated substrate layer to the base layer to form a laminate having said partially cured silicone coating in contact with a surface of the base layer; and exposing the laminate to ionizing radiation, to further cure the partially cured silicone coating and to bond the silicone coating to said surface of the base layer.

11. The wound dressing of claim 1, wherein the silicone coating is coated on a first side and a second side of the apertured substrate, wherein the first side of the apertured substrate is adapted to be bonded to the surface of the absorbent polyurethane base layer, and wherein the second side of the apertured substrate coated with the silicone coating is substantially non-adherent.

12. The wound dressing of claim 1, wherein the apertured substrate comprises a cellulose acetate gauze.

13. The wound dressing of claim 1, wherein the wound dressing is sterilized by ionizing radiation.

Description

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

(2) FIG. 1 shows a perspective view of a product according to the invention packaged in a microorganism-impermeable pouch;

(3) FIG. 2 shows a perspective exploded view of a first product according to the invention;

(4) FIG. 3 shows a partially cut away view of part of the product of FIG. 2;

(5) FIG. 4 shows a perspective exploded view of a second product according to the invention;

(6) FIG. 5 shows a partially cut away view of part of the product of FIG. 4;

(7) FIG. 6 shows a perspective exploded view of a third product according to the invention;

(8) FIG. 7 shows a perspective exploded view of a fourth product according to the invention;

(9) FIG. 8 shows a partially cut away view of part of the product of FIG. 7;

(10) FIG. 9 shows a perspective exploded view of a fifth product according to the invention;

(11) FIG. 10 shows a partially cut away view of part of the product of FIG. 9;

(12) FIG. 11 shows a perspective view of a sixth product according to the invention;

(13) FIG. 12 shows a perspective exploded view of a seventh product according to the invention;

(14) FIG. 13 shows a perspective view of the product of FIG. 12;

(15) FIG. 14 shows a perspective partially exploded view of an eighth product according to the invention;

(16) FIG. 15 shows a perspective exploded view of a ninth product according to the invention;

(17) FIG. 16 shows a perspective view of the product of FIG. 15;

(18) FIG. 17 shows a schematic drawing of the loop tack test configuration used in Procedure 1 below; and

(19) FIG. 18 shows a schematic drawing of the peel strength test configuration used in Procedure 2 below.

(20) Referring to FIG. 1, a packaged wound dressing 1 according to the invention is shown. The dressing 2 is sterile and packaged in a microorganism-impermeable envelope 3 of polypropylene or the like having a transparent window 4.

(21) Referring to FIGS. 2 and 3, the siliconized substrate 5 in this and all of the other embodiments shown in the drawings comprises a substrate of cellulose acetate gauze of density 107 grams per square meter nominal, coated with a hydrophobic, tacky, crosslinked silicone gel, prepared as described below. The silicone composition penetrates the gauze to form a single, chemically homogeneous silicone phase coating the strands of the gauze. The coated substrate 5 has an array of apertures extending through the substrate and the silicone to allow passage of wound fluid through the material. The nominal total coating weight of the silicone is 120-130 grams per square meter.

(22) The upper siliconized surface is bonded to a base layer 6, which in this embodiment is a semipermeable microporous polyurethane backing layer, which may or may not be coated with a polyurethane pressure-sensitive adhesive layer. The opposite surface of the siliconized substrate is covered by a release sheet 7 of siliconized paper that can be peeled off to expose the siliconized surface for application to a wound or to skin.

(23) Referring to FIGS. 4 and 5, the product 10 according to this embodiment comprises a siliconized substrate gauze 5 and releasable cover sheet 7 as before, but in this embodiment the base layer 11 is a sheet of water-absorbent hydrophilic polyurethane foam prepared as described in EP-A-0541391. The foam can absorb wound fluid and swell in use, while remaining strongly bonded to the siliconized gauze wound contacting layer 5.

(24) Referring to FIG. 6, the product according to this embodiment comprises a siliconized substrate gauze 5 as before, but in this embodiment the base layer 12 is a sheet of water-absorbent nonwoven textile, such as a nonwoven viscose web or a nonwoven alginate/nylon web. The absorbent textile 12 can absorb wound fluid and swell in use, while remaining strongly bonded to the siliconized gauze wound contacting layer 5. A backing sheet 14 of semipermeable film coated with adhesive 15 is applied over the opposite surface of the textile layer to prevent leakage of liquid from the back of the dressing.

(25) Referring to FIGS. 7 and 8, the product according to this embodiment comprises a siliconized substrate gauze 5 laminated to a hydrophilic foam layer and cover sheet as for the embodiment of FIG. 4. The embodiment of FIGS. 7 and 8 further comprises a backing sheet 14 of adhesive-coated semipermeable film as described for FIG. 6 that is applied over the opposite surface of the foam layer from the siliconized substrate to prevent leakage of liquid through the dressing.

(26) Referring to FIGS. 9 and 10, the product 16 according to this embodiment is an island dressing. It comprises a siliconized substrate gauze 5 laminated to a hydrophilic liquid-absorbent layer of textile material 17 and a polyurethane semipermeable backing sheet 14 as for the embodiment of FIG. 6. A silicone-coated paper release sheet 7 is provided over the wound-facing surface of the gauze 5. However, the area of the textile material 17 is less than that of the gauze 5 or the backing sheet 14, whereby a margin 18 of the backing sheet extends around all edges of the textile material. The siliconized gauze is therefore directly bonded to the backing sheet over the margin, as well as to the wound-facing surface of the textile layer 17. This bonding of the siliconized gauze to the margin 18 of the backing sheet 14 helps to keep the absorbent island in place on the backing sheet, and also provides the margin 18 with a skin-friendly, weakly adherent (tacky) siliconized surface for contact with the skin around a wound. The island dressings are less prone to leakage of wound fluids from the edges of the dressing than the simple laminates described above.

(27) Referring to FIG. 11, the product 20 is an envelope-type dressing formed from upper and lower sheets 5,19 of siliconized gauze, which may be separate sheets or a single sheet folded over. An island 17 of hydrophilic liquid-absorbent textile material is located centrally between the sheets 5,19. The sheets 5,19 are bonded to the island 17 and to each other in the marginal area around the island 17. The resulting envelope can be applied to a wound in either orientation.

(28) Referring to FIGS. 12 and 13, the product 21 according to this embodiment is an island dressing similar to that of FIGS. 9 and 10. It comprises a siliconized substrate gauze 5 laminated to a hydrophilic liquid-absorbent layer of textile material 17 and a polyurethane semipermeable backing sheet 14 as for the embodiment of FIG. 6. A layer of polyurethane pressure-sensitive adhesive 15 is provided over the wound-facing surface of the backing sheet 14. In certain alternative embodiments, the gauze 5 is coterminous with the island 17 so that the margin 18 is solely adhesive-coated to provide adhesion to skin around a wound.

(29) Referring to FIG. 14, an alternative island dressing structure is shown wherein the siliconized gauze layer 5 is laminated directly to a semipermeable polyurethane backing sheet 14, and an absorbent island 17 is laminated over and bonded to the gauze layer 5. In these embodiments, the gauze layer 5 acts as a tie layer to bond the absorbent island 17 to the backing sheet. A further siliconized gauze layer (not shown) may be bonded over the top of the absorbent layer, either coterminous with the absorbent layer 17 or coterminous with the backing sheet 14, in similar fashion as for the embodiments of FIG. 9-10 or 12-13.

(30) Referring to FIGS. 15 and 16, this embodiment is a sandwich structure having upper and lower sheets of siliconized gauze 5,19 sandwiching and bonded to a layer of nonwoven textile absorbent material 12. Suitably, the layers 5,12 and 19 are coterminous, or a small margin 24 of layers 5,19 directly bonded to each other may extend around the edges of the dressing.

(31) The products according to the invention may be made by a process according to the invention. This process starts from a continuous web of cellulose acetate gauze that is passed through a fluid silicone coating composition and nip rollers to coat and impregnate the gauze with the silicone composition. The silicone coating composition is prepared by mixing Components A and B of a soft silicone skin adhesive silicone elastomer kit supplied by Dow Corning under product reference Q7-9177, The components are mixed in weight ratio 50:50. Component A comprises a bis-dimethylvinyl terminated polydimethylsiloxane and a platinum catalyst. Component B comprises a bis-hydride terminated polydimethylsiloxane. To the mixture is added 2-methyl-3-butyn-2-ol inhibitor at a concentration of 0.02 wt. %.

(32) The coated substrate then passes over a blower 17 to open the apertures of the coated substrate that may have been occluded by the silicone.

(33) The coated gauze is then passed through an oven 18 held at 150 C. Typical conditions are 5 passes at 4.2 m/min, total residence time 1.5 minutes. This results in thermal partial cure of the silicone coating. The coated material is then allowed to cool, and the base layer and a release coated paper cover sheet are then continuously applied to the upper and lower surfaces.

(34) The material is then cut and packaged as shown in FIG. 1, followed by gamma irradiation with 35-50 kGy of Cobalt 60 radiation at 7-9 kGy/hr to sterilize the products and complete the cure. The irradiation curing results in a further increase in both hardness and tackiness of the silicone coating, and further bonds the silicone coating strongly to the base layer.

(35) Procedure 1: Measurement of Surface Tackiness by the Loop Tack Test

(36) The tackiness of the silicone coatings produced by the methods of the invention was measured in a tensile tester, such as an Instron tester, using the set-up shown in FIG. 17.

(37) Samples of the coated fully cured gauze laminates were cut to dimensions 59.5 cm. Margins of 1 cm were marked out along the long edges by drawing straight lines 1 cm from the long edges. The cover sheets were removed, and the sheet of coated gauze 30 was looped around and the 1 cm margins 30,32 on opposed edges of one surface (opposite the surface being measured) were applied firmly to opposite sides of a 2 mm thick metal spacer bar 34. Strips of polypropylene film 1 cm wide 36,37 were then applied to the opposite surfaces of the coated gauze opposite the spacer bar 34 to prevent the coated gauze from adhering to the jaws of the measurement device.

(38) The assembly of polypropylene strips, coated gauze and spacer bar was then gripped in the jaws 38 of the Instron tester. The loop of coated gauze 40 having the surface under test outermost was then lowered onto a clean polycarbonate surface 42 of dimensions 15.5 cm3.8 cm so that the loop adheres to the surface, and raised to detach the loop from the surface. Lowering and raising are performed at 300 mm/min, and the minimum distance between the jaws 38 and the polycarbonate surface 42 is 15 mm. The measured tack (in Newtons) is the maximum force measured while detaching the loop from the surface. Average of three measurements was used.

(39) Procedure 2: Measurement of Peel Strength

(40) The peel strength of the laminates produced by the methods of the invention was measured in a tensile tester, such as an Instron tester, using the set-up shown schematically in FIG. 18. The test strip 50 is positioned horizontally with the substrate layer and base layer in respective jaws 52,54 of the tester to give 180 degree peel. The test was performed on strips of laminate of dimensions 25.4 mm254 mm. The pull rate was 400 mm/minute. The reported peel strength was the average over the length of the strip in grams force (gf), whereby 1 gf=3.86 mN/cm (cm refers to the width of the strip in cm).

EXAMPLE 1

(41) Samples were prepared by the method of the present invention. The first sample comprises a silicone-coated gauze (ADAPTIC TOUCH available from Systagenix Wound Management Manufacturing Ltd., Gargrave, UK) laminated to a polyurethane hydrophilic foam sheet (TIELLE, available from Systagenix Wound Management Manufacturing Ltd., Gargrave, UK).

(42) Peel strength tests on the laminate before and after the final gamma sterilization and crosslinking step are shown in Table 1 below.

(43) TABLE-US-00001 TABLE 1 Average Load (gf) TIELLE + TOUCH (separate sterilisation) 1 5.71 2 4.87 3 4.58 Average 5.05 TIELLE + TOUCH (sterilised together) 1 126.36 2 141.45 3 142.90 Average 136.90

(44) It can be seen that the siliconized substrate adheres only weakly to the foam before irradiation, but exhibits strong bonding after irradiation.

EXAMPLE 2

(45) The method of Example 1 was repeated to prepare a laminate of a silicone-coated gauze (ADAPTIC TOUCH available from Systagenix Wound Management Manufacturing Ltd., Gargrave, UK) laminated to a semipermeable wound dressing backing sheet formed of 0.4 mm high-density polyurethane foam of a blocked toluene di-isocyanate nature coated with an aliphatic polyurethane adhesive.

(46) Peel strength tests on the laminate before and after the final gamma sterilization and crosslinking step are shown in Table 2 below. It can be seen that the siliconized substrate adheres only weakly to the foam before irradiation, but exhibits strong bonding after irradiation.

(47) TABLE-US-00002 TABLE 2 Average Load (gf) Backing + Substrate (after separate sterilisation) 1 3.44 2 3.94 3 too low to register Average 3.69 Backing + Substrate (sterilised together) 1 84.44 2 73.26 3 95.59 Average 84.43

(48) It can be seen that gamma sterilization of the silicone coated substrate laminated to the base layer results in a very large increase in the bonding strength of the laminate. The siliconized apertured substrate can thus provide a non-adherent wound contacting surface to the polyurethane backing sheet.

EXAMPLE 3

(49) The method of Example 1 was repeated to prepare a laminate of a silicone-coated gauze (ADAPTIC TOUCH available from Systagenix Wound Management Manufacturing Ltd., Gargrave, UK) laminated to second sheet of the same silicone-coated gauze.

(50) Peel strength tests on the laminate before and after the final gamma sterilization and crosslinking step are shown in Table 3 below.

(51) TABLE-US-00003 TABLE 3 Average Load (gf) Substrate + Substrate (sterilised separately) 1 13.14 2 15.90 3 21.71 Average 16.92 Substrate + Substrate (sterilised together) 1 151.19 2 156.12 3 174.84

(52) It can be seen that the siliconized substrate adheres only weakly to itself before irradiation, but exhibits strong bonding after irradiation.

EXAMPLE 4

(53) The method of Example 1 was repeated to prepare a laminate of a silicone-coated gauze (ADAPTIC TOUCH available from Systagenix Wound Management Manufacturing Ltd., Gargrave, UK) laminated to sheet of nonwoven textile (SILVERCEL available from Systagenix Wound Management Manufacturing Ltd., Gargrave, UK). The textile is a calcium alginate needled felt dressing incorporating metallic-silver-coated nylon fibers. The composition is as follows, by weight: 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 total silver content of the fabric is about 8 wt. %.

(54) Peel strength tests on the laminate before and after the final gamma sterilization and crosslinking step are shown in Table 3 below.

(55) TABLE-US-00004 TABLE 4 Average Load (gf) Silvercel + substrate (sterilised separately) 1 2.87 2 3.05 Average 2.96 Silvercel + Substrate (sterilised together) 1 299.18 2 336.4 Average 317.79

(56) It can be seen that the siliconized substrate adheres only weakly to itself before irradiation, but exhibits strong bonding after irradiation. In fact, under the peel test conditions the siliconized substrate does not peel from the surface of the textile, but instead the textile itself peels apart.

(57) The above examples have been described by way of illustration only. Many other embodiments falling within the scope of the accompanying claims will be apparent to the skilled reader.