Silver-containing foam structure

(54) Title: FOAM STRUCTURE CONTAINING SILVER (51) Int.CI .: A61L 15/18; A61L 15/24; A61L 15/42 (30) Unionist Priority: 01/03/2007 EP 07004275.9 (73) Holder (s): MÕLNLYCKE HEALTH CARE AB (72) Inventor (s): STEFAN ARESKOUG; ULF JOHANNISON; MALIN PRYDZ

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The present invention relates to an antibacterial and hydrophilic polyurethane foam structure. More

FOAM STRUCTURE CONTAINING SILVER specifically, the antibacterial and hydrophilic polyurethane foam structure contains an increased amount of silver both in the polymeric matrix and within the foam cells. Furthermore, the present invention provides a method for the manufacture of said structure in antibacterial and hydrophilic polyurethane foam.

Technical Background WO 97/42985 describes a dressing comprising a layer of absorbent foam material that includes a pattern of holes. The holes are opened on the side of the foam material that is close to the user's skin when the dressing is used, and the layer of foam material is coated with a layer of hydrophilic gel attached to the skin, where the extreme parts of the hole walls in the foam material that are close to the user's skin when the dressing is used are coated with gel. Nothing is described about the inclusion of particular antimicrobial or antibacterial compounds in the dressing.

US 5,662,913 describes the use of silver salts which are stabilized by the formation of complexes with acyclic polyether polymers. In addition, silver salt anions are present in excess of silver ions. The stabilized silver salt complexes of US patent 5,662,913 can be included in foam structures. The purpose of the invention described in this patent is to provide photo-stable, non-staining, antimicrobial metallic compositions

2/20 for protection against infections, which make the foam object the base of antimicrobial polyurethane. Nothing is described about the controlled release of silver from the polyurethane structure.

WO 2004/007595 describes a flexible cellular polyurethane foam product that was produced in the presence of a controlled release silver component. The release of silver from the structure is often slow, which is advantageous in some applications, but may not be sufficient in other applications.

EP-Al-1 486 523 and US 4,937,273 both refer to polyurethane foams containing antimicrobial silver bound to zeolite particles. The release of silver from the structure is often slow, which is advantageous in some applications, but may not be sufficient in other applications.

WO 2002/062403 describes the production of dressings with releasable silver complexes formed with group IV metals of the periodic element system, and in particular zirconium and silver salts. Nothing is described with respect to the silver salts of claim 1 of the present application.

EP-Al-0 059 049 relates to dressings containing silver sulfadiazine. Nothing is described with respect to the silver salts of claim 1 of the present application.

Different dressings require different patterns of release of antimicrobial agents, such as silver. For infected wounds and wounds that can be easily infected, it would therefore be desirable to use a dressing that was initially capable of releasing large amounts of antimicrobial part and which was capable of maintaining such release for an extended period of time.

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Summary of the Invention

The present invention provides a method of producing an antibacterial and hydrophilic polyurethane foam structure that can be used as a dressing. The method comprises the steps of:

a) providing an aqueous phase containing a surfactant;

b) provision of an isocyanate-terminated polyether having a functionality of more than 2;

c) mixing of said aqueous phase and said isocyanate-terminated polyether, immediately transferring the resulting mixture to a mold or a continuous mesh, whereby the foam structure is obtained; and

d) drying said foam structure until its moisture content is at most 10% (by weight), preferably at most 8% (by weight), and even more preferably at most 5% (by weight).

The essential feature of the method is that the aqueous phase in step (a) also contains a silver salt. The portion of said silver salt is dispersed in said aqueous phase. The advantage of this method is that silver antimicrobial ions are released from the foam in a favorable manner over an extended period of time. 0 silver salt mentioned above is chosen from the group consisting of sulfate, silver, silver citrate, silver acetate, silver carbonate, silver lactate and silver phosphate, or a mixture of these salts.

In addition, it is preferable to coat said mold or continuous mesh with molding paper before the mixture is added in step (c). Said molding paper is removed before the drying step (d).

In the presence of a catalyst, it is also preferable to add one or more gel-forming silicone components, which on curing form a silicone gel

4/20 cross-linked, to a surface of the foam structure obtained in step (d). Said catalyst is preferably a platinum complex.

Finally, the present invention provides a structure in antibacterial and hydrophilic polyurethane foam having a pore size between 30 and 1000 gm, where said structure can be produced by the method described above. Preferably, the accumulated silver release per cm² foam structure after 48 hours reaches more than 0.2 mg / cm², more preferably more than 0.25 mg / cm² and more preferably more than 0.30 mg / cm². In addition, the accumulated silver release per cm² of the foam structure after 72 hours preferably reaches more than 0.3 mg / cm², more preferably more than 0.35 mg / cm² and more preferably more than 0.40 mg / cm². Preferably, the accumulated silver release reaches a maximum of 0.80 mg / cm²after 48 hours, more preferably after 96 hours, and more preferably after 120 hours.

Preferably, the antibacterial characteristics of the foam structure are such that a circular sample of said foam having a diameter of 20 mm and a thickness of 5 mm, when exposed to 10 ml simulated wound fluid containing bacteria (a 1: 1 solution of fetal bovine serum and aqueous peptone (aqueous solution containing 0.9% (by weight) of NaCl and 0.5% (by weight) of peptone)) at a temperature of 3 5^sC ± 2²C according to the ASTM E 2149 reference method, is able to reduce the number of viable Pseudomonas aeruginosa cells by 10⁶ for less than 10² within 72 hours, and reduce the number of viable Staphylococcus aureus cells by 10⁶ for less than 10² in 120 hours.

The present invention also provides a dressing comprising said foam structure that releases silver.

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Detailed description of the invention

Thus, the present invention provides a method for the manufacture of an antibacterial and hydrophilic foam structure showing increased release of silver antibacterial ions over time.

The hydrophilic foam structure of the present invention is basically a hydrophilic polyurethane foam. Suitable hydrophilic polyurethane foams include those known with Hypol (trademark) foams. Hypol foams can be made from hydrophilic Hypol prepolymers marketed by Dow Chemicals.

Conformable hydrophilic polyurethane foam can be obtained by mixing an isocyanate-terminated polyether having more than two functionality with a surfactant and water and molding the mixture on a surface.

Preferred isocyanate-terminated polyethers include Hypol, FHP 2000, 2001, 3000, 2002 and 2000HD marketed by Dow Chemicals. Hypol is described in a booklet published by WR Grace and Co. Hypol foamable hydrophilic polymers — laboratory procedures and foam formulations. Its preparation and use are described in British patent applications no.^the 1429711 and 1507232.

Surfactants suitable for forming conformable hydrophilic polymer foams include nonionic surfactants. Favored non-ionic surfactants are oxypropylene-oxyethylene block copolymers known as Pluronic (registered trademark) marketed by BASF Wyandotte. Preferred Pluronic surfactants include L65, F87, P38, P75 and L62.

Suitable silver sources are silver salts with moderate water solubility. It is important that the silver salts are stable under sterilization conditions and that

6/20 are pharmaceutically acceptable. In an embodiment of the invention, silver salts with moderate water solubility are mixed with silver salts having low water solubility. It is essential that a portion of the silver salt is dispersed in the aqueous reaction mixture during the manufacturing process. Examples of silver salts that can be used according to the present invention are found in the group consisting of silver sulfate, silver citrate, silver acetate, silver carbonate, silver lactate and silver phosphate, or a mixture of these salts .

To prepare a typical foam, 100 parts by weight of Hypol FHP 2000, 2001, 3000, 2002 or 2000HD are mixed with 0.3 to 7 parts by weight of surfactant or mixtures of surfactants, 2 to 9 parts by weight of a salt of silver, such as silver sulfate, and 30 to 300 parts by weight of water, and the foaming mixture is molded onto a surface. Typical foaming mixes have a crema time of about 20 - 30 seconds, a rise time of about 60 - 250 seconds and a curing time of about 400 - 800 seconds. In addition, suitable foam pore sizes can vary between 30 and 1000 pm.

As already mentioned, the antibacterial and hydrophilic polyurethane foam structure of the present invention can be coated on one side with a silicone gel, by adding one or more gel-forming silicone components and allowing the added silicone to form a crosslinked gel for curing. The cross-linked silicone gel used as a coating for the hydrophilic antibacterial polyurethane foam of the present invention can conveniently be characterized in terms of its tensile strength, penetrability and peeling resistance. As used here, the term voltage resistance means the maximum voltage load that can be

7/20 applied (using a standard Instron tester) to a 5 cm wide and 3 mm thick tape of the silicone gel in question.

The cross-linked silicone gel can be formed from various gel-forming silicone components and mixtures thereof, such as, for example, linear silicones having reactive groups, as known in the art. Preferably, the gels are formed by the reaction between a vinyl substituted silicone component and a hydride containing silicone component in the presence of a suitable catalyst such as a platinum catalyst.

The gel-forming silicone components used can have a viscosity in the range of 100 - 10000 mPas, an average molecular weight value in the range of 350 to 40,000, and and can, for example, have from 0.004 to 0.4 mmol of reactive groups / g.

When silicone gels are formed by crosslinking a mixture of two or more silicone components, the molecular weights of the various components and / or their degrees of substitution by different reactive groups. This makes possible the formation presenting different physical properties varying the proportions of the components.

The components for forming the lattices suitable for use in the hydrophilic antibacterial polyurethane structure of the present invention are available, for example, from Wacker, under the reference Wacker Silgel 612.

As already mentioned, the structures of the present invention are formed by coating a sheet of foam material with one or more non-cross-linked silicone components and then causing cross-linking to occur. In the case of gels formed by the reaction of vinyl groups of one component with hydride groups of the other component, such curing may be made of

8/20 will generally be conducted in the presence of a catalyst such as a platinum complex at a concentration of 5 to 15 ppm. In such a case, the gel can be formed by curing at room temperature over a period of time of several days, however elevated temperatures are preferably employed. For example, silicone gels can be formed by curing at a temperature of 40²C to 120 ^sC and preferably at a temperature between 80 ²C and 100^sC. At a temperature of 80²C, curing usually takes 10 seconds to 10 minutes, for example, 1 to 5 minutes. At a temperature of 50²C, curing usually takes 10 minutes to 2 hours, for example, 15 minutes to 1 hour.

An example of a chemically suitable gel-forming silicone component (polydimethyl siloxane gel) is a 2-component platinum catalyzed RTV silicone, such as SilGel 612 from WackerChemie GmbH, Burghausen, Germany, and MED- 6340 from NuSil Technology, Carpinteria, USA.

Thus, the present invention provides a dressing that is characterized by an absorbent layer, a polyurethane foam material containing antibacterial and hydrophilic silver ion that includes a pattern of holes that open on the side of the foam material that is close to the skin of the user when in use. Preferably, the foam material has a coating of a layer of hydrophobic cross-linked silicone gel that adheres to the skin, and where the walls of the holes in the foam material are coated with gel on those end parts of said walls that are close to the skin. of the user when the dressing is being used.

In a first preferred embodiment intended for wounds from which fluid is exuded only slightly or in normal amounts, the foam structure has a pattern of holes comprised of pores in the material in question.

9/20 antibacterial foam. In the event that a crosslinked silicone gel is applied, said gel also extends slightly within the open pores of the foam material that are at the edges of the gel layer, without closing all pores.

Preferably, the foamed material is coated with a layer of liquid impermeable material on the side of the foamed material that is opposite the user's skin when in use.

The dressing comprising the antibacterial foam structure and containing a silicone gel coating on the side facing the users' skin presents a form of adhesion to the skin F1 from 0.1 to 2.0 N, appropriately 0.2 to 1.3 N is preferably 0.2-0.7 N.

In a first embodiment, the silicone gel layer has a thickness of 0.05-1.0 mm.

In a second embodiment, a pattern of holes is created in the foam material before placing said mat on the layer of mixing gel-forming silicone components.

The invention will now be described in more detail with reference to the accompanying drawings, in which:

Figure 1 is a schematic perspective view of a dressing piece of the invention according to an embodiment.

Figure IA is an enlarged view of a feature in the illustration in Figure 1.

Figure 2 schematically illustrates an apparatus for applying one or more gel-forming silicone components to a foam structure to obtain a silicone gel coating according to the present invention.

Figure 3 shows schematically how the release of silver from the silver-containing structure is determined.

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Figure 4 shows silver release diagrams comparing the material presented here (Sample A) with two commercially available silver foams (Sample B as described in WO 2002/062403 and Sample C as described in US patents 5,681,575 and US 5,837 .275). Figure 4A shows the amount of silver released at specific points in time, while Figure 4B shows the accumulated silver release.

Figure 5 shows diagrams of the sustained antimicrobial effect of the invention presented here (Sample A) compared to two commercially available silver foam products (Sample B as described in WO 2002/062403 and Sample C as described in US patents 5,681. 575 and US 5,837,275). Figure 5A shows the effect on Staphylococcus aureus and Figure 5B shows the effect on Pseudomonas aeruginosa. For both types of bacteria, the antibacterial foam obtained by the invention presented here shows an antimicrobial efficiency, that is, antibacterial, higher than that of the reference samples.

Figure 6 outlines the manufacture of a dressing containing a structure according to the present invention. Silver foam manufacturing is shown. The aqueous phase contains water, a silver salt, such as silver sulfate, and surfactants.

Figure 6 describes the manufacturing process. Polyurethane polymers are mixed with an aqueous phase containing surfactants, a silver salt dispersed and dissolved in a dispensing and mixing equipment. The reaction mixture is subsequently transferred to a mold or a continuous mesh, which has been coated with molding paper. After the completion of the polymerization reaction, the molding paper is removed from the molds and the foam obtained is dried to a moisture content of a maximum of 10% (by weight),

11/20 preferably at most 8% (by weight), more preferably at most 5% (by weight). The foam is then wrapped in plastic cores with paper between the layers and packed.

The Figure illustrates a piece of a dressing according to an embodiment of the invention. The dressing is comprised of an absorbent foam material (2) that is coated with a gel layer (3) on the side that is close to the user's wound or skin when the dressing is in use. As illustrated schematically in Figure IA, the gel layer (3) is arranged in such a way that even a part of the open cell walls or pores (4) in the foam material that open on the gel-coated side, is coated with gel . Since the gel layer (3) does not close, but only covers, a part of the walls at a pore end part of the foam material that faces the wound, the excess fluid from the wound can be removed by foam material (2) and absorbed there. The gel layer also forms a spacing layer that prevents the foam material from coming into direct contact with the user's wound or skin. The thickness of the total gel layer, i.e., including the penetration depth of the pores of the foam material, is 0.1-2.0 mm. Some of the pores in the foam material that face the wound are closed by the gel layer.

In order to provide a dressing that has a dry outer surface, a liquid-impermeable layer (5) is provided on the side opposite the gel layer (3). This liquid-impermeable layer (5) may conveniently comprise a plastic film, liquid-impermeable but vapor-permeable, thin, for example, a polyurethane film.

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The dressing shown in Figure 1 is intended for use with wounds that exude fluid in amounts ranging from mild to normal. The foam layer has a thickness of 1-10 mm, preferably 2-6 mm. As mentioned earlier, the foam material works both as an absorbent and as a gel carrier, and the dressing as a whole will, for this reason, be very soft and pleasant. Once the gel adheres to the skin surrounding the wound, the dressing will be kept in place while the gel allows a seal and prevents maceration, that is, it prevents the wound fluid from draining over healthy skin, softening and eventually damaging the epidermis. The open structure of the gel layer and foam material also allows the skin to breathe. The nature of the adhesive gel used in this invention differs entirely from the nature of the adhesives that are typically used for dressing dressings, for example, the acrylate adhesives or hot melt adhesives that are used today for this purpose. The significant difference between these adhesives and the gel used according to the invention is that the gel is much softer and has a better wetting capacity than said adhesives. This makes it possible for the gels to have a much lower specific adhesion capacity, that is, less adhesion per unit of surface contact area, than the specific adhesion capacity that must be given to harder adhesives in order to obtain an adhesion total equally effective than that offered by the gel.

Figure 2 is a highly schematic illustration of an apparatus for use in applying a layer of one or more gel-forming silicone components to a structure according to the present invention. The illustrated apparatus includes a conveyor (not shown) in which a plastic film (8) is transported from left to left.

13/20 right in Figure 2. An uncured gel mixture layer (9) is placed over the film (8). By gel mixing is meant a mixture of the components that form a gel after curing, including polymers that can react with each other to form a cross-linked structure. A layer (10) of absorbent foam material is applied to the uncured gel mixture layer (9) with the aid of a cylinder (11), and the layers (9, 10) are then transported to an oven (12) . The gel mixture is cured by passing through the oven (12) and forms a gel layer on the bottom of the foam material.

It was observed that with an adequate selection of one or more gel-forming components and mixtures and proportions thereof, pressure force F, amount of gel mixture, time between application of the foam material and heating of the layers, curing temperature, and so on, a discontinuous gel coating will be formed on the foam material. This is due to the fact that the gel mixture is removed by capillary action into the pores or holes in the foam material that open on the side of the foam material that is in contact with the gel mixture. When applying a gel-forming coating to the foam material that has no holes other than pores, the gel mixture should be applied in a layer of thickness such as to ensure that an excessively large number of pores opens at the bottom foam material is not clogged or blocked by the gel coating. The viscosity of the gel mixture and the pore size in the foam material also influences the tendency of the mixture to penetrate the pores. It has been observed that the gel mixture layer should preferably be applied to a thickness of 0.05-1.00 mm. A large part of the gel mixing layer is aspirated into the

14/20 foam, so the total gel layer, including air and foam, will have a thickness of 0.10-2.00 mm.

In a first application of the above method for coating the underside of an antibacterial polyurethane foam sheet with silicone gel, an open cell soft hydrophilic polyurethane foam sheet having a density of 80-150 kg / m³ and a thickness of 5 mm.

The silicone mixture was prepared from SilGel 612 obtained from Wacker, in a mixture of component A and component B with a ratio of 1.0: 0.9. the uncured mixture had a viscosity of about 1000 mPa.

The polyurethane sheet was placed on a silicone mixture having a thickness of 0.2 mm, without applying pressure F of the cylinder (11), in other words, the silicone mixture was subjected only to the weight of the foam sheet. The time taken to transport the foam material (10) and the silicone mixture (9) from the bottom cylinder (11) to the oven (12)

<td colspan="3">was a minute and the temperature</td><td>in</td><td>cure</td><td>was 130^andÇ.</td><td> 0</td><td></td>

<td>silicone</td><td>was</td><td>cured with a time</td><td>in</td><td colspan="2">residence in the oven</td><td>in</td><td></td>

<td>minutes.</td><td>a</td><td>polyurethane film</td><td>in</td><td>high</td><td>permeability</td><td>to</td><td></td>

<td>steam and</td><td>an</td><td>0.025 thickness</td><td>mm</td><td>was</td><td colspan="2">so firmly</td><td> -</td>

glued to the foam on the side opposite the gel coating. In this mixing ratio, the silicone gel had a penetration value of 16 mm, and the adhesive strength to the dressing skin was measured as 0.42 N. Under these conditions, it was observed that the gel mixing layer will present preferably a thickness of at least 0.1 mm, so as to obtain a suitable discontinuous gel coating on the foam material.

When the thickness of the gel mixture layer was above 0.4 mm, an excessively high percentage of

15/20 pores in the foamed material became blocked, resulting in insufficient permeability of the gel coating.

It will be evident from the following that when carrying out the method described with reference to Figure 2, the quality of the final product will depend on many factors. Thus, it is not possible to provide these factors with general limit values, and such limit values ​​must be established empirically in relation to the mixture of gel and foam material used.

The method described thus makes it very easy to produce a dressing of the type described with reference to Figure 1. The method is also very flexible and allows dressings of mutually different absorbencies to be produced, in principle, in the same way and with the aid of the same device.

The described dressing can certainly be sterilized, for example, by sterilization with ethylene oxide or steam sterilization, and is intended to be supplied in different sizes and for different types of wounds, both in sterile packaging and in non-sterile packaging. sterile. In view of their softness, they are suitable for use in combination with bandages and can be used beneficially on blisters, ulcers and similar wounds. Their high degree of flexibility also makes them suitable for use on injured joints, such as injured knees and taught elbows, even in advanced stages of the injury healing process. Dressings can also be cut to a size suitable for the size of the injury or injury in question.

It should be understood that the exemplary embodiments described above can be modified within the scope of the invention, particularly with regard to the described materials and applied process parameters.

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The invention will now be described further in the following examples.

Example 1: Preparation of the foam structure

An aqueous phase for the foam manufacturing process was prepared by solubilizing / dispersing the nonionic surfactant Pluronic F87, silver sulfate and activated carbon. The final concentrations of these constituents in the aqueous phase reached 0.5 (by weight) of Pluronic F87, and 2.2% (by weight) of silver sulfate. The concentration of dissolved silver sulfate reached 0.8% (by weight) and the rest of the silver sulfate was dispersed in the aqueous phase.

Simultaneously, a mold coated with mold paper was prepared. The mold was sufficiently deep to produce foams molded in the shape of a blade having a thickness of 5 mm.

The Hypol 2001 prepolymer (an isocyanate-terminated polyether) was added to the aqueous phase in a dispensing and mixing equipment in an amount of 40% (by weight) at room temperature. The resulting mixture was immediately transferred to the mold. The foaming process reached 30 seconds, and then the foam was cured for 10 minutes. After curing, the mold papers were removed and the foam was dried to a maximum moisture content of 10% (by weight) at a temperature of 120^TheC. (See Figure 1 and Figure 2).

Example 2: Absorption of foam material

Samples of the foam product produced in Example 1,

Sample A, and two commercially available products,

Sample B as described in WO 2002/062403 and

Sample C as described in US patents 5,681,575 (A) and US

5,837,275 (A), were cut into 6 x 6 cm test pieces

17/20 and heavy. Subsequently, the test pieces were soaked in an excess amount of warm water. After three hours, the pieces were weighed again. The results obtained are shown in Table 1:

Table 1

<td colspan="2"></td><td>Dry weight (g)</td><td>Wet weight (g)</td><td>Absorption (g / 36 cm²)</td><td>Absorption (g / cm²)</td>

<td>Sample</td><td>THE</td><td> 2,82</td><td> 35,5</td><td> 32,7</td><td> 0,91</td>

<td>Sample</td><td>B</td><td> 3,52</td><td> 28,5</td><td> 25,0</td><td> 0,69</td>

<td>Sample</td><td>Ç</td><td> 3,31</td><td> 33,0</td><td> 29,7</td><td> 0,82</td>

Example 3: Silver release

Circular samples having a diameter of 20 mm were taken from the material produced according to Example 1, referred to here as Sample A, and two commercially available products, Sample B as described in WO 2002/062403 and Sample C as described in US patents. 5,681,575 (A) and US 5,837,275 (A). Figure 3 shows a device for determining the release of silver, namely a 6-well Falcon ™ Multiwell unit (2) and a corresponding cell culture insert both from Becton Dickinson Labware (4) (The bottom diffusion membrane of the cell culture insert (4) was removed and replaced with a waterproof polyamide film). An opening (6) having a diameter of 12 mm was made in the bottom film. The dry sample (10) was placed in the cell culture insert (4) at the top of the opening (6). A weight made of stainless steel, weighing 15 g and having a diameter of 20 mm was placed on top of the sample (10) in order to compress and fix said sample on the bottom film.

A defined amount of a 0.15 M aqueous solution of NaN0₃ (hereinafter called the test solution (8)) was

18/20 added to the Multiwell ™ unit (2) according to the following scheme (Table 2):

Table 2

<td>0 h</td><td>6 h</td><td>24 h</td><td>48 h</td><td>72 h</td><td>96 h</td><td>120 h</td><td>144 h</td><td>168 h</td>

<td>3.5 ml</td><td>1.5 ml</td><td>1.5 ml</td><td>1.5 ml</td><td>1.5 ml</td><td>1.5 ml</td><td>1.5 ml</td><td>1.5 ml</td><td>0 ml</td>

The cell culture insert (4) was placed in the Multiwell ™ unit (2), thus allowing contact between the test solution (8) and the sample (10). The cover of the two-compartment model has been closed. At each sample time, the test solution that was not absorbed by the sample (10) was collected. After each sample time, a new test solution was added to a clean Multiwell ™ unit, where the cell culture insert (4) was placed, still containing the same sample (10). All six samples were tested in triplicate throughout the test. At each sample time, the amount of silver released was assessed with a silver ion electrode.

<td>Sample</td><td>0 h mg Ag / cm²</td><td>0 h accumulated mg Ag / cm²</td><td>6 h mg Ag / cm²</td><td>6 h accumulated mg Ag / cm²</td>

<td>THE</td><td> 0</td><td> 0</td><td> 0,006</td><td> 0,006</td>

<td>B</td><td> 0</td><td> 0</td><td> 0,005</td><td> 0,005</td>

<td>Ç</td><td> 0</td><td> 0</td><td> 0,002</td><td> 0,002</td>

<td>Sample</td><td>24 h mg Ag / cm²</td><td>24 h accumulated mg Ag / cm²</td><td>48 h mg Ag / cm²</td><td>48 h accumulated mg Ag / cm²</td><td>72 h mg Ag / cm²</td><td>72 h accumulated mg Ag / cm²</td>

<td>THE</td><td> 0,134</td><td> 0,14</td><td> 0,18</td><td> 0,32</td><td> 0,15</td><td> 0,47</td>

<td>B</td><td> 0,010</td><td> 0,015</td><td> 0,002</td><td> 0,017</td><td> 0,010</td><td> 0,027</td>

<td>Ç</td><td> 0,005</td><td> 0,007</td><td> 0,010</td><td> 0,017</td><td> 0,020</td><td> 0,037</td>

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<td>Sample</td><td>96 h mg Ag / cm²</td><td>96 h accum. mg Ag / cm²</td><td>120 h mg Ag / cm²</td><td>120 h accum. mg Ag / cm²</td><td>144 h mg Ag / cm²</td><td>144 h accum. mg Ag / cm²</td><td>168 h mg Ag / cm²</td><td>168 h accum. mg Ag / cm²</td>

<td>THE</td><td> 0,13</td><td> 0,60</td><td> 0,09</td><td> 0,69</td><td> 0,07</td><td> 0,76</td><td> 0,07</td><td> 0,83</td>

<td>B</td><td> 0,010</td><td> 0,037</td><td> 0,014</td><td> 0,051</td><td> 0,010</td><td> 0,061</td><td> 0,010</td><td> 0,071</td>

<td>Ç</td><td> 0,014</td><td> 0,051</td><td> 0,014</td><td> 0,065</td><td> 0,010</td><td> 0,075</td><td> 0,08</td><td> 0,083</td>

The results obtained are shown in Figures 4A and 4B. The product of Example 1 releases about 70% of its silver content during a one-week trial period. The highest release rate is achieved after about 48 hours.

Example 4: Antibacterial activity

Antibacterial activity was measured using a method based on the ASTM E 2149 reference method. Samples (20 mm in diameter) of the silver foam derived from Example 1 (Sample A) and the reference material (Sample B as described in the document WO 2002/062403, Sample C as described in US patents 5,681,575 (A) and US

5,837,275 (A) and a control sample; a foam as described in Example 1, but without any silver content) were placed in vials with bacteria (Staphylococcus aureus or Pseudomonas aeruginosa) and 10 ml of simulated wound fluid (SWF), that is, a 1: 1 solution of serum fetal bovine and aqueous peptone (0.9% NaCl with 0.5% peptone). The flasks were shaken for about 10 seconds and then incubated at 35 ± 2^TheC. In order to measure the antimicrobial effect of the products, samples were taken after every 24 hours for up to 8 days. The number of viable cells in the samples was determined using a standard plaque counting method.

The results of this experiment show a greater reduction in the viable count for Staphylococcus aereus

20/20 with the silver foam shown here than with the other products tested (see Figure 5A). The reduction in the viable count of Pseudomonas aeruginosa by Mepilex Ag was also greater than that for the other products (see Figure 5B).

The results are also shown in Tables 4A and 4B.

Table 4A: Sustained antimicrobial effect on

Staphylococcus aureus

<td>Sample</td><td>0 h log CFU / ml</td><td>24 h log CFU / ml</td><td>24 h log CFU / ml</td><td>72 h log CFU / ml</td><td>96 h log CFU / ml</td><td>120 h log CFU / ml</td><td>144 h log CFU / ml</td><td>168 h log CFU / ml</td>

<td>Control</td><td> 6,3</td><td> 8,6</td><td> 8,6</td><td> 8,3</td><td> 8,3</td><td> 8,2</td><td> 8,1</td><td> 8,1</td>

<td>THE</td><td> 6,3</td><td> 5,1</td><td> 4,6</td><td> 3,2</td><td> 2,4</td><td> 2,0</td><td> 2,1</td><td> 2,0</td>

<td>B</td><td> 6,3</td><td> 6,6</td><td> 5,5</td><td> 4,1</td><td> 3,5</td><td> 2,7</td><td> 2,6</td><td> 2,3</td>

<td>Ç</td><td> 6,3</td><td> 6,2</td><td> 5,1</td><td> 4,5</td><td> 4,3</td><td> 4,3</td><td> 4,2</td><td> 4,6</td>

Table 4B: Sustained antimicrobial effect on

Pseudomonas aeruginosa

<td>Sample</td><td>0 h log CFU / ml</td><td>24 h log CFU / ml</td><td>24 h log CFU / ml</td><td>72 h log CFU / ml</td><td>96 h log CFU / ml</td><td>120 h log CFU / ml</td><td>144 h log CFU / ml</td><td>168 h log CFU / ml</td>

<td>Control</td><td> 6,52</td><td> 9,95</td><td> 9,48</td><td> 8,75</td><td> 8,55</td><td> 9,00</td><td> 9,13</td><td> 9,15</td>

<td>THE</td><td> 6,51</td><td> 3,58</td><td> 2,26</td><td> 2,00</td><td> 2,00</td><td> 2,00</td><td> 2,00</td><td> 2,00</td>

<td>B</td><td> 6,38</td><td> 6,55</td><td> 3,20</td><td> 2,95</td><td> 2,59</td><td> 2,00</td><td> 2,00</td><td> 2,00</td>

<td>Ç</td><td> 6,35</td><td> 5,89</td><td> 5,90</td><td> 5,55</td><td> 6,03</td><td> 4,90</td><td> 5,49</td><td> 4,59</td>

detection limit is 2.00 log CFU / ml

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