Particle-containing foam structure

Abstract

A method of producing a hydrophilic polyurethane foam structure containing inert activated carbon particles, includes the steps of: (a) providing a water phase containing a surfactant and dispersed inert particles; (b) providing a isocyanate-terminated polyether having functionality of more than 2; (c) mixing the water phase and the isocyanate-terminated polyether, immediately transferring the resulting mixture to a mold or a continuous web, whereby a foam structure is obtained; and (d) drying the foam structure until it has a moisture content of at most 10% (wt). A foam structure produced by the method and a wound dressing containing the foam structure are also disclosed.

Claims

1. A hydrophilic polyurethane foam structure having a pore size between 30 and 1000 m, wherein the structure contains dispersed inert activated carbon particles, and wherein the structure is obtained by a method comprising the steps of a) providing a water phase containing a surfactant; b) providing an isocyanate-terminated polyether having functionality of more than 2; c) mixing the water phase and the isocyanate-terminated polyether, immediately transferring the resulting mixture to a mould or a continuous web, whereby a foam structure is obtained; and d) drying the foam structure until it has a moisture content of at most 10% (wt); wherein the water phase in step a) also contains dispersed inert activated carbon particles, wherein the inert activated carbon particles improve the maximum water absorption of the foam structure.

2. A wound dressing comprising the foam structure of claim 1.

3. An article comprising a wound dressing comprising a hydrophilic polyurethane foam structure having a pore size between 30 and 1000 m, wherein the structure contains dispersed inert activated carbon particles, wherein the inert activated carbon particles improve the maximum water absorption of the foam structure.

4. The article of claim 3, wherein the inert activated carbon particles improve the water retention capacity of the foam structure.

5. The foam structure of claim 1, wherein the inert activated carbon particles improve the water retention capacity of the foam structure.

6. The wound dressing of claim 2, wherein the inert activated carbon particles improve the water retention capacity of the foam structure.

7. The article of claim 3, wherein the wound dressing further comprises a cross-linked silicone gel.

8. A method of preventing wound fluid from running over skin surrounding a wound, comprising applying the article of claim 7 over a wound and to skin surrounding the wound, wherein the cross-linked silicone gel adheres to the skin surrounding the wound, thereby preventing wound fluid from running over the skin surrounding the wound.

9. A method of using the article of claim 3, comprising applying the article of claim 3 over a wound and to skin surrounding the wound.

10. The article of claim 3, wherein the gram per gram water absorption capacity of the hydrophilic polyurethane foam structure is from 18% to 41% higher than a hydrophilic polyurethane foam structure without the dispersed inert activated carbon particles when the hydrophilic polyurethane foam structure comprises 1% wt of inert activated carbon particles.

Description

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

(2) FIG. 1 is a schematic perspective view of a piece of an inventive dressing 1 according to one embodiment;

(3) FIG. 1A is an enlarged view of one feature of the FIG. 1 illustration;

(4) FIG. 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; and

(5) In one embodiment of the invention, the polyurethane pre-polymers are mixed with a water phase containing surfactants and inert particles such as activated carbon in dispensing and mixing equipment. The reaction mixture is subsequently transferred to a mould or a continuous web that has been lined with casting paper. After the termination of the polymerisation reaction, the casting paper is removed from the castings and the obtained foam is dried to a moisture content of at most 10% (wt). A plastic liquid-impervious core is coated.

(6) FIG. 1 illustrates a piece of a dressing 1 according to one embodiment of the invention. The dressing is comprised of an absorbent foam material 10 comprising activated carbon particles 7, which is coated with a gel layer 3 on that side which lies proximal to the wound or skin of the wearer when the dressing is used. As illustrated schematically in Figure IA, the gel layer 3 is disposed so that even a part of the walls of the open cells or pores 4 in the foam material that open into the gel-coated side thereof are gel coated. Because the gel layer 3 does not close, but only covers, a part of the walls in an end portion of the pores of the foam material that face the wound, excess wound fluid can be drawn into the foam material 10 and absorbed thereby. The gel layer also prevents the foam material from coming into direct contact with the wound or skin of the wearer. The thickness of the total gel layer, i.e. including the depth of penetration into the pores of the foam material, is 0.1-2.0 mm. Some of the pores in the foam material that face towards the wound are closed by the gel layer.

(7) With the intention of providing a dressing that has a dry outer surface, the dressing is given a liquid-impervious layer 5 on the side opposite to the gel layer 3. This liquid-impervious layer 5 may conveniently comprise a thin liquid-impervious, but vapour-permeable, plastic film, for instance a polyurethane film.

(8) The dressing illustrated in FIG. 1 is intended to be used with wounds that exude fluid in quantities ranging from slight to normal. The foam layer has a thickness of 1-10 mm, preferably 2-6 mm. As mentioned before, the foam material functions both as an absorbent and as a gel carrier, and the dressing as a whole will therefore be very soft and pliant. Because the gel adheres to the skin surrounding the wound, the dressing will be held in place while the gel affords a sealing function and prevents maceration, i.e. prevents wound fluid from running over healthy skin and softening and eventually damaging the epidermis. The open structure of the gel layer and the foam material also enables the skin to breathe. The nature of the adhesive gel used in this invention differs totally from the nature of glues that are typically used to secure dressings, for instance the acrylate glues or the hot melt glues that are used today to this end. The significant difference between these glues and the gel used in accordance with the invention is that the gel is much softer and has a better wetting ability than said glues.

(9) This enables the gels to be given a much lower specific adhesiveness, i.e. lower adhesion per unit of contact surface area, than the specific adhesiveness that must be given to harder glues in order to achieve an equally effective total adhesion as that offered by the gel.

(10) FIG. 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 conveyer (not shown) on which a plastic film 8 is conveyed from left to right in FIG. 2. A layer of uncured gel mixture 9 is placed on the film 8. By gel mixture is meant a mixture of those components which form a gel after curing, including polymers that can react with one another to form a cross-linked structure. A layer of absorbent foam material 10 is applied to the layer of uncured gel mixture 9 with the aid of a roller 11, and the layers 9, 10 are then transported into an oven 12. The gel mixture is cured in its passage through the oven 12 and forms a gel layer on the underside of the foam material.

(11) It has been found that with suitable selection of the one or more gel-forming components and mixtures and proportions thereof, pressure force F, quantity of gel mixture, time between applying foam material and heating the layers, curing temperature, and so on, there will be formed a discontinuous gel coating on the foam material. This is because the gel mixture is drawn by capillary action into those pores or holes in the foam material that open out in that side of the foam material which lies in abutment with the gel mixture. When applying a gel-forming coating to foam material that lacks holes other than pores, the gel mixture must be applied in a layer of such thinness as to ensure that an excessively large number of the pores opening into the underside of the foam material will not be clogged or blocked by the gel coating. The viscosity of the gel mixture and the size of the pores in the foam material also influence the tendency of the mixture to penetrate into the pores. It has been found that the gel mixture layer should preferably be applied at a thickness of 0.05-1.00 mm. A larger part of the gel mixture layer is sucked into the foam, wherewith the total gel layer, including air and foam, will have a thickness of 0.10-2.00 mm.

(12) In a first application of the above method for coating the underside of an polyurethane foam sheet with silicone gel, there was used an open cell, soft hydrophilic polyurethane foam sheet having a density of 130 kg/m and a thickness of 5 mm.

(13) The silicone mixture was prepared from SILGEL 612 obtained from Wacker, in an A-component and B-component mixing ratio of 1.0:0.9. The uncured mixture had a viscosity of about 1000 mPa.

(14) The polyurethane foam material was placed on a silicone gel mixture having a thickness of 0.2 mm, without applying pressure F from the roller 11, in other words the silicone mixture was subjected solely to the weight of the foam sheet. The time taken to transport the foam material 10 and the underlying silicone mixture 9 from the roller 11 to the oven 12 was one minute and the curing temperature was 130 C. The silicone cured in an oven within minutes. A polyurethane film of high vapour permeability and a thickness of 0.025 mm was then firmly glued to the foam on the side thereof opposite to the gel coating. At this mixture ratio, the silicone gel had a penetration death of 16 mm, and the skin adhesion force of the dressing was measured as 0.42 N. Under these conditions, it has been found that the gel mixture layer will preferably have a thickness of at least 0.1 mm, so as to obtain a suitable discontinuous gel coating on the foam material.

(15) When the thickness of the gel mixture layer was greater than 0.4 mm, an excessively large percentage of the pores in the foam material became blocked, resulting in insufficient permeability of the gel coating.

(16) It will be evident from the aforegoing that when carrying out the method described with reference to FIG. 2, the quality of the end product will depend on many factors. It is therefore not possible to provide these factors with general limit values, and such limit values must be established empirically with respect to the gel mixture and the foam material used.

(17) The described method thus enables a dressing of the kind described with reference to FIG. 1 to be produced very easily. The method is also very flexible and enables dressings of mutually different absorbencies to be produced in principle by the same way and with the aid of the same apparatus.

(18) The described dressing can, of course, be sterilized, e.g. by ethylene oxide sterilization or steam sterilization, and is intended for delivery in different sizes and for different types of wounds, both sterile packed and non-sterile packed. Because of their softness, they are suitable for use in combination with compression bandages and can be used beneficially on blisters, leg ulcers and like wounds. Their high degree of flexibility also makes them suitable for use on joint sores, such as knee sores and elbow sores, even in later phases of the sore healing process. The dressings can also be cut to a size suitable for the size of the sore or wound in question.

(19) It will be understood that the above described exemplifying embodiments can be modified within the scope of the invention, particularly with respect to the described materials and process parameters applied.

(20) The invention will now be further described in the enclosed examples.

Example 1: Manufacturing a Hydrophilic Polyurethane Foam Structure

(21) A water phase for the foam-manufacturing process was prepared by dissolving/dispersing the non-ionic surfactant PLURONIC F87, and activated carbon. The final concentrations of these constituents in the water phase amounted to 0.1% (wt) of PLURONIC F87, and 1.0% (wt) of active carbon.

(22) Simultaneously, a mould lined with casting paper was prepared. The mould had a sufficient depth so that sheet-formed foam castings having a thickness of 5 mm could be produced. The pre-polymer HYPOL 2001 (a isocyanate-terminated polyether) was added to the water phase in a dispensing and mixing equipment in an amount of 40% (wt) at room temperature. The resulting mixture was immediately transferred to the casting mould. The foaming amounted to 30 s, and then the foam was cured for 10 minutes. After curing, the casting papers were removed and the foam was dried to a moisture content of at most 10% (wt) at a temperature of 120 C.

Example 2: Water Absorption of the Hydrophilic Polyurethane Foam Structure

(23) Seven batches of hydrophilic polyurethane foam structures were prepared in accordance with the process of Example 1. Four of the batches contained 1% (wt) of particles of activated carbon. Samples from each batch were soaked in tap water and allowed to absorb for 2 minutes. Subsequently, the samples were hung in one corner to drip off for 9 minutes. The length was measured in the cross direction (CD) and the width in the machine direction (MD). The length and width in the wet state were measured after the samples had dripped off. At least three samples have punched out of each batch.

(24) The results obtained can be found in Table 1:

(25) TABLE-US-00001 TABLE 1 Original Absoption Swelling Swelling Swelling Number Activ. thickness Density capacity length width thickness Of Batch carbon? (mm) (kg/m.sup.3) (g/g) (%) (%) (%) samples 1 No 5.58 90.1 9.86 21.7 21.3 32.0 3 2 No 5.38 88.6 9.80 22.5 21.3 33.2 3 3 No 5.48 86.0 10.62 20.8 21.8 31.2 4 4 Yes 5.25 89.6 12.60 23.0 21.3 28.5 3 5 Yes 5.87 86.0 13.85 23.0 19.8 n.d. 4 6 Yes 5.11 91.7 13.60 21.9 21.2 26.8 3 7 Yes 5.27 92.4 12.48 22.9 20.8 26.8 4 n.d. = not detected

(26) The results show that the absorption capacity is about 30% higher for batches containing inert particles compared to batches without particles.

Example 3: Retention of a Saline Under Pressure

(27) Seven batches of hydrophilic polyurethane foam structures were prepared in accordance with the process of Example 1. Four of the batches contained 1% (wt) of particles of activated carbon. Samples from all batches were punched as 1010 cm pieces with rounded corners. First of all, the maximum absorption capacity was determined. The samples were weighed, subsequently soaked in a 0.9% (wt) aqueous solution of NaCl for five minutes and then drained for two minutes by hanging in a clip fastened in a corner. Finally, the samples were reweighed and the maximum absorption capacity was determined.

(28) Dry samples were weighed, and then exposed to an amount of saline corresponding to 80% of the maximum absorption capacity of the samples. The areas of the samples were determined after the samples had been exposed to the saline. Subsequently, the samples were exposed to a static pressure of 40 mmHg for 5 minutes and finally reweighed. The retention of saline is calculated as the difference between the mass after the pressure treatment and the mass of the dry sample.

(29) The results obtained can be found in Table 2, below:

(30) TABLE-US-00002 Batch 1 2 3 4 5 6 7 Active carbon? No No No Yes Yes Yes Yes Added liquid 80 80 80 87 80 80 80 % of max. absorption Area of sample 0.0132 0.0132 0.0132 0.0132 0.0132 0.0132 0.0132 (m.sup.2) Dry weight of sample 6.57 6.69 6.66 6.65 6.66 6.68 6.92 (g) Retention after static pressure 7.27 9.13 9.61 18.51 16.12 17.93 10.86 (g) Retention after static pressure 18 23 23 34 32 33 25 (% of max. absorption) Amount of samples 5 5 5 5 5 5 5

(31) The obtained results show that the retention after static pressure is significantly higher for foam structures containing inert particles.