The present invention relates to a polyurethane foam dressing material with improved moisturizing rate. More precisely, the present invention relates to a hydrophilic dressing material in which a wound contact layer (10) having a sponge structure composed of multiple open cells (12) and pores (15) passing through the cells (12) is laminated with a protective film (20). The lamination is characteristically performed at 150.about.250.degree. C. under a pressure of preferably 0.25.about.1 kgf/cm.sup.2, the moisturizing rate of the wound contact layer (10) is 300.about.1200% and the pore area (membrane opening) takes 10.about.35% of the total cell area.The polyurethane foam dressing material of the present invention prevents the invasion of foreign materials, releases absorbed exudation after changing it into water vapor or arresting the absorbed exudation inside the foam to maintain constant moisturizing, has excellent exudation absorption capacity, has a wound healing effect resulting from not adhering to a wound, is easy to change, and enhances the wound healing effect by maintaining optimum moisturizing conditions resulting from the improved moisturizing rate.

Description of the Invention

RELATED APPLICATIONS

This application claims priority to Korean Application Serial No. 10-2006-0130194, filed Dec. 19, 2006, which is specifically incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a polyurethane foam dressing material with improved moisturizing rate. More precisely, the present invention relates to a hydrophilic dressing material in which a wound contact layer, having a sponge structure composed of multiple open cells and pores that make a tunnel from cell to cell, is laminated with a protective film. The lamination is characteristically performed at 150.about.250.degree. C. under a pressure of 0.25.about.1 kgf/cm.sup.2, the moisturizing rate of the wound contact layer is 300.about.1200%, and the pore area (membrane opening) takes 10.about.35% of the total cell area.

The polyurethane foam dressing material of the present invention has the advantages of maintaining desired moisturizing conditions by blocking the invasion of foreign materials, releasing absorbed exudation to the outside after changing it into water vapor or arresting the absorbed exudation inside the foam, having a wound healing effect owing to its excellent exudation absorption without adhering to the wound, ease of dressing replacement, particularly promoting wound healing by maintaining optimum moisturizing conditions due to the improved moisturizing, and preventing contamination of clothes or sheets by avoiding exudation release due to an external force.

BACKGROUND ART

Once the skin has a wound, a huge amount of exudation is generated, which is called the `inflammatory phase`, then the proliferative phase occurs, in which granulation takes place, and finally the growing phase occurs in which newly generated skin becomes firm as the wound heals. The most important factor in the process of wound healing is to minimize the inflammatory phase by quickly absorbing exudation generated in the early inflammatory phase and to maintain proper moisturizing conditions during the growing phase to provide various cell growth factors (PDGF, TGF-.beta., EGF, FGF, VEGF, IGF, etc) or cytokines (IL-1, IL-6, IL-8, TNF, etc) to accelerate wound healing by helping cell migration and proliferation. It is preferable to use a dressing material that does not adhere to the wound.

The conventional gauze dressing absorbs wound exudate easily, but at the same time has the disadvantages of not-defending itself against infection by bacteria, keeping the wound area dry which delays recovery, and difficulty in changing dressings because it adheres to the wound, possibly damaging nascent tissues and causing pain. In the early treatment phase, a lot of exudate is generated so the dressing has to be changed frequently (for example, several times a day). As an alternative to overcome the disadvantages of the conventional gauze dressing, various obstructive dressing materials have been developed, but these new dressings are expensive, lack adequate absorption, and cannot regulate their water vapor permeability. Thus, the obstructive dressing materials are only applied to some specific types of wounds.

The obstructive dressing materials in use are films, hydrocolloids, hydrogels, polyurethane foams, etc. Particularly, hydrocolloids, hydrogels and polyurethane foams are favored because of their high treatment effect.

U.S. Pat. No. 5,503,847 and No. 5,830,932 describe a hydrocolloid dressing material which is composed of an adhesive composition layer, a hydrocolloid layer that absorbs impact and exudation, and a film layer that prevents the invasion of bacteria and impurities.

The hydrocolloid dressing material absorbs a small amount of wound exudate to form a gel and is able to provide humid conditions and maintain the pH as weakly acidic for a long time to prevent the disturbance of tissues and promote cell growth. However, water vapor permeability and exudation absorption are not satisfactory. During the change or removal of the dressing, the gel adheres to the wounded area and remains there, requiring secondary treatment to eliminate the residue. Thus, this dressing is not suitable for application to a wounded area that generates a large amount of exudate.

U.S. Pat. No. 5,501,661 and No. 5,489,262 describe a hydrogel dressing material. According to these descriptions, the hydrogel dressing material contains a non-permeable polymer film coated with hydrogel. The polymer film prevents dehydration or dryness of the hydrogel, and the hydrogel layer absorbs exudation by adhering to a wounded area and maintains humid conditions to accelerate wound healing. However, this dressing material is not suitable for application to a severe wound that generates a lot of exudation because of its low water vapor permeability and water absorptiveness. Excessive absorption of the dressing material deforms the dressing material itself, thereby making it difficult to change the dressing, and causes infection of normal tissues.

U.S. Pat. No. 5,445,604 and No. 5,065,752 describe a hydrophilic polyurethane foam dressing material having a triple layer structure in which both sides of the polyurethane foam are laminated with a film. Particularly, a wound contact layer film, which is laminated to prevent the huge wound contact layer pores from adhering to the wounded area, is designed to have a hole through which exudation is absorbed into the wound contact layer. However, exudation and blood cannot be completely absorbed from the wounded area, which generates blood clots on the area. Because of the generated blood clots, wound healing is retarded or the dressing adheres to the wound, and nascent tissues might also adhere to the dressing through the huge mechanically made pores, making it difficult to change the dressing and resulting in a dot shaped scar. When this dressing material is applied to a wound generating lots of exudation, the dressing has to be changed frequently because of the insufficient absorptiveness per unit area and the patient's clothes or sheets have to be changed often because exudation flows out through the dressing due to external forces owing to its weak moisturizing rate. In addition, the dryness around the wound or dryness of the wounded area itself when applied on a wound generating less exudation is another problem of this dressing material (J Korean Soc. Plast. Reconstr. Sur., Vol. 29, No. 4, 297-301, 2002; J Korean Burn Soc., Vol. 6, No. 1, 45-51, 2003).

U.S. Pat. No. 5,064,653 and No. 5,254,301 also describe a hydrophilic polyurethane foam dressing material. According to these descriptions, the dressing material has a triple layer structure in which a polyurethane foam produced by in situ reaction of a hydrophilic isocyanate-capped polyether prepolymer with a hydrotrope, water, an adjuvant and a wetting agent is laminated with films by two-part adhesive, which used to be added during continuous line foaming. Hydrophilicity and moisturizing rate have been improved by applying a hydrotrope and a wetting agent on the wound contact layer. However, the dressing material is still not suitable for operation wounds which produce a lot of exudation including blood, because excessive exudation is not absorbed in the dressing material and flows out through the wound contact layer to the patient's clothes or a sheet. In addition, the remaining blood generates blood clots on the wounded area, retarding wound healing, and the pore of the wound contact layer is bigger than a human cell so re-generated tissues adhere to the dressing, making it difficult to change the dressing (J Korean Burn Soc., Vol. 6, No. 1, 45-51, 2003).

The alternative to overcome the above mentioned problems has been proposed by the present inventors and described in Korean Patent No. 553078. According to the description, the polyurethane foam dressing material having a double-layer structure, in which an absorption layer having a water absorptiveness of 400.about.2,000 weight % is laminated with a protective film having a water vapor permeability of 200.about.1,500 g/m.sup.2day, is a ground-breaking development in wound healing. However, it still has a problem with regard to dryness around the wounded area when it is applied on a wound generating less exudation. Thus, a novel dressing material needs to be developed with an improved moisturizing rate that enables a hydrogel-like effect after absorbing exudation to provide comfortable humid conditions.

DISCLOSURE OF THE INVENTION

It is an object of the present invention, in order to solve the above problems, to provide a polyurethane foam dressing material with improved moisturizing rate, which is characterized by the ability to prevent the invasion of foreign materials, releasing absorbed exudation as water vapor or arresting it inside the foam to maintain humid conditions, the promotion of wound healing owing to its excellent exudation absorptiveness and non-adhesion to the wound contact layer, ease of dressing change, and accelerated wound healing by maintaining optimum humidity due to the improved moisturizing rate.

To achieve the above object, the present invention provides a hydrophilic dressing material in which a wound contact layer (10) having a sponge structure composed of multiple open cells (12) and pores (15) passing through the cells (12) is laminated with a protective film (20). The lamination is performed at 150 .about.250.degree. C. at a pressure of 0.25.about.1 kgf/cm.sup.2, the moisturizing rate of the wound contact layer (10) is 300.about.1200%, and the pore area (membrane opening) takes 10.about.35% of the total cell area.

If the temperature for the lamination is lower than 150.degree. C., the lamination of the protective film layer on the polyurethane foam absorption layer will not be successful. On the contrary, if the temperature is higher than 250.degree. C., a color change will be observed in the polyurethane foam absorption layer.

If the pressure for the lamination is lower than 0.25 kgf/cm.sup.2, the lamination of the protective film layer on the polyurethane foam absorption layer will not be successful. On the other hand, if the pressure is higher than 1 kgf/cm.sup.2, the membrane opening will be increased in the polyurethane foam absorption layer, resulting in the decrease of moisturizing rate.

The mean diameter of the open cells (12) is preferably 50.about.300 .mu.m and the mean diameter of the pores (15) is 5.about.85 .mu.m.

If the mean diameter of the open cells is more than 330 .mu.m, the moisturizing rate will be significantly decreased. If the mean diameter of the open cells is less than 10 .mu.m, exudation absorption will be decreased and the absorption speed will also be very slow, resulting in a pool of exudation from incomplete elimination of wound exudation.

If the mean diameter of the pores is more than 85 .mu.m, human cells migrate into the dressing material which causes the dressing to adhere to the wound and re-injures the wound during dressing change. If the mean diameter of the pores is less than 5 .mu.m, clean elimination of the wound exudation will be difficult.

The preferable content of the open cells in the wound contact layer (10) is 20.about.80%.

If the open cells take more than 80% of the wound contact layer, the moisturizing rate will be significantly decreased, making it difficult to ensure humid conditions around the wounded area. If the open cells take less than 20% of the wound contact layer, exudation absorption will be significantly decreased.

The preferable density of the wound contact layer (10) is 0.15.about.0.45 g/cm.sup.3.

If the density is more than 0.45 g/cm.sup.3, the percentage of the open cells will be lowered to at best 20%, which decreases exudation absorption. If the density is less than 0.15 g/cm.sup.3, the percentage of the open cells will be at least 80%, which means the moisturizing rate will drop significantly and the humidity around the wound will be poor.

The water absorptiveness of the wound contact layer (10) is preferably 400.about.2,000 weight %.

If the water absorptiveness is higher than 2,000 weight %, the inside structure of the foam requires a cell diameter of at least 300 .mu.m and 90% open cells. If this is the case, the moisturizing rate of the dressing material will be significantly reduced and the humidity around the wound will be poor. If the water absorptiveness is less than 400 weight %, frequent dressing changes will be required.

Herein, the wound contact layer (10) is prepared by the steps of mixing 40.about.70 weight % of a polyurethane prepolymer with 15.about.45 weight % of a foaming agent, 5.about.35 weight % of a cross-linking agent, 0.1.about.2 weight % of a surfactant and 0.5.about.15 weight % of an adjuvant with stirring; pour-foaming the mixture in a mold to prepare a polyurethane foam; and slicing thereof.

The polyurethane prepolymer herein is preferably synthesized from an isocyanate (1.about.4 mol) and a polyetherpolyol (0.15.about.2 mol).

The isocyanate herein can be selected from a group consisting of isophoronediisocyanate, 2,4-toluenediisocyanate and its isomer, diphenylmethanediisocyanate, hexamethylenediisocyanate, lysinediisocyanate, trimethylhexamethylenediisocyanate, bis(2-isocyanateether)-fumarate, 3,3'-dimethyl-4,4'-diphenylmethanediisocyanate, 1,6-hexanediisocyanate, 4,4'-biphenylenediisocyanate, 3,3'-dimethylphenylenediisocyanate, p-phenylenediisocyanate, m-phenylenediisocyanate, 1,5-naphthalenediisocyanate, 1,4-xylenediisocyanate and 1,3-xylenediisocyanate. Particularly, diphenylmethanediisocyanate, 2,4-toluenediisocyanate and its isomer, p- henylenediisocyanate, isophoronediisocyanate and hexamethylenediisocyanate are more preferred.

The polyethylenepolyol can be prepared by mixing a ethyleneoxide/propyleneoxide random copolymer having at least three hydroxyl groups, a molecular weight of 3,000.about.6,000 and an ethyleneoxide content of 50 .about.80% with a polypropyleneglycol having at least two hydroxyl groups and a molecular weight of 1,000.about.4,000 at the ratio of 30:70, and it is more preferred to select the above ethyleneoxide/propyleneoxide random copolymer alone as the polyethylenepolyol. However, other isocyanate compounds and polyols can be added to regulate the physical properties of the product.

The foaming agent can be selected from a group consisting of chlorofluorocarbon (CFC-141b), methylenechloride and distilled water, with distilled water being more preferred.

The cross-linking agent can be a single compound or a mixture of compounds having at least two hydroxyl groups selected from a group consisting of 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentylglycol, propyleneglycol, ethyleneglycol, polyethyleneglycol (MW: 200.about.2,000), glycerol, trimethylolethane, trimethylolpropane, pentaerythritol, sorbose and sorbitol. In particular, glycerol, sorbitol, polyethyleneglycol (MW: 200.about.2,000) and trimethylolpropane are more preferred.

The surfactant is one or more compounds selected from a group consisting of ethyleneoxide/propyleneoxide copolymers such as L-62, L-64, P-84,P-85, P-105, F-68, F-87, F-88, F-108, F-127 or a mixture thereof (Basf, Germany), and silicon-based surfactants such as L-508, L-5305, L-5302 and L-3150 (Osi).

As an adjuvant, a moisturizing agent and a wound healing accelerator, a pigment, an antimicrobial agent, and a growth factor can be added.

The moisturizing agent and the wound healing accelerator herein can be one or more compounds selected from a group consisting of high-absorptive polymers and natural substances such as polyacrylic acid, polyvinylalcohol, polyoxyethylene, polyethyleneoxide, polysaccharide, polymethacrylic acid, polyacrylamide, polyethyleneoxide, cellulose, carboxymethylcellulose, pectin, guar gum, sodiumalginate, chitin, chitosan, gelatin, starch, hyaluronic acid, keratan, collagen, dermatansulfate, sodiumcarboxymethylcellulose, locust bean gum, hydroxyethylcellulose, xanthan gum, pulp and karaya gum.

The antimicrobial agent used in the present invention can be selected from a group consisting of gluconate chlorohexidine, acetate chlorohexidine, hydrochloride chlorohexidine, silversulfurdiazine, povidone iodine, benzalkonium chloride, furagin, idokine, hexachlorophene, chlorotetracycline, neomycin, penicillin, gentamycin or acrinol.

The growth factor of the present invention can be one or more compounds selected from a group consisting of PDGF, TGF-.beta., EGF, FGF and VEGF.

The protective layer (20) of the present invention is a waterproof breather film 10.about.300 .mu.m thick, which is laminated directly on the wound contact layer (10) having a sponge structure, or indirectly laminated over the adhesive layer.

The tensile strength of the protective layer (20) is 45.about.700 kg and the elasticity is preferably 200.about.1,000%.
 

Claim 1 of 9 Claims

1. A method for preparing a two layer hydrophilic polyurethane foam dressing material with improved moisturizing rate, said method comprising laminating a wound contact layer (10), having a sponge structure composed of multiple open cells (12) and pores (15) passing through the cells (12), with a protective film (20) at 150.about.250.degree. C. under a pressure of 0.25.about.1 kgf/cm.sup.2, wherein said laminating is by heat-press; wherein the wound contact layer (10) has a moisturizing rate of 510.about.1050% and the pore area (membrane opening) takes 10.about.20% of the total cell area; wherein the mean diameter of the open cells (12) is 50.about.300 .mu.m and the mean diameter of the pores (15) is 5.about.85 .mu.m; wherein the ratio of the open cells to the wound contact layer (10) is 30.about.50%; wherein the wound contact layer (10) has a density of 0.15.about.0.45 g/cm.sup.3; and wherein the wound contact layer (10) has a water absorptiveness of 700.about.1800 weight %.

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