WO2008156285A1

WO2008156285A1 - Method for producing hydrophilic foam dressing and hydrophilic foam dressing produced thereby

Info

Publication number: WO2008156285A1
Application number: PCT/KR2008/003414
Authority: WO
Inventors: Won Il Kim; Seoung Wan Jang; Woo Kyun Kim; Oh Hyeong Kwon
Original assignee: Wonbiogen Co., Ltd.; Kumoh National Institute Of Technology Industry-Academic Cooperation Foundation; Lee, Hyang Lim
Priority date: 2007-06-21
Filing date: 2008-06-17
Publication date: 2008-12-24

Abstract

Disclosed herein is a method for producing a polyurethane foam dressing that protects injuries such as wounds or burns and is useful for wound healing. More particularly, the present invention provides a method for manufacturing a polyurethane foam dressing with remarkably improved productivity and processing efficiency, which can improve physical properties of the polyurethane foam dressing. The method comprises: preparing a moisture permeable waterproof polyurethane film layer; preparing a polyurethane prepolymer; preparing a polyurethane foaming mixture; obtaining a tacky gel type polyurethane foam layer; laminating the tacky gel type polyurethane foam layer on the polyurethane film layer; and winding the produced polyurethane foam dressing in a roll form and then ageing the foam dressing. The method further includes, impregnating the polyurethane foam with a moisturizer and drying the foam and, then, treating the foam with oxygen plasma to modify a surface of the foam dressing, thereby improving absorption rate of the foam dressing. The method of the present invention has advantages such as remarkably improved productivity and processing efficiency allowing mass production of foam dressings, thereby considerably reducing production costs and enabling supply of low cost foam dressings with improved physical properties.

Description

METHOD FOR PRODUCING HYDROPHILIC FOAM DRESSING AND HYDROPHILIC FOAM DRESSING

PRODUCED THEREBY

Technical Field

[1] The present invention relates to a method for producing a hydrophilic foam dressing that protects injuries such as burns and/or wounds and conducive to wound healing, and a hydrophilic foam dressing produced thereby. More specifically, the present invention relates to a method for manufacturing a hydrophilic polyurethane foam dressing with remarkably improved productivity and processing efficiency, which can improve physical properties of the polyurethane foam dressing, and a hydrophilic polyurethane foam dressing produced by the same.

[2]

Background Art

[3] Wound care is the basis of medical sciences and technologies and has a long history.

Ancient papyrus documents report that animal fats, honey and/or raw cotton were applied to wounds beginning in 5,000 B.C. Wound care technologies have greatly varied and developed over a long period of time. A zoologist, Winter reported in 1962 that it is better to keep a wound wet for healing than to leave the wound dry, forming a scab to cover the wound. Since then, benefits of moist wound healing have been further proven and detailed. At present, a wet dressing method for preventing bodily fluids, which are excreted from a wound, from being dried or dehydrated is considered as an easy wound healing.

[4] An ideal dressing must maintain a wet condition between a wound and the dressing, have favorable absorbability and moisture permeability, and prevent drying of a wound and skin festering around the wound. Furthermore, the dressing needs other properties including, for example, gas exchange and inhibition of bacterial invasion, and must not adhere to a surface of the wound and must not cause damage to granulation tissue on the wound during the dressing change. Additionally, a dressing enabling convenient observation of healing progress, and having non-stimulation, favorable availability and economic advantage may also be preferable. Research and investigations continue into development of an improved dressing that can satisfy the requirements described above. [5]

[6] Dressing materials that have recently become available will now be described. In the

TM early 1970s, OpSite was introduced as a semi-transparent thin film that keeps a wound wet, facilitates lysis of necrotic tissues and formation of granulation tissues, thereby promoting wound care, tbwever, wound exudates are excessively gathered in the wounded area, causing skin festering and/or leakage of the exudates from the wound, thus, the film is inconvenient because the exudates must be occasionally removed from the wound.

TM

[7] In 1982, DuoDERM was developed in the United States as a hydro-colloidal dressing, which reacts with wound exudates to provide a moist condition in a gel state when adhered to a wound and to promote epithelialization of the wound, tbwever, this dressing has disadvantages that gas such as oxygen and carbon dioxide or water vapor cannot permeate the dressing so that wound exudates are excessively gathered in the wound area and that gel may remain on the wound after the dressing change.

[8] Dressings using polymers were generally manufactured by gellation but, in recent years, foam production methods have been proposed to prepare a polymer foam using, for example, polyurethane, so as to form open cells.

[9] US Patent Nos. 4,664,662 (July 31, 1985), 4,860,737 (August 11, 1983) and

5,147,338 (June 17, 1991) disclose a polyurethane foam dressing manufactured by admixing a hydrophilic polyurethane prepolymer having at least two isocyanate terminals and a foaming agent such as water, a non-ionic surfactant and/or an antibacterial agent such as silver sulfadiazine and foaming the mixture. The disclosed polyurethane foam dressing typically has a thickness of 0.5 to 20mm, permeability of 300 to 5,000g/m724hrs (at a relative hunidity of 10 to 100% at 3TC), an open cell size of 30 to 700/M, open porosity (open cell rate) of 20 to 70%, and a three-layered structure with an outer film thickness of 12.5 to 37.5/M.

[10] Also, US Patent Nos. 4,773,409 (September 20, 1985) and 4,773,408 (September 25,

1985) disclose a hydrophilic polyurethane foam having a thickness of 1 to 10cm and a density of 0.16 to 0.8g/cnf. This dressing is manufactured by mixing a hydrophilic material such as sodiun carboxymethylcellulose, calciun carboxymethylcellulose, pectin, gelatin, guar gun, locust bean gun, collagen, karaya gun and the like together

TM TM wwiitthh aann iinnssoolluubbllee hhyyddrroopphhiilliicc ppoollyymer such as Aqualon , Water Lock available from Grain Processing Corp., etc.

[H]

[12] Korean Patent No. 0404140 discloses a method of producing a polyurethane foam dressing which comprises mixing a hydrophilic polyurethane prepolymer having an isocyanate terminal, a cross-linking agent, a foaming agent, an additive and the like under stirring, placing the mixture in a mold, and foaming the mixture. IHbwever, in order to manufacture the polyurethane foam dressing with desired different thicknesses, various types and/or forms of molds are required. Above all, the above method mostly produces the dressing in a single-sheet form with a constant size, thus having poor productivity.

[13] Korean Patent No. 0553078 describes a method for manufacturing a polyurethane foam dressing which comprises pouring a hydrophilic polyurethane prepolymer, a cross-linking agent, a foaming agent, an additive and so on into a large mold, foaming the mixture in the mold to prepare a block type polyurethane foam, and removing a skin layer and cutting the foam into a certain thickness using a horizontal cutter and laminating an additional outer film layer on the cut foam. IHbwever, the conventional method disclosed above has a limitation of adopting a mold foaming process. That is, this method requires multiple steps including, for example: mixing a hydrophilic polyurethane prepolymer having an isocyanate terminal, water as a foaming agent and other additive(s) and foaming the mixture in a frame having a certain size, thickness and/or shape to form a block type polyurethane foam; cutting the produced block type foam into pieces having a constant thickness; and combining the cut piece with an outer film layer. Therefore, the conventional method may encounter a problem of processing complexity, which in turn, results in considerably decreased productivity and processing efficiency. Moreover, when raw materials are mixed together in a mold, instant foaming occurs, leading to limited 'pot life.' As a result, the conventional method also has disadvantages in view of shape-forming processes. The polyurethane foam dressing manufactured by the conventional method disclosed above typically has open cells with a large size on a skin facing side thereof, thus having high absorption rate of wound exudates, tbwever, the foam dressing may merge with skin tissues regenerated in the wound and possibly cause pain or secondary damage when the dressing is removed from the skin.

[14] In this regard, the present inventors previously filed patent applications under Korean

Patent Application Nos. 10-2005-0107898 (Korean Patent No. 716658) and 10-2006-0026887, disclosing a dressing with a three-layered structure, which comprises: a non-porous polyurethane film layer to isolate a wound from ambient atmosphere; a polyurethane foam based inner absorptive layer with high absorbability, which has open cells with a size of 1 to 600/M and is located below the non-porous film layer; and a wound contact layer that does not adhere to wounds, has microfine open cells with a size of 1 to 50/M and absorbs wound exudates. Especially, in order to solve the problems of the conventional method disclosed above, these patent applications proposed a dressing manufactured by a series of processes including: mixing a hydrophilic polyurethane prepolymer, water and a surfactant under stirring to prepare a foaming mixture, applying the foaming mixture to a release sheet to a certain thickness using a comma coater, foaming the coated sheet and winding the foamed sheet in a roll form, thereby accomplishing noticeably improved productivity and processing efficiency thereof.

[15] IHbwever, although the inventions claimed in the previous patent applications filed by the present inventors achieved remarkably increased productivity compared to conventional techniques, these also have a limited 'pot life.' More specifically, in these inventions, since the foaming mixture applied to a surface of the comma coater cures after two (2) hours in terms of production time, manufacturing a product having a constant thickness becomes more difficult with passage of time. In addition, it was noted that the published patent applications have a problem of decreased absorption rate of wound exudates and/or blood, so that the polyurethane foam cannot actively absorb the wound exudates and/or blood.

[16]

Disclosure of Invention Technical Problem

[17] Accordingly, the present invention is directed to solve the problems of the conventional methods described above and, in particular, is devised to complement the sheet forming processes disclosed in Korean Patent No. 716658 and Korean Patent Application No. 10-2006-0026887, owned by the present inventors. Therefore, an object of the present invention is to provide a simple and effective process for manufacturing a foam dressing with a three-layered structure comprising: a film layer; an inner absorptive layer; and a wound contact layer, thereby noticeably improving productivity and processing efficiency thereof.

[18] In particular, the inventions disclosed in Korean Patent No. 716658 and Korean

Patent Application No. 10-2006-0026887 had difficulty in manufacturing products with a constant thickness with passage of time, since a foaming mixture applied to a surface of a coater cured after 2 hours in terms of production time due to a limited 'pot life.' Therefore, another object of the present invention is to solve the above problem and to provide a process for manufacturing products with a constant thickness regardless of 'pot life' even if the process is continued for a long time, thereby remarkably improving workability thereof.

[19] A still further object of the present invention is to provide a polyurethane foam dressing with improved physical properties, especially, one which exhibits considerably increased absorption rate through surface modification of the foam.

[20] Details of the above objects and other features of the present invention will be more clearly understood from the following detailed description of preferred embodiments and examples, which are proposed for illustrative purposes only and are not intended to restrict the spirit and scope of the invention.

[21]

Technical Solution

[22] In accordance with one aspect of the present invention to achieve the above purposes, there is provided a process for manufacturing a polyurethane foam dressing comprising:

[23] (a) adding 20 to 70 parts by weight ("wt. parts") of methylethylketone and 5 to 30 wt. parts of dimethylformamide to 100 wt. parts of polyurethane resin, removing air bubbles from the mixture, applying the mixture to a release sheet, and drying the coated sheet to prepare a non-porous waterproof polyurethane film layer;

[24] (b) introducing isocyanate into a mixture including polyol, diol and an antioxidant and proceeding a reaction to prepare a polyurethane prepolymer;

[25] (c) preparing a foaming composition comprising 60 to 120 wt. parts of deionized water as a foaming agent, 0.5 to 40 wt. parts of a cross-linking agent and 1 to 10 wt. parts of a surfactant;

[26] (d) mixing 50 to 150 wt. parts of the foaming composition obtained in step (c) with

100 wt. parts of the polyurethane prepolymer obtained in step (b) under stirring at a high speed to prepare a foaming mixture;

[27] (e) feeding the foaming mixture obtained in step (d) to a release sheet fixed at a certain angle such that the foaming mixture flows along an inclined surface of the release sheet and becomes foam to produce a tacky gel type polyurethane foam layer before being cured to a thickness of 1 to 20mm; and

[28] (f) laminating the polyurethane foam layer obtained in step (e) on the non-porous waterproof polyurethane film layer obtained in step (a) and pressing the laminate while maintaining a certain gap therebetween to regulate a thickness of the foam dressing.

[29] The process of the present invention may further include a step of impregnating the polyurethane foam dressing obtained in step (f) with a moisturizer and drying the treated foam dressing and/or treating the polyurethane foam dressing with oxygen plasma, so that the foam layer has an increased absorption rate. The process of the present invention may also include a step of ageing the polyurethane foam dressing in a hot air dryer after the lamination step (f). The foaming composition of step (c) may additionally include 0.01 to 20 wt. parts of a drug(s). [30] In accordance with another aspect of the present invention, there is provided a process for manufacturing a hydrophilic foam dressing comprising: impregnating a polyurethane foam dressing with a moisturizer and drying the treated foam dressing, and/or treating the polyurethane foam dressing with oxygen plasma to increase the absorption rate of the foam and a hydrophilic foam dressing manufactured by the same. [31]

Brief Description of the Drawings [32] The above and other aspects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: [33] FIGS. 1 to 4 are schematic views illustrating polyurethane foam dressing according to the present invention; [34] FIG. 5 is scanning electron microscope (SEM) photographs showing an absorptive layer and a wound contact layer of a polyurethane foam dressing according to

Production Example 15 of the present invention; [35] FIG. 6 is SEM photographs showing an absorptive layer and a wound contact layer of a polyurethane foam dressing according to Production Example 16 of the present invention; [36] FIG. 7 is SEM photographs showing an absorptive layer and a wound contact layer of a polyurethane foam dressing according to Production Example 17 of the present invention; [37] FIG. 8 is SEM photographs showing an absorptive layer and a wound contact layer of a polyurethane foam dressing according to Production Example 21 of the present invention;

TM

[38] FIG. 9 is SEM photographs showing MEDIFOAM-N available from IL DONG

Pharmaceutical Co., LTD.; [39] FIG. 10 is SEM photographs showing MEDIFOAM-F™ available from IL DONG

Pharmaceutical Co., LTD.; TM

[40] FIG. 11 is SEM photographs showing ALLEVYN available from SMITH &

NEPHEW;

[41] FFIIGG.. 1122 iiss SEM photographs showing CAREFOAM™ available from SAERON Pharmaceutical Co., LTD.;

[42] FIG. 13 is SEM photographs showing BIATAIN™ available from COLOPLAST

Wound Care;

[43] FIGS. 14 to 16 are graphs illustrating absorption rate behaviors of polyurethane foam dressings according to production examples (especially, Production Examples 7 to 14) of the present invention; and

[44] FIG. 17 is a schematic diagram illustrating introduction of a foaming mixture along a fixed and sloped release sheet 3OA according to the present invention.

[45]

Best Mode for Carrying Out the Invention

[46] In the description, the term "hydrophilic polyurethane" as herein used means polyurethane having hydrophilic groups, which exhibits stronger affinity for water than typical polyurethane. Also, "moisture permeable film" means a polyurethane film with higher moisture permeability than typical polyurethane films manufactured using hydrophilic polyurethane having hydrophilic groups as a raw material. Additionally, "moisture permeable waterproof film" means a polyurethane film with moisture permeability as well as water resistance, which is manufactured using hydrophilic polyurethane having hydrophilic groups.

[47] The process for manufacturing a polyurethane foam dressing according to the present invention may include the steps of: preparing a polyurethane film layer that is both water permeable and waterproof; preparing a polyurethane prepolymer; preparing a foaming composition; preparing a foaming mixture; regulating a thickness of the foam dressing while laminating a polyurethane foam layer in a tacky gel state on the polyurethane film layer; and carrying out surface modification of the foam layer to increase the absorption rate of the foam layer and/or ageing the polyurethane foam dressing.

[48]

[49] Hereinafter, individual steps will be described in more detail.

[50]

[51] Preparation of moisture permeable waterproof polvurethane film layer

[52] After 20 to 70 wt. parts of methylethylketone and 5 to 30 wt. parts of dimethyl- formarnide were added to 100 wt. parts of polyurethane resin under stirring, air bubbles were removed from the mixture. The mixture was applied to a release sheet. Drying the coated release sheet resulted in a non-porous waterproof polyurethane film layer. If needed, 1 to 10 wt. parts of a pigment may be added to the polyurethane resin. In an exemplary embodiment of the present invention, air bubbles were removed using a vacuun agitation defoaming device. After the polyurethane solution without air bubbles was applied to a matt release sheet using a coating gauge to a certain thickness, drying the coated sheet yielded a non-porous polyurethane film layer. Herein, using a moisture permeable waterproof polyurethane resin, that is, a polyurethane resin having hydrophilic groups introduced into a main chain which is same as the polyurethane resin used to form the polyurethane foam layer, it is possible to produce a moisture permeable waterproof polyurethane film layer. The polyurethane film layer is duly used to form an outer layer of a dressing manufactured according to the present invention.

[53]

[54] Preparation of polvurethane prepolvmer

[55] Isocyanate was introduced into a mixture containing polyol, diol and an antioxidant, followed by reaction therebetween to prepare a polyurethane prepolymer.

[56] A particular embodiment of preparing the polyurethane prepolymer will be described below. First, polyol and diol were placed in a container and, after increasing a temperature of the mixture to 5O⁰C under stirring at about 150 rpm, stirring was continued for 30 minutes. Next, isocyanate was introduced to the mixture under a nitrogen atmosphere, initiating a reaction therebetween. The reaction was allowed to proceed until NCO content (%) reaches a theoretical value thereof.

[57] The polyol used herein is not particularly limited but includes, for example: polypropyleneoxide glycol; polyethyleneoxide glycol; poly tetrame thy lene etherglycol; ethyleneoxide/propyleneoxide copolymer; polytetrahydrofuran/ethyleneoxide copolymer; polytetrahydrofuran/propyleneoxide copolymer; polybutylene carbonate glycol; polyhexame thy lene carbonate glycol; polycaprolactone glycol; polyethylene adipate; polybutylene adipate; polyneopentyl adipate; polyhexamethylene adipate, which may be used alone or as a combination of two or more thereof.

[58] The polyurethane prepolymer used to prepare polyurethane foam according to the present invention preferably includes a hydrophilic polyurethane prepolymer having hydrophilic groups. It is well known that ethyleneoxide is a hydrophilic group and ethyleneoxide content is important to make the prepolymer hydrophilic, as described in Journal of Cellular Plastics 1976; 12; 285, Journal of Cellular Plastics 1983; 19; 259, and US Patent No. 4,008,189 (November 4, 1975), which are each hereby incorporated by reference. Most preferable is poljol, especially, an ethyleneoxide/propyleneoxide copolymer having at least two hydroxyl groups, a molecular weight of 500 to 6,000 and an ethyleneoxide content of 20 to 90%.

[59] Isocyanate used in the present invention may include aromatic, aliphatic, alicjclic isocyanate and/or mixtures thereof. For example, isocyanate is not particularly limited but includes: 2,4-toluene diisocyanate; 2,6-toluene diisocyanate; methylenedipheyl di- isocyanate; 1,5 -naphthalene diisocyanate; tolidine diisocyanate; hexamethylene- 1,6-diisocyanate; isophorone diisocyanate; xylene diisocyanate; cjclohexylene- 1,4-diisocyanate; lysine diisocyanate; tetramethylene-xylene diisocyanate, which may be used alone or as a combination of two or more thereof. Preferred is the use of isophorone diisocyanate; 2,4-toluene diisocyanate; 2,6-toluene diisocyanate; methylenedipheyl diisocyanate.

[60] Diol compounds described above are not particularly limited but include, for example: ethylenegljcol; propylenegljcol; 1,3-butandiol; 1,4-butandiol; 1,5-pentandiol; 1,6-hexanediol; trie thy lenegljcol; diethylenegljcol; tetraethyelnegljcol; dipropylenegljcol; dibutylenegljcol; neopentylgljcol; l,4-c}clohexandimethanol; 24nethyl-l,3-pentandiol, which may be used alone or as a combination of two or more thereof. Preferable is at least one of ethylene glycol, propylene glycol and 1,4-butandiol or a combination of two or more thereof. The diol compound acts as a chain extender for the polyurethane prepolymer so as to increase the molecular weight of the prepolymer and, in addition, increases a content of hard segment, thereby enhancing mechanical properties thereof. IHbwever, if much of the diol compound is added to the prepolymer, the prepolymer exhibits a high viscosity, preventing the prepolymer from being homogeneously mixed with a foaming composition. Also, using the high viscosity prepolymer, a mixture of the prepolymer and the foaming composition which is prepared under stirring and flows along an inclined surface of the release sheet exhibits poor fluidity on the release sheet, thus complicating shape-forming. On the other hand, if the viscosity of the prepolymer is too low, the mixture of the prepolymer and the foaming composition flows too quickly along the inclined surface of the release sheet and is also difficult to be used in shape- forming. A prepolymer synthesized with addition of a diol compound preferably has a viscosity of 3,000 to 20,000 cps at 3O⁰C. IHbwever, it is clearly understood that the viscosity of the prepolymer can be easily varied by those skilled in the related art depending on processing conditions including, for example, viscosity of a foaming composition, shape-forming temperature and so on.

[61]

[62] With regard to the method for preparing polyurethane prepolymer according to the present invention, other known additives may be further added to the prepolymer by any conventional method. Especially, the additives may include an antioxidant. The antioxidant is not particularly limited but includes, for example: phenyl- beta-naphthalamine; cysteine hydrochloride; dibutylhydroxy toluene; nordihy- droguaiaretic acid; butylhydroxyanisole; phosphoric acid; citric acid; ascorbic acid; erythorbic acid; propyl gallate; and IRGANOX 1010, IRGANOX 1035, IRGANOX 1076, IRGANOX 1330, IRGANOX 1425WL, IRGANOX 3114, IRGANOX B215, IRGANOX B220, IRGANOX B225, IRGANOX B561, IRGANOX B313, IRGANOX B501W, IRGANOX B900, IRGANOX B1411, IRGANOX B1412, IRGANOX PS800, IRGANOX PS802, and IRAGAFOS P-EPQ, which are all available from Ciba Specialty Chemicals. More preferable is at least one selected from phosphoric acid, citric acid, dibutylhydroxytoluene, butylhydroxyanisole, IRGANOX 1010, IRGANOX 1035, IRGANOX 1076 and IRGANOX 1330, and/or combinations of two or more thereof. The antioxidant may be added in an amount of 0.05 to 5wt.% with respect to weight of the polyurethane prepolymer.

[63]

[64] Preparation of foaming composition

[65] As a foaming agent, a foaming composition is prepared by mixing water, a cross- linking agent and a surfactant. The foaming composition may comprise 60 to 120 wt. parts of deionized water, 0.5 to 40 wt. parts of a cross-linking agent and 1 to 10 wt. parts of a surfactant. If necessary, the foaming composition may further include 0.01 to 2 wt. parts of a pigment, 0.01 to 20 wt. parts of a drug(s) and 0.1 to 40 wt. parts of a moisturizer and/or an absorption enhancer.

[66] The cross-linking agent includes gljcerin, trimethylolpropane, 1,2,4-butane triol and sorbitol, without being limited thereto, which may be used alone or as a combination of two or more thereof. The cross-linking agent functions to improve mechanical properties of the polyurethane foam through cross-linkage during formation of the foam.

[67] The surfactant may be applied according to a conventional method and usage of the surfactant is well known in the art. For example, ethyleneoxide/propyleneoxide block copolymers may include F-68, F-87, F-88, F- 108 and F- 127, which are all available from BASF Corp., while silicon based surfactants may be exemplified by L-580, L- 603, L-688, L-5420, SZ-1703, L-6900, L-3150, Y-7931, L-1580, L-5340, L-5333, L- 6701, L-5740M, L-3002, L-626, etc. The surfactant may control a size of pores in a wound contact layer 11 and an inner absorptive layer 12 of a polyurethane foam dressing, as well as open porosity of the pores. In particular, F-68 as the ethyleneoxide/propyleneoxide block copolymer available from BASF Corp. is well known as the most preferable surfactant that does not damage human tissue, aids in wounds washing, and is non-toxic.

[68] The present invention may also use a moisturizer to maintain a moist environment around the wound, thereby substantially inhibiting formation of a hardened scab over the wound while facilitating wound healing. Therefore, the term "moisturizer" as herein used means not only commonly known moisturizers but also wound healing aids that maintain a moist wound environment to inhibit formation of a scab to cover a wound while allowing early wound healing. Such a moisturizer is not particularly limited but includes, for example: propyleneglycol alginate; methylcellulose; sodiun carboxymethylcellulose; calciun carboxymethylcellulose; sodiun carboxymethyl starch; sodiun alginate; arrmoniun alginate; potassiun alginate; calciun alginate; sodiun caseinate; guar gun; locust bean gun; xanthan gun; cyclodextrin; gun Arabic; gellan gun; carrageenan; gun karaya; casein; Tara gun; Tamarind gun; Tragacanth gun; pectin; glucomannan; gun ghatti; arabinogalactan; furcelleran; pullulan; glucosamine; carboxymethyl cellulose; chitin; chitosan; hyaluronic acid; amino acid; L-aspartic acid; sodium L-aspartate; DL-alanine; L-isoleucine; lysine hydrochloride; glycine; glycerin; L-glutamine; L-glutamic acid; L-glutamic acid sodium; pyridine acid; L-threonine; sericine; serine; L-tyrosine; heparin; sodiun chondroitin sulfate; gelatin, and the like, which are each added to a foaming mixture in an amount typically used according to conventional methods within the scope defined above.

[69] Among the above moisturizers, celluloses such as carboxymethyl cellulose may improve mechanical properties of a final product, compared to typical products without the moisturizer. This is substantially considered a "filler," which means a material added to prevent ageing, reinforce performance and/or increase dose of the product in practical uses of rubber or plastic products. For example, when the polyurethane film undergoes a shape-forming process together with urea formalin resin or phenol resin in synthetic leather production, the resin alone does not have sufficient strength. As a result, many of the conventional technologies have produced resins with reinforced mechanical properties by adding cellulose, asbestos, wood flour, etc. [70] The term "drug" as herein used includes not only typical drugs and antibiotics but also wound healing aids with exhibiting bacteriostasis and promoting proliferation of granulation tissue. Therefore, the drug used in the present invention may also include sugars which are well known to exhibit bacteriostasis and to promote granulation tissue proliferation. Such sugars are not particularly limited but include sucrose, sorbitol, mannitol, fructose, glucose, xylitol, lactose, maltose, maltitol, trehalose, etc. The wound healing aids promoting granulation tissue proliferation may include fibroblast growth factor (FGF), hepatocyte growth factor (FCF), epidermal growth factor (EGF), and so on.

[71] The drug may include, especially, natural materials which are well known to exhibit anti- inflammatory, anti-bacterial, anti-fungal and/or skin regeneration effects. Such materials include, for example: bioflavonoids derived from tea tree oil, Sophora An- gustifolia extract, iris extract, Gljcyrrhiza Glabra extract and/or grapefruit seed extract; naringin; polypeptides; tocopherols; asiatic acid derived from Centella Asiatica; and plant derived natural ingredients such as madecasic acid, β-glucan derived from mushrooms, Neem extract, Witch hazel extract, allantoin, Portulace oleracea extract, Ponciri fructus extract, phytosphingosin, aloe extract and the like. These natural materials may be used alone or as a combination of two or more thereof and added to the foaming composition of the present invention in an amount typically used according to conventional methods within the scope defined above.

[72] Moreover, other known antibiotics may be used to inhibit saprophyte infection and growth. For example, the foaming composition of the present invention may include silver sulfadiazine, povidone iodide, iodine, ionic iodide, fradiomycin sulfate, acrinol, chlorhexidine, benzalkoniun chloride, benzenetoniun chloride, fucidic acid and salts thereof, etc., in an amount typically used according to conventional methods within the scope defined above.

[73] If necessary, the dressing of the present invention may further include other known drugs for purposes of treatment and/or protection.

[74]

[75] Meanwhile, the foaming composition described above may include an absorption enhancer such as super absorbent polymers commonly used in the art in order to improve absorbability of the polyurethane foam according to the present invention within the scope defined above.

[76] In addition, the foaming composition of the present invention may include additives with traditionally known effects such as a stabilizing agent, a preservative, a physical property regulator and the like in a small amount for desired purposes thereof. [77] [78] Preparation of foaming mixture and formation of polvurethane foam layer

[79] 50 to 150 wt. parts of the foaming composition was added to 100 wt. parts of the polyurethane prepolymer prepared above and the mixture was stirred at high speed. The prepared foaming mixture was fed over a silicon release sheet 30A, which was fixed at a certain angle. The foaming mixture was foamed while flowing along an inclined surface of the release sheet, thus forming a polyurethane foam layer. The release sheet is preferably fixed at an angle of 30 to 70 to a straight line along which the foaming mixture was fed. If the angle is below 30°, the foaming mixture poorly flows over the inclined surface of the release sheet and is difficult to form a shaped pro duct. When the angle exceeds 70°, the foaming mixture flows too quickly over the inclined surface of the release sheet thereby causing a problem in shape-forming. Since the slope angle is defined in the desired range sufficient to suitably feed the foaming mixture over the release sheet, the present invention can continuously manufacture products with a constant thickness without a limited "pot life." FIG. 17 shows that the foaming mixture is fed over the release sheet 30A fixed at a desired angle "d".

[80] The formed foam layer was subjected to a lamination step, preferably, in a tacky gel state before being cured. That is, the polyurethane foam layer was combined with a polyurethane film layer immediately after the foam layer was formed in a tacky gel state on the release sheet. Accordingly, the lamination of the foam layer on the polyurethane film layer was simply achieved without any alternative process using an adhesive agent or a sticking agent, resulting in improved efficiency of the lamination process.

[81] The release sheet used in the present invention preferably includes a polymeric film or a paper release sheet, both being surface treated with silicon.

[S]

[83] Lamination (preparation of polvurethane foam dressing)

[84] After the prepared polyurethane foam layer was combined with the polyurethane film layer prepared as described above, the laminated layers were pressed at a constant gap therebetween to control a thickness of a foam dressing. The lamination of the polyurethane foam layer on the polyurethane film layer was simply performed without additional adhesives and/or sticking agents since the polyurethane foam layer was in the tacky gel state before being cured. Fbwever, the lamination process used in the present invention is not particularly limited and may include conventional methods such as use of adhesives or sticking agents, application of pressure, etc.

[85] Preferably, after laminating the prepared foam layer on the polyurethane film layer and drying the laminate in a hot air dryer at 10(FC for 1 minute, the release sheet was peeled from the film layer. The laminate is often preferably subjected to a following curing step after the hot air drying. This is because the resulting polyurethane foam dressing curls due to shrinkage if the laminate is directly cured in the hot air dryer without the hot air drying step, thereby causing difficulty in winding the foam dressing in a roll form. Another reason is that may inhibit evaporation of moisture remaining in the foam layer. If the moisture is not suitably removed, a wound contact layer of the polyurethane foam dressing has problems of decreased absorption and low absorption rate. Removing the release sheet attached to the film layer after the hot air drying yielded a polyurethane foam dressing of the present invention, which has only the release sheet in contact with the polyurethane foam layer. The release sheet in contact with the polyurethane foam layer is peeled off when the foam dressing is applied to a patient such that a side of the foam layer having the release sheet peeled off and directly contacts the patient's wound.

[86] According to an exemplary embodiment of the present invention, the polyurethane prepolymer and the foaming composition were agitated at 3,000 rpm to form a foaming mixture, which in turn, was fed over the release sheet fixed at a constant angle. After about 2 minutes, the foaming mixture applied to the release sheet began to form a tacky gel-like polyurethane foam. In this case, bringing a moisture permeable waterproof film in contact with a laminating face of the polyurethane foam layer, (which is the opposite side to the release sheet), to directly form a laminate thereof, followed by drying in a hot air dryer at 100⁰C for 3 minutes.

[87]

[88] Ageing

[89] The polyurethane foam dressing obtained from the previous lamination step, may further be subjected to an ageing step using the hot air dryer.

[90] According to an exemplary embodiment of the present invention, after hot air drying in the lamination process, the release sheet in contact with the film layer was peeled from the polyurethane foam layer. The foam layer was aged in the hot air dryer at 50 to 7O⁰C for a certain period of time. As a result of the ageing step, the polyurethane foam dressing shrank some extent and, at the same time, the film layer laminated on an outer side of the polyurethane also shrank to create natural wrinkles. Alternatively, using a specific release sheet with wrinkles such as AR-175 available from Asahi Roll Co., Ltd. may result in similar effects as described above. Moreover, the ageing process effectively increases mechanical properties of the foam dressing such as tensile strength, modulus of elongation, etc.

[91]

[92] Surface modification of polvurethane foam

[93] The polyurethane foam prepared in the previous steps, was impregnated with a moisturizer and/or dried, followed by oxygen plasma treatment to increase hydrophilic properties and, thus, absorption rate thereof.

[94] The moisturizer may include, for example, glycerin, triacetin, propyleneglycol, sorbitol, polyethyleneglycol, etc., which may be used alone or as a combination of two or more thereof. Especially, since glycerin content is proportional to pretreatment effects, the polyurethane foam is preferably impregnated with a mixture comprising 5 to 20wt. parts of glycerin in lOOwt. parts of 50% ethanol solution. In addition to ethanol, methanol, isopropyl alcohol and the like may be used, although ethanol is most preferable.

[95] The oxygen plasma treatment is suitably conducted for 10 seconds to 2 minutes and, more preferably for 30 to 60 seconds.

[96] Surface modification may be accomplished by any one selected from the use of moisturizer and the oxygen plasma treatment and/or a combination thereof such that the oxygen plasma treatment is carried out after moisturizing the polyurethane foam. The combined treatment is more preferable in view of surface modification effects. The surface modification is preferably carried out after completion of the manufacture of foam dressing through the steps described above, however, the present invention is not limited thereto. If necessary, the surface modification may be performed in any one of following steps after preparing a foam layer.

[97] According to an exemplary embodiment of the present invention, the polyurethane foam was fixed on a sample fixing part. A rotary vane vacuum punp was used to apply a vacuun to a reactor. A flow rate controller controlled the internal pressure of the reactor by oxygen injection. After the reactor pressure was set to 250 mTorr, oxygen was injected to the reactor for 10 minutes to generate oxygen plasma for 30 to 60 seconds, which in turn, was used to treat a surface of the polyurethane foam.

[98] FIGS. 14 to 16 are graphs illustrating absorption rate behaviors of the polyurethane foam dressing according to the present invention. As shown in the graphs, saturated absorption of the foam dressing is proportional to oxygen plasma treatment time. Also, a foam dressing treated with oxygen plasma after impregnating the dressing with a moisturizer such as glycerin and drying, exhibited shorter time reaching the saturated absorption than that of a foam dressing prepared without a pre-treatment using the moisturizer. From FIG. 16, it was found that, even without the oxygen plasma treatment, concentration of glycerin in a solution for impregnation of a dressing is proportional to the saturated absorption.

[99]

[100] Structure of polvurethane foam dressing

[101] The polyurethane foam dressing of the present invention manufactured by the previous process includes a foam layer comprising polyurethane foam and a polyurethane film layer, wherein the foam layer is divided into two layers. Hereinafter, a detailed description of a structure of the polyurethane foam dressing will be given.

[102] FIGS. 1 to 4 are schematic views illustrating a polyurethane foam dressing according to an exemplary embodiment of the present invention. FIG. 1 is a schematic cross- sectional view showing the polyurethane foam dressing, which comprises a foam layer 10 and an outer film layer 20 made of waterproof polyurethane. The foam layer 10 is characterized by a bilayer structure that includes a skin contact layer 11 having microfine open cells with a diameter of 1 to 50/M and an internal absorptive layer 12 having a nunber of open cells with a diameter of 1 to 1,000/M. In particular, the open cell has numerous pores perforating the open cell. Each of the pores has an average diameter of 1 to 50/M.

[103] FIG. 2 is a schematic view showing the polyurethane film layer 20. This layer is formed by defoaming polyurethane resin using a vacuun agitation defoaming device to remove air bubbles, applying the defoamed resin to a matt release sheet 30B, and drying the coated sheet. The polyurethane resin used in this case may include moisture permeable waterproof polyurethane resin having at least one hydrophilic group in a main chain, which is substantially identical to polyurethane resin used in preparing the polyurethane foam layer, thereby producing a polyurethane film layer that is both moisture permeable and waterproof.

[104] FIG. 3 is a schematic view showing a polyurethane foam layer 10. The polyurethane foam layer 10 is prepared by mixing a polyurethane prepolymer and a foaming composition, stirring the mixture at a high speed and feeding the homogeneous mixture over a silicon treated release sheet 30A fixed at a certain angle such that the mixture is foamed while flowing over an inclined face of the release sheet. The foam layer is divided into two layers 11 and 12 naturally formed due to difference in pore conditions, by mixing the polyurethane prepolymer and a foaming composition and allowing the mixture to come into direct contact with the release sheet 3OA to form a skin layer. The mixture forms finer open cells in a region in contact with the release sheet 30A than in a region in contact with the skin layer. The contact region with finer open cells is called 'a wound contact layer 11' while another region with a nunber of larger open cells is 'an absorptive layer 12.' The absorptive layer 12 mainly serves to absorb wound exudates in the polyurethane foam dressing.

[105] FIG. 4 is a schematic view showing a polyurethane foam dressing to which a release sheet is attached. The release sheet 30B attached to a film layer 20 is peeled off during production of the foam dressing while another release sheet 30A adhered to a foam layer 10 is removed immediately before using the foam dressing.

[106] In the polyurethane foam dressing of the present invention, the wound contact layer 11 which has microfine open cells with a diameter of 1 to 50/M, absorbs wound exudates while not adhering to the wound. The absorptive layer 12 at an inner side of the foam dressing, which has a plurality of open cells with a diameter of 1 to 1,000/M, can absorb and hold 100 to l,000wt.% of liquid fractions therein and has a density of 0.1 to 0.8g/cnf . Both of the open cells have pores that perforate the open cells and have an average diameter of 1 to 50/M. The film layer as a moisture permeable waterproof film at an outer side of the foam dressing, has high moisture permeability of 400 to 3,000g/m7day (with relative humidity of 10 to 90% at 3TC as determined by the Desiccant Method), inhibits invasion of bacteria and/or viruses from the outside, prevents exudates from leaking from the dressing, and forms a moist environment around the wound.

[107] FIGS. 1 to 4 are only given for illustration of the polyurethane foam dressing according to the present invention and the foam dressing of the present invention can be manufactured in various dimensions and/or morphologies according to uses and requirements thereof.

[108]

[109] Hereinafter, the present invention will be described in more detail in conjunction with specific examples and comparative examples. Fbwever, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

[HO]

[111] EXAMPLES [112] Synthesis Examples 1 to 3: synthesis of polvure thane prepolvmer [113] A polyurethane prepolymer was synthesized under conditions and methods according to the following Table 1 :

[114] Table 1 [Table 1]

[115] [116] As shown in the Table 1, it was found that addition of a chain extender such as ethyleneglycol or 1,4-butandiol and/or an increased content of hard segment increased the viscosity of the polyurethane prepolymer.

[117] [118] Synthesis Example: synthesis of moisture permeable waterproof polyurethane resin

[119] A moisture permeable waterproof polyurethane resin was synthesized under conditions and methods according to the following Table 2:

[120] Table 2 [Table 2]

[121] [122] Preparation Example: preparation of moisture permeable waterproof polyurethane film

[123] To 100 wt. parts of a moisture permeable waterproof polyurethane resin prepared as shown in Table 2 were added 50 wt. parts of methylethylketone, 15 wt. parts of dimethylformamide and 5 wt. parts of a pigment, followed by mixing and stirring to prepare a polyurethane mixture.

[124] The polyurethane mixture was applied to a matt release sheet available from Youlchon Chemical Co., Ltd. to a predetermined thickness using a thickness gauge. The sheet was dried in a hot air dryer at 100°C for 30 minutes to form a moisture permeable waterproof polyurethane film on one surface of the matt release sheet. The formed moisture permeable waterproof polyurethane film had a thickness of 20/M. [125] [126] Preparation Examples 1 to 3: preparation of foaming composition [127] Foaming compositions No. 1, 2 and 3 were prepared under conditions according to the following Table 3:

[128] Table 3 [Table 3]

[129] [130] Production Examples 1 to 21: production of polvurethane foam dressing

[131] (1) To 100 wt. parts of the polyurethane prepolymer prepared in the previous synthesis examples was added 80 wt. parts of the foaming composition prepared in the previous preparation examples under stirring at 3,000 rpm for 10 seconds. The foaming mixture was fed over a silicon release sheet A available from Youlchon Chemical Co., Ltd., which was fixed at an angle of 45°, to flow along an inclined surface of the sheet. The prepolymer and the foaming composition as well as processing conditions are shown in the following Table 4. Foaming compositions No. 1, 2 and 3 were prepared under conditions according to the following Table 4.

[132] (2) 2 minutes after flowing the foaming mixture along the inclined surface of the sheet as described above, a polyurethane foam layer with a certain thickness in a tacky gel state was observed. The moisture permeable waterproof polyurethane film with a thickness of 20/M was laminated on the resulting polyurethane foam layer such that a gap with a controlled width was kept therebetween. The laminate was pressed while maintaining the gap so as to control a thickness of a final product and then dried in a hot air dryer at 100°C for 3 minutes. The thickness and mechanical properties of the polyurethane foam layer before ageing are shown in the following Table 4. [133] (3) After drying the laminate, a matt release sheet B provided on the moisture permeable waterproof polyurethane film was peeled off and the resulting laminate was aged in a hot air dryer at 7(FC for 24 hours to produce a polyurethane foam dressing. Thicknesses of the polyurethane foam dressing and an outer film layer of the dressing as well as physical properties after ageing are shown in the following Table 4.

[134]

[135] Processing Example: Oxygen plasma treatment

[136] Each of the polyurethane foam dressings produced in the previous production examples was subjected to oxygen plasma treatment using a plasma reactor Model EPPS 2000 available from PLASMART Inc. for 30 seconds and 60 seconds, respectively. The oxygen plasma treatment was performed at a pressure of 250 mTorr. Herein, an internal pressure of the reactor was measured using a vacuum gauge Model 801 (Varian) while a flow rate of fluid was determined using a mass flow controller MFC (Brooks, Japan, Model 5850E). Observation of color plasma lights in the reactor resulted in determination of stable plasma generation. Table 4 also includes times required for the oxygen plasma treatment of the polyurethane foam dressings prepared in the previous production examples.

[137]

[138] Processing Example: moisturizer treatment

[139] 5, 10 and 20 wt. parts of glycerin as a moisturizer, respectively, were added to 100 wt. parts of 50% ethanol solution, thereby preparing three (3) mixtures with different concentrations of glycerin. Each of the polyurethane foam dressings produced in the previous production examples was impregnated with each of the mixtures for 1 minute, followed by drying in a vacuun dryer at 8O⁰C for 24 hours. The concentrations of glycerin in this processing example are shown in the following Table 4.

[140] Table 4

[Table 4]

[141] [142] Experimental Example [143] Physical properties of the polyurethane foam dressings produced in the previous production examples as well as polyurethane foam dressings produced in the following comparative examples were determined according to test procedures illustrated as follows. Test results are shown in the following Table 5. Moreover, internal structures of the polyurethane foam dressing according to the present invention as well as commercially available polyurethane foam dressings were observed by microscopy. These results are shown in FIGS. 5 to 13. Also, absorption rate behaviors of the polyurethane foam dressings manufactured as final products are shown in graph form in FIGS. 14 to 16.

[144] [145] (1) Mechanical properties (tensile strength, modulus of elongation)

[146] Mechanical properties of a polyurethane foam layer without an outer moisture permeable waterproof polyurethane film layer were measured using a universal test machine (Instron) under conditions of: 5ON load cell, a gauge width of 20mm, a gauge length of 30mm and a cross head speed of lOOmm/min.

[147] (2) Saturated absorption time (sec)

[148] A sample of the foam dressing was prepared with a size of 3cmx3cm and left at room temperature for 24 hours. Then, after dipping and storing the sample in distilled water at 3TC, the sample was subjected to measurement to determine time when the weight of the sample no longer increased.

[149] (3) Moisture absorption

[150] Moisture absorption of the foam dressing was measured using a thermohydrostat SH- CTH 150 available from SAMHEUNG INSTRUMENT according to ASTM E 96-94 (desiccant method). The thermohydrostat had a temperature of 37C+2 and a relative humidity of 80%+5.

[151] (4) Morphology

[152] Observation of the polyurethane foam dressing according to the present invention using a scanning electron microscope (SEM) resulted in determination of shapes of open cells and pores in the foam dressing and a thickness of the film layer in the foam dressing.

[153]

[154] Comparative Example 1

TM

[155] For comparison of the physical properties, a foam dressing, CAREFOAM commercially available from SAERON Pharmaceutical Co., LTD. was used. The physical properties of this foam dressing were measured according to the above experimental example. Test results are shown in the following Table 5.

[156]

[157] Comparative Example 2

TM

[158] For comparison of the physical properties, a foam dressing, ALLEVYN commercially available from SMITH & NEPHEW was used. Test results are shown in the following Table 5.

[159] Table 5 [Table 5]

* Conventional products' tensile strength and modulus of elongation were measured for the product having an outer film layer

[160] [161] As can be seen from Table 5 and FIGS. 14 to 16, it was confirmed that the foam dressing faster reaches saturated absorption with increase of the oxygen plasma treatment under the same condition. Increased saturated absorption increases the speed of wound exudate absorption and exudate retention. For the foam dressing without the moisturizer and the oxygen plasma treatment in Production Example 7, it was observed that the foam dressing had an absorption equilibriun time of 115 sec. Fbwever, the foaming dressing treated by the oxygen plasma for 30 seconds in Production Example 8 exhibited a remarkably improved absorption equilibrium time of 85 sec. Likewise, for the foaming dressing treated by oxygen plasma for 60 seconds in Production Example 9, the absorption equilibriun time was 70 sec, which is considerably shorter than that of the foam dressing without the oxygen plasma treatment in Production Example 7. Compared to the foam dressings with only the oxygen plasma treatment in Production Examples 8 and 9, the foam dressings manufactured in Production Examples 11 and 12, which moisturize the foam dressing in a mixture comprising 5 wt. parts of gljcerin in 100 wt. parts of 50% ethanol solution and then, perform the oxygen plasma treatment, exhibited reduced absorption equilibrium times of 70 sec and 60 sec, respectively. Alternatively, it was found that the foam dressings manufactured in Production Examples 13 and 14, including only a pre-treatment that impregnates the foam dressing with a high concentration moisturizer such as gljcerin and dries the impregnated foam dressing, without the oxygen plasma treatment, also exhibited greatly reduced times required to reach saturated absorption. Therefore, it is understood that time taken to reach saturated absorption can be appropriately controlled by regulating the duration of oxygen plasma treatment and/or the concentration of moisturizer, or by impregnating the foam dressing with the moisturizer.

[162] Referring to Production Examples 1 to 7, it is identified that, when a chain extender such as ethylenegljcol or 1,4-butandiol is added to polyurethane prepolymer during synthesis thereof, improvement in physical properties of the prepolymer is proportional to a content of hard segment while the time required to reach the saturated absorption time is reversely proportional to the content of hard segment. Additionally, if a triol compound such as gljcerin as a cross-linking agent is added, the foam dressing exhibits increased cross-linking, thus improving physical properties thereof. As a result, it is expected that the foam dressing can have controlled physical properties depending on the content of hard segment and whether the cross-linking agent is added or not.

[163] Referring to Production Examples 15, 16 and 17, the foam dressing manufactured by pressing a thickness control gap many times to cause a decrease in sizes of open cells and a reduction in nunber of pores perforating the open cells shows reduced saturated absorption rate. IHbwever, referring to Production Example 18, 19 and 20, it is confirmed that the oxygen plasma treatment and/or the pre-treatment using a moisturizer can preferably improve the saturated absorption rate of the foam dressing. Additionally, as the nunber of times that the thickness control gap is pressed increases, the sizes of the open cells and pores are substantially reduced while increasing a density of foam materials in the foam dressing, resulting in improved physical properties of the foam dressing.

[164] Referring to Production Examples 1 and 3, it is found that addition of carboxymethyl cellulose to a foaming composition improves physical properties of the foam dressing, compared to foaming compositions without carboxymethyl cellulose.

[165] Consequently, it is understood that mechanical properties of a polyurethane foam dressing can be controlled by various parameters such as addition of a chain extender, a content of hard segment, addition of a cross-linking agent and/or powdery additive such as carboxylmethyl cellulose, control of gap in a thickness control part of the foam dressing, etc. and, in addition, a polyurethane foam dressing with different physical properties and other features can be manufactured by adopting an oxygen plasma treatment and/or using a moisturizer.

[166]

[167] FIGS. 5 to 8 are SEM photographs showing polyurethane foam dressings of the present invention, in particular, FIGS. 5, 6, 7 and 8 illustrate SEM photographs of the polyurethane foam dressings manufactured in Production Examples 15, 16, 17 and 21, respectively. A in the figures represents an internal absorptive layer 12, while B represents a wound contact layer 11. The internal absorptive layer is larger than the wound contact layer. The internal absorptive layer has larger and more open cells and pores perforating the open cells than those in the wound contact layer. Also, it can be observed that repeatedly pressing the thickness control gap results in a decrease in sizes of open cells in the absorptive layer, an increase in nunber of skin layers at the wound contact layer, a variation in shape of the open cell from a round form to an elliptical form, and a reduction in number of the perforated pores. The above structure may not be effective to absorb wound exudates. Fbwever, this is not important since a foam dressing shows an improvement of saturated absorption rate through surface modification by pre-treatment using a moisturizer and/or oxygen plasma treatment.

[168] FIG. 9 is SEM photographs showing a polyurethane foam dressing, MEDIFOAM-N

TM available from IL DONG Pharmaceutical Co., LTD. (LOT. 01N22506, Date of manufacture: Feb. 7, 2006, Korea). "A" shows an internal absorptive layer with homogeneous and microfine open cells, while "B" shows a wound contact layer having a number of skin layers S with no open cells and including very small open cells, thus, can be clearly distinguished from conventional products. [169] FIG. 10 is SEM photographs showing another polyurethane foam dressing,

TM

MEDIFOAM-F available from IL DONG Pharmaceutical Co., LTD. (LOT. 02F01007, Date of manufacture: April 5, 2007, Korea). This is manufactured by preparing a block form dressing using a mold and removing a skin layer from the dressing using a horizontal cutter. The foam dressing includes an internal absorptive layer and a wound contact layer which have substantially the same structure. If there are too many open cells in the wound contact layer and/or the open cells are too large, although the foam dressing can have large open cells on a skin facing side, thus improving absorption rate of wound exudates, the skin facing side may adhere to epithelial tissue regenerated at or around a wound site, thus, cause a problem of pain or secondary damage during removal of the dressing.

[170] FIG. 11 is SEM photographs showing another polyurethane foam dressing,

ALLEVYN™ available from SMITH & NEPHEW (LOT. 0611 60229, Date of manufacture: March 13, 2006, United Kingdom). Similar to other conventional products, this dressing has open cells and perforated pores through the open cells and the open cells are somewhat large. Also, "B" as a wound contact layer has at least one skin layer S formed by laminating polymer films in a net form.

[171] FIG. 12 is SEM photographs showing another polyurethane foam dressing,

CAREFOAM ™ available from SAERON Pharmaceutical Co., LTD. (LOT.C05002, Date of manufacture: December 22, 2005, Korea). This is similar to the foam dressing shown in FIG. 10, but, has open cells with irregular sizes and morphologies compared to the foam dressing shown in FIG. 10. Additionally, since there are too many open cells in a wound contact layer and the open cells are too large, the open cells on a skin facing side may adhere to epithelial tissue regenerated at or around a wound site, thus, cause a problem of pain or secondary damage during removal of the dressing.

[172] FIG. 13 is SEM photographs showing another polyurethane foam dressing,

TM

BIATAIN available from COLOPLAST Wounded Care (LOT. 743794, Date of manufacture: March, 2006, Denmark). This dressing has an internal absorptive layer with a structure similar to that of the dressing shown in FIG. 8. Fbwever, a wound contact layer of the dressing has a nunber of open cells containing a few skin layers S.

[173]

[174] As apparent from the above detailed description, the polyurethane foam dressing manufactured according to the present invention has different morphologies. The present invention can provide a variety of polyurethane foam dressings with appropriate structure and absorption rate depending on states and conditions of various wounds. If necessary, hydrophilic properties of the polyurethane foam dressing may be controlled by surface modification such as pre-treatment using a moisturizer, oxygen plasma treatment, etc.

[175]

Industrial Applicability

[176] According to the present invention, there is provided a method, comprising: mixing a hydrophilic polyurethane prepolymer, deionized water, a surfactant and/or a cross- linking agent under stirring at high speed to prepare a foaming mixture; feeding the foaming mixture over a silicon release sheet fixed at a certain angle such that the foaming mixture is foamed while flowing over an inclined surface of the release sheet; and laminating the resulting polyurethane foam layer in a tacky gel state on a moisture permeable waterproof polyurethane film layer then pressing the laminated foam dressing while maintaining a certain gap therebetween to regulate a thickness of the foam dressing. As a result, the method of the present invention has advantages such as noticeably improved productivity and processing efficiency. Especially, the method of the present invention allows mass production of foam dressings as 'pot life' is unlimited, thereby considerably reducing production costs and enabling sufficient supply of low cost foam dressings with improved physical properties.

[177] Additionally, after impregnating the prepared polyurethane foam with a moisturizer and drying, the resulting foam is subjected to oxygen plasma treatment to improve absorption rate thereof, thereby producing a polyurethane foam dressing with enhanced performance. Also, controlling conditions for surface modification such as a time required for oxygen plasma treatment, concentration of the moisturizer and/or depending on whether the foam dressing is impregnated with the moisturizer or not, it is possible to manufacture a variety of foam dressings with appropriate absorption rates depending on conditions and states of various wounds.

[178] The present invention can considerably improve productivity of foam dressings by adopting novel and efficient processes and also provide a polyurethane foam dressing that has superior physical properties to expensive foam dressings manufactured by conventional methods and is capable of being easily formed in various shapes and different sizes.

[179]

[180] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

[1] A method for manufacturing a polyurethane foam dressing comprising:

(a) adding 20 to 70 parts by weight ("wt. parts") of methylethylketone and 5 to 30 wt. parts of dimethylformamide to 100 wt. parts of polyurethane resin, removing air bubbles from the mixture, applying the mixture to a release sheet, and drying the coated sheet to prepare a non-porous waterproof polyurethane film layer;

(b) introducing isocyanate into a mixture including polyol, diol and an antioxidant, and allowing reaction therebetween to prepare a polyurethane prepolymer;

(c) preparing a foaming composition comprising 60 to 120 wt. parts of deionized water as a foaming agent, 0.5 to 40 wt. parts of a cross-linking agent and 1 to 10 wt. parts of a surfactant;

(d) mixing 50 to 150 wt. parts of the foaming composition obtained in step (c) with 100 wt. parts of the polyurethane prepolymer obtained in step (b) under stirring at a high speed to prepare a foaming mixture;

(e) feeding the foaming mixture obtained in step (d) to a release sheet fixed at a certain angle such that the foaming mixture flows along an inclined surface of the release sheet and is foamed to produce a tacky gel type polyurethane foam layer before being cured to a thickness of 1 to 20mm; and

(f) laminating the polyurethane foam layer obtained in step (e) on the non-porous waterproof polyurethane film layer and pressing the combined laminate while maintaining a certain gap therebetween to regulate a thickness of the foam dressing.

[2] The method according to claim 1, wherein the release sheet is fixed at an angle ranging from 30 to 70°.

[3] The method according to claim 1, wherein step (f) includes hot air drying the laminate after laminating the polyurethane foam layer on the polyurethane film layer.

[4] The method according to claim 1, further including: ageing the polyurethane foam dressing in a hot air dryer after step (f).

[5] The method according to claim 1, wherein the foaming composition further includes 0.01 to 20 wt. parts of a drug(s).

[6] The method according to claim 1, wherein the foaming composition further includes 0.01 to 20 wt. parts of an absorption enhancer and a moisturizer.

[7] The method according to any one of claims 1 to 6, further including: impregnating the polyurethane foam layer with a moisturizer then drying the treated foam layer so as to increase absorption rate thereof.

[8] The method according to claim 7, further including: treating the polyurethane foa m layer with oxygen plasma after impregnating the foam layer with the moisturizer and then drying the treated foam layer.

[9] The method according to claim 7 or 8, wherein the moisturizer is at least one selected from a group consisting of: glycerin; triacetine; propyleneglycol; sorbitol; and polyethyleneglycol.

[10] The method according to any one of claims 1 to 6, further including: treating the polyurethane foam layer with oxygen plasma to increase absorption rate thereof.

[11] The method according to any one of claims 1 to 6, wherein polyol has at least two hydroxyl groups and comprises an ethyleneoxide/propyleneoxide copolymer having a molecular weight of 500 to 6,000 with an ethyleneoxide content in a range of 20 to 90%.

[12] The method according to any one of claims 1 to 6, wherein isocyanate is at least one selected from a group consisting of: isophorone diisocyanate; 2,4-toluene di- isocyanate; 2,6-toluene diisocyanate; and methylenediphenyl diisocyanate.

[13] The method according to any one of claims 1 to 6, wherein the diol compound is at least one selected from a group consisting of: ethylene glycol; propylene glycol; 1,3-butanediol; 1,4-butanediol; and 1,6-hexanediol.

[14] A method for manufacturing a polyurethane foam dressing comprising: impregnating polyurethane foam with a moisturizer and drying the treated foam to increase absorption rate thereof. [15] The method according to claim 14, further including: treating the polyurethane foam with oxygen plasma after impregnating the foam with the moisturizer and drying the same. [16] The method according to claim 14 or 15, wherein the moisturizer is at least one selected from a group consisting of: glycerin; triacetine; propylene glycol; sorbitol; and polyethylene glycol. [17] A method for manufacturing a polyurethane foam dressing comprising: treating polyurethane foam with oxygen plasma to increase absorption rate of the foam. [18] A polyurethane foam dressing manufactured by any one of the methods as set forth in claims 14, 15 and 17.