US 3526224 A
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United States Patent  Inventor Richard M. Potts I East Brunswick, New Jersey  Appl. No. 644,583  Filed June 8, 1967  Patented Sept. 1, 1970  Assignee Johnson & Johnson a corporation of New Jersey  DRESSING 4 Claims, 8 Drawing Figs.
 U.S.Cl 128/156, 161/1 12  1nt.C1 A61t'15/00  Field otSearch 128/155, 156,157, 580, 5 17; 161/109, 1 12, 76, 79,150, 151, 88, 89,148; 156/77  References Cited UNlTED STATES PATENTS 2,485,725 10/1949 Francis 161/77 3,253,598 5/1966 Spanel 3,331,728 7/1967 Lane 16l/ll2X 161/112 ABSTRACT: An occlusive dressing designed to act as a synthetic skin, the dressing comprising a laminate of an elastomeric polyurethane film having a water vapor transmission rate within the range of 150 to 500 g/m /24 hours and a sheet of knitted velour fabric. The sheet of velour fabric has a surface of looped pile which is adapted to contact the surface of the wound and into which body tissue will grow during the healing process. The dressing is flexible and the fiber loop surface when placed in intimate contact or engagement with the wound surface eliminates pockets or voids between the dressing surface and the substrate tissue.
Patented Sept. 1, 1970 3,526,224
INVENTOR flaw/=0 M 0775 ATTORNEY DRESSING BRIEF SUMMARY OF THE INVENTION The dressings of the present invention comprise an elastomeric polyurethane film laminated to a knitted fabric velour. The dressings, which are designed to act as a protective skin or membrane over a wound such, for example, as burn wounds, are, because of their structure, both flexible and extensible. They also provide a surface to which underlying wound tissue can adhere while controlling the amount of moisture leaving the surface. The dressings differ from normally conceived dressings in that they are not designed primarily for the absorption of fluids exuding from the wound or solely for protecting the wound from outside contact, but rather are designed to act as an artificial skin permitting natural healing and growth to take place under the dressing. The dressing is then removed after healing, by surgery if necessary. The artificial skin dressing thus protects the wound area permitting normal growth and healing thereunder and prevents excess loss of moisture by the patient through the wound area. The artificial skin dressing may remain in place until the pa- DESCRIPTION OF THE INVENTION For dressings of the synthetic skin type to be satisfactory the same must be sufficiently flexible to allow the surface of the dressing to come into intimate contact with the substrate wound surface over which they are placed. They should also have sufficient flexibility and extensibility to permit movement of the underlying wound surface without separation from the surface of the dressing. Further, the dressings must act as a shield against external contact and/or abrasion thereby giving the protection normally provided by intact skin.
The dressings are of the occlusive type in that the dressings either substantially prevent the escape of moisture from the wound area or permit only a relatively small amount of moisture vapor to escape. Although wound healing has been observed to occur more readily under an occlusive type dressing, one of the difficulties encountered is that in any pocket or open space formed between the dressing surface and the underlying wound tissue bacterial growth becomes excessive. Apparently such areas act as excellent media for the growth of bacteria such as Staphylococcus aureus or Pseudomonas aeruginosa. Where, however, the surface of the dressing is in intimate contact with the underlying tissue and the surface of the dressing is such that adhesion develops in a relatively short time, this adhesion prevents the formation of pockets or voids and bacterial growth between the dressing and the underlying tissue is substantially reduced.
In accordance with the present invention the synthetic skin dressings are prepared by using a film of polyurethane as the moisture barrier in the dressing. Films of this material in thicknesses of one to four mils regulate the escape of moisture from the wound surface in a range such as to give the advantages of occlusive dressings while at the same time permitting some moisture to escape and thus more closely approach the action of normal skin.
The polyurethane films also have the extensible nature of skin in that the same can be readily extended while being slightly elastic so as to return to substantially their original dimension. A still further advantage of utilizing polyurethane film as the moisture barrier in the dressing is that the polyurethane film has the characteristic of binding to itself thus permitting the assembly of two dressing elements through contact and pressure of the film surfaces to provide a composite dressing having a velour surface also on the outside; a structure that is desirable where substantial abrasion of the outer surface may be expected to occur.
In accordance with the present invention the preferred polyurethane films are formed through solvent casting of elastomeric thermoplastic polyurethanes of the block polymer type made from 4,4-diphenylmethane diisocyanate, (MDI), a low molecular weight polyester derived from adipic acid and 1,4-butanediol, and l,4-butanediol. These polymers, which have the following general structure, can be made with varying lengths of polyester and also varying lengths of aromatic blocks:
These materials can be dissolved in tetrahydrofuran, dioxane, cyclohexanone and dimethyl formamide. Many of these polymers are also soluble in acetone and methyl ethyl ketone.
The wound contacting surface of the dressing is formedas previously indicated by the nap surface of a knitted nylon velour in which the fiber on one side of the fabric has been brushed up to form a dense looped pile or nap. This pile provides small interstices or spaces into which the substrate tissue can readily move to produce significant adhesion to the substrate tissue within the first hour of application. Good adherence of the laminate to substrate tissue with virtual freedom from dead spaces or voids is essential to the successful application of a synthetic skin dressing.
Synthetic skin dressings would normally be applied to a wound area using the standard techniques for making living skin grafts which are well known to surgeons skilled in this art. Thus, the synthetic skin dressing may be held in place initially by suitable sutures or skin clips around the periphery as is the usual case in skin grafting, although in some cases the surgeon may choose to use an overlying compress or bandage for this purpose.
The synthetic skin dressing offers several important advantages. It canv be used as a temporary or even semi-permanent replacement for damaged skin. Since it is a manufactured item available in unlimited quantities, it completely avoids the problem of the short supply, or, in the case of extensive burn victims, the completely inadequate supply of autograph skin. The dressing is of a soft, flexible, conformable material which produces a minimum foreign body response. The host tissue will accept it as a completely adequate skin substitute. Due to its small but definite moisture vapor transfer, it allows limited transpiration similar to that of healthy skin while still avoiding the extreme insensible water loss of severe burn victims.
Reference is now made to the drawings wherein are set forth by way of illustration and example certain embodiments of the present invention. Referring to the drawings:
FIG. 1 is a perspective view of a sheet of dressing material made in accordance with the present invention;
FIG. 2 is an enlarged cross-sectional view taken along lines 2-2 of FIG. 1; FIG. 3 is a perspective view of a dressing of the present invention in place on a wound; I FIG. 4 is a microphotograph of a sectional slice througha wound to which a dressing has been applied illustrating the intimate contact of the undersurface of the dressing with the substrate tissue of the wound surface and the growing of tissue into the dressing;
FIG. 5 is a perspective view of a different modification of dressing of the present invention;
FIG. 6 is a cross-sectional view taken along lines 6-6 of the dressing of FIG. 5;
FIG. 7 is a perspective view ofa dressing of FIG. 1 on a carrier sheet; and
FIG. 8 is a cross-sectional view taken along lines 88 of FIG. 7.
Referring to FIG. 1, the dressing 10 comprises a knitted nylon velour fabric 11 having a hooked pile or nap 12 on one side and having laminated to the other side an elastommeric polyurethane film 13.
The synthetic skin dressing 10 is preferably adhered, as best illustrated in FIGS. 7 and 8, to a paper carrier sheet 14 containing a release coating 15 such, for example, as a cured silicone polymer release coating on one surface.
The synthetic skin dressing 10 is carried by the carrier paper 14 through light adhesion of the surface of film 13 to the release coating 15 on the carrier sheet.
Preferably, a portion of the knitted velour fabric 11 extends beyond the film 13 laminated thereto for ready grasping for removal of the dressing 10 from the carrier sheet 14. However, this is not necessary as the dressing 10 can be relatively I easily stripped from the carrier sheet.
In using the synthetic skin dressing the desired dressing size can be cut while still on the support paper 14 or can be cut after removal from such support paper to the size desired by the surgeon. The same is then secured to the wound area, as best illustrated in FIG. 3, by suturing around the edge as indicated at 16. In applying the dressing the edge of the dressing should come up to the edge of the intact skin, fully covering the wound area.
After application of the dressing the underlying tissue 17, during the healing process, is found to grow up into the nap 12 and around and through the loops 18, as best illustrated in FIG. 4. Adherence of the dressing to the underlying wound surface is found to occur within about 1 hour of application after which tissue growth seems to occur in much the same manner as under natural skin.
As previously indicated in some instances, either from the standpoint of appearance, or to give a better wearing surface, it is desirable to have a velour outer covering also present in the synthetic skin dressing when applied. This can be readily accomplished by the surgeon through folding over a section of the synthetic skin dressing illustrated in FIG. 1 onto itself with the two exposed film areas 13 being brought into intimate contact through pressure. If desired, some heat can be employed to obtain a more rapid bond or sealing between the two surfaces. Such a dressing might also be formed by pressing together two separate sheets rather than folding over a single sheet. Such a dressing is illustrated in FIGS. 5 and 6. Referring to FIG. 5, the dressing 19 has a velour 11 on each side. Either surface may be used to cover the wound while the other surface would be the outer surface of the dressing when applied. Such a dressing would comprise in cross section two outer velour surfaces of looped pile 24, the same being secured to the knitted base fabric 21 which contains the polyurethane film 22 bonded thereto, the films 22 in turn are bonded to each other to form a central film portion 23 which controls the occlusive nature ofthe dressing.
If desired, irrigation tubes may be placed between the two film surfaces 22 and the one film 22 which would be on the wound contacting the side of the dressing formed with small perforations. The irrigating tube would be a small perfusion tubing through which a fluid, such as a topical antibacterial fluid, may be introduced so that the same could pass into the bottom layer of the velour facing which is in contact with the wound and thence into contact with the substrate tissue should the surgeon so desire. The bonding characteristics of the polyurethane film, wherein the film is easily bonded to itself, make such film particularly suitable for the construction of such synthetic skin dressings with irrigation channels built therein.
A typical example of a dressing material such as that illustrated in FIG. 1. and its construction is as follows:
A 2 mil polyurethane film is prepared by casting from a solution of a polyester-based polyurethane of the type previously described and sold, for example, under the trade name Eastane 5703. The polymer has a specific gravity of 1.20 (ASTMD-12 27) and the film is cast from a suitable solvent such as methyl ethyl ketone onto a carrier paper having a release coating of a cured silicone resin.
The film so prepared has a M.V.T. of around 300, a Shore A durometer of 70 (ASTMD-676). a tensile strength in excess of 5000 pounds per square inch (p.s.i.)(ASTMD-4l 2), a 300 percent modulus ofless than 500 psi. and an elongation of700 percent. The moisture vapor transmission rate (M.V.T.) is the weight of water lost by evaporation through a film membrane of 25C. over a period of 24 hours. The weight loss is determined by sealing a film over the mouth ofa beaker, containing water. weighing the beaker, letting the beaker stand for 24 hours at atmospheric pressure in an environment having a humidity of 26 percent and temperature of 25C. and then again weighing the beaker to determine weight loss. To the film is laminated a knitted tricot fabric made from 30 denier textured nylon 6.6 yarn. the base of the fabric opposite to the side containing the looped nylon nap being laminated to the film. The lamination of film to velour is preferably carried out before complete drying of the film so that the polyurethane is still tacky with residual solvent. No separate laminating adhesive is required. If desired. however, an alternate method may be used in which the film is completely dried and then laminated with heat under low pressure l 2 psi.) at C. for 2 minutes. The velour knitted tricot fabric is laminated to the film while the same is still on the carrier paper. as best illustrated in FIGS. 7 and 8.
Particular embodiments of the invention have been used to illustrate the same. The invention, however, is not limited to these specific embodimentsv In view of the foregoing disclosure, variations or modifications thereof will be apparent, and it is intended to include within the invention all such variations and modifications except as do not come within the scope of the appended claims.
1. A surgical dressing having a wound adhering surface and a moisture controlling film barrier comprising a laminate of a flexible extensible fabric having a fiber pile on one side thereof formed offibers extending outwardly from the surface of said fabric and a flexible elastomeric polyurethane block polymer film adhered to the other side of said fabric. said polymer film having a water permeability rate of 150 to 500 grams per square meter per 24 hours and said fiber pile forming the wound adhering surface of said film, the extending fibers of said pile providing small interstices or spaces into which wound tissue, when the dressing is applied, can readily move to provide adhesion between said dressing and the underlying wound surface.
2. A dressing of claim 1 wherein said elastomeric polyurethane is a block polymer made from 4,4-diphenylmethane diisocyanate and 1,4-butanediol.
3. A dressing of claim 1 wherein said elastomeric polyurethane block polymer film is laminated to the fabric side of a knitted velour fabric, the nap side of said knitted velour fabric forming the wound adhering surface of said dressing.
4. A dressing of claim 3 wherein said dressing comprises a laminate consisting essentially of a knitted velour fabric, a polyurethane film, a polyurethane film and a knitted velour fabric. the polyurethane film portion of the laminate being in the center thereof and the outer surface of said dressing being formed of the nap of said knitted velour fabrics.