CA1094422A - Polymeric sheets - Google Patents

Abstract

Abstract of the Disclosure A polymeric sheet, useful as a burn dressing, that has an ultra-thin pinhole-free polymeric membrane on one side, formed from two or more layers of polymer, and a fabric texture on the other side, formed from a fabric-textured sheet, embedded in the polymer. The polymeric sheet features physiologic properties similar to human skin, excellent drapability characteristics, and recessed portions which provide a reservoir for debris from a burn. The poly-meric sheet can be made by: (1) applying two or more layers of polymer to a forming surface; (2) partially embedding a sheet having a fabric texture in the top layer of polymer;
(3) curing the polymer to form a composite of the fabric-textured sheet and polymer; and (4) separating the composite from the forming surface.

Description

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Background of_the Invention This invention relates to synthetic medical dressings or coverings for wounds and to processing techniques for preparing such dressings or coverings.
More particularly, it relates to thin drapable sheets of polymeric material which have physiologic properties similar to human skin plus other desirable properties which made the sheets especially useful'in the treatment of thermal wounds, conventionally classified as "burns". The medical problems posed by burn wounds and the general requirements for the successful treatment of such wounds are known to those skilled in the art. See, for example, the discusslon in U.S. Patent 3,648,692, entitled "Medical-Surgical Dressing For Burns And The Like", particularly that at column 1, lines 10-69.
~he major problem with'a burn wound is that the protective layer of skin is either missing or bad'ly damaged at the wound site, so that the normal physiologic functions of the skin are ab~sent or, at be~3t, materially impaired.
Two important physiologic functions of the skin are to serve as an antimicrobial barrier layer to prevent infection and to prevent the undue loss of body fluids, proteins and electrolytes. Once the skin can no longer adequately per-form these functions, the body fluids, proteins and electro-lytes are continuously lost and the invasion of harmful micro-organisms and other harmful agents into the body can proceed with predictable adverse results. For example, normal human skin has a water vapor phase transfer rate of about 2 mg./hr.-cm.2, whereas the rate for burned skin can be 25 to 45 mg./hr.-cm. or ~ven higher during the

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first few hours after the burn. To alleviate these pro-blems, the standard medical treatment for burns involves a combination of therapy and dressing to cover the burn site as soon as possible with a protective layer, the properties of which resemble the burned-away skin. While the use of topical and systemic antibacterial agents can reduce the extent of infection in a burn patient, coverage of the wound site with a skin-like dressing before the onset of infection remains a major factor in burn management.
At the present time, most of the burn dressincs used by the medical profession are either human or animal skin. The more common of these dresslngs are generally referred to as "autografts", "allografts" (also sometimes called "homografts") and "xenografts" (also sometimes called "heterografts"). An autograft is a portion of the burn victim's own skin taken from an uninjured part of the bo~
The limitations of this dressing are apparent, especially in cases where the victim has suffered extensive dermal des-truction. A homograft is skin taken from a cadaver. A
xenograft is skin taken from a different species. Pigskin is the most commonly used xenograft. Autografts are gene-rally preferred to homografts and pigskin xenografts.
The various human and animal skin dressings are expensive and are difficult to s1:ore for prolonged periods of time. Perhaps the most serious disadvantage of such materials, especially of homo~ra-ts, is their limited avai1abi1ity. Over 100,000 burn victims are hospitalized in the United States alone every year. While not all such patients require a covering for :heir burn sites, it is estimated that 50 to 75% of those hospitalized would benefit from such a covering.

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Recently, efforts have been made to develop synthetic burn dressings having physiologic properties similar to human skin which could be ineY.pensively prepared in large quantity and stored for long periods of time without degradation. See, for example, the polyurethane foam burn dressing described in U.S. Patent 3,648,692. Kornberg and his coworkers have described a synthetic burr, dressing com-posed of an ultra-thin (0.5 to 2 mils), pinhole-free silicone rubber membrane, to one surface of which a sheet of spun-bonded nylon, open-weave nylon or double-knit Dacron* is laminated. See "Ultra Thin Silicone Polymer Membrane:
A New Synthetic Skin Substitute", Kornberg et al, Transactions of the American Society of Art ficial Internal Orqans, Vol. 18, pp. 39-44 (1972). The Kornberg et al dressing is impervious to bacteria, inert, non-antigenic, -has a water vapor permeability similar to intact human skin, and is transparent and relatively inexpensive to produce.
Much of the success of the Kornberg et al dressing is attributed to the work of Nora E. Burns on techniques for mass-producing ultra-thin, pinhole-free silicone rubber membranes for use in membrane oxygenatorsO
This work is described in "Production of Silicone Rubber Film for the Membrane Lung", N. Burns, Biomedical Engineer-ng, VolO 4, pp. 356-359 (1969). Briefly, Burns prepares her ultra-thin silicone rubber membranes by applying an extremely thick dispersion of silicone rubber to a moving horizontal surface and spreading the dispersion into a film of uniform thickness using an accurately ground doctoring ~lade. Major processing problems generally arise because of the extreme thinness of the silicone rubber membrane, * Trademark i09~4ZZ
which makes it very difficult to handle without damaging it, and the need for uniform thickness in order to obtain uniform properties throughout the membrane and establish satisfactory quality control.
Among the desired properties of a synthetic burn dressing are that it have water vapor phase transfer rates and anti~microbial barrier layer properties approximating those of human skin, that it adhere well to a wound, and that it preferably have voids in the surface applied to the wound for fibroblastic ingrowth of tissue and to serve as a debris reservoir for necrotic tissue and other debris from the wound, so that such materials are removed from the wound. ~he dressing should also be transparent or trans-lucent, so the progress of the wound can be observed without removing the dressing. Two dimensional elasticity ~s another desira~le property because it permits the dressing to expand and contract if applied to an elbow, knee~or other body location where it is likely that the dressing .
will be flexed. The dressing should be drapable and readily conform to the-shape of the body. It should possess a sufficiently high tensile and tear strength, so that the dressing can be handled and stretched without damage to the dressing. The uniformity throughout the dressing of such properties as the water vapor phase transfer rate and the ~25~ anti-microbial barrier layer properties is also important, as is control of the characteristics of the dressing which affect these properties. Preferably, the dermal surface has .
controlled wicking characteristics to remove some but not all the fluid from the wound site, so as to maintain a medically acceptable, balanced fluid level on the wound site, and, of course, the dressing must be constructed frcm biologically innocuous and inert materials which are acce~t-able to the medical professian for use with human beings.

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It is an object of this invention to provide improved synthetic polymeric wound dressings having the above properties and characteristics.
It is another object of this invention to provide processing techniques for preparing these improved synthetic dressings by which the properties and characteristics of the dressings can be varied in accordance with the contemplated end use of the dressings.
It is another objeet of this invention to provide improved silicone rubber burn dressings and processing tech-niques for preparing such dressings.
These and other objects of the invention will be apparent to those skilled in the art upon a consideration of the specification and attached drawings, taken in their entirety.

Summary of the Invention The above objectives of the invention are accomplished in accordance with the invention by providing a drapable synthetic burn dressing having 1) a fabrie texture on one surface thereof which provides a reservoir for debris from a burn and 2) substantially uniform physiologic properties approximating those of human skin. The burn dressing includes a first layer of cured high-release non-stieking silieone rubber, having a thiekness of about 1 mil or less and forming one surfaee of the burn dressing.
A second layer of eured silieone rubber having a tensile strength and tear strength for a 25 mil thiek cured film thereof of at least about 400 pounds per square inch and at least about 20 pounds per inch, respeetively, is joined to the first layer of silieone rubber. The first and second layers of silicone rubber have a total thickness of about 2 mils or less and form an ultra-thin, pinhole-free, substantial]y non-porous and voids-free membrane. A third layer of fabric texture is joined to the second layer of silicone rubber and forms the other surface of ~-;7 -6-10~4422 the burn dressing. The above burn dressing has a water vapor phase transfer rate of about 2 to 10 mg./hr.-cm , two dimensional elongation of at least about 100~ in each direction, and antl-microbial barrier layer properties.
The third layer of fabric texture may comprise a knit or woven sheet of continuous multifilament strands.
The third layer of fabric texture may be formed of continuous multifilament strands having a polymer at the surfaces of the individual filaments, and the third layer of fabric texture preferably has a two dimensional elongat-ion of about 100 to 300~ in each direction.
The silicone rubber of the first layer may have a 180 degree peel strength less than about 50 grams per inch and preferably of about 40 or less grams per inch and the silicone rubber of the second layer may have a tensile strength and tear strength for a 25 mil thick cured film of at least about 700 pounds per square inch (preferably at least about 750 psi) and at least about 25 pounds per inch (and preferably at least about 25 pounds per inch), respectively. Furthermore, the silicone rubber of the first layer and the silicone rubber of the second layer may be the same silicone rubber.
The layer of fabric texture, joined to the second layer, may comprise substantially oil-free, at least about 70 denier, nylon strands; each strand comprising at least about 18 filaments; the layer of fabric texture havina a weight of at least 10 g./ft.2, a thickness of at least about 20 mils and a wettability, in relation to a 0.004 cc. drop of dye solution, defined by a wetted area of at least about 0.8 cm.2 and an absorption time of about 2 seconds or less; the fabric textured side of the burn dressing having a wettability defined by a wetted area of at least about .~ cm. and an absorption time of less than about 1 minute.

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The first layer of silicone rubber preferably has a thickness of about 0.1 -to 0.3 mil. The second layer of silicone rubber preferably has a thickness of about 0.5 to 1.5 mils. Also, the first and second layers of silicone rubber preferably have a total thickness of about 0.5 to 1.5 mils.
In a further aspect of the invention there is provided a process for preparing a sheet of polymeric material having a fabric texture on one surface thereof, which comprises: (1) applying to a forming surface a liquid containing a high-release non~sticking polymer, to form on the surface a first layer of polymer which upon curing will produce a layer of polymer of about 1 mil or less in thickness that can be separated intact from the surface; (2) applying to the forming surface containing the first layer of polymer a liquid containing a polymer to form a second layer of polymer which upon curing has a tensile strength and tear strength for a 25 mil thick cured film of at least about 400 pounds per square inch and at least about 20 pounds per inch, respectively, and which results upon curiny in an overall thickness of the first and second layers of polymer of about 2 mils or less; (3) embedding one surface of a sheet having a fabric texture-on at least one surface thereof in the second liquid layer of polymer~ with the surface having the fabric texture out of contact with the second layer of polymer; (4) curing the polymer layers while the surface of the sheet of fabric texture is embedded in the second layer of polymer, to form a bonded composite of cured polymer and sheet of fabric texture; and (5~ separating the composite from the forming surface.
Further aspects of the invention are set forth in the claims appended hereto.

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The sheets of the invention can be fabricated with substantially uniform physiologic properties approximating those of human skin. They have excellent strength and two-dimensional elongation characteristics and can be fabricated from biologically inert and medically acceptable materials such as silicone rubber.
The texture of at least one surface of each sheet provides a reservoir for wound debris, so that the debris does not remain in place on the wound site. The sheets are transparent or translucent, easy to handle, and can be stably stored for prolonged periods of time. Their drapability and conformability characteristics are excellent. Because the sheets are prepared from readily available synthetic materials, they can be made available in abundant supply.
The sheets of the invention and the processing techniques for preparing them are described in greater detail below, in conjunction with the accompanying drawings and the description of the preferred embodiments of the invention.

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Brief Description of the Drawin~s Figure 1 is a schematic flow sheet of a preferred embodiment of the invention, showing the preparation of a polymeric sheet having a fabric texture on each surface and containing elongated continuous channels in the interior of the sheet.
Figures lA-lD are enlarged sectional views taken generally along the lines lA-lD in Figure 1, with background structure eliminated for clarity of illustration.
Figures lB', lB'', lC', lC'', lD' and lD'I are enlarged views similar to Figures lB-lD illustra~ing varia-tions in the extent of polymer build-up on the multifilament strands of Figure lA.
Figure 2 is an enlarged ragmentary plan view taken genexally along the line 2-2 of Figure lD.
Figures 3 and 4 are enlarged fragmentary sectional views taken generally along the lines 3-3 and 4-4 of Figures lD' and 2, respectively.
Figure 5 is a schematio flow sheet of another preferred embodiment of the invention, showing the prepara-tion of a polymeric sheet having a coarse fabric texture on one surface only and optionally containiny elongated channels in the interior of the sheet at the fabric side.
Figures 5A-5I are enlarged sectional views taken generally along the lines 5A-5I of Figure 5, with background structure eliminated for clarity of illustration. Figures 5F-5I are e~en more enlarged thar. Figures 5A-5E.

109~4Z2 Figure 6 is a schematic flowsheet of still another preferred embodiment of the invention, showing the prepara-tion of a non-laminated polymeric sheet having a coarse fabric texture on one surface only and optionally containing elongated channels in the interior of the sheet at the fabric side.
Figures 6A-6D are enlarged sectional views taken generally along the lines 6A-6D of Figure 6, with back-ground structure eliminated for çlarity of illustration.
Figures 6C-6D are even more eniarged than Figures 6A-6s.
None of the drawings is drawn to scale or blue-print specification. This is particularly true of Figures 5C to 5I and 6A to 6D, where the thickness of the membrane layers 54, 54' and lll is greatly enlarged for clarity of lS illustration.
Figure 5 occupies sheets 5 and 6 of`the drawings .
- and is best viewed by placing sh~ets 5 and 6 end-to-end along their short dimension, with sheet 6 to the right of sheet 5.
Figures 5A to 5I occupy sheets 7 and 8 of the drawings and are best viewed by placing sheets 7 and 8 end-to-end along their short dimension, with sheet 8 to the right of sheet 7.
Figure 6 ocaupies sheets 9 and 10 of the drawings and is best vi~wed by placing sheets 9 and 10 ~25~ end-to-end along their short dimension, with sheet 10 to the right of sheet 9.
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Figures 6A to 6D occupy sheets 11 and 12 of the drawings and are best viewed by placing sheets 11 and 12 end-to-end along their short dimension, with sheet 12 to the right of sheet 11.

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Description of the P~eferred ~mbodiments The polymeric sheets of the invention are readily understood by a consideration of the processes by which they are prepared.
Polymeric Sheet With A Fabric Texture On Both Surfaces Referring to Figure 1, the initial starting material i5 a sheet 10, preferably having a coarse uneven fabric texture on both sides thereof. Sheet 10 serves as a skeleton or superstructure to carry the polymer from which the sheet of the invention is ultimately formed until such time as the polymer on the skeleton sheet can be cured, rigidified, hardened or otherwise rendered self-supporting.
Thereafter, skeleton sheet 10 is removed by solvent leaching or other suitable techniques, leaving an integral, self-supporting polymeric shell generally conforming in shape to the leached skeleton sheet and containing elongated channels or voids formed by the removal of sheet 10.
Skeleton sheet 10 can be of virtually any type of construction, e.g., woven, knit, molded, mesh, gauze, net-ting, expanded, etc., provided it has a fabric texture on both sides. Thus, for example, sheet 10 can be woven or knit fabric formed of monofilament or multifilament yarn strands. The mesh weave shown schematically in Figure 1 is for purposes of illustration only. Other conventional weaves and knits, such as, for example, the weft knit construction shown in Figure 9 of U.S. Patent 3,463,15~, also provide suitable skeleton sheets.

Preferably, skeleton sheet lO is composed of a plurality of continuous multifilament yarn strands 14 (see Figure l) in which the individual continuous filaments 15 (see Figure lA) forming each strand can be twisted, braided, plaited, laid parallel, or in any other suitable construc-tion. Generally, the axes of strands 14 and filaments 15 are substantially parallel to the plane of sheet 10, with the strands 14 and filaments 15 extending from edge to edge of sheet 10.
The thickness of the skeleton sheet can vary widely, depending largely upon the thickness and other properties and characteristics, such as the water vapor phase transfer rate, desired in the finished polymeric sheet. Illustrative thicknesses of sheet 10 are about 2 to 50 mils, preferably about 5 to 30 mils, particularly about lO to 30 mils, and quite particularly about 20 to 30 mils.
The amount of open-area in the skeleton shbet lO
also can vary widely depending on the extent of open area and other properties and characteristics, such as the water vapor phase transfer rate, desired in the finished polymeric sheet. Illustratively, sheet 10 has an open area of zero to about 60% and prefera~ly about lO to 50~.
The thickness of the multifilament strands 14 making up skeleton sheet 10 and the number and size of the individual filaments 15 in each strand also can vary con-siderably depending largely upon the overall thickness of - the finished sheet and the number and size of the elongate~
channels desired in the sheet. For example, the multifilament strands 14 can vary from about 2 to 100 or more individual filaments per strand having diameters o about 0.1 to 5 mi~s ~09~4ZZ

or more. Preferably, the multifilament strands 14 are less than about 20 mils in diameter and contain 10 to 50 indi-vidual filaments 15 with diameters ranging from 0.5 to 2 mils. When sheet 10 is composed of monofilament strands, each monofilament is illustratively about 1 to 50 mils in diameter and preferably less than about 20 mils in diameter~
The choicé of material from which the skeleton sheet 10 is made is based on the ability of the material to dissolve in a solvent in which the polymer applied to it is substantially insoluble. Consequently, numerous materials can serve as sheet 10. Some illustrative materials for sheet 10 include cellulose; cotton; rayon; silk; linen;
polyamides such as nylon, including nylon velours r poly-esters such as Dacron~ polyacrylonitriles such as Orlon*or Creslan~ halogenated polyalkylenes such as tetrafluoroethylene, Teflon*, Xel-F* and FEP~ polyalkylenes such as polyethylene and polypropylene; polyvinylalcohols; polyvinylacetates;
polyglycolic acid; polylactic acid; metals such as stainless steel; and the like. Sheet 10 is preferably fabricated from a polymeric medically-acceptable material such as nylon.
Skeleton sheet 10 is mounted on a suitable frame (not shown). If sheet 10 is a biaxially stretchable fabric such as a woven or knit mesh, it is desirable to biaxially stretch it somewhat on the frame to the extent of about 5 to 75% in each direction. Stretching sheet 10, while preferred, is not mandatory.
- The stretched skeleton sheet 10 is then immersed one or more times in a bath 12 which can be a solution, dispersion or other suitable form of the polymer from which * Trademark A~

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the finished polymeric sheet is ~o be formed, for a time sufficient to cover sheet 10 with polymer to the extent desired. Figure lA is a greatly enlarged cross-sectional view of the individual multifilament strands 14 in sheet 10 prior to their immersion in ~ath 12. Strand 14 is composed of a plurality of individual monofilaments 15 which are separated from each other by void spaces 16. As sheet 10 is immersed in the bath 12, the ~olution or dispersion of polymer impregnates, penetrates and fills the voids 16 and covers or coats the surfaces of the individual filaments 15 as shown in Figures lB to lB''. The extent to which the strands 14 are also covered or coated by polymer depends upon such factors as the concentration of polymer in the bath and the residence time and num~er of dips of sheet 10 in the bath. Thus, the amount of polymer build-up on sheet 10 can be controlled to produce as thick or as thin an encapsuiating coating 12' of polymer dispersion or solution 12 as desired on strands 14, as shown in Figures lB to lB" .
; This al]ows the open area of sheet 10 to be reduced as much ~20 as desired or even totally eliminated (see Figure lB''), depending on how much polymer is applied to sheet 10.
Figures lB to lB'' show the progressive reduction of the open~space 18 between strands 14 until, in Figure lB'', space 18 is totally eliminated and replaced by a bridge 12'' of~solution or dispersion between adjoining strands 14.
The particular polymer which is selected for application to skeleton sheet 10 depends largely upon the haracteristics and properties desired in the finished polymeric sheet. Any of the numerous polymers which have heretofore been used in or disclosed for use in medical and surgical dreRsings, bandages or other medical products and applications can be employed as coating polymers for ~09~42Z

sheet 10. These polymers are well known to those skilled in the art and need not be repeated in detail herein. Some illustrative polymers include polyurethanes, polyethylenes, polypropylenes, natural rubber, polybutadiene, silicone rubber and other syntheti~ and natural elastomeric polymers, such as those of isoprene, neoprene, chlororoprene, styrene-butadiene and various copolymers of the above.
Silicone rubbers are preferred polymers for appli-cation to skeleton sheet 10. Silicone rubbers are composed of high molecular weight linear polysiloxanes, such as polydimethylsiloxane and other polysiloxanes in which the methyl groups are replaced by groups such as ethyl, phenyl, vinyl and others. A wide variety of useful silicone rubbers of widely varying properties, chemical compositions and cure properties and characteristics are available com~.. ercially from suppliers such as General Electric Co., Dow Corning Corp. and Union Carbide Corp. See, for example, the silicone rubbers disclosed in "The Science and Technology of Silicone Rubber" by F. M. ~ewis, Rubber Chemistry.and ~echnoloay, Vol. XXXV, No. 5, December 1962 (pp. 1222-1275).- Other silicone rubbers are disclosed in U.S. Patents 3,334,067,

3,592,795 and 3,708,467 and in the numerous patents on silicone rubbers assigned to the above-mentioned three suppliers.
Preferred silicone rubhers for use in bath 12 are those which cure at or close to loom temperature to produce transparent films and which, when cured, have a tensile strength for a 25 mil thick film of at least about 400, pre-~erably at least about 700, especially at leas~ about 750 -16~

109 ~4Z2 pounds per square inch and a tear strength for a 25 mil thick film of at least about 20, preferably at least about 25, especially at least about 75, pounds per inch. Ar,ong such silicone rubbers, especially preferred are the silicone rubbers available under the trade designations RTV-615* and RTV-7000*(now discontinued) and the equivalents thereof from General Electric Co., Schenectady, N. Y. and the silicone rubbers available under the trade designation MD~-4-4210*
Elastomer from Dow Corning Corp., ~Sidland, Michigan.
The polymer can be provided in bath 12 as a solution, dispersion, or the like by mixing the polymer with an organic solvent. In bath 12, any conventional inert organic solvent or mixture thereof can be utilized. Among the solvents which can be used are: the straight chain, branched chain, and cyclic aliphatic hydrocarbon solvents, such as pentane, hexane, heptane and cyclohexane the aromatic hydrocarbon solvents, such as xylene, toluene and benzene; methylethylketone; and tetrahydrofuran. Where the polymer is a silicone rubber, bath 12 is preferably formed as a dispersion of the silicone rubber in a hydrocarbon solvent such as hexane. The concentration of polymer in bath 12 can vary widely, e~g., from about 10 to 60%, depend-ing upon factors such as the extent of polymer pick-up desired and the type of polymer used.
Once skeleton sheet 10 has picked up a sufficient amount of bath 12 to permea~e the voids 16 between the individual filaments 15 in each strand of sheet 10 (see Figures l~-lB) and build up as thick a coatin~ 12' as desired on strand 14 (contrast Figures lB-lB''), the polymer treated sheet 17 is then removed from the bath 12 and pre-ferably air-dried for 15 minutes to two hours to remove * Trademark .

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part of the solvent and increase the polymer concentration on sheet 17. The air-drying step is optional and coulcl be omitted if desired.
If the skeleton sheet is dipped in bath 12 more than one time, it is preferable to air-dry the dipped sheet, as described above, or use other drying techniques prior to each subsequent dip and again after the final dip.
Sheet 17, air-dried or otherwise, is then sub-jected to-conditions which will cure the polymer. The term "cure" as used herein means the conversion of the polymer from a low viscosity form, such as a solution or dispersion wherein the polymer is not self-supporting, to a significantly more viscous or solid form in which it is self-supporting.
Curing is generally a "time at temperature" phenomenon, with shorter times re~uired at higher temperatures and longer times at lower temperatures. Conditions for curing the common polymers are well known to those skilled in the art and need not be repeated in detail herein. In general, most polymer curing conditions involve treatments at room temperature (23C.) to about 200C. for about 15 minutes to 48 hours. A silicone rubber film of MDX-4-4210*Elastomer, for exampleS will cure in about 24 hours at room temperature, in about 30 minutes at 75C., and in about 5 minutes at 150C. Thick films may take longer to cure than thin films.

If the skeleton sheet 10 is dipped into bath 12 more than one time, the polymer optionally can be dried and/or cured or partially cured after each dip, as well as after the final dip. Any combination of drying alone or drying plus curing could also be employed after each dip.

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Figures lC-lC'' show the condition o~ the multi-filament strands 14 in the cured sheet 20 for the three different loadings of polymer depicted in Figures lB-lB''.
The cure~ or hardened polymer 21 is located in the void spaces 16 (see Fig. lA) between the individual monofilaments 15, and it forms a shell 21' around the strands 14, the thickness of which depends upon how much polymer was applied to strands 14 in bath 12. Figure lC " depicts the condition where the skeleton sheet picked up enough polymer on adjoin-ing strands 14 to form a bridge 21'' of cured polymer betweenthe adjoining strands 14, which totally fills in the open space 18 that existed between the strands 14 prior to the immersion of skeleton sheet 10 in bath 12. At this point in the processing, the sheet 20 comprises a plurality of poly-meric ribs or struts 24 interbonded at points 26 (see Figure1), which may or may not also be interbonded along substan-tialIy their entire length and which contain.a multifilament core strand 14 of the skeleton material.
~he sheet 20 of cured polymer is then im~ersed :in a bath 30 of a material which is a solvent for the material . .
rom which the skeleton sheet 10 is mad~ but not for the polymer 21, 21', 21''. Solvents for the normal materials from which sheet 10 is fabricated are well known to those s~illed in the art. For exam~lej formic acid, hydrochloric ~25 acid and phenol are well known solvents for nylon, a pre-ferred material for the skeleton sheet. The solvent dis-solves out the individual filaments 15 which formed the skeleton or super-structure of the cured sheet 20, leaving a plurality of elongated continuous channels or voids 32 30 interiorly located in the structural framework of the fin.ish-ed polymeric sheet 33, as shown in Figures lD to lD" .

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~9~zz In Figures lD' and lD" , the elongated channels 32 are located within the interior of the polymeric framework of polymexic sheet 33 that is composed of a plurality of polymeric ribs or struts 33' which are interbonded at points 34 (Figure 1) and which may (Figure lD") or may not (Figs. lD and lD') also be interbonded along substantlally their entire lengths. In Figure lD'', the ribs 33' are connected by the bridge 21'' of cured polymer, which is of a thinner dimension than ribs 33'. Channels 32 are interiorly located because all the filaments 15 which provided the channels 32 were completely enclosed within a shell 21, 21', 21'' of cured polymer prior to leaching out the individual filaments 15 (see Figures lC' and lC''). However, in Figure lD, the surface of sheet 33 also contains elongated channels 32' similar to channels 32 but which are located e~terioxly on ribs 33' instead of interiorly like channels 32. This is because not all the filaments 15 which provided the channels 32 were completely enclosed within a shell of cured polymer prior to leaching o~t the filaments 15. Thus, note in Figure lC that certain of the fi~aments, designated 15', were still at or close to the surface of the ribs 24 after curing of the polymer. When strands 15' were leached out, they created the elongated voids 32l (see Figure lD) in the surfaces of polymeric sheet 33.
The elongated channels both on the surface (chan-nels 32') and in the interior (channels 32) of polymeric sheet 33 generally h~ve the same configuration as the leached solid material from which they were formed. Thus, the network of voids created in sheet 33 by the leaching of the skeleton sheet 10 is an approximate image of sheet 10.
Illustratively, channels 32' and 32 are of a continuous .

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filamentary configuration and have a length to diameter ratio of at least 100 and diameters ranging from about 0~1 to 5 mils and preferably from about 0.5 to 2 mi]s.
The number of channels 32 and 32' present in each rib 33', as well as their total length, internal surface area and volume, can vary considerably depending on such factors as the size and quantity of the precursor filaments 15 and strands 14 from which they were formed. For example, the number of internal channels 32 found in a given rib 33' is illustratively about 10 to 40. The total length of internal channels 32 present in a polymeric sheet 33 can vary widely, e.g., from about 1 to 8 miles of such channels per square foot of sheet. The internal surface area o~
channels 32 is illustratively about 2 to lO square feet per square foot of sheet 33. The volume of channels 32 can range from akout 1 to 6 cubic centimeters per square foot of sheet, and the channels can occupy about 20 to 60% of the total volume of the sheet. Preferably, the sheets 33 con-tain about 12 to 35 channels per xib, and the channels have a total length of about 2.5 to 6.5 miles per square foot of sheet, an internal surface area of about 3 to 8.5 square feet per square foot of sheet, a ~olume of about 1.5 to 4.75 cubic centimeters per square foot of sheet, and occupy about 30 to 52% of the total volume of -the sheet.
In polymeric sheet 33, ~hannels 32 and 32' can be essentially parallel to each othe~, as shown in Figures 2-A, or they can extend in a random or haphazard fashion, as shown in Figures 2'-4'. It is not uncommon, for example, for the sùrface channels 32' to descend into the in~erior of the polymeric framework as shown in Figures 2' and 4'. ~or is ~0~42Z

it uncommon for the surface channels 32' or the interior channels 32 to intercommunicate as at locations 36 in Figures 3' and 4'. ~owever, the channels 32 and 32' norm-ally extend in a direction generally parallel to the plane of sheet 33, with most of the channels extending between the thin edges of the sheet and not between the two sides or faces of the sheet. This produces a network of voids 32, 32' which is oriented to provide continuous communication between the edges instead of between the faces of the sheet.
As will now be apparent, virtually any type of a network of voids can be built into the polymeric frameworX
of the sheet 33 by appropriate selection of the skeleton sheet 10. For example, the number and size of channels provided is readily controlled by the number and size of the filaments which make up sheet 10. The ability to vary the voids or poxosity of polymeric sheet 33 in this fashion can also be utilized to vary propertles of the sheet 33 which are related to its porosity, such as its water vapor phase transfer rate and its anti-microbial barrier layer properties.
The elongated channels 32, 32' also provide a reservoir for one or more medicating agents which can be releasel to a wound covered by the polymeric sheet 33 over a period of time. The channels can be loaded with a medicat-ing agent by immersing sheet 33 in a solution or dispersion of the agent until the desired loading is achieved. The sheet can then be removed from the solution or dispersion and dried if nacessary. Illustrative medicating agents include medicines, antibiotics, antiseptics, germicides, antimicrobial agents, and other materials useful in treating wounds or burns. For example, the elongated channels ~f sheet 33 can be impregnated with PVP-Iodine (polyvinyl-~101l3~

pyrrolidone iodine) comple~ by i~ersing sheet 33 in a lo~
aqueous solution of the PVP-Iodine sollds. PVP-Iodine is a water soluble, non irritating microbiocide with broad spectrum activity and is available from the General Aniline and Film Corp.
Polymeric sheet 33 has a fabric texture on each of its surfaces similar to the texture of the leached skeleton sheet 10 on which it was constructed. This type of surface provides pockets or reservoir spaces to accept the necrotic tissue and other debris from a wound site.
Water vapor phase transfer rates through sheet 33 can be controlled by varying the thickness of sheet 33, the extent of the open area in the sheet and the porosity imparted to the sheet by the elongated channels. Thickness and open area are largely controlled by .he thickness and open area of skeleton sheet 10 and the extent of polymer build-up on sheet 10, while porosity is largely controlled by the nature of the skeleton sheet as previously discussed.
Polymeric sheets 33 are integral, continuous, non-laminated, non-woven, non-fibrous, non-filamentary, non-foamed, gauze or mesh-like sheets, preferably formed from a single polymeric enkity and ha~ing a fabric texture on each side thereof. They have a structural framewQrk comprising a plurality of interconnecting polymeric ribs or struts 33' which are spaced from each other along their length either by open area 18 (Figures lD-lD') or a bridging layer 21'' (Figure lD'') which is thinner than ribs 33'. The ribs 33' define between them recessed portions 18 (in Figures lD-lD') and 18' (in Figure lD'') in both sides of sheet 33. The ribs 3~' contain the elongated, continuous filamentary channe]s 32, 32' in their interior and, optionally, on ~23-~,o~3442~

their surface, with the axis of most of the ribs and elon-gated channels being generally parallel to the plane of the sheet 33 and extending between the edges of the sheet.
The size of the ribs 33' can vary widely depending on how they were formed. Illustratively, ribs 33' have a diameter of about 4 to 30, preferably about 5 to 10, mils.
The len~th of the ribs 33' is typically about 650 to 2600, preferably about 975 to 2300, feet per square foot of sheet 33. The outer surface area of the ribs 33' is typically about 1 to 4, preferably about 1.5 to 3, square fee~ per square foot of sheet 33.
A number of polymeric sheets 33 were pxepared using the procedures illustrated in Figure 1. For example, multifilament nylon (nylon 66) meshes of sizes 1 x 40 (denier per strand) / 13 (filaments per strand), 1 x 50/13 and 1 x 50/17, obtained from Hanes Corporation, were stretched on 9 1/4 inch by 11 inch stainless steel frames and then immersed in a silicone rubber-hexane dispersion (RT~-7000*~
General Electric Co.). The number of dips in the silicone rubber dispersion and the concentration of solids in the dispersion were varied. Each dip was carried out by immers-ing the stretched nylon mesh sleeves in the silicone rubber-hexana dispersion and then immediately removing the sleeves from the dispersion at a constant withdrawal rate of about 38 inches per minute. Each sample required about 15 seconds before it was completely withdrawn from the dispersion.
Between dips, the coated nylon samples were air dried for about 10 minutes. The silicone rubber on the nylon samples was then cured at about 75C. for 1 1/2 hours. The coated nylon samples were then immersed in formic acid at room temperature for about 16 hours or longer to dissolve out * Trademark ~0'3~4ZZ

the nylon. The silicone rubber sheets which remained were dried, and various physical properties of the finished sheets were then measured. The physical properties measured are shown in Table 1, which follows.
As the data in Table l show, polymeric sheets 33 with a wide variation in properties are obtainable. The open area of the sheets 33 can be varied from 0 to about 60%, as desired, and water vapor phase transfer rates of about 2 to 20 mg./hr.-cm.2 or more are obtainable. Pre-ferably, the percent open axea is about lO to 50%, and the water vapor phase transfer rate is about 2 to lO mg./hr.-cm.2 in order to prevent excessive drying of a wound surface.
By varying the thickness and/or extent of open area, varyina degrees of transparency can be imparted to the sheets. The sheets have excellent drapability and conformability charac-teristics and have thicknesses of, for example, about 5 to 30 mils The sheets elongate easily in both directions by as much as 100~ or more and pref~rably by as much as 200~ or more. Illustratively, a 1 x 3 inch strip will stretch lO0 in a direction parallel to the 3 inch dimension at a force of less than about 0.5 pound pe~ inch and will stretch 200 at a force of less than about l pound per inch. Typically, a force of about 0.1 to 0.3 pound is required for lO0 stretch and a force of about 0.2 to 0.5 pound for 200 stretch.
The particular properties of the polymeric sheets 33 are normally selected in accordance with the desired end use of the sheets. For example, if the sheets are to be used as a burn dressing, a low w~ter vapor phase transfer rate approaching that of human s~in would be desired.

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~dditional polymeric sheets 33 were prepared in a manner similar to that just described for the sheets of Table 1, using a variety of different nylon meshes as the extractable components. The nylon mesh samples used were -;
obtained from Hanes Corporation, ~mtex, Inc. and Finetex Elastic Corporation. The Hanes sample was identified as a 1 x 40/13 nylon, as described above. The Amtex sample was identified as Style No. 224~2. The three Finetex samples were identified as ~2, ~9, and #15.
Each sample of nylon was immersed in a 22% solids dispersion of General Electric RTV-7000*silicone rubber in hexane and then removed from the dispersion, using the procedure described above. The samples were air-dried for 20 minutes and reimmersed in the 22% RTV-7000*silicone rubber dispersion as before. The samples were subsequently air-dried for 20 minutes and cured at 75C. for two hours.
The resulting products were then leached with 88% ormic acid for at least 8 hours, after which, the leached products were rinsed in water for 10 minutes and dried at room temperature.
Data on the microchannels 32 and the ribs 33' of the polymeric sheets 33, made in this way, are set forth in Tables 2, 3 and 4, which follow.

* Trademark . j ~(~9 ~22 rl'~ 2 D~ r ~ 2 Extractable ~lanes ~mtex Finetex Finetex Finetex Sleeve i~aterial lx40/13 224-2 #2 ~9 #1~
_ . _ _ _ _ __ __ _ __ _ _ _ __ __ _ . _ . _ _ Average Number of Channels Per Rib 33' 13 28 12.5 28 31.5 Diameter of Channels 32 (mils) 0.84 0~76 0.88 0.94 1.18 Calculated Total Length of Channels 32 (miles/sq.ft.) 2.68 6.47 5.63 6.50 4.84 Calculated Total Internal Surface Area ~f Channels 32 (sq.ft./sq.ft.) 3.1 6.8 6.9 8.4 7.9 ~o~ z~

TABLF~ 3 VOLUME OF CIIANN~LS 32 _ _ _ _ _ ~xtractable ~Janes Amtex Finetex Yinetex Finetex Sleeve l~aterial lx40/13 224-2 ~2 #9 #15 Volume of Channels 32 (cc/sq.ft.) 1.55 3.02 3.57 4.66 5.44 Total Volume of Sheet (cc/sq.ft.) 4.86 10.07 8.31 12.94 10.46 Silicone ~ubber Volume (cc/sq.ft.) 3.31 7.05 4.74 8.28 5.02 Total Sheet Volume Occupied by Chan-nels 32 (%) 30 32 36 43 52 ~ -29-109~422 T BL~ 4 DIMENSIONS OF RIBS 33' Extractable Hanes Amt~x Finetex Finetex Finetex Sleeve Material _ _ lx40/13 _ _2_-2 _ _~2 _ ~9_ 15 Thickness of Sheet (mils) 8 13 13 23 23 Calculated Diameter of Ribs 33' (mils) 5.38 7.31 4.75 8.26 9.13 Calculated Length of Ribs 33' (ft./
sq.ft.) 1,0~41,200 2,380 1,230 ~11 Calculated Surface Area of Ribs 33' (sq.ft./s~.ft.) 1.532.33 2.96 2.65 1.94 ~ ~30-....

~0'3~42Z
The process illustrated in Figure 1 could be readily performcd on a continuous basis by advancing a web or continuous strand of the skeleton sheet 10 sequentially through (1) a bath 12 of polymer to coat it with polymer, (2) a curing cha~ber or oven to cure the polymer on sheet 10, and (3) a leach tank containing a solvent to selectively dissolve sheet 10 but not the cured polymer, and finally ~4) a drying chamber to remove solvent from the finished pro-duct.
Polymeric Sheet With A Fabric Textur~ On One Surface Only Figure 5 depicts a process for preparing polymeric sheets having a coarse fabric texture on one side only. The other side or non-fabric side is a pinhole-free, ultra-thin polymeric membrane which is an anti-microbial barrier layer but remains sufficiently permeable to water VapGr to permit its usage as a wound dressing. Preferably, the polymeric membrane is composed o silicone rubber. A plurality of filamentary micro-channels can be optionally provided at the fabric side of the sheet.
Briefly, polymeric sheets of this type are pre-pared by forming the ultra-thin membrane layer of uncured silicone rubber or the like and embedding in one side of the silicone rubber layer a material which will impart a fabric texture to the one surface. The silicone rubber is then cured to produce a sheet having one surface which is smooth and one which has a fabric texture. The fabric embedded in the me~brane layer can be a gauze or mesh or other equivalent, either coated or uncoated with a polymer, or it can be the fabric-textured sheets prepared by the process of Figure 1.
If the fabric sheet is coated with a polymer, the fabric sheet i~ optionally leached out to create a network of voids at one side of the sheet corresponding in configuration to the leached fabric sheet.

4~ZZ

~eferring to Figure 5, a suppor~ing or forrning surface such as pl~te 50 is immersed in a bath 52 of sili-cone rubber to coat each surface of the plate with a layer 53 of silicone rubber (see Figure 5B). Since a main concern is the eventual separation of the finished polymeric sheet intact from plate 50, it is desirable to employ a non-stick-ing, high-release silicone rubber in bath 52 and a plate 50 having a smooth surface with good release or non stick pro-perties. Removal of the silicone rubber from the plate becomes a serious problem because normally the silicone rubber layer must be kept very thin, e.g., about 0.2 to 2 mils, in order to obtain desirable water vapor phase transfer rates. The thinness of the sheet detracts from its strength, and unless care is taken, the sheet can tear or otherwise rupture as it is being separated from the support plate.
This tendency can be greatly minimized by using a combina-tion of a high-release silicone rubber as the layer in contact with plate 50 and a plate with a non-sticking sur-face.
Plates 50 having a smooth, highly polished or mirror surface are preferred. For example, me~al plates surface-coated with chrome are quite satisfactory, as is highly polished metal foil such as aluminum foil. In addi-tion, any smooth surface of low surface tension can be used, including Teflo~, polyethylene, polypropylene, Teflon*
coated metal, and the like. Release agents or non-stick agents such as various polyvinylchlorides, soaps and other fatty materials can also be advantageously applied ~o the surface of plate 50 before it is immersed in bath 52.

_, * Trademark ~32-.. ~

~09442Z

The silicone rubber in bath 52 is preferably one which is characterized by hi~h-release or non-stick properties.
For example, a preferred silicone rubber for bath 52 is one which, after curing, can be separated intact from plate 50 by the application of a 1~0 degree peel strength of less than about 50, preferably about 40 or less, especially less than about 25, particularly less than about 15, gra~s per inch. As used herein, lgO degree peel strength is the maximum force required to peel away intact an ultra-thin (i.e., about 2 mils or less in thickness) strip of material at an angle of 180 degrees, divlded by the width of the strip of material. For example, if a strip dimension was 1 inch by 3 inch and the direction of peel was substantially perpendicular to the l inch dimension, the strip width to be used in calculating the peel strength would be the one inch dimension, not the three inch dimensionO
If peel strengths become excessive, the silicone rubber sheet, because of its thinness and relatively low strength, tends to tear or rupture in the effort to remove it from plate 50. This problem cannot be overcome by resort-ing to increased sheet thicknesses because, once the sheet thickness exceeds the ultra-thin levei of about 2 mils, the water vapor phase transfer rate declines sharply to values which are too low to permit usage of the sheet as a burn dressing.
General Electric's RTV-61~ silicone rubber is one example o~ a high-release silicone rubber preferred for use in bath 52. It is a dimethyl type silicone rubber with a relatively low molecular weight. ~nother high-release silicone rubber, suitable for bath 52, is Dow Cornin~'s ~lDX-4-421~ Elastomer.

-* Trademark ~(~9~li2~

Of course, other materials besides silicone rubbers can be used in bath 52, provided they are capable of pro-viding water vapor phase transfer rates comparable to silicone rubbers. The problem with many materials is that they have much lower permeabilities to water vapor than silicone rubbers, making it necessary to use such thin films of the materials in order to obtain acceptable water vapor phase transfer rates that the strength of the films is too low for practical usage, The polymer in bath 52 could be any non-sticking, high-release polymer which could be se-parated from plate 50 with a 180 degree peel strength of less than about 50 grams per inch and which would have ~ater vapor phase permeability characteristics essentially equiva-lent to those of silicone rubbers.
The coated forming plate 54 then is preferably but not necessarily air-dried at room,temperature for about 15 minutes to two hours to evaporate the solvent from the silicone rubber coating and increase the concentration of silicone rubber on the plate.
The dried plate subsequently is immersed in a second bath 58 of a silicone rubber, which can be of a different type than is used in bath 52, in order to add to each side thereof a second layer 60 of silicone rubber (see Figure 5C). The silicone rubber in bath 58 is selected for its high tensile strength and tear strength characteristlcs.
The high-release silicone rubbers used in bath 52 generally tend to have poor tensile and tear strengths. To compensate for this, bath 58 builds onto the first silicone rubber layer 53 a second layer 60 to ad~ tensile and tear str~ngths to the finished sheet. In gener;~l, any silicone rubber can ~r 2'Z

be used in bath 58 which, upon curing, has a tensile strength for a 25 mil thick cured film of at least about 400, preferably at least about 700, especially at lcast akout 750, pounds per square inch and a tear strength for a 25 mil thick cured film of at least about 20, preferably at least about 25, especially at least about 75, pounds per inch.
Polymers other than silicone rubbers could be used in bath 58 provided they have the above strength characte-ristics and water vapor phase transfer rates equivalent to those of silicone rubber~
The plate 70 from the second dip tank is then preferably although not necessarily air-dried in the same manner as described above for plate 54.
General Electric's RTV-7000*silicone rubber (now discontinued) and Dow Corning's MDX-4-421~ ~lastomer, as well as their equivalents, are examples of silicone rubbers which have been found suitable for use in bath 58. RTV-7000*
has a molecular weight after cure which is substantially greater than that of the RTV-615*silicone rubber of bath 52.
The amount of silicone rubber applied to the plate in baths 52 and 58 can be varied as desired by altering such variables as the concentration of solids in the baths, the residence time in the baths and the number of times the pIate is dipped into the baths. Illustratively, the con-centration of solids in the baths is about 10 to 60%, and anywhere from 1 to 5 dips of a few seconds duration, e.g., 5 to 60 seconds, normally suffices.
Illustratively, only enough of the high-release silicone rubber is applied in bath 52 to form a uniform layer 53 (see Figure 5B) of sufficient thickness to cover the surface of support plate sn and thus facilitate easy -* Trademark 109~422 release of thc finished po]ymeric sheet from the plate.
Normally, only enough silicone rubber is applied to pla~e 50 in bath 52 to form a layer of about 1 mil or less in the finished sheet and preferably about 0.1 to 0.3 mil. This thin layer 53 forms one part of a transparent, pinhole-free, anti-microbial barrier layer 5~, while the layer 60 of silicone rubber applied in bath 58 forms the other part.
The high tensile strength, high tear strength silicone rubber used in bath 58 is applied to the plate in sufficient a~ounts to provide an overall membrane thic}-ness (which includes the thickness of the high-release silicone rubber layer 53) of about 2 rils or less in the finished polymeric sheet and preferably about 0.5 to 1.5 mils.
Illustrativelyr the thickness of the high strength layer 60 can vary from about 0.2 to 2 mils in the finished ~embrane and preferably is about .5 to 1.5 mlls.
Because the water vapor phase transfer rate is strongly dependent on the overall thickness of the pinhole-free ~embrane 54 formed by the two layers 53, 60 of silicone rubber picked up in baths 52 and 58, respectively, it is important that the overall thickness of the membrane portion of the finished sheet be kept highly uniform, e.g., -about 0.2 mil. The vertical dipcoating techniques shown in Figure 5 have been especially useful in producing sheets, the membrane component of which is of substantially uniform thickness throughout, at least for sheets whose vertical dimension does not exceed about 12 inches. This results in finished polymeric sheets of highly uniform water vapor ' phase transfer rate characteristics, an important con-sideration in a burn dressing.

, , -36-"

~o944Z~

~lthough Figure 5 depic~s the application of two silicone rubbers having diferent characteristics to plate 50 in two separate steps, it is to be understood that, in accordance with the process shown in Figure 5, acceptable laminates could also be produced by fabricating the pinhole-free membrane layer 54 from a single silicone rubber material by one or more immersions of plate 50 in a single bath instead of two. For example, the pinhole free membrane 54 could be formed solely from RTV-615*silicone rubber, especially in applications where water vapor phase transfer rates were not particularly important, so that strength could be increased by increasing the overall thickness of the RTV-615*rubber.
i Similarly, the pinhole free membrane could be formed solely from RTV-7000*silicone rubber or equivalents thereof in applications where water vapor phase transfer rates were not particularly important, so that thickness could be increased to avoid tearing or rupturing the sheet when it was removed from plate 50.
Eaths 52 and 58 comprise a liquid which contains a polymer. The baths can be a solution or dispersion of the polymer, a latex, or any other form of the polymer which will coat the surace of plate 50 with polymer.
If plate 50 is immersed more than one time in baths 52 or 58, the dipped plates can be optionally dried and/or cured or partially cured between each dip, as well as after the final dip. Any combination of drying alone or drying plus curing could be employed after each dip. Pre-ferably, at least one curing step is carried-out before the final dipping o plate 50 in a polymer bath.
Returning now to Figure 5, the next step following build-up of the membranc layer 5~ on plate 50 is to apply, to the outermost layer 60 of the silicone rubber membrane, the material which will provide the fabric te~ture at o~e * Trademark ~09442Z
side of the finished sheet.. Normally, this is done by applying to layers 60 on the air dried plate 70 a sheet 71 having a coarse fabric texture or other type of coarse or rou~h surface (see Figure 5D). Sheets 10, 17, 20 and 33, discussed above in connection with Eigure 1, are examples of the sheet materials which can be used as sheet 71. The nature of sheets 10, 17, 20 and 33 has already been ex~
plained in detail. Sheets 10 and 17 are preferred sources of sheet 71 for this embodiment of the invention. Although Figures 5D-5~ show sheet 71 as being composed of a plurality of strands 71' separated by open spaces 72, sheets 17, 20 and 33 (from Figures lB'', lC'' and lD''), which have no open spaces between the strands, could also be employed as sheet 71.
For the case where sheet 10 from Figure 1 is used, the sheet preferably will stretch or elongate at least about 1004 and preferably about 100 to 300% in each direction.
For example, sheet 10 preferably will stretch 100~ in a given direction by the application of a force less than about 0.5 pound (for a 1 x 3 inch strip) and will stretch 200~ in a given direction by the application of a force less than ab~ut 3 pounds on the same basis. Sheet 10 preferably also hàs good wicking and liquid absorption characteristics to aid in removing liquids from a wound site at medically acceptable rates. Sheet 71 is preferably formed from a plurality of multifilament yarn strands.
Once sheet 71 has been placed on the silicone rubber layer 60, it is forced into layer 60 deep enough to form a good ~ond therewith but not deep enough to pierce through to the surface of the support plate 50 or to totally embed sheet 71 in the silicone rubber (see Figure 5E).

'10'3~4Z2 ~t is important that one side of sheet 71 remain exposed and substantially silicone rubber-free, so as to provide the coarse fabric-like surface in the finished sheet for ad-herence to the wound area and so as to not unduly impair the wettability characteristics of the fabric texture surface of the sheet~
The silicone rubber in layers 53 and 60 is then cured while one side of sheet 71 is embedded in the silicone rubber to bond sheet 71 to the pinhole-free silicone rub~er membrane portion 54. This is conveniently done by sand-wiching plate 70 with its adhering sheets 71 between t~;o sheets 73 of cured silicone rubber whose surfaces adjzcer_ sheet 71 are preferably covered by a material, such as aluminum foil or a relatively thick layer of nylon fabric.
The resulting composite is then placed bet~Jeen two platens 75 of a conventional press, which may be heated by electrical resistance wires 77. Pressure is applied to the composite while it is bein~ heated by the platens to cure the silicone rubber. Enough pressure is used to embed sheet 71 to the desired level in the silicone rubber. The pressure selected can depend on a number of actors, such as the viscosity of the silicone rubber and the percent open area of sheet 71.
Illustratively, pressures of about 10 to 200 psi suffice for many applications. Curing temperatures and times for sili-cone rubbers are well known to those skilled in the art.
Illustrative cure cycles involve treatments at room tempera-ture to about 200C. for about 1.5 to 48 hours, e.g., a treatment at 100C. for 2 hours.
As the silicone rubber cures, it securely bon~s to the individual strands 71' o~ she~t 71, thereby anchoring sheet 71 to the pinhole-ree, cured, silicone rubber, ~e~brane portion 54', composed of cured silicone rubber layers 53' and 10~ L1~ 4 ;2Z
60', as best seen in Figure 5E. The curing step ~ill also cure any polymer on the surfaces of sheet 71. ~or example, if sheet 71 originates from sheet 17 of Figure 1, the polymer 12, 12' and 12'' on sheet 71 will cure in the curing step.
After curing, the composite 80 of membrane 54' and sheet 71 can take one of two routes, depending upon the nature of sheet 71 and the desired end product. If sheet 71 originated from sheets 10, 17, 20 or 33 of Figure 1 and if there is no need to remove the skeleton for~ed ky the pre-sence of sheet 10 in sheets 17 and 20, the composite ~0 of membrane 54' and sheet 71 is separated from plate 50 to produce the finished polymeric sheet 81 having, or one side, a generally smooth even surface 82 and, on the other side, a coarse, uneven, fabric-like surface 83, as best seen in Figures. 5F and 5G. Figure 5F exemplifies the situation where sheet 71 was a sheet of multifilament strands 14, each containing a plurality of individual monofilants 15 (such as sheet 10 in Figures. 1 and lA) which had not been coated uith a polymer prior to its application to the silicone rubber layer 60. It is evident that, if sheets 17 or 20 from Figure 1 were used instead of sheet 10, the voids 16 between the individual filaments 15 in each yarn strand 14 (see Figure 5F) would be filled with cured polymer 21 (as shown in Figures. lC to lC'' and 5G), and each multifilament strand 14 would be encased within a sheath of cured polymer 21' ~as also shown in Figure 5G), the thickness of which would depend on the degree of polymer coating on sheets 17 and 20. In short, the finished sheet would be the same as the sheet shown in Figure 5F, except that the voids 16 in Figure 5F would ~e filled with cured polymer 21, 21', . -40-,~ .

~109 L~ ~ Z,Z, as shown in Figure 5G. If sheet 33 from Figure 1 was used as sheet 71, the filaments 15 would have already been leached out, so that ~he finished sheet, after removal from plate 50, would be as shown in Figure 5I, with the voids 32 re-placing the former location of the filaments 15.
On the other hand, if sheet 71 originated from sheets 10, 17 or 20 in Figure 1 and it is desired to remove the skeleton sheet 10 contained therein to provide a network of elongated continuous voids in the sheet similar to voids 10 32 and 32' in Figures lD to lD'', the composite sheet 80 (see Figure 5E) is immersed in a solvent 90 in which the skeleton sheet 10 is soluble but in which the cured polymer coating on the skeleton sheet is substantially insoluble.
The solvent 90 leaches or dissolves out the skeleton sheet 15 10, creating a plurality of elongated channels or voids 32, 32' in the finished polymeric sheet 93 ~see Figures 5~-5I), as described above in connection with Figures lD to lD''.
The nature of the coarse surface 83 of the finished polymeric sheet 93 and the voids 3Z, 32' in sheet 93 depends on the 20 nature of the skeleton sheet 10. If sheet 10 was composed of a multifilament yarn which ha~ not been coated tJith a polymer prior to its application to the silicone rubber~
membrane layer 54, the finished product would appear as in Figure 5H, with a combination of internal voids 32 and 25 surface voids 32' where filaments 15 had once been ~compare Figures 5F and 5H~. If sheet 10 had been coated t~ith a polymer prior to its application to membrane laye.r 54, the finished product would appear as in Figure 5I. It can be appreciated that the coarse surf.lce 83 of polymeric sheet 93 30 in Figure 5I is essentially shee~ 33 from Figure 1 and, accordingly, can be varied as desired in the manner discussed above for shèet 33 and as described in Fi~ures lD to lD''.

10~4~2Z ~
The skeleton sheet 10 can, of course, be leached from the composite 80 either before or after its separation from plate 50. Preferably the sheet is leached prior to separation from plate 50, provided plate 50 is substantially insoluble in the leaching solvent, and is then air-dried and separated from plate 50 to produce the finished poly-meric sheet 93.
As shown in Figures-5H and 5I, polymeric sheet 93 has a smooth uniform surface 82 on one side and a coarse, fabric-textured surface 83 on the other. The coarse sur~ace 83 in Figure 5I comprises a plurality of cured silicone rubber ribs or struts 33', each containing a plurality of filamentary voids 32 therein where the leached skeleton filaments 15 were at one time located. As pointed out in connection with Figures lD, 2 and 2', ribs 33' could also contain elongated surface channels such as channels 32' in Figures lD, 2 and 2', depending upon the extent to which the leached skeleton strands 14 were coated with polymer in the process of preparation, The finished polymeric sheets 81 and 93 have a ~mooth-surfaced, thin, pinhole-free, substantially non-p~rous and voids-free, non-foamed membrane layer 54' on one side thereof which has antimicrobial barrier layer pro-perties and desirable water vapor phase transfer rates. The other side of sheets 81 and 93 has a fabric texture imparted to it by the ribs 14 (Figure 5F), 24 (Figure 5G) or 33' ~Figure 5I) joined to membrane 541 or by the elongated voids 32' (Figure SH). Sheets 81 and 93 can be formed from one or more polymeric entities. The axis of most of the elongated channels 32, 32l and of the ribs is generally parallel to the plane of sheets 81 and 93, as discussed above in con-nection with sheet 33. The polymeric sheets 81 and 93 also are very thin and drapable.

1 0~4ZZ
The finished polymeric sheets 81 and 93 have properties similar to those discussed above for the sheets 33 produced by the process of Figure 1. The water vapor phase transfer rate is a function of the thickness of the pinhole-free, anti-microbial barrier or membrane layer 54' and the open area of the fabric-side 83 of the respective sheets. Generally, it is necessary to keep the merbrane layer 54' quite thin, e.g., 2 mils or less, in order to obtain water vapor phase transfer rates which approximate those of human skin. The ribs 14, 21' and 33' in sheets ~1 and 93 are normally significantly thicker than the membrane 54' and illustratively are about 10 to 60 mils, preferably about 15 to 35 mils, in thickness.
Wettability of the coarse or fabric-textured sides of polymeric sheets 81 and 93 is important in many medical applications. ~'ettability is deLined and cornpared herein by applying, to the fabric-textured side of a polymeric sheet of the invention, a 0.004 cubic centimeter drop of 1~ by weight C~ngo Red dye in water. The diameter of the spread of the cye solution, as absorbed into the sheet surface, is then me~sured, and the area of the spread is computed from the measured diameter. The time re~uired for the dye to be completely absorbed into the sheet surface, as viewed with the naked eye, also is measured. Higher wetted area values and lower times fox absorption mean increased wettability characteristics. Using this test procedure, illustrative spread areas of anywhere from approximately .15 to 1, pre-ferably at least ~bout .4, especially at least about .6, square centimeter and absorption times of about 0 seconds to 6 minutes, preferably less than about 1 minute, especially less than about 20 seconds, particularly less than about 2 seconds, quite particularly significantly less than about 1 ~os~z2 second, i.e., about 0 seconcls, have been obtained with the fahric-textured sides of the polymeric sheets of the invention, when such fabric sides have been formed from sheets of multifilament yarns~ The variations in wett-ability can be largely attributed to differences in the materials and structures used to form the fabric-textured sides of the polymeric sheets of the invention. Such varia-tions also indicate that the polymeric sheets can be fabri-cated with a wide range of wettability characteristics on their fabric sides.
Medicating agents of the types previously dis-cussed can be incorporated into the coarse or fabric-tex-tured sides of sheets 81 and 93 by impregnation of the elongated voids 32, 32' or voids 16 in the case of the embodiment of Figure 5F.
An especially preferred embodiment of the laminate polymeric sheet 81 of Figure 5F, having a fabric texture on one side thereof, can be made in a relatively simple fash1on, according to the process of Figure 5, with a very high de~ree of wettability. Such an cspecially preferred, poly-meric sheet 81 comprises; one or more layers of a cured, high-release and high-strength silicone rubber which form a pinhole free membrane 54'; and a skeleton sheet 10 of a relatively heavy and thick, wettcble nylon fabric, joined to an outer layer 60 of the silicone ruhber membrane 54'. This polymeric sheet 81 is considered to provide superior burn covering properties in that, besides having a water va~or phase trans~er rate of about 2 to 10 mg./hr.cm.2, a two-dimensional elongation of at lea~t 100% in each direction, and anti-microbial barrier layer properties, the fabric side of the sheet 81 can rapidly absorb ~luids, such as the ~0944ZZ

bodily fluids secreted at a burn site, to maintain a medi-cally acceptable, balanced fluicl level at the burn site.
The nylon skeleton sheet 10 used in the especially preferred, laminate polymeric sheet 81 should be made of at least about 70 denier, preferably about 100 denier or greater, especially about 100 denier, nylon strands, each strand of which is made up of at least about 18 filaments, preferably at least about 25 filaments. In the nylon skeleton sheet 10 of the especially preferred polymeric sheet 81 of Figure 5F, more filaments per strand are preferred, and the nylon sheet 10 sùitably contains, for example, up to about 75 filaments per strand, e.g., fifty 2-denier nylon filaments per strand.
The nylon skeleton sheet 10 also should be in a substan-tially oil-free condition, as results from heating the nylon sheet, should ha~e a weight of at least about lOg./ft.2, preferably at least about l~g./ft.2, and should have a thickness of at least about 20 mils, preerably at least about 25 mils. Most importantly, the nylon sheet 10 should have a wettability, in relation to a 0.004 cc. drop of dye solution, defined by a wetted area of at least akout 0.8 cm.2, preferably at least about 1.0 cm.2, and an absoxpti~n time of about 2 6econds or less, preferably about 1 second or less. A particularly preferred nylon sheet of the type described above is available under the trade designation Amtex 11002 T66T from Amtex, Inc., Cleveland, Tennessee and is a substantially oil-free, 100 denier, nylon fabric, having thirty-four 3-denier filaments per strand, a thick--ness of about 25 mils, a weight of about 14.4 g./ft.2, and a wettability defined by a wetted area of 1.26 cm.2 and an absorption time of significantly less than 1 second.

~L0~3~42Z

The silicone rubber used in the layers of the pinhole free me~brane 54' of the especially preferred, laminate polymeric sheet 81 should have both relatively high-release characteristics, i.e., a 180 degree peel strength, after curing, of less than about 50 grams per inch, preferably about 40 grams per inch or less, and re-latively high strength characteristics, i.e., a 25 mil thick cured film has a tensile strength of at least about 400 pounds per square inch, preferably at least about 700 pounds lG per square inch, and a tear strength of at least about 20 pounds per inch, preferably at least about 25 pounds per inch. Among the preferred, high release and high-strength, silicone rubbers which can be used is the silicone rubber available under the trade designation MDX-4-4210*Elastomer from Dow Corning, which has a 180 peel strength of about 30 grams per inch after curing and a tensile strength of about 700 pounds per square inch and a tear strength of about 90 pounds per inch ~or a 25 mil thick cured film. In the laminated polymeric sheet 81 of Figure 5F, two or more layers of the same cured silicone rubber preferably make up the pinhole free membrane 54'.
The especially preferred laminate sheet 81 of Figure SF, when made from an Amtex 11002 T66T nylon skeleton sheet 10 and a membrane 54' of two layers of MDX 4-4210*

Elastomer, can be provided with a wettability on its fabric-textured side defined by a wetted area of .66 cm.2 or better and an absorption time of 19 seconds or less, as well as a water vapor phase transfer rate o~ about 2-10 mg./hr.-cm.2, a two-dimensional elongation of at least 100% in each direction, and anti-microbial barrier properties. Thereby, a superior burn covering can be produced.

* Trademark 10~4~2Z

Figure 6 depicts another process for preparing a polymeric sheet having a smooth membrane layer on one side and a coarse fabric texture on the other side. The advantage of the processing technique of Figure 6 as compared to that of Figure 5 is that it results in a completely non-laminated product, thereby eliminating the undesirable possibility of ~ the various layers of the composite delaminating.
- ~eferring to Figure 6, a sleeve lO0 of fabric material of the same type as described above in connection with skeleton sheet lO is fitted over a cylindrical drum 101 in such manner that sleeve 100 is stretched on drum 101, thereby causing it to be uniformly pressed toward the external surface of the drum. Illustratively, sleeve lO0 can be circumferentially stretched anywhere from lO to 200 on drum 101.
Sleeve 100 serves as a skeleton on which the polymeric sheet of the invention is constructed. Drum 101 serves as a supporting surace for sleeve lO0 during the build-up of polymer on sleeve lO0. Drum 101 also serves as a surface on which an ultra-thin membrane layer of polymer can build-up in such a way that it forms a continuous phase with the polymer which coats the surfaces of the sleeve 100.
Drum 101 preferably has a smooth uniform surface, although a coarse surface can be used if a coarse rather ~5 than smooth texture is desired for the membrane side of the finished sheet. Teflon*and polypropylene are two examples of materials which can be used to fabricate drum lOl.
The composite 102 of sleeve 100 and drum lOl is then immersed in a bath 103 of a polymer using the handles lO~ which are provided at the top o the drum. Preferably, bath 103 is a solution or dispersion of a silicone rubber.

* Trademark 4~122 A preferred silicone rubber is General Electric's RTV-7000*
or an equivalent thereof, as discussed above. The amount of silicone rubber applied in bath 103 can be varied as desired by altering such parameters as the concentration of solids in the bath, the residence time of sleeve 100 in the bath and the number of times the composite 103 is dipped into the bath. Illustratively, the concentration of rubber solids in the bath is about 10 to 60~ and anywhere from 1 to 5 dips of a few seconds duration, e.g., 5 to 60 seconds, normally suffices. Different type silicone rubbers can be used in successive baths if desired.
Sleeve 100 is preferably composed of a plurality of multifilament strands 14, each composed of a plurality of individual filaments 15 with void spaces 16 between them, as best seen in Figure 6A. The polymer bath 103 permeates the void spaces 16 to the degree desired and forms an ultra-thin layer 106 o~ polymer on the surface 107 of drum 101, between surface 107 and the strands 14, as best seen in Figure 6B.
Layer 106 e~tends between the individual strands 14, to form a sheet of polymer to which each of the strands 14 is joined It is this ultra-thin layer 106 which, upon curing, provides the thin smooth membrane layer of the finished sheet.
After the stretched sleeve 100 has been treated with bath 103 for a sufficient time, the composite 102 of drum 101 and sleeve 100 is removed from bath 103. The polymer is then cured, as previously described, and removed from drum 101 to produce the finished polymeric sheet 110 (see Figure 6C). Sheet 110 has a membrane layer 111 of cured polymer and a coarse fabric-textured layer 112 also formed of cured polymer. The yarn strands 14 which make up sleeve 100 are encapsulated in cured polymer layer 112 and -* Trademark -4~-109~422 also partly in layer 111. Layer 111 has a smooth surface 113 whereas layer 112 has a coarse fabric-textured s~rface.
This coarse surface is formed by the portions 114 of cured polymer which project from membrane layer 111 and for~ a continuous polymeric phase with layer 111. In contrast to the sheets shown in Figures 5F to 5I, the smooth and coarse layers 111, 112 of sheet 110 are formed from a continuous phase of cured polymer, not from two separate pieces which are laminated together to provide the smooth and coarse sides of the sheet, respectively. This avoids delamination problems by providing a sheet which is ~ormed of a single integral unlaminated piece of polymer.
If desired polymeric sheet 110 can be immersed in a solvent llS (see Figure 6) which dissolves the sleeve 100 but not the cured polymer. As sleeve 100 dissolves, it creates a polymeric sheet 120 (see Figure 6D) containing elongated channels 32 in the coarse side of the sheet.
Channels 32 are o~ the same type as those previously dis-cussed in connection with other embodiments of the invention.
Illustratively, the th.ckness of the ultra-thin membrane layer 111 in polymeric ~heets 110 and 120 is about 0.5 to 2 mils, while the thickenc;s of layer 112 can vary from about 10 to 60 mils.
The polymeric sheet~ 110 and 120 shown in Figures 6C and 6D have essentially the same characteristics as those o Figures SG and 5I, respectively.
Although polymeric sheets 110 and 120 were pre-pared by stretching the sleeve lC0 on a cylindrical surface such as drum 101, sheets 110 and 120 could also be prepared by mounting a suitable skeleton cheet, such as sheet 10 of ~. ~

~0'34~22 Figure l, against an appropriate surface, e.g., a flat surface, to form a composite of the sheet and surface and then immersing the composite in bath 103. In such a case, the skeleton sheet would not necessarily have to have a sleeve configuration and could be, for example, a piece o~
knit or woven cloth formed from a plurality of multifilament yarn strands~
It can be appreciated that the polymeric sheets of this invention are particularly useful as dressings or coverings for wounds and, in particular, for burns because of their antimicrobial barrier layer properties and water vapor phase transfer rates. The sheets are applied to wound sites in such a manner that their fabric-textured side is toward the wound. If a non-sticking dressing is desired, the fabric-textured side should be formed from a low surface energy material, such as silicone rubber, Teflon*, polyethy-lene, polypropylene or the like whereas, if an adherent dressing is desired, the fabric-textured side should be formed from a high surface energy material such as nylon, rayon, Dacron*or cotton.
The polymeric sheets can be sutured to wound sites or adhesively applied. The voids or open areas in the coarse surface provide a reservoir for wound debris. The sheets have excellent conformability or drapability chara-cteristics and the desirable ability to stretch signifi-cantly in two directions because of their elastomeric nature.

* Trademark . ~ , . .

The presence of the elongated voids ~2, 32' is important for several reasons. They provide a means for varying the water vapor phase transfer rate through the polymeric sheets by imparting more or less voids to the sheets. They also provide reservoirs for medications which can be released to wound sites and reservoirs for wound debris. Finally, the voids can remove liquids from wound sites by capillary action.
When the polymeric sheets are ultra-thin, as is preferred when they are to be used as burn dressings, they are also transparent or translucent, thus permitting doctors to examine the progress of wounds without having to remove the dressings.
The polymeric sheets of the invention can be readily sterilized using ethylene oxide. For example, exposure to ethylene oxide vapors at a pressure of about 9 psi for 4 hours at 130F. will suffice for most applica-tions.
The specific and detailed information presented above was for purposes of illustration only, and such alterations~ modifications and equivalents thereof as would suggest themselves to those skilled in the art are deemed to fall within the scope and spirit of the invention, bearing in mind that the invention is defined by the following claimsO

~I -51-

Claims (31)

CLAIMS:

1. A drapable synthetic burn dressing having 1) a fabric texture on one surface thereof which provides a reservoir for debris from a burn and 2) substantially uniform physiologic properties approximating those of human skin, comprising:
(a) a first layer of cured high-release non-sticking silicone rubber, having a thickness of about 1 mil or less and forming one surface of the burn dressing;
(b) a second layer of cured silicone rubber having a tensile strength and tear strength for a 25 mil thick cured film thereof of at least about 400 pounds per square inch and at least about 20 pounds per inch, respectively, joined to the first layer of silicone rubber; the first and second layers of silicone rubber having a total thickness of about 2 mils or less and forming an ultra-thin, pinhole-free, substantially non-porous and voids-free membrane; and (c) a third layer of fabric texture joined to the second layer of silicone rubber and forming the other surface of the burn dressing;

the burn dressing having a water vapor phase transfer rate of about 2 to 10 mg./hr.-cm.2, two dimensional elongation of at least about 100% in each direction, and anti-microbial barrier layer properties.

2. The burn dressing of claim 1 wherein the third layer of fabric texture comprises a knit or woven sheet of continuous multifilament strands.

3. The burn dressing of claim 1 wherein the third layer of fabric texture is formed of continuous multifilament strands having a polymer at the surfaces of the individual filaments.

4. The burn dressing of claim 1 wherein the third layer of fabric texture has a two dimensional elongation of about 100 to 300% in each direction.

5. The burn dressing of claim 4 wherein the third layer of fabric texture comprises a knit or woven sheet of continuous multifilament nylon strands.

6. The burn dressing of claim 1 wherein the sili-cone rubber of the first layer has a 180 degree peel strength of less than about 50 grams per inch and the silicone rubber of the second layer has a tensile strength and tear strength for a 25 mil thick cured film of at least about 700 pounds per square inch and at least about 25 pounds per inch, respectively.

7. The burn dressing of claim 1 wherein the silicone rubber of the first layer has a 180 degree peel strength of about 40 or less grams per inch and the silicone rubber of the second layer has a tensile strength and tear strength for a 25 mil thick cured film of at least about 750 pounds per square inch and at least about 75 pounds per inch, respectively.

8. The burn dressing of claim 7 wherein the silicone rubber of the first layer and the silicone rubber of the second layer are the same silicone rubber.

9. The burn dressing of claim 8 wherein the layer of fabric texture, joined to the second layer, comprises substantially oil-free, at least about 70 denier, nylon strands; each strand comprising at least about 18 filaments;
the layer of fabric texture having a weight of at least 10 g./ft.2, a thickness of at least about 20 mils and a wettability, in relation to a 0.004 cc. drop of dye solution, defined by a wetted area of at least about 0.8 cm.2 and an absorption time of about 2 seconds or less; the fabric textured side of the burn dressing having a wettability defined by a wetted area of at least about .4 cm.2 and an absorption time of less than about 1 minute.

10. The burn dressing of claim 9 wherein the layer of fabric texture comprises about 100 denier or greater, nylon strands.

11. The burn dressing of claim 10 wherein the layer of fabric texture comprises at least about 25 fila-ments per strand and has a weight of at least about 14 g./ft.2, a thickness of at least about 25 mils, and a wettability, in relation to a 0.004 cc. drop of dye solution, defined by a wetted area of at least about 1.0 cm.2 and an absorption time of about 1 second or less; the fabric tex-tured side of the burn dressing having a wettability defined by a wetted area of at least about .6 cm.2 and an absorption time of less than about 20 seconds.

12. The burn dressing of claim 11 wherein the layer of fabric texture comprises substantially oil-free, about 100 denier, nylon strands, having thirty-four 3-denier filaments per strand, a thickness of about 25 mils and a weight of about 14.4 g./f-t.2; the fabric textured side of the burn dressing having a wettability defined by a wetted area of about 1.26 cm.2 and an absorption time of signific-antly less than 1 second.

13. The burn dressing of claim 1 wherein the first layer of silicone rubber has a thickness of about 0.1 to 0.3 mil.

14. The burn dressing of claim 13 wherein thew second layer of silicone rubber has a thickness of about 0.5 to 1.5 mils.

15. The burn dressing of claim 1 wherein the second layer of silicone rubber has a thickness of about 0.5 to 1.5 mils.

16. The burn dressing of claim 1 wherein the first and second layers of silicone rubber have a total thickness of about 0.5 to 1.5 mils.

17. A process for preparing a sheet of polymeric material having a fabric texture on one surface thereof, which comprises:
(1) applying to a forming surface a liquid containing a high-release non-sticking polymer, to form on the surface a first layer of polymer which upon curing will produce a layer of polymer of about 1 mil or less in thickness that can be separated intact from the surface;
(2) applying to the forming surface containing the first layer of polymer a liquid containing a polymer to form a second layer of polymer which upon curing has a tensile strength and tear strength for a 25 mil thick cured film of at least about 400 pounds per square inch and at least about 20 pounds per inch, respectively, and which results upon curing in an overall thickness of the first and second layers of polymer of about 2 mils or less;

(3) embedding one surface of a sheet having a fabric texture on at least one surface thereof in the second liquid layer of polymer, with the surface having the fabric texture out of contact with the second layer of polymer;
(4) curing the polymer layers while the surface of the sheet of fabric texture is embedded in the second layer of polymer, to form a bonded composite of cured polymer and sheet of fabric texture; and (5) separating the composite from the forming surface.

18. The process of claim 17 wherein the sheet of fabric texture embedded in the second layer of polymer is a woven or knit sheet of continuous multifilament strands.

19. The process of claim 17 wherein the sheet of fabric texture embedded in the second layer of polymer is an integral, continuous, non-laminated, substantially non-woven, non-fibrous, non-filamentary, non-foamed, drapable polymeric sheet, each side of which has a fabric texture, the sheet of fabric texture comprising a plurality of inter-bonded continuous polymeric ribs defining between them recessed portions on each side of the sheet of fabric text-ure, the ribs containing a plurality of elongated continuous channels interiorly located therein which extend in a direc-tion generally parallel to the plane of the sheet of fabric texture to form a network of voids within the ribs which extend continuously throughout the ribs, the sheet of fabric texture having a water vapor phase transfer rate of about 2 to 20 mg./hr.-cm.2, two dimensional elongation of at least about 100% in each direction and an open area between the ribs of zero to about 60%.

20. The process of claim 17 wherein the sheet of fabric texture embedded in the second layer of polymer is a woven or knit sheet of fibers having on their surfaces an uncured polymer different from the material of the fibers, which polymer is also cured in step (4) with the polymer layers; and further including the step of treating the composite with a solvent in which the fibers are soluble but in which the cured polymer on their surfaces and the polymer layers are substantially insoluble, to thereby dissolve the fibers and produce, at one side of the composite, a cured polymer having substantially the same surface texture as the dissolved fibrous sheet and containing a network of voids conforming to the configuration of the solids portion of the dissolved fibrous sheet.

21. The process of claim 20 wherein the sheet of fabric texture embedded in the second layer of polymer is also of a polymer.

22. The process of claim 17 wherein the first layer of polymer is cured before forming the second layer of polymer on the forming surface.

23. The process of claim 17 wherein the sheet of fabric texture embedded in the second layer of polymer is a woven or knit sheet of fibers having on their surfaces a cured polymer different from the material of the fibers; and further including the step of treating the composite with a solvent in which the fibers are soluble but in which the cured polymer on their surfaces and the polymer layers are substantially insoluble, to thereby dissolve the fibers and produce, at one side of the composite, a cured polymer having substantially the same surface texture as the dis-solved fibrous sheet and containing a network of voids con-forming to the configuration of the solids portion of the dissolved fibrous sheet.

24. The process of claim 23 wherein the sheet of fabric texture embedded in the second layer of polymer is also of a polymer.

25. The process of claim 17 wherein the sheet of fabric texture embedded in the second layer of polymer is of a material other than a polymer; and further including the step of treating the composite with a solvent in which the material of the sheet of fabric texture is soluble but in which the polymer layers are substantially insoluble, to thereby dissolve the sheet of fabric texture and produce at one side of the second layer of polymer a fabric texture.

26. The process of claim 25 wherein the sheet of fabric texture embedded in the second layer of polymer is a woven or knit sheet of continuous multifilament strands.

27. The process of claim 17 wherein the liquids containing the polymers are applied to the forming surface by a vertical dip coating technique.

28. The process of claim 17 wherein the polymer of the first layer, when cured, has a 180 degree peel strength of less than about 50 grams per inch and the polymer of the second layer has a tensile strength and tear strength for a 25 mil thick cured film of at least about 700 pounds per square inch and at least about 25 pounds per inch, respect-ively.

29. The process of claim 17 wherein the polymer of the first layer, when cured, has a 180 degree peel strength of about 40 grams or less per inch and the polymer of the second layer has a tensile strength and tear strength for a 25 mil thick cured film of at least about 750 pounds per square inch and at least about 75 pounds per inch, respect-ively.

30. The process of claim 17 wherein the polymer of the first layer and the polymer of the second layer are each a silicone rubber.

31. The process of claim 30 wherein the silicone rubber of the first layer and the silicone rubber of the second layer are the same silicone rubber.