US 3709221 A
A composite surgical dressing that is highly absorbent, capable of preventing leakage or exudation from open wounds and capable of preventing contamination from entering or escaping from the wound, comprising an outer microporous, liquid-repellent fibrous layer having a maximum pore size of 0.5 micron, and a voids volume of at least 50 percent; an inner macroporous, fibrous layer, the body-contacting face of which is non-wetted by body fluids; and a highly absorbent intermediate layer between the outer and inner layers.
Description (OCR text may contain errors)
United States Patent 1191 Riely Jan. 9,1973
MICROPOROUS NONADHERENT SURGICAL DRESSING Inventor: Phyllis Riely, Massapequa, N.Y. Assignee: Pall Corporation, Glen Cove, N.Y.
Filed: Nov. 21, 1969 Appl. No.2 878,716
U.S. c1 Q. ..128/156 1m. (:1. ..A6ll 15/00 Field of Search ..l28/l56, 155, 296
References Cited UNITED STATES PATENTS Gallovich 128/156 Bierenbaum et al. ..l28/l56 Gander et a1 ..l28/l56 X OTHER PUBLICATIONS Pioneering Uses of Fiberglas Materials in Medicine, Owens-Corning Fiberglas Corp. (3/21/45).
Meier ..l28/l56 Primary Examiner-Robert W. Michell Attorney-lanes and Chapman [5 7] ABSTRACT A composite surgical dressing that is highly absorbent,
capable of preventing leakage or exudation from open wounds and capable of preventing contamination from entering or escaping from the wound, comprising an outer microporous, liquid-repellent fibrous layer having a maximum pore size of 0.5 micron, and a voids volume of at least 50 percent;- an inner macroporous, fibrous layer, the body-contacting face of which is non-wetted by body fluids; and a highly absorbent intermediate layer between the outer and inner layers.
11 Claims, 2 Drawing Figures MICROPOROUS NONADHERENT SURGECAL DRESSING Dressings are applied to large area wounds, whether massive abrasions or burns or deep open wounds, in order to protect the wound surface, absorb fluids exuded from the wound and to let air into the surface of the wound. It is important to prevent the contamination of the wound without impeding the progress of the natural healing process of the body, and in some cases, to protect the environment against contamination from the wound.
It is also important to avoid, or at least impede, the formation of an adherent bond between the wound surface and the bandage; such a bond can be formed when the body fluids exuded from the wound into the dressing dry to a crust and the dry crust adheres to the healing flesh and to the dressing. This makes very difficult the removal of the bandage without causing great pain to the patient and, even more important, without reopening a partially healed wound.
A further problem is absorbing the body fluids which tend to exude from an open wound or massive burn area, so as to remove the fluids from the surface of the wound, permitting it to dry; this furthers the healing process; it is also necessary at the same time to control the loss of fluid. It is most advantageous, especially when dealing with massive burns, to insure against shock by preventing the excessive loss of the salts from the body which generally are dissolved an any body fluids which may be exuded. Therefore, by limiting the loss of body fluids, the loss of salts is also impeded, thereby decreasing the chances of severe shock.
Previous attempts have been made to prepare bandages which are impermeable to the passage of liquids, but selectively permeable to specific gases and vapors. In US. Pat. No. 3,367,329, patented Feb. 6, 1968, to Dibelius, there is described a surgical bandage including a nonporous membrane, impermeable to liquids and infectious organisms but selectively permeable to specific gases and vapors. In other words, the material is a membranous material that permits the diffusion of vapors, which diffusion is due to the partial pressure differential and is not related to the conventional filtering process (column 2, lines 67 and 68). Such a material is insufficiently permeable compared to the usual porous bandage material, and thus fails to provide the necessary transpiration from the wound surface. Further, there is no provision for absorption of any body fluids exuded from a wound or burn area. The Dibelius membrane is indicated as being a thin, permeable silicone rubber membrane having the desired permeability. I
U.S. Pat. No. 3,426,754, patented Feb. H, 1969, to Bierenbaum et a]. describes a medicaldressing comprising a film having a pressure-sensitive adhesive applied thereto. The film is described as a porous material having an open celled structure permeable to gases. The void or pore sizes of the open cell structure accessible to the exterior of the film is described as being under 5,000 angstrom units, e.g., 100 to 500 angstrom units. The film of Bierenbaum et al. is prepared from a group of relatively crystalline film-forming polymers having a defined elasticity. These films are prepared by a special process which forms the open cell structure in the film. The film can be formed from various hydrocarbon polymers, acetal polymers or a miscellaneous group of polymers including polyalkylene sulfides, polyphenylene oxides, polyamides polyesters. Films of this type are also relatively inefficient and fail to provide the necessary amounts of air and moisture vapor to and from the wound surface; they have a low dirt capacity, so that the amount of air which can be passed in quickly decreases once the film is exposed to even a slightly dusty environment. Bierenbaum et a1. further disclose the use of the porous film in combination with a pad or facing, covered by a wrapping or cover which functions to hold the facing in position.
It is an object of the present invention to provide a surgical dressing which provides all of the usual at-' tributes of a surgical dressing, including the ability to absorb the body fluids exuded from the wound, to protect the wound surface, and to permit the transpiration of air and moisture between the atmosphere and the wound surface. It is a further object of the present invention to provide a surgical dressing which, in addition to all of the usual attributes of a surgical dressing, also prevents the passage of microorganisms to or from the wound surface while retaining the ability to permit full transpiration of air and moisture during use.
it is a further object to provide a surgical dressing which is highly absorbent and capable of retaining, after absorbing, the body fluids exuded from the wound, so as to prevent the passage of the exuded liquid outside of the bandage.
In accordance with the present invention, a composite surgical dressing is provided comprising an outer microporous, liquid repellent fibrous layer, an intermediate absorbent layer, and an inner macroporous layer for separating the absorbent layer from a wound. The body-contacting face of the inner layer is 1 not wetted by body fluid and thus has the property of being relatively non-adherent to a wound surface.
The dressing according to this invention is especially useful for large open wounds or massive burn areas,
where there is heavy exudation of body fluids from the wound which must be absorbed, and the loss of which must be controlled and limited, together with a need for maintaining the wound or burn area aseptic and free from dirt, dust or other contaminants or irritants. It is further useful to prevent the influx of liquids from the exterior while permitting the free passage of air to the wound surface. The surgical dressing has a large capacity to absorb exuded body liquids without permitting loss of such liquids through the upper layer of the dressing, thus controlling the loss of fluids and the salts dissolved therein from the body.
The three layers of the composite'surgical dressing of this invention can be held together by mechanical means or by a bonding agent. Optimally, the layers are bonded together around their periphery, or at the outer edges of the composite. This avoids obstructing or decreasing the absorbency of the central layer of the dressing at the central portion which will be over the wound area. Holding or bonding the layers together around their periphery so that the edges of the dressing are sealed also serves to prevent any loss or escape of the central absorbent layer from between the inner and outer layers; this is especially important where the absorbent layer is formed of a fluffy fibrous mass in which and the individual fibers are not bonded together. Further, imperviously sealing the edges prevents the entry of bacteria or other contaminants into the absorbent layer; this prevents the circumvention of the protective upper, microporous, liquid-repellent layer by these contaminants.
The surgical dressing preferably also comprises an adherent layer, which serves to bond the dressing pad to the flesh of the user; the adherent layer preferably bonds the dressing pad to the flesh of the patient, around the periphery of the wound, to complete the seal around the periphery of the dressing; this further inhibits the by-passing of the microporous outer layer by organisms or particles that could contaminate the wound surface.
The outer microporous fibrous sheet of the dressing of the present invention must be liquid-repellent, to
' water. Thus, if the outer layer were not liquid repellent,
as moisture condenses or is deposited upon the exterior of the outer layer, bacteria could be carried by the water through the pores ofthe outer fabric into the absorbent layer and then to the open wound or burn surface. It is a well-known fact that filters can retain airborne particles of a smaller size than liquid-borne particles. A large liquid-borne particle can be pushed through the filter pores by the flowing liquid that could not be pushed through by dry air. Accordingly, the pores need be no smaller than the largest dimension of a microorganism or particle.
The microporous fibrous outer layer of the dressing of the present invention provides an open passage for the atmosphere to the space within the dressing, and especially that immediately above the wound.- The outer microporous layer is sufficiently porous to permit the passage of air at a substantially zero pressure differential across the surface. The outer layer does not pass the air by a diffusion process, as in the case of a membrane, but rather by direct gas flow through open pores. The outer layer must have a fluid flow capacity sufficient to maintain transpiration over the-wound area. The open structure of the microporous fibrous layer is obtained by utilizing a filter material having a voids volume of at least 50 percent and preferably at least 75 percent.
The outer fibrous layer preferably has a pore size which excludes the passage of air-borne particles of greater than 0.5 micron diameter and optimally of greater than 0.2 micron diameter. This is referred to in the claims as effective maximum pore diameter. This is sufficiently small to prevent the passage of substantially all harmful air-borne bacteria or other microorganisms such as molds, fungi and spores. The liquidrepellent properties of the outer fibrous layer prevent the passage of liquid and thus a smaller pore size is unnecessary.
The outer microporous fibrous layer of the present invention must also be capable of withstanding the abrasion to which it may be subjected during useQFor example, if worn by an ambulatory patient, who then proceeds to carry out his normal daily activities wearing the surgical dressing, the outer layer can be subjected to severe abrasive stress. The outer layer must have sufficient wear resistance to maintain its useful ness over a period of time when worn by an active pattent.
Accordingly, preferred types of microporous liquidrepellent fibrous layers are prepared from a woven glass cloth, which gives the fabric great abrasion resistance and flexibility; the glass cloth preferably has deposited within the weave glass fibers which are bonded in place with a fluorocarbon polymer, including a chlorofluoroc arbon polymer, impregnant or a silicone impregnant. The impregnants are preferably inert and nontoxic to the patient. These impregnants are liquid-repellent and thus prevent the passage of aqueous liquids through the microporous fabric. The glass fabric has great strength and ability to withstand the stresses to which it would be subjected during a days wearing by an ambulatory patient. An example of such a material is described in U.S. Pat. No. 3,053,762, patented Sept. 1 l, 1962 to Adiletta.
Examples of suitable fluorocarbon and chlorofluorocarbon polymer impregnants include polytetrafluoroethylene, fluorinated ethylenepropylene polymer, polyhexafluoropropylene and polychlorotrifluoroethylene. Polytetrafluoroethylene is the preferred impregnant.
The silicone impregnants can be silicone resins or silicone rubbers. The dimethylsiloxane polymers are preferred because of their physiological inertness.
The use of a woven glass fiber fabric and deposited glass fibers is especially preferred, when utilizing a fluorocarbon polymer impregnant. The fluorocarbon polymers require a relatively high curing temperature,
after impregnating the fabric to cure the polymer and to bond the fibers in place; glass is especially suited to withstand such high temperatures. Other impregnating fibers and woven fiber fabrics, however, can be used including such synthetic fibers, and fabrics made therefrom, such as polyamides, polyesters, rayons and polyacrylic resins and even such natural fibers as wool and cotton. The silicone impregnants are especially useful when the fabric and the impregnating fibers are not formed of glass because the silicone impregnants do not require a high curing temperature.
Nonwoven fabrics can also be utilized for the upper layer of the dressing of this invention if they are strong enough and have sufficient abrasion resistance. Excellent microporous woven and nonwoven fibrous sheet materials can be prepared according to any of the following U.S. Pat. Nos. 3,238,056 to Pall et al., dated Mar. 1, 1966; No. 3,246,767 to Pall et al., dated Apr.
bency required. Preferred materials include folded crepe tissue of cotton fibers or of wood pulp fibers, cotton wadding, certain synthetic fibers such as acetate rayon or regenerated cellulose, pulp fluff fibers (obtained by disintegrating chemical cellulose pulp prepared by the sulfate or sulfite methods in such a way that the fibers are set free from the pulp while at the same time avoiding the formation of fiber bundles or knots and cutting of the fibers), absorbent cotton fluff, such as cotton linters, garnetted white cotton waste, and fibrous layers formed from ramie, jute, hemp and bagasse fibers.
The absorbent portion can be formed of mats or pads of fibers, such as a mixture of cotton linters and crimped viscose rayon staple fibers, eg in the proportions of about 60 percent cotton linters and 40 percent viscose rayon staple fibers by weight. The fibers can have a denier within the range of from about 3 to about 15.
Cotton linters comprise cotton fibers of short length usually within the range of one thirty-second to about three-sixteenths of an inch. The viscose rayon fibers are preferably crimped or crinkled and generally of longer lengths, for example from about one-fourth to about three-fourths inch. The viscose fibers tend to add additional resiliency, if needed, to the absorbent layer to further protect the wound area. In addition, if the absorbent material is to be compressed, which results in a greater absorptivity per volume of absorbent material, the rayon fiber component permits additional resilience or springiness in the absorbent pad.
Generally, any highly absorbent, usually cellulosic fibrous material ofa bulky character can be used as the absorbent layer in the dressing of the present invention. Although noncellulosic materials can be used, they are not as preferred because the fibers, per se, are. generally nonabsorbent, or if they are absorbent tend to be far more expensive than the cellulosic materials.
Certain sponge materials, such as an artificial regenerated cellulosic sponge as conventionally produced and commercially available, have suitable properties of texture, porosity, resilience and absorptivity suitable for use as'an absorbent layer in the dressing of the present invention. Composite fiber-surfaced sponges, such as are described in US. Pat. No. 3,156,242, patented Sept. 3, 1968, to Crowe, Jr. et al., having hydrophilic fibers extending from the surface of the sponge into the main body thereof, are especially useful for forming the absorbent layer of the dressing of the present invention. Generally, any hydrophilic material is useful for the absorbent layer, including any combination of the above fibrous and/or spongy materials.
The inner layer of the dressing of the present invention, which is intended to contact the wound area, is of a macroporous fibrous sheet material, preferably woven to obtain increased strength and greatest porosity, and nonadherent to the wound. The porosity must be great enough to allow body fiuids to pass through the pores with insufficient pressure drop, despite the non-wetted characteristic, and small enough to prevent fibers of the absorbent layer from extending through to contact the wound. It is important that the inner face of the inner layer, which is intended to rest against the wound area, be nonadherent to the wound surface.
Otherwise, fibers might be left behind on the wound, causing possible future complications, and the dressing might tend to pull open a partially healed wound, when being pulled off. To avoid this problem, the fibers on the body-contacting face of the inner layer, i.e. the face intended to rest against the wound, are formed of, or coated or impregnated with, a material which is not wetted by body fluids, so that when the body fluids dry, they do not form an adherent bond to that face of the layer.
The macroporous, non-wetted, physiologically inert inner layer is preferably formed of a loosely woven glass fiber scrim. Other fibrous material can be used, including the various fabrics listed above for the microporous outer layer. The inner fabric is preferably impregnated, at least on the body-contacting face, with a nonadherent, physiologically inert, liquid-repellent polymer such as the fluorocarbon, including the chlorofiuorocarbon, polymers or silicone polymers discussed above as the impregnant for the microporous outer layer. All of the body-contacting face of the inner layer must be non-wetted by body fluids, to insure that it is nonadherent, and macroporous. Hence, any impregnation should cover the fibers forming the outer' face of the fabric, i.e. the face touching the wound area, but should not block the pores between the fibers. Generally, polytetrafluoroethylene is the preferred impregnating agent. for the nonadherent lower layer, because of its inertness, and its ability to form a thin film on the fibers of the fabric, without blocking the pores.
Alternatively, the fibers forming the coarse fabric can be coated with the liquid-repellent preliminary to formation of the fabric, whether by weaving, knitting or laying down to form a nonwoven web or mat, to insure that all of the fibers are completely coated. This, however, may render more difficult the fabric forming process, as the coated fibers may not be as easily handled because they become too thick.
The use of a polytetrafluoroethylene impregnation on the inner macroporous layer, as with the upper layer, tends to favor the utilization of a glass fabric, or other inorganic high temperature-resistant material. A preferred material for forming the lower layer is a coarsely woven glass fiber fabric which is coated with Teflon and then cured at the high temperatures required for Teflon curing.
Making the inner fabric layer non-wetted by body liquid and non-adherent to the open wound enables the bandage to be removed without reopening a large oozing wound. The liquid being exuded from the wound surface flows through the macroporous inner layer, to
be absorbed by the intermediate layer. The inner layer is not wetted by the liquid exuded from a wound, and
separates the absorbed liquid in the absorbent layer from the wound surface. The liquid absorbed by the absorbent layer is thus separated from the wound area by the non-wetted inner fabric layer, so that when the abupper and lower fabric surfaces. Preferably, the tape is microporous, as is the upper fabric, or non-porous to air so as to prevent the passage of microorganisms.
Alternatively, the upper and lower layers can be bonded together by applying a bonding agent to the layers and pressing them together, and curing the bonding agent, if necessary. Preferably, the microporous layer extends out beyond the absorbent layer and is folded around and under the inner macroporous layer. This latter system is desirable, because it protects the absorbent layer from being contaminated and thus prevents contaminants from being absorbed by the absorbent layer and passing through the macroporous layer to the wound surface.
The dressing pad can be attached onto a patient in various ways. An adhesive layer can be applied to the dressing pad. The adhesive can be applied around the outer periphery of the lower fabric layer; it can be applied to the lower side of the tape that is folded around the edges of the dressing pad, if that is the method used to hold the composite together; or, it can be applied to a portion of the upper microporous layer if the upper layer extends out beyond the main body of the pad or if the upper microporous layer is folded around and under the lower macroporous layer. Alternatively, the composite dressing can be applied to a patient and held in place by a bandage, generally a coarsely woven fabric, or by tape, wrapped about the patient.
Referring to the drawings,
FIG. 1 is a perspective view of a dressing pad prepared according to the present invention with portions of the upper microporous layer and of the middle absorbent layer broken away.
FIG. 2 is a sectional side view of the dressing pad of F IG. 1.
In the drawings, the upper microporous fabric 1 is a woven glass cloth having glass fibers deposited in the weave and impregnated with Teflon. The fabric is prepared according to the procedure set out in the Example in U.S. Pat. No. 3,053,762, utilizing a polytetrafluoroethylene impregnant. The microporous layer 1 has a maximum effective pore size of 0.2 microns, as determined by 100 percent removal of the bacteria Pseudomonas Diminutia in air suspension.
The middle absorbent layer 4 is formed of compressed wood cellulose fluff deposited as a layer upon the upper microporous fabric and held in place between the lower macroporous woven glass scrim 3 and the upper fabric. The scrim 3 is formed ofa woven glass fabric impregnated with polytetrafluoroethylene to insure body liquid repellency. in forming the dressing, the glass scrim is placed over the layer of fluff deposited upon the microporous layer 1 and the composite is compressed to decrease volume and thus increase unit-volume absorptivity. Finally, the microporous adhesive tape 2 is attached around the periphery of the dressing and folded over to bind the structure together and to maintain the middle fluff layer in compression. Folding the tape 2 completely around the periphery of the pad insures against loss of the middle fluff layer 4. However, folding the tape around only two of the four sides could be sufficient.
Alternatively, the middle layer can be formed of folded sheets of cotton wadding or wood pulp crepe tissue or several layers of a nonwoven fibrous material interleaved between supporting sheets of woven fabrics such as gauze; this type of an absorbent layer can be precompressed and then held between the microporous and macroporous outer layers; the composite can be then held together as explained above.
Alternatively, as a substitute for the microporous tape 2, which is applied around the sides and folded over both the upper and lower layer as shown in the drawing, the upper and lower macroporous and microporous fabrics can be bonded together with a bonding agent applied around the edges of the fabrics and cured subsequent to placing the absorbent layer between the two outer layers.
To further prevent contamination of the wound area and to prevent escape of wound exudation, means should be provided for sealing the periphery of the inner layer of the dressing to the flesh of the patient.
Such sealing means can include an adherent area around the periphery of the dressing, such as is shown in the drawing in FIG. 1, where the tape 2 folded around the inner and outer layers can have a portion of its undersurface, 5, i.e. adjacent. the outer face of the inner layer 3, adhesive on two sides, such that when it is pressed against the patient the outer edges will adhere to the patient forming an air-tight, or preferably a microporous, water-resistant bond. Preferably the adhesive material is permeable or porous to air but non permeable to microorganisms. The permeable or porous adhesive is formed so as to autogenously develop a vast number of pores producing a microporous, adhesive film that remains visibly continuous, but provides a microporous adhesive web suitable to prevent the contamination of the area under the dressing when the dressing is applied and bonded to a patient. Such a microporous adhesive is capableof admitting air, even to the area directly under the adhesive, thereby preventing any maceration of the wound border area, but prevents the passage of bacteria. Such maceration of the skin often occurs when a nonporous layer is applied over the skin, preventing the skin from transpiring properly. Such maceration is evidenced by a wrinkling and paleness of the flesh. An especially useful embodiment of such adhesive is shown in U.S. Pat. No. 3,426,754, to Bierenbaum et al., see particularly, the portion beginning on column 7, line 57 through column 8, line 60.
As a further preferred embodiment of the invention, a germicide can be applied either to the absorbent layer or to'the outer microporous layer of the dressing. Such a germicide would insure that any microbes which do penetrate the outer layer will be inactivated or killed. The germicide should, of course, be nontoxic and nonirritating to the patient. However, if the germicide is applied to the outer microporous layer or the the upper portion of the absorbent layer immediately adjacent the outer layer, and it cannot migrate through the absorbent layer and macroporous inner layer, to contact the patient, the nonirritating nature. of the germicide becomes less significant.
Antiseptic or medicating agents or other biologically active agents can be introduced into the dressing, especially into the macroporous layer or the absorbent layer, by incorporating a liquid or dry medicating agent and applying it to the desired layer. Such materials can be coated on the inner layer so as to react with the fluids exuded from the wound and thus be applied to aid in healing and disinfecting the wound surface. The germicide is preferably applied to the outer layer subsequent to curing, especially if the impregnant in the outer microporous layer is a tetrafluoroethylene polymer. Such materials require a high curing temperature which would decompose most organic germicides. Further, a disinfectant or biocide which is intended to act on the wound surface by reacting with the body fluids to either disinfect the wound area or to aid in the healing process can be applied to the inner macroporous layer, also subsequent to application and curing of the liquid-repellent coating to impart the nonwetted characteristic.
The fibrous layers and the composite dressing should be flexible, so as to be able to conform to the bodys surface. Where desirable, such as where the dressing is to be placed over an area which is subject to constant flexing, as at a joint in the body, e.g. an elbow or a knee, so that the dressing would require an added degree of flexibility, the fibrous layers can be formed only in part of the microporous or macroporous fabric, having intermediate portions formed of an impermeable, but elastic, material. In this construction, the microporous or macroporous fabric material can be formed in alternating strips along the length of the dressing, extending in a direction perpendicular to the direction in which the dressing is to be flexed, with the portions intermediate the microporous or macroporous material formed of the elastic material. This increases the elasticity of the dressing subjected to extreme flexing by the bodily member, while limiting the stress on the microporous or macroporous material, thereby decreasing the chances of ripping the microporous or macroporous layers, or of expanding or warping the pore openings of the layers, and thereby exposing the wound to exterior contaminants.
The intermediate absorbent layer, if it is highly porous to the flow of air, can aid to ensure that the air passing through the permeable portions of the outer layer is distributed over the entire surface of the wound, through the microporous outer layer and the macroporous inner layer. Generally, however, to permit the greatest amount of air to pass over the wound area, it is preferred that all of the outer layer be formed of the microporous material, which must, therefore, be sufficiently supple to withstand almost continuous flexure.
The inner macroporous layer should also be elastic, in this situation. However, because there is no need to avoid stretching the pores of the material or to avoid warping it in any way, the fabric itself may be made elastic, or it can be formed, at least in part of elastic fibers. Methods of preparing both woven and nonwoven elastic materials are well known to the art.
Having regard to the foregoing disclosure, the following is claimed as the inventive and patentable embodiments thereof:
1. A composite surgical dressing having a high degree of absorbency for body fluids exuded from a wound area, capable of preventing microbiological contamination of the wound area from without, and nonadherent to the wound during healing, comprising an outer microporous liquid-repellent fibrous layer having an effective maximum pore size not in excess of ill 0.5 micron, inhibiting passage of body fluids and passage of microorganisms in either 1 Y direction therethrough, and having a voids volume of at least 50 percent, an inner macroporous fibrous layer, the bodycontacting face of which is permeable to but not wetted by body fluids and impregnated so as to coat the fibers thereof with a nonadherent physiologically inert liquid- 1 repellent polymer thereby rendering the body-contacting face nonadherent to the wound, and bonding the fibers of the face together, and a highly absorbent intermediate layer between the outer and inner layers capable of absorbing body fluids passing through the inner macroporous layer.
2. The dressing of claim 1 wherein the outer and the inner layers are bonded together so as to compress the absorbent layer between them.
3. The dressing of claim 2 wherein the outer and inner layers are bonded together by an adhesive tape applied around the edges of the dressing and folded over each of the outer and inner layers.
4. The dressing of claim 1, including an adhesive applied to the outside surface of the inner layer of the dressing, around the periphery thereof, to bond the dressing to a patient.
5. The dressing of claim 1 comprising in addition a biologically-active ingredient applied to one of the layers of the dressing.
6. A composite surgical dressing having a high degree of absorbency for body fluids exuded from a wound area, capable of preventing microbiological contamination of the wound area from without, and nonadherent to the wound during healing, comprising an outer microporous liquid-repellent glass fiber fabric fibrous layer having an effective maximum pore size not in excess of 0.5 micron, inhibiting passage of body fluids and passage of microorganisms in either direction therethrough, and having a voids volume of at least 50 percent, an inner macroporous fibrous layer, the body-contacting face of which is not wetted by body fluids and impregnated so as to coat the fibers thereof with a nonadherent physiologically inert liquidrep'ellent polymer thereby rendering the body-contacting face nonadherent to the wound, and bonding the fibers of the face together, and a highly absorbent intermediate layer between the outer and inner layers capable of absorbing body fluids passing through the inner macroporous layer.
7. The dressing of claim 6 wherein the glass fiber fabric has glass fibers embedded in the weave thereof.
8. The dressing of claim 6 wherein the glass fiber fabric is coated with a resinous material imparting liquid repellency to the fabric. i
9. The dressing of claim 6 wherein the inner fibrous layer is a coarsely woven glass fiber fabric coated with a fluorocarbon resin imparting liquid repellency to the fabric and improving its resistance to adhesion to the body, while permitting the passage of fluids and air through the fabric.
10. The dressing of claim 6 wherein the outer layer is microporous glass fiber fabric impregnated with glass fibers and a fluorocarbon resin imparting liquid repel lency to the fabric, the'intermediate layer is a layer of absorbent cellulose fibers, and the inner layer is a macroporous glass fiber fabric having the body-contacting face impregnated with a fluorocarbon resin imparting liquid repellency to the fabric and improving its resistance to adhesion to the body, while permitting the passage of fluids and air through the fabric.
1 1. The dressing of claim 1 wherein the microporous layer has an effective maximum pore diameter of less than 0.2 micron.