Hydrophobic Non-adherent Wound Dressing

Abstract

A resilient, substantially flat, non-adherent flexible wound dressing which remains flexible when dry, of hydrophobic material capable of retaining substantial quantities of fluid wound exudate. One or both major surfaces may be non-adherent wound-contacting surfaces which may include fenestrated film or interrupted exposed portions of flattened sheetlike fused fibers having a filmlike appearance, or both. The interior of hydrophobic fibers is arranged to retain fluid wound exudate by capillary action. If superimposed fenestrated film is used, it may be united to the hydrophobic fibers either at or inside the dressing edges, or both, preferably by melt sealing. Dressings may be prepared by pressing (with substantially no relative movement) the hydrophobic fibrous material, preferably a carded or air laid batt together with any fenestrated film between closely adjacent parallel uni-directionally moving surfaces of a foam and a stainless steel belt which is heated and then cooled. In the absence of a covering fenestrated film, the surface fibers of the batt, pressed against the heated belt, are softened, flattened, fused and subsequently congealed in contact with the polished belt, thereby forming sheetlike interrupted surface areas of filmlike appearance. When a fenestrated film is added to the dressing, it passes in contact with the stainless belt and may be melt sealed in passage to the fibrous batt with sheetlike interrupted areas of fused fibers being formed, or not formed depending upon the temperature the fibers reach, through the holes in the fenestrated film. A melt edge version of the dressing with soft edges may be made with a cooled perimeter clamp adjacent which a hot perimeter knife cuts and seals the dressing edge.

Description

This invention relates to that class of wound dressings including a contact surface which is non-adherent to wounds and wound exudates, the dressing providing for removal from the wound site of liquid wound exudates, thus causing the formation of a very thin flexible eschar.

BACKGROUND OF THE INVENTION

An early dressing of the subject type disclosed in U.S. Pat. No. 2,923,298 to W. B. Dockstader et al., comprised a fenestrated smooth wound-contacting film united at points between the openings to an absorbent unified backing including nonwoven sheets and cotton gauze. A thinner version of the Dockstader dressing, using a single layer of cotton gauze, is disclosed in the Fukuda U. S. Pat. No. 3,446,208. Numerous other variations of the Dockstader dressing, largely concerned with the wound-contact surface, have been proposed, among which are the dressings described in the Eldredge et al. U. S. Pat. No. 3,285,245, and those described in the Davies U. S. Pat. No. 3,006,338. In the Eldredge variation the contact film is a particular discontinuous film of fused and coalesced nonwoven fine denier polypropylene fibers. The Davies patent impregnates a nonwoven fabric of about the weight of cleaning tissue with a polyethylene emulsion which after drying is calendered to produce a contact surface. Both of these variations and others unite the wound-contacting film or layer with an absorbent material, preferably in the form of cotton, rayon, cellulosic batts, etc., to produce a complete dressing, however. Such absorbent materials form excellent dressing components when the dressing is changed frequently before the exudate saturated absorbent portions of the dressings become dried. Exudate saturated absorbent materials do have the detrimental feature when dried, however, of becoming stiff, harsh and inflexible. If, after drying, they remain in contact with the wound which is already in traumatic condition, they are extremely uncomfortable and frequently aggravate the trauma. While the reason for stiff drying is not entirely clear, a possible explanation may be that the exudate and the absorbent material have an affinity for water which is known to swell absorbent fibers. Hence there is an intimate association possibly with some exudate being imbibed with its water into the fiber, forming when dried a continuous matrix reinforced by the exudate stiffened absorbent material. Additionally, whatever water is absorbed in the absorbent fiber comes from the exudate and hence the absorbent material more quickly reduces the dressing to the stiff dried condition than would be the case if no absorbent material were present.

SUMMARY OF THE INVENTION

It is a primary object of this invention to provide a suitably non-adherent dressing which not only will retain adequate amounts of wound exudate, thereby avoiding frequent dressing changing, but one which remains soft and flexible even when the retained exudate has dried. The primary object of the invention is attained by eliminating absorbent material from the dressing. The intimate association of absorbent material and wound exudate, which is the most significant factor in stiff drying of wound dressings, is thereby avoided. The dressing of this invention is, therefore, wholly hydrophobic, not only with regard to the wound-contact surface which because of its porous nature permits the exudate to contact the subsurface capillaries of the dressing, but also with regard to the fibrous layers which are themselves hydrophobic and whose capillary interstices draw the exudate away from the wound into the dressing interior. Wound dressings of this invention are filled from the wound side with exudate by capillary action, the interconnecting interstices causing the dressings to fill until the capillary space is occupied, thus avoiding contact between the drying atmosphere and the wound exudate except at the peripheral surface areas. But even when the exudate is completely dry, the dressing does not have the characteristics of a solid matrix but rather remains flexible. A possible explanation may be that the exudate which fills only capillary interstices dries into an extremely fragile three dimensional network of individual dried strands which remain flexible because of their thinness.

The hydrophobic dressings of this invention are of two species, one of which is wholly fibrous initially but one or more surfaces of which are softened, flattened and formed by contact against a hot polished surface and cooled thereon, forming a soft comfortable non-adherent wound-contact surface including interrupted sheetlike areas of fused hydrophobic fibers having a filmlike appearance. The interrupted filmlike areas are bridged by underlying subsurface fibers of the fibrous capillary interior of the dressing. The contact surface wicks the wound exudate into the dressing interior where it dries, leaving the dressing still flexible. Only a thin layer of exudate is left in contact with the wound. This thin layer dries to a flexible eschar film adherent to the wound.

The other species of dressing of the invention, which is the preferred one, may simply be the first species with a fenestrated thin film between what would be the contact surface otherwise and the wound. The film may be united to the underlying fibrous material either in the manner illustrated in the Dockstader patent, around the holes, at points between the holes, or only at the peripheral edges. The underlying fibrous pad which forms the interior of the dressing, being somewhat resilient, tends to press its surface fibers against and even somewhat into the fenestrated film holes to make its capillarity available to the wound exudate. However, it is unnecessary when a fenestrated film is interposed that the underlying fibrous surface have interrupted sheetlike areas of fused hydrophobic fibers having a filmlike surface. Moreover, when fenestrated film is used on both major surfaces and the films are sealed together around the dressing edges, it is even unnecessary to have an integrated fibrous interior although it is preferred that the fibrous layer be integrated. Obviously, if the film is on one surface only, at least the exposed fibrous back should be integrated to prevent fiber shedding. But when fenestrated film-faced dressings are prepared by passing them through the apparatus of FIG. 7, they may be passed through at a faster rate or at reduced temperatures whereby fusion between the film and the underlying structure is achieved without appreciably flattening the surface fibers bridging the film holes. However, if there are protruding fiber ends, these are softened, bent back and usually fused to the edges of the holes or to other fibers. All of these variations are suitable, although some give better results than others.

While it is preferred that the layers of hydrophobic fibers used in the preparation of the dressings of this invention be assembled by air laying or carding, the method of assembly is not critical nor is the spacial relationship of the fibers or, if integrated, their method of unification, either by the use of binders, solvents, heat, mechanical intermeshing or by other means. What is critical is that the layers must have capillarity. Fibrous layers of hydrophobic material can normally be made to exhibit capillarity since if the interfiber spacing is too great to support capillary action, the layers may be compressed until the inter-fiber spacing will support capillary action.

Preferred hydrophobic fibers for the hydrophobic fibrous layers used in the preparation of the dressings of this invention are those prepared from polyolefins, polyesters, acrylics, polyvinyls, polyamides and various mixtures thereof, although all of the known flexible hydrophobic polymeric fibers are suitable. Fibers as coarse as 50 denier and above, while not preferred because of their stiffness and comparatively high resiliency in some cases, are suitable so long as the layers assembled from them have capillarity. The stiffness of such higher denier fibers may be somewhat alleviated by non-toxic plasticizers, as is well known.

But finer fibers in the denier range, from the finest commercially available to 8 denier, are preferred because dressings made in accordance with the invention from such fibers display softness, conformability and adequate resiliency to provide cushioning protection to wounds from normally encountered forceful contacts.

It is characteristic of hydrophobic fibrous capillary layers that when compressed there is a distinct tendency for sheetwise capillary flow as compared with penetrating flow. Penetrating flow is more pronounced in less compressed areas or layers of the same fibers prepared under the same conditions. A possible explanation might be that, in compressing the layers, the fibers and hence the capillary channels are bent or deflected in sheetwise direction to a greater degree. At any rate, the phenomenon exists and advantage is taken of it in the preferred dressings of the invention by incorporating at least one densified or compressed layer. In one such dressing, the outer layers of the fibrous thickness are separated by a more compressed or densified layer, which while being penetrated spreads the fluid over a greater sheetwise area of the dressing. The spread fluid then moves from this enlarged area into both outer layers by capillary action, thus avoiding saturation in a local area.

In this invention, the size of the holes in any fenestrated film, preferably in the range of 0.025 inch to 0.035 inch in diameter and the open area, (hole area)/(total area), preferably 10 to 25 percent, and not critical so long as the open area is sufficient and the holes are large enough to permit passage of the exudate. This latter varies somewhat in that exudate which is more viscous requires a larger hole than blood or burn fluids. Larger holes which might otherwise be objectionable because of the fibrous nature of the underlying capillary layer may be used when the holes are at least partially bridged by the interrupted skinlike smooth porous film areas of softened flattened and fused surface fibers of the underlying fibrous layer.

The thickness of the interposed fenestrated film, where such film is used, again is not critical. However, in addition to the fact that thin films are generally softer and more conformable than thick films, they are preferred because of the fact that the thickness and flexibility of the eschar remaining covering the wound is related to the film thickness. For that reason, films in the range of 0.00025 inch to 0.001 inch are preferred although flexible films of considerably greater thickness can be used less effectively.

The properties of the dressings of this invention can perhaps best be illustrated by comparison with the most widely used non-adherent dressing marketed today, dressing "A" made in accordance with the Dockstader et al. patent teaching and sold under the trademark "TELFA" by The Kendall Company, 225 Franklin Street, Boston, Mass. This dressing comprises an outer envelope of 1/4 mil fenestrated polyethylene terephthalate film and an absorbent nonwoven feltlike layer of cotton united to the film at points between the holes therein. Dressing "B" of this invention, with which the "TELFA" non-adherent dressing was compared, consisted of an outer envelope of 1/4 mil fenestrated polypropylene film and a filling layer of partially fused polypropylene fibers averaging 3 denier with a fiber length of about 1 1/2 inches. This dressing was passed twice through the apparatus of FIG. 7 and the film and fibrous layer were fused together around the holes at least but in only a few of the holes were any of the interrupted skinlike film areas shown in FIG. 6 exhibited. The dressing was edge sealed on the apparatus of FIG. 8.

In testing the fluid take-up rate of the dressings, an apparatus was used which delivers the fluid to a well and maintains the well level at dressing-contact level. The dressing was placed wound-contact surface down over the liquid-filled well and the time necessary for the dressing to take up 5 ml. of fluid was recorded.

The fluid retention test was the so-called "dunk and drain" test in which the dressings were immersed in water until thoroughly saturated and then after draining for 10 minutes were weighed to determine the gain over the dry weight under ambient conditions. The test utilized was ASTM No. D1117.

Figures given in Table I below are average figures.

TABLE I

Dressing A Dressing B Size 3 .times. 8 inches 3 .times. 8 inches Weight 2.45 grams 2.60 grams Fluid up-take rate 5 ml in 20 sec. 5 ml in 15 sec. "Dunk & Drain" Fluid retention 25.25 grams 27.16 grams

The comparative stiffness of the dressings were measured before wetting and after being wetted with 10 ml. of blood, and dried. Stiffness was measured using a modified cantilever method whereby similar size dressings were similarly clamped to a rotatable cantilever arm with the dressing initially horizontal and just contacting but not depressing a knife edge on a balance arm. As the cantilever arm was rotated through 90.degree. toward the balance, the amount of downward force exerted by the bending dressing against the balance knife edge was recorded for each 10.degree. of rotation. When the dressings were compared before wetting, the force exerted by the dressings was very similar, varying from about 0.6 gram to 2.3 grams in bending from 10.degree. through 90.degree.. After being wetted with the same amount of blood and dried, however, the force exerted by the two dressings was as follows:

TABLE II

Dressing A Dressing B 10.degree. 6.0 grams 2.5 grams 20.degree. 10.3 grams 4.0 grams 30.degree. 13.9 grams 5.3 grams 40.degree. 15.7 grams 6.0 grams 50.degree. 17.3 grams 6.1 grams 60.degree. 17.7 grams 5.5 grams 70.degree. 18.4 grams 5.3 grams 80.degree. 18.0 grams 5.3 grams 90.degree. 18.1 grams 5.3 grams

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a preferred wound dressing of the invention 10 with a turned up corner including a fenestrated contact film 11 with openings 13 which are bridged by hydrophobic fibrous surface areas 16 of a hydrophobic fibrous layer 15 (FIG. 2). The preferred dressing has a melt sealed continuous edge 14 and a carded hydro-phobic fiber back surface 12.

FIG. 2 is a cross section of the dressing along the line 2 - 2' of FIG. 1 looking in the direction of the arrows, showing the internal hydrophobic fibrous layer 15 which must demonstrate capillarity.

FIG. 3 is a variation of the invention with films similar to 11 on both sides of the dressing of FIG. 1, the illustrated cross section 20 showing fenestrated films 21 and 21', the openings in which are bridged by hydrophobic fibrous surface areas similar to 16 in FIG. 1, the continuous edge 24 and the internal fibrous structure 25 also being similar to respective edge 14 and fibrous structure 15 of FIGS. 1 and 2. While in the embodiment of FIG. 3 the internal fibrous structure 25 and the film 21 and 21' are sealed together at the edge 24, in a non-preferred but workable embodiment the fibrous structure is merely contained in the film envelope without being sealed or otherwise fastened thereto.

FIG. 4 is another variation of the wound dressing of FIG. 1 wherein the dressing 30 has major surfaces 36 and 36' which have no superimposed fenestrated film 11. These surfaces include interrupted skinlike smooth porous film areas of fused and melted surface fibers of a hydrophobic fibrous layer (preferably of fibers similar to those of the interior 35) with underlying and bridging hydrophobic fibers. The internal structure of hydrophobic fibers 35 and the sealed edge 34 are similar to their counterparts in FIGS. 1 and 2.

FIG. 5 shows a cross section of a dressing of the invention in one of its most simple forms. The dressing 50 consists of integrated layers of hydrophobic fibers 75, 75' and 78 of demonstrated capillarity and a wound-contact major surface 76 of interrupted skinlike smooth porous areas of fused and melted surface fibers of fibrous layer 75. The back major surface 79 of the dressing 50 is not different from the fluid retaining body 75'. The layer 78 is a layer of more compacted hydrophobic fibers which tends to spread the fluid as it passes through.

Obviously, dressings may be constructed within the invention incorporating one or more of the illustrated non-critical variations and others, so long as the dressings respond to the claims.

FIG. 6 illustrates a typical microphotographic appearance 70 of wound-contact surfaces 36, 36' and 76 of the dressings of FIGS. 4 and 5 at 150 magnification showing the interrupted skinlike smooth porous film areas 71 of softened and fused hydrophobic fibers with openings 73 (between the smooth film areas 71) bridged by underlying fibers 72.

FIG. 7 illustrates schematically apparatus 80 useful in producing from a fibrous batt the wound-contact surfaces similar to FIG. 6 on the dressings of the invention similar to those illustrated in FIGS. 4 and 5. The apparatus comprises two endless contacting belts, one (51) of polymeric foam and the other (52) of stainless steel, which press the preferably continuous fibrous dressing and optionally fenestrated film between them, wound-contact surface against the stainless steel belt. Whenever both major surfaces of the dressing are to be wound-contact surfaces, the dressing must be inverted and run through the machine again, or two such machines could be used. Alternatively, a spring loaded stainless steel belt could replace the foam belt. The belts are stretched taut between drums 53 and 54 (which turn with their respective shafts 55 and 56 in fixed bearings) and respective drums 57 and 58 whose shafts 59 and 60 are in adjustable bearings being movable with respect to the frame 67 on crossheads 61 and 62 by respective adjustment screws 63 and 64. Similar adjustable features are at the opposite side of the respective belts. The stainless steel belt 52 is heated by means of gas burners 65 whose flame contacts the under side of the belt. The burners are insulated from cold water jets 66 which rapidly cool the previously heated stainless steel belt with which the softened and flattened surface fibers of the hydrophobic dressing on the fenestrated film are still in contact. Passage through the apparatus at proper temperatures forms skinlike smooth film areas of the surface fibers which contact the hot belt. The interrupted fibrous surface retains capillarity because the softened fibers are allowed to flow only to a limited extent and are chilled before the interstices can be closed. Capillaries also exist in the areas bridging the fused surface fibers.

In FIG. 8 a device 40 is illustrated schematically for forming thin flexible melt fused edges such as the edge 14 of FIGS. 1 and 2 on the dressings of the invention. The device consists of a chilled peripheral hold-down clamp 44 which has means for raising and lowering it into clamping relationship. A contour die 42 heated by means of heater coil 41 melts through and seals the thermoplastic dressing material as it descends, compressing spring 43, the elements of which obviously must have sufficient spacing to permit such action. The peripheral heated edge 45 moves closely adjacent the cooled peripheral clamp edge 46. The die is withdrawn by the action of spring 43 when the downward pressure is released. While it is preferred that when a fenestrated film is to be used on the dressings of the invention it be fastened to the underlying fibrous batt by the apparatus of FIG. 7, the film may be fastened by other means including those described in the above mentioned Dockstader et al. patent, or alternatively the fenestrated film such as 11 in FIG. 1 may be completely unsecured to the underlying batt except at the edges which may be sealed by the heated edge 45 or otherwise. In the envelope embodiment of FIG. 3, it is not essential that the fibrous structure and the film be fastened together.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The preferred embodiment of this invention is a dressing similar to that illustrated in FIG. 1 except that the fibrous portion which retains the wound exudate is in three layers which are carded and compressed, with the central layer compressed more than the two outer layers. All layers are preferably made of 3 denier polypropylene fibers about 1 1/2 inches in length with the total weight of the fibrous portion being in the range of 100 to 200 grams per square yard. The film is 1/4 mil polypropylene fenestrated with 0.025 to 0.035 inch diameter holes to give an open area of about 10 to 25 percent. The dressing fabric is run through the apparatus (FIG. 7) at such speed that the film is heated to about 300.degree. F. and then is rapidly cooled in contact with the stainless steel belt as it moves through the apparatus. The individual dressings are then edge sealed on the apparatus of FIG. 8.

The next preferred dressing is made with the same fibrous layers from the same materials with the film omitted. The material is again run through the apparatus of FIG. 7 under the same conditions as with film but the fibrous surface which is in contact with the stainless steel roll has its contacting fibers softened, flattened and fused to form a wound-contact surface similar to that illustrated in FIG. 6 (magnified). Both of the preferred dressings retain adequate amounts of wound exudate, are satisfactory as to non-adherence to wounds and wound exudates, and remain flexible when retained blood is dried.

Claims

We claim:

1. In a unitary non-adherent flexible wound dressing capable of removing from the wound site appreciable quantities of fluid wound exudate and retaining it separated therefrom, that improvement wherein the surfaces on both sides of the dressing are hydrophobic and the dressing includes

a flexible noncellular nonwoven layer of discrete fibers, all of which are hydrophobic, providing fluid retentive inter-fiber capillarity with the major portion of said discrete fibers of said layer being located in the interior of said layer to provide bulk to the dressing and

at least one of said surfaces being a porous non-adherent wound-contact surface.

2. The dressing of claim 1 wherein the contact surface includes areas of interrupted sheetlike fused hydrophobic fibers having a filmlike appearance.

3. The dressing of claim 2 wherein the interrupted areas of sheetlike fused hydrophobic fibers and a wound-contact surface are coextensive.

4. The dressing of claim 2 wherein the interrupted areas of sheetlike fused hydrophobic fibers are coextensive with both major surfaces thereof.

5. The dressing of claim 1 wherein the wound-contact surface includes at least one fenestrated hydrophobic film, the openings in which are bridged by surface fibers of the flexible hydrophobic fibrous layer.

6. The dressing of claim 5 wherein the openings are at least partially bridged by interrupted areas of sheetlike fused hydrophobic fibers having a filmlike appearance.

7. The dressing of claim 5 wherein the layer of fibers is integrated at least on the exposed surfaces thereof.

8. The dressing of claim 5 wherein surface fibers of the hydrophobic fibrous layer are sealed to the fenestrated hydrophobic film.

9. The dressing of claim 5 having two major wound-contact surfaces including fenestrated hydrophobic film united at the dressing edges.

10. The dressing of claim 1 wherein the hydrophobic fibers are polyolefin fibers.

11. In a unitary non-adherent flexible wound dressing capable of removing from the wound site appreciable quantities of fluid wound exudate and retaining it separated therefrom, that improvement wherein the dressing is hydrophobic and comprises

at least two flexible noncellular nonwoven layers of discrete hydrophobic fibers, providing fluid retentive inter-fiber capillarity, one of which layers is more dense than another layer, and wherein the major portion of said discrete fibers of said layers is located in the interior of said layers and provides bulk to the dressing and

at least one major porous hydrophobic non-adherent wound-contact surface.

12. The dressing of claim 11 wherein the contact surface includes interrupted areas of sheet-like fused hydrophobic fibers at the surface of the outermost layer of the dressing, said surface having a film-like appearance.

13. The dressing of claim 11 wherein the wound-contact surface includes at least one fenestrated hydrophobic film, the openings in which are bridged by surface fibers of the outermost surface of said hydrophobic fibrous layers.