Patent Application
20200323694
This invention relates to a novel wound dressing design. Particularly, this invention relates to a wound dressing which incorporates multiple distinct layers, each providing useful features and together providing a novel method of managing a variety of wound types. Moist healing, exudate management, ease of use and patient comfort are provided.
In the field of wound care there exist several general categories of commonly used dressings, each with its own unique set of advantages and disadvantages. Each is indicated for certain wound conditions and user preferences. For example, conventional gauze is inexpensive and widely available, but tends to integrate into the wound as eschar forms in the wound bed and healing progresses. As a result, dressing changes can be painful and counterproductive. Hydrogel and hydrocolloid dressings are soft and gentle on the wound but are bulky and can sometimes cause tissue maceration due to excessive moisture accumulation resulting from poor exudate management. Semi-occlusive, thin polymer films coated with a pressure sensitive adhesive (“PSA”) are readily available and provide a moist healing environment with some level of exudate management. A common example of this type of dressing is a polyurethane thin film coated with an acrylic PSA. These dressings are easily applied and maintained, but can aggressively adhere to adjacent tissue complicating removal and potentially causing irritation due to the PSA.
Woven or nonwoven meshes and various types of apertured films or nettings are likewise used for a wide variety of wound dressing designs. The mesh may serve as a wound contacting surface and/or as a mechanical reinforcing mechanism for handling purposes.
Impregnated mesh dressings may use a multitude of apertured materials including but not limited to woven monofilament structures, nonwoven spunlace webs, extruded apertured materials (“scrims”), knitted textiles and even 3D printed structures, collectively “apertured meshes.” These types of dressings are easy to handle and fix in place. Yet while open porosity is helpful for exudate management, it can be problematic due to integration into the wound bed—or in extreme cases wound desiccation.
In more recent years silicones have been increasingly utilized for wound care applications, particularly for “gentle” skin adhesion. Examples include silicone impregnated into various porous substrates or coated onto thin films.
Bio Med Sciences, Inc. of Allentown, Pa. manufactures and markets the Rylon® brand of wound dressings comprised of woven polyester monofilament mesh impregnated or coated with a tacky silicone gel on one or both sides (Rylon-1 or Rylon-2 respectively). The gel is partially impregnated into the mesh so that a portion of the apertures remain open for exudate management. The mesh further provides a reinforcing mechanism sufficient enough for the retention of surgical staples when required. While these products are easy to handle and manage copious amounts of exudate, they do not typically provide a semi-occlusive environment for moist healing.
Prior art further includes silicone coated thin films that provide a semi-occlusive environment and a non-adherent wound contacting surface. While providing moist healing, these types of dressings tend to wrinkle or slip on the wound making stability and fixation problematic. An example of such a dressing is described in U.S. Pat. No. 4,832,009, which is incorporated herein by reference, and which discloses a dressing made from an interpenetrating polymer network (“IPN”) of polytetrafluoroethylene (“PTFE”) and silicone, and is presently marketed by Bio Med Sciences, Inc. as Silon-TSR® Temporary Skin Replacement. An IPN is a type of polymer/polymer composite wherein each polymer forms a continuous matrix which mutually interpenetrates the other.
As with wound dressings, there are a wide variety of wound types. Wounds can be categorized as chronic or acute. Examples of chronic wounds include venous stasis ulcers, decubitus ulcers and diabetic ulcers. Examples of acute wounds include burns, skin graft donor sites, skin graft recipient sites, abrasions and the like. Wounds are also either wide surface area or linear in nature. Wide surface area wounds such as burns are particularly problematic in comparison to linear wounds such as incisions or lacerations. With linear wounds, the tissue edges are in close proximity so there is less wound to be bridged—each side of the injured tissue is held in direct contact with the other by use of tape, sutures or staples. With wide area wounds, healing must occur from the wound bed upward. With deep wounds where the dermis is damaged or destroyed, skin grafting is required. Whether grafted or not, wide area healing is a slow, painful process.
Not only do the features required for the proper performance of a wound dressing depend on the wound type, the location on the body can have a major impact as well. The issue is particularly challenging for skin graft sites on the back or buttocks of a patient, where ordinary movement and contact with bedding can easily displace a dressing. In the case of a graft recipient site, the graft itself can even be dislodged. Similarly, chronic wounds are a challenge because they tend to produce copious amounts of exudate which often precludes the use of semi-occlusive films. This is particularly problematic for decubitus ulcers in the sacral region.
Even the same wound may require different dressings at different stages of the healing process. A venous stasis ulcer will produce copious amounts of exudate in the early stages of healing. Hydrocolloid dressings are often used on these wounds because of their high absorption capabilities. But as wounds of these type heal, the fragile epithelium can easily be damaged during dressing changes; so a non-adherent dressing may be substituted later in the healing process.
Since infection is a constant threat and potentially serious complication for any wound condition, various antimicrobial agents are used in combination or incorporated into a wide variety of wound dressings in the field. Commonly used antimicrobials include bacitracin, neomycin and polymyxin. Additionally, silver-based compounds and dressings containing silver-based compounds have become commonplace in wound care. Silver-based compounds which contain high valence states of silver (Ag2+ and Ag3+) are preferred. Furthermore, non-leaching polymeric antimicrobial agents composed of polyquat salts such as 3-methoxysilylpropyldimethyloctadecyl ammonium chloride have been used to inhibit microbial colonization.
For the reasons elucidated above no one dressing is a panacea for all wound types, circumstances or phases of healing.
In the field of polymer films, in addition to polyurethane as previously mentioned, materials such as polyethylene, polyester, polycaprolactone, vinyl and other materials including copolymers and composites (collectively “polymeric films”) are used. These polymeric films may or may not be porous or microporous. An example of such a polymeric film is described in U.S. Pat. No. 4,945,125, which is incorporated herein by reference, and which discloses a microporous polymeric IPN membrane of PTFE and silicone and is of particular interest to the present invention. For purposes of this specification, the terms “film” and “membrane” may be used interchangeably, with the term “web” applying to lengths of membranes or films that are manufactured in a continuous process of producing roll goods of such materials.
In the field of adhesives a plethora of chemical systems exist, including acrylics, hydrogels and silicones (collectively “surface adhesives.” For clarity, surface adhesives are not to be confused with contact adhesives such as cyanoacrylate glues.
In the field of silicone chemistry, there is likewise a plethora of systems known in the art. Of particular interest to the present invention are polysiloxane formulations, and in particular platinum catalyzed polydimethylsiloxane systems which are common to the medical field. In general, these formulations are two-part systems where one component contains a crosslinking agent and the other a catalyst. The two components are mixed together in liquid form. Crosslinking between polymer chains (usually accelerated with heat) causes the polysiloxane to cure or vulcanize and form a cohesive solid which can range in character from rigid elastomers to soft & pliable gels depending largely on crosslink density. Elastomers tend to have nonadherent surfaces and high durometer values while gels tend to have low durometer values and are adhesive or tacky to the touch. Such low crosslink density formulations find utility in the wound care field as “gentle adhesives” being semi-adhesive in that their tacky nature clings to the skin or wound surface but does not aggressively adhere to the point of causing wound disruption upon removal. For the purposes of this invention we shall call these types of polymer formulations (whether silicone-based or otherwise) “gels.” An example of a suitable elastomeric silicone is Dow Corning (Midland, Mich.) product code MDX4-4210. An example of a suitable silicone gel is Dow Corning product code 7-9700.
In an effort to improve the art, I have created a dressing with a unique layered design which mitigates the problematic characteristics of silicone thin films and silicone impregnated meshes while leveraging their positive attributes.
In a preferred embodiment, the new inventive dressing comprises an IPN/gel film, which is preferably fenestrated or perforated, laminated to a silicone impregnated apertured mesh, preferably a woven mesh coated on one side (coating the second side would be superfluous in this case). For the purposes of this invention the terms “partially impregnated” and “coated” can be used interchangeably to describe the application of a polymer to an apertured mesh regardless if the polymer actually penetrates into the mesh or simply is bound to its surface. Preferably, the IPN/gel film is fenestrated or perforated, and comprises a thin layer of silicone gel continuously coated onto a silicone/PTFE IPN membrane. (For the purposes hereof, the terms fenestrated and perforated may be used interchangeably.) Due to geometry and the relative frequency of hole patterns in each layer, open holes are created in defined patterns through the entire dressing. This construction improves handling and fixation but also provides a semi-occlusive wound environment capable of managing copious amounts of exudate.
By applying the new dressing to the wound site with the gel surface of the IPN/gel membrane against the wound, the non-adherent/non-integrating advantages of the Silon-TSR dressings are preserved. At the same time, however, the handing and fixation advantages of Rylon dressings are maintained.
Fenestrations or perforations are cut through the IPN/gel material and the apertured mesh is substantially open, thereby allowing wound exudate to freely migrate from the wound through the dressing and optionally into a secondary dressing. By controlling the geometry and design of the fenestrations in the IPN/gel film relative to the apertures and holes of the impregnated mesh, a balance between moist healing and exudate management can be tailored. Consider that a large number of small holes may result in different wound management features than a small number of large holes—even if the hole area is equal. Varying the fenestration and aperture patterns of the layers of the dressings of this invention provides the ability to engineer a number of dressing designs of clinical significance. The combination of fenestrations and apertures is additive when openings align and provide a pathway for exudate to flow. Conversely it is subtractive when they do not align and moisture is retained. Given the nature of repetitive patterns superimposed upon one another, a sort of harmonic beat design occurs. Minor adjustments in one pattern or another greatly influence the overall pattern of openings that extend through the dressing. As long as the relative spacing of fenestrations to apertures is not a whole number multiple of one to the other, there is no need to register the two main layers of the dressing with each other. In other words, if the holes in the wound contacting layer exactly matched the spacing of the apertures in the mesh layer, one would have to position the two layers precisely so that openings through the combined layers are maintained. If the spacing of the holes to apertures is anything other than a whole number multiple of one to the other, every so many repeats of the patterns will cause a hole to align with an aperture. In this fashion the dressing may be engineered to provide a desired flow rate of exudate passage (e.g., a low, medium or high).
Thus, with the present invention the relative geometry of film fenestrations to mesh apertures affords a great ability to tailor exudate management versus moist healing characteristics while also providing non-adherent properties and good handling features.
A web (340) of at least partially impregnated apertured mesh material (that is, the web (340) comprising a web (45) of apertured mesh material (50) at least partially impregnated with silicone (110) and having a silicone coated surface (40)) on carrier substrate (150b) (together identified in
The constructed material (370) of layered apertured web (45) bound to the IPN side (10) of layer (15) on slit release liner (260) is then passed through a die cutting apparatus (380) to punch-cut the final wound dressing shapes. The remaining matrix not cut from web (370) (that is, the remaining material (390) left behind from the cutting process) is then rewound onto a roll (400) to be discarded or preferably recycled. The individual dressings (60) (identified in
Turning now to
As with dressing (60), dressing (60′) may be engineered to provide a desired flow rate (e.g., a low, medium or high) rate of exudate passage.
A preferred embodiment of this invention includes fenestrations through the wound contacting polymer film layer, however it is contemplated that the use of porous or microporous polymeric films may be utilized so that fenestrations or perforations are not necessary to achieve the same basic function of the present invention.
The following examples are not intended to be limiting, as variations on these designs, configurations and processes would be obvious to those skilled in the art. It is obvious that the relative layers of the dressing of this invention may be substantially varied. Example 1 shows an IPN/gel film of approximately 40 microns thickness, but at between 10 and 200 microns is sufficient. Example 1 also shows a woven mesh of 380 microns in thickness with a final partially impregnated apertured mesh of approximately 420 microns; however, these layers may range from 100 microns 600 microns in combination or independently.
Likewise, it is believed that other materials could be used to achieve the same dressing design. Throughout this specification the use of fenestrations of the polymer film layer is described as a preferred embodiment; however, microporous thin films, particularly those that resorb or dissolve also may be used regardless of being fenestrated or not.
Finally, in addition to the cut dressing shapes described herein, a useful alternative is to provide small rolls of the inventive material without a release liner for “tape-like” or circumferential wrap style application.
A continuous web of polydimethylsiloxane and polytetrafluoroethylene IPN was manufactured according to established methods on a suitable carrier substrate, and then coated with a silicone gel using the equipment and process shown and described in connection with
A web of woven mesh approximately 380 microns thick was manufactured according to established methods, and then partially impregnated with silicone gel on a suitable carrier substrate using the equipment and process shown and described in connection with
Using the equipment and process shown and described in connection with
Using bench-top analogs of the processes described in connection with
Examples 1 and 2 are repeated, except a silicone gel containing 3% by weight of a non-leaching, polyquat antimicrobial (3-trihydroxysilylpropyldimethyloctadecyl ammonium chloride) is used. That is, the uncured liquid silicone (180a) in the reservoir shown in
Examples 1, 2 and 3 are repeated, except a silicone gel containing 3% by weight of silver oxysalts is used. That is, the uncured liquid silicone (180a) in the reservoir shown in
Examples 1 through 4 are repeated except that a silicone gel containing 3% by weight of silver oxysalts is used. That is, the uncured liquid silicone (180b) in the reservoir shown in
Examples 1 through 5 are repeated except a silicone gel containing 3% by weight of a non-leaching, polyquat antimicrobial (3-trihydroxysilylpropyldimethyloctadecyl ammonium chloride) is used. That is, the uncured liquid silicone (180b) in the reservoir shown in
Examples 1 through 6 are repeated, except a PTFE/silicone IPN (10′) is formulated using a silicone gel so that wound contacting surface (30′) is inherently tacky and except the step of coating the IPN with a silicone gel using the equipment and process shown and describe in connection with
Example 7 are is repeated, except a microporous resorbable polymeric membrane made of a copolymer of polylactic acid, polylactide, trimethylene carbonate, e-caprolactone is used instead of a PTFE/silicone IPN film (10′) so that the wound contacting surface (30′) is semi-adherent by means of microporous capillary action and except curing is done by passing through the oven (230) at low temperature due to temperature sensitivity of the copolymer.
Preferably, in accordance with the invention, a method of managing a variety of wound types comprises the steps of providing a wound dressing of the invention, in which the wound dressing comprises multiple layers, wherein a first wound contacting layer is fenestrated or perforated semi-occlusive thin film membrane which is a semi-adhesive gel or other polymeric formulation that is inherently tacky, a second more distal layer is a non-continuous silicone gel partially penetrating or otherwise adhering to an apertured mesh, and applying the wound dressing to a wound with the first wound contacting layer being against the wound, so that wound exudate passes through the wound dressing, while integration of the wound dressing into the wound and slippage and wrinkling of the wound dressing on the wound are limited. In this embodiment, the first wound contacting layer of the wound dressing, as well as the non-continuous silicone gel partially penetrating or otherwise adhering to an apertured mesh may include an antimicrobial substance, such as 3% by weight of a non-leaching polyquat antimicrobial (for example, 3-trihydroxysilylpropyldimethyloctadecyl ammonium chloride) or 3% by weight of silver oxysalts.
In accordance with the invention, a method of managing a wound comprises providing a wound dressing of the invention, in which the wound dressing comprises multiple layers, wherein a first wound contacting layer is a semi-adhesive gel or other polymeric film, a second more distal layer is an apertured mesh thus providing a moist healing environment for the wound, while (a) limiting slippage and wrinkling of the wound dressing on the wound, (b) permitting wound exudate to pass through the wound dressing, and (c) limiting integration of the wound dressing into the wound. In this embodiment, the first wound contacting layer of the wound dressing, as well as the silicone gel of the at least partially impregnated apertured mesh may include an antimicrobial substance, such as 3% by weight of a non-leaching polyquat antimicrobial (for example, 3-trihydroxysilylpropyldimethyloctadecyl ammonium chloride) or 3% by weight of silver oxysalts.
The apertured mesh may be woven or knitted textile material, or a nonwoven material, or an extruded scrim.
Preferably, in accordance with the invention, a method of manufacturing a multilayered wound dressing also comprises the steps of (1) creating a thin film with a suitable wound contacting gentle adhesive surface (that is, creating a thin film with a suitable wound contacting low tack surface), (2) creating an at least partially impregnated apertured mesh by at least partially impregnating an apertured mesh with a polymer gel so that apertures of the at least partially impregnated apertured mesh remain open to the passage of wound exudate, the apertured mesh having an outer surface that faces away from a wound application site, and (3) adhering the thin film and the at least partially impregnated apertured mesh together creating a multilayered wound dressing having a wound contacting surface and a distal surface, the wound contacting surface being the wound contacting gentle adhesive surface (that is, the wound contacting tacky surface) of the thin film and the distal surface being the outer surface of the apertured mesh. In a preferred embodiment of the method of manufacturing the multilayered wound dressing, the method may include a step of fenestrating the thin film to create openings for exudate passage. The thin film may be, for example, a semi-occlusive polymeric membrane such as a silicone/PTFE IPN membrane formulated to be inherently tacky and therefore have a gentle adhesive surface.
