Abstract:
A dressing for an open wound includes a cover layer dimensioned for positioning relative to a wound bed. The cover layer permits an evacuation of the space around the wound bed such that a sub-atmospheric pressure may be established to stimulate healing and facilitate the removal of fluid from the wound. Multiple performance zones in the cover layer allow the wound dressing to remain in position through repeated cycles of evacuation without placing undue strain on the wound bed. An outer peripheral zone may include a high peal-strength adhesive while an intermediate zone may include a shear resistant adhesive. A central zone may be devoid of any coating to maximize moisture transmission through cover layer.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present disclosure relates generally to a wound dressing for treating an open wound with a vacuum wound therapy treatment. In particular, the disclosure relates to a dressing having a cover layer employing a plurality of zones of variable performance characteristics to promote healing of the wound. 
         [0003]    2. Background of Related Art 
         [0004]    The body&#39;s natural wound healing process is a complex series of events beginning at the moment of injury. Initially the body reacts by delivering proteins and other factors to the wound through the blood stream to minimize the damage. Blood clots to prevent blood loss while cells engulf bacteria and debris to carry it away from the wound site. Next, the body begins to repair itself in a stage of healing often referred to as the proliferate phase. This phase is characterized by the deposition granulation tissue in the wound bed. Granulation tissue provides a base structure over which cells may migrate inwardly from the periphery to close the wound. Finally the process ends as collagen gives strength to new tissue over time often forming a scar. 
         [0005]    One technique for promoting the natural healing process, particularly, but not exclusively during the proliferate phase, is known as vacuum wound therapy (VWT). Application of a reduced pressure, e.g. sub-atmospheric, to a localized reservoir over a wound has been found to assist in closing the wound. The reduced pressure may be effective to promote blood flow to the area to stimulate the formation of granulation tissue and the migration of healthy tissue over the wound in the natural process. Also a reduced pressure may assist in removing fluids exuding from the wound, which may inhibit bacterial growth. This technique has proven effective for chronic or non-healing wounds, but has also been used in for other purposes such as post-operative wound care. 
         [0006]    The general VWT protocol provides for the introduction of a filler material into the wound to absorb exudates. The filler material may comprise such materials as non-reticulated foams, non-woven fabrics or gauze. The wound and the filler material may then covered by moisture vapor permeable cover layer that permits oxygen exchange with the environment, which may be essential for wound healing. The cover layer often includes an adhesive periphery that forms a substantially fluid tight seal with the healthy skin surrounding the wound. The cover layer thus defines a vacuum reservoir over the wound where a reduced pressure may be maintained over time by individual or cyclic evacuation procedures. 
         [0007]    An aspect of concern in a VWT treatment is the management of forces generated in the dressing when a vacuum is applied. Such forces may cause the separation of the dressing from the skin, thereby limiting the effect of the VWT treatment and increasing the probability that microorganisms will infect the wound. Also, such forces may damage newly forming granulation tissue. The application of a vacuum can deform a flexible cover layer such that it compresses the filler and increases its tendency to adhere to the wound bed. Additionally, the deformation of the cover layer creates transverse shear forces along the skin-adhesive interface at the peri-wound area. These shear forces can cause the dressing to shift and/or pull away from the skin where gaps and wrinkles may develop. Such movement, and the mentioned results thereof, can inhibit the dressing&#39;s ability to provide a seal that is suitable for both the maintenance of a vacuum and for prohibiting the infiltration of contamination. 
         [0008]    Adhesives applied to a cover layer to strengthen or reinforce the dressing&#39;s attachment to the skin may diminish the moisture vapor permeability of the dressing affecting its ability to permit oxygen exchange with the environment. Diminished moisture vapor permeability could also lead to the accumulation of moisture at the skin-adhesive interface. Permitting such an accumulation undermines the dressing&#39;s adhesion to the skin at the peri-wound area, thereby reducing the wear-time of the dressing, the effectiveness of the treatment and the health of the peri-wound area. Accordingly a need exists for a dressing suitable for use in a VWT procedure. 
       SUMMARY 
       [0009]    The present disclosure describes a dressing for use in a vacuum wound therapy procedure to promote healing of a wound. The dressing includes a cover layer having a plurality of zones of variable performance characteristics. A central zone is defined by a portion of a moisture vapor permeable membrane devoid of any coating that would otherwise inhibit the transmission of moisture through the membrane. A peripheral zone adjacent a periphery of the cover layer is adapted to provide a seal around the perimeter of the wound. At least one intermediate zone is disposed between the central zone and the peripheral zone to impart a therapeutic effect or benefit to the wound. 
         [0010]    The peripheral zone may include a high peal-strength adhesive while a first intermediate zone may include a shear-resistant adhesive. A second intermediate zone may include a coating adapted for medicament delivery, a hydrogel for maintaining a moist wound environment, or at least one of an anti-infective agent, an antimicrobial, antibiotic, analgesic, healing factor, vitamins, growth factors, debridement agents or nutrients. 
         [0011]    The moisture variable permeable membrane may extend to a periphery of the cover layer so as to constitute a backing layer for the attachment of an adhesive defining the peripheral zone. The peripheral zone and at least one intermediate zone may be arranged concentrically with respect to the central zone. The cover layer may also include a port for permitting access to a vacuum reservoir defined beneath the cover layer for a vacuum tube. 
         [0012]    According to another aspect of the disclosure a wound dressing apparatus for use in a vacuum wound therapy procedure includes a contact layer and a filler material positioned in a wound bed and covered by a cover layer. The cover layer defines a vacuum reservoir above the wound bed and permits access of a vacuum tube to the vacuum reservoir. The cover layer includes a peripheral zone to provide a seal around the wound bed, at least one intermediate zone for imparting a therapeutic effect or benefit to the wound bed, and a central zone formed from a moisture vapor permeable membrane. 
         [0013]    The contact layer may be formed from a conical apertured film to promote unidirectional flow of exudates from the wound. The absorbent filler material may include polyolefin filaments arranged in a multi-strand bundle. Also, a vacuum system in fluid communication with the vacuum reservoir may include a vacuum source, a collection canister and a one-way valve. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the detailed description of the embodiments given below, serve to explain the principles of the disclosure. 
           [0015]      FIG. 1  is an exploded perspective view of a vacuum wound therapy system in accordance with the present disclosure; 
           [0016]      FIG. 2A  is a perspective view of the vacuum wound therapy system of  FIG. 1  assembled for use on a patient; 
           [0017]      FIGS. 2B and 2C  depict alternate assemblies of the vacuum wound therapy system; 
           [0018]      FIG. 3A  is a reverse angle perspective view of the cover layer of  FIG. 1 ; 
           [0019]      FIG. 3B  depicts an alternate embodiment of the cover layer; 
           [0020]      FIG. 4A  is a cross sectional view of the vacuum wound therapy system of  FIG. 1  in a first condition exhibiting a vacuum reservoir; and 
           [0021]      FIG. 4B  depicts the vacuum wound therapy system in a second condition wherein the vacuum reservoir is evacuated. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0022]    The wound dressing of the present disclosure promotes healing of a wound by providing a reservoir over the wound where a reduced pressure may be maintained. The reservoir subjects the wound to a sub-atmospheric pressure to effectively draw wound fluid, including liquid exudates, from the wound without the continuous use of a vacuum pump. Hence, vacuum pressure may be applied once, or in varying intervals depending on the nature and severity of the wound. The use of a wound dressing in this manner has been found to promote healing by reducing the probability of infection, stimulating the deposition of granulation tissue and other beneficial processes. The wound dressing of the present disclosure includes a cover layer having multiple performance zones to enhance the effect of a vacuum wound therapy treatment. 
         [0023]    The attached figures illustrate exemplary embodiments of the present disclosure and are referenced to describe the embodiments depicted therein. Hereinafter, the disclosure will be described in detail by explaining the figures wherein like reference numerals represent like parts throughout the several views. 
         [0024]    Referring initially to  FIG. 1 , a vacuum wound therapy system according to the present disclosure is depicted generally as  10  for use on a wound “w” surrounded by healthy skin “s.” The vacuum wound therapy system  10  includes a vacuum system  12  in fluid communication with a vacuum reservoir  14  ( FIG. 4A ) defined by or within the wound dressing  16 . The vacuum system  12  includes a vacuum source  18  coupled to the dressing  16  through a one-way valve  20  and a vacuum tube  24 . A collection canister  28  is provided for wound drainage and debris. The vacuum system  12  is adapted to provide a reduced pressure to the vacuum reservoir  14  appropriate to stimulate healing of the wound. A more detailed description of an appropriate vacuum system  12  is found in commonly assigned U.S. Patent Application Publication 2007/0066946, the entire contents of which are incorporated herein by reference. 
         [0025]    Wound dressing  16  generally includes a contact layer  34 , filler  38  and a cover layer  40  defining a plurality of performance zones. A backing layer  44  may be coated with various materials in a juxtaposed relation to define a peripheral zone  48 , a first intermediate zone  52 , a second intermediate zone  56  and a central zone  58  ( FIG. 3A ). Alternatively, each zone may comprise an independent layer positioned adjacent the wound bed “w.” Each layer is described in greater detail below. 
         [0026]    Contact layer  34  may be sufficiently conformable to be positioned in direct contact with an irregularly shaped surface of a wound bed “w.” A thin film of polyethylene or other suitable non-adherent material may form the contact layer  34  to limit the adherence of filler  38  and other substances to the wound “w.” Apertures or perforations in the film permit fluids to pass through the contact layer  34 , allowing for the sub-atmospheric pressure to penetrate into the wound “w” and for exudates to flow freely out of the wound “w.” By selecting an appropriate film material, the passage of wound exudate through contact layer  34  may be controlled so as to be substantially unidirectional to prevent wound exudate from flowing back into the wound. To promote a unidirectional flow, a conical apertured film, such as those provided by Tredegar Film Products of Richmond, Va., may be selected for forming contact layer  20 . This type of film is arranged with apertures positioned at the peaks of cone shaped formations in the film material such that exudate encounters the film as an array of micro-funnels in one direction and an array of collecting basins in the other. Unidirectional flow of exudates may also be promoted by the selection of other materials including a lamination of layers having varying absorptive characteristics. One exemplary material, which may be used as a contact layer is sold under the trademark XEROFLO® by Kendall Corp., a division of Covidien. 
         [0027]    Filler  38  may be arranged over contact layer  34  to fill wound “W” to the level of the surrounding healthy skin “s,” or alternatively the wound “w” may be overfilled with filler  38 . An absorbent material such as non-woven gauze or reticulated foam may be used for filler  38  to trap any exudate that migrates through contact layer  34 . An antimicrobial dressing sold under the trademark KERLIX™ AMD™ by Kendall Corp., a division of Covidien, may be suitable for use as filler  38 . To prevent adhesion to the wound “w,” the filler  38  may also comprise a material configured such that its fibers do not tend to protrude through apertures of contact layer  34  where they may become engulfed by newly forming granulation tissue. One particular type of material exhibiting this characteristic is often referred to as “tow.” The manufacturing process for synthetic fibers often includes an extrusion of an indeterminate length of continuous filaments, which are spun together to form fibers. Continuous lengths of un-spun filaments may be arranged in multi-strand bundles which are referred to as tow. A single length of tow formed from a hydrophobic material such as polyolefin may be laid in the wound bed “w” to form filler  38 . This arrangement allows for a complete removal of filler  50  when the dressing  16  is changed without re-injuring the wound “w.” 
         [0028]    Cover layer  40  may be placed over the wound “W” enclosing the contact layer and filler therein. The periphery of cover layer  40  extends laterally beyond the perimeter of the wound bed “w” so as to contact the healthy skin “s” to form a seal over the wound “w.” As depicted in  FIG. 2A , an opening  60  may be provided or formed through the cover layer  40  to provide access for the vacuum tube  44  to communicate with the vacuum reservoir  14 , or the vacuum tube  44  may be sealed under the periphery of the cover layer  40  as depicted in  FIG. 2B . Alternatively, a distinct portal member or port  62  may be provided to facilitate fluid communication between the vacuum system  12  and the vacuum reservoir  14  as depicted in  FIG. 2C . Port  62  may be configured as a rigid or semi rigid, low-profile component adapted to receive the vacuum tube  24  in a releasable and fluid-tight manner. The vacuum port  62  may be configured to include a wide and flexible flange  64  about its perimeter. The flange  64  permits an adhesive to be attached to either an underside of flange  64  for securement to an outer surface of cover layer  40 , or to a top side of flange  64  to provide for mounting to the underside of the cover layer  40 . 
         [0029]    Referring now to  FIG. 3A , cover layer  40  includes multiple performance zones  48 ,  52 ,  56  and  58  comprising various materials. A backing layer  44  may extend to the periphery of the cover layer  40  to provide a substrate for various coatings or materials defining the various performance zones  48 ,  52 ,  56  and  58 . As depicted, each of the performance zones  48 ,  52 ,  56  and  58  is a continuous band arranged concentrically with respect to the others. The size, shape and position of the zones, however, may be varied according to the needs of the particular wound or treatment. For example, a cover layer  40 A as depicted in  FIG. 3B  may be provided comprising a first intermediate zone  52  formed from a pattern of distinct shapes surrounded by second intermediate zone  56 A. The various coatings may be laminated to the backing layer  44  or affixed by other appropriate means. The various materials forming layer  40  are described in greater detail herein below. 
         [0030]    Backing layer  44  may be formed from a flexible polymeric membrane to act as a fluid barrier to allow for a sub-atmospheric pressure to be established in vacuum reservoir  14 . The material&#39;s flexibility accommodates the pressure changes associated with the evacuation cycles in a VWT procedure. Backing layer  44  also serves as a microbial barrier preventing contaminants from entering the wound area. Preferably, the backing layer  44  is formed from a moisture vapor permeable membrane to promote the exchange of oxygen and moisture between the wound site and the atmosphere. A membrane that provides a sufficient moisture vapor transmission rate (MVTR) and is simultaneously impervious to liquid may be selected for use as backing layer  44 . Another preferred membrane characteristic is the ability to stretch and conform to the compressed wound filler or wound bed. A membrane&#39;s tendency for elongation when subjected to a vacuum reduces the shear forces transitioned to the peri-wound area. One exemplary material for use in backing layer  44  is a transparent membrane sold under the trade name DURAFLEX® by Deerfield Urethan, a Bayer Material Science Company. Other materials which may be suitable for use in a backing layer include the thin films marketed under the names POLYSKIN®II by Kendall Corp., a division of Covidien, TEGADERM™ by 3M of St. Paul, Minn. and OPSITE™ by Smith and Nephew PLC of London, UK. A central zone  58  of the cover layer is defined by the area of the backing layer  44  not covered with any material which would tend to lessen the MVTR. 
         [0031]    At the periphery of the cover layer  40  is a peripheral zone  48  defined by a continuous layer of high peal-strength, pressure sensitive adhesive. The adhesive forms a seal with the skin “s” around the perimeter of the cover layer to prevent the ingress of atmospheric fluids under the edges of the cover layer  40  when a reduced pressure is established in the reservoir  14 . The adhesive defining the peripheral zone  48  is adapted to prevent the loss of adhesion to the skin even when exposed to environmental factors such as exudates from the wound “w” or body movements by the patient. In general, the high peal-strength adhesive is adapted to resist inadvertent lift-off, roll or “flagging,” i.e., a failure of the dressing to adhere to itself, at the edges of the cover layer. The adhesive defining the peripheral zone  48  may include, for example, those adhesives included with the dressing sold under the trademark GELVA® Multipolymer Solutions by CYTEC Surface Specialties Inc. 
         [0032]    The high peal-strength adhesive defining peripheral zone  48  may be bonded to backing layer  44 , or applied directly to the skin “s” surrounding the wound bed “w.” The adhesive should preferably be non-irritating and non-sensitizing to the contacted skin, and may be vapor moisture permeable to permit the contacted skin to transmit moisture. Preferably, the peripheral zone  48  and first intermediate zone  52  are positioned so as not to overlap the contact layer  34  as seen in  FIGS. 4A and 4B . This arrangement facilitates the changing of certain individual components of the dressing, such as filler  38  without removing the entire dressing  16 . 
         [0033]    Disposed between the peripheral zone  48  and central zone  58  are first and second intermediate zones  52  and  56  respectively. First and second intermediate zones  52 ,  56  are defined by a layer of a substance for imparting a therapeutic effect or benefit to the wound “w.” As indicated above, first and second intermediate zones  52 ,  56  may be arranged as continuous bands concentric with central zone  58  as seen in  FIG. 3A , as a pattern of distinct shapes as seen in  FIG. 3B , or any other convenient arrangement. 
         [0034]    First intermediate zone  52  may, for example, be defined by a layer of an adhesive that laterally stabilizes the dressing when a reduced pressure is applied to evacuate the reservoir. As seen in  FIG. 4B , when the reservoir is evacuated, the cover layer may tend to flatten against the wound “w.” This may result in an outwardly directed force in the dressing  16  which may tend to separate the cover layer  40  from the skin “s.” Also, the shear forces in the cover layer  40  may be transmitted to the skin “s,” pulling apart newly forming granulation tissue and re-injuring the wound “w.” To counteract these tendencies, a shear-resistant adhesive may be selected for use in first intermediate zone  52 . Since many high peal-strength adhesives are adapted primarily to resist upwardly directed forces, i.e., those forces tending to lift the cover layer from the skin, a high peal-strength adhesive defining the peripheral zone  48  may be supplemented with an adhesive particularly adapted to resist lateral forces defining the first intermediate zone  52 . A shear-resistant adhesive, such as GMS 1753 manufactured by CYTEC Surface Specialties Inc., that is moisture vapor permeable and suitable for use on the skin, may be used to define first intermediate zone  52 . 
         [0035]    Second intermediate zone  56  may be defined by a layer of a distinct material for providing a therapeutic effect or benefit to the wound. For example, second intermediate zone  56  may be adapted for transdermal medicament delivery. A substance such as an anti-infective agent, an antimicrobial, antibiotic, analgesic, healing factor, vitamins, growth factors, debridement agents or nutrients may be coated on portions of backing layer  108  to define second intermediate zone  56 . Alternatively, a hydrogel may be selected for use in second intermediate zone  56  to maintain a moist wound environment. As seen in  FIG. 4B , second intermediate zone  56  may be in contact with filler  38  when the reservoir  14  is evacuated to permit transfer beneficial agents thereto. Filler  38  and contact layer  34  may be eliminated if appropriate allowing for second intermediate zone  56  to contact the wound bed directly. It is also contemplated that an additional attachment adhesive may be beneficial for use in second intermediate zone  56 . 
         [0036]    Although the foregoing disclosure has been described in some detail by way of illustration and example, for purposes of clarity or understanding, it will be obvious that certain changes and modifications may be practiced within the scope of the appended claims.