Patent Description:
The body'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.

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 by 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.

The general VWT protocol provides for the introduction of a filler material into the wound to absorb exudates and promote fluid transport away from the wound bed. The wound filler may comprise such materials as non-reticulated foams, non-woven reinforcements or gauze. The wound and the absorbent wound filler material may then be covered by a flexible cover layer having 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. <CIT> and <CIT> each describe different systems for vacuum wound therapy.

An aspect of concern in a VWT treatment is the management of forces generated in the dressing when a reduced pressure is applied. These forces may undesirably deform a flexible cover layer, draw the peri-wound margins into the wound and put the surrounding skin in tension. These same forces may significantly compress the absorbent filler such that it forms a rigid mass. In such a state, the filler adopts an increased tendency to adhere to the wound bed, restricts the fluid passages available for exudate transport and inhibits penetration of the reduced pressure there through. Accordingly, a need exists for a dressing suitable for use in a VWT procedure.

The present disclosure describes a dressing for use in a vacuum wound therapy procedure to promote healing of a wound. The dressing according to the invention is defined in claim <NUM>. The dressing includes a cover layer having an integrated support structure to manage forces associated with a VWT procedure. The cover layer includes a backing layer formed from a flexible polymeric membrane, an adhesive layer to affix the backing layer over a wound and provide to a seal around the wound bed, and a reticulated or net-like reinforcement layer affixed to the backing layer and extending to a peripheral region of the cover layer. The net-like reinforcement layer stiffens the cover layer and contributes to the ability of the cover layer to resist the deformation in the wound area commonly associated with a VWT procedure. Thus, the wound filler may be compressed to a minor degree such that it continues to provide exudate transport and vacuum penetration. The use of the net-like reinforcement layer may also lessen the degree to which the wound margin collapses, and may contribute to the manifestation of forces generated by the application of a reduced pressure as compression forces rather than shear forces. Compression forces applied to a wound is well known to be a beneficial wound treatment.

The reinforcement layer may be formed from such structures as a mesh of polyethylene terephthalatae fibers and thermoplastic netting. The adhesive layer may be affixed to a peripheral region of the backing layer and may include an opening such that the adhesive layer does not extend to a central region of the cover layer. The adhesive layer may overlap a portion of the reinforcement layer such that the reinforcement layer is firmly affixed to the backing layer. Alternatively, the reinforcement layer may contain an appropriate adhesive coating to more firmly attach it to the backing layer. The backing layer may be formed from a polyurethane film having a thickness from about <NUM> mils to about <NUM> mils, and includes an aperture therein for facilitating connection of a vacuum port to the cover layer. The vacuum port incorporates a filter screen defining a plurality of openings. The backing layer may be formed from a moisture vapor permeable membrane.

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 a single strand of a polyolefin filament. Also, the vacuum system may include a vacuum source, a collection canister and a one-way valve.

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention, in the following also described as "the present disclosure", and, together with the detailed description of the embodiments given below, serve to explain the principles of the disclosure.

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. To facilitate fluid transport from the wound, a filler material is included within the reservoir to promote the wicking of wound fluids subject to a reduced pressure. 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 a reinforcement structure to enhance the effect of a vacuum wound therapy treatment.

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.

Referring initially to <FIG>, a vacuum wound therapy system according to the present disclosure is depicted generally as <NUM> for use on a wound "w" surrounded by healthy skin "s. " The vacuum wound therapy system <NUM> includes a vacuum system <NUM> in fluid communication with a vacuum reservoir <NUM> (<FIG>) defined by or within wound dressing <NUM>. The vacuum system <NUM> includes a vacuum source <NUM> coupled to the dressing <NUM> through a one-way valve <NUM> and a vacuum tube <NUM>. A collection canister <NUM> may be provided for wound drainage and debris. The vacuum system <NUM> is adapted to provide a reduced pressure to the vacuum reservoir <NUM> appropriate to stimulate healing of the wound "w. " A more detailed description of an appropriate vacuum system <NUM> is found in commonly assigned <CIT>.

A vacuum port <NUM>, depicted in greater detail in <FIG>, is included to facilitate connection of the vacuum system <NUM> to the dressing <NUM>. The vacuum port <NUM> may be configured as a rigid or semi-rigid, low-profile component adapted to receive the vacuum tube <NUM> in a releasable and fluid-tight manner. The vacuum port <NUM> may be configured to include a wide and flexible flange <NUM> about its perimeter. The flange <NUM> permits an adhesive to be attached to either an underside of flange <NUM> for securement to an outer surface of cover layer <NUM>, or to a top side of flange <NUM> to provide for mounting to the underside of the reinforcement layer <NUM>. Either configuration provides a mechanism for connecting to the dressing <NUM>. A hollow interior of the vacuum port <NUM> provides fluid communication between the vacuum tube <NUM> and the reservoir <NUM> defined by or within dressing <NUM>. A connector segment <NUM> extends above the flange <NUM> for facilitating connection with the vacuum tube <NUM>. It is envisioned that because of the possible intimate proximity of the vacuum port <NUM> to either reservoir <NUM> or wound filler <NUM>, the performance of vacuum port <NUM> may be enhanced by the incorporation of a filter screen <NUM> as depicted in <FIG>. Filter screen <NUM> may inhibit the migration of large particles that may otherwise be drawn into the vacuum port <NUM> and consequently create a restriction or blockage of the vacuum tube <NUM>. The filter screen <NUM> may be integral to the configuration of the vacuum port <NUM> as part of the port flange <NUM>. The filter screen <NUM> may include a number of openings, each smaller than a cross-sectional area of the vacuum tube <NUM> or the opening in the vacuum port <NUM> adapted to receive the vacuum tube <NUM>, and collectively greater than the cross-sectional area of vacuum tube <NUM> or the opening in the vacuum port <NUM> adapted to receive the vacuum tube <NUM>. For example, the filter screen <NUM> of vacuum port <NUM> may include four relatively large openings, while the filter screen 58A of vacuum port 30A depicted in <FIG> may include six relatively small openings. The openings in the filter screens <NUM>, 58A are dimensioned to minimize the passage of tissue particles of a predetermined dimension through the respective vacuum port <NUM>, 30A.

Another alternate embodiment of a vacuum port is depicted generally as 30B in <FIG>, <FIG>, <FIG> and <FIG>. Vacuum port 30B is configured to accept a filter screen <NUM> or <NUM> as a
distinct or independently manufactured component as depicted in <FIG>, <FIG> and <FIG>. An opening or cavity <NUM> depicted in the plan view of <FIG> and shown in phantom in <FIG> on an underside of vacuum port 30B may be adapted to permit filter screen <NUM> to be permanently bonded therein such that filter screen <NUM> is substantially flush with the underside of vacuum port 30B. Alternatively, filter screen <NUM> may be bonded to the opening on the underside of vacuum port 30B. Filter screen may <NUM> includes a generally flat base <NUM> through which the openings <NUM> extend, and a pair lips <NUM> projecting from the base <NUM> along opposite edges of the filter screen <NUM>. The lips <NUM> may be dimensioned to be flush with a patient facing under surface of the flange when received within the cavity <NUM>. Alternatively the lips <NUM> may extend beyond the under surface of the flange to extend beyond the cavity <NUM> in the portal member 30B as depicted in <FIG>. Filter screen <NUM> may exhibit an increased surface area available for bonding within cavity <NUM> of vacuum port 30B. Filter screen <NUM> may be secured within cavity <NUM> by bonding, cements, adhesives or the like. In one embodiment, filter screen <NUM> is positioned within cavity <NUM> with lips <NUM> facing toward the wound (<FIG> and <FIG>). In another embodiment, filter screen <NUM> is positioned within lips <NUM> facing toward vacuum port 30B and away from the wound (<FIG>). In another embodiment, base <NUM> is devoid of lips <NUM> as shown in <FIG>, and is substantially planar.

It is also envisioned that filter screens <NUM> and <NUM> may be provided in combination with a treatment element <NUM> comprising a therapeutic material as depicted in <FIG>. Treatment element <NUM> may be inserted between filter screens <NUM>, <NUM> and may secured to vacuum port 30B by an appropriate adhesive bond. The treatment element <NUM> and filter screens <NUM>, <NUM> may define an insert for reception into cavity or opening <NUM> on the underside of portal member 30B. This arrangement may provide a convenient method of treating the wound exudate as it is drawn from the wound "w. " Treatment element <NUM> may comprise fibrous or granulated materials contained in a porous container or wrap to facilitate placement between filter screens <NUM> and <NUM>. Treatment element <NUM> may include materials such as activated charcoal or other odor control or neutralizing substances. Treatment element <NUM> may include anti-bacterials such as polyhexamethylene biguanide (PHMB). Also, antimicrobials such as ionic metals or biguinides may be included to reduce the bio-burden of the exudate or microbials within the exudate as the exudate is drawn in to a collection canister <NUM>. In the alternative, filter screens <NUM>, <NUM> may comprise charcoal, antimicrobials, anti-odor substances.

Vacuum tube <NUM> may be configured to accept a variety of tubing geometries such as round, oblong or elliptical. Vacuum port <NUM> may be provided as a pre-affixed component of dressing <NUM>, as part of vacuum system <NUM> or entirely independently. Also vacuum port <NUM> may not be necessary depending on the configuration of dressing <NUM>.

Wound dressing <NUM> generally includes a contact layer <NUM>, filler <NUM> and a reinforced cover layer <NUM>. Reinforced cover layer <NUM> is formed from a composite including a backing layer <NUM>, a reinforcement layer <NUM> and an adhesive layer <NUM>. Each layer of wound dressing <NUM> is described in greater detail below.

Contact layer <NUM> 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 <NUM> to limit the adherence of filler <NUM> and other substances to the wound "w. " Apertures or perforations in the film permit fluids to pass through the contact layer <NUM>, 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 <NUM> 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 <NUM>. 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. Though it is depicted in a square configuration, the shape of the contact layer <NUM> can be customized to better suit the wound geometry. 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.

Filler <NUM> may be arranged over contact layer <NUM> to fill wound "w" to the level of the surrounding healthy skin "s" or may over-fill the wound "w" as depicted in <FIG>. An absorbent material such as non-woven gauze or reticulated foam may be used for filler <NUM> to trap or transport any exudate that migrates through contact layer <NUM>. An antimicrobial dressing sold under the trademark KERLIX® by Kendall Corp. , a division of Covidien, may be suitable for use as filler <NUM>. To prevent adhesion to the wound "w," the filler <NUM> may also comprise a material configured such that any stray fibers do not tend to protrude through apertures of contact layer <NUM> 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. It is the continuous lengths of un-spun filaments 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 <NUM>. This arrangement allows for a complete removal of filler <NUM> when the dressing <NUM> is changed without re-injuring the wound "w.

Cover layer <NUM> may be placed over the wound "w" enclosing the contact layer <NUM> and filler <NUM> therein. The periphery of cover layer <NUM> 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>, adhesive layer <NUM> may extend to the periphery of cover layer <NUM> to provide the seal with the use of a medical-grade, pressure-sensitive adhesive. The adhesive layer <NUM> may be adapted to provide a fluid-tight and bacteria-tight seal around a peripheral region of dressing <NUM> such that exudate cannot escape through the edges of the dressing <NUM> and external air and contaminants may not enter the wound area. To provide such a barrier, the adhesive layer <NUM> may, for example, be on the order of <NUM> to <NUM> mils thick depending on the adhesive used. In general, a high peal-strength adhesive may be used to resist inadvertent lift-off, roll or "flagging," i.e., a failure of the dressing to adhere to itself or the patient, at the edges of the cover layer <NUM>. The adhesive defining the adhesive layer <NUM> may include, but is not limited to, medical grade acrylics, rubber base or silicone adhesives. Preferably, those adhesives included with the dressing sold under the trademark Polyskin II Transparent Dressings by Kendall Corp. , a division of Covidien, may be used. Adhesive layer <NUM> forms a continuous band around the peripheral region of cover layer <NUM>, but contains an opening such that the adhesive layer does not extend inwardly to the central areas of cover layer <NUM>.

As depicted in <FIG>, reinforcement layer <NUM> may overlap adhesive layer <NUM> at an outer edge such that an outer periphery of reinforcement layer <NUM> is firmly affixed to backing layer <NUM>. Reinforcement layer <NUM> extends to a peripheral region of cover layer <NUM>, but not necessarily to an outer perimeter of the cover layer <NUM>. Reinforcement layer <NUM>, particularly any portion not overlapping the adhesive layer <NUM>, may be affixed to backing layer <NUM> with a light coat of an adhesive <NUM> applied to the appropriate side of the reinforcement layer <NUM> or the backing layer <NUM>. A portion of a wound facing side <NUM> of the reinforcement layer <NUM> carries no adhesive to prevent adhesion of the cover layer <NUM> to the filler <NUM>. An aperture <NUM> extends through the reinforcement layer <NUM> to permit fluid communication between the reservoir <NUM> and vacuum system <NUM>.

The reinforcement layer <NUM> may comprise a mesh of polyethylene terephtalate (PET) fibers, which offer good liquid resistance making it suitable for use in a moist wound environment. PET fibers may be used to form woven or non-woven reinforcements having large pore sizes. Some PET reinforcement manufacturing methods provide for interlinking the fiber junctions to yield a mesh that is flexible in multiple directions and also does not unravel when cut. One such method is known as hydro-entanglement. PET reinforcements thus manufactured tend to have a high shear stiffness that may be useful in reinforcing cover layer <NUM>. One exemplary material, which may be suitable for incorporation into reinforcement layer <NUM>, is sold under the trademark Sontara® by DuPont. Alternatively, reinforcement layer <NUM> may be formed from another reinforcement or mesh structure having suitable shear stiffness. Examples of suitable structures include extruded netting.

Suitable materials for use in such alternate structures include PET, polyethylene, nylon and polypropylene. Additionally, woven structures may be used for reinforcement layer <NUM>. Acceptable woven materials may include cotton gauze, woven acetate and nylon.

Extending to the periphery of the cover layer <NUM> is backing layer <NUM>. Backing layer <NUM> provides a substrate to which reinforcement layer <NUM> and adhesive layer <NUM> may be affixed. An aperture <NUM> extends through the backing layer <NUM> to permit fluid communication between the reservoir <NUM> and vacuum system <NUM>. Backing layer <NUM> is formed from a flexible polymeric membrane to serve as a fluid barrier to allow for a sub-atmospheric pressure to be established in vacuum reservoir <NUM>, and also as a microbial barrier preventing contaminants from entering the wound area. For example, backing layer <NUM> may comprise a polyurethane film having a thickness from about <NUM> mils to about <NUM> mil. Preferably, the backing layer <NUM> is formed from a moisture vapor permeable membrane to promote the exchange of oxygen and moisture vapor between the wound site and the atmosphere. One exemplary material is a transparent membrane sold under the trade name POLYSKIN® II by Kendall Corp. , a division of Covidien. Other materials which may be suitable for use in a backing layer include the thin films marketed under the names TEGADERM™ by <NUM> of St. Paul, MN and OPSITE™ by Smith and Nephew PLC of London, UK.

As seen in <FIG>, reservoir <NUM> is defined by or within wound dressing <NUM> when applied to the skin. Filler <NUM> is included to fill the reservoir <NUM>. Evacuating atmospheric gasses from the reservoir <NUM> may impart a tendency for cover layer <NUM> to flatten against the wound "w" as depicted in <FIG>. This tendency of cover layer <NUM> to deform may draw the peri-wound margins into the wound "w" and put the surrounding skin "s" in tension. This tendency may be counteracted or resisted by the shear stiffness in reinforcement layer <NUM> such that the cover layer <NUM> may better main its shape. Because reinforcement layer <NUM> extends to a peripheral region of cover layer <NUM> and backing layer <NUM> anchored to healthy skin "s," the forces associated with evacuating reservoir <NUM> may be transferred beyond the perimeter of the wound "w," and may be manifested as compression forces. Thus reinforcement layer <NUM> reinforces cover layer <NUM> and vacuum reservoir <NUM>.

Claim 1:
A dressing (<NUM>) for use in a vacuum wound therapy procedure comprising: a cover layer (<NUM>) including a backing layer (<NUM>) formed from a flexible polymeric membrane extending to the periphery of the cover layer,
and an aperture (<NUM>) extending through the backing layer,
an adhesive layer (<NUM>) to affix the backing layer over a wound bed and
provide a seal around the wound bed, and a reticulated or net-like reinforcement layer (<NUM>) affixed to the backing layer and extending to a peripheral region of the cover layer;
a contact layer (<NUM>);
a filler (<NUM>); and
a vacuum port (<NUM>, 30A, 30B)
characterized in that the vacuum port comprises a filter screen (<NUM>, 58A, <NUM>, <NUM>) incorporated therein.