Patent Description:
<CIT> discusses how the device includes a housing that is preferably constructed from a rigid or semi-rigid type material. <CIT> mentions different types of oxygen absorbers such as those that absorb oxygen through the oxidation of iron metal. <CIT> further mentions silver oxide, metal peroxides, silver metal, and antimicrobial organic compounds. Placing these types of oxygen absorbers in the cavity formed by a gas or fluid impermeable housing to cover a wound would result in no oxygen (or a nearly undetectable amount) within the cavity unless the reacting agent in the oxygen scavenger was specifically designed to limit the amount of oxygen scavenged within the cavity, which <CIT> does not discuss in any particularity.

<CIT> discusses how the reactor can consume oxygen, which may result in an approximate <NUM>% reduction from atmospheric pressure in an enclosed volume around a wound.

The range of negative pressures currently used for popularly available negative pressure wound therapy (NPWT) systems is in the range of about -<NUM>% to about -<NUM>% of atmospheric pressure, or about -40mmHg to about -150mmHg from atmospheric pressure. A negative pressure of less than -<NUM>% (about -40mmHg) could be considered to be outside the range of therapeutic negative pressure, and there may be instances, where removing oxygen from around the wound may be desirable, but the need for typical therapeutic negative pressure ranges may not be necessary.

In view of the foregoing, a dressing according to claim <NUM> includes an application site covering and an oxygen scavenger provided with or positioned with respect to the application site covering so as to remove oxygen from a volume beneath the application site covering and around an application site covered by the application site covering. The application site covering and the oxygen scavenger are configured to maintain gas pressure beneath the application site covering around the application site that is above a therapeutic negative pressure while the oxygen scavenger is consuming oxygen beneath the application site covering.

<FIG> depicts a dressing <NUM> including an application site covering in the form of a drape <NUM>, an adhesive <NUM> on a skin-facing surface <NUM> of the drape <NUM> and an oxygen scavenger <NUM>. <FIG> depicts an application site covering in the form of two films where an oxygen scavenger is incorporated in a film-forming polymer that is used to make the oxygen scavenger film <NUM>, which is applied to the drape <NUM>. In each instance, the oxygen scavenger <NUM> or the oxygen scavenger incorporated into the oxygen scavenger film <NUM> is designed to react with gaseous oxygen (O<NUM>), removing it from any air that is in contact with the oxygen scavenger. With the dressing <NUM> sealed to the skin, this results in a topical hypoxic or very low oxygen environment around an application site covered by the application site covering, which can be beneficial for certain skin conditions. Accordingly, the oxygen scavenger can be provided with or positioned with respect to the application site covering so as to remove oxygen from a volume beneath the application site covering and around an application site covered by the application site covering. As will be described in more detail below, the application site covering and the oxygen scavenger are configured to maintain gas pressure beneath the application site covering around the application site that is above the therapeutic negative pressure discussed above. The dressing is configured so that the gas pressure beneath the dressing is at atmospheric pressure or nearer to atmospheric pressure as compared to one used in a typical NPWT system.

<FIG> and <FIG> depict a gasket <NUM>, wicking material <NUM>, and a release layer <NUM>, which can also be provided with the dressing <NUM>. <FIG> also depicts a sealed package, which can be made up of a lower foil layer <NUM> and an upper foil layer <NUM> that can be affixed to one another, in which the dressing <NUM>, when assembled, is sealed. The sealed package inhibits ambient oxygen from reacting with the oxygen scavenger until after the dressing <NUM> has been removed from the sealed package. <FIG> depicts the application site covering being made from the oxygen scavenger film <NUM> described above.

The drape <NUM> may be made from a flexible material and can be made from a thin, flexible elastomeric film. Unlike a rigid or semi-rigid type gas or fluid impermeable housing, the drape <NUM> (and other application site coverings) are conformable to the wicking material <NUM> and skin to which it is applied. Examples of such materials include polyurethane or polyethylene films. The thin film from which the drape <NUM> is made can be substantially impermeable to liquids but somewhat permeable to water vapor and other gases. For example, the thin film material from which the drape <NUM> is made may be constructed of polyurethane or other semipermeable material such as that sold under the Tegaderm® brand or <NUM> TPU tape available from <NUM>. Similar films are also available from other manufacturers.

<FIG> depicts the oxygen scavenger film <NUM> applied to the drape <NUM>. The oxygen scavenger film <NUM> can be made in accordance with the teachings of <CIT> or the patent documents discussed therein. If desired, the oxygen scavenger film <NUM> can be provided as the application site covering itself, which is shown in <FIG> and can be made in accordance with the teachings of <CIT> or the patent documents discussed therein. In either instance, the oxygen scavenger film <NUM> acting as the drape or the oxygen scavenger film <NUM> applied to the drape <NUM>, the oxygen scavenger film <NUM> or the drape <NUM> in combination with the oxygen scavenger film <NUM> results in a film or films that is as flexible or nearly as flexible as films sold under the Tegaderm® brand or <NUM> TPU tape available from <NUM>. The oxygen scavenger film <NUM> could also be conformable to the wicking material <NUM> and skin to which it is applied. This conformability of the application site covering, whether it be the drape <NUM> or the oxygen scavenger film <NUM>, can allow for the application site covering to be drawn toward the skin as oxygen is being removed from beneath the application site covering, which allows for volume reduction beneath the application site covering.

With reference to <FIG>, the gasket <NUM> can include silicone <NUM> such as a polysiloxane gel adhesive with good moisture and gas barrier properties, such as P-DERM PS-<NUM> from Polymer Science, Inc. The gasket <NUM>, which can include an inner through hole <NUM>, is formed by providing the silicone <NUM> on a gasket backing film <NUM>, which can be a polyurethane, polyethylene, polypropylene, or co-polyester film. The gasket backing film <NUM> can be brought in contact with the adhesive <NUM> on a skin-facing surface <NUM> of the drape <NUM> to affix the gasket <NUM> to the drape. The gasket <NUM> can attach to the oxygen scavenger film <NUM> in similar manners. A variation on gasket constructions can include using a hydrogel instead of silicone as the gasket. Other materials that provide a better seal than acrylic adhesives against skin can also be used as the gasket.

One example of the oxygen scavenger <NUM> for use in the embodiment depicted in <FIG> is a porous composite of zinc powder (Zn), carbon powder (C), potassium bromide (KBr), and a binder such as polyfluoroethylene (PTFE), with or without added water (H<NUM>O) similar to a Rechargeable Battery Company (dba Exothermix) Air Activated Heater. Another variation is an oxygen scavenger including a reactive material from iron fines, or any other material that can react with O<NUM> present at the application site covered by the drape <NUM> and absorbing it when in contact after activation.

<FIG> depicts the oxygen scavenger <NUM> where the reducing agent, which can include aluminum, zinc or iron, can be provided on, e.g., printed on, a thin substrate, hereinafter referred to as the reducing agent substrate <NUM>. An electrolyte solution <NUM>, which can be provided in a rupturable package <NUM>, is shielded from the reducing agent substrate <NUM>, and thus the reducing agent, until the dressing <NUM> is ready to be placed on the skin obviating the need for a hermetically sealed package to contain the dressing <NUM>. Small protuberances <NUM>, which can be similar in shape and size to solid microneedles used in touch-actuated microneedle array patches, can be fixed to or provided below (relative to the application site) the skin-facing surface <NUM> of the drape <NUM>. The small protuberances <NUM> can be used to rupture the rupturable package <NUM> so that the electrolyte solution <NUM> is introduced to the reducing agent on the reducing agent substrate <NUM>. One presses on the drape <NUM> in the vicinity of the protuberances to rupture the rupturable package <NUM>. The rupturable package <NUM> can be ruptured in other manners.

With reference back to <FIG> and <FIG>, the wicking material <NUM> can be any appropriate material with the capability of removing moisture from the skin. In certain instances, however, the wicking material <NUM> can be configured to shrink when atmospheric pressure pushing on the drape <NUM> exceeds an internal air pressure beneath the drape <NUM> and around an application site covered by the drape plus a mechanical compression resistance pressure of the wicking material. This will be described in more detail below.

The adhesive <NUM> may be a pressure-sensitive acrylic-based adhesive applied on the skin-facing surface <NUM> of the drape <NUM>. Other types of adhesives could be applied to the drape <NUM>, for example, a photoresponsive adhesive polymer such as those described in <CIT>. A pressure-sensitive acrylic-based adhesive is known to provide strong initial tack that can last for a relatively long time, for example a few days, when in contact with the skin. The adhesive <NUM> can be applied over an entirety of the skin-facing surface <NUM> of the drape <NUM>, which can also be useful to retain other components of the dressing <NUM> during assembly. Known pressure-sensitive acrylic-based adhesives, however, are not known for providing a good seal so as to preclude or greatly inhibit the ingress and egress of air, thus the gasket <NUM> in addition to the adhesive <NUM> can be provided with the dressing <NUM>.

The release layer <NUM> protects the gasket <NUM> and the adhesive <NUM> until ready for application to the application site, e.g., a patient's skin. The release layer <NUM> can be coated with a fluoropolymer release coating on the side of the release layer <NUM> that contacts the adhesive <NUM> on the drape <NUM> and the appropriate surfaces of the gasket <NUM> and the wicking material <NUM>. The release layer <NUM> can be a polyester film coated on one side with the fluoropolymer release coating, which can be used with silicone. This release coating is also compatible with pressure-sensitive acrylic-based adhesives. The release layer <NUM> has a larger area than the drape <NUM> and is removed from the drape <NUM> prior to the drape being affixed to application site.

The drape <NUM>, oxygen scavenger <NUM>, gasket <NUM>, wicking material <NUM>, and release layer <NUM> can be assembled in different manners in the dressing <NUM>. Additionally, there are different manners in which the oxygen scavenger <NUM> might be formulated including: (<NUM>) with a reducing agent, e.g., zinc, iron, aluminum, and an electrolyte solution needed to support the reaction of the reducing agent with oxygen, (<NUM>) with the reducing agent and an electrolyte salt but not the solvent water so there is no electrolyte solution, or (<NUM>) with the reducing agent but without either the electrolyte salt or solvent water.

When the reducing agent is provided with the electrolyte solution, the oxygen scavenger <NUM> is in an activated state and must be protected from contact with air until use. At the time of use, the dressing <NUM> is removed from its protective packaging (shown in <FIG> as the lower foil layer <NUM> and the upper foil layer <NUM>) and applied quickly to the application site. The protective packaging can be, for example, a sealed metallized, e.g., foil-type, package that precludes air from entering the package until after opened. After the dressing <NUM> is removed from the protective packaging, the oxygen scavenger <NUM> begins immediately to remove oxygen from the air. With the dressing <NUM> being applied quickly to the application site, the oxygen scavenger <NUM> removes oxygen from the air trapped between the dressing <NUM> and the skin, and achieves an oxygen-free or nearly oxygen-free environment in minutes to hours. Ease of use is simplest, but requires swift application of the dressing <NUM> after opening its packaging. The drape <NUM> and the gasket <NUM> provide an adequate barrier to slow O<NUM> permeation to the oxygen scavenger <NUM> from the external environment, so that the main access of O<NUM> to the reducing agent is through the wicking material <NUM> from the trapped air within the dressing <NUM> sealed to the skin. This produces the desired oxygen-free or nearly oxygen-free environment on the skin within the area bounded by the gasket <NUM>.

If the oxygen scavenger <NUM> includes an electrolyte salt (such as KBr) but not solvent water, it will not be in an active state until water is added. The oxygen scavenger <NUM>, and thus the dressing <NUM>, will need to be protected from moisture vapor, but oxygen exclusion will not be important. The water addition could be drops of water, contact with perspiration on the skin, or even condensation of water vapor from the humidity in the trapped air driven by moisture vapor from the skin, since the electrolyte salt can be expected to be deliquescent. Use requires addition of water, which is readily available in most environments. Timing between opening the dressing package and applying the dressing <NUM> to the target skin is less critical than in the case of the oxygen scavenger <NUM> being active as packaged. The solvent water could also be provided in a rupturable package similar to the rupturable package <NUM> shown in <FIG>.

If the oxygen scavenger <NUM> does not include an electrolyte salt or solvent water, an electrolyte solution must be added at the time of use to enable the oxygen scavenger <NUM> to react with oxygen in the air. If the period of use of the dressing <NUM> is short enough, a solution of table salt could activate the oxygen scavenger <NUM> without causing rapid corrosion of an active component of zinc. This would not require complete protection of the oxygen scavenger <NUM>, and thus the dressing <NUM>, from exposure to air or moisture.

Removal of O<NUM> from an enclosed volume of air reduces its pressure. In a rigid container, removal of O<NUM> would cause a <NUM>% reduction in pressure (assuming some humidity). However, comfortable dressing materials are not rigid, and typical wicking materials are compressible, so the volume of trapped air will shrink when the internal air pressure is less than the external air pressure. This shrinkage in air volume restores at least part of the pressure lost by the removal of O<NUM>. Applying the ideal gas law equation to the nitrogen only and specifying that PN2,before shrinkage = PN2,atm: <MAT> or <MAT>.

If there is no resistance to wicking material air volume shrinkage, then <MAT> <MAT>.

However, the wicking material <NUM> will have resistance to the compression required to shrink the air volume. The dressing <NUM> will shrink until there is a balance between the atmospheric pressure pushing down on the drape <NUM> (or outermost material of the dressing <NUM>, for example, when an drape <NUM> is not provided) and the combination of internal air pressure and the mechanical compression resistance pressure of the wicking material <NUM>.

The internal dressing air pressure will be determined by the compressibility of the wicking material <NUM>. The more easily compressed the wicking material <NUM> (lower Pmechanical), the closer PN2,after will be to Patm and the less negative air pressure will be beneath the dressing <NUM>: <MAT> NP = Pmechanical compression resistance.

Since the O<NUM> removed from the dressing <NUM> air represents only <NUM>% of its air, the air volume beneath the dressing <NUM> cannot shrink more than <NUM>% under the influence of atmospheric pressure. At <NUM>% shrinkage, the remaining N<NUM> pressure beneath the dressing <NUM> would be equal to the total atmospheric pressure Patm.

The range of negative pressures currently used for popularly available negative pressure wound therapy systems is in the range of -60mmHg to -150mmHg, or -<NUM>% to -<NUM>% of atmospheric pressure. A negative pressure of <NUM>% (-40mmHg) or less could be considered to be outside the range of therapeutic negative pressures.

A wicking material "spongy" enough that up to 40mmHg of external pressure would compress its air volume by <NUM>% would produce an atmosphere of N<NUM> at under the dressing <NUM> at a pressure equal to or less than 40mmHg below atmospheric pressure.

In other words, a wicking material whose air volume can be compressed <NUM>% by 40mmHg of pressure could produce an environment beneath the dressing <NUM> free of O<NUM> with a negative pressure of 40mmHg.

For an open-pore wicking material whether fibrous or foam, the material from which the wicking material <NUM> is made is chosen to have its air volume compressed by <NUM>% or more at 40mmHg pressure to make a dressing <NUM> with up to 40mmHg negative pressure beneath the dressing <NUM>.

If the wicking material <NUM> starts at about <NUM>% porous, compressing <NUM>% of <NUM>% would require compressing the bulk dimensions by only <NUM>%. If the wicking material <NUM> starts at about <NUM>% porous, compressing <NUM>% of that <NUM>% would require compressing the bulk dimensions by only <NUM>%.

The dressing <NUM> can be assembled in different manners. In one example and with reference to <FIG> and <FIG>, the drape <NUM> can be flood coated on the skin-facing surface <NUM> with the adhesive <NUM>. The gasket <NUM>, which can include the inner through hole <NUM>, can be attached to the drape <NUM> by providing the silicone <NUM> on the gasket backing film <NUM>, which can be a polyurethane, polyethylene, polypropylene, or co-polyester film. The gasket backing film <NUM> is brought in contact with the adhesive <NUM> on the skin-facing surface <NUM> of the drape <NUM>. The oxygen scavenger <NUM>, which can be deposited or printed onto a carrier film, can be positioned within the through hole <NUM> in the gasket <NUM>. The carrier film for the oxygen scavenger <NUM> is brought in contact with the adhesive <NUM> on the skin-facing surface <NUM> of the drape <NUM>. If desired, a liquid-impermeable but gas-permeable membrane <NUM> can be provided between the oxygen scavenger <NUM> and the wicking material <NUM>. The wicking material <NUM>, which is larger in area that the carrier film for the oxygen scavenger <NUM>, is also brought in contact with the adhesive <NUM> on the skin-facing surface <NUM> of the drape <NUM>. The release layer <NUM> is then brought in contact with the adhesive <NUM> on the skin-facing surface <NUM> of the drape <NUM> to cover also the gasket <NUM> and the wicking material <NUM> to provide the assembled dressing <NUM>.

The dressing <NUM> could also be assembled without the drape <NUM> or the application site covering in the form of the oxygen scavenger film <NUM>, an example of which is shown in <FIG>. In this construction, the application site covering can be in the form the silicone <NUM>, which does not include a through hole, but instead includes a cavity <NUM> to allow the silicone <NUM> to receive while covering the oxygen scavenger <NUM> and the wicking material <NUM> with respect to ambient atmosphere. The oxygen scavenger <NUM>, which can be printed or deposited on a thin carrier film, is placed in the cavity <NUM> in the silicone <NUM> and then is covered with the wicking material <NUM>. Adhesive <NUM>, which may or may not be provided on a carrier film similar to the gasket backing film <NUM> described above, can be provided around the perimeter of the silicone <NUM> to facilitate adhesion of the dressing <NUM> to the skin. The release layer <NUM> is then brought in contact with the adhesive <NUM> to cover also the silicone <NUM> and the wicking material <NUM> to provide the assembled dressing <NUM>.

The dressing <NUM> could also be assembled where the drape <NUM> does not contact the skin, but rather provides a carrier for stacking the components that make up the dressing <NUM>. Such an example is shown in <FIG>.

A variation on the dressing constructions described above include using a hydrogel instead of the silicone <NUM> to establish a seal to the skin. The electrolyte and reducing agent, with or without the PTFE, could be mixed into the hydrogel. Use of a hydrogel would require moisture barrier packaging to preserve the water content of the hydrogel.

The speed with which the oxygen tension decreases under the dressing <NUM> can be slowed by interposing an oxygen permeable membrane between the wicking material <NUM> and the oxygen scavenger <NUM> or between the wicking material <NUM> and the skin. Combining an oxygen permeable membrane between wicking material <NUM> and oxygen scavenger <NUM>, accompanied by an oxygen permeable drape over the part of the wicking material <NUM> not covered by the oxygen scavenger <NUM> would allow a non-zero O<NUM> level on the skin.

In another alternative and with reference to <FIG> and <FIG>, a valve <NUM> can be provided with the drape <NUM> or the oxygen scavenger film <NUM> and cooperate with an opening <NUM> provided in each. The valve <NUM> can be similar in construction to that described in <CIT>. Operation of the valve <NUM> will be described in detail with reference to the drape <NUM> with the understanding that the valve would operate similarly with the oxygen scavenger film <NUM>. The valve <NUM> can be configured to open and allow air into the volume beneath the drape <NUM> to allow the volume beneath the drape <NUM> to maintain gas pressure beneath the drape <NUM> above a therapeutic negative pressure, and preferably nearer to atmospheric pressure than to the therapeutic negative pressure. For example, the valve <NUM> can be configured to open at a pressure differential between the volume beneath the drape <NUM> and ambient at less than -<NUM> mmHg or even less than -40mmHg. As such, when the valve <NUM> is open, air enters through the valve <NUM> and the opening <NUM> into the volume beneath the drape <NUM> raising the gas pressure towards ambient atmospheric pressure. The system will then equilibrate dynamically to a nearly pure nitrogen atmosphere at nearly atmospheric pressure. A mechanical pump could be inserted into or over the top of the valve <NUM> to remove air under the patch to reduce the pressure to -<NUM> to - 40mmHg.

<FIG> depicts a two-piece dressing having a top assembly <NUM> and a bottom assembly <NUM>. The bottom assembly <NUM> includes the drape <NUM>, the gasket <NUM>, the wicking material <NUM> and adhesive <NUM> on the skin-facing surface <NUM> of the drape <NUM>. The wicking material <NUM> can be an anti-microbial pad, which could also hold the water or electrolyte solution to activate the reducing agent of the oxygen scavenger <NUM>. The wicking material <NUM> may also include a layer of silver, which is not shown. The top assembly <NUM> includes the oxygen scavenger <NUM>, which can be printed or deposited on a thin flexible carrier <NUM> having an adhesive layer <NUM>, e.g., tape. Also, the oxygen scavenger <NUM> could be any of the aforementioned oxygen scavengers. The oxygen scavenger <NUM> can be packaged in an active state within a sealed package (for example, similar to the foil layers <NUM>, <NUM>) so to have depleted the oxygen in the sealed package before being applied and adhered to the drape <NUM>.

After the bottom assembly <NUM> is applied over the application site, the top assembly <NUM> is applied over the bottom assembly <NUM>. To apply the top assembly <NUM>, lay the top assembly <NUM> top-down on a surface. Remove a release liner (not shown) to expose the adhesive layer <NUM> and the oxygen scavenger <NUM>. Position the top assembly <NUM> over a porous or perforated area <NUM> of the drape <NUM> and adhere the adhesive layer <NUM> to an outer surface <NUM> of the drape <NUM>. The porous or perforated area <NUM> of the drape <NUM> is confined within the area bound by the gasket <NUM> beneath the drape <NUM> and the top assembly <NUM> covers the porous or perforated area <NUM> of the drape <NUM> when properly applied and adhered to the drape <NUM>. Alignment marks <NUM> that remain visible when the top assembly <NUM> is adhered to bottom assembly <NUM> can be provided on the outer surface of the drape <NUM>. The top assembly <NUM> and the bottom assembly <NUM> can be individually packaged, and top assembly <NUM> could be replaced as required without removing the bottom assembly <NUM>.

Claim 1:
A dressing (<NUM>) comprising:
an application site covering;
an oxygen scavenger (<NUM>) provided with or positioned with respect to the application site covering so as to remove oxygen from a volume beneath the application site covering and around an application site covered by the application site covering,
a wicking material (<NUM>) including air voids, wherein the wicking material (<NUM>) is configured to shrink when atmospheric pressure pushing on the application site covering exceeds an internal air pressure beneath the application site covering plus a mechanical compression resistance pressure of the wicking material (<NUM>), and wherein 40mmHg of external pressure on the wicking material compresses an air volume of the wicking material by at least <NUM>%;
the application site covering and the oxygen scavenger being configured to maintain gas pressure beneath the application site covering around the application site that is above a therapeutic negative pressure while the oxygen scavenger (<NUM>) is consuming oxygen beneath the application site covering.