Patent ID: 12232933

DETAILED DESCRIPTION

FIG.1depicts a dressing10including an application site covering in the form of a drape12, an adhesive14on a skin-facing surface16of the drape12and an oxygen scavenger18.FIG.2depicts 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 film24, which is applied to the drape12. In each instance, the oxygen scavenger18or the oxygen scavenger incorporated into the oxygen scavenger film24is designed to react with gaseous oxygen (02), removing it from any air that is in contact with the oxygen scavenger. With the dressing10sealed 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.

FIGS.3and4depict a gasket26, wicking material28, and a release layer32, which can also be provided with the dressing10.FIG.3also depicts a sealed package, which can be made up of a lower foil layer34and an upper foil layer36that can be affixed to one another, in which the dressing10, when assembled, is sealed. The sealed package inhibits ambient oxygen from reacting with the oxygen scavenger until after the dressing10has been removed from the sealed package.FIG.4depicts the application site covering being made from the oxygen scavenger film24described above.

The drape12may 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 drape12(and other application site coverings) are conformable to the wicking material28and skin to which it is applied. Examples of such materials include polyurethane or polyethylene films. The thin film from which the drape12is 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 drape12is made may be constructed of polyurethane or other semi-permeable material such as that sold under the Tegaderm® brand or 9834 TPU tape available from 3M. Similar films are also available from other manufacturers.

FIG.2depicts the oxygen scavenger film24applied to the drape12. The oxygen scavenger film24can be made in accordance with the teachings of U.S. Pat. No. 7,781,018 B2 or the patent documents discussed therein. If desired, the oxygen scavenger film24can be provided as the application site covering itself, which is shown inFIG.4and can be made in accordance with the teachings of U.S. Pat. No. 7,781,018 B2 or the patent documents discussed therein. In either instance, the oxygen scavenger film24acting as the drape or the oxygen scavenger film24applied to the drape12, the oxygen scavenger film24or the drape12in combination with the oxygen scavenger film24results in a film or films that is as flexible or nearly as flexible as films sold under the Tegaderm® brand or 9834 TPU tape available from 3M. The oxygen scavenger film24could also be conformable to the wicking material28and skin to which it is applied. This conformability of the application site covering, whether it be the drape12or the oxygen scavenger film24, 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 toFIG.3, the gasket26can include silicone42such as a polysiloxane gel adhesive with good moisture and gas barrier properties, such as P-DERM PS-1050 from Polymer Science, Inc. The gasket26, which can include an inner through hole46, is formed by providing the silicone42on a gasket backing film48, which can be a polyurethane, polyethylene, polypropylene, or co-polyester film. The gasket backing film48can be brought in contact with the adhesive14on a skin-facing surface16of the drape12to affix the gasket26to the drape. The gasket26can attach to the oxygen scavenger film24in 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 scavenger18for use in the embodiment depicted inFIG.1is 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 (H2O) 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 with02present at the application site covered by the drape12and absorbing it when in contact after activation.

FIG.5depicts the oxygen scavenger18where 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 substrate60. An electrolyte solution62, which can be provided in a rupturable package64, is shielded from the reducing agent substrate60, and thus the reducing agent, until the dressing10is ready to be placed on the skin obviating the need for a hermetically sealed package to contain the dressing10. Small protuberances66, 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 surface16of the drape12. The small protuberances66can be used to rupture the rupturable package64so that the electrolyte solution62is introduced to the reducing agent on the reducing agent substrate60. One presses on the drape12in the vicinity of the protuberances to rupture the rupturable package64. The rupturable package64can be ruptured in other manners.

With reference back toFIGS.3and4, the wicking material28can be any appropriate material with the capability of removing moisture from the skin. In certain instances, however, the wicking material28can be configured to shrink when atmospheric pressure pushing on the drape12exceeds an internal air pressure beneath the drape12and 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 adhesive14may be a pressure-sensitive acrylic-based adhesive applied on the skin-facing surface16of the drape12. Other types of adhesives could be applied to the drape12, for example, a photoresponsive adhesive polymer such as those described in U.S. Pat. No. 10,336,923 B2. 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 adhesive20can be applied over an entirety of the skin-facing surface16of the drape12, which can also be useful to retain other components of the dressing10during 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 gasket26in addition to the adhesive14can be provided with the dressing10.

The release layer32protects the gasket26and the adhesive14until ready for application to the application site, e.g., a patient's skin. The release layer32can be coated with a fluoropolymer release coating on the side of the release layer32that contacts the adhesive14on the drape12and the appropriate surfaces of the gasket26and the wicking material28. The release layer32can 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 layer32has a larger area than the drape12and is removed from the drape12prior to the drape being affixed to application site.

The drape12, oxygen scavenger18, gasket26, wicking material28, and release layer32can be assembled in different manners in the dressing10. Additionally, there are different manners in which the oxygen scavenger18might be formulated including: (1) with a reducing agent, e.g., zinc, iron, aluminum, and an electrolyte solution needed to support the reaction of the reducing agent with oxygen, (2) with the reducing agent and an electrolyte salt but not the solvent water so there is no electrolyte solution, or (3) 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 scavenger18is in an activated state and must be protected from contact with air until use. At the time of use, the dressing10is removed from its protective packaging (shown inFIG.3as the lower foil layer34and the upper foil layer36) 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 dressing10is removed from the protective packaging, the oxygen scavenger18begins immediately to remove oxygen from the air. With the dressing10being applied quickly to the application site, the oxygen scavenger18removes oxygen from the air trapped between the dressing10and 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 dressing10after opening its packaging. The drape12and the gasket26provide an adequate barrier to slow O2permeation to the oxygen scavenger18from the external environment, so that the main access of O2to the reducing agent is through the wicking material28from the trapped air within the dressing10sealed to the skin. This produces the desired oxygen-free or nearly oxygen-free environment on the skin within the area bounded by the gasket26.

If the oxygen scavenger18includes an electrolyte salt (such as KBr) but not solvent water, it will not be in an active state until water is added. The oxygen scavenger18, and thus the dressing10, 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 dressing10to the target skin is less critical than in the case of the oxygen scavenger18being active as packaged. The solvent water could also be provided in a rupturable package similar to the rupturable package64shown inFIG.5.

If the oxygen scavenger18does not include an electrolyte salt or solvent water, an electrolyte solution must be added at the time of use to enable the oxygen scavenger18to react with oxygen in the air. If the period of use of the dressing10is short enough, a solution of table salt could activate the oxygen scavenger18without causing rapid corrosion of an active component of zinc. This would not require complete protection of the oxygen scavenger18, and thus the dressing10, from exposure to air or moisture.

Removal of O2from an enclosed volume of air reduces its pressure. In a rigid container, removal of O2would cause a 20% 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 O2. Applying the ideal gas law equation to the nitrogen only and specifying that PN2,before shrinkage=PN2, atm:

PN⁢⁢2,atm⁢Vbefore⁢⁢shrinkage=PN⁢2,after⁢⁢shrinkage⁢Vafter⁢⁢shrinkage,orPN⁢2,after⁢⁢shrinkage=(Vbefore⁢⁢shrinkage⁢/⁢Vafter⁢⁢shrinkage)⁢PN⁢⁢2,atm

If there is no resistance to wicking material air volume shrinkage, then

Negative⁢⁢pressure⁢⁢NP=Pa⁢t⁢m-PN⁢2,after⁢⁢shrinkageNP=Pa⁢t⁢m-PN⁢⁢2,atm⁡(Vbefore⁢/⁢Vafter)

However, the wicking material28will have resistance to the compression required to shrink the air volume. The dressing10will shrink until there is a balance between the atmospheric pressure pushing down on the drape12(or outermost material of the dressing10, for example, when an drape12is not provided) and the combination of internal air pressure and the mechanical compression resistance pressure of the wicking material28.

Pa⁢t⁢m=PN⁢⁢2,after+⁢Pmechanical⁢⁢compression⁢⁢resistance

The internal dressing air pressure will be determined by the compressibility of the wicking material28. The more easily compressed the wicking material28(lower Pmechanical), the closer PN2,afterwill be to Patmand the less negative air pressure will be beneath the dressing10:

Negative⁢⁢Pressure⁢⁢(NP)=Pa⁢t⁢m-PN⁢⁢2,after=(PN⁢⁢2,after+Pm⁢e⁢c⁢h⁢a⁢n⁢ical)-PN⁢⁢2,afterNP=Pmechanical⁢⁢compression⁢⁢resistance

Since the O2removed from the dressing10air represents only 20% of its air, the air volume beneath the dressing10cannot shrink more than 20% under the influence of atmospheric pressure. At 20% shrinkage, the remaining N2pressure beneath the dressing10would 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 −60 mmHg to −150 mmHg, or −8% to −20% of atmospheric pressure. A negative pressure of 5% (−40 mmHg) or less could be considered to be outside the range of therapeutic negative pressures.

A wicking material “spongy” enough that up to 40 mmHg of external pressure would compress its air volume by 20% would produce an atmosphere of N2at under the dressing10at a pressure equal to or less than 40 mmHg below atmospheric pressure.

Initial⁢⁢state⁢:⁢Pa⁢t⁢m⁢Vbefore⁢⁢shrinkage=(nN⁢⁢2+nO⁢⁢2)⁢RT=PN⁢⁢2,atm+PO⁢⁢2,atmAfter⁢⁢removal⁢⁢of⁢⁢O2⁢:⁢PN⁢⁢2,atm⁢Vbefore⁢⁢shrinkage=nN⁢2⁢RTAfter⁢⁢shrinkage⁢:⁢PN⁢⁢2,patch⁢Vafter⁢⁢shrinkage=nN⁢2⁢RTNegative⁢⁢pressure⁢:⁢(NP)=Pa⁢t⁢m-PN⁢⁢2,patch=Pa⁢t⁢m-nN⁢2⁢RT⁢/⁢Vafter⁢⁢shrinkageN⁢P=Pa⁢t⁢m-PN⁢⁢2,atm⁢Vbefore⁢⁢shrinkage⁢/⁢Vafter⁢⁢shrinkageFor⁢⁢NP=5⁢%⁢⁢of⁢⁢Pa⁢t⁢m⁢:⁢0.05⁢Pa⁢t⁢m=Pa⁢t⁢m-PN⁢⁢2,atm⁢Vbefore⁢/⁢VafterKnowing⁢⁢PN⁢⁢2,atm=0.8⁢0⁢Pa⁢t⁢m⁢:⁢0.0⁢5⁢Pa⁢t⁢m=Pa⁢t⁢m-0.8⁢0⁢Pa⁢t⁢m⁢Vbefore⁢/⁢VafterVbefore⁢/⁢Vafter=0.9⁢5⁢Pa⁢t⁢m⁢/⁢0.8⁢0⁢Pa⁢t⁢m=1.1875Shrinkage⁢⁢as⁢⁢fraction⁢⁢of⁢⁢starting⁢⁢volume=(Vb-Va)⁢/⁢Vb=1-Va⁢/⁢Vb=1-(1⁢/⁢1.187⁢5)=1-0.8⁢4=0.1⁢6=16⁢%

In other words, a wicking material whose air volume can be compressed 16% by 40 mmHg of pressure could produce an environment beneath the dressing10free of O2with a negative pressure of 40 mm Hg.

For an open-pore wicking material whether fibrous or foam, the material from which the wicking material28is made is chosen to have its air volume compressed by 16% or more at 40 mmHg pressure to make a dressing10with up to 40 mmHg negative pressure beneath the dressing10.

If the wicking material28starts at about 80% porous, compressing 16% of 80% would require compressing the bulk dimensions by only 13%. If the wicking material28starts at about 60% porous, compressing 16% of that 60% would require compressing the bulk dimensions by only 10%.

The dressing10can be assembled in different manners. In one example and with reference toFIGS.3and6, the drape12can be flood coated on the skin-facing surface16with the adhesive14. The gasket26, which can include the inner through hole46, can be attached to the drape12by providing the silicone42on the gasket backing film48, which can be a polyurethane, polyethylene, polypropylene, or co-polyester film. The gasket backing film48is brought in contact with the adhesive14on the skin-facing surface16of the drape12. The oxygen scavenger18, which can be deposited or printed onto a carrier film, can be positioned within the through hole46in the gasket26. The carrier film for the oxygen scavenger18is brought in contact with the adhesive14on the skin-facing surface16of the drape12. If desired, a liquid-impermeable but gas-permeable membrane68can be provided between the oxygen scavenger18and the wicking material28. The wicking material28, which is larger in area that the carrier film for the oxygen scavenger18, is also brought in contact with the adhesive14on the skin-facing surface16of the drape12. The release layer32is then brought in contact with the adhesive14on the skin-facing surface16of the drape12to cover also the gasket26and the wicking material28to provide the assembled dressing10.

The dressing10could also be assembled without the drape12or the application site covering in the form of the oxygen scavenger film22, an example of which is shown inFIG.7. In this construction, the application site covering can be in the form the silicone42, which does not include a through hole, but instead includes a cavity40to allow the silicone42to receive while covering the oxygen scavenger18and the wicking material28with respect to ambient atmosphere. The oxygen scavenger18, which can be printed or deposited on a thin carrier film, is placed in the cavity40in the silicone42and then is covered with the wicking material28. Adhesive14, which may or may not be provided on a carrier film similar to the gasket backing film48described above, can be provided around the perimeter of the silicone42to facilitate adhesion of the dressing10to the skin. The release layer32is then brought in contact with the adhesive14to cover also the silicone42and the wicking material28to provide the assembled dressing10.

The dressing10could also be assembled where the drape12does not contact the skin, but rather provides a carrier for stacking the components that make up the dressing10. Such an example is shown inFIG.8.

A variation on the dressing constructions described above include using a hydrogel instead of the silicone42to 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 dressing10can be slowed by interposing an oxygen permeable membrane between the wicking material28and the oxygen scavenger18or between the wicking material28and the skin. Combining an oxygen permeable membrane between wicking material28and oxygen scavenger18, accompanied by an oxygen permeable drape over the part of the wicking material28not covered by the oxygen scavenger18would allow a non-zero O2level on the skin.

In another alternative and with reference toFIGS.3and4, a valve70can be provided with the drape12or the oxygen scavenger film24and cooperate with an opening72provided in each. The valve70can be similar in construction to that described in EP 1 958 883 B1. Operation of the valve70will be described in detail with reference to the drape12with the understanding that the valve would operate similarly with the oxygen scavenger film24. The valve70can be configured to open and allow air into the volume beneath the drape12to allow the volume beneath the drape12to maintain gas pressure beneath the drape12above a therapeutic negative pressure, and preferably nearer to atmospheric pressure than to the therapeutic negative pressure. For example, the valve70can be configured to open at a pressure differential between the volume beneath the drape12and ambient at less than −60 mmHg or even less than −40 mmHg. As such, when the valve70is open, air enters through the valve70and the opening72into the volume beneath the drape12raising 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 valve70to remove air under the patch to reduce the pressure to −1 to −40 mmHg.

FIG.9depicts a two-piece dressing having a top assembly84and a bottom assembly86. The bottom assembly86includes the drape12, the gasket26, the wicking material28and adhesive14on the skin-facing surface16of the drape12. The wicking material28can be an anti-microbial pad, which could also hold the water or electrolyte solution to activate the reducing agent of the oxygen scavenger18. The wicking material28may also include a layer of silver, which is not shown. The top assembly84includes the oxygen scavenger18, which can be printed or deposited on a thin flexible carrier88having an adhesive layer92, e.g., tape. Also, the oxygen scavenger18could be any of the aforementioned oxygen scavengers. The oxygen scavenger18can be packaged in an active state within a sealed package (for example, similar to the foil layers34,36) so to have depleted the oxygen in the sealed package before being applied and adhered to the drape12.

After the bottom assembly86is applied over the application site, the top assembly84is applied over the bottom assembly86. To apply the top assembly84, lay the top assembly84top-down on a surface. Remove a release liner (not shown) to expose the adhesive layer92and the oxygen scavenger18. Position the top assembly84over a porous or perforated area94of the drape12and adhere the adhesive layer92to an outer surface96of the drape12. The porous or perforated area94of the drape12is confined within the area bound by the gasket26beneath the drape12and the top assembly84covers the porous or perforated area94of the drape12when properly applied and adhered to the drape12. Alignment marks102that remain visible when the top assembly84is adhered to bottom assembly86can be provided on the outer surface of the drape12. The top assembly84and the bottom assembly86can be individually packaged, and top assembly84could be replaced as required without removing the bottom assembly86.

It will be appreciated that various features and functions of the above-disclosed embodiments and other features and functions, or alternatives or varieties thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.