OXYGEN PRODUCING DEVICE FOR WOUNDCARE

[0001] This application is a Continuation-in-Part of and claims the benefit of prior U.S. Patent Application Serial No. 10/520,410 filed December 12, 2002, which claims priority to PCT Application No. PCT/US02/39680, filed December 11, 2002, which claims priority to U.S. Provisional Application Serial No. 60/341 ,076, filed on December 12, 2001.

BACKGROUND

[0002] The present embodiments relate to the promotion of wound healing on skin and tissue repair. More particularly, the present embodiments relate to the application of oxygen using an oxygen producing device containing an ion conducting membrane to promote the healing of skin wounds. [0003] It is known that providing a supply of oxygen to a wound to or through the skin (e.g., ulcers, abrasions, cuts, sores, etc.) promotes healing of the wound. Oxygen therapy is used for inducing the growth of new skin tissue to close and heal ischemic wounds. Topical oxygen therapy calls for applying oxygen directly to an open wound. The oxygen dissolves in tissue fluids and improves the oxygen content of the intercellular fluids. Injuries and disorders which may be treated with topical oxygen include osteomyelitis, tendon and cartilage repair, sprains, fractures, burns and scalds, necrotizing fasciitis, pyoderma gangrenosum, refractory ulcers, diabetic foot ulcers and decubitus ulcers (bed sores) as well as cuts, abrasions, and surgically induced wounds or incisions.

[0004] In light of the documented benefits of such oxygen therapy, there have been several proposed methods for providing such an oxygen supply to a wound or regulating the oxygen concentration in the vicinity of a wound. Prior art teaches the application of topical hyperbaric oxygen by placing the entire affected limb of a person in a sealed chamber that features controlled pressure sealing and automatic oxygen regulation control. Not only are such

oxygen chambers expensive and difficult to sterilize, but they are also cumbersome in that the chamber must be hooked up to an external oxygen tank, limiting the patient's mobility. In addition, because the entire limb is placed in a chamber or bag, large areas of skin may be unnecessarily subjected to high levels of oxygen. Such high levels of oxygen present risks of vasoconstriction, toxicity and tissue destruction. U.S. Pat. No. 4,328,799 to LoPiano describes such a system in which a recumbent patient is connected to a gas chamber attached to an oxygen supply.

[0005] U.S. Patent Nos. 5,578,022 and 5,788,682 describe systems in which oxygen producing devices are incorporated into a patch or bandage which is placed directly over a wound. Both of these patents describe devices in which oxygen is produced electrochemically. These electrochemical devices use a membrane electrode assembly which incorporates a proton exchange membrane. Proton exchange membranes need water to maintain their low ionic resistance. Water, however, has a relatively high vapor pressure and will evaporate. As water in the membrane evaporates, the membrane loses its ability to effectively conduct ions. Attempting to keep the membrane hydrated by adding water externally can result in complications in the design of a practical device. For example, the inclusion of a water source to keep the membrane moist can make the device cumbersome, mitigating one of the key benefits of such a device. In addition, water presents a potential breeding ground for microbes. This is highly undesirable in such an oxygen generating device, which is often placed on or near open wounds that are susceptible to microbial infection.

[0006] The parent application describes a device overcoming some of these drawbacks. Nevertheless, there is a continued need for oxygen producing devices for wound care that are more convenient and inexpensive.

BRIEF DESCRIPTION OF THE INVENTION

[0007] In one aspect, there is provided a device for supplying oxygen to a patient for treatment of a wound or condition including: a) a wound dressing adapted for receipt over a wound or injury treatable with oxygen; b) a portable oxygen generating device remote from the wound dressing for supplying oxygen to the skin wound, the device including: a housing having mating top

and bottom portions, wherein the top portion has an outlet; a membrane electrode assembly for electrochemically producing oxygen comprising an anode, a cathode and an ion conducting membrane; and a circuit board having an associated power source; wherein the membrane electrode assembly is mounted to the top portion of the housing, thereby forming a sealed cavity between the anode and the top portion of the housing such that the outlet is fluidly connected to the cavity; and c) a conduit fluidiy connecting the outlet with the wound dressing.

[0008] In a second aspect, there is provided a portable oxygen generating device for supplying oxygen to a skin wound, the device including: a housing having mating top and bottom portions, wherein the top portion has an outlet; a membrane electrode assembly for electrochemically producing oxygen including an anode, a cathode and an ion conducting membrane; and a circuit board having an associated power source; wherein the membrane electrode assembly is mounted to the top portion of the housing, thereby forming a sealed cavity between the anode and the top portion of said housing such that the outlet is fluidly connected to the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present embodiments may take physical form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail in this specification and illustrated in the accompanying drawings which form a part hereof.

[0010] FIGURE 1 is an exploded ^Z A overhead view of an oxygen producing device in accordance with one embodiment.

[0011] FIGURE 2 is a view of an underside of a top portion of an oxygen producing device in accordance with one embodiment.

[0012] FIGURE 3 is a cutaway side view of an oxygen producing patch with tubing in accordance with one embodiment of the invention deployed on a patient.

[0013] FIGURE 4 is a schematic diagram of a membrane electrode assembly (electrochemical cell) for use in the present embodiments.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0014] The present embodiments relate to oxygen producing devices for wound care application. The present embodiments simplify the construction and operation of portable, self-contained devices for the topical application of oxygen to promote wound healing described in US Patent Nos. 5,578,022 and 5,788,682, as well as parent application Serial No. 10/520,410. These concerns include:

[0015] Membranes made from presently available ionically conducting polymers dry out when exposed to ambient conditions. When dry, such membranes show high ionic resistance resulting in device failure. [0016] For wound healing application, the oxygen generating device is secured with adhesive tapes and is exposed to several impurities, which poison the catalyst for oxygen reduction and/or generation. [0017] The present embodiment devices operate based on similar principles as those described in our earlier patent, U.S. Patent No. 5,578,022, (incorporated herein by reference in its entirety) which has been commercialized by Ogenix Corporation under the name EpiFLO ^SD ®, and cleared by the FDA for the treatment of certain types of wounds. More specifically, it uses oxygen reduction at a high area gas permeable cathode yielding water as a product, and water oxidation at a high area gas permeable anode to generate pure oxygen. Both electrodes are attached to opposite surfaces of a thin polymer electrolyte membrane (PEM), e.g., Nafion®, in much the same way as in PEM fuel cells. The anode and cathode sides of the cell are isolated from each other. As the gas permeability of the assembly is very low, operation of the device enriches the oxygen content of the side facing the anode, and, at the same time, depletes the oxygen content of the side facing the cathode.

[0018] Referring now to the drawings wherein the showings are for purposes of illustrating a preferred embodiment and not for purposes of limiting the same, the figures show a new design for generating oxygen to heal wounds.

[0019] With reference to Figures 1 and 2, an exploded view of an oxygen producing device in accordance with one aspect of the present invention is shown. The device includes a housing having top 12 and bottom 14 portions. The top and bottom portions may be designed to be detachable.

This can be done using various attachment options, such as simple clip structures 16. Inside of the housing is a circuit or control board 18. This board contains electronics for harnessing power from a power source, such as a set of batteries 20, and for running and controlling the oxygen producing device. Oxygen is produced in the device by an electrochemical cell or membrane electrode assembly 22, which, as seen in Figure 4, includes a porous cathode, an ion conducting membrane and a porous anode. [0020] The electrochemical cell is attached to the top portion 12 of the housing using any conventional means. When attached, the anode of the cell 22 is preferably sealed in an airtight manner to the top portion of the housing such that air or other gases are prevented from being transferred to the anode side of the cell from the interior of the housing (Figure 2). When attached to the top portion 12 of the housing, a small cavity or headspace 32 is formed between the anode and the interior surface of the top portion 12 of the housing. This cavity on the anode side of the cell is fluidly connected with an outlet 30 in the top portion 12 of the housing. This fluid connection between the cavity and the outlet may be accomplished with a sealed passageway 32 molded into the top portion 12 of the housing. The outlet 30 can be equipped with a Luer or Luer-Loc type attachment.

[0021] In operation, the cathode is exposed to the atmosphere, such as through a vent (not shown) in the bottom portion 14 of the housing. As detailed above, the anode is in fluid communication with the outlet 30, which itself may be in fluid communication with a skin wound through the use of a conduit or cannula (described in more detail below). The cavity becomes filled with gaseous oxygen evolved at the anode. The oxygen flows from the cavity to the outlet, where it can be delivered to the wound site via a cannula. [0022] With reference to Figure 4, the oxygen producing device of the present invention suitable for use in any of the above described embodiments can be described generally as comprising a membrane electrode assembly (MEA) or electrochemical cell 100 (which is labeled 22 in Figure 1 above) for the electrochemical concentration of oxygen from air. An ion conducting membrane 102 is positioned between two electrodes 104, 106, which in turn are connected to a power source 108, such as a battery, capable of passing a current across the electrodes.

[0023] As shown in Figure 4, oxygen in ambient air is reduced to water at an interface region 110 between the cathode 104 held at a reducing potential and the membrane 102 using the protons supplied by the membrane according to a reaction as described below. The product water migrates (or diffuses) through the membrane 102 to the anode 106 held at an anodic potential, which oxidizes the water back to oxygen while releasing protons at an interface region 112 between the anode and the membrane. The protons move through the membrane to the cathode 104 to make possible continued reduction of oxygen from air. Atmospheric nitrogen and carbon dioxide are electrochemically inert under the reaction conditions required for oxygen reduction and, thus, are effectively rejected at the cathode. The reduction product of oxygen alone moves through the membrane, resulting in near 100% pure oxygen on the anode. This oxygen is then directed to the tubing for delivery to a wound site.

[0024] Thus, the following reaction mechanisms may be used in the present invention for the production of oxygen: [0025] At the cathode: O ₂ + 4H ⁺ + 4 e- → 2H ₂ O [0026] At the anode: 2H ₂ O → O ₂ + 4H ⁺ + 4e-

[0027] with the net reaction being the depletion of a gaseous oxygen (from ambient air) on the cathode side of the membrane and an increase of the oxygen concentration on the anode side.

[0028] Preferably attached to a perimeter of an underside of the bottom housing 14 is an adhesive strip (not shown), which is used to secure the housing to the patient's skin. The oxygen pressure in the cavity will vary depending on the size of the cavity as well as the size of the outlet and cannula as well as the rate of oxygen production. However, the pressure will preferably not be so high so as to cause vasoconstriction. [0029] The bandage itself may have multiple layers to promote patient comfort and healing, including but not limited to layers of cotton gauze, polyethylene oxide-water polymer, as well as layer(s) containing topical ointments and other medicinals including antibiotics, antiseptics, growth factors and living cells. Preferably, the bandage is occlusive on all sides to enable the maintenance of an oxygen rich atmosphere.

[0030] As described above, the device will preferably use one or more batteries as a power source. The circuit board may have an electronic timing device that can be set for a defined period of oxygen delivery, e.g. seven day or 15 day oxygen therapy treatment. The unit as shown in FIG. 1 may be powered by a variety of primary or secondary battery power sources, including alkaline manganese-dioxide, zinc-air, lithium thionyl chloride, lithium manganese dioxide, lithium ion, nickel metal hydride and the like. [0031] With reference to Figure 3, an oxygen producing device and patch assembly 80 according to a second embodiment of the invention is shown generally and includes a dressing or bandage 82 to be placed over a wound, a portable oxygen producing device 84 as described above for supplying oxygen to the wound, and a conduit such as a flexible tubing or cannula 86 fluidly connecting the oxygen producing device with the bandage 82 and the underlying wound. The flexible tubing may include a Luer type connection or similar type. The tubing 86 is preferably made from a polymeric material suitable for use in hospital applications. Suitable materials for use in the tubing include, but are not limited to, silicone, polyethylene, polypropylene, polyurethane and various other thermoplastics.

[0032] Oxygen is produced at the oxygen producing device 84 via an electrochemical reaction. The oxygen then travels through the flexible tubing 86 to the bandage covered wound. Depending on the type of wound and the dressing used to cover it, the tubing can contact the dressing in various ways. For example, the end of the cannula may be placed directly above the wound and under fully occlusive dressings, thereby making an ordinary bandage "oxygen enriched".

[0033] The present embodiments allow delivery of oxygen to a wound in a variety of ways. That is, the present embodiment may allow delivery of oxygen subdermally, transdermally, and/or topically, allowing for a variety of treatments.

[0034] For in vivo uses, the end of the cannula can be implanted to the site where treatment is desired. The implanted end of the cannula may be perforated with multiple holes or made of material that would allow oxygen to diffuse through the tubing wall into ischemic tissue or the bloodstream. In addition, a syringe can be attached to the end of the tubing to facilitate the

introduction of oxygen subdermally. Site specific oxygen delivery to promote localized angiogenesis or ischemic reperfusion and elevated metabolism is beneficial for orthopedic and organ repair as well as tissue, bone, tendon, and cartilage regeneration. Localized oxygenation of tissue and tumors for improved radiological oncology applications may benefit with the present device.

[0035] Thus, the present device may be considered a universal remote supply of oxygen in that it can be used with a wide variety of bandages or dressings already on the market. Additional types of dressings with which the present invention may be used include fully occlusive thin film dressings, hydrocolloid dressings, alginate dressings, antimicrobial dressings, biosynthetic dressings, collagen dressings, foam dressings, composite dressings, hydrogel dressings, warm up dressings, and transparent dressings. [0036] In other applications, the device is capable of treating venous leg ulcers where the patient must wear woven four part compression dressings to control swelling and edema. The remote oxygen producing device 84 with a tubing 86 can be placed on the top layer of the compression dressing, thus avoiding compressing the device tightly against the leg as would be necessary with prior art devices. The tubing 86 may be woven between the four individual layers of the compression dressing to conform directly to the leg without unduly compressing the oxygen generator, batteries and hardware comprising the oxygen producing device 84 against fragile skin surrounding the wound. Positioning the device on top of the compression dressing also provides the further advantage of assuring unrestricted delivery of oxygen from atmospheric air to the wound, rather than relying on atmospheric diffusion through the dressing.

[0037] The remote device can be positioned on the patient wherever convenient and comfortable. Patients with wounds on the bottom of their feet, for example, can wear a thin bandage, add the soft tubing and attach the device away from the wound on the ankle or leg. The patient is thus able to wear a shoe while being treated with oxygen without having size and comfort restraints created by the prior art. For patients with wounds to the sacrum, heel, back or other pressure points, the device can be remotely placed away

from the wound and pressure point for optimum comfort. Then, the relatively soft tubing can be directed to the wound site.

[0038] While microbes from a wound site may contaminate a bandage or dressing placed over it, the use of the remote device with disposable, sterile tubing prevents microbial reflux from reaching the device. The tubing serves as a microbial barrier to the device. When in operation, the tubing provides positive gas pressure from the device to the wound and is separated by a sufficient distance to prevent reflux contamination of the device. Optionally, a microbial biofilm interrupting mechanism, such as a semi-permeable membrane may be implemented with the device within or at either end of the tubing as a further safeguard.

[0039] The ion conducting membrane may be any of a number of known ion conducting membranes which are capable of conducting protons and other ionic species. Suitable membranes include various perfluoronated ionomer membranes that include a poly(tetrafluoroethylene) backbone and regularly spaced perfluoronated polyether side chains terminating in strongly hydrophilic acid groups. A preferred group of membranes suitable for use in the present invention include those containing sulfonic acid terminating groups on the side chains and available under the trademark Nafion® from E. I. Dupont Co. Nafion ^® is a perfluorinated polymer that contains small proportions of sulfonic or carboxylic ionic functional groups. Its general chemical structure can be seen below, where X is either a sulfonic or carboxylic functional group and M is either a metal cation in the neutralized form or an H ⁺ in the acid form. Other suitable membranes include partially fluorinated membrane materials and those based on hydrocarbon polymer backbones.

[0040] The electrodes used in the membrane electrode assembly can be in the form of a mesh or a thin coating on the opposite surfaces of the membrane. They can be made of any materials which are electrically conductive and which will catalyze the reduction of gaseous oxygen into water, and catalyze the oxidation of the product water to release oxygen. Suitable electrode materials include, but are not limited to, platinum, iridium, rhodium, ruthenium as well as their alloys and oxides in a pure finely divided form or as supported catalysts.

[0041] In one embodiment of the present invention, Nafion® membrane is treated or imbibed with 85-100% phosphoric acid. In Nafion®, water normally provides the hydrogen bonding network and enables the rapid movement of protons through the polymer (and hence the high ionic conductivity). However, when left under ambient conditions, Nafion® loses water to the surroundings (due to the relatively high vapor pressure of water), which results in the loss of ionic conductivity. Phosphoric acid can also provide a hydrogen bonding network similar to that of water, but unlike water, has a very low vapor pressure - at room temperature the vapor pressure of phosphoric acid is so low that it can be considered zero. It is also hygroscopic to a degree, such that it may absorb water from the atmosphere. This combination of properties makes it possible to replace most of the water in Nafion® with phosphoric acid under appropriate conditions. [0042] A method of making a membrane electrode assembly that is capable of accomplishing the above goal consists of bonding a Pt/C electrode and a Pt black electrode to either side of a Nafion® 117 (or similar) membrane. The electrical connections from the electrodes to the voltage source are normally provided through conducting end plates that are normally made of thick graphite or metallic material. To reduce weight and improve mobility of the device, a thin (e.g., 1-5 mil), electronically conducting and electrochemicaily inert wire is placed in between the membrane and electrode during the bonding process, thereby making the electrical connection an integral part of the membrane electrode assembly. Examples of such wires include: gold, Pt, gold or Pt plated or deposited Ta, and similar materials.

[0043] In addition, a catalyst may be used to improve the electrochemical production of oxygen in the above reactions. The addition of a catalyst in one or both electrodes aids in overcoming the kinetic reaction barriers. Preferably, a Pt-Ru, Pt-Ir, or similar noble metal alloy catalyst that is poison resistant is used to coat the electrodes. The use of such poison resistant catalysts will prevent impurities introduced from the adhesive and other components of the device from reducing the catalyst activity and deactivating the device. Suitable non-limiting examples of anode catalysts include Pt-Ir, Pt-Sn, and ternary combinations thereof. Suitable non-limiting examples of cathode catalysts include Pt-Ru/C, Pt-Sn, Pt-Ir, Pt-C, and ternary combinations thereof. A preferred catalyst is Pt-Ir.

[0044] The electronic circuit board or controller may contain an on-off switch and a current monitoring port. The amount of oxygen generated by the device can be varied by changing the voltage applied across the electrodes. Typically, the device will produce between about 1 and about 50 ml oxygen/hr, more preferably between about 1 and about 10 ml/hr. [0045] The invention has been described with reference to various preferred embodiments. Obviously, modifications and alteration will occur to others upon a reading and understanding of this specification. It is intended to include all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalent thereof.

What is claimed is: