News Column

Patent Issued for Medical Device

August 26, 2014



By a News Reporter-Staff News Editor at Life Science Weekly -- According to news reporting originating from Alexandria, Virginia, by NewsRx journalists, a patent by the inventors Flick, A. Bartholomew (Lakemont, GA); Silver, Gregg (Chicago, IL); Miller, Thomas (Willowbrook, IL), filed on October 21, 2005, was published online on August 12, 2014 (see also Argentum Medical, LLC).

The assignee for this patent, patent number 8801681, is Argentum Medical, LLC (Chicago, IL).

Reporters obtained the following quote from the background information supplied by the inventors: "The disclosure generally relates to a medical device for the care or treatment of a pathology. In particular, the disclosure relates to a wound dressing, for example conductive wound dressings having anti-microbial, therapeutic or prophylactic properties, and methods for making the dressings.

"The treatment of wounds has become a highly developed area of scientific and commercial investigation because increased rates of healing reduces healthcare costs and decreases the risk of complications due to secondary infections. It is currently believed that healing is related to the degree of injury, the immunological and nutritional status of the host, contamination of the wound, the maintenance of the moisture level, pH and oxygen tension of the wound surface, and the electrical parameters of the wound site in relation to the surrounding intact, uninjured tissue. In particular, regeneration in amphibians and fracture healing in mammals are associated with complex changes in the local direct current (DC) electric field. It is believed that the electric field gradually returns to normal pre-injury levels as the injury heals. Conversely, failure of the normal healing process, for example as in fracture non-unions, is associated with, among other things, the absence of appropriate electrical signals at the site of the injury or infection.

"There have been numerous studies conducted on wound healing in amphibians because their rate of healing is significantly greater than that of mammals. Wound healing in mammalian skin occurs over days or even weeks, with epithelial cell migration rates ranging from 7 (dry wound) to 20 (wet wound) micrometers/hour. Amphibian skin wounds heal within hours, with epithelial cell migration rates ranging from 60 to more than 600 micrometers/hr. The expedited rates of healing in amphibian skin may be partially explained by the aqueous environment that bathes the outer surface of the epithelium. Amphibian wounds in an aqueous environment are provided with the appropriate ions to re-establish the electrical potential on the surface of the wound as well as provided with an environment favorable to cell migration and reproduction.

"It is generally recognized that dry wounds in mammals heal more slowly than wounds that are kept moist by occlusive dressings. Keeping the epidermis surrounding a wound and the wound itself moist stimulates the wound to close. Wound dressings have been designed to retain moisture from the exudates produced by the wound and function by preventing evaporation of fluid. Wounds that are dry and lack production of .quadrature.bsorben must depend upon the moisture within a self contained wound dressing. If the wound dressing dries out, the needed moisture level for optimum wound healing will not be maintained and the dressing will stick to the wound surface and cause disruption of cellular processes. The lack of moisture often results in the formation of an eschar or scab, and a general slowing of the wound healing process.

"Wounds that produce an extensive amount of moisture are thought to create another problem called skin maceration. Skin maceration is a softening of the skin or wearing away of the skin as a result of continual exposure to bodily fluids or moisture. It is known to cause a breakdown of the cornified epithelium, thereby reducing the physical microbial barrier function as well as the moisture regulation function of the epidermis. With a reduction of the microbial barrier function, the wound surface has a significantly greater risk of contamination by pathogenic microbes from the surrounding environment. Therefore, it is common practice to design wound dressings to reduce or prevent skin maceration by wicking away wound fluids and storing the fluids in absorbent layers.

"A common practice in the treatment of wounds is the application of impermeable backing sheets to a wound dressing. The backing sheet functions as a moisture retention layer as well as a physical barrier to prevent microbial penetration. The backing sheet typically consists of a material with specified moisture vapor transmission rates (MVTR) and provides control of the rate of evaporation of moisture from the absorbent layer. Therefore, the backing sheet is generally impervious to liquid.

"There are a variety of venting systems that can be contained within the dressing structure for the purpose of directing wound exudates via specific pathways to provide a controlled leakage of fluids from the wound surface to a contained absorbent layer.

"For example, in certain perforated films, the perforations are sufficient to permit wound exudates to diffuse through the film at a rate that precludes pooling on the wound surface, which is a common cause of maceration. These dressings must be removed when they become saturated with exudates.

"While there are numerous dressings designed to retain the moisture content of wounds, there are still many areas of inefficiency in current treatment methods. For example, these dressings are only effective for moist wounds and do not provide any significant benefit for dry wounds. Wounds vary significantly in the amount of exudates or moisture produced throughout the healing cycle. In order to maintain an effective level of moisture it is necessary to continually change the dressings as the absorbent component reaches maximum capacity. Conversely, it is necessary to remove the dressings and add fluid to dry wounds, then replace the dressings. In either situation, removal of the dressing can cause disruption of the cellular process of the wound and increase the risk of contamination by microbes.

"Furthermore, it is necessary to change the types of dressings throughout the healing process of the wound as the moisture content changes.

"Besides the effect of moisture on wound healing, microbial growth at the site of injury has a great effect on healing. In normal skin, a microbial barrier is created by the cornified epithelium. Wounds cause destruction of the cornified epithelium as well as deeper layers thereto, and the loss of the natural anti-microbial barrier.

"The presence of microbial species at the wound site creates a bioburden that can retard the healing process. As the bioburden of the wound decreases to bacterial counts less than 103 CFU/ml, wound healing is enhanced. Treatment of wounds typically involves preventing contamination by pathogenic microbes from the external environment as well as reducing the microbial bioburden of the wound.

"While there are many antibacterial and antifungal agents that can be used to treat wounds, the anti-microbial and antifungal properties of silver have been of particular interest. However, the effectiveness of silver as an anti-microbial agent is at least partly determined by the delivery system. Most silver compounds that dissociate readily and produce large numbers of free silver ions are highly toxic to mammalian tissues. Less-toxic compounds, including silver sulfadiazine cream, widely used in the treatment of burns, do not dissociate readily and therefore do not release large numbers of silver ions. Therefore, these compounds must be re-applied frequently to maintain their clinical efficacy.

"Silver has been used in the construction of wound dressings to actively or passively release metallic silver particles or silver ions into the wound. Active release of silver ions require the presence of an electrical potential that actively drives silver ions from a source into the wound dressing or wound itself. This has been accomplished with a battery or other power source known to those skilled in the art. Passive release of silver ions is dependent upon the solubility of silver in aqueous solutions. The passive release of silver ions has been called the oligodynamic release process and includes the passive dissolution of silver into a solution.

"The anti-microbial efficiency of metallic silver or silver ions is dependent upon the microbe coming into direct contact with the surface of the metallic silver or coming into contact with a released silver ion. Therefore, the total surface area of metallic silver and the number of silver ions released is directly related to the level of anti-microbial activity.

"Various methods have been used to create mechanisms for metallic ion transfer.

"For example, the vacuum vapor deposition technique has been utilized in the construction of wound dressings to plate metallic silver and silver salts onto a variety of substrates. The vacuum vapor deposition technique has been modified so as to create 'atomic disorder' of the plated silver that has been reported to enhance the anti-microbial effect by allowing the release of nanocrystaline particles of metallic silver. However, the technique provides a flat plating pattern and does not uniformly coat the entire three-dimensional surface of fibers.

"Another mechanism used for passive release of silver ions and particles from a wound dressing includes imbedding or placing silver particles of varying sizes in a variety of substrates. Finely divided metallic silver in collagen has been incorporated into surgical dressings of reconstituted collagen foam laminated to a thick continuous layer of inert polymer. This does not allow for direct contact of the maximum number of ions with the wound.

"When connected to a voltage source, a metal anode and a return electrode have been used as a means to deliver silver ions iontophoretically to a wound or within a wound dressing. Electrically conductive silver-impregnated meshes, including silver-protein colloids, have been disclosed with current densities as low as IOIA/mm2. This requires an external power source and stationary equipment and is cumbersome for the patient.

"Silver foils have been incorporated into wound dressings as a means of supplying silver ions as an anti-microbial agent, as well as acting as an electrode for dispensing medications. In addition, silver has been fabricated into devices that incorporate a means of applying a therapeutic voltage to the wound. Foils do not provide for circulation of air, and are limited in surface area.

"Compounds that slowly release silver into the wound environment have been disclosed in substances such as water soluble glass, phosphorus pentoxide and silver oxide.

"The silver impregnated glass may be in the form of a powder, granules, or woven into a dressing. The water soluble glass releases silver secondary to the dissolution of the glass.

"Such compositions have a high volume resistance and very poor conductivity.

"Regardless of whether silver is provided in the form of silver ions or as a topical composition (silver nitrate solution, silver sulfadiazine cream, or the like), its beneficial effects are manifested primarily at the treated surface and immediately adjacent tissues, and are limited by the achievable tissue concentration of silver ions. Despite the availability of numerous techniques for the delivery of silver and silver compounds in vitro and in vivo, there remains a need for a delivery system that is capable of supplying clinically useful concentrations of silver ions to a treatment site without the need for adjuvant electrical stimulation.

"None of the available metallic ion treatment devices provide an efficient and convenient means to restore the homeostatic electromagnetic environment for areas of wounds. They also do not provide for maximum surface area for release of metallic ions. In addition, the prior art does not address the need to regulate the moisture content of a wound without manually changing the dressings, or applying liquids or medicants. This is true in part because of the belief that a wound dressing must serve as a microbial barrier and prevent the movement of fluids from the wound exudates. The currently available treatments for wounds prevent microbial contamination by providing a physical barrier which must be manipulated and interrupted as part of the treatment process. Such activities allow for microbe contamination and interrupt the healing process.

"It is believed that wound healing occurs with maximum speed and efficiency when the wound is maintained in a moist condition without excessive wetness or dryness.

"Negative pressure or sub-atmospheric pressure has been used in combination with wound dressings for the treatment of soft tissue damage and wound closure. Negative pressure wound therapy assists in wound closure by applying localized negative (sub-atmospheric) pressure to help promote wound healing. Generally, vacuum pressure is applied to a special dressing positioned in the wound cavity or over a flap or graft. This pressure-distributing wound packing helps remove fluids from the wound and promote the normal healing process.

"Some negative pressure therapies use open-cell reticulated foam that can be cut to the shape of the wound, or can be placed side by side or layered to treat very large wounds. A tube in contact with the foam allows the application of vacuum pressure for the removal of excess wound fluid. The dressing and distal evacuation tube are covered by a transparent, occlusive drape that provides a seal which allows the application of vacuum pressure to the system.

"The free end of the evacuation tube is attached to a canister reservoir, which fits into a microprocessor-controlled vacuum unit and collects the fluids drawn away from the wound. The vacuum unit provides continuous or intermittent negative pressure selected to meet the needs of the wound being treated. The pressure can be adjusted within a range that has been demonstrated to provide optimal fluid removal without placing the delicate wound tissue at risk of injury.

"The application of negative pressure therapy to a wound provides a moist wound-healing environment. A moist wound-healing environment is the standard of care for wound healing. Removal of excess interstitial fluid also can lead to removal of excess proteinases present in the periwound environment. Metalloproteinases are known to bind and degrade growth factors before the growth factor can reach its target tissue. With inhibitors removed, growth factors can stimulate cell proliferation and migration. Removal of excess interstitial fluid can naturally help decrease periwound induration (swelling) further helping to promote wound healing.

"Problems associated with applying a negative pressure to a wound include: tissue growth into the dressing; potential damage of delicate structures such as blood vessels and internal organs and adhesion of the dressing to the wound base causing repeated trauma (therefore increasing pain and increased healing time) with dressing changes.

"Accordingly, there is a need for additional devices and methods for treating or preventing a pathology."

In addition to obtaining background information on this patent, NewsRx editors also obtained the inventors' summary information for this patent: "Aspects of the present disclosure generally relate to compositions and methods for treating a pathology of an organism. An exemplary device comprises at least one conformable, conductive layer comprising one or more fibers or foams, wherein the one or more fibers or foams are coated with an antimicrobial metal in an amount sufficient to provide the conductive layer with a surface resistance of less than about 1,000 ohms/cm.sup.2 or less, 5 ohms/cm.sup.2 or less, or 1 ohm/cm.sup.2 or less and wherein the at least one layer comprises a plurality of apertures sufficient to provide the device with a liquid wicking value of at least about 5%. In other aspects, the device can have a liquid wicking value of at least about 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or more.

"In certain aspects, the disclosed compositions can aid in restoring the transepithelial skin potential, maintain a moist wound healing environment, create a functional microbial barrier, reduce microbial bio-burden of the wound, deliver an antimicrobial metal, aid in reducing pain, or a combination thereof. For example, certain embodiments of the disclosed devices can reduce the wound potential or make the wound potential more negative by about 1 mV, about 5 mV, about 10 mV, about 20 mV, about 30 mV, about 40 mV, about 50 mV or more.

"The present disclosure also provides devices, medical devices, wound dressings and methods of using the disclosed compositions. Devices such as wound dressings of the present disclosure comprise one or more layers of materials. One of the layers can be a layer comprising conductive fibers, non-conductive fibers, conductive foams, non-conductive foams or combinations thereof. This layer, referred to as the conductive layer, comprises fibers, foams or a combination of fibers and foams that have from approximately 0% to approximately 100% of the surface or surfaces of the fiber or foam covered with a metal plating, and all ranges there between. In certain aspects, one or more fibers or foams are coated with an amount of antimicrobial metal effective to provide the conductive layer with a surface resistance of about 1,000 ohms/cm.sup.2 or less, typically, about 5 ohms/cm.sup.2 or less, even more typically about 1 ohm/cm.sup.2 or less. Fibers or foams that do not have metal plating are referred to as nonconductive and fibers or foams with metal plating are referred to as conductive.

"Another aspect provides a device having at least two layers of conformable conductive fabric separated by a plurality of supports. Other devices of the present disclosure can comprise a second layer that is an absorbent layer as well as an optional third layer that is a moisture control layer, which may be impermeable to gases or liquids or may have apertures therein that allow transmission of differing materials such as gases, liquids or microbial or environmental contaminants.

"Preferably, the at least one conductive layer can be placed in contact with a wound. At least a portion of the conductive layer comprises substrates coated with metal. Fibers include but are not limited to polysaccharides, for example alginates, chitosans, natural or synthetic polymers, such as polyamides, polyesters, silk, cotton, proteins, or a combination thereof. Fibers may vary in composition and three dimensional structure.

"A preferred conductive layer comprises a plurality of fibers wherein at least one fiber comprises a three dimensional structure and the fiber is substantially coated with a metal.

"Another preferred conductive layer comprises a polymeric foam structure wherein at least a portion of the foam surfaces are substantially coated with a metal, or the layer comprises a combination of fibers and foams. The plurality of fibers or foams within the conductive layer comprise at least one fiber or foam, having its surfaces coated with metal and include fibers or foams that are shaped to provide a spontaneous movement of fluids such as capillary action or wicking of fluids. Such fibers or foams are designed with grooves or channels along the longitudinal axis of the fiber or foam and these channels serve as ducts to move fluids, store or trap substances and provide a large surface area for a given denier per fiber or surface area of a foam.

"Preferably, additional layers of the dressing include at least one absorbent layer and at least one moisture regulation layer having a plurality of apertures disposed primarily in the moisture regulation layer. It will be appreciated that one or more of the layers of the disclosed devices can have one or more apertures. The apertures may vary in size from a layer with no apertures to apertures in a size range that is occlusive to liquids but not to gases, to a size range that allows liquids and gases to pass through, to a size that is open to microbes, such as bacteria, viruses, fungi, parasites, and environmental contaminants.

"An additional aspect of the disclosure relates to wound dressings that provide for a capacitive effect formed by the alternation of conductive layers of fiber with non-conductive layers.

"Another aspect of the disclosure relates to wound dressings having a plurality of layers arranged according to the ratio of conductive to nonconductive fibers comprising each layer. Additional aspects of the disclosure relate to various configurations of the functional shape of the novel dressings. Another aspect of the disclosure relates to methods of using the novel dressings to treat wounds in a human or an animal. Further aspects of the disclosure relate to methods of making the disclosed devices."

For more information, see this patent: Flick, A. Bartholomew; Silver, Gregg; Miller, Thomas. Medical Device. U.S. Patent Number 8801681, filed October 21, 2005, and published online on August 12, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8801681.PN.&OS=PN/8801681RS=PN/8801681

Keywords for this news article include: Argentum Medical LLC.

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Source: Life Science Weekly


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