Stock material or miscellaneous articles – Structurally defined web or sheet – Edge feature
Reexamination Certificate
1997-03-17
2001-12-25
Dixon, Merrick (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Edge feature
C428S198000, C428S221000, C428S328000, C428S354000
Reexamination Certificate
active
06333093
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to anti-microbial coatings formed from one or more anti-microbial metals and to multilayer laminated wound dressings.
BACKGROUND OF THE INVENTION
Burns and related wounds present a serious problem in infection control. Noble metal ions such as silver and gold ions are known for their anti-microbial activity and have been used in medical care for many years to prevent and treat infection. Water soluble silver nitrate has been widely used as an astringent and as a potent anti-microbial solution. For example, 10% silver solution preparations are applied directly to ulcers of the mouth; dressings wetted with 0.5% silver nitrate solutions are used to cover second and third degree burns, especially to protect against gram negative infections; and drops of a 1% silver nitrate solution in the eye is still a legally required treatment in many areas of the world for prophylaxis of ophthalmia neonatorum.
The anti-microbial effect of these known silver nitrate solutions appears to be directly related to the concentration of the silver ions. Unfortunately, water soluble silver nitrate solutions provide very little residual activity due to the reactivity of silver ions with chloride, etc. in body fluids. To compensate for this lack of in use longevity, soluble silver solutions, such as silver nitrate, are used at far higher concentrations (3000 to 3500 mg/L) than are required for bacterial control (2 to 5 mg/L) in an effort to extend the duration of the antimicrobial effect. As a result, the solution can have irritating and astringent effects on wounds. For instance 1% solutions used prophylactically for ophthalmia neonatorum must be followed in a few seconds with a 0.85% sodium chloride rinse to prevent conjunctivitis. Burn wound treatment in current use for second degree burns employs 0.5% silver nitrate solutions which must be added frequently throughout the day (usually 12 times daily) in order to replenish the active Ag
+
ion. Also in use are silver sulphadiazine creams, which need frequent reapplication and scraping to remove the debris and chemical barrier, and which may also cause sensitivity or allergic reaction to the sulpha component.
Significant improvements to minimize adverse properties have been sought since the turn of the century. Some efforts have focussed on the use of colloidal solutions of insoluble, poorly ionized salts such as oxide complexes with proteins to reduce the rate of release of silver ions. Other efforts focussed on producing silver in an activated form, for example by depositing it on porous carbon to provide slower release of silver ions, or by activating the silver after deposition, for example by treatment with strong oxidizing agents. Still other efforts were directed at electrical activation of the silver coatings to drive the release of silver, or depositing with an electochemically different, more noble metal so as to use dual metal galvanic action as the driving force to release silver ions. To date, improvements in anti-microbial agents derived from anti-microbial metals such as silver, and wound treatment procedures using same are sought to improve the anti-microbial efficacy of the metal ions, to reduce the frequency of the application of the anti-microbial agent, and to improve infection control in wound treatment. Also needed is a visible indicator of the anti-microbial activity and effect, so as to minimize over application of the anti-microbial agents and unnecessary wound dressing removal, and thus improve patient comfort and minimize sensitivity reactions to anti-microbial metals.
Applicants have developed anti-microbial materials which provide efficacious and sustainable anti-microbial effect. Such materials are described in, for example U.S. Pat. No. 5,454,886, issued Oct. 3, 1995, to Burrell et al. The materials are formed as powders, foils, flakes, coatings or thin films from one or more anti-microbial metals so as to contain atomic disorder.
SUMMARY OF THE INVENTION
The inventors made a number of surprising discoveries when working on improvements to the anti-microbial materials formed with atomic disorder described in their previous patent applications. Firstly, they discovered that a thin film of an anti-microbial metal material on a reflective base layer coating, such as a reflective silver coating, was capable of producing an interference colour. By altering the refractive index and/or the thickness of the top layer, different, discernible interference colours were produced. Secondly, they discovered that if the top anti-microbial metal layer was formed with atomic disorder so as to produce an anti-microbial effect when exposed to alcohol or electrolyte, sharp interference colours were produced, providing a useful indicator of activation (release of ions etc.) from medical devices and the like carrying such a coating. Even minor dissolution or composition changes of the top layer of the coating, such as a fingertip touch, was discovered to cause a detectable colour change. Thirdly, they discovered that a single layer of an anti-microbial metal formed with atomic disorder could be produced with an initial colour which changed on contacting an alcohol or electrolyte so as to generate an interference colour which was different from the initial colour. Without being bound by the same, it is believed that contacting the atomically disordered material forms a thin layer at the top of the material (hereinafter termed as “in situ generated top layer”) which has a composition different enough from the underlying base layer that it is capable of providing an interference colour. Thus, the present invention extends to a method of indicating exposure of multilayer anti-microbial material formed with atomic disorder to an alcohol or electrolyte through the use of interference colours.
In one broad aspect, the invention provides a multilayer anti-microbial material comprising a) a base layer of a partly reflective material capable of generating an interference colour when covered with a partly reflective, partly light transmissive top layer; and b) a top layer formed over said base layer, said top layer being a partly reflective, partly light transmissive thin film containing at least one anti-microbial metal and having a thickness such that an interference colour is produced, said top layer having a refractive index different from that of the base layer, and the anti-microbial metal being formed with sufficient atomic disorder such that the top layer, in contact with an alcohol or water based electrolyte, releases ions, atoms, molecules or clusters of the anti-microbial metal into the alcohol or water based electrolyte at a concentration sufficient to provide a localized anti-microbial effect on a sustainable basis. The invention extends to anti-microbial materials in which the top layer is formed above the base layer by such techniques as vapour deposition, and to materials having an in situ generated top layer.
The base layer might be provided as a substrate (ex. medical device) which is partly reflective such that it can provide an interference colour when covered with a partly reflective, partly transmissive top layer. Preferably the base layer is formed from a metal selected from Ag, Au, Pt, Pd, Cu, Ta or Al, with Au, Ag, Pt, Pd and Cu being most preferred. Preferably both the top and base layers are formed from anti-microbial metals formed with atomic disorder. The top layer is most preferably formed from Au or Ag.
Most preferably, the top layer is a composite material formed by depositing the anti-microbial metal in a matrix with atoms or molecules of a different material, wherein the different material provides atomic disorder in the matrix. The different material may be a biocompatible metal such as Ta, Ti, Nb, V, Hf, Zn, Mo, Si or Al, or oxides, nitrides, carbides, borides, halides, sulphides or hydrides of such biocompatible metals. Alternatively, the different material may be atoms or molecules absorbed or trapped from the atmosphere used in a vapour deposition process, including
Burrell Robert Edward
Precht Roderick John
Dixon Merrick
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Westaim Biomedical Corp.
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