WO2013155618A1

WO2013155618A1 - Anodized metal product with antimicrobial properties and method for producing the same

Info

Publication number: WO2013155618A1
Application number: PCT/CA2013/000389
Authority: WO
Inventors: Jocelyn LAMBERT; Maxime DUMONT; Jean-Denis CÔTE; Daniel Rivard; François PARADIS; Steve Arsenault; Daniel Gaudet
Original assignee: 9163-0384 Québec Inc.
Priority date: 2012-04-20
Filing date: 2013-04-19
Publication date: 2013-10-24
Also published as: CA2909198A1; CA3079855A1; CA2909198C

Abstract

The invention relates to a metal product having an anodized surface with antimicrobial properties. The invention also concerns methods for producing such a metal product and articles of manufacture comprising the same. The antimicrobial metal product of the invention comprises a porous surface layer formed by anodization, the porous surface layer comprising an electrodeposit of at least one metal and at least one antimicrobial compound. The methods of the invention may be performed on different metals and on metals of different quality and/or of different sizes including aluminum, titanium, zinc, magnesium, niobium, tantalum and anodizable alloys thereof. The metal product has an antimicrobial surface effective in killing a broad spectrum of microorganism, including various pathogens.

Description

ANODIZED METAL PRODUCT WITH ANTIMICROBIAL PROPERTIES AND METHOD FOR PRODUCING THE SAME

FIELD OF THE INVENTION

[0001] The invention relates to metal products having an anodized surface with antimicrobial properties. It also concerns methods for producing the same and articles of manufacture comprising such metal products.

BACKGROUND OF THE INVENTION

[0002] Aluminum alloys materials are light, have strength, softness and provide some durability against corrosion once anodized. Applications of aluminum alloys products are numerous and include kitchen wares, household furniture, appliances, door knobs, and medical devices. Unfortunately, aluminum does not have antimicrobial property of its own and microorganisms can easily stay alive on its surface.

[0003] Various methods have been developed for treating the surface of aluminum or aluminum alloy products for improving its antimicrobial properties. The following documents are selected examples of such methods: US patent No. 5,753,322 (Yamaduchi ef a/.); US 6,168,869 (Tomioka et a/.); European patent No. 1 207 220 (Takayssy ef a/.); Japanese patent application No. 11 323 597 (Kazuo ef a/.); Japanese patent publication No. 10 168 597 (Hisao et a/.); Japanese patent publication No. 10 168 598 (Hisao et a/.); Japanese patent publication No. 10 168 598 (Hisao ef a/.); Chi ef a/., Antibacterial activity of anodized aluminum with deposited silver, Surface and Coatings Technology, 157, (2002) 162-165; Chi ef a/., Antibacterial surface treatment of aluminum materials, Chinese J. Chem. Eng., 10(5), (2002), 622-624. However, these methods and the products obtained therefrom are less than optimal because antimicrobial activity is either weak or limited to few bacterial species and/or because antibacterial treatment is not compatible to dying of the aluminum product. Furthermore, these methods may not be applicable to antimicrobial treatment of other anodizable metals such as magnesium, zinc, niobium, tantalum and titanium.

[0004] There is thus a need for improved methods for treating the surface of anodizable metals such as aluminum in order to obtain a colored metal product having antimicrobial properties. There is also a need for anodizable metal products having a surface which has been coated such that it is effective in killing a broad spectrum of microorganism, including Gram-positive microbial pathogens, Gram-negative microbial pathogens and yeasts. There is also a need for antimicrobial solutions useful for impregnating anodizable metal products and providing metal products with an antimicrobial coating.

[0005] The present invention addresses these needs and other needs as it will be apparent from review of the disclosure, drawings and description of the features of the invention hereinafter.

BRIEF SUMMARY OF THE INVENTION

[0006] The invention relates to metal products having an anodized surface with antimicrobial properties. [0007] One particular aspect of the present invention concerns an antimicrobial metal product. According to one particular embodiment, the antimicrobial metal product comprises a porous surface layer formed by anodization, the porous surface layer comprising an electrodeposit of at least one metal and at least one antimicrobial compound. [0008] According to another embodiment, the antimicrobial metal product comprises an anodized metal substrate and an antimicrobial surface coating. The antimicrobial surface coating comprises a porous surface layer formed by anodization of the metal substrate. The porous surface layer comprises an electrodeposit of at least one metal and at least one antimicrobial compound in the pores of the surface layer. [0009] The metal product may be selected from aluminum, titanium, zinc, magnesium, niobium, tantalum and anodizable alloys thereof. The electrodeposited metal may be selected from silver, gold, copper, nickel, zinc, tin, palladium, cadmium and platinum.

[00010] The antimicrobial compound may be selected from antivirals, antibiotics, and antifungals. The antimicrobial compound(s) may be selected such that the antimicrobial surface coating of the antimicrobial metal product possesses antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria and/or yeast. In preferred embodiments the antimicrobial compound is not irreversibly captured in the pores such that it can diffuse outside the pores. [00011] In preferred embodiments, the antimicrobial compound is a quaternary ammonium such as Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC). More preferably, the porous surface layer comprises at least two quaternary ammonium compounds i.e. Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC) and Didecyl Dimethyl Ammonium Chloride (DDAC).

[00012] The porous surface layer may further comprise a dye and the surface layer may also be sealed partially or completely.

[00013] A preferred aspect of the invention concerns an antimicrobial piece of aluminum. The piece of aluminum comprises a porous surface layer formed by anodization and the porous surface layer comprises an electrodeposit of silver and at least one quaternary ammonium compound. More preferably, at least one quaternary ammonium compound is in the pores of the surface layer.

[00014] The invention also concerns all kinds of articles of manufacture incorporating an antimicrobial metal product and/or an antimicrobial piece of aluminum as defined herein. Particular articles covered by the invention include kitchen wares, kitchen countertops, hospital countertops, furniture, appliances, office equipment, door knobs, medical devices, laminar flow hoods, laboratory incubators, wall panels, floor panels, boat hulls, pipes, etc.

[00015] The invention further relates to a method for obtaining an antimicrobial metal product having an antimicrobial surface coating. In one embodiment, the method comprises the steps of:

- providing an anodized metal product having a porous surface layer formed by anodization;

- electrodepositing a metal to the porous surface layer; and

- impregnating the porous layer with at least one antimicrobial compound.

[00016] The anodized metal product, the metal electrodeposited and the antimicrobial compound may be selected as defined previously. In one particular embodiment, electrodeposition of silver is carried out in an aqueous solution of sulfuric acid.

[00017] The method may further comprise a sealing or clogging step which is carried out simultaneously or after the impregnation. In particulars embodiments, the sealing is carried out by soaking in a solution or by exposing the porous layer to steam at ambient pressure or in an autoclave. The method may further comprise a dying step before impregnating the porous layer with the at least one antimicrobial compound. [00018] A related aspect on the invention concerns an antimicrobial solution for impregnating a porous layer of an anodized metal product. In a preferred embodiment, the antimicrobial solution comprises at least two quaternary ammonium compounds having antimicrobial activity. More preferably, the at least two quaternary ammonium compounds consists ADBAC and DDAC.

[00019] The antimicrobial solution may further comprises a metallic salt such as AgN0₃, Cu(N0₃)₂, Zn(N0₃)₂, Ni(N0₃)₂ and mixtures thereof. The antimicrobial solution may also comprise additional antimicrobial agent(s) selected from antivirals, antibiotics, and antifungals. [00020] A related aspect on the invention method for controlling growth of microorganisms and/or microbial pathogens on a metallic surface, comprising impregnating the metallic surface with an antimicrobial solution as defined herein prior to contacting the metallic surface with microorganism(s) or pathogen(s). The invention also encompasses the use of an antimicrobial solution as defined herein for impregnating a porous layer of an anodized metal product, thereby creating an antimicrobial coating on the surface of the anodized metal product.

[00021] An advantage of the present invention is that it provides simple, cheap and relatively fast and efficient means for treating the surface of anodizable metals for conferring antimicrobial properties to these metallic surfaces. The methods of the invention may be performed on different metals and alloys of different quality and/or of different sizes. The invention also provides anodizable metal products having a surface effective in killing a broad spectrum of microorganisms, including various pathogens. Preferably, the killing action may require only a very short contacting period (e.g. less than 5 minutes). [00022] Additional aspects, advantages and features of the present invention will become more apparent upon reading of the following non-restrictive description of preferred embodiments which are exemplary and should not be interpreted as limiting the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS [00023] Figures 1 is bar graph showing antimicrobial activity of paper disks treated with different antimicrobial solutions. Solutions 1 to 5 are as defined in Example 1. Antimicrobial activity was evaluated using a disk diffusion assay against the following bacterial strains: E. coli (EC), P. aeruginosa (PA), S. aureus (SA), B. subtilis (BA), and C. albicans (CA).

[00024] Figure 2 is a panel showing pictures of Petri dishes illustrating antimicrobial activity against Gram positive bacteria, Gram negative bacteria and yeast of aluminum disks treated with various antimicrobial solutions: A: benzalkonium chloride (2,12 % W/V) + silver nitrate (1.02 % W/V) or B: Benzalkonium chloride (0,96%) + Didecyl dimethyl ammonium chloride (1 ,44 %) + silver nitrate (1.02 % W/V)). Antimicrobial activity of the disks against the following microbial strains was assessed: E. coli ATCC 8739; P. aeruginosa ATCC 9027; S. aureus ATCC 6538; B. subtilis ATCC 6633; and C. albicans ATCC 10231. For each dish, lanes 1 and 3 shows growth of bacteria for a pair of disks treated with the antimicrobial solution whereas lanes 2 and 4 growth of bacteria for a pair of untreated disks (negative control).

[00025] Figure 3 is a panel of microscopic pictures made at 500X of transversal cuts of aluminum disks anodized for 11 min (#2467), 22 min (#2468), 33 min (#2469) or 44 minutes (#2469). As expected, the thickness of porous aluminum anodic film (lined area at the top of each picture) increases with the duration of the anodization period (i.e. 4 pm, 8 μιη, 13 pm, 19 pm respectively).

[00026] Figure 4 is a schematization of a process for making an anodized metal product with antimicrobial properties according to one embodiment of the invention. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Antimicrobial metal product and Methods for making same

[00027] One particular aspect of the present invention relates to an antimicrobial metal product comprising an anodized metal substrate and an antimicrobial surface coating. The invention also concerns methods for obtaining an antimicrobial metal product having an antimicrobial surface coating.

[00028] As it is well known, anodization increases the thickness of the natural oxide layer on the surface of metal parts. Anodization changes the microscopic texture of the surface and changes the crystal structure of the metal near the surface. Typically, the end result of the anodization is the formation of a porous surface layer which is harder, stronger, more adherent, and more brittle than unanodized products.

[00029] The invention adds to the known advantageous properties on anodized metals by providing an anodized metal substrate having an antimicrobial surface coating. The antimicrobial surface coating comprises a porous surface layer formed by anodization. In addition, the porous surface layer comprises an electrodeposit of at least one metal and it further comprises at least one antimicrobial compound.

[00030] According to an embodiment of the methods of invention, an anodized metal product having a porous surface layer formed by anodization is first provided. Any metal which can be anodized is suitable according to the invention, including, but not limited to aluminum, titanium, zinc, magnesium, niobium, tantalum and anodizable alloys thereof (e.g. aluminum alloys and others). Anodization of such metals in well known to those skilled in the art and any anodization process resulting in the formation of a porous surface layer at the surface of the metal is acceptable according to the invention. In various embodiments according to the invention, the porous surface layer formed by anodization has a thickness ranging from about 1 pm to about 150 pm, preferably a thickness ranging from between 2 pm to about 35 pm, more preferably a thickness ranging from between 10 pm to about 20 pm. Typically the pores are nanopores having a diameter ranging from 5 nm to about 100 nm.

[00031] Prior to its anodization the metal substrate may be subjected to one or more pretreatment steps of such as degreasing, electropolishing, etching, etc. according to procedures known in the art. In one particular embodiment, for obtaining an aluminum product with a antimicrobial surface coating, the following steps are carried out: aluminum is degreased with acetone; etched with 10% weight/vol NaOH for 2 min at 50- 60°C; neutralized in 35% vol/vol HN0₃ for 30 sec. at room temperature; and submitted to a P2 etch treatment for 10 min at 50-60°C with 33% v/v sulfuric acid and ferrite (Russell and Garnis, 1977, Chromate-Free Method of Preparing Aluminum Surfaces for Adhesive Bonding. An Etchant Composition of Low Toxicity, Army Armament Research and Development Center, Dover NJ, Large Caliber Weapon Systems Lab).

[00032] It is within the skill of those in the art to anodize various anodizable metals and alloys. According to particular embodiments, the aluminum substrate is anodized in a 15 % v/v stirred sulfuric acid solution. A current of 1.5 Amps (13 volts) is applied to the aluminum piece for 44 minutes (given the selected size of the anodized piece, this allows an anodic/cathodic area ratio of 3/1 (the anode is anodized aluminum with a surface area 3 time the cathode surface) (the ratio can be to 1/1 to 4/1)). This leads to a layer of anodization of approximately 20 pm. The temperature of the solution is maintained between 21 °C and 23 °C. [00033] Electrodeposition (also known as electroplating) is well known to those skilled in the art. According to particular embodiments of the invention, once an anodized metal product having a porous surface layer is obtained, the porous surface layer created by the anodization is subjected to a step of electrodeposition of a metal. The metal to be electrodeposited may be selected among silver, copper, gold, nickel, zinc, tin, palladium, cadmium, platinum and combinations thereof. The metal to be electrodeposited can be selected according to the desired properties of the final product, including desired coloration, desired antimicrobial activity, desired durability and/or combination of these properties. In preferred embodiments, silver (Ag) is electrodeposited to the porous surface layer.

[00034] Any suitable electrodeposition process may be used according to the invention. In one particular embodiment, silver is electrodeposited onto aluminum and electrodeposition is carried out for about 30 sec to about 10 minutes in an aqueous solution comprising about 1.5 % vol/vol sulfuric acid and about 5.1 g/l silver nitrate (AgN0₃) at room temperature, Ac voltage 18 V. The invention also encompasses additional electrodeposition methods and conditions. In another particular embodiment, the method uses 8 g/l stannous sulphate (SnS0₄), 20 g/l nickel sulphate (NiS0₄), 17 g/l sulfuric acid (H₂S0₄) and 10 g/l tartaric acid (C₄H₆0₆) at room temperature, Ac voltage 15 V, for 1 to 10 minutes. In another particular embodiment, electrodeposition is carried out with 40 g/l nickel sulphate (NiS0₄), 25 g/l boric acid (H₃B0₃), 20 g/l magnesium sulphate (MgS0₄), 50 g/l ammonium sulphate ((NH₄)₂S0 ) and 5 g/l Tri-Ammonium citrate (C₆H-17 3O7) at room temperature, Ac voltage 5 V, for 1 to 10 minutes. Another method is 35 g/L copper sulfate (CuS0₄), 10 g/L sulfuric acid (H₂S0₄), 2 g/l sodium sulfate (Na₂S0 ) at 40°C with a voltage of 30 V for 50 min. Preferably, theses techniques should use metals with demonstrated or potential antimicrobial activity. The general process of the invention may be applicable to electrodeposition of Ag and additional metals (e.g. Au, Cu, Ni, Sn, Zn, Pt, Pd, Cd) with either documented and/or with potential antimicrobial activity.

[00035] In some embodiments, electrodeposition is used mainly to color and/or improve the visual aesthetic properties of the anodized metal product. Various metals can be electrodeposited according to the invention for coloration purposes including, but not limited to, silver, gold, copper, nickel, zinc, tin, palladium, cadmium, platinum and combinations thereof. In preferred embodiments, it is silver (Ag) which is electrodeposited to the porous surface layer because this metal possesses combined aesthetic and antimicrobial properties. [00036] According to some embodiments of the invention, after the electrodeposition step, the porous surface layer of the anodized metal is next impregnated with at least one antimicrobial compound. Suitable antimicrobial agent or compound includes antivirals, antibiotics, and/or antifungals, and these can consists of an organic or inorganic chemicals or salts. Impregnation may be carried out using any suitable method known to those skilled in the art. In preferred embodiments, the anodized metal is soaked in a product solution (with or without agitation) for about 1 second to about 12 hours or more at about 0°C to about 200°C. More preferably, the anodized metal is soaked at about 97°C for about 30 min. Various antimicrobial chemicals are compatible with the invention, including but not limited to quaternary ammonium compound, antibiotics, sulfamides, detergents, colorant, meal conservators, antifungal agent, antivirals, metallic ions (salts), alcohols (e.g. ethyl alcohol, methanol, isopropyl alcohol), acids (e.g. hydrochloric acid, phosphoric acid, ethylenediaminetetraacetic (EDTA)), etc. Depending of the particular compound(s), the concentration of the antimicrobial chemical in the solution may vary from about 0.001 % to about 100%.

[00037] In a preferred embodiment, the porous layer is impregnated with at least one quaternary ammonium compound. As used herein, the term "quaternary ammonium compound" refers to any compound having antimicrobial activity and comprising positively charged polyatomic ions of the structure NR₄ ⁺ with R being an alkyl group. Suitable examples according to the invention include, but are not limited to, Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC), Didecyl Dimethyl Ammonium Chloride (DDAC), Benzyldimethyl(2-dodecyloxyethyl)-ammonium chloride, Benzyldimethyl(2- hydroxyethyl)ammonium chloride, benzyldimethyl

(hexadecylcarbamoylmethyl)ammonium chloride, benzyldimethyl (tetradecylcarboamoylmethyl)ammonium chloride, benzyloxycarbonylmethyl-trimethyl- ammonium chloride, bis-(2-hydroxyethyl)-ciannamyl(2-dodecyloxymethyl)ammonium chloride, Benzyltriethylammonium chloride, Tetramethylammonium chloride, Tetramethylammonium iodide, Tetraethylammonium hydroxide, Tetramethylammonium hydroxide, Benzyltrimethylammonium hydroxide, Dimethyldioctadecylammonium chloride, Dodecyltrimethylammonium choride, Trimethylphenylammonium chloride, Octadecyltrimethyl ammonium bromide, Tetrabutyl ammonium bromide, Tetramethylammonium nitrate, Tetrabutylammonium hydroxide, Didodecyldimethyl ammonium bromide, Didodecyldimethylammonium chloride, Dimethyldioctadecyl ammonium bromide, (2-(Methacryloyloxy)ethyl)trimethylammonium chloride, Dioctyl dimethyl ammonium chloride, Tetrapropylammonium chloride, Didecyldimethylammonium chloride, Bezyldodecyldimethyl ammonium bromide, Diallyl dimethyl ammonium chloride, Benzalkonium bromide, Ammonium bromide, Benzyltributylammonium chloride, Octyldecyl dimethyl ammonium chloride, Tetrabutylammonium hydrogen sulfate, Tetrabutylammonium tribromide, Methyltributylammonium chloride, Bis(hydrogenated tallow)dimethylammonium chloride, N-Alkyl dimethyl benzyl ammonium chloride, Tetrabutylammonium fluoride trihydrate.

[00038] In a preferred embodiment, the porous layer comprises at least one inorganic compound. As used herein, the term "inorganic compound" refers to any compound having antimicrobial activity which is not an organic compound. Suitable examples according to the invention include, but are not limited to metallic salts such as silver nitrate (AgN0₃), silver chloride (AgCI), copper nitrate (Cu(N0₃)₂), copper chloride (CuCI₂), zinc nitrate (Zn(N0₃)₂), nickel nitrate (Ni(N0₃)₂), etc.

[00039] In selected embodiment, the porous layer comprises at least one antibacterial agent. As used herein, the term "antibacterial" refers to any compound having antibacterial activity included but not limited to detergents, meal conservators, alcohols (e.g. ethyl alcohol, methanol, isopropyl alcohol), acids (e.g. hydrochloric acid, phosphoric acid, ethylenediaminetetraacetic (EDTA)), etc.

[00040] In selected embodiments, the porous layer comprises at least one antibiotic. As used herein, the term "antibiotic" refers to any compound having antibacterial activity including, but not limited to beta-lactams (ex: penicillin, cephalosporin, etc.), aminoglycosides (ex: streptomycin, neomycin, kanamycin, etc.), cyclins (ex: tetracycline), amphenicols (ex: chloramphenicol, thiamphenicol, etc.), macrolides (erythromycin, clarithromycin, etc), glycopeptides (ex: vancomycin, bleomycin, etc.), quinolones (ciprofloxacin, levofloxacin, etc.), polypeptides (actinomycin, bacitracin, polymyxin B, etc.), nitrofurans (furazolidone, nitrofurazone, etc.), [00041] In preferred embodiments, the antimicrobial surface coating may possess antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria and/or yeasts. In preferred embodiments, the porous layer comprises at least one antimicrobial. As used herein, the term "antimicrobial" or "antimicrobial activity" refers to killing or inhibiting growth of microbes including, but not limited to, bacteria, viruses, algae, yeasts and mold. In preferred embodiments, the antimicrobial surface coating possesses antimicrobial activity of at least 90%, preferably at least 99%, and more preferably of at least 100%, as measured by bioburden testing (microorganism spike/recovery experiments). In particular embodiments, the microbe is a Gram-positive bacteria. In other embodiments, the microbe is a Gram-negative bacteria. [00042] Examples of Gram-positive bacteria include, but are not limited to, many well- known genera such as Staphylococcus, Streptococcus, Enterococcus and Bacillus. Examples of Gram-negative bacteria includes, but are not limited to, Escherichia coli, Salmonella, Shigella, and other Enterobacteriaceae, Pseudomonas, Moraxella, Helicobacter, Stenotrophomonas, Bdellovibrio, acetic acid bacteria, Legionella and alpha-proteobacteria as Wolbachia and numerous others. Other notable groups of Gram- negative bacteria include the cyanobacteria, spirochaetes, green sulfur and green non- sulfur bacteria. Examples of yeasts include, but are not limited to, Saccharomyces cerevisiae and pathogenic yeast such as Candida. In preferred embodiments, the anodized metal products according to the invention have an antimicrobial activity against one or more of the following pathogens: Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans.

[00043] In selected embodiments, the porous layer comprises at least one antifungal agent. As used herein, the term "antifungal agent" refers to any compound having antifungal activity including, but not limited to polyene (Natamycin, rimocidin, candicin, etc.), imidazole, triazole, thiazole (miconazole, fluconazole, abafungin, etc.), allylamines (terbinafine, naftifine, etc.), echinocandin (caspofungin, micafungin, etc.), others (ciclopirox, griseofulvin, etc.).

[00044] In selected embodiments, the porous layer comprises at least one antiviral. As used herein, the term "antiviral" refers to any compound having the potential of destruction of a virus or the potential to inhibit the penetration of the virus into a host cell. Examples include, but are not limited to, glutaraldehyde, amantadine and combination thereof.

[00045] The methods of the invention may further comprise sealing or clogging the impregnated metal material in order to ensure an increased durability of the metal product and to ensure a longer durability of the antimicrobial activity. The more the impregnated metal material is sealed, lower the speed of diffusion of the antimicrobial agent(s) is going to be. Accordingly, sealing may be suitable to modulate (increase or decrease) speed of diffusion of the antimicrobial agent. In one embodiment, the sealing step is used to slow down the diffusion of the product and the impregnated metal material is sealed (i.e. at about 1 % to about 100%, or about 25% to about 75%). Those skilled in the art know how to assess sealing using various methods.

[00046] The sealing can be concurrent (i.e. during) or not with the impregnation. In some embodiments, sealing is carried simultaneously with impregnation by heating the metallic material from 50°C to 100°C. In another embodiment, sealing is achieved by treating the metal under pressurized vapor (for instance in an autoclave, with steam at 100°C to 140°C) or with chemical treatments at 30°C to 50°C (with salts). In one embodiment, the metal is submitted to pressurized vapor at about 100°C to 130°C. Various treatment combinations are conceivable for achieving sealing. For instance, one can simultaneously impregnate and seal the metal product by soaking the anodized metal substrate in the antimicrobial solution. Another possibility is to impregnate the anodized metal substrate and then seal it with steam at room temperature or in an autoclave. In the alternative, the anodized metal substrate can be impregnated then sealed by heating (e.g. about 50°C to about 100°C), sealed by soaking in water, sealed with steam (e.g. about 100°C to about 140°C) or sealed with chemical treatment (e.g. salts).

[00047] Depending on the anticipated use for the metal product (e.g. for decorative purposes), it may be advantageous to color the antimicrobial metal product. Accordingly, in some embodiments, the methods of the invention further comprise a dying or coloring step. The invention encompasses any dying or coloration procedure compatible with obtaining an anodized metal product with an antimicrobial surface coating according to the methods of the invention. For instance, it is well known to electrolytically deposit (i.e. by electrodeposition) various metals in the pores of an aluminum anodic coating to provide lightfast colors (e.g. bronze shades and pale champagne to black). Alternatively, the color may be produced integral to the coating during the anodizing process using organic acids mixed with a sulfuric electrolyte and a pulsed current. It is also possible to dye the unsealed porous surface of the metal in lighter colors and then splashing darker color dyes onto the surface. Another approach comprises impregnation of the metal substrate in a dying solution.

[00048] In preferred embodiments, manufacture of colored antibacterial metal products is carried out in two consecutive steps: 1) coloration and 2) impregnation (i.e. the dying step precedes impregnation of the porous layer with the antimicrobial compound(s)). This order is preferred for ensuring that the desired colored metal product possesses acceptable antibacterial properties. In one particular embodiment a colorant solution is heated at about 50°C to about 70°C and the metal substrate is soaked 30 min with the heated colorant solution, then the metal substrate is impregnated with the antimicrobial substance. Specific conditions may also vary depending of the colorant and the metal material. For instance, in particular embodiments heating of the colorant solution is facultative (ambient temperature is acceptable). [00049] An example of method for obtaining an antimicrobial metal product having an antimicrobial surface coating according to a preferred embodiment of the invention is schematized in Figure 4. Step A: An anodizable metal substrate (10) (e.g. a sheet of aluminum) is degreased with acetone to remove impurities (2) from the surface of the substrate (10); Step B: The metal substrate (10) is anodized, which results in the formation of a porous surface layer (20) comprising nanopores (22); Step C: Metal ions (24) (e.g. Ag) are electrodeposited to the porous surface layer (20); Step D: The porous surface layer (20) and its pores (22) are impregnated with an antimicrobial solution (26); Steps E and F: The pores (22) of the porous surface layer (20) are sealed either partially (Step E) or completely (Step F).

Antimicrobial solutions

[00050] An additional aspect of the invention concerns antimicrobial solutions and uses thereof for impregnating a porous layer of an anodized metal product in order to create an antimicrobial coating on the surface of the anodized metal product. [00051] In one particular embodiment, the antimicrobial solution comprises at least two quaternary ammonium compounds selected among quaternary ammonium compounds having antimicrobial activity, including but not limited to those mentioned hereinbefore. Preferably, the quaternary ammoniums are Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC) and Didecyl Dimethyl Ammonium Chloride (DDAC). More preferably, ADBAC is present at a concentration of about 1 mM to about 1 M and DDAC is present at a concentration of about 1 mM to about 1 M. Even more preferably, ADBAC is present at a concentration of about 10 mM to about 50 mM and wherein DDAC is present at a concentration of about 10 mM to about 100 mM.

[00052] The antimicrobial solution of the invention may further comprises a metallic salt, including but not limited to AgN0₃, Cu(N0₃)₂, Zn(N0₃)₂, Ni(N0₃)₂ and mixtures thereof.

[00053] The antimicrobial solution may further comprise at least one antimicrobial agent including, but not limited to, antivirals, antibiotics, and antifungals as defined herein. Controlling growth of microorganisms and pathogens

[00054] An additional aspect of the invention concerns a method for controlling growth of microorganisms and/or microbial pathogens on a metallic surface. In one embodiment, the method comprises impregnating the metallic surface with an antimicrobial solution as defined herein prior to contacting the metallic surface with microorganism(s) or pathogen(s). In another embodiment, the method comprises providing an antimicrobial metal product having an antimicrobial porous surface layer as defined herein prior to contacting the antimicrobial porous surface of the metal product with microorganism(s) or pathogen(s).

[00055] As used herein, "controlling" include, but is not limited to, preventing adhesion of the microorganism(s) to the metallic surface; preventing formation of a microbial biofilm on the metallic surface; inhibiting or slowing growth of the microorganism(s) on the metallic surface; killing, and/or eradicating the microorganism(s), etc.

[00056] As used herein, the term "microbial pathogen" refers to any microorganism susceptible to harm a human being. The term microbial pathogen encompasses bacteria (e.g. Gram-positive or Gram-negative bacteria), viruses (orthomyxoviridae, retroviridae, adenovirus, papillomavirus, etc.), mold (e.g. Aspergillus, Penicillium, Fusarium, etc.), yeasts (e.g. Candida, Saccharomyces, Rhodotorula, etc.) and algae (e.g. Cyanobacteria, Euglenophyta, Rhodophyta, etc.). The invention encompasses controlling microbial pathogens including, but not limited to Gram-positive bacteria, Gram-negative bacteria, viruses and yeast. Accordingly, the invention encompasses controlling microbial pathogens which may be harmful to humans. Human pathogens against which the methods and compositions of the invention may be useful include, but are not limited to, Escherichia coli, Staphylococcus aureus, Salmonella species, Listeria species, Mycobacterium tuberculosis, viruses responsible for humans diseases such as flu, foot and mouth disease, swine fever, etc. and yeasts (e.g. Candida).

[00057] The invention encompasses controlling microbial pathogens including, but not limited to viruses. Viruses against which the methods and compositions of the invention may be useful include, but are not limited to orthomyxoviridae, retroviridae, adenovirus, papillomavirus, etc.

Articles of manufacture

[00058] A large variety of articles of manufacture may benefit from incorporating an antimicrobial metal product as described herein. These include, but are not limited to, kitchen wares, kitchen countertops, hospital countertops, furniture, office equipment (e.g. pen, stapler, computers and keyboards, etc), appliances, door knobs, medical devices, jewellery, laminar flow hoods, laboratory incubators, wall panels, air purification systems, gloves, masks, panels (e.g. walls, floors, ceilings), boat hulls and pipes. The invention encompasses all these articles of manufacture. Preferably the metal product is made of aluminum or aluminum alloy.

[00059] Conceivably, air filters and filter masks comprising a metal product having an antimicrobial surface coating according to the invention may be useful for the removal and killing of germs. Such product could be used in air systems (circulation, heating, climatization) for buildings (e.g. for reducing risk of contamination by Legionella), for decontamination (e.g. bioterrorism) or for individual use (e.g. mask).

[00060] The invention may also find applications in buildings and room constructions. For instance, antimicrobial metal products entering in the construction of buildings may prevent mould contamination (e.g. inside walls, ceilings and floors).

[00061] Similarly, the invention may be helpful to manufacture safer clean rooms and sterile rooms (e.g. rooms and laboratories of hospitals and pharmaceutical companies) and replace current walls and floors made of stainless steel. Using an antimicrobial metal product in the construction of such rooms may help to obtain and maintain a sterile environment and reduce the need of cleaning or decontamination.

[00062] Office supplies and hardware (keyboard, mice, pens, etc.) made with the metal products or methods of the invention would be desirable since their antimicrobial activity could prevent the spread of microorganisms.

[00063] Additional medical applications include manufacture of medical devices requiring sterilization (e.g. endoscope, scalpels, dentist tools, etc.). Use of medical equipment comprising an antimicrobial surface according to the invention may help preventing contamination and infections in humans and animals.

[00064] The invention may also be helpful to manufacture jewellery (e.g. earrings, piercings, etc.) thereby minimizing risks of infections and/or stimulating healing (particularly for new body piercings).

[00065] The invention may also find sanitary applications, for instance in the manufacture of toilets (seat, handle, whole toilet, etc.), distributors (hand soap distributors, paper towel distributors, etc.) for either personnel use or public uses (e.g. public restrooms, planes, buses, etc.). [00066] The invention may also find naval applications, for instance in the construction of boats having a hull comprising an antimicrobial metal product according to the invention. According to that particular use, the antimicrobial surface could prevent the formation of bacterial biofilms and/or prevent attachment of organisms (e.g. algae, mussel, etc), which is undesirable since such attachment increases the friction coefficient of the hull. A boat comprising an antimicrobial hull according to the invention could consume significantly less energy to reach a desired speed. Preventing attachment of living organisms to the hull may also prevent undesirable propagation of undesirable living organisms in different countries.

[00067] Metal products according to the invention could also be used in pipes (e.g. purified water systems) to avoid formation of bacterial biofilms in the pipes.

[00068] Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, numerous equivalents to the specific procedures, embodiments, claims, and examples described herein. Such equivalents are considered to be within the scope of this invention and covered by the claims appended hereto. The invention is further illustrated by the following examples, which should not be construed as further limiting.

EXAMPLES

EXAMPLE 1 : Preparation and testing of antimicrobial solutions

[00069] Before their application to anodized aluminum surface, various antimicrobial solutions were tested, alone or in combination, for assessing their potential antimicrobial activity:

[00070] Antimicrobial activities of the solutions were tested on various microorganisms, including Escherichia coli (ATCC 8739), Pseudomonas aeruginosa (ATCC 9027), Staphylococcus aureus (ATCC 6538), Bacillus subtilis (ATCC 6633) and Candida albicans (ATCC 10231). All strains were freshly grown at 35°C on agar plates prior to the analysis. Microbial colonies were picked and resuspended into MHB bacterial growth medium to an O.D.660 nm of approximately 0.4. [00071] The antimicrobial properties of various agents were initially tested using a disk diffusion method and different microbial strains. Five (5) mm Whatman™ filter paper punches were dipped into serial dilutions of antimicrobial solutions and deposited onto agar plate microbial lawns prior to incubation overnight at 35°C. Antimicrobial activities were compared by measuring in duplicates the diameter of the growth inhibited zone (Figure 1).

[00072] As shown in Figure 1 , Silver nitrate at 60 mM (solution 1) was more effective on Gram-negative bacteria (Escherichia coli (EC), Pseudomonas aeruginosa (PA)) than on Gram-positive bacteria (Staphylococcus aureus (SA), Bacillus subtilis (BS)) or yeast (Candida albicans (CA)). However, solutions 2, 3, 4 and 5 were more effective against Gram-positive bacteria and yeast than Gram-negative bacteria. Overall, solutions 3 and 5 were the most effective against all microorganisms types.

EXAMPLE 2: Preparation and testing aluminum with antimicrobial property

Experimental

Anodization of the Aluminum surfaces

[00073] Anodization was used to increase the thickness of the natural oxide layer on the surface of aluminum plates and for creating at their surface an anodic film having nanopores. Aluminum plates of the 6000 serie were used throughout this study. Plates of 2.3 mm thickness were cut using a laser into 22.2 mm disks attached in groups of five by a 5 mm linker region. The resulting necklaces were degreased with acetone; etched with 10% weight/vol NaOH for 2 min at 50-60°C; neutralized in 35% vol/vol HN0₃ for 30 sec. at room temperature; and submitted to a P2 etching (33% v/v sulfuric acid and ferrite ) for 10 min at 50-60°C and electrochemically oxidized at room temperature in 15% vol/vol sulfuric acid solution at 1.5 amps for 11 min, 22 min, 33 min or 44 minutes prior to rinsing with distilled water.

[00074] The standardized time of anodization according to the theoretical formula was used to obtain the needed thickness. The theoretical thickness was measured using the following equation* :

Oxide thickness (μηι) = 0.3 x current density (A/dm²) x anodizing time (min)

^*Equation obtained from: Anodizing and coloring of aluminum alloys (2002), S. Kawai editor, Publisher: ASM International, p.170. [00075] Efficiency of the anodization process was estimated by microscopy at 500X coupled to an image processor (Figure 3) and by impedance using 500-4000 wavelength cm^"1 to verify the exactness of the theoretical formula (Table 1 hereinafter). Impregnation and sealing

[00076] The anodized aluminum necklaces were next immerged into various antimicrobial solutions at 97°C for 11 minutes while mixing with a magnetic stir bar. This immersion allowed impregnation the antimicrobial agents into the nanopores and a concurrent partial sealing of the nanopores (through water hydration process) estimated to about 25%. Thereafter the anodized and impregnated aluminum disks were separated using a metal cutter, rinsed twice with distilled water, sterilized with ethanol and kept in a sterile environment until further use.

Electroplating of the anodized aluminum surfaces

[00077] The anodized aluminum surface was electroplated with AgN0₃ (30 mM) in 150 mM sulfuric acid for 30 sec and up to 10 min for a constant tension of 18 volts AC at room temperature.

Measurement of antimicrobial activity

[00078] For semi-quantitative assays, microbial lawns were first prepared by spreading the microbial dilutions onto agar plates using cotton swabs. The aluminum disks were deposited onto the agar surfaces for 5 min, then removed and plates were incubated at 35°C until the next day. The inhibition zone (diameter) was measured for semi-quantitative results.

[00079] Quantitative analyses were performed by spreading 10 μΙ_ of the initial bacterial suspensions onto the aluminum disks and by incubating the disks at room temperature for 5 min. The disks were transferred into 5-10 mL of MHB growth medium, vortexed to disperse and to recover the microorganisms, diluted and aliquots were plated in triplicates onto agar plates. After overnight incubation, the CFU were counted and positive and negative controls were compared. The amounts of CFU/mL for each of the initial microbial suspension were determined by serial dilutions followed by plating 10 and 100 pl_ aliquots onto MHA plates in triplicates followed by incubation at 35°C for at least 18 hrs. The average counts were used to determine the amounts of CFU deposited onto the aluminum surfaces. Results

Anodization efficiency

[00080] Efficiency of the anodization process was estimated by using two different approaches (by impedance and by microscopy).

[00081] Table 1 : Thickness of the anodized aluminum surfaces as measured using different methods

[00082] These results indicate that the theoretical thicknesses estimated using the equation was highly comparable to those obtained by impedance and microscopy. As expected, impedance was less precise at higher thicknesses.

Antimicrobial activity of the treated aluminum

[00083] Antimicrobial solutions for treatment of aluminum were chosen based on results of antimicrobial-like test (Figure 1). The antimicrobial property of the chosen antimicrobial solutions incorporated into the aluminum oxide nanopores was evaluated using two different approaches.

[00084] Figure 2 illustrates the qualitative results of the first approach where the aluminum disks were laid onto microbial lawns for 5 min. Disks impregnated with the benzalkonium chloride (2,12 % WW) + silver nitrate (1.02 % WA ) [solution 5, (A)] prevented the growth of the Gram-positive strains and yeast C. albicans (column 1) whereas the anodized aluminum alone did not (column 2). E. coli showed a slight reduced growth whereas P. aeruginosa growth was not inhibited at all. None of the anodized disks without antimicrobial solution prevented microbial growth (columns 2 and 4). However, disks impregnated with the Benzalkonium chloride (0,96%) + Didecyl dimethyl ammonium chloride (1 ,44 %) + silver nitrate (1.02 % W/V) [solution 3, (B)] prevented the growth of all the strains tested (column 3).

[00085] The antimicrobial activity was maintained for a long period since the disks with the benzalkonium chloride (2.12 % WA/) + silver nitrate (1.02 % WA/) solution were still active when tested on S. aureus after 1 , 3, 5, 7, 12, 14 and 24 months of storage at room temperature (data not shown) confirming that antimicrobial metal products according to the invention can withstand time.

[00086] Table 2A and 2B hereinafter show the results of quantitative analyses of anodized aluminum disks incorporating two types of antimicrobial solutions. Aluminum disks impregnated with the benzalkonium chloride (2.12% W/V) + silver nitrate (1.02 % W/V) solution (Solution 5, Table 2A) did not prevent the growth of E. coli and of P. aeruginosa. However, these disks had strong antimicrobial activity against S. aureus 25923 and S. aureus 6538 with >99.99% and 100% efficiency, respectively. The efficiency against B. subtilis and C. albicans strains was also remarkable since for these two strains, the bacteria in the original inoculums were completely eliminated. Aluminum disks impregnated with the Benzalkonium chloride (0.96%) + Didecyl dimethyl ammonium chloride (1 ,44 %) + silver nitrate (1.02 % W/V) solution (Solution 3, Table 2B) had even a stronger antimicrobial activity since they killed almost completely all the strains, including the Gram-negative strains E. coli and P. Aeruginosa.

[00087] Table 2A: Antimicrobial activity of aluminum incorporating the benzalkonium chloride (2,12 % W/V) + silver nitrate (1,02 % W V) solution [Solution 5]

Strains Input CFU % survival % killing

E. Coli 8739 4.8 x 10⁸ 100 0

P. Aeruginosa 9027 4.4 x 10⁸ 88 12

S. Aureus 25923 2.0 x 10⁹ 0.0032 99.9968

S. Aureus 6538 1.3 x 10⁹ 0 100

B. Subtilis 6633 4.7 x 10⁵ 0 100

C. Albicans 10231 6.5 x 10⁶ 0 00

Table 2B: Antimicrobial activity of aluminum incorporating the Benzalkonium chloride (0,96%) + Didecyl dimethyl ammonium chloride (1,44 %) + silver nitrate (1,02 % WW) solution [Solution 3]

Strains Input CFU % survival % killing

E. Coli 8739 4.4 x 10⁸ 0 100

P. Aeruginosa 9027 6.4 x 10⁸ 1 99

S. Aureus 25923 1.2 x 10⁹ 0 100

S. Aureus 6538 1.3 x 10⁹ 0 100

B. Subtilis 6633 4.7 x 10⁵ 0 100

C. Albicans 10231 1.0 x 10⁶ 0 100 [00088] As can be appreciated, the quantitative results of Table 2A and 2B

corroborate qualitative results illustrated in Figure 2.

Abrasion test

[00089] An abrasion test was developed to assess the effectiveness against the wear of the antimicrobial surface on antimicrobial activity. Briefly, anodized aluminum disks impregnated with Solution No 3 was submitted to a controlled to and fro movement (110 cycles/min) with a puck of sandpaper (caliber 320) for 120 minutes. A continuous pressure of 12.8 KPa was applied onto the puck to ensure a constant friction of the sandpaper on the aluminum disks. After the abrasion period, residual antimicrobial activity anodized aluminum disks was assessed by laying the disks over microbial lawns of Staphylococcus aureus ATCC 6538 for 5 min. The results are shown in Table 3 hereinafter:

Table 3: Effect of abrasion on antimicrobial activity

Untreated disk shown no zone of inhibition (surface [00090] As can be appreciated, abrasion had a limited impact on antimicrobial activity, confirming that metal products according to the invention can withstand wearing and maintain their effectiveness under harsh conditions.

[00091] Altogether these results demonstrate the antimicrobial metal products according to the invention, including aluminum anodized surfaces, have interesting antimicrobial properties. Therefore, metallic articles comprising the same may have numerous applications in various household, hospital and industrial environments.

* * *

[00092] Headings are included herein for reference and to aid in locating certain sections. These headings are not intended to limit the scope of the concepts described therein under, and these concepts may have applicability in other sections throughout the entire specification. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

[00093] As used herein and in the appended claims, the singular forms "a", "an", and "the" include plural referents unless the context clearly indicates otherwise. [00094] Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, concentrations, properties, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". At the very least, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the present specification and attached claims are approximations that may vary depending upon the properties sought to be obtained. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the embodiments are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contain certain errors resulting from variations in experiments, testing measurements, statistical analyses and such.

[00095] It is understood that the examples and embodiments described herein are for illustrative purposes only and that various modifications or changes in light thereof will be suggested to persons skilled in the art.

Claims

CLAIMS:

1. An antimicrobial metal product, wherein said metal product comprises a porous surface layer formed by anodization, and wherein said porous surface layer comprises an electrodeposit of at least one metal and at least one antimicrobial compound.

2. The antimicrobial metal product of claim 1 , wherein the metal product is selected from the group consisting of aluminum, titanium, zinc, magnesium, niobium, tantalum and anodizable alloys thereof.

3. The antimicrobial metal product of claim 1 or 2, wherein the electrodeposit of at least one metal is selected from the group consisting of an electrodeposit of silver, an electrodeposit of gold, an electrodeposit of copper, an electrodeposit of zinc, an electrodeposit of nickel, an electrodeposit of tin, an electrodeposit of cadmium, an electrodeposit of palladium and an electrodeposit of platinum.

4. The antimicrobial metal product of any one of claims 1 to 3, wherein the at least one antimicrobial compound is carried out in nanopores of the porous surface layer.

5. The antimicrobial metal product of any one of claims 1 to 4, wherein the at least one antimicrobial compound is selected from the group consisting of antibacterials, antivirals, antibiotics, and antifungals.

6. The antimicrobial metal product of any one of claims 1 to 5, wherein the at least one antimicrobial compound comprises a quaternary ammonium, preferably Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC).

7. The antimicrobial metal product of any one of claims 1 to 6, wherein the porous surface layer comprises at least two quaternary ammonium compounds selected from the group consisting of Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC), Didecyl Dimethyl Ammonium Chloride (DDAC).

8. The antimicrobial metal product of any one of claims 1 to 7, wherein said antimicrobial surface coating possesses antimicrobial activity against Gram-positive bacteria, Gram-negative bacteria and/or yeast.

9. The antimicrobial metal product of any one of claims 1 to 8, wherein said porous surface layer further comprises a dye.

10. The antimicrobial metal product of any one of claims 1 to 9, wherein said porous surface layer is sealed.

11. An antimicrobial piece of aluminum, wherein said piece of aluminum comprises a porous surface layer formed by anodization, and wherein said porous surface layer comprises an electrodeposit of silver and at least one quaternary ammonium compound in pores of the surface layer.

12. An article of manufacture incorporating an antimicrobial metal product according to any one of claims 1 to 10 and/or an antimicrobial piece of aluminum according to claim 11.

13. The article of manufacture of claim 12, wherein said article of manufacture is selected from the group consisting of kitchen wares, kitchen countertops, hospital countertops, furniture, appliances, office equipment, door knobs, medical devices, laminar flow hoods, laboratory incubators, wall panels, floor panels, boat hulls and pipes.

14. A method for obtaining an antimicrobial metal product having an antimicrobial surface coating, comprising the steps of:

- electrodepositing a metal to said porous surface layer; and

- impregnating the porous surface layer with at least one antimicrobial compound.

15. The method of claim 14, wherein the anodized metal is selected from the group consisting of aluminum, titanium, zinc, magnesium, niobium, tantalum and anodizable alloys thereof.

16. The method of claim 14 or 15, wherein the metal electrodeposited is selected from the group consisting of silver, gold, copper, nickel, zinc, tin, cadmium, palladium and platinum.

17. The method of claim 16, wherein electrodeposition is carried out in an aqueous solution comprising about 1 to about 5% vol/vol sulfuric acid and about 0.1 to about 5 % W/v AgN0₃ at temperature of about 0°C to about 100°C.

18. The method of any one of claims 14 to 17, wherein the at least one antimicrobial compound is selected from the group consisting of antibacterials, antivirals, antibiotics, and antifungals.

19. The method of any one of claims 14 to 18, further comprising a sealing or clogging step which is carried out simultaneously or after the impregnation.

20. The method of claim 19, wherein the sealing is carried out by soaking in a solution or by exposing the porous layer to steam at ambient pressure or in an autoclave.

21. The method of any one of claims 14 to 20, further comprising a dying step before impregnating the porous layer with the at least one antimicrobial compound.

22. An antimicrobial solution for impregnating a porous layer of an anodized metal product, said antimicrobial solution comprising at least two quaternary ammonium compounds having antimicrobial activity.

23. The antimicrobial solution of claim 22, wherein said at least two quaternary ammonium compounds consists of Alkyl Dimethyl Benzyl Ammonium Chloride (ADBAC) and Didecyl Dimethyl Ammonium Chloride (DDAC).

24. The antimicrobial solution of claim 23, wherein ADBAC is present at a concentration of about 1 mM to about 1 M and wherein DDAC is present at a concentration of about 1 mM to about 1 M.

25. The antimicrobial solution of claim 23 or 24, wherein ADBAC is present at a concentration of about 10 mM to about 50 mM and wherein DDAC is present at a concentration of about 10 mM to about 100 mM.

26. The antimicrobial solution of any one of claims 22 to 25, wherein said antimicrobial solution further comprises a metallic salt.

27. The antimicrobial solution of claim 26, wherein the metallic salt is selected from the group consisting of AgN0₃, Cu(N0₃)₂, Zn(N0₃)₂, Ni(N0₃)₂ and mixtures thereof.

28. The antimicrobial solution of any one of claims 22 to 27, wherein said antimicrobial solution further comprises at least one antimicrobial agent selected from the group consisting of antibacterials, antivirals, antibiotics, and antifungals.

29. A method for controlling growth of microorganisms and/or microbial pathogens on a metallic surface, comprising impregnating the metallic surface with an antimicrobial solution as defined in any one of claims 22 to 28 prior to contacting the metallic surface with microorganism(s) or pathogen(s).

30. Use of an antimicrobial solution as defined in any one of claims 22 to 28 for impregnating a porous layer of an anodized metal product, wherein said impregnation creates an antimicrobial coating on the surface of said anodized metal product.