Abstract
The invention relates to a hybrid material, in particular provided as an additive relating to materials, substances and/or coating materials for producing an antimicrobial, antiviral and/or fungicidal effect, and which comprises particles, each of which comprising at least one carrier material being at least partially coated with at least two different metals, wherein at least one first metal and one second metal are, at least with their respective surfaces, in electrically conductive contact to each other. According to the invention the first metal comprises at least one semiconductive compound of at least one transition metal element, which exhibits multiple oxidation states and allows a change of the oxidation states by means of catalytically active centers, and the second metal comprises at least one electrically conductive silver semiconductor, wherein both metals establish half cells which are short-circuited in the presence of water and oxygen and thus develop an antimicrobial, antiviral and/or fungicidal effect, wherein the carrier material comprises at least one material being adapted to the substance and/or the coating material and their use. The hybrid material according to the invention can be advantageously used as antimicrobial additive for various materials, substances and/or coating materials, preferably lacquers, paints, plastering, polymers and/or cellulose.
Claims
1. Hybrid material provided as an additive relating to materials, substances and/or coating materials for producing an antimicrobial, antiviral and/or fungicidal effect comprising: particles, each of which comprising at least one carrier material being at least partially coated with at least two different metals, wherein at least one first metal and one second metal of the two different metals are, at least with their respective surfaces, in electrically conductive contact to each other, wherein the first metal comprises at least one semiconductive compound of at least one transition metal element, which exhibits multiple oxidation states and allows a change of the oxidation states via catalytically active centers, and the second metal comprises at least one electrically conductive silver semiconductor, wherein both, the first metal and the second metal, establish half cells which are short-circuited in presence of water and oxygen and thus develop an antimicrobial, antiviral and/or fungicidal effect, and wherein the carrier material further comprises at least one material adapted to the substance and/or the coating material and a use of the substance and/or the coating material.
2. The hybrid material according to claim 1, wherein the carrier material comprises at least one material selected from the group consisting of cellulose, glass, zeolite, silicate, metal or metal alloy, metal oxide, ceramic, graphite, and a polymer.
3. The hybrid material according to claim 1, wherein the carrier material comprises cellulose.
4. The hybrid material according to claim 1, wherein the hybrid material is modified with organic polymers, and/or with ascorbic acid or derivatives of ascorbic acid.
5. The hybrid material according to claim 1, wherein the first metal and the second metal establish half cells which are short-circuited in presence of water and oxygen and thus develop an antimicrobial effect, wherein the strength of the antimicrobial effect is specifically adjustable through adjusting the amount of at least one of both metals and/or the proportion of both metals on the surface of the particles.
6. The hybrid material according to claim 1, wherein the transition metal element is at least one metal of the group consisting of ruthenium, iridium, vanadium, manganese, nickel, iron, cobalt, cerium, molybdenum, and tungsten.
7. The hybrid material according to claim 1, wherein the transition metal compound of the first metal comprises ruthenium present in one or both of the oxidation states VI and IV.
8. The hybrid material according to claim 1, wherein the transition metal compound of the first metal comprises at least one metal oxide, metal oxyhydrate, metal hydroxide, metal oxyhydroxide, metal halogenide and/or at least one metal sulfide of the transition metal element.
9. The hybrid material according to claim 1, wherein the silver semiconductor comprises at least one silver oxide, silver hydroxide, silver halogenide or silver sulfide, or a combination of silver and a corresponding silver compound.
10. The hybrid material according to claim 1, wherein the particles have a spherical or polyhedric shape and a mean diameter of at most 100 .Math.m including at most 50 .Math.m or at most 5 .Math.m, and/or that the particles have a fiber-like shape and a mean length of at most 1 mm including at most 100 .Math.m at most 75 .Math.m or at most 60 .Math.m.
11. A method for producing a hybrid material having antimicrobial effect including the hybrid material according to-claim 1 comprising a) providing or producing a particle-shaped carrier material, b) at least partly applying a first metal onto the carrier material, and c) at least partly applying a second metal, which differs from the first metal, onto the carrier material and/or onto the first metal, wherein both, the first metal and the second metal, are applied such that they are, at least with their respective surfaces, in electrically conductive contact to each other.
12. The method according to claim 11, wherein at least one of the first metal and second metal is applied onto the carrier material and/or onto the other metal of the first and second metal in cluster-shaped form, nanoporously, microcrackly and/or in form of single particles.
13. The method according to claim 11, wherein after a) and/or c), the carrier material and/or the metals is/are modified with organic polymers including polyethylene glycol, polydopamine and/or chitosan, and/or with ascorbic acid or derivatives of ascorbic acid.
14. The method according to claim 11, wherein a link layer is generated on at least one of the first or second metal, wherein the link layer comprises at least one metal compound of the corresponding first or second metal, which is selected from the group consisting of halogenides, oxides, and sulfides.
15. The method according to claim 11, wherein a strength of an antimicrobial effect of the hybrid material is adjusted by adjusting the an amount of at least one of the first and the second metal and/or the proportion of the first and the second metal on a surface of particles comprising the carrier material being at least partially coated with the first and/or second metal.
16. The method according to claim 11, wherein the the first and second metals are applied sequentially or simultaneously via electrochemical deposition, chemical-reductive deposition, electrophoretic coating, calcinating, PVD, CVD and/or sol-gel processes.
17. The method according to claim 11, wherein application of the second metal onto the carrier material and/or the first metal comprises at least one step having a strong oxidative effect.
18. The method according to claim 11, wherein , after applying the first and second metals, a thermal post-treatment is applied thereby adjusting specific oxidation states.
19. A material, including a coating material, or substance, comprising, as an additive, the hybrid material according to claim 1, wherein the additive confers to the material or substance an antimicrobial, antiviral and/or fungicidal effect.
20. The hybrid material according to claim 4, wherein the organic polymers are polyethylene glycol, polydopamine and/or chitosan.
Description
BRIEF DESCRIPTION OF THE FIGURES
[0067] FIG. 1 shows a schematic diagram of an exemplary embodiment of the hybrid material according to the invention.
[0068] FIG. 2 shows photographic images of different antimicrobial variants of the hybrid material according to the invention prepared on silver-coated glass beads S3000S of the company Potters Industries Inc. with an average diameter of about 40 .Math.m.
[0069] FIG. 3 shows REM images of silver-coated glass beads S3000S of the company Potters Industries Inc. at 300x magnification (top left) and at 10,000x magnification (top right). Ruthenium-coated samples are shown at 10,000x magnification: Samples 513 (center left), 514 (center right), 515 (bottom left), and 516 (bottom right).
[0070] FIG. 4 shows a bar graph of the catalytic formation of hydrogen peroxide at the surface of the particulate antimicrobial hybrid materials 513, 514, and 515 according to FIG. 3.
[0071] FIG. 5 shows a photographic image of an inhibition zone test. A suspension culture of E. coli bacteria (DSM 498) was plated onto an agar plate. Silver-coated glass particles S3000S and antimicrobial hybrid materials 513, 514, and 515 were plated onto the agar as samples according to FIG. 3 and incubated at 37° C. for 18 h. The samples were then added to the agar plate.
[0072] FIG. 6 shows growth curves of MRSA cultures (source: Robert Koch Institute) in the presence of the glass particles S3000S and the antimicrobial hybrid materials 513, 514, and 515 according to FIG. 3.
[0073] FIG. 7 shows photographic images of exemplary embodiments of the hybrid material according to the invention. [0074] a) Uncoated cellulose powder; [0075] b) coated antimicrobial cellulose powder with a silver content of 20% by weight and a ruthenium content of 1% by weight; [0076] c) distribution of the two metals on the cellulose fiber; and [0077] d) inhibition zone test powder prepared according to the invention.
[0078] FIG. 8 shows growth curves of MRSA cultures (source: Robert Koch Institute) in the presence of the hybrid material (powder) according to the invention as shown in FIG. 7. [0079] (a) Determination of the minimum inhibitory concentration; and [0080] (b) dependence of antimicrobial efficiency of cellulose particles on ruthenium content.
[0081] FIG. 9 shows photographic images, a bar diagram and a table relating to the antimicrobial efficacy of a cellulose film or yarn produced by a lyocell process. [0082] a) Cellulose film; [0083] b) inhibition zone test for antimicrobial activity of the cellulose filament produced according to the invention against E. coli (DSM 498); and [0084] c) antimicrobial activity of a particulate cellulose-based silver-ruthenium hybrid (720b) against S. aureus (DSM 799).
[0085] FIG. 10 shows a graphical representation (curve) of a virus plaque test for the efficacy of one embodiment of the hybrid material according to the invention against SARS-CoV-2 and Feline Coronavirus (FCoV). [0086] (a) Feline coronavirus (FCoV); and [0087] (b) SARS-CoV-2.
[0088] FIG. 11 shows photographic images of an exemplary embodiment of the hybrid material according to the invention (microparticles or antimicrobial powder). [0089] a) Uncoated silver powder; [0090] b) antimicrobial powder coated according to the invention; [0091] c) REM image of a powder particle at 100,000x magnification. [0092] d) Inhibition zone test for antimicrobial activity of the microparticles or powder according to the invention.
[0093] FIG. 12 shows a growth curve of MRSA for microparticles according to the invention as shown in FIG. 11b.
[0094] FIG. 13 shows photographic images of a further exemplary embodiment of the hybrid material according to the invention (microparticles or antimicrobial powder) on a catalytic basis. [0095] a) Powder after filtration, washing and drying; [0096] b) mortared, black powder; [0097] c) REM image of a powder particle at 100,000x magnification; and [0098] d) inhibition zone test for antimicrobial activity of the microparticles or powder according to the invention.
[0099] FIG. 14 shows a growth curve of the microparticles or powder according to FIG. 13.
[0100] FIG. 15 shows photographic images of several samples of commercial facade paint, to which increasing concentrations (0.1 wt.%, 0.5 wt.% and 1.0 wt.%) of an exemplary embodiment of the hybrid material according to the invention prepared on glass particles have been added.
[0101] FIG. 16 shows photographic images of several samples of a commercial antifouling paint to which increasing concentrations (2.0 wt%, 4.0 wt% and 8.0 wt%) of another exemplary embodiment of the hybrid material according to the invention prepared on cellulose powder have been added.
[0102] FIG. 17 shows photographic images of Ultramid C33 samples containing 1 wt% of an exemplary embodiment of the hybrid material of the invention prepared with commercial silver powder. [0103] a) Granules; [0104] b) plates; and [0105] c) inhibition zone test of the samples against E. coli bacteria.
[0106] FIG. 18 shows a photographic image of fibers of polyamide containing 3 wt% of an exemplary embodiment of the catalytic-based hybrid material of the invention (a) and a bar diagram of the antimicrobial efficacy of these fibers (b).
[0107] FIG. 19 shows photographic images of an antimicrobial hybrid material prepared according to the invention, the core of which consisting of ferromagnetic iron powder (a and b), as well as a bar diagram showing the lysis of gram-positive B. subtilis germs by this hybrid material (c).
[0108] FIG. 20 shows photographic images of an exemplary embodiment of the hybrid material according to the invention, which is uniformly distributed in the water by vigorous stirring. [0109] a) Particles of the hybrid material without post-coating; and [0110] b) particles of hybrid material subsequently treated with dopamine hydrochloride solution (2 mg/ml) and phosphate buffer (0.1 M, pH 8.5) at RT.
[0111] FIG. 21 shows a photographic image of an inhibition zone test for the antimicrobial efficacy of an exemplary embodiment of the cellulose-based hybrid material according to the invention, the efficacy of which is not impaired by post-treatment.
[0112] FIG. 22 shows photographic images of a cellulose-based antimicrobial hybrid material that has been integrated into siloxanes to provide them with antimicrobial activity. [0113] a) Siloxane coatings H 2084 and H 5055; and [0114] b) antimicrobial assay results for E. coli on an agar with polypropylene platelets coated on one side with siloxane.
[0115] FIG. 23 shows growth curves of MRSA bacteria using two ruthenium / ruthenium oxide // silver / silver chloride (Ru/RuOx // Ag/AgCI) powders (AP 383 and AP 823) prepared by different ruthenium deposition processes for different powder amounts.
[0116] FIG. 24 shows an XPS surface analysis (Ru3d spectra) of the electroplated Ru/RuOx // Ag/AgCl powder samples 825 and 392 and the Ru/RuOx // Ag/AgOx PVD coatings on polyethylene films (samples Ru and RuOx).
[0117] FIG. 25 shows O1s spectra for samples 825, 392, Ru, RuOx.
DESCRIPTION OF EXEMPLARY AND PREFERRED EMBODIMENTS OF THE INVENTION
[0118] According to the invention, the particulate hybrid material is produced on the basis of a core substance (carrier material), whereby, for example, a first closed layer with one of the two electrode metals according to the invention is first applied to the core material (cellulose, metal, glass, ceramic, graphite, polymer). Subsequently, the second electrode metal is applied as a non-closed, cluster-shaped, porous or micro-cracked thin second layer on the core material and/or the first electrode layer. These coatings can be applied by conventional electrolytic processes, chemically-reductive processes, or via vapor deposition. Preferably, chemical-reductive processes are used, in which the metals are deposited on the selected carrier material by chemical reduction. Suitable reducing agents include aldehydes, ascorbic acid, hydrazine, hydroxylamine or metal hydrides. To prevent the reducing agent from depositing the metal ions already in solution rather than on the particle cores, which would decompose the solution and result in metal loss, suitable inhibitors known to experienced electroplating personnel can be added to the electrolyte. In ruthenium deposition, for example, ethylenediamine can be added as a suitable inhibitor. Depending on the reducing agent used, the surface of the carrier material must be activated with a catalyst. Since silver causes the decomposition of sodium borohydride, no additional activation is necessary for this combination.
[0119] The deposition of the two metals on the carrier material can be carried out, for example, in a two-stage process, since both metals can usually be deposited galvanically from electrolytes with different compositions. Preferably, the chemical-reductive metal deposition is carried out batchwise, with the amount of metal contained in the electrolyte being completely deposited on the particle cores. Verification of the complete elaboration of the electrolyte can be performed by classical analytical methods, such as AAS or ICP, which is essential not only for quality control, but especially when precious metals are used as antimicrobial coating materials. In order to achieve uniform and complete deposition of the metals on the particle cores, the metered addition of the metal compounds, reducers as well as other chemical additives into the reactor must be carried out with simultaneous high electrolyte movement, e.g. by stirrers or mixers (kneaders in the case of cellulose). Temperature control or cooling and classical electrolyte controls such as measurement of the pH value are important for quality assurance of the hybrid antimicrobial particles as well as process reliability.
[0120] Post-coating of the antimicrobial hybrid material is carried out in separate reactors, for example by adding it with uniform stirring to an aqueous solution containing the reactant. In this process, a chemical reaction or chemisorption takes place on the surface of the metals on the hybrid material of the invention at the metal surface of the hybrid system, for example, by using halide- or sulphide-containing water-soluble compounds, ascorbic acid, chitosan, polyethylene glycol, polydopamine .
[0121] FIG. 1 schematically shows the structure of the particulate antimicrobial hybrid material, the shape and size of which are largely determined by the particle core (1). The particle size is usually < 50 .Math.m, preferably < 5 .Math.m. In the case of fibrous particles, the linear extension, depending on the application, can be < 1 mm, preferably < 60 .Math.m, preferably, < 1 .Math.m.
[0122] A first, largely closed metal layer (2), preferably a silver layer, is applied to the core (1).
[0123] Over the first layer (2) of the hybrid system, the second metal, preferably ruthenium, is applied as a very thin nanoporous layer (3). First (2) and second layer (3) over the core (1) are constructed in such a way that oxygen from the moist environment, is reduced at the cathodic part of the applied material of the hybrid surface and oxygen radicals are formed.
[0124] The metallic components of the first (2) and second layer (3) can each be converted by chemical reactions at the surface into a metal compound (4), e.g. a metal halide or metal sulfide, or form an oxide layer by an oxidizing solution, or convert an existing oxide layer into a mixed oxide layer with altered valencies. The hybrid layer system on the particles can alternatively be provided with a chemisorbed ascorbic acid layer (5).
[0125] The hybrid system can additionally be provided with a polymeric layer (6) of chitosan, polyethylene glycol or polydopamine, which do not inhibit the antimicrobial effect.
[0126] Depending on the required property profile, the chemically-reductively deposited metals and chemically applied inorganic or organic layers can be variably adjusted in their lateral distribution, thickness and structure.
[0127] FIG. 2 shows different antimicrobial variants of the hybrid material according to the invention prepared on silver-plated glass beads S3000S from Potters Industries Inc. with an average diameter of approx. 40 .Math.m. Silver serves here as the anode material, on which ruthenium was deposited with different layer thicknesses as the catalytically active cathode material. For the ruthenium coating, the glass spheres were dispersed in alkaline solution with vigorous stirring. Then solutions of ruthenium (III) chloride and sodium borohydride were added as reducing agents. Particles with different layer thicknesses of ruthenium were prepared. The calculated average layer thickness of ruthenium is about 0.4 nm for sample 513, about 0.8 nm for sample 514, and about 1.9 nm for sample 515. The surface of the samples becomes slightly darker with increasing layer thickness of ruthenium. Sample 515 exhibits a faint brownish hue.
[0128] FIG. 3 shows SEM images of the chemically-reductively coated particles. The silver-coated glass particles S3000S are shown at 300x magnification (top left) and at 10,000x magnification (top right). Furthermore, samples coated with ruthenium are shown at 10,000x magnification. Samples 513 (middle left), 514 (middle right) and 515 (bottom left) show a very uniform coating. For sample 516 (bottom right) with an average coating thickness of about 9.4 nm, the porous structure of the catalytically active ruthenium coating can be seen.
[0129] FIG. 4 shows the catalytic formation of hydrogen peroxide on the surface of particulate antimicrobial hybrid materials 513, 514, and 515. 50 mg of each bead was incubated in a solution of ferrous ions and xylenol orange for 1 h on the shaker at 225 rpm. The iron (II) ions were oxidized by the formation of hydrogen peroxide. The generated ferric ions immediately formed a colored complex with xylenolorange, the concentration of which was determined photometrically at a wavelength of 585 nm. As the thickness of the ruthenium layer increases, the concentration of hydrogen peroxide formed increases.
[0130] FIG. 5 shows the determination of the antimicrobial efficiency of the powder samples after the inhibition zone test. A suspension culture containing 10.sup.7/ml bacteria of E. coli (DSM 498) was plated out with 50 .Math.l. The samples were plated on the agar and incubated for 18 h at 37° C. The silver-coated glass particles S3000S already showed moderate antimicrobial activity. The antimicrobial efficiency of powders 513, 514 and 515 is very high. A difference between these samples is not discernible after microbiological agar testing.
[0131] FIG. 6 shows growth curves of the powders S3000S, 513, 514 and 515. 30 ml of a culture of MRSA (source: Robert Koch Institute) was adjusted to an optical density of 0.1 in an Erlenmeyer flask. Subsequently, 200 mg of each of the different samples were incubated in a shaking incubator at 37° C. and 150 rpm. The optical density (OD.sub.600) of the samples was then determined at hourly intervals. No inhibition of MRSA culture growth was determined for the silver-coated glass beads after this very sensitive antimicrobial assay method. With increasing layer thickness of ruthenium on the beads, the growth inhibition increases significantly. For sample 515, complete growth inhibition is observed for the selected weight of powder. The minimum inhibitory concentration (MIC) for this powder is thus 200 mg.
[0132] FIG. 7 shows an antimicrobial particulate hybrid material prepared on the basis of cellulose powder with an average fiber length of 60 .Math.m. The cellulose powder was first impregnated with a solution of silver nitrate. Then the silver ions were reduced by adding ascorbic acid. Gray-white silver-coated cellulose powder was obtained. The silvered cellulose powder was then dispersed in alkaline solution with vigorous stirring. Then solutions of ruthenium (III) chloride and sodium borohydride were added as reducing agents. Dark gray powder was obtained, the color of which depends largely on the ruthenium content. FIG. 7a shows the uncoated cellulose powder and FIG. 7b shows the coated antimicrobial powder with a silver content of 20 wt.% and a ruthenium content of 1 wt.%. The SEM image of the fiber surface at 10,000x magnification shown in FIG. 7c shows the uniform distribution of the two metals on the cellulose fiber. The inhibition zone test according to FIG. 7d shows that various batches of the powder produced by this process have high antimicrobial activity.
[0133] FIG. 8 a shows the determination of the minimum inhibitory concentration of the antimicrobial powder on coated cellulose by generating MRSA growth curves. A sample without addition of the antimicrobial powder served as a control. The minimum inhibitory concentration for the prepared powder was only 15 mg. FIG. 8 b shows that the antimicrobial efficiency of the prepared cellulose-based antimicrobial particles also depends on its ruthenium content. For a ruthenium content of 0.2 wt%, only a slight inhibition of bacterial growth of MRSA can be seen according to the growth curve determined, while for a ruthenium content of 1.0 wt%, complete inhibition of growth occurs. A sample without addition of the antimicrobial powder again served as a control. The weight of the powders was 20 mg in each case.
[0134] Although all hybrid silver-ruthenium particles on cellulose carrier material exhibit an antimicrobial effect, the antimicrobial efficacy can be differentiated once again in terms of its strength on the basis of growth curves with MRSA germs. Table 1 shows that both the ruthenium and silver contents (quantities) have an influence on the strength of the efficacy against MRSA. Both metals can be used to control the antimicrobial efficacy of the hybrid material of the invention in terms of the strength required. Table 1 shows the amounts of silver and ruthenium analyzed [wt %] in relation to the entire hybrid material, with the respective antimicrobial strength evaluated as (x+) according to the legend. In principle, it can be stated that ultimately all material variants show a complete antimicrobial effect if sufficient quantities are present. In terms of measurement, therefore, the particle quantity was reduced until a differentiation could be made, because not all variants achieve complete MRSA killing. If a 100 % effect of a silver-ruthenium variant was still detectable with a lower weighting, this was classified as a particularly effective composition. Table 1 thus shows the evaluation for the variants indicated according to the weights.
TABLE-US-00001 C-720 Silver (wt. %) Ruthenium (% by weight) Antimicrobial efficacy 1.1 18.13 1.44 +++++ 2.2 10.93 1.01 ++++ 2.1 18.4 0.1 +++ 2.3 10.9 0.11 ++ +++++ = very strong; ++++ = strong; +++ = medium; ++ = weak
[0135] FIG. 9 a shows an antimicrobial cellulose film produced via the Lyocell process, which has been produced by adding the cellulose-based antimicrobial hybrid material produced according to the invention to the Lyocell process. Similarly, antimicrobial cellulose filaments could also be produced after the Lyocell process. FIG. 9 b shows the antimicrobial efficacy of the cellulose filament produced according to the invention against E. coli (DSM 498) on the basis of the inhibition zone formed around the thin filament. FIG. 9 c shows the significant antimicrobial activity against S. aureus (DSM 799) determined according to DIN EN ISO 20743 by the addition of only 3% of the particulate cellulose-based silver-ruthenium hybrid (720b) to the cellulose spinning solution.
[0136] FIG. 10 shows the efficacy of the particulate antimicrobial hybrid material produced according to the invention against SARS-CoV-2 and the Feline Coronavirus (FCoV), which is even more difficult to inhibit. Testing was performed at FU Veterinary Medicine using the so-called plaque assay. Virus plaque assays determine the number of plaque-forming units (pfu) in a virus sample, which is a measure of the amount of virus. This assay is based on a microbiological method performed in Petri dishes or multiwell plates. A viral plaque is formed when a virus infects a cell within the fixed cell monolayer. The virus-infected cell lyses and the infection is transmitted to neighboring cells where the infection-lysis cycle is repeated. The infected cell area forms a plaque (an area of infection surrounded by uninfected cells) that can be visualized with a light microscope or visually. In FIG. 10 a, the plaque reduction assay shows that the cellulose-based antimicrobial particles prepared according to the invention have an antiviral effect against the Feline Coronavirus already at a concentration of about 0.2 mg/ml (IC50: kills 50% of the viruses). In the case of the antiviral effect of the antimicrobial cellulose-based particulate hybrid material according to the invention against SARS-CoV-2 shown in FIG. 10 b, the IC50 is even significantly lower at approx. 0.05 mg/ml. Thus, the antimicrobial hybrid system according to the invention is suitable for combating viruses by integrating the particles into paints, coatings, plastics.
[0137] FIG. 11 shows microparticles (antimicrobial powder) prepared on silver particles according to the invention, where commercially available spherical silver powder with a particle size of 1 .Math.m - 100 .Math.m was coated with ruthenium. The silver powder was dispersed in alkaline solution with vigorous stirring. Then solutions of ruthenium(III) chloride and sodium borohydride were added as reducing agents. Dark gray powder with a ruthenium content of 3.2 wt.% was obtained. FIG. 11 a shows the uncoated silver powder and FIG. 11 b the coated antimicrobial powder. FIG. 11 c shows the SEM image of a powder particle at 100,000x magnification with a diameter of about 1 .Math.m. The porous structure of the ruthenium coating is clearly visible. FIG. 11 d shows the inhibition zone test, which demonstrates a high antimicrobial efficiency of the microparticles or powder according to the invention.
[0138] FIG. 12 shows the growth curve of MRSA for antimicrobial microparticles based on silver particles according to FIG. 11b. The minimum inhibitory concentration of the particles is 20 mg. A sample without addition of the antimicrobial powder served as a control.
[0139] FIG. 13 shows microparticles (antimicrobial powder) according to the invention on a catalytic basis, where the silver powder used as a basis was previously prepared by a chemical-reductive process. Ascorbic acid was used as a reducing agent. In addition, gum arabic was used as an inhibitor. The silver powder prepared was filtered off, washed and coated with ruthenium immediately after filtering. Again, solutions of ruthenium (III) chloride and sodium borohydride were added as reducing agents. FIG. 13 a shows the powder after filtration, washing and drying. Larger, hard, gold-colored particles were formed. These were then ground. FIG. 13 b shows the mortared, black powder. The particle size of the powder varies from 0.1 .Math.m - 5 .Math.m. The ruthenium content is 3.2% by weight. FIG. 13 c shows the SEM image of a powder particle at 100,000x magnification. The diameter is about 0.7 .Math.m.
[0140] FIG. 14 shows the growth curve of the microparticles or powder according to FIG. 13. The minimum inhibition concentration of the powder is only 5 mg. This small value is due to the large relative surface area of the small powder particles. A sample without addition of the antimicrobial powder served as a control.
[0141] FIG. 15 shows several samples of commercial facade paint to which increasing concentrations of an antimicrobial hybrid material prepared on glass particles according to the invention have been added. The concentration of the powder is 0.1 wt%, 0.5 wt% and 1.0 wt%. The antimicrobial activity of the samples against E. Coli bacteria after the inhibition zone test was determined. All samples showed significant antimicrobial efficiency, which increased with increasing concentration of the powder. The antimicrobial function of the hybrid material is not inhibited by the facade paint. Film preservation of facade paint does not require a pronounced long-distance effect, so much lower concentrations of the hybrid material powder are sufficient for this application. A reference sample with high antimicrobial activity served as a control.
[0142] FIG. 16 shows several samples of a commercial antifouling paint to which increasing concentrations of hybrid antimicrobial material powder prepared on cellulose powder have been added. The concentrations of the powder were 2.0 wt%, 4.0 wt% and 8.0 wt%. The antifouling coating without the addition of the antimicrobial powder served as a control. The samples were stored in the North Sea for 6 weeks. After this time, the control sample already showed significant fouling, while the sample with 2.0 wt.% of antimicrobial powder showed fouling only in isolated areas. As the concentration of antimicrobial hybrid material powder increases, the low level of fouling decreases further.
[0143] FIG. 17 shows samples of Ultramid C33 containing 1% by weight of antimicrobial microparticles prepared with commercial silver powder. FIG. 17 a shows granules, and FIG. 17 b shows plates. FIG. 17 c shows the inhibition zone test of the samples against E. coli bacteria. Both samples have medium antimicrobial activity. One sample of the plate was incubated for 18 months in deionized water, which was replaced at regular intervals. The antimicrobial activity of the sample is unchanged after incubation because its antimicrobial activity is not due to the leaching of a biocide, but is due to a catalytic process.
[0144] FIG. 18 shows polyamide fibers containing 3% by weight of catalytic-based antimicrobial microparticles (FIG. 18 a). The microparticle powder used was produced by reducing silver ions in a chemical-reduction process and subsequent coating with ruthenium. For the powder to be incorporated into the fibers, the size of the particles must be < 5 .Math.m. The fibers have good antimicrobial activity (FIG. 18 b).
[0145] FIG. 19 a shows an antimicrobial hybrid material produced according to the invention, the core of which has been made from ferromagnetic iron powder. FIG. 19 b shows how the hybrid particles equipped with a ferromagnetic core can be manipulated completely in the glass container from the outside through a glass wall with a strong permanent magnet. Such a hybrid system can be used, for example, in biological measuring apparatus. FIG. 19 c shows results of the hybrid antimicrobial particle system (arrows) according to the invention for PCR genome analysis on gram-positive B. subtilis germs. The antimicrobial particle system according to the invention had the task of lysing B. subtilis (approx. 1x10exp6 cells) in a 21 .Math.l suspension with PBS for 15 min at RT. Here, the particles could be completely removed from the instrument after the end of the experiment with the aid of a magnet.
[0146] FIG. 20 shows an antimicrobial hybrid material coated according to the invention and uniformly distributed in water by vigorous agitation. The particles of the hybrid material in (a) are without post-coating, while the particles of the hybrid material in (b) are subsequently treated in a dopamine hydrochloride solution (2 mg/ml) and a phosphate buffer (0.1 M, pH 8.5) at RT. The dopamine hydrochloride treatment converted the particle surface from the previously hydrophobic state to a hydrophilic one. This resulted in the particles that were hydrophobic without post-coating with dopamine hydrochloride immediately sinking to the bottom of the vessel after agitation, while a stable dispersion can be maintained for a longer time due to the hydrophilized particles (FIG. 20 b).
[0147] FIG. 21 shows a cellulose-based antimicrobial hybrid material produced according to the invention, the antimicrobial efficacy of which is not impaired by post-treatment. FIG. 21 a shows the antimicrobial activity of the cellulose-based hybrid particles produced according to the invention without post-treatment against an E. coli (DSM 498) suspension culture (10exp7/ml with 200 .Math.l plated out) on the basis of the pronounced inhibition zone on the agar. In FIG. 21 b, the same size Hemmhof shows that the cellulose-based hybrid particles posttreated with ascorbic acid do not negatively alter the antimicrobial activity of the particles prepared according to the invention. The same applies to the post-treatments with chitosan (FIG. 21 c) and polydopamine (FIG. 21 d).
[0148] FIG. 22 shows a cellulose-based antimicrobial hybrid material that has been integrated into sol-gel coating materials (e.g. siloxanes) and provides the sol-gel coating with antimicrobial activity. The two siloxane coatings H 2084 and H 5055 (FIG. 22 a) were used as sol-gel coatings. Hybrid cellulose-based particles were used as antimicrobial additive, which were added to the siloxane coating at a concentration of 5 wt.%. After mixing, the dispersion was applied to the sample support by spraying. The coating was then crosslinked in the drying oven at the appropriate temperature. The powder particles showed good distribution on the sample surface. FIG. 22 b shows antimicrobial test results for E. coli on the agar of polypropylene plates coated on one side with siloxane and coated with 5% by weight of the cellulose-based hybrid antimicrobial material of the invention. The inhibition yard test with E. coli (DSM 498) shows the high antimicrobial activity of the two samples. This was also true for samples that had been subsequently incubated for 5 min in a 1% solution of potassium sulfide. The partially irregular inhibition halo is due to the uneven spray application. It can be seen that the antimicrobial activity of the antimicrobial particles produced according to the invention is hardly affected by the siloxane coating. In this case, the subsequent sulphide post-treatment even leads to an increase in the antimicrobial efficacy of the dispersion coating system. Since siloxane coatings are hard and scratch-resistant in the polymerized state, this antimicrobial dispersion coating system is particularly suitable for surfaces subject to wear and tear.
[0149] FIG. 23 shows the growth curves of MRSA bacteria in which the two ruthenium/ruthenium/silver/silver oxide powders have been used with different amounts of powder. Ruthenium can be deposited with different strong reducing agents (e.g., NaBH.sub.4, N.sub.2H.sub.4) by direct, one-step chemical-reduction route, for example, on silver surfaces, and ruthenium/ruthenium oxides can be deposited on the silver surface accordingly. However, ruthenium/ruthenium oxides can also be deposited in a two-step process, in which ruthenium is first oxidized in the first step and the oxidized ruthenium is reduced to ruthenium and ruthenium oxides only in the second step. It was expected that the different process routes for ruthenium/ruthenium oxide deposition on silver particles would lead to comparable antimicrobial efficacy. Surprisingly, however, the two-step process was found to have almost an order of magnitude greater antimicrobial activity of the silver/silver oxide/ruthenium/ruthenium oxide against S. aureus (MRSA) and P. aeruginosa compared to the direct, one-step ruthenium deposition process. Unlike the direct, one-step reduction of Ru (III) ions by a strong reducing agent, the indirect, two-step process relies on the oxidation of Ru (III) ions to ruthenium (VIII) oxide [Chen 2011]. RuO.sub.4 is a strong oxidizing agent that is converted to ruthenium (IV) oxide by suitable reducing agents, coating the carrier material with a layer of ruthenium (IV) oxide. The oxidation of Ru (III) ions to RuO.sub.4 is carried out by sodium hypochlorite. To stabilize RuO.sub.4, the process is carried out in alkaline medium. The reduction to RuO.sub.2 is carried out by sodium nitrite.
Preparation of Semiconducting Silver / Silver Oxide // Ruthenium / Ruthenium Oxide Powders by Chemical Reductive Deposition of Ru/RuO.SUB.x on Silver Particles Using an Indirect, Two-Step Process for Ruthenium Deposition (AP 383)
[0150] 50 g silver powder (Toyo Chemical Industrial, SBA10M27) was slurried in a 2000 ml three-neck flask in an ultrasonic bath with 1000 ml deionized water. Additional agitation was performed with the KPG stirrer at 300 rpm. After 2 h, the brown suspension was transferred to another 2000 ml three-neck flask by decantation. In the ultrasonic bath and stirring with the KPG stirrer, 10 ml of Ru(NO)(NO.sub.3).sub.3 solution (10.83 g/l) was added. Then a mixture of the following solutions was added to the suspension: [0151] 300 ml NaClO solution (14 %), [0152] 100 ml NaOH solution (10 g/l), [0153] 87.5 ml NaNO2 solution (10 g/l).
[0154] The silver powder immediately turned dark. The suspension was then stirred for 1 h in an ultrasonic bath. After sedimentation of the coated powder, the yellow supernatant was decanted off. The powder was taken up with deionized water and filtered off. After washing with deionized water, the powder was taken up with ethanol, filtered off and dried in a drying oven at a temperature of 60° C.
Antimicrobial Effect
[0155] Surprisingly, silver / silver oxide // ruthenium / ruthenium oxide powders in which the ruthenium oxide was deposited by the one-step and two-step chemical reduction processes, respectively, show strikingly large differences in antimicrobial testing against MRSA bacteria (Gram-positive). Silver / silver oxide // ruthenium / ruthenium oxide powders (AP823) deposited by direct ruthenium reduction on silver particles with the strong reducing agent sodium borohydride (NaBH4) exhibited antimicrobial activity nearly an order of magnitude lower than silver / silver oxide // ruthenium / ruthenium oxide powders (AP383) deposited by the two-step method. FIG. 23 shows the growth curves of MRSA bacteria in which the two ruthenium / ruthenium oxide // silver / silver oxide powders have been used with different amounts of powder. As can be seen from the shape of the growth curves, the two-step silver / silver oxide // ruthenium / ruthenium oxide powder (AP383) showed complete killing of MRSA bacteria at a weighed powder amount of 2.5 mg, whereas the one-step silver / silver oxide // ruthenium / ruthenium oxide powder (AP823) showed complete killing only at 15 mg powder amount. Thus, the 2-stage ruthenium deposition was found to have significantly increased antimicrobial efficacy compared to the 1-stage method, as indicated by the fact that complete germicide over the entire 8 h experimental period required only 2.5 mg of powder for sample 383(veequivalent Ru deposition method as 392) and > 10 mg for sample 823, i.e., about 4-6 times less. A comparably large difference in antimicrobial activity (approx. one order of magnitude) was found in studies of the antimicrobial activity of both types of powder (AP823) and (AP383) against P. aeruginosa PA 14 (gram-negative).
[0156] The antimicrobial effect is particularly high for samples containing ruthenium (VI) oxide in the first half cell (Table 2). Apparently, the ruthenium (VI) oxide can be obtained in both electrochemical and PVD deposition of ruthenium when a process step with strong oxidative effect is present in the ruthenium deposition (392 and RuOx). The XPS surface analyses indicate a correlation between the antimicrobial effect and the composition of the ruthenium oxides, possibly depending on a certain ruthenium (VI) oxide / ruthenium (IV) oxide ratio. In any case, the presence of ruthenium (VI) oxide is beneficial or even necessary for the enhanced antimicrobial activity.
TABLE-US-00002 XPS analysis results - manufacturing process-antimicrobial activity Sample designation Basic material Ruthenium deposition process Chemical composition (XPS 3d spectra) * Antimicrobial effect Ru(0) RuO2 RuO3 825 Silver particles Chemical Reductive Direct Reduction 280, 1 eV 280.7 eV ++++ ++++ n. d. ++ 392/383 Silver particles Chemical-Reductive 2-stage Stage 1: Oxidation Stage 2: Reduction Very low share Contained in the broad red peak RuO2 (hydrated). Substantial part is RuO3 282.9 eV + ++ +++ ++++ “Ru” PE film PVD sputtering 280.0 eV Low proportion in Ru(0) peak ++++ + n. d. ++ “RuOx” PE film PVD Reactive Sputtering (Oxidative) 282, 1 eV + n.d. ++++ ++++ *) Reference spectrum: silver (The binding energies of the high-resolution spectra were corrected using the Ag3d spectra.
[0157] Literature binding energies (eV): [0158] Ru (0): Ru 3d: 280, 2 eV; J. F. Moulder, W. F. Stickle, P. E. Sobol and K. D. Bomben: Handbook of X Ray Photoelectron Spectroscopy: A reference of Standard Spectra for identification and interpretation of XPS Data, J. Chastain and J. R. C. King, Editors, p. 115, Physical Electronics Eden Prairie, Minnesota (1995). [0159] RuO2: Ru 3d: 280, 66 eV; T. P. Luxton, M. J. Eick, K. G. Schekel; Journal of Colloid and Interface Science 359, (2011) 30-39. [0160] RuO3: Ru 3d: 282, 5 eV; T. P. Luxton, M. J. Eick, K. G. Schekel ; Journal of Colloid and Interface Science 359, (2011) 30-39. RuO3: Ru 3d: 282.4 eV; R. Kötz, H. J. Lewerenz and S. Stucki; J. Electrochem. Soc. 130, No. 4, 1983, 825-829.
[0161] In addition to the wet chemical 2-step Ru deposition on silver, ruthenium and silver were also deposited by PVD coating on a PE foil, which has the advantage that no silver chloride is present on the PVD samples and any differences that may be detected can be attributed to the ruthenium half cell more unequivocally.
[0162] (A) PVD deposition: [0163] (a) Ruthenium sputtering on silver (sample designation “Ru”). [0164] (b) Reactive sputtering (O.sub.2) of silver and ruthenium (sample designation “RuOx”).
[0165] (B) Chemical-reductive ruthenium deposition: [0166] (c) direct reduction for ruthenium deposition on silver (sample designation “825”). [0167] (d) Reduction of ruthenium to deposit on silver in the 2-step process already described (oxidation + subsequent reduction, (sample designation “392”).
[0168] These 4 samples were analyzed by growth curves and surface composition (XPS analysis). As a result, it has been shown that in both investigations differences occurred within the respective group (A) or (B), but also between groups (A) and (B), with an increased antimicrobial efficiency corresponding to a striking distinction in the surface composition, according to the XPS analysis.
[0169] FIG. 24 shows XPS spectra of the samples Ru (a), RuOx (b) as well as 825 (c), 392 (d). Antimicrobial studies had shown, as described above, that there are significant differences in the chemical-reductive deposition and PVD deposition of Ru/RuOx // Ag/AgCI and AgOx-half cell combinations, respectively. The XPS analyses show differences in a striking manner, which correspond to the different antimicrobial efficacies. As can be seen in the Ru3d spectra (FIG. 24), there are the following striking differences both in the group of chemically-reductively prepared samples 825 (c) (curve (1)), 392 (d) (curve (2)) and the group of PVD-coated samples Ru (a) (curve (3)), RuOx (b) (curve (4)) within one group and between the two groups: [0170] A narrow signal from metallic ruthenium (BE = 280.1 eV) is found in sample 825 (a) curve 1. The spectrum of sample Ru consists mostly (65%) of metallic ruthenium and about 24% is assigned to RuO2. [0171] The RuOx (b) sample (curve (4) - PVD oxidation sputtered) contains significantly less Ru(0), making the carbon components more prominent. The largest component (BE = 284.4 eV) would be attributed to metal carbide (C apparently originates from PVD cleaning of the PE film). The ruthenium component of the spectrum is dominated by the signal at BE = 282.1 eV, which accounts for about 85% and can be assigned to RuO3**. The half-width of this component is quite large, so that a contribution of other compounds to the signal cannot be excluded. The remaining Ru components of the spectrum are caused by oxide hydrates of Ru(VI) or higher oxidation states of ruthenium.
[0172] Sample 392 (d) curve (2) is similar to sample RuOx (b) curve 4 and also contains RuO3** in significant concentration. In addition, however, other compounds are present which may be oxide hydrates. But Ru compounds with greater valence are also possible. The Ru(0) and RuO2 content is small.
[0173] **) According to literature data (Table 1), between 282.2 eV and 282.6 eV RuO.sub.3 is located.
[0174] In the oxygen O1s spectra (FIG. 25), one sees a grouping of the samples as described for the Ru3d spectra. The Ru and 825 samples give virtually identical spectra shapes, which can be matched with three components. Metal oxides are expected at BE = 530 eV. The components at larger BE may represent hydroxides and hydrates. However, in all likelihood, significant portions of these are attributable to adsorbates. The RuOx sample is probably significantly influenced by the adsorbates. In addition, the O atoms can be seen in the ruthenium oxides. Sample 392 shows only small proportions of oxidic oxygen atoms. The predominant part is bound in hydrates. In between, hydroxides are probably still to be found.
[0175] The XPS analyses show several differences in the oxidic composition of the samples studied. Striking, and possibly a main culprit for the increased antimicrobial efficacy, could be the presence of the hexavalent oxidation state of ruthenium, in addition to the RuO.sub.2 and the metallic Ru(0), in the samples with high antimicrobial efficacy. In particular, in the PVD samples where AgCl is not present, there may be no influence from this side to increase the antimicrobial efficacy.
