Patent Application
20230200381
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. The invention further relates to a method for producing a particulate hybrid material having antimicrobial activity, and to the use of such a particulate hybrid material.
As a rule, additives must possess a number of properties that often cannot be achieved on the basis of a base material alone. Desired property profiles can be adjusted by means of surface technology. Often, properties are required that cannot be achieved by one material alone, but only by several surface materials consisting of different components. Such multi-component systems are also referred to as hybrid material systems.
Antimicrobial devices and products have been used in sensitive areas such as medical and hygiene technology and food processing for some time. The current SARS-CoV-2 pandemic, but also many previous epidemics, have brought the topic of hygiene and protection against pathogenic microorganisms very far into the consciousness of the population and extended the need for antimicrobial protection to all areas of life. Due to the huge negative impact on the global economy, the current situation highlights the importance of antimicrobial protection and that the need for highly effective antimicrobial protection materials will increase significantly. Especially for items that are frequently touched or serve as antimicrobial protective equipment, such as mouth masks, there is an increasing need for more powerful and durable antimicrobial systems that can be well processed and integrated into products.
Previous solutions in the field of antimicrobial additives have been limited to the use of conventional biocidal substances released by leaching. Oligodynamic metals such as silver, copper or zinc, their chemical modifications, organic substances such as triclosan and isothiazolinones, and organometallic substances such as zinc pyrithione are used. These substances are stored in a depot in the carrier matrix. Once the depot is exhausted, the antimicrobial effect of the carrier material is no longer present. New developments in the field of antimicrobial additives mostly relate to the production of particles for powder coating, to improved dispersion of biocides in a polymeric carrier matrix, to the prevention of discoloration of the carrier matrix by the added biocides, and to the controlled release of the biocidal active ingredients by encapsulation. However, future-proof antimicrobial systems are expected to exert sufficient spontaneous action to prevent the growth of microorganisms and, at the same time, to be antimicrobially effective over long periods of time by slowly releasing toxicologically and ecotoxicologically tolerable amounts of the active substance.
From WO 2008/046513 A2 a bioactive metallic coating containing silver, ruthenium and a vitamin is known, which is used for sterilization, disinfection and decontamination of water or aqueous solutions. The combination of silver with ruthenium and a vitamin, for example ascorbic acid, leads to faster and more efficient killing of microorganisms. At the same time, these bioactive metal surfaces prevent colonization with microorganisms and the attachment or stable deposition of problematic biomolecules such as DNA, RNA or proteins. The coating creates a self-cleaning surface which, when in contact with water or aqueous solutions, very quickly and efficiently establishes its sterility and maintains it over longer periods of time.
Patent EP 0 677 989 B1 discloses the preparation of an antimicrobially active powder that can be used as an additive for products made of plastic. The powder comprises a core of inorganic material coated with an antimicrobially active metal or metal compound. A second coating consists of aluminum silicate, aluminum oxide, aluminum phosphate, silica, silicate, borosilicate or mixtures of these substances. The porosity of the coating is intended to regulate the diffusion of antimicrobially active substances so as to prevent possible discoloration of the plastics used. A third coating of hydrous metal oxides of aluminum, magnesium, zirconium or the rare earths is intended to reduce the agglomeration of the particles and improve their dispersion in the plastics. The content of the antimicrobial coating is 0.05 to 20 wt% based on the carrier material. For the second coating, the content is 0.5 to 20 wt%, also based on the carrier material. The antimicrobial powder can be added to a variety of aliphatic or aromatic polymers.
EP 0 270 129 A2 discloses a process for the production of an antimicrobial powder based on zeolites and its use as an additive for resins. Both natural and synthetic zeolites are used. The antimicrobial function is based on complete exchange with ammonium ions as well as with ions of the metals silver, copper, zinc, mercury, tin, lead, bismuth, cadmium, chromium and thallium. The metal content is 0.1 to 15 wt% for silver and 0.1 to 8 wt% for copper or zinc. The antimicrobial zeolite is added to resins such as polyethylene, polypropylene, polystyrene or PVC.
Patent US 5 147 686 discloses the production of antimicrobial powders using powdered titanium oxide as a carrier material. The powder particles have a size of 0.01 µm - 3 µm. The particles are provided with an antimicrobially active coating. The coating consists of copper, zinc and their alloys such as Cu—Zn, Cu—Ag, Cu—Sn, Cu—Al, Zn—Sn, Zn—Sn—Cu, Zn—Al—Cu—Mg or similar alloys. The metal content is 0.001 to 35 wt%. The coating is applied by external currentless deposition, whereby the surface of the carrier particles is first activated with palladium or tin. In addition to its antimicrobial properties, the powder excels as an additive in various media.
US 2016/0369405 A1 discloses a method for producing particles coated with metal in a liquid. Particles of silicon, tin, germanium, gallium, lead, zinc, aluminum or carbon are used as the base particles, which are coated with a metal in a reactor, the metal being elemental silver, copper, platinum, palladium, iron, cobalt, rhodium, nickel, vanadium, ruthenium, iridium or gold. A reducing agent, for example ascorbic acid, is used to initiate the plating reaction. In particular, the production and use of silicone particles coated with silver is described.
Materials that are incorporated into products or materials in a particle form in order to ensure or enhance the required product properties are also designed as hybrid systems with different surface compositions and structures in order to integrate them into other materials so that they impart therein their specific particle properties in the desired manner. Multicomponent hybrid particle systems must therefore be specifically adapted to the desired material and the required material properties by the right choice of particle material, particle size and structure, and additionally applied layer systems, or by chemical post-treatment of one or more components of the hybrid particle system. This also applies to particulate systems with antimicrobial properties that are intended to introduce these antimicrobial properties into products or materials. However, there is a risk that during particle processing or particle-material integration, their desired core property - the antimicrobial effect - is weakened or even lost.
It is the object of the invention to develop an antimicrobially active particulate hybrid material that can maintain its antimicrobial property even after processing, material integration and/or as an additive in products.
According to the invention, the object is solved by a hybrid material of the type mentioned above, in which 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. Overall, the invention thus provides a hybrid, adaptable particulate multi-component system of different materials that can transport its broad-spectrum antimicrobial effect (for the sake of simplicity, the efficacy against bacteria, viruses, fungi, and other microorganisms is hereinafter referred to as “antimicrobial”) into a wide variety of materials, substances and/or coating materials without losing the antimicrobial property in the molding process, material integration or the ready-to-use product. The material components needed for the molding process or material integration and use of the finished antimicrobial product, in particular the carrier material, are selected in such a way that they do not negatively affect the antimicrobial property of the hybrid particulate system, but rather strengthen it. Furthermore, the hybrid material according to the invention is an antimicrobially active particulate system which, adjustable via the hybrid particle structure, is suitable for use with different products or primary materials or substances and/or coating materials. In this context, the hybrid material according to the invention can, for example, be integrated into the substance and/or the coating material. The combination with the hybrid particle system imparts an antimicrobial property to the product or primary material, wherein the carrier material comprises at least one material which is selected, designed and/or modified in such a way that the hybrid material according to the invention is optimally adapted to the substance and/or the coating material and its use. Thus, in addition to maintaining the antimicrobial effect, a further advantage of the hybrid material according to the invention is that it can be specifically adapted to the material, the substance and/or the coating material and the required material properties as well as the desired applications thereof, for example, by the correct selection of the particle material, the particle size and structure as well as additionally applied layer systems or by chemical post-treatments of one or more components of the hybrid particle system.
According to the invention, two metals with high chemical stability and different electrochemical potentials are deposited on the carrier material. Preferably, these are transition metals of the d group, preferably noble metals. The metal combination according to the invention is deposited on the carrier material in such a way that both metals are in electrically conductive contact with each other and are distributed on the surface of the carrier material in the form of a plurality of nano- or microgalvanic elements short-circuited via the aqueous phase. Thus, the present invention advantageously comprises an antimicrobially active metal coating each consisting of a semiconductive, catalytically active transition metal compound (half cell I of a galvanic element) and a semiconductive, hardly soluble silver compound (e.g., silver oxide, silver hydroxide, silver sulfide, silver-halogen compounds, or combinations thereof; half cell II of the galvanic element), both being in direct, electrically conductive contact with each other. The transition metal element of the first half cell is selected in such a way that it has several oxidation states and thus permits a (relatively easy) change of oxidation states via catalytically active centers. Particularly suitable half cells are therefore those which have multiple valences and at which highly reversible redox reactions can occur over a wide potential range. The high catalytic activity of such half cells for oxygen reduction is due to the easy change of oxidation states and the easy exchange of oxygen, which preferentially occurs at the active centers of the semiconductor surface. In this process, the transition metal element is only changed in its valence, resulting in the actual redox reaction. Therefore, no transition metal compound is consumed or formed, only the oxidation states are changed. The transition metal compound binds the molecular oxygen, allowing it to be catalytically reduced. Therefore, the presence of multiple valences is a prerequisite for the catalytic effect and the redox reaction. Thus, no transition metal compound needs to be formed. Special metal oxides or metal sulfides and hardly soluble silver compounds exhibit catalytic properties, electrical conductivity and high stability in water. By suitable combination of materials, two metals are in electrical contact with each other, which have a different electrochemical potential and thus form a galvanic cell. If this cell is short-circuited via the aqueous phase, a high electric field strength is generated due to the small distance (nm or µm range) between the two contacting metals. This contributes significantly to germ elimination. Redox reactions occur at both electrodes of the microgalvanic element, each of which kills the microorganisms. At the first half cell (cathode), molecular oxygen is reduced to oxygen radicals, which then have a toxic effect on the microorganisms. At the second half cell (anode), electrons are transferred from the microorganisms to the silver semiconductor, thereby destroying them by oxidation.
The electrochemical potential difference of the transition metals of the hybrid system deposited on the carrier material is thereby adjusted in such a way that the oxygen present in the moist environment can be reduced by redox processes and antimicrobially active oxygen radicals can be formed. The hybrid antimicrobial particle system according to the invention, whose antimicrobial efficacy is not based on the release of biocides or metal ions but on the catalytically assisted generation of oxygen radicals, preferably on a noble metal combination of silver oxide / ruthenium oxide and/or silver chloride / ruthenium oxide, does not change its composition even with long-term antimicrobial use and, unlike biocides or oligodynamic metals, does not require a depot or devices regulating the biocide or metal ion release.
The two metals (half cells) can, for example, be applied as a layer system on the surface of the particulate carrier (carrier material), with the layer of one metal lying at least partially above that of the other metal. In this case, the respective upper layer can be porous (in particular nanoporous) or microcracked, in particular cluster-shaped, applied to or deposited on the other metal, so that the aqueous solution or moisture has access to both half cells and the galvanic element is short-circuited. Alternatively or additionally, however, the two metals (half cells) can also be applied to the surface of the particulate carrier (carrier material), for example, in the form of individual particles. These may be, for example, bimetallic particles comprising both metals and/or metal particles each comprising only one of the two metals. The latter can be applied sequentially, i.e. first particles of the first metal and then particles of the second metal (or vice versa), or simultaneously as a mixture of particles of both metals in such a way that they are in electrically conductive contact with the carrier material. The particles can be applied to the carrier material in a single layer (lying next to each other) and/or at least partially in multiple layers (lying on top of each other).
Unlike biocides and oligodynamic metals, which have to release toxic substances into the environment in order to be effective, only water is ultimately produced from the oxygen radicals formed when the hybrid material of the invention is used. Since the metal combination is a catalytically supported system, its antimicrobial effect is advantageously dependent exclusively on the active surface and not, as in the case of biocides or the oligodynamic systems (silver, copper and zinc or their salts or compounds), on their quantity and rate of leaching.hg
In an advantageous embodiment of the invention, it is provided that the carrier material comprises at least one material selected from the group consisting of cellulose, glass, zeolite, silicate, metal or a metal alloy, metal oxide (e.g. TiO2), ceramic, graphite, and a polymer. The hybrid material according to the invention can be targeted by the selection of the carrier material with respect to integration requirements with other materials as well as specific applications of use. For example, in terms of temperature resistance when integrated into e.g. plastics (e.g. silver particles as carrier), water absorption/absorbency (e.g. cellulose as carrier), magnetic particles, e.g. for analytical or production applications in apparatus from which particle removal is only possible from outside with a magnet (iron particles as carrier), cellulose integration in a Lyocel process in which the cellulose doped with the hybrid material of the invention dissolves in the organic cellulose solution and finely distributes the hybrid material particles in the cellulose slurry from which cellulose filaments can then be spun, or color design (e.g. white color: carrier cellulose). Surprisingly, in one of the embodiments of the antimicrobial hybrid system according to the invention, the selection of cellulose as a carrier material has provided a new manufacturing opportunity for antimicrobial textile fibers and films.
For example, cellulose (C)- or its derivatives as microcrystalline (MCC) or nanocrystalline cellulose powder (NCC) can be used as a carrier material, which provide a number of inherent properties that support the antimicrobial effect of the hybrid particle system, such as their hydrophilicity and a high water binding capacity, which is still about 5-8% in the dry state. The cellulose fibers can be varied not only in fiber length but also in fiber cross-section, which can significantly increase the fiber surface area. Thus, in addition to the “standard cellulose” which is cloud-shaped in cross-section, fibers with star-like (Trilobal) or letter-like (Umberto) cross-sections are also available. The cellulose carrier surface can also be significantly increased by so-called bacterial cellulose (BC) due to its tissue-like, fine network structure. BC also has an increased water absorption capacity and is therefore popular in medical applications.
Cellulose is the most abundant biopolymer on earth, with a formation rate of 1.5 trillion tons per year, making it the world’s most important renewable raw material.
Cellulose is used not only in the textile, paper and building materials industries, but also in the medical sector. The widespread use of cellulose materials, particularly their use in medical applications, has led to the development of antimicrobial cellulose particles. Cellulose itself does not have antimicrobial activity that could prevent infections. The majority of work to date on the production of antimicrobial cellulose has focused on the incorporation of biocidal nano-silver particles onto or into cellulose fibers through various deposition processes. Surprisingly, the present invention has succeeded in depositing not only silver but also ruthenium on the cellulose in an adherent manner. In this context, it was achieved in the manner according to the invention that the catalytically supported oxygen radical formation on the silver-ruthenium precipitates is also given on the cellulose carrier.
In a further advantageous embodiment of the invention, it is provided that the hybrid material is modified with organic polymers, preferably polyethylene glycol (PEG), polydopamine and/or chitosan, and/or with ascorbic acid or ascorbic acid derivatives. In this context, the modification can be carried out by pretreating the carrier material before applying the metals, for example to facilitate coating, and/or posttreating the hybrid material after applying the metals. In this way, certain properties of the product (material and/or coating material) doped with the hybrid material according to the invention can be changed or improved. For example, the flowability and/or dispersibility of particles or powders can be specifically adjusted by post-treatment of the hybrid material with, for example, polydopamine or propylene glycol (PG).
In an advantageous embodiment of the invention, it is further provided that 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. Thus, the antimicrobial strength of the selected antimicrobial hybrid material is adjustable not only by varying the amount of particles but also by varying its structure. The hybrid system according to the invention can be specifically adjusted with respect to the strength of its antimicrobial effect (often the highest effect is not desired, adjustment by growth curves) and the requirements for use or integration with other material(s) as well as for the specific applications of use. For example, by varying the coating process, the thickness of at least one metal layer can be adjusted. For example, the shape of the carrier material and/or the reduction process during coating can be used to selectively influence the structure of the metal layers. Furthermore, the strength of the antimicrobial effect of the hybrid material according to the invention can be specifically adjusted, for example, by using a defined amount of at least one metal (e.g. proportion of the metal in the total hybrid material in % by weight).
In another advantageous embodiment of the invention, it is provided that 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.
In a particularly advantageous embodiment of the invention, it is provided that the transition metal compound of the first metal comprises ruthenium present in one or both of the oxidation states VI and IV. Ruthenium is a noble metal that has multiple oxidation states and is capable of forming, for example, different ruthenium oxides due to its different valencies. Surface redox transitions such as Ru(VIII)/Ru(VI), Ru(VI)/Ru(IV), Ru(IV)/Ru(III), and possibly Ru(III)/Ru(II) are the cause of the high catalytic activity of the mixed ruthenium compounds and their good electrical conductivities. The unusually pronounced catalytic and electrocatalytic properties of the ruthenium compounds depend on the variation of the oxidation states. For example, the antimicrobial activity is particularly high in compositions according to the invention comprising ruthenium (VI) oxide in the first half cell.
The transition metal compound of the first metal may thereby comprise at least one corresponding metal oxide, metal oxyhydrate, metal hydroxide, metal oxyhydroxide, metal halogenide and/or at least one metal sulfide of the transition metal element.
In an advantageous embodiment of the invention, it is further provided that 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 (for example, metallic silver having on its surface a silver compound such as silver oxide or silver chloride).
In a further advantageous embodiment of the invention, it is provided that the particles have a spherical or polyhedric shape and a mean diameter of at most 100 µm, preferably at most 50 µm, in particular at most 5 µm. For example, such spherical particles may have a mean diameter between 0.1 and 70 µm, preferably between 0.1 and 50 µm or 0.1 and 10 µm, in particular between 1 and 5 µm. Alternatively or additionally, the particles may have a fiber-like shape and a mean length of at most 1 mm, preferably at most 100 µm, in particular at most 75 µm or at most 60 µm. For example, such elongated particles may have a mean length between 0.1 and 100 µm, preferably between 0.1 and 50 µm or 0.1 and 10 µm, in particular between 0.1 and 1 µm. Particle size and shape play an important role, for example, in nozzle problems during the spinning of polymer threads (e.g. fine silver particles) or when a large surface area is required (e.g., due to different cellulose fiber cross-sections or fine silver particles). Since the antimicrobial effect of the hybrid material according to the invention is based on a catalytic process at the particle surface, the particle efficiency increases while the surface fraction of the particles increases in relation to the particle volume. Therefore, particle efficiency is particularly advantageous for smaller particle sizes.
The invention is further solved by a method for producing a hybrid material having antimicrobial activity, in particular the hybrid material described above, comprising the following steps:
In principle, all the materials initially mentioned can be used as carrier materials, preferably cellulose, metals, metal oxides (e.g. TiO2), glass, ceramics, graphite and polymers. In a particular embodiment, the antimicrobial hybrid system is provided with a magnetizable particle core. For example, the antimicrobial coating may be deposited on a ferromagnetic core (e.g., nickel, iron, cobalt powder). Such antimicrobial hybrid systems are needed, for example, where, after use of the particles, their complete removal from reaction or analytical vessels that are difficult to access is required. The antimicrobial, magnetizable particle hybrids can be pulled from outside the reactor with a strong magnet to an accessible location of a reactor where they can be removed.
Preferably, a first metal is applied to the carrier material, which comprises at least one electrically conductive silver semiconductor. A second metal is also applied to the carrier material and/or the first metal, wherein the second metal comprises at least one transition metal element that has multiple oxidation states and allows a change of oxidation states via catalytically active centers. Alternatively, a first metal can be applied to the carrier material, which comprises at least one transition metal element that has multiple oxidation states and allows a change of oxidation states via catalytically active centers. In this case, a second metal is also applied to the carrier material and/or the first metal, the second metal comprising at least one electrically conductive silver semiconductor. In both alternatives, the second metal is applied to the carrier material and/or the first metal in such a permeable manner that the two metals are in electrically conductive contact with one another at least with their respective surfaces and are each in contact with an electrolyte and can thereby develop an antimicrobial effect (see above).
For the production of a hybrid material according to the invention, for example, silver can be deposited chemically-reductively on the carrier material (e.g. glass beads). Silver nitrate (AgNO3) is preferably used as the silver salt. Various reducing agents can be used as reducing agents, for example aldehydes, ascorbic acid, metal hydrides (preferably sodium borohydride), hydrazine and/or a hydrazinium salt, and/or hydroxylamine and/or a hydroxylammonium salt. In the case of cellulose as the carrier material, ascorbic acid is preferably used as the reducer. This first step may also be omitted in the case where commercially available silver-coated carrier materials (e.g., pre-silver-coated glass beads) are available and used. Ruthenium, for example, can then also be applied to the silver layer by chemical reduction. For ruthenium coating, the silver-coated carrier material (e.g. glass beads) is dispersed in alkaline solution under strong stirring. Solutions of ruthenium (III) chloride and sodium borohydride are then added as reducing agents.
In an advantageous embodiment of the method according to the invention, it is provided that at least one of both metals is applied onto the carrier material and/or the respective other metal in cluster-shaped form, nanoporously, microcrackly and/or in the form of single particles.
In an advantageous embodiment of the method according to the invention, it is further provided that, after step a) and/or step c), the carrier material and/or the metals is/are modified with organic polymers, preferably polyethylene glycol, polydopamine and/or chitosan, and/or with ascorbic acid or derivatives of ascorbic acid. Consequently, the hybrid material can be modified by pretreatment of the carrier material prior to application of the metals, for example to facilitate coating, and/or post-treatment after application of the metals. In this way, certain properties of the product (material and/or coating material) doped with the hybrid material according to the invention can be modified or improved. According to the invention, for example, the carrier material with the antimicrobial metal coating, without or with a chemically generated compound layer (see below), can be modified to optimize the properties of the hybrid material. This concerns, for example, the flowability, dispersibility or long-term stability. According to the invention, despite the modification of the hybrid particle system, its antimicrobial properties are maintained or even improved.
In a further advantageous embodiment of the method according to the invention, it is provided that a link layer is generated on at least one metal, which comprises at least one metal compound of the corresponding metal, which is selected from the group consisting of halogenides, oxides, and sulfides. To enhance the function, the two metals are thereby activated with a chemically stable compound of the metals. For this purpose, a link layer is created on the metals, which may consist of a halide, oxide or sulfide, for example. The influence of the post-treatment of the particulate surfaces can be determined or adjusted accordingly, for example, using suitable microbiological methods or measurement procedures, such as growth curves.
In an advantageous embodiment of the method according to the invention, it is further provided that the strength of the antimicrobial effect is specifically adjusted by adjusting the amount of at least one of both metals and/or the proportion of both metals on the surface of the particles. For example, the strength of the antimicrobial effect of the hybrid particle system can be controlled by appropriately selecting the deposition conditions for the two metals on the surface of the carrier material, wherein the areal proportions of the two metals on the hybrid surface are varied with respect to each other. The surface composition sought for desired antimicrobial action of the hybrid particulate material of the invention can be determined by suitable microbiological methods, such as growth curves, based on the variation of particle composition and structure.
In a further advantageous embodiment of the method according to the invention, it is provided that the respective metal is applied sequentially or simultaneously by means of electrochemical deposition, chemical-reductive deposition, electrophoretic coating, calcinating, PVD, CVD and/or sol-gel processes. In this context, the two metals (half cells) can also be deposited, for example, in the form of individual particles on the surface of the carrier material. The particles can be applied to the carrier material, e.g., sequentially, i.e. first particles of the first metal and then particles of the second metal (or vice versa), or simultaneously as a mixture of particles of both metals (or possibly in the form of bimetallic particles).
In calcination, thermally easily decomposable compounds containing the desired transition metals (usually anhydrous), e.g., in alcohols (e.g., ethanol or isopropanol), are intensively mixed, applied to the surface to be coated and then thermally decomposed at high temperatures (e.g., 200-500° C.) in the presence of air. In this process, any desired composition of the two half cell metals can be adjusted by mixing the two metal salts to obtain the appropriate oxidic compounds. Easily decomposable ruthenium compounds include, for example, RuCl3 (halides in general).
In a particularly advantageous embodiment of the invention, it is further provided that the application of the second metal onto the carrier material and/or the first metal comprises at least one step having a strong oxidative effect. For example, ruthenium/ruthenium oxides can be applied in a two-step process, wherein in the first step ruthenium is first oxidized and only in the second step the reduction of the oxidized ruthenium to ruthenium and RuOx is accomplished. Unlike the direct, one-step reduction of Ru (III) ions by a strong reducing agent, this indirect, two-step process relies on the oxidation of Ru (III) ions to ruthenium (VIII) oxide (RuO4). RuO4 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. For example, the formation of ruthenium (VI) oxide can be achieved in both electrochemical and PVD deposition of ruthenium if the ruthenium deposition includes a process step with a strong oxidative effect.
In a further advantageous embodiment of the invention, it is provided that, after applying both metals, a thermal post-treatment is accomplished for adjusting specific oxidation states. Provided that the carrier material is thermally resistant, the applied oxidic metal coatings or metal compounds can be subjected to thermal oxidation or reduction in a suitable atmosphere in order to set specific oxidation states.
The invention further relates to a hybrid material with antimicrobial activity produced by means of the method described above.
The invention also relates to the use of the hybrid material according to the invention for joint application with any materials, substances and/or coating materials, preferably lacquers, paints, plasters, polymers and/or cellulose. In this regard, the hybrid material may be associated with the materials, substances and/or coating materials in any manner. For example, the materials, substances and/or coating materials may be coated with or blended with the hybrid material particles. Preferably, the hybrid material particles of the invention are integrated into the materials, substances and/or coating materials.
The hybrid cellulose-silver-ruthenium particle variant of the hybrid material according to the invention surprisingly offers the possibility to produce antimicrobial cellulose fibers and cellulose films based on the antimicrobial hybrid system according to the invention with the help of the innovative and environmentally friendly Lyocell technology, since the cellulose-silver-ruthenium particle additive, despite its catalytic activity, does not have a decisive influence on the decomposition temperature of the solvent used in the Lyocell process (N-methymorpholine N-oxide (NMMO)) and can thus be processed in the Lyocell process. In the Lyocell process, the carrier material cellulose dissolves in the NMMO and releases the silver-ruthenium particles deposited on the cellulose fibers evenly distributed in the cellulose-containing solvent, so that antimicrobial Lyocell fibers can be produced from them for the textile industry, but also for nonwovens and other technical applications such as films, e.g., for packaging.
The invention also relates to microparticles, in particular bimetallic particles, for forming an antimicrobially active powder, which comprise particles of a first metal coated with a cluster-shaped, nanoporous and/or microcracked layer comprising a second metal, the particles of the first metal having an average diameter of at most 50 µm, preferably at most 10 µm. A particular embodiment of the invention is established if one of the two active components (metals) of the hybrid system is both surface and carrier material at the same time. For economic reasons alone, this applies only to very small noble metal carrier particles (e.g. 0.1 - 50 µm, preferably < 5 µm). In processing operations for integrating the hybrid antimicrobial particle system according to the invention (e.g., into certain plastics), which have to take place at high temperatures, this hybrid system variant is an option. For this purpose, the metal particles used as carrier material must be appropriately small so that the costs for the hybrid particle system can be overcompensated by correspondingly smaller amounts of noble metal due to the more favorable surface-to-volume ratio.
In an advantageous embodiment of the microparticles according to the invention, it is provided that the first metal is silver and the second metal is a metal selected from the group consisting of ruthenium, iridium, vanadium, manganese, nickel, iron, zinc, cobalt, cerium, molybdenum, and tungsten, or that the first metal is a metal selected from the group consisting of ruthenium, iridium, vanadium, manganese, nickel, iron, zinc, cobalt, cerium, molybdenum, and tungsten and the second metal is silver.
The invention also relates to a method for the preparation of microparticles, in particular bimetallic particles, having antimicrobial activity, comprising the following steps:
In an advantageous embodiment of the method according to the invention, it is provided that the reducing agent is sodium borohydride, hydrazine and/or a hydrazinium salt, and/or hydroxylamine and/or a hydroxylammonium salt.
The invention further includes microparticles, in particular bimetallic particles, for forming an antimicrobial powder prepared by the method described above.
The microparticles or bimetallic particles according to the invention can advantageously be used together with any materials, substances and/or coating materials, preferably lacquers, paints, plasters, polymers and/or cellulose. In this regard, the microparticles may be associated with the materials, substances and/or coating materials in any manner. For example, the materials, substances and/or coating materials may be coated or blended with the microparticles. Preferably, the microparticles are integrated into the materials, substances and/or coating materials.
Preferably, the microparticles or bimetallic particles according to the invention are a component of the hybrid material according to the invention, wherein the carrier material is at least partially coated with the microparticles or bimetallic particles.
The microparticles or bimetallic particles according to the invention can thus be used in an advantageous manner to produce a hybrid material according to the invention by applying them to the carrier material. The microparticles can be applied to the carrier material in a single layer (lying side by side) and/or at least partially in multiple layers (lying on top of each other).
The particulate materials of the invention are suitable, for example, for providing coatings and paints, plasters, polymers, textiles and packaging materials with antimicrobial properties. In principle, a wide range of materials such as cellulose, metals or metal oxides (e.g. TiO2), ceramic/mineral or polymer materials are available as carrier materials. A hybrid antimicrobial particle system is particularly advantageous if, in addition to the active component, the other constituents of the hybrid system can contribute additional positive properties that can support or improve the effect, processing or integration into the desired semi-finished product or finished product.
“Particle”, “particle-shaped” or “particulate” in the sense of the invention refers to single particle-shaped bodies that are delineated as a whole from other particles and their surroundings. In this context, all possible particle shapes and sizes, regardless of geometry and mass, are included within the scope of the invention. Particles may be characterized, for example, by their shape, weight, volume and/or size (e.g., length, diameter, circumference).
“Half cell” in the sense of the invention refers to a part of a galvanic element forming the latter in combination with at least one further half cell. In this context, a half cell comprises a metal electrode which is at least partially located in an electrolyte.
“Galvanic element” in the sense of the invention refers to the combination of two different metals, each of which forming an electrode (anode and cathode, respectively) in a common electrolyte. If the two metal electrodes are in direct contact with each other or are electrically conductively connected to each other via an electron conductor, the less noble metal with the lower redox potential (electron donor, anode) donates electrons to the more noble metal with the higher redox potential (electron acceptor, cathode) and subsequently initiates the redox processes at the electrodes.
“Electrolyte” in the sense of the invention refers to a compound (e.g., ions in aqueous solution) that conducts electric current under the influence of an electric field by the directional movement of ions.
“Substance” in the sense of the invention refers to a material of which a part, component, structural element or assembly of an article or product is made. In particular, the term “substance” includes, but is not limited to, parts made of at least one polymer (plastic; including films as packaging material), textiles (natural and/or synthetic textile fibers; woven, knitted, crocheted and braided fabrics), nonwovens, metals, glass and ceramics.
“Coating material” in the sense of the invention refers to a material or substance with which an object or product is or can be at least partially covered. The coating material may be applied to the object or product in one or more (preferably thin) layer(s). In particular, the term “coating material” includes, among others, liquid or pasty coating materials such as lacquers, paints and plasters, as well as solid coating materials such as powders and films.
“Metal” in the sense of the invention refers to atoms of a chemical element of the periodic table of the elements (all elements that are not nonmetals) that form a metal lattice by means of metallic bonds and thereby a macroscopically homogeneous material that is characterized, among other things, by high electrical conductivity and high thermal conductivity. The term “metal” also includes alloys comprising at least two different metals, metal compounds such as metal oxides, metal oxyhydrates, metal hydroxides, metal oxyhydroxides, metal halides and metal sulfides, and combinations of metals and corresponding metal compounds.
“Layer” or “layered” in the sense of the invention refers to a two- or three-dimensional structure that has a horizontal extension and is bounded by at least two surfaces, the layer bottom and the layer top. In this context, a layer may comprise a coherent material or substance and/or particles that are at least partially in contact with each other. In the sense of the invention, a layer may be homogeneous, heterogeneous, continuous (i.e., uninterrupted), clustered, nanoporous, and/or microcracked. “Coated” in the sense of the invention is a material, particle or other body, if at least a part of its (outer or inner) surface is provided with a “layer” (see above).
The invention is further explained in more detail by the following figures and examples.
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.
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.
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 .
A first, largely closed metal layer (2), preferably a silver layer, is applied to the core (1).
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.
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).
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.
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.
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.
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)(NO3)3 solution (10.83 g/l) was added. Then a mixture of the following solutions was added to the suspension:
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.
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.
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.
Literature binding energies (eV):
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.
(A) PVD deposition:
(B) Chemical-reductive ruthenium deposition:
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.
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.
**) According to literature data (Table 1), between 282.2 eV and 282.6 eV RuO3 is located.
In the oxygen O1s spectra (
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 RuO2 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.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20176476.8 | May 2020 | EP | regional |
| 20189686.7 | Aug 2020 | EP | regional |
| 20195711.5 | Sep 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/064115 | 5/26/2021 | WO |
