Process for the preparation of porous sintered metal materials

FIELD OF THE INVENTION

The present invention relates to a process for the manufacture of porous metal- containing materials, the process comprising the steps of providing a composition comprising particles dispersed in at least one solvent, the particles comprising at least one polymer material and at least one metal-based compound; substantially removing the solvent from said composition; substantially decomposing the polymer material, thereby converting the solvent free particles into a porous metal- containing material. The inventive materials can be used as coatings or bulk materials for various purposes, particularly for coated medical implant devices. BACKGROUND OF THE INVENTION

Porous metal-based ceramic materials like cermets are typically used as components for friction-type bearings, filters, fumigating devices, energy absorbers or flame barriers. Constructional elements having hollow space profiles and increased stiffness are important in construction technology. Porous metal-based materials are becoming increasingly important in the field of coatings, and the functionalization of such materials with specific physical, electrical, magnetic and optical properties is of major interest. Furthermore, these materials can play an important role in applications such as photovoltaics, sensor technology, catalysis, and electro- chromatic display techniques.

Generally, there may be a need for porous metal-based materials having nano-crystalline fine structures, which allow for an adjustment of the electrical resistance, thermal expansion, heat capacity and conductivity, as well as superelastic properties, hardness, and mechanical strength.

Furthermore, there may be a need for porous metal-based materials which may be produced in a cost efficient manner. Conventional porous metal-based materials and cermets can be produced by powder- or melt- sintering methods, or by infiltration methods. Such methods can be technically and economically complex and costly, particularly since the control of the desired material properties can often depend on the size of the metal particles used. This parameter may not always be adjustable over an adequate range in certain applications like coatings, where process technology such as powder coating or tape casting may be used. According to

conventional methods, porous metals and metal-based materials may typically be made by the addition of additives or by foaming methods, which normally require the addition of pore- formers or blowing agents.

Also, there may be a need for porous metal-based materials, where the pore size, the pore distribution and the degree of porosity can be adjusted without deteriorating the physical and chemical properties of the material. Conventional methods based on fillers or blowing agents, for example, can provide porosity degrees of 20-50%. However, the mechanical properties such as hardness and strength may decrease rapidly with increasing degree of porosity. This may be particularly disadvantageous in biomedical applications such as implants, where anisotropic pore distribution, large pore sizes, and a high degree of porosity are required, together with long-term stability with respect to biomechanical stresses.

In the field of biomedical applications, it may be important to use biocompatible materials. For example, metal-based materials for use in drug delivery devices, which may be used for marking purposes or as absorbents for radiation, can preferably have a high degree of functionality and may combine significantly different properties in one material. In addition to specific magnetical, electrical, dielectrical or optical properties, the materials may have to provide a high degrees of porosity in suitable ranges of pore sizes. SUMMARY OF EXEMPLARY EMBODIMENTS OF THE INVENTION

It is one object of the present invention to provide, e.g., a material based on metallic precursors which can be modifiable in its properties and composition, which allows for the tailoring of the mechanical, thermal, electrical, magnetical and optical properties thereof. Another object of the present invention is to provide, e.g., porous metal- containing materials at relatively low temperatures, wherein the porosity of the formed material can be reproducibly varied for use in a large range of application fields, without adversely affecting the physical and chemical stability.

A further object of the present invention is to provide, e.g., a porous material and a process for the production thereof which may be used as a coating as well as a bulk material.

Still another object of the present invention is to provide, e.g., a material obtainable by a process such as those described herein, which may be in the form of a coating or in the form of a porous bulk material.

A still further object of the present invention is to provide, e.g., a porous sintered metal-based material, obtainable by the processes as described herein, which may have bioerodible or biodegradable properties, and/or may be at least partially dissolvable in the presence of physiologic fluids.

Yet a further object of the present invention is to provide, e.g., such porous metal- containing materials for use in the biomedical field, as implants, drug delivery devices, and/or coatings for implants and drug delivery devices.

For example, these and other objects of the invention can be achieved by one exemplary embodiment of the present invention which relates to a process for the manufacture of porous metal- containing materials, comprising the following steps: providing a composition comprising particles dispersed in at least one solvent, the particles comprising at least one polymer material and at least one metal-based compound; substantially removing the solvent from said composition; and substantially decomposing the polymer material, thereby converting the solvent free particles into a porous metal- containing material.

In a further exemplary embodiment of the process of the invention, the particles include at least one of polymer-encapsulated metal-based compounds, polymer particles being at least partially coated with the at least one metal-based compound, or any mixtures thereof, and may be produced in a solvent-based polymerization reaction.

In another exemplary embodiment of the present invention, the particles in the above mentioned process comprise at least one metal-based compound encapsulated in a polymer shell or capsule, and wherein the particles may be prepared as follows: providing an emulsion, suspension or dispersion of at least one polymerizable component in at least one solvent; adding the at least one metal-based compound into said emulsion, suspension or dispersion; polymerizing said at least

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one polymerizable component, thereby forming said polymer-encapsulated metal- based compounds.

In still another exemplary embodiment of the present invention, the particles in the above mentioned process comprise metal-based compound coated polymer particles, wherein the particles are prepared as follows: providing an emulsion, suspension or dispersion of at least one polymerizable component in at least one solvent; polymerizing said at least one polymerizable component, thereby forming an emulsion, suspension or dispersion of polymer particles; adding the at least one metal-based compound into said emulsion, suspension or dispersion, thereby forming polymer particles coated with said metal-based compound.

It has to be noted, that all aspects of the exemplary embodiments of the present invention described herein are combinable with each other as desired. DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE INVENTION According to one exemplary embodiment of a process of the present invention, metal-based compounds may be encapsulated in a polymer material. This can be accomplished, e.g., by typical, conventional solvent-based polymerization techniques. In a generally applicable, exemplary procedure, the particles comprising at least one metal-based compound encapsulated in a polymer shell or capsule, being dispersed in a solvent, can be prepared by providing an emulsion, suspension or dispersion of polymerizable monomers and/or oligomers and/or prepolymers in a solvent, adding at least one metal-based compound into said emulsion, suspension or dispersion, and polymerizing said monomers and/or oligomers and/or prepolymers, thereby forming polymer-encapsulated metal-based compounds. According to another exemplary embodiment of the present invention, particles of polymer material may be combined and/or at least partially coated with at least one metal- based compound. In a generally applicable procedure of certain exemplary embodiments of the present invention, polymer particles coated with metal-based compound may be prepared by providing an emulsion, suspension or dispersion of polymerizable components such as monomers and/or oligomers and/or

prepolymers in a solvent, polymerizing said monomers and/or oligomers and/or prepolymers, thereby forming an emulsion, suspension or dispersion of polymer particles, and adding the at least one metal-based compound into said emulsion, suspension or dispersion, thereby forming polymer particles being at least partially coated with said metal-based compound.

These exemplary embodiments may require essentially the same polymerization methods, and differ by the point of time at which the at least one metal-based compound is added to the reaction mixture. In a first exemplary embodiment, the metal-based compound is typically added before or during the polymerization step, whereas in a second exemplary embodiment, the addition is done after the polymer particles had already formed in the reaction mixture.

Surprisingly it has been found, that from metal-based compounds, particularly metal-based nanoparticles, porous sintered metals, alloys, oxides, hydroxides, ceramic materials and composite materials may be produced, and the porosity and pore sizes of the resulting material can be reproducibly and reliably adjusted over wide ranges, e.g., by appropriate selection of the polymers used and metal-based compounds, their structure, molecular weight, and the overall content of solids in the reaction mixture. Furthermore, it has been found that the mechanical, tribological, electrical and optical properties may be easily adjusted, e.g., by controlling the process conditions in the polymerization reaction, the solids content of the reaction mixtures and the kind and/or composition of the metal-based compounds. Metal-based compounds

For example, the metal-based compounds may be selected from zero-valent metals, metal alloys, metal oxides, inorganic metal salts, particularly salts from alkaline and/or alkaline earth metals and/or transition metals, preferably alkaline or alkaline earth metal carbonates, -sulphates, -sulfites, -nitrates, -nitrites, -phosphates, - phosphites, -halides, -sulfides, -oxides, as well as mixtures thereof; organic metal salts, particularly alkaline or alkaline earth and/or transition metal salts, in particular their formiates, acetates, propionates, malates, maleates, oxalates, tartrates, citrates,

benzoates, salicylates, phtalates, stearates, phenolates, sulfonates, and amines as well as mixtures thereof; organometallic compounds, metal alkoxides, semiconductive metal compounds, metal carbides, metal nitrides, metal oxynitrides, metal carbo- nitrides, metal oxycarbides, metal oxynitrides, and metal oxycarbonitrides, preferably of transition metals; metal-based core- shell nanoparticles, preferably with CdSe or CdTe as the core and CdS or ZnS as the shell material; metal- containing endohedral fullerenes and/or endometallofullerenes, preferably of rare earth metals like cerium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium; as well as any combinations of any of the foregoing. In certain exemplary embodiments, solders and/or brazing alloys are excluded from the metal-based compounds.

In further exemplary embodiments of the present invention, the metal-based compounds of the above mentioned materials may be provided in the form of nano- or microcrystalline particles, powders or nanowires. The metal-based compounds may have an average particle size of about 0.5 nm to 1.000 nm, preferably about 0.5 nm to 900 nm, or more preferably from about 0.7 nm to 800 nm.

The metal-based compounds to be encapsulated or coated on polymer particles can also be provided as mixtures of metal-based compounds, particularly nanoparticles thereof having different specifications, in accordance with the desired properties of the porous metal- containing material to be produced. The metal-based compounds may be used in the form of powders, in solutions in polar, non-polar or amphiphilic solvents, solvent mixtures or solvent- surfactant mixtures, in the form of sols, colloidal particles, dispersions, suspensions or emulsions.

Nanoparticles of the above-mentioned metal-based compounds may be easier to modify due to their high surface to volume ratio. The metal-based compounds, particularly nanoparticles, may for example be modified with hydrophilic ligands, e.g., with trioctylphosphine, in a covalent or non-covalent manner. Examples of ligands that may be covalently bonded to metal nanoparticles include fatty acids, thiol fatty acids, amino fatty acids, fatty acid alcohols, fatty acid ester groups of

mixtures thereof, for example oleic acid and oleylamine, and similar conventio nal organometallic ligands.

The metal-based compounds may be selected from metals or metal- containing compounds, for example hydrides, inorganic or organic salts, oxides and the like, as described above. Depending on the thermal treatment conditions and the process conditions used in the exemplary embodiments of the present invention, porous oxidic as well as zero- valet metals may be produced from the metal compounds used in combination with the polymer particles or capsules.

In certain exemplary embodiments of the present invention, metal-based compounds may include, but are not limited to powders, preferably nanomorphous nanoparticles, of zero- valent- metals, metal oxides or combinations thereof, e.g. metals and metal compounds including the main group of metals in the periodic table, transition metals such as copper, gold and silver, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, rhenium, iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium or platinum; or rare earth metals.

The metal-based compounds which may be used include, e.g., iron, cobalt, nickel, manganese or mixtures thereof, such as iron-platinum- mixtures. Magnetic metal oxides may also be used, such as iron oxides and ferrites. To provide materials having magnetic or signaling properties, magnetic metals or alloys may be used, such as ferrites, e.g. gamma- iron oxide, magnetite or ferrites of Co, Ni, or Mn. Examples of such materials are described in International Patent Publications WO83/03920, WO83/01738, WO85/02772, WO88/00060, WO89/03675, WO90/01295 and WO90/01899, and in U.S. Patent Nos. 4,452,773; 4,675,173; and 4,770,183. Additionally, semiconducting compounds and/or nanoparticles may be used in further exemplary embodiments of the present invention, including semiconductors of groups II- VI, groups III- V, or group IV of the periodic table. Suitable group II- VI- semiconductors include, for example, MgS, MgSe, MgTe, CaS, CaSe, CaTe, SrS, SrSe, SrTe, BaS, BaSe, BaTe, ZnS, ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe or mixtures thereof. Examples of group III- V

semiconductors include, for example, GaAs, GaN, GaP, GaSb, InGaAs, InP, InN, InSb, InAs, AlAs, AlP, AlSb, AlS, or mixtures thereof. Examples of group IV semiconductors include germanium, lead and silicon. Also, combinations of any of the foregoing semiconductors may be used. In certain exemplary embodiments of the present invention, it may be preferable to use complex metal-based nanoparticles as the metal-based compounds. These may include, for example, so-called core/shell configurations, which are described, e.g., in Peng et al., Epitaxial Growth of Highly Luminescent CdSe/CdS Core/Shell Nanoparticles with Photo stability and Electronic Accessibility, Journal of the American Chemical Society (1997, 119: 7019 - 7029).

Semiconducting nanoparticles may be selected from those materials listed above, and they may have a core with a diameter of about 1 to 30 nm, or preferably about 1 to 15 nm, upon which further semiconducting nanoparticles may be crystallized to a depth of about 1 to 50 monolayers, or preferably about 1 to 15 monolayers. Cores and shells may be present in nearly any combination of the materials as listed above, including CdSe or CdTe cores, and CdS or ZnS shells.

In a further exemplary embodiment of the present invention, the metal-based compounds may be selected based on their absorptive properties for radiation in a wavelength ranging anywhere from gamma radiation up to microwave radiation, or based on their abilitiy to emit radiation, particularly in the wavelength region of about 60 nm or less. By suitably selecting the metal-based compounds, materials having non- linear optical properties may be produced. These include, for example, materials that can block IR-radiation of specific wavelengths, which may be suitable for marking purposes or to form therapeutic radiation- absorbing implants. The metal-based compounds, their particle sizes and the diameter of their core and shell may be selected to provide photon emitting compounds, such that the emission is in the range of about 20 nm to 1000 nm. Alternatively, a mixture of suitable compounds may be selected which emits photons of differing wavelengths when exposed to radiation. In one exemplary embodiment of the present invention, fluorescent metal- based compounds may be selected that do not require quenching.

Metal-based compounds that may be used in further exemplary embodiments of the present invention include nanoparticles in the form of nanowires, which may comprise any metal, metal oxide, or mixtures thereof, and which may have diameters in the range of about 2 nm to 800 nm, or preferably about 5 nm to 600 nm. In further exemplary embodiments of the present invention, the metal-based compound may be selected from metallofullerenes or endohedral carbon nanoparticles comprising almost any kind of metal compound such as those mentioned above. Particularly preferred are endohederal fullerenes or endometallofullerenes, respectively, which may comprise rare earth metals such as cerium, neodynium, samarium, europium, gadolinium, terbium, dysprosium, holmium and the like. Endohedral metallofullerenes may also comprise transition metals as described above. Suitable endohedral fullerenes, e.g. those which may be used for marker purposes, are further described in U.S. Patent No. 5,688,486 and International Patent Publication WO 93/15768. Carbon-coated metal nanoparticles comprising, for example, carbides may be used as the metal-based compound. Also, metal- containing nanomorphous carbon species such as nano tubes, onions; as well as metal- containing soot, graphite, diamond particles, carbon black, carbon fibres and the like may also be used in other exemplary embodiments of the present invention. Metal-based compounds which may be used for biomedical applications include alkaline earth metal oxides or hydroxides, such as magnesium oxide, magnesium hydroxide, calcium oxide, or calcium hydroxide, or mixtures thereof. Polymer encapsulation

The metal-based compounds as described above may be encapsulated in a polymeric shell or capsule. The encapsulation of the metal-based compounds into polymers may be achieved by various conventional solvent polymerization techniques, e.g. dispersion-, suspension- or emulsion-polymerization. Preferred encapsulating polymers include, but are not limited to, polymethylmethacrylate (PMMA), polystyrol or other latex- forming polymers, polyvinyl acetate. These polymer capsules, which contain the metal-based compounds, can further be modified, for example by linking lattices and/or further encapsulation with polymers,

or they can be further coated with elastomers, metal oxides, metal salts or other suitable metal compounds, e.g. metal alkoxides. Conventional techniques may optionally be used to modify the polymers, and may be employed depending on the requirements of the individual compositions to be used. Without wishing to be bound to any particular theory, the applicants believe that the use of encapsulated metal-based compounds may prevent aggregation of the metals, and when applied into molds or onto substrates, the polymer shells provide a three-dimensional pattern of metal centers spaced apart from each other, by the polymer material, leading to a highly porous precursor structure which is at least partly preserved in the thermal decomposition step. Thus, after the polymer has completely decomposed, a porous sintered metal structure remains. The same concept applies for metal-coated polymer particles. This makes it possible to control the pore size and/or overall porosity of the resulting sintered metal materials mainly by controlling the size of the metal- containing polymer particles or capsules, which can easily be achieved by selecting suitable reaction conditions and parameters for the polymerization process.

It may be possible to adjust the porosity and pore sizes of the materials over a wide range to the desired values, depending on the intended use of the material. The process of the exemplary embodiments of the invention may allow for materials having a pore size in the micro-, meso- or macroporous range. Average pore sizes achievable with the processes described herein can be at least about 1 nm, preferably at least about 5 nm, more preferably at least about 10 nm or at least about 100 nm, or from about 1 nm to about 400 μm, preferably about 1 nm to 80 μm, more preferably about 1 nm to about 40 μm. In the macroporous region, pore sizes may range from about 500 nm to 400 μm, preferably from about 500 nm to about 80 μm, or from about 500 nm to about 40 μm, or from 500 nm to about 10 μm, wherein all the values above are combinable with each other, and the materials may have an average porosity of from about 30 % to about 80 %.

The encapsulation of the metal-based compounds can lead to covalently or non- covalently encapsulated metal-based compounds, depending on the individual

components used. The encapsulated metal-based compounds may be provided in the form of polymer spheres, particularly micro spheres, or in the form of dispersed, suspended or emulgated particles or capsules. Conventional methods suitable for providing or manufacturing encapsulated metal-based compounds or polymer particles, dispersions, suspensions or emulsions, particularly preferred mini- emulsions, thereof can be utilized.

Conventional methods suitable for providing or manufacturing encapsulated metal-based compounds, dispersions, suspensions or emulsions, particularly preferred mini- emulsions, thereof can be utilize. Suitable encapsulation methods are described, for example, in Australian publication AU 9169501, European Patent Publications EP 1205492, EP 1401878, EP 1352915 and EP 1240215, U.S. Patent No. 6380281, U.S. Patent Publication 2004192838, Canadian Patent Publication CA 1336218, Chinese Patent Publication CN 1262692T, British Patent Publication GB 949722, and German Patent Publication DE 10037656; and in S. Kirsch, K. Landfester, O. Shaffer and M. S. El-Aasser, "Particle morphology of carboxylated poly-(n-butyl acrylate)/(poly(methyl methacrylate) composite latex particles investigated by TEM and NMR," Acta Polymerica 1999, 50, 347-362; K. Landfester, N. Bechthold, S. Fδrster and M. Antonietti, "Evidence for the preservation of the particle identity in miniemulsion polymerization," Macromol. Rapid Commun. 1999, 20, 81-84; K. Landfester, N. Bechthold, F. Tiarks and M. Antonietti, "Miniemulsion polymerization with cationic and nonionic surfactants: A very efficient use of surfactants for heterophase polymerization" Macromolecules 1999, 32, 2679-2683; K. Landfester, N. Bechthold, F. Tiarks and M. Antonietti, "Formulation and stability mechanisms of polymerizable miniemulsions," Macromolecules 1999, 32, 5222- 5228; G. Baskar, K. Landfester and M. Antonietti, "Comb- like polymers with octadecyl side chain and carboxyl functional sites: Scope for efficient use in miniemulsion polymerization," Macromolecules 2000, 33, 9228-9232; N. Bechthold, F. Tiarks, M. Willert, K. Landfester and M. Antonietti, "Miniemulsion polymerization: Applications and new materials" Macromol. Svmp. 2000, 151, 549- 555; N. Bechthold and K. Landfester: "Kinetics of miniemulsion polymerization as

revealed by calorimetry," Macromolecules 2000, 33, 4682-4689; B. M. Budhlall, K. Landfester, D. Nagy, E. D. Sudol, V. L. Dimonie, D. Sagl, A. Klein and M. S. El- Aasser, "Characterization of partially hydrolyzed polyvinyl alcohol). I. Sequence distribution via H-I and C-13-NMR and a reversed- phased gradient elution HPLC technique," Macromol. Symp. 2000, 155, 63-84; D. Columbie, K. Landfester, E. D. Sudol and M. S. El- Aasser, "Competitive adsorption of the anionic surfactant Triton X-405 on PS latex particles," Langmuir 2000, 16, 7905-7913; S. Kirsch, A. Pfau, K. Landfester, O. Shaffer and M. S. El- Aasser, "Particle morphology of carboxylated poly-(n-butyl acrylate)/poly(methyl methacrylate) composite latex particles," Macromol. Symp. 2000, 151, 413-418; K. Landfester, F. Tiarks, H.-P. Hentze and M. Antonietti, "Polyaddition in miniemulsions: A new route to polymer dispersions," Macromol. Chem. Phys. 2000, 201, 1-5; K. Landfester, "Recent developments in miniemulsions - Formation and stability mechanisms," Macromol. Svmp. 2000, 150, 171-178; K. Landfester, M. Willert and M. Antonietti, "Preparation of polymer particles in non-aqueous direct and inverse miniemulsions," Macromolecules 2000, 33, 2370-2376; K. Landfester and M. Antonietti, "The polymerization of acrylonitrile in miniemulsions: 'Crumpled latex particles' or polymer nanocrystals," Macromol. Rapid Comm. 2000, 21, 820-824; B. z. Putlitz, K. Landfester, S. Fδrster and M. Antonietti, "Vesicle forming, single tail hydrocarbon surfactants with sulfonium- headgroup," Langmuir 2000, 16, 3003-3005; B. z. Putlitz, H.-P. Hentze, K.

Landfester and M. Antonietti, "New cationic surfactants with sulfonium- headgroup," Langmuir 2000, 16, 3214-3220; J. Rottstegge, K. Landfester, M. Wilhelm, C. Heldmann and H. W. Spiess, "Different types of water in film formation process of latex dispersions as detected by solid-state nuclear magnetic resonance spectroscopy," Colloid Polym. Sci. 2000, 278, 236-244; K. Landfester and H.-P. Hentze, "Heterophase polymerization in inverse systems," in Reactions and Synthesis in Surfactant Systems, J. Texter, ed.; Marcel Dekker, Inc., New York, 2001, pp 471-499; K. Landfester, "Polyreactions in miniemulsions," Macromol. Rapid Comm. 2001, 896-936; K. Landfester, "The generation of nanoparticles in miniemulsion," Adv. Mater. 2001, 10, 765-768; B. z. Putlitz, K. Landfester, H.

Fischer and M. Antonietti, "The generation of 'armored latexes' and hollow inorganic shells made of clay sheets by templating cationic miniemulsions and latexes," Adv. Mater. 2001, 13, 500-503; F. Tiarks, K. Landfester and M. Antonietti, "Preparation of polymeric nanocapsules by miniemulsion polymerization," Langmuir 2001, 17, 908-917; F. Tiarks, K. Landfester and M. Antonietti, "Encapsulation of carbon black by miniemulsion polymerization," Macromol. Chem. Phys. 2001, 202, 51-60; F. Tiarks, K. Landfester and M. Antonietti, "One- step preparation of polyurethane dispersions by miniemulsion polyaddition," J. Polym. ScL, Polym. Chem. Ed. 2001, 39, 2520-2524; F. Tiarks, K. Landfester and M. Antonietti, "Silica nanoparticles as surfactants and fillers for latexes made by miniemulsion polymerization," Langmuir 2001, 17, 5775-5780.

These polymerization methods may be principally used with all of the exemplary embodiments of the present invention, the major difference will be the time point at which the metal-based compounds are added to the polymerization mixture, before, during or after the polymerization reaction.

The encapsulated metal-based compounds may be produced in a size of about 1 nm to 500 nm, or in the form of microparticles having sizes from about 5 nm to 5 μm. Metal-based compounds may be further encapsulated in mini- or micro- emulsions of suitable polymers. The term mini- or micro- emulsion can be understood as dispersions comprising an aqueous phase, an oil phase, and surface active substances. Such emulsions may comprise suitable oils, water, one or several surfactants, optionally one or several co- surfactants, and one or several hydrophobic substances. Mini- emulsions may comprise aqueous emulsions of monomers, oligomers or other pre-polymeric reactants stabilised by surfactants, which may be easily polymerized, and wherein the particle size of the emulgated droplets is between about 10 nm to 500 nm or larger.

In such reactions, the particle size may be controlled, e.g., by the kind and/or amount of surfactant added to the monomer mixture. Normally it is observed, that the lower the surfactant concentration, the larger the particle size of the polymer particles or capsules. The amount of surfactant used in the polymerization reaction can

therefore be a suitable parameter for adjusting the pore size and/or overall porosity of the resulting porous metal- containing material.

Furthermore, mini- emulsions of encapsulated metal-based compounds can be made from non- aqueous media, for example, formamide, glycol, or non-polar solvents. In principle, pre-polymeric reactants may be selected from thermosets, thermoplastics, plastics, synthetic rubbers, extrudable polymers, injection molding polymers, moldable polymers, and the like or mixtures thereof, including pre- polymeric reactants from which poly(meth)acrylics can be used.

Examples of suitable polymers for encapsulating the metal-based compounds or for being coated with metal-based compounds include, but are not limited to, homopolymers or copolymers of aliphatic or aromatic polyolefins such as polyethylene, polypropylene, polybutene, polyisobutene, polypentene; polybutadiene; polyvinyls such as polyvinyl chloride or polyvinyl alcohol, poly(meth)acrylic acid, polymethylmethacrylate (PMMA), polyacrylocyano aery late; polyacrylonitril, polyamide, polyester, polyurethane, polystyrene, polytetrafluoroethylene; bio- polymers such as collagen, albumin, gelatine, hyaluronic acid, starch, celluloses such as methylcellulose, hydroxypropyl cellulose, hydroxypropyl methylcellulose, carboxymethylcellulose phthalate; casein, dextranes, polysaccharides, fibrinogen, poly(D,L-lactides), poly(D,L-lactide coglycolides), polyglycolides, polyhydroxy- butylates, polyalkyl carbonates, polyorthoesters, polyesters, polyhydroxyvaleric acid, polydioxanones, polyethylene terephthalates, polymaleate acid, polytartronic acid, polyanhydrides, polyphosphazenes, polyamino acids; polyethylene vinyl acetate, silicones; poly(ester urethanes), poly(ether urethanes), poly(ester ureas), polyethers such as polyethylene oxide, polypropylene oxide, pluronics, polytetramethylene glycol; polyvinylpyrrolidone, poly(vinyl acetate phthalate), shellac, and combinations of these homopolymers or copolymers. In certain exemplary embodiments of the present invention, polyurethanes are excluded as the polymer material, i.e. the polymer material does not include polyurethane materials, and their monomers, oligomers or prepolymers

Further encapsulating materials that may be used can include poly(meth)- acrylate, unsaturated polyester, saturated polyester, polyolefines such as polyethylene, polypropylene, polybutylene, alkyd resins, epoxy-polymers or resins, polyamide, polyimide, polyetherimide, polyamideimide, polyesterimide, polyester- amideimide, polyurethane, polycarbonate, polystyrene, polyphenole, polyvinylester, polysilicone, polyacetale, cellulosic acetate, polyvinylchloride, polyvinylacetate, polyvinylalcohol, polysulfone, polyphenylsulfone, polyethersulfone, polyketone, polyetherketone, polybenzimidazole, polybenzoxazole, polybenzthiazole, polyfluoro- carbons, polyphenylenether, polyarylate, cyanatoester-polymere, and mixtures or copolymers of any of the foregoing are preferred.

In certain exemplary embodiments of the present invention, the polymers for encapsulating the metal-based compounds may include at least one of mono(meth)- acrylate-, di(meth)acrylate-, tri(meth)acrylate-, terra- acrylate and pentaacrylate- based poly(meth)acrylates. Examples of suitable mono(meth)acrylates include hydroxy- ethyl acrylate, hydroxy ethyl methacrylate, hydroxypropyl methacrylate, hydroxy- propyl acrylate, 3-chloro-2-hydroxypropyl acrylate, 3 -chloro- 2- hydroxypropyl methacrylate, 2,2-dimethylhydroxypropyl acrylate, 5-hydroxypentyl acrylate, diethylene glycol monoacrylate, trimethylolpropane monoacrylate, pentaerythritol monoacrylate, 2,2- dimethyl- 3-hydroxypropyl acrylate, 5-hydroxypentyl meth- acrylate, diethylene glycol monomethacrylate, trimethylolpropane monometh- acrylate, pentaerythritol monomethacrylate, hydroxy- methylated N- (1,1 -dimethyl- 3- oxobutyl)acrylamide, N- methylolacrylamide, N- methylolmethacrylamide, N-ethyl- N- methylolmethacrylamide, N- ethyl- N- methylolacrylamide , N,N- dimethylol- acrylamide, N-ethanolacrylamide, N-propanolacrylamide, N- methylolacrylamide, glycidyl acrylate, and glycidyl methacrylate, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, ethylhexyl acrylate, octyl acrylate, t-octyl acrylate, 2-methoxyethyl acrylate, 2-butoxyethyl acrylate, 2-phenoxy ethyl acrylate, chloroethyl acrylate, cyanoethyl acrylate, dimethylaminoethyl acrylate, benzyl acrylate, methoxybenzyl acrylate, furfuryl acrylate, tetrahydrofurfuryl acrylate and phenyl acrylate; di(meth)acrylates may be selected from 2,2-bis(4- methacryloxy-

phenyl)propane, 1,2-butanediol-diacrylate, 1,4-butanediol-diacrylate, 1,4-butanediol- dimethacrylate, 1 ,4- cyclohexanediol- dimethacrylate, 1,10- decanediol- dimeth- acrylate, diethyleneglycol-diacrylate, dipropyleneglycol-diacrylate, dimethyl- propanediol- dimethacrylate, trie thy leneglycol- dimethacrylate, tetraethyleneglycol- dimethacrylate, 1,6-hexanediol-diacrylate, Neopentylglycol-diacrylate, polyethylene - glycol- dimethacrylate, tripropyleneglycol- diacrylate, 2,2-bis[4- (2- acryloxyethoxy) - phenyl]propane, 2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane, bis(2- methacryloxyethyl)N,N- 1 ,9-nonylene-biscarbamate, 1 ,4-cyclohexane- dimethanol- dimethacrylate, and diacrylic urethane oligomers; tri(meth)acrylates may include tris(2-hydroxyethyl)isocyanurate-trimethacrylate, tris(2-hydroxy-ethyl)- isocyanurate- triacrylate, trimethylolpropane - trimethacrylate, trimethylo 1- propane - triacrylate or pentaerythritol- triacrylate; tetra(meth)acrylates may include pentaerythritol-tetraacrylate, di-trimethylopropan- tetraacrylate, or ethoxylated pentaerythritol- tetraacrylate; suitable penta(meth)acrylates may be selected from dipentaerythritol-pentaacrylate or pentaacry late- esters; and copolymers thereof.

In medical applications, biopolymers or acrylics may be preferably selected as polymers for encapsulating or for carrying the metal-based compounds.

Encapsulating polymer reactants may be selected from polymerizable monomers, oligomers or elastomers such as polybutadiene, polyisobutylene, polyisoprene, poly(styrene-butadiene-styrene), polyurethanes, polychloroprene, or silicone, and mixtures, copolymers and combinations of any of the foregoing. The metal-based compounds may be encapsulated in elastomeric polymers solely or in mixtures of thermoplastic and elastomeric polymers or in a sequence of shells/layers alternating between thermoplastic and elastomeric polymer shells. The polymerization reaction for encapsulating the metal-based compounds may be any suitable conventional polymerization reaction, for example, a radical or non- radical polymerization, enzymatic or non-enzymatic polymerization, including a poly- condensation reaction. The emulsions, dispersions or suspensions used may be in the form of aqueous, non- aqueous, polar or non-polar systems. By adding suitable surfactants, the amount and size of the emulated or dispersed droplets can be

adjusted as required. The surfactants may be anionic, cationic, zwitterionic or non- ionic surfactants or any combinations thereof. Preferred anionic surfactants may include, but are not limited to soaps, alkylbenzolsulphonates, alkansulphonates like e.g. sodium dodecylsulphonate (SDS) and the like, olefinsulphonates, alkyether- sulphonates, glycerinethersulphonates, a-methylestersulphonates, sulphonated fatty acids, alkylsulphates, fatty alcohol ether sulphates, glycerine ether sulphates, fatty acid ether sulphates, hydroxyl mixed ether sulphates, monoglyceride(ether) sulphates, fatty acid amide(ether)sulphates, mono- and di-alkylsulfosuccinates, mono- and dialkylsulfosuccinamates, sulfotriglycerides, amidsoaps, ethercarboxylicacid and their salts, fatty acid isothionates, fatty acid arcosinates, fatty acid taurides, N-acyl- aminoacids such as acyllactylates, acyltartrates, acylglutamates and acylaspartates, alkyoligoglucosidsulfates, protein fatty acid condensates, including plant derived products based on wheat; and alky(ether)phosphates.

Cationic surfactants suitable for encapsulation reactions in certain exemplary embodiments of the present invention may be selected from the group of quaternary ammonium compounds such as dimethyldistearylammoniumchloride, Stepantex ^® VL 90 (Stepan), esterquats, particularly quaternised fatty acid trialkanolaminester salts, salts of long-chain primary amines, quaternary ammonium compounds like hexadecyltrimethylammoniumchloride (CTMA-Cl), Dehy quart ^® A (cetrimonium- chloride, Cognis), or Dehy quart ^® LDB 50 (lauryldime thy lbenzylammonium chloride, Cognis). Preferably, cationic surfactants are, however, avoided in certain exemplary embodiments of the present invention.

The metal-based compounds, which may be in the form of a metal-based sol, can be added before or during the start of the polymerization reaction, and may be provided as a dispersion, emulsion, suspension or solid solution, or solution of the metal-based compounds in a suitable solvent or solvent mixture, or any mixtures thereof. The encapsulation process can require the polymerization reaction, optionally with the use of initiators, starters or catalysts, wherein an in- situ encapsulation of the metal-based compounds in the polymer produced by the polymerization in polymer capsules, spheroids or droplets is provided. The solids

content of the metal-based compounds in such encapsulation mixtures may be selected such that the solids content in the polymer capsules, spheroids or droplets can be about 10 weight% to 80 weight% of metal-based compound within the polymer particles. Optionally, the metal-based precursor compounds may also be added after completion of the polymerization reaction, either in solid form or in a liquid form. In such an instance, the metal-based compounds are bonded to or coated onto the polymer particles and cover the surface thereof at least partially, typically by stirring the metal-based compounds into the liquid polymer particle dispersion, which results in a binding to the polymer particles, spheroids or droplets covalently or non- covalently, or simply a physical adsorption to the polymer particles. The droplet size of the polymers and/or the solids content of metal-based compounds may be selected such that the solid content of the metal-based compounds is in the range of about 5 weight- % to 60 weight- %. In an exemplary embodiment of the present invention, the in- situ encapsulation of the metal-based compounds during the polymerization may be repeated by addition of further monomers, oligomers or pre-polymeric agents after completion of the first polymerization/encapsulation step. By providing at least one similar repeated step, like this multilayer- coated polymer capsules may be produced. Also, metal-based compounds bound or coated to polymer spheroids or droplets may be encapsulated by subsequently adding monomers, oligomers or pre-polymeric reactants to overcoat the metal-based compounds with a polymer capsule. Repetition of such process steps can provide multilayered polymer capsules comprising the metal-based compound. Any of these encapsulation steps may be combined with each other. In a further exemplary embodiment of the present invention, polymer encapsulated metal- based compounds may be further encapsulated with elastomeric compounds, so that polymer capsules having an outer elastomer shell may be produced.

In further exemplary embodiments of the present invention, polymer encapsulated metal-based compounds may be further encapsulate in vesicles,

liposomes or micelles, or overcoatings. Suitable surfactants for this purpose may include the surfactants described above, and compounds having hydrophobic groups which may include hydrocarbon residues or silicon residues, for example, polysiloxane chains, hydrocarbon based monomers, oligomers and polymers, or lipids or phosphorlipids, or any combinations thereof, particularly glycerylester such as phosphatidyl-ethanolamine, phosphatidylcholine, polyglycolide, polylactide, polymethacrylate, polyvinylbuthylether, polystyrene, polycyclopentadienylmethyl- norbornene, polypropylene, polyethylene, polyisobutylene, polysiloxane, or any other type of surfactant. Furthermore, depending on the polymeric shell, surfactants for encapsulating the polymer encapsulated metal-based compounds in vesicles, overcoats and the like may be selected from hydrophilic surfactants or surfactants having hydrophilic residues or hydrophilic polymers such as polystyrensulfonicacid, poly-N-alkylvinyl- pyridiniumhalogenide, poly(meth)acrylic acid, polyaminoacids, poly-N-vinyl- pyrrolidone, polyhydroxyethylmethacrylate, polyvinylether, polyethylenglycol, polypropylenoxide, polysaccharides such as agarose, dextrane, starch, cellulose, amylase, amylopektine or polyethylenglycole, or polyethylennimine of a suitable molecular weight. Also, mixtures from hydrophobic or hydrophilic polymer materials or lipid polymer compounds may be used for encapsulating the polymer capsulated metal-based compounds in vesicles or for further over-coating the polymer encapsulating metal-based compounds.

The incorporation of polymer- encapsulated metal-based compounds into the materials produced in accordance with exemplary embodiments of the present invention can be regarded as a specific form of a filler. The particle size and particle size distribution of the polymer-encapsulated metal-based compounds in dispersed or suspended form may correspond to the particle size and particle size distribution of the particles of finished polymer- encapsulated metal-based compounds, and they can have a significant influence on the pore sizes of the material produced. The polymer- encapsulated metal-based compounds can be characterized by dynamic light scattering methods to determine their average particle size and monodispersity.

Additives

With the use of additives in the inventive materials, it is possible to further vary and adjust the mechanical, optical and thermal properties of the resultant material. The use of such additives may be which is particularly suitable for producing tailor-made coatings having desired properties. Therefore, in certain exemplary embodiments of the present invention, further additives may be added to the polymerization mixture or the dispersion of polymer particles, which do not react with the components thereof.

Examples of suitable additives include fillers, pore- forming agents, metals and metal powders, and the like. Examples of inorganic additives and fillers can include silicon oxides and aluminum oxides, aluminosilicates, zeolites, zirconium oxides, titanium oxides, talc, graphite, carbon black, fullerenes, clay materials, phyllosilicates, suicides, nitrides, metal powders, in particular those of catalytically active transition metals such as copper, gold, silver, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, manganese, rhenium, iron, cobalt, nickel, ruthenium, rhodium, palladium, osmium, iridium or platinum.

Further suitable additives can include crosslinkers, plasticizers, lubricants, flame resistants, glass or glass fibers, carbon fibers, cotton, fabrics, metal powders, metal compounds, silicon, silicon oxides, zeolites, titan oxides, zirconium oxides, aluminium oxides, aluminium silicates, talcum, graphite, soot, phyllosilicates and the like.

Fillers can be used to modify the size and the degree of porosity. In some certain exemplary embodiments of the present invention, non-polymeric fillers may be preferred. Non-polymeric fillers can be any substance which can be removed or degraded, for example, by thermal treatment or other conditions, without adversely affecting the material properties. Some fillers might be resolved in a suitable solvent and can be removed in this manner from the material. Furthermore, non-polymeric fillers, which can be converted into soluble substances under chosen thermal conditions, can also be used. These non-polymeric fillers may comprise, for

example, anionic, cationic or non- ionic surfactants, which can be removed or degraded under thermal conditions.

In another exemplary embodiment of the present invention, the fillers may comprise inorganic metal salts, particularly salts from alkaline and/or alkaline earth metals, including alkaline or alkaline earth metal carbonates, sulfates, sulfites, nitrates, nitrites, phosphates, phosphites, halides, sulfides, oxides, or mixtures thereof. Other suitable fillers include organic metal salts, e.g., alkaline or alkaline earth and/or transition metal salts, including formiates, acetates, propionates, malates, maleates, oxalates, tartrates, citrates, benzoates, salicylates, phtalates, stearates, phenolates, sulfonates, or amines, as well as mixtures thereof.

In yet another exemplary embodiment of the present invention, polymeric fillers may be applied. Suitable polymeric fillers can be those as mentioned above as encapsulation polymers, particularly those having the form of spheres or capsules. Saturated, linear or branched aliphatic hydrocarbons may also be used, and they may be homo- or copolymers. Polyolefins such as polyethylene, polypropylene, polybutene, polyisobutene, polypentene as well as copolymers thereof and mixtures thereof may be preferably used. Polymeric fillers may also comprise polymer particles formed of methacrylates or polystearine, as well as electrically conducting polymers such as polyacetylenes, polyanilines, poly(ethylenedioxythiophenes), polydialkylfluorenes, polythiophenes or polypyrroles, which may be used to provide electrically conductive materials.

In some or many of the above-mentioned procedures, the use of soluble fillers can be combined with addition of polymeric fillers, wherein the fillers may be volatile under thermal processing conditions or may be converted into volatile compounds during thermal treatment. In this way the pores formed by the polymeric fillers can be combined with the pores formed by the other fillers to achieve an isotropic or anisotropic pore distribution. Suitable particle sizes of the non- polymeric fillers can be determined based on the desired porosity and/or size of the pores of the resulting composite material.

Solvents that can be used for the removal of the fillers after thermal treatment of the material may include, for example, (hot) water, diluted or concentrated inorganic or organic acids, bases, and the like. Suitable inorganic acids can include, for example, hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, as well as diluted hydrofluoric acid. Suitable bases can include, for example, sodium hydroxide, ammonia, carbonate, as well as organic amines. Suitable organic acids can include, for example, formic acid, acetic acid, trichloromethane acid, trifluoromethane acid, citric acid, tartaric acid, oxalic acid, and mixtures thereof. In certain exemplary embodiments of the present invention, coatings of the inventive composite materials may be applied as a liquid solution or dispersion or suspension of the combination in a suitable solvent or solvent mixture, with subsequent drying or evaporation of the solvent. Suitable solvents may comprise, for example, methanol, ethanol, N-propanol, isopropanol, butoxydiglycol, butoxyethano 1, butoxyisopropanol, butoxypropanol, n-butyl alcohol, t-butyl alcohol, butylene glycol, butyl octanol, diethylene glycol, dimethoxydiglycol, dimethyl ether, dipropylene glycol, ethoxydiglycol, ethoxyethanol, ethyl hexane diol, glycol, hexane diol, 1,2,6-hexane triol, hexyl alcohol, hexylene glycol, isobutoxy propanol, isopentyl diol, 3-methoxybutanol, methoxydiglycol, methoxyethanol, methoxy- isopropanol, methoxymethylbutanol, methoxy PEG- 10, methylal, methyl hexyl ether, methyl propane diol, neopentyl glycol, PEG-4, PEG-6, PEG-7, PEG-8, PEG-9, PEG- 6- methyl ether, pentylene glycol, PPG- 7, PPG-2-buteth-3, PPG- 2 butyl ether, PPG- 3 butyl ether, PPG- 2 methyl ether, PPG- 3 methyl ether, PPG- 2 propyl ether, propane diol, propylene glycol, propylene glycol butyl ether, propylene glycol propyl ether, tetrahydrofurane, trimethyl hexanol, phenol, benzene, toluene, xylene; as well as water, any of which may be mixed with dispersants, surfactants, or other additives, and mixtures of the above-named substances.

Any of the above-mentioned solvents can also be used in the polymerization mixtures. Solvents may also comprise one or several organic solvents such as ethanol, isopropanol, n-propanol, dipropylene glycol methyl ether and butoxyisopropanol (1,2- propylene glycol-n-butyl ether), tetrahydrofurane, phenol,

methylethylketone, benzene, toluene, xylene, preferably ethanol, isopropanol, n-propanol and/or dipropylene glycol methyl ether, wherein isopropanol and/or n-propanol may be preferably selected, and water.

The fillers can be partly or completely removed from the resultant material, depending on the nature and time of treatment with the solvent. A complete removal of the filler may be preferable in certain embodiments of the present invention. Thermal decomposition of polymer

The polymer- encapsulated metal-based compounds or metal-coated polymer particles formed by the process according to exemplary embodiments of the invention can be converted into a solid porous metal- containing material, e.g., by means of a thermal treatment.

It may be preferred that the solvent is removed before a thermal treatment. This can be most conveniently achieved by drying the polymer particles, e.g. by filtration or thermal treatment. In exemplary embodiments of the present invention, this drying step itself may be a thermal treatment of metal- containing polymer particles, in the range of about -200 ⁰ C to 300 ⁰ C, or preferably in the range of about -100 ⁰ C to 200 ⁰ C, or more preferably in the range of about -5O ⁰ C to 15O ⁰ C, or about O ⁰ C to 100 ⁰ C, or yet even more preferably about 5O ⁰ C to 8O ⁰ C; or simply by an evaporation of the solvents at approximately room temperature. Drying may also be performed by spray drying, freeze drying, filtration, or similar conventional methods.

A suitable decomposition treatment may involve a thermal treatment at elevated temperatures, typically from about 20 ⁰ C to about 4000 ⁰ C, or preferably from about 100 ⁰ C to about 3500 ⁰ C, or more preferred from about 100 ⁰ C to about 2000 ⁰ C, and even more preferred from about 150 ⁰ C to about 500 ⁰ C, optionally under reduced pressure or vacuum, or in the presence of inert or reactive gases.

A thermal treatment step can be further performed under various conditions, e.g., in different atmospheres, for example inert atmospheres such as in nitrogen, SF ₆ , or noble gases such as argon, or any mixtures thereof, or it may be performed in an oxidizing atmosphere like oxygen, carbon monoxide, carbon dioxide, or nitrogen

oxide, or any mixtures thereof. Furthermore, an inert atmosphere may be blended with reactive gases, e.g., air, oxygen, hydrogen, ammonia, C ₁ -C ₆ saturated aliphatic hydrocarbons such as methane, ethane, propane and butene, mixtures thereof, or other oxidizing gases. In certain exemplary embodiments of the present invention, the atmosphere during thermal treatment is substantially free of oxygen. The oxygen content may be preferably below about 10 ppm, or more preferably below about 1 ppm. In certain exemplary embodimentsof the present invention, a thermal treatment can be performed by laser applications, e.g. by selective laser sintering (SLS). The porous sintered material obtained by a thermal treatment can be further treated with suitable oxidizing and/or reducing agents, including treatment of the material at elevated temperatures in oxidizing atmospheres. Examples of oxidizing atmospheres include air, oxygen, carbon monoxide, carbon dioxide, nitrogen oxides, or similar oxidizing agents. The gaseous oxidizing agent can also be mixed with inert gases such as nitrogen, or noble gases such as argon. Partial oxidation of the resultant materials can be accomplished at elevated temperatures in the range of about 5O ⁰ C to 800 ⁰ C, in order to further modify the porosity, pore sizes and/or surface properties. Besides partial oxidation of the material with gaseous oxidizing agents, liquid oxidizing agents can also be applied. Liquid oxidizing agents can include, for example, concentrated nitric acid. Concentrated nitric acid can contact the material at temperatures above room temperature. Suitable reducing agents such as hydrogen gas or the like may be used to reduce metal compounds to the zero- valent metal after the conversion step.

In further exemplary embodiments of the present invention, high pressure may be applied to form the resultant material. In exemplary embodiments of the present invention, suitable conditions such as temperature, atmosphere and/or pressure, depending on the desired property of the final material, and the polymers used in the inventive process may be selected, to ensure a substantially complete decomposition and removal of any polymer residues from the porous sintered metal- containing materials.

By oxidative and/or reductive treatment or by the incorporation of additives, fillers or functional materials, the properties of the resultant materials produced can be influenced and/or modified in a controlled manner. For example, it is possible to render the surface properties of the resultant composite material hydrophilic or hydrophobic by incorporating inorganic nanoparticles or nanocomposites such as layer silicates.

Coatings or bulk materials from the materials obtained by a process according to exemplary embodiments of this invention may be structured in a suitable way by folding, embossing, punching, pressing, extruding, gathering, injection molding and the like, either before or after being applied to a substrate or being molded or formed. In this way, certain structures of a regular or irregular type can be incorporated into the coatings produced with the material.

Coatings of the resultant materials may be applied in liquid, pulpy or pasty form, before a decomposition treatment, for example, by painting, furnishing, phase- inversion, dispersing atomizing or melt coating, extruding, slip casting, dipping, or may be applied as a hot melt, followed by the thermal treatment to decompose the polymer.

Dipping, spraying, spin coating, ink-jet- printing, tampon and micro drop coating or 3-D- printing and similar conventional methods can be used. A coating of the polymeric materials before the thermal decomposition can be applied to an inert substrate, subsequently dried and then thermally treated, where the substrate is sufficiently thermally stable.

Furthermore, the materials can be processed by any conventional technique such as folding, stamping, punching, printing, extruding, die casting, injection molding, reaping and the like.

Depending on the temperature and the atmosphere chosen for the thermal treatment, and/or depending on the specific composition of the components used, porous metal- containing materials can be obtained,, e.g., in the form of coatings, e.g. on medical implant devices, or bulk materials, or also in the form of substantially pure metal-based materials, e.g. mixed metal oxides, wherein the structures of the

materials can be in the range from amorphous to crystalline. Porosity and pore sizes may be varied over a wide range, e.g., simply by varying the particle size of the encapsulated metal-based compounds.

Furthermore, by suitable selection of the components and processing conditions, the production of bioerodible or biodegradable coatings, or coatings and materials which are dissolvable or may be peeled off from substrates in the presence of physiologic fluids can be produced, which makes the materials particularly suitable for the production of medical implant devices or coatings on such devices. For example, coatings comprising the resultant materials may be used for coronary implants such as stents, wherein the coating further comprises an encapsulated marker, e.g., a metal compound having signaling properties, and thus may produce signals detectable by physical, chemical or biological detection methods such as x- ray, nuclear magnetic resonance (NMR), computer tomography methods, scintigraphy, single-photon-emission computed tomography (SPECT), ultrasonic, radiofrequency (RF), and the like. Metal compounds used as markers may be encapsulated in a polymer shell or coated thereon and thus cannot interfere with the implant material, which can also be a metal, where such interference can often lead to electrocorrosion or related problems. Coated implants may be produced with encapsulated markers, wherein the coating remains permanently on the implant. In one exemplary embodiment of the present invention, the coating may be rapidly dissolved or peeled off from a stent after implantation under physiologic conditions, allowing a transient marking to occur.

Magnesium-based materials as exemplified in the examples described hereinbelow can be one example for dissolvable materials under physiological conditions, and they may further be loaded with markers and/or therapeutically active ingredients.

If therapeutically active metal-based compounds are used in forming the resultant materials or loaded onto these materials, they may preferably be encapsulated in bioerodible or resorbable porous sintered metal- containing matrices, allowing for a controlled release of the active ingredient under physiological

conditions. Production of coatings or materials which, due to their tailor- made porosity, may be infiltrated with therapeutically active agents, which can be resolved or extracted in the presence of physiologic fluids can also be achieved. This allows for the production of medical implants providing, e.g., for a controlled release of active agents. Examples include, without excluding others, drug eluting stents, drug delivery implants, or drug eluting orthopaedic implants and the like.

Also, the production of optionally coated porous bone and tissue grafts (erodible and non-erodible), optionally coated porous implants and joint implants as well as porous traumatologic devices like nails, screws or plates, optionally with enhanced engraftment properties and therapeutic functionality, with excitable radiation properties for the local radiation therapy of tissues and organs, can be achieved.

Furthermore, the resultant materials may be used, e.g., in non- medical applications, including the production of sensors with porous texture for venting of fluids; porous membranes and filters for nano- filtration, ultrafiltration or microfiltration, as well as mass separation of gases. Porous metal- coatings with controlled reflection and refraction properties may also be produced from the resultant materials.

The invention will now be further described by way of the following non- limiting examples. Analyses and parameter determination in these examples were performed by the following methods:

Particle sizes are provided as mean particle sizes, as determined on a CIS Particle Analyzer (Ankersmid) by the TOT- method (Time- Of- Transition), X-ray powder diffraction or TEM (Transmission- Electron- Microscopy). Average particle sizes in suspensions, emulsions or dispersions were determined by dynamic light scattering methods. Average pore sizes of the materials were determined by SEM (Scanning Electron Microscopy). Porosity and specific surface areas were determined by N ₂ or He absorption techniques, according to the BET method.

Example 1

In a mini emulsion polymerization reaction, 5.8 g of deionized water, 5.1 mM of acrylic acid (obtained from Sigma Aldrich), 0.125 mol of methylmethacrylic acid MMA, (Sigma Aldrich) and 0.5 g of a 15 wt.-% aqueous solution of a surfactant (SDS, obtained from Fischer Chemical) were introduced into a 250 ml four-neck flask, equipped with a reflux condenser under a nitrogen atmosphere (nitrogen flow 2 1 per minute). The reaction mixture was stirred at 120 rpm for about 1 hour in an oil bath at 85 ⁰ C, resulting in a stable emulsion. To the emulsion, 0.1 g of a homogenous ethanolic magnesium oxide sol (concentration 2 g per liter) having an average particle size of 15 nm, prepared from 100 ml of a 20 weight- % solution of magnesium acetate tetrahydrate (Mg(CH ₃ COO) ₂ x 4H ₂ O in ethanol and 10 ml of a 10 % nitric acid at room temperature, were added and the mixture was stirred for another 2 hours. Then, a starter solution comprising 200 mg of potassium peroxodisulphate in 4 ml of water was slowly added over a time period of 30 minutes. After 4 hours of stirring, the mixture was neutralized to pH 7 and the resulting mini emulsion comprising PMMA encapsulated magnesium oxide particles was cooled to room temperature. The average particle size of the encapsulated magnesium oxide particles in the emulsion were about 100 nm, determined by dynamic light scattering. The emulsion containing the encapsulated magnesium oxide particles was sprayed onto a metallic substrate made of stainless steel 316 L with an average coating weight per unit area of 4 g/m ² , dried under ambient conditions and subsequently transferred into a tube furnace and treated at 32O ⁰ C in an air atmosphere for 1 hour. After cooling to room temperature, the sample was analyzed by scanning electron microscopy (SEM), revealing that an about 5 nm thick porous magnesium oxide layer with a mean pore size of about 6 nm had formed. Example 2

A stable mini emulsion of acrylic acid and methylmethacrylic acid was prepared as described in Example 1 above. The emulsion was polymerized upon addition of the starter solution as described in Example 2. In contrast to the

procedure described in Example 1, the ethanolic magnesium oxide sol was added after the polymerization was completed and the emulsion had been cooled to room temperature. After addition of the magnesium oxide, the reaction mixture was stirred for a further 2 hours. The resulting dispersion of PMMA capsules coated with magnesium oxide was subsequently sprayed onto a metallic substrate made of stainless steel 316 L with an average coating weight per unit area of about 8 g/m ² . After drying under ambient conditions, the sample was transferred into a tube furnace and treated under oxidative conditions in an air atmosphere at a temperature of 32O ⁰ C for 1 hour. SEM analysis revealed a porous magnesium oxide layer having a mean particle size of about 140 nm. Example 3

A mini emulsion was prepared in accordance with Example 1, however the amount of surfactant was reduced to 0.25 g of the 15 wt.-% aqueous SDS solution, leading to larger PMMA capsules. As in Example 1, a magnesium oxide sol was added to the monomer emulsion, which was subsequently polymerized and resulted in PMMA encapsulated magnesium oxide particles having a mean particle size of about 400 nm. The resulting dispersion was sprayed onto a metallic substrate made of stainless steel 316 L with an average coating weight per unit area of about 6 g/m ² and, after drying at room temperature, subsequently thermally treated as described in Example 1. The SEM analysis revealed that the porous coating of magnesium oxide had an average pore size of about 80 nm. Example 4

As described above in Example 2, a mini emulsion of the monomers was prepared and subsequently polymerized with a lower amount of surfactant as described in Example 3, i.e. 0.25g of the 15 wt.-% aqueous SDS solution instead of 0,5g. Then, the magnesium sol was added to the dispersion of polymer particles and the mixture was stirred for 2 hours. The average particle size of the PMMA capsules coated with magnesium oxide was about 400 nm.

The resulting dispersion was sprayed onto a metallic substrate (stainless steel 316 L) and subsequently dried under ambient conditions (average coating weight per

unit area 6 g/m ² ). The sample was thermally treated as described in Example 2. The resulting porous magnesium oxide layer had an average pore size of about 700 nm. Example 5

In a typical mini emulsion polymerization reaction, 5.8 g of deionized water, 5.1 mM of acrylic acid (obtained from Sigma Aldrich), 0.125 mol of acid (obtained from Sigma Aldrich) and 0.5 g of a 15 wt.-% aqueous solution of a surfactant (SDS, obtained from Fischer Chemical) were introduced into a 250 ml four- neck flask equipped with a reflux condenser under a nitrogen atmosphere as described above. The reaction mixture was stirred at 120 rpm for about 1 hour in an oil bath at 85 ⁰ C, resulting in a stable emulsion. To the emulsion, 0.1 g of an ethanolic iridium oxide sol (concentration 1 g per liter) having a mean particle size of about 80 nm, produced by vacuum- drying of a 5% aqueous nanoparticle dispersion of powdered iridium oxide (purchased from Meliorum Inc., USA) and re- dispersion in ethanol, was added and stirring was continued for another 2 hours. Then, a starter solution containing 200 mg of potassium peroxodisulphate in 4 ml of water was slowly added over a time period of 30 minutes. After 4 hours, the mixture was neutralized to pH 7 and the resulting mini emulsion comprising encapsulated iridium oxide particles was cooled to room temperature. The resulting emulsion comprised encapsulated iridium oxide particles with an average particle size of about 120 nm. The emulsion was sprayed onto a metallic substrate made of stainless steel 316 L with an average coating weight per unit area of about 5 g/m ² , dried under ambient conditions and subsequently treated under oxidative conditions in an air atmosphere at 32O ⁰ C for 1 hour. SEM analysis revealed a 3 nm thick porous iridium oxide layer having a mean pore size of about 80 nm. * * *

Having thus described in detail several exemplary embodiments of the present invention, it is to be understood that the invention described above is not to be limited to particular details set forth in the above description, as many apparent variations thereof are possible without departing from the spirit or scope of the present invention. The embodiments of the present invention are disclosed herein or

are obvious from and encompassed by the detailed description. The detailed description, given by way of example, is not intended to limit the invention solely to the specific embodiments described.

The foregoing applications, and all documents cited therein or during their prosecution ("appln. cited documents") and all documents cited or referenced in the appln. cited documents, and all documents cited or referenced herein ("herein cited documents"), and all documents cited or referenced in the herein cited documents, together with any manufacturer' s instructions, descriptions, product specifications, and product sheets for any products mentioned herein or in any document incorporated by reference herein, are hereby incorporated herein by reference, and may be employed in the practice of the invention. Citation or identification of any document in this application is not an admission that such document is available as prior art to the present invention. It is noted that in this disclosure and particularly in the claims, terms such as "comprises," "comprised," "comprising" and the like can have the broadest possible meaning; e.g., they can mean "includes," "included," "including" and the like; and that terms such as "consisting essentially of and "consists essentially of can have the broadest possible meaning, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the invention.