Tubes having internal diameters in the nanometer range

Abstract

Hollow fibers having an internal diameter from 1 nm to 100 nm can be produced by coating degradable materials with nondegradable materials and then degrading the degradable materials. The hollow fibers are useful in separation technology, catalysis, microelectronics, medical technology, materials technology or the clothing industry.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates to nanotubes, i.e., tubes or hollow fibers having an internal diameter in the nanometer range, to a process for their production and to the use of these tubes or hollow fibers.

[0003] 2. Discussion of the Background

[0004] Hollow fibers, mesotubes and nanotubes are generally tubes having an internal diameter of less than 0.1 mm.

[0005] Tubes or hollow fibers having a small internal diameter are known and are employed in particular for separation duties, for example in medical dialysis, for gas separation or osmosis of aqueous systems, for example for water treatment (see Kirk Othmer, Encyclopedia of Chemical Technology, 4th Ed., Vol. 13, pp. 312-313). The fiber material usually comprises polymers, which may in addition have pores, i.e. properties of semipermeable membranes. The hollow fibers used for separation duties usually have a surface area of 100 cm2/cm3 of volume coupled with an internal diameter of from 75 &mgr;m to 1 mm.

[0006] A further application of hollow fibers is in micro electronics. Here, superconducting fibers about 60 &mgr;m in diameter are produced using superconducting material by filling hollow polymeric fibers with a material which, after thermodegradation of the polymer, possesses superconducting properties (J. C. W. Cien, H. Ringsdorf et al., Adv. Mater., 2 (1990) p. 305).

[0007] Tubes having a small internal diameter are generally produced by extrusion spinning processes. A number of extrusion spinning processes are described in Kirk-Othmer, Encyclopedia of Chemical Technology, 4th Ed., Vol 13, pp. 317-322.

[0008] Extrusion spinning processes provide hollow fibers having an internal diameter of down to 2 &mgr;m. However, the production of hollow fibers having smaller internal diameters is not possible by these processes.

[0009] Very thin fibers without internal cavity can be produced by electrostatic spinning, or electrospinning. In electrospinning, polymer melts or polymer solutions are extruded through cannulas under a low pressure in an electric field. The principles of this technique are described, for example, in EP 0 005 035, EP 0 095 940, U.S. Pat. No. 5,024,789 or WO 91/01695. Electrospinning provides solid fibers which are 10-3000 nm in diameter; but not hollow fibers.

[0010] Hollow fibers having a very small internal diameter have hitherto only been obtainable by electrochemical synthesis, as described in L. A. Chernozantonskii, Chem. Phys. Lett. 297, 257, (1998), by methods of supra molecular chemistry (S. Demoustier-Champagne et al., Europ. Polym. a. 34, 1767, (1998)) or using self organizing membranes as templates (E. Evans et al., Science; Vol. 273, 1996, pp. 933-995). Hollow carbon fibers based on fullerene chemistry (carbon nanotubes) having single- or multi-walled structures made of a single rolled-up graphite layer (layer of six-membered carbon rings fused to one another on all sides) or concentrically arranged graphite cylinders are described for example in “Fullerenes and Related Structures”, Ed. A. Hirsch, Springer Verlag, 1999, pp. 189-234 or N. Grobert, Nachr. Chem. Tech. Lab., 47, (1999).

[0011] However, these methods can only be applied to specific materials and cannot be employed to produce industrially useful, i.e. mechanically and chemically stable, hollow fibers.

[0012] Hollow fibers having internal diameters in the &mgr;m range are known. For instance, WO 97/26225, EP 0 195 353 and U.S. 5,099,906 disclose hollow fibers which are composed of ceramic materials and have an internal diameter of at least 1 &mgr;m. Hollow fibers which are composed of metals and have an internal diameter of 1-1 000 &mgr;m are described in FR 12 11 581 and DE 28 23 521.

[0013] WO 01/09414 discloses meso- and nanotubes having internal diameters in the range from 10 nm to 50 pm that are preferably produced by electrospinning. However, the electrospinning process disclosed therein does not allow the production of smaller fibers, since a fiber produced when the material to be spun is thinned out to any degree is irregular and has thick portions.

[0014] There are many applications, for example the separation of gases, in which it is desirable to employ hollow fibers having very small external and/or internal diameters that are composed of various materials optimized to the particular area of application. More particularly, the materials should be capable of withstanding thermal, mechanical and chemical stresses, if desired have a porous structure, selectively be electrical conductors or insulators and be composed of polymers, inorganics or metals.

SUMMARY OF THE INVENTION

[0015] It is therefore an object of the present invention to provide hollow fibers of industrially usable materials that have an internal diameter in the nm range.

[0016] This and other objects have been achieved by the present invention the first embodiment which includes a hollow fiber having an internal diameter from 1 nm to 100 nm and an outer wall comprising a metal-containing inorganic compound, a polymer, a metal or a combination thereof.

[0017] In another embodiment the present invention provides a process for preparing a hollow fiber, comprising:

[0018] coating a fiber of a first, degradable material with at least one coating of at least one second material; and

[0019] degrading the first, degradable material to obtain the hollow fiber;

[0020] wherein said hollow fiber has an internal diameter from 1 nm to 100 nm.

[0021] In yet another embodiment the present invention relates to a method for removal of a metabolite or an enzyme from cytoplasm, comprising:

[0022] contacting said cytoplasm with the hollow fiber.

BRIEF DESCRIPTION OF DRAWINGS

[0023] FIG. 1 shows an electrospinning apparatus, embodiments of hollow fiber, and a process for production of the hollow fiber.

[0024] FIG. 2 shows a scanning electron photomicrograph of polylactide template fibers.

[0025] FIG. 3 shows a tunneling electron micrograph of polylactide template fibers.

[0026] FIG. 4 shows a tunneling electron photomicrograph of polyamide template fibers.

[0027] FIG. 5 shows a scanning electron micrograph of poly(p-xylene) fibers.

[0028] FIG. 6 shows a scanning electron micrograph of poly(p-xylene) fibers.

[0029] FIG. 7 shows a tunneling electron photomicrograph of poly(p-xylene) fibers.

[0030] FIG. 8 shows a tunneling electron micrograph of poly(p-xylene) fibers.

[0031] FIG. 9 shows a wide angle X-ray graph.

DETAILED DESCRIPTION OF THE INVENTION

[0032] It has been surprisingly found that hollow fibers having an internal diameter in the desired run range are producible in a precise manner from a wide variety of materials such as polymers, inorganics or even metals.

[0033] The present invention accordingly provides a hollow fiber having an internal diameter from 1 nm to 100 nm and an outer wall constructed of metal-containing inorganic compounds, metals and/or polymers or combinations thereof.

[0034] The internal diameter of the hollow fibers according to the invention is preferably in the range from 1 nm to 5 nm, more preferably in the range from 1 nm to 9 nm and most preferably in the range from 1 nm to 5 nm. The internal diameter includes all values and subvalues therebetween, especially including 1.5, 2.5, 3, 3.5, 4 and 4.5 nm.

[0035] The hollow fiber length is determined by the intended use and is generally in the range of from 50 &mgr;m up to several mm or cm. The hollow fiber length includes all values and subvalues therebetween, especially including 100, 200, 300, 400, 500, 600, 700, 800, 900 &mgr;m; 1, 2, 3, 4, 5, 6, 7, 8, 9 mm; 1, 2, 3, 4, 5, 6, 7, 8 and 9 cm.

[0036] The wall thickness, i.e., the thickness of the outer wall of the hollow fiber, is variable and is generally in the range from 1 to 500 nm, preferably in the range of from 1 to 100 nm and more preferably in the range from 10 to 25 nm. The thickness of the outer wall includes all values and subvalues therebetween, especially including 10, 50, 100, 150, 200, 250, 300, 350, 400 and 450 nm.

[0037] Hollow fibers according to the present invention as well as the very small internal diameters, have a number of properties which make them suitable for use in the fields of medicine, electronics, catalysis, chemical analysis, gas separation, osmosis or optics.

[0038] Thus, the outer wall of the hollow fiber according to the present invention can be constructed from the most diverse materials, for example from polymers, metals or metal containing inorganic compounds. The outer wall can have one layer of these materials, i.e., consist entirely thereof or have a plurality of layers composed of the same or different materials. The very small internal diameter ensures a very high ratio of hollow fiber surface area to volume which can be between 500 and 2 000 000 cm2/cm3, preferably in the range from 5 000 to 1 000 000 cm2/cm3 and more preferably in the range from 5 000 to 500 000 cm2/cm3. The ratio of hollow fiber surface area to volume includes all values and subvalues therebetween, especially including 1,000; 10,000, 50,000, 100,000, 200,000, 300,000, 400,000, 500,000, 600,000, 700,000, 800,000, 900,000, 1,000,000, 1,200,000, 1,400,000, 1,600,000 and 1,800,000 cm2/cm3.

[0039] The metal-containing inorganic compounds of the hollow fiber according to the invention are for example metal oxides, metal mixed oxides, spinel, metal nitrides, metal sulfides, metal carbides, metal aluminates or metal titanates. Boron compounds or metal-doped carbon nanotubes having single- and multi-wall structures made from a single rolled-up graphite layer (layer of six-membered carbon rings fused to one another on all sides) or concentrically arranged graphite cylinders are not metal-containing compounds for the purposes of the present invention. Materials similar to carbon nanotubes having concentrically arranged polyhedral or cylindrical layer structures such as for example WS2, MoS2 and VS2 are likewise not metal-containing compounds for the purposes of the present invention.

[0040] For the purposes of the present invention, the polymers are polycondensates, polyaddition compounds or products of chain growth polymerization reactions, but not graphite-like compounds composed of pure or doped carbon.

[0041] The present invention further provides a process for producing the hollow fiber.

[0042] The process for producing the hollow fiber according to the present invention comprises coating a fiber of a first, degradable material with at least one further material. Subsequently, the first material is degraded in such a way that the hollow fiber thus obtained has an internal diameter from 1 nm to 100 nm.

[0043] In a preferred embodiment of the process, the first, degradable material may be admixed with 0.1-10% by weight of a basic compound, such as pyridine which is preferable when polyamides are used and can be used for example as a solvent additive in electrospinning. The amount of basic compound includes all values and subvalues therebetween, especially including 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9 and 9.5% by weight.

[0044] In another preferred embodiment of the process, the degradable material is admixed with 10-60% by weight and preferably 25-50% by weight of a noble metal salt. The amount of noble metal includes all values and subvalues therebetween, especially including 20, 30, 40 and 50% by weight. Preference is given to platinum, nickel, cobalt, rhodium and palladium salts of organic acids, such as acetate or formate. It is also possible to add the hereinbelow specified metals of groups I to XIII, a and b of the periodic table. This embodiment of the process makes is possible to produce nanotubes having small noble metal crystals on the inner surface. These nanotubes are especially useful as catalysts. It is also possible to apply the above two embodiments of the process at the same time.

[0045] Preferred embodiments of the hollow fiber and of the process for production thereof are illustrated in FIG. 1 (b and c).

[0046] In another embodiment preferred of the process, the initial step comprises subjecting a fiber (FIG. 1, b, I) composed of a first, degradable material to a coating operation (FIG. 1, b, II). This fiber may be composed of a material which is degradable thermally, chemically, radiochemically, physically, biologically or by means of plasma, ultra-sound or extraction with a solvent. These fibers may be produced by electrospinning.

[0047] Details concerning electrospinning technology are described, for example in D. H. Reneker, I. Chun., Nanotechn. 7, 216 (1996). The basic construction of an electrospinning apparatus is shown in FIG. 1 (a).

[0048] The diameter of the degradable fibers should be in the same order of magnitude as the later desired internal diameter of the hollow fibers. In general, the later cavity in the hollow fibers is of approximately the same size as the diameter of the degradable fibers or coatings. The precise dimensions depend on the materials used and their changes during the degradation operation and can be determined without difficulty by preliminary experiments. Useful degradable fiber materials include organic or inorganic materials, especially polymers such as polyesters, polyethers, polyolefins, polycarbonates, polyitrethanes, natural polymers, polylactides, polyglycosides, poly-a-methylstyrene and/or polyacrylonitriles. The electrospinning process also makes it possible to produce multicomponent fibers, i.e., fibers having different materials in different layers or fibers having a certain surface topography, i.e., having smooth or porous surfaces.

[0049] The surface finish of the fiber or layer of degradable materials also determines the surface topography of the subsequent coatings. If, for example, a rough or micro structured inner surface is desired for the hollow fibers, this can be achieved by means of a correspondingly rough fiber of a degradable material. Rough or microstructured fibers can be obtained by electrospinning a polymer solution containing a volatile solvent. Furthermore, additives such as salts, for example sodium sulfate, metallic nanopowders, conductive polymers such as polypyrroles or graphite can distinctly enhance the conductivity of the spun material.

[0050] The coating with the at least one further nondegradable material can be effected by gas phase deposition, plasma polymerization or application of the material in a melt or in solution. The coating can be effected in various layers and using various materials and forms the outer wall of the hollow fiber.

[0051] This coating, i.e. the construction of the outer walls can be effected for example by gas phase deposition, knife coating, spin coating, dip coating, spraying or plasma deposition of polymers such as poly(p-xylylene), polyacrylamide, polyimides, polyesters, polyolefins, polycarbonates, polyamides, polyethers, polyphenylene, polysilanes, polysiloxanes, polybenzimidazoles, polybenzothiazoles, polyoxazoles, polysulfides, polyester amides, polyarylenevinylenes, polylactides, polyether ketones, polyurethanes, polysulfones, ormocers, polyacrylates, silicones, aromatic copolyesters, poly-N-vinylpyrrolidone, polyhydroxyethyl methacrylate, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polymethacrylonitrile, polyacrylonitrile, polyvinyl acetate, neoprene, Buna N, polybutadiene, polytetrafluoroethene, cellulose (modified or unmodified), alginates or collagen, homopolymers or copolymers and/or blends thereof.

[0052] Furthermore, the degradable layers or fibers may be coated with a further material obtained by polymerization of one or more monomers. Preferred monomers for the homo- or copolymerization include, for example, methacrylate, styrene, styrenesulfonate, 1,6-hexamethylene diisocyanate (HDI), 4,4′-methylenebiscyclo-hexyl-diisocyanate (HMDI), 4,4′methylenebis-(benzyl-diisocyanate) (MDI), 1,4-butanediol, ethylenediamine, ethylene, styrene, butadiene, 1-butene, 2-butene, vinyl alcohol acrylonitrile, methyl methacrylate, vinyl chloride, fluorinated ethylenes and/or terephthalates.

[0053] The coating, i.e., the construction of the outer wall of the hollow fibers, can be composed of metals of the groups la, Ib, Ia, IIb, IIa, IIIb, IVa, IVb, Vb, VIb, VIIb and/or VIIIb of the periodic table, each as a pure metal or as an alloy. Preferred metals include for example gold, palladium, aluminum, platinum, silver, titanium, cobalt, ruthenium, rhodium, sodium, potassium, calcium, lithium, vanadium, nickel, tungsten, chromium, manganese and/or silicon. The coating can be effected by vapor deposition of the metals or by decomposition of suitable organometal-containing compounds using chemical vapor deposition (CVD) methods.

[0054] Polymeric coating materials may further bear functional groups such as esters, amides, amines, silyl groups, siloxane groups, thiols, hydroxyl groups, urethane groups, carbamate groups, nitrite groups, C═C groups, C═C groups, carboxylic acid halide groups, sulfoxide groups, sulfone groups, pyridyl groups, arylphosphine groups or else ionic groups such as carboxylic acids, sulfonic acids or quaternary amines. The functional groups can be attached to the inner and/or outer surface of the hollow fibers to improve the surface properties of the hollow fibers in separation or osmosis processes. The functional groups can also be chemically modified subsequently by polymer-analogous reactions, for example by hydrolysis of esters.

[0055] Appropriate functionalization, furthermore, can be used to have active ingredients such as antibiotics, anesthetics, proteins such as insulin, antifouling agents and agrochemicals such as herbicides or fungicides reversibly fixed in the hollow fibers and/or gradually released again in specific concentrations at a controlled rate.

[0056] The outer wall of the hollow fibers, i.e., the nondegradable further material, can also be constructed of glass, glass ceramics, SiOx, perovskite, ceramics, aluminas or zirconias, optionally of silicon carbide, boron nitride, carbon and metal oxides. Useful methods here likewise include gas phase deposition processes (CVD or physical vapor deposition (PVD)) or else hydrothermal processes.

[0057] Preferred perovskites have the general formula

LaXYMgO

[0058] wherein X=Ca, Sr or Ba; and Y=Ga or Al; (without stoichiometry) which have oxygen ion conductance properties.

[0059] The degradation of the degradable material can be effected thermally, chemically, radiation-induced, biologically, photochemically or by means of plasma, ultrasound or extraction with a solvent. Thermal degradation is particularly preferred in practice. The decomposition conditions vary with the material ranging from 100 to 500° C. and from 0.001 mbar to 1 bar, particularly preferably from 0.001 to 0.1 mbar. The decomposition temperature includes all values and subvalues therebetween, especially including 150, 200, 250, 300, 350, 400 and 450° C. The decomposition pressure includes all values and subvalues therebetween, especially including 0, 005, 0.01, and 0.05 mbar. Degradation of the material provides a hollow fiber whose wall material is composed of the coating materials.

[0060] As shown in FIG. 1 (b and c), it is also possible for a plurality of layers of different materials to be applied to the fiber. This provides hollow fibers having different inner and outer surfaces or hollow fibers where the outer walls can be constructed of a plurality of layers. The different layers can perform different functions in that, for example, the inner layer can have particular separation properties for chromatographic purposes, for example, and the outer layer can have high mechanical stability.

[0061] The following layer sequences for the hollow fibers according to the invention may be mentioned by way of example:

[0062] glass/metal

[0063] metal/glass

[0064] glass/polymer

[0065] polymer/glass

[0066] polymer/polymer

[0067] metal/metal

[0068] metal-containing inorganic compound/metal-containing inorganic compound

[0069] ceramic/ceramic

[0070] polymer/metal

[0071] metal/polymer

[0072] ceramic/polymer

[0073] polymer/ceramic

[0074] metal/ceramic

[0075] ceramic/metal

[0076] polymer/metal/polymer

[0077] metal/polymer/metal

[0078] metal/ceramic/metal

[0079] polymer/ceramic/polymer

[0080] ceramic/polymer/ceramic

[0081] polymer/glass/polymer

[0082] glass/polymer/glass.

[0083] Hollow fibers according to the present invention are useful in particular as a separation or storage medium for gases, liquids or particle suspensions and for filtering or purifying compositions of matter. Preferred applications here are as a membrane for gases, especially H2 or liquids, for particle filtration, in chromatography, for oil/water separation, as an ion exchanger in dialysis, for size separation of cells, bacteria or viruses, as a constituent of an artificial lung, for desalination, for drainage or irrigation or as a filter for dewatering power fuels.

[0084] Hollow fibers according to the invention may further be used in sensor technology for solvent, gas, moisture or biosensors, in capillary electrophoresis, in catalytic systems, in scanning probe microscopy or as materials of construction in superlightweight building construction, as a mechanical reinforcement similar to glass fibers, as a noise or vibration abate, as a composite material or filler, as a controlled release or drug delivery system, in medical separation technologies, in dialysis, as an artificial lung, as a protein store or in tissue engineering.

[0085] The hollow fibers according to the invention may be used in the clothing/textile industry as a thennal insulator in clothing or sleeping bags, in photo- or thermochromic clothing through embedding of dyes in the tube interior or as an authenticator through markers in the tubes interior.

[0086] Hollow fibers according to the invention also find use in electronics, optics or energy production the hollow fibers can be used to produce wires, cables or capacitors, micromachines (for example for piezoelectric, shaping, nanoperistaltic pumps or for shaping photoadrressable polymers) or interlayer dielectrics. Further uses for hollow fibers according to the invention are microreactors, for example for catalytic reactions, template reactions and bioreactions, heat generation through conversion of sunlight (solar a systems) or in chip technology as flexible devices or microscopy as a sensor constituent (for example; as tips or probes for scanning probe microscopes br SNOM instruments).

[0087] The hollow fibers according to the present invention have a very low dielectric constant and therefore can also be used as a dielectric, in particular as an interlayer dielectric in electronic components. For example, in chip manufacture, interlayer dielectrics having a low dielectric constant are important in the production of new chip generations having even smaller dimensions or higher storage densities due to the high proportion of included air per unit volume. The hollow fibers according to the invention have a dielectric constant of less than 4, preferably less than 3, most preferably less then 2, ideally less than 1.5.

[0088] The hollow fibers are preferably used as a web or mat for dielectric applications due to the large surface area of the hollow fibers according to the invention, these can also be used in fuel cells, batteries or electrochemical reactions. For such uses, the outer wall of the hollow fibers is advantageously composed of oxygen ion conductors, for example perovskites. In oxidation reactions, the hollow fibers may be surrounded by the reactant, an olefin for example, while oxygen is passed through the cavities of the fibers. The oxidation product is formed on the outside of the hollow fibers and transported away.

[0089] The hollow fibers according to the present invention can be used as a catalytic system. It is thus possible, for example, to use hollow fibers composed of noble metals such as platinum or palladium as denoxing catalysts in motor vehicles.

[0090] Hollow fibers according to the invention which are composed of cell-compatible materials or have appropriately modified surfaces can be incorporated introduced into cell membranes and used for the separation and also recovery or removal of metabolites, enzymes and other components of the cytoplasm within cells or cytoplasmic components and hence for the recovery of biopharmaceuticals.

[0091] Having generally described this invention, a further understanding can be obtained by reference to certain specific examples which are provided herein for purposes of illustration only, and are not intended to be limiting unless otherwise specified.

EXAMPLES

Example 1

Production of Polylactide Template Fibers by Electrospinning

[0092] A 5% solution of poly-L-lactide in dichloromethane (conductivity <10−7 &mgr;s/cm) containing 50% by weight of Pd(OAc)2, based on the polylactide, was electrospun at a voltage of 48 kV in the apparatus of FIG. 1 (a). The separation of the cannula tip (diameter 0.3 mm) from the substrate plate (glass) was 10 cm. The fibers were further used without further treatment. A scanning electron photomicrograph of the fibers is shown in FIG. 2. FIG. 3 shows a tunneling electron micrograph of the material thus obtained.

Example 2

Production of Polyamide Template Fibers by Electrospinning

[0093] An 8% solution of nylon 46 containing 2% by weight of pyridine, based on N46, in formic acid was electrospun at a voltage of 55 kV in the apparatus shown in FIG. 1(a). The separation of the cannula tip (diameter 0.3 mm) from the substrate plate (glass) was 15 cm. The fibers were further used without further treatment. A tunneling electron photomicrograph of the fibers is shown in FIG. 4.

Example 3

Production of poly(p-xylylene) Hollow Fibers by Coating from the Gas Phase

[0094] Polyamide template fibers produced by electrospinning as per Example 1 were placed in a gas phase deposition apparatus. Subsequently 37 mg of analytically pure [2.2] paracyclophane were evaporated at 220° C./0.1 mbar and pyrolyzed at 800° C., causing the formation of 25 poly(p-xylene) (PPX) in the sample space at about 20° C.

[0095] The poly(p-xylylene) polylactide composite fabric was extracted with chloroform for 24 hours. The formation of poly(p-xylylene) hollow fibers having an internal diameter from about 6 to 20 nm was confinmed by scanning electron microscopy (FIGS. 5, 6).

Example 4

Production of poly(p-xylylene) Hollow Fibers by Coating from the Gas Phase

[0096] Polyamide template fibers produced by electros: pinning as per Example 2 were placed in a gas phase deposition apparatus. Subsequently 37 mg of analytically pure [2.2]paracyclophane were evaporated at 220° C./0.1 mbar and pyrolyzed at 800° C., causing the formation of poly(p-xylylene) (PPX) in the sample space art about 20° C.

[0097] The poly(p-xylylene) polyamide composite was extracted with fonmic acid for 24 hours. The formation of the hollow fibers having an internal diameter of 45 nm is discernible from the tunneling electron photomicrograph in FIG. 7.

Example 5

Production of poly (p-xylylene)/Hollow Fibers by Coating from the Gas Phase

[0098] Polylactide template fibers produced by electrospinning as per Example 1 were placed in a gas phase deposition apparatus. Subsequently 40 mg of analytically pure [2.2]paracyclophane were evaporated at 220° C./10.1 mbar and pyrolyzed at 700° C., causing the formation of poly(p-xylylene) in the sample space at about 20° C. The poly(p-xylylene) polylactide composite fabric was thenmally treated in a vacuum oven at 285° C./0.01 mbar for 8 hours. The fonmation of poly(p-xylylene)/hollow fibers laving an average internal diameter of about 17 nm was confirmed by scanning electron microscopy (FIG. 8).

[0099] Thermal degradation gives palladium crystallites 4-10 nm in size on the inner surface of the tube is shown in FIG. 8. FTIR spectroscopy confirms the degradation of the polylactide. The conversion of palladium acetate to metal-containing palladium is confirmed by wide angle X-ray spectroscopy (FIG. 9).

[0100] German patent application 10133393.5, filed Jul. 13, 2001, is incorporated herein by reference.

[0101] Numerous modifications and variations on the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.

Claims

1. A hollow fiber having an internal diameter from 1 nm to 100 nm and an outer wall comprising a metal-containing inorganic compound, a polymer, a metal or a combination thereof.

2. The hollow fiber according to claim 1, wherein said internal diameter is from 1 nm to 10 nm.

3. The hollow fiber according to claim 1, wherein said outer wall comprises a homopolymer, a copolymer or a blend of compounds selected from the group consisting of poly(p-xylylene), polyacrylamide, polyimides, polyesters, polyolefins, polycarbonates, polyamides, polyethers, polyphenylene, polysilanes, polysiloxanes, polybenzimidazoles, polybenzothiazoles, polyoxazoles, polysulfides, polyester, amides, polyarylenevinylenes, polylactides, polyether ketones, polyurethanes, polysulfones, ormocers, polyacrylates, silicones, aromatic copolyesters, poly-N-vinylpyrrolidone, polyhydroxyethyl methacrylate, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polymethacrylonitrile, polyacrylonitrile, polyvinyl acetate, neoprene, Buna N, polybutadiene, polytetrafluoroethene, modified cellulose, unmodified cellulose, alginates, and collagen.

4. The hollow fiber according to claim 1, wherein said outer wall comprises a metal or an alloy of metals selected from the group consisting of metals of groups Ia, Ib, Ia, IIb, IIIa, IIIb, IVa, IVb, Vb, VIb, VIb, VIIb of the periodic table, and mixtures thereof.

5. The hollow fiber according to claim 1, wherein said outer wall comprises glass, glass ceramics, SIOx, perovskite, ceramics, aluminas or zirconias.

6. The hollow fiber according to claim 1, wherein said outer wall comprises a plurality of layers.

7. The hollow fiber according to claim 1, having a dielectric constant of less than 4.

8. A process for preparing a hollow fiber, comprising:

coating a fiber of a first, degradable material with at least one coating of at least one second material; and

degrading the first, degradable material to obtain the hollow fiber;

wherein said hollow fiber has an internal diameter from 1 nm to 100 nm.

9. The process according to claim 8, wherein the first, degradable material comprises 10-60% by weight of a noble metal salt.

10. The process according to claim 8, wherein the first, degradable material further comprises a basic compound.

11. The process according to claim 8, wherein the second material comprises an inorganic compound, a polymer, a metal or a mixture thereof.

12. The process according to claim 8, wherein the second material comprises homopolymers, copolymer or blends of compounds selected from the group consisting of poly(p-xylylene), polyacrylamide, polyimides, polyesters, polyolefins, polycarbonates, polyamides, polyethers, polyphenylene, polysilanes, polysiloxanes, polybenzimidazoles, polybenzothazoles, polyoxazoles, polysulfides, polyester amides, polyarylenevinylenes, polylactides, polyether ketones, polyurethanes, polysulfones, ormocers, polyacrylates, silicones, aromatic copolyesters, poly-N-vinylpyrrolidone, polyhydroxyethyl methacrylate, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polymethacrylonitrile, polyacrylonitrile, polyvinyl acetate, neoprene, Buna N, polybutadiene, polytetrafluoroethene, modified cellulose, unmodified cellulose, alginates, and collagen.

13. The process according to claim 8, wherein the second material comprises a metal or an alloy of metals selected from the group consisting of metals of groups Ia, Ib, Ia, IIb, IIa, IIIb, IVa, IVb, Vb, VIb, VIb, VIIb of the periodic table, and mixtures thereof.

14. The process according to claim 8, wherein the second material comprises metal oxides, glass, glass ceramics SiOx, perovskite, ceramics, aluminas, silicon carbide, boron nitride, carbon or zirconias.

15. The process according to claim 8, wherein the second material is obtained by polymerization of one or more monomers.

16. The process according to claim 15, wherein the second material is obtained by homopolymerization or copolymerization of a compound selected from the group consisting of methacrylate, styrene, styrene sulfonate, 1,6-hexamethylene diusocyanate, 4,4′-methylenebiscyclohexyl dilsocyanate, 4,4′-methylenebis(benzyl-diisocyanate), 1,4butanediol, ethylenediamine, ethylene, styrene, butadiene, 1-butene, 2-butene, vinyl alcohol, acrylonitrile, methyl methacrylate, vinyl chloride, fluorinated ethylenes, terephthalate or mixtures thereof.

17. The process according to claim 8, wherein the degrading of the first, degradable material is effected thermally, chemically, biologically, radiation-induced, photochemically, by plasma, by ultrasound or by extraction with a solvent.

18. A separation medium or storage medium for gases, liquids or particle suspensions, comprising:

the hollow fiber according to claim 1.

19. A method for removal of a metabolite or an enzyme from cytoplasm, comprising:

contacting said cytoplasm with the hollow fiber according to claim 1.