| Porous ceramic, polymer and metal materials with pores created by biological fermentation -> Monitor Keywords |
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Porous ceramic, polymer and metal materials with pores created by biological fermentationRelated Patent Categories: Chemistry: Molecular Biology And Microbiology, Micro-organism, Tissue Cell Culture Or Enzyme Using Process To Synthesize A Desired Chemical Compound Or CompositionPorous ceramic, polymer and metal materials with pores created by biological fermentation description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070042455, Porous ceramic, polymer and metal materials with pores created by biological fermentation. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a divisional of U.S. patent application Ser. No. 10/885,488 filed Jul. 7, 2005, now U.S. Pat. No. ______, and the complete contents thereof is herein incorporated by reference. FIELD OF THE INVENTION [0002] The present invention relates generally to methods for creating porous materials. More specifically, it relates to a method for creating pores in materials by biological fermentation (e.g. with bacteria or yeast or enzymes). BACKGROUND OF THE INVENTION [0003] Porous ceramic materials have been made previously by adding organic materials to the ceramic during fabrication, and then burning out the organic materials to leave holes or voids therein. For example, in brick manufacturing, sawdust or wood powder (i.e., "fugitive material") has been added to make the bricks lighter. On firing, the sawdust burns out, leaving a void where the wood once resided. This methodology has a number of drawbacks. In particular, it requires a significant amount of additional energy input (e.g., heating of the ceramic to combust the sawdust) and time. If the bricks are fired too fast, burning sawdust can cause the bricks to fracture. In addition, the burning process can leave a significant amount of residue to remove from the resulting porous ceramic material depending on the time and temperature of heating. Finally, the fugitive material adversely impacts profitability for the manufacturer by requiring space in the plant to store the material before use. This involves both an expense for storage and a decrease in the production capacity of the plant since some of the area is used up for storage purposes. [0004] Porous polymeric materials can be made by a process wherein hollow glass spheres are combined with the polymer forming material. The density of the polymer composite can be varied by varying the density of the glass spheres and the volume fraction of spheres added. However, similar to prior porous ceramic structure manufacturing techniques, techniques for forming porous polymeric materials suffer from the fact that a very large volume of usable plant space must be reserved to store the large volumes of the glass spheres. This usage of space for storage of the glass spheres carries a very high cost both in overhead costs and in lost production capacity. [0005] U.S. Pat. No. 5,071,747 to Hough et al. describes porous polymeric material, which in one embodiment, includes yeast within the pores of the material. The Hough invention contemplates formation of an emulsion from monomers and pre-polymers, followed by polymerizing the monomers and pre-polymers to yield a porous polymeric material, and finally, incorporation of the yeast within the pores. The yeast does not function to create the pores in the Hough device. Rather, the yeast provides biological activity in the device that is ultimately produced. [0006] U.S. Pat. No. 4,603,111 to Keller describes a process for making a polyacrylamide bead, which in one embodiment incorporates yeast. The process involves combining the yeast with the acrylamide monomers, followed by polymerization. The resulting product is a bead with yeast immobilized thereon and therein. It was determined that the immobilized yeast retained the same activity of non-immobilized yeast. Thus, the beads could then be ideally used in later processes. It is noted that the yeast in Keller do not function in any capacity to form pores in the polyacrylamide bead. [0007] U.S. Pat. No. 5,705,118 to Hayes describes a process for forming a ceramic material which includes combining an organic material such as gluten with a ceramic, followed by firing the ceramic material to form a green body. The gluten functions as a binder, and is ultimately eliminated by heat treatment in the manner discussed above in conjunction with prior technologies. Hayes indicates that minor amounts of yeast or enzymes, as well as many other constituents, may be included with the gluten, and that a "risen loaf" from the ceramic/gluten/yeast or enzyme mixture is ultimately fired. [0008] U.S. Patent Publication 2003/0171822 to Lo describes a process for creating a porous synthetic bone graft wherein ceramic powder, binder and a pore-forming agent are combined in an inert liquid. The pore forming agent is then allowed to create the pores, and the porous structure is then fixed by a heat treatment. A high temperature heating is then used to eliminate the binder and the pore forming agent, and to fuse the structure together. Lo suggests that the pore forming agents could be yeast cells, alkali metal salts, and inorganic salts of acids derived from carbon and phosphorous. Lo indicates that a carbohydrate powder, and, in the case of yeast being used as the pore forming agent, sugar, are added to the slurry. Lo does not contemplate combining metal materials with the ceramic. Rather, in Lo, it is important to have pores in order to allow osteoblasts to attach in order to promote mineralization. Further, the Lo process methodology is not applicable to polymer materials as it requires the use of a binder, and a post pore forming, ceramic fusing heat step. Likewise, the Lo process suffers from the requirement of using carbohydrate powders and binders, which may result in porous structure where the pores are less uniform in size and/or are larger in size than is desired for certain industrial applications as opposed to applications in the human body. [0009] It would be an advance in the art to provide a method for making porous materials that does not require large volumes of fugitive material. It would also be an advance to provide methods for making porous materials that can be used with metals, semiconductors, and polymers. SUMMARY OF THE INVENTION [0010] The present invention includes a porous polymeric material having closed pores, wherein the closed pores contain a biologic agent or a residue of biological agent. The residue can be a decomposition or desiccation product of yeast, bacteria or enzyme, for example. Carbon dioxide generated by the biological agent can also be trapped within the closed pores, but may also diffuse through the polymer material over time. The polymeric matrix material can be epoxy or a variety of other polymers or combinations of polymers. [0011] The present invention also includes a method for making a porous polymeric material. In the method, a polymer forming material is mixed with a biological agent (e.g., yeast), and a growth substrate (e.g., sugar). The biological agent is allowed to act on the growth substrate and form gas bubbles. Then, the polymer forming material is polymerized, and in the process of polymerization, it traps gas bubbles therein. The size of the bubbles will vary depending on the polymer forming materials used, rate of polymerization, and other processing conditions. The biological agent can act on the growth substrate at the same time that the polymer forming material is polymerizing. [0012] The present invention also includes a method for making a porous ceramic or porous semiconductor material. In this method, a powder of ceramic or semiconductor material is mixed with a biological agent (e.g., yeast), a growth substrate (e.g., sugar), and a ceramic forming liquid binder (e.g., polysilazane). The biological agent is allowed to act on the growth substrate to form gas bubbles which separate powderized ceramic or semiconductor material except at particular points on the surfaces of the powder. The binder may hold the powderized ceramic or semiconductor material together at the points of contact. Then, the mixture is heated so that the ceramic forming liquid is converted to an oxide material, thereby binding the ceramic or semiconductor particles together. The material may be further heated to sinter the ceramic or semiconductor particles together. [0013] The present invention also includes a method for making a porous metal material. In this method, a powder of metal material is mixed with a biological agent (e.g., yeast), and a growth substrate (e.g., sugar). The biological agent is allowed to act on the growth substrate to form gas bubbles. Then, the mixture is heated to bond the metal particles together. The metal particles, depending on the metal particles chosen, may also be sintered by further heat treatment. [0014] The present invention also includes a porous ceramic with embedded metal wires. The ceramic can be made of many different ceramic materials, and the metal wires can be made of many different metal materials. The ceramic can be dried or baked at relatively low temperature, or may be sintered at relatively high temperature. DESCRIPTION OF THE DRAWING FIGURES [0015] FIG. 1 shows a porous polymer material made according to the present invention. [0016] FIG. 2 shows a porous ceramic with metal wires according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION [0017] The present invention provides several methods for making porous polymers, metals, semiconductors and ceramics. [0018] For making porous polymers according to the present invention, polymer forming material (e.g., monomers or oligomers) or an already formed polymer is mixed with a combination of biologically active material (preferably yeast, but also may include bacteria or enzymes), a growth substrate (preferably sugar, but also may include polysaccharides, mixtures of sugars, and other materials which can be acted upon by the biologically active material to produce a gaseous byproduct), and preferably a fluid carrier (e.g., preferably water, but any fluid which allows mixing of the polymer forming material or polymer, biologically active material and growth substrate, and which does not inhibit the activity of the biologically active material would be acceptable). In the most preferred embodiment, yeast, sugar and water are used in combination with a polymer forming material. In this embodiment, the yeast is allowed to ferment the sugar to produce carbon dioxide bubbles in the polymer as the polymer forming material is polymerized. Polymerization can proceed by a variety of different mechanisms including without limitation condensation or step-type polymerizations, free-radical polymerizations, ionic and coordination polymerization, ring opening polymerization, and photolytic or electrolytic polymerization. Polymerization can be initiated by a variety of different mechanisms including addition of a catalyst, addition of one or more reactants, application of radiant energy (e.g., UV radiation), and application of heat. The polymer formed can be aqueous (i.e. water-soluble) or non-aqueous (immiscible in water). Continue reading about Porous ceramic, polymer and metal materials with pores created by biological fermentation... 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