WO1999022861A1

WO1999022861A1 - Biomimetic materials for filtration, chemical processing and detoxification

Info

Publication number: WO1999022861A1
Application number: PCT/US1998/023589
Authority: WO
Inventors: Donald E. Ingber; Quing Liu; Zewen Liu; Antonios G. Mikos; Raman V. Bahulekar
Original assignee: Molecular Geodesics, Inc.; Rice University
Priority date: 1997-11-05
Filing date: 1998-11-05
Publication date: 1999-05-14
Also published as: WO1999022861B1

Abstract

Materials that utilize porous skeleton materials coated with hydrogels to provide an improved, low resistance filtration capability for removal of pathogens, toxins, or other contaminants from a contaminated gas or liquid and an enhanced capacity for binding, sequestering, or catalytic processing of chemical, biological, or molecular substrates.

Description

BIOMIMETIC MATERIALS FOR FILTRATION. CHEMICAL PROCESSING AND DETOXIFICATION

This application claims priority under 35 U.S.C. §119(e) to United States

Provisional application no. 60/032,408 filed December 4, 1996, entitled "Biomimetic

Materials", which is hereby incorporated in its entirety by reference.

Background of the Invention There are many applications which require filtration of gas or liquids to remove contaminating pathogens, toxins, or other particulates. These techniques typically use filters that contain pores or filtration pathways which are smaller than the diameter of the contaminating particles and thus, which greatly increase the mechanical resistance to gas and fluid flow. Increased mechanical resistance reduces the efficiency of the filter and may increase the discomfort level in the user where the filter is used in air filtration apparatus.

One commonly used air cleaner is designed primarily to filter out the particulate matter or contaminants from the air. This filter removes the particulate matter by forcing the air through a filter medium which blocks the contaminant. The filter medium may be comprised of a variety of materials, such as glass fibers, wire screens, steel wool, animal hair or hemp fiber. Conventional cartridge type filter or respirator may use a cartridge of porous or perforated end walls containing relatively large mesh granulated or pelletized activated carbon. The relatively large mesh size of the granules or pellets packed between the porous end walls minimizes resistance to flow; however, minimization of air resistance in this manner results in reduced surface area exposure of the active material.

Many filters also rely on the use of tiny pores to restrict passage of biological pathogens. For example, filters used for removal of biological pathogens, such as HEPA filters or Nitex filters, rely on the use of a solid membrane containing pores with diameters smaller than the pathogen to prevent their passage across a barrier. As the size of the pore decreases, the mechanical resistance to gas or fluid flow increases. This feature can greatly restrict the usefulness of these filtration devices, especially when air flow is restricted, for example, in surgical masks. In certain applications, filters may be treated with chemical processing agents and enzymes which are effective in the immobilization and/or deactivation of biologically active contaminants, e.g., "biofiltersX The effectiveness of these biofilters is limited by the surface area available for reaction to take place and, when used with contaminated gases, often lack the aqueous or hydrophilic environment required for optimal filtration.

United States Patent No. 5,529,609 describes an air cleaner which relies on adsorption of the contaminants onto the filter surface, rather than physical obstruction. The air filter includes a three dimensional matrix of a cross-linked polymer, such as acrylamide, swelled with a liquid medium. The hydrogel was demonstrated to be effective in the removal of contaminants from an air stream; however, the hydrogel matrix lacks the mechanical strength to provide a highly porous structure and tends to collapse in on itself.

It is the object of the present invention to provide a filter for the filtration of contaminated gas and liquids which overcome the disadvantages of prior art filters as noted above and as generally recognized in the industry.

It is an object of the invention to efficiently remove particulate matter, gases and vapors, molecular contaminants and/or biological contaminants from gases and liquids. It is a further object of the present invention to provide a filtration system which is highly porous and which nonetheless can efficiently entraps and removes contaminants.

It is yet a further object of the invention to provide a new active filter material having a high active surface area with relatively low pressure drop across the filter membrane and low resistance to flow.

It is a further object of the invention to provide a filter which is effective in the immobilization and/or deactivation of biological pathogen. Summary of the Invention

These and other objects of the invention are achieved with a filter having a porous skeleton of high porosity and surface area coated with a hydrogel (water-seeking) material that is capable of absorbing contaminants due to the hydroscopic character of many contaminants in liquids and gases, including particulates, biological pathogens and toxins. By holding the hydrogel open in a porous configuration, the skeleton supports and reinforces the hydrogel, increase its surface area and provides it with enhanced tensile and compressive strength. Surface area of the hydrogel may be increased further by incorporating pores or porosity into the hydrogel coating. These features improve the filtration efficiency and capacity of the filter. The present invention mimics biological design principles to provide a filtration system that will remove pathogens, molecular toxins, and other organic contaminants without greatly restricting gas or fluid flow.

The filtration system may additionally include additives to improve the filtration properties of the system. The open network provided by the skeleton/hydrogel structure may be impregnated with materials selected for their ability to remove and/or neutralize particulates and/or chemicals from a fluid medium. The highly porous configuration of the filter optimizes availability of chemical reactants and other additives useful in the deactivation or sequestration of contaminants.

Additives may be located in the structure in at least four ways. Large particles may be placed in spaces between neighboring gel surfaces, e.g. , see filtration space 16 in Figure 1. Water-soluble additives may be added to the water phase of the hydrogel. For example, peroxides and light-sensitive dyes that release free radicals are well-suited to addition into the water phase. Thirdly, additives, such as immobilized enzymes, may also be connected to the backbone of the porous skeleton. Lastly, additives, such as immobilized ligands, enzymes or antibodies, may be connected to the backbone of the hydrogel polymer. The same additives may be suitable for location in more than one site. Typical additives include, but are in no way limited to, surface adsorbents, such as charcoal particles, immobilizing or binding agents, such as liposomes, lipid foams and affinity binding ligands, detoxifying enzymes or catalysts, sterilizing agents, such as antibodies and ultraviolet light sources (optical fibers). Once deactivated, the filter of the invention is also ideal for the removal of reaction products (deactivated or complexed pathogens, toxins, etc.) by their sequestration and adsorption into the hydrogel phase.

In one embodiment of the invention, the additives may be imbedded in the fluid phase of the hydrogel or immobilized by adsorption, bonding, conjugation, etc. onto the polymer backbone of the hydrogel polymer. In another embodiment of the invention, the additives could be similarly immobilized on the skeletal backbone. In yet another embodiment of the invention, additives, and in particular, large particulate additives, may be located in the open spaces of the porous network.

The high surface area of the hydrogel phase and the ability to tailor the chemical reactivity of the hydrogel phase makes the composition of the invention well-suited to additional applications. In another aspect of the invention, as scaffold is provided which is porous to permit fluid flowthrough and coated with a hydrogel coating. The hydrogel and/or any additives to the scaffold are capable of effecting a desired chemical transformation upon the fluid which passes therethrough. The scaffold may be used in applications such as, but not limited to, catalysis, distillation and enzymatic filtration. By "fluid" as that term is used herein, it is meant either a gas or liquid medium.

By "pores" as that term is used herein, it is meant an opening or channel on the surface or wall of the skeleton or hydrogel coating through which fluid may pass. The pore size is a measurement the mesh size of the openings. The actual pore size is relevant to the ability of the filter to trap or entrain contaminants.

By "porous" or "porosity" as those terms are used herein, it is meant a feature of the filter, either residing in the skeleton or the hydrogel coating, relating to open spaces or channels throughout the volume of the article through which a fluid (gaseous or liquid medium) may pass. Porosity measures the void volume fraction of the material. The porosity preferably provides an open network, as a closed network would not facilitate fluid flow therethrough. The degree of porosity is a factor in the low resistance to flow of the filter. The porosity may be introduced by the presence of pores: however, the openness of the article may be due to other structural features, such as the filamentous, foamlike or rodlike nature of the skeleton or hydrogel.

When addressing the size or dimension of pores or porosity in the article of the invention, it is meant a largest dimension of the cross-sectional area of the pore or porosity in the article, skeleton or hydrogel. The dimension may be, but is not required to be, measured relative to a direction substantially transverse to the direction of fluid flow.

By "contaminant" as that term is used herein, it means any agent, be it a particle, molecule, biological organism, gas or vapor, which is viewed as undesirable in the fluid medium. The contaminant may be particulate irritants, biological or chemical toxins, toxic or noxious fumes or microbiological agents or pathogens.

By "scaffold" as that term is used herein, it is meant a porous structure which maintains its porosity even when stressed and which permits continuous fluid inflow and outflow. The scaffold is typically rigid, but may possess some degree of flexibility so long as porosity is maintained upon deformation. Tensegrity structures as disclosed in co-pending United States Application No. 60/032,402, entitled "Biomimetric Materials", which is hereby included in its entirety by reference, are considered particularly suitable for such structures.

Brief Description of the Drawing

The invention is described with reference to the Figures, which are presented for the purpose of illustration only and are not intended to be limiting of the invention and in which,

Figure 1 is an illustration of a hydrogel coated filter of the invention; Figure 2 is an illustration of a hydrogel-coated tensegrity structure skeleton for use as a filtration system according to the invention;

Figure 3 is an illustration of a face mask incorporating the filter of the invention;

Figure 4 is a scanning electron photomicrograph of (A) uncoated Saratoga BDO fabric and (B) Saratoga BDO fabric coated with p(HEMA) hydrogel; Figure 5 is a scanning electron photomicrograph of (A) the surface of a p(HEMA) hydrogel and (B) a cross-section through the same hydrogel sample showing the size and distribution of pores;

Figure 6 is a scanning electron photomicrograph of a cross-section of a hydrogel prepared using the cast and leach method;

Figure 7 is a reaction scheme for the preparation of 4-O-β-D- galactosopyranosyl-D-glucopyranose-functionalized glycidylmethacrylate; and

Figure 8 is reaction scheme for the synthesis of p(HEMA-cø-GMA) functionalized with -aminophenyl-β-D-galactose sugar.

Detailed Description of the Invention The present invention exploits fundamental design principles utilized by living cells and tissues to create "biomimetic" materials designed for more efficient filtration and chemical processing. Much of the cell's metabolic machinery effectively functions in a "solid-state", that is, many of the enzymes that mediate biochemical reactions are physically immobilized on insoluble molecular polymers that comprise the cytoskeletal framework of the cell. Substrates and products can channel between adjacent enzymes due to the presence of an aqueous phase which surrounds these insoluble biopolymers. Because the cytoskeleton is a highly porous, three dimensional lattice, the surface area available for binding and processing of chemical and molecular substrates is greatly enhanced. In addition, the living cell and its cytoskeleton are also part of a higher order structure, the tissue, which is composed of many cells that are mechanically connected to each other and to a common extracellular matrix supporting lattice. This matrix lattice provides an additional skeletal backbone on a larger size scale which mechanically stabilizes the cytoskeletal framework while at the same time holding pores open that permit substrates and reactants to percolate through the entire tissue matrix. Finally, many enzymes also function in a solid-state while immobilized to the biopolymers that comprise the extracellular matrix using the aqueous phase of the interstitial fluid to deliver and removal chemical reactants and products. Thus, pathogens, toxins, and other destructive agents are prevented from reaching critical cellular and molecular targets due to the high tortuosity and porosity of the tissue matrix containing immobilizing enzymes and other binding agents which permits biochemical sequestration and removal of these destructive agents.

A filtration system of the invention is illustrated in Figure 1. The filter 10 includes a porous skeleton 12 coated with a hydrogel polymer 14 thereby providing the desired high surface area of active material. In addition, pore size and/or filtration pathway 16 of the porous skeleton is greater in size than the pathogen, toxin or contaminant particles to be removed so that fluid flow resistance through the material is minimized. The pore size dimension typically can range from five micrometers (μm) to 5 cm, and is preferably 25 μm-5 cm and most preferably 1-5 cm. The preferred range may vary for particular applications. For example, preferred range for face masks would be 100 microns to 1 centimeter. The preferred range for a fabric would be much smaller, such as 25 μm to 250 μm.

The support skeleton is not limited to any particular design, so long as it is strong enough to support the hydrogel and possesses pore size and/or air pathways of the requisite dimensions. Suitable support skeletons may be fabrics, textiles, felts, nets, foams, honeycombs, screens or meshes of two or three dimensions. The porous skeleton may have a random or repeating geometry. In preferred embodiments, the skeleton possesses a three-dimensional lattice which resembles the cytoskeletal framework of cells. In other preferred embodiments, the porous skeleton comprises integrally connected modules having tensegrity and/or geodesic structural features, such as sheets composed of linked tensegrity units, in which each unit consists of six rigid compression elements (struts) and twenty four cables, variously linked to adjacent units. A hydrogel-coated rigid octet truss such as shown in Figure 2 is an example of a porous scaffold material possessing geodesic and tensegrity elements suitable for high flowthrough applications of the invention.

The porous skeleton may be made from almost any material, including but not limited to organic polymers, plastics, paper, metal, glass and ceramic. Commercially available porous, 3-D matrices, such as plastic foams or fibers, metallic fibers or meshes, commercially available fabrics, such as Lycra®-based elastic materials, such as Maxxam®. conventional cotton, nylon, and polyester materials, polyurethanes foams, metal and plastic screening and the like may be used as the porous skeleton. Exemplary polymers include non-erodible polymers such as, poly aery lates, epoxides, polyesters, polyurethanes, poly (methacry late) , and polyimides. In preferred embodiments, the porous skeleton is comprised of siloxanes, such as polydimethylsiloxanes, polyethylenes, Kevlar®, nylon or polyurethanes. A particularly preferred porous skeleton may be a geodesic or tensegrity-based structure, which uses the principles of tensegrity (self-stabilizing structures) to prepare skeletons which are highly porous, yet possess great compressive and tensile strength. Exemplary tensegrity structures are described in U.S.S.N. 60/032,408, entitled "Biomimetric Materials", which is hereby incorporated by reference. The surface of the skeleton may be treated to improve adhesion of the hydrogel onto the porous network. For example, the skeleton may be treated with hydrophilic agents to improve hydrogel affinity for the skeleton. As a further example, a hydrophilic coating as described in U.S. Patent No. 5,503,746 to Gagnon may be used. In another embodiment, the surface of the porous skeleton could be roughened or textured to enhance hydrogel adhesion. Surface treatment may be accomplished by chemically etching the surface or by altering the vertical height of the polymerization layer using stereolithography. Polymer layers applied to the skeleton typically leaves a sedimentary rock-like patterning on the skeleton surface which could be used to enhance hydrogel adhesion.

The porous skeleton, and tensegrity structures in particular, may be prepared using well known polymer synthesis and microfabrication techniques including, but not limited to. stereolithography, three dimensional microprinting, microscale patterning, micromolding techniques and self-assembly. These fabrication techniques may be facilitated by the use of mathematical models for cell and cytoskeletal mechanics based on tensegrity. These mathematical principles are described in "A Microstructural Approach to Cytoskeletal Mechanics based on Tensegrity" J. Theor. Bid. 181:125 (1996) and U.S.S.N. 60/032,408, which are herein incorporated in their entirety by reference.

Other well-known microfabrication techniques may be used in the preparation of the scaffold material. By way of example only, stereolithography techniques, three dimensional microprinting, three dimensional laser-based drilling or etching techniques and micromolding, may be used in the preparation of the material of the invention. The interested reader is directed to Science and Technology of Microfabrication R.E. Howard, E.L. Hu, S. Namba, S. Pang (Eds.) Materials Research Society Symposia Vol. 76 (1987), for further information on microfabrication.

The hydrogel polymer is swollen with water or other suitable solvent. The skeleton supports the hydrogel polymer and provides it with the requisite mechanical strength so that it does not collapse and thereby reduce porosity. In other embodiments of the invention, the hydrogel coating may itself be porous. The hydrogel porosity desirably increases the active surface area of the filter. As with the porous skeleton, the porosity of the hydrogel desirably is greater than the pathogens or particulate or vaporous contaminants which are to be removed from fluid. Porosity includes incorporation of pores within the hydrogel, use of a hydrogel foam, and the like. Porosity dimension is greater than 5 μm. and preferably in the range of 20-150 μm. Porous hydrogels are known in the art and can be prepared according to known methods. For example, pores may be introduced into the hydrogel using conventional methods, such as introduction of porosigens into the hydrogel, control of dehydration process or casting and leaching techniques.

The hydrogel coating is sufficiently thick to attract and adsorb the contaminants of interest, while retaining sufficient open space that resistance to flow is minimized. The coating thickness is preferably in the range of 10 to 500 μm, but may be smaller or greater as the situation dictates.

Suitable hydrogel polymers desirably demonstrate chemical and thermal stability, high swelling efficiency and flexibility. In particular, the hydrogels should not be readily biodegradable. Exemplary hydrogels include, but are not limited to, poly(2-hydroxyethyl methacrylate) , poly(2-hydroxyethylmethacry late-co-methyl methacrylate), poly(methacrylic acid) (PMAA), poly (acrylic acid) (PA A), linear polyesters, cellulosics, poly (vinyl alcohol) (PVA), poly (aery lamides), poly(N-vinyl pyrolidone) (PNVP), poly (vinyl acetate), poly(ethylene oxide) (PEO), poly(ethylene glycol) (PEG), and copolymers and terpolymers thereof.

Although not bound by a particular mechanism, it is believed that the hydrogel polymer removes contaminants from the fluid medium due to their inherent hydroscopic (water-seeking) properties. The open porous network of the filtration system does not necessarily trap contaminants by physical obstruction, but instead relies on attractive hydrophilic forces between the contaminant and the hydrogel polymer to remove contaminants from the air. The water-swollen hydrogel is very hydrophilic and has a high affinity for hydrophilic contaminants, which become adsorbed into the fluid phase of the hydrogel. Furthermore, the moist surface of the hydrogel is capable of wetting the surfaces of most airborne contaminants, so that even hydrophobic or particulate contaminants may be retained within the porosity of the hydrogel polymer. Because the contaminant is adsorbed into the interior of the hydrogel polymer, the surface of the filter is constantly being cleansed and is therefore capable of removing a significantly larger amount of airborne particles than prior art devices which rely on entrapment to remove contaminants. Thus, the hydrogel polymer filtration system is capable of removing various types of contaminants over a wide size range.

In the instance where the fluid to be filtered is a liquid, it is anticipated that flow rate would be slower than for gases in order to provide sufficient time for contaminants to diffuse into and out of the hydrogel phase. Due to the increased surface area of the filter of the invention as compared to conventional filters, however, the flow rate will not have to be as slow as conventional systems in order to be as effective. As an additional advantage, contaminants taken up by the hydrogel phase are not readily released, thus continually cleansing the liquid. The adhesive and adsorptive properties of the hydrogel polymer make it particularly well-suited for the sequestration of microbiological organisms. Since pathogens and toxins typically are much smaller in size, e.g., 1-3 μm, than the porosity of the filter, e.g., >5 μm, there is little chance that the contaminants will clog the filter and reduce air flow, as in prior art filtration systems. Once the pathogen is adsorbed into the hydrogel polymer liquid phase, it is sequestered and deactivated. It has been demonstrated that the hydrogel alone is capable of sequestering biological pathogens. See, Example 10. Thus the filter system is well suited for use in face masks and, in particular surgical masks, as well as in protective clothing and breathing apparatus for biological warfare or other biological threats. To enhance the biocidal activity of the filter, additives may be included which have antifungal, antibacterial and antibiotic effects. A non-limiting list of suitable additives includes antibiotics, antiseptics, deactivating enzymes or other chemical agents, oxidizing agents, such as hydrogen peroxide, iodine compounds, and potassium permanganate, dendrimers, and bacteriocidal agents, such as copper salts and copolymers as described in U.S. Patent No. 5,006,267.

It also should be possible to provide additional protective activity against biothreat by incorporating molecules that inactivate or destroy the biothreat. The molecules may be located in the liquid phase of the hydrogel or may be bound to either the porous skeletal structure or the hydrogel polymer, e.g., "immobilized". Immobilized enzymes are a preferred embodiment. The enzyme or other biological agent may specifically target against pathogens or release free radicals which can kill microorganisms and sterilize the site. For example, proteases such as lysozyme may be included to breakdown toxins or enzymes such as peroxidases may be included which generate free radicals in the hydrogel. Enzymes, such as myeloperoxidase, may be incorporated into the hydrogel to release free radicals into the fluid phase. Soluble photosensitive molecules may be incorporated which release oxygen free radicals on exposure to specific light wavelengths, e.g., via optical fibers. Such agents are biomimetric since they use mechanisms used by living cells and tissues, e.g., lysozyme is found in saliva and free radical release mediates killing in macrophages.

In addition, enzymes that inactivate and/or destroy chemical toxins, such as organophosphorus nerve gases (e.g., acetylcholinesterase, organophosphorus acid anhydrolase, phosphotriesterase), also could be incorporated within the gel to provide additional protection against these chemical warfare agents. By way of example only, acetylcholinesterase enzyme may be conjugated to a hydrogel using carbonyldiimidazole. The efficiency of protein binding can be assessed by radiolabeling or surface analysis (X-ray photoelectron spectroscopy). Suitable additives which are reactive with the contaminant to be removed are enzymes, antimicrobials, chemical substrates reactive with the contaminant, proteins, lipids, nucleic acids, oxidants, free radical generators, photosensitive molecules capable of generating oxygen free radicals upon exposure to light as well as sterilizing radiation and means to deliver it to the filter site. For example, the additives include peroxides, potassium permanganate, iodine, aldehydes, magainins, dendrimers, novasomes and liposomes. In an alternative embodiment, pathogenic organisms (e.g., bacteria, viruses, protozoa) and toxins (e.g., ricin toxin, botulinum toxin, vibrio cholerae neuraminidase) may be bound and sequestered by incorporation of specific binding ligands into the filter. The binding ligand is selected to bind specifically to the contaminant to be removed from the environment. The binding ligands maybe introduced into the liquid phase of the hydrogel or may be conjugated onto the backbone of a hydrogel which has been coated onto the scaffold material. Use of such specific binding ligands mimic cell activity since they take advantage of mechanisms used by cells in confronting toxins and pathogens. Biological toxins and pathogenic organisms adhere to living cells and enter the body by binding to specific ligands on the cell surfaces. Exemplary binding ligands include simple sugars (e.g., galactose), complex carbohydrates (e.g., heparin sulfate), and membrane phospholipids (e.g., phosphatidylinositol). Synthetic antibodies, e.g., plastics with ligand-shaped binding sites on their surfaces, may also be employed. Monoclonal antibodies also have been generated which may be used in the filter of the invention to bind to specific biothreat agents (e.g., ricin toxin) with high affinity.

In other embodiments of the invention, particulate additives are incorporated into the filter, typically in the interstitial spaces of the filter, which are capable of adsorbing contaminants. Suitable adsorbent additives include charcoal particles or beads or zeolites.

The hydrogel polymer is also capable of absorbing gases and volatile liquids, such as volatile organic liquids (VOCs). Additives may also be included which promote the removal of VOCs from the fluid. In order to improve the interactive forces between the hydrophilic phase of the hydrogel and the organic contaminant, surfactants desirably may be employed to alter the surface properties of the hydrogel. The filter also could be used to purify organic solvents or hydrocarbons by removal of hydrophilic contaminants. Suitable additives include, zeolites, alkali or alkaline earth bases and bifunctional amphoteric oxides. Where such additives are large particulates, they may be added to the porous spaces of the filter. Additives may be introduced into the hydrogel phase by mixing with the hydrogel prior to its application to the skeleton. They also may be introduced into the hydrogel or porous skeleton by swelling the hydrogel with an aqueous solution containing the additive, either before or after coating onto the porous skeleton. Additives also may be chemically bonded to the hydrogel by reaction of the additive with reactive sites of the hydrogel or porous skeleton.

The filter of the invention may be incorporated into face masks, breathing apparatuses, fabrics and textiles. The filter may be used as air conditioner filters, air room cleaners and window screens, in water purification systems and catalytic converters for removal of hydrocarbons and other detoxification networks. Figure

3A is an illustration of a face mask 30 which incorporates a filter 32 of the invention. A portion of the outer surface of the face mask is removed to indicate location of the filter. Possible architectures for the filter are shown in Figures 3B-D and consist of stacked layers of open geodesic units ("cassettes"). Prototype cassettes may include baffles 34 as illustrated in Figures 3C and 3D. The baffles aid in retarding the flow of air-borne particles and aerosols through the filter to thereby maximize contact with the pathogen-binding hydrogels, while at the same time maintaining ample air flow for breathing.

The hydrogel-coated porous structure may also useful in bioprocessing operations. For example, living organisms may be cultured in the liquid phase of the hydrogel and may be used in place of microcarrier beads or suspension cultures in the culturing process. In order to accomplish this, the hydrogel may include immobilized enzymes or living "bugs" growing in the hydrogel.

It is further contemplated that the porous structure and hydrogel may be useful in the chemical processing or catalysis of a variety of reactions. Reactants could be volatilized or dissolved in the fluid medium and passed through a scaffold including a hydrogel impregnated with a co-reactant or catalyst. The reactants would be adsorbed into the hydrogel phase, where they could be chemically transformed or detoxified. Suitable uses include as a catalytic converter or in the distillation of alcohol in the production of liquor. In such instances, the porous skeleton is preferably made of a more chemically inert material such as glass or ceramic.

The invention is described in the examples which follow, which are presented for the purpose of illustration only and which are in no way intended to be limiting of the invention. The true scope of the invention is set forth in the claims which follow the specification. Example 1. Preparation of a hydrogel-coated filter.

A typical filter may be prepared as follows. A CAD application may be used to design a three dimensional network using a commercially available program such as Alias Wavefront, Softimage, Proengineer, or SDRC. The CAD is then translated into an .STL file and fabricated using stereolithography.

The scaffold may then be immersed in a monomer, crosslinking agent and initiator, for example, 2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA), and ethyleneglycol dimethacrylate (EGDMA), purged with nitrogen to remove oxygen, and then polymerization is initialized. In the preparation of poly(HEMA-co-MMA), the monomers, 2-hydroxy ethyl methacrylate (HEMA) and methyl methacrylate (MMA), are liquid and will be mixed with a crosslinking agent (EGDMA) and an ] initiator to polymerize and form a hydrogel according to standard procedures. See, "Adsorption of Proteins from Artificial Tear Solutions to Poly(methyl methacrylate) Copolymer", by F.H. Royce, Jr.; B.D. Ratner and T.A. Horbett, in Biomaterials: Interfacial Phenomena and Applications. Advances in Chemistry Series American Chemical Society (1982), S.L. Cooper, N.A. Peppas, Eds.; pp453-462, which is herein incorporated by reference. The relative amount of HEMA confers hydrophilicity and also pliability whereas the MMA confers hydrophobicity and mechanical rigidity to the hydrogel. The engineering of the HEMA/MMA copolymer ratio and the EGDMA crosslinking ratio allows one to synthesize hydrogels with tailored permselective and mechanical properties.

The residual resin adherent to the surface of the porous skeleton will be polymerized by adding an initiator to form a hydrogel coating. This hydrogel would in turn be chemically conjugated or reacted to bioactive molecules such as carbohydrates containing galactose dimers to remove ricin toxins, antibodies against different pathogenic organisms, and enzymes, such as acetylcholinesterase, that may deactivate nerve gases. The scaffold spaces may also be impregnated with charcoal microparticles to remove air-borne chemical toxins as well as liposomes or lipid foams to remove lipophilic agents and organisms. The monomer HEMA has a pendant hydroxyl group so it will allows one to use alcohol chemistry to attach carbohydrates and proteins. The tensile strengths and moduli of the materials may be determined by an axial/torsional test system. Water binding capacities can be measured in dynamic and equilibrium swelling studies. Porosity and pore size of dry specimens can be measured by mercury intrusion porosimetry. The porosity and pore size of wet specimens can be estimated morphometrically using environmental scanning electron microscopy.

Example 2. Preparation of a p(HEMA)-coated face mask cassette is described. The face mask cassette was a geodesic design prepared using stereolithography and has the geometry as shown in either Figure 2 or Figure 3. A HEMA homopolymer, p(HEMA), was prepared according to the general procedure outlined in Example 1. The structure was precoated with a p(HEMA) alcohol solution, followed by polymerization of HEMA and crosslinking using EGDMA in 0.7 M NaCl using a redox initiating system. The structure was coated as follows: a. dip coating the geodesic skeleton coated with p(HEMA) ethanol solution (5-

10% w/w, followed by air drying at room temperature for 10 minutes; b. immersing in ammonium persulfate aqueous solution (5% w/w) to swell the p(HEMA) coating, followed by drying the coated geodesic structure in air at room temperature for 10 minutes; c. repeating the coating process of step a; d. introducing the coated skeleton in ascorbic acid (0.3% w/v), HEMA (40% w/w), EGDMA (0.6% molar to monomer) solution which also contains NaCl (0.7M) and gently stirring until the desired coating thickness is achieved.

The porous skeleton was coated with solutions having a variety of monomer and initiator concentrations, as well as coating times, which provided a uniform p(HEMA) hydrogel coating of differing thicknesses. Results of the various coating conditions are found in Table 1. Table 1.

Example 3. Preparation of a p(HEMA)-coated fabric is described. This example demonstrates the application of the hydrogel to a fabric which may be used in manufacturing clothes for protection against biothreats, e.g., battledress overgarments (BDO).

A battledress overgarment obtained from Saratoga Corporation was coated with p(HEMA) hydrogel by immersing the fabric in a solution of HEMA, EGDMA and initiator. The dipped fabric was then irradiated with UV light for 90 minutes to initiate polymerization. Examination of the dipped fabric showed a consistently even coating of hydrogel, even at high magnification. See, Figure 4 in which Figure 4A depicts the uncoated fabric and Figure 4B depicts the fabric coated with p(HEMA) hydrogel.

Example 4. Preparation of porous hydrogels is described. A porous hydrogel was prepared using UV irradiation to initiate polymerization of HEMA to form p(HEMA). p(HEMA) gels having pores sizes ranging from 1 μm to 50 μm were prepared. The porosity of the hydrogel may be modified by varying the concentration of sodium chloride in the gel solution. Figure 5 shows a photomicrograph of a poly(HEMA) hydrogel prepared using 0.3M sodium chloride which demonstrates that the pores are evenly distributed throughout the hydrogel.

The porosity of these hydrogels was further modified by using a casting and leaching method which involved changing the concentration of sodium chloride particles (crystals) that were embedded within the hydrogel during polymerization and where were later dissolved away to create pore space. Figure 6 shows a photomicrograph of a porous hydrogel prepared according to this method. By varying both the pore size and porosity, the surface area of the hydrogel available for coating with bioactive ligands, e.g., lectins, antibodies, and enzymes, may be greatly increased which may used to optimize pathogen capture.

Example 5. This example describes the effect of different solvents on pore size and porosity to enable increase of the surface area of the hydrogel and facilitation of immobilization of a maximal amount of specific binding ligands for neutralization of pathogens. p(HEMA) gels were prepared by polymerization in toluene, 50/50 toluene/propanol and 70/30 toluene/propanol. Scanning electron microscopy (SEM) studies demonstrate that the resultant p(HEMA) has different pore size and porosity. An increase in the ratio of toluene to propanol was shown to increase the porosity and the specific surface area of the hydrogel, but result in smaller pore size. Example 6. Quantification of water uptake by hydrogels. Hydrogels were demonstrated to be capable of holding a substantial amount of water.

Water uptake and hydrogel swelling depends upon various factors such as the polymer chemical composition, crosslink density and environment, i.e., ionic strength an pH. The effect of varying chemical composition and pH on water absorbing capacity of homo- and copolymers of HEMA and glycidylmethacrylate (GMA) was investigated. HEMA and GMA homo- and copolymers were synthesized using a bulk polymerization technique. Tertiary butyl hydroperoxide (0.6343 wt%) was used as initiator and ethylene glycol dimethacrylate (0.102 mole%) was used as the crosslinking agent. GMA content in the copolymers was varied at 15, 34, 50, 67 and 100 mole%. The polymerization was initially allowed to proceed at 65 °C for 20 hour and then at 70 °C for another 20 hours. The polymers obtained were in the form of solid transparent cylinders which were cut into 1-2 mm thick disks for the water uptake studies. Water uptake was studied in distilled water and in buffers of various pH with constant ionic strength (0.5 M) at 35 ± 0.05 °C. Two sets of experiments were carried out. In the first set, crosslinking density was held at 1 mole% and initiator concentration was 1 wt% of monomers. The relative concentration of GMA:HEMA was varied at 1 :2 and 2:1 moles. Polymerization ws carried out for 16 hours at 80 °C. This initial approach produced solid polymers with bubbles (voids) trapped inside. This was most likely due to the high concentration of initiator. In the second series of experiments, the initiator concentration and crosslinking density were decreased to 0.5 wt% and 0.1 mole% of monomers, respectively. The ratio of GMA:HEMA was varied as 1 :0, 2:1. 1:1, 1 :2 and 0:1 moles. Polymerization was allowed to proceed for 48 hours. This produced solid polymers with very few or no bubbles. The polymers were cut into 1 mm disks for the swelling experiments. These studies showed that water uptake decreases as the amount of GMA is increased in the GMA/HEMA copolymer. Increasing the amount of GMA also reduced the amount of hydrogel swelling. This is not surprising due to the hydrophobic nature of GMA. Furthermore, water uptake decreased in HEMA homopolymers as the pH of the medium is lowered whereas the effect of pH on water uptake in the HEMA GMA copolymers was minimal.

Additional studies have shown that the post-polymerization drying process will greatly affect the water up-take ability of the hydrogels. Porous hydrogels prepared in NaCl solution have different water up-take capabilities when dried in different ways. Hydrogels dehydrated directly by evaporation of water in an oven have the lowest water up-take, while hydrogels dehydrated by a gradient hydration method using propanol and toluene gives the highest water up-take. Dehydration in propanol (replacement of water by propanol) has an intermediate result. It is desirable to maximize the water up-take of the hydrogel in order to improve aerosol capture ability of the hydrogel.

Example 7. A monomer with a β-lactose sugar functional group was synthesized. The sugar group may be used to bind and immobilize living cells and toxins.

A glycidyl methacrylate (GMA) monomer was functionalized with the β- lactose sugar, 4-O-β-D-galactospyranosyl-D-glucopyranose, according to the reaction scheme shown in Figure 7. Characterization by 'H-NMR and by FTTR confirmed the sugar-GMA adduct. Preliminary investigation using ¹ C-NMR indicates the incorporation of carbonyl groups, indicating glycidyl methacrylate functionalization since the starting sugar does not contain a carbonyl functional group. The solubility characteristics of the starting sugar (β-lactose) and functionalized monomer (β-lactose-GMA adduct) are very different. The simple sugar is insoluble in methanol, whereas the adduct is completely soluble in methanol. Also, the β-lactose-GMA adduct is highly hydroscopic, whereas the starting material are hydrophobic and insoluble in water.

The homopolymer of β-lactose-GMA monomer and terpolymers of HEMA, GMA and β-lactose-GMA were synthesized by free radical polymerization at 65 °C using tert-butylhydroperoxide as the initiator. Terpolymers containing β-lactose sugar-functionalized GMA, GMA and HEMA were also prepared. The composition is given in Table 2.

Table 2.

Example 8. A copolymer gel was functionalized with a sugar group. Functionalization of HEMA-co-GMA was accomplished using p- aminophenyl-β-D-galactose, as shown in Figure 8. Porous poly(HEMA-cø-GMA) (70 mol% HEMA; 30 mol% GMA) was swelled in N,N-dimethylformamide (DMF) for 24 hours, and the swollen polymer was reacted with/?-aminophenyl-β-D-galactose in methanol:0.3 M K₂C0₃ solution (1 :1 v/v) for 24 hours at ambient. The resulting polymer was crosslinked with EGDMA. Incorporation of the sugar group into the polymer was confirmed by FTIR.

Example 9. A terpolymer including cationic monomers is described. The positively charged functional group is intended to adsorb bacteria efficiently.

Terpolymers comprising HEMA, GMA and [(3-methacrylamino) propyl] trimethylammonium chloride (MAAmPTAC) were prepared by polymerization of the monomers using EGDMA as the crosslinking agent and t-butyl hydroperoxide (TBHP) as the free radical initiator at 60 °C for 20 hours.

Example 10. Uptake of bacteria by hydrogels. Studies were conducted to characterize the ability of an unmodified porous hydrogel to restrict passage of living pathogens.

A 100%) poly(HEMA) hydrogel prepared by the casting and leaching method was used to investigate its ability to bind and retain Escheria coli K-12 (ATCC 10798), a wild type, motile, gram-positive rod. Using a hydrogel with a pore size of 50-150 μm and 2.5 mm thickness, no bacteria were able to pass through the porous gel. More than 90% of the bacteria remained sequestered within the interstices of the gel, even after 24 hours incubation. This results suggested that the poly(HEMA) hydrogel alone has the capacity to sequestrate live bacteria with out using any bioactive ligands, i.e., antibodies or enzymes and to capture and kill pathogens when bactericidal agents and the like are included in the hydrogel phase. The hydrogel's ability to capture pathogens will be further improved if bacteria-binding ligands and germicidal enzymes are incorporated into the hydrogel.

Example 11. Pathogen-neutralizing capabilities of porous hydrogels. The purpose of this experiment is to demonstrate the capability of functionalized hydrogels to trap, bind and kill living bacteria. Three different bacterial strains, Escherichia coli K-12 (ATCC 10798, gram negative, motile), Bacillus subtilus (ATCC 6051a, gram-positive, motile) and Staphylococcus aureus (ATCC 27217, gram-positive, pathogenic), which represent both gram-positive and negative bacteria as well as a real pathogen, were used in this study. The bacteria were cultured at 37 °C, harvested at stationary growth phases, washed twice in water and suspended at concentrations ranging from 10⁵ - 10⁸ cells/ml. Hydrogels used for these experiments consisted of macroporous p(HEMA) fabricated using the enhanced phase separation method of polymerization of HEMA in sodium chloride solution in order to introduce macropores in the hydrogel (see, Example 4). For testing the bactericidal capabilities of the hydrogels, the 2 mm thick hydrogels were first cut into lxl cm pieces and 20 μl of different concentrations of suspended bacteria were added to the top of the hydrogel for 30 min. The hydrogels were then placed in bacteria culture media and incubated for 48 hour at 37 °C and the number of live bacteria present were measured using the standard plate measure.

E. coli, a highly motile (20 μm/sec) facultative anaerobe, was used to examine the trapping capability in the pores of the unmodified hydrogel. In these experiments, 20 μl bacterial suspension with a concentration of about 10⁸ cells/ml was added to the top of a lxl cm piece of hydrogel, both hydrated and non-hydrated. The hydrogels were then placed on a solid culture medium and incubated at 37 °C. After 48 hours, no bacteria were detected under the hydrogels, which indicated that the added bacteria did not pass through the hydrogel. The bactericidal properties of the hydrogels containing hydrogen peroxide was examined. Different concentrations of hydrogen peroxide were used to hydrate the hydrogels that, in turn, tested for their ability to kill bacteria. The same three bacterial strains were used to test bactericidal effectiveness. All three strains of bacteria at 10⁸ cells/ml were killed in hydrogels containing low (0.3%) peroxide levels. The bactericidal properties of the hydrogels containing antibiotics also was examined. Hydrogels loaded with 100 μg/ml gentamicin as described above were found to kill E. coli and S. aureus at concentrations of up to 10⁸ cells/ml.

What is claimed is:

Claims

CLAIMS:

1. A filter for removing a contaminant from a fluid, comprising: a porous skeleton coated with a hydrogel material in which the pore size of the porous skeleton is greater in dimension than a contaminant to be removed from an environment.

2. The filter of claim 1 , wherein the pore size is of a dimension effective to remove biological pathogens and toxins.

3. The filter of claim 1 , wherein the pore size is of a dimension effective to remove molecular and chemical contaminants.

4. The filter of claim 1 , wherein the pore size is of a dimension effective to remove vaporous or gaseous contaminants.

5. The filter of claim 1, wherein the hydrogel material is selected from the group consisting of poly(2-ethylhydroxyethyl methacrylate), poly(2- hydroxyethylmethacry late-co-methyl methacrylate), poly(methacrylic acid) (MAA), poly (aery lie acid) (AA), linear polyesters, cellulosics, poly(vinylalcohols) (PVA), poly(acrylamides) , poly (n-vinylpyrollidone) , poly(vinylacetates) , poly(ethyleneoxide) (PEO), poly(ethylene glycol) (PEG), and copolymers and terpolymers thereof.

6. The filter of claim 1 , wherein the hydrogel material further comprises additives selected to enhance removal of the contaminants.

7. The filter of claim 6, wherein the additive comprises an affinity binding ligand selected to have a binding affinity to a contaminant to be removed.

8. The filter of claim 7, wherein the affinity binding ligand is selected from the group consisting of sugars, carbohydrates, proteins, lipids and nucleic acid, membrane phospholipids and plastic antibodies. _╬¢,ΓÇ₧ΓÇ₧_o^ 9/22861

9. The filter of claim 6, wherein the additive is reactive with a contaminant in order to inactivate or destroy the contaminant.

10. The filter of claim 9, wherein the reactive additive is selected from the group consisting of enzymes, antimicrobials, chemical substrates reactive with a contaminant, proteins, lipids, nucleic acids, oxidants, free radical generators, photosensitive molecules capable of free radicals generation, sterilizing radiation, peroxides, potassium permanganate, iodine, aldehydes, magainins, dendrimers, novasomes and liposomes.

11. The filter of claim 6, wherein the additive is capable of adsorbing contaminants from the fluid.

12. The filter of claim 11, wherein the additive is selected from the group consisting of charcoal particles and zeolites.

13. The filter of claim 6, wherein the additive is located in a liquid phase of the hydrogel.

14. The filter of claim 6, wherein the additive is chemically bound or coordinated to a polymer comprising the hydrogel.

15. The filter of claim 6, wherein the additive is chemically bound or coordinated to the porous skeleton.

16. The filter of claim 1 , wherein the pore size of the porous skeleton is in the range of about 5 ╬╝m to 5 cm.

17. The filter of claim 1 , wherein the pore size of the porous skeleton is in the range of about 25 ╬╝m to 5 cm.

18. The filter of claim 1 , wherein the filter is incorporated into a face mask and the pore size the porous skeleton is in the range of 100 ╬╝m - 1 cm.

19. The filter of claim 1, wherein the filter is incorporated into a fabric and the pore size the porous skeleton is in the range of 25 ╬╝m - 250 ╬╝m.

20. The filter of claim 1 , wherein the hydrogel is porous.

21. The filter of claim 20, wherein the hydrogel porosity is in the range of 5-150 ╬╝m.

22. The filter of claim 1, wherein the porous skeleton is selected from the group consisting of fabrics, textiles, felts, nets, foams, honeycombs, screens, and meshes of two or three dimensional materials.

23. The filter of claim 1, wherein the porous skeleton is comprised of a material selected from the group consisting of inorganic or organic polymers (non-erodible or erodible), metals, ceramics, glasses, carbon, proteins, lipids, nucleic acids, carbohydrates, collagens, elastins and spectrins.

24. The filter of claim 1, wherein the porous skeleton is comprised of a geodesic material or a material which can rearrange to form a fully geodesic material.

25. The filter of claim 1, wherein the porous skeleton comprises a predetermined arrangement of integrally connected modules, each said module comprised of a plurality of integrally connected elongated members forming at least a portion of a polyhedron, the members arranged such that at least a portion of said members form geodesic or tensegrity elements.

26. The filter of claim 1 , wherein the filter is incorporated into an device selected from the group consisting of a face mask, protective fabric, air filter, water filter, breathing apparatus and catalytic air detoxification system.

27. A scaffold for chemical processing, catalysis, or detoxification, comprising: porous skeleton coated with a hydrogel material, said scaffolding being porous, such that a fluid medium comprising a chemical substrate may pass freely therethrough, said hydrogel selected to transform on said chemical substrate into a desired product.

28. A scaffold for biological processing, comprising: porous skeleton coated with a hydrogel material, said scaffolding being porous, such that a fluid medium comprising a living organism may pass freely therethrough, said hydrogel selected to be compatible with viability of the living organism.

29. The scaffold of claim 28, further comprising a molecule capable of interacting with or exerting an effect on the living organism.

30. The scaffold of claim 29, wherein said molecule comprises an enzyme.

31. A method of filtration, comprising: contacting a fluid with a filter comprising a porous skeleton coated with a hydrogel material in which the porosity of the filter is greater in size than a contaminant to be removed, whereby the contaminant is removed from the fluid.