Bilayer film

Abstract

There is provided a porous membrane comprising: an upstream porous asymmetric layer having an asymmetric layer thickness and a porous structure that reduces passage of bacteria therethrough; a downstream porous isometric polymer layer in contact with the porous asymmetric layer, the porous isometric layer having an isometric layer thickness and a porous structure that reduces passage of bacteria therethrough; wherein the porous membrane has a total membrane thickness; and the isometric layer thickness is 45% to 80% (e.g., 48-80%) of the asymmetric layer thickness.

Description

Background Technology

[0001] Membranes with isotropic (symmetric) and anisotropic (asymmetric) structures, such as multilayer membranes and composite membranes, are known in the art. However, conventional membranes are not suitable for some applications, for example, they cannot reliably provide one or more of the following: the required flux, sterile filtration, and robustness. This disclosure aims to improve at least some of the disadvantages of the prior art. These and other advantages of this disclosure will be apparent from the description set forth below. Summary of the Invention

[0002] In one aspect, this disclosure provides a porous membrane comprising: an upstream porous asymmetric layer having an asymmetric layer thickness and a porous structure that reduces bacterial passage therethrough; a downstream porous isometric polymer layer in contact with the porous asymmetric layer, the porous isometric layer having an isometric layer thickness and a porous structure that reduces bacterial passage therethrough; wherein the porous membrane has a total membrane thickness; and the isometric layer thickness is 45% to 80% (e.g., 48% to 80%) of the asymmetric layer thickness.

[0003] In another aspect, this disclosure provides a method for processing a fluid, the method comprising passing the fluid through a porous membrane described herein in a direction from an asymmetric layer toward an isometric layer.

[0004] In a further aspect, this disclosure provides a method for preparing the porous membrane described herein, the method comprising preparing a first solution comprising a first polymer and a solvent for the first polymer, and a second solution comprising a second polymer and a solvent for the second polymer. According to an embodiment of this disclosure, the method includes casting the first solution onto a support at a first velocity, and casting the second solution onto the first solution to form a membrane precursor. In an embodiment, the method further includes quenching the membrane precursor in a fluid at a second velocity, leaching the membrane precursor, and drying the membrane. Attached Figure Description

[0005] Figure 1A and 1B Depicting asymmetric layers ( Figure 1A ) and equal-metric layers ( Figure 1B A representative scanning electron microscope (SEM) image. Figure 1A The four zones of the asymmetric layer are further shown.

[0006] Figure 2A and 2B The results of a bacterial challenge study of isobaric layers of porous membranes as described herein are shown. Figure 2A This is a scatter plot, which shows the bubble point (K) along the x-axis for samples with equal thickness of film. L(), in psi, and bacterial recovery rate from the filtrate along the y-axis, in CFU. Figure 2B This is a scatter plot showing the K values ​​of equal-weight film samples along the x-axis. L The units are psi and the logarithmic decrease value (LRV) along the y-axis. A total of 44 samples were tested and grouped according to thickness in mils, as shown in the legend. The line marked "Cliff" indicates the critical point (cliff) for bacterial challenge (BC), and the line marked "LSL" indicates the lower limit of specification. Data points marked as attributable causes were identified as deformations that caused damage to the test samples and prevented proper testing conditions.

[0007] Figure 3 The results of a bacterial challenge study of asymmetric membranes with porous membranes as described herein are shown. Figure 3 This is a scatter plot showing the bubble points (K) of the asymmetric membrane sample along the x-axis. L The values ​​are in psi and the logarithmic decrease (LRV) along the y-axis. A total of 69 samples were tested, although 17 were excluded as representative due to deformation or damage that prevented proper testing conditions. The vertical dashed line marked "38 psi" indicates the BC critical point, and the horizontal line marked "3.5LRV" ​​indicates the minimum LRV value used to determine the BC critical point.

[0008] Figure 4A and Figure 4B An illustrative filter assembly (filter capsule) is depicted in an exploded view, which can be used with the membrane described herein. Figure 4A The top view shows a filter capsule having a hollow cylindrical filter element comprising a pleated membrane according to one aspect of this disclosure, and a structure disposed between the lower end of the filter element and the outlet portion of the housing for reducing stagnant (dead) volume. Figure 4B The same filter capsule is shown in the view below.

[0009] Figure 5A and 5B An illustrative filter assembly (filter capsule) is depicted in an exploded view, which can be used with the membrane described herein. Figure 5A The top view shows a filter capsule comprising a housing with at least one planar filter element, the planar filter element comprising a membrane according to one aspect of the invention, and protrusions of the housing and the membrane therein to reduce retention volume. Figure 5B The same filter capsule is shown in the view below. Detailed Implementation

[0010] One aspect of this disclosure provides a porous membrane comprising an upstream porous asymmetric layer and a downstream isometric layer, both of which reduce the passage of bacteria, wherein the membrane has a total thickness, and wherein the isometric layer has a thickness of 45% to 80% of the thickness of the asymmetric layer. The asymmetric layer can act as a bacterial pre-filter that reduces the amount of bacteria entering the isometric layer. Advantageously, this allows the isometric layer to have a reduced thickness while unexpectedly maintaining the ability to filter aseptically. This allows the membrane to have a reduced total thickness compared to conventional bilayer membranes. Advantageously, according to embodiments of this disclosure, the reduction in membrane thickness can result in higher flux and / or improved filtration during the filtration process, as more membrane (e.g., when pleated) can be loaded into the filter device, for example, as a filter element, cartridge, or box.

[0011] In one aspect, this disclosure provides a porous membrane comprising: an upstream porous asymmetric layer having an asymmetric layer thickness and a porous structure that reduces bacterial passage therethrough; a downstream porous isometric polymer layer in contact with the porous asymmetric layer, the porous isometric layer having an isometric layer thickness and a porous structure that reduces bacterial passage therethrough; wherein the porous membrane has a total membrane thickness; and the isometric layer thickness is 45% to 80% of the asymmetric layer thickness.

[0012] According to various aspects of this disclosure, the layers of the membrane are formed from the same polymer and solvent; however, different viscosities, additives and treatments, or different polymers, additives and / or viscosities may be used for different layers.

[0013] In some embodiments, the equimetric layer thickness is 45% to 80% of the asymmetric layer thickness. For example, according to embodiments of this disclosure, the equimetric layer thickness is 50% to 80% relative to the asymmetric layer thickness, such as 55% to 80%, 60% to 80%, 65% to 80%, 70% to 80%, 75% to 80%, 45% to 75%, 50% to 75%, 55% to 75%, 60% to 75%, 65% to 75%, 70% to 75%, 45% to 70%, 50% to 70%, 55% to 70%, 60% to 70%, 65% to 70%, 45% to 65%, 50% to 65%, 55% to 65%, 60% to 65%, 45% to 60%, 50% to 60%, 55% to 60%, 45% to 55%, 50% to 55%, or 45% to 50%, etc.

[0014] The porous membranes described herein can have any suitable average flow pore size (MFP). As used herein, the term "average flow pore size" (also referred to as "MFP size") refers to the mean or average pore size calculated as described in the Washburn equations relating pore size and pressure. (Where P is pressure, y is surface tension, θ is contact angle, and r is aperture).

[0015] As described herein, MFP dimensions are measured using mercury porosimetry or capillary flow aperture measurement. Capillary flow aperture measurement can be used to characterize the pore size and pore size range of symmetric films, and also to characterize films deformed under high pressure, as this method can be performed at relatively low pressures (<35 psi). Alternatively, mercury porosimetry can provide useful pore size characterization information for asymmetric films, as this method measures all diameters of open and blind aperture sizes. In some embodiments, the MFP size of isometric layers is 310 nm to 400 nm. For example, according to embodiments of this disclosure, the MFP size of isometric layers is 320 nm to 400 nm, such as 330 nm to 400 nm, 340 nm to 400 nm, 350 nm to 400 nm, 360 nm to 400 nm, 370 nm to 400 nm, 380 nm to 400 nm, or 390 nm to 400 nm, etc. In some implementations, the MFP of the asymmetric layer is 390 nm to 420 nm, such as 400 nm to 420 nm, or 410 nm to 420 nm, etc.

[0016] The porous membranes described in this article can have any suitable quantitative bubble point (K). L As used in this article, the term "bubble point" (also known as "K") refers to the point at which a substance is quantified. L "Bubble point" and / or "WBP" ​​refer to the point at which air is forced through the membrane at a given rate until a certain pressure is reached, at which point the air velocity increases dramatically, and this can be visually observed by the appearance of bubbles. In some embodiments, the K of the isometric layer... L The psi ranges from 45 psi to 75 psi. For example, according to the embodiment of this disclosure, the K of the isometric layer... L The psi ranges from 48 psi to 75 psi, for example, 48 psi to 70 psi, 48 psi to 65 psi, 48 psi to 60 psi, 48 psi to 55 psi, 55 psi to 75 psi, 55 psi to 70 psi, 55 psi to 65 psi, 65 psi to 75 psi, or 70 psi to 75 psi, etc. In some implementations, the K of the asymmetric layer... L The psi ranges from 25 psi to 55 psi. For example, according to the embodiment of this disclosure, the K of the asymmetric layer... LThe range is 30 psi to 55 psi, for example, 30 psi to 50 psi, 30 psi to 45 psi, 30 psi to 40 psi, 35 psi to 55 psi, 35 psi to 50 psi, 35 psi to 40 psi, 40 psi to 55 psi, 40 psi to 45 psi, 45 psi to 55 psi, or 50 psi to 55 psi, etc.

[0017] The porous membranes described herein can have any suitable level of logarithmic reduction. As used herein, the term "level of logarithmic reduction" or "LRV" refers to the reduction in bacteria after passing through the membrane, where each unit represents a reduction to the power of 10. LRV is expressed using an equation. The calculations are performed. The total challenge is the amount of bacteria loaded into the membrane, and the total recovery is the amount of bacteria that pass through the membrane; both are typically measured as colony-forming units (CFU).

[0018] As described in this article, LRV is measured using a bacterial challenge test, where the challenge load is 10. 7 CFU / cm 2 Up to 10 8 CFU / cm 2 Defective shortwave monoclonal bacteria ( Brevundimonas diminuta Bacteria. As used herein, the term "reduced bacterial permeability" refers to a membrane or membrane layer having an LRV greater than 1. As used herein, the term "significantly reduced bacterial permeability" refers to a membrane or membrane layer having an LRV of 7 or greater. In some embodiments, the LRV of an isometric layer is 7 to 10. In some embodiments, the LRV of an asymmetric layer is 2.5 to 7.5. For example, according to embodiments of this disclosure, the LRV of an asymmetric layer is 3 to 7.5, such as 4 to 7.5, 5 to 7.5, or 6 to 7.5, etc.

[0019] The advantages of porous membranes as described herein can be seen across a variety of layer densities. For example, in some embodiments, the isometric layer thickness is 55 µm to 125 µm. According to embodiments of this disclosure, the isometric layer thickness is 60 µm to 125 µm, for example, 65 µm to 125 µm, 70 µm to 125 µm, 75 µm to 125 µm, 80 µm to 125 µm, 85 µm to 125 µm, 90 µm to 125 µm, 95 µm to 125 µm, 100 µm to 125 µm, 105 µm to 125 µm, 110 µm to 125 µm, 115 µm to 125 µm, 120 µm to 125 µm, etc. In some embodiments, the asymmetric layer thickness is 75 µm to 120 µm. For example, according to embodiments of this disclosure, the asymmetric layer thickness is 80 µm to 120 µm, 85 µm to 120 µm, 90 µm to 120 µm, 95 µm to 120 µm, 100 µm to 120 µm, 105 µm to 120 µm, 110 µm to 120 µm, 115 µm to 120 µm, etc. In some embodiments, the total film thickness is 130 µm to 245 µm. For example, according to the embodiments of this disclosure, the total membrane thickness is 135 µm to 245 µm, 140 µm to 245 µm, 145 µm to 245 µm, 150 µm to 245 µm, 155 µm to 245 µm, 160 µm to 245 µm, 165 µm to 245 µm, 170 µm to 245 µm, 175 µm to 245 µm, 180 µm to 245 µm, 185 µm to 245 µm, 190 µm to 245 µm, 195 µm to 245 µm, 200 µm to 245 µm, 205 µm to 245 µm, 210 µm to 245 µm, 215 µm to 245 µm, 220 µm to 245 µm, 225 µm to 245 µm, 230 µm. µm to 245 µm, 235 µm to 245 µm, 240 µm to 245 µm, etc.

[0020] In some embodiments, the asymmetric layer includes four zones, each having a certain thickness and porosity: (a) a first zone having a thickness of 20 µm to 40 µm and a porosity of 40% to 55%, (b) a second zone having a thickness of 10 µm to 30 µm and a porosity of 30% to 50%, (c) a third zone having a thickness of 10 µm to 30 µm and a porosity of 20% to 50%, and (d) a fourth zone having a thickness of 5 µm to 15 µm and a porosity of 10% to 50%. Figure 1A The image shows a representative scanning electron microscope (SEM) image of the asymmetric layer, in which four bands can be seen: band 1 at the top of the image, followed by bands 2 and 3, and band 4 at the bottom of the image.

[0021] The porous membranes described herein can have any suitable porosity. In this regard, as used herein, the term "porosity" refers to the percentage of pores in the membrane. As described herein, porosity is measured using representative SEM images or the mercury porosimetry method. Representative SEM images are used to measure porosity, for example... Figure 1A and 1B The images are SEM images of the asymmetric layer (including its four zones) and the isometric layer, respectively. Porosity was calculated as the percentage of pores in the membrane using representative SEM images and software, specifically ImageJ (developed by the National Institutes of Health). Alternatively, porosity was measured using the mercury porosimetry method. In the mercury porosimetry method, mercury is propelled through the membrane, and the amount of mercury occupying the pores is used to calculate the percentage of pores in the membrane, as well as the pore size and distribution.

[0022] In some embodiments, the asymmetric layer comprises four zones: (i) a first zone having an average pore size of 1300 nm to 1800 nm, (ii) a second zone having an average pore size of 700 nm to 1200 nm, (iii) a third zone having an average pore size of 400 nm to 800 nm, and (iv) a fourth zone having an average pore size of 400 nm to 900 nm.

[0023] As used herein, the term “average pore size” refers to the mean or average size of the pores calculated by obtaining a representative SEM image of the membrane and using software such as ImageJ to measure the pore size.

[0024] The surface properties of the layer can be modified by wet or dry oxidation, by coating or depositing polymers on the surface, or by grafting reactions (e.g., to influence CWST, including surface charge, such as positive or negative charge, and / or to change the polarity or hydrophilicity of the surface). Modifications include, for example, irradiation, polar or charged monomers, coating and / or curing the surface with charged polymers, and chemical modification to attach functional groups to the surface. Grafting reactions can be activated by exposure to an energy source (e.g., gas plasma, vapor plasma, corona discharge, heat, van der Graft generator, ultraviolet light, electron beam, or various other forms of radiation) or by surface etching or deposition using plasma treatment. Illustrative modifications include, for example, those described in U.S. Patent 9,469,737 and U.S. Patent 6,083,393, each of which is incorporated herein by reference.

[0025] In some embodiments, the membrane further includes an interface between an asymmetric layer and an isometric layer, the interface layer having a first portion in contact with the asymmetric layer and a second portion in contact with the isometric layer; and (a) the asymmetric layer has a region in contact with the first portion of the interface layer, the region including a cell with a first diameter; (b) the isometric layer has a region in contact with the first portion of the interface layer, the region including a cell with a second diameter; and the first portion of the interface layer includes a cell with the first diameter, and the second portion of the interface layer includes a cell with the second diameter, wherein each portion of the interface layer includes a mixture of cells with the first diameter and cells with the second diameter.

[0026] In some embodiments, the interface membrane comprises a first polymer from the asymmetric layer and a second, different polymer from the isometric layer.

[0027] In various aspects, this disclosure provides methods for handling fluids, including passing the fluid through or contacting the membrane described herein in a direction from the asymmetric layer toward the isometric layer. Membranes according to various aspects of this disclosure can be used in a wide range of applications, including, for example, sterile filtration applications, fluid filtration for the electronics industry, fluid filtration for all process stages in the pharmaceutical and biopharmaceutical industries, such as, but not limited to, filtering fluids containing antibodies (especially monoclonal antibodies) and / or proteins; final pharmaceutical formulations, such as nanosuspensions including liposomes, emulsions, exosomes, and nanospheres; recombinant proteins including monoclonal antibodies, antibody fragments, bispecific antibodies, and antibody-drug conjugates; blood products including IVIG and human serum albumin; small molecule drugs, such as doxorubicin; viruses; fluid filtration, clarification, and cell culture medium filtration for the food and beverage industry.

[0028] In various respects, this disclosure provides a method for preparing the porous membrane described herein, the membrane having an upstream porous asymmetric layer and a downstream porous isometric polymer layer in contact with the porous asymmetric layer, the method comprising: preparing a first solution comprising a first polymer and a solvent for the first polymer; preparing a second solution comprising a second polymer and a solvent for the second polymer; casting the first solution onto a support at a first velocity; casting the second solution onto the first solution and forming a membrane precursor; quenching the membrane precursor in water at a second velocity; leaching the membrane precursor; and drying the membrane.

[0029] In various respects, this disclosure provides suitable solutions comprising polymers, such as polyaromatics; sulfones (e.g., polysulfones, including aromatic polysulfones such as polyethersulfone (PES), bisphenol A polysulfone, polyarylsulfone, and polyphenylene sulfone), polyamides, polyimides, polyvinylidene halides (including polyvinylidene fluoride (PVDF)), polyolefins such as polypropylene and polymethylpentene, polyesters, polystyrene, polycarbonates, polyacrylonitrile (including polyalkylacrylonitrile), cellulose polymers (e.g., cellulose acetate and cellulose nitrate), fluoropolymers, and PEEK. Solutions comprising polymers may contain mixtures of polymers, such as hydrophobic polymers (e.g., sulfone polymers) and hydrophilic polymers (e.g., polyvinylpyrrolidone).

[0030] In some embodiments, in addition to one or more polymers, the solution also contains at least one solvent and may further contain at least one non-solvent. Suitable solvents include, for example, dimethylformamide (DMF); N,N-dimethylacetamide (DMAC); N-methylpyrrolidone (NMP); tetramethylurea; dioxane; diethyl succinate; dimethyl sulfoxide; chloroform; and tetrachloroethane; and mixtures thereof. Suitable non-solvents include, for example, water; various polyethylene glycols (PEGs; e.g., PEG 400, PEG 1000); various alcohols, such as methanol, ethanol, isopropanol (IPA), pentanol, hexanol, heptanol, and octanol; alkanes, such as hexane, propane, nitropropane, heptane, and octane; and ketones, ethers, and esters such as acetone, butyl ether, ethyl acetate, and amyl acetate; and various salts, such as calcium chloride, magnesium chloride, and lithium chloride; and mixtures thereof.

[0031] In some embodiments, the polymer-containing solution may further contain, for example, one or more polymerization initiators (e.g., any one or more of peroxides, ammonium persulfate, aliphatic azo compounds (e.g., 2,2'-azobis(2-amidinylpropane) dihydrochloride (V50)) and combinations thereof), and / or small amounts of components such as surfactants and / or release agents.

[0032] In some embodiments, a polymer-containing solution is cast into a thin film, one layer on top of another, exposed to a gaseous environment for a predetermined period of time, and then quenched in a non-solvent for the polymer. In some embodiments, a first solution is spread as a layer (bottom layer) on a support (e.g., a non-porous support), and a second solution is spread as a layer (top layer) on the first solution, and then the film is separated from the support after quenching. However, in some embodiments, a support (porous or non-porous) is incorporated into the final structure, if desired. In some embodiments, the support is a strip.

[0033] Various devices known in the art are used for casting. Suitable devices include, for example, mechanical coaters that include doctor blades, spatulas, or spray / pressurization systems. An example of a coating apparatus is an extrusion die or slit coater that includes a casting chamber, into which the casting formulation (a solution containing a polymer) is introduced and extruded under pressure through a narrow slit. Various air gaps are suitable for some embodiments of this disclosure, and the air gaps may be the same or different for the doctor blade / spaniper. As known in the art, various casting speeds are suitable. In some embodiments, the casting speed is 6 to 8 feet per minute. In some embodiments of this disclosure, the casting speed is 7 feet per minute. In some aspects, casting is performed at a certain temperature. In some embodiments, the casting temperature is 20°C to 30°C. In some embodiments of this disclosure, the casting temperature is 26°C. In some aspects, casting is performed at a certain humidity. In some embodiments, the humidity is 60% to 100%. In some embodiments of this disclosure, the humidity is 75%. In some embodiments, the casting solution is exposed to air after casting but before quenching. In some embodiments, air (e.g., humid air) is circulated (e.g., using one or more fans) to enhance contact with the casting solution. In some embodiments, the air is not circulated. In some embodiments, a support having the casting solution on it is immersed in a quenching bath to achieve phase separation of the polymer solution in a continuous layering sequence to form a monolithic multilayer (i.e., layers bonded together such that the membrane exhibits a single structure that does not layer or separate under normal operating conditions) microporous polymer membrane. In some embodiments, the quenching fluid is water. In some embodiments, the quenching fluid has a specific temperature. In some embodiments, the temperature of the quenching fluid is 20°C to 60°C, 45°C to 55°C, or 45°C to 50°C, etc. In some embodiments, after formation, the membrane is washed to remove residual solvent, dried, and wound onto a mandrel. In some embodiments, the washing solution is deionized water or ethanol.

[0034] In some embodiments, there is a time interval between casting the first solution and casting the second solution on top of the first solution. In some embodiments, the time interval is from 1 second to 60 seconds. In some embodiments, the time interval is from 2 seconds to 30 seconds.

[0035] In some implementations, the membrane includes a corrugated membrane.

[0036] Various aspects of the membrane can be used in a variety of cartridges, tubes, and / or filter assemblies (filter capsules). In some embodiments, the membrane is used in cartridges or tubes and / or filter assemblies (filter capsules), for example, as described in U.S. Patent Application 63 / 539,405, filed September 20, 2023, jointly assigned, and jointly pending, and incorporated herein by reference.

[0037] In short, in one embodiment, a box or cylinder may be arranged in a filter assembly comprising a first housing and a second housing. In some embodiments, the first housing includes an inlet, a first chamber, and at least two first guide pins, and the second housing includes an outlet, a second chamber, and at least two second guide pins. Further, the box may include a first planar side and a second planar side having at least two first guide pin openings and at least two second guide pin openings, together with the box outlet. However, the guide pins and guide pin openings are optional for any embodiment of the invention. While the illustrated embodiments show two first guide pins, two second guide pins, two first guide pin openings, and two second guide pin openings, embodiments of the invention may include at least one first guide pin and at least one first guide pin opening and / or at least one second guide pin and at least one second guide pin opening; or an embodiment of the invention may not include first guide pins and first guide pin openings and / or second guide pins and second guide pin openings. Illustratively, an embodiment without guide pins and guide pin openings may be produced by, for example, using an external guide on either side of the box to guide the box into place, or, for example, temporarily inserting a pin through the box to guide the box into the housing, and then removing the pin. Each planar side (e.g., a first planar side and a second planar side) includes an inner surface and an outer surface. The inner surface of the planar side defines the cavity.

[0038] Regarding the first and second housings, in some embodiments, the housings are configured to engage such that the cartridge is disposed within the first and second cavities, such that one or more optional first guide pins each penetrate one or more optional first guide pin openings, and one or more optional second guide pins each penetrate one or more optional second guide pin openings. An inlet is in fluid communication with an outlet via the cartridge cavity and a cartridge outlet.

[0039] In one embodiment, the filter cartridge is configured for arrangement within a pressurized filter capsule. The cartridge may include a first planar side and a second planar side. The first and second planar sides define a first and a second outer surface of the cartridge, respectively. A second outer surface of the cartridge is opposite to the first outer surface. Additionally, according to some embodiments, the cartridge further includes a first and a second inner surface further defining a cartridge cavity, wherein at least one of the first and second outer surfaces includes an open grid in fluid communication with the cartridge cavity. In one embodiment, the cartridge includes an outlet projecting from the first and second planar sides and in fluid communication with the cartridge cavity, and a membrane disposed on the open grid upstream of the cartridge cavity.

[0040] An illustrative embodiment of a filter assembly (filter capsule) that can be used with the porous membrane described herein is shown in Figure 4A and 4B middle. Figure 4A A top view of a decomposed capsule filter assembly according to one embodiment of the present disclosure is depicted. Specifically, an upper housing and its internal components, and a filter cartridge with a pleated membrane, are shown, configured to be disposed within the filter capsule assembly, and partially within and between the upper and lower housings. The illustrated filter cartridge comprises a hollow cylindrical filter element including a pleated membrane according to one aspect of the present disclosure, and the filter capsule further includes a structure disposed between the lower end of the filter element and the outlet portion of the housing to reduce stagnant (dead) volume. This structure helps reduce stagnant volume by filling and thus reducing the open space within the filter capsule. Reducing stagnant volume in this way advantageously allows for increased recovery of the filtered fluid. Figure 4B Depicting Figure 4A The bottom view of the same decomposition filter capsule.

[0041] Another illustrative embodiment of a filter assembly (filter capsule) that can be used with the porous membrane described herein is shown in Figure 5A and Figure 5B middle. Figure 5AAn exploded view of a filter capsule assembly according to one embodiment of this disclosure is shown. Specifically, an upper housing and its internal components are shown, as well as a cartridge configured for arrangement within the filter capsule assembly, and partially within and between the upper and lower housings. The upper housing includes an upper housing cavity in which a plurality of ribs are arranged, and in some embodiments, one or more guide pins are arranged. The ribs help secure the cartridge and / or membrane within the upper housing and guide the flow and flow distribution of liquid received within the upper housing via its inlets, thereby ensuring predictable and balanced flow of the liquid to be filtered toward one or more outer surfaces of the cartridge, which provides filtration of the liquid. The ribs also reduce the surface area of ​​the cartridge and / or the membrane fixed thereon directly exposed to contact the liquid to be filtered, thereby reducing the internal wetting area. If present, one or more guide pins are arranged in a similar manner to the ribs to extend and to assist in securing the cartridge within the upper housing.

[0042] The size and shape of the upper housing cavity are configured as a receiving box. The upper housing also includes circumferential and lateral supports, which provide structural rigidity to the upper housing as a whole, strengthen it to improve pressure ratings, and allow for a reduction in the amount of material required to form the upper housing as a whole. The hemispherical shape of the upper housing further contributes to its rigidity and the ability to form a pressure vessel capable of withstanding increases in internal pressure. The upper housing includes an upper mating surface through which it engages with the lower housing.

[0043] The cartridge includes a protruding outlet extending from the first planar side and providing fluid connection between the exterior of the cartridge and its internal cavity. Therefore, only filtered liquid (e.g., through one or more membranes) can exit the cartridge via the outlet. The membrane protrusion is configured to be fixed to the outlet. The protrusion ensures that stagnation openings, such as grid openings along the protruding outlet of the cartridge, are covered by the membrane, thereby ensuring that the stagnation volume in the filter capsule can be reduced and that liquid flowing too deep below the grid of the cartridge can still be filtered and discharged from the filter capsule.

[0044] Figure 5B The view below shows Figure 5A The filter capsule assembly, shown in the lower view, more clearly displays the features of the cartridge and the internal features of the lower housing. The cartridge includes a grid formed by multiple openings that provide fluid communication between the internal cavity of the cartridge and the external environment, or, in the assembled state of the filter capsule, provide fluid communication between the internal cavity of the cartridge and the internal volume of the filter capsule configured to receive the liquid to be filtered. The illustrated cartridge further includes an O-ring configured to seal against the inner surface of the lower housing, thereby preventing the liquid to be filtered from bypassing the cartridge and flowing out of the filter capsule without prior filtration. However, the O-ring is not essential. For example, the cartridge may be welded in place, with the weld acting as a seal.

[0045] Similar to the upper housing, the lower housing may include multiple ribs within its cavity, and in some embodiments, one or more guide pins. The upper and lower housing cavities are configured to engage together to form a larger single cavity in which a box is disposed. The lower housing also includes circumferential and lateral supports that provide structural rigidity to the lower housing as a whole and reinforce it to improve its pressure rating. The hemispherical shape of the lower housing further contributes to its rigidity and the ability to form a pressure vessel capable of withstanding increases in internal pressure. The lower housing includes a lower engagement surface through which it engages with the upper housing.

[0046] Further embodiments of the filter cartridge will be apparent to those skilled in the art, including the illustrative embodiments shown and described by reference in U.S. Patent Application 63 / 539,405, which is incorporated herein by reference.

[0047] This disclosure is further illustrated by the following exemplary aspects. However, this disclosure is not limited to these aspects.

[0048] (1) A porous membrane or a method for preparing a porous membrane as described herein.

[0049] (2) A porous membrane comprising: (a.) an upstream porous asymmetric polymer layer having an asymmetric layer thickness and a porous structure reducing the passage of bacteria therethrough; (b.) a downstream porous isometric polymer layer in contact with the porous asymmetric layer, the porous isometric layer having an isometric layer thickness and a porous structure reducing the passage of bacteria therethrough; wherein the porous membrane has a total membrane thickness; and the isometric layer thickness is 45% to 80% (e.g., 48% to 80%) of the asymmetric layer thickness.

[0050] (3) The membrane of aspect 2, wherein the average flow pore (MFP) diameter of the isometric layer is 310 nm to 400 nm (e.g., 311 nm to 393 nm).

[0051] (4) The membrane of aspect 2 or 3, wherein the MFP of the asymmetric layer is 380 nm to 420 nm (e.g., 384 nm to 412 nm).

[0052] (5) A membrane of any one of aspects 2-4, wherein the quantitative bubble point (K) of the isometric layer L The range is 45 psi to 75 psi (e.g., 48 psi to 72 psi).

[0053] (6) A membrane of any one of aspects 2-5, wherein the K of the asymmetric layer LThe range is 25 psi to 55 psi (e.g., 29 psi to 54 psi).

[0054] (7) A membrane of any one of aspects 2-6, wherein the log reduction level (LRV) of the isometric layer is 7 to 10 (e.g., 7.2 to 9.8).

[0055] (8) A membrane of any one of aspects 2-7, wherein the LRV of the asymmetric layer is 2.5 to 7.5 (e.g., 3 to 7.4).

[0056] (9) A membrane of any one of aspects 2-8, wherein the thickness of the isometric layer is 55 µm to 125 µm (e.g., 60 µm to 124 µm).

[0057] (10) A membrane of any one of aspects 2-9, wherein the thickness of the asymmetric layer is 75 µm to 120 µm (e.g., 78 µm to 118 µm).

[0058] (11) A membrane of any one of aspects 2-10, wherein the total membrane thickness is 130 µm to 245 µm.

[0059] (12) A membrane of any one of aspects 2-11, wherein the asymmetric layer comprises four zones each having a certain thickness and porosity: (a.) a first zone having a thickness of 20 µm to 40 µm and a porosity of 40% to 55% (e.g., 41% to 54%), (b.) a second zone having a thickness of 10 µm to 30 µm and a porosity of 30% to 50% (e.g., 31% to 49%), (c.) a third zone having a thickness of 10 µm to 30 µm and a porosity of 20% to 50% (e.g., 23% to 46%), and (d.) a fourth zone having a thickness of 5 µm to 15 µm and a porosity of 10% to 50% (e.g., 12% to 46%).

[0060] (13) The membrane of aspect 12, wherein (i.) the first zone has an average pore size of 1300 nm to 1800 nm, (ii.) the second zone has an average pore size of 700 nm to 1200 nm, (iii.) the third zone has an average pore size of 400 nm to 800 nm, and (iv.) the fourth zone has an average pore size of 400 nm to 900 nm.

[0061] (14) A membrane of any one of aspects 2-13, wherein the isobaric layer can significantly reduce the passage of bacteria.

[0062] (15) A membrane of any one of aspects 2-14, wherein the membrane further comprises an interface between an asymmetric layer and an isometric layer, the interface layer having a first portion in contact with the asymmetric layer and a second portion in contact with the isometric layer; and (a.) the asymmetric layer has a region in contact with the first portion of the interface layer, the region including a pore having a first diameter; (b.) the isometric layer has a region in contact with the first portion of the interface layer, the region including a pore having a second diameter; and the first portion of the interface layer includes a pore having a first diameter, and the second portion of the interface layer includes a pore having a second diameter, wherein each portion of the interface layer includes a mixture of pores having a first diameter and pores having a second diameter.

[0063] (16) A method of processing a fluid, comprising passing the fluid through a membrane of any one of aspects 2-15 in a direction from the asymmetric layer toward the isometric layer.

[0064] (17) A method for preparing a porous membrane of any one of aspects 2-15, the membrane having an upstream porous asymmetric layer and a downstream porous isometric polymer layer in contact with the porous asymmetric layer, the method comprising: (a.) preparing a first solution comprising a first polymer and a solvent for the first polymer; (b.) preparing a second solution comprising a second polymer and a solvent for the second polymer; (c.) casting the first solution onto a support at a first velocity; (d.) casting the second solution onto the first solution and forming a membrane precursor; (e.) quenching the membrane precursor in a fluid at a second velocity; (f.) leaching the membrane precursor; and (g.) drying the membrane.

[0065] It should be noted that the foregoing aspects are illustrative and not restrictive. Other exemplary combinations will be apparent from the overall description herein. Those skilled in the art will also understand that the various embodiments can be used in various combinations with other embodiments provided herein.

[0066] The following embodiments further illustrate the invention, but of course, they should not be construed as limiting its scope in any way.

[0067] Example 1 This embodiment illustrates an illustrative scheme for preparing porous membranes according to one embodiment of the present disclosure.

[0068] A formulation was prepared comprising the following components and percentages by weight of the formulation: polyethylene glycol (PEG) comprising approximately 60% to 70%; poly(ethylene glycol 400 dimethacrylate) (DM 400) comprising approximately 0.1% to 1%; poly(ethylene glycol monomethacrylate) (MM) comprising approximately 0.1% to 1%; 2-hydroxyethyl methacrylate (HEMA) comprising approximately 0.01% to 0.5%; tetraacrylate (Tetracylate) comprising approximately 0.1% to 1%; WAKO 201 comprising approximately 0.1% to 1%; 2,2'-azobis(2-methylpropanediamine) dihydrochloride (V50) comprising approximately 0.01% to 0.1%; H2O comprising approximately 1% to 5%; and high molecular weight polyethersulfone (HMW) comprising approximately 8% to 15%. PES; including dimethylformamide (DMF) in approximately 8% to 15%; and N-methyl-2-pyrrolidone (NMP) in approximately 1% to 10%.

[0069] The formulation is mixed at approximately 40°C to 50°C for approximately 40 to 50 hours and cast onto a tape at a temperature of approximately 20°C to 30°C and a humidity of approximately 70% to 80%, at a rate of approximately 90 to 100 inches per minute (in / min). The cast membrane is leached with DI water for approximately 5 to 15 minutes, followed by 50% ethanol / 50% DI water for approximately 5 to 15 minutes, and then with DI water at approximately 80°C to 90°C for approximately 5 to 15 minutes. The membrane sample is then passed through an oven at approximately 55°C to 65°C for approximately 5 to 15 minutes.

[0070] Example 2 This embodiment illustrates an illustrative scheme for preparing porous membranes according to one embodiment of the present disclosure.

[0071] A formulation was prepared having the following components and percentages by weight of the formulation: polyethylene glycol (PEG) comprising about 30% to 40%; trimethylolpropane trimethacrylate (TMPTMA) 400 comprising about 0.05% to 0.5%; 2-hydroxyethyl methacrylate (HEMA) comprising about 0.05% to 0.5%; poly(ethylene glycol) dimethacrylate (PEGDM) comprising about 0.1% to 1%; ammonium persulfate (AMPS) comprising about 0.01% to 0.1%; RO water comprising about 1% to 10%; Plasdone K90 comprising about 1% to 5%; polyethersulfone (PES) comprising about 5% to 15%; and N-methyl-2-pyrrolidone (NMP) comprising about 40% to 50%.

[0072] The formulation is mixed at approximately 40°C to 50°C for approximately 40 to 50 hours and quenched with water at a rate of approximately 5 to 10 feet per minute at a temperature of approximately 45°C to 50°C. The cast membrane is leached with DI water for approximately 5 to 15 minutes, followed by 50% ethanol / 50% DI water for approximately 5 to 15 minutes, and then with DI water at approximately 80°C to 90°C for approximately 5 to 15 minutes. The membrane sample is then passed through an oven at approximately 55°C to 65°C for approximately 5 to 15 minutes.

[0073] Example 3 This embodiment demonstrates the method used to determine the thickness and K of the porous membranes in Examples 1 and 2. L An illustrative scheme.

[0074] Membrane thickness: Manually lift the plunger, insert the membrane into the Federal thickness gauge, and then manually lower the plunger. The thickness value is then displayed and recorded.

[0075] membrane K L The porous membrane was cut into squares and wetted with water. The wetted membrane was then loaded onto K. L Inside the sample rack on the test bench. K L The point is defined as the point where the air velocity increases sharply under a given air pressure.

[0076] Tables 1 and 2 show the thickness and K of the porous membranes in Examples 1 and 2, respectively. L .

[0077] Table 1. K values ​​of the porous membrane in Example 1 L And thickness. membrane Thickness (mil) KL (psi) 1 2.35 52.35 2 2.52 50.67 3 3.28 47.93 4 3.93 51.47 5 4.36 55.00 6 4.87 55.77 7 4.41 56.23 8 3.59 58.33 9 2.88 60.03 10 2.59 60.87 11 2.61 66.10 12 2.93 64.77 13 3.65 62.80 14 4.48 60.70 15 2.56 54.75 16 2.85 54.48 17 3.55 54.23 18 3.44 64.65 19 3.48 63.80 20 3.42 55.90 21 3.45 61.77 22 3.53 68.20 23 3.43 63.43 24 3.40 57.57 25 3.47 65.33 26 3.47 64.97 27 3.55 70.20

[0078] Table 2. K values ​​of the porous membrane in Example 2 L And thickness. membrane Thickness (µm) KL (psi) 1 95.3 40.8 2 98.4 29.1 3 78.3 37.1 4 98.5 42.2 5 90.8 30.2 6 100.0 40.7 7 101.8 38.6 8 105.0 32.8 9 103.8 47.6 10 97.4 54.2 11 88.3 38.8 12 78.1 33.0 13 94.7 37.9 14 85.8 45.2 15 83.9 46.0 16 98.5 43.5 17 117.8 49.4 18 113.0 38.6

[0079] As can be seen in Tables 1 and 2, the thickness and K were determined for the 27 porous membranes of Example 1. L It has a thickness of 2.35 mil to 4.87 mil and exhibits a K0 of 47.93 psi to 70.20 psi. L Values ​​were also determined for the thickness and K of the 18 porous membranes in Example 2. L It has a thickness of 78.1 µm to 117.8 µm and exhibits a Ki of 29.1 psi to 54.2 psi. L value.

[0080] Example 4 This embodiment illustrates an illustrative scheme for determining the bacterial challenge level / log reduction value of the porous membranes of Examples 1 and 2.

[0081] The porous membrane, the required solution, and the equipment were autoclaved. A membrane with approximately 10⁻⁶ ppm was prepared. 5 CPU / mL up to 10 10 Defective shortwave monoclonal bacteria with a titer of CPU / mL ( B. Dim Bacterial challenge solution. The membrane is loaded into the bacterial challenge test bench, and a capture membrane (e.g., a GN membrane) is attached downstream of the membrane sample. The membrane is wetted with sterile water, and at membrane K... L Pre-challenge was performed using sterile air at approximately 75% to 85% of the pressure. A solution of defective shortwave monocytogenes bacteria was then passed through the membrane sample. The membrane was then subjected to pre-challenge at membrane K. L Post-challenge was performed using sterile air at approximately 75% to 85% of the pressure. The capture membrane was incubated at approximately 30°C to 40°C for approximately 1 to 3 days to form plaques. Bacterial density was counted to determine the logarithmic reduction value, which was calculated as follows: The total recovery rate was measured as CFU in the filtrate.

[0082] Bacterial recovery and retention rate (LRV) and K L The relationship between the membranes in Example 1 is shown in Figure 2A and 2B The bacterial challenge (BC) threshold was determined to be 56 psi, and this threshold was defined as K. L Above a threshold value, LRV will be stable and bacterial recovery will reach zero. Therefore, the lower limit of specification for the membrane of Example 1 was determined to be 62 psi, calculated as 10% above the BC critical value. This figure confirms that, for the isobaric membrane of Example 1, K... L The value has a greater impact on bacterial rejection rate than membrane thickness. This suggests that thinner, isobaric layers can be used in bilayer membranes without loss of bacterial rejection capacity.

[0083] The relationship between bacterial rejection rate (LRV) and bubble point (WBP) for the membrane of Example 2 is shown in... Figure 3 In the middle. The bacterial challenge (BC) threshold was determined to be 38 psi, defined as the WBP threshold above which the LRV would be greater than 4.0 (within a range of ±0.5). This figure confirms that for the asymmetric membrane of Example 2, K L The value has a greater impact on bacterial rejection rate than membrane thickness. This suggests that thinner asymmetric layers can be used in bilayer membranes without loss of bacterial rejection capacity.

[0084] Tables 3 and 4 show the bacterial challenge level and LRV of the porous membranes in Examples 1 and 2, respectively.

[0085] Table 3. Bacterial challenge data for the porous membrane of Example 1. Pre-challenge (psi) 44.24 – 68.17 Post-challenge (psi) 44.96 – 68.17 Total Challenge Total CFU 1.8E+09 – 6.0E+09 Total recovery rate Total CFU 0.0E+00 –>200 titer reduction 2.7E+07 – 6.0E+09 <![CDATA[CFU / cm 2 ]]> 1.4E+07 – 4.8E+07 Logarithmic decrease value 7.2 – 9.8

[0086] Table 4. Bacterial challenge data for the porous membrane of Example 2. Pre-challenge (psi) 26.11 – 55.84 Post-challenge (psi) 26.11 – 55.11 Total Challenge Total CFU 1.40E+09 – 8.85E+09 Total recovery rate Total CFU 3.20E+02 – 1.30E+09 titer reduction 4.31– 2.77E+07 <![CDATA[CFU / cm 2 ]]> 1.10E+07 – 6.97E+07 Logarithmic decrease value <![CDATA[0.63 * – 7.44]]>

[0087] As can be seen in Tables 3 and 4, bacterial challenge levels and LRVs were determined for the 27 porous membranes of Example 1. The bacterial challenge level was determined to be 1.4E+07 CFU / cm³. 2 – 4.8E+07 CFU / cm 2 The logarithmic reduction values ​​were 7.2–9.8. Bacterial challenge levels and LRVs were also determined for the 18 membranes from Example 2. The bacterial challenge level was determined to be 1.10E+07 CFU / cm³. 2 -6.97E+07 CFU / cm 2 The logarithmic reduction values ​​are 0.63–7.44. *The lower LRV values ​​for some membranes in Example 2 can be attributed to several variables. For example, pressure may be unavailable for pre-challenge and post-challenge purposes, possibly due to the presence of small defects. Alternatively, a lower thickness of the retention portion can result in a low LRV. The retention rate is a function of both the pore size and effective thickness of the retention portion, not the total thickness. Therefore, if the thickness is too low, the retention rate may also be low.

[0088] Example 5 This embodiment illustrates an illustrative scheme for determining the average flow pore size of the porous membranes of Examples 1 and 2.

[0089] The porous membrane was cut into small discs of approximately 20 mm to 30 mm and wetted with Porefil at 16 dynes / cm. The wetted membrane samples were then loaded into a Porolux instrument, commercially available from Porometer, headquartered in Belgium. ™ Within a 1000-sample holder. The pressure range is set to approximately 95 psi to 105 psi. Set approximately 45 to 55 steps and start the porosimeter. The porosimeter reports the average flow pore size based on the gas flow rate versus gas pressure function.

[0090] Tables 5 and 6 show the average flow pore size of the porous membranes in Examples 1 and 2, respectively.

[0091] Table 5. Average flow pore size of the porous membrane in Example 1. membrane Average flow orifice diameter (nm) 1 313 2 311 3 329 4 391 5 343 6 340

[0092] Table 6. Average flow pore size of the porous membrane in Example 2. membrane Average flow orifice diameter (nm) 1 384 2 385 3 412

[0093] As can be seen in Tables 5 and 6, the porous membrane of Example 1 exhibits an average flow pore size of 311 nm to 391 nm, and the porous membrane of Example 2 exhibits an average flow pore size of 384 nm to 412 nm.

[0094] Example 6 This embodiment illustrates an illustrative method for determining the porosity of the porous membrane of Example 2.

[0095] Scanning electron microscope: A Phenom microscope, commercially available from Thermo Fisher Scientific, Inc. (Waltham, Massachusetts), was used. ™ The XL G2 Desktop Scanning Electron Microscope is used to image porous membranes. ImageJ software is used to calculate the porosity of the porous membranes.

[0096] Porosity measurement instrument: The porous membrane sample is loaded into a Mercury Poremaster GT 33, commercially available from Quantachrome Instruments (Boynton Beach, Florida). The instrument pushes mercury through the membrane pores and records the amount of mercury entering the membrane sample as pressure changes. Based on this data, the instrument calculates the pore size and distribution.

[0097] Table 7 shows the average flow pore size of the porous membrane in Example 2.

[0098] Table 7. Porosity of the membrane in Example 2 Membrane 1 Membrane 2 Membrane 3 Membrane 4 Membrane 5 Membrane 6 Zone 1 53% 54% 46% 47% 42% 41% Zone 2 42% 42% 31% 34% 49% 49% Zone 3 30% 30% 23% 26% 46% 46% Zone 4 27% 25% 12% 16% 46% 44% As can be seen in Table 7, the porous membrane of Example 2 has a porosity of approximately 41% to 54% in zone 1, approximately 31% to 40% in zone 2, approximately 23% to 46% in zone 3, and approximately 12% to 46% in zone 4.

[0099] Example 7 This embodiment illustrates an illustrative method for determining the water flow rate in a porous membrane.

[0100] Use a water flow rate test stand. Cut the porous membrane into a square and wet it with water. Load the membrane sample into the sample holder and clamp it using a pneumatic device. The instrument forces water through the membrane at an approximate pressure of 5 to 15 psi. After expelling air bubbles and stabilizing the instrument, record the average water flow rate over 5 to 30 seconds using a mass flow meter.

[0101] The membrane of Example 1 exhibited a water flow rate of 20 to 60 mL·min⁻¹·cm⁻² at 10 psi and 29°C. The membrane of Example 2 exhibited a water flow rate of 40 to 120 mL·min⁻¹·cm⁻² at 10 psi and 29°C.

[0102] Example 8 This embodiment illustrates an illustrative method for determining the burst tensile strength, burst strength, and burst elongation of a porous membrane.

[0103] Utilizing Instron, headquartered in Norwood, Massachusetts ® Commercially available Instron ® A 5543 burst testing machine or equivalent equipment is used. Porous membranes are cut into discs with a diameter of approximately 75 mm to 100 mm and inserted into a sample holder. The instrument applies a force of approximately 0.1 to 5 psi to the membrane until it ruptures. The distance traveled and / or the membrane elongation are recorded simultaneously. The maximum force at which the membrane ruptures is defined as the membrane burst force. The maximum elongation at rupture divided by the original membrane size is defined as the membrane stretch percentage. The burst force divided by the membrane thickness is defined as the normalized burst force.

[0104] All references cited in this article, including publications, patent applications and patents, are incorporated herein by reference to the same extent that each reference is individually and specifically indicated to be incorporated by reference and is expounded in its entirety in this article.

[0105] In the context of describing this disclosure (especially in the context of the appended claims), the use of the terms “a,” “an,” “the,” and “at least one,” and similar indicators, should be interpreted to cover both the singular and the plural, unless otherwise stated herein or obviously contradicted by the context. The use of the term “at least one,” which follows a list of one or more items (e.g., “at least one of A and B”), should be interpreted to mean one item selected from the list (A or B), or any combination of two or more of the listed items (A and B), unless otherwise stated herein or obviously contradicted by the context. Unless otherwise stated, the terms “comprising,” “having,” “including,” and “containing” should be interpreted as open-ended terms (i.e., meaning “including but not limited to”). Unless otherwise stated herein, the description of numerical ranges herein is merely intended to serve as a shorthand method of individually referring to each separate value falling within the range, and each separate value is incorporated into the specification as if it were individually described herein. Unless otherwise stated herein or obviously contradicted by the context, all methods described herein can be performed in any suitable order. The use of any and all instances or exemplary language (e.g., "for example") provided herein is intended merely to better illustrate the contents of this disclosure and does not constitute a limitation on the scope of this disclosure unless otherwise stated. No language in this specification should be construed as indicating that any unclaimed element is necessary for the practice of this disclosure.

[0106] This document describes preferred embodiments of the present disclosure, including the best modes known to the inventors for carrying out the present disclosure. Variations of those preferred embodiments will become apparent to those skilled in the art upon reading the foregoing description. The inventors expect those skilled in the art to appropriately employ such variations, and the inventors anticipate practicing the present disclosure in ways different from those specifically described herein. Accordingly, the invention includes all modifications and equivalents to the subject matter set forth in the appended claims, as permitted by applicable law. Furthermore, unless otherwise stated herein or clearly contradicted by the context, this disclosure covers any combination of the foregoing elements with all possible variations.

Claims

1. A porous membrane comprising: a. An upstream porous asymmetric polymer layer having an asymmetric layer thickness and a porous structure that reduces the passage of bacteria; b. A downstream porous isometric polymer layer in contact with the porous asymmetric layer, the porous isometric layer having an isometric layer thickness and a porous structure that reduces the passage of bacteria therethrough; The porous membrane has a total membrane thickness; and The thickness of the equal-weighted layer is 45% to 80% (e.g., 48% to 80%) of the thickness of the asymmetric layer.

2. The membrane of claim 1, wherein the average flow pore (MFP) diameter of the isometric layer is 310 nm to 400 nm (e.g., 311 nm to 393 nm).

3. The membrane according to claim 1 or 2, wherein the MFP of the asymmetric layer is 380 nm to 420 nm (e.g., 384 nm to 412 nm).

4. The membrane of any one of claims 1-3, wherein the isometric layer has a quantitative bubble point (K L ) of 45 psi to 75 psi.

5. The membrane according to any one of claims 1-4, wherein the K of the asymmetric layer L The range is from 25 psi to 55 psi.

6. The membrane according to any one of claims 1-5, wherein the log reduction level (LRV) of the isometric layer is 7 to 10 (e.g., 7.2 to 9.8).

7. The membrane according to any one of claims 1-6, wherein the LRV of the asymmetric layer is 2.5 to 7.

5.

8. The membrane according to any one of claims 1-7, wherein the thickness of the isometric layer is from 55 µm to 125 µm.

9. The membrane according to any one of claims 1-8, wherein the thickness of the asymmetric layer is from 75 µm to 120 µm.

10. The membrane according to any one of claims 1-9, wherein the total membrane thickness is from 130 µm to 245 µm.

11. The membrane according to any one of claims 1-10, wherein the asymmetric layer comprises four zones, each having a certain thickness and porosity: a. A first zone having a first zone thickness of 20 µm to 40 µm and a porosity of 40% to 55% (e.g., 41% to 54%); b. A second zone having a second zone thickness of 10 µm to 30 µm and a porosity of 30% to 50% (e.g., 31% to 49%); c. A third zone having a thickness of 10 µm to 30 µm and a porosity of 20% to 50% (e.g., 23% to 46%); and d. A fourth zone having a fourth zone thickness of 5 µm to 15 µm and a porosity of 10% to 50% (e.g., 12% to 46%).

12. The membrane according to claim 11, wherein: i. The first zone has an average pore size of 1300 nm to 1800 nm; ii. The second zone has an average pore size of 700 nm to 1200 nm; iii. The third zone has an average pore size of 400 nm to 800 nm; and iv. The fourth zone has an average pore size of 400 nm to 900 nm.

13. The membrane according to any one of claims 1-12, wherein the isobaric layer can significantly reduce the passage of bacteria.

14. A method of processing a fluid, comprising passing the fluid through a membrane according to any one of claims 1-13 in a direction from an asymmetric layer toward an isometric layer.

15. A method for preparing a porous membrane according to any one of claims 1-13, the membrane having an upstream porous asymmetric layer and a downstream porous isometric polymer layer in contact with the porous asymmetric layer, the method comprising: a. Prepare a first solution comprising a first polymer and a solvent for the first polymer; b. Prepare a second solution comprising a second polymer and a solvent for the second polymer; c. Flow the first solution onto the support at a first velocity; d. The second solution is cast onto the first solution to form a membrane precursor; e. Quench the membrane precursor in the fluid at a second velocity; f. Filter the membrane precursor; and g. Dry the membrane.

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