Abstract: A method and apparatus for purifying an aqueous suspension comprising feeding an aqueous suspension containing fine particles comprising an inorganic component from the outer surface of a wavy hollow fiber membrane having an outer diameter of from 0.5 to 3.1 mm to filter, followed by physical wash of the hollow fiber membrane. The purifying method can reduce the damage of the membrane outer surface during the physical wash step, prevent open pores on the surface from covering and achieve stable filtration. The hollow fiber membrane bundle can be produced by having a pulsation flow contacted with the hollow fiber material being extruded from the double spinning nozzle under specific conditions and cooling and solidifying or coagulating it while shaking.

Abstract: The method relates to bringing about a mixed state of at least two fluids in a second part (34) of a line, which have flowed through a first part (32) of this line. This is attained in that a fractional flow of the fluids is withdrawn from the second part (34) of the line at a point (43), and this fractional flow is resupplied to the second part (34) of the line at a different point (45). A employment to avoid clogs in modules in a crossflow filtration system is described, along with apparatuses for performing the employment.

Abstract: An apparatus for filtering a liquid in a tank has a plurality of elements and a frame for holding the elements while they are immersed in the liquid. The elements have a plurality of hollow fibre membranes attached to and suspended between an upper header and a lower header. The membranes are in fluid communication with one or more permeate channels in one or more of the headers. Releasable attachments between the headers and the frame allow the frame to releasably hold the elements by their headers. The size and configuration of the frame determines the positions of the upper and lower headers of each element relative to each other. Connections between the permeate channels and one or more permeate collection tubes attached to the frame are releasable and resealable connections which are made or broken automatically by the movements involved in inserting or removing an element into or out of the frame.

Abstract: A manufacturing method of an artificial organ formed of a material having a solubility parameter &dgr; of not more than 13 (cal/cm3)½ involves filling micropores of the body fluid treatment membrane with a filling solution having no or little solubility with respect to a fat-soluble modifier solution, and coating a portion of the body fluid treatment membrane with the fat-soluble modifier by contacting the fat-soluble modifier solution. With this method substantially only the necessary portions need to be coated with the fat-soluble modifier so that a smaller amount of the fat-soluble modifier may be employed. A microporous membrane is formed of a synthetic polymer substrate having a solubility parameter &dgr; of not more than 13 (cal/cm3)½, with not less than 50 wt % of fat-soluble modifier included in the hollow fiber membrane being held on a surface which may contact body fluid. The membrane possesses the following sieve coefficients measured by dextrans: no more than 0.

Abstract: A membrane filtration unit comprises a housing having a feedstock inlet, a permeate outlet and a retentate outlet, at least one bundle of tubular membranes accommodated in the housing, sealing bodies which hold end parts of the membranes sealed in a fixed position with respect to the housing, and at least one flexible, permeable sleeve element which encloses the bundle of membranes and holds it together. The sleeve element encloses a center part, which is situated between the held end parts, of the bundle. Socket members are provided, which delimit transitional parts of the bundle, which transitional parts are situated at the location of the transitions from the end parts to the center part. Part of each socket member is fixedly connected with respect to the housing and part of each socket member movably encloses an end of the sleeve element.

Abstract: The present invention provides a gas-permeable hollow fiber membrane having an inner diameter of 50 to 500 &mgr;m and a membrane thickness of 10 to 150 &mgr;m, which is preferably a composite hollow fiber membrane having a three-layer structure consisting of a nonporous layer having porous layers disposed on both sides thereof. Dissolved gases present in an ink can be removed by passing the ink through the bores of hollow fibers comprising such a hollow fiber membrane, and evacuating the outer surface side of the hollow fibers. This method makes it possible not only to degas inks with a slight pressure loss, but also to degas inks stably even if pressure changes occur during degassing.

Abstract: A method of potting a plurality of hollow fiber membranes into a mass of solidified potting liquid is described. Open ends of a plurality of hollow fiber membranes are enclosed in a first material held in a container which may be a part of a permeate collection means, for example, a permeate pan or header enclosure. A potting liquid is flowed into the container over the first material. The potting liquid surrounds each hollow fiber membrane and then becomes a solid mass that provides a fluid-tight seal to the outside of the hollow fiber membranes. The first material prevents the potting liquid or solid mass from closing the ends of the membranes. The first material is later removed from the ends of the hollow fiber membranes.

Abstract: A filter device having two flow paths. The first flow path having at least one cap and fluid port. The second flow path surrounding the first fluid flow path and having at least one cap that overlaps the cap of the first fluid flow path. The second flow path also having at least one fluid port. The filter device providing a simple arrangement that is easily disinfected or sterilized.

Abstract: An aerator for immersed filtering membranes has an aerator shell with openings for discharging bubbles from its upper surface and a shape capable of temporarily containing a volume of air in fluid communication with the openings. The shell is open to tank water below it and located so that discharged bubbles will rise through an assembly of the filtering membranes. The shell may be wholly or partially made of parts of the assemblies of filtering membranes. A supply of air is provided to the air space in the aerators alternating between a high flow rate and a low flow rate in short cycles of between about 10 seconds and 100 seconds. A filtration system has an inlet for adding substrate and an outlet for retentate are located so as to create a horizontal flow of substrate through the tank. Membrane assemblies are located within the horizontal flow of substrate. Aerators as described above are provided and operated as described above.

Abstract: The present invention provides a gas-permeable hollow fiber membrane having an inner diameter of 50 to 500 &mgr;m and a membrane thickness of 10 to 150 &mgr;m, which is, preferably a composite hollow fiber membrane having a three-layer structure consisting of a nonporous layer having porous layers disposed on both sides thereof. Dissolved gases present in an ink can be removed by passing the ink through the bores of hollow fibers comprising such a hollow fiber membrane, and evacuating the outer surface side of the hollow fibers. This method makes it possible not only to degas inks with a slight pressure loss, but also to degas inks stably even if pressure changes occur during degassing.

Abstract: A filter device has two flow paths. The first flow path has at least one cap and fluid port. The second flow path surrounds the first fluid flow path and has at least one cap that overlaps the cap of the first fluid flow path. The second flow path also has at least one fluid port. The filter device provides a simple arrangement that is easily disinfected or sterilized.

Abstract: A method for preventing activation of the contact phase of blood or plasma which comes into contact with a semi-permeable membrane based on polyacrylonitrile bearing fixed negative charges, which is fitted in apparatus for the treatment of blood or plasma, by extra-corporal circulation, said method comprising contacting blood or plasma with said semi-permeable membrane, wherein: a neutral or cationic polymer is combined with said semi-permeable membrane before or after formation of the membrane, and before sterilization of the membrane; the overall ionic capacity of the semi-permeable membrane, based on polyacrylonitrile bearing fixed negative charges and containing a neutral or cationic polymer, is negative; the overall ionic capacity of the semi-permeable membrane, based on polyacrylonitrile bearing fixed negative charges and containing a neutral or cationic polymer, is, as an absolute value, not more than 10% less than the overall ionic capacity of the same semi-permeable membrane without a neutral or cati

Abstract: A blood processing apparatus which retains little residual blood is provided by a hollow fiber flux fixed to a housing by a partition, with the end portion opened. A blood port provided with a blood intake is attached to the opened end plane. The angle of the blood intake interior wall of the blood port has an inclination &thgr; of 1.5° or less as to the center axis of the blood port. The distance h of the interior face of the blood port and the flux-holding partition it faces is 0.08 D≦h≦0.13 D where Q represents the intersection between a hypothetical line which passes through the end portion P of the inner plane of the blood port and is orthogonal with the partition and a hypothetical extension line from the ceiling plane of the blood port, h represents the distance between the partition and the intersection Q, and D represents the diameter at the end portion of the inner plane of the blood port. The blood processing apparatus is used for blood purifying, dialysis, ultrafiltration, and the like.

Abstract: The reactor includes a hollow fiber membrane bundle. Pressurized hydrogen and water are introduced into a volume containing the fiber bundle. The fibers are free to separate and more independently over most of their length. The fibers have microporous inner and outer layers and a nonporous layer sandwiched between the inner and outer layers and are sealed on one end. Hydrogen is introduced inside the fibers, which are sealed on one end to prevent direct escape of the hydrogen gas. The H2 gas dissolves then diffuses through the nonporous layer. Water is introduced around the fibers, and the biofilm reaction occurs on the outer surface of the fibers. Oxidized contaminants are removed from the water by the biofilm reaction, which consumes H2 gas that diffuses through the membrane. The individual fibers are free, over most of their length, to separate in response to the water flow. This prevents excessive biofilm-to-biofilm contact.

Abstract: The invention relates to a filter device for the physical elimination of microbes, suspended matter and solids from water, which in a housing has a filter insert made of 200 to 10000 hollow-fiber membranes with a defined pore width between 0.001 and 1.0 &mgr;m and which can be mounted on a water tap with its top side. A disadvantage of previously known filter devices is that deposits will adhere to the fibers. In order to remedy this drawback, the bottom side of the device of the invention features separate outlets for filtered and unfiltered water and at least in the outlet for the unfiltered water a valve is fitted with which this outlet can be closed.

Abstract: A filter includes a plurality of filter units formed of a porous ceramic medium arranged and housed in a casing, and having therethrough a circulatory line for passing a feed fluid and a discharging route for passing a permeated fluid. The circulatory line and the discharging route are separated from each other by partially sealing those portions of the filter units which are fixed to opposite ends of the casing. The filter unit is structured to basically have a large number of open channels communicating with the circulatory line and passing the feed fluid and closed channels passing the permeated fluid, and a large number of discharge holes penetrating a solid portion of the porous ceramic medium to discharge the permeated fluid. As seen in any cross section of the filter orthogonal to one direction thereof, the plurality of filter units occupy an area corresponding to at least 35% of an internal area of the casing.

Abstract: The present invention provides a device for concentrating a blood fraction. The device includes an ultrafiltration unit connected to a fluid delivery system for delivering the blood fraction to be concentrated into the ultrafiltration unit. The device also includes a purge fluid delivery system for expelling concentrate from the ultrafiltration unit. In one embodiment, the device accommodates multiple cycles of concentration. A blood fraction concentration method is also provided. The device and method of the present invention are particularly useful for preparing a plasma concentrate suitable for use in a coagulum-based wound sealant.

Abstract: A method and apparatus for cleaning a membrane module, the membrane module having a plurality of porous membranes, the membranes being arranged in close proximity to one another and mounted to prevent excessive movement therebetween and means for providing, from within the module, by means other than gas passing through the pores of the membranes, gas bubbles entrained in a liquid flow such that, in use, the liquid and bubbles entrained therein move past the surfaces of the membranes to dislodge fouling materials therefrom, the gas bubbles being entrained in the liquid by flowing the liquid past a source of gas to draw the gas into the liquid flow. The gas bubbles are preferably entrained into the liquid using a venturi type device. The membranes are preferably partitioned into discrete groups to assist cleaning while maintaining high packing density.

Abstract: A filtering element has ultrafiltration or microfiltration hollow fibre membranes extending horizontally between a pair of opposed horizontally spaced, vertically extending headers. Side plates extending between the pair of vertically extending headers define a vertical flow channel through the element. Modules are created by placing the elements side by side or in an orthogonal grid. A frame restrains the elements in place without obstructing the vertical flow channels. Each element may be released from the frame, however, and removed by sliding it in a direction substantially normal to its headers without disassembling the remainder of the module. The elements have associated releasable water tight fittings between the elements and a permeate collector, the releasable water tight fittings being releasable by removing of an element from the frame. An aerator is located below the module with a plurality of air holes.

Abstract: The invention relates to a filtering device comprising a pressure vessel provided with a feed connection and a filtrate connection, and one or more capillary filtration membrane modules, said membrane modules comprising an inlet coupled with the feed connection, an outlet coupled with the filtrate connection, and a filter housing provided with a membrane compartment accommodating a bundle of capillary filtration membranes, and said capillary filtration membranes being cased at both ends of the membrane module in membrane holders. At least one of the membrane modules is provided with at least one feed-through conduit extending substantially in the longitudinal direction through the membrane module.

Abstract: A dual-stage hemodiafiltration cartridge is presented and includes a first hemodiafiltration stage including a first housing with first filtering elements disposed therein. The first housing has a blood inlet and a first dialysate outlet at one end and a first dialysate inlet at an opposite end. The cartridge further includes a second hemodiafiltration stage having a second housing with second filtering elements disposed therein. One end of the second housing has a blood outlet and a second dialysate inlet. An opposite end has a second dialysate outlet. An inter-stage connector is connected to one end of the first housing and to one end of the second housing and is adapted to allow flow of blood from a blood side of said first filtering elements to a blood-side of the second filtering elements and flow of dialysate fluid therethrough from the second stage to the first stage.

Abstract: The filter has hollow fiber membranes which are spaced apart from each other and are held in a substantially linear fashion between a first bonded layer and second bonded layer. This allows the membranes to work effectively without having to be looped. This placement also avoids the kinking of the membranes and stretching in the membrane which in turn would undesirably increase the pore size. The filter thus has a plurality of porous membranes, each membrane having a hollow passage therein and having a first end and second end, and each end having an opening. The first bonded layer is affixed to the first ends so as to block fluid entry through the openings of the first ends. The second bonded layer is affixed to the second ends so as to leave the openings of the second ends exposed for fluid exit from the hollow fiber membranes.

Abstract: To pot membranes in a header, a dense, viscous liquid, suspension or, preferably, a thixotropic, water soluble gel, is placed in a header pan in space reserved for a permeate channel. A plurality of hollow fiber membranes are collected together and their open ends are inserted into the gel. A fixing liquid, typically a resin, is placed over the gel. The fixing liquid surrounds each membrane and then solidifies, simultaneously sealing the outer surfaces of the membranes and forming a plug in the opening of the header to complete the permeate channel. After the fixing liquid has solidified, the gel is removed by various means. The space initially occupied by the gel becomes part of the permeate channel after the gel is removed. In one embodiment, membranes are grouped by a cushioning adhesive which later surrounds the membranes where they exit the completed header.

Abstract: A hollow fiber separation membrane element and a module thereof which comprise a bundle of a great number of bunches of hollow fiber separation membranes, the bunches of hollow fiber separation membranes being each reinforced with a filament wound therearound. Breakage or rupture of the hollow fiber separation membranes is prevented during production and use.

Abstract: The present invention provides a module for cell culture comprising a structure comprising hollow fibers and at least two spacers, wherein the spacers have small pores regularly arranged therein and the hollow fibers pass through the small pores and are arranged regularly at a very small distance, a hybrid artificial liver module wherein hepatocytes are immobilized in this module, and a method of cell culture wherein cells are immobilized in the lumen or extra-fiber space of the module of this module by the use of a centrifugal force and wherein the immobilized cells are cultured. The present invention also provides a method for cell culture wherein hepatocytes are cultured in a culture medium containing DMEM as a basal medium.

Abstract: This invention provides an apparatus and method for desalting a low volume solution for use in connection with an electronically addressable microarray. The apparatus comprises a tubular molecular weight cut-off membrane embedded within a ion exchange resin filled chamber. The apparatus provides a very high surface to volume ratio of membrane pore surface to exchange resin capacity for absorbing charged molecules. The design facilitates the speedy removal of charged molecules from test solutions with the resultant desalted solution having a very low ionic strength suitable for use in the electronic transport of nucleic acids, proteins, and cells.

Abstract: A membrane separator assembly for separating solids from water includes opposing enclosure wall structures, a membrane module unit, and a gas diffuser disposed below the membrane module unit. The membrane module unit includes a plurality of membrane modules respectively having at least one separating membrane extending between at least two membrane fixing members. At least one of the membrane fixing members has a main passage which is in fluid communication with a membrane passageway. The membrane passageway is accessible to water via permeation through the separating membranes and is inaccessible to solids which are impermeable relative to the separating membranes. The membrane separator assembly is preferably used with a detergent containing percarbonate, preferably sodium percarbonate. The assembly also includes a gas diffuser with two opposing main pipes and branch pipes extending therebetween to avoid undesired pressure differentials when cleaning the assembly.

Abstract: The present invention provides a hollow fiber membrane module of immersing type and a method for manufacturing such a hollow fiber membrane module, in which it is difficult for polluted substances to accumulate between hollow fiber membranes, and increase in pressure difference, reduction in flow rate and inter-fiber clogging can be prevented for a long time period. The module is provided at its both ends with water collecting portions having water collecting plates, and hollow fiber membranes are connected to the water collecting plates in such a manner that the hollow fiber membranes are not in contact with each other, and the hollow fiber membranes are mounted between the plates in a relaxed condition.

Abstract: A filter assembly 1 comprising an elongate housing 2 having therein a plurality of discrete filter bundle lengths 3 disposed end to end in a series configuration. Each filter bundle length 3 comprises a multitude of micro-porous polymeric hollow fibers of the kind wherein feed to be filtered is fed to the outside of the bundle of fibers and permeate is extracted from one or both permeate discharge ends 4 of the fiber lumens. The system also includes one or more longitudinally extending feed passages 6 and 7 and one or more longitudinally extending permeate return passages, each of the permeate return passages being in fluid flow communication with each of the permeate discharge ends 4 of the fiber lumens, desirably via connecting passages 9.

Abstract: A membrane filtration module, comprising a housing, a semi-permeable membrane, which is accommodated in the housing and has a liquid side for the introduction of liquid to be filtered and a concentrate side opposite the liquid side, as well as a permeate chamber, which surrounds the membrane and is in communication with a permeate-discharge line for discharging permeate. According to the invention, the wall of the housing comprises one or more channels which are closed towards the liquid side and the concentrate side and are in communication with the permeate chamber. These channels act as a permeate discharge.

Abstract: A reactor for carrying out gas/liquid/solid phase reactions, comprises a housing (1) which encloses an essentially closed reaction chamber (2) for holding a first liquid phase, the solid phase and a gas phase fed through the chamber; at least one feed (3), connected to the reaction chamber, for feeding a first liquid phase to the reaction chamber (2); at least one hollow fiber (4), the wall of which defines an internal flow channel for at least removing a second liquid phase, such that exchange of matter can take place between the reaction chamber (2) and the flow channel through the wall of hollow fiber (4); at least one discharge (6), connected to the flow channel, for removing the second liquid phase; at least one gas inlet (7) and at least one gas outlet (8), connected to reaction chamber (2) such that, in the use position, the at least one gas inlet (7) opens essentially into the bottom of the reaction chamber (2) and the at least one gas outlet (8) is located essentially at the top of the reaction chamb

Abstract: An appliance for fragmenting heterogeneous elements of a fluid medium comprising a filter module with an inlet connected to a supply line for the fluid medium including heterogeneous elements and an outlet connected to a fluid medium outlet line. The filter module comprises a series of channels inside which the fluid medium is to be circulated. The appliance further comprises a planar fragmentation device which is located upstream of the inlet and comprises passages. In accordance with the invention, the planar device constitutes a screen comprising passages which have one dimension equal to the smallest dimension of the cross section of flow of the channels divided by n, where n is in the range 1.4 to 10. The passages are formed from cutting separator elements which define the passages and have a minimum thickness in the range 0.1 mm to 2 mm to ensure fragmentation of heterogeneous elements of the fluid medium.

Abstract: A filter element includes a bundle of hollow fiber type separation membranes made of a natural or synthetic macromolecular material and a sealed part made of a thermoplastic resin. The bundle has an opening in at least one terminal part thereof. The sealed part is bonded to the bundle at a temperature not higher than the melting or decomposing temperature of the macromolecular material and adapted to seal watertightly the opening of the bundle in a half-bonded state showing no compatibility with the macromolecular material and permitting persistence of the mutual interface of bondage.

Abstract: A hollow fiber membrane device adapted for bore side feed includes a split annular disk as a tube sheet support. The device may be assembled without integrating tube sheet support means into the hollow fiber bundle and tube sheet combination and without in situ tube sheet formation.

Abstract: A membrane filter having one or more ducts is disclosed herein. Each of the ducts has a porous wall defining a lumen surrounded by helical grooves in the respective wall. The groove can be a single, double, or triple start groove defining a flow direction along the groove. The cross sectional area of the groove in the case of a single start groove, or aggregate cross sectional area of the groove in the case of a double or triple start groove, perpendicular to the flow direction along the lumen is within a range of 75% to 125% of the cross sectional area of the lumen. The helical grooves create vortices which reduce concentration polarization while increasing membrane area.

Abstract: An object is to provide a highly integrated hollow fiber membrane module and hollow fiber membrane module unit as filtration processing devices which are appropriate for miniaturization, and to also provide a purification tank with a hollow fiber membrane module unit installed therein. To achieve this there is provided a hollow fiber membrane module in which at least one end of a hollow fiber membrane with hollow fibers deployed in a plane is fixed with a fixing resin to a collector pipe in a fluid tight manner, constructed such that an open ended tip of the hollow fiber membrane is inserted into an aperture provided in the collector pipe, and in this condition, fixing resin is filled into the aperture and hardened, thereby securing the open ended hollow fiber membrane to the collector pipe.

Abstract: An apparatus and process for substance-specific treatment of fluids, whereby the apparatus comprises a housing with a distribution space and a collection space, between which is arranged a structure of adjacent flat first and second layers containing first and second hollow-fiber membranes, respectively, and a matrix on which groups acting in a substance-specific manner for fluid treatment are immobilized, whereby the filling ratio &egr; of the housing determined by the hollow-fiber membranes and the matrix is greater than 0.55. The first hollow-fiber membranes are open in the direction of the distribution space and closed in the direction of the collection space, and the second hollow-fiber membranes are open in the direction of the collection space and closed in the direction of the distribution space, and the hollow fiber membranes are embedded at least at their open end in the sealing compounds.

Abstract: The invention relates to an improved separation device in which a plate unit containing the filter comprises a separate abutment ring and a cassette which can be easily connected thereto, said cassette comprising at least one filter together with, if required, a frame belonging thereto so as to support the filter. If the filter consists of a flexible membrane, this is fitted into a special frame. However, if the filter is a rigid self-supporting filter of a porous material, for example, a ceramic filter or the like, a separate frame is not needed to support the filter.

Abstract: A bioreactor (10) comprises an elastic housing (12) and a plurality of hollow, porous fibers (14) disposed within the housing. The lumens of the fibers define an intrafiber compartment, and the outer surfaces of the fibers and the housing define an extrafiber compartment. A variable flow device (34) varies the flow of the perfusate through the intrafiber compartment. The variable flow device can include a flow restrictor (34) that variably restricts the discharge of a perfusate (26) from the intrafiber compartment or a pump for increasing the flow of the perfusate into the intrafiber compartment. The elastic housing can include a wall (28) with perforations (30) extending therethrough and an elastic membrane (32) tightly surrounding the wall or a wall with at least one expansion port extending therethrough and at least one extrafiber space expander 38 coupled to a one of the at least one expansion port.

Abstract: The membrane module includes tube membranes (6), which are arranged in the membrane module in coiled, curved form (8). As a result, a greater total membrane surface area per unit of volume, simplified assembly, and processing of material mixtures with a high solid proportion are all attained. The modules are arranged to facilitate cross flow filtration over membrane surfaces disposed between a supply conduit manifold and a discharge conduit manifold. Optionally, the coils are aligned in parallel and are in coaxial relation to each other.

Abstract: A system for preparing autologous plasma comprises a single use filter unit having two inlets in fluid communication with each other, an outlet, and a filtration membrane selectively permeable to blood plasma separating the inlets from the outlet. Manually operable, single use pumps, preferably syringes, connect to the inlets. A flow path is defined along the membrane between the pumps, whereby, whole blood can be repeatedly exchanged between the two pumps, past the membrane, to cause plasma to flow across the membrane and out of the outlet. A syringe can collect plasma from the outlet. Plasma thus collected can be simultaneously applied with a thrombin solution to a site on the body, thereby forming a fibrin gel.

Abstract: A filter module for filtering raw liquid that includes an outer housing having a longitudinal axis and raw liquid inlet and outlet ends. A non-porous member is attached to each end of the outer housing to form a seal between a hollow tube and the outer housing. A plurality of fins are disposed among hollow fiber filter elements to separate the elements into a plurality of bundles. Each of the fins has a plurality of spacers abutting the hollow tube to form liquid pathways between each of the respective fins in the hollow tube.

Abstract: An antimicrobial microfiltration filter is made from a bundle of polymeric semipermeable hollow fibers treated with an antimicrobial agent and a microporous filter medium which may also be treated with an antimicrobial agent.

Abstract: A novel hydrophilic composite porous membrane is obtained by applying a specific copolymer solution onto the overall surface of an oriented polyolefin membranous matrix comprising a plurality of microfibrils and a plurality of knotted portions cross-connected to the microfibrils, followed by drying. The copolymer is water-insoluble and is comprised of hydrophilic monomeric units and hydrophobic monomeric units in a specific ratio. In the obtained composite porous membrane, the microfibrils are bonded together by means of the copolymer, thereby forming bundles and a coat of the copolymer is formed on the overall surface of the bundles and knotted portions. The membrane has therewithin pores which are substantially elliptic in the cross section taken along the same direction as the longitudinal direction of the microfibril bundles and has on both surfaces thereof openings which are substantially elliptic as viewed against the surface of the membrane.