Method for producing porous separation membrane having biocompatible polymer immobilized thereon

Abstract

To provide a method for producing a porous separation membrane in which the occurrence of membrane fouling is suppressed without greatly changing the liquid permeation performance or fractional molecular weight of a porous membrane as a material.SOLUTION: A method for producing a porous separation membrane in which a biocompatible polymer is chemically fixed to at least a first surface of the porous separation membrane includes bringing the biocompatible polymer into contact with at least the first surface of the porous separation membrane and heating and drying the porous separation membrane in a state where a polyhydric alcohol is filled in pores of the porous separation membrane.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for producing a porous separation membrane having a biocompatible polymer immobilized thereon. [Background technology]

[0002] In recent years, porous membranes have been used in a wide range of applications, including medical applications such as hemodialysis membranes (Patent Document 1), industrial applications such as wastewater and waste oil treatment (Patent Documents 2 and 3), industrial fields such as water treatment membranes, and medical fields such as blood treatment. Medical applications include hemodialysis, hemofiltration, protein separation, cell separation, bacterial cell separation, separation and purification of extracellular vesicles, and drug efficacy evaluation using separation membranes (Hollow-Fiber Infection Model: HFIM).

[0003] On the other hand, as described in Patent Document 1, when separating biologically derived microorganisms (hereinafter referred to as organic matter) using a porous membrane, the organic matter may be adsorbed and deposited on the membrane, causing clogging of the membrane pores (membrane fouling), which can significantly reduce separation efficiency.

[0004] A technique for coating with biocompatible polymers is known as a method for suppressing the adsorption of organic substances. For example, the biocompatible polymer 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer is a polymer into which phospholipid polar groups, which are components of biological membranes (cell membranes), have been introduced. It has been shown that coating with this biocompatible polymer suppresses the adsorption of proteins and blood cells (Non-Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 06-343842 [Patent Document 2] Japanese Patent Application Laid-Open No. 2002-361049 [Patent Document 3] Japanese Patent Publication No. 2022-036298 [Non-patent literature]

[0006] [Non-Patent Document 1] Colloids and Surfaces B: Biointerfaces, 134, 2015, 384-391 Summary of the Invention [Problem to be solved by the invention]

[0007] However, it has become clear that coating a biocompatible polymer using the method described in Non-Patent Document 1 results in the pores being blocked or the pore size becoming extremely small, significantly altering the liquid permeability and the molecular weight cutoff of the membrane, making it unusable as a separation membrane.

[0008] The present disclosure has been made in consideration of the above circumstances, and aims to provide a method for producing a porous separation membrane in which the occurrence of membrane fouling is suppressed without significantly changing the liquid permeability or molecular weight cutoff of the porous membrane used as the material. [Means for solving the problem]

[0009] The present inventors have surprisingly discovered that by contacting at least the first surface of a porous membrane with a biocompatible polymer and heating and drying the porous membrane while the pores of the porous membrane are filled with a polyhydric alcohol, it is possible to produce a porous separation membrane in which the occurrence of membrane fouling is suppressed without significantly changing the liquid permeability or molecular weight cutoff of the porous membrane used as the material, and have thus completed the present invention.

[0010] In the present disclosure, the following means can be adopted to solve the above problems. [1] A method for producing a porous separation membrane having a biocompatible polymer chemically fixed to at least the first surface thereof, the method comprising contacting a biocompatible polymer with at least the first surface of the porous membrane, and heating and drying the porous membrane while the pores of the porous membrane are filled with a polyhydric alcohol. [2] A porous separation membrane having a biocompatible polymer chemically fixed to a first surface of the porous membrane, the porous membrane being made of cellulose acetate. [3] A method for chemically fixing a biocompatible polymer to a porous membrane, comprising contacting a biocompatible polymer with at least a first surface of the porous membrane, and heating and drying the porous membrane while the pores of the porous membrane are filled with a polyhydric alcohol. [Effects of the Invention]

[0011] According to the present disclosure, the first or second problem can be solved, that is, a method for producing a porous separation membrane in which the occurrence of membrane fouling is suppressed can be provided without significantly changing the liquid permeability or molecular weight cutoff of the porous membrane used as a material, or the effect of providing a porous separation membrane in which the occurrence of membrane fouling is suppressed can be achieved. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic explanatory diagram illustrating one step in a method for producing a porous separation membrane according to one embodiment of the present disclosure. [Figure 2] FIG. 1 is a schematic explanatory diagram illustrating one step in a method for producing a porous separation membrane according to one embodiment of the present disclosure. [Figure 3] FIG. 1 is a schematic explanatory diagram illustrating one step in a method for producing a porous separation membrane according to one embodiment of the present disclosure. [Figure 4] FIG. 1 shows the results of a BSA adsorption test. [Figure 5] FIG. 1 shows the results of a gamma globulin filtration test. DETAILED DESCRIPTION OF THE INVENTION

[0013] An embodiment of the present disclosure will be described below. The present disclosure is not limited to the following embodiment and can be implemented with appropriate modifications within the scope that does not impair the effects of the present disclosure. When a specific description of one embodiment also applies to other embodiments, that description may be omitted in other embodiments. Furthermore, when multiple upper and lower limit values ​​are described for a specific parameter, any of these upper and lower limit values ​​can be combined to form a suitable numerical range. Furthermore, the lower and / or upper limit values ​​of a numerical range described in this disclosure are numerical values ​​within that numerical range and may be replaced with numerical values ​​shown in the examples. In this specification, the expression "X to Y" indicating a numerical range means "not less than X and not more than Y." The configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible as appropriate without departing from the spirit of the present disclosure. The present disclosure is not limited by the embodiments, but is limited only by the claims. Each aspect disclosed in this specification can be combined with any other feature disclosed in this specification.

[0014] [Method of manufacturing porous separation membrane] The manufacturing method of the present disclosure includes contacting a biocompatible polymer with at least a first surface of a porous membrane, and heating and drying the porous membrane while the pores of the porous membrane are filled with a polyhydric alcohol. According to the manufacturing method of this embodiment, it is possible to manufacture a porous separation membrane in which the occurrence of membrane fouling is suppressed without significantly changing the liquid permeability or molecular weight cutoff of the porous membrane used as the material. By the above manufacturing method, it is possible to manufacture a porous separation membrane in which a biocompatible polymer is chemically fixed to at least the first surface.

[0015] (porous membrane) In this embodiment, the porous membrane refers to a membrane (untreated membrane) that has not been treated to immobilize a biocompatible polymer and is used as a material for a porous separation membrane. A porous membrane usually has two surfaces, one of which constitutes a first surface and the other of which constitutes a second surface. Examples of porous membranes that can be used include nanofiltration membranes, ultrafiltration membranes, and microfiltration membranes. The molecular weight cutoff of the porous membrane is preferably 2,000 Da or more and 2,000,000 Da or less, more preferably 10,000 Da or more and 1,000,000 Da or less, and even more preferably 50,000 Da or more and 500,000 Da or less. The molecular weight cutoff of a porous membrane can be determined by dissolving various proteins or peptides with known molecular weights in a buffer solution consisting of sodium phosphate (0.05 M) and sodium chloride (0.1 M) to a concentration of 250 mg / L and adjusting the pH to 5-7. The solution is filtered at a transmembrane pressure of 0.1 MPa, and the protein or peptide concentration in the permeate after 30 minutes is quantified using an absorbance spectrometer (wavelength 277 nm). The rejection rate of each protein or peptide is calculated, and the molecular weight at which the rejection rate reaches 90% is used as the molecular weight cutoff. Proteins and peptides used for molecular weight cutoff measurement include ovalbumin (molecular weight 46,000), trypsin inhibitor (molecular weight 28,000), myoglobin (molecular weight 16,800), cytochrome C (molecular weight 12,500), and insulin (molecular weight 5,800).

[0016] In one embodiment, the average pore size of the porous membrane is preferably 0.001 to 10 μm, more preferably 0.002 to 5 μm, and even more preferably 0.005 to 1 μm. The average pore diameter of a porous membrane can be determined by obtaining a scanning electron microscope (SEM) image of the widthwise cross section of the porous membrane and using analysis software to calculate the average diameter of 50 nearby pores at each distance from the inner surface.

[0017] The material of the porous membrane is not particularly limited as long as it does not impair the effects of the present disclosure, and examples thereof include resins such as polyethersulfone, polysulfone, polyvinylidene fluoride, polyacrytonitrile, polyethylene, polytetrafluoroethylene, polyvinyl alcohol, polyethylene vinyl alcohol, regenerated cellulose, and cellulose acetate. When the biocompatible polymer is an MPC polymer, the material of the porous membrane preferably contains a hydroxyl group in order to covalently bond it to the porous membrane surface, and polyvinyl alcohol, polyethylene vinyl alcohol, regenerated cellulose, and cellulose acetates such as cellulose diacetate and cellulose triacetate are preferred. Cellulose acetates such as cellulose diacetate and cellulose triacetate are more preferred because of their biocompatibility and relatively easy membrane formation.

[0018] [Porous separation membrane] The porous separation membrane produced by the production method of the present disclosure is a porous separation membrane having a biocompatible polymer chemically fixed to at least a portion of its first surface, and is usable as a separation membrane. The material of the porous separation membrane is the same as that of the porous membrane, but is preferably cellulose acetate. A biocompatible polymer is chemically fixed to the first surface of the porous separation membrane produced by the production method of the present disclosure, thereby suppressing membrane fouling. Porous separation membranes typically have two surfaces, one of which constitutes the first surface and the other the second surface. The target substance to be treated is not limited, and examples include bacterial culture solution, cell culture solution, protein solution, blood, various biological product solutions, tap water, river water, lake water, seawater, and wastewater. For example, bacterial culture solution can be treated with a porous separation membrane to separate the bacterial cells from the culture solution.

[0019] "Chemically fixed" means fixed via a chemical bond such as a covalent bond or an ionic bond, and does not exclude physical fixation via physical interaction, and a portion may be physically fixed. Fixation via a covalent bond is particularly preferred. For example, when the biocompatible polymer is an MPC polymer, fixation via a covalent bond can be confirmed by thoroughly washing the porous separation membrane with running water such as pure water or ethanol, and then examining the presence or absence of phosphorus (P) in X-ray photoelectron spectroscopy (XPS) analysis of the porous membrane surface.

[0020] "A biocompatible polymer is chemically fixed to the first surface" means that a specific detection peak of the biocompatible polymer can be prominently confirmed on the first surface, and it is most preferable that the intensity of the specific detection peak is at least 1.3 times, preferably at least 1.5 times, and even more preferably at least 2 times that of other peaks.

[0021] In one embodiment, no biocompatible polymer is immobilized on the second surface of the porous separation membrane. "No biocompatible polymer is immobilized on the second surface" means that no biocompatible polymer is predominantly immobilized on the second surface, and the intensity of the detection peak specific to the biocompatible polymer is preferably less than 1.3 times, more preferably 1.2 times or less, and particularly preferably 1.1 times or less. For example, in the case of an MPC polymer, the intensity of the detection peak specific to the biocompatible polymer can be determined by X-ray photoelectron spectroscopy (XPS) analysis, using the ratio of the peak intensity at the phosphorus binding energy (138 eV) to the average intensity at other binding energies.

[0022] In one embodiment, the inner surfaces of the pores of the porous separation membrane are substantially free of a biocompatible polymer. Here, "the inner surfaces of the pores of the porous separation membrane are substantially free of a biocompatible polymer" means that the intensity of the specific detection peak of the biocompatible polymer is less than 1.3 times.

[0023] When the biocompatible polymer is an MPC polymer, the intensity of the specific detection peak of the biocompatible polymer can be measured by detecting phosphorus (P) by X-ray photoelectron spectroscopy (XPS) analysis. XPS analysis can be performed, for example, using the following apparatus and conditions. Analytical equipment: "KARATOS Nova" (Shimadzu Corporation) X-ray source: AlKα ray (1486.6eV) X-ray spot diameter: 100 μm Neutralization conditions: Neutralization electron gun (accelerating voltage adjusted depending on the element, current 100 μA)

[0024] In one embodiment, the average pore size of the porous separation membrane is preferably 0.001 to 10 μm. The average pore size of the porous separation membrane is more preferably 0.002 to 5 μm, and even more preferably 0.005 to 1 μm. By setting the average pore size of the porous separation membrane to 0.001 μm or more, high permeability as a separation membrane can be achieved, and by setting it to 10 μm or less, the separation accuracy of the target substance can be improved. The average pore size of the porous separation membrane can be measured by the same method as that for measuring the average pore size of a porous membrane.

[0025] In one embodiment, the molecular weight cutoff of the porous separation membrane is preferably 2,000 Da or more and 2,000,000 Da or less, more preferably 10,000 Da or more and 1,000,000 Da or less, and even more preferably 50,000 Da or more and 500,000 Da or less. The molecular weight cutoff of the porous separation membrane can be measured by the same method as that for measuring the molecular weight cutoff of a porous membrane.

[0026] In one embodiment, the pure water permeability (PWP) of a porous separation membrane can be determined by measuring the flow rate of pure water permeating the porous separation membrane per unit membrane area and per unit time when pure water at 25°C is filtered through the porous separation membrane at a filtration pressure of 0.1 MPa, and is generally in the range of 100 to 50,000 L m -2 h -1 It is preferable that the temperature is 200 to 10,000 L m-2 h -1 It is more preferable that the temperature is 300 to 5,000 L m -2 h -1 It is more preferable that the pure water permeability of the porous separation membrane is 100 L m -2 h -1 By increasing the pure water permeability of the porous separation membrane to 50,000 L m or more, high treatment capacity can be achieved. -2 h -1 By setting the following, it is possible to obtain high separation accuracy of the substances to be separated.

[0027] (Biocompatible polymer) Biocompatible polymers are polymers that do not naturally occur in living organisms and are unlikely to cause inflammation or toxic reactions in living organisms. Examples of biocompatible polymers that can be used include 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer, polyethylene glycol (PEG), poly(2-methoxyethyl acrylate) (PMEA), polycarboxybetaine (PCMB), etc. Biocompatible polymers can be used alone or in combination of two or more types.

[0028] The MPC polymer may be a homopolymer or a copolymer of an MPC monomer and a monomer copolymerizable with the MPC monomer. Examples of monomers copolymerizable with the MPC monomer include organosilanes such as tris(3-methacryloyloxypropyl)tris(trimethylsiloxy)silane (MPTSSi) and tris(3-methacryloyloxypropyl)tris(trimethylsiloxy)silane (MPTMSi), as well as butyl methacrylate (BMA) and methacrylic acid N-hydroxysuccinimide ester (MNHS). When the MPC polymer is a copolymer, it may be a random copolymer or a block copolymer, but a random copolymer is preferred from the viewpoint of the effect of inhibiting protein adhesion to the porous separation membrane surface. The proportion of the MPC monomer-derived constituent units constituting the MPC polymer is preferably 30 mol% to 100 mol%, more preferably 40 mol% to 95 mol%, and even more preferably 50 mol% to 90 mol% of the total constituent units (100 mol%). The proportion of the MPC monomer-derived constituent units in all constituent units is: 1 It can be measured by known methods such as H-NMR.

[0029] The polyethylene glycol may be a homopolymer or a copolymer of polyethylene glycol and a monomer copolymerizable with polyethylene glycol. As the monomer copolymerizable with polyethylene glycol, organosilanes such as tris(3-methacryloyloxypropyl)tris(trimethylsiloxy)silane (MPTSSi) and tris(3-methacryloyloxypropyl)tris(trimethylsiloxy)silane (MPTMSi) can be used. The average molecular weight of the polyethylene glycol is preferably 200 to 1500, more preferably 300 to 1000. Specific examples include polyethylene glycol 200, polyethylene glycol 400, polyethylene glycol 1000, and polyethylene glycol 1500.

[0030] (Hollow fiber porous separation membrane) In one embodiment, the porous separation membrane may be a hollow fiber porous separation membrane (hollow fiber porous separation membrane) having a configuration in which the first surface forms the inner surface and the second surface forms the outer surface, that is, a biocompatible polymer is chemically fixed to the inner surface of the hollow fiber porous separation membrane.

[0031] The molecular weight cutoff of the hollow fiber porous separation membrane is preferably 2,000 Da or more and 2,000,000 Da or less, more preferably 10,000 Da or more and 1,000,000 Da or less, and even more preferably 50,000 Da or more and 500,000 Da or less. The molecular weight cutoff of the hollow fiber porous separation membrane can be measured by the same method as that for measuring the molecular weight cutoff of a porous membrane.

[0032] In one embodiment, the hollow fiber porous separation membrane has an average inner diameter of 0.2 to 2.0 mm. By setting the average inner diameter of the hollow fiber porous separation membrane to 0.2 mm or more, it is possible to suppress the pressure loss when a solution passes through the hollow fiber membrane module to a certain level or less. Furthermore, by setting the average inner diameter of the hollow fiber porous separation membrane to 2.0 mm or less, it becomes easier to increase the number of hollow fiber porous separation membranes in a hollow fiber membrane module. Note that the "average inner diameter of the hollow fiber porous separation membrane" in the present disclosure is a value calculated by cutting one hollow fiber porous separation membrane along an arbitrary plane perpendicular to the longitudinal direction and calculating the diameter of the smallest circle inscribed in the hollow portion of the cut surface. In the present disclosure, the diameters are measured at 10 to 100 arbitrary locations on the cut surface, and the average value is defined as the "average inner diameter."

[0033] In one embodiment, the average outer diameter of the hollow fiber porous separation membrane is preferably 0.3 to 3.0 mm. By setting the average outer diameter of the hollow fiber porous separation membrane to 3.0 mm or less, the number of hollow fiber porous separation membranes in a hollow fiber membrane module can be increased. The "average outer diameter of the hollow fiber porous separation membrane" is a value calculated from the diameter of the smallest circle encompassing the outer edge of a cut surface of a hollow fiber porous separation membrane cut in the same manner as the average inner diameter of the hollow fiber porous separation membrane described above. In the present disclosure, the diameters are measured at any 10 to 100 locations on the cut surface, and the average value is defined as the "average outer diameter."

[0034] In one embodiment, the membrane thickness of the hollow fiber porous separation membrane is preferably 30 to 500 μm, more preferably 40 to 400 μm, and even more preferably 50 to 300 μm. By making the membrane thickness of the hollow fiber porous separation membrane 30 μm or more, the strength and elongation of the hollow fiber porous separation membrane can be ensured. Furthermore, by making the membrane thickness of the hollow fiber porous separation membrane 500 μm or less, a decrease in the effective membrane area of ​​the hollow fiber membrane module can be suppressed.

[0035] In one embodiment, the rejection rate of gamma globulin (molecular weight: approximately 150 kDa) of the hollow fiber porous separation membrane is preferably 50 to 95%, more preferably 60 to 95%, and even more preferably 70 to 95%.

[0036] [Hollow fiber membrane module] The hollow fiber membrane module of this embodiment has a hollow fiber membrane bundle in which hollow fiber porous separation membranes are bundled together. In one embodiment, the hollow fiber membrane module comprises a cylindrical housing having a solution inlet at a first end and a solution outlet at a second end, and a plurality of hollow fiber porous separation membranes housed within the cylindrical housing and oriented in the direction between the first end and the second end. The hollow fiber porous separation membranes contained in the hollow fiber membrane bundle may be hollow fiber porous separation membranes having the same properties or hollow fiber porous separation membranes having different properties, but are preferably hollow fiber porous separation membranes having the same properties. The number of hollow fiber porous separation membranes contained in the hollow fiber membrane module is not particularly limited as long as the effects of the present disclosure are achieved, but is 100 to 5,000, preferably 200 to 4,000, and more preferably 300 to 3,000.

[0037] In one embodiment, the pure water permeability (PWP) of the hollow fiber membrane module is 100 to 50,000 L m -2 h -1 It is preferable that the temperature is 200 to 10,000 L m -2 h -1 It is more preferable that the temperature is 300 to 5,000 L m -2 h -1 The pure water permeability of the hollow fiber membrane module can be measured in the same manner as for the porous separation membrane described above.

[0038] (cylindrical housing) The cylindrical housing in this embodiment has a solution supply port at a first end and a solution discharge port at a second end. The cylindrical housing may be configured as a housing used in known hollow fiber filters, artificial dialysis, artificial kidneys, HFIMs, etc., and cylindrical housings having a solution supply port at a first end and the solution discharge port at a second end are also known. The cross-sectional shape of the cylindrical housing in the width direction can be, for example, a circle or a polygon (preferably a polygon close to a circle). The cylindrical housing may be made of metal, synthetic resin, or the like. The size of the cylindrical housing (size of the internal volume) can be determined depending on the total number of hollow fiber membranes to be housed therein.

[0039] Each step in the manufacturing method of the present disclosure will be briefly described below. (Step of contacting the porous membrane with the biocompatible polymer: First step) In the first step, a biocompatible polymer is brought into contact with a first surface of the porous membrane, and the area of ​​the first surface in contact with the biocompatible polymer is preferably at least 80% of the total area of ​​the first surface, more preferably 90% or more, even more preferably 95% or more, particularly preferably 98% or more, and most preferably 100%.

[0040] In a case where the porous separation membrane is a hollow fiber type, the biocompatible polymer can be brought into contact with the first surface by immersing the porous membrane in a polyhydric alcohol and circulating the biocompatible polymer around the inside (first surface) of the hollow fiber porous membrane, as shown in Figure 1. To explain the process shown in Figure 1 in detail, the apparatus used includes a hollow fiber porous membrane 1 placed in a resin tube 5, and the two ends of the hollow fiber porous membrane 1 are connected to a liquid feed tube 6 via needles 4. The liquid feed tube 6 is connected to a pump 7 and a receiver 8 in which a biocompatible polymer 3 is stored. When the pump 7 is operated, the biocompatible polymer 3 stored in the receiver 8 passes through the liquid feed tube 6 and is introduced into the interior (hollow portion) of the hollow fiber porous membrane 1 from the first end of the hollow fiber porous membrane 1. The biocompatible polymer 3 introduced into the hollow fiber porous membrane 1 flows toward the second end of the hollow fiber porous membrane 1, with a portion of the polymer being in contact with the inner surface (first surface) of the hollow fiber porous membrane 1, and passes from the second end through the liquid delivery tube 6 to be stored in the receiver 8. This series of operations circulates the biocompatible polymer 3 inside the hollow fiber porous membrane 1 (first surface), thereby bringing the biocompatible polymer into contact with the first surface. In another embodiment, the polyhydric alcohol is not used, and the first surface of the porous membrane is contacted with the biocompatible polymer by immersing the porous membrane in the biocompatible polymer. In this embodiment, the first surface, the second surface, and the interior of the pores are in contact with the biocompatible polymer.

[0041] When the porous membrane is a flat sheet membrane, as shown in Figure 2, a cross-flow type flat membrane test cell such as "C10-T" (manufactured by Nitto Denko Corporation) can be used to circulate the biocompatible polymer solution to the first surface while keeping the second surface in contact with a polyhydric alcohol, thereby bringing the biocompatible polymer into contact with the first surface. In another embodiment, the flat porous membrane is immersed in a biocompatible polymer without using a polyhydric alcohol, so that the first surface is in contact with the biocompatible polymer. In this embodiment, the first surface, the second surface, and the interior of the pores are in contact with the biocompatible polymer.

[0042] (Step of heating and drying the porous membrane: second step) In the second step, the porous membrane is heated and dried while the pores of the porous membrane are filled with the polyhydric alcohol. At least the first surface is heated and dried. It is believed that by heating and drying while the pores of the porous membrane are filled with the polyhydric alcohol, clogging of the pores due to heating is suppressed. The state in which the pores of the porous membrane are filled with the polyhydric alcohol preferably means a state in which the polyhydric alcohol penetrates into the pores so as to fill the pore volume of the porous membrane. The polyhydric alcohol preferably fills 50% or more of the pore volume of the porous membrane, more preferably 70% or more, and even more preferably 90% or more. As long as the pores of the porous membrane are filled with the polyhydric alcohol, the polyhydric alcohol may also be in contact with the second surface, i.e., the polyhydric alcohol may be filled in the pores of the porous membrane and in contact with the second surface, whereas it is preferable that the polyhydric alcohol is not in contact with the first surface.

[0043] The porous membrane is heated, whereby the biocompatible polymer is chemically fixed to the resin material of the porous membrane. In one embodiment, the chemical fixation is preferably by covalent bonding. The heating temperature is preferably 30 to 80° C., more preferably 30 to 70° C., and even more preferably 40 to 60° C. Heating at 20° C. or higher makes it easier for the biocompatible polymer to be chemically fixed to the resin material of the porous membrane, while heating at 80° C. or lower can suppress changes in the membrane structure. The heating time is preferably 1 to 40 hours, more preferably 1 to 30 hours, and even more preferably 1 to 10 hours. By setting the drying time to 1 hour or more, the biocompatible polymer can be sufficiently dried, and by setting it to 40 hours or less, the production efficiency of the porous separation membrane can be improved.

[0044] A more specific heat-drying method is a method in which a gas is blown onto the first surface. When the porous separation membrane is a hollow fiber type, heat-drying can be performed by flowing a gas inside the hollow fiber porous membrane, as shown in FIG. 3. For example, after the step of contacting the first surface of the porous membrane with a biocompatible polymer is completed, the liquid delivery tube 6 is removed from the needle 4, and a syringe 9 is connected to the first end of the hollow fiber porous membrane 1 via the needle 4. The end of the needle 4 on the second end side, which is not connected to the hollow fiber porous membrane 1, is open. Heat-drying can be performed by blowing heated dry air from the syringe 9 into the hollow fiber porous membrane 1, thereby flowing the gas inside the membrane. When the porous membrane is a flat membrane in sheet form, the cross-flow type flat membrane test cell described above can be used to heat and dry the porous membrane while the pores of the porous membrane are filled with polyhydric alcohol.

[0045] In the heat drying step, the temperature of the gas is preferably 30 to 90° C., more preferably 40 to 70° C., and even more preferably 50 to 60° C. Furthermore, the humidity of the gas is not necessarily limited, but is preferably 1% or less, more preferably 0.6% or less, and even more preferably 0.5% or less. Other methods include drying the membrane by directly heating it after contacting it with a biocompatible polymer in a dryer, drying the membrane under vacuum, and drying the membrane with radiant heat.

[0046] The step of contacting the porous separation membrane with a biocompatible polymer (step 1) and the step of heating and drying the porous membrane (step 2) can also be performed using a hollow fiber membrane module in which the hollow fiber membrane is mounted in a case, and when a hollow fiber membrane module is used, the operations in both steps become simpler.

[0047] In one embodiment, it is preferable to remove excess biocompatible polymer by blowing dry air onto the porous membrane before heating and drying it.

[0048] (Polyhydric alcohol) Examples of polyhydric alcohols include diol compounds such as ethylene glycol, diethylene glycol, propylene glycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, triethylene glycol, bis-hydroxyethyl terephthalate, cyclohexanedimethanol, octanediol, diethylpropanediol, butylethylpropanediol, 2-methyl-1,3-propanediol, and 2,2,4-trimethylpentanediol, as well as hydrogenated bisphenol A, an ethylene oxide adduct of hydrogenated bisphenol A, a propylene oxide adduct of hydrogenated bisphenol A, trimethylolethane, trimethylolpropane, glycerin, pentaerythritol, trishydroxyethyl isocyanurate, and hydroxypivalyl hydroxypivalate. Among these, glycerin or ethylene glycol is preferably used.

[0049] Glycerin The glycerin may be monoglycerin, polyglycerin, or a mixture of both. Polyglycerin having an average degree of polymerization of 2 to 30 is preferably used, and one having an average degree of polymerization of 2 to 15 is more preferably used. Specific examples of polyglycerin include diglycerin, tetraglycerin, hexaglycerin, octaglycerin, and decaglycerin. The concentration of glycerin is preferably 80% or more, more preferably 90% or more, even more preferably 98% or more, and particularly preferably 100%.

[0050] (Manufacturing method for hollow fiber membrane module) The method for storing multiple hollow fiber membranes in a cylindrical housing is not particularly limited, but examples include the following method. First, the hollow fiber porous separation membranes are cut to an appropriate length, the required number are bundled together, and then placed in the cylindrical housing. Then, temporary caps are placed on both ends, and a solidifying sealant, such as a potting agent, is poured into both ends of the hollow fiber porous separation membranes. At this time, the sealant can be poured while rotating the cylindrical housing with a centrifuge to ensure uniform filling. After the sealant has solidified, both ends of the hollow fiber porous separation membranes are cut so that both ends are open, and a header is attached to obtain a hollow fiber membrane module.

[0051] A non-limiting list of exemplary embodiments and combinations of exemplary embodiments of the present disclosure are disclosed below. [1] A method for producing a porous separation membrane having a biocompatible polymer chemically fixed to at least the first surface thereof, the method comprising contacting a biocompatible polymer with at least the first surface of the porous membrane, and heating and drying the porous membrane while the pores of the porous membrane are filled with a polyhydric alcohol. [2] The manufacturing method according to [1], which comprises fixing the porous membrane and the biocompatible polymer by covalent bonding by the heat drying. [3] The method according to [1] or [2], wherein the temperature for the heat drying is 30 to 80°C. [4] A porous separation membrane having a biocompatible polymer chemically fixed to a first surface of the porous membrane, the porous membrane being made of cellulose acetate. [5] The porous separation membrane according to [4], wherein the biocompatible polymer comprises a 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer. [6] The porous separation membrane according to [4] or [5], wherein the biocompatible polymer is a random copolymer containing an MPC polymer. [7] The porous separation membrane according to any one of [4] to [6], which has an average pore size of 0.001 to 10 μm. [8] The porous separation membrane according to any one of [4] to [7], which is a hollow fiber porous separation membrane, wherein the first surface forms an inner surface and the second surface opposite the first surface forms an outer surface. [9] A hollow fiber membrane module comprising a hollow fiber membrane bundle in which the porous separation membranes according to [8] are bundled together.

[10] A method for chemically fixing a biocompatible polymer to a porous membrane, comprising contacting a biocompatible polymer with a first surface of the porous membrane, and heating and drying the porous membrane while the pores of the porous membrane are filled with a polyhydric alcohol. The configurations and combinations thereof in each embodiment are merely examples, and additions, omissions, substitutions, and other modifications of the configurations are possible as appropriate within the scope that does not deviate from the gist of this disclosure. [Example]

[0052] The following examples are provided, but none of the examples should be construed as limiting.

[0053] The various raw materials used in the examples and the methods for producing them are as follows. (porous membrane) Hollow fiber porous membrane (FUC1582, manufactured by Daisen Membrane Systems Co., Ltd.), material: cellulose triacetate (CTA), molecular weight cutoff: 150 kDa (gamma globulin rejection rate: 85%), inner diameter: 800 μm, pure water permeability (PWP): 600 L m -2 h-1 ) Hollow fiber porous membrane (material: cellulose diacetate (CDA), molecular weight cutoff: 150 kDa (gamma globulin rejection rate: 85%), inner diameter: 800 μm, pure water permeability (PWP): 650 L m -2 h -1 ) This hollow fiber porous membrane was produced by the method described in Example 1 of Japanese Patent No. 2688564. (Biocompatible polymer) MPC polymer (A): Random copolymer of MPC monomer ("Lipidure (registered trademark)" manufactured by NOF Corporation), MPTSSi (manufactured by Tokyo Chemical Industry Co., Ltd.), and MPTMSi (manufactured by Tokyo Chemical Industry Co., Ltd.) (ratio of constituent units derived from MPC monomer: 80 mol%) MPC polymer (A'): Random copolymer of MPC monomer ("Lipidure (registered trademark)" manufactured by NOF Corporation), MPTSSi (manufactured by Tokyo Chemical Industry Co., Ltd.), and MPTMSi (manufactured by Tokyo Chemical Industry Co., Ltd.) (ratio of constituent units derived from MPC monomer: 60 mol%) MPC polymer (B): Block copolymer of MPC monomer ("Lipidure (registered trademark)" manufactured by NOF Corporation), MPTSSi (manufactured by Shin-Etsu Chemical Co., Ltd.), and MPTMSi (manufactured by Shin-Etsu Chemical Co., Ltd.) (ratio of constituent units derived from MPC monomer: 80 mol%) Polyethylene glycol copolymer (A): Block copolymer of polyethylene glycol (average molecular weight (Mw) 400), MPTSSi (manufactured by Tokyo Chemical Industry Co., Ltd.), and MPTMSi (manufactured by Tokyo Chemical Industry Co., Ltd.): Block PEG polymer "b-160 (PME-400) Blenmar (registered trademark) PME-400" (manufactured by NOF Corporation) Polyethylene glycol copolymer (B): Block copolymer of polyethylene glycol (average molecular weight (Mw) 1000), MPTSSi (manufactured by Tokyo Chemical Industry Co., Ltd.), and MPTMSi (manufactured by Tokyo Chemical Industry Co., Ltd.): Block PEG polymer "b-160 (PME-1000) Blenmar (registered trademark) PME-1000" (manufactured by NOF Corporation) (Polyhydric alcohol) Glycerin ("Glycerol" (Fujifilm Wako Pure Chemical Industries, Ltd.))

[0054] The pure water permeability (PWP) was determined by measuring the amount of pure water passing through when pure water was passed from the inside of the hollow fiber porous separation membrane to the outside of the hollow fiber membrane at a transmembrane pressure difference of 0.1 MPa (=100,000 Pa), similar to the method for measuring the pure water permeability coefficient described in Japanese Patent No. 06649779. The membrane permeation resistance is the value obtained by dividing the transmembrane pressure difference by the product of the permeation flux J, which is converted into units of pure water permeability (PWP), and the viscosity of water. The viscosity of water is a value relative to the temperature of the water when measuring the amount of pure water permeation; for example, when the water temperature is 25°C, it is 0.00089 (Pa·s).

[0055] Synthesis of MPC polymer (A) The procedure for preparing MPC polymer (A) is described below. (1) The initiator (AIBN (2.5 mM)) and monomers (MPC (0.4 M), MPTSSi (0.05 M), MPTMSi (0.05 M)) were dissolved in methanol. (2) Dissolved oxygen was removed by nitrogen bubbling (15 minutes). (3) Free radical polymerization was carried out with stirring (65°C, 6 hours). (4) The polymer was reprecipitated in a mixed solvent of acetone and ethanol (volume ratio 20:1, respectively). (5) The obtained polymer was dissolved in methanol and stored. [ka]

[0056] Synthesis of MPC polymer (A') The synthesis was carried out in the same manner as for MPC polymer (A), except that the molar ratio of the monomers was MPC (0.3 M), MPTSSi (0.15 M), and MPTMSi (0.05 M).

[0057] Synthesis of MPC polymer (B) MPC polymer (B) was synthesized by a two-step reversible addition-fragmentation chain transfer (RAFT) polymerization method. In the first step, poly-MPC (PMPC) was synthesized. MPC monomer (0.5 M), AIBN as a radical initiator, and CPD as a RAFT agent were dissolved in 1-propanol and polymerized at 65 °C for 24 hours. The second copolymerization step was carried out without reprecipitation. A 1-propanol solution containing MPTSSi and MPTMSi monomers was added to the reaction solution containing PMPC produced in the first polymerization. The second polymerization was carried out at 65 °C for 24 hours to obtain a block polymer. The resulting block polymer was reprecipitated in a mixture of diethyl ether and hexane (volume ratio 7:3). The block polymer was dissolved in ethanol and stored. [ka]

[0058] (Preparation of hollow fiber porous separation membrane) [Example 1] As shown in Figure 1, a hollow fiber porous membrane (FUC1582, manufactured by Daisen Membrane Systems Co., Ltd.) was used. Material: cellulose triacetate (CTA). Molecular weight cutoff: 150 kDa (γ-globulin rejection rate: 85%). Inner diameter: 800 μm. Outer diameter: 1300 μm. Pure water permeability (PWP): 600 L m. -2 h -1 ) (length: approximately 20 cm) was connected to a tube and a pump via a needle, and the outside of the porous membrane was immersed in a glycerin (100%) solution. Next, using the pump, a solution of 0.1 wt% MPC polymer (A) in methanol and 0.1 M acetic acid in water, mixed at a volume ratio of 10:1, was circulated inside the hollow fiber porous membrane at room temperature for approximately 1 hour. Then, as shown in Figure 3, the hollow fiber porous membrane was connected to a syringe via a needle and immersed in glycerin. Dry air (humidity 0.5% or less, 40°C) was passed inside the hollow fiber porous membrane for 20 hours to dry it, thereby obtaining a hollow fiber porous separation membrane. Furthermore, X-ray photoelectron spectroscopy (XPS) analysis was performed using the following equipment and conditions, confirming that the MPC polymer (A) was fixed to the inner surface of the hollow fiber porous membrane. The inner surface of the hollow fiber porous separation membrane was washed with approximately 1 L of pure water at a flow rate of approximately 20 cm / s to remove the MPC polymer physically attached to the porous membrane surface, and then X-ray photoelectron spectroscopy (XPS) analysis of the porous membrane surface revealed predominantly phosphorus components, confirming that the MPC polymer had been chemically fixed. Analytical equipment: "JPS-9010MS type photoelectron spectrometer" (manufactured by JEOL Ltd.) X-ray source: AlKα ray (1486.6eV) X-ray spot diameter: 100 μm Neutralization conditions: Neutralization electron gun (accelerating voltage adjusted depending on the element, current 100 μA)

[0059] [Examples 2 to 5] A hollow fiber porous separation membrane was obtained in the same manner as in Example 1, except that the following polymer was used. Example 2: MPC polymer (A') Example 3: MPC polymer (B) Example 4: Polyethylene glycol copolymer (A) Example 5: Polyethylene glycol copolymer (B) [Example 6] As shown in Figure 1, a hollow fiber porous membrane (material: cellulose diacetate (CDA), molecular weight cutoff: 150 kDa (gamma globulin rejection: 85%), inner diameter: 800 μm, outer diameter: 1300 μm) (length: approximately 20 cm) was connected to a tube and a pump via a needle, and the outside of the porous membrane was immersed in a glycerin (100%) solution. Next, a solution consisting of a 0.1 wt% methanol solution of MPC polymer (A) and a 0.1 M acetic acid aqueous solution mixed at a volume ratio of 10:1 was circulated inside the hollow fiber porous membrane using a pump at room temperature for 1 hour. Then, as shown in Figure 3, the hollow fiber porous membrane was connected to a syringe via a needle and immersed in glycerin. Dry air (humidity 0.5% or less, 50°C) was passed inside the hollow fiber porous membrane for 4 hours to dry it, thereby obtaining a hollow fiber porous separation membrane. [Example 7] A flat-type porous cellulose triacetate separation membrane was obtained by the following procedure. (1) Cellulose triacetate (LT75 (Daicel Corporation)) was dissolved in polyethylene glycol 200 (Fujifilm Wako Pure Chemical Industries, Ltd.) and dimethyl sulfoxide (Fujifilm Wako Pure Chemical Industries, Ltd.) at 60°C for 5 hours to obtain a membrane-forming solution. (2) The membrane-forming solution obtained above was cast onto a glass plate, and the membrane-forming solution was applied using an applicator (gap 200 μm), and then the glass plate was placed in a water tank adjusted to 60°C. (3) After about 5 minutes, the glass plate was removed from the water tank, and a flat porous membrane was obtained on the glass plate. (4) The flat porous membrane obtained above was placed in a flat porous membrane cell so that a 0.1 wt % MPC polymer (A) solution similar to that in Example 1 was uniformly adhered to the first surface of the porous membrane, and 100% glycerin was uniformly adhered to the second surface, as shown in Figure 2, and left to stand at room temperature for about 1 hour. Thereafter, only the MPC polymer (A) solution was discharged from the cell and heated and dried in a dryer at 50°C for about 4 hours. [Comparative Example 1] In Example 1, a hollow fiber porous membrane to which no biocompatible polymer (MPC polymer (A)) was immobilized was used as the membrane of Comparative Example 1. Comparative Example 2 A hollow fiber porous membrane was prepared as Comparative Example 2 in the same manner as in Example 1, except that glycerin was not used. Comparative Example 3 In Example 6, a hollow fiber porous membrane to which no biocompatible polymer (MPC polymer (A)) was immobilized was used as Comparative Example 3. Comparative Example 4 In Example 7, a flat porous membrane to which no biocompatible polymer (MPC polymer (A)) was immobilized was used as Comparative Example 4.

[0060] The films prepared in the examples and comparative examples were evaluated as follows.

[0061] (Measurement of the effect of biocompatible polymer immobilization on pure water permeability) The membranes of Examples 1 to 7 and Comparative Examples 1 to 4 were examined for pure water permeability. Furthermore, the membranes of Examples 1 to 7 and Comparative Example 2 were examined for the retention of pure water permeability (pure water permeability after immobilization of biocompatible polymer / pure water permeability before immobilization of biocompatible polymer).

[0062] (Measurement of the effect of immobilization of biocompatible polymer on gamma globulin rejection rate) The gamma globulin rejection rates of the membranes of Example 1 and Comparative Example 1, and Example 6 and Comparative Example 3 were examined. The results are shown in Table 1.

[0063] [Table 1]

[0064] As shown in Table 1, particularly from a comparison between the Examples and Comparative Example 2, when the membrane was produced without using glycerin, pore clogging occurred and it became impossible to use it as a separation membrane. However, by using the production method of the present invention, it was possible to fix the biocompatible polymer without significantly affecting the pure water permeability and gamma globulin rejection rate (molecular weight cutoff), or while maintaining a certain level of pure water permeability.

[0065] (Measurement of the effect of bovine serum albumin (BSA) adsorption on pure water permeability) For the membranes obtained in Examples 1, 3 to 5 and Comparative Example 2, BSA (molecular weight 64 kDa) was adsorbed onto the membranes under the conditions described below, and the change in pure water permeability before and after the adsorption was examined. BSA immersion adsorption conditions: 1) Dissolve BSA in phosphate buffer to prepare a BSA solution with a concentration of 100 ppm. 2) Vacuum degass the solution at room temperature (decompression level: 0.03 MPa, 5 minutes) 3) The hollow fiber porous separation membrane is left to soak for approximately 17 hours at room temperature. The results are shown in Figure 4. ◆ indicates before BSA adsorption, and ■ indicates after BSA adsorption.

[0066] As can be seen from Figure 4, in the hollow fiber porous separation membrane of the example in which a biocompatible polymer was immobilized, pure water permeability did not decrease significantly before and after BSA adsorption, and membrane fouling by BSA was suppressed. In particular, the membrane fouling suppression effect was greatest when MPC polymer (A) was used. On the other hand, in the porous membrane of Comparative Example 2, a decrease in pure water permeability was observed due to BSA adsorption.

[0067] The membrane obtained in Example 7 was placed in a flat membrane cell (50 mL Amicon Stirred Cell: manufactured by Millipore), and 15 mL of a solution of BSA (concentration: 4500 ppm) dissolved in phosphate buffer was added to the cell and left at room temperature for approximately 1 hour. After that, the BSA solution was discharged from the cell, and the inside of the cell was washed with pure water. Then, pure water was introduced into the cell, and the pure water permeability (PWP) was measured at a pressure of 0.03 MPa. The results are shown in Table 2.

[0068] [Table 2] As shown in Table 2, the membrane of Comparative Example 4, which did not have a biocompatible polymer immobilized thereon, showed a significant decrease in pure water permeability due to BSA adsorption, whereas the membrane of Example 7, which had a biocompatible polymer immobilized thereon, was found to suppress the decrease in pure water permeability even when BSA was adsorbed.

[0069] (Measurement of the effect on filtration rate change using gamma globulin solution) A gamma globulin solution (dissolved in phosphate buffer at a concentration of 100 ppm) was injected into the inside of the membranes of Example 6 and Comparative Example 3 under a pressure of 0.02 MPa and circulated while undergoing cross-flow filtration (filtration linear velocity: 0.5 m / s), and the change in the filtration rate over time was measured. All of the filtrate was recovered and returned to the gamma globulin solution.

[0070] The results are shown in Figure 5. ● indicates Example 6 and ○ indicates Comparative Example 3. The hollow fiber porous separation membrane of Example 6, which had a biocompatible polymer immobilized thereon, showed a smaller decrease in filtration rate and a higher filtration flux than the membrane of Comparative Example 3, even when a gamma globulin solution was subjected to cross-flow filtration.

[0071] (Fabrication of hollow fiber membrane module) A hollow fiber membrane module was fabricated using hollow fiber porous membranes, the outside of the hollow fiber porous membrane (extra-capillary space, ECS) in the hollow fiber membrane module was filled with glycerin, MPC polymer (A) was brought into contact with the inside of the hollow fiber porous membrane, and then the membrane was heated and dried, thereby confirming that MPC polymer (A) could be fixed to the inside of the hollow fiber porous membrane. The obtained hollow fiber membrane module was examined for the retention of pure water permeability (pure water permeability after immobilization of biocompatible polymer / pure water permeability before immobilization of biocompatible polymer). The results are shown in Table 3.

[0072] [Table 3] It was found that the manufacturing method of the present disclosure can also be used when a biocompatible polymer is immobilized on the porous membrane in a hollow fiber membrane module, and it was also confirmed that the pure water permeability of the hollow fiber membrane module is not significantly reduced by the immobilization of the biocompatible polymer. [Explanation of symbols]

[0073] 1. Hollow fiber porous membrane 2. Glycerin 3. Biocompatible polymers 4 needles 5 Resin tube 6 Liquid transfer tube 7. Pump 8 Receiver 9 syringes

Claims

1. A method for producing a porous separation membrane having a biocompatible polymer chemically fixed to at least the first surface thereof, the method comprising contacting a biocompatible polymer with at least the first surface of the porous membrane, and heating and drying the porous membrane while the pores of the porous membrane are filled with a polyhydric alcohol.

2. The method according to claim 1 , further comprising the step of covalently bonding the porous membrane and the biocompatible polymer by the heat drying.

3. The method according to claim 1 or 2, wherein the heat drying temperature is 30 to 80°C.

4. A porous separation membrane having a biocompatible polymer chemically fixed to a first surface of the porous membrane, the porous membrane being made of cellulose acetate.

5. The porous separation membrane according to claim 4, wherein the biocompatible polymer comprises 2-methacryloyloxyethyl phosphorylcholine (MPC) polymer.

6. The porous separation membrane according to claim 4 or 5, wherein the biocompatible polymer is a random copolymer containing an MPC polymer.

7. The porous separation membrane according to claim 4 or 5, having an average pore size of 0.001 to 10 μm.

8. The porous separation membrane according to claim 4 or 5, wherein the first surface forms an inner surface and a second surface opposite the first surface forms an outer surface.

9. A hollow fiber membrane module comprising a hollow fiber membrane bundle in which the porous separation membranes according to claim 8 are bundled together.

10. A method for chemically fixing a biocompatible polymer to a porous membrane, comprising contacting a biocompatible polymer with a first surface of the porous membrane, and heating and drying the porous membrane while the pores of the porous membrane are filled with a polyhydric alcohol.

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