JPH0364150B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an anionic porous membrane suitable for the treatment of body fluid components, particularly for efficiently concentrating serum albumin, which is the main component of body fluids. More specifically, the present invention relates to a highly water-permeable vinyl alcohol-based porous membrane having a negative charge and suitable for separation and fractionation of various body fluid components having a molecular weight of 100,000 or less and 1,000 or more. Including hemodialysis treatment using dialysis membranes,
Various blood treatments are widely practiced clinically, such as blood purification using membrane membranes, ascites hyperconcentration, and blood purification using adsorbents. In the case of membrane treatment of body fluids, the performance required of the membrane is solute permeability, ultraviolet capacity (UFR), blood compatibility, and mechanical strength.
The solute permeability and water permeability differ depending on the purpose of body fluid treatment, but in the case of hemofiltration, ascites concentration, etc., it is preferable that the solute permeability and water permeability be as high as possible without allowing serum albumin to permeate. In other words, in normal hemodialysis, albumin does not substantially permeate, and the water permeability is 1 to 10 ml/mm.
While a Hg・m ²・hr membrane is required, in the case of body fluid filtration such as hemofiltration and ascites concentration, it does not substantially allow albumin to pass through, and the water permeation rate is low.
A membrane of 20ml/mmHg・m ²・hr or more is required. As such membranes, polyacrylonitrile membranes, polymethyl methacrylate membranes, etc. are already known. For example, JP-A-57-136903 describes a membrane containing carboxyl groups and/or amide groups that prevents protein adsorption to membranes. An acrylonitrile-based semipermeable membrane has been disclosed that has the following effects. Also, JP-A-57-
No. 147404 discloses a polymethyl methacrylate-based anti-permeable membrane that is given mechanical strength by polyion complex crosslinking. However, it has recently become clear that such conventionally known membranes cannot remove substances with a molecular weight of 20,000 to 30,000, which are thought to be accumulated in the bodies of long-term dialysis patients. The present inventors conducted intensive research to eliminate these drawbacks, and as a result, surprisingly, the vinyl alcohol-based porous membrane containing anionic groups substantially does not allow albumin to pass through, allowing substances with a molecular weight of 20,000 to 30,000 to pass through. The present invention has been completed based on the discovery that it can be efficiently removed. That is, the present invention provides a body fluid treatment membrane made of a polymer containing at least 25 mol% of vinyl alcohol residues and 0.3 to 45 mol% of groups that can be dissociated into anions in water, which has pores with a pore diameter of 80 to 1000 Å on at least one surface.
The membrane has a dense layer with many micropores, and the inside of the membrane has a microporous structure with a porosity of 40 to 80%, and has a water permeability of 20 ml/mmHg・m ²・hr or more, which inhibits serum albumin. It is an anionic body fluid permeable membrane characterized by an anionic body fluid permeability of 85% or more. The present invention will be explained in more detail below. In the present invention, body fluids include blood, plasma, serum, lymph fluid, bone marrow fluid, ascites fluid, and fluids that have undergone some kind of treatment, such as removing white blood cells,
It is a general term for products that have cholesterol removed, are cooled (heated) to form a protein gel, or have hydroxyethyl starch added to them. As the material for the membrane in the present invention, it is necessary to use a polymer containing at least 25 mol% of vinyl alcohol residues. Such polymers include polyvinyl alcohol or vinyl alcohol copolymers, such as at least one of olefins such as ethylene and propylene, styrene, vinyl chloride, acrylonitrile, acrylic acid and derivatives thereof, and vinyl esters such as vinyl acetate. Examples include saponified products of copolymers with
Among these copolymers, ethylene vinyl alcohol copolymers are preferred because they have excellent antithrombotic properties. The content of ethylene residues in the ethylene vinyl alcohol copolymer is at least 10 mol%, preferably 20 to 50 mol%. The vinyl alcohol residue in the polymer is at least
It is necessary that the content be 25 mol%. If it is less than 25 mol%, affinity with blood decreases. The reason for this is not clear, but the balance between hydrophilicity and hydrophobicity of the polymer, which is one of the important factors for anticoagulation,
It is thought that the hydration of the hydroxyl group exerts a gradual adjustment effect. The preferred content of vinyl alcohol residues is 50 to 95 mol%. The content of vinyl alcohol residues herein refers to the ratio of the number of vinyl alcohol monomers to the number of unit monomers (residues) of the polymer constituting the membrane. The content of groups that can be ionized into anions in water (hereinafter referred to as anionic groups) in the polymer is 0.3.
The amount is mol % to 45 mol %, preferably 1 to 10 mol %. The ionic group content here is the ratio of the number of moles of anionic groups to the number of unit monomers of the polymer constituting the membrane. If the content of anionic groups is less than 0.3 mol%, the separation and fractionability of substances with a molecular weight of 1,000 to 100,000 will not improve.
The decrease in overspeed over time is also large. On the other hand, if it exceeds 45 mol %, the membrane will swell to a large extent and its pressure resistance will drop significantly, making it necessary to carry out a large amount of crosslinking, which is unsuitable because a large overspeed cannot be achieved. For the crosslinking reaction, known general methods can be used. Examples include crosslinking reactions caused by radiation and light such as rays and electron beams. A crosslinked structure can be introduced by copolymerization with a polymer having a crosslinked structure in advance. Further, a crosslinking reaction can also be carried out during polymerization and film formation. In particular, a step in which only a crosslinking reaction is performed may be performed. If necessary, a crosslinking reaction can be carried out after film formation. Also, acetalization, esterification,
Various reactions including etherification can also be carried out at any time. Although these are not crosslinks, they are useful in adjusting the hydrophilicity and hydrophobicity of the membrane to control blood compatibility. Examples of ionic groups include carboxyl groups, sulfonic acid groups, sulfinic acid groups, phosphonic acid groups, phosphinic acid groups, and salts thereof, phenolic hydroxyl groups and salts thereof, esters such as sulfates and phosphates, and esters thereof. There is salt, etc. Two or more types of these groups may be present in the same residue, or two or more types of these groups may be present in the polymer forming the membrane. The ionic groups can be introduced into the membrane-forming polymer by copolymerizing vinyl monomers, polymers, or multicomponent copolymers containing them with other monomers. Or after polymerization, during film formation, after film formation,
Furthermore, it may be introduced after modularization. Photoreaction or radiation may be used to introduce ionic groups, or acetalization, esterification, etherification,
Known reactions such as sulfonation, oxidation, reduction, addition, substitution, exchange, and grafting may be used. The body fluid permeable membrane of the present invention has an active dense layer having a large number of micropores of 80 to 1000 Å on at least one surface of the membrane. Further, the inside of the membrane has a microporous structure having many pores larger than the above-mentioned micropores, and the porosity thereof is 40% or more and 85% or less. The water permeability of this body fluid treatment membrane is 20ml/mmHg・m ²・
hr or more, preferably 50ml/mmHg・m ²・hr or more,
Serum albumin (molecular weight 67000) inhibition rate is 85%
or more, preferably 95% or more. If the porosity is smaller than this, or if the water permeability is smaller than this, the overspeed of body fluid, which is a concentrated protein solution, will be small, and the overspeed will decrease over time due to clogging. Furthermore, if the porosity exceeds 85%, the mechanical strength of the membrane will be extremely insufficient, making it difficult to modularize it. If the serum albumin inhibition rate is less than 85%, the loss of albumin during body fluid removal is too large, and expensive albumin preparations and plasma replacement are required in cases such as hemofiltration, which is inconvenient. Such loss of serum albumin reduces the micropores provided in the lamina densata to less than 1000 Å, preferably 400 Å.
This can be prevented by setting it to Å or less. Next, the method for forming the body fluid permeable membrane of the present invention will be explained in more detail. The average molecular weight of the polymer forming the membrane is approximately 30,000 or more. Usually 35,000 to 20
Approximately 10,000 is used. The higher the average molecular weight, the better the mechanical properties of the membrane. As the solvent for the polymer, a solvent is selected from among water and organic solvents that can completely dissolve the raw material polymer and can be quickly dissolved in the coagulation bath. For example, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, tetrahydrofuran, pyrrolidone, N-methylpyrrolidone, monohydric alcohols such as methanol, ethanol, isopropanol, polyhydric alcohols such as ethylene glycol, propylene glycol, glycerin, phenol, metacresol, formic acid. , water or a mixture thereof. In order to obtain the porous membrane referred to in the present invention, a solution containing only a polymer and a solvent may be used as a membrane-forming stock solution, but additives are often added to the membrane-forming stock solution in order to form pores. Examples of additives include inorganic acids and inorganic salts such as boric acid, mirabilite, calcium carbonate, and calcium chloride; organic acids and their salts; alkalis; non-solvents such as polyethylene glycol, polypropylene glycol, acetone, hexane, and benzene; Dispersoids such as colloidal silica can be used. The amount of these substances added is 10% or more and 300% or less, preferably 50% or more and 200% relative to the polymer.
It is as follows. If the amount added is smaller than this, clogging pores are likely to be formed, and if the amount is larger than this, it is difficult to form a film. The concentration of the polymer in the membrane forming stock solution is in the range of 5 to 50% by weight, preferably 10 to 35% by weight. At a concentration lower than this, the viscosity is too low, and at a concentration higher than this, the viscosity is too high, making it difficult to stably obtain a uniform film. The temperature of the membrane forming stock solution is 0°C to 120°C, preferably 5°C.
~95℃ is good. If the temperature is lower than this, the viscosity becomes too high and film formation becomes difficult, and if the temperature is higher than this, the polymer may be decomposed or deteriorated. The film-forming stock solution obtained in this way is formed into a film by various known wet coagulation methods or wet-dry coagulation methods. For example, a method in which the membrane-forming stock solution is extruded through a nozzle with elongated slit-like holes and solidified by contacting or immersing it in a coagulation bath to form a flat film; Examples include a method of forming a hollow fiber membrane. If necessary, an irregularly shaped cap with a hole of a more complex shape may be used. In addition, after casting the membrane forming stock solution into the desired shape,
Alternatively, the film may be formed by contacting or immersing in a coagulation bath while casting. Applying the so-called Loeb membrane film forming technology, the process of discharging, spreading, and
Alternatively, by evaporating an appropriate amount of solvent from the surface of the cast membrane-forming stock solution, an asymmetric membrane having a dense structure only on the surface can be obtained. An asymmetric membrane can also be formed by bringing coagulation baths having different coagulation rates into contact with each side of the discharged, spread, or cast membrane-forming solution. The coagulation bath used is one that has high compatibility with the solvent of the membrane-forming stock solution and has substantially no compatibility with the part that forms the membrane. Generally, water, monohydric alcohols such as methanol and ethanol, polyhydric alcohols such as ethylene glycol, diethylene glycol, and glycerin, acetone, or mixtures thereof are used. In order to adjust the coagulation rate or control gelation or phase separation, miscible organic solvents, inorganic salts such as boric acid, mirabilite, calcium chloride, acids, alkalis, etc. may be added to the coagulation bath. be. In special cases, only one side of the film is in contact with the coagulation bath, and the other side is exposed to a gas such as air or nitrogen, or to the solvent of the film forming stock solution such as benzene, toluene, hexane, or mercury, or to the coagulation bath. It is carried out in contact with immiscible liquids. In some cases, as in JP-A-55-148209, the material is passed through a gas phase immediately before contacting the coagulation bath. Usually, the solidification rate of water or a mixture of water and the solvent used in the membrane forming stock solution is suitable for forming the membrane structure. The temperature of the coagulation bath is an important factor in obtaining a membrane with performance suitable for body fluid filtration, and is generally between -10℃ and 50℃.
℃, preferably in the range of 10 to 40℃. At temperatures lower than this, solidification is slow and it is difficult to form a porous film. Further, at higher temperatures, the viscosity during film formation is too low and spots are likely to occur. After finishing solidification, stretching, heat treatment, and washing are performed as necessary. The membrane according to the invention can also be used as a wet or dry membrane. Drying methods include direct drying using air current, heat rays, electromagnetic waves, etc., as well as methods such as replacing the water contained in the film with an organic solvent that is water-miscible and does not dissolve the polymer (such as acetone, methanol, tetrahydrofuran, etc.), and then using an organic solvent. Methods of removing the solvent by reducing pressure, heating, etc., or using glycerin, ethylene glycol, etc. during or after film formation.
A method of treating with an aliphatic polyhydric alcohol such as polyethylene glycol and subsequent drying, or a method of freezing the water-containing film with liquid nitrogen or carbon dioxide gas and freeze-drying it, etc. can be used. When the membrane of the present invention is made into a module, the best shape is a hollow fiber type, but other known shapes such as a flat membrane type, keel type, coil type, spiral type, and tubular type can also be used. . Especially when utilized in the form of hollow fiber membranes, the inner diameter is 40~3000μ,
Preferably, the film thickness is 80 to 800μ, and the film thickness is preferably in the range of 200μ or less. The anionic porous membrane of the present invention obtained as described above has the characteristics of high blood affinity, excellent permeability to low-molecular-weight proteins, and small decrease in body fluid transit rate over time. It is particularly suitable for use in hemofiltration and ascites concentration. When using the membrane of the present invention for these applications, as mentioned above, the pore diameter provided in the dense layer should be approximately 80 Å or more.
Suitable are those having an anionic group content of 1 to 10 mol %, with a diameter of 1000 Å or less, preferably 400 Å or less.
Those in this range have a blocking rate of 90% or more against serum albumin, and myoblobin (molecular weight
17,000), showing a high separation property of less than 60%, and has a high ability to remove, for example, substances with a molecular weight of 20,000 to 30,000, which are thought to accumulate in the bodies of long-term dialysis patients. The reason for this effect of anionic porous membranes is not clear, but serum albumin, the main component in body fluids, has a low isoelectric point of 4.6, so it becomes negatively charged in body fluids and is specific to the membrane. It is thought that this shows a large repulsion force, and as a result, the blocking rate improves. It is also presumed that the suppression of gelation of albumin on the membrane surface as a result of this electrical repulsion also affects the improvement in separation performance. In this application, water permeability, porosity, and rejection were measured as follows. (1) Water permeability was measured at 37℃ and 20-100mmHg, and membrane water permeability K' was determined. K'=V/A・t・ΔP (ml/m ²・hr・mmHg) v: permeated water amount (ml), A: dialysis membrane area (m ² ) t: permeation time (hr), ΔP: measurement pressure ( mmHg) (2) The porosity was calculated using the following formula. (1-P _D /P _W ) x 100 (%) P _D : Weight of dry membrane P _W : Weight of water-containing membrane (dry membrane immersed in water,
Weight after sufficiently permeating water into the micropores and removing water from the membrane surface) (3) Unless otherwise specified, rejection rates are based on solute concentration.
Using 0.1%, isotonic phosphorus buffer with pH 7.4, 37℃, TMP 100mmHg, Q _B = 200ml/min,
Measurements were made under the condition that the membrane area was 1.0 m ² . Next, the present invention will be further explained by examples. Example 1 A saponified ethylene-vinyl acetate copolymer (ethylene content: 32 mol%, degree of saponification: 99.9 mol%) was heated and dissolved in dimethyl sulfoxide to prepare a membrane-forming stock solution with a polymer concentration of 20%. This solution was casted onto a glass plate placed on a hot plate, and each glass plate was immersed in a 10% aqueous solution of CaCl ₂ adjusted to 20°C (solubility of CaCl ₂ in water at 20°C: 82 g/dl). Wet coagulation resulted in a white film. As a result of observing the cross section of the obtained film with a scanning electron microscope,
A clear active dense layer was observed on the free surface side. This membrane was immersed in a polyethylene glycol (molecular weight 400) maleate solution containing 15% maleic anhydride, esterified at 70°C for 4 hours to introduce carboxyl groups, and then washed with warm water. The maleated ethylene vinyl alcohol flat film had a vinyl alcohol residue content of 64.8 mol%, a maleic acid group content of 3.2 mol%, a film thickness of 305 μm, and a porosity of 68%. In addition, using a laminar flow device manufactured by Amicon, the membrane performance was measured under the conditions of 25℃, 0.1% protein solution, PH7.4 isotonic phosphorus buffer, and TMP 0.5Kg/ ^cm2 , and the membrane before maleation was measured. Table 1 shows the results of performance comparison as a control. It can be seen that the difference in the rejection rate between albumin and myoglobin is clearly improved in the anionic porous membrane, and the separation of serum albumin from a low molecular weight protein with a molecular weight of 20,000 to 30,000 is improved.

[Table] Example 2 250 g of saponified ethylene-vinyl acetate copolymer (ethylene content: 44 mol%, saponification degree: 98 mol%) was dissolved in a mixed solvent of 720 g of dimethyl sulfoxide and 30 g of water, and this was used as a stock solution to prepare the following hollow Performed fiber spinning. The nozzle used was a 40-hole type made by Kasensen Nozzle Co., Ltd., with an inner diameter of 600μ at the part that extruded the stock solution.
The one with an outer diameter of 1200μ was used. The stock solution temperature was kept at 50 °C, and the hollow injection solution was 10% of _CaCl2 at 15 °C.
Water adjusted to 20°C was used as a coagulation bath for the aqueous solution. The raw solution transfer speed is gear pump discharge volume 120ml/
Wet spinning was performed at a bath separation yarn speed of 8 m/min. The obtained hollow fiber membrane has an outer diameter of 800μ and an inner diameter of 500μ.
The porosity was 74%. This hollow fiber
A cylindrical module with a membrane area of 1.0 m ² was fabricated by bundling 2560 pieces using a conventional method. 2% for this module
Sodium orthobenzaldehyde sulfonate and 10
A sulfonation solution consisting of 10% sulfuric acid and 10% Glauber's salt was introduced, and the mixture was reacted at 40°C for 6 hours. The sulfonated hollow fiber has an inner diameter of 570μ, an outer diameter of 940μ, and a porosity.
80%, the degree of sulfonation was 4.9 mol%, and therefore the content of vinyl alcohol residues was (100-44)×0.98−4.9×2=45.1 mol%. The results of measuring excess performance against 0.1% protein solution using the module before sulfonation as a control, and α-
Table 2 shows the overtest results for bovine blood to which chymotrypsin (molecular weight 25,000) was added. It is clear that the porous membrane having a sulfone group shows less decrease in transit rate over time than the control membrane, and has a greater separation ability (difference in rejection rate) between a substance with a molecular weight of 20,000 to 30,000 and serum albumin.

[Table] Example 3 Chips of a saponified ethylene-vinyl acetate copolymer with an ethylene content of 32 mol% and a degree of saponification of 99.8 mol% were placed in a mixed aqueous solution of 10% sulfuric acid, 10% Glauber's salt, and 2.5% sodium benzaldehyde sulfonate. disperse, 70
The acetalization reaction was carried out at ℃ for 5.5 hours, resulting in a concentration of 3.4 mol%.
Introducing sulfone group, vinyl alcohol residue content
A polymer with an average molecular weight of 42,000 and an average molecular weight of 61.1 mol% was obtained. After thorough washing and drying, the polymer was dissolved in dimethyl sulfoxide at 80°C to determine the polymer concentration.
A 20% membrane forming stock solution was obtained. Apply this stock solution to the nozzle hole diameter
Discharges from an annular nozzle with a diameter of 700μ and a needle diameter of 300μ.
It was coagulated in a 15° C. bath containing 15% CaCl ₂ while expelling water from the needle. The inner diameter of the obtained hollow fiber is 200μ, the outer diameter is 370μ,
The porosity was 65%. 1.0 by a conventional method.
When molded into a m ² cylindrical module and evaluated its performance, water permeability was 26 ml/mmHg・m ²・hr, serum albumin inhibition rate was 98%, and myoglobin inhibition rate was 30%.
It had excellent performance in both water permeability and protein separation.

Claims (1)

[Claims] 1 At least 25 mol% vinyl alcohol residue
Contains 0.3 groups that can be ionized into anions in water.
A body fluid permeation membrane consisting of a polymer containing ~45 mol%,
It has a dense layer with many micropores with a pore diameter of 80 to 1000 Å on at least one surface, and the porosity inside the membrane is 40 to 85.
% microporous structure and water permeability of 20ml/
An anionic body fluid permeation membrane characterized by exhibiting mmHg・m ²・mmhr or more and a serum albumin rejection rate of 85% or more.