JP3995228B2 - Hollow fiber membrane for blood purification - Google Patents

Description

【００３０】
【発明の効果】
以上の説明で明らかなように、本発明によれば透析合併症誘因物質の除去性や臨床症状の改善効果があるとされる分子量2 万程度の物質の除去性に優れ、かつアルブミンの漏出の少ないシャープなカットオフ性を有する血液浄化用中空糸膜が得られる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a blood purification membrane used for hemodialysis and the like. More particularly chronic renal failure in efficiency stable when used in the treatment often beta ₂ - microglobulin can be removed the molecular weight of the uremic substances represented by (hereinafter, beta ₂ referred to as M), albumin, a useful protein The present invention relates to a hollow fiber membrane for blood purification capable of suppressing leakage of blood.
[0002]
[Prior art]
In recent years, dialysis complications associated with an increase in long-term dialysis patients have attracted attention, and the removal targets are expanding not only to low molecular weight substances such as urea and creatinine but also to medium high molecular weight substances (low molecular weight proteins). It has also been suggested that the removal of substances with a molecular weight of about 20,000 has the effect of improving clinical symptoms such as pruritus and pain, and improving lipid metabolism. There are also membranes reported to be effective in reducing itching and irritation (kidney and dialysis separate volume 36 high performance membrane '94: 70, 1994, kidney and dialysis separate volume 36 high performance membrane '94: 132, 1994).
[0003]
However, these membranes have too much albumi leakage per treatment, and long-term use can cause hypoproteinemia and conversely worsen the patient's prognosis. Synthetic polymer membranes typified by polysulfone have been reported to have an albumin leakage of 1 g or less per treatment and excellent β ₂ M removal performance. _{Although the 2} M removal performance was low, it was inferior to the membrane with low albumin leakage. In other words, in order to ensure the safety of patients, no membrane has been obtained that has an excellent ability to remove a substance having a molecular weight of about 20,000 that has a small amount of albumin leakage and leads to a reduction in itchiness and irritation.
[0004]
[Problems to be solved by the invention]
The present invention is intended to solve the above-mentioned drawbacks, and its purpose is not only excellent in the removal of a dialysis complication inducer having a molecular weight of about 10,000 represented by β ₂ M but also an effect of improving clinical symptoms. An object of the present invention is to provide a hollow fiber membrane for blood purification that is excellent in the removal of a substance having a molecular weight of about 20,000 and that suppresses leakage of albumin, which is a useful protein, as much as possible.
[0005]
In order to efficiently remove a substance having a molecular weight of about 20,000, which is a causative substance of itchiness and irritation, a pore size larger than that of a normal dialysis membrane is required. However, with the current membrane manufacturing technology, it is impossible to completely separate albumin, which is a protein necessary for the human body, from a substance with a molecular weight of about 20,000, and it is quite difficult to improve clinical symptoms such as itchiness and irritation. An amount of albumin leak occurs at the same time. As a specific figure, improvement of clinical symptoms such as itchiness and irritation is particularly well recognized when the protein concentration in the filtrate (mostly albumin occupies) when blood is filtered is 200 mg / dl or more. However, if the protein concentration in the filtrate is 200 mg / dl or more, about 3 L of filtration is performed per treatment in normal dialysis, so that the amount of aluminium leaking out in one treatment becomes 6 g or more, and as described above, hypoproteinemia occurs. May cause. Therefore, it seemed impossible to achieve both the improvement of clinical symptoms such as itching and irritation and the safety of albumin leakage.
[0006]
However, as a result of further investigation, if the protein concentration in the filtrate at the initial stage of blood filtration is 200 mg / dl or more, and the protein concentration in the filtrate decreases with time due to blood filtration, it remains within a certain range. As a result, it was found that the removal performance of a substance having a molecular weight of about 20,000 was kept high throughout the treatment time.
[0007]
[Means for Solving the Problems]
That is, the present invention provides the following hollow fiber membrane for blood purification. 15 when a hematocrit 30 ± 3%, protein concentration 6.5 ± 0.5 g / dl was flowed into a module with a membrane area of 1.5 m ^{2 at} a flow rate of 200 ml / min and blood filtration was performed at a filtration flow rate of 15 ml / min. The protein concentration in the filtrate after 200 minutes / min is 600 mg / dl or less , the protein concentration in the filtrate after 120 minutes is 50 mg / dl or more and 200 mg / dl or less, and β2-microglobulin 15 minutes after the start of filtration. A blood purification hollow fiber membrane comprising cellulose triacetate having a sieving coefficient of 0.85 or more, a dextran having a molecular weight of 20,000 and a sieving coefficient of 0.5 or more, and a water permeability of 10 ml / m ² / hr / mmHg or more.
[0008]
In the present invention, the protein concentration in the filtrate after 15 minutes should be 200 mg / dl or more and 1000 mg / dl or less. Preferably it is 300-800 mg / dl, More preferably, it is 400-600 mg / dl. By setting it to 200 mg / dl or more, a molecular weight substance having a molecular weight of about 20,000 can be efficiently removed. Even if it is less than 200 mg / dl, a substance with a molecular weight of up to about 10,000 can be removed relatively efficiently, but clinical symptoms such as itching and irritation are difficult to improve. On the other hand, the protein concentration in the filtrate after 15 minutes is preferably 1000 mg / dl or less. If it exceeds 1000 mg / dl, it will be difficult to keep the total protein removal during treatment within the safe range even if the protein concentration in the filtrate decreases with time.
[0009]
In the present invention, the measurement of the protein concentration in the filtrate immediately after the start of blood filtration is 15 minutes later for the following reason.
In the present invention, as apparent from the object of the invention, the pore diameter of the membrane immediately after blood filtration must be greater than a certain value, so that the protein concentration in the filtrate is accurately measured as early as possible after the start of blood filtration. It is desirable to do. However, the membrane is pre-primed with physiological saline before coming into contact with blood, and the filtrate side in the membrane and the module is filled with physiological saline. For this reason, even if blood is flowed and filtration is started, the filtrate obtained first is diluted with physiological saline, and it is difficult to obtain an accurate protein concentration in the filtrate. When the filtrate flow rate is about 15 ml / min, the shortest time in which the influence of dilution with physiological saline can be ignored is 15 minutes after the start of filtration.
[0010]
In the present invention, the protein concentration in the filtrate after 120 minutes should be 50 mg / dl or more and 200 mg / dl or less. If the protein concentration in the filtrate after 120 minutes is 50 mg / dl or more, removal of molecular weight substances with a molecular weight of about 20,000 can be efficiently performed over the entire treatment time. If it is less than 50 mg / dl, the substance removal performance at the beginning of the treatment is high, but the removal effect cannot be maintained over the entire treatment time, which is not preferable. Also, if the protein concentration in the filtrate after 200 minutes exceeds 200 mg / dl, protein leakage increases throughout the treatment time, and hypoproteinemia tends to occur.
[0011]
The causative agent for itching and irritation is estimated to have a molecular weight of about 20,000, but has not yet been identified. Also, if the molecular weight is the same but the molecular shape is different, the removal characteristics when filtered through a membrane cannot be defined unconditionally. In our study, when the protein concentration in the filtrate after 15 minutes is 200 mg / dl or more, the sieving coefficient of fluorescently labeled dextran having a molecular weight of 20,000 is recognized to be 0.5 or more. We introduced the sieving coefficient of fluorescently labeled dextran with a molecular weight of 20,000 as a standard for objectively judging clinical effects in the laboratory, and thought that it was possible to eliminate itchiness and irritability when this sieving coefficient was 0.5 or more. .
[0012]
The present invention provides a hollow fiber membrane having both high removal efficiency and safety by adjusting the protein concentration in the filtrate to an appropriate range. However, the hollow fiber membrane of the present invention is generally a high flux dialysis membrane. It belongs to the category called. That is, since the removal efficiency has a correlation with the water permeability of the dialysis membrane, the water permeability of the hollow fiber membrane of the present invention is preferably 10 ml / m ² / hr / mmHg or more, more preferably 20 ml / m ² / hr / mmHg or more. With such a high water permeability, an excellent therapeutic effect can be expected by setting the above filtrate protein concentration range.
[0013]
The hollow fiber membrane of the present invention requires that the sieving coefficient of albumin measured using a 5 wt% albumin-containing phosphate buffer (pH 7.4) is 0.15 to 0.6. When the sieving coefficient of albumin is less than 0.15, β ₂ M and the like are not sufficiently removed when blood purification is actually performed. If the sieving coefficient for albumin exceeds 0.6, the amount of albumin leakage necessary for the human body increases. That is, it can be said that the necessity that the sieving coefficient of albumin in the aqueous solution is in the range of 0.15 to 0.6 is the size added with the pore diameter that is reduced by the protein gel layer formed during actual blood purification.
[0014]
Examples of the hollow fiber membrane material in the present invention include regenerated cellulose, modified cellulose, polysulfone, acrylonitrile and the like, and any cellulose acetate that is excellent in water permeability and solute permeability is preferable as long as the amount of protein adsorption is small. From the viewpoint of biocompatibility, cellulose triacetate is particularly preferable.
[0015]
The spinning method of the hollow fiber membrane of the present invention is not particularly limited and can be obtained by a known spinning method such as melting, dry, wet, and dry wet, but a hollow forming agent is used in order to widen the range of phase separation control. It is preferable to form a film by the dry and wet spinning method used. The hollow forming agent may be inert to the spinning solution. For example, liquid paraffin or isopropyl myristate can be used as the liquid, and dry air, nitrogen, helium, argon, or the like can be used as the gas.
[0016]
The hollow fiber membrane of the present invention can be produced, for example, as follows, but the present invention is not limited to the following. A spinning stock solution consisting of 16 to 25 parts by weight of cellulose acetate, 45 to 75.6 parts by weight of solvent, and 8.4 to 39 parts by weight of non-solvent is heated to 130 to 190 ° C. to dissolve and extruded from the outside of the double-tube spinneret. Extrudes the hollow forming agent. The extruded spinning dope passes through a gas atmosphere and is then coagulated in a coagulating liquid at 0 to 50 ° C., and the excess solvent and non-solvent are washed in a water washing bath. In order to obtain the hollow fiber membrane of the present invention, a spinning stock solution composed of a membrane material such as cellulose triacetate, a solvent, and a non-solvent is discharged from a tube-in-orifice type spinneret into a gas atmosphere, and then guided to a coagulation bath. It is preferable to use a spinneret with an outer diameter of 1000 μm or more and adjust the gas passage time to 0.5 seconds or more when manufacturing the membrane. Here, the gas passage time is calculated from the linear velocity of the spinning dope discharged from the spinneret and the gas atmosphere passage length. Although it depends on the spinning speed, the AG length is preferably 50 mm or more, more preferably 100 mm or more. Moreover, it is preferable to adjust the draft ratio represented by the ratio of the roller speed at the coagulation bath outlet and the linear speed of the spinning dope discharged from the spinneret between 10-30. Furthermore, it is preferable to adjust the temperature of the coagulation bath to 30 ° C. or higher. By using these combinations, the obtained hollow fiber membrane has an appropriate balance between the amorphous region and the crystalline region, and obtains a blood purification membrane satisfying the parameters of the present invention with good water permeability and solute permeability. I found it possible.
[0017]
Thereafter, the hollow fiber is passed through a 30 to 70% by weight glycerin aqueous solution by a conventional method to impregnate the membrane pores with glycerin, and wound through a drying step. The solvent is not particularly limited as long as it dissolves cellulose acetate, but N, N-dimethylacetamide, N, N-dimethylformamide, γ-butyrolactone, N-butylpyrrolidone, dimethylsulfoxide, N, N- It is preferable to use a polar solvent such as dimethylimidazolidinone. These can be used alone or in combination. Examples of the non-solvent include polyhydric alcohols such as ethylene glycol, triethylene glycol, polyethylene glycol, and glycerin, or lower alkyl ether derivatives thereof, which can be used alone or in combination.
[0018]
The hollow fiber membrane for blood purification produced by such a method has a good balance between the pore size and the number of pores, the permeability of low-molecular solute to medium-molecular solute (low-molecular protein), and the cutoff of albumin, which is a useful protein. Since it has excellent properties, it is suitably used for ultrafiltration, dialysis, diafiltration, and specifically used for hemodialysis, hemodiafiltration, and the like.
Although the theoretical basis of the present invention has not been confirmed, the inventor thinks as follows.
In other words, it is necessary to make the pore size larger than that of a normal dialysis membrane in order to remove the causative agent of itchiness and irritation. Therefore, the sieving coefficient of albumin measured using a 5 wt% albumin-containing phosphate buffer and the start of filtration 15 It will be clear that the filtrate protein concentration after the minute must be set within a certain range.
It has a specific adsorption form with plasma protein on the blood contact surface of the membrane when the blood and the membrane come into contact with each other by having a pore size within the above range and having an appropriate balance between the amorphous region and the crystalline region. It is considered that it acts as the next separation membrane and exhibits an excellent separation efficiency that cannot be achieved with the current membrane production technology, that is, a high degree of separation between albumin and a substance having a molecular weight of about 20,000.
[0019]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited at all by an Example.
[0020]
[Example 1]
19 parts by weight of cellulose triacetate, 56.7 parts by weight of N-methylpyrrolidone and 24.3 parts by weight of triethylene glycol were dissolved by heating at 170 ° C., and vacuum degassed to obtain a spinning solution of cellulose triacetate. This was filtered through a sintered filter having a pore diameter of 20 μm to remove impurities, and then discharged from the outside of the double-tube structure having an outer diameter of 1400 μm at a discharge linear velocity of 321 cm / min, and at the same time, liquid paraffin was discharged from the inside of the base. The hollow fiber spinning dope passes 7.5 cm in a gas atmosphere for 1.4 seconds, and then led to a coagulation bath at 40 ° C. consisting of N-methylpyrodon / triethylene glycol / water = 10.5 / 4.5 / 85, and the coagulation bath outlet roller speed is 73.8 m. Withdrawn from the coagulation bath at / min. The draft ratio at this time was 23.0 when calculated from the spinning solution discharge linear velocity and the coagulation bath outlet roller velocity. Subsequently, it was wound in a cheese shape with a winder through a water washing bath, a 60% glycerin water bath, and a drying step.
[0021]
10400 hollow fibers having an inner diameter of 200 μm and a film thickness of 15 μm thus obtained were bundled and filled into a plastic case to produce a performance evaluation module (effective membrane area 1.5 m ²⁾ having an effective length of 23 cm.
[0022]
Measurement method 1. Measurement of ultrafiltration coefficient The above-prepared module was thoroughly washed with pure water, and pure water adjusted to 37 ° C was poured into the hollow fiber membrane, and the pressure difference (TMP) between membranes was 50, 100, 150 and 200mmHg. The water permeability was measured.
The ultrafiltration coefficient at each TMP was calculated from the obtained water permeability using the following formula.
UFR (ml / m ² · hr · mmHg) = Permeability x 60 / TMP / Membrane area module's ultrafiltration coefficient is the average limit based on the slope of the regression line obtained from the above 4 points TMP and ultrafiltration coefficient The filtration coefficient was obtained.
[0023]
2. Measurement of sieving coefficient of albumin Dissolve albumin in phosphate buffer and add saline to adjust the albumin concentration to 5 wt%, pH 7.4, 37 ° C. This solution was passed through a module having a membrane area of 1.5 m ^{2 at} a flow rate of 200 ml / min and a filtration flow rate of 15 ml / min. After 15 minutes, the concentrations of albumin at the module inlet and outlet and the filtrate were measured using a commercially available measurement kit. The sieving coefficient (SC) of albumin was calculated according to the following formula.
SC = filtrate concentration / ((entrance concentration + outlet concentration) / 2)
[0024]
3. Fluorescence labeling (FITC)-Determination of dextran sieving coefficient FITC-dextran (molecular weight 20,000) to a concentration of 1.9 mg / dl in bovine blood prepared with hematocrit 30 ± 3% and protein concentration 6.5 ± 0.5 g / dl And flow into a module with a membrane area of 1.5 m ² at a flow rate of 200 ml / min. After 5 minutes from the start of blood flow, blood filtration starts at a filtration rate of 15 ml / min, and after 15, 30, 60 and 120 minutes, the blood and filtrate at the inlet and outlet of the module are sampled and the FITC-dextran concentration is measured by fluorescence spectrophotometry. Measured using a meter. The sieving coefficient of dextran was calculated from the following formula using each obtained measurement value.
SC = filtrate concentration / ((entrance concentration + outlet concentration) / 2)
[0025]
4. beta ₂ microglobulin (β ₂ M) sieve measured hematocrit 30 ± 3% of the factor, flow protein concentration 6.5 ± 0.5 g / dl in the prepared bovine blood film area 1.5 m ² module 200 ml / min. After 5 minutes from the start of blood flow, blood filtration is started at a filtration rate of 15 ml / min. After 15, 30, 60 and 120 minutes, the blood and filtrate at the inlet and outlet of the module are sampled, and an enzyme immunoassay (eg, Glazyme) is sampled. measuring a beta ₂ M concentration with β ₂ -Microglobulin-EIA Ltd. Test Wako Pure Chemical Industries) and the like.
In addition, an appropriate amount of human-derived β ₂ M is added to the bovine blood flowing into the module in this measurement, and the sampled blood is centrifuged as necessary to be used for β ₂ M measurement. A sieve coefficient was calculated from the measured β ₂ M concentration according to the following formula.
SC = filtrate concentration / ((entrance concentration + outlet concentration) / 2)
[0026]
5. Measurement of protein concentration in the filtrate Bovine blood prepared to a hematocrit of 30 ± 3% and protein concentration of 6.5 ± 0.5g / dl was poured into the module at 200ml / min, and after starting blood filtration at a filtration rate of 15ml / min, 15, 30, After 60 and 120 minutes, the blood and filtrate at the inlet and outlet of the module were sampled, and the protein concentration was measured by a colorimetric method (Micro TP Test Wako, etc.). The amount of protein leakage at the time of 3L water removal was calculated from the average value of 15 minutes to 120 minutes.
[0027]
[Comparative Example 1]
17 parts by weight of cellulose triacetate, 49.8 parts by weight of N-methylpyrrolidone, and 33.2 parts by weight of triethylene glycol were dissolved by heating at 170 ° C., and vacuum degassing was performed to obtain a spinning solution of cellulose triacetate. This was filtered through a sintered filter having a pore size of 20 μm to remove impurities, and then discharged from the outside of the double tube cap having an outer diameter of 540 μm at a discharge linear velocity of 1064 cm / min, and at the same time, liquid paraffin was discharged from the inside of the cap. The hollow fiber-shaped spinning dope is passed through 25 mm in air for 0.14 seconds and then led to a 55 ° C. coagulation bath consisting of N-methylpyrrolidone / triethylene glycol / water = 18/12/70, and 7 3.8 m as in Example 1. Withdrawn from the coagulation bath at / min. In this case, the draft ratio was 7.0. Subsequently, it was wound in a cheese shape with a winder through a water washing bath, a 60% glycerin water bath, and a drying step.
[0028]
[Example 2]
17.5 parts by weight of cellulose triacetate, 66.0 parts by weight of N-methylpyrrolidone and 16.5 parts by weight of triethylene glycol were heated and dissolved at 170 ° C., and vacuum degassed to obtain a spinning solution of cellulose triacetate. This was filtered through a sintered filter having a pore diameter of 20 μm to remove impurities, and then discharged from the outside of the double-tube base having an outer diameter of 1200 μm at a discharge linear velocity of 364 cm / min. At the same time, liquid paraffin was discharged from the inside of the base. The hollow fiber spinning stock solution passed through 60 mm in the air for 0.99 seconds, then led to a coagulation bath at 36 ° C. consisting of N-methylpyrrolidone / triethylene glycol / water = 40/10/50, and 73.8 m / min as in Example 1. Withdrawn from the coagulation bath. The draft ratio at this time was 20.6. Subsequently, it was wound in a cheese shape with a winder through a water washing bath, a 60% glycerin water bath, and a drying step.
[0029]
[Comparative Example 2]
Performance evaluation was similarly performed using a commercially available module (manufactured by Fresenius, product name F60, membrane area 1.25 m ² ) and compared.
[Table 1]

[0030]
【The invention's effect】
As is apparent from the above explanation, according to the present invention, the removal of substances causing dialysis complications and the removal of substances with a molecular weight of about 20,000, which are said to have an effect of improving clinical symptoms, are excellent. A blood purification hollow fiber membrane having a small sharp cut-off property is obtained.

Claims (1)

When a hematocrit 30 ± 3%, protein concentration 6.5 ± 0.5 g / dl was passed through a module with a membrane area of 1.5 m ^{2 at} a flow rate of 200 ml / min, and blood filtration was performed at a filtration flow rate of 15 ml / min. Protein concentration in the filtrate after 15 minutes is 200 mg / dl to 600 mg / dl , protein concentration in the filtrate after 120 minutes is 50 mg / dl to 200 mg / dl and β2-microglobulin 15 minutes after the start of filtration A hollow fiber membrane for blood purification comprising cellulose triacetate having a sieving coefficient of 0.85 or more, a dextran having a molecular weight of 20,000 and a sieving coefficient of 0.5 or more, and a water permeability of 10 ml / m ² / hr / mmHg or more.