CA1237260A - Hollow fiber membrane for dialysis - Google Patents
Hollow fiber membrane for dialysisInfo
- Publication number
- CA1237260A CA1237260A CA000451497A CA451497A CA1237260A CA 1237260 A CA1237260 A CA 1237260A CA 000451497 A CA000451497 A CA 000451497A CA 451497 A CA451497 A CA 451497A CA 1237260 A CA1237260 A CA 1237260A
- Authority
- CA
- Canada
- Prior art keywords
- hollow fiber
- fiber membrane
- dialysis
- membrane
- yield strength
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/02—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor characterised by their properties
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/08—Hollow fibre membranes
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D69/00—Semi-permeable membranes for separation processes or apparatus characterised by their form, structure or properties; Manufacturing processes specially adapted therefor
- B01D69/08—Hollow fibre membranes
- B01D69/084—Undulated fibres
Abstract
Abstract:
The invention provides a hollow fiber membrane suitable for dialysis made of a cellulose ester. The hollow fiber membrane has a membrane thickness of less than 20µ, and a yield strength Sb (g/filament) after being heat-treated at 80°C for 20 hours which satisfies the following formula (I):
0.90 < Sb/Sa < 1.10 (I) wherein Sa is the yield strength (g/filament) of the hollow fiber membrane measured before the heat treatment. The present invention further provides a method for producing the hollow fiber membrane which comprises extruding a spinning solution of a cellulose ester through circular slits around an inner tube of a spinneret while simultaneously extruding a core solution through the inner tube of the spinneret, passing the spinning solution extruded from the circular slits through a gaseous atmosphere, introducing the same into an aqueous coagulation bath, washing the coagulated hollow fibers, passing the fibers through a glycerin bath, drying the fibres, reeling the fibres onto a bobbin and then heat treating the reeled fibers. The membrane is suitable for the dialysis of body liquids, and particularly for the dialysis of blood, because it has good dialysis performance while maintaining good storage stability and good UFR retention during storage and during hemodialysis.
The invention provides a hollow fiber membrane suitable for dialysis made of a cellulose ester. The hollow fiber membrane has a membrane thickness of less than 20µ, and a yield strength Sb (g/filament) after being heat-treated at 80°C for 20 hours which satisfies the following formula (I):
0.90 < Sb/Sa < 1.10 (I) wherein Sa is the yield strength (g/filament) of the hollow fiber membrane measured before the heat treatment. The present invention further provides a method for producing the hollow fiber membrane which comprises extruding a spinning solution of a cellulose ester through circular slits around an inner tube of a spinneret while simultaneously extruding a core solution through the inner tube of the spinneret, passing the spinning solution extruded from the circular slits through a gaseous atmosphere, introducing the same into an aqueous coagulation bath, washing the coagulated hollow fibers, passing the fibers through a glycerin bath, drying the fibres, reeling the fibres onto a bobbin and then heat treating the reeled fibers. The membrane is suitable for the dialysis of body liquids, and particularly for the dialysis of blood, because it has good dialysis performance while maintaining good storage stability and good UFR retention during storage and during hemodialysis.
Description
12371Z6~
Hollow fiber membrane for dialysis The present invention relates to a novel hollow fiber membrane. More particularly, it relates to a hollow fiber membrane made of a cellulose ester which is suit-able for artificial kidneys.
It is known that cellulose esters can be processed to form hollow fiber membranes which may be used for various processes. For example, these membranes may be used for separation processes involving energy savings, such as processes for desalinating sea water or salt water, and ultrafiltration of aqueous solutions containing various solutes.
It is also known that cellulose esters are suitable for the preparation of hollow fiber membranes useful for artificial kidneys because they have good biocompatibility and are easily produced, and hence, extensive studies have been carried out in this regard. Generally, in order to be suitable for artificial kidneys, the material used for the hollow fibers should satisfy the following six conditions:
(1) it should have good dialysis performance, i.e. a suitable ultrafiltration rate (hereinafter referred to as 'IUFRn) and also excellent permeability by solutes such as urea, creatinine, etc.;
(2~ the hollow fiber membrane made therefrom should not permit leakage of blood;
(3) it should have good compatibility with blood, i.e.
it should have low thrombogenicity and hemolysis;
(4) after the hemodialysis, no blood should remain in the module (i.e. the hollow fiber membrane assembly of the separation apparatus);
(5) an acceptably small amount of material should be dissolved out of the hollow fiber membrane; and (6) during storage or during hemodialysis, no change of the dialysis performance, particularly UFR, should be observed.
A hollow fiber membrane which satisfies all of the above conditions has not previously been produced. It is known that when the thickness of the hollow fiber membrane is reduced, the product shows better perme-ability by solutes such as urea, uric acid, creatinine, etc. and higher dialysis efficiency, so dialysis modules incorporating such membranes can be made smaller and the amount of blood which has to be circulated outside the patient's body is advantageously reduced. However, when the membrane thickness is reduced, the hollow fiber membrane disadvantageously exhibits poor maintenance of dialysis performance, i.e. the sixth requirement of those given above, namely a change of dialysis performance, particularly lowering of UFR, during storage or during hemodialysis. A conventional hollow fiber membrane made of cellulose ester should therefore have a thickness of not less than about 20 ~ in order to prevent this dis-advantage, but such a membrane still has some problems with respect to dialysis performance, that is, it is difficult to provide improved UFR and a high permeability for urea.
The present inventors have carried out extensive research for improved hollow fiber membranes having no change of dialysis performance during storage or during hemodialysis while maintaining the advantages of thin membranes.
1237~
According to one aspect of the invention there is provided a hollow fiber membrane suitable for di-alysis comprising cellulose ester and having a membrane thickness of less than 20 ~, and a yield strength Sb (g/filament) after being heat-treated at 80C for 20 hours which satisfies the following formula (I):
0.90 ~ Sb/Sa ~ 1.10 (I) wherein Sa is the yield strength (g/filament) of the hollow fiber membrane measured before the heat treatment.
Suitable cellulose esters used for the preparation of the dialysis membrane of the present invention include cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate pro-pionate and the like, which may be used alone or in combination of two or more thereof.
The hollow fiber membrane of the present invention should essentially satisfy the condition that it has a membrane thickness of less than 20 ~, and the condition of the above formula (I). Although it is known that when the membrane has a reduced thickness, it shows better permeability by solutes such as urea or creatinine, hollow fiber membranes having a membrane thickness of about 20 ~ or more are normally employed to provide acceptable storage stability and stability during the dialysis procedure. In contrast, the hollow fiber membrane of the present ~nvention can be made thin while maintaining a strong membrane structure. When the ratio of Sb/Sa is less than 0.9, the hollow fiber membrane shows an undesirable lowering of yield strength during storage over a long period of time, and hence, when it is used for hemodialysis, it has unstable strength and leakage of blood may be induced, which is a fatal draw-back for artificial kidneys. On the other hand, when the ratio of Sb/Sa is over 1.1, the hollow fiber membrane tends to become dense in structure when exposed to high temperatures during storage or transportation, and hence, ~237260 the dialysis performance is decreased and the original hemodialysis capacity can not be obtained, which can have a severe effect on patients. The yield strength of the hollow fiber membrane is measured by a universal tensile tester, that is, by subjecting a fixed length of the hollow fiber (50 mm) to stretching at a tensile rate of 10 mm/minute to obtain a stress-strain curve, followed by calculating the yield strength from the yield point obtained from the curve.
Thus, the hollow fiber membrane of the present in-vention is characterized in that, owing to a desirable membrane thickness and dynamic properties, the dialysis performance, particularly UFR, is not lowered during storage or transportation, or during hemodialysis. For example, a hollow fiber membrane of the present invention showed the following UFR reten~ion in a storage test and in a bovine blood filtration test. That is, a module for dialysis was prepared from a hollow fiber membrane of the present invention and was kept at 55C for 15 days, and then the storage UFR retention (%) was calculated by the following formula:
Storage UFR retention = UFR value after storage x 100 (%) UFR value before storage The hollow fiber membrane of the present invention showed . a storage UFR retention of more than 90 ~.
Besides, a module for dialysis prepared from a hollow fiber membrane of the present invention was subjected to a filtration test of bovine blood wherein the hematocrit value was controlled to 40 % under a transmembrane pressure of about 300 mmHg, and the change of UFR was measured with lapse of time, and the UFR retention (%) in the bovine blood filtration test was calculated by the following formula:
~23726~
UFR retention UFR value 120 minutes after in bovine _ initiation of filtration test blood filtration UFR value 15 minutes after x 100 test (%) initiation of filtration test The hollow fiber membrane of the present invention showed a UFR retention in the bovine blood filtration test of more than 90~.
In practice, the hollow fiber membrane of the present invention has a membrane thickness of not less than 5 ~, because according to known techniques, a round, uniform hollow fiber membrane having a thickness of less than 5 cannot be produced by spinning. The cellulose ester hollow fiber membrane of the present invention generally has an inner diameter of 100 ~ to 400 ~, preferably 150 to 300 ~. It is advantageous to provide appropriate crimps in the hollow fiber membrane in order to increase the dialysis efficiency. This allows the membrane thick-ness to be reduced while preventing an undesirable biased flow within the module. Preferably 10 to 35 crimps are provided per 10 cm length of the hollow fiber membrane and the crimp amplitude L (unit: micron) (which expresses the size of the crimp) is preferably in the range of from 65 %
of the outer diameter of the hollow fiber membrane to the outer diameter of the hollow fiber membrane plus 50 ~.
When the crimp amplitude is within the above range, the hollow fiber membrane can be used to form a module having improved dialysis performance while preventing undesirable biased dialysate flow, and further, the module can be made compact and the membrane can be made sufficiently thin.
The cellulose ester hollow fiber membrane of the present invention can be prepared in the following manner.
A spinning solution of a cellulose ester may be extruded through circular slits around an inner tube of a spinneret having a double structure comprising an inner tube and an outer tube while simultaneously extruding a core solution through the inner tube of the spinneret, passing the spinning solution extruded from the , ., circular slit throuyh a gaseous atmosphere, introducing the same into an aqueous coagulation bath, washing the coagulated hollow fibers with hot water, passing them through a glycerin bath, drying with hot air, reeling them onto a bobbin, and then heat-treating the reeled hollow fibers.
In order to obtain the desired hollow fiber membrane~
the spinning should be done under the following conditions, all of which should be satisfied simultaneously.
The spinning solution should have a cellulose ester concentration of 27 to 37 % by weight; the coagulation bath should have a water content of 65 to 90 % by weight, preferably 70 to 85 % by weight; the washing with hot water should be done with water having a temperature of 40 to 80C; the glycerin bath should have a glycerin concentration of 25 to 60 % by weight and the temperature of the glycerin solution should be 35 to 80C; and the heat treatment of the reeled fibers should be carried out under a humidity of lO to 20 g-H2O/kg-dry air and at a dry-bulb temperature of 60 to 100C.
When the above conditions are satisfied, a desirable hollow fiber membrane can be produced, but when such a hollow fiber membrane of rather thin wall thickness is used for dialysis, e.g. for the dialysis of blood, sub-stances remaining in the cellulose ester material tend to leach out and flow to the patient. Accordingly, it is preferable to reduce the amount of such substances remaining in the thin hollow fiber membrane as much as possible. For such a purpose, it is preferable to control the starting materials very thoroughly ~i.e. by checking the impurities in the starting materials) and also to ensure that the washing with hot water takes place thor-oughly. In particular, with regard to the cellulose ester used as the starting material, which is a solid material and is difficult to control as far as impurities are concerned, it is preferable first to extract it with 1~3726~
fifteen times its volume of a mixed solvent consisting of acetone and water (55 : 45 by volume) at 20C for 1 hour~
A cellulose ester having an extraction rate of less than 0.5 % by weight is particularly preferred.
The hollow fiber membrane thus obtained has a membrane thickness of less than 20 and a yield strength Sb after heat treatment according to formula (I~ as mentioned hereinbefore and shows a suitable UFR as well as good maintenance of the dialysis performance during storage and during the dialysis procedure without undesirable problems such as leakage of blood, thrombogenicity, hemolysis and retaining of blood. Thus, the hollow fiber membrane of the present invention is useful for the dialysis of body liquids, and particularly for the dialysis of blood.
The present invention is illustrated by the follow-ing Examples, but should not be construed to be limited thereto.
Example 1 Cellulose diacetate (extraction rate with acetone, water = 55/45 by volume: 0.32 % by weight, 33 part~
by weight), N-methyl-2-pyrrolidone (54 parts by weight) and ethylene glycol (13 parts by weight) were mixed and dissolved to form a spinning solution. The spinning solution was spun in a spinning machine provided with a circularorifice nozzle.
The spinning solution was supplied from the outer tube and liquid paraffin was extruded as a core solution from the inner tube. The hollow spinning solution extruded from the circular orifice was run through air for a length of 5 cm and then introduced into a coagulation bath containing 75 parts by weight of water. The coagulated hollow fibres were thoroughly washed with hot water at 50C, passed through an aqueous solution of glycerin having a glycerin concentration of 45 % by weight at 40C, passed through a drying zone having a counter flow of drying air at 60C, and then reeled by a winder onto :~23726~
a bobbin. The hollow fibers eeled onto the bobbin were heat-treated within a sealed room at a humidity of 14 g-H2O/kg-dry air and at a temperature of 70C
for 15 hours.
The cellulose diacetate hollow fibers thus obtained were round and had an inner diameter of 200~ , a membrane thickness of 15~ , a crimp number of 17 crimps/10 cm, and a crimp amplitude of 180~ .
A module for dialysis (1.1 m2) was assembled employ-ing the hollow fiber membrane thus produced. The module for dialysis had a UFR of 5.9 ml/hr.mmHg when measured according to the dialyzer performance evaluation standard provided by the Nippon Artificial Organs Association. When this module for dialysis was used for the dialysis of blood at a blood flow rate of 200 ml/minute, the clearance of urea was 174 ml/minute.
The yield strength of the hollow fiber membrane for dialysis was measured before and after the heat treatment at 80C for 20 hours, and the retention ratio (Sb/Sa) was calculated therefrom. The retention ratio was found to be 1.03. When the module for dialysis was kept at 55C for 15 days (said 55C representing the highest temperature to which the module might be exposed during transportation), the retention of UFR was an excellent 93 %. In a bovine blood filtration test, the module for dialysis also showed an excellent 95 ~ retention of UFR.
Reference Example 1 A hollow fiber membrane having an inner diameter of 200 ~ and a membrane thickness of 27 ~ was produced in the same manner as described in Example 1 except that the extrusion amount of the starting spinning solution and the spinning rate were changed~
A module suitable for dialysis (1.1 m20 was assembled from the resulting hollow fiber membrane. This module showed a yield strength retention ratio tSb/Sa) (before and after the heat treatment at 80~C for 20 hours) of 1.01.
~Z37Z6~
g However, when the dialysis performance of the module for dialysis was tested in the same manner as described in Example 1, it showed a UFR of 3.5 ml/hr.mmHg and a clearance of urea of 1~0, which were insuf f icient for dialysis.
Reference Example 2 The same spinning colution and core solution as used in Example 1 were spun through a circular orifice. The hollow spinning solution extruded from the cyclic orifice was run in air for a length of 5 cm and then introduced into a coagulation bath containing 60 parts by weight of water. The coagulated hollow fibers were thoroughly washed with water at room temperature, passed through an aqueous solution of glycerin having a glycerin con-centration of 45 ~ by weight at 40C, passed through a drying zone having a counter flow of drying air at 60C, and then reeled with a winder onto a bobbin.
The cellulose diacetate hollow fibers thus obtained had an inner diameter of 200 ~, and a membrane thickness of lS ~.
A module for dialysis (1.1 m2) was assembled from the resulting hollow fiber membrane. This module for dialysis showed a yield strength retention ratio (Sb/Sa) ~before and after the heat treatment at 80C for 20 hours) of 1.15.
However, when the module for dialysis was kept at 55C
for 15 days, it showed a UFR retention of 83 %, which was insufficient for dialysis. Besides, it also showed an insufficient 81 % UFR retention in a bovine blood filtration test.
Example 2 A cellulose diacetate hollow fiber membrane having a membrane thickness of 15 ~ was produced in the same manner as described in Example 1 except that the amount of water in the coagulation bath was 80 parts by weight and the concentration of glycerin in the glycerin bath was 50 by weight.
.~
12:~726tll A module for dialysis (1.1 m2) was assembled from the resulting hollow fiber membrane. The UFR of the module for dialysis was measured in the same manner as described in Example 1. As a result, it had a UFR of 6.1 ml/hr.mmHg and a clearance of urea of 176 ml/minute.
Besides, the yield strength of the hollow fiber membrane was measured before and after the heat treatment at 80C
for 20 hours and then the retention ratio (Sb/Sa) was calculated. As a result, the ratio was found to be 1002 Moreover, the UFR retention during storage and that in a bovine blood filtration test were tested and were found to be 94 % and 94 %, respectively.
Hollow fiber membrane for dialysis The present invention relates to a novel hollow fiber membrane. More particularly, it relates to a hollow fiber membrane made of a cellulose ester which is suit-able for artificial kidneys.
It is known that cellulose esters can be processed to form hollow fiber membranes which may be used for various processes. For example, these membranes may be used for separation processes involving energy savings, such as processes for desalinating sea water or salt water, and ultrafiltration of aqueous solutions containing various solutes.
It is also known that cellulose esters are suitable for the preparation of hollow fiber membranes useful for artificial kidneys because they have good biocompatibility and are easily produced, and hence, extensive studies have been carried out in this regard. Generally, in order to be suitable for artificial kidneys, the material used for the hollow fibers should satisfy the following six conditions:
(1) it should have good dialysis performance, i.e. a suitable ultrafiltration rate (hereinafter referred to as 'IUFRn) and also excellent permeability by solutes such as urea, creatinine, etc.;
(2~ the hollow fiber membrane made therefrom should not permit leakage of blood;
(3) it should have good compatibility with blood, i.e.
it should have low thrombogenicity and hemolysis;
(4) after the hemodialysis, no blood should remain in the module (i.e. the hollow fiber membrane assembly of the separation apparatus);
(5) an acceptably small amount of material should be dissolved out of the hollow fiber membrane; and (6) during storage or during hemodialysis, no change of the dialysis performance, particularly UFR, should be observed.
A hollow fiber membrane which satisfies all of the above conditions has not previously been produced. It is known that when the thickness of the hollow fiber membrane is reduced, the product shows better perme-ability by solutes such as urea, uric acid, creatinine, etc. and higher dialysis efficiency, so dialysis modules incorporating such membranes can be made smaller and the amount of blood which has to be circulated outside the patient's body is advantageously reduced. However, when the membrane thickness is reduced, the hollow fiber membrane disadvantageously exhibits poor maintenance of dialysis performance, i.e. the sixth requirement of those given above, namely a change of dialysis performance, particularly lowering of UFR, during storage or during hemodialysis. A conventional hollow fiber membrane made of cellulose ester should therefore have a thickness of not less than about 20 ~ in order to prevent this dis-advantage, but such a membrane still has some problems with respect to dialysis performance, that is, it is difficult to provide improved UFR and a high permeability for urea.
The present inventors have carried out extensive research for improved hollow fiber membranes having no change of dialysis performance during storage or during hemodialysis while maintaining the advantages of thin membranes.
1237~
According to one aspect of the invention there is provided a hollow fiber membrane suitable for di-alysis comprising cellulose ester and having a membrane thickness of less than 20 ~, and a yield strength Sb (g/filament) after being heat-treated at 80C for 20 hours which satisfies the following formula (I):
0.90 ~ Sb/Sa ~ 1.10 (I) wherein Sa is the yield strength (g/filament) of the hollow fiber membrane measured before the heat treatment.
Suitable cellulose esters used for the preparation of the dialysis membrane of the present invention include cellulose diacetate, cellulose triacetate, cellulose propionate, cellulose butyrate, cellulose acetate pro-pionate and the like, which may be used alone or in combination of two or more thereof.
The hollow fiber membrane of the present invention should essentially satisfy the condition that it has a membrane thickness of less than 20 ~, and the condition of the above formula (I). Although it is known that when the membrane has a reduced thickness, it shows better permeability by solutes such as urea or creatinine, hollow fiber membranes having a membrane thickness of about 20 ~ or more are normally employed to provide acceptable storage stability and stability during the dialysis procedure. In contrast, the hollow fiber membrane of the present ~nvention can be made thin while maintaining a strong membrane structure. When the ratio of Sb/Sa is less than 0.9, the hollow fiber membrane shows an undesirable lowering of yield strength during storage over a long period of time, and hence, when it is used for hemodialysis, it has unstable strength and leakage of blood may be induced, which is a fatal draw-back for artificial kidneys. On the other hand, when the ratio of Sb/Sa is over 1.1, the hollow fiber membrane tends to become dense in structure when exposed to high temperatures during storage or transportation, and hence, ~237260 the dialysis performance is decreased and the original hemodialysis capacity can not be obtained, which can have a severe effect on patients. The yield strength of the hollow fiber membrane is measured by a universal tensile tester, that is, by subjecting a fixed length of the hollow fiber (50 mm) to stretching at a tensile rate of 10 mm/minute to obtain a stress-strain curve, followed by calculating the yield strength from the yield point obtained from the curve.
Thus, the hollow fiber membrane of the present in-vention is characterized in that, owing to a desirable membrane thickness and dynamic properties, the dialysis performance, particularly UFR, is not lowered during storage or transportation, or during hemodialysis. For example, a hollow fiber membrane of the present invention showed the following UFR reten~ion in a storage test and in a bovine blood filtration test. That is, a module for dialysis was prepared from a hollow fiber membrane of the present invention and was kept at 55C for 15 days, and then the storage UFR retention (%) was calculated by the following formula:
Storage UFR retention = UFR value after storage x 100 (%) UFR value before storage The hollow fiber membrane of the present invention showed . a storage UFR retention of more than 90 ~.
Besides, a module for dialysis prepared from a hollow fiber membrane of the present invention was subjected to a filtration test of bovine blood wherein the hematocrit value was controlled to 40 % under a transmembrane pressure of about 300 mmHg, and the change of UFR was measured with lapse of time, and the UFR retention (%) in the bovine blood filtration test was calculated by the following formula:
~23726~
UFR retention UFR value 120 minutes after in bovine _ initiation of filtration test blood filtration UFR value 15 minutes after x 100 test (%) initiation of filtration test The hollow fiber membrane of the present invention showed a UFR retention in the bovine blood filtration test of more than 90~.
In practice, the hollow fiber membrane of the present invention has a membrane thickness of not less than 5 ~, because according to known techniques, a round, uniform hollow fiber membrane having a thickness of less than 5 cannot be produced by spinning. The cellulose ester hollow fiber membrane of the present invention generally has an inner diameter of 100 ~ to 400 ~, preferably 150 to 300 ~. It is advantageous to provide appropriate crimps in the hollow fiber membrane in order to increase the dialysis efficiency. This allows the membrane thick-ness to be reduced while preventing an undesirable biased flow within the module. Preferably 10 to 35 crimps are provided per 10 cm length of the hollow fiber membrane and the crimp amplitude L (unit: micron) (which expresses the size of the crimp) is preferably in the range of from 65 %
of the outer diameter of the hollow fiber membrane to the outer diameter of the hollow fiber membrane plus 50 ~.
When the crimp amplitude is within the above range, the hollow fiber membrane can be used to form a module having improved dialysis performance while preventing undesirable biased dialysate flow, and further, the module can be made compact and the membrane can be made sufficiently thin.
The cellulose ester hollow fiber membrane of the present invention can be prepared in the following manner.
A spinning solution of a cellulose ester may be extruded through circular slits around an inner tube of a spinneret having a double structure comprising an inner tube and an outer tube while simultaneously extruding a core solution through the inner tube of the spinneret, passing the spinning solution extruded from the , ., circular slit throuyh a gaseous atmosphere, introducing the same into an aqueous coagulation bath, washing the coagulated hollow fibers with hot water, passing them through a glycerin bath, drying with hot air, reeling them onto a bobbin, and then heat-treating the reeled hollow fibers.
In order to obtain the desired hollow fiber membrane~
the spinning should be done under the following conditions, all of which should be satisfied simultaneously.
The spinning solution should have a cellulose ester concentration of 27 to 37 % by weight; the coagulation bath should have a water content of 65 to 90 % by weight, preferably 70 to 85 % by weight; the washing with hot water should be done with water having a temperature of 40 to 80C; the glycerin bath should have a glycerin concentration of 25 to 60 % by weight and the temperature of the glycerin solution should be 35 to 80C; and the heat treatment of the reeled fibers should be carried out under a humidity of lO to 20 g-H2O/kg-dry air and at a dry-bulb temperature of 60 to 100C.
When the above conditions are satisfied, a desirable hollow fiber membrane can be produced, but when such a hollow fiber membrane of rather thin wall thickness is used for dialysis, e.g. for the dialysis of blood, sub-stances remaining in the cellulose ester material tend to leach out and flow to the patient. Accordingly, it is preferable to reduce the amount of such substances remaining in the thin hollow fiber membrane as much as possible. For such a purpose, it is preferable to control the starting materials very thoroughly ~i.e. by checking the impurities in the starting materials) and also to ensure that the washing with hot water takes place thor-oughly. In particular, with regard to the cellulose ester used as the starting material, which is a solid material and is difficult to control as far as impurities are concerned, it is preferable first to extract it with 1~3726~
fifteen times its volume of a mixed solvent consisting of acetone and water (55 : 45 by volume) at 20C for 1 hour~
A cellulose ester having an extraction rate of less than 0.5 % by weight is particularly preferred.
The hollow fiber membrane thus obtained has a membrane thickness of less than 20 and a yield strength Sb after heat treatment according to formula (I~ as mentioned hereinbefore and shows a suitable UFR as well as good maintenance of the dialysis performance during storage and during the dialysis procedure without undesirable problems such as leakage of blood, thrombogenicity, hemolysis and retaining of blood. Thus, the hollow fiber membrane of the present invention is useful for the dialysis of body liquids, and particularly for the dialysis of blood.
The present invention is illustrated by the follow-ing Examples, but should not be construed to be limited thereto.
Example 1 Cellulose diacetate (extraction rate with acetone, water = 55/45 by volume: 0.32 % by weight, 33 part~
by weight), N-methyl-2-pyrrolidone (54 parts by weight) and ethylene glycol (13 parts by weight) were mixed and dissolved to form a spinning solution. The spinning solution was spun in a spinning machine provided with a circularorifice nozzle.
The spinning solution was supplied from the outer tube and liquid paraffin was extruded as a core solution from the inner tube. The hollow spinning solution extruded from the circular orifice was run through air for a length of 5 cm and then introduced into a coagulation bath containing 75 parts by weight of water. The coagulated hollow fibres were thoroughly washed with hot water at 50C, passed through an aqueous solution of glycerin having a glycerin concentration of 45 % by weight at 40C, passed through a drying zone having a counter flow of drying air at 60C, and then reeled by a winder onto :~23726~
a bobbin. The hollow fibers eeled onto the bobbin were heat-treated within a sealed room at a humidity of 14 g-H2O/kg-dry air and at a temperature of 70C
for 15 hours.
The cellulose diacetate hollow fibers thus obtained were round and had an inner diameter of 200~ , a membrane thickness of 15~ , a crimp number of 17 crimps/10 cm, and a crimp amplitude of 180~ .
A module for dialysis (1.1 m2) was assembled employ-ing the hollow fiber membrane thus produced. The module for dialysis had a UFR of 5.9 ml/hr.mmHg when measured according to the dialyzer performance evaluation standard provided by the Nippon Artificial Organs Association. When this module for dialysis was used for the dialysis of blood at a blood flow rate of 200 ml/minute, the clearance of urea was 174 ml/minute.
The yield strength of the hollow fiber membrane for dialysis was measured before and after the heat treatment at 80C for 20 hours, and the retention ratio (Sb/Sa) was calculated therefrom. The retention ratio was found to be 1.03. When the module for dialysis was kept at 55C for 15 days (said 55C representing the highest temperature to which the module might be exposed during transportation), the retention of UFR was an excellent 93 %. In a bovine blood filtration test, the module for dialysis also showed an excellent 95 ~ retention of UFR.
Reference Example 1 A hollow fiber membrane having an inner diameter of 200 ~ and a membrane thickness of 27 ~ was produced in the same manner as described in Example 1 except that the extrusion amount of the starting spinning solution and the spinning rate were changed~
A module suitable for dialysis (1.1 m20 was assembled from the resulting hollow fiber membrane. This module showed a yield strength retention ratio tSb/Sa) (before and after the heat treatment at 80~C for 20 hours) of 1.01.
~Z37Z6~
g However, when the dialysis performance of the module for dialysis was tested in the same manner as described in Example 1, it showed a UFR of 3.5 ml/hr.mmHg and a clearance of urea of 1~0, which were insuf f icient for dialysis.
Reference Example 2 The same spinning colution and core solution as used in Example 1 were spun through a circular orifice. The hollow spinning solution extruded from the cyclic orifice was run in air for a length of 5 cm and then introduced into a coagulation bath containing 60 parts by weight of water. The coagulated hollow fibers were thoroughly washed with water at room temperature, passed through an aqueous solution of glycerin having a glycerin con-centration of 45 ~ by weight at 40C, passed through a drying zone having a counter flow of drying air at 60C, and then reeled with a winder onto a bobbin.
The cellulose diacetate hollow fibers thus obtained had an inner diameter of 200 ~, and a membrane thickness of lS ~.
A module for dialysis (1.1 m2) was assembled from the resulting hollow fiber membrane. This module for dialysis showed a yield strength retention ratio (Sb/Sa) ~before and after the heat treatment at 80C for 20 hours) of 1.15.
However, when the module for dialysis was kept at 55C
for 15 days, it showed a UFR retention of 83 %, which was insufficient for dialysis. Besides, it also showed an insufficient 81 % UFR retention in a bovine blood filtration test.
Example 2 A cellulose diacetate hollow fiber membrane having a membrane thickness of 15 ~ was produced in the same manner as described in Example 1 except that the amount of water in the coagulation bath was 80 parts by weight and the concentration of glycerin in the glycerin bath was 50 by weight.
.~
12:~726tll A module for dialysis (1.1 m2) was assembled from the resulting hollow fiber membrane. The UFR of the module for dialysis was measured in the same manner as described in Example 1. As a result, it had a UFR of 6.1 ml/hr.mmHg and a clearance of urea of 176 ml/minute.
Besides, the yield strength of the hollow fiber membrane was measured before and after the heat treatment at 80C
for 20 hours and then the retention ratio (Sb/Sa) was calculated. As a result, the ratio was found to be 1002 Moreover, the UFR retention during storage and that in a bovine blood filtration test were tested and were found to be 94 % and 94 %, respectively.
Claims (5)
1. A hollow fiber membrane suitable for dialysis comprising cellulose ester and having a membrane thickness of less than 20 µ, and a yield strength Sb (g/filament) after being heat-treated at 80°C for 20 hours which satisfies the following formula (I):
0.90 < Sb/Sa < 1.10 (I) wherein Sa is the yield strength (g/filament) of the hollow fiber membrane measured before the heat treatment.
0.90 < Sb/Sa < 1.10 (I) wherein Sa is the yield strength (g/filament) of the hollow fiber membrane measured before the heat treatment.
2. A hollow fiber membrane according to claim 1, wherein the membrane has a thickness of 5 to less than 20 µ, and an inner diameter of 100 to 400 µ.
3. A hollow fiber membrane according to claim 1, wherein the membrane is provided with crimps, the number of said crimps being in the range of 10 to 35 per 10 cm length of the membrane and the crimp amplitude being in the range of from 65 % of the outer diameter of the hollow fiber membrane to 50 µ plus the outer diameter of the hollow fiber membrane.
4. A method for producing a cellulose ester hollow fiber membrane suitable for dialysis having a membrane thickness of less than 20 µ, and a yield strength Sb (g/filament) after being heat-treated at 80°C for 20 hours which satisfies the following formula (I):
0 90 < Sb/Sa < 1.10 (I) wherein Sa is the yield strength (g/filament) of the hollow fiber membrane measured before the heat treatment, which method comprises extruding a spinning solution of a cellulose ester having a concentration of the cellu-lose ester of 27 to 37 % by weight through circular slits around an inner tube of a spinneret having a double structure while simultaneously extruding a core solution through the inner tube of the spinneret, passing the spinning solution extruded from the circular slits through a gaseous atmosphere, introducing the same into an aqueous coagulation bath having a water content of 65 to 90 % by weight, washing the coagulated hollow fibers with hot water at 40° to 80°C, passing the fibers through a glycerin bath having a glycerin concentration of 25 to 60 % by weight and a temperature of 35° to 80°C, drying the fibres with hot air at 60° to 80°C, reeling the fibres onto a bobbin, and then heat-treating the reeled fibers under a humidity of 10 to 20 g-H2O/kg-dry air and a dry-bulb temperature of 60° to 100°C.
0 90 < Sb/Sa < 1.10 (I) wherein Sa is the yield strength (g/filament) of the hollow fiber membrane measured before the heat treatment, which method comprises extruding a spinning solution of a cellulose ester having a concentration of the cellu-lose ester of 27 to 37 % by weight through circular slits around an inner tube of a spinneret having a double structure while simultaneously extruding a core solution through the inner tube of the spinneret, passing the spinning solution extruded from the circular slits through a gaseous atmosphere, introducing the same into an aqueous coagulation bath having a water content of 65 to 90 % by weight, washing the coagulated hollow fibers with hot water at 40° to 80°C, passing the fibers through a glycerin bath having a glycerin concentration of 25 to 60 % by weight and a temperature of 35° to 80°C, drying the fibres with hot air at 60° to 80°C, reeling the fibres onto a bobbin, and then heat-treating the reeled fibers under a humidity of 10 to 20 g-H2O/kg-dry air and a dry-bulb temperature of 60° to 100°C.
5. A method according to claim 4, wherein the starting cellulose ester which is in solid form is washed with a mixed solvent consisting of acetone/water of 55 : 45 by volume until the extraction rate becomes 0.5 % by weight or less.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP5036284A JPS60193504A (en) | 1984-03-15 | 1984-03-15 | Hollow fiber membrane for dialysis |
| JP50362/1984 | 1984-03-15 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1237260A true CA1237260A (en) | 1988-05-31 |
Family
ID=12856778
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000451497A Expired CA1237260A (en) | 1984-03-15 | 1984-04-06 | Hollow fiber membrane for dialysis |
Country Status (3)
| Country | Link |
|---|---|
| JP (1) | JPS60193504A (en) |
| BE (1) | BE903876A (en) |
| CA (1) | CA1237260A (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4587168A (en) * | 1984-04-05 | 1986-05-06 | Toyo Boseki Kabushiki Kaisha | Hollow fiber membrane for dialysis |
| JPH01307404A (en) * | 1988-06-04 | 1989-12-12 | Asahi Chem Ind Co Ltd | Reformed cellulose-based dialyzing membrane and its production |
| JP5299617B2 (en) * | 2008-11-21 | 2013-09-25 | 東洋紡株式会社 | Method for producing hollow fiber membrane |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS55107505A (en) * | 1979-02-13 | 1980-08-18 | Nippon Zeon Co Ltd | Production of hollow fiber |
| JPS569420A (en) * | 1979-07-04 | 1981-01-30 | Nippon Zeon Co Ltd | Method of production of hollow fiber |
| JPS57133211A (en) * | 1981-02-09 | 1982-08-17 | Toyobo Co Ltd | Production of hollow fiber of cellulose ester |
| JPS60168502A (en) * | 1984-02-10 | 1985-09-02 | Toyobo Co Ltd | Dialytic hollow yarn membrane |
-
1984
- 1984-03-15 JP JP5036284A patent/JPS60193504A/en active Pending
- 1984-04-06 CA CA000451497A patent/CA1237260A/en not_active Expired
-
1985
- 1985-12-17 BE BE0/216024A patent/BE903876A/en not_active IP Right Cessation
Also Published As
| Publication number | Publication date |
|---|---|
| BE903876A (en) | 1986-04-16 |
| JPS60193504A (en) | 1985-10-02 |
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