MEMBRANE TYPE ARTIFICIAL LUNG AND METHOD FOR MANUFACTURE THEREOF

Abstract: A membrane type artificial lung uses a gas-exchange membrane having at least the surface thereof for exposure to blood or the minute pores therein coated or blocked with a vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain. The gas-exchange membrane of the artificial lung is manufactured by a method which comprises bringing at least the surface of the gas-exchange membrane for exposure to blood into contact with a solution of the vinyl type copolymer and subsequently vaporizing the solvent in the solution.

Description: This invention relates to a membrane type artificial lung and to a method for the manufacture thereof. More particularly, this invention relates to a membrane type artificial lung for removing carbon dioxide gas from blood and adding oxygen to blood during the course of extra­ corporeal blood circulation, which artificial lung abounds with biocompatibility, suffers only insignificant loss of platelets, and excels in gas-exchange ability, and to a method for the manufacture thereof. Description of the Prior Art: Heretofore, as auxiliary means for the cardiotomy, an artificial lung which is adapted to effect exchange of gases by exposing the blood in circulation therethrough to an oxygen-containing gas through the medium of a gasexchange membrane possessed of satisfactory permeability to gas has been in use. The gas-exchange membranes which are used in membrane type artificial lungs of the class described above fall under two kinds, homogeneous membranes and porous membranes. As homogeneous membranes, silicone membranes are currently used prevalently. Due to the use of silicone membranes, however, the homogeneous membranes have no sufficient strength when they have to be produced in a small thickness below 100 µm. They consequently have limited permeability to gas and exhibit particularly poor permeability to carbon dioxide gas. When some tens of thousand hollow fiber membranes are bundled for the purpose of attaining a desired gas-exchange ability, the apparatus designed to operate with this bundle of membranes inevitably occupies a large volume, requires a large amount of priming, and proves very costly. The porous membranes heretofore known in the art are made of various materials such as, for example, polyethylene, polypropylene, polytetrafluoroethylene, polysulfones, polyacrylonitrile, polyurethane, and polyamides. As a further example, document US 4008 047 (PETERSEN) discloses a gas-permeable coating that uses Fluorocacylated etyl cellulose having a combined Fluorine content of at least 10% by weight and a degree of substitution ranging from about 1.0 to 2.75. These gas-exchange membranes are required to possess large permeability coefficients with respect to O₂ and CO₂, refrain from inducing leakage of blood plasma during a protracted circulation of blood, and avoid afflicting upon the blood such damage due to physical contact as coagulation of blood, formation of microthrombosis, loss of platelets, degeneration of blood plasma proteins, and hemolysis. None of the gas-exchange membranes so far developed satisfies all these requirements. Particularly in terms of damage to blood or biocompatibility, even silicone membranes which are rated as superior to all the other membranes are not satisfactory. In the extracorporeal circulation of blood carried out with the help of an artificial lung, therefore, it has been customary to perform simultaneously a chemotherapy for suppressing thrombosis by addition of heparin, for example. It has been found, however, that while the heparin can be expected to be effective in suppressing coagulation, it has virtually no effect upon agglutination and aggregation of platelets. The porous membranes literally possess numerous minute pores extending throughout in the direction of wall thickness. Since the membranes are hydrophobic, they permit addition of oxygen from the feed gas to blood and removal of carbon dioxide gas from blood into the gas without suffering passage of blood plasma through the minute pores, i.e. leakage of blood plasma from the blood path side of the membrane to the gas path side thereof. Owing to their high permeability to steam, however, the porous membranes not only suffer from degradation of performance by dew but also induce leakage of blood plasma actually during a protracted service in circulation of blood. This adverse phenomenon is witnessed even in the case of those porous membranes which have successfully passed the water leakage test performed during the course of manufacture of an artificial lung. With a view to eliminating the various drawbacks suffered by the conventional porous membranes as described above, we have proposed an artificial lung using porous membranes having the minute pores thereof blocked with silicone oil (Japanese Patent Application SHO 58 (1983) 92,325) and a further improved artificial lung using porous membranes having the minute pores thereof blocked with silicone rubber (Japanese Patent Application SHO 59 (1984) 105,384). The artificial lung which uses porous membranes having the minute pores thereof blocked with silicone rubber no longer entail the problem of blood plasma leakage which is observed in the artificial lungs using the conventional porous membranes. It nevertheless has no sufficient ability to remove carbon dioxide gas. As the result, it has experienced difficulty in removing the amount of carbon dioxide gas produced in the living body with such a low flow volume of blood as in the extracorporeal circulation such as, for example, the ECCO₂R (extracorporeal CO₂ removal). An object of this invention, therefore, is to provide a novel membrane type artificial lung and a method for the manufacture thereof. Another object of this invention is to provide a membrane type artificial lung adapted to remove carbon dioxide gas from blood and add oxygen to the blood during the course of the extracorporeal circulation of blood, which artificial lung has a high ability to remove carbon dioxide gas and has no possibility of inducing leakage of blood plasma during a protracted use and a method for the manufacture thereof. A further object of this invention is to provide a membrane type artificial lung which is most suitable for ECCO₂R and a method for the manufacture thereof. The objects described above are accomplished by a membrane type artificial lung which is characterized in that the gas-exchange membranes incorporated therein have at least the surfaces thereof intended for exposure to blood coated with a vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoro­ alkyl side chain. This invention discloses a membrane type artificial lung, wherein the vinyl type copolymer is a (meth)acrylate type copolymer having as one of the components thereof a (meth)acrylate monomer possessing a perfluoroalkyl side chain. This invention also discloses a membrane type artificial lung, wherein the vinyl type copolymer is a block copolymer. This invention further discloses a membrane type artificial lung, wherein the weight ratio in the block copolymer of the polymer component formed of a vinyl monomer possessing a perfluoroalkyl side chain to the polymer component formed of the other monomer of the copolymer is in the range of 0.25 to 1.5. This invention discloses a membrane type artificial lung, wherein the perfluoroalkyl side chain is -CH₂CH₂(CF₂)₇CF₃.Thisinvention also discloses a membrane type artificial lung, wherein the gas-exchange membranes are porous membranes. This invention further discloses a membrane type artificial lung, wherein the porous membranes are made of an olefin type resin. This invention discloses a membrane type artificial lung, wherein the porous membranes are made of polypropylene. This invention also discloses a membrane type artificial lung, wherein the gas-exchange membranes are homogeneous membranes. This invention further discloses a membrane type artificial lung, wherein the gas-exchange membranes are hollow fiber membranes. This invention also discloses a membrane type artificial lung, wherein the vinyl type copolymer having as one of the component thereof a vinyl monomer possessing a perfluoroalkyl side chain is coated in a thickness in the range of 0.001 to 10 µm. The objects described above are accomplished by a membrane type artificial lung using as gas-exchange membranes thereof porous membranes having a wall thickness in the range of 5 to 80 µm, a porosity in the range of 20 to 80%, and a pore diameter in the range of 0.01 to 5 µm, which artificial lung is characterized by having the minute pores thereof blocked with a vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain. This invention discloses a membrane type artificial lung, wherein the vinyl type copolymer is a (meth)acrylate type polymer having as one of the components thereof a (meth)acrylate monomer possessing a perfluoroalkyl side chain. This invention also discloses a membrane type artificial lung, wherein the vinyl type copolymer is a block copolymer. This invention further discloses a membrane type artificial lung, wherein the weight ratio in the vinyl type block copolymer of the polymer component formed of a vinyl monomer a possessing a perfluoroalkyl side chain to the polymer component formed of the other monomer of the copolymer is in the range of 0.25 to 1.5. This invention discloses a membrane type artificial lung, wherein the perfluoroalkyl side chain is -CH₂CH₂(CF₂)₇CF₃. This invention discloses a membrane type artificial lung, wherein the gas-exchange membranes are made of an olefin type resin. This invention discloses a membrane type artificial lung, wherein the gas-exchange membranes are made of polypropy­ lene. This invention also discloses a membrane type artificial lung, wherein the gas-exchange membranes are hollow fiber membranes. This invention further discloses a membrane type artificial lung, wherein the hollow fiber membranes have an inside diameter in the range of 100 to 1,000 µm. The above objects are accomplished by a method for the manufacture of a membrane type artificial lung, which method comprises the step of bringing at least the surfaces of gas-­ exchange membranes intended for exposure to blood into contact with a solution of a vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain and the step of subsequently vaporizing a solvent of the solution thereby forming a coating of the vinyl copolymer on the surfaces intended for exposure to blood. The above objects are further accomplished by a method for the manufacture of a membrane type artificial lung using as gas-exchange membranes thereof porous membranes having a wall thickness in the range of 5 to 80 µm, a porosity in the range of 20 to 80%, and a pore diameter in the range of 0.01 to 5 µm, which method comprises the step of bringing the porous hydrophobic membranes into contact with a solution of vinyl type copolymer having as one components thereof a vinyl monomer possessing a perfluoroalkyl side chain thereby blocking the minute pores of the membranes with the copolymer. This invention also discloses a method for the manufacture of a membrane type artificial lung which further comprises the step of bringing the surfaces intended for exposure to blood into contact with a cleaning liquid for the copolymer and the step of subsequently vaporizing the cleaning liquid. Fig. 1 is a model diagram illustrating one embodiment of the gas-exchange membrane to be used in the membrane type artificial lung of this invention, Fig. 2 is a model diagram illustraing another embodiment of the gas-exchange membrane, Fig. 3 is a model diagram illustrating yet another embodiment of the gas-exchange membrane, Fig. 4 is a model diagram illustrating a further embodiment of the gas-exchange membrane, Fig. 5 is a model diagram illustrating still another embodiment of the gas-exchange membrane, and Fig. 6 is a partial cross section of a hollow fiber membrane type artificial lung showing one embodiment of the membrane type artificial lung of this invention. Now, the present invention will be described in detail below with reference to the accompanying drawings. Fig. 1 and Fig. 2 are magnified cross sections illustrating microstructures of membranes in typical membrane type artificial lungs embodying this invention. The gas-exchange membrane 2 in the membrane type artificial lung 1 of the present invention is a porous membrane as illustrated in Fig. 1. It is otherwise a homogeneous membrane as illustrated in Fig. 2. When the gas-exchange membrane 2 is a porous membrane, the material used for the membrane is a macromolecular substance. Examples of the macromolecular substance include hydrophobic macromolecular substances such as polypropylene, polyethylene, polytetrafluoroethylene, polysulfones, polyacrylonitrile and cellulose acetate, and hydrophilic macromolecular substances, although hydrophobic ones are preferable. Among other materials enumerated above, olefin type resins are desirable and polypropylene is particularly desirable. To be specific, a polypropylene membrane having minute pores formed therein by the stretching method or the solid-liquid layer separation method is desirable. This porous membrane has a wall thickness in the range of 5 to 80 µm, preferably 10 to 60 µm, a porosity in the range of 20 to 80%, preferably 30 to 60%, and a pore diameter in the range of 0.01 to 5.0 µm, preferably 0.01 to 1.0 µm. The gas-exchange membrane 2 of the present embodiment is a hollow fiber membrane having an inside diameter in the range of 100 to 1,000 µm, preferably 100 to 300 µm. When the gas-exchange is a homogeneous membrane, the material for the membrane is a silicone rubber, preferably a silicone rubber containing no silica. This homogeneous membrane has a wall thickness in the range of 50 to 300 µm, preferably 80 to 150 µm. The gas-exchange membrane 2 in this embodiment is a hollow fiber membrane having an inside diameter in the range of 100 to 1,000 µm, preferably 100 to 300 µm. Further, the gas-exchange membrane 2 has at least the surface thereof intended for exposure to blood coated with a layer of a vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoro­ alkyl side chain. The vinyl type copolymer having as one component thereof a vinyl monomer possessing a perfluoroalkyl side chain is a copolymer of a desired vinyl type polymer with a vinyl monomer possessing a perfluoroalkyl side chain. Preferably, this copolymer is the so-called A-B type block copolymer which has a block of a homopolymer of a vinyl monomer possessing a perfluoroalkyl side chain linked to a mother block of a desired vinyl type polymer (which may be a homopolymer, a block copolymer, or a random copolymer). Typical examples of the vinyl monomer possessing a perfluoroalkyl side chain include perfluoroacrylates and perfluoromethacrylates which possess such perfluoroalkyl groups as -CH₂(CF₂)₂H, -CH₂(CF₂)₄H, -CH₂CF₃, and -CH₂CH₂(CF₂)₇CF₃, preferably -CH₂CH₂(CF₂)₇CF₃, as side chains thereof. Typical examples of the vinyl monomer which forms the mother block alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate, and alkyl acrylates such as methyl acrylate, ethyl acrylate, and butyl acrylate. In the vinyl type block copolymer having as one component thereof a vinyl monomer possessing a perfluoroalkyl side chain, the weight ratio of the polymer component formed of a vinyl monomer possessing a perfluoroalkyl side chain to the other vinyl monomer of the copolymer is in the range of 0.25 to 1.5, preferably 0.25 to 1.2. If this weight ratio is not more than 0.25, there is the possibility that the microstructural phase separation necessary for inhibiting agglutination of platelets will fail to manifest. If the weight ratio exceeds 1.5, there is the possibility that the solution of the copolymer with a solvent will become difficult and the fabricability of the copolymer will be degraded. This block copolymer is obtained by preparing a vinyl type polymer intended to constitute a mother block possessing a peroxy bond in the main chain thereof and polymerizing a perfluoroacrylate by dispersion polymerization using the vinyl polymer as a polymerization initiator. The vinyl type block copolymer having as one component thereof a vinyl monomer possessing a perfluoro­ alkyl side chain is soluble in organic solvents embracing ketones such as acetone, methylethyl ketone, methylisobutyl ketone, and cyclohexanone, alcohols such as methanol, ethanol, n-butanol, and sec-butanol, esters such as ethyl acetate and butyl acetate, ethers such as dimethylformamide, tetrathydrofuran, diethyl ether, methyl cellosolve, and ethyl cellosolve and chloroform. The formation of a coating 4 of a vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluroalkyl side chain on at least the surface of the gas-exchange membrane 2 intended for exposure to blood can be carried out easily as follows. To be specific, it is effected by bringing the surface of the gas-exchange membrane 2 intended for exposure to blood into contact, as by immersion, with a solution having the vinyl type copolymer dissolved therein in a concentration of 1 to 10% by weight, preferably 3 to 5% by weight and subsequently vaporizing the solvent of the solution. As the solvent to be used for this solution, though any of the solvents enumerated above can be adopted, it is preferable to adopt one member or a mixture of two or more members of the group aforementioned of ketones or a mixture of a ketone with an alcohol. Since it is necessary to control the vaporization of the solvent for the sake of the formation of a coating, it is proper to use a mixed solvent such as, for example, a 4/6 (volumetric ratio) mixture of methylethyl ketone/methylisobutyl ketone or a (4/6) /10 (volumetric ratio) mixture of (methylethyl ketone/methylisobutyl ketone)/ethanol. Although this coating of the gas-exchange membrane 2 with the vinyl type copolymer can be carried out before the membrane type artificial lung is assembled, it is carried out preferably after the assembly of the lung modules, as the surface of the membrane type artificial lung intended for exposure to blood other than the gas-exchange membrane can be coated simultaneously with that of the gas-exchange membrane. The coating 4 of the vinyl type copolymer has a thickness in the range of 0.01 to 10 µm, preferably 0.1 to 5 µm. If this thickness exceeds 10 µm, there is the possibility that the ability of the gas-exchange membrane to exchange gases will be lowered and there is also the possibility that, when the gas-exchange membrane is a hollow fiber membrane, the blood passed in the hollow fiber will cause a contraction of the blood path. When the gas-exchange membrane is coated with the vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain as described above, the otherwise possible damage done as to the platelet component of blood due to contact with the membrane will be suppressed to a great extent. Moreover, since the vinyl type copolymer possesses highly satisfactory permeability to gas, the coating has no possibility of substantially degrading the membrane type artificial lung's ability to add oxygen to blood and remove CO₂ from blood. Fig. 3 is a magnified cross section illustraing the microstructure of a gas-exchange membrane for use in a typical membrane type artificial lung embodying the present invention. As illustrated in Fig. 3, the gas-exchange membrane 2 of the membrane type artificial lung is a hydrophobic porous membrane which has a wall thickness in the range of 5 ot 80 µm, preferably 10 to 60 µm, a porosity in the range of 20 to 80%, preferably 30 to 60%, and a pore diameter approximately in the range of 0.01 to 5 µm, preferably 0.01 to 1.0 µm. In the present embodiment, the gas-exchange membrane is a hollow fiber membrane having an inside diameter in the range of 100 to 1,000 µm, preferably 100 to 300 µm. The minute pores 3 in the gas-exchange membrane 2 are blocked with a vinyl type block copolymer 5 having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain. For the purpose of this blocking, it suffices to close the greater part, if not all, of the minute pores. Preferably, all the minute pores are to be blocked. The minute pores 3 in the case of the present embodiment are blocked in a manner having the interiors thereof filled up with the vinyl type copolymer 5. Alternatively, they may be blocked in a manner having the copolymer 5 deposited only on the surface parts of the minute pores on the inner surface side (or the outer surface side) of the gas-exchange membrane 2 as illustrated in Fig. 4 or in a manner having the copolymer 5 deposited in the form of a continuous film on the entire inner surface (or the outer surface) of the gas-exchange membrane 2 as illustrated in Fig. 5. Particularly, since the copolymer to be described in detail below not only excels in permeability to gas but also possesses extremely high biocompatibility, it is desirable that the inner surface intended for exposure to blood should be covered with a coating of the copolymer. The material for the gas-exchange membrane 2 is a macromolecular substance. Examples of the material include hydrophobic macromolecular substances such as polypropylene, polyethylene, polytetrafluoroethylene, polysulfones, polyacrylonitrile, and cellulose acetate, and hydrophilic macromolecular substances, although hydrophobic one is preferable. Among other materials cited above, olefin type resins are desirable and polypropylene is particularly desirable. A polypropylene membrane having minute pores formed therein by the stretching technique or the solid-­ liquid layer separation technique is desirable. The expression "vinyl type block copolymer having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain" has the same meaning as defined above. This block copolymer is used in the form of a solution in an organic solvent as described above. The blocking of the minute pores 3 of the gas-exchange membrane 2 with the vinyl type copolymer 5 having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain can be carried out easily as follows. To be specific, it is accomplished by bringing the gas-exchange membrane 2 in the form of a hollow fiber membrane into thorough contact, as by inflow or immersion, with a solution containing the vinyl type copolymer in a concentration in the range of 1 to 20% by weight, preferably 3 to 10% by weight, optionally removing the part of the solution adhering to the part other than the minute pores 3 with a cleaning liquid (bad-solvent) incapable of dissolving the vinyl type copolymer such as hexanes, heptanes, octanes, petroleum ether, etc., and subsequently vaporizing the liquid. This cleaning liquid is desired to be intimately mixable with the solvent in the solution of the copolymer. For the solution of the vinyl type copolymer, any of the aforementioned solvents can be used. Desirably, one member of a mixture of two or more members selected from the group of ketones or a mixture of a ketone with an alcohol is used. It is nevertheless necessary to control vaporization of the solvent. It is, therefore, proper to use a 4/6 (volumetric ratio) mixed solvent of methylethyl ketone/methylisobutyl ketone or a (4/6)/10 (volumetric ratio) (methylethyl ketone/methylisobutyl ketone)/ethanol, for example. Although the blocking of the minute pores 3 of the gasexchange membrane 2 with the vinyl type copolymer may be carried out before the assembly of the membrane type artificial lung, it is performed desirably after the assembly of the lung modules. Fig. 6 illustrates the state in which a hollow fiber membrane type artificial lung as one embodiment of this invention is assembled. The hollow fiber membrane type artificial lung, is provided with a housing 15. This housing 15 comprises a cylindrical housing body 16 and annular externally threaded fitting covers 17, 18 disposed one at each of the opposite ends of the annular housing body 16. Inside the housing 15, is provided a multiplicity of, specifically, 10,000 to 60,000, either porous or homogeneous hollow fiber gasexchange membranes 2 having at least the surfaces thereof intended for exposure to blood coated with a vinyl type copolymer including as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain described above or hollow fiber gas-exchange membranes 2 having the minute pores thereof blocked with a vinyl type copolymer including as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain as described above. These hollow fiber membranes 2 are disposed parallel along the direction of length of the housing 15 as mutually separated and spread away from each other throughout the ends of the gas-exchange membranes 2 are water-tightly supported in position respectively with bulkheads 19, 20 inside the fixing covers 17, 18 in such a manner that their openings will remain intact. The bulkheads 19,20 form an oxygen chamber 21, a chamber for transfer of a first substance, jointly with the outer surfaces of the gas-exchange membranes 2 and the inner surface of the housing 15, block the oxygen chamber 21, and separate the oxygen chamber 21 from a space for passage of blood (not shown), a space for flow of a second substance, which is formed inside the gas-exchange membranes 2. The fixing cover 17 is provided with an inlet 22 for feeding oxygen as the fluid for transfer of the first substance. The other fixing cover 18 is provided with an outlet 23 for discharging oxygen. Desirably on the inner surface of the cylindrical housing body 16 of the housing 15, a constricting part 24 for squeezing the bundle of gas-exchange membranes is annularly raised at the central part in the axial direction. Specifically, the constricting part 24 is integrally formed with the cylindrical housing body on the inner surface of the cylindrical housing body so as to squeeze the periphery of the hollow fiber bundle 25 comprising the multiplicity of gas-exchange membranes 2 inserted in the cylindrical housing body 16. As a result, the hollow fiber bundle 25 is squeezed radially to form a squeezed part 26 at the center in the axial direction as illustrated in Fig. 6. The packing ratio of gas-exchange membranes 2 varies at different parts along the axial direction and is highest at the central part. For the reason to be described later, desirable packing ratios at different parts are shown below. The packing ratio at the central squeezed part 26 is approximately in the range of 60 to 80%, that inside the cylindrical housing body 16 is approximately in the range of 30 to 60%, and that at the opposite ends of the hollow fiber bundle 25, namely on the outer sides of the bulkheads 19, 20 is approximately in the range of 20 to 40%. Now, the bulkheads 19, 20 will be described below with respect to their formation. As pointed out above, the bulkheads 19, 20 fulfill the important function of separating the interiors of the gas-exchange membranes 2 from the exteriors thereof. Generally, the bulkheads 19, 20 are produced by causing a macromolecular potting material of high polarity such as, for example, polyurethane, silicone, or epoxy resin by the centrifugal casting method into the cavities defined by the inner walls of the opposite ends of the housing 15 and by curing the cast material. To be more specific, a multiplicity of hollow fiber membranes 2 of a length greater than the length of the housing 15 are prepared, with the openings at the opposite ends thereof provisionally stoppered with highly viscous resin, and are parallelly disposed inside the cylindrical housing body 16 of the housing 15. Then, mold covers of a diameter greater than the diameter of the fixing covers 17, 18 are placed to cover the opposite ends of the gas-exchange membranes 2 completely and, with the housing 15 kept rotated around the axis thereof, the macromolecular potting material is injected inwardly from the opposite ends. When the injection is completed and the resin is cured, the mold covers are removed and the outer end surfaces of the cured resin are cut away with a sharp blade to expose the opposite opening ends of the gas-exchange membranes 2. In this manner, the bulkheads 19, 20 are completed. The outer surfaces of the bulkheads 19, 20 are covered respectively by flow path forming members 27, 28 each provided with an annular projection. The flow path forming members 27, 28 comprises respectively liquid distributing members 29, 30 and threaded rings 31, 32. The end surfaces of raised strips 33, 34 formed as annular protuberances near the peripheries of the liquid distribut­ ing members 29, 30 are held fast respectively against the bulkheads 19, 20 and fixed in position by having helically fitting the threaded rings 31, 32 respectively into the covers 17, 18, with the result that an inflow chamber 35 and an outflow chamber 36 are formed for handling blood as the fluid for transfer of the second substance. In the flow path forming members 27, 28, an inlet 37 and an outlet 38 for the blood as the fluid for transfer of the second substance are formed. The gaps formed around the peripheries of the bulkheads 19, 20 by the bulkheads 19, 20 and the flow path forming members 27, 28 are sealed tightly with the bulkheads 19, 20 by being filled with packing agents 43, 44 introduced through at least two holes 41, 42 communicating with the gaps. Otherwise, the gaps may be sealed with O-rings (not shown). In the hollow fiber membrane type artificial lung described above, the fluid for transfer of the first substance is an oxygen-containing gas such as air or blood and the fluid for transfer of the second substance is blood or an oxygen-containing gas. When the fluid for transfer of the first substance is a gas, the fluid for transfer of the second substance is blood. When the fluid for transfer of the first substance is blood, then the fluid for transfer of the second substance is a gas. The present invention has been described with respect to the hollow fiber membrane type artificial lung. In the case of a flat membrane type artificial lung using a plurality of superposed membranes, or a coiled membrane, or a membrane folded in a zigzag pattern, the invention may also be carried out with membranes having at least the surfaces thereof intended for exposure to blood coated with a vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain of the minute pores in the gas-­ exchange membranes blocked with the copolymer. In this case, there is also obtained a membrane type artificial lung which abounds with biocompatibility, suffers only insignificant loss of platelets, excels in gas-exchange ability, particularly in the removal of CO₂, and avoids inducing any leakage of blood plasma during the course of a protracted use. Now, the present invention will be described more specifically below with reference to working examples. Example 1 and Control 1 A hollow fiber membrane type artificial lung having a membrane area of 1.6 m² and constructed as illustrated in Fig. 6 was produced using hollow fiber membranes of silicone rubber having an inside diameter of 200 µm and a wall thickness of 100 µm. Separately, a 3 wt% solution was obtained by dissolving a (methyl methacrylate/butyl methacrylate)-­ perfluoropropyl acrylate block copolymer [weight ratio (25 : 25) : 50] in a 4/6 mixed solvent of methylethyl ketone/methylisobutyl ketone. This (methyl methacrylate/­ butyl methacrylate)-perfluoropropyl acrylate copolymer solution was left in contact for 1 minute with the blood-­ flow surface of the aforementioned hollow fiber membrane type artificial lung. Then, the artificial lung was emptied of the solution and swept with air to remove the solvent and form a coating. To test the membrane type artificial lung thus endowed with the coating (Example 1) and the membrane type artificial lung which had not undergone the coating treatment (Control 1) for gas-exchange ability, a venous blood adapted to have a partial pressure of oxygen of 35 mmHg and a partial pressure of carbon dioxide gas of 45 mmHg was prepared using fresh heparin-added bovine blood and caused to pass through the blood path of the artificial lung. The bovine blood used for this test had a hemoglobin content of 12 g/dl and a temperature of 37°C. The relation between the flow volume of blood on one part and the ability to add oxygen gas and the ability to remove carbon dioxide gas on the other part where the ratio of the flow volume of oxygen to that of blood is 1 is as shown in Table 1. It is noted from Table 1 that substantially no difference of gas-exchange ability is recognized between the membrane type artificial lung of Example 1 and that of Control 1. When these membrane type artificial lungs were subjected to 6 hours′ vein-artery extracorporeal circulation each using a dog, the loss of platelets was found to be 3% in the membrane type artificial lung of Example 1 and 15% in that of Control 1. Example 2 and Control 2 A hollow fiber membrane type artificial lung having a membrane area of 1.6 m² and constructed as illustrated in Fig. 6 was produced using porous hollow fiber membranes of polypropylene having an inside diameter of 200 µm, a wall thickness of 25 µm, a porosity of 45%, and an average pore diameter of 700 Å. Separately, a 30 wt% solution was prepared by dissolving a (methyl methacrylate/butyl methacrylate)-­ perfluoropropyl acrylate block copolymer [weight ratio (25:25) : 50] in a 4/6 mixed solvent of methylethyl ketone/methylisobutyl ketone and then was diluted with ethanol to 3% by weight. With this diluted solution, a coating was formed on the blood flow surface of the hollow fiber membrane type artificial lung by following the procedure of Example 1. The membrane type artificial lung endowed with the coating (Example 2) and the membrane type artificial lung which had not undergone the coating treatment (Control 2) were tested for gas-exchange ability by following the procedure of Example 1 and Control 1. The results were as shown in Table 1. It is noted from Table 1 that substantially no difference of gas-exchange ability was recognized between the membrane type artificial lung of Example 2 and that of Control 2. When these membrane type artificial lungs were subjected to 30 hours′ vein-artery extracorporeal circulation each using a mongrel dog, the loss of platelets was found to be 10% in the membrane type artificial lung of Example 2 and 25% in that of Control 2. Example 3 and Control 3 A hollow fiber membrane type artificial lung having a membrane area of 1.6 m² and constructed as illustrated in Fig. 6 was produced using hollow fiber membranes of polypropylene having an inside diameter of 200 µm, a wall thickness of 25 µm, a porosity of 45%, and an average pore diameter of 700 Å. Separately, a 30 vol% solution was prepared by dissolving a (methyl methacrylate/butyl methacrylate)-­ perfluoropropyl acrylate block copolymer [ weight ratio (25: 25) : 50] in a 4/6 mixed solvent of methylethyl ketone/methylisobutyl ketone and then diluted with ethanol to 6 wt%. The hollow fiber membranes of the hollow fiber membrane type artificial lung were kept filled for 3 minutes with the (methyl methacrylate/butyl methacrylate)-perfluoro­ propyl acrylate copolymer solution, then emptied of the solution, divested of the residual solvent, and dried, in order to give rise to a coating serving to block the minute pores in the membrane. To test the membrane type artificial lung endowed with the coating (Example 3) and the membrane type artificial lung which had not undergoen the treatment with the (methyl methacrylate/butyl methacrylate)-perfluoropropyl acrylate copolymer (Control 3) for gas-exchange ability, a venous blood adapted to have a partial pressure of oxygen gas of 35 mmHg was produced using fresh heparin-added bovine blood and passed though the blood path of the artificial lung. The bovine blood used in the test had a hemoglobin content of 12 g/dl and a temperature of 37°C. The relation between the flow volume of blood on one part and the ability to add oxygen gas and the ability to remove carbon dioxide gas on the other hand existing when the ratio of the flow volume of oxygen to that of blood is 1 is as shown in Table 2. It is noted from Table 2 that substantially no difference of gas-exchange ability is recognized between the membrane type artificial lung of Example 3 and that of Control 3. When the membrane type artificial lungs were subjected to 30 hours′ vein-artery extracorporeal circulation each using a mongrel dog, absolutely noleakage of blood plasma occurred in the membrane type artificial lung of Example 3, whereas leakage of blood plasma started after 8 hours′ circulation in the membrane type artificial lung of Control 3. Example 4 and Control 4 A hollow fiber membrane type artificial lung having a membrane area of 3.3 m² and constructed as illustrated in Fig. 6 was produced using the same hollow fiber membrane of polypropylene as used in Example 3. The hollow fiber membranes of the hollow fiber membrane type artificial lung were kept filled for 3 minutes with the same (methylethyl ketone/methylisobutyl ketone)/ethanol solution of a (methyl methacrylate/butyl methacrylate)-perfluoropropyl acrylate block copolymer as used in Example 3, emptied of the solution, and n-hexane was passed through the membranes which then were dried. Consequently, the minute pores in the hollow fiber membranes were blocked with the methyl methacrylate/butyl methacrylate)-perfluoropropyl acrylate copolymer (Example 4). Then, the hollow fiber membranes of the hollow fiber membrane type artificial lung were kept filled for 1 minute with a trifluorochloroethane 60 wt% silicone solution, emptied of the solution, then swept with a toluene/dipropylene glycol solution to wash out the residual silicone rubber solution adhering to the interiors of the hollow fiber membranes with silicone rubber (Control 4). When the two artificial lungs were tested for ability to exchange carbon dioxide gas by circulating blood at a flow rate of 1,500 ml/min and feeding oxygen gas at a flow volume of 15 liters/min, the exchange ability was found to be 250 ml/min in Example 4 and 160 ml/min in Control 4, indicating that the artificial lung of Example 4 filled with the (methyl methacrylate/butyl methacrylate)-perfluoropropyl acrylate copolymer was applicable to LFPPV-ECCO₂R, whereas the artificial lung of Control 4 filled with the silicone rubber had too poor ability to exchange carbon dioxide gas to be applied effetively to LFPPV-ECCO₂R. Since the present invention is directed to a membrane type artificial lung characterized by causing at least the surface of the gas-exchange membrane intended for exposure to blood to be coated with a vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain, the membrane type artificial lung inflicts upon the blood being circulated therethrough only insignificant damage as far as is concerned coagulation of blood, formation of microthrombosis, loss of platelets, degeneration of blood plasma proteins, hemolysis, etc. and thus, enjoys high biocompatibility. Further, the membrane type artificial lung possesses sufficient gas-­ exchange ability because the coating of the vinyl monomer possessing a perfluoroalkyl side chain has extremely high permeability to gas and does not impair at all the gas-exchange ability inherent in the gas-exchange membrane. This invention, therefore, provides a literally excellent membrane type artificial lung. This invention, as described above, is directed to a membrane type artificial lung using as gas-exchange membranes having a wall thickness in the range of 5 to 80 µm, a porosity in the range of 20 to 80%, and a pore diameter in the range of 0.01 to 5 µm, which membrane type artificial lung is characterized by having the minute pores in the membranes blocked with a vinyl type copolymer having as one of the components thereof a vinyl monomer possesing a perfluoroalkyl side chain. In spite of its extremely high ability to exchange gases, particularly to remove carbon dioxide gas, this membrane type artificial lung has no possibility of inducing leakage of blood plasma during a protracted use. It is, therefore, capable of removing the amount of carbon dioxide gas produced in the living body with such a small extracorporeal circulation volume as ECCO₂R. The membrane type artificial lung of this invention exhibits the gas-exchange ability to great advantage when the vinyl type copolymer is a (meth) acrylate type copolymer having as one of the components thereof a (meth)acrylate monomer possessing a perfluoroalkyl side chain, when the vinyl copolymer is a block copolymer, when the weight ratio in the vinyl type block copolymer of the polymer component formed of a vinyl monomer possessing a perfluoroalkyl side chain to the polymer component formed of the other monomer of the copolymer is in the range of 0.25 to 1.5, and when the perfluoroalkyl side chain is - CH₂CH₂(CF₂)₇CF₃. The membrane type artificial lung enjoys particularly high biocompatibility when the vinyl type block copolymer of the foregoing description further coats the surface of the artificial lung destined to contact blood. The gas-exchange membranes have sufficient mechanical strength to warrant compaction of the artificial lung when they are made of an olefin type resin, preferably polypropylene. The membrane type artificial lung is enabled to exhibit outstanding performance when the gas-exchange membranes are hollow fiber membranes.

Claims: 1. A membrane type artificial lung (1) comprising gas-exchange membranes (2), characterized in that at least the surface of a gas-exchange membrane intended for exposure to blood is coated with vinyl type copolymer (4) having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain. 2. A membrane type artificial lung (1) according to Claim 1, wherein said gas-exchange membrane (2) is a porous membrane. 3. A membrane type artificial lung (1) according to Claim 1, wherein said gas-exchange membrane (2) is a homogeneous membrane. 4. A membrane type artificial lung (1) according to Claim 3, wherein said homogeneous membrane (2) is made of a silicone rubber. 5. A membrane type artificial lung according to Claim 1, wherein the coating (4) of said vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain applied to said gas-exchange membrane (2) has a wall thickness in the range of 0.001 to 10µm. 6. A membrane type artificial lung (1) using as a gas-exchange membrane (2) a porous membrane having a wall thickness in the range of 5 to 80 µm, a porosity in the range of 20 to 80%, and a pore diameter in the range of 0.01 to 5 µm, characterized in that minute pores (3) of said membrane are blocked with a vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain. 7. A membrane type artificial lung (1) according to Claim 1 or 6, wherein said vinyl type copolymer is a (meth)acrylate type copolymer having as one of the components thereof a (meth)acrylate monomer possessing a perfluoroalkyl side chain. 8. A membrane type artificial lung (1) according to Claim 1 or 6, wherein said vinyl type copolymer is a block copolymer. 9. A membrane type artificial lung (1) according to Claim 8, wherein the weight ratio in said vinyl type block copolymer of the polymer component formed of a vinyl monomer possessing a perfluoroalkyl side chain to the polymer component formed of the other monomer of the copolymer is in the range of 0.25 to 1.5. 10. A membrane type artificial lung (1) according to Claim 1 or 6, wherein said perfluoroalkyl side chain is -CH₂CH₂(CF₂)₇CF₃. 11. A membrane type artificial lung (1) according to Claim 2 or 6, wherein said gas-exchange membrane (2) is made of an olefin type resin. 12. A membrane type artificial lung (1) according to Claim 11, wherein said gas-exchange membrane (2) is made of polypropylene. 13. A membrane type artificial lung (1) according to Claim 1 or 6 wherein said gas-exchange membrane (2) is a hollow fiber membrane. 14. A membrane type artificial lung (1) according to Claim 13, wherein said hollow fiber membrane (2) has an inside diameter in the range of 100 to 1,000 µm. 15. A membrane type artificial lung (1) according to Claim 6, wherein the surface of said membrane (2) to which blood is exposed is coated with said vinyl type copolymer. 16. A method for the manufacture of a membrane type artificial lung (1) characterized by the step of bringing at least the surface of a gas-exchange membrane intended for exposure to blood into contact with a solution of a vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain and by the step of subsequently vaporizing the solvent of said solution thereby forming a coating of said vinyl type copolymer on said surface intended for exposure to blood. 17. A method for the manufacture of a membrane type artificial lung (1) using as a gas-exchange membrane (2) a porous membrane having a wall thickness in the range of 5 to 80 µm, a porosity in the range of 20 to 80%, and a pore diameter in the range of 0.01 to 5 µm, characterized by the step of bringing said porous membrane into contact with a solution of vinyl type copolymer having as one of the components thereof a vinyl monomer possessing a perfluoroalkyl side chain thereby blocking minute pores thereof with said copolymer. 18. A method according to Claim 17, characterized in that it further comprises the step of bringing the membrane surface intended for exposure to blood into contact with a cleaning liquid and the step of subsequently vaporizing said cleaning liquid. 19. A method according to Claim 16 or 17, wherein said vinyl type copolymer is a (meth)acrylate type copolymer having as one of the components thereof a (meth)acrylate monomer possessing a perfluoroalkyl side chain. 20. A method according to Claim 16 or 17, wherein said vinyl type copolymer is a block copolymer. 21. A method according to Claim 20, wherein the weight ratio in said block copolymer of the component formed of a vinyl monomer possessing a perfluoroalkyl side chain to the polymer component formed of the other monomer of the copolymer is in the range of 0.25 to 1.5. 22. A method according to Claim 16 or 17, wherein the concentration of said vinyl type monomer in said solution is in the range of 1 to 20% by weight.

Inventors: FUKAZAWA, HIROMICHI, HAGIWARA, KAZUHIKO
Applicants: TERUMO KABUSHIKI KAISHA TRADING AS TERUMO CORPORATION
Application year: 1986
Main classification: A61M1
IPC codes: B01D67, A61L33