Liquid purification or separation – Filter – Material
Reexamination Certificate
2000-12-15
2003-08-12
Kim, John (Department: 1723)
Liquid purification or separation
Filter
Material
C210S500100, C210S500410
Reexamination Certificate
active
06605218
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semipermeable membrane for blood treatment which exhibits little change in performance upon drying and reduced elution of a hydrophilic polymer therefrom; a dialyzer for use in blood treatment using the same; and a processes for producing a dialyzer having incorporated therein a semipermeable membrane which exhibits little change in performance before and after drying and reduced elution of a hydrophilic polymer therefrom.
2. Description of the Related Art
As a material for a semipermeable membrane for blood treatment such as an artificial kidney, there have been used a number of materials. For example, a natural material cellulose and its derivatives, e.g., cellulose diacetate and cellulose triacetate, were originally used, and synthetic polymers were then developed, such as polysulfone, polymethyl methacrylate (PMMA) and polyacrylonitrile. Recently, modified cellulose membranes have also been used which is prepared by treating cellulose with polyethylene glycol (PEG) or the like to modify the compatibility to blood. In semipermeable membranes for blood treatment in patients suffering from chronic renal failure, attempts have been made to reduce the leakage of albumin to a minimum while positively removing low molecular proteins other than albumin. In addition to such improvement in the membranes, hemodiafiltration (HDF) procedures and push-and-pull procedures have been developed for increasing the dialysis efficiency and positive removal of undesirable low molecular proteins. Polysulfone, which has a high water permeability, is now widely used since it meets the above-mentioned requirements. In a polysulfone membrane, a hydrophilic polymer is generally blended to impart an affinity for blood to the membrane. However, the polysulfone membrane has such a defect that once it is dried the properties tend to be changed to a great extent. Hence, it is difficult to produce a dry type of polysulfone membrane dialyzer which is light-weight and easy to handle.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a dialyzer using a dry or semi-dry type of semipermeable membrane which has advantages such as light-weight and resistance to freeze, wherein the semipermeable membrane is improved in water permeability and dialyze performance (which are poor in a conventional one) to the same level as those of a wet type one.
It is another object of the present invention to provide a dry or semi-dry type of dialyzer having advantages such as light-weight and resistance to freeze, wherein the dialyzer is improved in water permeability and dialyze performance (which are poor in a conventional one) to the same level as those of a wet-type one and exhibits a reduced elution of a hydrophilic polymer therefrom.
That is, in an aspect of the present invention, there is provided a dialyzer for blood treatment having incorporated therein a semipermeable membrane which comprises a hydrophobic polymer and a hydrophilic polymer, the water permeating performance of the semipermeable membrane after drying being ½ or higher relative to that before drying and the dialyzer satisfying any of the following requirements:
(A) the vitamin B12 clearance is not smaller than 135 ml/min per 1.6 m
2
; and
(B) the amount of the hydrophilic polymer that is eluted from the semipermeable membrane is not higher than 10 ppm.
In another aspect of the present invention, there is provided a process for producing a dialyzer having incorporated therein a semipermeable membrane which comprises a hydrophobic polymer and a hydrophilic polymer, the process comprising:
drying the semipermeable membrane; and
saturating the dried semipermeable membrane with water ratio of not smaller than 100% based on the dry weight of the semipermeable membrane, providing an inert gas atmosphere to the inside of the dialyzer, and then irradiating the semipermeable membrane with gamma-ray in the inert gas atmosphere.
In still another aspect of the present invention, there is provided a process for producing a hollow fiber membrane for use in blood treatment through dry/wet spinning from a spinning solution comprising 15 to 18% by weight of a hydrophobic polymer and 4 to 8% by weight of a hydrophilic polymer, the dry zone being filled with dry mist.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In the present invention, the hydrophobic polymer to be used in the semipermeable membrane includes a number of engineering plastics, such as polysulfone, polyamide, polyimide, polyphenyl ether and polyphenylene sulfide. Preferably, the hydrophobic polymer is polysulfone represented by the formula below, which shows the skeleton of the polysulfone. Polysulfone derivatives in which the benzene ring in the skeleton is modified are also usable in the present invention.
The hydrophilic polymer to be used in the semipermeable membrane includes, for example, polyethylene glycol, polyvinyl alcohol, carboxymethyl cellulose and polyvinyl pyrrolidone, which may be used alone or in combination. Polyvinyl pyrrolidone (hereinafter, sometimes referred to as “PVP”) is preferred since it is relatively high in industrial availability. It is preferable to use two or more of hydrophilic polymers having different molecular weights. In this instance, the hydrophilic polymers preferably have different weight average molecular weights from one another by five times or more.
The spinning solution to be used for the preparation of the semipermeable membrane preferably comprises a hydrophobic polymer, a hydrophilic polymer, a solvent and an additive. The solvent may be an amphiprotic solvent which can fully dissolve all of the hydrophobic polymer, the hydrophilic polymer and the additive. Specific examples of the solvent include dimethylacetamide, dimethylformamide, dimethylsulfoxide, acetone, acetaldehyde and 2-methyl pyrrolidone. Dimethylacetamide is particularly preferred from the viewpoints of safety, stability and toxicity. The additive may be one which is a poor solvent for the hydrophobic polymer but is miscible with the hydrophilic polymer, such as an alcohol, glycerin, water and an ester. Water is particularly preferred from the viewpoint of process suitability.
The viscosity of the spinning solution for membrane production may depend on the molecular weight of the hydrophilic polymer, since commercially available hydrophilic polymers have low molecular weights. A decreased viscosity of the spinning solution could cause breakage or swinging of fibers during the preparation of a hollow fiber membrane, leading to a decreased stability of the resulting hollow fiber membrane. Accordingly, when PVP is used as the hydrophilic polymer, PVP with a high molecular weight is preferred. When two or more types of PVP are used in a mixture, the PVP mixture preferably has an average molecular weight of 200,000 or higher.
Next, the contents of the hydrophobic and hydrophilic polymers in the spinning solution is described. As stated above, as the polymer content increases, a membrane can be formed more effectively but the porosity of the resulting membrane decreases, leading to a decreased water permeability. Accordingly, there is an optimum range for the polymer content. To obtain a membrane that can exert both a high permselectivity and a low albumin permeability even when dried, like one produced in the present invention, the concentration of the hydrophobic polymer is preferably 10 to 20% by weight, more preferably 12 to 18% by weight, and the concentration of the hydrophilic polymer is preferably 2 to 20% by weight, more preferably 3 to 15% by weight. In the case where two or more hydrophilic polymers having different molecular weights are used, it is preferable that the content of hydrophilic polymers having molecular weights of 100,000 or higher in the spinning solution is 1 to 10% by weight. If this content is too large, the viscosity of the spinning solution increases, which may cause difficulty in formation of a membrane, as well as decrease in water permeabil
Kozawa Hidetoshi
Nakashima Hidekazu
Wada Shigehisa
Kim John
Nixon & Vanderhye P.C.
Toray Industries Inc.
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