Liquid purification or separation – Filter – Material
Patent
1995-11-06
1998-12-15
Fortuna, Ana
Liquid purification or separation
Filter
Material
210490, 21050023, 21050029, 21050032, 264199, 264200, B01D 6300
Patent
active
058491899
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a hollow fiber blood purifying membrane, and particularly to a blood purifying membrane made of high-performance hollow cellulose acetate fibers having a specific internal/external surface ratio and cross-section condition, and having a specific selective permeability. More specifically, the present invention provides a blood purifying membrane made of hollow fibers composed of a cellulose acetate polymer with a high degree of polymerization, which excels at removing middle to high molecular proteins of molecular weight 10,000 to 20,000, such as .beta..sub.2 -microglobulin (.beta..sub.2 -MG), has excellent blood plasma albumin permeation blockage, has a small difference in in vivo and in vitro ultrafiltration rate (UFR) values, undergoes little change in performance with time, and is excellently suited for living organisms. The present invention also provides a process for the production of such a blood purifying membrane.
BACKGROUND ART
Selectively permeable hollow fibers have been used in common practice for blood dialysis. The blood purifying apparatuses used for blood dialysis comprise a plurality of dialysis membranes, for example hollow fiber membranes, arranged in parallel in a cage-like housing, and the patient's blood is allowed to flow through the inner hollow while the dialyzing fluid is allowed to flow on the outside, i.e. between the hollow fibers, for dialysis through the hollow fiber membranes to remove waste products from the blood and rectify electrolyte concentrations, with ultrafiltration carried out due to the differential pressure between the inside and outside of the hollow fibers, to remove excess water from the blood.
The hollow fibers for blood processing must be selectively permeable to specific substances, depending on the purpose. Their performance is determined based on the material of the hollow fibers as well as the porosity (size and number of pores, etc.) and membrane thickness.
Cellulose and cellulose acetate are two materials commonly used in hollow fibers for blood purifiers. In particular, cellulose acetate fibers are relatively easy to produce by commonly used spinning methods such as plasticizing melt spinning or wet spinning, and when the resultant hollow fibers are used for blood dialysis therapy, they provide the advantage of allowing some degree of suppression of complement activity in contrast to, for example, hollow cellulose fibers.
Conventional blood purification membranes made of cellulose acetate, however, even with pore sizes large enough to allow removal of .beta..sub.2 -MG, have become clogged by adsorption of proteins, etc. during the dialysis procedure, leading to deterioration with time accompanied by a marked decrease in the ultrafiltration rate, whereas membranes which are too dense have lacked the ability to remove middle to high molecular weight proteins such as .beta..sub.2 -MG.
On the other hand, hollow fibers produced by melt spinning cellulose acetate are disclosed in Japanese Unexamined Patent Publication No. 54-42420 which describes a process for obtaining a dialysis membrane by adding a homogeneous mixture of polyethylene glycol and glycerine to a cellulose ester to produce hollow fibers and then extracting the mixture. The membrane obtained by this process, however, is limited to permeability to low molecular weight substances, and being a dense membrane it is vastly different from the membrane obtained by the production process of the present invention.
In Japanese Examined Patent Publication No. 3-62447, some of the present inventors have proposed a process by which hollow fibers are made from a composition prepared by mixing a cellulose ester with given proportions of a water-soluble polyhydric alcohol and an additive selected from the group consisting of polyethers one of whose residues is glycerin, which substantially has no plasticizing effect on the cellulose ester and is compatible with the polyhydric alcohol, after which the additive is removed by extraction. For this purpose the
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Emi Shingo
Fukuhara Satoshi
Soga Kouji
Fortuna Ana
Teijin Limited
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