Liquid purification or separation – Filter – Supported – shaped or superimposed formed mediums
Reexamination Certificate
2000-10-23
2003-10-07
Kim, John (Department: 1723)
Liquid purification or separation
Filter
Supported, shaped or superimposed formed mediums
C210S483000, C210S488000
Reexamination Certificate
active
06629613
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to leukocyte filters and filtration generally.
BACKGROUND OF THE INVENTION
Filters are commonly used to remove leukocytes from blood and blood products in order to minimize various adverse effects of white cell transfusion. Examples of adverse effects include non-hemolytic febrile reaction, alloimmunization and graft versus host disease. Commercial leukoreduction filters are mostly composed of non-woven materials, which are made up of discrete fibers bonded or pressed together.
Another filter known in the art is a membrane filter, which, instead of having discrete fibers, is a continuous structure containing a network of pores. The membrane enables efficient capture of leukocytes and a reasonably good passage of the desired blood components (e.g., erythrocytes, platelets or plasma). However, membrane filters known in the art are either lacking in performance or require specific materials of construction, unusual pore morphology, a very narrow pore size distribution or pore size gradation within the filter.
One example of a membrane filter is described in U.S. Pat. No. 5,895,575 assigned to the present applicant/assignee, the disclosure of which is incorporated herein by reference. The '575 patent describes a filter composed of nitrocellulose membranes and non-woven materials.
U.S. Pat. No. 5,476,587 (Kuroki et al.) describes a membrane with a most frequent pore diameter of 1-5 &mgr;m, and a pore size weight average to number average ratio of 1.5 to 2.5, the ratio gradually changing from the top to the bottom of the filter.
U.S. Pat. No. 5,707,526 (a continuation-in-part of Kuroki et al.'s '587 patent) describes a membrane having a most frequent pore diameter of 1-5 &mgr;m, and a specific dust permeability, enclosed in a housing of a specially designed structure.
U.S. Pat. No. 5,478,470 (Fukuda et al.) describes membranes with a specific set of properties, including pores of 2-30 &mgr;m having a combined pore volume equal to or greater than 94% of the total pore volume.
U.S. Pat. No. 5,665,233 (a division of Fukuda et al.'s '470 patent) describes the use of porous materials, including membranes, having a specific set of properties, among them certain pore volumes, pore size gradation, leukocyte retention per layer, and layer thickness of less than 0.5 mm.
European Patent Application Publication No. 0406,485 A1 (now abandoned) describes membrane containing filters, wherein the membranes are strongly asymmetric, having a median pore size at the upstream surface substantially larger than at the downstream surface.
Japanese Patent Application No. 526,2656 describes membranes with a negative charge. Japanese Patent Application No. 503,4337 describes membranes made specifically of polyvinyl format or polyurethane. Japanese Patent Application No. 514,8150 describes a filter containing both porous materials and a non-woven fabric with fibers of 0.8-3 &mgr;m diameter. Japanese Patent Application No. 54-44270 (filed Apr. 13, 1979) describes a polyester foam used to trap leukocytes.
Other membrane filters are described in European Patent Publication No. 408,462 B1 and U.S. Pat. No. 5,234,593, both of which have unusual pore structures, and in U.S. Pat. Nos. 4,985,153 and 5,783,094. The disclosures of all publications mentioned in the present specification are incorporated herein by reference.
In general in the prior art, membrane filters are constructed of specialized or non-commercial materials with narrow ranges of pore sizes. In addition, the filters generally have a non-homogeneous pore structure throughout their bulk, i.e. they employ membranes wherein the pores of the membranes have large diameter on one side of the membrane and a narrower diameter on the other side. Also, it has been assumed in the prior art that in order to obtain good throughput and prevent filter clogging, the filter must have a multilayer structure with a gradual decrease in pore size in the direction of flow.
SUMMARY OF THE INVENTION
The present invention seeks to provide an improved leukocyte filter, a filtering method and a filtered blood product, including a filtered whole blood product.
There is thus provided in accordance with a preferred embodiment of the present invention a leukocyte filter comprising: a prefilter portion; and a membrane filter portion downstream of the prefilter portion, the membrane filter portion having a pore size distribution having a median pore size between 3 and 12 microns and having at least 40% of the pore volume being constituted by pores having a pore cross section diameter of between 3 and 10 microns and having at least 5% of the pore volume being constituted by pores having a pore cross section diameter larger than 10 microns.
In accordance with a preferred embodiment of the invention, no more than 60% of the pore volume is constituted by pores having a pore cross section diameter larger than 10 microns. In accordance with a preferred embodiment of the invention, the membrane filter portion is characterized in that no more than 30% of the pore volume is constituted by pores having a pore cross section diameter less than 3 microns. In accordance with a preferred embodiment of the invention, the membrane filter portion is characterized in that no more than 30% of the pore volume is constituted by pores having a pore cross section diameter less than 3 microns.
There is also provided, in accordance with a preferred embodiment of the invention, a leukocyte filter comprising: a prefilter portion; and a membrane filter portion downstream of the prefilter portion, the prefilter portion being characterized in that it captures less than 60% of incoming leukocytes, and the membrane filter portion being characterized in that it is non-cellulosic and generally homogeneous. In accordance with a preferred embodiment of the invention, the membrane filter portion is characterized in that it has a pore surface area/membrane volume ratio larger than 6 square meters per milliliter of membrane volume. In accordance with a preferred embodiment of the invention, the membrane filter portion is characterized in that it has a pore surface area/membrane mass ratio larger than 12 square meters per gram of membrane. In accordance with a preferred embodiment of the invention, the membrane filter portion comprises at least one layer of a generally homogeneous non-cellulosic membrane, wherein the total pore volume of pores having a diameter between 1-30 microns is less than 90% of the total pore volume. In accordance with a preferred embodiment of the invention, the membrane filter portion is characterized in that it has a pore size distribution having a median pore size between 3 and 12 microns and having at least 40% of the pore volume being constituted by pores having a pore cross section diameter of between 3 and 10 microns and having at least 5% of the pore volume being constituted by pores having a pore cross section diameter larger than 10 microns. In accordance with a preferred embodiment of the invention, no more than 60% of the pore volume is constituted by pores having a pore cross section diameter larger than 10 microns. In accordance with a preferred embodiment of the invention, the membrane filter portion is characterized in that at least 40% of its pore volume is constituted by pores having a pore cross section diameter of between 3 and 10 microns. In accordance with a preferred embodiment of the invention, the membrane filter portion is characterized in that at least 5% of the pore volume is constituted by pores having a pore cross section diameter larger than 10 microns. In accordance with a preferred embodiment of the invention, the membrane filter portion is characterized in that no more than 30% of the pore volume being constituted by pores having a pore cross section diameter less than 3 microns. In accordance with a preferred embodiment of the invention, the membrane filter portion is characterized in that it has a pore size distribution having a median pore size between 3 and 12 microns and having at lea
Gamlieli Yefet
Kraus Menachem
Kim John
Ladas & Parry
Teva Medical Ltd.
LandOfFree
Leukocyte filter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Leukocyte filter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Leukocyte filter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3153140