Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF T~IE INVENTION
This invention concerns a novel device for membrane
plasmapheresis, and more particularly, a disposable filter
; cell for membrane plasmapheresis.
Typical plasmapheresis techniques utilize the
collection of whole blood from donors in bags, and removal
of the bags to a centrifuge where the plasma is separated
from the whole blood. The plasma is withdrawn from the
bag and the remaining blood is returned to the donor.
More recently, automated centrifuges have been
devised which continuously withdraw whole blood from the
donor, centrifuge the whole blood to separate the plasma,
harvest the plasma, and return the remaining blood in its
plasma-poor condition to the donor in a continuous fashion.
It has been proposed that plasmapheresis be carried
out without using a centrifuge, because of the inherent
complexity and cost of c~ntrifugation equipment. To this
end, the filtration of cells from whole blood using a
microporous membrane has been disclosed, for example, in
Blatt, et al. U.S. Patent No. 3,705,100~ It has been
found that a membrane-type plasmapheresis device yields
platelet-free plasma while ce~trifuge~devices yield
plasma containing some platelets. Further, it has been
~ound that the membrane plasmapheresis devices can also
be designed to ~ield much greater quantities of plasma in
shorter times than the centrifuge devices.
In co-pending application Serial No~ ~ ,it~7
q
filed , and en~itled "Apparatus For
Membrane Plasmapheresisl', a parallel membrane type of
membrane plasmapheresis apparatus is disclosed An advan-
tage of the type of membrane plasmapheresis apparatus
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disclosed in application Serial No. g4~,-077 ~s that such
apparatus is capable of comprising an inexpensive, dis~
posable package and, in addition, the apparatus utilizes
a substantially large amount of membrane surface area.
The present invention is an improvement upon the
membrane plasmapheresis apparatus of appliaation Serial
No. g ~ ~77~in that the present invention concerns a
disposable filter cell for membrane plasmapheresis which
is extremel~ simple in construction and inexpensive to
produce, ~et the filter cell of the present invention is
capable of achieving efficient plasmapheresis.
Other objects and advantages of the present inven-
tion will become apparent as the description proceeds.
SUMMARY OF THE INVENTION
In accordance with the present invention~ a
disposable filter cell is provided for membrane plasma-
pheresis. The filter cell includes a first flexible sheet
having a roughened undersurface and a second flexible
sheet having a roughened upper surface. A pair of filter
membranes are provided, having pore sizes of about 0.1
micron to 2 microns, and these filter membranes are posi-
tioned adjacent each other to form a blood flow path
therebetween.
The first and second flexible sheets are posi-
tioned on opposite sides of the membranes to sandwich the
membranes between the flexible sheets, with the roughened
surface of each flexible sheet facing the respective
membrane.
The first flexible sheet and the first Eilter
membrane define a first plasma filtrate volume, and the
second flexible sheet and the second filter membrane
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define a second plasma filtrate volume. Blood inlet and
outlet ports communicate with the blood flow path and a
plasma outlet port is in communication with the plasma
filtrate volumes.
In the illustrative embodiment, each of the first
and second filter membranes defines an opening whiah
provides the communication between the first plasma
filtrate volume and the second plasma filtrate volume.
A seal traverses the filter membranes to close one side
of the blood flow path defined by the filter membranes,
in order to segregate the blood flow path from the openings
defined by the filter membranes.
In the illustrative embodiment, the flexible sheets
each comprise plastic sheets which are extruded with the
roughened surfaces formed in the extrudate.
A more detailed explanation of the invention is
provided in the following description and claims, and is
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
..... .... . . _ ... .. .. . . .
FIGURE 1 is an exploded perspective view of a
disposable filter cell constructed in accordance with the
principles of the present invention; and
FIGURE 2 is a perspective view of a disposable
filter cell constructed in accordance with the principles
of the present invention, with portions broken away for
clarity.
DETAILED DESCRIPTION OF THE
ILLUSTRATIVE EMBODIMENT
Referring to the drawings, a disposable filter
cell for membrane plasmapheresis is shown thexein
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comprising a first ~lexible sheet 4, a second flexible
sheet 6, a first filter membrane 8, and a second filter
membrane 10.
Flexible sheet 4 has a roughened undersurface that
corresponds to the roughened upper surface 12 of flexible
sheet 6. Sheets 4 and 6 are preferably formed of ~ ible
plastic material, such as polyeth~lene or PVC that has
been extruded and has a thickness of about 0.015 inch,
with the roughened surface comprising a plurality of
longitudinal grooves defined by the extrudate with each
of the grooves being about 0~010 inch deep.
It is to be understood that the roughened under-
surface of sheet 4 and the roughened suxface 12 of sheet 6
could comprise any type of roughened surface that allows
for the flow of plasma to a plasma collection chamber, as
will be described below. The roughened surface, therefore,
could comprise a criss-cross grooved configuration, a
plurality of spaced projections, a mesh screen member in
contact with the flexible sheet material, or a combination
of these.
Although for economy it is preferred that flexible
sheets 4 and 6 be formed of an extruded plastic material,
it may be desired to form flexible sheets 4 and 6 of a
metallic sheet material, such as aluminum foil. In addi-
tion, the alumninum foil may have a roughened surface
defined by the aluminum foil itself or may be coated with
a plastic material to form the roughened surface.
Membranes 8 and 10 are each formed of a sheet-like
microporous membrane having a pore size that permits the
filtration of plasma *rom whole blood, preferably between
about 0.1 micron and 2 microns, with the average pore size
preferably being about 0.65 microns. The membranes 8 and 10
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have a void volume of greater than 60 percent, with an
average void colume of about 80 percent. The membranes
are preferably formed of a polymeric material, with the
pores defining a relatively tortuous path. The thickness
of each of the membranes is preferably between 0.002 inch
and 0.008 inch.
Sheets 4 and 6 and membranes ~ and 10 are recti-
linear as illustrated, with the four edges A, B, C and D
being aligned with each other. Edges A-D of sheets 4 and
6 and membranes 8 and 10 are sealed to each other to form
a compact unit, such as illustrated in FIGURE 2.
Filter membranes 3 and 10 define circular openings
13. The membrane package, which comprises membranes 8 and
10, defines a blood flow path 14 between the m~mbranes.
Membrane 8 defines openings 16 and 18 and sheet 4 carries
a blood inlet port 20 which communicates with opening 16
~and is sealed around opening 16) and a blood outlet port
22 which communicates with opening 18 (and is sealed
around opening 18), thereby forming communication between
inlet and outlet ports 20, 22, respectively, and the blood
flow path 14.
A heat seal E traverses the membranes 8 and 10 to
close one side of the blood flow path 14 and to segregate
the blood flow path 14 from aligned openings 13. Openings
13 communicate with a first plasma filtrate volume 24 that
is formed between membrane 8 and sheet 4 and with a second
plasma filtrate volume 26 that is formed between membrane
10 and sheet 6. A plasma outlet port 30, which is aligned
with openings 13, is provided in communication with plasma
filtrate volumes 24 and 2~, for connection to a suitable
conduit through which the plasma is removed.
It is preferred that the sheets 4 and 6 and
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membranes 8 and 10 be formed of a thermoplastic material
so that the seals mentioned above may be heat seals.
: Alternatively, these seals may be formed of bonding
materials, sonic welds, or other types of fluid-tight
seals.
In operation, the disposable filter cell is
placed in a preferably permanent fixture and the conduit
is coupled to port 20 into which blood is introduced from
the patient's vein, a conduit is coupled to port 22 for
forming a red blood cell return line and a plasma recovery
conduit is coupled to port 30. The plasmapheresis filter
cell described above may be used in the system illustrated
3~ ~ 3 53
and described in co-pending application Serial No. ~4~,~77,
filed Se~3mb~E~ 7~.
Although an illustrative embodiment of the inven-
tion has been shown and described, it is to be understood
that various modifications and substitutions may be made
by those skilled in the art without departing from the
novel spirit and scope of the present invention.
