Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION --
This invention concerns a novel device for membrane
plasmapheresis, and more particularly, a disposable filter
cell for membrane plasmapheresis.
T~pical plasmapheresis techniques utilize th~
collection of whole blood from donors in bag~, and removal
of the bays 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 The plasma is withdrawn from the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 ~o 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 centrifugation 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 centrifuge-devices yield
plasma containing some platelets. Further, it has been
found that the membrane plasmapheresis devices can also be
designed to yield much greater ~uantities of plasma in
shorter times than the centrifuge devices. ~ 3
~n co-pending application Serial No.~ rT,
filed ~ e ~ ~ and entitled "Apparatus For
Membrane Plasmapheresis", 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. ~42,~'17 is 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 application Serial
No. 5-42~-077 in that the present invention concerns a
disposable filter cell fox memhrane plasmapheresis which
is extremely simple in construction and inexpensive to
produce, yet 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 i5 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.l
micron to ~ microns, and these filter membranes are posi-
tioned adjacent each other to orm 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 filter
3~ membrane define a plasma filtrate volume, and the second
flexible sheet and the second filter membrane define a
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plasma filtrate volume. The first and second flexible
sheets include poxtions spaced from the filter membranes
which portions define a plasma collection chamber.
Blood inlet and outlet ports communicate with the
blood flow path and a plasma outlet port is in communica-
tion with the plasma collection chamber.
In the illustrative embodiment, the sheets and
filter membranes have three aligned edges and the sheets
have larger surface areas than the membranes~ In this
manner, the plasma collection chamber is formed by portions
of the sheets that are not aligned with portions of the
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
clarit~.
DETAILED DESCRIPTION OF T~IE
ILLUSTRATIVE EMBODIMENT
Referring to the drawings, a disposable filter
cell for membrane plasmapheresis is shown therein
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comprising a first flexible 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
coxresponds to the roughened upper surface 12 o flexible
sheet 6. Sheets 4 and 6 are preferably formed of flexible
plastic material, such as polyethylene 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 surface 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 aluminum 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
iltration of plasma from whole blood, preferably between
about 0.1 micron and 2 microns, with the average pore size
preferably being about 0.65 micronsO The membranes 8 and 10
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have a void volume of greater than 60 percent, with an
average void volume 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 preferabl~ between 0.002 inch
and 0.008 inch.
Sheets 4 and 6 and membranes 8 and 10 are recti-
linear as illustrated, with sheets 4 and 6 having a greater
surface area than membranes 8 and 10~ As illustrated in
FIGURE 1, three of the edges A, B and C of sheets 4 and 6
and membranes B and 10 are aligned with each other, while
edges D of sheets 4 and 6 are aligned with each other and
edges E of membranes 8 and 10 are sealed to each other or,
if desired, the seal may comprise a fold defined by a
single sheet which forms membranes 8 and 10. Edges A of
sheets 4 and 6 and membranes 8 and 10 are sealed to each
other as are edges B and C of these sheets and membranes.
Edges D of sheets 4 and 6 are sealed to each other and a
compact unit, such as illustrated in FIGURE 2, is formed.
The membrane package, which comprises membranes 8
and 10 with their outer edges sealed to each other, defines
a blood flow path 14 between the membranes. 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 15) 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 plasma filtrate volume 24 is formed between
membrane 8 and sheet 4, while a plasma filtrate volume 26
is formed between membrane 10 and sheet 6. Because of
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the larger surface area of sheets 4 and 6 than the surface
areas of membranes 8 and 1~, a plasma collection chamber 28
is formed between the surface portions of sheets 4 and 6
which are not aligned with membranes 8 and 10. A plasma
outlet port 30 is provided in communication with plasma
collection chamber 28 for connection to a suitable conduit
to which the plasma is removed.
It is preferred that the sheets 4 and 6 and
membranes 8 and lQ 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 and
described in co-pending application Serial No.
filed Se~te ~ ~r~ g~.
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.
