Note: Descriptions are shown in the official language in which they were submitted.
~ETH~D QF M~KING MASS TRANSFER APPARATUS
TAe present invention relates to a mass transfer
apparatus ~or- the flow of fluids separated by a planar
semipermeable membrane element folded several times upon
itself and to a method of manufacturing such an apparatus.
The invention more particularly relates to an
improvement in an apparatus comprising a semipermeable membrane
folded to ~orm a stack of accordion pleats, disposed inside of
a casing, and provided with the necessary ports for the intro-
duction and evacuation of blood, dialysate and/or ultrafiltrate,
the pleats of the stack on one side of the membrane containing
a plurality of porous or open-mesh support members.
, An apparatus of this general type is known, as
disclosed in U. S. patent 3,788,482. Generally the stack of
the membrane in accordion pleats and of the support members
is enclosed in a fluid-tight manner inside a housing. This
housing may be either a box consisting of essentially two
or more pieces suita~ly joined together for example, or an
envelope made out of a suitable plastic materLal and molded
about said stack. These boxes, being made according to a
given model, have all exactly the same dimensions and, on the
other hand, the mold being the same for all these envelopes,
their external dimensions are all identical. Also it has been
thought advantageous to have identical apparatuses which
have especially stacks of exactly the same height. However,
it- has now been found that in actual practice the thickness
cf the ~e~rane, and particularly of the support members,
may vary slightly ~rom one apparatus to another and that such
slight variations, when multiplied by the number of pleats
or number o~ support elements in a stack, may result in
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apprecia~le ~ar~at~ons in the thickness of the bl~od films
for~ed ~n d2~ferent apparatuses of the same stack height
and same external dimensions. Consequently, the performance
and efficiency of these apparatuses may vary at random from
one apparatus to another in an undesirable manner, presenting
potentially serious problems in a field where reliability and
uniformity of operation are deemed essential.
One aspect of this invention therefore lies in
recognizing the nature of this problem and its cause; another
aspect is concerned with the discovery of a solution to that
problem. Specifically, it is an object of the present invention
to provide an apparatus having reproducible performance
characteristics so that the performance from one such apparatus
to another will be substantially identical. It is an object
of the present invention to provide an apparatus of the kind
indicated that eliminates or at least greatly minimizes
problems and disadvantages of the prior art devices.
It is also an object of the present invention to
provide an apparatus of simple and economical construction
which allows an easy flow of blood under a small pressure
drop and with uniform distribution of blood over the entire
membrane, and within successive pleats of the same membrane,
and which requires only a limited volume of blood within the
body of the apparatus.
This invention, in one aspect, resides in a mass
tr~nsfer apparatus comprising two rigid and essentially
rectangular plates, and a stack made up of membrane and
membrane support members disposed between said plates,
characterised in that connecting means are provided which
- 30 are bonded to opposite side edges of said plates to maintain
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a compre~sIye lQad Q~ predeter~ined value on said stack.
M~Pe ~articularly, the invention in one aspect,
provides a ~ass trans~er apparatus which comprises two rigid
and essentiall~ rectangular plates which have uniform
thickness and ~lat opposing surfaces, a semipermeable
membrane disposed between said plates, said membrane being a
planar membrane folded to form a stack of accordion pleats
between the whole internal or opposing surfaces of said plates,
a support me~ber ~eing disposed within each pleat on one side
only of said membrane, connecting means bonded (by sticking,
sealing, melting, welding, soldering, brazing, potting, casting,
or the like) to each o~ said plates along opposite side edges
thereof for securing said two plates in parallel positions
while maintaining the stack under a uniformly-distributed load
: lS of predetermined value, at least three ports for the flow of
fluids on both sldes of the membrane stack, a housing about
said stack, said plates, and said ports, and means for embed-
ding or imperviously sealing the edges of the membrane over
its whole length in a fluid-tight manner.
In another aspect the present invention resides in a
method of manufacturing the above-mentioned mass transfer appara-
tus, comprising the steps of making up a stack of membrane and
: membrane support members, locating said stack between two rigid
and essentially rectangular plates, exerting a compressive load
25 of predetermined value on said plates whereby said load is
exerted on said stack, and bonding connecting means to opposite
side edges of said plates to maintain a compressive load on
said stack~
More particularly, the method aspect of this inven-
tion resides in a method of manufacturing a mass transfer
apparatus which comprises the following steps:
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(a~ ~aking up an assembly ~y folding a semi-
per~e~ble me~r~ne ln accordiQn-like manner into a number
of closely spaced pleats around support members inserted
into or between the pleats on one side only of said membrane,
~nd placing the accordion-folded stack between a pair of
rigid plates each having ~lat, parallel surfaces;
(b) introducing said assemblage between the two
platens of a press, at least one of which is movable with
respect to the other, their opposite faces remaining constantly
parallel during all positions of the platens;
(c) exerting a uniformly-distributed predetermined
compressive load on said asse~blage by means of said press;
~d) positioning rigid connecting means, preferably
in the form of headers having ~low ports, adjacent the side
edges of said lower and upper rigid plates of the assemblage,
and rigidly bonding them to said plates by sticking, sealing,
melting, welding, soldering, ~razing, potting, casting, or
the like while said assem~lage is maintained under said
uniformly distributed predetermined compressive load; and
(e) completing the overall housing of said
assemblage (the plate~ thereof having been rigidly secured by
said connecting means) ~y any desired per se known means.
A still better understanding of the features of the
present invention and its inherent advantages will become
appar~nt from the following description and reference to the
accompanying drawing in which the sole ~igure is a perspective
view of a hemodlalyzer disposed during its construction
between the two platens o~ a press.
Referring now to the drawing, it will be seen that
the semiper~ea~le me~brane 10 is ~olded in accordion pleats
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around ~u~po~t ~embers 11 wh~ch are disposed only on one side
o~ the ~em~rane, Mem~rane pleats cover the whole surface of
; a lo~er rig~d plate 12 ~hich is preferably made of polvmethyl-
methacrylate or other rigid plastic material and whose shape
is generally rectangular.
~ n upper rigid plate 13, generally identical with
the lower rigid plate 12, covers the whole surface of the top
pleat of the membrane. Each plate is rigid and has flat,
parallel upper and lower sur~aces. The upper and the lower
ends of the membrane may be sealed in a leakproof manner by
any desired per se known means respectively to the upper and
lower plates, ~or instance, by means of epoxy, polyurethane
resin or other suitable adhesive agent.
Plates 12 and 13 are disposed between the platens
14 and 15 of the press. The opposite faces of the platens 14
and 15 are exactly parallel and must remain parallel when mov-
ing one with respect to the other. For example, the platen 14
is fixed while the platen 15 is movable, being attached to the
piston 16 of a press. T~e other elements of the press, being
conventional and not critical for an understanding of the
present invention, are not shown.
The support members used in this apparatus within
the pleats of the membrane may be of ~arious types per se
well known in the art for maintaining a suitable spacing between
adjacent folds and yet providing a minimum impediment to flow
;~ o~ dialysate. Each takes the ~orm o~ a spacer comprising
a plastic non-woven ~esh (e.g., of polyolefin) which has two
layers o~ threads dlsposed at substantially right angles to
each other and then heat sealed, each layer originally being
in a dif~erent plane. A support member may generally comprise
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one or two spacers between pleats o~ the membrane. The
~e~r~ne ~ay ~e an~v ~lex~ble and semipermeable membrane of
":
various types ~s well known in the art, for example known
me~branes suitable for hemodialysis and treatment of blood
by ultrafiltration such as "Cuprophan",* polyacrylonitrile,
etc.
The stack o~ me~r~ne and support members consti-
tutes a compressible and elastic assemblage whose height may
vary depending on the compressive force applied. Furthermore,
when the same load or compressive force is applied to different
stacks ~ormed of membrane and spacer materials taken from the
same sources, stack height variations of from 0.5~ to 10~ may
occur, such variations commonly falling in the range of 2% to
; 6%. Such variatons arise because of minute irregularities or
differences in the thickness of materials used for the support
elements and membranes of the dialyzers, and because such
differences may be magnified by the multiplicity of pleats and
support elements required in each apparatus.
According to the present in~ention, it has been
found that greater reproducibility, and in general better
results, may ~e ~tained i~, although always employing the
same conventional elements such as membrane, support members
and plates, the stacks of these elements are produced under a
uniform predetermined load without regard to whether the final
height of one stack differs from another stack having the same
; number of pleats and spa~ers. It is to be understood that one
may employ either a constant pressure, or a weight or any
other suitable means which results in a uniform load distrib-
uted evenly o~er and throughout the stack of membrane and
*Trademark for a commercially available form of regenerated
cellulose.
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suppQrt ~e~ber~ by reason of the rigid plates.
This uniform load Q~ a predetermined value may be
readily established ~or an assemblage of any given size and
number of pleats, using any given membrane and spacer materials,
by a series o~ simple tests. If the loading is too high, the
pressure drop of ~luids when traversing the apparatus may be
too high and the liquid ~ilms may be locally too thin and/or
the flow of fluids may be at rates that are too slow, thus
adversely affecting the operation and efficiency of the
apparatus. In the case of blood, there even may be the risk
of coagulating the blood because of the reduced flow. If, on
the contrary, the uniform load is too low, the channels offered
for fluid flow may be too large and the distribution of fluid
inside the apparatus may become preferential as between the
different pleats feed~ng in parallel from a co~non header, and
the rate of circulation locally may become too slow, leading to
the same drawbacks mentioned above. At optimum loading, ~he
cross sectional dimensions of the fluid layers within the
membrane pleats and the rates o~ ~luid flow therein will provide
the best exchange or transfer characteristics for the materials
and construction used. Once an optimum compressive loading
value has been established to achieve the desired operating
characteristics ~or an apparatus o~ given size and materials,
repeated use of that same loading in the fabrication of
~imilar units will result in apparatuses having essentially
the same operating characteristics. Moreover, such
reproducibility of operating characteristics will be obtainable
even though the stack height of one assembly may differ from
that of the next ~ecause o~ virtually indetectable variations
3d in the thlckness of the ~ultiple support members, and sometimes
even of the membranes, used in successive assemblies.
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According t~ the p~esent invention, the uniform
c~mpre$sive load ls applied to rigid plates which have flat,
parallel ~aces and which remain constantly parallel to each
other, the stack o~ membrane pleats and spacer elements being
disposed there~etween. It has been found that this disposition
promotes the uniform distribution of fluids witnin the pleats
of the membrane when the apparatus so formed is put to use.
Thus, according to the invention, rigid plates 12 and 13 are
maintained parailel to each other under a uniform pre-
established loading, and without regard to differences in the
spacing of such plates from one apparatus to another, and
are thereafter fixed to each other by connecting means bonded
to the opposite longitudinal side edges of the upper and lower
plates. Advantageously, the connecting means comprises a
plurality of rigid elements which extend vertically and are
bonded to the side edges of the plates adjacent the corners
thereof.
The connecting elements may take the form of bars,
rods, sheets, plates, etc., which extend from one plate to the
other adjacent the creases of the membrane. Such elements
may be stuck, sealed, melted, welded, soldered, brazed, potted,
cast, or the like, to form rigid links between the side edges
of the two plates. If desired, they may be integral with one
or the other of the two plates.
A preferred embodiment o~ the invention consists
in using fluid-conducting headers such as 17, 18, 19 as the
rigid connecting elements between the lower plate and the
upper plate. Each header has an inwardly-facing vertical
channel which communicates with all the pleats of the stack
on the side of the membrane facing that header and is otherwise
closed except for a port advan~ageously provided with a short
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pipe such as 2Q, 21, 22 to which a suitable tube may be
connected in ~ ~luid~tight manner. Such headers are bonded
to the s~de edges of the lower and the upper plates, for
exa~ple at the points 23, 24, 25, 26, etc., while the
assemblage ~s maint~ined under a predetermined, uniform, and
constant load. Since the headers are bonded to the plates,
rather than being mechanically latched to such plates, the
step of securin~ the headers may be easily achieved without
i~posing any~orces on the plates which might alter their
spacing or which might per~it any significant changes in such
spacing after the ~onding action is completed and the
assembled structure is removed from the press.
The desired construction of the apparatus is then
achieved by bringing about the peripheral fluid-tightness by
; lS means known per se to the art. For instance, it is possibleto introduce the assemblage (with the headers) into a mold
and to cast in the mold a fluid resin for enclosing that
assemblage. It is also possible to employ a box (equipped
with port openlngs for receiving tubes or pipes 20, 21, 22,
etc.), for example in two pieces, and to cast a fluid resin
around the assemblage inside the assembled box. Thus the
edges of the me~branes may be sealed over their whole length.
The apparatus has been described in a form
particularly adapted for use as a hemodialyzer provided with
- 25 four ports, two for blood and two for dialysate, for treatment
of blood. Alternatively, there may be provided one port
only for the exit of ultrafiltrate. In each of these cases,
the features described above improve the circulation of blood
or other ~luid and hence the efficiency of the apparatus.
This apparatus is also convenient for any other
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treatm,ent Q~ ~lood, for instance as ~ blQod ox~v~enator in
~n art~Ic~al lung.
Moreover, the terms "blood" and "dialysate" are
e~ployed herein ~erely by way of example and to identify any
f'luids flowin~ through the channels and ports, and are used
merely for convenience o~ exposition and are to be construed
- as including other fluids. Also other types of membranes or
folded sheets ~ay be emplo~ed, as dictated by the particular
fluids and by the nature of the desired transfer between the
fluids.
It is to be particularly emphasized that one of the
main advantages of the present invention is that it enables
one to manufacture a series of like devices which, because of
; the application of the same predetermined uniform load or
force during manufacture of each of the devices of the series,
will have essentially the same operating characteristics during
use, despite minute differences in the thickness of the
membranes and/or support members of each of the devices of
the series.
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