Note: Descriptions are shown in the official language in which they were submitted.
1118367
The present invention relates broadly to a mass
transfer apparatus including a semipermeable membrane element
folded several times upon itself. For convenience, it is
described hereinafter for the particular case where such an
apparatus is used for the treatment of blood by hemodialysis
and/or by ultrafiltration; and more particularly, such an
apparatus which is of relatively small size, economical, suit-
able to be used at home, and discarded after use.
The invention relates more particularly to an appara-
tus comprising, inside of a fluid-tight casing provided with
the necessary ports for introduction and evacuation of blood,
dialysate and/or ultrafiltrate, a semipermeable membrane
folded upon itself to form a stack of accordion pleats to
thereby define two fluid chambers, with support members or
spacers disposed within all those pleats which are on one
side of the membrane.
Apparatus of this general type is known: for ex-
ample, see U.S. Patent 3,788,482 to Markley. With the usual
hemodialyzer membranes of relatively low middle molecule
clearance characteristics, however, only narrow pleats can
be used, as otherwise blood enters and leaves with difficulty
and does not become uniformly spread over all the surfaces
of the pleats of the membrane. With membranes allowing better
performance, particularly in ultrafiltration, such as the
polyacrylonitrile membranes described in British Patent
1,327,990, it becomes still more difficult to secure the
penetration of blood through the apparatus with uniform
distribution over the entire membrane and with a flow having
an acceptable low pressure drop.
For solving these problems, some solutions have
been already proposed. Thus, U.S. Patent 3,780,870 to Esmond
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suggests the provision of two support members folded upon
themselves, thereby forming four superposed layers in the
compartments filled with dialysate with only one of those
support members extending to the ends of the apparatus.
Additional supports are disposed in the blood chamber. This
design provides some channels at each end for the flow of
blood. On the other hand, the size of such an apparatus for
a given overall surface of membrane is greatly increased and
the apparatus is not sufficiently economical. Besides, blood
of which a greater volume is necessary comes directly into
contact with the support members disposed at the ends of the
apparatus. As these support members are generally constituted
by screens which may have sharp edges on at least two opposite
sides, it is necessary to take care (as indicated in U.S.
Patent 3,565,258 to Lavender et al) not to risk coagulation
of the blood. See also U.SO Patents 3,862,031 and 3,757,955
to Leonard.
It is an object of the present invention to provide
an apparatus of the kind indicated that eliminates or at least
substantially minimizes problems and disadvantages of prior
art devices.
More precisely, it is 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, which requires only a limited volume of
blood within the apparatus, and which nowhere permits the
blood to come into contact with sharp edges of support
members.
In accordance with the present invention, a fluid
flow apparatus is provided which has a semipermeable membrane
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folded to form a stack of accordion pleats defining two series
of fluid chambers extending inwardlyfrom opposite sides of
said stack, and planar support members disposed within the
chambers of only one of said series ~on the dialysate side
where the transfer apparatus is a dialyzer), the planar support
members consisting of a plurality of discrete open-mesh inserts
having cut-outs adjacent opposite ends thereof to facilitate
the flow of fluid into and out of the chambers not containing
such support members. In a modified form of the invention, a
pair of superimposed support members or mesh inserts is dis-
posed within each of the chambers of the one series and, in
a further modification, only one of the inserts of each such
pair is provided with such cut-outs.
The present invention further provides a mass trans-
fer apparatus for use in hemodialysis and ultrafiltration
comprising a housing; a semipermeable membrane disposed with-
in said housing, said membrane being folded to form a stack
of accordion pleats; a plurality of discrete perforated sup-
port members associated with the membrane, at least one
support member being disposed within every pleat on one side
only of the membrane, said membrane.being so constructed
and arranged that two separate fluid chambers for blood and
dialysate are thereby formed, said dialysate chamber being
on said one side of said membrane and said blood chamber
being on the other, and ports directing the flow of blood
and dialysate into and out of the respective fluid chambers,
the improvement wherein said support members are provided
with cut-out openings in substantial alignment with at least
one of said ports for directing the flow of blood, said cut-
out openings being situated and arranged such that whenblood flows into and out of the blood chamber said semi-
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permeable membrane is caused to collapse into said cut-out
openings under pressure of said blood, thereby providing, in
use, a flow path of enlarged cross-section for the blood in
said blood chamber and thereby facilitating the flow of blood
in said blood chamber.
A still better understanding of the features of the
present invention and its inherent advantages will become
apparent from the following description and reference to the
accompanying drawings in which:
Fig. 1 is a perspective view of a hemodialyzer
built in accordance with the present invention, partially
broken away to expose its interior structure;
Fig. 2 is a plan view of the hemodialyzer of Fig. 1,
partially in section, and with the membrane being drawn aside
to expose one support member according to the present inven-
tion;
Fig. 3 is a somewhat schematic vertical transverse
sectional view of the hemodialyzer taken along the line 3-3
of Fig. 2, showing a first embodiment of the present invention
which comprises two support members disposed between every
pair of pleats;
Fig. 4 (located in the first sheet Gf drawings, with
Fig. 1) is a somewhat schematic transverse sectional view taken
along the line 4-4 of Fig. 2, showing that only one of the
two support members is provided with a cut-out and that the
membrane is supported in the region of the cut-out only by
the other support member,
Fig. 5 is an enlarged somewhat schematic sectional
view taken along the line 5-S of Fig. 2, showing the flow
pattern at one end only of the hemodialyzer, and especially
the enlarged flow path for the blood provided by the cut-out;
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Fig. 6 is a view similar to Fig. 5 but of a second
e~bodiment of the present invention, which comprises cut-outs
in each of the two support members disposed between every pair
of pleats;
Fig. 7 is a view similar to Fig. 5 but of a third
embodiment of the present invention, which comprises only one
slotted support member disposed betw~en every pair of pleats;
and
Fig. 8 is a partial plan view of the right end of
another embodiment of the hemodialyzer of Figs. 1 and 2,
broken away, the membrane being drawn aside to expose one
support member according to the present invention.
Referring now to the drawings in detail, it will be
seen that there is illustrated in Fig. 1 a hemodialyzer
construction in accordance with the present invention and
identified by the numeral 10. This hemodialyzer includes a
housing, preferably rectangularr generally identified by the
numeral 11, and a core, generally identified by the numeral
12. This hemodialyzer is provided on one side with a blood
inlet port 13 and a blood outlet port 14 and on the opposite
side with a dialysate inlet port 15 and a dialysate outlet
port 16.
The core is formed of a single length of a flat
semipermeable membrane 17 which is folded into a large number
of closely spaced pleats which extend along the length of
the housing and, as is most clearly seen in Figs. 3 and 4,
undulates back and forth across the width of the housing 11
and between the walls thereof. The two ends of the folded
membrane are attached to or anchored in a conventional sealing
plastic or potting compound 26.
The semipermeable membrane may be of any desired
type permitting the diffusion of water and/or low and middle
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molecular weight substances (e.g., urea and vitamin B12) from
blood to another fluid through the membrane under conditions
of relatively low transmembrane pressures. As suitable examples
one may mention "Cuprophan"* (a commercially available form
of regenerated cellulose) or a polyacrylonitrile membrane as
described in the British patent cited above or a polycarbonate
membrane, the last two having a permeability of at least .05
cc H2O/minute/sq. meter/mm. Hg. The present invention al-
though adapted for use in hemodialysis in connection with
"Cuprophan"* membranes, is especially well adapted for use
in connection with polyacrylonitrile or polycarbonate mem-
branes where the optimum transmembrane pressure differential
is lower than that for "Cuprophan"* and especially for ultra-
filtration.
Support members such as 18 and 19 are disposed with-
in all those pleats which are on one side of the membrane 17,
while those pleats on the opposite side of membrane 17 do not
contain support members. The support members such as 18 and
19 are disposed in those pleats on the side of the membrane
17 which communicates with the dialysate inlet port 15 and the
dialysate outlet port 16. Owing to this arrangement, only the
dialysate (and never the blood) comes into contact with any
support members.
The two perforated support members, such as 18 and
19, are preferably non-woven plastic mesh supports of per se
conventional design and configuration. As an example of a
suitable material for the support members, one may employ
"Vexar"** which is a commercially-available polyolefin mesh
material. Such a thermoplastic mesh may be readily fabricated
for the support members by criss-crossing one set of filaments
of polypropylene or the like with another set of similar
* Trademark
** Trademark
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~11836~7
filaments at an angle of approximately 90 to each other, and
heat-sealing the juxtaposed filaments to give the desired open
mesh arrangement having a thickness substantially equal to the
diameter of the filaments except at the cross-over points
where the thickness (due to the heat sealing) will be somewhat
less than twice that of the filaments. In general, the total
thickness of such a mesh should be of the order of 15 to 50
mils. The resulting structure assures good support for the
semipermeable membrane at the numerous cross-over points while
affording intermediate portions within which the membrane may
collapse to thereby provide ample paths to facilitate the
substantially uniform distribution and flow of blood on the
blood side of the membrane.
The edges at both ends of the accordion-folded semi-
permeable membrane 17 are sealingly embedded within plastic
potting material (not shown). Similarly, both longitudinal
sides of the membrane (i.e., the edges at~pposite ends of
the stack) are sealingly embedded within a plastic potting
material 26, so that the membrane defines within the housing
two separate chambers. The potting material may be a
conventional epoxy or polyurethane blood-compatible material
having a relatively short curing time at ordinary temperatures.
After curing, the potted assembly is generally disposed with-
in a separate housing 11 made of any suitable material such
as polycarbonate, polystyrene, polymethylmethacrylate or the
like or, where the header cavities are part of the housing 11
as shown, the potting of the stack and its sealing attachment
within the housing may be performed simultaneously.
The interior walls of the unsupported pleats of the
semipermeable membrane are essentially in contact with each
other over the largest part of their surface in the absence
1~18367
of a fluid and therefore these pleats are essentially closed
when the apparatus is not in use. While in the drawings
(Figures 1 and 3-7) spaces have been shown between the two
interior walls of the unsupported pleats for the sake of
clarity, it should be understood that in fact the opposing
surfaces are essentially in contact and the unsupported pleats
are normally closed. These unsupported pleats are capable
of opening under a fluid pressure so that, when blood is
introduced into the hemodialyzer through blood inlet portion
13, it flows into the unsupported pleats and opens them to
permit the flow of blood therein. The flowing blood within
the hemodialyzer is always maintained at a pressure slightly
greater than the pressure of the dialysate (e.g., by applying
vacuum to the dialysate side) in order to drive water from
the blood into the dialysate across the membrane, as it is a
normal kidney function to remove excess water from the blood
by ultrafiltration, and this greater pressure of the blood
relative to that of the dialysate causes the separation of
the normally closed unsupported pleats, thereby opening
passages for the blood flow. As indicated above, some other
components may also pass through the membrane.
Similarly, Figures 1 and 3-7 show the membrane 17
spaced from support members 18 and 19, and the paired support
members in each fold or chamber spaced from each other; how-
ever, it is to be understood that such spacing is shown only
for clarity of illustration and does not exist in a fully
assembled apparatus.
According to the prior art, when the blood is
introduced into the hemodialyzer, with a positive difference
of pressure between blood and dialysate, the membrane 17
distends into the spaces in the mesh supports 18 and 19,
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thereby opening the closed unsupported pleats and providing
passages for blood flow through the hemodialyzer. But, as
said before, with the usual hemodialysis membrane only narrow
pleats can be used, as otherwise blood distribution is not
uniform within the pleats, being greater on the side of the
dialyzer near the blood ports and diminishing towards the
side having the dialysate ports. With membranes allowing
better performance, particularly in ultrafiltration and middle
molecule clearance, i.e., membranes generally thicker and
stiffer than the earlier membranes of lower water permeability
and middle molecule clearance, it becomes still more difficult
to secure the penetration of the blood in and through the
apparatus, as well as its uniform distribution over the entire
surface of the membrane and its flow with an acceptably low
pressure drop and acceptable level of ultrafiltration. These
stiffer and thicker membranes tend to form folds of greater
radius at their leading edges, with the contacting leading
edges at adiacent folds forming an obstruction to throttle
blood flow even under negative dialysate pressure.
It has now been found that an improved flow of blood
can be obtained if at least one of the support members within
each pleat (on the dialysate side) is provided with at least
one cut-out such as 20 and 21 opening on the same side of the
support member and preferably in front of the inlet 13 and/or
the outlet port 14 for blood -- see Fig. 2. In this way the
membrane billows out as it were into each cut-out, such as 22
and 23, for example, downwardly into such cut-outs as shown
in Fig. 5, to form a blood flow path of enlarged cross-section,
from which blood is substantially evenly distributed as from
a header or manifold, over substantially the entire surface
of the membrane. The throttling effect at the leading edges
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~1183~;?7
of the folds (on the blood side) which would otherwise occur,
particularly with use of the relatively stiff membranes of
higher middle molecule clearance characteristics, is thereby
substantially eliminated or at least greatly reduced.
Dialysate enters the hemodialyzer through dialysate
inlet port 15 and distributes itself across the width of the
supported pleats. Dialysate flows within the supported pleats
according to the broken-line arrows f (see Fig. 2), along the
length of the assembly toward dialysate outlet port 16, from
which it exits from the hemodialyzer.
Blood enters the dialyzer through blood inlet port
13 and diStributes itself in parallel across the width of the
unsupported pleats, opening them for flow in the recess such
as 22 as described above. The blood then flows within the
unsupported pleats in a direction generally parallel to the
creases of the pleats along the length of the housing accord-
ing to the solid-line arrows F; see Figs. 1 and 2. The blood
flows on the opposite side of the semipermeable membrane 17
from the dialysate, and preferably countercurrently to the
flow of dialysate, toward the recess 23 and the opposite end
where it exits from the hemodialyzer through blood outlet
portion 14.
Under transmembrane pressure, the portion of the
membrane in contact with a slotted support member 18 bulges
into the cut-out 22 (or 23) and into contact with the unslotted
member 19 contiguous with member 18. Therefore, the paired
support members 18-19 in each pleat or chamber on the dialy-
sate side of the dialyzer accurately control the size of the
enlarged transverse blood flow paths shown most clearly in
Figs. 2 and 5. In that connection, it is particularly sig-
nificant that the planar support members 18 and 19 are
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separate or discrete elements without folds or other edge con-
nections which might otherwise cause slight but unacceptable
variations in their combined thickness and prevent the support
members of the entire stack from assuming precisely parallel
relation to each other. Such parallelism is essential in
achieving control and reproducibility in the flow of fluid
through the dialyzer and in accurately establishing the
pressure drop associated with such flow.
One may have other embodiments falling with the
spirit and scope of the invention. Thus, according to this
invention, each of two support members may have a cut-out,
opening on the same side, in front of the corresponding ports.
Preferably these cut-outs are located one above each other
(see Fig. 6). According to this embodiment, dialysate cannot
always easily flow longitudinally between the deeper recesses
formed by the membrane, but the passage for blood is increased.
This embodiment therefore is of special interest with rela-
tively thick and/or relatively stiff membranes.
Another embodiment is shown in Fig. 7, wherein only
o~e support member is introduced within every pair of pleats
of the membrane. Each support member is provided with a cut-
out near each of its ends and opening on the same side. The
membrane is flattened against each support member and against
itself in front of the cut-out, and thus the desired enlarged
passage for blood is provided on the blood side of the membrane.
The cut-outs extend for at least a significant part
of the width of the support member. Thus the length of the
cut-outs is at least about 0.040 of an inch and may be as
great as 9/10 of the width of the support member, although
these exact limits are not critical. Preferably, the cut-outs
extend over the greater part of the width of the support
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members. The average width of the cut-outs is from about 1/lO
to 1 inch.
The support members, such as 18 and l9, may have any
desired dimensions, although a particularly useful configura-
tion is represented by a length of about 12 3/8 inches, a
width of about 2 3/4 inches, and a combined thickness for each
pair of about 3/64 inch, with cut-outs about 3/8 inch x 2
3/16 inches spaced about 7/8 inch from both ends.
Generally, the apparatus is symmetrical with respect
to the transverse vertical plane P (see Fig. 2) passing through
the center of the apparatus, and the cut-outs in the support
members are also generally symmetrical with respect to this
plane.
As shown in Fig. 2, the ports 13 and 14 for the blood
communicate with the inside of the apparatus via enlarged
channels such as 24a and 25a provided by the special shape of
the wall of the housing, over the whole height of the core 12,
thus constituting manifolds for the flow of blood to and from
the blood side of the membrane. As there shown, the cut-outs
20, 21 are widened at the edge of the support member 18 to
about the same width as channels 24a, 25a, thereby enabling
the blood to enter and leave the blood side via relatively
large regions 22 and 23 resulting from the collapse of the
membrane into the cut-outs as shown in Figs. 5, 6 and 7.
The channels 24b, 25b which are in communication
with the dialysis ports 15 and 16 insure an even better
distribution of dialysate over the whole height of the appara-
tus.
The axes of the dialysis inlet and outlet ports
may be substantially in registry or slightly out of registry
with the ends of the cut-outs in the support members. Thus,
:
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Fig. 8 shows such a modification (right end only for
simplicity) where the axes of the ports are displaced slightly
outwardly with respect to the ends of the cut-outs. The
slight displacement may instead by slightly inwardly.
The support members, or spacers, used in this
apparatus may be of various types per se well known in the
art for maintaining a suitable spacing between adjacent folds
and yet providing a minimum impediment to flow of dialysate.
They are preferably formed of a plastic non-woven mesh made
from two layers of threads and heat-sealed, each layer being
in a different plane.
Two separate support members or only one support
member may be introduced within single pleats of the semi-
permeable membrane. In any event, such discrete support mem-
bers are located in the pleats on only one side (the dialy-
sate side) of the membrane, do not come into contact with
the blood, and result in a dialyzer which is remarkably
compact and efficient. As already described, such efficiency
results in a large part from the slotting of the members
which permits substantial blood flow with more uniform
distribution and at a relatively low pressure drop, without
the necessity (and undesirable consequences) of providing
spacers in the folds on the blood side of the membrane.
The cut-outs in the support members may be formed
by various means per se well known in the art, for example,
by cutting, punching, sawing, melting and/or dissolving in
a suitable solvent.
The apparatus has been described in a form partic-
ularly adapted for use as a hemodialyzer provided with four
ports, two for blGod and two for dialysate, for
of blood. Alternatively, there may be one port only for the
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exit of ultrafiltrate. In each of these cases, the features
described above improve the circulation of blood or other
fluid and hence the efficiency of the apparatus. This appara-
tus is also convenient for any other treatment of blood, for
instance, as a blood oxygenator in an artificial lung.
Moreover, the terms "blood" and "dialysate" are
employed herein to identify broadly any fluids flowing through
the channels and ports, and are used merely for convenience
of exposition and are to be construed as including other
fluids. Also other types of membranes or folded sheets may
be employed, as dictated by the particular fluids and by the
nature of the desired transfer between the fluids.
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