Note: Descriptions are shown in the official language in which they were submitted.
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This inVention relates ta fluid flow t~ansfer devices using
separatory membranes and fluid 10w manifolds at the inlet and outlet.
In constructing a fluid flow transfer device such as a hemodialyzer
that uses a pleated membrane, it is desirable to pot the membrane tips to the
interior of the housing on the blood side of the membrane to force the blood
down into the membrane folds and thereby prevent shunting of the blood from
inlet to outlet without being dialyzed within those folds. Such potting is
effectively done with an initially easily flowable material such as low
viscosity polyurethane. It is important, however, to keep the potting from
flowing into the blood inlet and outlet manifold areas and into the membrane
folds opposite those areas, or blood flow into or out of those folds will
be undesirably blocked and the dialyzer will have a reduced capacity.
We have discovered that by applying a thixotropic adhesive around
the manifold areas prior to potting and contacting the membrane tips with
the still-wet adhesive, we can provide a formed-in-place gasket that will
prevent liquid potting from entering the manifold areas or wicking into the
membrane folds exposed to those areas. Our invention thus prevents blockage
of the manifold areas and yields a more efficient fluid flow transfer
apparatus.
Thus, according to one aspect of the present invention, there is
provided in a method of forming a fluid flow manifold for a fluid flow transfer
apparatus having a pleated membrane stack and a housing, wherein said membrane
is folded and the fold edges form tips that are bonded to an interior surface
of said housing by a potting material that is introduced in a flowable state,
and wherein said housing has a channel portion formed along said interior
surface, said channel communicating through a fluid port to the exterior of
said housing, and said channel forming a manifold with said membrane stack,
the improvement comprising the steps of: applying a gasket material to said
housing interior surrounding said channel portion prior to bonding tlle tips
of said pleated membrane to said housing~ said gasket material being flowable
enough to conform to the shape of the membrane tips and to penetrate into the
; spaces formed between the tipswhile viscous enough to avoid wicking of itself
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along said spaces into the maniold area, that is, thixotropic, and placing
said membrane tips against said applied gasket material while said material
is still deformable, to cause said material to conform to said tips and to
penetrate far enough into said spaces between tips to prevent capillary
flow of subsequently-introduced potting material through said spaces, whereby
when said potting material is introduced it is prevented from blocking the
manifold area.
According to another aspect of the present invention, there is
provided in a fluid flow transfer apparatus having a pleated membrane stack
and a housing, wherein said membrane is folded and the fold edges form tips
that are bonded to an interior surface of said housing by a potting material
that is introduced in a flowable state, and wherein said housing has a channel
portion formed along said interior surface, said ch2nnel communicating through
a fluid port to the exterior of said housing, and said channel forming a
manifold with said membrane stack, the improvement comprising a formed-in-
place gasket adjacent said channel portion, said gasket being formed of a
material different from said potting material, said gasket conforming to said
interior surface and to said membrane tips, and said gasket protruding far
enough into the spaces formed between adjacent tips to prevent capillary flow
of potting material through said spaces into the manifold area and resulting
blockage of the area.
In particular aspects, our invention includes forming ribbed
portions around the manifold areas and placing the adhesive on the sides of
the ribbed portions remote from the manifold areas, and using silicone rubber
adhesive.
The invention will now be described in greater detail with refer-
ence to the accompanying drawings, in which:
Pigure 1 is a perspective view of a dialyzer utilizing the presently
preferred embodiment;
Figure 2 is a somewhat diagrammatic sectional view along 2-2 of
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11351~7
Figure 1;
Figure 3 is an exploded view of a portion of the membrane and
support netting of the dialyzer of Figure l;
Figure 4 is an enlarged perspective view of a portion of the
support netting of Figure 3;
i Figure 5 is a sectional view along 5-5 of Figure 1; and
Figure 6 is a greatly erlarged vertical sectional view like that
of Figure 2 of a portion of the membrane and support nettirg of the dialyzer
of Figure 1.
The embodiment shown in the drawings and its operation are now
described.
1. Embodiment
Figures 1 and 2 show dialyzer 10, which includes a two-part
housing comprising trough-shaped polycarbonate casing 12 and interfitting
polycarbonate casing 14, which is open at both longitudinal ends and has a
pair of longitudinal fins 16. Casing 12 includes inlet 18 and outlet 20,
both integrally molded therewith. Casing 14 includes integrally molded
inlet 22 and outlet 24. Inlets 18 and 22 and outlets 20 and 24 become char~
nels of steadily decreasing cross section when they enter their respective
casings. A pair of stub shafts 26, formed by mating semicircular portions
on casings 12 and 14, and a pair of cooperating stops 28 (only one is
shown in Figure 2), spaced equidistantly longitudinally from the right stub
shaft, permit rotatable, vertical mounting of the dialyzer on a bracket, for
degassing and normal operation.
Dialysis membrane 30, a Cuprophan (trademark of Enka Glanzstoff
AG) cuprammonium cellophane sheet having a generally accordion pleated con-
figuration and to which glycerin has been added as a plasticizer and humectant
for smooth processing, is squeezed between fins 16, and is sealed with poly-
urethane potting 32 along its outermost flaps to the outer faces of the fins.
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The folded upper tips of membrane 30, shown somewhat rounded in Figure 2~
are affixed to casing 12 by being anchored in polyurethane potting 32, there-
by forming a series of separate parallel fluid flow passages, indicated by
B in Figure 3, in the valleys above the membrane. Potting of the upper tips
prevents shunting of fluid directly from inlet 18 to outlet 20 without
entering passages B. Support netting 34, a nonwoven polypropylene mesh
(see the arrangement of its strands 35 in Figure 4) sold under the Du Pont
trademark Vexar, is also in the form of an accordion pleated sheet, and
is positioned within membrane 30 on the membrane side adjacent casing 14
(Figure 3). By this configuration, support netting 34 spaces apart the
underside faces of adjacent membrane walls with two layers of the netting
shown in Figure 4, and provides parallel fluid flow passages underneath the
membrane, indicated by D in Figure 3. Netting 34 is not bonded to either
casing, except at its longitudinal ends, as will be described hereinafter,
and unlike membrane 30 does not fold over fins 16.
Both membrane 30 and netting 34 are pleated along generally
parallel lines, and strands 35 run at 45 to those lines.
Casing 12 has a continuous peripheral ridge 50 that seats in
continuous peripheral groove 52 of shelf portion 54, which surrounds casing
14. When casing 12 and casing 14 are so interfitted, the tips of fins 16
are vertically spaced from the adjacent inner surface of casing 12 and from
ribs 36 running transversely on that surface, to avoid cutting of membrane
30 between the pointed fin tip and casing 12.
Longitudinal ends of membrane 30 and netting 34 are bonded to
casings 12 and 14 by pottirg 32 (Figure 5). Transverse ribs 36 (one shown
in Figures 2 and 5) of casing 12 space the folded tips of membrane 30 from
the casing ceiling to provide channels for flow of potting 32 during con-
struction of dialy~er 10, described hereinafter. Ribs 36 have arcuate por-
tions 56 which laterally space fins 16 from the angled and vertical sidewalls
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of casing 12 by tangential contact with fins 16 through membrane 30;
portions 56 perlnit the flow channels to extend from the central fluid chamber
between fins t6 to the side compartments between each fin and the corresponding
sidewall of casing 12. A continuous ridge of General Electric RTV 108
thixotropic silicone rubber adhesive 38 adjacent casing ribs 40 surrounds
the channel portion of outlet 20 (and in the same way inlet 18, though not
shown) and bonds to the membrane tips, to act as a formed-in-place gasket
in order to prevent flow of potting 32 into the channel area during conr
struction. The adhesive needs to be thixotropic so that it will not itself
wick across the membrane folds in the manifold area and thus block entrances
to passages B. Inlet 18 and outlet 20 thus cooperate along their channel
portions with membrane 30 to form inlet and outlet manifolds into and out
of the fluid passages indicated at B in Figure 3. Likewise inlet 22 and
outlet 24 cooperate along their channel portions with membrane 30 on its
underside to form inlet and outlet manifolds into and out of the fluid
passages indicated at D in Figure 3.
In constructing dialyzer 10, one pleats a sheet of membrane 30,
pleats a sheet of netting 34, and combines the two by placing each fold of
netting within a corresponding fold of membrane (Figure 3). The resultant
membrare-netting stack is squeezed together and placed in a casing 14
between fins 16, with each of the two outermost flaps of membrane 30 folded
over its respective fin. Each outermost flap is then sealed to the outer
face of the adjacent fin 16 with polyurethane potting 32. Casing 12 is then
provided, and two ridges of silicone rubber adhesive 38, each having a
weight of approximately one gram, are then applied around the outer edges
of the channel portions of inlet 18 and outlet 20 of casing 12, adjacent
ribs 40 and on end shoulders 41 (one shown in Figure 5). Casing 14 is then
interfitted with casing 12. Ridge 50 is wetted with solvent and then pressed
- into groove 52, to which it bonds on drying. A ramp portion 48 running along
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the base of each fin 16 serves to guide ridge 50 into groove 52. The
interfitting is done while the silicone adhesive 38 is still wet so that it
will seep a short way (about 1/16 to 1/8 inch) into the membrane folds to
prevent wicking of polyurethane potting in the folds in the manifold area
and consequent undesirable blockage of fluid flow into or out of the folds.
The membrane and netting longitudinal ends are then potted in polyurethane
32, which is applied through holes 42 in casing 14 at each end thereof by
a needle inserted through tapes (not shown) placed on raised portions 58
and covering the holes 42 (only one hole is shown in Figure 5). Dialyzer
10 is held vertical during this process, with the end to be potted at the
bottom. After curing of the potting at the end, the dialyzer is rotated
180, with the other end at the bottom, ready to receive its potting. Potting
seeps into the netting side of the membrane but not generally into the other
side (Figure 5). Holes 42 are sealed with the hardened potting, and the
tapes are removed.
The potting of the membrane tips and flaps to casing 12 now takes
place. Dialyzer 10 is positioned horizontally with the membrane tips to
be potted below the membrane body and horizontally aligned with casing 12
on the bottom (inverted from Figure 2). Plugs (not shown) are placed in
inlet 22 and outlet 24, and a needle is inserted through one of the plugs
to apply 300 mmHg positive pressure from a pressure source through netting
34 against the face of membrane 30 adjacent casing 14. The pressure source
is removed after pressurization is complete, and a pressure gauge is used
to check for leaks. The plug maintains the pressure. Inlet 18 and outlet
20 are open to atmospheric pressure. Approximately 60cc of polyurethane
potting 32, which comprises an initially liquid mixture of~Polyol 936 and
~orite 689, a urethane prepolymer, both manufactured by N. L. Industries,
Bayonne, New Jersey, is then pumped into dialyzer 10 through hole 44 (Figure
2) in one sidewall of casing 12. The potting flows into the side compartment
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formed between the sidewall of casing 12 and one fin 16 through channels
between arcuate rib portions 56, down into the trough of casing 12, trans-
versely through channels formed by 0.06 inch deep transverse ribs 36 (Figure
5), and again through channels between arcuate portions 56 up into the other
side compartment between the other sidewall of casing 12 and the other fin
16. Arcuate portions 56 prevent fins 16 from flaring outward to contact
the sidewalls of casing 12 and thereby block potting Mow into or out of
the side compartments. A pair of pinholes (not shown) in casing 14, one
adjacent inlet 22 and the other adjacent outlet 24, let air escape as the
potting is pumped in. The potting settles uniformly on the inner surface
of casing 12 and reaches the same level in each side compartment. Because
of the positive pressure maintained on the opposite side of membrane 30,
passages B are closed up, and the potting cannot wick or otherwise flow
up between the folds. After a curing time o~ 60 minutes, one of the plugs
is removed to permit a vacuum to be applied to the membrane side that ini-
tially received the higher pressure. Ten dialyzers 10 are connected in
parallel to a vacuum pump through a 25 gauge one inch long needle acting as
a pneumatic resistor, and the evacuation produces a negative pressure from
20 to 24 inches of mercury. The resistor chosen gives a desirable rate of
evacuation. If evacuation is either too fast or too slow, unwanted bubbles
; will form in the polyurethane potting.
As a result of the evacuation, the folds of membrane 30 are drawn
back from each other, enlarging the spaces between the folds, and are drawn
tightly and even crushed against the folds of netting 34 (Figure 6), which
then support the membrane and prevent it from pulling away from the inner
surface of casing 12. The nowimore viscous potting can seep up through the
entrances to the spaces between the membrane folds and into those spaces
to increase the bonding surface area provided by the membrane tips and
thereby further improve the casing-membrane bond effected by the potting.
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However, the potting is too viscous to seep undesirably far into those
spaces so as to interfere with flow passages B. Curing time between the
pressure and evacuation steps is important; if the time chosen for the par-
ticular potting compound is too short, the potting will not be viscous
enough and will seep too far into the spaces between the membrane folds
when the vacuum is applied, thus interfering with fluid flow passages B.
If the time is too long, unwanted bubbles will form in the potting because
of its increased viscosity.
After further curing, dialyzer 10 is ready for use.
Dimensions of dialyzer 10 are as follows. Its housing is approxi-
mately 12 inches by 3 5/8 inches by 2 inches. Membrane 30 has a dry thick-
ness of 13.5 microns and an actual surface area of approximately 1.54 m2.
Netting 34 has 16 strands per inch and a mean thickness of 0.022 inch. Both
membrane and netting have 66 folds ("folds" meanirlg adjacent pairs of me~
brane or netting walls joined along a crease), which is equivalent to the
number of upper tips of membrane 30 affixed to casirg 12 (far fewer folds
are shown in the somewhat diagrammatic view of Figure 2). There are 65
fluid flow passages B along the folds. The channel portions of inlet 18
and outlet 20 are approximately 2 3/4 inches long, 3/8 inch wide and 5/32
inch deep adjacent the tubular portion of the inlet or outlet, which acts
as a port, and 3/8 inch wide and 1/16 inch deep at the narrower channel
tip. There are seventeen ribs 36, spaced about 1/2 inch apart, and seven-
teen corresponding pairs of arcuate portions 56. Additionally, there is
a pair of arcuate portions 56 (not shown) between each longitudinal end of
casing 12 and inlet 18 and outlet 20.
2. Operation
When used as a hemodialyzer, dialyzer 10 operates as follows.
Blood tubing is connected to inlet 18 and outlet 20, and dialysate tubing
is colmected to inlet 22 and outlet 24. Dialyzer 10 is mounted vertically,
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11351~7
with inlet 18 and outlet 24 on top. Blood is introduced into inlet 18,
Mows along its channel portion, and then, partly because of the potting
32~ flows into the spaces B between the folds of membrane 30 and in the
general direction indicated by arrows in Figure 3, until it is collected
in the channel portion of outlet 20 and then passes out of dialyzer 10.
Dialyzing fluid or dialysate is introduced into irlet 22 and flows along
its channel portion where it is distributed into all of the dialysate flow
passages D (Figure 3), and flows in the general direction indicated by
arrows in Figure 3, countercurrently with blood flow. It has been found
that the membrane tips adjacent casing 14 dolnot need to be potted to it,
when dialysate is introduced on this side. Dialysate is collected in the
channel portion of outlet 24 and then passes out of dialyzer 10, from which
it is collected for regeneration or disposal. Dialysis occurs across membrane
30. Blood is introduced into its inlet port with use of a pump while dialy-
sate is introduced into its irlet port at a lower pressure. Thus in addition
to removal of unwanted substances from the blood by dialysis, dialyzer 10
effects removal of water from the blood through membrane 30 because of the
pressure difference across the membrane.
In normal operation dialysate flows upward because of the vertical
positioning of dialyzer 10, and the dialysate flow paths D (Figure 3) are
constantly being degassed as dialysate flows in that direction. The blood
flow paths B (Figure 3) are degassed prior to dialysis by inverting dialyzer
10, introducing a saline primirg solution, and having that solution flow
upward for a predetermined time.
An enlarged view of the arrangement of support netting 34 and
membrane 30 is shown in Figure 6. Potting 32 has seeped somewhat into the
space between the folds shown, to increase the bonding area and hence im-
prove the bond between membrane tips and the potting. The pleated sheet con-
figuration of nettirg 34 provides a spacer between adjacent membrane folds
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that is two layers thick. The effect i9 to increase the dialysate flow
passages and to lower the dialysate pressure drop through the dialyzer. The
double layer of netting tends not to entrap air bubbles, which on accumulating
would impede dialysate flow and increase the pressure drop. Instead the
bubbles desirably wash on through. As to blood flow, strands 35 ten~ to
pinch adjacent folds of membrane 30 at spaced points designated P in Figure
6. Between points P portions of folds of membrane 30 sag into inter-strand
spaces of netting 34 to create separate blood flow passages 46. Pressure from
the blood helps keep the membranes apart for blood flow.
Dialyzer 10 provides the following specifications and results
when used in hemodialysis:
Pressure DroPs
Blood (at flow rate, QB~ of 200 ml/min. and - 15 m~Hg
Transmembrane Pressure (TMP) of 100 mmHg)
(Hematocrit = 30%)
Dialysate (at flow rate, Qn, 500 ml/min. and 2 mmHg
TMP of 100 mm~g~
In Vitro Clearances *
- (QB = 200 ml/min.
QD = 500 ml/min.TMP = 100 mmHg)
Urea 140 ml/min.
Creatinine 120 ml/min.
B-12 31 ml/min.
Ultrafiltration Rate (in vitro) * 3.6 ml/hr/mmHg TMP
Blood Volume
100 mmHg TMP85 ml
200 mmHg TMP120 ml
Dialysate Volume730 ml
Maximum TMP500 mmHg
* Performance subject to variations in Cuprophan membrane.
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Variations and Modifications
The fluid flow manifold of the present invention has other uses
beside that in hemodialysis; for example, it can be used in laboratory di-
alysis.
Other embodiments of the invention will be obvious to those
skilled in the art.
Other Inventions
The method of injecting liquid potting material into a housing for
uniform potting of the membrane tips to the housing was the invention of
Thomas E. Goyne.
The fin-membrane sealing construction was the invention of Donn D.
Lobdell.
The pressure-evacuation two-step method for anchoring the membrane
tips to the casing was the invention of Dennis J. Hlavinka, and is the sub-
ject matter of Canadian patent application Serial No. 300321 filed on`April
3, 1978,
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