CA1046426A - Plate dialyzer with asymmetrically tensioned membrane - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A diffusion device has a plurality of stacked plates and overlying membranes with the plates defining a plurality of rows of spaced projections of uniform height to form flow channels. The membranes overlying the plates are selectively tensioned in one direction with respect to other directions over the projections. The center-to-center spacing of the projections in the one direction is greater than in a direction transverse thereto.

Description

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This invention relates to a plate dialyzer with membranes located between the plates.
Dialyzers have an extensive field of use. They are used for separating solvent-containing liquids, particularly for separa-ting colloids from molecularly dispcrscd smaller substances which are contained therein. When differently constructed, these plate dialyzers can also be used for exchange between liquids and gases, for example, as artificial lungs; for gas exchange, for example, as artificial gills; or as heat exchangers between two media capable of flowing, depending upon the selection of the m0mbranes which separate the media taking part in the material exchange or heat exchange.
A special field of use for platc dialyzers is that of extra-corporeal hemodialysis. In that case, the semipermeable mem-brane takes over the task of the physiological filter of the glomerulus capillaries. According to the laws of osmosis and diffusion, an exchange of material then takes place between, on the one hand, a blood film applied to one side of the membrane and, on the other hand, a scavenging solution flowing past the other side of the mem-brane. This use of a plate dialyzer as an artificial kidney is becoming more and more important at the present time, and for that reason, hereinafter special refcrence will be made to a blood dialyzer. However, the devices of this invention are also intended for use as blood oxygenators and for other uses not involving blood.
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3L~Z6 An object o~ the pre~nt invention i5 to climinate drawbacks of prior art constructions through the provision of a plate dialyzer of greatly simp].ified construction which provides improved diffusion characteristics by improvlng the flow characteristics of blood and dialysis solution passing through the device, and providing ease and reliability of manufacture.
This application is a division of copending Canadian application Serial No. 190,16~ filed January 15, 1974.
The invention as defined in the above-identified parent application provides, in a diffusion device, a stack of plates separated by semi-permeable membranes to provide a pair of separated, isolated flow paths through the diffusion devicé on opposite sides of the membranes, the plate having a membrane-supporting profiled surface co~prising a plurality of rows of upstanding projections, in which the membranes are disposed across the plates over the projections while stretched in one direction, the spacing of the centers of the projections in rows in the general direction of stretching being greater than .~.
the center-to-center spacing of the projections in rows trans-verse to the general direction of stretching to prevent undue sagging of the membrane upon wetting in the transverse direction while permitting lo.w flow resistance across the plates, the sur~ace also comprising a plurality of support ridges extending in continuous, uninterrupted fashion across the plate in the general direction of the flow paths to abut corresponding support ridges on an ad~acent plate o the 9tack to control the spacing between facing plates.
On the other hand the invention of this application _ 3 dap/~?

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~)4~;Z 6 provides, in a diffusion device comprisiny a plurality o stacked plates and overlying membranes, the plates defining a plurality of rows of spaced projections o~ uniform height for forminy flow channels, in which the memhranes overlying the pla-tes are asymmetrically tensioned in one direction with respect to other directions over the projections, the center-to-center spacing of the projections in the one direction being grea-ter than the center-to-center spacing of the projection in a direction transverse to the one direction.
In the drawings, preferred embodiments of this invention are illustrated. The particular embodiments are improvements on the dialyzer disclosed in United States Patent No. 3,730,350, and except as otherwise indicated herein, can be manufactured in accordance with the teachings of that patent.
Figure 1 is a perspective view of a preferred embodiment of the dialyzer of this invention in an intermediate state of manufacture of the casing Figure 2 is an enlarged, partial side elevational view, taken partly in section, of the dialyzer of ~igure 1 after complete assembly.
Figure 3 is a full side elevational view with portions broken away of the dialyzer of Figure 1 after compiete assembly.
Figure 4 is a diagrammatic view showing the relationship of a plate used iIl the dialyzer of Figure 1 and its overlying membrane, and the respective typical flow paths of dialysis soluti~n and blood.

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' : ' , -1046~26 Flgure 5 is a plan vlew of a preferred plate deslgn used ln the dlalyzer of thls lnventlon.
Figure 6 ls a diagrammatlc view of a stack of plates and assoclated membranes.
Figure 7 (appearing on the same sheet of drawings as Figure 1) i9 a sectlonal vlew taken along llne 14-14 of the stack of plates of Figure 6, with the respective parts slightly vertically separated for purposes of clarity.
Figure 8 is a partial, greatly enlarged plan view of one corner of the plate of Figure 5.
Figure 9 is a plan view of another preferred embodi-ment of a plate for use in this invention.
Figure 10 is a greatly enlarged perspective view of a portion of the edge of the plate of Figure 9 and a fragment of overlying membrane.
Figure 11 is a greatly enlarged plan view of one corner of the plate of Figure 9.
Figure 12 is a transverse sectional view of another embodiment of a dialy~er essentially identical to that of Figure 1, but with a different plate design.
Figure 13 is a diagrammatic plan view of one corner of the stack of plates of the device of Figure 12, showing in phantom how ridges of an ad~oining facing plate are positioned with respect to the ridges of the plate shown.
Figure 14 i9 a sectlonal vlew taken through the plates of the device of Figure 12, showing the relatlonshlp of the membranes and respective ridges of the plates.
Figure 15 (appearing on the same sheet of drawings as Figure 12) i8 an enlarged transverse diagrammatic sectional view showing the shape of the blood manifold in the device of Flgures 1 and 12.

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Figure 16 (appearing on tha sams sheet of drawlngs as Flgure 12) 18 a fragmentary plan vlew of che inslde corner of a shell used to enclose the plates in the device of Pigures 1 and 12.
~ igure 17 tappearlng orl the same sheet of drawings as Figure 13) 19 an elevatlonal vlew, taken partly in section, of a modlfied dialysls of this invention.
The stacked plate diffusion device of this applica-tlon is partlcularly capable of exhibiting a high efficiency of diffusion, so that liquid such as blood passed through the device can be essentially completely processed by a single pass through the device. This i8 accomplished because the device of this invention can be designed with an extremely thin flow path for blood, slnce the profiled surface on the stack of plates may have flow channels which are no more than 0.5 mm. and even less in depth. Also, the dialyzer of this ~nvention can be fabricated in a manner suitable for supporting ultrathin membranes, which will accelerate the diffusion process in a manner unavailable to the designs of the prior art.
Referring to the diffusion device of Figures 1 through 9, a stack of plates and membrances is assembled in the manner generally de~cribed in U.S. Patent ~lo. 3,730J750, and then placed between a pair of hollow shells 30, 32 which may be of molded plastic. Shells 30, 32 face together to define a chamber inside, the parting line between the two shells being brscketed by a pair of flange6 34, 36.
Prlor to insertion of tha ~ack of plates and meu~branes (portions of which are illustrated in Figure 6), 30 the stack of plates is compressed, desirably at a pressure of about 14 to 28 kg. per square cm., to cause the facing rear sides of the plate6 and the membrane ends batween them t~p/~

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~L0~69~26 to become pressed to~ether, to prevent the passage of significant amount~ of fluid between the facing rear sides, The above pressure ~alues are particularly effective for rectangular plates having a length of about 12 cm. and a width of about 6 cm., being about 1 mm.
in thickness, and being made of polystyrene plastic with adjoining ultrathin membranes of about 10 microns thickness. When the above dimensions are significantly varied, the optimum pressure on the stack of plates and membranes to achieve the desired effect above may also change.
The stack typically has been about 100 and lS0 separate plates and overlying membranes.
A relatively thick pressure plate 37 is placed at each end of the stack of plates, preferably prior to the pressure step, for ~ro-tecting and positioning the plates, and to uniformly distribute the compressi~e pressure placed on said stack in the pressure step and thereafter by said casing.
After the pressure step on the stack of plates and membranes, they are placed inside hollow shells 32, 34, along with spacers 37, and the shells brought together under pressure so that flanges 34, 36 are in facing contact with each other as shown in Figure 8. Groove and 0 ring system 35 ~Figures 1 and 15) is disposed around manifold chamber 44 and the corresponding oudlet manifold chamber, for sealing purposes.
Flanges 34, 36 can then be sealed together by any conventional ~- means, It is preferred to injection mold a frame of plastic 38 [Figures

2 and 9 ) about the periphery of flanges 34, 36 to enclose the peripheral portions of thç flanges and to permanently bond them together in firm, abutting relation. Figure 17 also shows an identical frame 38 as appl~ed to a pair of modified shells.
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Ridges 40 arc tormed in sections of nanges 34, 36 to retain the molded frame 38 in tight-fitting relationship. Anothsr set of ridges (not shown) are typically placed on flange portions 41 on the other ~ide of the dialyzerO
Typically, blood enters the device of Figure 1 through port 42, and is distributed by way of manifold chamber 44 (Figure 15) along the ~ide edge surfaces of the stacked plates and membranes through the beveled mamfold areas 46 (Flgure 6) of the plates which function in the manner of connecting chambers 10, as shown in Figure 3 of U. S.
Patent No. 3, 370~ 350. Manifold chamber 44 decreases in depth in all directions as it radiates from inlet 42, and terminates with a spacer ridge 50, to position the plates 52. Alternatively, an outer portion of chamber 44 can be in actual contact with plates 52, with the shells 30, 32 being sufficiently flexible to expand slightly when pressurized as blood enters inlet 42, so that a ilOw channel having a depth of a few microns or 80 i9 formed by the pressure. The advantage of this is that the v olume of blood contained in the device is brought to an absolute minimum, which i8 desirable. Otherwise, the minimum depth of chamber 44 can be about 1 mm. or less while in uslpressuri~ed condition.
The reduction of the depth of manifold chamber 44 in a manner - dependent on its distance from inlet 42 also assists in the distribution of blood or other fluid across the sides of plates 52 in a manner which corresponds to the demand for nuid passing between the plates, resulting in improved uniformity of flow with a minimum of blood volume in the device.
The optimum flow of blood or other fluid through manifold cham-ber 44 i~ combined with a minimum blood volume in the manifold cham-b~r when the manifold chamber defines a generally uniform curve in all direction~ which approximates th~ following: d--- 2/ - ~ C.

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~0~64Z6 - -d (Figure lS) 18 the depth of all points of chamber 44 along lines 43 which extend radially from the peripheral wall 45 of fluid port 42 to meet a line, in perpendicular relation thereto, constituting an extension of a peripheral edge 47 of chamber 44. do is the depth of the manifold chamber directly underneath peripheral wall 45 multiplied by the circumference of port 42; S is the distance of the point measured along a said perpendicular line 43, measured from wall 45; S0 is the total distance along line 43 from wall 45 to the peripheral edge 47 of said manifold; and C is the minimum desired d,epth of manifold 44 at peripheral edge 47.
C is preferably about 0. 5 to 1 mm. while, for a dialyzer of the ~pecific type described herein, d 0 is suitably about 0. 5 sq. cm., and S0 about 3 cm. for a dialyzer having about one hundred eighteen 12 cm.
by 6 cm. by 1 mm. plates made of polystyrene plastic and having adjoining ultrathin membranes of about 10 microns thickness.

Blood from manifold chamber 44 passes between facing mem-branes of adjacent plates, and then i9 collected in a manifold chamber defined by shell 32, which is similar in structure to chamber 44. The blood i~ then conveyed from the device by outlet 54.

Dialy~is solution (or oxygen, if the device is intended for use as a blood oxygenator) can enter the device by inlet 56, where it enters a manifold space 60 (Figures 3, 15, and 16) for distribution of the dialysis solution to the ends of the stack of plates 52. The dialysis solution then passes into plate inlet ports 62, which constitute a groove 10~6~26 de~ned in the back side of each plate which is open to ends 64 of each plate. Thus dialysis solution passes into the plate stack without disruption of sealing shoulders 66.
Inlet ports 62 extend through sealing shoulders 66 a distance 0ufficient to insure adequate sealing of the ends of the plates. A hole 68 passes entirely through each plate 52 to serve as a connection between inlet port 62 and flow channel 70. Channel 70 is a groove inscribed in the front side of each plate for the distribution of dialysis solution across one side of the plate.
The dialysis solution then passes from flow channel 70 across profiled surface 72 to a second flow channel 74 (Figure 5 ) for collection of dialysis solution.
The second flow channel then communicates with plate outlet port means 76, which is typically identical in design and function to inlet port 62 and hole 68.
As is seen from Figure 5, each plate 52 is symmetrical in its initial condition, having ports communicating with the exterior at both ends of flow channels 70 and 74. This simplifies the assembly of the stack of plates, since they can be placed together in face-to-face relatior without as much concern about assembly accuracy as is required when a3yrnmetrical plates are brought together in face-to-face relation.
After the plates have been assembled in a stack, the respecti~re second open ends 78 of channels 70, 74 are heat sealed with a hot bar or otherwise occluded, as at 78a in Figure 2, so that channels 70, 74 are open at only ports 62, 76. This heat sealing step is 1 ypically per-~ormed after the pressure squeezing step described previously, but before the stack of plates is placed inside of shells 30, 32.

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~0916~;Z 6 Small support plates 79 are placed at each end o~ plates 52 to prevent the dialyzate manifold spaces 60 at each end of the plates Yrom collapsing under the pressures encountered during the injection molding step which creates frame 38 for sealing the shells together.
Figure ~ shows schematically the blood flow path 49 running transversely across plate 52 and separated therefrom by membrane 39, while the dialy~ate flow path 80 is shown to pass into the plate by inlet port 62 and to move as previously described.
Profiled surface 72 of plate 52 is shown in Figure 8 to con-stitute rows of upstanding projections 82 which are typically generally pyramidal structures having a height of 0. 05 to 0. 5 mm.; for example, 0.15 mm. projections 82 cover most of the plate. Preferably, the alternate rows of projections are laterally shifted with respect to their adjacent rows, so that both blood and dialysis solution flow in crossing grooves 83 running between dialysis fluid flow channels 70, 74, for improved gentle mixing of both the blood and dialysis fluid as it passes across the plate face.
The centers of these projections are spaced a distance Dl of about 0. 3 to 1. 5 mm. apart in the rows which are transverse to the - 20 general direction of blood flow 81 across the plate face, and generally parallel to flow channels 70, 74, to provide narrow grooves 83.
The advantage of this is particularly found when ultrathin mem-brane o~ no more than about 20 microns thickness is used, in that the great multitude of tiny and closely spaced projections provides adequate support for the thin membrane, preventing the membrane from ripping, or from sagging into the nOw channels between the projections. Thus, , . .
lQ -lO~Z6 since this plate structure permits an ultrathin membrane to be used, the diffusion rate between fluid passing on opposite sides of the mem-brane is substantially improved over the known and conventional diffusion membranes, which are substantially thicker.
The now resistance across plates 52 is reduced by spacing the centers of the projections 82 in rows extending parallel to the blood flow direction 81 a greater distance apart than the spacing in the trans-verse rows described above. This spacing D2 is typically about two to three times the distance Dl, that is, about 0. 5 to 5 mm., preferably about three times that of Dl. A preferred spacing Dl is 0. 5 mm., while a preferred spacing D2 is 1. 5 mm. .
Pyramidal projections 82 are typically about 0. 5 mm. long on their long axis and 0. 2 to 0. 3 mm. long on their short axis as shown in Figure 15.
It is preferred for the dialysis membrane to be placed across the plates 52 and projections 82 while stretched in such a direction that the center-to-center spacing between projections 82 in the stretched direction of the membrane is g~eater than the center-to-center spacing of the projections transverse to the stretched direction of the membrane. In other words the membrane, which is typically a cellulose-based membrane for blood dialyzers, is laid across plate 52 while being gently stretched in a direction generally parallel to direction 81. Ae stated above, the projection spacing in a direction perpendicular to direction 81 is about one-third the distance of the projection spacing in direction 81.

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Thc ~dvanta~eof this is that, when wetted, cellulose-based dia.lysis mcmbranes and the like tend to expand, and the degree of expansion in the direction perpendicular to their stretched direction is greater than in their stretched direction. If the degree of e~cpan-sion of the wetted membrane is too great, it will sag and occlude the dialyzate flow channels 83 between the projections 82. Thus, pro-jections 82 are spaced more closely together perpendicular to direc-tion 81 to acco-mt for this increased degree of sagging of the membrane.
If the membrane is stretched onto the plates in a direction transverse to direction 81, the spacing of projections 82 can be modified accord-ingly to prevent undue membrane sagging.
Ridges 84 are positioned to mate with corresponding ridges on the faces of adjacent plates to serve as spacer members, thus preventing the projections 82 on facing plates from collapsing between each other during the squeezing or pressurization step of the stack of plates.
Figure 16 shows a portion of the inside view of shells 30, 32.
Dialyzate inlet tube 56 is shown solvent-sealed in position in an appro-priate receptacle for the inlet port. Spacer ridge 50 is 3hown in position to space the plates in uniform manner.
Referring to Figuree 9 through 11, an alternate plate embodi-ment 85 is disclosed having a profiled surface comprising projections 86 (Figure 11~. Plate 85 h~s a pair of sealing shoulders 88 in a manner similar to the previous plates, but with several dialysis fluid entrance por;s 90, which are grooves defined on the rear side of plate 84 in a manner similar to that shown in Figure 8 as inlet 62. Holes 92 corres-pond to holes 68, and four dialy~ate channels 94 convey dialysis solution, .~ . , .

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. ! . ' , ' . ' ' . , ' : ' ~0~ 26 extending transversely to the crossinL~ ~rooves 87 defined by projec-tions 86 across plate 85. Channels ~4 are of differing length to pro-vide uniformly distributed dialysis solution to the space between each plate and its associated membrane. The arrangement insures that adequate supplies of dialysis solution are provided to the areas of plate 84 which are remote from entry ports 90. If desired, projec-tions 86 rnay be spaced in the arrangement as shown in Figure 8 .
Correspondingly, a plurality of take-up channels 96 are pro-vided to convey fluid away from the plate by means of holes 98 which communicate with ports 100, defined on the back of plate 85, to permit solution to be conveyed to the exterior without breaking the seal provided by sealing shoulder 88.

Tooth-like structures 102 are provided on one side of plate 85 as a means to provide a manifold chamber for blood. The blood is, as previously described, conveyed across plates 85 between associated membranes (one of which is shown as membrane 106 in Figure 10) and correspondingly expelled from the other side of plate 85~

In this embodiment, the plates are stacked so that tooth-like structures 102 of adjacent facing plates are located at opposite sides from each other. One set of the teeth 102 then will serve as an inlet manifold for the blood while the other set on the other plate will serve as an outlet manifold.
Support ridges 108 function in the same manner as ridges 84 (Figure 5 ) to prevent the projections 86 of plates in face-to-face relation from being forced together.
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Referring to F;3Lgures 12 through 14, a longitudinal sectional ~rieW o~ a device similar to Figure 1 i~ shown having a modified plate design. Blood enters through inlet 42 as before and departs through outlet 54. Dialysis solution enters through inlet 56 into manifold chaDnber 60, which is supported by blocks 79, as previously shown, to prevent collapse of manifold chambers 60 during the injection molding of frame 38. Dialysis solution passes from manifold charn-ber B0 through a plurality of channels 110 defined on the rear side of each plate underneath sealing shoulders 112. Channels 110 communi-cate with holes 114, which pass entirely through each plate just adjacent the sealing shoulders 112 to provide access from channels 110 to the front side of the plate.
The majority of the plate is provided with alternating rows of parallel, short ridges 116, t~rpically no more than 0. 05 to 0. 5 mm.
high, about 1 to 1. 5 mm. long, and substantially less in width 10. 3 mm. ), in which the ridges of alternating rows define angles to the ridges of adjacent rows. Preferably, all of the short ridges 116 define acute angle~ to the edges of their respective plates between the sealing shoul-ders 112, and an odd number of rows of short ridges are provided on the plate in at least one, and preferably bo~h directions, so that the ~ ~
8hort ridges 116 of plates disposed in face-to-face relation are in ;
abutting, angular relation to corresponding ridges 116' of the adjacent i~ace-to-~ace plate, to provide spacing and support between the plates.
This i illustrated in Figure 14, in which a pair of adjacent membraner are 8hown to be retained and held together by crossing ridges 116, 116' oi~ ad~acent plates. The phantomed ridges 116' of Figure 20 illustrate the same principle. When crossing ridges 116 are used, the long ridges 84 IFigure 5 ~ are no longer nece9Qary, and mole uniform plate . ' .

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support i8 pro~ided. Dialysis solution is then collected in corres-ponding collection channels 118 (of identical structure to members 110, 114), which solution is then withdrawn through another manifold 60 and outlet 57. ,~
In Figure 12, ridges 116 are shown enlarged and with fewer rows than would be customarily used, for purposes of clarity. A
typical ridge spacing 117 between ridges of adjacent rows is about 0.2 mm.
Referring now to Figure 17~ a modified device of this inven-tion comprising a pair of shells 120, 122 is disclosed. Blood inlet 54 is essentially the same as in Figures I and 12, as is blood outlet 42, frame 38, and an exemplary stack of plates and membranes having ridges 116 and functioning as described above. ~Iowever, the dialysis solution inlet and outlet have been moved with respect to the casing of Figures 1 and 12 to avoid the molding problems which result when the dialysis inlet and outlet are involved with the molding opera-tion of frame 38. Thus, new dialysis inlet 124 is located below frame 38, while dialysis solution outlet 126 is located above frame 38.
Dialysis manifold chambers 128 are providedJ corresponding to mani-fold chambcrs 60 in Figures 12 and 15, but having sufficient depth and - volume to eliminate any possiblc nonuniformity of flow caused by the asymmetric locations of inlet 124 and outlet 126.
It can be seen that shells 120 and 122 can be manufactured from the same mold, and assembled simply by facing the two shells in opposite direction during assembly.
The above has been offered for illustrative purposes only, and i8 not to be considered to limit the invention, which is defined in the .. . . . . . . . . . ...
claims below.

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Claims (5)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In a diffusion device comprising a plurality of stacked plates and overlying membranes, said plates defining a plurality of rows of spaced projections of uniform height for forming flow channels, in which said membranes overlying said plates are asymmetrically tensioned in one direction with respect to other directions over said projections, the center-to-center spacing of said projections in said one direction being greater than the center-to-center spacing of said pro-jections in a direction transverse to said one direction.

2 The diffusion device of claim 1 in which the general path of fluid flow across adjacent membranes approximates said one direction.

3. The diffusion device of claim 2 in which said projections are spaced in rows in said one direction at least two times farther apart than in said transverse direction.

4. The diffusion device of claim 3 in which said membrane is made of a cellulosic material.

5. The diffusion device of claim 4 in which each plate has a front side with sealing shoulders on opposed side edges, said rows of projections being defined between the sealing shoulders, the front side of each plate being covered by a said membrane folded at opposed ends about the edges of said plate between the sealing shoulders, so that opposed membrane ends lie adjacent to the rear side of said plate, the plates being arranged in face-to-face and back-to-back relation respectively with adjacent plates to clamp said membranes between the rear sides of adjacent plates and to clamp membrane edges between said sealing shoulders, first manifold means for con-ducting a fluid across said plates through said fluid flow channels between the plate and its associated membrane, and second manifold means for conducting fluid across said plates between the membranes of plates lying in face-to-face relation.