GB1602896A - Forming fluid manifold for a fluid flow transfer device - Google Patents

Description

(54) FORMING FLUID MANIFOLD FOR A FLUID FLOW TRANSFER DEVICE (71) We, COBE LABORATORIES, INC., a corporation organised under the laws of the State of Colorado, United States of America, of 1201 Oak Street, Lakewood, Colorado 80215, United States of America, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to fluid flow transfer devices using separatory membranes and fluid flow manifolds at the inlet and outlet.

In constructing a fluid flow transfer device such as a haemodialyzer 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.

According to a first aspect of the 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 the 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 tips while viscous enough to avoid wicking of itself along said spaces into the manifold 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 subsequentlyintroduced potting material through said spaces, whereby when said potting material is introduced it is prevented from blocking the manifold area.

According to a second aspect of the 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 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 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.

We turn now to description of the presently preferred embodiment of the invention. In the accompanying drawings: Fig. 1 is a perspective view of a dialyzer utilizing the presently preferred embodiment; Fig. 2 is a somewhat diagrammatic sectional view along 2-2 of Fig. 1; Fig. 3 is an exploded view of a portion of the membrane and support netting of the dialyzer of Fig. 1; Fig. 4 is an enlarged perspective view of a portion of the support netting of Fig. 3; Fig. 5 is a sectional view along 5--5 of Fig. 1; and Fig. 6 is a greatly enlarged vertical sectional view like that of Fig. 2 of a portion of the membrane and support netting of the dialyzer of Fig. 1.

The embodiment shown in the drawings and its operation are now described.

1. Embodiment Figs. 1 and 2 show a dialyzer 10, which includes a two-part housing comprising a trough-shaped polycarbonate casing 12 and an interfitting polycarbonate casing 14, which is open at both longitudinal ends and has a pair of longitudinal fins 16. The casing 12 includes an inlet 18 and an outlet 20, both integrally moulded therewith. The casing 14 includes an integrally moulded inlet 22 and outlet 24. The inlets 18 and 22 and outlets 20 and 24 become channels of steadily decreasing cross section when they enter their respective casings. A pair of stub shafts 26, formed by mating semicircular portions on the casings 12 and 14, and a pair of co-operating stops 28 (only one is shown in Fig. 2), spaced equidistantly longitudinally from the right stub shaft, permit rotatable, vertical mounting of the dialyzer on a bracket, for degassing and normal operation.

A dialysis membrane 30, a Cuprophan (trademark of Enka Glanzstoff AG) cuprammonium Cellophane (Registered Trade Mark) sheet having a generally accordion pleated configuration and to which glycerin has been added as a plasticizer and humectant for smooth processing, is squeezed between the fins 16, and is sealed with polyurethane potting 32 along its outermost flaps to the outer faces of the fins. The folded upper tips of the membrane 30, shown somewhat rounded in Fig. 2, are affixed to the casing 12 by being anchored in polyurethane potting 32, thereby forming a series of separate parallel fluid flow passages, indicated by B in Fig. 3, in the valleys above the membrane. Potting of the upper tips prevents shunting of fluid directly from the inlet 18 to the outlet 20 without entering the passages B. Support netting 34, a nonwoven polypropylene mesh (see the arrangement of its strands 35 in Fig.

4) sold under the Du Pont trademark Vexar, is also in the form of an accordion pleated sheet, and is positioned within the membrane 30 on the membrane side adjacent the casing 14 (Fig. 3). By this configuration, the support netting 34 spaces apart the underside faces of adjacent membrane walls with two layers of the netting shown in Fig. 4, and provides parallel fluid flow passages underneath the membrane, indicated by D in Fig. 3. The netting 34 is not bonded to either casing, except at its longitudinal ends, as will be described hereinafter, and unlike the membrane 30 does not fold over the fins 16.

Both the membrane 30 and the netting 34 are pleated along generally parallel lines, and the strands 35 run at 450 to those lines.

The casing 12 has a continuous peripheral ridge 50 that seats in a continuous peripheral groove 52 of a shelf portion 54, which surrounds the casing 14. When the casing 12 and the casing 14 are so interfitted, the tips of the fins 16 are vertically spaced from the adjacent inner surface of the casing 12 and from ribs 36 running transversely on that surface, to avoid cutting of the membrane 30 between the pointed fin tip and the casing 12.

The longitudinal ends of the membrane 30 and the netting 34 are bonded to the casings 12 and 14 by potting 32 (Fig. 5).

Transverse ribs 36 (one shown in Figs. 2 and 5) of the casing 12 space the folded tips of the membrane 30 from the casing ceiling to provide channels for flow of potting 32 during construction of the dialyzer 10, described hereinafter. The ribs 36 have arcuate portions 56 which laterally space the fins 16 from the angled and vertical sidewalls of the casing 12 by tangential contact with the fins 16 through the membrane 30; the portions 56 permit the flow channels to extend from the central fluid chamber between the fins 16 to the side compartments between each fin and the corresponding sidewall of the casing 12. A continuous ridge of General Electric RTV 108 thixotropic silicone rubber adhesive 38 adjacent casing ribs 40 surrounds the channel portion of the outlet 20 ( and in the same way the 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 construction. 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. The inlet 18 and outlet 20 thus co-operate along their channel portions with the membrane 30 to form inlet and outlet manifolds into and out of the fluid passages indicated at B in Fig. 3. Likewise the inlet 22 and outlet 24 co-operate along their channel portions with the membrane 30 on its underside to form inlet and outlet manifolds into and out of the fluid passages indicated at D in Fig. 3.

In constructing the 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 (Fig. 3).

The resultant membrane-netting stack is squeezed together and placed in a casing 14 between the fins 16, with each of the two outermost flaps of the 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 the silicone rubber adhesive 38, each having a weight of approximately one gram, are then applied around the outer edges of the channel portions of the inlet 18 and outlet 20 of casing 12, adjacent ribs 40 and on end shoulders 41 (one shown in Fig.

5). The casing 14 is then interfitted with the casing 12. The ridge 50 is wetted with solvent and then pressed into the groove 52, to which it bonds on drying. A ramp portion 48 running along the base of each fin 16 serves to guide the ridge 50 into the 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 the 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 Fig. 5). The 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 1800, 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 (Fig. 5).

The 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. The dialyzer 10 is positioned horizontally with the membrane tips to be potted below the membrane body and horizontally aligned, with the casing 12 on the bottom (inverted from Fig. 2). Plugs (not shown) are placed in the 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 the membrane 30 adjacent the 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. The inlet 18 and outlet 20 are open to atmospheric pressure. Approximately 60 cc of polyurethane potting 32, which comprises an initially liquid mixture of Polyol 936 and Vorite (Trade Mark) 689, a urethane prepolymer, both manufactured by N. L.

Industries, Bayonne, New Jersey, is then pumped into the dialyzer 10 through hole 44 (Fig. 2) in one sidewall of the casing 12. The potting flows into the side compartment formed between the sidewall of the casing 12 arid one fin 16 through channels between the arcuate rib portions 56, down into the trough of the casing 12, transversely through the channels formed by the 0.06 inch deep transverse ribs 36 (Fig. 5), and again through channels between the arcuate portions 56 up into the other side compartment between the other sidewall of the casing 12 and the other fin 16. The arcuate portions 56 prevent fins 16 from flaring outward to contact the sidewalls of casing 12 and thereby block potting flow into or out of the side compartments. A pair of pinholes (not shown) in the casing 14, one adjacent the inlet 22 and the other adjacent the outlet 24, let air escape as the potting is pumped in. The potting settles uniformly on the inner surface of the casing 12 and reaches the same level in each side compartment. Because of the positive pressure maintained on the opposite side of the membrane 30, passages B are closed up, and the potting cannot wick or otherwise flow up between the folds. After a curing time of 60 minutes, one of the plugs is removed to permit a vacuum to be applied to the membrane side that initially 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 of 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 the 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 the netting 34 (Fig. 6), which then supports the membrane and prevent it from pulling away from the inner surface of the casing 12. The now more 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. 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 particular 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, the dialyzer 10 is ready for use.

The dimensions of the dialyzer 10 are as follows. Its housing is approximately 12 inches by 3-5/8 inches by 2 inches. The membrane 30 has a dry thickness of 13.5 microns and an actual surface area of approximately 1.54 mZ. The netting 34 has 16 strands per inch and a mean thickness of 0.022 inch. Both membrane and netting have 66 folds ("folds" meaning adjacent pairs of membrane or netting walls joined along a crease), which is equivalent to the number of upper tips of the membrane 30 affixed to the casing 12 (far fewer folds are shown in the somewhat diagrammatic view of Fig. 2). There are 65 fluid flow passages B along the folds. The channel portions of the 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 seventeen corresponding pairs of arcuate portions 56. Additionally, there is a pair of arcuate portions 56 (not shown) between each longitudinal end of the casing 12 and the inlet 18 and outlet 20.

2. Operation When used as a haemodialyzer, the dialyzer 10 operates as follows. Blood tubing is connected to the inlet 18 and outlet 20, and dialysate tubing is connected to the inlet 22 and outlet 24. The dialyzer 10 is mounted vertically, with the inlet 18 and outlet 24 on top. Blood is introduced into the inlet 18, flows along its channel portion, and then, partly because of the potting 32, flows into the spaces B between the folds of the membrane 30 and in the general direction indicated by arrows in Fig. 3, until it is collected in the channel portion of the outlet 20 and then passes out of the dialyzer 10. Dialyzing fluid or dialysate is introduced into the inlet 22 and flows along its channel portion where it is distributed into all of the dialysate flow passages D (Fig. 3), and flows in the general direction indicated by arrows in Fig. 3, countercurrently with blood flow. It has been found that the membrane tips adjacent the casing 14 do not need to be potted to it, when dialysate is introduced on this side.

Dialysate is collected in the channel portion of the outlet 24 and then passes out of the dialyzer 10, from which it is collected for regeneration or disposal. Dialysis occurs across the membrane 30. Blood is introduced into its inlet port with use of a pump while dialysate is introduced into its inlet port at a lower pressure. Thus in addition to removal of unwanted substances from the blood by dialysis, the dialyzer 10 effects removal of water from the blood through the membrane 30 because of the pressure difference across the membrane.

In normal operation dialysate flows upward because of the vertical positioning of the dialyzer 10, and the dialysate flow paths D (Fig. 3) are constantly being degassed as dialysate flows in that direction.

The blood flow paths B (Fig. 3) are degassed prior to dialysis by inverting the dialyzer 10, introducing a saline priming solution, and having that solution flow upward for a predetermined time.

An enlarged view of the arrangement of the support netting 34 and membrane 30 is shown in Fig. 6. Potting 32 has seeped somewhat into the space between the folds shown, to increase the bonding area and hence improve the bond between the membrane tips and the potting. The pleated sheet configuration of the netting 34 provides a spacer between adjacent membrane folds that is two layers thick. The effect is 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 tend to pinch adjacent folds of membrane 30 at spaced points designated P in Fig. 6.

Between points P portions of folds of the 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.

The dialyzer 10 provides the following specifications and results when used in haemodialysis: Pressure Drops Blood (at flow rate, QB. of 200 mVmin. and Transmembrane Pressure (TMP) of 100 mmHg) (Haematocrit=30%) 15 mmHg Dialysate (at flow rate, QD 500 ml/min. and TMP of 100 mmHg) 2mmHg 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 TMP 85 ml 200 mmHg TMP 120 ml Dialysate Volume 730 ml Maximum TMP 500 mmHg The fluid flow manifold of the present invention has other uses beside that in haemodialysis; for example, it can be used in laboratory dialysis.

Other embodiments of the invention will be obvious to those skilled in the art.

WHAT WE CLAIM IS: 1. 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 the tips of said pleated membrane to said housing, said gasket material being flowable enough to conform *Performance subject to variations in Cuprophan membrane.

to the shape of the membrane tips and to penetrate into the spaces formed between the tips while viscous enough to avoid wicking of itself along said spaces into the manifold 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 subsequentlyintroduced potting material through said spaces, whereby when said potting material is introduced it is prevented from blocking the manifold area.

2. A method according to claim 1 wherein said gasket material is silicone rubber.

3. A method according to claim 1 or 2, wherein said potting material is polyurethane.

4. A method according to any one of the preceding claims wherein said channel portion is about 2-3/4 inches long, about 3/8 inch wide and 5/32 inch deep adjacent said fluid port, and tapers to a depth of about 1/16 inch and width of 3/8 inch at its opposite end, and approximately one gram of adhesive is applied around said channel.

5. A method according to any one of the prece.ding claims wherein said method includes forming a ribbed portion in said housing longitudinally surrounding said channel portion and said gasket material is applied on the sides of said ribbed portion away from said channel portion.

6. 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 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 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.

7. An improvement as claimed in claim 1 or 6 wherein said gasket material is adhesive.

8. An improvement as claimed in claim 1, 6 or 7, wherein said gasket material extends fully around said channel portion.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

1. **WARNING** start of CLMS field may overlap end of DESC **.

   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.

   The dialyzer 10 provides the following specifications and results when used in haemodialysis: Pressure Drops Blood (at flow rate, QB. of 200 mVmin. and Transmembrane Pressure (TMP) of 100 mmHg) (Haematocrit=30%) 15 mmHg Dialysate (at flow rate, QD 500 ml/min. and TMP of 100 mmHg) 2mmHg 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 TMP 85 ml

   200 mmHg TMP 120 ml Dialysate Volume 730 ml Maximum TMP 500 mmHg The fluid flow manifold of the present invention has other uses beside that in haemodialysis; for example, it can be used in laboratory dialysis.

   Other embodiments of the invention will be obvious to those skilled in the art.

   WHAT WE CLAIM IS: 1. 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 the tips of said pleated membrane to said housing, said gasket material being flowable enough to conform *Performance subject to variations in Cuprophan membrane.

   to the shape of the membrane tips and to penetrate into the spaces formed between the tips while viscous enough to avoid wicking of itself along said spaces into the manifold 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 subsequentlyintroduced potting material through said spaces, whereby when said potting material is introduced it is prevented from blocking the manifold area.
2. 2. A method according to claim 1 wherein said gasket material is silicone rubber.
3. 3. A method according to claim 1 or 2, wherein said potting material is polyurethane.
4. 4. A method according to any one of the preceding claims wherein said channel portion is about 2-3/4 inches long, about 3/8 inch wide and 5/32 inch deep adjacent said fluid port, and tapers to a depth of about 1/16 inch and width of 3/8 inch at its opposite end, and approximately one gram of adhesive is applied around said channel.
5. 5. A method according to any one of the prece.ding claims wherein said method includes forming a ribbed portion in said housing longitudinally surrounding said channel portion and said gasket material is applied on the sides of said ribbed portion away from said channel portion.
6. 6. 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 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 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.
7. 7. An improvement as claimed in claim 1 or 6 wherein said gasket material is adhesive.
8. 8. An improvement as claimed in claim 1, 6 or 7, wherein said gasket material extends fully around said channel portion.
9. 9. A fluid flow apparatus as claimed in

   claim 6 wherein said housing interior has a ribbed portion longitudinally surrounding said channel portion and said gasket is formed on the sides of said ribbed portion away from said channel portion.
10. 10. A method of forming a fluid flow transfer device substantially as hereinbefore described with reference to the accompanying drawings.
11. 11. A fluid flow transfer device formed by a method according to any one of claims I to 5.
12. 12. A fluid flow transfer device substantially as hereinbefore described with reference to the accompanying drawings.