CA1132914A

CA1132914A - Method of potting the ends of a bundle of hollow fibers positioned in a casing

Info

Publication number: CA1132914A
Application number: CA320,991A
Authority: CA
Inventors: Bert S. Bodnar; William J. Schnell
Original assignee: Baxter Travenol Laboratories Inc
Current assignee: Baxter International Inc
Priority date: 1978-03-20
Filing date: 1979-02-05
Publication date: 1982-10-05
Also published as: CH641720A5; IL56618A0; FR2420413A1; AU529112B2; FR2420413B1; ES484194A1; JPS54128197A; GB2016358A; AU4523679A; IT7921089A0; GB2016358B; SE7902408L; BR7901523A; ES478813A1; DE2910214A1; NL7902163A; IL56618A; JPS6317464B2; IT1112039B

Abstract

ABSTRACT OF THE DISCLOSURE

A method of potting the ends of a bundle of hollow fibers positioned in a casing is provided, for example, in the manufacture of hollow fiber artificial kidneys. The bundle is inserted into the casing through an open end there-of and the casing ends are enclosed with sealed casing clos-ure member means. The casing ends are spun, while curable liquid sealant is inserted through side apertures in the casing. Accordingly, the liquid sealant migrates by the centrifugal force of the spinning to the interior sealed ends of the casing. After the liquid sealant has cured, the closure member means, sealant and hollow fibers are cut through at each casing end to expose the bores of the hollow fibers. Alternatively, the closure means can be removed prior to the cutting step.

Description

113Z9i4 BACkGROUND OF THE INVENTION
Hollow fiber dialyzers are a well-known and in-creasingly popular form of dialyzer for use as artiicial kidneys, as well as other desired uses. One liquid for dialysis, typically blood, passes through the bore of a bundle of hollow, semi-permeable fibers, while a second dial-ysis li~uid flows through the bundle against the exterior surfaces of the ~ibers.
Conventionally, as in U.S. Patent Nos. 3,4~2,698 and 3,442,002, the hollow fiber bundles are placed in a generally tubular casing, and the ends are potted within the casing to provide a seal. After cure of the potting compound, the potted areas are sliced to expose the bores of the fibers in the bundle, and exterior manifold members are placed over the ends of the casing so that blood or other liquid can be conveyed to the ends of the fibers at one end of the casing, and collected from the other ends of the fibers at the other end of the casing.
In the usual manufacturing techniques, the casing is spun about an axis of rotation extending through the center of the casing, so as to place a centrifugal force upon the potting compound at opposite ends of the casing while potting compound is added through the ends, and as it cures. The ends of the casing are typically sealed by a temporary mechanical end seal of the centrifuge apparatus, to prevent the loss of sealant out of the open ends of the casing.

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ll~Z9i4 It has been found that it is difficult to seal the potting compound since the open ends are under a sub-stantial G-force from the centrifuge. Accordingly, some leakage of sealant often takes place, even when expensive, S high-performance mechanical end seals are provided to the centrifuge and apparatus.
The invention of this application provides a means for potting the ends of a hollow fiber dialyzer without the use of a mechanical end seal, providing a sim-plification of the system during centrifugation. Also, thisinvention provides a potting system in which less sealant per unit may be used in each potting operation.
~ ikewise, further efficiencies of operation may be provided, for example, by providing a carousel-type of assembly operation, in which a series of potting centrifuges are placed upon a carousel platform which moves the potting centrifuges in a circular path, presenting them one by one to the operator for unloading and reloading, with a substan-tial saving of sealant in the operations.

'`` 113Z9~4 DESCRIPTION OF THE INVENTION

In accordance with this invention, a method is provided for potting the ends of a bundle of hollow fibers positioned in a usually tubular casing comprising a central casing having at least one open end, and closure member means for said end. The fiber bundle is inserted into the central casing through an open end thereof. Then the end or ends of the central casing are sealingly closed with the closure member means (which are preferably rigid) to effectively seal the casing ends, for example by solvent or ultrasonic sealing of the closures to the casing to integrally incor-porate the cIosures and casing. Alternatively, the casing ends and casing closure members may carry screw threads so that the closure members may be screwed on the ends for sealing and later removed.
Opposed side-mounted outlet ports of a hollow, elongated potting boat member are then attached to side apertures positioned in fluid communication with casing and curable liquid sealant is placed into the hollow, elongated member.
One then spins the casing ends about an axis of rotation extending through a central portion of the casing.
Accordingly, the liquid sealant migrates by the centrifugal force of the spinning to the interior ends of the casing through said side apertures to pot the ends of the fiber bundle within the casing. After the liquid sealant is cured, end portions of the casing are removed, and the . sealant and hollow fibers are cut through at each end of the fiher bundle to expose the bores of the hollow fibers.

~ - 4 -Upon centrifugation as described above, the sealant is driven to the respective ends of the potting boat, and from there through the outlet ports and side apertures into the casing, where it migrates radially outwardly into the casing closure member means to surround and seal the ends of the fiber bundle. This is done without spilling, because the casing closure member means can provide an absolute seal, greatly improved over any temporary seal member carried by the centrifuge which has been previously used to pot the ends of a casing from the exterior, while at the same time attempting to hold the sealant in position against the centrifugal force generated by the centrifuge.
Manifold means may be conventionally placed on each end of the casing to facilitate liquid flow through the open bores of the fibers in the bundle.
After the sealant has cured, the casing clos- -ure member means is then opened, and the potted bundle end may be cut in a two-step process as follows: first, a circumfer-ential channel or notch may be cut through the casing or casing closure member,for example, by the use of a parting tool, to expose the potted bundle underneath the generally rigid plas-tic of the casing closure members. Alternatively, the casing closure member may be simply removed, for example, by unscrewing it. Thereafter, the potted bundle end may be conventionally sliced with a precision meat slicer or the like, through the cut circumferential channel or notch, or at its exposed end where the closure member is removed, to provide a flat surface which includes the opened bores of the fibers in the bundle.
If desired, the rigid casing closure means may comprise plastic cup-shaped members, each sealed at their rims to an end of the tubular casing. A portion of each cup-shaped member adjacent the rim may be of relatively en-larged diameter, relative to the tubular casing, to serve as a manifold means for side apertures in the casing, which in their ultimate use may serve as the inlet and outlet ports for one of the fluids to be dialyzed.
Each`of the cup-shaped members may also define an extended cylindrical portion, preferably of equal or greater length than the enlarged diameter portion, positioned re-motely from the rim and having a diameter of less than the relatlvely enlarged-diameter portion. This segment of the cup-shaped member receives an end of the hollow fiber bundle, and is filled with the potting compound. Because of its reduced diameter, the amount of potting compound used is reduced over various prior art techniques.
Alternatively, the casing closure means may simply be separate end plates, attached to and sealing each end of the casing after insertion of the fiber bundle. In this case, the casing itself may be cut open after the centri-fugation step.
Referring to the drawings, Figure 1 is an elevation-al view, shown in partially diagramatic form, of a hollow fiberbundle positioned in a casing and carried by a centrifuye in accordance with this invention.
Figure 2 is a longitudinal sectional view of one end of the casing and fiber bundle shown in Figure 1, also ~13Z914 showing the sealant migrating from the potting boat to the respective ends of the casing.
Figure 3 is a view similar to Figure 2 showing how the closure member means is cut through by cutting of s a circumferential channel about the closure member.
Figure 4 is a view similar to Figure 2 showing how the end portion of the closure member is removed and the potted ends of the fiber bundles are sliced.
Figure S is a perspective view of a separate, hollow tubular casing of this invention into which a fiber bundle is placed, and a separately molded closure member, which is adapted to be sealed to an end of the casing.
Figure 6 is a perspective view of the finished, cut tubular casing and a manifold member about to be attached thereto.
Figure 7 is a plan view of an indexing carousel for semi-automated mass production of potted hollow fiber bundles in casings, in accordance with this invention.
Figure 8 is an elevational view of the end of a hollow fiber bundle in another embodiment of the casing and associated cup-shaped casing closure member of this inven-tion.
Figure 9 is a fragmentary elevational view of an end of the casing and fiber bundle shown in Figure 8, showing how the projected potted fiber bundle end may be cut.
Figure 10 is a fragmentary perspective view of an end of the casing and fiber bundle shown in Figure 9 at the completion of the cutting step.

~13Z914 Referring to Figures 1 through 6, a method and apparatus for assembling a potted, hoilow fiber bundle within a casing is disclosed. A central, hollow tubular casing 10 is shown to be initially loaded with a hollow fiber bundle 12, which preferably may be made in accor-dance with the disclosures of Fitzgerald, et al-, Canadian Patent application No. 291,548 filed November 23, 1977, or by any other desired technique for assembling fiber bundles. Hollow fiber bundle 12 is shown to be longer than central casing 10, so that it protrudes out of both ends of the casing 10 by a predetermined length. It is also pre-ferable for the ends of fiber bundle 12 to be surrounded and secured with tape 14 prior to insertion of the bundle into casing 10, for ease of insertion and to prevent disrup-tion of the bundled array of fibers.
Thereafter, generally cup-shaped casing closure members 16 are sealed onto the ends 18 of casing 10, to surround and enclose the fiber bundle 12 by ultrasonic welding or the like for a permanent, hermetic seal bond.
As shown, the sealing cup member 16 defines a closed end wall 2~, which may be positioned to be slightly spaced from its associated end of the fiber bundle 12.
Also, in this embodiment, the cup-shaped closure member means 16 carries side aperture member 22 as an inte-gral part thereof.
Furthermore, a portion 24 of the cup-shaped seal-ing member 16 is of relatively enlarged diameter, relative to tubular casing 10, to serve as a manifold area for fluids passing into or out of side apertures 22. Another extended, ~, .~, -~l~Z9~4 Cylindrical portion 26 of the cup-shaped sealing member 16, which is preferably of equal or greater length to section 24, has a diameter which is less than the relatively en-larged diameter portion 24 and is, as stated before, posi-tioned to receive an end of the hollow fiber bundle 12.
The structure as shown in Figure 2 typically represents the structure as it is at both ends of the casing, with one end being omitted for purposes of simplicity of disclosure.
Inner flange 25 may be used to help center bundle 12.
After sealing of a cup~shaped, rigid casing closure member means 16 at each end of casing 10, by ultra-sonic welding or any other desired technique, the resulting assembly is mounted on a centrifuge rotor 28, operated by centrifuge 36, both of which may be of conventional design, being adapted to firmly hold casing 10 and its related parts.
Arms 29 of the rotor grip casing 10 and end members 16.
A hollow, elongated potting boat 30 which may be made of thermoformed plastic or the like, is attached with its outlet ports 32 positioned within side aperture members 22 as illustrated in Figure 2. Any desired retention means may be used. For example, the end of each outlet port 32 may be slightly bulbous, as shown, for a friction fit within aperture members 22, and the boat 30 may be attached to casing 10 by rubber bands 31.
The top of potting boat 30 defines an open aperture 34 into which liquid-curable sealant, for example polyurethane .: .

~132914 sealant, may be inserted, typically while the centrifuge is in operation. This is after installation of casing 10 and the potting boat 30 on centrifuge rotor 28.
The centrifuge 36 spins casing 10 about an axis - 5 of rotation extending through the center of the casing.
The urethane sealant 3~ is driven radially outwardly toward both ends of the potting boat 30. From there, the sealant migrates through outlet port 32 and side aperture member 22, to continue the flow radially outwardly along the upper edge of sealing cup members 16, to fill the remotely posi-tioned portion 26 of the sealing cup member, surrounding and enveloping the ends of fiber bundle 12. Typically, an amount of sealant is used sufficient to permit the filling of portion 26 of the sealing cup member up to about the level of flange 38, which defines the junction between portion 26 and portion 24 of the sealing cup member.
As a result of this, less sealant is used, while at the same time the bundle 12 is thoroughly potted at its ends, and bonded to the interior of the casing assembly.
After the sealant 39 has sufficiently cured, cen-trifuge 36 is stopped. Casing 10 and its related parts may be removed from the centrifuge, and potting boat 30 may be removed as well, for either reuse or discard as desired.
After the sealant is completely cured, the casing assembly may be opened at its ends, typically by the initial step of cutting a circumferential channel or notch 40 through each closure member means, specifically in section 26 of the closure mer~er cup. This is as shown in Figure 3, and may be done with a parting tool if desired, to expose fiber ,. ~
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ll~Z9~4 bundle and cured sealant at the bottom of notch 40. There-after, a commercial meat slicer or equivalent machine may be used to cut through groove 40 to sever the potted bundle end and remove the ends of the casing assembly 10.
As shown in Figure 4, several sequential slicing cuts may be used as desired in order to obtain a smooth cut, in which the maximum number of fibers i~ the bundle have open, exposed bores, and also to provide a smooth surface which does not stimulate blood clotting.
Thereafter, a conventional manifold member 41 may be added to each end. It is preferable for the side port members 22 of the casing to be parallel to each other, to facilitate attachments to the potting boat 30.
Referring to Figure 7, an industrial layout making use of the apparatus and method of this invention is dis-closed.
Carousel platform 42 carries a plurality of centri-fuges 36 in a series of stations for continuous and multiple manufacture of potted, hollow fiber bundle casings on a semi-automated basis. Each centrifuge station 36 is adapted forpracticing the present invention as described above.
Accordingly, as each centrifuge station 36 is in-dexed to position 44 by rotational indexing of the carousel 42 on a predetermined schedule, it may be unloaded of its processed hollow fiber bundle casing, and reloaded with a new casing and potting boat. Then, the predetermined amount of sealant is inserted into the potting boat after the cen-trifuge 36 is turning, and the carousel platform index onward to present another centrifuge 36 to work station 44, while .,~.. ... .. . .... ..

~1329i4 the freshly-loaded centrifuge is rotationally moved away from the station 44 for automatic centrifugal processing for any desired length of time.
Accordingly, one operator can, if desired, service all of the centrifuges on the carousel platform 42, while the remaining centrifuges 36 operate until the allotted cure time has elapsed, Preferably, carousel platform 42 is enclosed in a housing 46, equipped with a vent pipe 48 to remove fumes re-sulting from the curing of the sealant.
Also, carousel platform 42 may carry recirculating forced air heaters 50 to heat the hollow fiber bundle casings 10 and their related members to a temperature which is pre-ferably higher than that of the polyurethane sealant, prior to injecting of the polyurethane into the casing 10 for pot-ting. The urethane then tends to bond first to the dialyzer casing wall, and then as it builds in volume, moves slowly inwardly to bond the fibers together, providing an improved overall seal. Generally, a temperature of 130F. is desir-able.
Alternatively, a second operating station could be provided, for example 180 around from the first work station 44, or any other arrangement may be used as may be desirable.
Referring now to Figures 8 through 10, another embodiment of the invention of this application is disclosed which may be identical in structure and manufacturing tech-nique to the embodiment described in Figures 2 through 7, except as otherwise indicated below.

Hollow tubular casing lOa contains a hollow fiber bundle 12a in a manner similar to the previous embodiment, with the ends of bundle 12a projecting from each end of casing lOa.
In this embodiment, side aperture member 22a may be carried by end member 16a, which is sealed to tubular casing lOa, as in the previous embodiment.
In distinction from the previous embodiment, end member 16a defines a terminal sleeve member 52 which is equipped with helical screw threads 54. The opposed end of casing lOa and end member 16a may be of similar design to that shown in Figure 8.
After insertion of fiber bundle 12a into tubular casing lOa a generally cup-shaped casing closure member 55 is provided at each end of end member 16a~ Closure member 55, which carries mating helical screw threads 56 at its lip, may be simply screwed onto each end of member 16a to provide a hermetic seal to the ends of casing lOa. The emplaced cup-shaped casing closure member 55 is shown in phantom lines in Figure 8.
Closure member 55 defines a diametrically disposed blade 57 across its outer end to facilitate the emplacement and removal of closure 55 on and from casing end members 16a.
Casing lOa and the respective closure members 16a, 55 at each end of casing lOa may be attached through side apertures 22a to a potting boat 30 in a manner similar to that shown in Figure 1. The centrifuge is activated to cause the urethane sealant 39a to flow to the ends of casing lOa and to cure in a manner analogous to that shown and described in .

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the previous embodiment. The urethane sealant 39a is added to fill each of the sealing members 55 and preferably part of members 16a so that the inner edge of the sealant is at least substantially within sleeve 52. As shown in Figure 8, the sealant is then cured to assume the outline of the inner chamber of each cup-shaped casing closure member 55. If desired, the apparatus of Figure 7 and the preferred methods of potting described previously may be used.
After the potting and curing step has taken place, the centrifugation process is terminated, and each of the closure members 55 is removed by simple unscrewing of the closure member from the threaded sleeve 52 on end members 16a.
Thereafter, the ends of fiber bundle 12a, potted with cured sealant 3~a, are cut off, preferably by means of a round knife 60 positioned adjacent each end of the casing lOa.
Preferably, the casing lOa may be placed within a rotatable drum with its ends projecting, and then rotated about its longitudinal axis while being brought into cutting contact with a pair of knives 60, positioned to make the cut at each end of casing lOa at the desired positions. Arrow 62 indicates the direction of rotation of casing lOa and its associated parts.
The result of this step is to expose the bores of the hollow fibers of bundle 12a in a flat end surface 64, which comprises the ends of the fibers of bundle 12a and cured sealant, with surface 64 generally projecting slightly outwardly from the outer end of each sleeve 52 defined by end member 16a.

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~l~Z914 Following this, a conventional manifold member 41 of the type used in the previous embodiment, but preferably equipped with screw threads, may be simply screwed anto threads 54, to provide a tightly sealed manifold member at each end of the casing lOa, resulting in a finished dialyzer.
By the above techniques, a simple means is pro-vided to eliminate complex sealing apparatus carried by the centrifuge for preventing the outward migration and leakage of the sealant from the ends of the casing 10 or lOa, with the complex centrifuge seals being replaced with a simple and disposable cup-shaped member having improved sealing reliability.
The above has been offered for illustrative pur-poses only and is not intended to limit the invention of this application, which is as defined in the claims below.

Claims

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

1. The method of potting the ends of a bundle of hollow fibers in a casing comprising a central casing having at least one open end and closure member means for closing said end, the method comprising:
inserting said bundle of hollow fibers into said central casing through said open end; sealingly closing the central casing by attaching said casing closure member means to the central casing; attaching opposed, side-mounted outlet ports of a hollow, elongated potting boat member to side aper-tures positioned in fluid communication with said casing;
placing curable liquid sealant into said hollow, elongated member; and spinning the casing ends about an axis of rotation extending through a central portion of said casing; whereby said liquid sealant migrates by the centrifugal force of said spinning to interior ends of said casing through said side apertures to pot the ends of the fiber bundle within the casing; and, after said liquid sealant has cured, removing end portions of the casing and cutting through said sealant and hollow fibers at each end of the fiber bundle to expose the bores of the hollow fibers.

2. The method of claim 1 in which said apertures are positioned adjacent opposite ends of said casing and generally pointing in the same direction.

3. The method of claim 2 including the further step of surrounding the ends of said bundle with tape prior to in-sertion of said bundle into said casing.

4. The method of claim 2 comprising the further step of practicing said method by simultaneously spinning the casing ends of a plurality of separate casings in centrifuges posi-tioned in a series of stations mounted on a rotating carousel platform, and initiating said spinning, terminating said spinning, and loading and unloading said casings from the centrifuges at at least one station positioned at said carousel platform.

5. The method of claim 1 in which said closure member means is provided at each end of the central casing and is removably attached by interlocking helical threads to the central casing, and wherein said step of removing end portions of the casing comprises removing said closure member means from the central casing, without cutting, prior to the step of cutting of said sealant and hollow fibers.

6. The method of claim 1 in which said closure member means is provided at each end of the central casing and in which the step of removing end portions of the casing comprises cutting a circumferential channel about each said closure mem-ber means adjacent each end of said central casing, and then slicing through said sealant and hollow fibers.

7. The method of claim 1 comprising the further step of practicing said method by simultaneously spinning the casing ends of a plurality of separate casings in centrifuges posi-tioned in a series of stations mounted on a rotating carousel platform, and initiating said spinning, terminating said spinning, and loading and unloading said casings from the centrifuges at at least one station positioned at said carousel platform.

8. The method of claim 1 in which closure member means is provided at each end of the central casing and in which said step of removing end portions of the casing comprises totally removing said closure member means after said liquid sealant is cured.

9. The method of claim 1 in which the entire amount of curable liquid sealant used is placed centrally into said potting boat member prior to spinning said casing.

10. The method of claim 1, wherein closure member means is provided at each end of the central casing and comprises a cup-shaped member having a rim connected in sealing relation to one of said ends of said central casing, a portion of said cup-shaped member adjacent said rim being of relatively en-larged inner diameter, relative to said tubular casing, each said cup-shaped member also defining an extended cylindrical portion, positioned remotely from said rim, having an inner diameter less than said relatively enlarged inner diameter portion and receiving an end of said hollow fiber bundle.