CA1199280A - Microporous hollow fiber membrane assembly and its method of manufacture - Google Patents

Abstract

MICROPOROUS HOLLOW FIBER MEMBRANE
ASSEMBLY AND ITS METHOD OF MANUFACTURE

ABSTRACT OF THE DISCLOSURE

A bundle of microporous hollow fibers comprises a sheet member and a plurality of microporous hollow fibers generally uniformly arranged along one side of the sheet member. The ends of each fiber are closed to the ingress of fluid in a manner which also bonds the fiber ends to the sheet member. The sheet member can be inwardly rolled upon itself with the fibers disposed inwardly facing the center of the bundle. The bundle can be potted without permanently occluding the fibers with the potting compound or disturbing the distribution of the fibers on the sheet member.

Description

MICROPOROUS HOLLOW ~IBER MEMBRANE ~
ASSEMBLY AND ITS METHOD OF MANUFACTURE

FIELD OF THE INVENTION

This application generally relates to perm selective membrane assemblies and, more particularly, to permselective membrane assemblies utilizing bundles of microporous hollow fibers.

DESCRIPTION OF THE PRIOR ART

The use of hollow fiber membranes in selective permeation separation and purification devices and processes is well know. For example, hollow fiber membranes made o a cellulose deriv~tive material find widespread use in hemodialysis. A bundle of these hollow cellulose fibers can be mounted within a tubular housing using con~entional potting techniquesi such as those disclosed in U.S. Patents 3,492,698; 3,442,002; and 4,227,295.

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During the potting oper~tions disclosed in these patents, a liquid potting compound, typically polyurethane, is introduced into opposite ends of ~he housing in which the fiber bundle is carried. The potting compound impre~nates the ex~eriQr areas of the bundle about and between the ends of the individual fibers.
The potting compound can, and typically does, also enter into both ends of the fiber bores through a process known as "wicking". However, the depth of the potting compound penetrating both ends of the bores is substantially less than the depth of the po~ting compound impregnating the exterior areas of the bundle. This is because, due to the non-air permeable character of the cellulose fibers, the air inside the bores is successively trapped and compressed as the potting compound advances into the bores, and an interior counterpressure is created which eventually inhibits further penetration of potting compound. Thus, once the potting compound has ~ured, one can cut transversely through the potting compound in 20 advance of the penetrated fiber portions to expose open fiber bores.
Besides cellulose derivative materials, hollow fiber membranes made from a microporous material also find use in selective permeation separation and purifi-25 cation devices and processes. ~xamples of such useinclude blood oxygenation, membrane plasmapheresis, and other ultrafiltration processes.
The mounting of a bundle of microporous hollow fiber membranes within a housing utilizing conventional 30 potting techniques can pose difficulties. Unlike the cellulose derivative fibers, microporous fibers are generally air~permeable in character. Thus, during pottin~

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operations, the potting compoulld penetrates, or "wicks", a substantial distance into the bores of the ~ibers. Th:is is because, as air within the bores escapes through the air-permeable fibers outwardly of the bores in advance of the potting compound, there is no counterpressure developed to inhibit the penetration. ~s a result, the depth of the potting compound penetrating the bores becomes essentially equal to the depth of the potting compound outside of the bores. It is thus difficult, or even impossible, to open the bores by cutting a transverse section through the cured potting compound.
Known methods of preventing the penetration of the potting compound into the bores of the fibers include plugging the ends of the fibers with a solid material, such as wax, which can be easily and completely removed after the application of the potting compound; or casting an end fitting about the end portion of the bundle inwardly of the exposed bore ends and thereafter severing the projecting ends of the fiber flush with the outer face of the end mold; or forming looped ~nd portions in the fibers which are thereafter cut away after potting. All of these known methods require additional steps and only complicate and add to the cost of the potting operation.
In addition to the difficulties heretofore 2S outlined, the mere ac~- of handling microporous hollow fibers before and during potting operations can also pose a problem. This is because these fibers are typically quite flimsy and without a substan ial amount of axial rigidity. Thus, during handling, they are easily stre~ched, twisted, collapsed, or otherwise damaged, as well as easily moved out of the desired distribution pattern.

One of the principal objects of this invention is to provide a bundle of microporous hollow .fibers which can be mounted within a housing using known potting techniques, without the presently existing fear of permanently occluding the bores of the fibers due to the ingress of potting compound.
Another principal object of this invention is to provide a bundle of microporous hollow ftibers which, in addition to accommodating known potting techniques, protects the fibers from damage and maintains a desired distribution of the fibers during handling both before and during potting operations.
It is still another principal object of this invention to provide a bundle of microporous hollow fibers 15 which is easily manufactured, whether on a small or large scale, without the need for complicated machinery.

SUMMARY OF THE INVENTION

To achieve these and other objects, the invention provides a bundle of hollow ibers comprising a generally 20 planar sheet member and a plurality of hollow fibers which are ~enerally uniformly arranged along one side of the sheet member. Means is provlded for closing th~ ends of each fiber to the ingress of fluid in a manner which also bonds the ends of each fiber to the sheet member.
In the preferred embodiment, the microporous hollow fibers are made of a thermoplastic polymer, such as polypropylene. In this embodiment, the sheet member is also made of a similar thermoplastic polymer. Heat is uniformly applied to occlude the ends of each fiber.
30 Simultaneously, the application of hea-t thermally bonds the occluded fiber ends to the sheet member.

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The invention also provides a permselective membrane device comprising a tubular housing in which the hollow fibex bundle as above generally described is mounted using known potting techniques.
In this e~bodiment, prior to pottingJ the sheet member is loosely rolled inwardly upon itself about an axis with the hollow fibers disposed along the interior of the inwardly rolled member generally pa~allel to the axis.
The invention also provides a method for manufacturi.ng the hollow fiber bundle as well as a method for manufacturing the membrane device as above generally described.
By occluding the ends of the fibers in accordance with the invention, the ingress of potting compound into the bores of the fibers during potting operations is prevented.
Thus, after the potting compound is cured, a transverse cut through the potting compound serves to sever the occluded ends from the remainder of the bundle and exposes open fiber bores.
Furthermore, by simultaneously bonding the occluded fiber ends to the sheet member in accordance with the invention, a desired uniform distribution of fibers upon the sheet member can be achieved during manufacture of the bundle and can thereafter be maintained during subsequent potting operations. Additionally, the sheet member, in both its normal and its inwardly rolled configurations, serves to protect the fibers from damage or collapse occassioned by handling before and during potting 30 operations.
The bundle of hollow fibers as above described also lends itself to a manufacturing process which is straightforward and does not require the use of overly complicated machinery.

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Other Eeatures and adYantages o the inyention will be polnted out in, or will be apparent from, the speclflcatlon and claims, as will obvious modiflcation of the embodiments shown in the drawings.

5 DFSCRIPTION OF THE DRAWI~GS

Fig. 1 is an exploded, persp~ctive view of a bundle of microporous hollow fibers which embodles various of the features of the inventlon;
Fig. 2 ~s a perspective VieW of the bundle 10 shown in Fig. 1 in an assembled condition;
Fig. 3 is a perspective view of the bundle shown in Fig. 2 in a position inwardly rolled upon itself;
Fig. 4 is a perspective, and partially diagrammatic view of one device which can be utilized to manufacture 15 the bundle shown in Fig. 2 on a large scale basis;
Fig. 5 is a perspective, and partially diagrammatic, view of another device which can be utilized to manufacture the bundle shown in Fig. 2 on a large scale basis;
Fig. 6 is a side view of a permselective membrane device utilizing the hollow fiber bundle shown in Fig. 3 during centrifugal potting operations;
Fig. 7 is a side view of the permselective membrane device shown in Fig. 6 after the completion of 25 potting operations; and Fig. 8 is an end section Yiew Qf the permselective mer~rane device taken generally along line 8-8 in Fig. 7.

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Before explaining the embodiments o~ the invention in detail, it is ~o be unders~ood that the invention is n~t limited in its application to the details of construction and the arrangement of components set forth in the following description and as illustrated in the drawings. The invention is capable of other embodiments ~nd of being practiced and caxried out in various ways.
~lso, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A bundle 10 of microporous hollow fibers applicable for use in various permselective membrane devices is shown in Figs. 1 through 3. Generally~ the bundle 10 includes a flexible sheet member 12 on which a plurali~y of the microporous hollow fibers 14 are carried.
By the ~erm "microporous", it is intended to mean that the walls of the fibers have pores which are permeable to air and other ~ases, thereby permitting air 20 and gases to readily pass therethrough. However, notwith-standing the air-permeable nature, the fiber walls still retain a semi-permeable or permselective characteristic and serve to restrict the flow of a liquid passing through them, as in blood Qxygenators, or to ~estrict the ~low a 25 component of the liquid fro~ passing th~ough, such as blood cells in membrane plasmapheresis devices, and in other comparable ultrafiltration processes.
Materials from which a microporous hollow fiber can be made include thermoplastic polymers, such a5 30 polypropylene. These polymers can be formed into hollow fibers by know processes such as solution spinning or melt spinning.

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For example, a polypropylene hol]ow fiber can be manufactured which has a wall thickness of approximately 150 microns, an interior diameter of approximately 320 microns, a maximum pore size of approximately .55 microns, and an average pore size of approximately .30 microns.
Such a hollow fiber is commercially available from Enka, A. G., Federal Republic of Germany, and is well suited for use in a plasmapheresis procedure to separate the plasma from whole blood.
Because of its air permeable nature, this polypropylene hollow fiberl as well as all microporous hollow fibers in general, does not readily accommodate potting using known potting techniques. This is because~
during potting operations, the potting compound can and 15 does easily penetrate and permanently occlude the bores of the fibers.
Furthermore, this polypropylene hollow fiber, as , well as most microporous hollow fibers in general, is easily deformed, lacks substantial a~ial rigidity, and is quite flimsy. It can be easily stretched, crimped, or collapsed during handling, and the maintenance of a uniform arrangement of the fibers before and during potting Gan pose additional difficulties.
With these problems in mind, the invention 25 provides means 18 for closing the ends 16 of each fiber 14 to the ingress of fluid in a manner which simultaneously bonds the fiber ends 16 to one side 20 of the sheet member 12.
As will be soon become apparent, the resulting 30 bundle lO shown in Fi~s. 1 through 3 is compact, easily handled without damaging or collapsing the fibers, and readily accommodates potting using known techniques.

q3 The means 18 for si:multaneously closing and bonding the ends 16 of each fiber 14 to the sheet member 1.2 can vary accordiny ~o the particular fiber and sheet mat.erials utilized. In the particular embodiment illustratedr in which the fiber 14 is a thermoplastic polymer (i.e. polypropylene), the application of heat to melt and occlude the fiber ends 16 is preferred as being fast and effective. To accommodate this procedure, the sheet member 12 is made of a thin, thermoplastic, and preferably foraminous, material; for example, a flexible, non-woven, polypropylene screen, such as Shell Enjay CD476 or Dart PL 381. The application of heat to occlude the fiber ends 16 thus also simultaneously forms a thermal bond between the occluded ends 16 and the underlying thermoplastic sheet member 12.
It should be appreciated that, by appropriately preselecting and matching the materials utilized for the bundle 10, a thermoplastic resin or an ultrasonic or radiofrequency procedure could be utilized instead of heat to occlude the fiber ends 16 and simultaneously bond the ends 16 to the underlying sheet member 12.
The bundle 10 as heretofore described lends itself to straightforward manufacturing processes. For example, an essentially manual technique can be utilized for 25 small scale production purposes. In this procedure, and as shown in Figs. 1 and 2, the sheet member 12 is cut to a desired width and length, and the fibers 14 pre-cut ~o the same length (see Fig. 1~. The fibers 14 are then manually arranged uniformly alon~ one side of the sheet 30 member 12. The fibers 14 can be arranged in single, double, or multiple layers, depending upon the number of fibers 14 in the bundle 10. The fiber ends 16 are thereafter simultaneously occluded and bonded to the edges of the ~10--sheet member 12 by the formation of a heat seal line 42 uniformly across the fiber ends 16 (see Fiy. 2), utilizing any commercially available electric hea~ sealing machine (not shown).
The bundle 10 may a:Lso be assembled utilizing mechanized mass production techniques. For example, and as shown in Fig~ 4, the material from which of the sheet member 12 is made may be mounted in a continuous length between two rollers 22 and 24, one of which (roller 24 in Fig. 4) is operatively coupled to a drive motor 26 for rvtation. The sheet material 12 can thus be fed from the roller 22 and advanced in a conveyor belt fashion onto the roller 24.
Between the two rollers 22 and 24, and spanning the width of the sheet material 12, is a heat sealing mechanism 28. The mechanism 28 may be variously constructed.
In the embodiment illustrated in Fiy. 4, it includes a movable heat sealing element 30 disposed above the sheet material 12. The movable element 30 is carried by a 20 pneumatic ram 36 which, in turn, is coupled to a pneumatic control circuit 38. The mechanism 28 also includes a stationary heat sealing element 32 disposed below the sheet material 12. Both of the elements 30 and 32 are heated by a suitable electrical control circuit 34 to 25 form the desired heat seal.
In this arran~ement, the hollow fibers 14 are carried in continuous lengths on spools 40 disposed adjacent to and behind the feed roller 22.
In operation, the fibers 14 are initially 30 manually distributed on the sheet 12 adjacent to the mechanism 28. The mechanism 28 is then pneumatically operated (using control circuit 38) to bring the movable heat sealing element 30 do~n to sandwich an area of the sheet ~aterial 12 between the two heat sealing elements 30 and 32. The two elements 30 and 32 are thereafter electrically heated (using control circuit 343 to form the continuous heat seal line 42 which simul~aneously 5 occludes the fibers 14 and thermally bonds the fibers 14 to the sheet material 12 along the line 42.
The drive motor 26 is thereafter actuated to to advance the sheet material 12 and the attached hollow fibers 14 for a predetermined distance. Guides 43 are 10 provided to maintain the desired distribution of fibers 14 on the sheet 12. The drive motor 26 then is stopped, and the heat sealing mechanism 28 again actuated to form another continuous heat seal line 42.
The above described sequence is repeated.
lS Preferably, the drive motor 26, the electrical control circuit 34, and the pneumatic control circuit 38 are electrically interconnected (as shown by phantom lines in Fig. 4) to function automatically to follow the sequence.
Heat seal lines 42 are thereby formed at desired intervals along the sheet material 12 as the sheet material 12 is wound upon the drive roller 24, along which lines 42 the ~i.bers 14 are occluded and bonded to the sheet 12.
The sheet material 12 can then be unwound off the drive roller 24, and separated along the heat seal lines 42, such 25 as by cutting, to form a plurality of individual bundles 10, one of which is shown in Fi~. 2.
Another method suited for mass production techniques is shown in Fig. 5. In this method, the sheet material 12 is mounted upon a drum 44. The drum 44 is 30 operatively coupled to a drive motor 46 for rotation.
Disposed axially of the rotatable drum 44 (and similar to the arrangement shown in Fig. 4~ is a first heat sealiny element 48, which is mounted for movement above the drum 44l and a second heat sealing element 50, -~2-which is carried by the drum 44 for common rotation the:rewith and which is disposed beneath the sheet material 12 carried by the drum 44. Both heat sealing elements 48 and 50 are coupled to an electrical control circuit 52, just as the members 30 and 32 in the Fig. 4 embodiment are connected to the electrical control circuit 34.
Also like the Fig. 4 embodiment, the movable element 48 is carried by a pneumatic ram 5~ which, in turn; is coupled to a pneumatic control circuit 56.
In this arrangement, the hollow fiber 14 is wound in a continuous length upon a spool 58 disposed axially of the drum 44. The hollow fiber 14 is then evenly distributed from the spool 58 in one or more concentric layers onto the drum-mounted sheet material 12 during rotati.on of the drum 44 by means of a feeder mechanism 6G. The feeder mechanism 50 includes a feeder member 62 which is operatively carried in an axial path along one side of the drum 44 by a worm gear 64 which, in turn, is coupled for rotation to a drive motor 6Ç. The direction of travel of the feeder mernber 62 (shown by arrows in Fig. 5) is controlled by the direction of rotation of the worm gear 64.
In this arrangement, after the fibers 14 are initia7ly fastened to the sheet member 12, such as by a solve~ ta_k bond, he drive moto~s 46 and 66 ~re operated to rotate the drum 44 and drive the feeder mechanism 60. The hollow fibers 14 are evenly distributed back and forth along the sheet ~ember 12. When a desired fiber distribution is achieved, the drive motors 44 and 66 30 are stopped to place the heat sealing elements 48 and 50 in a facing relationship, as shown in Fig. 5. The control circuits 52 and 56 are then operated, as above described in the Fig. 4 embodiment, to form a continuous heat seal line 42, along which the fibers 14 are occluded ancl thermally bonded to the sheet material 12.
The sheet member 12 is thereafter separated, such as by cutting,along the heat seal line 42 to form an individual bundle 10 as shown in Fig. 2.
Alternately, by increasing the circumfexence of the drum 44, and by including addi~ional heat sealing elements 50 disposed at desired arcuate inter~als along the expanded drum circumference (as shown in phantom lines in Fig. 5), an increased length of sheet material 12 can be accom~odated. Periodic heat seals 42 can then be formed along this circumference, and a plurality of individual bundles 10 may be thus fabricated.
The opera~ive parameters surrounding the formation of the heat seal can, of course, vary according to the particular thermoplastic materials used. It has been observed that, utilizing the polypropylene materials heretofore discussed, and uniformly distributing approximately 800 fiber lengths across an 8 inch width of sheet material, the fibers can be effectively occluded and heat sealed to the sheet material by the application of heat beginning at temperatures approximating 200 to 300F and gradually raised by operation of the associated control circuit to tempera~ures approximating 400 to 500F.
The bundle 10 as heretofore described facilitates the handling of the microporous hollow fibers 14 without fear of damaging or collapsing the fibers 14~ Because the fibers 14 are disposed along only one side 20 of the sheet member 12, the bundle 10 may be handled with a minimum of physical contact to the fibers 14. Furthermore, since the fiber ends 16 are bonded to the sheet material 12, the fibers 14 are protected against stretching, kinking, or other deformations during handling.

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The bundle 10 also ~Eacilitates the construction of a permselective membrane device 68 (see Fig. 7) utilizing kno~n potting techniques, such as those techniques disclosed in U.S~ Patent 4,227,245.
Referring first principally to ~ig. 7, the device 68 includes a tubular housing 70 or cannister having opposite ends 72 and 74 and an open interior 76 extending therebetween. The bundle 10 as heretofore,described is carried within the interior 76 of the housing 70 n a loose, inwardly rolled configurati.on.
More parti.cularly, and referring now principally to Figs. 3 and 8, to accommodate its mounting within the tubular housing 70, the sheet member 12 on which the plurality of hollow fibers is attached can be manually rolled inwardly upon itself in a loose fashion without the need for a central core member about an axis 7~ extending generally parallel to the fibers 14.
Because the f.ibers 14 are disposed only along one side 20 of the sheet member 12, the sheet member 12 may be inwardly rolled with the fibers 14 disposed along only the interior surface of the roll, and thus generally shielded from physical contact as the sheet 12 is being rolled.
When in this loose, inwardly rolled configur-ation, the bundle 10 defines in transverse cross-section one or more convoluted layers 80, with the fibers 14 arranged along the interior, or inwardly facing, side 20 of each layer 80. The loose, inwardly rolled configuration of the bundle 10 prevents tight, pressing contact between the fibers 14, which could collapse or otherwise cause damage ~Q the fibers 14.
The loose, inwardly rolled bundle 10 can be next manually inserted into the interior 76 of the housing, after which potting operations can proceed on an unintex-rupted "one shot" basis.

ReEerring now principally to Fig. 6/ during thepotting operations, the housing ends 72 and 74 are each sealingly capped by a cup-shaped closure member 82, which can be attached by solvent bonding. The resulting intermediate assembly 69 is then centrally mounted on a centrifuge rotor 84. An elongated potting boat 86 is attached to -the assembly 69 with its outlet ports 88 positioned within aperatures 90 formed outwardly of the side of the housing 70.
The centrifuge rotor 84 is thereafter spun about an axis of rotation 71 which generally extends through the center of the housing 70. Potting compound, typically a polyurethane sealant 92, is driven radially outwardly toward both ends of the potting boat 86. From there, the sealant migrates thxough the outlet ports 88 and side apertures 90 to fill each closure member 82. The flow of sealant 92 is generally shown by arrows in Fig. 6. The inwardly rolled ends of the bundle 10 confined within the closure members 82 are thereby surrounded and enveloped by the sealant 92 ~see Fig. 8).
During this step of the potting operation, the ingress of sealant 92 into the bores of the fibers 14 is blocked by the occluded fibers 14 along the heat seal lines 42. The sealant 92 thus impregnates only the exposed exterior portions of the bundle 10, as shown in Fig. 8, en~eloping each concentric la~er 80 and the exteriors of the holloT~ fibers 14 disposed therebetween.
Furthermore~ because the ends 16 of the fibers 14 are also bonded to the sheet member 12, nesting or movement of the fibers 14 out of their prearranged configuration on the sheet 12 during this step of the procedure is prevented. The desired arrangement of fibers 14 is thus maintained.

The potting sealant 92 is thereafter cured.
A transverse cut 91 is then made generally through the middle of the cured sealant 92 at each end 72 and 74 of the housing 70 (the cut lines 91 being shown by phantom lines in Fig. 6). The sealed and bonded ends 16 of the fibers 14 and underlying sheet material 12 are thus severed and removed from the remainder of ~he bundle 10. Open fiber ends 17 sealingly enveloped by the cured potting sealant 92 (see Fig. 8) are exposed.
It should now be apparent that, by virtue of the invention, the potting characteristics of the bundle 10 of air-per~eable microporous hollow fibers 14 approximates the potting characteristics of fibers which are not air permeable, such as those made of a cellulose-derivative material.
After severing the sealant 92 along lines 91, end caps 94 (see Fig. 7) of conventional design (such as those shown in Schnell Patent Application Serial No.
58,5~9, filed January 18, 1979) may be sealed to the potted ends 72 and 74 of the housing 70. The assembly of the permselective microporous hollow fiher membrane device 68 as shown in Fig. 7 is completed.
When assembled (and still referring to Fig. 7), the device 68 includes a blood inlet port 96 formed on one of the end caps 94, and a blood outlet port 98 formed on the other end cap 94. Blood introduced through the port 96 enters the open ends 17 of the fibers 14. By maintaining a desired level of blood inlet pressure, the plasma will proceed through the micropores of the fibers 14 and out into the open volume 100 circumferentially surrounding the bundle 10. The foraminous character of the sheet member 12 facilitates this plasma flux into the volume 100.

One of the side apertures 90 of the housing 70 is preferably plugged by a plug member 102, and the other aperture 90 is preferâbly left open to collect the plasma filtratate from the volume 100.
The plasma poor blood ~containing red ce]ls, leukocytes, and platelets? exits the open ends 17 of the fibers 14 through port 98, typically for return to the patient~dorlor .
It should be appreciated that the bundle 10 can be handled and rolled without collapsing and damaging the fibers 14 and without altering the desired distribution of fibers 14 before and during potting operations. Thus a maximum desired plasma flux from the fibers 14 can be achieved. ~he bundle 10 also permits the use of conventional potting techniques on an uninterrupted basis, without the fear of permanently occluding the bores of the fibers 14 to render them useless for their intended purpose.
It should also be appreciated that the bundle 10 is easily manufactured, whether on a small or large 20 scale, without the need of complicated machinery, such as those involved in winding hollow fibers or otherwise involved in the formation of loops in the end portions of the fibers to prevent the ingress of potting compound.
Lastly, it should be appreciated thât various 25 changes and modifications can be made without departing from the spirit of the invention or from the scope of the appended claims.

Claims (15)

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

1. A hollow fiber bundle accommodating a potting operation which generally follows the steps of impregnating the ends of said bundle with a curable fluid sealant, curing the sealant, and thereafter transversely cutting through the sealant-impregnated ends of said bundle to expose open bores of the hollow fibers which are surrounded on their exterior by the cured sealant, said hollow fiber bundle comprising a single generally planar sheet member having opposite side edges, a plurality of microporous hollow fibers each having opposite ends normally open to the ingress of the curable fluid sealant, said plurality of hollow fibers being arranged generally uniformly along only one side of said single sheet member with said normally open opposite ends of said fibers positioned adjacently along said opposite side edges of said sheet member, and means for closing said hollow fiber ends to the ingress of the curable fluid sealant prior to the sealant impregnating step of the potting operation by bonding said hollow fiber ends to said adjacent side edges along said one side of said single sheet member, said closure means forming a uniform, continuous closure line along each of said adjacent side edges positioned for complete severance from the remainder of said bundle during the transverse cutting step of the potting operation to remove said closure means and thereby reopen said hollow fiber ends.

2. A hollow fiber bundle accommodating a potting operation which generally follows the steps of impregnating the ends of said bundle with a curable fluid sealant, curing the sealant, and thereafter transversely cutting through the sealant-impregnated ends of said bundle to expose open bores of the hollow fibers which are surrounded on their exterior by cured sealant, said hollow fiber bundle comprising a single, generally planar sheet member having opposite side edges and capable of being loosely rolled inwardly upon itself about an axis to define in transverse cross-section one or more convoluted layers, a plurality of microporous hollow fibers each having opposite ends normally open to the ingress of the curable fluid sealant, said fibers extending generally parallel to said axis and arranged generally uniformly along only the inwardly facing sides of said convoluted layers with said normal open opposite ends of said fibers positioned adjacently along said opposite side edges of said sheet member, and means for closing said hollow fiber ends to the ingress of the curable fluid sealant prior to the sealant impregnating step of the potting operation by bonding said hollow fiber ends to said adjacent side edges along said inwardly facing side of said sheet member, said closure means forming a uniform, continuous line along each of said adjacent side edges for complete severance from the remainder of said bundle during the transverse cutting step of the potting operation to remove said closure means and thereby reopen said hollow fiber ends.

3. A bundle according to claim 1 or 2 wherein said closure line comprises a heat seal line disposed uniformly across each of said fiber ends to occlude said fiber ends and simultaneously bond said ends to said sheet member.

4. A method of manufacturing a bundle of hollow fibers comprising the steps of arranging a plurality of hollow fibers fabricated of a microporous material generally uniformly along one side of a sheet member, and bonding the ends of each of the hollow fibers to the sheet member in a manner which also closes the fiber ends to the ingress of fluid.

5. A method of according to claim 4 and further including, after said bonding step, the step of rolling the sheet member inwardly upon itself about an axis extending generally parallel to the fibers to define in transverse cross-section one or more convoluted layers between which the fibers attached to the sheet member are disposed.

6. A method according to claim 4 wherein said step of arranging the hollow fibers includes advancing a continuous length of material from which the sheet member is made, and uniformly distributing along the length of the sheet material a plurality of hollow fibers each having a continuous length, and wherein said bonding step includes forming a bond between the fibers and the sheet material at preselected intervals, which bond also occludes the fibers at that point, thereby forming a plurality of bonded areas along the continuous length of sheet material, and separating the continuous length of the sheet material along the bonded areas to form a plurality of individual bundles each having a plurality of hollow fibers the end portions of which are occluded and bonded to the sheet material.

7. A method according to claim 4 wherein said step of arranging the hollow fibers includes mounting a length of the material from which the sheet member is made upon a rotating drum, distributing about the circumference of the rotating sheet member a plurality of hollow fibers each having a continuous length, and wherein said bonding step includes bonding the fibers to the sheet material along an area extending axially of the axis of drum rotation in a manner which also occludes the fibers at that point, and separating the sheet material along the bonded area to form a generally planar bundle having a plurality of hollow fibers the end portions of which are occluded and bonded to the sheet material.

8. A method according to claim 7 wherein said bonding step further includes bonding the fibers to the sheet material along more than one axially extending area, which areas are arcuately spaced about the circumference of the drum, and wherein said separation step includes separating the sheet material along each of the bonded areas to form a plurality of individual generally planar bundles each having a plurality of hollow fibers the end portions of which are occluded and bonded to the sheet material.

9. A method according to claim 4 or 5 wherein said bonding step includes heat-sealing the ends of the hollow fibers to the sheet material to attach the ends of each fiber to the sheet material and simultaneously close the fiber ends to the ingress of fluid.

10. A method of manufacturing a bundle of hollow fibers comprising the steps of arranging a plurality of hollow fibers fabricated of a thermoplastic microporous material generally uniformly along one side of a sheet member which is also made of a thermoplastic material, and heat-sealing the ends of each of the hollow fibers to the sheet member to attach the ends of each fiber to the sheet member and simultaneously close the fiber ends to the ingress of fluid.

11. A method according to claim 10 and further including the step of rolling the sheet member inwardly upon itself about an axis extending generally parallel to the fibers to define in transverse cross-section one or more convoluted layers between which the fibers which are heat-sealed to the sheet member are disposed.

12. A method of manufacturing a permselective membrane device comprising the steps of arranging a plurality of hollow fibers fabricated of a microporous material generally uniformly along one side of a sheet member, bonding the ends of each of the hollow fibers to the sheet member in a manner which also closes the fiber ends to the ingress of fluid, locating the sheet member within the confines of a hollow housing, impregnating the closed ends of the hollow flbers and adjacent area of the sheet member with a curable, fluid sealant, curing the sealant, and cutting transversely through the sealant-impregnated, closed ends of the fibers and adjacent sheet member to open the hollow fiber ends to communication with the atmosphere.

13. A method according to claim 12 and further including, after said bonding step, the step of rolling the sheet member inwardly upon itself about an axis extending generally parallel to the fibers to define in transverse cross-section one or more convoluted layers between which the fibers attached to the sheet member are disposed, and wherein said sheet member locating step includes locating the inwardly rolled sheet member within the confines of a hollow tubular housing.

14. A method of manufacturing a permselective membrane device comprising the steps of arranging a plurality of hollow fibers fabricated of a thermoplastic microporous material generally uniformly along one side of a sheet member also made of a thermoplastic material, and heat-sealing the ends of each of the hollow fibers to the sheet member to thermally attach the ends of each fiber to the sheet member and simultaneously thermally occlude the fiber ends to the ingress of fluid.
locating the sheet member within the confines of a hollow housing, impregnating the closed ends of the hollow fibers and adjacent area of the sheet member with a curable, fluid sealant, curing the sealant, and cutting transversely through the sealant-impregnated, closed ends of the fibers and adjacent sheet member to open the hollow fiber ends to communication with the atmosphere.

15. A method according to claim 14 and further including, before said sheet member location step, the step of rolling the sheet member inwardly upon itself about an axis extending generally parallel to the fibers to define in transverse cross-section one or more convoluted layers between which the fibers which are heat-sealed to the sheet member are disposed.