IE46551B1 - Diffusion device separation elements - Google Patents

Abstract

This application discloses an apparatus and method for preparing an elongated, coreless bundle of homogeneously distributed hollow, generally longitudinally-directed, semipermeable filaments, free of direct mechanical attachment to each other, for use as a fluid separation element in a diffusion device such as a dialyzer. The filaments are positioned in the bundle whereby the majority of the lengths thereof, and the overall directions thereof, define an angle to the longitudinal axes of the said filament bundle. The filaments are positioned in crossing, overlying relation with adjoining filaments, said filaments essentially occupying individual, parallel, flat planes. The filaments define first sets of generally parallel strands defining a first angular relation to said longitudinal axis and second sets of generally parallel strands defining an opposite angular relation to said longitudinal axis, a first filament of a first set being overlaid by a first filament of a second set, which first filament of said second set is, in turn, overlaid by a second filament of said first set, which second filament of said first set is, in turn, overlaid by a second filament of said second set. The said relationship continues throughout the majority of the filaments of the first and second sets to define interleaving releationships, in which the filaments of each set overly the immediatelypreceding filaments of the other associated set, and are overlaid by the immediately-following filaments of said other set, the majority of individual filaments thereof extending across 15 to 50 percent of the width of said filament bundle.

Description

This invention relates to a fluid separation element for use in a diffusion device, especially for a hollow-fibre dialyzer of the type used in artificial kidney systems.

A hollow-fibre dialyzer includes an elongate and generallycylindrically shaped casing within which many very fine, hollow and semi-permeable fibres are positioned and secured adjacent their terminal ends to the casing. Blood from the patient flows through the dialyzer inside the fibres. Dialysis solution flows through the dialyzer and surrounds and contacts the fibres so as to receive bodily waste products from the blood and remove them from the dialyzer.

The fibres are made from a long hollow filament of Cellophane (R.T.M.) or of a cellulose derivative, such as sold under the trade name Cuprophan (T.M). The filament is continuous and is supplied on a spool.

In manufacture the dialyzer it is impractical to individually cut the filament into individual fibres, group or bunch the fibres, and then assemble the dialyzer. One suggested process for bunching the fibres is to form the filament into a hank or bundle by winding the filament on a wheel, grasping the wound filaments at two points and removing the hank from the wheel. The hank or bundle is then pulled into a cylindrical casing. In this form the filament is still continuous, and after further preparation the looped ends of the hank are cut so as to form the open-ended fibres. As can be appreciated, only one device can be made from each hank.

In other winding systems the filament is wound on a support, which support ultimately becomes a part of the device. Unfortunately, in the dialyzer the support is an inactive element which occupies space and thereby reduces the efficiency of the device.

Hollow fibre dialyzers of other diffusion devices are made from bundle., of fibres which are positioned in generally parallel relation to the longitudinal axis of the fibre bundle. The result of this is to create, during use, relatively inhomogeneous flow spaces about the exterior of the fibres, where shunting of the dialysis or other solution passing around the exterior of the fibres takes place, providing uneven and poor dialysis results. Also, stagnant areas are formed in the dialyzer which can enhance blood clotting.

Some commercial hollow fibre dialyzers of the prior art use fibres made from cellulose acetate, which is then regenerated into cellulose. These fibres, when wet, ,4 6 5^5 4are very soft and do not provide a good, generally selfsupporting, fibre matrix for providing generally homogenous flow channels through the bundle of fibres.

As a result, the longitudinally arrayed parallel fibre bundles, particularly when made of cellulose regenerated from a cellulose ester, have exhibited dialysis clearance rates and blood clotting characteristics which are below optimum.

Furthermore) the soft cellulose filaments generally are packed together to provide an undesirably low void fraction (which is the fraction of the fibre bundle v/hich is not occupied by fibres, and which constitutes in a dialyzer the flow path for dialysis fluid). Since the wet, soft filaments are not very self-supporting, if a void fraction of as much as 0.4 is utilised, the tendency of the soft filaments to permit the formation of fluid shunt paths through the space between the filaments becomes very pronounced.

Stiffer hollow cellulose filaments can be obtained through the cuprammonium-regenerated cellulose process, which is an old and well-known process. Such filaments are commercially available, for example, from Enka Glanzstoff A.G. in Wuppertal, West Germany. However, these fibres have been difficult to assemble on a commercial basis into an effective dialyzer. - 4 46 5 5 1 In accordance with this invention there is provided a fluid separation element, for a diffusion device, comprising an elongate, coreless bundle of hollow, semi-permeable filaments, free of direct mechanical attachment to each other, the bundle being of substantially rectilinear cross-section when first manufactured, each of said filaments extending lengthwise of the bundle for the entire length of the bundle, the great majority of the filaments defining an angle of 2° to 3° to the longitudinal axis of the bundle, the filaments being positioned in crossing, overlying relation with adjacent filaments, the majority of filaments extending across fifteen to fifty percent of the width of said filament bundle, in its as-manufactured state.

The filaments also preferably occupy individual, parallel planes..

The result of this is to create an improved and generally more uniform configuration in the flow space exterior of the filaments in the bundle, resulting in a substantial improvement in diffusion and dialysis characteristics.

Preferably, the individual filaments extend across about twenty to thirty-five percent of the width of the bundle.

The majority and preferably substantially all of the °0 lengths of the filament are disposed at preferably a generally uniform angle to the longitudinal axis of the bundle, and also at an angle to a plane passing through the longitudinal aids of the bundle, which plane is perpendicular to the planes which contain individual filaments. Preferably, such a 'plane perpendicular to the planes of the individual filaments will intersect from fifteen to fifty percent of the filaments in the bundle, and generally most preferably from twenty to thirty-five percent, to provide a bundle which exhibits an improved fluid flow path, particularly for dialysis solution, through the bundle outside of the filaments.

A further characteristic of the preferred filament bundles of this invention is that they have the property of exhibiting increased resistance to being pulled apart, due to their structure, in a direction transverse to the longitudinal axis and parallel to the planes which contain individual filaments, when compared with the direction transverse the longitudinal axis and perpendicular to the planes which contain individual filaments. Thus, the filament bundles exhibit an increased independent self-supporting characteristic despite the fact that they are nonwoven and free of direct mechanical attachment to each other.

Thus they tend to remain together in a coherent, generallyordered bundle while it ls being assembled into a dialyzer.

Preferably, the void fraction as defined above, in the bundles of this invention is in excess of 0.4, and most preferably between about 0.6 and 0.8. As a result of this, there is more room for dialysis solution or other fluid passing through the bundle between the filaments, to provide an improved dialysis solution flow path which, in particular, provides good access of the dialysis solution to the filaments in the central region of the bundle. In the filament bundles of the prior art, the void fraction can be as low as 0.1 Reference is now made to the accompanying drawings, wherein;Figure 1 is a perspective view of one side of the winding machine used to manufacture the filament bundle of this invention, showing the take-up reel, two filament supply spools and the filament guide; Figure 2 is a diagrammatic and perspective view of a drive system for driving the take-up reel and for moving the filament guide; Figure 3 is a perspective view, partially in 20 section, showing a two-cam system for controlling the movement of the filament guides on each side of the machine; FIGURE 3Δ shows an alternative single cam system for controlling the guides; FIGURE 4 is an enlarged perspective view showing a filament guide assembly·; FIGURE 5 is a side elevational view showing the take-up reel; FIGURE 6 is a sectional view taken substantially along line 6-6 of FIGURE 5 and showing a hub-and-locking mechanism for the take-up reel; FIGURE 7 is a greatly enlarged elevational view showing a portion of the take-up reel; FIGURE 8 is a view taken substantially along line 8-8 of FIGURE 7 and showing the filament crossover; FIGURE 9 is a perspective view showing a split sleeve for use in bundling the filament for cutting into the fibres; and FIGURE 10 is an end view of the split sleeve with one side opened; FIGURE 11 is a schematic view of a filament bundle of this invention showing the typical arrangement of a few of the filaments in the bundle for illustrative purposes; FIGURE 12 is a sectional view taken along line 12-12 of FIGURE 11; FIGURE 13 is a perspective view of a dialyzer utilising the filament bundle in accordance with this invention.

Referring now to FIGURE 1, winding machine 10 for making the filament bundle of this invention includes a body 12 on each side of which is provided a winding mechanism. The body includes a boxlike main section 14 which is supported by a pair of legs 16 and 18. A control console and supply spool mounting section 20 is supported in a cantilever fashion from the back end of the main body section 14.

Two substantially identical winding mechanisms are provided, one on each side of the body. Thus, two winding operations can be performed simultaneously, if desired.

Each winding mechanism includes upper and lower spool support shafts 22 and 24, which extend laterally from the mounting section 20. Two filament supply spools 26 and 28, each having wound thereon a continuous hollow filament, are mounted on the shafts 22 and 24. The filaments and 32 extend from the spools through the filament guide assembly 34 and to tne driven take-up reel assembly 36.

A protective and transparent case, such as 38, having two access doors 38a and 38b is carried by the main body section so as to enclose the guide assembly and take-up reel.

The rotation of the take-up reel assembly 36 and movement of the filament guide assembly 34 are controlled by a drive system, which is enclosed with the main body section 14. The system includes an electric motor 40, which drives both the reel assemhly and the guide assembly. The motor speed can be varied between 0-2000 rpm.

The Reel Drive. The motor 40 is connected to the take-up reel through a gear and timing belt system as described hereinafter. The motor 40 is connected to a 5:1, worm-gear-type speed reducer 42 having an output gear 44. A geared output drive timing belt 46 is trained about the gear 44, as well as the driven gear 48, which is mounted on the cross shaft 50. A counter, take-off gear 52 is mounted on the cross shaft 50 and is connected to a rpm counter 54 by a counter timing belt 56. The gearing system is arranged such that the counter is synchronised with the take-up reel rpm.

A reel drive gear 58 is also mounted to the shaft 50 and is connected to a reel drive shaft 60 by a gear 62 on the shaft 60 and a timing belt 64. The take-up reel assembly 36 is mounted to an end of the shaft 60. Thus the take-up reel is driven; by the motor 40; through the gear reducer 42; through the gear 44, belt 46 and gear 48; through shaft 50; through gear 58; 46S5 1 belt 64 and gear 62; and through shaft 60. Through this system the take-up reel can be driven at between 0-400 rpm.

The Guide Drive. The guide assembly 34 is mounted so as to cause the filament to reciprocate or move laterally with respect to the take-up reel assembly 36 at a rate related to the rotation of the take-up reel. The motor 40 drives the guide assembly. A variable speed control 64 is mounted to the motor 40. The speed control includes a manual speed adjuster 65 and an output gear 66. The speed of the output gear 66 is controllable between 0-400 rpm. A drive timing belt 68 is trained about the output gear 66 and a smaller driven gear 70. For each revolution of the output gear 66, the driven gear 70 revolves 2.25 times, so as to provide a 2.25:1 gear ratio. The driven gear 70 is secured to one end of a shaft 72, which enters a gear box 74. A second aligned shaft 76 exits the gear box and a gear 78 is secured to the outer end of the shaft 76. A rotatable cam drive shaft 80 extends upwardly from the gear box and is driven by the shaft 72. A bevel gear arrangement (not shown) is provided within the gear box for driving the shafts 76 and 80.

Another timing belt 82 is trained about the gear 78 and a gear 84 for driving a second rotatable cam drive shaft 86 and a counter 88, through a gear box arrangement 89, which is similar to that previously described in Π connection with the gear box 74. The counter 88 is synchronized with the rotation of the shafts 80 and 86, which, in turn, is related to the rate of reciprocation of the guide arm, so that the counter indicates the rate of guide arm reciprocation or oscillation.

Referring now to FIGURE 3, each of the shafts 80 and 86 carry at their upper end a cam, such as 90 and 92, which controls the reciprocation of the guide assembly 34 and the filaments. A reciprocating control rod 94 extends from within the body 14 through a sidewall 14a and connects at its outer end to the guide assembly 34.

At the inner end, the rod 94 includes a cam follower 96, which is biased against the cam 90 by a coiled compression spring 98 that bears against a bearing plate 100 and the cam follower 96. Rotation of the cam 90 causes the rod 94 to reciprocate. It will be appreciated that the guide arm on the other side of the machine (not shown) is controlled in a similar manner.

With this arrangement the rate of reciprocation of the guide arm can be controlled between 0-900 oscillations per minute.

In the alternative cam construction shown in FIGURE 3A, there is a single grooved cam 102. Here there is only one drive shaft 80a which drives the single cam, which, in turn, controls the two control rods 93a and 94a. •46551 It will be appreciated that the speed of the cam drive shaft 80 relative to the take-up reel drive shaft 60 can be controlled and adjusted with the speed control adjuster 65. If no adjustment is made, the ratio of guide arm reciprocation to take-up reel rotation remains constant regardless of the speed of the take-up reel. However, use of the adjuster 65 permits adjustment and control of the ratio of guide arm reciprocation to take-up reel rotation.

The guide arm assembly 34 is mounted to the outside of sidewall 14a by a vertically adjustable mounting plate 101, a pivotally adjustable side plate 102 and a forwardly and rearwardly adjustable lateral support plate 104. An upper filament sensing switch 106 is mounted to the top side of the plate 104 and a lower filament sensing switch 108 is supported by and is positioned below the plate 104. Each switch includes leaf-like member, such as 110, which is biased toward the filament and which engages and senses the presence of the filament, such as 30. In the event the filament breaks during winding, the member 110 moves upwardly and actuates means (not shown) for disabling the drive system and for applying a controlled braking action to the supply spool shafts and the take-up reel to minimize breakage of filaments on other reels.

An elongated and swingable guide arm 112 is pivotally mounted at its back end to the support plate 104, forwardly of-the switch 106, by a pin 114. The control rod 94 is connected to the arm at a point intermediate the ends of the arm by a universal-type joint 116. The head 112a at the forward end of the guide arm carries upper and lower spring-like filament guides such as 118, which co-operates with the spring-like filament guides, such as 119, associated with the switches. As the control rod reciprocates, the head 112a swings back and forth in a manner controlled by the cam 90.

The take-up reel assembly 36, as shown in FIGUKES 5 and 6, includes a filament winding plate 120 and a hub-and-locking system 122 for removably securing the plate to the machine.

The Winding Plate. The plate 120 has a large, circular and centrally positioned opening whioh defines the inner edge 124, and has six support edge carrying sections 126, 128, 130, 132, 134 and 135. Each of the sections are positioned radially outwardly from the centre of the plate and equally about the periphery.

A V-shaped filament support assembly, such as 136, is mounted on the plate at each of the support sections, such as 126. Each of the support assemblies, such as 136, includes a pair of outwardly extending U-shaped filament supports 138 and 140, each of which terminates in a lower beveled edge, such as 138a and 140a. Each of the supports, such as 138 and 140, is bolted to the plate through bolt-receiving apertures in the plate 120. As can be seen in FIGURE 5, the filament support assemblies can be movably positioned in one of three different radial positions. Thus the supports 138 and 140 can be moved from the inner position as shown to an intermediate position at 142 and 144, or to an outer position at 146 and 148.

It will be appreciated that such changes in 10 position can increase or decrease the length of the filaments bundles between the sets of supports. For example, by moving the supports radially outwardly, the length of the bundles between the adjacent supports is lengthened. This permits the manufacture of hollow fibre dialyzers of different lengths.

The Hub-and-Locklng-System. The system 122 for securing the plate 120 to the machine is shown in both FIGURES 5 and 6. That system includes a hub assembly 150, which is secured to an end of the winding shaft 60 by a set screw 151. The hub assembly includes a flanged, boss-like member 152 to which a wheel-like support plate 154 is secured. The support plate includes three radial spokes 156, 158 and 160, each of which has an elongated guide slot, such as 162. The outer periphery of the plate is L-shaped in section and defines an axial 6'S 5 Γ or laterally-extending shoulder 164 and a circumferential shoulder 166.

The take-up reel winding plate 120 is constructed such that the inner edge 124 can be fitted onto the shoul5 der 164 with the plate against the circumferential shoulder 166. This fit prevents radial movement of the reel plate 120 relative to the hub 150. The plate 120 is removably secured in driving relation to the hub assembly by six studs, such as 167a, which extend outwardly from the shoulder 166 and which engage six stud-receiving apertures, such as 167b, in the winding plate.

Three generally radially-extending locking arms 168, 170 and 172 are provided to secure the winding plate 120 to the support plate 154 by preventing axial movement of the winding plate with respect to the support plate shoulder 166. The arms are secured at their inner ends to the hub 150 by·a pin, such as 174, and a pivotable collar-like member 176. Each arm carries a guide block, such as 178, which moves radially within the slot 162 in the arm. The guide block 178 is secured to the arm and in the slot by a pin 180. Each of the locking arms is of a length such that when the arms are in the extended, radial and locking position, the outer end of the arm is positioned radially outwardly over the shoulder 164 and in overlying relationship to the plate 120. With this construction 46531 the arm can lock and hold the take-up plate on the winding machine in fixed relation to the shaft 60.

The collar 176 is pivotable with respect to the shaft 60 and to the support arms, such as 160. As can be seen in FIGURE 5, a stop pin 182 defines the limits of movement for the collar 176. The collar is held in the locked position by a spring-loaded detent assembly (not shown). In the position shown in FIGURE 5, in full line, the arms arc positioned to lock the plate in position.

Pivoting of the collar 176 causes the arms to retract and the guide members, such as 178, slide within the slots 162, until the outer ends of the arms move within the inner edge of the shoulder 164. With the locking arms retracted, the take-up plate 120 can be removed from the machine by pulling it axially outwardly.

As can be seen from the drawings, the two spools of hollow-fibre filaments are mounted on the shafts 22 and 24 and each filament is guided through the guide assembly 34 and started on the take-up reel 36.

The machine is actuated so that the motor rotates the take-up reel assembly 36. As this occurs, the takeup reel draws filament from the supply reel through the guide assembly. The action of the cams, such as 90, causes the guide arm 112 to oscillate or move laterally, inwardly and outwardly as the take-up reel rotates. The <16 5 51 cam is designed in a manner such as to provide an even distribution of the filament on the guides. The shape of the cam co-operates in preventing build-up of filament at the edges of the guide by increasing the arm speed at each end of the oscillation. Also, the cam can be shaped to lay down a filament which exhibits a generally constant angle to the axis of the bundle. Furthermore, the cam prevents close-packing of the filament windings and causes the filament which is being wound to crossover the pre10 vious winding of the filament. This crossover is diagrammatically shown in FIGURE 8 where it can be see: that an upper filament winding 190 crosses over a lower filament winding 192.

It has also been found that the use of the two reels is beneficial fron the point of view that a sufficient quantity of filament is supplied so as to continuously feed the take-up reel and thereby avoid the need to stop the winding operation and start a second spool.

This stopping has been found to be detrimental to the ef20 ficiency of the dialyzer since undesirably large flow channels may be formed where one spool ended and the other began. It is believed that the channel may be formed as a result of differences in filament tension at the end of the first spool and at the beginning of the second spool.

During winding it has been found to be often 6 5 5 1 desirable to rotate the take-up reel at a speed greater than the speed at which the guide arm oscillates. This, at the maximum, can provide, after cutting of ten percent of the length of the bundle during removal from the reel, individual filaments which occupy about thirty percent of the width of the bundle. In one particular operation the take-up reel is driven at 200 rpm and the guide arm is oscillated at 160 or 180 oscillations per minute. Overall, it is generally preferred for there to be from about 0.45 to 1.7 back and forth oscillations per rotation of the takeup reel, especially in a reel of the design shown where six bundles are simultaneously manufactured. The above ratio may correspondingly vary for take-up reels which make different numbers of lengths of filament bundles.

Thus it will be appreciated that as the geometry of the take-up reel, for example the size and diameter of the take-up reel, changes, the oscillations of the r guide arm must also change in order to effectuate proper crossover.

Once the filaments are wound on the take-up reel and the bundles are of a sufficient size for use in hollow fibre dialyzers, the winding operation is stopped.

An elongate split case 200 as shown in FIGURE 9 is used in forming the fibre bundles from the filaments and for removing the bundles from the take-up reel. The split case includes an upper semi-cylindrical member 202 and a lower semi-cylindrical member 204, which are joined by a pair of flexible hinges 206 and 208. As can be seen in FIGURE 10, the sections can be opened and positioned and clamped about the wound bundles of the filament.

Referring now to FIGURE 7, once the members are in position, they tightly grasp the bundles of filament therebetween and the filament may then be cut at either end of the case so as to form open-ended fibres and permit removal of the bundles from the reel. The cutting converts the continuous filament to the individual hollow fibres used in the dialyzer. After cutting and removal, the individual bundles are then treated and formed into the hollow fibre dialyzers.

Referring to Figure 11, a schematic view of a filament bundle 210 made in accordance with this invention is shown, with the great majority of the filaments being omitted for a clearer disclosure of the filament relationships. Basically, most of the filaments shown in the bundle 210 fit the overall relationships of the filaments in the bundle as schematically illustrated In Figure 8, resulting from the winding technique utilized as described in this invention. The winding tension is preferably from about 0.5 to 5 gm. per filament being wound, preferably less than one j 25 gram per filament. ί ( ί t ' 1 It should also be added that when two or more filaments are wound onto the reel at once, as specifically disclosed herein, the pair of filaments lie side by side in a relationship in which each filament as shown in Figures 8 and 11 can represent separate multiple, parallel filament members, locatad adjacent to one another in the filament bundle. The term filament as utilized herein is intended to include this plural structure.

Filament bundle 210 may, in one embodiment, be 10 at least five thousand generally longitudinally directed, semi-permeable, individual filaments, free of mechanical attachment to each other, made of cellulose for dialysis, or any other appropriate material for other diffusion functions. Preferably, the dialysis filaments are made of cuprammonium regenerated cellulose, the individual filaments having a sufficient wet tenshe strength (e.g. at least about 100 grams) and are still enough to retain, in the main, the crossing, overlying structure into which they are formed, as illustrated in Figure 8 and 11.

Softer fibres, such as cellulose acetate derived filaments, when wet, may sag at random throughout the bundle, to form uneven flow paths outside of the filaments.

Preferably, the individual cellulose filaments used herein define an outer diameter of 100 and 400 microns, there being preferably at least nine thousand separate 4655i filaments which exhibit an aggregate surface area of at least 0.5 square metre and preferably one to two square metres. The wall thickness of the individual filaments is preferably from 10 to 30 microns, for example, 16 microns.

As shown in FIGURE 8, the array of filaments 190, 192 are in angular relation to each other and to longitudinal axis 212 of the filament bundle (FIGURE 11). In the manufacture of the filament bundle of this invention, filaments 190 are laid down as guide arm 112 is swinging transversely of the longitudinal axis 212 in one direction. Filaments 192 are laid down while the guide arm 112 is swinging in the opposite transverse direction.

As shown in the detail of FIGURE 8, filament 190a is laid down by a first swing of the guide arm 112 in a first transverse direction as the reel assembly 36 rotates. Filament 192a is then laid down on top of filament 190a by the further rotation of reel assembly 36, as arm 112 swings back in the opposite transverse direction, so that filament 192a overlies filament 190ji. Then, on the next rotation of reel 36 as guide arm 112 swings back in the first transverse direction again, filament 190b is laid down, over-lying filament 192a. Thereafter, as guide arm 112 is swung back again in the opposite transverse direction, and reel 36 rotates, filament 192b is laid down, to overlie filament 190b, and so on through the 4655 1 entire assembly operation, to form the resulting filamentbundled loop, which is cut into six filament bundles 210 in the specific embodiment shown.

Filament bundle 210, in its completed form, may 5 be about 15 to 25 cm., specifically, 20.5 cm., in length prior to assembly into a dialyzer housing, and may comprise about 11,500 individual filaments having an outer diameter of 247 microns and an inner diameter of 215 microns, to provide a dialyzer unit having the useful surface area of about 1.5 square metres. Each filament may traverse about percent of the width of the bundle, except for angled filaments 216.

It should be noted that the crossing points 214 of the respective filaments as shown in Figure 8 are in roughly linear arrangement with each other. This does not necessarily have to be the case. The arrangment of the various crossing points is dependent upon the revolutions per minute of the reel, compared with the number of oscillations per minute of arm 112. It is, in fact, generally preferable for the crossing points to lie in different positions with each rotation of the reel member, to avoid uneven fibre buildup or resonance.

Filaments 216 should also be noted (Figure 11 ) as a category of filament which is likely to be found in most filament bundles 210. As can be seen, these filaments are 23laid down on the reel during the time that guide arm 112 reaches a lateral limit of its swing, and begins to swing back again in the opposite direction, causing the resulting filament to first travel in one angular direction with respect to axis 212, and then to turn and be oriented in the opposite, similar angular direction to axis 212, defining a lateral apex 218 at the edge of the bundle. In fact, in the actual bundles of this invention, it is noted that some of these and other fibres can straighten out and form other wavy bends to some degree, and thus do not assume the ideal configuration which is as shown in Figure ll. Nevertheless, the bundle as a whole substantially exhibits the structure, characteristics, and advantages described herein.

The ideal angles of filaments 190, 192, and 216 to axis 212 are constant, at 2° to 3° for example, 2.15° or 2,59°, In tha particular filament bundle which is specifically described herein, the void fraction may be about 0.64, resulting in a very substantial increase in dialysis clearance when placed in a dialyzer housing.

Also, the dialyzer using the bundle structure of this invention, made of cuprammonium regenerated cellulose filaments can exhibit low blood clotting.

The filament bundle of this invention exhibits the 6 5 51 remarkable characteristic in that it resists being laterally pulled apart in .direction 218 (Figure 12) to a degree which is perceptibly and significantly greater than its resistance to being laterally pulled apart in direction 220. The resistance of being pulled apart at direction 220 is substantially equal to the similar resistance of conventional filament bundles, which is indeed very low. Accordingly, while the filament bundle of this invention requires some outside retention to hold together, it exhibits a better tendency to retain its structure while being assembled into a dialyzer than the conventional filament bundles .

Referring to FIGURE 13, a dialyzer for blood is shown incorporating filament bundle 210 of this invention. Basically, the dialyzer may, if desired, be of conventional structure as currently used with filament bundles.

Bundle 210 is encased in a tubular housing 222, which encloses the squaxxsh bundle 210 as wound (as in Figure 12), and holds it in a cylindrical configuration for optimum flow characteristics. The filament ends of bundle 210 pass through cured potting compound members 224, which are specifically each in the shape of a disc, and sealingly positioned inside enlarged chamber ends 226 of housing 222, so that the filaments of bundle 210 pass through the discshaped structures 224 to permit flow through the filaments.

Caps 228 are placed on the ends of tubular housing 222 in sealing manner, and each carry a port 230. Potted discs 224 are slightly spaced from the inner ends of caps 228, to provide a manifold chamber, for providing a fluid flow path between the ports 230 through the hollow filaments of bundle 210 In a sealed flow path.

A second flow path is provided to the dialyzer by means of second ports 232, which may be laterally posi10 tioned adjacent the ends of housing 222 on opposite sides thereof as shown. Enlarged portions 226 of the housing serve as a second manifold means to uniformly distribute fluid around the exterior of bundle 210 in the annular chamber defined between the bundle and the inner wall of the housing in that area. In the central, constricted portion of housing 222, bundle 210 fits snugly within the housing wall, without any outside space as there is in enlarged chamber portions 226. f Accordingly, a second fluid flow path passes from one port 232, about an enlarged chamber 226, and then in a percolating flow path through the crossing filaments of bundle 210 to the opposite enlarged changer 226, and the other port 232..

The flow path between ports 230 is typically used for blood, while the flow path between ports 232 is for 6 5 51 dialysis solution.

The two flow paths are sealed from each other so that there is no mixing of the fluids passing through them, except by means of diffusion through the walls of· the filaments of bundle 210.

Preferably, a countercurrent flow pattern is utilized, in which blood flows in one direction through the dialyzer, and dialysis solution flows in the opposite direction.

Dialyzers made as specifically described herein, having about 11,500 thin-walled capillaries of about 16 microns thickness, and defining an active surface area of about 1.5 square metres, have been shown to provide superior clearance characteristics in the small and middle molecule ranges, coupled with wide range, managable ultrafiltration capabilities. The priming volume of such a dialyzer, made in accordance with this invention, may be 125 ml. in the blood compartment, with a volume change which Is relatively insensitive to pressure variations.

The dialyzer of this invention, utilizing Cupraammonium derived cellulose fibres, may be packed dry, eliminating the formaldahyde flushing procedure used in some prior art dialyzers.

Claims (5)

1. » substantially as herein described with reference toy the accompanying drawings. 14. A dialyzer for blood incorporating a tubular Figures 8, 11 and 12 of rence toy

1. A fluid separation element, for a diffusion device, comprising an elongate, coreless bundle of hollow, semipermeable filaments, free of direct mechanical attachment to each other, the bundle being of substantially recti5 linear cross-section when first manufactured, each of said filaments extending lengthwise of the bundle for the entire length of the bundle, the great majority of the filaments defining an angle of 2° to 3° to the longitudinal axis of the bundle, the filaments being positioned, in crossing, 10 overlying relation with adjacent filaments, the majority of filaments extending across fifteen to fifty percent of the width of said filament bundle, in its as-manufactured state.

2. A fluid separation element according to Claim 1 in which the majority of said individual filaments extend across 20 15 to 35 percent of the width of said bundle.

3. A fluid separation element according to claim 1 or 2 which is made of cellulose and exhibits sufficient wet stiffness so as not to substantially collapse out of crossing overlying relation with adjoining filaments when wet. - 28 4 6 5 5 1 4. 6 5 51 A fluid separation element according to Claim

4. A fluid separation element according to Claim 1, 2, 3 or 4, which is made of cuprammonium-regenerated cellulose, said filaments having a wet tensile strength of at least one hundred grams. 55. A fluid separation element according to any preceding claim in which each of said hollow filaments has an outer diameter of 100 to 400 microns, there being at least five thousand filaments present in said bundle to provide an aggregate filament surface area 10 of at least 0.5 square meter, said filaments occupying individual, substantially parallel planes. 6. A fluid separation element according to Claim 5 in which each of said filaments has a wall thickness of 10 to 30 microns. 15 7. a fluid separation element according to Claim 5 or 6 which comprises at least nine thousand separate filaments which exhibit an aggregate surface area of one to two square meters. 5. A fluid separation element according to any 20 preceding Claim, in which the individual filaments extend across no more than thirty percent of the width of said bundle. 9. A fluid separation element according to any preceding claim, in which the void fraction of the filament 25 bundle is in excess of 0.4. - 29 10. A fluid separation element according to Claim ί 9 in which the void:·fraction is 0.6 to 0.8. 11. A fluid separation element according to any preceding claim, wherein said filaments occupy individual, 5 parallel, flat planes, said filaments defining a first set of generally parallel strands defining a first angular relation to said longitudinal axis, and a second set of generally parallel strands defining an opposite angular relation to said longitudinal axis, when compared with 10 said first set, and positioned in the following relationship: a first filament of the first set being overlaid by a first filament of the second set, which first filament of the second set is, in turn, overlaid by a second filarcant of the first set, which second filament of the 15 first set is, in turn, overlaid by a second filament of the second set, such relationship continuing throughout the majority of the filaments of the first and second sets to define an interleaving relationship, in which each filament of each set overlies the immediately20 preceding filament of the other set, and is overlaid by the immediately following filament of the other set. 12. A fluid separation element according to any preceding claim wherein each filament comprises a group of separate, parallel filament members located adjacent 25 one another. - 30 13.

5. Casing which sealingly encloses a fluid separation element according to any preceding claim, and first manifold means for providing a fluid flow path through said diaryzer via the interior of the hollow filaments of said element and second manifold means for conveying fluid through said 10 bundle about the exterior of said filaments.