GB2061761A

GB2061761A - A hollow fibre dialyzer

Info

Publication number: GB2061761A
Application number: GB8035095A
Authority: GB
Original assignee: Akzo NV
Current assignee: Akzo NV
Priority date: 1979-11-02
Filing date: 1980-10-31
Publication date: 1981-05-20
Also published as: IT8050056A0; SE446690B; SE8007663L; DE2944172A1; IT1127911B; FR2468396A1; DE2944172C2; GB2061761B; JPS5681107A

Abstract

A hollow fibre dialyzer comprises a longitudinally curved hollow fibre sheath (1) housing a bundle of hollow fibres (2) cut from a longer length wound on a reel, the fibres being arranged parallel to the sheath curvature and combined in the bundle parallel to their winding curvature. The free ends of the bundle are connected to the sheath adjacent feed and delivery connections (5, 6) by a pourable sealing compound (4). The use of a curved sheath enables the fibre bundle to be cut directly on the surface of a correspondingly curved reel. <IMAGE>

Description

SPECIFICATION A hollow fibre dialyzer The present invention relates to a hollow fibre dialyzer comprising a bundle of hollow fibres and a housing which comprises a hollow fibre sheath and feed and delivery connections to which the free ends of the hollow fibre bundle are connected in a water-tight manner by means of a pourable sealing compound.

Hollow fibre dialyzers of the known type are quite well known, for example from U.S.

Patent No. 3 339 341, and are produced in designs which differ slightly from each other.

The housings of previously known dialyzers have the form of a cylinder or a prism.

Cylinders and prisms are defined as bodies defined by two parallel planes which are congruent to each other. The line connecting corresponding points in the intersecting faces of the body are straight lines which are parallel to each other. In the case of a cylinder, the surface of the cylinder is defined by a closed directrix. In the case of a prism, the bases are parallel congruent triangles, rectangles or polygons. The lateral faces of the prism are parallelograms.

In order to build a dialyzer, thousands of hollow fibres, which generally come from bobbins, are assembled by adopting techniques known in the processing of textile threads.

Thus, the hollow fibres from a defined number of bobbins can be assembled into a strand of parallel adjacent fibres, to a strand with the individual layers crossing each other, to an irregular bundle cut into lengths, to a regular bundle, by adopting weaving, knitting and bonding methods, and are then inserted in a large enough number depending on the desired membrane surface of the dialyzer, into a housing in which the head ends are sealed by providing a pourable sealing compositions between the fibres in order to separate the interior of the hollow fibres from the exterior in an air and water-tight manner.

As hollow fibres are generally produced industrially in a continuous process, it is desirable to wind them on circular yarn holders, as it is only possible in this way to adjust the winding speed uniformly and in conformity with the delivery speed on the production machines.

Now great problems arise when transferring the fibre packages wound on a round or polygonal (almost round) support into a stretched, rectilinear package form, which is necessary because all dialyzer housings form a straight line in their longitudinal axis.

The problems include: Disturbance of the selected bonding order; assistance in the formation of channels due to splitting of the package; bending and kinking of fibres; uneven lengths between the internal and external winding radius and thus multiple cutting, and high wastage at polygon support points.

Although the disadvantages of bending from the curved form into a rectilinear form are avoided in the above-mentioned weaving, knitting and bonding methods by placing the longitudinal axis of the fibres in a stretched form into the subsequent longitudinal direction of the dialyzer housing during assembly and only curving it in the direction running perpendicularly thereto, such processes demand a considerable outlay in specially adapted machines.

The hollow thread packages for known dialyzers are produced nowadays by windign on polygonal reels in which the straight portions are used and the markedly bent intermediate portions are rejected as they lead to decentralised head ends in the bundle and to pressure points in the hollow fibres.

A relatively high wastage also occurs during production from closed strands since the completely bent ends form a substantial proportion of the total length of the dialyzer.

An object of the present invention was to reduce the above-mentioned disadvantages of the previously conventional dialyzer structure without adversely affecting the effectiveness of the dialyzer.

According to the present invention there is provided a hollow fibre dialyzer comprising a bundle of hollow fibres and a housing which comprises a hollow fibre sheath and feed and delivery connections, to which the free ends of the hollow fibre bundle are connected in a water-tight manner by means of a pourable sealing compound, the hollow fibre sheath being curved longitudinally and the hollow fibres of the hollow fibre bundle being combined parallel to their winding curvature and arranged in the housing parallel to the housing curvature.

The lines of curvature of the hollow fibre sheaths are preferably parallel circular arcs.

The better the radius of curvature of the dialyzer coincides with that of the circular take-up member for the hollow fibres and thus also the winding curvature of the hollow threads, the better the fibres maintain the orderliness imparted to them during winding and the less the risk of bending or kinking of the hollow fibres.

The radii of curvature for winding and for the dialyzer housing are preferably selected equal in size by mounting curved half dishes or partial dishes of the dialyzer housing on the periphery of a drum and depositing the hollow fibres into the half or partial dishes during rotation of the drum.

The wound strand is now cut, without wastage, into desired lengths which are determined beforehand by suitable housing portions or the entire strand is cut up into equally long partial bundles simultaneously with the housing section which had previously been placed on the winding roller as a closed ring.

The tendency of the strand to shrink, due to the wihding tension, causes the cut ends to gape apart during the first cut on the periphery of the roll. Only the remaining total length needs to be cut into equally long portions.

The dish-shaped curved housing sections are sealed from above by a similarly curved cover or a partial dish and removed from the winding roller. The hollow fibre bundle lo abated in the sheath is then further processed in the conventional way, i.e. covered at both ends in an air and water-tight manner with a pourable synthetic resin, cut up to open all fibres and equipped with sealing caps which are provided for the admission and discharge of the liquid into and out of the inner compartment of the hollow fibres.

However, it is also possible firstly to empty the internal liquid necessitated by the spinning operation, to dry the hollow fibre bundle and then to embed it. Although the threads are wound in the dry state, it is surprising how well the orderliness imparted in the laying operation during winding is maintained in the case of the curved type of housing of a dialyzer according to the invention. This is important for achieving a good throughput of dialysate. The flow resistance in the dialysate can therefore be regulated very simply by varying the angle at which the hollow threads cross each other.

A very small crossing angle, i.e. an almost parallel winding, leads to a high degree of filling and a high flow resistance whereas a large crossing angle leads to a low degree of filling and low flow resistance.

These important parameters for a good dialyzer can be achieved quite simply and demand no fixing by extraneous threads, weaving, knitting or by other means, since the orderliness of the threads once deposited, is maintained by maintaining the curved shape.

Another significant advantage of the hollow fibre dialyzer according to the invention lies in the fact that an orderly hollow fibre bundle can be produced not only with one hollow thread, but preferably with a plurality of up to about 100 hollow threads without difficulty and this very significantly influences the averaging and regularisation of the permeability values of dialyzers. Thus, the divergence of the ultrafiltration rate of dialyzers composed of 100 bobbins drops to the a < 100 th value = ~~~~~ 10 relative to the divergence of dialyzers composed of only one bobbin, for, for example, statistical reasons. Such an increase to 100 bobbins cannot yet be made in the currently known weaving-knitting machines for the production of orderly hollow fibre mats.

The radius of the winding roller, which is preferably equal to the radius of curvature of the dialyzer housing should be selected as large as possible so that: 1. the external periphery of the wound pack age does not differ significantly, i.e. by less than 5% from the internal periphery, and 2. the dialyzer remains manageable and is not too bulky during packaging.

In a preferred embodiment of the invention, the radius of curvature of the arcs is from 30 cm to 4 m, the term radius of curvature referring to that of the shortest connecting line. The radius of curvature of the longest connecting line is then greater by the height of the end face. 100 cm, for example, is a# useful average for the radius. In this case, the difference in periphery for a 2 cm tlhicln bundle is only 2% and is thus unimportant for the flow resistance, and the curvature appears to be quite low for a 25 cm long dialyzer, remaining manageable. Much higher radii of curvature make the dialyzer more similar in its external appearance to the currently conventional dialyzers, but make a corresponding winding unit inconvenient, but not impossible.

Much smaller radii of curvature than, for example, 10 cm would produce a difference in periphery of 20% in the case of a 2 cm thick wound package, and this is too great for the flow resistance and would be impermissibly high for the non-permeable hollow fibre content lying in the pouring compound.

An advantage of the production method for a dialyzer according to the invention lies in the avoidance of wastage of hollow fibres.

Virtually no cutting wastage occurs during winding on a winding drum with incisions made in a radial direction. This method of splitting the hollow fibres is permitted for the first time by the invention, as such hollow fibres can only be used in a hollow fibre dialyzer according to the invention.

The selection of the cross-sectional shape and size of the end faces can also be used, to a certain extent, for adjusting the degree of filling and the flow resistance. Depending on the desired flow conditions and permeation characteristics, end faces of the housing which are defined by a circle, an ellipse or by a rectangle are preferred. The corners are preferably rounded in the case of a rectangle.

This rectangle obviously also includes a square.

One advantage of the hollow thread dialyzer according to the invention lies in the fect that the hollow threads in the hollow thread bun dle can be produced at a high production rate in an on-line process using a hollow thread machine.

The careful method of winding on to a relatively slightly curved winding body, the avoidance of disorderliness in the thread due to stretching of the originally curved shape and the utilization of the very uniform round shape of the hollow threads in the unwound condition, which is maintained up to the complete dialyzer without disturbance or damage, are decisive advantages produced by the hollow thread dialyzer according to the invention.

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 shows a schematic section through an embodiment of a hollow thread dialyzer according to the invention, and Figures 2 to 5 show the preferred crosssectional shapes of the end faces of the sheath.

As shown in Fig. 1, a sheath 1 contains hollow fibres 2 of a hollow fibre bundle. The sheath 1 bears inlet and discharge connections 3. The free ends of the hollow fibre bundle are joined in a water-tight manner to the inlet and discharge connections 3 by means of a pourable sealing compound. The liquid to be dialyzed, for example blood, is introduced into the hollow fibres and recirculated from them again via the connections 5.

The dialysate fluid is introduced and discharged via the connections 6.

The radii of curvature 7 of the parallel, curved connecting lines are greater than that allocated to the shortest connecting line by a maximum of the height of the end faces of the sheath. All radii of curvature have the same centre of curvature.

Figs. 2 to 5 shows respectively sheath end faces of circular elliptical rectangular and rectangular with rounded corners, cross-sections.

Claims

1. A hollow fibre dialyzer comprising a bundle of hollow fibres and a housing which comprises a hollow fibre sheath and feed and delivery connections, to which the free ends of the hollow fibre bundle are connected in a water-tight manner by means of a pourable sealing compound, the hollow fibre sheath being curved longitudinally and the hollow fibres of the hollow fibre bundle being combined parallel to their winding curvature and arranged in the housing parallel to the housing curvature.

2. A hollow fibre dialyzer according to Claim 1, wherein the lines of curvature of the hollow fibre sheath lie on parallel circular arcs.

3. A hollow fibre dialyzer according to Claim 2, wherein the radis of curvature of the circular arcs correspond to the radius of curvature of the winding curvature of the hollow fibres.

4. A hollow fibre dialyzer according to Claim 2 or 3, wherein the radius of curvature of the circular arcs is from 30 cm to 4 m.

5. A hollow fibre dialyzer according to Claim 4, wherein the radius of curvature of the circular arcs is from 1 to 2 m.

6. A hollow fibre dialyzer according to any of Claims 1 to 5, wherein the end faces of the hollow fibre sheath are defined by a circle.

7. A hollow fibre dialyzer according to any of Claims 1 to 5, wherein the end faces of the hollow fibre sheath are defined by an ellipse.

8. A hollow fibre dialyzer according to any of Claims 1 to 5, wherein the end faces of the hollow fibre sheath are defined by a rectangle.

9. A hollow fibre dialyzer according to Claim 8, wherein the corners of the rectangle are rounded.

10. A hollow fibre, dialyzer substantially as herein described with reference to Fig. 1 with or without reference to any one of Figs.

2 to 5 of the accompanying drawings.