GB2037614A

GB2037614A - Disposable filter cell for membrane plasmapheresis

Info

Publication number: GB2037614A
Application number: GB7943246A
Authority: GB
Original assignee: Baxter Travenol Laboratories Inc
Current assignee: Baxter International Inc
Priority date: 1978-12-21
Filing date: 1979-12-14
Publication date: 1980-07-16
Also published as: DK544879A; SE7910450L; AU5329079A; DE2948597A1; ES487198A0; FI793994A; IT7928293A0; ES8102825A1; IT1127307B; IL58787A0; NO794150L; BR7908156A; FR2444471A1

Abstract

The cell comprises a pair of flexible sheets (4, 6) facing each other. A pair of membranes (8, 10) is sandwiched between the sheets. A blood flow path (14) is defined between the membranes and plasma filtrate volumes (24, 26) are defined between each membrane and the adjacent sheet. Ports (20, 22, 30) are provided for input and output of blood and for output of plasma from the plasma filtrate volumes. The surfaces 12 of the sheets facing the membranes may be textured or provided with a mesh screen member to form a plasma flow path. <IMAGE>

Description

SPECIFICATION Disposable filter cell for membrane plasmapheresis This invention concerns a disposable filter cell for membrance plasmapheresis.

Typical plasmapheresis techniques utilize the collection of whole blood from donors in bags, and removal of the bags to a centrifuge where the plasma is separated from the whole blood. The plasma is withdrawn from the bag and the remaining blood is returned to the donor.

More recently, automated centrifuges have been devised which continuously withdraw whole blood from the donor, centrifuge the whole blood to separate the plasma, harvest the plasma, and return the remaining blood in its plasma-poor condition to the donor in a continuous fashion.

It has been proposed that plasmapheresis be carried out without using a centrifuge, because of the inherent complexity and cost of centrifugation equipment. To this end, the filtration of cells from whole blood using a micro-porous membrane has been disclosed, for example, in Blatt, et al. U.S.

Patent No. 3,705,100. It has been found that a membrane-type plasmapheresis device yields platelet-free plasma while centrifuge-devices yield plasma containing some platelets. Further, it has been found that the membrane plasmapheresis devices can also be designed to yield much greater quantities of plasma in shorter times than the centrifuge devices.

The present invention concerns a disposable filter cell for membrane plasmapheresis which can be extremely simple in construction and inexpensive to produce, yet the filter cell of the present invention is capable of achieving efficient plasmapheresis.

In accordance with the present invention, a disposable filter cell is provided for membrane plasmapheresis. The filter cell includes a first flexible sheet having a roughened undersurface and a second flexible sheet having a roughened upper surface. A pair of filter membranes are provided, having pore sizes of about 0.1 micron to 2 microns, and these filter membranes are positioned adjacent each other to form a blood flow path therebetween.

The first and second flexible sheets are positioned on opposite sides of the membranes to sandwich the membranes between the flexible sheets, with the roughened surface of each flexible sheet facing the respective membrane.

The first flexible sheet and the first filter membrane define a plasma filtrate volume, and the second flexible sheet and the second filter membrane define a plasma filtrate volume.

In one illustrative embodiment. each of the first and second filter membranes defines an opening which provides the communication between the first plasma filtrate volume and the second plasma filtrate volume. A seal traverses the filter membranes to close one side of the blood flow path defined by the filter membranes, in order to segregate the blood flow path from the openings defined by the filter membranes. Blood inlet and outlet ports communicate with the blood flow path and a plasma outlet port is in communication with the plasma filtrate volumes.

In another illustrative embodiment, the sheets and filter membranes have three aligned edges and the sheets have larger surface areas than the membranes. In this manner, a plasma collection chamber is formed by portions of the sheets that are spaced from the filter membranes and that are not aligned with portions of the membranes. Blood inlet and outlet ports communicate with the blood flow path and a plasma outlet port is in communication with the plasma collection chamber.

In the illustrative embodiments, the flexible sheets comprise plastic sheets which are extruded with the roughened surfaces formed in the extrusion.

Figure 1 is an exploded perspective view of said one illustrative embodiment of a disposable filter cell constructed according to the present invention; Figure 2 is a perspective view of the embodiment of Figure 1, with portions broken away for clarity; Figure 3 is an exploded perspective view of said another illustrative embodiment of a disposable filter cell constructed in accordance with the present invention; and Figure 4 is a perspective view of the embodiment of Figure 3, with portions broken away for clarity.

Referring to the drawings, both of the embodiments illustrated include a disposable filter cell for membrane plasmapheresis comprising a firstfiexi- ble sheet 4, a second flexible sheet 6, a first filter membrane 8, and a second filter membrane 10.

Flexible sheet 4 has a roughened undersurface that corresponds to the roughened upper surface 12 of flexible sheet 6. Sheets 4 and 6 are preferably formed of flexible plastics material, such as polyethylene or PVC that has been extruded and has a thickness of about 0.015 inch, with the roughened surface comprising a plurality of longitudinal / grooves defined by the extrusion with each of the grooves being about 0.010 inch deep.

It is to be understood that the roughened undersurface of sheet 4 and the roughened surface 12 of sheet 6 could comprise any type of roughened surface that allows for the flow of plasma to a plasma collection chamber, as will be described below. The roughened surface, therefore, could comprise a criss-cross grooved configuration, a plurality of spaced projections, a mesh screen member in contact with the flexible sheet material, or a combination of these.

Although for economy it is preferred that flexible sheets 4 and 6 be formed of an extruded plastics material, it may be desired to form flexible sheets 4 and 6 of a metallic sheet material, such as aluminium foil. In addition, the aluminium foil may have a roughened surface defined by the aluminium foil itself or may be coated with a plastics material to form the roughened surface.

Membranes 8 and 10 are each formed of a sheet-like microporous membrane having a pore size that permits the filtration of plasma from whole blood, preferably between about 0.1 micron and 2 microns, with the average pore size preferably being about 0.65 microns. The membranes 8 and 10 have a void volume of greater than 60 percent, with an average void volume of about 80 percent. The membranes are preferably formed of a polymeric material, with the pores defining a relatively tortuous path. The thickness of each of the membranes is preferably bwetween 0.002 inch and 0.008 inch.

Sheets 4 and 6 and membranes 8 and 10 are rectilinear as illustrated. Edges A of sheets 4 and 6 and membranes 8 and 10 are sealed to each other as are edges B and C of these sheets and membranes.

In the embodiment illustrated in Figures 1 and 2, edges D of sheets 4 and 6 and of membranes 8 and 10 are sealed to each other and a compact unit, such as illustrated in Figure 2, is formed, with filter membranes 8 and 10 defining circular openings 13.

In the embodiment illustrated in Figures 3 and 4, sheets 4 and 6 have a greater surface area than membranes 8 and 10 are aligned with each other and edges E of membranes 8 and 10 are sealed to each other or, if desired, the seal may comprise a fold defined by a single sheet which forms membranes 8 and 10.

The membrane package, which comprises membranes 8 and 10, shown in Figure 4 with their outer edges sealed to each other, defines a blood flow path 14 between the membranes. Membrane 8 defines openings 16 and 18 and sheet 4 carries a blood inlet port 20 which communicates with opening 16 (and is sealed around opening 16) and a blood outlet port 22 which communicates with opening 18 (and is sealed around opening 18), thereby forming communication between inlet and outlet ports 20, 22, respectively, and the blood flow path 14.

With reference to the embodiment illustrated in Figures 1 and 2, a heat seal E' traverses the membranes 8 and 10 to close one side of the blood flow path 14 and to segregate the blood flow path 14 from aligned openings 13. Openings 13 communicate with a first plasma filtrate volume 24 that is formed between membrane 8 and sheet 4 and with a second plasma filtrate volume 26 that is formed between membrane 10 and sheet 6. A plasma outlet port 30, which is aligned with openings 13, is provided in communication with plasma filtrate volumes 24 and 26, for connection to a suitable conduit through which the plasma is removed.

Regarding the embodiment illustrated in Figures 3 and 4, a plasma filtrate volume 24 is formed between membrane 8 and sheet 4, while a plasma filtrate volume 26 is formed between membrane 10 and sheet 6. Because of the larger surface area of sheets 4 and 6 then the surface areas of membranes 8 and 10, a plasma collection chamber 28 is formed between the surface portions of sheets 4 and 6 which are not aligned with membranes 8 and 10. A plasma outlet port 30 is provided in communication with plasma collection chamber 28 for connection to a suitable conduit to which the plasma is removed.

It is preferred that the sheets 4 and 6 and membranes 8 and 10 be formed of a thermoplastic material so that the seals mentioned above may be heat seals. Alternatively, these seals may be formed of bonding materials, sonic welds, or other types of fluid-tight seals.

In operation, the disposable filter cell is placed in a preferably permanent fixture and the conduit is coupled to port 20 into which blood is introduced from the patient's vein, a conduit is coupled to port 22 for forming a red blood cell return line and a plasma recovery conduit is coupled to port 30.

Claims

1. A disposable filter cell for membrane plasmapheresis which comprises first and second flexible sheets having respectively a roughened undersurface and a roughened upper surface; first and second filter membranes each having a pore size of 0.1 micron to 2 microns; the first and second filter membranes being positioned adjacent each other to form a blood flow path therebetween; said first and second flexible sheets being positioned on opposite sides of said membranes to sandwich the membranes between the flexible sheets, with the roughened surface of each flexible sheet facing the respective membranes; said first flexible sheet and said first filter membrane defining a first plasma filtrate volume; said second flexible sheet and said second filter membrane defining a second plasma filtrate volume; a blood inlet port and a blood outlet port, each communicating with said blood flow path; and a plasma outlet port communicating with at least one of said plasma filtrate volumes.

2. The disposable filter cell of Claim 1, wherein each of said first and second filter membranes has an opening which provides communication between the first and second plasma filtrate volumes.

3. The disposable filter cell of Claim 2, including means segregating the blood flow path from said openings in the filter membranes.

4. The disposable filter cell of Claim 3, wherein the segregating means comprises a seal traversing the filter membranes to close one side of the blood flow path defined by the filter membranes, with said seal being located inwardly of said openings.

5. The disposable filter cell of any one of Claims 1 to 4, wherein said first and second flexible sheets and said first and second filter membranes are rectilinear and are sealed to each other along four edges thereof.

6. The disposable filter cell of Claim 1, wherein said first and second flexible sheets include portions spaced from the filter membrane, and defining a plasma collection chamber, and the plasma outlet port communicates with the plasma collection chamber.

7. The disposable filter cell of Claim 6, wherein said first and second flexible sheets and said first and second filter membranes are rectilinear.

8. The disposable filter cell of Claim 7, wherein said first and second flexible sheets and said first and second filter membranes are sealed to each other along three edges thereof.

9. The disposable filter cell of Claim 7, wherein said sheets and filter membranes have three aligned edges, said sheets have larger surface areas then said membranes, and said plasma collection chamber is formed by portions of said sheets that are not aligned with portions of said membranes.

10. The disposable filter cell of any one of Claims 1 to 4 or 6, wherein said first and second filter membranes are sealed to each other around their peripheries.

11. The disposable filter cell of any one of Claims 1 to 4,6, or 10, wherein said first and second flexible sheets are sealed to each other around their peripheries.

12. The disposable filter cell of Claim 10, wherein at least one of said seals comprises a fold.

13. The disposable filter cell of any preceding Claim, wherein said roughened surfaces comprise grooves defined by the respective surfaces.

14. The disposable filter cell of Claim 13, wherein said sheets are elongate and the grooves extend longitudinally.

15. The disposable filter cell of any one of Claims 1 to 12, wherein said roughened surfaces comprise a plurality of spaced projections carried by the respective surfaces.

16. The disposable filter cell of any one of Claims 1 to 12, wherein said roughened surfaces comprise mesh members in direct contact with the respective surfaces.

17. The disposable filter cell of any one of Claims 1 to 14, wherein said first and second flexible sheets are formed of plastics material and are extruded, the extrusions defining the roughened surfaces.

18. The disposable filter cell of Claim 17, wherein each extrusion is about 0.15 inch thick and the roughened surface comprises longitudinal grooves about 0.010 inch deep.

19. The disposable filter cell of any one of Claims 1 to 14, wherein said first and second flexible sheets are formed of flexible sheet metal.

20. A disposable filter cell for plasmapheresis constructed substantially as herein described with reference to Figures 1 and 2, or Figures 3 and 4 of the accompanying drawings.