WO1999013927A2

WO1999013927A2 - Apparatus for conducting the flow of multiple fluids

Info

Publication number: WO1999013927A2
Application number: PCT/US1998/018810
Authority: WO
Inventors: Mark J. Brierton; John J. Kappus; Jeffery L. Blakeslee
Original assignee: Cobe Laboratories, Inc.
Priority date: 1997-09-12
Filing date: 1998-09-10
Publication date: 1999-03-25
Also published as: AU9311698A; WO1999013927A3

Abstract

Disclosed is an apparatus (10) for conducting the flow of multiple fluids. The apparatus (10) includes a novel design allowing for the crossover of two fluid conduit paths (12, 26) to allow for more flexibility in placement of fluid conduits and greater utility of space. The apparatus (10) can also include a novel design which enables testing of the apparatus for leaks in fluid conduit paths (12, 26) and which also identifies leaks during operation and prevents contamination of one fluid path with leaked fluid from another fluid path. The apparatus (10) is useful in applications for conducting the flow of multiple fluids, including in extracorporeal blood processing systems such as apheresis systems, blood oxygenation systems and hemodialysis systems.

Description

APPARATUS FOR CONDUCTING THE FLOW OF MULTIPLE FLUIDS

Field of the Invention The present invention relates to an apparatus for conducting the flow of multiple fluids and, more particularly, to apparatus and methods of manufacture and testing of such apparatus.

Background of the Invention

There are a number of industrial and medical devices which direct and control the flow of multiple fluids. For example, in the field of medical devices, extracorporeal blood handling systems direct the flow of blood from the body, treat it or separate it into multiple components and return the treated blood or components back to the body. In such systems, the multiple fluids include untreated blood, treated blood and blood components, as well as other fluids which are used to treat the blood. As an example of such an extracorporeal blood processing system, an apheresis system is disclosed in U.S. Patent No. 5,653,887. Such systems need to control the flow of blood from the body through various treatment apparatus and back to the body. Control of the fluids includes the use of pumps, valves, pressure sensors, and other similar devices. The system disclosed in U.S. Patent No. 5,653,887 describes the use of a cassette assembly for controlling the flow of multiple fluids in an apheresis system. Such assemblies can be used to control the flow and processing of fluids in a disposable part of the system. There exists a need in the design of the layout for such apparatus to increase the flexibility of placement of the flow paths as well as to increase the compactness of such apparatus. Thus, there is a need for improved manufacturing and assembly techniques to allow for such flexibility.

In addition, apparatus which control the flow of multiple fluids can have leaks from a given fluid conduit. In such instances, it is important that the leaks be detected by the operator as soon as possible so that, if necessary, the procedure can be terminated and other remedial measures can be taken.

In addition, it is possible that a first fluid will leak from the conduit designed for its flow into an interior portion of the apparatus, and subsequently into a conduit designed for a second fluid. Such leakage and subsequent contamination not only cause misfunctioning of the device, but also can constitute health hazards in the event of medical devices in the event that fluids for introduction to the body are contaminated. Thus, there is a need for apparatus which can be readily tested during manufacture for any leaks and which will identify any leaks that develop during use.

Summary of the Invention One embodiment of the present invention is an apparatus for conducting the flow of multiple fluids. The apparatus includes the first fluid conduit path which occurs in a first plane. The first fluid conduit path has an entry port and an exit port from the apparatus . The first fluid conduit path, thus, defines first and second areas in the apparatus. The apparatus also includes a second fluid conduit path which has an entry port and an exit port from the apparatus. The entry port of the second fluid conduit path occurs in the first area defined by the first fluid conduit path, and the exit port of the second fluid conduit path occurs in the second area. Thus, the first and second conduit paths crossover at a point. At the point of cross-over of the first and second fluid conduit paths, the second fluid conduit occurs in a second plane. In preferred embodiments the apparatus is a cassette assembly for directing fluid flows in an extracorporeal blood processing system, such as an apheresis system, a perfusion system, a blood oxygenation system, and a hemodialysis system.

A second embodiment of the present invention is a disposable assembly for use in an extracorporeal blood processing system. The assembly includes a blood removal conduit for transferring blood from a donor/patient and a blood return conduit for transferring blood to a donor/patient. The assembly also includes a molded cassette member which includes integral passageways that partially define the blood removal and blood return conduits . The molded cassette member includes a first fluid path which occurs in a first plane. The first fluid conduit path has an entry port and an exit port and thereby defines first and second areas in the molded cassette member. The molded cassette member also includes a second fluid conduit path which has an entry port and an exit port. The entry port of the second fluid conduit path occurs in the first area defined by the first fluid conduit path and the exit port occurs in the second area. At a point of cross-over the first and second fluid conduit paths, the second fluid conduit path is in a second plane. A further embodiment of the present invention is an apparatus for conducting the flow of multiple fluids. The apparatus includes a first fluid conduit path and a second fluid conduit path. The apparatus also includes a void or space between the first and second fluid conduit paths. The apparatus also includes an opening or bleedhole which communicates with the void. This apparatus can be used in an extracorporeal blood processing system. A further embodiment of the present invention is a method for testing the integrity of fluid conduit paths in an apparatus for conducting the flow of multiple fluids. The method includes using an apparatus which has a first and second fluid path, each of which have an entry port and an exit port. The apparatus also includes a void between the first and second fluid conduit paths and an opening communicating with the void. The method includes sealing the entry and exit ports of the first and second fluid conduit paths. It further includes pressurizing the first and second fluid conduit paths and evaluating whether the pressure in the first and second fluid conduit paths remains constant after accounting for material relaxation of the apparatus .

A further embodiment of the present invention is a method for manufacturing an apparatus for conducting the flow of multiple fluids. The apparatus includes a first fluid conduit in a first plane and a second fluid conduit which occurs in the first plane and in a second plane. The second fluid conduit is in the second plain at a point of crossover between the first and second fluid conduits. The method includes injection molding a top plate by using a mold having a positive structure to form channels in the top plate to partially define the first and second fluid conduit paths . The method also includes injection molding a bottom plate using a mold which has a (i) a positive structure to form channels in the bottom plate to partially define the first and second fluid conduit paths and (ii) a core pin to form at least a portion of the second fluid conduit path in the second plane. The method further includes assembling the top and bottom plates to complete the apparatus.

Brief Description of the Drawings Fig. 1 is a top view of an apparatus of the present invention; Fig. 2 is a sectional side view of an apparatus of the present invention;

Fig. 3 is a top view of an alternative embodiment of an apparatus of the present invention; Fig. 4 is an end view of an apparatus of the present invention;

Fig. 5 is a sectional top view of an apparatus of the present invention;

Fig. 6 illustrates a top piece for forming an assembly of the present invention;

Fig. 7 illustrates a bottom piece for forming an assembly of the present invention.

Detailed Description The present invention relates to an apparatus for conducting the flow of multiple fluids . More particularly, in one aspect, the apparatus has an improved structure for allowing the crossover of two or more fluid paths. In this manner, the apparatus can have improved designs in terms of flexibility for placement of entry and exit outlets from the apparatus while also allowing for a more compact apparatus . In another aspect of the present invention, the apparatus includes a novel system for detection of leaks from a fluid path. An embodiment of the first aspect of the invention is illustrated in Figs. 1 and 2. With reference to Figs. 1 and 2, the apparatus for conducting the flow of multiple fluids 10 includes a first fluid conduit path 12, which occurs in a first plane 14. It should be noted that, while the first fluid conduit path 12 is defined as occurring in a first plane 14, it should be understood that the first fluid conduit path 12 can also occur, in part, in other planes, such as a second plane 16. The first fluid conduit path has an entry port 18 and an exit port 20. Thus, the first fluid conduit path 12 can conduct a fluid entering the entry port 18 through the length of the first fluid conduit path 12 and out through the exit port 20. In this manner, the first fluid path conduit 12 sections the apparatus 10 into a first area 22 and a second area 24. It should be noted that the first fluid conduit path 12 can follow a straight line, as shown in Fig. 1, or it can follow a curved or angular path.

The apparatus 10 also includes a second fluid conduit path 26 which also includes an entry port 28 and an exit port 30. The second fluid conduit path entry port 28 occurs in the first area 22 defined by the first fluid path 12. The second fluid conduit path exit port 30 occurs in the second area 24 defined by the first fluid path 12. Thus, the second fluid path 26 conducts fluid from its entry port 28 along its path, which can also be straight, curved, or angular, to its exit port 30. Thus, the second fluid conduit path 26 crosses the first fluid conduit path 12 at the point where the second fluid conduit path 26 crosses from the first area 22 to the second area 24. With reference to Fig. 3, it should be appreciated that, in addition to the embodiment of having a first fluid path 12 and second fluid path 26, apparatus of the present invention can include any number of fluid paths and can form complex patterns depending on the application for the apparatus. Thus, for example, in Fig. 3, an apparatus is illustrated showing a fourth fluid path 32 having an entry port 34 and exit port 36. The fourth fluid path crosses over fifth, sixth, and seventh fluid paths 38, 40, 42 having entry ports 44, 46, 48 and exit ports 50, 52, 54.

The apparatus as generally described herein provides significant advantages in terms of manufacturing, operation and use. By allowing for the crossover of multiple fluid paths, placement of entry and exit ports in the layout and design of such apparatus is made more flexible. Thus, if it is desirable for an entry port to be located on a first side of the apparatus to be in close proximity to a supply line and to have an exit port located on the opposite side of the apparatus to be in close proximity of a receiving line, the ability to have improved crossover structures allows for placement of the entry and exit ports in the most economical positions. In this manner, the need for extra connections and tubing is reduced.

Apparatus of the present invention can be used for any device, mechanism or system which has a need for conducting the flow of multiple fluids. Such apparatus are particularly useful as part of a disposable assembly, wherein the apparatus is connected via tubing to hardware which can include pumps, processing equipment, and other similar devices. For example, such systems can include medical device systems where body fluids, such as blood, are treated. More specifically, extracorporeal blood processing systems typically include disposable components for contacting, transporting, storing and processing blood in addition to hardware such as pumps, processing equipment and supporting structures. Thus, in a preferred embodiment of the present invention, the apparatus of the present invention is used as part of a disposable assembly for use in extracorporeal blood processing systems.

A disposable assembly for extracorporeal blood processing includes a blood removal conduit for transferring blood from a donor/patient. Such an assembly also includes a blood return conduit for transferring blood to a donor/patient. It should be recognized in this context that reference to a "donor" in the term "donor/patient" can refer to a person donating blood or blood components, such as during an apheresis procedure. In addition, the term "donor" can refer to a blood container, such as a bag, in a procedure where blood, which is already outside the body, is processed. Such procedures are sometimes referred to as "bag-to-bag" procedures. Further, in this context, reference to a "blood removal conduit" refers to a conduit for removing blood from a blood container, and reference to a "blood return conduit" refers to a conduit for introducing blood to a blood container, even though the blood was not originally in that given container. The disposable assembly further includes a molded cassette member which includes integral passageways which partially define the blood removal conduit and the blood return conduit. Such a molded cassette member can be an apparatus of the present invention as broadly described above. As noted, such a disposable assembly can be used in extracorporeal blood processing systems. For example, such systems can include apheresis systems for componentizing blood, blood oxygenation systems, and hemodialysis systems. Other components of various types of extracorporeal blood processing systems are well-known in the art. For example, an apheresis system is generally described in U.S. Patent No. 5,653,887; a perfusion system is generally described in U.S. Patent No. 4,663,125; a blood oxygenation system is generally described in U.S. Patent No.5,489,413 and a hemodialysis system is generally described in U.S. Patent No.4, 683,053 and 5,603,902, all of which are hereby incorporated by reference.

Apparatus of the present invention can be produced by a variety of manufacturing processes known to those skilled in the art. For example, such an assembly can be produced by providing an interior housing or body that is appropriately compartmentalized and assembling front and back panels to complete the structure. Such a method of assembly (but not the present invention) is illustrated in U.S. Patent No. 5,462,416 to Dennehey et al. In a preferred embodiment, however, such apparatus are produced by injection molding of top and bottom plates or pieces, as described in more detail below. The apparatus can be formed from a variety of materials including polymeric materials, metals, and composite materials. In a preferred embodiment, the apparatus of the present invention is formed from polymeric materials which are thermoforming medical grade plastics . With reference to Fig. 2, a side view of an apparatus of the present invention is illustrated. As illustrated, the apparatus is formed by assembly of a top plate 56 and a bottom plate 58. At least a portion of the first fluid path 12 and a portion of the second fluid path 26 are defined by channels in the surfaces of the top and bottom plates 56, 58. As the top and bottom plates 56, 58 are fixed together, the channels in the interfacing surfaces of the top and bottom plates define the fluid conduit paths 12, 26. As seen in Fig. 2, the portion of the second fluid path 26 which occurs in the second plane 16 is entirely within the bottom plate 58. This region of the second fluid path 26 is the point at which crossover with the first fluid path 12 occurs. As illustrated in Fig. 2, the first fluid path 12 and the second fluid path 26 do not have any fluid communication. In the manufacture of such an apparatus by injection molding, the mold for the top plate includes positive structures for forming of the channels defining the first fluid path 12 and the second fluid path 26. In addition, the bottom plate, is formed by use of a mold having positive structures for forming the channels in the bottom plate which interface with the top plate 56 to define the first fluid path 12 and the second fluid path 26. However, the portion 60 of the second fluid path 26 which occurs entirely in the second plane 16, cannot be formed by a positive structure in a mold for forming the bottom plate 58. Rather, the portion 60 is formed by a core pin or other similar structure inserted from the side of the mold to produce the portion 60 of the second fluid path 26 which does not directly appear on the interfacing surface of the bottom plate 58. Thus, such a core pin forms the portion 60 of the second fluid conduit 26 which occurs in the second plane 16. This portion 60 meets the cavity formed by a positive structure in the mold forming the bottom plate 58 to form the entire second fluid conduit 26.

A further aspect of the invention is a method for manufacturing an apparatus for conducting the flow of multiple fluids. The method includes forming top and bottom plates as described above, by injection molding. Thus, the molds include positive structures to form channels to define first and second fluid conduit paths. In addition, at least one of the molds includes a core pin to form a portion of a fluid path at a point of cross-over between two fluid paths such that the paths occur in separate planes. The method further includes assembling the top and bottom plates to form the apparatus .

As noted above, a second aspect of the present invention involves an apparatus for conducting the flow of multiple fluids with a system for detection of leaks from one fluid path. Such an apparatus includes a first fluid conduit path and a second fluid conduit path. The apparatus further includes a void or space between the first and second fluid conduit paths. The apparatus also includes an opening or bleed hole communicating with the void.

With reference to Fig. 4, an example of this apparatus is illustrated. Fig. 4 shows an end view of the apparatus. As shown, the apparatus includes a fluid conduit path 62 and a fluid conduit path 64.

Between the two fluid conduit paths 62, 64, is a void 66. The apparatus also includes an opening 68 which communicates from the outside to the void 66. Fig. 5 shows a sectional view of the apparatus in Fig. 4. As illustrated in Fig. 5, fluid conduit path 62 has an entry port 70 and an exit port 72. Fluid conduit path 64 has an entry port 74 and an exit port 76. In operation, as fluids are being conducted through fluid conduit paths 62,64, in the event a fluid conduit path 62 develops a leak, the fluid will leak from the path 62 into the void 66, and will drain through the opening 68 to the exterior. Alternatively, fluid can leak from the path 62 in the direction away from the void and external to the apparatus through the side of the apparatus. Thus, an operator of the system will be able to detect the presence of the fluid draining from the apparatus either through the opening 68 or through a side edge of the apparatus. In some circumstances, in the absence of such a structure, leakage from a fluid conduit path 62 could build up sufficient force to disrupt the integrity of the fluid conduit path 64 and result in a fluid communication between the paths 62,64 resulting in contamination of both paths 62,64 with fluid from the other. In addition, leaks in the system into the void or outside of the apparatus through an edge of the apparatus can be detected during operation by detecting a variance in the normal flow of fluids in the system. For example, detection of a change from the normal fluid pressure, when fluid pressures are otherwise being monitored, or detection of a change in the mass flow through the system will indicate a leak in the system. Leakage from a fluid conduit path into a void 66 may cause the system pressure to be significantly reduced, thus indicating a leak in the system if pressures are monitored. In addition to advantages of this apparatus during operation in detection of leaks and prevention of contamination, the present apparatus allows for testing of apparatus for leaks prior to use. For example, all fluid conduit entry and exit ports 70,72,74,76 can be sealed and the fluid conduit paths 62, 64 pressurized with air. If the pressure within the fluid conduit paths is maintained at a constant level after accounting for material relaxation of the apparatus, the integrity of the fluid conduit paths 62, 64 is confirmed. However, if the pressure in either of the fluid conduit paths significantly decreases, this result indicates leakage of air from a fluid conduit path 62,64 into the void 66 and out through the opening 68. Thus, such result indicates that the fluid conduit paths in the apparatus are not completely sealed. Alternatively, the flow of air into or out of the apparatus can be measured to indicate the leakage of air from or to a fluid conduit path. In addition to the foregoing descriptions of procedures for testing of leaks, any conventional leak testing procedures can be used as well .

The apparatus of this aspect of the present invention can be constructed using a variety of manufacturing techniques and structures known to those skilled in the art to achieve the functional attributes identified above. For example, such an assembly can be produced by providing an interior housing or body that is appropriately compartmentalized and assembling front and back panels to complete the structure. Such a method of assembly (but not the present invention) is illustrated in U.S. Patent No. 5,462,416 to Dennehey et al . In a preferred embodiment, however, this apparatus of the present invention is produced by assembly of two injection molded pieces. With reference to Figs. 6 and 7, a top piece 78 is shown in Fig. 6 and a bottom piece 80 is shown in Fig. 7. Each of the top and bottom pieces 78, 80 partially defines one conduit fluid path 82a, 82b and second fluid conduit path 84a, and 84b. The top and bottom pieces 78, 80 each partially define a void 86a, 86b. The bottom piece 80 also includes an opening 88 which occurs in the portion of the bottom piece 80 defining the void 86b. The apparatus is assembled so that the top and bottom pieces contact each other on interfacing surfaces 90a and 90b. The interfacing surfaces 90a, 90b are sealed to complete assembly of the top and bottom pieces 78, 80. Thus, in operation, fluids can be conducted through fluid conduit paths 82 and 84. In the event of a leak occurring in either fluid conduit path 82, 84 at a location that would otherwise migrate toward the other fluid conduit path, the leakage would first enter the void 86 and be able to drain through the opening 88. Thus, an operator of the system would be able to identify that a leak occurred by the presence of liquid in the void 86 or by drainage of liquid from the opening 88. In addition, as discussed in detail above, the apparatus illustrated in Figs. 6 and 7 can be tested prior to use to confirm the integrity of the fluid conduits 82, 84 by sealing the entry and exit ports of the fluid conduits 82, 84 and pressurizing them with air. Maintenance of the pressure after accounting for material relaxation indicates that no leakages occur from the fluid conduit into the void space 86 which is relieved by the opening 88. Moreover, no fluid pressure would build up that would cause a disruption in the seal between interfacing surfaces 90a, 90b resulting in leakage of fluid from fluid conduit 82 into fluid conduit 84.

The apparatus of the present invention can be used as an assembly for conducting the flow of multiple fluids for use in an extracorporeal blood processing system. Such systems are generally described above in regard to other embodiments of the present invention. In this regard, it will be apparent to those skilled in the art that an improved apparatus for detection of leaks and prevention of fluid contamination are of critical importance. For example, in the context of an extracorporeal blood processing system, if a fluid conduit for return of blood to a patient is contaminated with fluid from a different fluid conduit, the patient could suffer serious physical consequences, including death.

The foregoing description of the present invention has been presented for the purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the above teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described above are intended to explain the best mode known of practicing the invention, and to enable others skilled in the art to utilize the invention in such or other embodiments and with various modifications required by the particular applications or uses of the present invention. It is intended that the appended claims be construed to include alternative embodiments, to the extent permitted by the prior art ,

Claims

What is claimed is:

1. An apparatus for conducting the flow of multiple fluids, comprising: a first fluid conduit path in a first plane, said first fluid conduit path having an entry port and an exit port from said apparatus to define first and second areas in said apparatus; and a second fluid conduit path having an entry port and an exit port from said apparatus, wherein said second fluid conduit path entry port is in said first area and said second fluid conduit path exit port is in said second area and wherein, at a point of crossover of said first and second fluid conduit paths, said second fluid conduit path is in a second plane.

2. An apparatus, as claimed in Claim 1, wherein said apparatus is a cassette assembly for directing fluid flows in an extracorporeal blood processing system.

3. An apparatus, as claimed in Claim 2, wherein said extracorporeal blood processing system is selected from the group consisting of an apheresis system, a blood oxygenation system, and a hemodialysis system.

4. An apparatus, as claimed in Claim 1, wherein said apparatus is formed from a top and a bottom plate, wherein at least a portion of said first and second fluid conduit paths are defined by channels in interfacing surfaces of said top and bottom plates .

5. An apparatus, as claimed in Claim 4, wherein said top and bottom plates are formed by injection molding.

6. An apparatus, as claimed in Claim 5, wherein said bottom plate is formed by injection molding using a mold having a positive structure to form at least a portion of said first and second fluid conduit paths and having a core pin to form at least a portion of said second fluid conduit path in said second plane.

7. An apparatus, as claimed in Claim 1, wherein said entry port and exit port of said first fluid conduit path and said exit port of said second fluid conduit path are in said first plane.

8. An apparatus, as claimed in Claim 6, wherein said entry port of said second fluid conduit path is in said second plane.

9. A disposable assembly for use in an extracorporeal blood processing system, comprising: a blood removal conduit for transferring blood from a donor/patient ; a blood return conduit for transferring blood to a donor/patient; a molded cassette member comprising integral passageways partially defining said blood removal conduit and said blood return conduit; and wherein said molded cassette member comprises: a first fluid conduit path in a first plane, said first fluid conduit path having an entry port and an exit port from said molded cassette member to define first and second areas in said molded cassette member; and a second fluid conduit path having an entry port and an exit port from said molded cassette member, wherein said second fluid conduit path entry port is in said first area and said second fluid conduit path exit port is in said second area and wherein, at a point of crossover of said first and second fluid conduit paths, said second fluid conduit path is in a second plane.

10. A disposable assembly, as claimed in Claim 9, wherein said extracorporeal blood processing system is selected from the group consisting of an apheresis system, a blood oxygenation system, and a hemodialysis system.

11. A disposable assembly, as claimed in Claim 9, wherein said molded cassette member is formed from a top and a bottom plate, wherein at least a portion of said first and second fluid conduit paths are defined by channels in interfacing surfaces of said top and bottom plates.

12. A disposable assembly, as claimed in Claim

9, wherein said top and bottom plates are formed by injection molding.

13. A disposable assembly, as claimed in Claim 9, wherein said entry port and exit port of said first fluid conduit path and said exit port of said second fluid conduit path are in said first plane.

14. A disposable assembly, as claimed in Claim 13, wherein said entry port of said second fluid conduit path is in said second plane.

15. An apparatus for conducting the flow of multiple fluids, comprising: a first fluid conduit path and a second fluid conduit path, wherein said apparatus comprises a void between said first and second fluid conduit paths- and wherein said apparatus comprises an opening communicating with said void.

16. An extracorporeal blood processing system comprising the apparatus of Claim 15.

17. The extracorporeal blood processing system of Claim 16, wherein said extracorporeal blood processing system is selected from the group consisting of an apheresis system, a blood oxygenation system, and a hemodialysis system.

18. The extracorporeal blood processing system of Claim 16, wherein said first fluid is different from said second fluid.

19. A method for testing the integrity of fluid conduit paths in an apparatus for conducting the flow of multiple fluids, wherein said apparatus comprises a first fluid path an entry port and an exit port, and a second fluid path includes an entry port and an exit port, wherein said apparatus comprises a void between said first and second conduit paths, and wherein said apparatus comprises an opening communicating with said void, said method comprising;

(a) sealing said entry and exit ports of said first and second conduit paths;

(b) pressurizing said first and second fluid conduit paths, and; (c) evaluating whether the integrity of said first and said second fluid conduit paths is retained after accounting for material relaxation.

20. A method for manufacturing an apparatus for conducting the flow of multiple fluids, wherein said apparatus includes a first fluid conduit in a first plane and a second fluid conduit in said first plane and in a second plane, and wherein said second fluid conduit is in a second plane at a point of crossover of said first and second fluid conduits, said method comprising:

(a) injection molding a top plate, using a mold having a positive structure to form channels in said top plate to partially define said first and second fluid conduit paths;

(b) injection molding a bottom plate, using a mold having:

(i) a positive structure to form channels in said bottom plate to partially define said first and second fluid conduit paths; and

(ii) a core pin to form at least a portion of said second fluid conduit path in said second plane; and (c) assembling said top and bottom plates to form said apparatus for conducting the flow of multiple fluids.

21. A method, as claimed in Claim 20, wherein said apparatus is a cassette assembly for directing fluid flows in an extracorporeal blood processing system.

22. A method, as claimed in Claim 21, wherein said extracorporeal blood processing system is selected from the group consisting of an apheresis system, a blood oxygenation system, and a hemodialysis system.

23. A method, as claimed in Claim 20, wherein said positive structures form a void between at least a portion of said first and second fluid conduits and wherein said void comprises a bleedhole .