Patent Publication Number: US-2009236027-A1

Title: Blood Treatment Filter and Method of Manufacturing

Description:
PRIORITY DATA AND INCORPORATION BY REFERENCE 
     This application claims benefit of priority to U.S. Provisional Patent Application No. 60/593,888, filed Oct. 27, 2005 which is incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     One of the more expensive components of blood treatment systems, such as renal replacement therapy systems, are the filter devices used for blood purification and fluid sterilization. A common structure for such devices includes a molded housing that holds tubular membranes that open at opposite ends of the media in inlet and outlet headers. The cost of manufacture involves considerable capital expense for the molds used to create the housing. This first cost discourages providing multiple filter designs for the various applications of these filter devices. Also, there is a need for filter designs that require less material, are more robust, and which are amenable to consistent high quality manufacturing. 
     The inventive embodiments provide various other features and advantages in addition to or in lieu of those discussed above and below. Many of these features and advantages are apparent from the description below with reference to the following drawing. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-section view of a filter usable in a variety of different types of blood treatment systems oriented to trap air in one or two header portions of the filter. 
         FIGS. 2A through 2C  illustrate holders for use with the filter device embodiment described herein, including a particular example of application to a blood treatment device such as that of  FIG. 1 . 
         FIG. 2D  illustrates an example of a holder feature to restrict orientations of a filter ensure that the filter is oriented with respect to the force of gravity. 
         FIG. 3  illustrates a filter similar to that of  FIG. 1  but with a header port for removing air and/or disrupting or cleaning clots. 
         FIG. 4A  illustrates an assembly for use with the port of  FIG. 3  for removing air and/or disrupting or cleaning clots. 
         FIG. 4B  illustrates a drip-chamber (or bubble trap) embodiment similar to the embodiment of  FIG. 4A . 
         FIG. 5  illustrates a header cap with a hydrophobic membrane for automatically venting air. 
         FIGS. 6A through 9B  illustrate a method for manufacturing a filter having a two-piece header caps that allow the use of a cylinder for a majority of the filter. 
         FIGS. 10A ,  10 B, and  11  illustrate the filter whose manufacture is described with respect to  FIGS. 6A through 9B . 
         FIG. 12  shows an alternative configuration for connecting a dialysate manifold with a tubular body of the a filter according to an embodiment of the invention. 
         FIG. 13  illustrates a single element header component that uses a simple tube for the dialysate portion. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a cross-section view of a filter usable in a variety of different types of blood treatment systems oriented to trap air in one or two header portions of the filter. A filter  100 , which may be a dialyzer, hemofilter, hemodiafilter, or any other compatible blood treatment has a bundle of tubular media  132  connecting an arterial  160  and venous  155  head space which is isolated from a filtrate space  130 . Blood flows through ports  122  and  124  in header caps  110  and  136  as indicated by arrows  118  and  112  into and out of the arterial  160  and venous  155  head spaces, respectively. A cylindrical filter body  128  encloses the filtrate space  130  and contains filtrate (e.g., dialyzer) ports  126  and  120 . Arterial and venous headers  142  and  134  isolate the filtrate space  130  from the respective arterial  160  and venous  155  head spaces. 
     The orientation of the filter  100  with respect to the pull of gravity is shown with the understanding that gravity is assumed to pull down with respect to the profile orientation of the drawing page. If any air is entrained in the blood, it may settle in pockets  151  and  153  in the arterial  160  and venous  155  head spaces as indicated by air/liquid interfaces  152  and  150 . The flow of blood through the arterial  160  and venous  155  head spaces is extremely slow due to the very small cross-sectional areas of the filter fibers in the bundle  132 . As a result, the arterial  160  and venous  155  head spaces are an idea place for air to settle out. With the indicated orientation, with blood outlet  124  pointing down and away from the pocket  151 . Since the blood moves at a very slow rate in the arterial  160  and venous  155  head spaces, there is little risk of reentrainment and air settles out very effectively. 
     Air trapped in pocket  153  may travel through filter fibers in bundle  132  up to venous head space  155  and accumulate in pocket  151 . Since the pocket  153  is located near the top of the arterial head space  160 , air will tend to travel up a few of the fibers closest to the top and collect in the pocket  151  without mixing in with blood. This keeps the vast majority of fibers filled with blood. 
       FIGS. 2A through 2C  illustrate holder variations for the filter embodiments of the present patent disclosure. The variations are intended to illustrate examples and not intended to be comprehensive or limiting. In  FIG. 2A , a holder  175  of a blood treatment machine orients a filter such as that of  FIG. 1  and those of the further filter embodiments described below. The holder  175  may be attached at a base thereof (not shown separately) to a blood treatment machine  172  which may contain actuators, sensors, and control elements as well as a fluid circuit, here illustrated as a cartridge  180  enclosed between two parts  171  and  172  of the blood treatment machine  172 . A filter  100  that is preconnected to the fluid circuit can easily be mounted in such an apparatus. The holder  175  may be articulating to allow for some movement or change of orientation of the filter  100  and is preferably a spring-tensioned clamp that allows for one-handed insertion of a filter  100 . In an alternative embodiment, the holder  175  may be attached to the  180  cartridge such that its orientation is obtained when the cartridge  180  is positioned with respect to the blood treatment machine  170 . In  FIG. 2B , a holder  194  is integrated into a disposable unit  190  (such as the fluid circuit cartridge of  FIG. 2A ). For example, the holder  194  may be made of wire which is connected to a plastic panel support  191  of the disposable unit. Examples of such disposable units are disclosed in U.S. Pat. No. 6,955,655 for “Hemofiltration system” and U.S. Pat. No. 6,579,253 for “Fluid processing systems and methods using extracorporeal fluid flow panels oriented within a cartridge,” each of which is hereby incorporated by reference as if full set forth in its entirety herein and U.S. patent application Ser. No. 10/650,935 published as US 2004-0069709, which is incorporated by reference above. The holder  194  supports a filter  192  such that when the disposable unit  190  is mounted, in a treatment device such as  170 , the filter  192  is held at an angle as shown. 
     Another alternative arrangement shown in  FIG. 2C  is to provide a separate support  178  that is attached, or attachable, to a support  176 . 
       FIG. 2D  illustrates an example of a holder feature to restrict orientations of a filter ensure that the filter is oriented with respect to the force of gravity. The view is a sectional view. In the example, the filter  166  has tabs  162  and  164  that prevent the filter  166  from being received fully within a flexible trough  168  which functions as a holder. This may be confirmed by inspection. The flexible trough  168  allows the filter  166  body to fit into it fully in only one orientation, the holder providing an urging force that keeps the filter  166  in place when inserted. Note that the example illustrated in  FIG. 2D  is only one of many devices that may be used to restrict the orientation of the filter when attached to a holder and is not intended to be limiting of the scope of any of the inventions described in the present disclosure. 
       FIG. 3  illustrates a filter similar to that of  FIG. 1  but with a header cap  210  having an integrated header port  200  for removing air and/or disrupting or cleaning clots. Tubing  265  may be connected to the port and provided with a clamp  260 . The clamp  260  may be released, at intervals, by an operator, to vent air from the air pocket  251  and re-engaged to prevent blood loss. The clamp  260  may be a normally-closed type clamp with a strong spring so that it reclamps tubing  265  when released. The tubing  265  may be capped with a microporous filter end cap  253  to prevent any contamination re-entering the blood in the venous head space  155 . The entire assembly that includes the filter  100 , tubing  265 , and microporous filter end cap  253  may be fused, sealed, and sterilized as a unit. In addition the same may be fused, sealed and sterilized as a unit with an entire treatment circuit, combining it with the circuit described in U.S. patent application Ser. No. 10/650,935 published as US 2004-0069709, which is hereby incorporated by reference as if full set forth in its entirety herein. With this combination, the entire circuit may be isolated from contamination. 
       FIG. 4A  illustrates an assembly  350  for use with the port of  FIG. 3  for removing air and/or disrupting or cleaning clots. The port  200  has a tube  310  connecting the venous head space  155  with a multi-way valve (e.g., a stopcock as shown)  312 . The multi-way valve  312  is further connected to a syringe  320  and tubing  375  connecting a supply of blood normal saline  375 , heparin, drug, or other medicament (such as from a tube  360  and bag  365 ) such as anticoagulants, drugs, etc. The multi-way valve allows the syringe to be connected, in a first position, to draw saline from the source of saline  375  and, in a second position, to draw air from the venous head space  155 . In the second position, saline may be pushed into the head space  155  to clear clots or for prophylaxis by injecting medicament, for example, an anticoagulant such as heparin. In an illustrative usage method, the multi-way valve  312  is set in the second position and air is drawn from the head space  155 . Then it is set in the first position and saline is drawn into the syringe  320 . Then the multi-way valve  312  is set in the second position again and saline (or saline and heparin) is injected into the venous head space  155 . The apparatus including the multi-way valve  312 , syringe  320 , tubing  310 ,  375 ,  360  and clamp  260  may be pre-attached to the filter  100  and presterilized as a unit. 
     Note that besides using the multi-way valve and bag  365  to draw air from the header of a filter and inject medicaments into the filter header, the same devices may be used in connection with an air trap or drip chamber. Referring to  FIG. 4B , a drip chamber  393  (which could also be a bubble trap or other similar device in which air may accumulate and possibly be vented), has an inlet  391  and an outlet  394 . A connection  392  to the top of the drip chamber  393  may be connected to the line  310  shown in  FIG. 4A  and used in the manner described for removing air and/or injecting medicaments. 
       FIG. 5  illustrates a header cap  210  with cover  280  sealed to and covering the header port  200 . The cover includes a hydrophobic membrane  285  that allows air in the head space  155  to vent automatically while preventing any contamination from entering. Referring to  FIGS. 6A and 6B , a method for manufacturing a filter design that incorporates features of the foregoing examples begins with the insertion of a filter fiber bundle  420  into a cylindrical tube  405  which forms part of a housing (discussed with reference to  FIG. 11 ). The tube  405  is a straight tube with no other structural features, in the present example. As such, the tube  405  may be a thin walled structure allowing material to be saved. In addition, it may be made of a material that is not necessarily injection moldable, as filter housings generally are. A preferred material is glycol-modified polyethylene terephthalate, a copolyester (PETG) which may be a clear amorphous thermoplastic with high stiffness, hardness, and toughness as well as good impact strength. Other advantages of using a tube for the main part of the housing will become clear from the further description below. Note that in the drawing only one end of the tube is shown in the present and following figures, but a complementary operation may be performed at an opposite end of the tube  405  such that a mirror-image structure is obtained. 
     The filter fiber membrane bundle  420  may be inserted such that the fibers  415  extend beyond the end  407  of the tube  405  as indicated at  445 . Referring now to  FIGS. 7A and 7B , the resulting combination  430  of tube  405  and filter fibers  420  may be inserted in a dialysis cap  435 . Note that the term “dialysis cap” is for convenience is not intended to limit the scope of the invention to the manufacture of a dialyzer. The outer surface of the tube  405  lies adjacent an inner annular surface  440  of the dialysis cap and a  450  bond is formed by thermal welding or sealing using adhesive, solvent, or filling type bonding agent such as urethane to form a completed structure  480 . A symmetrical structure is formed at the opposite end so that both ends of the tube  405  have a dialysate cap  435 . 
     Referring now to  FIGS. 8A and 8B , potting caps (not shown) are placed over the ends of the structure  480  and the ends of the fiber bundle are potted as according methods that are known in the art of manufacturing filters. A preferred method of potting is described in U.S. Pat. No. 6,872,346 for a “Method and apparatus for manufacturing filters,” which is hereby incorporated by reference as if fully set forth in its entirety herein. The result of potting is the creation of a sealed end of potting material indicated at  440  which, after hardening, is cut along a planar surface indicated at  460 . The cut  460  is done in such a way that the end of the filter fibers  420  are open at the surface  465  forming. A portion of the dialysate cap  435  may be trimmed off in the process of cutting  460 , as illustrated, although it will be apparent to those skilled in the art that this is not essential and instead, the fibers  420  could extend beyond the end of the dialysate cap  435  before potting such that the fibers  420  can be opened by cutting without cutting the dialysis cap 
       435 . The completed end portion is shown in  FIG. 8B , and as discussed, a symmetrical end portion may be completed at the opposite end (not shown here). 
     Referring now to  FIGS. 9A through 11 , the two ends  600 A and  600 B of a single tube structure are indicated. Respective blood caps  505  and  605  are fitted to the ends  600 A and  600 B of the structure  480 . Each blood cap has a respective blood port  510 ,  610  and one of the blood caps has a secondary port  610  which will be recognized from the discussion of embodiments such as shown and discussed with respect to  FIGS. 3 through 5 . The blood caps  505  and  605  have respective header spaces  645  that are preferably hydraulically shaped to ensure that no, or a minimal number of, dead (stagnant flow of blood) spaces arise when in use. In the embodiment shown, a rim  515  fits into an annular recess  470  (or rim  615  into annular recess  471 ). Prior to fitting the blood caps  505  and  605 , a bead  605 ,  606 ,  607 ,  608  of adhesive or sealing material may be applied or injected in the annular recesses  470  and  471  to form a bond between the structure  480  and the respective blood caps  505  and  605 . The bonding may be done by thermal, friction, solvent welding, compression bonding, or other technique. Dialysate ports  30  and  531  in the dialysate caps  435  and  425 , respectively, allow dialysate to flow into and out of the space occupied by bundle  420  and in contact with the external surfaces of the filter bundle  420 . For a hemofilter or other kinds of filters, such as sterile filters, reverse osmosis filters, ultrafilters, etc.; only one “dialysate” port would be required. Blood ports  510  and  610  in blood caps  505  and  605 , respectively, supply blood into, and be recovered from, the header spaces  545  and  645 , respectively. Air can be removed from air removal/access port  610 . As explained above, removal/access port  610  can also be used for injection of anticoagulants, drugs, or other medicaments. 
     As best seen in  FIGS. 10A and 10B , a small gap  685 ,  686  is provided between the end  407  ( FIGS. 6A ,  7 A,  8 A) of the tube  405  ( FIGS. 6A ,  6 B) and the surface of the potting  440  to allow dialysate to flow into the space occupied by the filter bundle  420 . The dialysate (or filtrate, depending on the application) is distributed by an annular dialysate manifold space  626 ,  626 . Referring momentarily to  FIG. 12 , it is noted that instead of providing for the gap  685 ,  686  in the manner described, the fiber bundle may be extended all the way to the end  407  of the tube  405  and openings  705  can be provided to perform the function of the openings  685 ,  686 . The same features provide for extraction of filtrate or dialysate or other fluid depending on the application.  FIG. 11  shows a complete filter unit. One of the benefits of the design is that it makes it possible to confine the capital expense associated with injection molding to the dialysate and blood header reducing first costs in new filter designs. In addition, the design allows the tubular portion to be lengthened and shorted without requiring major design and manufacturing changes. Note that although injection molding is not contemplated to be a requirement for the practice of the invention or all its embodiments, it is a preferred means for achieving the high precision and economies of scale for articles of manufacture such as dialyzers, filters, and hemofilters, as well as other applications of the disclosed embodiments. Referring to  FIG. 13 , the benefit of using a tube for the filtrate/dialysate portion of the filter can be obtained by using a single element header cap rather than separate “dialysate” and “blood” caps. In the example shown, a one-piece cap  725  has an annular dialysate manifold  740  that is sealed by 0-rings  747  against the surface of a tube  760 . A blood header space  732  is in communication with a blood port  730  and the dialysate manifold  740  is in communication with a dialysate port  735 . Slits  750  (configured such as illustrated in  FIG. 11 ) allow fluid communication between the dialysate manifold  740  and the external surfaces of the fiber bundle  733 . A potting plug  745 , in addition to performing its normal function, serves to reinforce the cylindrical structure of the tube  760  against the pressure of the 0-ring  747  seals. In this embodiment, a tube is permitted to be used with a single-element cap  725  structure providing many of the benefits of the inventions discussed above. 
     A tension band  757  may be used to ensure a good seal and provide a final shape to the one-piece cap  725  if made of a somewhat compliant resin to allow it to be removed from an injection mold despite the recess defined by the dialysate manifold  740 . Alternatively, the one-piece cap  725  may have a discontinuous dialysate manifold that allows it to be created without requiring the cap to yield, the cap could be machined rather than molded, or the cap could be made of two molded pieces that are assembled into a single cap. Many variations are possible. 
     It will be understood that while the invention has been described above in conjunction with a few exemplary embodiments, the description and examples are intended to illustrate and not limit the scope of the invention. That which is described herein with respect to the exemplary embodiments can be applied to the measurement of many different formation characteristics. Thus, the scope of the invention should only be limited by the following claims.