Abstract:
A filter device made of less expensive material than comparable filter devices heretofore has basic filter components plus some unique design aspects and an additional ring component. The ring provides an interface inside the filter which enables the potting compound to adhere to the filter and create a seal between a first and second fluid compartment within the filter. An embedded region of the ring possesses a detailed geometry which helps ensure that a delamination would be localized and unable to propagate from the first to the second compartment, maintaining the structural integrity of the filter device. To ensure that the sealing interface remains intact and free from delamination, the ring is subjected to a surface treatment, which modifies the surface energy of the ring. This modified surface energy of the ring allows the hydrophilic potting compound to more effectively bond to the modified hydrophobic ring.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a continuation of Application Ser. No. 10/007,516, filed on Dec. 5, 2001, titled “Filtering Device With Associated Sealing Design And Method”, now U.S. Pat. No. ______, which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to the field of filtering devices, and more particularly, to a hollow fiber type filter device having a single use or disposable design together with a method for using and manufacturing the same. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]      FIG. 1  shows an overall side view of an embodiment of the filter device of the present invention.  
         [0004]      FIG. 2  shows an exploded isometric view of the filter device of  FIG. 1  in an embodiment of the present invention.  
         [0005]      FIGS. 3A-3D  show various views of the ring of  FIGS. 1 and 2  of an embodiment of the filter device of the present invention.  
         [0006]      FIG. 4  shows a cross-section view of a portion of the filter device of  FIG. 1  in an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0007]     Referring to the Figures, in which like numerals refer to like portions thereof,  FIG. 1  shows an overall side view and  FIG. 2  shows an exploded isometric view of an embodiment of the filter device of the present invention. Referring now to  FIGS. 1 and 2 , Filter Device  100  in this embodiment of the invention is a dialyzer used for hemodialysis. One skilled in the art will recognize that the filter device of the present invention could also be used for filtering other types of fluids besides blood, including, but not limited to water, sewage, or other types of chemical separation.  
         [0008]     Filter Device  100  is a dialyzer utilized by patients with kidney disease who suffer from the adverse effects of toxin build-up in their blood. Dialysis is a process which employs an artificial kidney to remove those toxins. In hemodialysis a dialyzer is used which contains a semipermeable membrane dividing the dialyzer into two compartments. Blood is pumped through one compartment and a dialysate solution through the second. As the blood flows by the dialysis fluid, separated by the semipermeable membrane, blood impurities such as urea and creatinine diffuse through the semipermeable membrane into the dialysis solution by diffusion, convection, and absorption. The electrolyte concentration of the dialysis fluid is set so as to maintain electrolytic balance within the patient.  
         [0009]     Dialyzers are known in a variety of configurations. The basic concept is to maximize the surface area of the membrane dividing the blood side from the dialysate side, so that the pressure gradient diffusing toxins from the blood side into the dialysate side and diffusing nutrients or pharmacological agents from the dialysate side into the blood side can operate over a wide area. On the other hand, there are size constraints to the overall three dimensional volume of the device, in order to fit into the hemodialysis apparatus.  
         [0010]     Filter Device  100  has a large number of Microfibers  104  (not shown in  FIG. 2 ) encased in a Housing  102 , which is a hollow cylinder open at both ends. In other designs, Housing  102  may be open only at one end, and Microfibers  104  are looped in a U-shape in Housing  102  such that both open ends of each microfiber are located at the one open end of Housing  102  (not shown). In either design, thousands of the hollow semipermeable Microfibers  104  carry blood in a pathway through one set of open ends of each Microfiber  104 , through the interior of each Microfiber  104 , and exiting out of the other open end of each Microfiber  104 .  
         [0011]     As shown in  FIG. 1 , thousands of the hollow semipermeable Microfibers  104  carry blood in a pathway that enters from one end through a first Blood Inlet/Outlet Port  118  to the opposite end and out through a second Blood Inlet/Outlet Port  118  so that blood flows through the interior of each Microfiber  104  in a first direction. Dialysate Inlet/Outlet Ports  110  are also present on opposite ends of Housing  102 . A first Dialysate Inlet/Outlet Port  110  carries dialysate in a pathway into Housing  102 , the dialysate flows through Housing  102  in a countercurrent direction to the blood flow and in the space between each Microfiber  104 , and a second Dialysate Inlet/Outlet Port  110  carries the dialysate out of Housing  102 . The material exchange thus takes place across the semipermeable membrane that is the walls of each Microfiber  104 . Label  114  is preprinted and applied after assembly. A Cap  112  screws into each Blood Inlet/Outlet Port  118  after sterilization, and is utilized to ensure an uncontaminated fluid pathway and is typically not removed until the technician is ready to connect the blood lines.  
         [0012]     The design of Filter Device  100  produces a high surface area for material exchange in a relatively low volume device. For example, a Filter Device  100  having a 6.3 cm cylindrical diameter and a 25.4 cm length can easily accommodate a bundle of about 12,000 to 13,000 Microfibers  104 . If each Microfiber  104  has a 0.60 cm circumference and is 24 cm long, the total surface area of all 12,000-13,000 Microfibers  104  is approximately 180 cm 2 .  
         [0013]     The manufacture of Filter Device  100  begins by joining Rings  108  into each end of Housing  102 . Each Ring  108  is then joined to Housing  102 . Many different joining techniques may be employed including, but not limited to, spin (friction) welding, laser welding, ultrasonic welding, high frequency welding, gluing, adhesive bonding, solvent bonding, screwing with threads, snap fitting, or any other suitable plastic joining technique. In this embodiment of the invention, spin welding is utilized. A plurality of Nubs  120  spaced apart on the outer surface of Ring  108  constitute the spin welding drive features to assist in the spin welding process. Next, open-ended Housing  102  is filled with a bundle of Microfibers  104  which extend in the longitudinal direction throughout the length of Housing  102  and extending a short distance beyond each end. A Potting Cap  202  ( FIG. 2 ) is attached to each Ring  108  to close off each end of Housing  102 . Housing  102  is then positioned in a centrifuge to allow rotation about an axis perpendicular to the central longitudinal axis, wherein the axis of rotation extends through the midpoint of Housing  102 . Potting Compound  116  is then injected into Dialysate Inlet/Outlet Ports  110  on each end of Housing  102 , is spun in a centrifuge, and the fibers are effectively potted in the dialyzer. Alternatively, each end of Housing  102  may be separately spin welded and injected in a two step process. In one embodiment of the invention, polyurethane is used for Potting Compound  116 . Epoxy or any other suitable compound may also be used as a potting material. The centrifugal force produced by the rotation in the centrifuge forces Potting Compound  116  to each end, where it sets and hardens.  
         [0014]     Housing  102  is then removed from the centrifuge, and each Potting Cap  202  is removed from each end to expose the hardened Potting Compound  116  encasing the ends of each Microfiber  104 . Potting Compound  116  and the encased Microfibers  104  at each end are then cut through in a plane perpendicular to the central longitudinal axis of Housing  102 , and the Microfibers  104  longitudinal axes, to expose the interior channels of each Microfiber  104 . The result is that the ends of each Microfiber  104  are open for blood flow through the interior channels of each Microfiber  104  extending through Housing  102 , but the rest of the space surrounding each Microfiber  104  at both ends of Housing  102  is filled with polyurethane, creating a seal between the blood and dialysate.  
         [0015]     After the potting and cutting process, a Flange Cap  106  is attached to each Ring  108  and spin welded together, permanently adhering it to Filter Device  100 . This design eliminates an O-ring typically used to assist in the sealing of the blood compartment of a dialyzer.  
         [0016]     Dialysate Inlet/Outlet Port  110  in the walls of Housing  102 , which are toward but not at the very ends, remain open for dialysate flow there through. A dialysate line is connected to one Dialysate Inlet/Outlet Port  110  and a dialysate return line is connected to the other Dialysate Inlet/Outlet Port  110 . The dialysate thus flows through the interior of Housing  102  in the space surrounding the Microfibers  104  in one direction. Blood flows from an arterial blood line from a patient connected to a first Blood Inlet/Outlet Port  118 , entering the exposed ends of each Microfiber  104  and flowing through the interior channels through the length of Housing  102  in a countercurrent direction, and then out of the other exposed ends of each Microfiber  104  and back to the patient through a venous blood line connected to a second Blood Inlet/Outlet Port  118 . The blood is thus separated from the dialysate by the semipermeable membranes of the microfiber walls, which allow the transfer of liquids, toxins, and nutrients by solute diffusion and pressure gradients.  
         [0017]     Typically, dialyzers are reused. After use in a hemodialysis session for a patient, the dialyzer is cleaned and sterilized for subsequent use by the same patient for a next hemodialysis session. The cleansing, sterilizing, storing, and cataloging of each dialyzer to ensure safe use by the same patient is an expensive and laborious task, and fraught with risk should the dialyzer not effectively have had all of the sterilizing chemicals removed from the dialyzer and the patient be exposed to the sterilizing agent itself. Additionally, if the sterilization process was not able to effectively sterilize the dialyzer, the patient may be subjected to a “non’ biocompatible medical device. Further logistic risk remain in the case the dialyzers get mixed up and the wrong dialyzer is used with the wrong patient. Heretofore, single use dialyzers have been too expensive to manufacture to be very practicable. To accommodate the growing demands of the hemodialysis market for single use or disposable dialyzers, the design of Filter Device  100  of the present invention has solved the high cost problem associated with the current manufacture of disposable dialyzers, but yet maintain the performance and medical requirements necessary for successful hemodialysis.  
         [0018]     Various seals in a dialyzer must remain intact, which is of special concern when replacing the currently proven expensive materials, from which many dialyzers are made, with less expensive materials in order to reduce costs. Any dialyzer inherently has at least two sealing regions in its respective design. First, the blood and dialysate compartments must be sealed from each other to ensure that a blood leak does not occur. The second seal consists of sealing either the blood or dialysate compartment from the exterior of the dialyzer.  
         [0019]     In nearly all dialyzers currently marketed throughout the world, polyurethane is used as a potting material to seal to the housing to ensure that the blood and dialysate compartments are sealed from each other. An O-ring is typically used to separate the blood from the exterior of the dialyzer.  
         [0020]     The seals in a dialyzer must not only maintain their integrity through a specified shelf life duration and during the dialysis treatment process, but must also maintain their integrity during the manufacturing process.  
         [0021]     The Filter Device  100  of the present invention utilizes molded parts, including Housing  102  and Flange Caps  106 , made with a polypropylene homopolymer that possess comparable general characteristics to the polycarbonate used in the molded components of the Fresenius Hemoflow series of dialyzers, but is considerably less expensive. The choice of materials for the dialyzer are heavily dependent upon the manufacturing processes employed. Though the optical property of the polypropylene homopolymer is significantly more “hazy” compared to polycarbonate, the blood and dialysate compartments are still readily visible to technicians.  
         [0022]     Polyurethane in one embodiment of the invention is used as Potting Compound  116  for Filter Device  100 . Instead of an O-ring, a separate Ring  108  molded from polypropylene is utilized. One Ring  108  is spin welded into each end of Housing  102 . Flange Caps  106  are then spin welded onto Rings  108  after Filter Device  100  has been potted and cut. Other joining techniques as listed above, including laser welding, may be used instead of spin welding. However, spin welding is based on a very simple concept and the process generally can be performed faster, less expensively, and with much less continuous maintenance and re-alignment as compared to laser welding. The weld joint designs utilized in Filter Device  100  are very robust and conducive to the rigors of large scale manufacturing.  
         [0023]     During the potting process, the interior portion of each Ring  108  becomes encased in Potting Compound  116 . This creates the first seal between the blood and the dialysate compartments. After potting, the potting caps are removed, the ends are cut, and Flange Caps  106  are spin weld onto Rings  108 . The spin welded region constitutes the second seal region, which seals the blood compartment from the outside of Filter Device  100  (a seal which has typically utilized an O-ring). Filter Device  100  is then conditioned during a low flux conditioning process, and then sterilized. Sterilization may be accomplished in a variety of ways, including ethylene oxide (EtO), steam, or radiation sterilization.  
         [0024]     A disadvantage of polypropylene is that its hydrophobic property has a tendency to delaminate from the hydrophilic polyurethane potting material due to the chemistry of surface adhesion between the two materials, resulting in leaks between the blood and dialysate compartments. A two-pronged approach has been taken to solve this delamination problem associated with the use of polypropylene. The first involves building a detailed geometry into the design of Ring  108  to minimize delamination or propagation of the delamination through the creation of physical stops, discussed more fully in relation to  FIGS. 3A-3D . The second involves the modification of the surface characteristics of the polypropylene to increase adhesion between it and the polyurethane, also discussed more fully in relation to  FIGS. 3A-3D .  
         [0025]      FIGS. 3A-3D  show various views of an embodiment of the ring of  FIGS. 1 and 2  in an embodiment of the single use dialyzer of the present invention.  FIG. 3A  shows a front view of Ring  108 .  FIG. 3B  shows a side view of Ring  108 .  FIG. 3C  shows an isometric cross-sectional view of a portion of Ring  108  as seen along lines B-B of  FIG. 3A .  FIG. 3D  shows a cross-sectional view of Ring  108  as seen along line A-A of  FIG. 3A .  
         [0026]     Referring now to  FIGS. 3A-3D , Ring  108  is shaped to coincide with Housing  102  and Flange Caps  106  that each Ring  108  is mated with. Typically, Housing  102 , Flange Caps  106 , and Rings  108  are circular, but other shapes may also be utilized. Ring  108  has Annular Tongue  316  which fits into an annular groove in Housing  102  formed by Annular Inner Lip  410  and Annular Outer Lip  412  in an interference based snap fit fashion in one embodiment of the invention (see  FIG. 4 ). Ring  108  also has Annular Outer Rim  312  and Annular Inner Rim  314  which form an annular groove which is designed to receive Flange Cap  106  in an interference based snap fit (see  FIG. 4 ). Potting Cap  202  used in the manufacturing process ( FIG. 2 ) is also designed to fit into this annular groove.  
         [0027]     Several methods are available to treat the surface of Ring  108  to modify its surface energy to increase adhesion between it and the polyurethane, including plasma, corona discharge, and flame treatments. By increasing the ability of the surface of Ring  108  to adhere to the polyurethane, Ring  108  has been shown to be effective in eliminating potential issues regarding delamination. A delamination could potentially allow the two fluid pathways to mix outside of the filtering microfibers. The detailed geometry of the design of Ring  108  increases the surface area treatable through surface treatment, enhancing the effects of modifying the surface energy of Ring  108 .  
         [0028]     In one embodiment of the invention, a typical surface treatment process which allows for the most practical integration into a clean room automated assembly process is the “corona discharge” surface treatment technique. This treatment method is currently utilized in industry to increase the adhesion of inks, coatings, and adhesives to polyolefins, such as polypropylene. The corona discharge consists of a high voltage electrical discharge that is created between two electrodes across a specified distance. This discharge ionizes the gases present between the electrodes and creates unstable chemical species (mainly free radicals), which possess sufficient energy to initiate bond cleavage at the polymer surface. A small fan is situated just above the corona discharge heads and blows the reactive chemical species onto the polymeric surface of the part being treated, Ring  108 , as shown by arrows  308  in  FIG. 3D . Ring  108  is especially well suited to accommodate the corona discharge treatment process, presenting a large surface area due to its geometric design. The corona discharge treatment process is based on the surface being treated to be directly exposed to the electrical discharge, and sections of the surface that are not directly in the “line of sight” of the discharge do not receive as effective treatment. Ring  108  is designed to ensure that the polyurethane interface regions of the ring receive optimal amounts of the surface treatment, while also forcing any delamination that may occur to follow a very difficult pathway. Annular Rounded Ridges  318  on the upper and lower surfaces of Annular Anchor  306  have relatively sharp transitions between them to ensure that optimal amounts of “treatable” area of Ring  108  are exposed to the corona discharge treatment process. When this entire section of Ring  108  is embedded in the Potting Compound  116 , delamination is forced to essentially “start” again and again after being initiated anywhere along the Ring  108 /Potting Compound  116  interface as shown in a close up cross-section of Ring  108 , Housing  102 , and Flange Cap  106  shown in  FIG. 4 . The effects of the corona discharge treatment may also be somewhat distributed onto Annular Rounded Ridges  318  in the lower surface of Annular Anchor  306  as the unreacted unstable chemical species will be blown into the center of Ring  108  and react with the lower surface of Ring  108 , which also is embedded in Potting Compound  116 . The thickness of Annular Anchor  306  tends to decrease or taper inwardly from Annular Outer Rim  312 , as opposed to increasing or expanding inwardly, which aids in this surface treatment process.  
         [0029]     Covalent bonds are produced on the surface of the polymer as the surface is oxidized during the treatment process. This oxidative coating on the polypropylene surface allows the hydrophilic polyurethane to effectively bond to the modified polypropylene. Because the oxidative coating on the polypropylene has the ability to interact with the oxygen present in the air, and simply the dynamic nature of polymers, the stability of the corona discharge treatment is limited to a specified amount of time. However, once potted, the modified surface of Ring  108  is permanent and does not degrade over time.  
         [0030]     A large portion of Ring  108 , Annular Anchor  306 , serves as a mechanical lock and is located at an interior portion of Ring  108  and is completely embedded in Potting Compound  116 . This portion of Ring  108  forces delamination to completely circumvent around and through the Annular Rounded Ridges  318  to create an actual delamination between the blood and dialysate compartments of Filter Device  100  as shown in  FIG. 4 .  
         [0031]     Another feature of Ring  108  are Radial Channels  302 . As the polyurethane potting mass “backfills” from the ends of Filter Device  100 , the residual air from the ends of Filter Device  100  becomes entrapped due to Annular Rounded Ridges  318  of Annular Anchor  306  portion of the design of Ring  108 . Not allowing the potting mass to bind to the corona discharge treated surface because of an air pocket could potentially create an initiation site for a delamination. To address this situation, Radial Channels  302  are periodically notched perpendicular to Annular Rounded Ridges  318  of the upper surface of Annular Anchor  306  of Ring  108 , which allows the air to escape and not become trapped during “backfilling” of Potting Compound  116 . The upper surface of each Annular Anchor  306  is that surface which faces outward toward the ends of Housing  102 .  
         [0032]      FIG. 4  shows a cross-section view of a portion of the single use dialyzer of  FIGS. 1 and 2  in an embodiment of the present invention. Referring now to  FIG. 4 , Dialysate Compartment  402  and Blood Compartment  404  are the regions of ingress and egress of dialysate and blood through Dialysate Inlet/Outlet Ports  110  and Blood Inlet/Outlet Ports  118  respectively. Annular Inner Lip  410  and Annular Outer Lip  412  of Housing  102  receives Annular Tongue  316  in an interference based snap fit fashion. This connection is spin welded as described above. Typically spin welding of polypropylene does not generally produce extensive spin welding particulate, but material does aggregate around the weld joint in the form of jagged flash (melted polymeric material) which aids in sealing welded parts together. Annular Channel  320  and Annular Channel  408  accommodate the flow of some of the melted flash material that is displaced during the spin welding process.  
         [0033]     After the potting and cutting process, in similar fashion Annular Interior Rim  414  and Annular Exterior Rim  416  form an annular groove for receiving Annular Outer Rim  312  of Ring  108 . This connection is spin welded as described above. Annular Channel  406  also accommodates the flow of some of the melted material that is displaced during the spin welding process. Annular Channel  422  is a specially designed area where Flange Cap  106  and Ring  108  seal off against each other during the spin welding process, entrapping additional amounts of melted flash material from the spin welding process. This design insures that no flash material is allowed to invade Blood Compartment  404 . Blood tends to coagulate on any rough surface exposed within Blood Compartment  404 , which would degrade the functioning of Filter Device  100 . One skilled in the art will recognize that Annular Channel  422  will also trap residue material from the other types of joining techniques mentioned above. The flat annular portions seal up against each other and ensure that the flash produced will not be introduced into the blood compartment of Filter Device  100 . However, the welding occurs only at the designated region and not at the flat annular regions where additional amounts of flash may be generated. Additional regions that are designed to contain spin weld flash, or residue material from other types of joining techniques, are located around the Housing  102 /Ring  108  weld interface as Annular Outer Lip  412  extends up from Housing  102  along the exterior of Ring  108 , and around the Flange Cap  106 /Ring  108  weld interface as Annular Exterior Rim  416  extends down from Flange Cap  106  along the exterior of Ring  108 . These areas also minimize the flow of flash, or residue material from other types of joining techniques, outside of Filter Device  100  improving the aesthetic features.  
         [0034]     The results of various studies on Filter Device  100  show that the design of Ring  108  provides an excellent surface for the corona discharge treatment prior to potting. Extensive quality and delamination testing from two separate experiments of nearly  600  separate Filter Device  100  samples determined that the current design would have a 0.00% chance of delaminating with an upper binomial confidence level of 0.09%. Extensive testing shows that the design of Filter Device  100  possesses excellent capability of resisting delamination, possesses high performance characteristics, and has significantly reduced manufacturing costs. In addition, the clearance characteristics of Filter Device  100  are among the highest currently available on the market.  
         [0035]     Having described the present invention, it will be understood by those skilled in the art that many and widely differing embodiments and applications of the invention will suggest themselves without departing from the scope of the present invention.