Abstract:
A biological fluid processing or fluid filtration system is provided having novel open and closed loop processing systems wherein the gases transferred into and out of the system during processing pass through a porous medium in upstream and/or downstream gas inlet or outlet housings or vents in a manner which precludes the fluid being processed or filtered from ever contacting the housings or vents. Each housing or vent is separated from the fluid by a column of gas in its respective transfer line. The upstream gas inlet housing or vent is in communication with the unfiltered biological fluid, and the downstream gas inlet housing or vent is in communication with the filtered biological fluid.

Description:
This application is claiming the benefit, Under 35 U.S.C. §119 (e), of the provisional application filed on Mar. 20, 1998, under 35 U.S.C. §111(b), which was granted Ser. No. 60/078,848, and of the provisional. application filed on Apr. 29, 1998, under 35 U.S.C. §111(b), which was granted Ser. No. 60/083,484. The provisional applications, 60/078,848 and 60/083,484 are hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method and apparatus for processing biological fluids into their therapeutically valuable components. More particularly, the present invention relates to a method and apparatus for processing donated blood into its therapeutically valuable components. Most particularly, the present invention relates to an improved method and apparatus for processing donated blood into its therapeutically valuable components which uses improved open-loop and closed-loop systems to substantially increase the recovery of all the blood products from the donated blood. 
     2. Discussion of the Related Art 
     Methods and apparatus for processing blood are well known in the prior art. U.S. Pat. No. 3,892,236 to Djerassi shows an apparatus for the continuous withdrawal of blood from a human donor, forced extracorporeal circulation of blood of the donor with separation of granulocytes, and return by gravity of the leukocyte-poor whole blood to the donor. 
     U.S. Pat. No. 5,126,054 to Matkovich shows a venting means for venting gas from the transfer line of a liquid delivery system comprising a housing, a first, liquid-wettable, microporous membrane carried in said housing so as to be in communication with the transfer line, and a second, non-liquid-wettable, gas permeable microporous membrane superimposed on said microporous membrane to the outward side of the housing. Gas in the delivery system is vented from the system so long as the first microporous membrane remains unwetted by the delivery liquid. 
     U.S. Pat. No. 5,451,321 to Matkovich shows biological fluid processing assemblies having a gas inlet, and/or a gas outlet. 
     While these devices are generally satisfactory, some of the methods and apparatus of the prior art leave a large amount of biological fluid trapped in various elements of the fluid processing apparatus. While the aforementioned U.S. Pat. No. 5,451,321 to Matkovich provides for liquid trapped in various elements of the blood processing system to be recovered either by causing a volume of gas behind the entrapped liquid to push the liquid through those elements and into the designated collection bag, or by pulling the entrapped liquid into the designated collection bag by a pressure differential (e.g. gravity head, pressure cuff, suction and the like), the system still has several drawbacks. One drawback is that they require one or more nonwettable, gas permeable, membranes. This requirement can lead to increased costs over wettable membranes. 
     Therefore, those skilled in the art continue to search for a method and apparatus to provide for optimal recovery of the biological fluid from biological fluid processing systems, cost reduction and ease of use, and have developed novel open and closed loop systems and methods associated therewith to achieve this goal. 
     SUMMARY OF THE INVENTION 
     The problems of the prior art are solved by the present invention utilizing novel open and closed loop biological fluid processing systems which all share the concept that the gases transferred into, out of, or within the biological fluid processing system have the transfer lines arranged or configured in a manner which precludes the biological fluid from ever contacting the upstream and downstream gas inlet or outlet housings or vents, or bypassing the fluid filtration or leukocyte depletion device. Gases are transferred into and out of the biological fluid processing systems through a porous medium in the upstream and downstream gas inlet housings or vents. Each housing or vent is separated from, and in communication with the biological fluid by a column of gas in the transfer lines. The upstream gas inlet housing or vent is in communication with the unfiltered biological fluid and the downstream inlet or vent is in communication with the filtered biological fluid. 
     In one embodiment of the present invention, a biological fluid filtration apparatus is provided which includes a fluid filtration or leukocyte depletion device having an inlet and an outlet, a fluid container upstream from and elevated above said fluid filtration or leukocyte depletion device and having an outlet, a first conduit in fluid communication with the outlet of said fluid container and the inlet of said fluid filtration or leukocyte depletion device, a receiving container downstream of said fluid filtration or leukocyte depletion device and having an inlet, a second conduit in fluid communication with the inlet of said receiving container and the outlet of said fluid filtration or leukocyte depletion device, an upstream gas inlet having one of its&#39; ends elevated above said fluid container, and having its&#39; other end in fluid communication with said first conduit, and a downstream gas inlet having one of its&#39; end elevated above said fluid container, and having its&#39; other end in fluid communication with said or leukocyte depletion or fluid filtration device. 
     In another embodiment of the present invention, there is provided a closed loop fluid filtration or leukocyte depletion device including a fluid filtration or leukocyte depletion device having an inlet and an outlet, a fluid container upstream from, and elevated above, said fluid filtration or leukocyte depletion device and having an outlet, a first conduit in communication with the outlet of said fluid container and the inlet of said fluid filtration or leukocyte depletion device, a receiving container downstream of said fluid filtration or leukocyte depletion device and having an inlet, a second conduit in fluid communication with the inlet of said receiving container and the outlet of said fluid depletion device and a bypass line in fluid communication with said fluid container and said receiving container and having a loop portion elevated above said fluid container. 
     In yet another embodiment of the present invention the upstream gas inlet is eliminated and the downstream gas inlet is connected to the receiving container instead of the fluid filtration or leukocyte depletion device. 
     In another embodiment of the present invention, the downstream gas inlet may be eliminated. 
     In still another modification of the present invention, the upstream gas inlet housing or vent and the downstream gas inlet housing or vent may be part of the same inlet device. 
     Thus, it is an object of the present invention to provide an improved method and apparatus for filtering biological fluids. 
     It is a further object of the present invention to provide an open gas vent that prevents premature gas introduction into the fluid stream in a biological fluid processing system. 
     It is a further object of the present invention to provide an open loop biological fluid processing system with transfer lines or conduits arranged or configured in a matter which precludes the biological fluid from contacting the upstream and downstream gas inlet housings or vents, or bypassing the biological fluid depletion device. 
     Another object of the present invention is to offer a wider choice of materials which may be used in the gas inlet housings or gas outlet housings or vents of biological fluid filtration systems. The present invention does not require wettable membranes. The choice of membranes for the present invention is not limited. 
     Another object of the present invention is to provide a system of the foregoing nature where gas is transferred into and out of the biological fluid processor through porous medium in the upstream and downstream gas vents. 
     A still further object of the present invention is to provide an open loop system of the foregoing nature where each gas vent is separated from, and in communication with the biological fluid by a column of gas in the transfer lines or conduits. 
     A still further object of the present invention is to provide an open loop biological fluid filtration system of the foregoing nature wherein the upstream gas inlet housing or vent, and the downstream gas inlet housing or vent may be a portion of the same inlet device. 
     A still further object of the present invention is to provide a closed loop biological fluid filtration system having a bypass line bypassing the biological fluid filtration device, the bypass line is arranged such that a column of gas separates the unfiltered biological fluid upstream of the filtration device from the filtered biological fluid downstream of the biological fluid filtration device. 
     A further object of the present invention is to provide an open loop biological fluid filtration system having an upstream gas inlet elevated above the level of the biological fluid container and having a satellite bag connected to the biological receiving fluid container. 
     Further objects and advantages of the present invention will be apparent from the following description and appended claims, reference being made to the accompanying drawings forming a part of the specification, wherein like reference characters designate corresponding parts in the several views. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of a prior art biological fluid filtration system. 
     FIG. 2 is an elevational view of a construction embodying the present invention. 
     FIG. 3 is an elevational view showing a modification of the construction shown in FIG.  2 . 
     FIG. 4 is an elevational view of a further modification of the construction shown in FIG.  2 . 
     FIG. 5 is an elevational view showing a further modification of the construction shown in FIG.  2 . 
     FIG. 6 is an elevational view of a closed loop construction embodying the present invention. 
     FIG. 7 is an elevational view showing a modification of the construction shown in FIG.  6 . 
     FIG. 8 is an elevational view of a further modification of the construction shown in FIG.  6 . 
     FIG. 9 is an elevational view showing a further modification of the construction shown in FIG.  6 . 
     FIG. 10 is an elevational view showing a further modification of the construction shown in FIG.  6 . 
     FIG. 11 is an elevational view showing a further modification of the construction shown in FIG.  6 . 
     FIG. 12 is an elevational view of a construction embodying the present invention utilizing a satellite bag. 
     FIG. 13 is a perspective view of a biological fluid filter construction embodying the present invention; 
     FIG. 14 is a front elevational view of the construction shown in FIG. 13; 
     FIG. 15 is a sectional view, taken in the direction of the arrows, along the section line  15 — 15  of FIG. 14; 
     FIG. 16 is a sectional view, taken in the direction of the arrows, along the section line  16 — 16  of FIG. 14 
     FIG. 17 is a sectional view, taken in the direction of the arrows, along the section line  17 — 17  of FIG. 14; 
     FIG. 18 is a front elevational view of the inlet portion of the construction shown in FIG. 13; 
     FIG. 19 is a rear elevational view of the construction shown in FIG. 18; 
     FIG. 20 is a front elevational view of the outlet portion of the construction shown in FIG. 13; 
     FIG. 21 is a rear elevational view of the construction shown in FIG. 20; 
     FIG. 22 is a modification of the construction shown in FIG. 13; 
     FIG. 23 is a diagrammatic view of the filter medium shown in the construction of FIG. 22; 
     FIG. 24 is a diagrammatic view of a further modification of the construction shown in FIG. 13; and 
     FIG. 25 is a diagrammatic view of the filter medium shown in the construction shown in FIG.  24 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The aforementioned U.S. Pat. No. 5,451,321 to Matkovich shows a biological fluid processing assembly for filter biological processes such as blood. An example of the Matkovich apparatus is illustrated in FIG.  1 . The apparatus has a blood collection bag  30  connected by a first conduit  31  to a leukocyte depletion device  32 . The leukocyte depletion device  32  is connected by a second conduit  33  to a blood receiving bag  34 . A gas inlet  35  having a cover or cap  36 , is provided in fluid communication with the first conduit  31  downstream of said collection bag  30 , and a gas outlet  37  is provided in second conduit  33  downstream of the leukocyte depletion device  32 . 
     In one embodiment of the prior art, a first clamp  38  is placed on first conduit  31  downstream of the blood collection bag  30  and upstream of the gas inlet  35 , and a second clamp  39  is placed on the second conduit  33  downstream of the gas outlet  37 . In a typical operation the blood collection bag  30  is sterile and is connected to the conduit  31  as illustrated. The gas inlet  35  is comprised of a housing  41  and a porous medium barrier  42  in addition to cover or cap  36 . Additional details of the barrier  42  may be obtained by reference to U.S. Pat. No. 5,451,321. 
     Prior to the start of blood processing, the inlet clamp  38 , the outlet clamp  39 , and the gas inlet  35  are all closed. The blood processing is initiated by opening the inlet clamp  38 , and allowing the blood to drain from the blood collection bag  30 . A column of blood flows through the first conduit  31  into the leukocyte depletion device  32  displacing any gas within the blood processing system. No blood enters the gas inlet device  35  since the gas inlet is closed. The displaced gas is expelled from the system through the gas outlet  37  since the second clamp  39  is closed. As substantially all the gas is expelled from the first conduit  31  and the portion of the second conduit  33  leading to the gas outlet  37 , the porous medium is wetted by the blood, and the blood flow seizes or stops at the liquiphobic bearer in the gas outlet  37 . 
     Once the gas outlet  37  is wetted, the second or outlet clamp  39  is opened, and filtered blood flows into the blood receiving bag  34 . The gas outlet  37  need not be closed prior to opening of the outlet clamp since the gas outlet is sealed by the wetted porous medium. Blood flows from the collapsible blood container or bag  30  through the leukocyte depletion device  32  and into the blood receiving bag  34  until equilibrium is reached within the system and blood ceases to flow. At this point, all of the blood has not been processed through the leukocyte depletion device  32 . The first conduit  31 , the filter device  32 , and the second conduit  33  are filled with blood. 
     Removing the cover or cap  36  from the gas inlet  35  allows gas to enter the processing system and drive the blood through the leukocyte depletion device  32 . However, since the filter medium  32 A within the leukocyte depletion device  32  is wetted, the flow of blood seizes when gas fills the upstream chamber of the filter. When the blood flow seizes, the second or outlet clamp  39  is closed. 
     It can be seen that, at this point, the downstream side of the leukocyte depletion device  32 , and the entire second conduit  33  are filled with blood. With ever increasing need for blood and blood products, those skilled in the prior art have strived to increase the recovery of blood, and such a relatively large quantity of blood being left in the device of the prior art is no longer satisfactory. 
     In order to solve the recovery problems present in the prior art devices, the open-loop construction shown in FIG. 2 has been developed. There is shown a biological fluid filtration system  44  having a leukocyte depletion device  45  with a filter medium  46 , an inlet  47 , and an outlet  48 . The leukocyte depletion device may be such as the biological fluid filter shown in provisional application Ser. No. 60/083,484, which has been incorporated herein by reference, or any other suitable fluid filtration or leukocyte depletion device. 
     A blood container  49  is provided upstream from, and elevated above said leukocyte depletion device  45 . Blood container  49  is connected to, or in fluid communication with, said leukocyte depletion device  45  through first conduit  50 . 
     There is also provided a blood receiving container  52  downstream of said leukocyte depletion device  45 . Leukocyte depletion device  45  is connected to blood receiving container  52  through second conduit  54 . An upstream gas inlet  56  is provided in fluid communication with said first conduit  50 , and a downstream gas inlet  58  is provided in fluid communication with said leukocyte depletion device  45 , downstream of said filter medium  46 . 
     An inlet clamp  60  and an outlet clamp  61  may be provided. It should be understood that one or more of inlet clamp  60  and/or outlet clamp  61  may be provided, and be well within the scope of the present invention. 
     Upstream gas inlet  56  may take the form of a vent line  62  being connected to an upstream gas inlet housing  64 . Vent line  62  may have a U-shaped portion  62 A to prevent drawing of gas into biological fluid filtration system  44  until substantially all of the biological fluid has drained from the biological fluid container  49 . The other end of vent line  62  should be at a sufficient height such that it is always positioned above the level of the fluid in the biological fluid container  49 . 
     Upstream gas inlet housing or vent  64  has an inlet  65  and an outlet  66 . Interposed between the inlet  65  and the outlet  66  in a sealing relationship is at least one layer of a porous medium  67 . The porous medium may be such as a bacterial retention medium, a viral retention medium, or other suitable medium. 
     In a similar manner, the downstream gas inlet  58  may comprise a second vent line  70  connected to a downstream gas inlet housing or vent  71  having an inlet  72  and an outlet  73 . A cap or other closure  74  may be used in connection with the opening and the closing of inlet  72 . Interposed in the housing  71 , between the inlet  72  and the outlet  73  is a second porous medium  76 . The second porous medium  76  may also be such as a bacterial retention medium, a viral retention medium, or other suitable medium. 
     As illustrated, upstream gas inlet housing  64  and downstream gas inlet housing  71  may be provided in a single novel inlet device  80  having a barrier or wall  81  which prevents fluid communication between the upstream gas inlet porous medium  67  and the downstream gas inlet porous medium  76 . The upstream medium  67  and the downstream medium  76  may then be formed of a single sheet. 
     The upstream gas inlet  56  and the downstream gas inlet  58  may be placed in any practicable location as long as they are located such that the blood product being filtered never contacts the porous medium  67 . In the preferred embodiment illustrated the porous medium  67  contained within the housing  64  is elevated above the blood container  49 , but other locations are well within the scope of the present invention. 
     In the method of blood processing embodying the present invention, the inlet clamp  60  and the outlet clamp  61  are initially closed. The cap or closure  74  covering the inlet  72  of downstream gas inlet device, housing, or housing portion  71  is also in place. 
     The blood processing is initiated by opening the inlet clamp  60  and allowing the biological fluid to flow through the first conduit  50 . As the fluid flows past the junction  50 A, some of the fluid will flow into the upstream gas inlet  56  through vent line  62 . A column of liquid of a predetermined, desired, length (shown as dimension A in FIG.  2 ), between the junction  50 A and the bottom of the loop portion of  62 A, prevents gas entry into the system until substantially all of the biological fluid has been drained from the biological fluid container  49 . 
     The upstream gas vent may be thought of as a manometer measuring the pressure at the junction  50 A. As the level of fluid within the biological fluid container  49  decreases, the pressure at the junction  50 A decreases and, therefore, the height of the fluid in the vent line  62  decreases. When substantially all of the biological fluid has drained from the biological fluid container  49 , the atmospheric pressure acting on the column of fluid within the vent line  62  will cause all of the fluid within the upstream gas inlet  56  to drain into the conduit  50 . The remaining fluid contained with the upstream gas inlet line  62  is drained into the conduit  50  because the upstream gas inlet is open to atmosphere. Thus, dimension A in FIG. 2 must be of sufficient distance such that the above described sequence of events occur. At this point, the leukocyte depletion device  45  downstream of the filter medium  46  and the second conduit  54  between the leukocyte depletion device  45  and the blood receiving container  52 , are all filled with filtered biological fluid. 
     The filtered biological fluid or blood downstream of the filter medium  46  in the leukocyte depletion device  45  may now be recovered by opening the cap or closure  74  covering the inlet  72  of downstream gas inlet device, housing, or housing portion  71 . In place of cap  74 , a clamp (not shown) could be used on second vent  70 . 
     After this step substantially all of the blood previously unrecovered by the prior art devices is in the blood receiving container  52 . Any gas in the receiving container  52  and/or second conduit  54  downstream of the disconnecting point of the blood receiving container  52  may be pushed back up into the second conduit  54  by gently squeezing the blood receiving container  52 , and then the outlet clamp  61  can be closed. 
     As is now evident, the construction shown in FIG. 2 provides an easy method of drainage of substantially all of the biological fluid from the receiving bag  52  through the leukocyte depletion device  45 . In addition, the biological fluid filtration system  44  in its preferred embodiment utilizes only a single housing in the inlet device  80 , and a single layer of porous medium and substantially all of the filtered biological fluid is recovered. The system has a lower number of parts, is easier to manufacture, and recovers more biological fluid at a lower per unit biological fluid processing cost. 
     Alternate embodiments of the construction shown in FIG. 2 are illustrated in FIGS.  3 - 5 , with like numerals designating corresponding parts in the several views. Their operation can easily be understood by those skilled in the art in view of the foregoing description. 
     A modification of the present invention utilizing only the upstream gas inlet  56  and a satellite bag  83  is shown in FIG.  12 . Satellite bag  83  is connected in fluid communication with blood receiving container  52  by satellite conduit  84 . Satellite clamp  85  opens and closes satellite conduit  84 . In this embodiment of the present invention, the satellite bag is used to vent the gas displaced from the receiving container  52 . The volume of the satellite bag  83  should be sufficient to accept all of the gas displaced. After all the blood has flowed into the receiving container  52 , the container is gently squeezed until all of the gas is vented past the satellite clamp  85 , at which time the satellite clamp  85  is closed. 
     Referring now to FIG. 6, there is shown a closed loop biological fluid filtration system  90 . As in previous embodiments of the present invention, there is a leukocyte depletion device  45  having a filter medium  46 , an inlet  47 , and an outlet  48 . The filter medium  46  is interposed in a sealing relationship between the inlet  47  and the outlet  48 . The system  90  also includes a blood container  49  connected by first conduit  50  to the inlet  47  of leukocyte depletion device  45 . Inlet clamp  60  is provided as before. 
     Provided downstream of the leukocyte depletion device  45  is a blood receiving container  52 . A second conduit  54  is connected between the outlet  48  of the leukocyte depletion device  45  and the inlet of the blood receiving container  52 . Used in place of the upstream gas inlet  56  and a downstream gas inlet  58  is a by-pass line  91 , which may be opened and closed by by-pass clamp  92 . A first end of the by-pass line  91  is connected in fluid communication with the blood container  49  proximate the outlet thereof, and the other end of the by-pass line  91  is connected in fluid communication with the blood receiving container  52  proximate the inlet thereof. The loop portion  93  of the by-pass line  91  is positioned such that when the blood container  49  is full of blood, the blood will not reach the loop portion  93  and thus, there can be no flow of blood through the by-pass line. One such position is illustrated in FIG. 6 with the loop portion  93  elevated above the blood container  49 . 
     In place of loop portion  93 , a one way check valve or other device may be used such that a column of gas will always separate the unfiltered biological fluid upstream of the filtration device from the filtered biological fluid downstream of the leukocyte depletion device  45 . The positioning of the loop portion  93 , and the bypass line  91  may also be varied to accomplish this. 
     The method of operating the the closed loop embodiment of the invention differs in several respects from the method used with the open loop embodiment. As illustrated in FIG. 6, the additional by-pass clamp  92  is needed because no gas inlet or gas outlet devices are provided, as were necessary in the prior art. Prior to the start of blood processing, the inlet clamp  60  is closed and the by-pass clamp  92  is open. The blood processing is initiated by opening the inlet clamp  60  and allowing blood to drain from the blood container  49  through first conduit  50  into the leukocyte depletion device  45  and therethrough to the blood receiving container  52 . The blood does not by-pass the leukocyte depletion device  45  because of the loop portion  93  of the by-pass line  91  being elevated to a sufficient height. The gas within the closed loop biological fluid filtration system  90  is displaced by the blood flow into the blood receiving container  52 . As the blood container  49  approaches its nearly empty condition, the gas stored within the receiving container  52  automatically flows through the by-pass line  91  into the blood container  49  and allows substantially all of the blood to be processed through the leukocyte filtration device  45 . It is important to note that the chamber of the leukocyte depletion device  45  downstream of the filter media  46  at this point will be filled with blood, as will the second conduit  54  between the leukocyte depletion device and the blood receiving container  52 . If there is any gas left in the receiving container  52  it may be displaced into the by-pass line  91  by closing the outlet clamp  61 , gently squeezing the blood receiving container  52  and closing the by-pass clamp  92 . In this embodiment of the invention comprising the closed loop biological fluid filtration system, the chamber downstream of the filter medium  46  in the leukocyte depletion device  45  is not drained of blood, nor is second conduct  54 . However, the inlet device and the outlet devices of the prior art are eliminated, and a simplified system is provided. 
     Additional modifications of the closed loop biological fluid filtration system  90  are shown in FIGS.  7 - 11 . Their operation can be understood by those skilled in the art from the foregoing description. A more detailed description of the biological fluid filter can be had by referring to FIGS.  13 - 25 . The biological fluid filter  100  consists of an inlet section  101  and an outlet section  102 . Referring to FIGS. 14 and 15, the inlet section  101  of biological fluid filter  100  has an inlet  103 , including port  103 A, communicating with first passage  104 , which is in fluid communication with first or inlet chamber  105  through first port or outlet  104 A. Further, biological fluid filter  100  has a second passage  106  in fluid communication with both, first or inlet chamber  105 , and first vent chamber  107 . 
     The outlet section  102  has a second vent chamber  110  in fluid communication with a third passage  111 . Third passage  111  is in fluid communication with outlet  112  through port  112 A. A fourth passage  113  is in communication with the third passage  111  and the second or outlet chamber  115 . A vent filter element  117  separates the first vent camber  107  from the second vent chamber  110 , and is held in place by means to be described in more detail hereinbelow. 
     Similarly, a biological filter element  119  separates the first or inlet chamber  105  from the second or outlet chamber  115 . Both the vent filter element  117  and the biological filter element  119  may consist of one or more layers, and be made of a wide variety of filter materials. In the embodiment illustrated, they are liquiphilic. 
     In the preferred embodiment, the vent filter element  117 , and the biological fluid filter element  119 , are made of the same filter medium, which may be such as glass or nylon fibers. In use, a fluid container (not shown), such as a blood container is placed in fluid communication with inlet port  103 A. Similarly, a biological fluid receiving bag (not shown) is placed in fluid communication, by means well known in the art, with outlet port  112 A. Fluid flow is initiated and blood flows in the inlet port  103 A, through the first passage  104  and through first outlet  104 A into inlet chamber  105 . 
     In operation, as the blood enters the inlet chamber  105 , the blood may wick into the filter element  119 . The blood may wick into the filter element  119  faster, or slower, than the blood level rises in the first or inlet chamber  105 . The rate at which the blood wicks into the filter element  119  will depend on the properties of the filter medium being chosen, and the biological fluid being filtered. These properties include the pore size of the medium, the density of the biological fluid, the surface tension of the biological fluid, and the contact angle of the solid-liquid-gas interface. While the blood level is rising in the inlet chamber  105 , any air entrapped in chamber  105  is either passing through a portion of the filter element  119  which is not yet wetted, or is proceeding through second passage  106  and being vented out the vent filter element  117 . 
     As the blood level continues to rise in inlet chamber  105 , at some point, the biological filter element  119  will be sufficiently “wetted”, and the biological fluid being filtered will “breakthrough” the filter element  119 , and will start flowing into outlet chamber  115 . The fluid breakthrough depends on the pore size of the material, the surface tension and the contact angle, as well as the pressure differential across the filter element  119 . 
     Due to the pressure differential across the biological filter element  119 , the biological fluid continues to flow up into second passage  106 . If the pressure differential is sufficient, the biological fluid will contact the vent filter element  117 , which is the preferred embodiment. If the vent filter element  117  is also made of a liquiphilic media, it will become “wetted out”. However, by this time all the gas entrapped in inlet chamber  105  has either passed previously through biological filter element  119  or through vent filter element  117  and accomplished one of the objects of the invention. 
     Referring now to FIGS.  14 - 19 , the construction of the inlet section  101  of the biological fluid filter  100  may be clearly understood. The biological fluid filter  100  includes an inlet section  101  which is bonded to an outlet section  102  by a seal  130 . The seal  130  is preferably an ultrasonic seal. It can be understood by those skilled in the art that other seals such as heat seals, adhesive seals, or any other air tight seal may be used. 
     Inlet section  101  includes a recessed top wall  131 , and down standing side walls  132  extending around the periphery of the recessed top wall  131 . A down standing peripheral ridge  133  extends around the periphery of the down standing side wall  132  and forms a part of the mechanism which holds the vent filter element  117  and the biological filter element  119  in place, as will be more fully explained hereinafter. A first protuberance  135  extends from the recessed top wall  131 , and carries the inlet  103  and first passage  104  as previously described. First or outlet port  104 A which is in fluid communication with the first passage  104  can be seen in FIG. 19. A recess  136 , provided by the combination of the top surface of the recessed top wall  131  and the peripheral side walls  137  almost completely surrounds the protuberance  135 . 
     A peripheral flange  138  depends from the peripheral sidewall  137  and forms a groove  139  extending around the periphery of the inlet section  101  of the biological fluid filter  100 . The groove  139  forms a portion of the means by which the seal  130  between the inlet section  101  and the outlet section  102  of the biological fluid filter  100  is formed. A plurality of down standing ribs  142  are provided on the lower surface of the recessed top wall  131  for purposes to be described. 
     The inlet portion  101  of the biological fluid filtration device also has an extended portion  145  which contains second passage  106  (FIG. 15) in fluid communication with first vent chamber  107 . The same flange  138  and groove  139  are provided in the extended portion  145  of the inlet section  101  as are provided in the remainder of the inlet section  101 , so that the inlet section  101  will properly mate with the outlet section  102  to be described. A circular ridge  147  is provided about the first vent chamber  107  to aid in holding the vent filter, as will be further described. 
     Referring now to FIGS.  15 - 17  and  20 - 21 , the construction of the outlet portion  102  of the biological fluid filter  100  will be clearly understood. The shape of the outlet section  102  of the biological fluid filter  100  is complimentary in shape to the inlet section  101  so that the inlet section  101  may act as a closure to the outlet section  102 , or vice versa. It can easily be understood by those skilled in the art that the biological fluid filter  100  may be of any desired shape, such as the generally oval shape thus far described, the diamond shape of the modification shown in FIGS. 22 or  24 , or any other desired shape. Similar to the inlet section  101 , the outlet section  102  of the biological fluid filter  100  has a bottom wall  150  and upstanding sidewall  151 . The top of the upstanding sidewall  151  fits into the groove  139  in the inlet portion  101 , and is preferably sonically welded to form the seal  130 . A second protuberance  154  is provided on the exterior portion of the bottom wall  150  and carries the third passage  111 , fourth passage  113 , and a portion of the vent chamber  110 . A second circular ridge  155 , complimentary in shape to the circular ridge  147 , is provided. The protuberance  154  covers a portion of the extended portion  156  of the outlet portion  102  of the biological fluid filter  100 . 
     As seen in FIG. 17, a further plurality of ribs  142  is provided on the interior surface of the bottom wall  150  to help support the biological filter element  119  and provide flow in the second or outlet chamber  115  of the biological fluid filter  100 . An upstanding ridge  157  is provided in a spaced apart relationship to the upstanding sidewall  151 . As with the circular ridges  147  and  155  when the outlet portion  22  and the inlet portion  21  are in mating relationship, the down standing ridge  133  and the upstanding ridge  157  will be in a 180° opposed relationship. As can be seen in FIG. 15 these ridges will provide the pinch seals  160  for the vent filter element  117  and the biological filter element  119 . An ultrasonic weld ridge  158  is provided to separate vent filter  117  and biological filter element  119 , and to provide additional support for the fluid filter  190 . 
     Referring to FIGS. 22 and 23, there is shown a modification of the biological fluid filter  100  previously described. In this modification of the invention, the biological fluid filter  100  has a housing  163 , which may be constructed in a manner similar to that just described, or may be constructed by other means well known in the art. The housing has an inlet  164  to which a biological fluid container of the type well known in the art would be in fluid communication during operation. The housing  163  also has an outlet  165  through which the filtered fluid passes. The outlet  165  would be in fluid communication with a biological receiving container (not shown). 
     A filter element  166  would be sealingly mounted within the housing between inlet  164  and outlet  165 . In this modification of the biological fluid filter  100 , instead of there being a separate and distinct vent filter element  117 , the vent filter element  117  is embedded in the biological fluid filter element  166 . The biological filter element  166  may be made of a liquiphilic filter medium, and the embedded vent filter element  167  may also be made of a liquiphilic filter medium, surrounded by a solid or liquiphobic barrier  168 . In operation, this modification of the biological fluid filter would operate in a similar manner to that just described because of the liquiphilic nature of the biological filter element  166 , until the element was completely saturated. As the blood was rising in the inlet chamber  161 , any entrapped gas would pass through the embedded vent filter element  167  until the level of the blood surpassed the solid or liquiphobic barrier  168 . At this time, virtually all of the entrapped gas would be downstream of the biological filter element  166 , the element would be completely saturated, and blood would now freely flow into the outlet chamber  162 . 
     Another modification of the biological fluid filter  100  is shown in FIGS. 24 and 25. As before, there is a filter housing  163  having an inlet  164  communicating with an inlet chamber  161 , and an outlet  165  communicating with an outlet chamber  162 . In this modification of the invention, the biological filter element  166  has a first embedded liquiphilic gas vent  167  surrounded by a solid barrier  168 , and a second embedded liquiphobic gas vent  173 . 
     In operation, a biological fluid container known in the art (not shown) will be in fluid communication with inlet  164 . As blood is released from the biological fluid container it will flow into the inlet chamber  161  and come into contact with the bottom of the biological fluid filter element  166 . Since filter element  166  may be a liquiphilic porous medium, the blood level may wick up in the liquiphilic porous medium  166  faster than the level in the chamber  161 . The blood will not pass through the liquiphobic second embedded gas vent  173 . The second embedded gas vent  173  will have no effect on the operation of the biological fluid filter  100  while the liquid level continues to rise in inlet chamber  161 . However, the difference between the embodiment of the invention shown in FIGS. 22 and 23, and  24  and  25 , becomes apparent when all of the blood has been released from the biological filter container and the level starts dropping in the inlet chamber  161 . The vent filter element  167  will stay wetted out as the level in the inlet chamber  161  drops because of the blood present in the outlet chamber  162 . However, as the level in the inlet chamber  161  continues to drop it will drop below the level of the liquiphobic second embedded gas vent  173 . Since gas vent  173  did not wet out, when the blood level drops, air will pass from the inlet chamber  161  through the second embedded gas vent  173 , and aid in draining the filter element  166 , as well as the outlet chamber  162 , through the outlet  165 . 
     Therefore, by carefully studying the problems present in prior art biological filtration fluid systems, I have developed a novel method and apparatus for biological fluid filtration. 
     In accordance with the provisions of the patent statutes, the present invention has been described in what is considered to represent its preferred embodiment. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope.