Abstract:
The present invention relates generally to the field of extracorporeal blood processing methods and apparatus which are particularly useful in blood component collection, and more specifically, the present invention relates to methods and apparatus for centrifugally separating buffy coat that reduce the surface available for separated buffy coat components to sediment on by varying the radius of the product collection bag.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/365,602 filed Jul. 19, 2010 
     
    
     FIELD OF THE INVENTION 
       [0002]    The instant invention relates to a centrifuge for processing blood and blood components and for pooling buffy coat collections. This invention would be useful in any system with a central compartment where blood components are collected during centrifugation. 
       BACKGROUND OF THE INVENTION 
       [0003]    Different types of centrifuges intended for processing blood and blood components and also several types of ring bags intended for use in these centrifuges are described in, for example, WO87/06857; U.S. Pat. No. 5,144,396; U.S. Pat. No. 5,732,050; WO97/30715; and WO98/35757. An apparatus for pooling buffy coat collections is described in U.S. Pat. No. 6,656,105. In the apparatus described in U.S. Pat. No. 6,656,105, the center well or central compartment or chamber to hold the platelet collection bag forms a cylindrical wall parallel to the axis of rotation of the centrifuge. This cylindrical wall provides a relatively large surface against which the platelets sediment under centrifugal force. This cylindrical wall also determines the sedimentation distance of the platelets. 
       SUMMARY OF THE INVENTION 
       [0004]    It is an object of this instant invention to reduce the sedimentation surface against a wall available for platelets in a centrifuge. This, in turn, increases the distance through which platelets must sediment before settling onto the wall. The result is that most of the platelets remain suspended in plasma or Platelet Additive Solution (PAS) when they are removed from the central chamber. Platelets in suspension are of a better quality than platelets that have sedimented onto the wall. 
         [0005]    This present invention includes a centrifuge for processing buffy coat, comprising a rotor with a central axis of rotation, a central chamber on the rotor capable of receiving a product collection bag, and a separation chamber capable of receiving a separation vessel containing buffy coat. The separation vessel is connected to the product collection bag where separated buffy coat components can pass from the separation chamber to the central chamber. The central chamber of the centrifuge has an inner wall with a varying radius from the central axis of rotation, an upper portion, and a lower portion. When the product collection bag is received in the central chamber, the bag extends adjacent to both the upper and lower portions of the inner wall. 
         [0006]    Another aspect of the present invention is a system for processing buffy coat comprising a bag assembly, and a centrifuge for processing buffy coat components. The bag assembly includes a separation vessel, a product collection bag, and at least one conduit connecting the separation vessel to the product collection bag. The centrifuge for processing buffy coat comprises a rotor with a central axis of rotation; a central chamber on the rotor, wherein the product collection bag is in the central chamber; and a separation chamber capable of receiving the separation vessel containing buffy coat. The central chamber of the centrifuge has an inner wall with a varying radius from the central axis of rotation, an upper portion, and a lower portion. The product collection bag extends adjacent to both the upper and lower portions of the inner wall. 
         [0007]    In one embodiment of the invention, the upper portion of the inner wall of the central chamber described above has a greater radius than any radius of the lower portion. In another embodiment of the invention, the lower portion has a greater radius than any radius of the upper portion. Also in one embodiment, the upper portion and/or the lower portion may have a constant radius with respect to the central axis of rotation. The inner wall may also have a middle portion that is between the upper and lower portions of the inner wall that may be sloped at an angle. The radius of the lower portion of the wall may decrease or increase from its top, defined by the middle portion, to its bottom, defined by the bottom of the central chamber. The radius with respect to the central axis of rotation of the upper portion may decrease or increase from its top, defined by the top of the central chamber, to its bottom, defined by the lower portion of the inner wall. In one embodiment of the present invention, the inner wall may comprise a removable insert for the central chamber. 
         [0008]    In one embodiment of the invention, the separated component of the buffy coat is platelets. The separated platelets are passed to the product collection bag, wherein the inner wall of the central chamber is configured such that the platelets sediment out on either the upper portion of the inner wall or the lower portion of the inner wall. 
         [0009]    Another aspect of the present invention includes a method for separating blood composites from buffy coat in a centrifuge. The centrifuge used in the method has a rotor with a central axis of rotation and a central chamber on the rotor, and the central chamber has an inner wall. The method includes loading a separation vessel onto the centrifuge, loading a product collection bag in the central chamber of the centrifuge, loading the separation vessel with buffy coat, rotating the centrifuge at a sufficient rate such that platelets separate from the buffy coat, collecting the separated platelets in the product collection bag, and reducing the surface area for the collected platelets to contact the product collection bag. 
         [0010]    In one embodiment of the invention, the reducing step may comprise preventing platelets from contacting the entire inner wall. The preventing step may comprise varying the radius of the product collection bag with respect to the central axis of rotation. The varying step may comprise providing the inner wall with an upper and a lower portion, where the upper portion has a greater radius than the lower portion and where the product collection bag extends adjacent to both the upper and lower portions of the inner wall. The varying step may alternatively comprise providing the inner wall with a lower portion that has a greater radius than any radius of the upper portion of the inner wall, and extending the product collection bag adjacent to both the upper and lower portions of the inner wall. 
         [0011]    In one embodiment of the invention, the reducing step may comprise shaping the product collection bag during the collecting step to conform the product collection bag to the inner wall of the central chamber. The shaping step may include varying the radius of the product collection bag with respect to the central axis of rotation. Additionally, the central chamber may have a top and a bottom and the reducing step may comprise decreasing or increasing the inner wall radius of the central chamber along the central axis of rotation from the top to the bottom, comprising providing the inner wall with an upper portion and a lower portion. In one embodiment of the invention, the upper portion may have a radius with respect to the central axis of rotation that is greater than any radius of the lower portion and the product collection bag extends adjacent to both the upper and lower portions of the inner wall. In another embodiment, the lower portion may have a radius with respect to the central axis of rotation that is greater than any radius of the upper portion and the product collection bag extends adjacent to both the upper and lower portions of the inner wall. 
         [0012]    In one embodiment, the reducing step may also comprise adding an insert inside the central chamber to form the inner wall and to vary the radius of the central chamber between the central axis of rotation and the inner wall. The inner wall may be provided an upper and a lower portion where the product collection bag extends adjacent to both portions of the inner wall. The upper portion may have a greater radius than any radius of the lower portion with respect to the central axis of rotation. In another embodiment, the lower portion has a greater radius than any radius of the upper portion. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  illustrates a cross-sectional view through a typical centrifuge in accordance with the prior art. 
           [0014]      FIG. 2  illustrates a cross-sectional view of an alternate central chamber in accordance with the invention for the centrifuge of  FIG. 1 . 
           [0015]      FIG. 3  illustrates a cross-sectional view of an alternate central chamber in accordance with the invention for the centrifuge of  FIG. 1 . 
           [0016]      FIG. 4  illustrates a cross-sectional view of an alternate central chamber in accordance with the invention for the centrifuge of  FIG. 1 . 
           [0017]      FIG. 5  illustrates a cross-sectional view of an alternate central chamber in accordance with the invention for the centrifuge of  FIG. 1 . 
           [0018]      FIG. 6  illustrates a cross-sectional view of an alternate central chamber in accordance with the invention for the centrifuge of  FIG. 1 . 
           [0019]      FIG. 7  is a cross-sectional view of a centrifuge with a central chamber wall in accordance with the invention. 
           [0020]      FIG. 8  is a top view of a ring or separation bag for the centrifuge of  FIG. 1  or  FIG. 5 . 
           [0021]      FIG. 9  is a schematic of a bag set intended for blood platelet production from buffy coat. 
           [0022]      FIG. 10  is a schematic view of a centrifuge equipped with buffy coat pooling. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The centrifuge  34  shown in  FIG. 1  has a rotor  1  with a central axis of rotation  100 , and a central chamber  2 , where, for example, the final storage, product collection or satellite bags for produced or collected separated products can be located during a centrifuging operation. The central chamber has an outer wall  61  and an inner wall  63 . The satellite bags, such as bag  33  in  FIG. 9 , are connected to a ring or annularly-shaped separation vessel  4 . Furthermore, a ring or separation chamber  3  is included on the rotor  1  to receive ring or separation vessel  4 . In one embodiment of the present invention, the separation chamber  3  surrounds the central chamber  2 . The area beneath the ring or separation vessel  4  in the separation chamber  3  forms a chamber  5 . The chamber  5  can be filled with a hydraulic fluid with the purpose of applying pressure or squeezing the ring or separation vessel  4 . Centrifuge rotor  1  further includes a rotating inner lid  6  which includes a securing portion  7  for the ring or separation vessel  4 . A sensor for sensing component movement is included at  52 . 
         [0024]    In  FIG. 1 , ring or separation vessel  4  is shown filled with fluid  8  which is a composite fluid or composite buffy coat (as described below) for separation. There are three supports  9 ,  10 , and  11  on the centrifuge rotor  1 . Of these, only support  9  is shown in  FIG. 1 , but see also  FIG. 8 . The supports  9 ,  10 , and  11  locate the position of ring or separation vessel  4  and also provide guide grooves  12 ,  21  and  22 , respectively, to secure different connecting tubes or tubing or conduits between the separation vessel  4  and the satellite or product collection bags as well as a tube, tubing or conduits from the diluting fluid or buffy coat composite fluid bags as will be described below. Supports  9 ,  10 , and  11  may be configured such that the guide grooves  12 ,  21  and  22  may be selectively reduced and/or increased in size to clamp or unclamp tubing or connecting tubes placed in the grooves. For example, a portion of the support  9  could be configured to move in the direction of arrow  13  so as to function as a clamp valve. Also, one or more of supports  9 ,  10 , and  11  may be configured to provide a welding function, which, when activated, seals and cuts the tubes positioned in the guide grooves  12 ,  21  and  22 . 
         [0025]    The welding function on the supports requires access to electric power in the centrifuge rotor and may also receive commands from a control system of the centrifuge. Any electrical connection occurs through slip ring connectors between the rotor and centrifuge stand where  14  indicates the centrifuge&#39;s rotor portion and  15  indicates the centrifuge stand. On  FIG. 1 , the centrifuge motor is marked as  16 . Motor  16  rotates the centrifuge rotor through driving belt  47 ; driving belt  47  is located between the motor&#39;s driving pulley  48  and the centrifuge&#39;s driving pulley  49 . The centrifuge&#39;s rotation bearing is  50  and the centrifuge&#39;s rotating guide is  51 . In the centrifuge&#39;s inner lid or cover  6 , there is a central opening  53  which permits central chamber  2  to be accessible externally even when the inner lid or cover  6  is closed. 
         [0026]    Ring or separation vessel  4 , as shown in  FIG. 8 , comprises two sheets of suitable plastic material joined together along the welded edges  17  and  18 . An external ring vessel for separation of a blood composite and buffy coat is formed between the welded edges  17  and  18 . Besides ring welds  17  and  18 , there are additional welded points for strengthening around the holes which are intended for locating ring or separation vessel  4  on supports  9 ,  10 , and  11 . All the ring or separation vessels shown in the Figures are formed with a central opening, where the central opening primarily corresponds to the center chamber  2  opening when the separation vessel  4  is in the centrifuge  34 . In  FIG. 8 , this opening is designated  19 . The ring or separation vessel  4  shown in  FIG. 8  has openings  109 ,  110 , and  111  for supports  9 ,  10 , and  11 , respectively. Input tube  20  and output tube  32  are attached to the ring or the separation vessel&#39;s top and bottom sides by means of the welded sleeve couplings  24 . Ports with flat securing collars  4   a  and  4   b  can be welded to the ring or separation vessel&#39;s top and bottom sides in which the connecting tubes  20  and  32  are secured by welding. Instead of being secured via the port and securing collar, the input tube  20  and output tube  32  can also be secured to each respective welded edge, i.e., welding  17  and welding  18  in  FIG. 8 . 
         [0027]      FIG. 9  shows the bag set for collecting blood platelets from buffy coat. This bag set includes ring or separation vessel  4 , a bag with diluting solution  23 , four connecting tubes or conduits  25 ,  26 ,  27 , and  28  (the number of connecting or separation tubes can vary with the number of buffy coat collections, but generally the number is between four and six). In use, each tube  25 ,  26 ,  27 , and  28  can be connected such as by welding or sterile connection to bags with buffy coat, such as bags  37 ,  38 ,  39 ,  40  in  FIG. 10 . A multi-way connector  29  is connected to the diluting solution bag  23  via tube or conduit  30 . Tube  20  is further connected to the tubes  25 ,  26 ,  27 , and  28  through the multi-way connector  29 . Tube  32  is connected from the ring or separation vessel  4  to a final storage, product collection, or satellite bag  33 . A leukoreduction filter  31  may also be included. Tube  30 , which extends from diluting solution bag  23  to multi-way connector  29 , is arranged in the guide groove  22  in support  11  to provide a clamp valve function for control of the addition of diluting solution. Bag  23  may also contain an optional openable closer or frangible closer at  45 . 
         [0028]    The bag set shown in  FIGS. 8 and 9  is used in the apparatuses of  FIG. 2 ,  3 ,  4 ,  5 ,  6  or  7 , and, in  FIG. 10 , for buffy coat pooling. In  FIG. 10 , the centrifuge  34  is shown with an outer lid  35  open and locked in position. The centrifuge&#39;s inner lid  6  has been omitted in this figure, but see  FIG. 7 . Also, the centrifuge rotor  1  and the ring or separation vessel  4  are drawn in a simplified manner. The centrifuge&#39;s control panel is shown schematically at  36 . Furthermore, a cassette  41  mounted on the inside of the centrifuge&#39;s outer lid  35  and rotatable as shown at  42 , holds blood bags  37 ,  38 ,  39 , and  40  which contain buffy coat. Bag  23 , containing a diluting solution, is mounted via holder  44  at a level vertically higher than bags  37 ,  38 ,  39 ,  40 . 
         [0029]    As shown in  FIG. 7 , in operation, when the bag set of  FIG. 9  is loaded on the centrifuge rotor  1 , final storage, product collection or satellite bag  33  is placed in the central chamber  2 . In the prior art  FIG. 1 , the sides  62  of the bag  33  are generally parallel to the outer wall  61  and the inner wall  63  of the central chamber. 
         [0030]    In  FIG. 2 , a removable insert  71  is provided for central chamber  2  to vary the radius of the inner wall of central chamber  2  with respect to the central axis of rotation  100 . The insert  71  includes a top side  72 , an outer side  73 , a bottom  74 , and a sloping inner side  75 . The insert  71  has a height between the top side  72  and bottom side  74  that is less than the height of the central chamber  2 . The top side of the insert  72  defines a middle portion of the inner wall of the central chamber  2 . The sloping inner side  75  of the insert  71  defines a lower portion of the inner wall of the central chamber  2 . The lower portion  75  of the inner wall has a radius with respect to the central axis of rotation  100  that decreases from its top, defined by the middle portion  72 , to its bottom, defined by the bottom of the insert  74 . The portion of the inner wall  76  above the insert  71  defines an upper portion of the inner wall of the central chamber  2 . The insert  71  fits inside the central chamber  2  to shape product collection bag  33  during centrifugation as is more fully described below. 
         [0031]      FIG. 3  illustrates an alternative removable insert  81  with a sloping top side  82 , inner and outer sides  85  and  83 , and a bottom  84 . This insert also has a height between the highest point  87  of top side  82  and bottom  84  that is less than the overall height of the central chamber  2 . The inner side  85  defines a lower portion of the inner wall of the central chamber, and the sloping top side  82  of the insert defines a middle portion of the inner wall of the central chamber. The middle portion  82  is sloped at an angle greater than 0 degrees and less than or equal to 90 degrees with respect to the outer wall of the central chamber  61 . The portion  86  of the central chamber above the insert  81  defines an upper portion of the inner wall of the central chamber  2 . Both the upper portion  86  and lower portion  85  of the inner wall have constant radii with respect to the central axis of rotation  100 . 
         [0032]    A third alternative removable insert  91  is shown in  FIG. 4 . This insert has parallel top side  92  and bottom  94 . An outer side  93  is parallel to an inner side  95 . The insert  91  has a height between the top side  92  and the bottom side  94  that is less than the overall height of the central chamber  2 . The portion  96  of the central chamber above the insert  91  defines an upper portion of the inner wall of the central chamber  2 . The inner side  95  defines a lower portion of the inner wall, and the top side  92  of the insert  91  defines a middle portion of the inner wall of the central chamber  2 . Both the upper portion  96  and lower portion  95  of the inner wall have constant radii with respect to the central axis of rotation  100 . 
         [0033]    A fourth alternative removable insert  201  is shown in  FIG. 5 . The insert  201  has a bottom  204 , an outer side  203 , an inner side  205 , and a top side  202 . The insert  201  extends the length of central chamber  2  from central chamber  2 &#39;s opening to its bottom. The inner side  205  of the insert  201  defines an inner wall of the central chamber  2 . The inner wall  205  is divided into portions. The portion  206  of the inner wall  205  defines an upper portion of the inner wall of the central chamber  2 . The portion  207  of the inner wall  205  defines a lower portion of the inner wall  205  of the central chamber  2 . Both the upper portion  206  and the lower portion  207  of the inner wall have decreasing radii with respect to the central axis of rotation  100  from the top of the central chamber  2  to the bottom of the central chamber  2 . 
         [0034]    A fifth alternative removable insert  301  is shown in  FIG. 6 . The insert  301  has a bottom  304 , an outer side  303 , an inner side  305 , and a top side  302 . The insert  301  extends the length of central chamber  2  from central chamber  2 &#39;s opening to its bottom. The inner side  305  of the insert  301  defines an inner wall of the central chamber  2 . The inner wall  305  is divided into portions. The portion  306  of the inner wall  305  defines an upper portion of the inner wall of the central chamber  2 . The portion  307  of the inner wall  305  defines a lower portion of the inner wall  305  of central chamber  2 . Both the upper portion  306  and the lower portion  307  of the inner wall have increasing radii with respect to the central axis of rotation  100  from the top of the central chamber  2  to the bottom of the central chamber  2 . 
         [0035]    As described, the inserts  71 ,  81 ,  91 ,  201  and  301  fit inside the central chamber  2  permitting the central chamber  2  to have an inner wall with a varied radius, shaping the product collection bag  33  during centrifugation. The product collection bag  33 , when received, is positioned in the central chamber  2  adjacent to both the upper portions  76 ,  86 ,  96 ,  206 ,  306  and the lower portions  75 ,  85 ,  95 ,  207 ,  307  of the inner wall of the central chamber  2 . The upper portions  76 ,  86 ,  96 ,  206  of the inner wall have a radius greater than any radius of the lower portions  75 ,  85 ,  95 ,  207  of the inner wall with respect to the central axis of rotation  100 . However, the upper portion may have a greater radius than the lower portion of the inner wall such as in  FIG. 6  and still accomplish the goal of reducing the surface area for platelets to sediment on. An insert consistent with such a configuration is shown in  FIG. 6 ; insert  301  has a lower portion  307  of the inner wall  305  with a radius with respect to the central axis of rotation  100  greater than any radius of the upper portion  306  of the inner wall  305 . In the case that the upper portion of the inner wall has a greater radius than the lower portion of the inner wall, then the middle portion of the inner wall will be sloped at an angle greater than or equal to 90 degrees and less than or equal to 180 degrees with respect to the outer wall of the central chamber. 
         [0036]      FIGS. 2 ,  3 ,  4 ,  5 , and  6  describe removable inserts. However, as shown in  FIG. 7 , the central chamber inner wall  171  can be manufactured having a varied radius without an insert. As shown in  FIG. 7 , the upper portion  176  of the inner wall has a constant radius from the central axis of rotation  100  greater than any radius of the lower portion  175  of the inner wall. A middle portion  172  divides the upper portion  176  of the inner wall from the lower portion  175  of the inner wall. A bottom of the lower portion of the inner wall is shown at  174 . As shown in  FIG. 7 , under centrifugal forces, a portion of product collection bag  33  extends adjacent to both the lower portion  175  of the inner wall and the upper portion of the inner wall  176 . 
         [0037]    Although only a wall configuration similar to  FIG. 2  is shown in  FIG. 7 , it is understood that wall configurations similar to  FIGS. 3 ,  4 ,  5 , and  6  could be used to define the inner wall of the central chamber  2  rather than using an insert. 
         [0038]    Before the buffy coat is separated into its components, the buffy coat in bags  37 ,  38 ,  39 ,  40  must be loaded into the separation vessel  4 . As ring or separation vessel  4  is loaded on the centrifuge rotor  1 , the product collection bag  33  is loaded into the central chamber  2  for product collection. Also, tube or conduit  30  is placed in groove  22  in support  11 , tube or conduit  20  is placed in groove  21  in support  10  and tube or conduit  32  is placed in groove  12  in support  9 . To begin the process of transferring or loading the buffy coat into the ring or separation vessel  4 , a small amount of diluting solution will be flowed through tube  30  after opening the valve in support  11  and optional frangible  45 , through multi-way connector  29 , and through tubes  25 ,  26 ,  27 ,  28  into bags  37 ,  38 ,  39 ,  40 , respectively. After the addition of diluting solution in sufficient amounts to bags  37 ,  38 ,  39 ,  40 , a motor operatively connected to cassette  41  is actuated to oscillate cassette  41  forward and backwards in a pendulum movement, shown as  42 , until all remaining concentrate substance in the buffy coat bags  37 ,  38 ,  39 ,  40  is suspended in the diluting solution. After sufficient agitation for suspension, the valve in support  10  on the rotor is opened through which tubing  20  passes from the multi-way connector  29  to drain or load the buffy coat into separation vessel  4 . The process of adding diluting solution to bags  37 ,  38 ,  39 ,  40 , agitating, and draining the mixture of buffy coat and diluting solution through multi-way connector  29  and into tube  20  can be repeated until there is no remaining buffy coat in bags  37 ,  38 ,  39 ,  40 . The buffy coat and diluting solution flow through tube  20  to ring or separation vessel  4 . 
         [0039]    After the buffy coat and diluting solution have been drained or loaded into ring or separation vessel  4 , tubes  20  and  30  can be cut and sealed in guide grooves  21  and  22 , respectively, by the welding function in supports  10  and  11 . Cassette  41 , holder  44 , bags  37 ,  38 ,  39 ,  40  and  23 , and all associated tubing are removed from the centrifuge lid whereby the centrifuge is closed for the centrifugation operation. 
         [0040]    The rotor  34  is rotated at  1800  rpm or at a sufficient rpm that the less dense platelets separate from the denser Red Blood Cells (RBC) and leukocytes of the buffy coat. The built-in valve in guide groove  12  in support  9  can be opened and separation vessel  4  can be squeezed using the hydraulic fluid in chamber  5  to permit the less dense platelets and any plasma or diluting solution to be transferred through tube  32  to product collection bag  33  to be collected. While being expressed or passed from the separation vessel  4  to the product collection bag  33 , the platelets can be pushed through the optional filter  31 , shown on  FIG. 9 , and collected into the product collection bag  33 . The transfer of the platelets and any plasma continues until a sensor  52  indicates the interface between the platelets and RBCs/leukocytes. After the final expression of platelets, tube  32  is sealed by sterile welding using the welding function on support  9 . The platelets in bag  33  will continue to be subjected to centrifugal force until the centrifuge slows to a stop. 
         [0041]    During centrifugation, the surface area is reduced for the collected platelets to contact the product collection bag and platelets are prevented from contacting the entire inner wall. Product collection bag  33  is extended adjacent to both the upper and lower portions of the inner wall and is shaped by the contour of central chamber  2 &#39;s inner wall during centrifugation. The inner wall of the central chamber has a varying radius with respect to the central axis of rotation  100  shaped either by an insert  71 ,  81 ,  91 ,  201  or  301  shown in  FIGS. 2 ,  3 ,  4 ,  56  or by the use of the central chamber inner wall  171  of  FIG. 7 . The product collection bag is shaped by the centrifugal force to conform to the shape of the inner wall of the central chamber  2 . Thus, the radius of the product collection bag is also varied by the shaping. When subjected to the centrifugal force, the platelets will form a layer farthest from the central axis of rotation  100  due to their sedimentation velocity. Decreasing or increasing the inner wall radius of the central chamber from top to bottom of the chamber either by manufacture  171  as shown in  FIG. 7  or by using an insert  71 ,  81 ,  91 ,  201  or  301  in  FIG. 2 ,  3 ,  4 ,  5  or  6  reduces surface area for the platelets to form a layer by preventing the platelets from contacting the entire inner wall. 
         [0042]    As shown in  FIGS. 2 ,  3 ,  4 ,  5  and  6 , adding an insert  71 ,  81 ,  91 ,  201  or  301  or using of the central chamber inner wall  171  of  FIG. 7  to vary the radius of the central chamber between the central axis of rotation  100  and the inner wall permits the platelets to pack or sediment out along the portion of the wall with the greatest radius, including upper portions  76 ,  86 ,  96 ,  206  or  176  of the inner wall or, alternatively, the lower portion  307  of the inner wall. This is because the platelets will sediment out faster than any remaining less dense plasma or diluting fluid. The denser platelets under centrifugal force that have been expressed tend to move to form a layer farthest from the rotation axis. If the layer forms only in the upper portions  76 ,  86 ,  96 , and  206  or, alternatively, the lower portion  307 , of the inner wall, there will be fewer numbers of platelets contacting the surface area of the bag  33  than if the platelet layer extended along the entire height of the bag parallel to the central axis of rotation  100 , as in the prior art  FIG. 1 . 
         [0043]    Platelets in plasma have a lower sedimentation velocity generally than platelets that are stored in a platelet additive solution (PAS). Generally, platelets in such an additive solution have a higher sedimentation velocity and thus may be more likely to form a film on the bag wall over its height. Thus, using the configurations of  FIGS. 2 ,  3 ,  4 ,  5 ,  6  and  7  reduce the ability of platelets in PAS to form such a film.