Patent Publication Number: US-11654408-B2

Title: Methods for operating a bioreactor with impeller assembly and related bioreactors

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 15/829,379, filed on Dec. 1, 2017, now U.S. Pat. No. 10,335,751, which is a continuation of U.S. application Ser. No. 14/660,405, filed Mar. 17, 2015, now U.S. Pat. No. 9,855,537, which claims priority to U.S. Provisional Patent Application No. 61/969,094 filed Mar. 22, 2014, which are incorporated herein by specific reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. The Field of the Invention 
     The present invention relates to methods for operating bioreactors having an impeller assembly and related bioreactors. 
     2. The Relevant Technology 
     The biopharmaceutical industry uses a broad range of mixing systems for a variety of processes such as in the preparation of media and buffers and in the growing, mixing and suspension of cells and microorganisms. Some conventional mixing systems, including bioreactors and fermentors, comprise a flexible bag disposed within a rigid support housing. An impeller is disposed within the flexible bag and is coupled with a drive shaft projecting into the bag. Rotation of the drive shaft and impeller facilitates mixing and/or suspension of the fluid contained within the flexible bag. 
     Although the current mixing systems are useful, they have some limitations. For example, where the drive shaft is secured within the flexible bag during the manufacturing process, the rigid drive shaft limits the ability to collapse or fold the flexible bag so as to reduce its size for transportation, storage and/or further processing. Likewise, where it is intended to reuse the drive shaft, such as when it is made of metal, this system has the disadvantage of needing to clean and sterilize the drive shaft between different uses. 
     In an alternative mixing system, a flexible tube is disposed within a flexible bag. A first end of the tube is rotatably coupled by a dynamic seal to the bag while an opposing second end of the tube is sealed to an impeller. During use, a rigid drive shaft is passed down into the tube and couples with the impeller. In turn, rotation of the drive shaft facilitates rotation of the tube and impeller for mixing the fluid within the flexible bag. In this design, before the drive shaft is inserted, the combined flexible bag and tube can be folded for ease of storage and transportation. In addition, the tube isolates the drive shaft from the fluid so that during use the drive shaft does not directly contact the fluid within the bag. As such, following use, the drive shaft can be removed and reused without the need for cleaning or sterilization. 
     Although the mixing system using the flexible tube has a number of improved advantages, it also has some limitations. For example, the flexible tube design is limited to a single impeller mounted on the end thereof. In larger volume mixing systems or in applications where higher rates of mixing are required, a single impeller may not be sufficient to achieve a needed mixing rate. Accordingly, what is needed in the art are mixing systems that retain all or some of the advantages of using the flexible tube to isolate the rigid drive shaft from the fluid but enable higher mixing rates relative to the single impeller design. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       To further clarify the above and other advantages and features of the present invention, a more particular description of the invention will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. It is appreciated that these drawings depict only illustrated embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
         FIG.  1    is a perspective view of a fluid mixing system; 
         FIG.  2    is a perspective view of the container assembly and drive motor assembly of the fluid mixing system shown in  FIG.  1   ; 
         FIG.  3    is a perspective view of the impeller assembly, drive shaft and drive motor shown in  FIG.  2   ; 
         FIG.  4    is a perspective view of the drive shaft in  FIG.  3    being coupled with the drive motor assembly; 
         FIG.  5    is an elevated side view of the impeller assembly and drive shaft shown in  FIG.  3   ; 
         FIG.  6    is an enlarged top perspective view of the rotational assembly shown in  FIG.  5   ; 
         FIG.  7    is an exploded perspective view of the second tubular connector and impellers shown in  FIG.  5   ; 
         FIG.  8    is an enlarged exploded perspective view of the first end of the second tubular connector and an impeller to be received thereon; 
         FIG.  9    is a perspective view of the components in  FIG.  8    assembled; 
         FIG.  10    is an enlarged exploded perspective view of the second end of the second tubular connector and an end cap to be received thereon; 
         FIG.  11    is a cross sectional side view of the second tubular connector with the impellers thereon; and 
         FIG.  12    is an elevated side view of an alternative embodiment of a drive shaft. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before describing the present disclosure in detail, it is to be understood that this disclosure is not limited to particularly exemplified apparatus, systems, methods, or process parameters that may, of course, vary. It is also to be understood that the terminology used herein is only for the purpose of describing particular embodiments of the present disclosure, and is not intended to limit the scope of the invention. 
     All publications, patents, and patent applications cited herein, whether supra or infra, are hereby incorporated by reference in their entirety to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. 
     The term “comprising” which is synonymous with “including,” “containing,” “having” or “characterized by,” is inclusive or open-ended and does not exclude additional, unrecited elements or method steps. 
     It will be noted that, as used in this specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to a “port” includes one, two, or more ports. 
     As used in the specification and appended claims, directional terms, such as “top,” “bottom,” “left,” “right,” “up,” “down,” “upper,” “lower,” “inner,” “outer,” “internal,” “external,” “interior,” “exterior,” “proximal,” “distal” and the like are used herein solely to indicate relative directions and are not otherwise intended to limit the scope of the invention or claims. 
     Where possible, like numbering of elements have been used in various figures. Furthermore, alternative configurations of a particular element may each include separate letters appended to the element number. Accordingly, an appended letter can be used to designate an alternative design, structure, function, implementation, and/or embodiment of an element or feature without an appended letter. For instance, an element “80” may be embodied in an alternative configuration and designated “80a.” Similarly, multiple instances of an element and or sub-elements of a parent element may each include separate letters appended to the element number. In each case, the element label may be used without an appended letter to generally refer to instances of the element or any one of the alternative elements. Element labels including an appended letter can be used to refer to a specific instance of the element or to distinguish or draw attention to multiple uses of the element. 
     Various aspects of the present devices, systems, and methods may be illustrated with reference to one or more exemplary embodiments. As used herein, the term “embodiment” means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other embodiments disclosed herein. 
     Various aspects of the present devices and systems may be illustrated by describing components that are coupled, attached, and/or joined together. As used herein, the terms “coupled”, “attached”, “connected” and/or “joined” are used to indicate either a direct connection between two components or, where appropriate, an indirect connection to one another through intervening or intermediate components. In contrast, when a component is referred to as being “directly coupled”, “directly attached”, “directly connected” and/or “directly joined” to another component, there are no intervening elements present. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present disclosure pertains. Although a number of methods and materials similar or equivalent to those described herein can be used in the practice of the present disclosure, the preferred materials and methods are described herein. 
     The present invention relates to fluid processing systems and related methods for mixing and sparging solutions and/or suspensions. The processing systems can be bioreactors or fermentors used for culturing cells or microorganisms. By way of example and not by limitation, the inventive systems can be used in culturing bacteria, fungi, algae, plant cells, animal cells, protozoans, nematodes, and the like. The systems can accommodate cells and microorganisms that are aerobic or anaerobic and are adherent or non-adherent. The systems can also be used in association with the formation and/or treatment of solutions and/or suspensions that are not biological but nevertheless incorporate mixing. For example, the systems can be used in the production of media, chemicals, food products, beverages, and other liquid products. 
     The inventive systems are designed so that a majority of the system components that contact the material being processed can be disposed of after each use. As a result, the inventive systems substantially eliminate the burden of cleaning and sterilization required by conventional stainless steel mixing and processing systems. This feature also ensures that sterility can be consistently maintained during repeated processing of multiple batches. In view of the foregoing, and the fact that the inventive systems are easily scalable, relatively low cost, and easily operated, the inventive systems can be used in a variety of industrial and research facilities that previously outsourced such processing. 
     Depicted in  FIG.  1    is one embodiment of an inventive fluid processing system  10  incorporating features of the present invention. In general, processing system  10  comprises a container  12  that is disposed within a rigid support housing  14 . A mixer system  18  is designed for mixing and/or suspending components within container  12 . The various components of fluid processing system  10  will now be discussed in greater detail. 
     With continued reference to  FIG.  1   , support housing  14  has a substantially cylindrical sidewall  20  that extends between an upper end  22  and an opposing lower end  24 . Lower end  24  has a floor  26  mounted thereto. Support housing  14  has an interior surface  28  that bounds a chamber  30 . An annular lip  32  is formed at upper end  22  and bounds an opening  34  to chamber  30 . Floor  26  of support housing  14  rests on a cart  36  having wheels  38 . Support housing  14  is removably secured to cart  36  by connectors  40 . Cart  36  enables selective movement and positioning of support housing  14 . In alternative embodiments, however, support housing  14  need not rest on cart  36  but can rest directly on a floor or other structure. 
     Although support housing  14  is shown as having a substantially cylindrical configuration, in alternative embodiments support housing  14  can have any desired shape capable of at least partially bounding a compartment. For example, sidewall  20  need not be cylindrical but can have a variety of other transverse, cross sectional configurations such as polygonal, elliptical, or irregular. Furthermore, it is appreciated that support housing  14  can be scaled to any desired size. For example, it is envisioned that support housing  14  can be sized so that chamber  30  can hold a volume of less than 50 liters or more than 1,000 liters. Support housing  14  is typically made of metal, such as stainless steel, but can also be made of other materials capable of withstanding the applied loads of the present invention. 
     In one embodiment of the present invention means are provided for regulating the temperature of the fluid that is contained within container  12  disposed within support housing  14 . By way of example and not by limitation, electrical heating elements can be mounted on or within support housing  14 . The heat from the heating elements is transferred either directly or indirectly to container  12 . Alternatively, in the depicted embodiment support housing  14  is jacketed with one or more fluid channels being formed therein. The fluid channels have a fluid inlet  42  and a fluid outlet  44  that enables a fluid, such as water or propylene glycol, to be pumped through the fluid channels. By heating, cooling or otherwise controlling the temperature of the fluid that is passed through the fluid channels, the temperature of support housing  14  can be regulated which in turn regulates the temperature of the fluid within container  12  when container  12  is disposed within support housing  14 . Other conventional means can also be used such as by applying gas burners to support housing  14  or pumping the fluid out of container  12 , heating or cooling the fluid and then pumping the fluid back into container  12 . When using container  12  as part of a bioreactor or fermentor, the means for heating can be used to heat the culture within container  12  to a temperature in a range between about 30° C. to about 40° C. Other temperatures can also be used. 
     Support housing  14  can have one or more openings  46  formed on the lower end of sidewall  20  and on floor  26  to enable gas and fluid lines to couple with container  12  and to enable various probes and sensors to couple with container  12  when container  12  is within support housing  14 . Further disclosure on support housing  14  and alternative designs thereof is disclosed in U.S. Pat. No. 7,682,067 and US Patent Publication No. 2011-0310696, which are incorporated herein by specific reference. 
       FIG.  2    shows container  12  coupled with mixer system  18 . Container  12  has a side  55  that extends from an upper end  56  to an opposing lower end  57 . Container  12  also has an interior surface  58  that bounds a compartment  50  in which a portion of mixer system  18  is disposed. In the embodiment depicted, container  12  comprises a flexible bag. Formed on container  12  are a plurality of ports  51  that communicate with compartment  50 . Although only two ports  51  are shown, it is appreciated that container  12  can be formed with any desired number of ports  51  and that ports  51  can be formed at any desired location on container  12  such as upper end  56 , lower end  57 , and/or alongside  55 . Ports  51  can be the same configuration or different configurations and can be used for a variety of different purposes. For example, ports  51  can be coupled with fluid lines for delivering media, cell cultures, and/or other components into and out of container  12 . 
     Ports  51  can also be used for coupling probes to container  12 . For example, when container  12  is used as a bioreactor for growing cells or microorganisms, ports  51  can be used for coupling probes such as temperatures probes, pH probes, dissolved oxygen probes, and the like. Examples of ports  51  and how various probes and lines can be coupled thereto is disclosed in United States Patent Publication No. 2006-0270036, published Nov. 30, 2006 and United States Patent Publication No. 2006-0240546, published Oct. 26, 2006, which are incorporated herein by specific reference. Ports  51  can also be used for coupling container  12  to secondary containers and to other desired fittings. 
     In one embodiment of the present invention, means are provided for delivering a gas into the lower end of container  12 . By way of example and not by limitation, as also depicted in  FIG.  2   , a sparger  54  can be either positioned on or mounted to lower end  57  of container  12  for delivering a gas to the fluid within container  12 . As is understood by those skilled in the art, various gases are typically required in the growth of cells or microorganisms within container  12 . The gas typically comprises air that is selectively combined with oxygen, carbon dioxide and/or nitrogen. However, other gases can also be used. The addition of these gases can be used to regulate the dissolved oxygen and CO 2  content and to regulate the pH of a culture solution. Depending on the application, sparging with gas can also have other applications. A gas line  61  is coupled with sparger  54  for delivering the desired gas to sparger  54 . Gas line  61  need not pass through lower end  57  of container  12  but can extend down from upper end  56  or from other locations. 
     Sparger  54  can have a variety of different configurations. For example, sparger  54  can comprise a permeable membrane or a fritted structure comprised of metal, plastic or other materials that dispense the gas in small bubbles into container  12 . Smaller bubbles can permit better absorption of the gas into the fluid. In other embodiments, sparger  54  can simply comprise a tube, port, or other type opening formed on or coupled with container  12  through which gas is passed into container  12 . In contrast to being disposed on container  12 , the sparger can also be formed on or coupled with mixer system  18 . Examples of spargers and how they can be used in the present invention are disclosed in United States Patent Publication Nos. 2006-0270036 and 2006-0240546 which were previously incorporated by reference. Other conventional spargers can also be used. It is appreciated that in some embodiments and uses that a sparger may not be required. 
     In the depicted embodiment, container  12  has an opening  52  that is sealed to a rotational assembly  82  of mixer system  18 , which will be discussed below in greater detail. As a result, compartment  50  is sealed closed so that it can be sterilized and be used in processing sterile fluids. During use, container  12  is disposed within chamber  30  of support housing  14  as depicted in  FIG.  1   . Container  12  is supported by support housing  14  during use and can subsequently be disposed of following use. In one embodiment, container  12  is comprised of a flexible, water impermeable material such as a low-density polyethylene or other polymeric sheets or film having a thickness in a range between about 0.1 mm to about 5 mm with about 0.2 mm to about 2 mm being more common. Other thicknesses can also be used. The material can be comprised of a single ply material or can comprise two or more layers which are either sealed together or separated to form a double wall container. Where the layers are sealed together, the material can comprise a laminated or extruded material. The laminated material comprises two or more separately formed layers that are subsequently secured together by an adhesive. 
     The extruded material comprises a single integral sheet that comprises two or more layers of different materials that can be separated by a contact layer. All of the layers are simultaneously co-extruded. One example of an extruded material that can be used in the present invention is the Thermo Scientific CX3-9 film available from Thermo Fisher Scientific. The Thermo Scientific CX3-9 film is a three-layer, 9 mil cast film produced in a cGMP facility. The outer layer is a polyester elastomer coextruded with an ultra-low density polyethylene product contact layer. Another example of an extruded material that can be used in the present invention is the Thermo Scientific CX5-14 cast film also available from Thermo Fisher Scientific. The Thermo Scientific CX5-14 cast film comprises a polyester elastomer outer layer, an ultra-low density polyethylene contact layer, and an EVOH barrier layer disposed therebetween. 
     The material is approved for direct contact with living cells and is capable of maintaining a solution sterile. In such an embodiment, the material can also be sterilizable such as by radiation. Examples of materials that can be used in different situations are disclosed in U.S. Pat. No. 6,083,587 which issued on Jul. 4, 2000 and United States Patent Publication No. US 2003-0077466 A1, published Apr. 24, 2003, which are hereby incorporated by specific reference. 
     In one embodiment, container  12  comprises a two-dimensional pillow style bag wherein two sheets of material are placed in overlapping relation and the two sheets are bounded together at their peripheries to form the internal compartment. Alternatively, a single sheet of material can be folded over and seamed around the periphery to form the internal compartment. In another embodiment, the containers can be formed from a continuous tubular extrusion of polymeric material that is cut to length and is seamed closed at the ends. 
     In still other embodiments, container  12  can comprise a three-dimensional bag that not only has an annular side wall but also a two dimensional top end wall and a two dimensional bottom end wall. Three dimensional containers comprise a plurality of discrete panels, typically three or more, and more commonly four or six. Each panel is substantially identical and comprises a portion of the side wall, top end wall, and bottom end wall of the container. Corresponding perimeter edges of each panel are seamed together. The seams are typically formed using methods known in the art such as heat energies, RF energies, sonics, or other sealing energies. 
     In alternative embodiments, the panels can be formed in a variety of different patterns. Further disclosure with regard to one method of manufacturing three-dimensional bags is disclosed in United States Patent Publication No. US 2002-0131654 A1, published Sep. 19, 2002, which is hereby incorporated by reference. 
     It is appreciated that container  12  can be manufactured to have virtually any desired size, shape, and configuration. For example, container  12  can be formed having a compartment sized to 10 liters, 30 liters, 100 liters, 250 liters, 500 liters, 750 liters, 1,000 liters, 1,500 liters, 3,000 liters, 5,000 liters, 10,000 liters or other desired volumes. The size of the compartment can also be in the range between any two of the above volumes. Although container  12  can be any shape, in one embodiment container  12  is specifically configured to be complementary or substantially complementary to chamber  30  of support housing  14 . It is desirable that when container  12  is received within chamber  30 , container  12  is at least generally uniformly supported by support housing  14 . Having at least general uniform support of container  12  by support housing  14  helps to preclude failure of container  12  by hydraulic forces applied to container  12  when filled with fluid. 
     Although in the above discussed embodiment container  12  has a flexible, bag-like configuration, in alternative embodiments it is appreciated that container  12  can comprise any form of collapsible container or semi-rigid container. Container  12  can also be transparent or opaque and can have ultraviolet light inhibitors incorporated therein. 
     Mixer system  18  is used for mixing and/or suspending a culture or other solution or suspension within container  12 . As depicted in  FIG.  2   , mixer system  18  generally comprises a drive motor assembly  59  that is mounted on support housing  14  ( FIG.  1   ), an impeller assembly  78  coupled to and projecting into container  12 , and a drive shaft  72  ( FIG.  4   ) that extends between drive motor assembly  59  and impeller assembly  78 . 
     Turning to  FIG.  3   , drive motor assembly  59  comprises a housing  60  having a top surface  62  and an opposing bottom surface  64  with an opening  66  extending through housing  60  between surfaces  62  and  64 . A tubular motor mount  68  is rotatably secured within opening  66  of housing  60  and bounds a passage  90  extending therethrough. As depicted in  FIG.  4   , the upper end of motor mount  68  terminates at an ends face  92  having a locking pin  94  outwardly projecting therefrom. A thread  96  encircles motor mount  68  adjacent to end face  92 . Returning to  FIG.  3   , a drive motor  70  is mounted to housing  60  and engages with motor mount  68  so as to facilitate select rotation of motor mount  68  relative to housing  60 . As depicted in  FIG.  1   , drive motor assembly  59  is coupled with support housing  14  by a bracket  53 . In alternative embodiments, however, drive motor assembly  59  can be mounted on a separate structure adjacent to support housing  14 . 
     Drive shaft  72  is configured to pass through motor mount  68  and thus through housing  60 . Turning to  FIG.  5   , drive shaft  72  has a first end  98  and an opposing second end  100  and generally comprises a shaft portion  101  with a head  103  mounted on the end thereof. Head  103  includes a substantially frustoconical engaging portion  102  that is complimentary to an engaging portion formed within the upper end of motor mount  68 . As a result, the two engaging portions can be complementary mated to facilitate contacting engagement between motor mount  68  and drive shaft  72  when drive shaft  72  is passed through motor mount  68 . 
     As depicted in  FIG.  4   , head  103  also includes a substantially circular plate  104  disposed on top of engaging portion  102 . Plate  104  extends to a perimeter edge  106  that radially outwardly projects beyond engaging portion  102 . A plurality of spaced apart notches  108  are formed on perimeter edge  106 . When drive shaft  72  is passed through motor mount  68 , plate  104  rests on or slightly above end face  92  of motor mount  68  so that locking pin  94  is received within a notch  108 . As a result, drive shaft  72  is locked to motor mount  68  so that rotation of motor mount  68  facilitates concurrent rotation of drive shaft  72 . A cap  115  ( FIG.  3   ) can be threaded onto the end of motor mount  70  to prevent drive shaft  72  from disengaging from motor mount  70 . 
     Returning to  FIG.  5   , shaft portion  101  comprises a first driver portion  112  and a second driver portion  114 . Driver portions  112  and  114 , as will be discussed below in greater detail, typically have a polygonal transverse cross section. For example, driver portions  112  and  114  can have 5, 6, 7, or more sides. In other embodiments, the transverse cross of section of driver portions  112  and  114  can be other non-circular shapes such as oval or irregular. The remainder of shaft portion  101  typically has a circular transverse cross section with a maximum diameter that is smaller than the maximum diameter of driver portions  112  and  114 . Second end  100  of drive shaft  72  terminates at a nose  105  that is inwardly tapered for easy insertion. 
     In one embodiment drive shaft  72  can comprise a single, unitary shaft. In other embodiments, draft shaft  72  can be comprised of multiple sections that are selectively threaded or otherwise secured together. For example, drive shaft can comprise a head section  74  and a separate shaft section  76  that can be coupled together as depicted in  FIG.  3   . Drive shaft  72  can be formed from 2, 3, 4, 5 or more sections that are selectively coupled together. Drive shaft  72  can be comprised of high strength polymers, ceramics, composites, metals, such as aluminum, stainless steel, or other metal alloys, or other materials. Furthermore, different sections can be made of different materials. 
     By forming drive shaft  72  from multiple sections, it is easy to form a shaft having a desired length by adding or removing sections. Furthermore, the modular drive shaft  72  can be used in a room with a low ceiling height. For example, a first section of drive shaft  72  can be partially advanced down through motor mount  68 . Additional sections can then be progressively attached thereto as the sections are progressively advanced down through motor mount  68 . Accordingly, the full length of drive shaft  72  need not be simultaneously raised above motor mount  68  for passing therethrough. Alternative embodiments of drive shafts that can be used in the present inventive system, including examples of how separate sections can be coupled together, are disclosed in U.S. Pat. No. 8,641,314 which issued on Feb. 4, 2014 and which is incorporated herein by specific reference. 
     As depicted in  FIG.  5   , impeller assembly  78  comprises an elongated first tubular connector  80  having rotational assembly  82  secured at one end and an elongated second tubular connector  84  coupled at the opposing end. A plurality of impellers  85 A-C are disposed along the length of second tubular connector  84 . More specifically, first tubular connector  80  has a first end  118  and an opposing second end  120  with an interior surface that bounds a passage  122  that extends along the length thereof. In one embodiment first tubular connector  80  comprises a flexible tube that can typically be bent along its length over an angle of 90° and more commonly 180° or 270° without plastic deformation. Tubular connector  80  is typically made from, comprises or consists of a sufficiently flexible material, such as an elastomeric material, so that tubular connector can withstand repeated bending and deformation without appreciable structural yield and can possess a durometer on the Shore OO scale that is typically less than 98 and often less than 60 or 30. Other values can also be used. First tubular connector  80  can be formed from a polymeric material such as flexible PVC or other polymers having the desired properties. 
     Rotational assembly  82  comprises an outer casing  86  and a tubular hub  88  that centrally extends through outer casing  86  and is rotatably coupled thereto. One or more dynamic seals can be formed between outer casing  86  and tubular hub  88  so that a sterile seal can be maintained therebetween. Furthermore, one or more bearings can be positioned between outer casing  86  and tubular hub  88  to enable easy rotation of hub  88  relative to casing  86 . As depicted in  FIG.  6   , hub  88  has an interior surface  124  that bounds a passage  126  extending therethrough. At least a section of interior surface  124  forms an engaging portion  128  that is complementary to the transverse cross section of first driver portion  112  on drive shaft  72  ( FIG.  5   ) or is otherwise configured to engage first driver portion  112  so that when first driver portion  112  is received within engaging portion  128 , rotation of drive shaft  72  facilitates rotation of hub  88  relative to casing  86 . 
     Returning to  FIG.  5   , hub  88  includes a barbed stem  89  that downwardly projects below casing  86 . Stem  89  is configured to be received within first end  118  of first tubular connector  80  so that a liquid tight seal is formed therebetween and so that stem  89  is secured to first tubular connector  80 . Casing  86  includes an annular, outwardly projecting flange  132  which, as depicted in  FIG.  2   , is welded or otherwise secured to container  12  so as to secure casing to container  12  within opening  52  thereof. In this configuration, first tubular connector  80  projects into compartment  50  of container  12 . 
     Returning to  FIG.  5   , second tubular connector  84  has a first end  136  and an opposing second end  138  with an interior surface  140  and an exterior surface  142  extending therebetween. Interior surface  140  bounds a passage  141  ( FIG.  11   ) extending therethrough. In one embodiment, second tubular connector  84  is more rigid than first tubular connector  80 . For example, in different embodiments second tubular connector  84  cannot be bent along its length over an angle of 20°, 40°, 90° or 120° without plastic deformation. Tubular connector  84  is typically not made from and does not comprise or consist of an elastomeric material. Rather, tubular connector  84  is typically comprised of a rigid plastic or other material so that tubular connector  84  has a durometer on the Shore D scale that is typically greater than 20 and often greater than 40 or 60. Other values can also be used. 
     As depicted in  FIG.  7   , formed at first end  136  is a tapered stem  144  that is configured to be received within second end  120  of first tubular connector  80  ( FIG.  5   ) so as to form a secure, liquid tight seal therebetween. A barbed stem  146  is formed at second end  138 . Exterior surface  84  extending between stems  144  and  146  has a transverse cross section that is polygonal, elliptical, or some other non-circular configuration. For example, the transverse cross section can be polygonal having 5, 6, 7 or more sides. Disposed at spaced apart locations along the length of exterior surface  142  are three pairs of annular grooves  148 A-C and  150 A-C that encircle second tubular connector  84 . 
     Exterior surface  142  of second tubular connector  84  is configured to receive impellers  85 A-C so that they can be fixed thereon. As used in the specification and appended claims, the term “impeller” is broadly intended to include all conventional types of impellers and impeller blades along with other structures that can be mounted on second tubular connector  84  so that when second tubular connector  84  is rotated within container  12 , the structures can uniformly mix the fluid within container  12 . In the current embodiment, as depicted in  FIG.  8   , each impeller  85  comprises a central hub  154  having a plurality of fins  156  outwardly projecting therefrom. Again, fins  156  can comprise any type of impeller blade that will function for mixing in the intended application. Hub  154  has an interior surface  158  that bounds an opening  160  extending therethrough. Interior surface  158  has a configuration complementary to exterior surface  142  of second tubular connector  84  or is otherwise configured to engage exterior surface  142  so that when second tubular connector  84  is advanced through opening  160  of impeller  85 , impeller  85  is keyed with or otherwise secured to second tubular connector  84  so that rotation of second tubular connector  84  along the longitudinal axis thereof causes impellers  85  to concurrently rotate therewith. 
     During assembly, each impeller  85 A-C is slid along second tubular connector  84  until hub  154  is centrally located between a pair of corresponding grooves  148  and  150 . Retainers  162  are received within grooves  148  and  150  to retain impellers  85  at the desired locations along second tubular connector  84 . In one embodiment, retainers  162  comprise O-rings that are made from an elastomeric material such as silicone. Other materials can also be used. The O-rings are configured so that when they are received within annular grooves  148 / 150 , the O-rings still radially outwardly project beyond exterior surface  142  of second tubular connector  84 . Thus, the O-rings can be slid onto second tubular connector  84  on opposing sides of each impeller  85  so that when the O-rings are received within annular grooves  148 / 150  with impeller  85  disposed therebetween, the O-rings preclude impeller from sliding along the length of second tubular connector  84  past the O-rings. This configuration provides a simple way to manufacture and assemble second tubular connector  84  with impellers thereon and eliminates complex molding procedures and mechanical fasteners, such as set screws, which can become loose or can form small holes or crevices into which cells or microorganisms can stagnate and die. The configuration also eliminates the required use of adhesives which can potentially leach into and contaminate a culture. 
     In alternative embodiments, it is appreciated that other retainers  162  can also be used. For example, snap rings or clips, such as those having a C-shaped configuration, could be received within grooves  148 / 150  to secure impellers  85 . In still other embodiments, it is appreciated that other conventional techniques, such as those discussed above, could be used to either permanently or removably secure impellers  85  to second tubular connector  84 . Furthermore, in other alternative embodiments it is appreciated that not all of exterior surface  142  of second tubular connector  84  needs to be complementary to interior surface  158  of impellers  85 . Rather, only the portion of exterior surface  142  between grooves  148  and  150  needs to have the complementary or otherwise engaging surface so as to mate with impellers  85 . 
     Turning to  FIG.  10   , an end cap  166 , such as made from a polymeric or elastomeric material, can be slid over stem  146  and secured by a fastener  168 , such as a pull tie or crimp, so as to form a liquid tight seal at second end  138  of second tubular connector  84 . 
     Turning to  FIG.  11   , interior surface  140  of second tubular connector  84  along the length thereof has a configuration that is complementary to the transverse cross section of second driver portion  114  on drive shaft  72  ( FIG.  5   ) or is otherwise configured to engage second driver portion  114  so that when second driver portion  114  is received within passage  141  of second tubular connector  84 , rotation of drive shaft  72  facilitates concurrent rotation of second tubular connector  84 . For example, interior surface  140  of second tubular connector  84  and second driver portion  114  on drive shaft  72  can have complementary polygonal or other non-circular configurations. 
     It is appreciated that second driver portion  114  need not engage the full length of second tubular connector  84 . However, because drive shaft  72  is typically stronger than second tubular connector  84 , the more length of drive shaft  72  that directly engages along the length of second tubular connector  84 , the more strength is imparted to second tubular connector  84 . Thus, in general, in situations where greater torque will be applied to second tubular connector  84 , more length of second driver portion  114  should engage second tubular connector  84 . For example, second driver portion  114  can be configured to engage at least 20% and more commonly at least 40% or 60% of the total length of second tubular connector  84 . Other percentages can also be used. 
     During assembly, impeller assembly  78  is coupled with container  12  as discussed above. The assembly can then be sterilized, such as by radiation, so that compartment  50  and the components therein are sterile. To facilitate shipping and storage, container  12  can be folded over at any location along the length of flexible first tubular connector  80  so as to minimize the length and size of the container assembly. During use, container  12  with impeller assembly  78  secured thereto is positioned within chamber  30  of support housing  14 . Rotational assembly  82  is then removably connected to bottom surface  64  of housing  60  of drive motor assembly  59  so that hub  88  is aligned with motor mount  68 . First end  100  of drive shaft  72  is advanced down through motor mount  68 , through hub  86  of rotational assembly  82 , through first tubular connector  80  and finally into second tubular connector  84 . 
     In this position, drive shaft  72  is locked to motor mount  68  with first driver portion  112  engaging hub  88  and second driver portion  114  engaging second tubular connector  84 , as discussed above. As a result, rotation of motor mount  68  by motor  70  facilitates rotation of drive shaft  72  which in turn facilitates the concurrent rotation of hub  88 , first tubular connector  80 , second tubular connector  84 , and impellers  85  mounted on second tubular connector  84 . In turn, rotation of impeller  85  facilities mixing and suspension of the fluid within compartment  50  of container  12 . Further disclosure with regard to drive motor assembly  59 , rotational assembly  82 , and drive shaft  72  and how these elements operate and couple together, along with alternative embodiments thereof, is disclosed in United States Patent Publication Nos. 2011-0188928 A1, published Aug. 4, 2011; 2011-0310696, published Dec. 22, 2011 and 2006-0280028, published Dec. 14, 2006 which are incorporated herein by specific reference. 
     Embodiments of the inventive system have a number of advantages. For example, by using second tubular connector  84  which is rigid, a plurality of impellers can be mounted thereon which significantly increases the ability to mix the fluid within container  12 . This is significantly helpful in situations such as where the fluid processing system is functioning as a fermentor for growing microorganisms. This is because fermentors typically require aggressive mixing to achieve and maintain the needed gas-liquid mass transfer with the fluid to keep the microorganisms alive and thriving. The system is also advantageous in that the container assembly is easy to manufacture, scalable, and disposable after use so that no cleaning or sterilization is required. As discussed above, by using first tubular connector  80  which is flexible, the container assembly can still be folded into a relatively small volume, thereby making it easier to sterilize, ship, and store. Furthermore, the system provides an easy, modular system for attaching impellers to second tubular connector  84 . For example, different systems having different numbers of impellers can be designed using the same second tubular connector  84 . In addition, because all of the impellers can be mounted on second tubular connector  84 , only one separate connection to first tubular connector  80  is required, thereby simplifying assembly and minimizing locations for potential contamination. Other advantages also exist. 
     It is appreciated that the inventive system also has a number of alternative embodiments. For example, although second tubular connector  84  is shown having three impellers  85  mounted thereon, in other embodiments second tubular connector  84  can have 1, 2, 4, 5 or more impellers  85  mounted along the length thereof. It is also appreciated that the relative lengths of first tubular connector  80  and second tubular connector  84  can be varied. For example, in some embodiments, the length of second tubular connector  84  is at least 20%, 40% or 60% of the combined total length of first tubular connector  80  and second tubular connector  84 . In other embodiments, the length of first tubular connector  80  is at least 20%, 40% or 60% of the combined total length of first tubular connector  80  and second tubular connector  84 . 
     Depicted in  FIG.  12    is an alternative embodiment of a drive shaft  72 A. Like features between drive shaft  72  and  72 A are identified by like reference characters. Drive shaft  72 A is substantially identical to drive shaft  72  except that first driver portion  112  ( FIG.  5   ) has been eliminated. As such, drive shaft  72  does not directly engage hub  88 . However, hub  88  can still rotate by torque produced by first tubular connector  80 . 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.