Abstract:
A probe assembly includes a tubular sleeve having a passage extending between a first end and an opposing second end. The tubular sleeve is movable between an extended position wherein the first end and the opposing second end are spaced apart and a collapsed position wherein the first end and the opposing second end are moved closer together. A connector is secured to the second end of the tubular sleeve, the connector having an opening extending therethrough that communicates with the passage of the tubular sleeve, a sealing layer removably covering the opening of the connector. An elongated probe has a first end and an opposing second end, the second end of the probe being positioned within the passage of the tubular sleeve, the second end of the probe being configured to pass through the opening of the connector when the sealing layer is removed therefrom.

Description:
[0001]    This application is a divisional of U.S. application Ser. No. 11/112,834, filed on Apr. 22, 2005, which claims the benefit of U.S. Provisional Application Ser. No. 60/565,908, filed Apr. 27, 2004, which applications are hereby incorporated by reference for all purposes. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. The Field of the Invention 
         [0003]    The present invention relates to a stirred-tank reactor system and methods of preparing such systems. The present invention further encompasses the use of the stirred-tank reactor system as a disposable bioreactor and in kits with disposable elements. 
         [0004]    2. The Relevant Technology 
         [0005]    Bioreactors or fermenters include containers used for fermentation, enzymatic reactions, cell culture, biologicals, chemicals, biopharmaceuticals, tissue engineering, microorganisms, plant metabolites, food production and the like. Bioreactors vary in size from benchtop fermenters to stand-alone units of various sizes. The stringent asepsis requirements for sterile production in some bioreactors can require elaborate systems to achieve the desired product volumes. Consequently, the production of products in aseptic bioreactors can be costly which provides the motivation for pursuing improved systems. 
         [0006]    Conventional bioreactors perfuse nutrient media through a single type of hollow fiber. The various disadvantages of such bioreactors may include heterogeneous cell mass, difficult procurement of representative cell growth samples, poor performance due to inefficient oxygenation and an inability to control oxygen levels, and problems with contamination of cell cultures. Moreover, micro-environmental factors such as pH may not be effectively controlled and a mixed culture or co-culture of cells may not be possible. Some known bioreactors include a reaction container, through which a central strand of porous hollow fibers extends, through which a nutrient solution is pumped. This central strand of hollow fibers is concentrically surrounded by a plurality of strands of hollow fibers, through which a gaseous medium is conveyed. The hollow fibers of these strands are also constituted in such a manner that the gaseous medium—for example oxygen or carbon dioxide- can at least partly emerge from these strands or enter into these strands respectively. This type of bioreactor can achieve enhanced nutrient media oxygenation as compared to other known devices. However, occasional contamination of cell cultures and an inability to control pH levels effectively may continue to present difficulties. 
         [0007]    The expense of producing cells, biopharmaceuticals, biologicals and the like in aseptic bioreactors is often exacerbated by the required cleaning, sterilization and validation of the standard bioreactors (i.e., stainless steel or glass reactors). Attempts have been made to solve this problem with the development of pre-sterilized disposable bioreactor systems that need not be cleaned, sterilized or validated by end users. The use of such disposable bioreactor systems could provide significant savings. Furthermore, plastics are lightweight, easy to transport, and require less room than stainless steel or glass reactors. Some have reported the use of disposable elements in bioreactors that include a reactor chamber with a support housing. The interior chamber of the support housing is lined with a disposable liner and sealed with a head plate attached to the liner to form a sealed chamber. As the liner is open at the top, it is typically used in a vertically oriented bioreactor to prevent the contamination of the head plate. Although this system provides a disposable liner, the head plate and the interior chamber may still require cleaning and sterilization. 
         [0008]    Others have attempted to develop flexible, disposable plastic vessels that do not require cleaning or sterilization and require only minimal validation efforts. Such approaches can include a flexible, disposable, and gas permeable cell culture chamber that is horizontally rotated. The cell culture chamber is made of two sheets of plastic fused together. In addition, the culture chamber is made of gas permeable material and is mounted on a horizontally rotating disk drive that supports the flexible culture chamber without blocking airflow over the membrane surfaces. The chamber is placed in an incubator and oxygen transfer is controlled by controlling the gas pressure in the incubator according to the permeability coefficient of the bag. The rotation of the bag assists in mixing the contents of the bag. However, the cell culture chamber will often be limited to use within a controlled gas environment. Particularly, the cell culture chamber may have no support apparatus and may be limited to small volumes. Furthermore, the chamber may not provide an inlet and an outlet for media to be constantly pumped into and out of the chamber during rotation. 
         [0009]    Some companies have developed a range of pre-sterile, disposable bioreactors that do not require cleaning or sterilizing. Such reactors are made of sheets of flexible, gas impermeable material to form a bag. The bag is partially filled with media and then inflated with air that continually passes through the bag&#39;s headspace. The media is mixed and aerated by rocking the bags to increase the air-liquid interface. However, since there is typically no solid housing that support the bags, the bags may become cumbersome and difficult to handle as they increase in size. Furthermore, the wave action within the rocking bag can create damaging turbulent forces. Certain cell cultures, particularly human cell cultures, may benefit from more gentle conditions. 
         [0010]    Thus, there is a continuing need to develop flexible, pre-sterilized, disposable bioreactors that are easy to handle and require little training to operate, yet provide the necessary gas transfer and nutrient mixing required for successful cell and tissue cultures. Such disposable bioreactors would be equally useful for the production of chemicals, biopharmaceuticals, biologicals, cells, microorganisms, plant metabolites, foods and the like. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    In a first aspect, the present invention provides a stirred-tank reactor system with disposable elements, such as a flexible plastic bag with an attached bearing, shaft, and impeller assembly. The instant invention further relates to the use of this novel stirred-tank reactor system as a disposable bioreactor and in kits with disposable elements. The advantages of the present invention are numerous. Particularly, the stirred-tank reactor system may be pre-sterilized and does not require a steam-in-place (SIP) or clean-in-place (CIP) environment for changing from batch to batch or product to product in a culture or production system. As such, the system may require less regulatory control by assuring zero batch-to-batch contamination and can, thus, be operated at a considerable cost-advantage and with minimal or no preparation prior to use. In addition, the system can be a true stirred-tank reactor system unlike other disposable reactors systems. This provides the added advantage that the instant invention can offer a hydrodynamic environment that can be scaled to various sizes similar to conventional non-disposable reactor systems. As the system typically does not require cleaning or sterilizing, it combines a flexible, easy-to-use, true stirred-tank reactor environment with zero cross-contamination during the cell culture or production process. 
         [0012]    One aspect of the present invention provides a stirred-tank reactor system, comprising a flexible bag with at least one opening, wherein the bag functions as a sterile container for a fluidic medium; a shaft situated within the bag; an impeller attachable to the shaft, wherein the impeller is used to agitate the fluidic medium to provide a hydrodynamic environment; and a bearing attached to the shaft and to the opening of the bag. The bag may be affixed to the shaft and the bearing through at least one seal or o-ring such that the inside of the bag remains sterile. The seals or o-rings can be affixed to the bag. The system may be disposable and pre-sterilized. The bag may further include a pH sensor and a dissolved-oxygen sensor, wherein the sensors are incorporated into the bag. In addition, the system may include at least one internal pouch sealed to the bag, wherein the pouch has one end that can be opened to the outside of the bag such that a probe (i.e., a temperature probe, a pH probe, a dissolved gas sensor, an oxygen sensor, a carbon dioxide (CO 2 ) sensor, a cell mass sensor, a nutrient sensor, an osmometer, and the like) can be inserted into the reactor. The system may also include at least one port in the bag allowing for the connection of a device such as a tube, a filter, a sampler, a probe, or a connection device to the port. A port allows for sampling; gas flow in and out of the bag; liquid or media flow in and out of the bag; inoculation; titration; adding of chemostat reagents; sparging; and the like. 
         [0013]    Another aspect of the present invention provides a stirred-tank reactor system, comprising a flexible bag with at least one opening, wherein the bag functions as a sterile container for a fluidic medium; a shaft situated within the bag; an impeller attachable to the shaft, wherein the impeller is used to agitate the fluidic medium to provide a hydrodynamic environment; and a bearing attached to the shaft and to the opening of the bag. The system may further include a housing, such as a reactor housing, on the outside of the bag, wherein the housing includes at least one support that holds the bearing and a motor, and wherein the bag is contained within the housing. The housing may further include a plurality of baffles such that the bag folds around the baffles. Optionally, the system further encompasses a heater (e.g., a heating pad, a steam jacket, a circulating fluid or water heater, etc.) that can be located between the bag and the housing. Alternatively, the heater may be incorporated into the housing (e.g., a permanent reactor housing with incorporated heating system). 
         [0014]    In another aspect of the invention, the stirred-tank reactor system includes a permanent housing with a product loop with flow past a pH sensor and a dissolved-oxygen sensor, wherein the sensors are incorporated into the housing. The permanent housing includes, but is not limited to, a metal barrel, a plastic barrel, a wood barrel, a glass barrel, and the like. 
         [0015]    The invention also contemplates a method for preparing a stirred-tank reactor system, comprising providing a flexible bag with at least one opening, wherein the bag functions as a sterile container for a fluidic medium; inserting a shaft with an impeller attachable to the shaft into the bag, wherein the impeller is used to agitate the fluidic medium to provide a hydrodynamic environment; attaching a bearing to the shaft and to the opening of the bag; and sealing the bag to the shaft and the bearing such that the inside of the bag remains sterile. The stirred-tank reactor system prepared by this method includes at least one disposable element including, but not limited to, the bag, the shaft, the impeller, and the bearing. 
         [0016]    The invention further encompasses a kit comprising a stirred-tank reactor system and instructions for use. The kit includes a disposable stirred-tank reactor system. The kit may also include a stirred-tank reactor system with at least one disposable element such as the bag, the shaft, the impeller, or the bearing. The bag may be affixed to the shaft and the bearing through at least one seal or o-ring such that the inside of the bag remains sterile. Furthermore, the bag may include a pH sensor and a dissolved-oxygen sensor, wherein the sensors are incorporated into the bag. The kit may also include at least one internal pouch sealed to the bag, wherein the pouch includes one end that can be opened to the outside of the bag such that a probe can be inserted into the reactor. In addition, the system may include at least one port in the bag allowing for the connection of a device to the port, wherein the device includes, but is not limited to, a tube, a filter, a sampler, and the like. 
         [0017]    Another aspect of the invention provides a bag for use in a stirred-tank reactor system. The bag may be a disposable, flexible, plastic bag. The bag may also include at least one disposable element including, but not limited to, a seal, an o-ring, a port, a pouch, a tube, a filter, a sampler, a probe, a sensor, a connection device, or the like. 
         [0018]    In one aspect, the present invention provides a reactor system that includes a container and a rotational assembly. The rotational assembly can be in sealed cooperation with an opening of a container. The rotational assembly can include a rotatable hub adapted to receive and releasably couple with a drive shaft, such that when the drive shaft is operatively coupled with the rotatable hub, rotation of the drive shaft facilitates a corresponding rotation of the rotatable hub. In a related aspect, the system can further include nn impeller coupled with the rotatable hub, such that the impeller is disposed within the container and adapted to couple with a distal end of the drive shaft. In other aspects, the rotational assembly can include a casing, whereby the rotational assembly is in sealed cooperation with the opening of the container via the casing. Similarly, the system can include a drive shaft, wherein the rotatable hub and the drive shaft are disposed to rotate relative to the casing. In still a related aspect, the rotational assembly can include a bearing assembly disposed between the casing and the rotatable hub. The rotational assembly may further include a sealing arrangement disposed circumferentially to the rotatable hub, between the rotatable hub and the casing. Relatedly, the bearing assembly can include a plurality of race bearings, and the sealing arrangement can include a rotating disk coupled with the rotatable hub, a wear plate coupled with the casing, and a dynamic seal disposed between the rotating disk and the wear plate. In other aspects, a seal can include two or more seal subunits disposed in co-planar arrangement. Relatedly, a bearing assembly can include a journal bearing, and the sealing arrangement can include a wear plate coupled with the rotatable hub, and a dynamic seal disposed between the casing and the wear plate. In a similar aspect, the impeller can include a spline adapted to couple with the drive shaft. Often, the container can comprise a flexible bag. In another aspect, the rotatable hub can be coupled with the impeller via a flexible tube. 
         [0019]    In one aspect, the present invention provides a reactor system that includes a container and a sparger assembly. The sparger assembly can be disposed within the container, and can include a flexible sheet of permeable material and a sparger conduit. In a related aspect, the sheet of permeable material can include a vapor-permeable and water-resistant material. In some aspects, the sheet of permeable material can include a high density polyethylene fiber. In related aspects, the sparger assembly can be in fluid communication with a port of the container. Similarly, the reactor system may include a rotational assembly in sealed cooperation with an opening of the container, and an impeller disposed within the container and coupled with the rotational assembly. The sparger body may be anchored to an interior surface of the container, and in some cases, the sparger body of the sparger assembly can be in a substantially spherical shape. 
         [0020]    In another aspect, the present invention provides a bioreactor system that includes a frame support coupled with a drive motor; a flexible bag disposed within a housing of the frame support. The flexible bag can include one or more ports for introducing a cell culture and a medium into the flexible bag; a rotational assembly coupled with a bracket of the frame support and in sealed cooperation with an opening of the flexible bag. The rotational assembly can include a hub adapted to house and couple with a drive shaft of the drive motor. The system can also include an impeller coupled with the hub for agitating the cell culture and medium. The impeller can be disposed within the flexible bag and adapted to couple with the drive shaft. In one aspect, the bioreactor system can include a probe assembly. The probe assembly can include a port coupled with the flexible bag, a Pall connector coupled with the port, a sleeve coupled with the Pall connector, a coupler coupled with the sleeve, and a probe configured to be coupled with the coupler and inserted through the sleeve, Pall connector, and port, and partially into the flexible bag. 
         [0021]    In one aspect, the present invention provides a method for manufacturing a reactor system. The method can include coupling a container with a rotational assembly. The rotational assembly can be in sealed cooperation with an opening of the container. The rotational assembly can include a hub adapted to house and couple with a drive shaft. The method may also include coupling an impeller with the hub, where the impeller is disposed within the container. The method may further include sterilizing the reactor system. In a related aspect, the sterilizing step can include treating the system with gamma radiation. 
         [0022]    In another aspect, the present invention provides a method for preparing a reactor system. The method can include coupling a casing of a rotational assembly of the reactor system to a frame bracket. The method can also include placing a container of the reactor system at least partially within a frame housing, and inserting a drive shaft into a hub of the rotational assembly. The hub can be disposed within the casing of the rotational assembly between a bearing and the casing. The method can further include coupling a distal end of the drive shaft to an impeller. The impeller can be disposed within the container and coupled with the hub. The method can also include introducing a reaction component into the container via a port. 
         [0023]    In one embodiment, the present invention provides a reactor system kit. The kit can have a reactor system that includes a container. The reactor system can also include a rotational assembly in sealed cooperation with an opening of the container. The rotational assembly can include a hub adapted to house and couple with a drive shaft, and an impeller coupled with the hub. The impeller can be disposed within the container and adapted to couple with the drive shaft. The kit also includes instructions for use. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0024]    The present invention is best understood when read in conjunction with the accompanying figures which serve to illustrate the preferred embodiments. It is understood, however, that the invention is not limited to the specific embodiments disclosed in the figures. 
           [0025]      FIG. 1  depicts a longitudinal cross-section of one embodiment of the stirred-tank reactor system, wherein the stirred-tank reactor system is placed into a permanent housing. 
           [0026]      FIG. 2  depicts one embodiment of a probe connection in order to illustrate that a probe can be attached to the stirred-tank reactor system via a sterile or aseptic connection. 
           [0027]      FIGS. 3A and 3B  illustrate cross-section views of a reactor system according to one embodiment of the present invention. 
           [0028]      FIG. 4A  illustrates a cross-section view of a rotational assembly according to one embodiment of the present invention. 
           [0029]      FIG. 4B  illustrates a cross-section view of a rotational assembly according to one embodiment of the present invention. 
           [0030]      FIG. 5  illustrates a cross-section view of a rotational assembly according to one embodiment of the present invention. 
           [0031]      FIG. 6  illustrates a partial cross-section view of a rotational assembly according to one embodiment of the present invention. 
           [0032]      FIG. 7  illustrates a perspective view of a rotational assembly according to one embodiment of the present invention. 
           [0033]      FIG. 8  illustrates a cross-section view of a rotational assembly according to one embodiment of the present invention. 
           [0034]      FIG. 9  illustrates a cross-section view of a rotational assembly according to one embodiment of the present invention. 
           [0035]      FIG. 10  illustrates a cross-section view of an impeller according to one embodiment of the present invention. 
           [0036]      FIG. 11  illustrates a partial cross-section view of an impeller according to one embodiment of the present invention. 
           [0037]      FIG. 12  illustrates a perspective view of drive shaft core according to one embodiment of the present invention. 
           [0038]      FIG. 13  illustrates a cross-section view of an impeller according to one embodiment of the present invention. 
           [0039]      FIG. 14A  illustrates a perspective view of an impeller according to one embodiment of the present invention. 
           [0040]      FIG. 14B  illustrates a perspective view of an impeller according to one embodiment of the present invention. 
           [0041]      FIG. 15  illustrates a cross-section view of a sparger body according to one embodiment of the present invention. 
           [0042]      FIG. 16  illustrates a cross-section view of a sparger assembly according to one embodiment of the present invention. 
           [0043]      FIG. 17  illustrates a cross-section view of a sparger assembly according to one embodiment of the present invention. 
           [0044]      FIG. 18  illustrates a cross-section view of a sparger assembly according to one embodiment of the present invention. 
           [0045]      FIG. 19  illustrates a cross-section view of a sparger assembly according to one embodiment of the present invention. 
           [0046]      FIG. 20  illustrates a partial perspective view of a reactor system according to one embodiment of the present invention. 
           [0047]      FIG. 21  illustrates a partial perspective view of a reactor system according to one embodiment of the present invention. 
           [0048]      FIG. 22  illustrates a partial perspective view of a reactor system according to one embodiment of the present invention. 
           [0049]      FIG. 23  illustrates a cross-section view of a reactor system according to one embodiment of the present invention. 
           [0050]      FIG. 24  illustrates a perspective view of a reactor system according to one embodiment of the present invention. 
           [0051]      FIG. 25  illustrates a perspective view of a reactor system according to one embodiment of the present invention. 
           [0052]      FIG. 26  illustrates a probe assembly  2600  according to one embodiment of the present invention. 
           [0053]      FIG. 27A  provides a illustration of a probe port subassembly of a probe assembly according to one embodiment of the present invention. 
           [0054]      FIG. 27B  illustrates a probe kit subassembly of a probe assembly according to one embodiment of the present invention. 
           [0055]      FIG. 27C  illustrates an autoclave subassembly of a probe assembly according to one embodiment of the present invention. 
           [0056]      FIG. 28A  illustrates a probe assembly according to one embodiment of the present invention. 
           [0057]      FIG. 28B  illustrates a probe assembly according to one embodiment of the present invention. 
           [0058]      FIG. 29  provides a graph of data that was generated using a reactor system according to one embodiment of the present invention. 
           [0059]      FIG. 30  provides a graph of data that was generated using a reactor system according to one embodiment of the present invention. 
           [0060]      FIG. 31  provides a graph of data that was generated using a reactor system according to one embodiment of the present invention. 
           [0061]      FIG. 32  provides a graph of data that was generated using a reactor system according to one embodiment of the present invention. 
           [0062]      FIG. 33  provides a graph of data that was generated using a reactor system according to one embodiment of the present invention. 
           [0063]      FIG. 34  provides a graph of data that was generated using a reactor system according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0064]    In some embodiments, the term “flexible bag” can refer to a container that holds a fluidic medium. The bag may include one or more layer(s) of flexible or semi-flexible waterproof material depending on size, strength and volume requirements. The inside surface of the bag may be smooth and provide a sterile environment (e.g., for culturing cells or other organism, for food production, etc.). The bag may include one or more openings, pouches (e.g., for inserting one or more probes, devices, etc.), ports (e.g., for the connection of one or more probes, devices, etc.) or the like. Furthermore, the bag can provide a disposable alternative to a solid vessel in a conventional stirred-tank bioreactor. The flexible bag may further include a shaft, an impeller, a bearing and seals or o-rings, and may be entirely disposable. 
         [0065]    In some embodiments, the term “fluidic medium” can refer to any biological fluid, cell culture medium, tissue culture medium, culture of microorganisms, culture of plant metabolites, food production, chemical production, biopharmaceutical production, and the like. The fluidic medium is not limited to any particular consistency and its viscosity may vary from high to medium to low. When the fluidic medium is a cell culture medium the system may be operated in, for example, batch mode, semi-batch mode, fed-batch mode, or continuous mode. 
         [0066]    In some embodiments, the term “impeller” can refer to a device that is used for agitating or mixing the contents of a stirred-tank reactor system (e.g., bioreactor). The impeller may agitate the fluidic medium by stirring or other mechanical motion. The impeller of the instant invention includes, but is not limited to, a Rushton, a marine, a hydrofoil, a pitched blade, and any other commercially available impeller. 
         [0067]    In some embodiments, a “hydrodynamic” environment of the instant invention may refer to an environment that is influenced by the motion of fluids and the forces acting on solid bodies immersed in these fluids within the stirred-tank reactor system. 
         [0068]    The present invention includes single use bioreactors, stirred tank reactors, and the like. Such reactors have a variety of applications, such as for the production of therapeutic proteins via batch cell culture. Relatedly, these systems can be used to provide for cell growth and antibody production for CHO and other cell lines. The hydrodynamic environment within the reactors can be well characterized, and, as such, may be scaled to other stirred tank bioreactors. 
         [0069]    Single use bioprocess containers can be used for the storage of biopharmaceutical media, buffers, and other products. Using these storage container systems, several mixing systems for preparation of media and buffers can be developed, often to commercial scale up to 10,000 liters or more. Such mixing systems and bioreactors can use various means for mixing the reactor contents, such as a pulsating disk, a paddle mixer, a rocking platform, an impeller, and the like. These systems are well suited for use in chemical processing. The operating characteristics of the reactors can be well defined, and can be readily predicted and scaled to various sizes. In the biopharmaceutical industry, such stirred tank bioreactors can be established as a means for manufacture of biologic products from a wide range of biological systems, including animal cell culture. Processes for biological systems can be developed using stirred tank bioreactors at the bench scale and transferred to stirred tank bioreactors at the commercial scale, up to 10,000 liters or greater, using well established scale-up methodologies. For a stirred tank bioreactor, design parameters such as tip speed, power input, Reynolds number, and oxygen transfer coefficient can be readily determined and used for scale-up. 
         [0070]    A single use portion of the system can include a flexible plastic container with the following single use integrated components: a bearing, shaft, and impeller assembly; a sparger assembly; ports for sterile attachment of sensor probes; and various ports for inlet and outlet of liquids and gases. A single use bioreactor can be manufactured using medical grade film. In some cases, other components of the single use bioreactor can be manufactured from readily machined materials that are not necessarily USP Class VI materials. The impeller can be a pitched-blade impeller that is attached to a bearing assembly by a flexible sheath. The impeller and sheath can rotate along with an inner bearing assembly, which is isolated from the exterior bearing assembly using various seal assemblies. An outer bearing assembly can be directly affixed to the single use container. A sparger can include a porous membrane that is sealed to the bottom of the single use container. Sparge gas can be introduced to the space between the porous membrane and bottom of the container through a port after passing through a pre-attached sterilization filter. The pH and dO2 sensors may or may not be part of the single use container and can connected to the bioreactor using Pall Kleenpack® connectors. Industry-standard 12 mm sensors can be calibrated, then steam sterilized with one half of the connector. The other half of the connector can be pre-attached to the container, allowing the sensor to be inserted in direct contact with the reactor contents. Ports and tubing for headspace gas, thermo well, media inlet, titrant, sampling, harvest, and various pulse feeds can be pre-attached and pre-sterilized with the container. 
         [0071]    A permanent support vessel that contains a motor and drive shaft assembly, heat jacket, and openings for inlets, outlets, and probes can hold a single use container. A drive shaft can fit through the single-use bearing, through the flexible sheath, and lock into the impeller. This shaft can be driven using a standard bioreactor mixer motor of sufficient power. Heat can be provided to the bioreactor contents, for example, by electric heat bands that are in direct contact with sides of the single-use container. The permanent support vessel can be mobile, and can be placed on a weigh scale for control of reactor volume. 
         [0072]    The system can be operated using standard sensors and controllers that have industry-accepted track records of performance. In some embodiments, no control system may be required for steam sterilization or clean in place, and a controller commonly used for bench-scale bioreactors may be sufficient for control of the pH, dO2 concentration, and temperature of the single use bioreactor. A single use bioeactor often requires no cleaning or sterilization in-place. As such, the capital and operating costs of control systems and utilities, such as clean steam, required for steam sterilzation of a large pressure vessel may be eliminated. The cost for fabrication of a rigid-walled pressure vessel designed to handle the stresses exerted during steam-in-place sterilization may also be eliminated. Likewise, the capital and operating costs for clean-in-place control systems and utilities may be unnecessary. The design elements of traditional stainless steel vessels dictated by cleanability requirements may similarly be eliminated. 
         [0073]    In some embodiments, a single use bioreactor can be a closed system that is discarded after use. This may eliminate the need for cleaning validation studies. The potential for cross contamination between production batches may also be reduced. In some embodiments, the capital expenditure required to accommodate multiple products simultaneously in single use bioreactors can be low compared to the cost of the fixed assets and utilities required to segregate traditional bioreactor systems. A single use bioreactor can be manufactured using medical grade film, and regulatory documentation for the film may be currently available. Other product contact components of a single use bioreactor can be manufactured from USP Class VI materials. Current applications of bioprocess containers manufactured from these materials include bioreactor feed and harvest, and transport and storage of bulk intermediate and final product. 
         [0074]    As note above, a stirred tank single use bioreactor according to the present invention can provide a well-characterized hydrodynamic environment for cell growth. Mixing characteristics can be readily calculated and can be translated to larger stirred tank reactors. Thus, processes developed at the lab or pilot scale may be scaled up directly to commercial scale, either in larger single use bioreactors or larger traditional stirred tank bioreactors. Scale-up parameters such as power input per unit volume, tip speed, oxygen transfer coefficient, or geometric similarity may be maintained at the larger scale. In some embodiments, the present invention provides a stirred tank reactor with a design that includes a rotating impeller driven by a drive shaft isolated through a series of rotating seals. Such designs can provide effective and efficient means of transmitting the energy required for mixing and mass transfer to the reactor contents. 
         [0075]    The present invention can also include or be compatible with industry-standard sensor and controller technology. A standard that has developed in the industry is the use of 12 mm diameter pH and dO2 sensors inserted through DN25 (Inglold-style) ports in direct contact with the reactor contents. Systems such as a single use bioreactor can incorporate the same 12 mm diameter pH and dO2 sensors in direct contact with the reactor contents. Calibration and standardization procedures for these sensors can be readily performed during operation of the bioreactor. In addition, outputs from these sensors can be compatible with current controllers used by industry. The use of PID controllers to maintain pH, dO2 concentration, and temperature can be used in such bioreactors. As a stirred tank bioreactor with standard sensors, these control strategies can be directly translatable to a single use bioreactor. Because it can be a stand-alone unit, the single use bioreactor may be controlled using whichever controller type that is preferred by a given facility. 
       A. THE STIRRED-TANK REACTOR SYSTEM  
       [0076]    In some embodiments, the stirred-tank reactor system of the present invention provides a flexible and disposable bag for a variety of purposes, including culturing cells, microorganisms, or plant metabolites as well as processing foods, chemicals, biopharmaceutical and biologicals. The disposable bag may include disposable elements such as a shaft, impeller and bearing and is designed to fit into a permanent housing such as a reactor housing. The bag may further include one or more openings, pouches, ports or the like. The stirred-tank reactor system allows a user to operate the culture or production with relative ease and little training. In particular, the disposable system may not require cleaning or sterilizing. Furthermore, the system may not need continuous validation between production runs. Thus, it combines a flexible, easy-to-use, true stirred-tank reactor environment with little or no cross-contamination during the production process. 
         [0077]    Referring to the drawings,  FIG. 1  depicts a flexible bag  104  with at least one opening and an agitation shaft  112  with an attachable impeller  113 . As shown, the agitation shaft  112  and attached impeller  113  are situated within the bag  104 . Further, the agitation shaft  112  is connectable to a bearing  105 , wherein the bearing  105  can be sealed to the bag by heat welding to the bag and/or through seal(s) or o-ring(s)  6 . The bag  104 , agitation shaft  112 , impeller  113 , and bearing  105 , including seals or o-rings  106  are optionally disposable. The disposable bag can be a flexible, plastic bag. The bag  104  can be affixed to the agitation shaft  112  and the bearing  105  through at least one seal or o-ring  106  such that the inside of the bag remains sterile. The seals or o-rings can be further affixed to the bag as is shown in  FIG. 1 . Additionally, the disposable stirred-tank reactor system may be connected to a support or one or more bracket(s)  103  that hold the bearing  105  and motor  101 . In one embodiment (as shown in  FIG. 1 ), the support  103  is a motor and bearing support  103 , wherein the upper end of the agitation shaft  112  is further connected to a motor coupling  102 . The motor coupling  102  is connected to the motor  101  which drives the stirring motion of the agitation shaft  12  and impeller  113  leading to a hydrodynamic environment within the bag  14 . The bag  14  is designed to fit into a housing  111  such as a barrel or chamber. The housing may be a metal barrel, a plastic barrel, a wood barrel, a glass barrel, or any other barrel or chamber made from a solid material. In one embodiment of the instant invention, the housing further includes a plurality of baffles, wherein the bag folds around the baffles. In another embodiment, the flexible bag  104  further includes a top port (single or multiple)  108 , a bottom port (single or multiple)  109 , and a side port (single or multiple)  110 , wherein flexible tubing  107  can be connected to one or more of these ports. 
         [0078]    The stirred-tank reactor system may optionally include a heater such as a heating pad, a steam jacket, or a circulating fluid or water heater. In one embodiment, the heater is located between the bag  104  and the housing  111 . In another embodiment, the heater is incorporated into the housing  111  (e.g., into a double wall between the reactor housing and the bag). In yet another embodiment, the stirred-tank reactor system is placed inside an incubator. The heater allows for heating or warming of a specific culture or production. This is particularly important for cell cultures which are often grown at 37° C. 
         [0079]    In one embodiment of the instant invention, the bag  104 , the bearing  105 , the seal(s) or o-ring(s)  106 , the tubing  107 , the top port(s)  108 , the bottom port(s)  109 , the side port(s)  110 , the shaft  112 , and the impeller  113  are disposable. The motor  101 , the motor coupling  102 , the bracket(s) or motor and bearing support  103 , and the housing  111  are permanent. 
       B. DEVICES AND PORTS  
       [0080]    The stirred-tank reactor system may also include sensors and other devices. In one embodiment, the bag includes a pH sensor and a dissolved-oxygen sensor, wherein the sensors are incorporated into the bag. As such, the sensors are disposable with the bag. In another embodiment, the sensors are attachable to the bag and are separate units. Such sensors may optionally be reusable after sterilization. In another embodiment, the system includes a product loop with flow past a pH sensor and dissolved-oxygen sensor, wherein the sensors are incorporated into the reactor housing. The system is flexible and provides alternative ways of supplying optional equipment of various kinds (e.g., sensors, probes, devices, pouches, ports, etc.). The system may also include one or more internal pouches that are sealed to the bag. In one preferred embodiment, the pouch has at least one end that can be opened to the outside of the bag to insert a probe into the reactor (i.e., the bag) while remaining on the exterior of the bag. The probe may be, for example, a temperature probe, a pH probe, a dissolved gas sensor, an oxygen sensor, a carbon dioxide sensor, a cell mass sensor, a nutrient sensor, an osmometer or any other probe that allows for testing or checking the culture or production. In another preferred embodiment, the system includes at least one port in the bag allowing for the connection of a device to the port. Such a device includes, but is not limited to, a tube, a filter, a connector, a probe, and a sampler. The incorporation of various ports into the bag allows for gas flow in and out of the bag as well as liquid flow in and out of the bag. Such ports also allow for sampling or testing the media or culture inside the bag. Tubing, filters, connectors, probes, samplers or other devices can be connected to the ports by using any desirable tubing connection technology. Pouches and ports that are sealed or affixed to the bag are disposable with the bag. The bag may also include a sparger (i.e., the component of a reactor that sprays air into the medium) sealed to the bag which can be disposed off with the bag. 
         [0081]    Particularly, ports may be incorporated at any place on the flexible bag to accommodate the following:
   Headspace gas in   Headspace gas out   Sparge gas in   Temperature probe   pH probe   Dissolved oxygen probe   Other desired probes   Sample apparatus   Media in   Titrant in   Inoculum in   Nutrient feeds in   Harvest out   
 
         [0095]    Each port may have flexible tubing attached to the port, to which media bags, sample devices, filters, gas lines, or harvest pumps may be attached with sterile or aseptic connections. In one embodiment, the ports are sealed onto the flexible bag during bag manufacture, and are sterilized with the bag assembly. 
         [0096]    Devices that may be used to make aseptic connections to the flexible tubing are the following:
   WAVE sterile tube fuser   TERUMO sterile tubing welder   PALL KLEENPAK connector   Connection made under a laminar flow hood, using aseptic techniques   BAXTER Hayward proprietary “HEAT-TO-HEAT” connection using metal tubing and an induction heater   
 
         [0102]    In another embodiment, flexible tubing that is attached to an appropriate stainless-steel valve assembly may be sterilized separately (e.g., via autoclave), and then used as a way to connect the disposable bioreactor to traditional reactors or process piping. The valve assembly is used to make a traditional steam-in-place (SIP) connection to a traditional reactor or other process, and the flexible tubing is used to make a sterile or aseptic connection to a port on the disposable reactor. 
         [0103]    Referring to the drawings,  FIG. 2  depicts a probe connection that can be employed with the stirred-tank reactor system according to one embodiment of the instant invention. As shown in  FIG. 2 , the probe  201  can be connected to a flexible sleeve  202  or bag which extends to one half of a PALL connector  203 . The PALL connector  203  can be connected to the other half of the PALL connector  205  to provide for a sterile connection between the probe and the stirred-tank reactor system. The PALL connectors  203 ,  205  include covers  204  and filters  207  to keep the connection site sterile. Sterile tubing  206  extends from the other half of the PALL connector  205  to a reactor port  208  of the reactor vessel  209  of the stirred-tank reactor system. In order to attach the probe, the PALL connection is made by removing the covers  204 , mating the connectors  203 ,  205 , removing the filters  207 , and sliding the movable part of the connector into position. The probe sensor tip  212  is then pushed into the reactor as the flexible sleeve or bag bunches or compresses  210 . The probe senor tip  212  is then in direct contact with the inside of the reactor vessel  209 . A clamp  211  is placed around the probe and tubing to seal the reactor contents from the PALL connection assembly. Thus, when a sterile connection is made between the two halves of the PALL connectors  203 ,  205 , the flexible sleeve  202  or bag becomes compressed  210  and the probe is in contact with the culture or production media. 
         [0104]    In one embodiment, the probes may be sterilized separately (e.g., via autoclave) then attached to the reactor via a sterile or aseptic connection. For example, a probe assembly may be made by inserting a probe  201  into one half of a PALL KLEENPAK connector  203  and sealing the probe to the connector using a flexible sleeve or bag  202  as described above and shown in  FIG. 2 . The sleeve extends from the outside end of the probe to the barb of the PALL connector. This assembly is sterilized separately. The other half of the PALL connector  205  is connected to a port  208  on the reactor  209  via flexible tubing  206  that will accommodate the probe. This assembly is sterilized as part of the reactor. The PALL connector is described in detail in U.S. Pat. No. 6,655,655, the content of which is incorporated herein by reference in its entirety. 
         [0105]      FIGS. 3A and 3B  illustrate cross-section views of a reactor system  300  according to one embodiment of the present invention. Reactor system  300  can include a rotational assembly  301  coupled with a container  302 . Optionally, reactor system  300  may include an impeller  340 . In some embodiments, rotational assembly  301  is in sealed cooperation with an opening or aperture in container  302 . Similarly, rotational assembly  301  may include a casing  360  that is coupled with the opening or aperture in container  302 . Typically, impeller  340  is disposed within the interior of container  302 . Rotational assembly  301  can be supported or held by bracket  308 . 
         [0106]    In some embodiments, rotational assembly  301  may include a hub  320  that is coupled with impeller  340 , and hub  320  may be coupled with impeller  340  via a connector  390 . Optionally, hub  320  may be directly coupled with impeller  340 . In some embodiments, hub  320  is tubular in shape and includes an interior surface which bounds a passageway  320   a  longitudinally extending therethrough. In one embodiment an annular barb  321  radially encircles and outwardly projects from the exterior surface of hub  320 . Barb  321  can be used for creating a sealed connection with connector  390 . 
         [0107]    Connector  390  can be tubular in shape, and can include an interior surface which bounds a passageway  390   a  extending longitudinally therethrough. In some embodiments, connector  390  includes a flexible tube having a first end connected in sealed engagement with hub  320  and an opposing second end connected in sealed engagement with impeller  340 . Hub  320 , either alone or in cooperation with connector  390 , can provide a sealed channel in which drive shaft  304  can be received and removably coupled with impeller  340 . Consequently, drive shaft  304  can be used repeatedly without sterilizing because it does not directly contact the contents of container  302 . Furthermore, by using a flexible tube as connector  390 , a flexible container  302  such as a bag assembly can be easily rolled up or folded for easy transport, storage, or processing. 
         [0108]    Often, rotational assembly  301  will include a bearing assembly  370  disposed between hub  320  and casing  360 . Bearing assembly  370  can include a journal bearing, which may be in fixed relation with casing  360 , and hub  320  can rotate relative to the journal bearing and casing  360 . Hub  320  may include a guide  324  for receiving a snap ring or retaining ring, which can help maintain hub  320  in place, relative to the journal bearing. 
         [0109]    Rotational assembly  301  may also include a sealing arrangement  380 , which can be disposed between hub  320  and casing  360 . Sealing arrangement  380  can include, for example, a wear plate  382  and one or more seals  384 , which may be, for example, dynamic seals. Wear plate  382  can be disposed circumferentially to, and coupled with, hub  322 . Seal(s)  384  can be disposed between wear plate  382  and casing  360 . Rotational assembly  301  may also include one or more seals  392  disposed between wear plate  382  and hub  322 , wherein seals  392  may be, for example, static seals. In some embodiments, seal(s)  384  include one or more V-rings and seals(s)  392  include one or more O-rings. In the embodiments shown in  FIG. 3A , seal(s)  384  include two V-rings, and seal(s)  392  include one O-ring. An annular flange  322  may also radially, outwardly project from the exterior surface of hub  320  and be disposed against seal  392 . 
         [0110]    In use, hub  320  is configured to receive or house a drive shaft  304  that is selectively coupled with a motor (not shown). In some embodiments, hub  320  may be configured to couple with one or more ears  306  located at an upper end of drive shaft  304  via one or more hub notches  322  formed on hub  322 . Impeller  340  may include a spline  342  configured to couple with a lower end of drive shaft  304 . Drive shaft  304  can be placed in hub  322 , and coupled with hub  322  and impeller  340 . For example, drive shaft  304  may extend through passageway  320   a . Similarly, drive shaft  304  may extend through passageway  390   a . Drive shaft  304  can be rotated by a motor, thereby rotating hub  320 , connector  390 , and impeller  340 . In turn, impeller  340  agitates the contents of container  302 . As hub  320  is rotated by drive shaft  304 , seal(s)  392  provide a seal between wear plate  382  and hub  320  as they both rotate in unison, relative to casing  360 . As casing  360  remains stationary, seal(s)  384  provide a seal between wear plate  382  and casing  360 , where wear plate  382  rotates relative to casing  360 . In some embodiments, seal(s)  384  provide a hermetic seal between wear plate  382  and casing  360 . As shown here, seal(s)  384  can be in co-planar arrangement with one another. 
         [0111]    In some embodiments, hub  320  may be removably engagable with drive shaft  304  such that annular rotation of drive shaft  304  facilitates annular rotation of hub  320 . Although the embodiment depicted in  FIG. 3A  shows drive shaft ears  306  coupled with hub notches  322 , the present invention contemplates any of a variety of coupling means for accomplishing this function. In yet other alternative embodiments, clamps, pins, collects, meshing teeth, or other fasteners can be used to removably secure drive shaft  304  to the hub  320  when the drive shaft  304  is coupled with hub  320 . Similarly, the present invention contemplates any of a variety of coupling means for removably engaging drive shaft  304  to impeller  340 , including the coupling means described above, such that rotation of drive shaft  304  facilitates rotation of impeller  340 . 
         [0112]    According to one embodiment of the present invention, reactor system  300  can be manufactured by coupling container  302  with rotational assembly  301 , such that container  302  and rotational assembly  301  are in sealed cooperation with one another. For example, rotational assembly  301  can be coupled with an opening of container  302 . Rotational assembly  301  can be manufactured to include hub  320 , and hub  320  can be coupled with impeller  340  such that impeller  340  is disposed within container  302 . Further, reactor system can be sterilized, for example by gamma radiation. 
         [0113]    According to another embodiment of the present invention, reactor system  300  can be prepared for use by coupling casing  360  of rotational assembly  301  to frame bracket  308 , and placing container  302  at least partially within a frame or container housing (not shown). Drive shaft  304  can be inserted into hub  320 , and a distal end of drive shaft  304  can be coupled with impeller  340 . Further, reaction components such as cells and culture media can be introduced into container  302  via a port  310 . 
         [0114]    Container  302  can include any of a variety of materials. In some embodiments, container  302  includes a flexible bag of water impermeable material such as a low-density polyethylene or other polymeric sheets having a thickness in a range between about 0.1 mm to about 5 mm, or between about 0.2 mm to about 2 mm. 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 can include two or more separately formed layers that are subsequently secured together by an adhesive. The extruded material can include a single integral sheet having two or more layers of different material that are each separated by a contact layer. All of the layers can be simultaneously co-extruded. One example of an extruded material that can be used in the present invention is the HyQ CX3-9 film available from HyClone Laboratories, Inc. out of Logan, Utah. The HyQ 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 HyQ CX5-14 cast film also available from HyClone Laboratories, Inc. The HyQ CX5-14 cast film comprises a polyester elastomer outer layer, an ultra-low density polyethylene contact layer, and an EVOH barrier layer disposed therebetween. In another example, a multi-web film produced from three independent webs of blown film can be used. The two inner webs are each a 4 mil monolayer polyethylene film (which is referred to by HyClone as the HyQ BM1 film) while the outer barrier web is a 5.5 mil thick 6-layer coextrusion film (which is referred to by HyClone as the HyQ BX6 film). 
         [0115]      FIG. 4A  illustrates a cross-section view of a rotational assembly  401  according to one embodiment of the present invention.  FIG. 4B  illustrates a cross-section view of the rotational assembly  401  depicted in  FIG. 4A  coupled with a connector  490  and an impeller  440 . Rotational assembly  401  may include a bearing assembly  470  disposed between a hub  420  and a casing  460 . As shown here, bearing assembly  470  includes two race bearings, which are in fixed relation with casing  460 . Hub  420  can rotate relative to the race bearings. Hub  420  may include guides  424 ,  424   a  for receiving a snap ring or retaining ring, which can help maintain hub  420  in place, relative to race bearings. 
         [0116]    Rotational assembly  401  may also include a sealing arrangement  480 , which can be disposed between hub  420  and casing  460 . Sealing arrangement  480  can include, for example, a wear plate  482 , one or more seals  484 , and a rotating disk  450 . Rotating disk  450  can be disposed circumferentially to, and coupled with, hub  420 . Seal(s)  484  can be disposed between rotating disk  450  and wear plate  482 . Wear plate  482  can be coupled with casing  460  via screws or bolts inserted through casing columns  428 . Rotational assembly  401  may also include one or more seals  492  disposed between rotating disk  450  and hub  422 . In some embodiments, seal(s)  484  include one or more V-rings and seals(s)  492  include one or more O-rings. In the embodiment shown in  FIGS. 4A and 4B , seal(s)  484  include three V-rings, and seal(s)  492  include one O-ring. Rotational assembly  401  may also include one or more seals  426  to provide a seal between hub  420  and the top of casing  460 , and one or more seals  462  to provide a seal between casing  460  and wear plate  482 . As shown here, seal(s)  426  include one V-ring and seal(s)  462  include one O-ring. 
         [0117]    In use, hub  420  is configured to receive or house a drive shaft (not shown). In some embodiments, hub  420  may be configured to couple with an ear of drive shaft via hub notch  422 . As hub  420  is rotated by drive shaft, seal(s)  492  provide a seal between rotating disk  450  and hub  420  as they both rotate in unison, relative to casing  460 . As casing  460  remains stationary, seal(s)  484  provide a seal between rotating disk  450  and wear plate  482 , where rotating disk  450  rotates relative to wear plate  482  and casing  460 . In some embodiments, seal(s)  484  provide a hermetic seal between rotating disk  450  and wear plate  482 . As shown here, seal(s)  484  can be in co-planar arrangement with one another. 
         [0118]      FIG. 5  illustrates a cross-section view of a rotational assembly  501  according to one embodiment of the present invention. Rotational assembly  501  may include a bearing assembly  570  disposed between a hub  520  and an inner casing  560 . As shown here, bearing assembly  570  includes two race bearings, which are in fixed relation with inner casing  560 . Hub  520  can rotate relative to the race bearings. Hub  520  may include guides  524 ,  524   a  for receiving snap rings or retaining rings, which can help maintain hub  520  in place, relative to race bearings. 
         [0119]    Rotational assembly  501  may also include a sealing arrangement  580 . Sealing arrangement  580  can include, for example, a bottom plate  583  and one or more seals  584 . Seal(s)  584  can be disposed between hub  520  and inner casing  560 . A top plate  587  can be coupled with inner casing  560  via screws or bolts inserted through casing columns  528 . Rotational assembly  501  may also include one or more seals  591  disposed between top plate  587  and an outer casing  561 . In some embodiments, seal(s)  584  include one or more V-rings and seals(s)  591  include one or more O-rings. In the embodiment shown in  FIG. 5 , seal(s)  584  include three V-rings, and seal(s)  591  include one O-ring. Rotational assembly  501  may also include one or more seals  526  to provide a seal between hub  520  and the top plate  587 . As shown here, seal(s)  526  include one V-ring. 
         [0120]    In use, hub  520  is configured to receive or house, and couple with, a drive shaft (not shown). As hub  520  is rotated by drive shaft, seal(s)  584  provide a seal between hub  520  and inner casing  560  as hub  520  rotates relative to inner casing  560 . In some embodiments, seal(s)  584  provide a hermetic seal between hub  520  and inner casing  560 . As shown here, seal(s)  584  can be in co-planar arrangement with one another. 
         [0121]      FIG. 6  illustrates a partial cross-section view of a rotational assembly  601  according to one embodiment of the present invention. Rotational assembly  601  may include a bearing assembly  670  disposed between a hub  620  and an inner casing  660 . As shown here, a lower race bearing of the bearing assembly  670  is in fixed relation with inner casing  660 . Hub  620  can rotate relative to the race bearing. Hub  620  may include a guide  624   a  for receiving snap rings or retaining rings, which can help maintain hub  620  in place, relative to race bearing. 
         [0122]    Rotational assembly  601  may also include a sealing arrangement  680 . Sealing arrangement  680  can include, for example, one or more seals  684 . Seal(s)  684  can be disposed between hub  620  and inner casing  660 . In some embodiments, seal(s)  684  include one or more V-rings. In the embodiment shown in  FIG. 6 , seal(s)  684  include three V-rings. 
         [0123]    In use, hub  620  is configured to receive or house, and couple with, a drive shaft (not shown). As hub  620  is rotated by drive shaft, seal(s)  684  provide a seal between hub  620  and inner casing  660 , as hub  620  rotates relative to inner casing  660 . In some embodiments, seal(s)  684  provide a hermetic seal between hub  620  and inner casing  660 . As shown here, seal(s)  684  can be in a tiered-planar arrangement with one another. 
         [0124]      FIG. 7  illustrates a perspective view of a rotational assembly  701  according to one embodiment of the present invention. Rotational assembly  701  can include a hub  720  having one or more hub notches  722 . In use, hub  720  is configured to receive or house, and couple with, a drive shaft  704 . Hub notch(es)  722  are configured to couple with one or more drive shaft ears  706 . A top plate  787  can be coupled with casing  760  via screws or bolts inserted through top plate apertures  787   a . As hub  720  is rotated by drive shaft  704 , hub  720  rotates relative to top plate  787  and casing  760 . Rotational assembly  701  may also include one or more seals  726  to provide a seal between hub  720  and the top plate  787 . As shown here, seal(s)  726  include one V-ring. 
         [0125]      FIG. 8  illustrates a cross-section view of a rotational assembly  801  according to one embodiment of the present invention. Rotational assembly  801  can include a hub  820  having one or more hub notches  822 . As shown here, a bearing assembly  870  is in fixed relation with a housing  823 . In use, hub  820  is configured to receive or house, and couple with, a drive shaft  804 . Hub notch(es)  822  are configured to couple with one or more drive shaft ears  806 , which may be at opposing ends of a drive shaft spindle  806 a. As hub  820  is rotated by drive shaft  804 , hub  820  rotates relative to housing  823 , bearing assembly  870 , and casing  860 . 
         [0126]    Rotational assembly  801  may also include a sealing arrangement  880 , which can be disposed between hub  820  and housing  823 . Sealing arrangement  880  can include, for example, one or more outer seals  884  and one or more inner seals  886 . Seal(s)  884  can be disposed between an outer surface of hub cup  820   a  and housing  823 , and seal(s)  886  can be disposed between an inner surface of hub cup  823  and housing  823 . Housing  823  can be fixed with casing  860 . In some embodiments, seal(s)  884  include one or more V-rings and seals(s)  886  include one or more oil seals. In the embodiment shown in  FIG. 8 , seal(s)  884  include one V-ring, and seal(s)  886  include one oil seal. Hub  820  can be coupled with a flexible tube  890 . 
         [0127]      FIG. 9  illustrates a cross-section view of a rotational assembly  901  according to one embodiment of the present invention. Rotational assembly  901  can include a hub  920  configured to releasably couple with a drive shaft  904 . As shown here, two bearings of a bearing assembly  970  are in fixed relation with a housing  923 . In use, hub  920  is configured to receive or house, and couple with, a drive shaft  904 . As hub  920  is rotated by drive shaft  904 , hub  920  rotates relative to housing  923 , bearing assembly  970 , and casing  960 . 
         [0128]    Rotational assembly  901  may also include a sealing arrangement  980 , which can be disposed between hub  920  and inner housing  923   a . Sealing arrangement  980  can include, for example, one or more outer seals  984  and one or more inner seals  986 . Seal(s)  984  can be disposed between hub  920  and seal(s)  986 , and seal(s)  986  can be disposed seal(s)  984  and inner housing  923   a . Housing  923  can be fixed with casing  960 , and in sealed relation with casing  960  via one or more seal(s)  962 . In some embodiments, seal(s)  984  include one or more V-rings, seals(s)  986  include one or more oil seals, and seal(s)  962  include one or more O-rings. In the embodiment shown in  FIG. 9 , seal(s)  984  include two V-rings, seal(s)  986  include two oil seals, and seal(s)  962  include two O-rings. Hub  920  can be coupled with a flexible tube  990 . 
         [0129]      FIG. 10  illustrates a cross-section view of an impeller  1040  according to one embodiment of the present invention. Impeller  1040  can be coupled with connector  1090 , which can be couple with hub (not shown). Impeller  1040  can include an impeller spline  1042  which can couple with a spline  1005  of drive shaft  1004 . 
         [0130]      FIG. 11  illustrates a partial cross-section view of an impeller  1140  according to one embodiment of the present invention. Impeller  1104  can include an impeller barb fitting  1141  that can couple with a rotational assembly hub (not shown) via a connector  1190 . Drive shaft  1104  can be attached to impeller  1140  by placing drive shaft  1104  into impeller aperture  1142 . When drive shaft  1104  is inserted into impeller aperture  1142 , end cap  1107  can reach the distal end of impeller base  1143 . As shown here, drive shaft  1104  is hollow and adapted to receive a core  1108 . Drive shaft  1104  is coupled with an end cap  1107 . Core  1108  includes a ball dent  1102  which operatively associates with a ball  1103 . In a first ball configuration  1103 a, ball  1103  is disposed at ball dent  1102 . As core  1108  is advanced along the inside of hollow drive shaft  1104  toward the distal end of impeller aperture  1142 , spring  1109  is compressed, and ball  1103  moves into opening  1104   a  in drive shaft opening  1104   a  and impeller base opening  1143   a , thus adopting a second ball configuration  1103   b.  Distal end of core  1108  can cause end cap  1107  to separate from drive shaft  1104 . In some embodiments, core  1108  is in threaded engagement with end cap  1107 , which can prevent spring  1109  from pushing core  1108  back out of hollow drive shaft  1104 . 
         [0131]      FIG. 12  illustrates a perspective view of drive shaft core  1208  according to one embodiment of the present invention. Drive shaft core  1208  includes ball dent  1202 , end cap  1207 , spring  1209 , and ball  1203 . As shown here, ball  1203  can adopt a first ball configuration  1203   a  and a second ball configuration  1203   b.    
         [0132]      FIG. 13  illustrates a cross-section view of an impeller  1340  according to one embodiment of the present invention. Impeller  1340  can include a square spline  1342  for coupling with a square spline  1305  of drive shaft  1304 . Impeller  1340  can be coupled with hub (not shown) via a connector  1390 . For the sake of clarity, the impeller blades are not shown in this figure. 
         [0133]      FIG. 14A  illustrates a perspective view of an impeller  1440   a  according to one embodiment of the present invention. Impeller  1440   a  can include one or more impeller blades  1445   a  coupled with an impeller body  1446   a . In some embodiments, impeller blades  1445   a  can be machined separately from impeller body  1446   a . Impeller blades  1445   a  may be constructed from a variety of materials, including Delrin, HDPE, and the like. Impeller body  1446   a  may be constructed from a variety of materials, including HDPE and the like. 
         [0134]      FIG. 14B  illustrates a perspective view of an impeller  1440   b  according to one embodiment of the present invention. Impeller  1440   b  can include one or more impeller blades  1445   b  and an impeller body  1446   b . In some embodiments, impeller  1440   b  can be molded as a single piece. Impeller  1440   b  may be constructed from a variety of materials, including medium low density polyethylene, low density polyethylene, Dow Engage® polyolefin elastomers, and the like. 
         [0135]      FIG. 15  illustrates a cross-section view of a sparger body  1500  according to one embodiment of the present invention. Sparger body  1500  can include a sheet of permeable material. In some embodiments, sparger body  1500  includes a vapor-permeable and water-resistant material. In related embodiments, sparger body  1500  includes a high density polyethylene fiber. For example, sparger body  1500  can include Tyvek® material. Sparger body  1500  can be in fluid communication with a port of a container (not shown) via a sparger conduit  1510 . As shown in  FIG. 15 , sparger body  1500  can be in the shape of a donut or ring. Relatedly, sparger body  1500  can include a base  1502  which is adapted to anchor to an interior surface of a container (not shown). The base may or may not include a gas permeable material. In other embodiments, one or more sheets of gas permeable material can be directly sealed with the interior of the container, whereby the interior of the sparger body  1500  includes a gas permeable material on one side (e.g. top side of body), and a corresponding portion of the container on the other side (e.g. bottom side of body). 
         [0136]    In some embodiments, the permeability of the sparger body is such that fluid is prevented from flowing into the sparger when not in use. Similarly, the sparger may be constructed so as to only allow gas to pass through the permeable material when it is subject to sufficiently high gas pressure. Often, a sparger body will include a soft, flexible material. In some embodiments, sparger body  1500  may be welded directly onto container so as to ensure proper placement and alignment. When coupled with a flexible container such as a flexible bag, sparger body  1500  can effectively be folded up with the bag for storage and transport, sterilized simultaneously with the bag, and disposed of so as to eliminate subsequent cleaning. Sparger body  1500  can provide for minute gas bubbles which can increase diffusion of gas into the fluid. It is appreciated that other types of spargers can be used with the present system. 
         [0137]    A variety of materials or assemblies can be used to provide gas transfer into growth chambers. These include, for example, porous materials in the form of tubing made of Teflon® (PTFE), polysulfone, polypropylene, silicone, Kynar® (PVDF), and the like. In some embodiments, used to provide gas transfer into growth chambers. As noted above, sparger body  1500  can include Tyvek® material, which can be used in a bioreactor for the use of active gas diffusion. Similarly, this material can be used in a growth chamber utilizing passive gas transfer. Permeability of Tyvek® film can be measured using the quantitative property of Gurley Hill Porosity. In some embodiments, such materials range in values between about 6 to about 30 (sec/100 cc IN 2 ). Permeability rated according to the methods of Bendtsen Air Permeability are often in a range between about 400 to about 2000 (ml/min). 
         [0138]    In some embodiments, a permeable material will have high permeability while maintaining hydrophobicity, strength, weldability, biocompatibility, and gamma stability. Often, it is desirable to have a flexible material that welds readily to common materials used in the film or port configurations, often found in the manufacture of bioprocessing containers (BPCs). For example, the flexible nature of a soft or paper like film can allow it to be folded during manufacturing, packaging, loading, and use of the bioreactor. It may also be desirous to allow for the surface area and shape of the sparge material to easily be modified or changed according to weld or cut pattern. Optionally, instead of providing a sparger body to be immersed in the contents of a container, a permeable envelope could be used encapsulate the liquid contents of the bioreactor, thus providing a broad area for diffusion. 
         [0139]    Welding the sparger body on a port or container surface can provide for a high level of surface area while providing a low-profile sparge. In some embodiments, this can reduce turbulence near the impeller and/or reduce the possibility of cells accumulating in cracks, seams, or crevices. Often, conventional sparge configurations rely on the use of sparging rings that have small hole perforations that are placed bellow the impeller. Spargers can also include the use of extremely small pore sizes. Such porous materials are commonly seen as sintered metal or ceramic materials. Using a single use disposable material such as Tyvek® may be helpful in avoiding or reducing contamination and cleaning issues that may be associated with some conventional spargers, which sometimes involve cleaning numerous holes, pores, and crevices of such units. For example, small void areas in some spargers may present areas for cell debris to lodge and accumulate leading to increased occurrence of contamination. In some cases, this may carry over in subsequent cell runs. 
         [0140]    One purpose of a sparge unit in a cell culture is to aid in the mass transfer of oxygen (kLa), which is often necessary for the respiration of the growing cells. An advantage of a sparge approach used in a single use bioreactor is that the tortuous pore structure of a gas permeable membrane such as Tyvek® can allow for a beneficial effect on mass transfer of oxygen from the bulk gas introduced through the sparger. In some embodiments, it is desirable to have small bubbles introduced into the bioreactor as they can benefit mass transfer. Mass transfer across a permeable membrane can occur independent of mass transfer resulting from a gas bubble. Relatedly, a long gas retention time within the fluid column and a higher surface to volume ratios are often desirable effects. It is generally accepted that the bubble size can be dominated by surface tension effects, inherently related to the component ratio of salts, proteins, sugars, and micro and macro components of the nutrient media. Experimentally calculated kLa values, visual observation, and data from bioreactor runs often indicate that bubble size and perhaps improved mass transfer are qualities of the present sparge approaches. The composition and rheological properties of the liquid, mixing intensity, turnover rate of the fluid, bubble size, presence of cell clumping, and interfacial absorption characteristics all influence mass transfer of gas such as oxygen to the cells. Main driving forces of mass transfer include surface area and concentration gradient. In many cases, a main source of resistance of oxygen mass transfer in a stirred tank bioreactor can be the liquid film surrounding the gas bubble. 
         [0141]    A sparging material such as Tyvek® can provide for the transfer of gas across the membrane. Relatedly, by incorporating Tyvek® and similar gas permeable membranes, the surface area can easily be increased. In some embodiments, the oxygen gradient between the membrane and the liquid interface can be maintained at a high level through constant replenishment directly through a sparge inlet. Further, a rapid mixing intensity can also benefit mass transfer as the impeller pumps media directly down onto a sparger surface. The use of a membrane can allow for mass transfer of oxygen across the bulk film surface, which can be in addition to the formation of bubbles that rise within the fluid column. In many cases, small bubbles can lead to greater foaming at the top of a bioreactor, which can have negative effects on cell viability and kLa according to Henry&#39;s law and the solubility of gases related to partial pressures. This boundary layer often results in a reduced ability to control dissolved oxygen levels within the bulk liquid. Typically, it is desirable to avoid or mitigate the presence of foam, as excessive amounts can result in exhaust filter blocking and run failure. The novel sparger approaches described herein can provide the desired mass transfer properties, often with reduced levels of foam generated as compared to conventional systems. This may be due to greater efficacy and less gas being introduced through the sparger to maintain a target oxygen solubility. 
         [0142]    Tyvek® is similar is some aspects to the material Gore-Tex® in that it has hydrophobic qualities but will still allow water vapor to pass through. For medical grades of Tyvek® a large relative pore size can be about 20 (micrometers) and the surface energy can be about 25 to about 32 (dynes/cm). As mentioned elsewhere herein, it may be beneficial to use a check valve in a gas inlet stream near a sparger to reduce undesirable transfer of water vapor through the membrane when the sparger is submerged while not in use. Actual moisture transmission rates may vary largely with the media used and the particular application. Moisture Vapor Transmission Rates (MTVR) often range from about 1500 to about 1640 (g/m 2 /24 hrs). The present invention also contemplates the use of these sparger approaches in the form of a replaceable retrofit kit, which may be adapted for use with conventional bioreactors. Such kits can improve kLa and replace a piece of hardware commonly used in steam sterilized bioreactors that may be difficult to sterilize or clean. 
         [0143]    It is appreciated that any of a variety of permeable membranes may be used as a sparging material. In some embodiments, such membranes may be comprised of high density polyethylene fibers that are heat sealed into a web having a thickness in a range between about 50 microns to about 250 microns. The fibers typically have a diameter in a range between about 2 microns to about 8 microns and can be produced by a flash spun process or other methods. 
         [0144]    In other embodiments, the sparging material may include a perforated film sheet, such as a sheet of low density PE film with small perforated holes. This may be in the form of a plastic tubing, molded plastic, shaped film, or flat film. The small perforated holes can be, for example, punched, molded, or embossed into the film. As described above, such sparging materials or constructions can be fixed to the container. In some embodiments, a sparging mechanism may include a combination of a permeable membrane and a perforated film. 
         [0145]      FIG. 16  illustrates a cross-section view of a sparger assembly  1600  according to one embodiment of the present invention. Sparger assembly  1600  can include a sheet of permeable material  1605  and a sparger conduit  1610 . As shown here, sheet of permeable material  1605  is annular in shape. Sparger assembly  1600  can be in fluid communication with a port of a container (now shown) via sparger conduit  1610 . An inner ring  1603  and an outer ring  1604  of sheet  1605  can each be anchored to the interior surface of a container  1602 , such that the sheet of permeable material  1605 , as coupled with container  1602 , defines a donut-shaped space. 
         [0146]      FIG. 17  illustrates a cross-section view of a sparger assembly  1700  according to one embodiment of the present invention. Sparger assembly  1700  can include any number of sheets of permeable material  1705 , a sparger tube  1730 , and a sparger conduit  1710 . Sparger assembly  1700  can be in fluid communication with a port  1720  of a container  1702  via a sparger conduit  1710 . As shown here, sparger assembly  1700  can include a sparger body  1706  that is constructed of two sheets of permeable material  1705  which are coupled together along their outer rings  1704 . It is appreciated that sparger body  1706  can be configured in any of a variety of shapes, including spheres, cylinders, boxes, pyramids, irregular shapes, and the like, and may include any combination of permeable and non-permeable materials or surfaces. 
         [0147]      FIG. 18  illustrates a cross-section view of a sparger assembly  1800  according to one embodiment of the present invention. Sparger assembly  1800  can include a sheet of permeable material  1805  and a sparger conduit  1810 . Sparger assembly  1800  can be in fluid communication with a port  1820  of a container  1802  via sparger conduit  1810 . As shown here, sheet of permeable material  1805  is circular in shape. An outer ring  1804  of sheet  1805  can each be anchored to the interior surface of a container  1802 , such that the sheet of permeable material  1805 , as coupled with container  1802 , defines a dome-shaped space. Sparger assembly configurations such as those described herein can allow the surface area and corresponding gas flow rate requirements of, for example, the permeable material  1805  to be adjusted by utilizing different size shapes such as the dome shown here. Some embodiments of the present invention may include a check valve inline coupled with a tubing that is attached to the sparger conduit  1810 , which can prevent fluid backflow. 
         [0148]      FIG. 19  illustrates a cross-section view of a sparger assembly  1900  according to one embodiment of the present invention. Sparger assembly  1900  can include a sheet of permeable material  1905  and a sparger conduit  1910 . Sparger assembly  1900  can be in fluid communication with a port of a container (not shown) via sparger conduit  1910 . As shown here, sheet of permeable material  1905  is circular in shape. An outer ring  1904  of sheet  1905  can be coupled with sparger conduit  1910 , such that the sheet of permeable material  1905 , as coupled with sparger conduit  1910 , defines a dome-shaped space. 
         [0149]      FIG. 20  illustrates a partial perspective view of a reactor system  2000  according to one embodiment of the present invention. Reactor system  2000  can include a drive motor  2095  coupled with a drive shaft  2004 . Reactor system  2000  can also include a frame support  2097  coupled with drive motor  2095 . In use, drive shaft  2004  can be coupled with a rotational assembly  2001  to mix or agitate the contents of a container (not shown) which is coupled with rotational assembly  2001 . In some embodiments, rotational assembly  2001  is coupled with frame support  2097  via a bracket (not shown).  FIG. 21  illustrates a partial perspective view of a reactor system  2100  according to one embodiment of the present invention. Reactor system  2100  can include a drive motor (not shown) coupled with a drive shaft  2104 . Reactor system  2100  can also include a frame support  2197  coupled with the drive motor. Drive shaft  2004  may include or be in operative association with a drive shaft ear  2006  that is configured to couple with a notch of a rotational assembly hub (not shown). Drive shaft ear  2006  is often used to transmit torque from the drive motor to the rotational assembly hub. 
         [0150]      FIG. 22  illustrates a partial perspective view of a reactor system  2200  according to one embodiment of the present invention. Reactor system  2200  can include a drive motor  2295  coupled with a drive shaft  2204 . In use, drive shaft  2204  can be coupled with a rotational assembly  2201  to mix or agitate the contents of a container (not shown) which is coupled with rotational assembly  2201 . A clamp  2205  may also be coupled with rotational assembly  2201 . In this embodiment, drive motor  2295  includes a right angle gearmotor, which can allow an operator to pass drive shaft  2204  through drive motor  2295  without moving the drive motor  2295 . Embodiments that include right angle gear motors, parallel shaft gear motors, and hollow shaft motors can provide enhanced alignment and ease of connection between drive motor  2295  and rotational assembly  2201 .  FIG. 23  illustrates a cross-section view of a reactor system  2300  according to one embodiment of the present invention. Reactor system  2300  can include a drive motor  2395  coupled with a drive shaft  2304 . Drive shaft  2304  may include or be coupled with a tapered element  2304   a  that is configured to associate with a corresponding receiving element  2395   a  of motor  2395 . Tapered element  2304   a  can provide enhanced alignment between drive shaft  2304  and drive motor  2395 . 
         [0151]      FIG. 24  illustrates a perspective view of a reactor system  2400  according to one embodiment of the present invention. Reactor system  2400  can include a container housing  2411  coupled with a support shelf  2413 . Support shelf  2413  may be adapted for supporting sensing probes (not shown) and other elements of a reactor system. Container housing  2411  can be coupled with a drive motor  2495  via a support frame  2497 .  FIG. 25  illustrates a perspective view of a reactor system  2500  according to one embodiment of the present invention. Reactor system  2500  can include a container housing  2511  coupled with a support shelf  2513 . Container housing  2511  can be coupled with a drive motor  2595  via a support frame  2597 . 
         [0152]      FIG. 26  illustrates a probe assembly  2600  according to one embodiment of the present invention. As seen here, probe assembly  2600  is in a retracted configuration, prior to engagement with a reactor container. Probe assembly  2600  can include a dissolved oxygen and pH probe  2610  and Pall Kleenpak connectors  2620  for providing an aseptic connection. Probe assembly  2600  can also include a port  2630 , a sleeve  2640 , and a coupler  2650 , and these three components can facilitate the integration of probe  2610  into the reactor utilizing Pall connectors  2620 . In some embodiment, port  2630  and female Pall connector  2620   f  can be part of or integral with the reactor container (not shown). Sleeve  2640 , coupler  2650 , and male Pall connector  2620   m  can be manufactured or provided to the user as a separate subassembly. The user can install the desired probe into such a subassembly and then can sterilize the complete probe assembly. Port  2630 , sleeve  2640 , and coupler  2650  can facilitate integration of probe  2610  into a bioreactor using Pall connector  2620 . 
         [0153]      FIG. 27A  provides a illustration of a probe port subassembly  2702  of a probe assembly according to one embodiment of the present invention. Probe port subassembly  2702  can include a bioprocessing container port  2730  coupled with female Pall connector  2620   f.  Port  2730  may be, for example, heat welded into a container (not shown) via flange plane  2734 . Port  2730  may also include a lip seal  2732  that can prevent backflow of fluid or material from container into probe assembly or beyond flange  2734  plane. In some embodiments, port  2730  and female Pall connector  2620   f  are constructed integrally with the container. 
         [0154]      FIG. 27B  illustrates a probe kit subassembly  2704  of a probe assembly according to one embodiment of the present invention. Probe kit subassembly  2704  can include a coupler  2750 , a sleeve  2740 , and a male Pall connector  2620   m.  Probe kit subassembly  2704  may be supplied to an end user as a separate kit. Sleeve  2740  may be coupled with coupler  2750  via a barb fitting (not shown) of coupler  2750 . Similarly, sleeve  2740  may be coupled with male Pall connector  2620   m  via a barb fitting (not shown) of male Pall connector  2620   m.    
         [0155]      FIG. 27C  illustrates an autoclave subassembly  2706  of a probe assembly according to one embodiment of the present invention. Autoclave subassembly  2706  can include a probe  2710 , coupler  2750 , sleeve  2740 , and male Pall connector  2620   m . An end user can install the desired probe  2710  into a probe kit subassembly  2704  as describe above, and sterilize the resulting autoclave assembly  2706 . After sterilization, the user can join the male Pall connector  2620   f  and the female Pall connector  2620   f , and complete the probe engagement into the fluid stream. In some embodiments, sleeve  2740  is a flexible member that can collapse and allow probe  2710  to be displaced, and coupler  2750  can provide an interface between sleeve  2740  and probe  2710 . 
         [0156]      FIG. 28A  illustrates a probe assembly  2800  according to one embodiment of the present invention. Probe assembly  2800  includes probe  2810 , coupler  2850 , sleeve  2850 , male Pall connector  2820   m , female Pall connector  2820   f , and port  2830 . Probe assembly  2800  is shown in a first connected configuration, wherein probe assembly is engaged with container, but the probe is not yet introduced into the fluid stream.  FIG. 28B  illustrates a probe assembly according to one embodiment of the present invention, wherein probe assembly  2800  is in a second connected configuration such that sleeve  2840  is collapsed and a distal end of probe  2710  is introduced into the fluid stream of the container. 
       C. CULTURES  
       [0157]    The stirred-tank reactor system can be designed to hold a fluidic medium such as a biological fluid, a cell culture medium, a culture of microorganisms, a food production, or the like. When the fluidic medium is a cell culture the system can be operated in, for example, batch-mode, semi-batch mode, fed-batch mode, or continuous mode. A batch culture can be a large scale cell culture in which a cell inoculum is cultured to a maximum density in a tank or fermenter, and harvested and processed as a batch. A fed-batch culture can be a batch culture which is supplied with either fresh nutrients (e.g., growth-limiting substrates) or additives (e.g., precursors to products). A continuous culture can be a suspension culture that is continuously supplied with nutrients by the inflow of fresh medium, wherein the culture volume is usually constant. Similarly, continuous fermentation can refer to a process in which cells or micro-organisms are maintained in culture in the exponential growth phase by the continuous addition of fresh medium that is exactly balanced by the removal of cell suspension from the bioreactor. Furthermore, the stirred-tank reactor system can be used for suspension, perfusion or microcarrier cultures. Generally, the stirred-tank reactor system can be operated as any conventional stirred-tank reactor with any type of agitator such as a Rushton, hydrofoil, pitched blade, or marine. With reference to  FIG. 1 , the agitation shaft  112  can be mounted at any angle or position relative to the housing  111 , such as upright centered, upright offset, or 15° offset. The control of the stirred-tank reactor system can be by conventional means without the need for steam-in-place (SIP) or clean-in-place (CIP) control. In fact, the system of the instant invention is not limited to sterile bioreactor operation, but can be used in any operation in which a clean product is to be mixed using a stirred tank, for example, food production or any clean-room mixing without the need for a clean-room. 
       D. THE KIT 
       [0158]    The invention encompasses a kit that includes a stirred-tank reactor system and instructions for use. In one embodiment, the kit includes a disposable stirred-tank reactor system. Accordingly, the kit includes at least one disposable element such as the bag, the shaft, the impeller, or the bearing. The kit can be entirely disposable. The flexible, disposable bag may be affixed to the shaft and the bearing through at least one seal or o-ring such that the inside of the bag remains sterile. In addition, the bag may include a pH sensor and a dissolved-oxygen sensor, wherein the sensors are incorporated into the bag and are disposable with the bag. The kit may also include one or more internal pouches that are sealed to the bag. The pouch has one end that can be opened to the outside of the bag such that a probe can be inserted into the reactor. The probe may be a temperature probe, a pH probe, a dissolved gas sensor, an oxygen sensor, a carbon dioxide (CO 2 ) sensor, a cell mass sensor, a nutrient sensor, an osmometer, and the like. Furthermore, the system may include at least one port in the bag allowing for the connection of a device to the port, wherein the device includes, but is not limited to, a tube, a filter, a sampler, a probe, a connector, and the like. The port allows for sampling, titration, adding of chemostat reagents, sparging, and the like. The advantage of this kit is that it is optionally entirely disposable and easy-to-use by following the attached instructions. This kit comes in different sizes depending on the preferred culture volume and can be employed with any desired reaction chamber or barrel. This kit is pre-sterilized and requires no validation or cleaning. The kit can be used for cell culture, culture of microorganisms, culture of plant metabolites, food production, chemical production, biopharmaceutical production, and others. 
         [0159]    In another embodiment the kit includes a housing or barrel that holds the disposable bag. Such a housing or barrel can be supplied with the bag or provided separately. 
       E. EXAMPLES  
       [0160]    The following specific examples are intended to illustrate the invention and should not be construed as limiting the scope of the claims. 
         [0161]    (1) A Disposable Bioreactor 
         [0162]    One example of a stirred-tank reactor system of the instant invention is a disposable bioreactor, or single use bioreactor (SUB). The bioreactor is similar to a 250 liter media bag with built-in agitation and attachable sensors (e.g., pH sensors, temperature sensors, dissolved oxygen (dO2) sensors, etc.). The reactor is operated via conventional controllers. The agitator (e.g., agitation shaft and impeller) and bearing are disposable and built into the bag. The motor attaches to a support (e.g., motor and bearing support) or bracket(s) on the 250 liter barrel that holds the bag. In size, shape, and operation, this bioreactor appears similar to a stainless steel reactor with a sterile liner, however, the bioreactor of this invention provides a multitude of advantages compared to a conventional stainless steel reactor. It can be appreciated that the size and volume of such media bags can be scaled both upward and downward, according to industry needs. 
         [0163]    Most importantly, the need for cleaning and steam sterilization is eliminated. The bag is pre-sterilized by irradiation and, thus, ready for use. In fact, no cleaning, sterilization, validation or testing is required at culture start-up or between culture runs. Consequently, the bioreactor provides a culture environment of zero cross-contamination between runs. In conventional systems, the majority of costs are related to clean-in-progress (CIP) and steam-in-progress (SIP) as well as the design of a skid and control system to oversee these functions. These costs are eliminated in the disposable bioreactor and multiple products may be cultured or manufactured simultaneously and with much greater ease. 
         [0164]    The disposable bioreactor can be easily scaled-up by using larger culture bags and larger barrels to hold the bags. Multiple bioreactors can be operated at the same time without any need for extensive engineering or cleaning. The bioreactor is a true stirred tank with well characterized mixing. As such, the bioreactor has the added advantage that it can be scaled and its contents transferred to a stainless steel reactor if desired. Notably, the bioreactor combines ease of use with low cost and flexibility and provides, thus, a new technical platform for cell culture. 
         [0165]    (2) Cell Culture 
         [0166]    The disposable bioreactor of the instant invention can be used for a batch culture in which cells are inoculated into fresh media. As the cells grow, they consume the nutrients in the media and waste products accumulate. For a secreted product, when the culture has run its course, cells are separated from the product by a filtration or centrifugation step. For viral-vector production, cells are infected with a virus during the growth phase of the culture, allowing expression of the vector followed by harvest. Since there is zero cross-contamination in the bioreactor it works well with batch cultures. 
         [0167]    The bioreactor can also be used for perfusion cultures, wherein product and/or waste media is continuously removed and the volume removed is replaced with fresh media. The constant addition of fresh media, while eliminating waste products, provides the cells with the nutrients they require to achieve higher cell concentrations. Unlike the constantly changing conditions of a batch culture, the perfusion method offers the means to achieve and maintain a culture in a state of equilibrium in which cell concentration and productivity may be maintained in a steady-state condition. This can be accomplished in the disposable bag as easily as in any conventional stainless steel reactor. For viral- vector production, the perfusion process allows for an increase in the cell concentration and, thereby the post-infection virus titer. For a secreted product, perfusion in the bioreactor offers the user the opportunity to increase the productivity by simply increasing the size of the culture bag. Most importantly, there is no need for sterilization, validation, or cleaning because the system experiences zero cross-contamination during the production process. 
         [0168]    (3) Batch Data  1   
         [0169]      FIG. 29  provides a graph of data that was generated using a reactor system according to one embodiment of the present invention. Human embryonic kidney (HEK) 293 cells in 200 liters of CDM4 culture medium were incubated in a 250 liter capacity reactor system. Among other parameters shown in the graph, the viable cell density of the reactor system culture increased for about the first 14 days of the batch run. 
         [0170]    (4) Batch Data  2   
         [0171]      FIGS. 30-34  illustrate data obtained from a single use bioreactor system for mammalian cell culture according to one embodiment of the present invention. The scaleable mass transfer characteristics of the single use stirred tank bioreactor are described. Cell growth and metabolism, antibody production, and antibody characterization data from batch culture using a 250-liter prototype system are presented and compared to results from a traditional stainless-steel bioreactor of similar scale. 
         [0172]    Materials and Methods—Mixing Studies. Mixing time in the bioreactor was estimated at various agitation rates by tracking the change in pH in the reactor over time in response to addition of a base solution. The reactor was filled to working volume of 250 liters with typical cell culture media. At time zero, 500 ml of 1N NaOH was added at the top of the reactor, and a combined pH glass electrode was used to measure pH from time zero until the pH had stabilized. The pH versus time was plotted, and the time required to reach 95% of the final pH was estimated from the graph. 
         [0173]    Key scale-up parameters were determined using standard calculations that have been well established in the chemical and pharmaceutical industry. 
         [0174]    The mixing Reynolds number, N Re  is the ratio of fluid kinetic and inertial forces and is used to determine the mixing regime, either laminar or turbulent: 
         [0000]        N   Re   =ND   u   2 ρ/μ 
         [0175]    The energy input into the reactor, P o , per volume of the reactor, V, relates to the scale at which fluid mixing and mass transfer occurs and is dependent on the impeller power number, N p : 
         [0000]        P   o   /V=N   p   ρN   3 D i   5   /V    
         [0176]    The impeller power number depends on the design of the impeller and is a function of number of blades, blade width, and blade pitch. Np is also a function of the clearance of the impeller from the sides and bottom of the reactor. For various impeller types, the power number is well documented. 
         [0177]    Tip speed of the impeller, v i , relates to the fluid shear stress in the vicinity of the impeller: 
         [0000]      v i =πND i    
         [0178]    In the above equations, N=impeller rotational speed, D=impeller diameter, ρ=fluid density, and μ=fluid viscosity. 
         [0179]    Materials and Methods—Oxygen Transfer Studies. The volumetric oxygen transfer coefficient, k L a, was estimated at various agitation and sparging rates by tracking the change in dissolved oxygen, dO 2 , concentration over time at the appropriate condition. The reactor was filled to the working volume of 250 liters with typical cell culture media, and a dO 2  sensor was installed in the reactor. To prepare for each experiment, nitrogen was sparged through the bioreactor until the dO 2  concentration dropped below approximately 20% saturation with air. For each experiment, the agitation rate was set, and then air was sparged at the desired rate. The dO 2  concentration was measured versus time until it reached approximately 80% saturation with air. The value of k L a can be estimated from a graph of C L  versus dC L /dt, based on the following mass balance equation: 
         [0000]        dC   L   /dt=k   L   a ( C*−C   L ) 
         [0180]    where C L  is the dO 2  concentration, and C* is the equilibrium value for C L . 
         [0181]    Materials and Methods—Cell Culture Procedures. A cell culture process that had been developed for a traditional stainless-steel reactor of 300-liter working volume was used to demonstrate the performance of the single use bioreactor. The cell line, media, and process parameters that had been demonstrated in the traditional reactor were repeated in the single use reactor. 
         [0182]    The cells used were CHO cells expressing a humanized monoclonal antibody. Cells were thawed and maintained in T-flasks using standard methods. Cells were then expanded from T-flasks into custom 1-liter expansion bags prior to being introduced into a traditional stainless-steel 110-liter inocula bioreactor. Once cells reached a concentration of 1.6×10 6  cells/ml, 45 liters from the traditional 110-liter bioreactor were used as inocula for the single use bioreactor. Thus, exponentially growing cells from a controlled bioreactor at a pre-determined cell concentration were provided as inocula for the single use bioreactor. 
         [0183]    A standard, commercially available, chemically defined cell culture medium was used. At a specified point in the batch culture, a commercially available nutrient feed that is of non-animal origin but is not chemically defined was added. Solutions of D-glucose and L-glutamine were added daily as required during the batch culture to maintain a concentration of D-glucose between 1 and 3 mg/liter and a concentration of L-glutamine between 1 and 3 mMol/liter throughout the batch. 
         [0184]    Control of the single use bioreactor was accomplished using standard, industry-accepted sensors and controllers. The temperature, pH, and dO 2  feedback controllers operated using proportional, integral, and differential (PID) control. Temperature was measured by a platinum resistance thermometer inserted in a thermo well in the reactor, and was controlled at 37° C. via a electric heat jacket. The pH was measured using a combined pH glass electrode that was in direct contact with the bioreactor contents. The pH was controlled at a value of 7.1 via addition of CO 2  into the headspace or addition of 1M Na 2 CO 3  to the culture. The dO 2  concentration was measured using a dO 2  sensor that was in direct contact with the bioreactor contents. The dO 2  concentration was controlled at 30% saturation with air via sparging of O 2  at approximately 0.2 liters/min. Agitation was not controlled by feedback but was maintained at a single set point of 110 rpm and checked daily. Level in the bioreactor was measured using a weigh scale. 
         [0185]    A sampling system was attached to the bioreactor using a sterile connection device, and was used to withdraw 10-ml samples as required during the batch culture. Samples were withdrawn at least once daily. Samples were immediately analyzed using a Nova BioProfile 200 analyzer, which provided culture pH, dO 2 , dCO 2 , D-glucose, and L-glutamine concentrations. The pH probe was standardized, as required, and D-glucose and L-glutamine solutions were added based on the Nova measurements. Viable and total cell concentrations were determined for each sample based on hemacytometer counts using trypan blue dye exclusion. Samples were filtered through a 0.2 μm filter and stored for later analysis using an Igen based assay for antibody titer. 
         [0186]    Key cell culture parameters were calculated based on the sample measurements. Maximum viable cell concentration, cumulative cell time at harvest, final antibody concentration, and total glucose and glutamine consumed were calculated directly from the sample data. As a batch culture, the specific growth rate of the cells, μ, was determined for only the exponential phase of the culture. Specific growth rate was calculated from a regression fit of viable cell concentration, X v , from days one through four following inoculation: 
         [0000]    
       
      
       dX 
       v 
       /dt=μt  
      
     
         [0187]    Results from a series of batch cultures using a traditional stainless-steel bioreactor of similar scale were available for comparison with the single use results. The ranges of values tabulated for the traditional bioreactor are the 95% prediction intervals for a single future observation: 
         [0000]        x   mean   ±t   α/2,n−1   ·s √(1+(1 /n )) 
         [0188]    where x mean =sample mean, s=sample standard deviation, n=sample size, and t α/2,n−1  is the appropriate Student&#39;s t-statistic. 
         [0189]    The single use bioreactor supernatant was harvested, clarified by filtration and purified (protein A-based affinity purification combined with ion exchange chromatography) using the procedures established for the traditional stainless bioreactor manufacturing process. The resultant purified antibody was characterized and compared to antibody derived from the traditional stainless steel process. Carbohydrate (CHO) profile, SDS-PAGE (reduced and non reduced), SEC-HPLC, SEC-MALS (Multi-Angle Light Scattering), BIACore Binding, RP-HPLC, Capillary Electrophoresis Isoelectric Focusing (CEIEF) and MALDI-TOF Mass Spectrometry assays were utilized to characterize the purified antibody derived from the single use bioreactor. The results obtained were compared to those seen for antibody produced in a traditional stainless steel bioreactor. 
         [0190]    Results—Mixing Studies. The time required to reach 95% homogeneity decreased with increasing agitation speed. Each experiment was repeated twice, and the average mixing times are shown in Table 1. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Single Use Bioreactor Mixing Studies 
               
             
          
           
               
                   
                 Agitation speed (rpm) 
               
             
          
           
               
                   
                 50 
                 100 
                 200 
               
               
                   
                   
               
             
          
           
               
                   
                 Characteristic mixing time (sec) 
                 90 
                 60 
                 45 
               
               
                   
                   
               
             
          
         
       
     
         [0191]    In addition, key scale-up parameters for the single use bioreactor could be readily calculated. The single use bioreactor was designed using design criteria for a typical stirred tank bioreactor, and the impeller was a typical pitched-blade design, as shown in Table 2. In the absence of baffles, vortex formation in the reactor was avoided by mounting the impeller at an offset from center and at a 20° angle from vertical. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
               
                   
               
               
                 Single Use Bioreactor Design Elements 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                   
                 Tank height (at working volume) 
                 1.5 tank diameter 
               
               
                   
                 Impeller diameter 
                 0.33 tank diameter 
               
               
                   
                 Impeller number of blades 
                 3 
               
               
                   
                 Impeller blade pitch 
                 45° 
               
               
                   
                 Impeller blade height 
                 0.5 impeller diameter 
               
               
                   
                 Impeller clearance from tank bottom 
                 1 impeller diameter 
               
               
                   
                 Impeller clearance from tank side 
                 0.5 impeller diameter 
               
               
                   
                 Impeller power number (calculated) 
                 2.1 
               
               
                   
                   
               
             
          
         
       
     
         [0192]    Using the power number from Table 2, characteristic scale-up parameters can be readily calculated for various agitation speeds, as listed in Table 3. 
         [0000]    
       
         
               
             
               
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Single Use Bioreactor Scale-Up Parameters 
               
             
          
           
               
                   
                 Agitation speed (rpm) 
               
             
          
           
               
                   
                 50 
                 100 
                 200 
               
               
                   
                   
               
             
          
           
               
                 Tip speed (cm/sec) 
                 53 
                 106 
                 213 
               
               
                 Power input per unit volume 
                 0.0022 
                 0.018 
                 0.143 
               
               
                 (hp/1000 liter) 
               
               
                 Mixing Reynolds number 
                 34,000 
                 69,000 
                 137,000 
               
               
                   
               
             
          
         
       
     
         [0193]    Results—Oxygen Transfer Studies. The volumetric oxygen transfer coefficient, k L a was determined for various flowrates of air through the sparger and for various agitation speeds, shown in  FIG. 30 . As expected, k L a increased with increasing air flowrate and with increasing agitation speed, with one exception. At 200 rpm, k L a was lower than that at 100 rpm. This discrepancy may be due to an increased surface effect on k L a at the higher agitation rate. (Due to the experimental procedure, the headspace contained a mixture of nitrogen and air.) Further experiments are required to quantify the surface effects. 
         [0194]    These results are comparable, as expected, with oxygen transfer characteristics of traditional stirred tank bioreactors of the same geometry. A typical literature value for the equilibrium oxygen concentration in cell culture media is 0.18 mMol/liter, and specific oxygen uptake rate for typical animal cell culture is 0.15 mMol/10 9  cells/hr. Operated in the middle of the range from the above chart (agitation=100 rpm; sparge rate=1.0 liter/min; kLa≈10 hr −1 ) the single use bioreactor is calculated to be capable of maintaining cell concentrations greater than 10×10 6  cells/ml using air as the sparge gas and greater than 50×10 6  cells/ml using oxygen as the sparge gas. 
         [0195]    Results—Batch Cell Culture. To demonstrate the suitability of the single use bioreactor for cell culture production, CHO cells producing a humanized monoclonal antibody were grown in batch culture and compared to historical results from the same cell line and process carried out in a traditional stainless steel bioreactor of similar scale. This process has been repeated five times in a 300-liter Abec traditional stainless steel reactor that is specifically designed for cell culture. Key cell culture parameters from the two reactors are compared in Table 4. 
         [0000]    
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Single Use and Traditional Bioreactor Batch Results 
               
             
          
           
               
                   
                 Single Use 
                 Traditional 
               
               
                   
                 Bioreactor 
                 Bioreactor 
               
               
                   
                 (n = 1) 
                 (n = 5)* 
               
               
                   
                   
               
             
          
           
               
                 Duration of Cell Culture (hours) 
                 285 
                 282 ± 8  
               
               
                 Maximum Viable Cell Concentration 
                 7.6 
                 7.4 ± 2.4 
               
               
                 (10 6  cells/mL) 
               
               
                 Cumulative Viable Cell Time at Harvest 
                 1214 
                 1019 ± 171  
               
               
                 (10 9  cell · hr/L) 
               
               
                 Specific Exponential Growth Rate of Cells 
                 0.027 
                 0.028 ± 0.010 
               
               
                 (1/hr) 
               
               
                 Antibody Concentration at Harvest 
                 112 
                 100 ± 33  
               
               
                 (% of historical) 
               
               
                 Total Glucose Consumed (mg/L) 
                 14.2 
                 15.7 ± 9.4  
               
               
                 Total Glutamine Consumed (mMol) 
                 16.4 
                 18.9 ± 2.4  
               
               
                   
               
               
                 *range is the prediction interval for a single future observation 
               
             
          
         
       
     
         [0196]    The single use bioreactor was an initial prototype. As a prototype being used for the first time, adjustments to the controller PID parameters were made several times during the batch culture. Temporary excursions in pH, dO2 concentration, sparger flowrate, and agitation speed occurred at times during the batch due to these adjustments. Despite these excursions, results from this bioreactor are equivalent to results from the traditional stainless steel bioreactor. Graphs of the pH, dO2, and dCO2 concentration from off-line samples measured by the Nova analyzer are shown in  FIG. 31 . 
         [0197]    Detailed results from the single use bioreactor are shown in the following figures. The single use bioreactor was inoculated at 0.33×10 6  cells/mL and reached a maximum cell density of 7.6×10 6  cells/mL. Viability remained above 90% during the growth portion of the batch curve. Total and viable cell concentration and percent viability are shown in  FIG. 32 . 
         [0198]    Antibody titer over time, as a percent of final titer at harvest, is shown in  FIG. 33 . As is typical for this cell line, approximately 50% of the antibody was produced in the second half of the batch as the cell concentration was declining. 
         [0199]    Cumulative glucose and glutamine consumption is shown in  FIG. 34 . Glucose and glutamine consumption for the single use bioreactor was comparable to historical results from the traditional stirred tank bioreactor. 
         [0200]    A summary of the assay results is contained in Table 5. In all cases, the antibody derived from the single use bioreactor showed equivalent results to that produced in the traditional stainless steel bioreactor. 
         [0000]    
       
         
               
             
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Single Use and Traditional Bioreactor Protein Assay Results 
               
             
          
           
               
                 Assay 
                 Traditional Bioreactor 
                 Single Use Bioreactor 
               
               
                   
               
               
                 Carbohydrate 
                 Comparable to reference 
                 Comparable to reference 
               
               
                 (CHO) profile 
               
               
                 SDS-PAGE 
                 Comparable to reference 
                 Comparable to reference 
               
               
                 Reduced 
               
               
                 SDS-PAGE 
                 Comparable to reference 
                 Comparable to reference 
               
               
                 Non-reduced 
               
               
                 SEC-MALS 
                 ~150 KD, &gt;98% monomer 
                 ~150 KD, &gt;98% 
               
               
                   
                   
                 monomer 
               
               
                 BIACore Binding 
                 Pass specification 
                 Pass specification 
               
               
                 CEIEF 
                 Pass specification 
                 Pass specification 
               
               
                 MALDI-TOF 
                 ~150 Kd 
                 Comparable to reference 
               
               
                 Mass Spec. 
               
               
                 RP-HPLC 
                 &gt;95% purity (Pass) 
                 &gt;95% purity (Pass) 
               
               
                 Peptide Mapping 
                   
                 Comparable to reference 
               
               
                   
               
             
          
         
       
     
         [0201]    Various modifications and variations of the present invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the claims.