Abstract:
Aeration device for bioreactors with a first aeration element with gas outlet openings of a first size and with at least one second aeration element with gas outlet openings of a second size, the aeration elements being formed by a common housing with separate aeration channels.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an aeration device for bioreactors with a first aeration element with gas outlet openings of a first size and with at least one second aeration element with gas outlet openings of a second size. 
     2. Description of the Related Art 
     Provision of an oxygen supply is a key factor in cellular metabolic processes. Although animal cell cultures consume substantially less oxygen than bacteria and yeast cultures, ensuring an efficient supply is the greatest challenge facing the operation of a cell culture bioreactor. In addition to supplying the cells with oxygen, the concentration of dissolved carbon dioxide also plays a part as a controlled variable. 
     There are two conventional aeration methods: aerating the headspace of the bioreactor and direct injection of the gases through aeration rings. For this purpose, use is made not only of the aeration rings known from fermenters with bores or gas outlet openings of for example 0.8 mm but also of “microspargers” made from sintered plastics with pore sizes of for example 20 to 45 μm, which likewise form gas outlet openings. Both kinds have specific advantages and drawbacks. The aeration ring produces larger bubbles, which means that higher gas throughput rates are required to achieve the same “oxygen transfer rate”. With its relatively large bubbles, the ring sparger is suitable for stripping or sweeping out CO2 with air, for example. With its relatively small bubbles, the microsparger is particularly suitable for supplying oxygen. One drawback, however, is that under unfavorable conditions foaming may occur due to the relatively smaller bubbles. 
     Aeration devices are used as part of automated bioreactor aeration systems, for example single-use reactors, the supply of air, oxygen, carbon dioxide and nitrogen being mutually independently controllable. Sensors for oxygen partial pressure and pH facilitate the control of these important process parameters. 
     WO 2009/122310 A2, WO 2009/115926 A2 and WO 2009/116002 A1 disclose a single-use bioreactor with a mixer and with an aeration device arranged on the bottom of the reactor interior. It is known here to arrange two aeration elements on the bottom which take the form of opposing, mating ring segments. 
     Drawbacks of this aeration device, which has in principle proved effective, are that, on the one hand, it must be fastened in relatively complex manner to the bottom of the reactor and that, on the other hand, it is difficult to arrange a plurality of such aeration elements optimally relative to the stirrer or mixer. 
     An aeration device for bioreactors is furthermore known from WO 2008/088371 A2, in which for example two aeration elements with different gas outlet openings may be fastened to the bottom of the reactor. 
     One drawback here is that the aeration elements are fastened in relatively complex manner to the bottom of the reactor. A further drawback is that the individual aeration element is here not optimally arranged relative to the mixer. 
     The object of the present invention is accordingly to improve the known aeration devices for bioreactors in such a manner that, on the one hand, they are simpler to fasten and, on the other hand, each aeration element is optimally positioned relative to a mixing element arranged in the reactor interior. 
     SUMMARY OF THE INVENTION 
     This object is achieved in conjunction with an aeration device for bioreactors with a first aeration element with gas outlet openings of a first size and with at least one second aeration element with gas outlet opening of a second size in that the aeration elements are formed by a common housing with separate aeration channels. 
     Thanks to the common housing, the aeration device may be arranged simply and centrally relative to a mixer while occupying little space. 
     According to a preferred embodiment of the invention, the housing takes the form of an annular disk in which the at least two aeration elements are arranged concentrically to one another. The concentric arrangement of the aeration elements enables an optimum arrangement relative to a mixer or stirrer. 
     According to a preferred embodiment of the invention, the first aeration element takes the form of a ring sparger with gas outlet openings of greater than 0.1 mm in diameter, while the second aeration element takes the form of a microsparger with gas outlet openings of less than 0.1 mm in diameter. The gas outlet openings of the microsparger are here formed of a porous material, for example a sintered plastics material. In this manner, both a ring sparger and a microsparger are compactly arranged in a common housing in a small space. 
     According to a further preferred embodiment of the invention, the first aeration element and the second aeration element take the form of a ring sparger with in each case two differently sized gas outlet openings, the gas outlet openings being larger than 0.1 mm. 
     According to a further preferred embodiment of the invention, the first aeration element and the second aeration element take the form of a microsparger with in each case two differently sized gas outlet openings, the gas outlet openings being smaller than 0.1 mm. 
     According to another preferred embodiment of the invention, the housing comprises a lower part, in which are arranged the aeration channels with in each case a radially extending inflow. In this manner, each of the separately arranged aeration channels comprises a dedicated radially extending inflow. 
     According to a further preferred embodiment of the invention, the lower part is covered by an upper part which covers the aeration channel of the ring sparger and comprises the gas outlet openings. 
     In the region of the microsparger, the upper part comprises segment-shaped openings towards the aeration channel, the aeration channel being covered or sealed by an annular aeration ring made from the porous material forming the gas outlet openings. It is, however, also possible in principle to insert the aeration ring directly into the upper part. 
     The upper part may be sealed relative to the lower part comparatively simply by seals, for example O-ring cord seals or O-rings. 
     In further preferred embodiments, the upper part may be either welded or adhesively bonded to the lower part. 
     According to a further preferred embodiment of the invention, the inflows for independent supply of the aeration channels in each case comprise a tube connection with a nonreturn valve. The nonreturn valves reliably prevent backflow of media from the reactor interior into the aeration device. 
     According to a further preferred embodiment of the invention, the housing comprises a central opening adjusted to a stirrer flange of the bioreactor and may be arranged upstream of a stirrer on the bottom of an interior of the bioreactor. Thanks to the central opening of the aeration device, the latter may be positioned optimally relative to a stirrer arranged in the reactor interior. The volumetric flow rates of the aeration elements may be adapted to the reactor volume by being differently dimensioned. In particular in the case of the ring sparger, the number of holes may be adjusted to the volume or effective volume of the reactor. For example, one hole may be arranged in the ring sparger for each 10 liters of effective volume. In the case of the microsparger, its surface area is likewise adapted to the reactor volume, for example 2 to 2.5 cm2 per 10 liters of effective volume. In this manner, a constant bubble size distribution may be achieved combined with any desired scalability of the reactor volume. 
     In addition to the number of gas outlet openings or holes, the size thereof may also be adapted to the desired volumetric flow rates. In the case of microspargers, the porosity and the surface area thereof may be correspondingly adapted. 
     According to another preferred embodiment of the invention, the lower part comprises a continuous, circular bottom and may be inserted in sealing manner into the bottom of the bioreactor by a screw, bayonet, latch, clamp, adhesive or clip connection. 
     Further details of the invention may be inferred from the following detailed description and the attached drawings, which illustrate preferred embodiments of the invention by way of example. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an enlarged plan view of a medium-sized aeration device. 
         FIG. 2  is a side view of the aeration device of  FIG. 1  suction sectioned along line II-II. 
         FIG. 3  is a side view of the aeration device of  FIG. 1  sectioned along line III-III. 
         FIG. 4  is a plan view of a further aeration device of a smaller size than the aeration device of  FIG. 1 . 
         FIG. 5  is a plan view of a further aeration device of a larger size than the aeration device of  FIG. 1 . 
         FIG. 6  is a side view of a bioreactor with stirrer and an aeration device. 
         FIG. 7  is a side view of a further bioreactor with an aeration device, the lower part of which, by means of a continuous bottom, may be inserted by a screw connection into the bottom of the bioreactor. 
         FIG. 8  is a side view of a further bioreactor with an aeration device, the lower part of which, by means of a continuous bottom, may be inserted by a latch connection into the bottom of the bioreactor. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An aeration device  1  substantially consists of a housing  2  with a first aeration element  3  and a second aeration element  4 . 
     The housing  2  consists of a lower part  5  and an upper part  6  positionable on the lower part  5 . The lower part  5  comprises two aeration channels  7 ,  8  arranged concentrically to one another. The aeration channels  7 ,  8  are downwardly delimited in the vertical direction by a bottom  9  of the lower part  5 . The first aeration channel  7  is laterally delimited by the outer wall  10  and, towards the second aeration channel  8 , by a partition wall  11 . The second aeration channel  8  is correspondingly delimited towards the first aeration channel  7  by the partition wall  11  and, on the side thereof remote from the first aeration channel  7 , by an inner wall  12  of the lower part  5 . 
     The second aeration channel  8  comprises on the side thereof remote from the bottom  9  an annular step  13 , into which may be inserted an annular aeration ring  14 , which closes off the second aeration channel  8  upwardly in a vertical direction. The aeration ring  14  consists of a sintered porous material which forms the gas outlet openings of the second aeration element  4 , which takes the form of a “microsparger”  15 . The aeration ring  14  correspondingly comprises gas outlet openings, the diameter of which is less than 0.1 mm. 
     The upper part  6  positionable on the lower part  5  closes the first aeration channel  7  and forms with the latter the first aeration element  3 . To this end, the upper part  6  comprises gas outlet openings  36  in the region of the aeration channel  7 , the diameter of which openings is greater than 0.1 mm. The first aeration element  3  consequently forms a “ring sparger”  16 . 
     In the region of the second aeration channel  8 , the upper part  6  comprises segment-shaped openings  17 , which leave the aeration ring  14  exposed in the substantial regions thereof comprising the gas outlet openings  36 . 
     Sealing between the lower part  5  and upper part  6  is provided by in each case arranging seals  18 ,  19 ,  20 , which take the form of O-ring cord seals or O-rings, on the walls  10 ,  11 ,  12 . 
     The first aeration channel  7  comprises a radially extending first inflow  21  which leads into a tube connection  22 . The second aeration channel  8  correspondingly comprises a second radially extending inflow  23  which leads into a tube connection  24 . Nonreturn valves (not shown) may be arranged in the tube connections  22 ,  24  or in the inflows  21 ,  23 . 
       FIGS. 4 and 5  show two further exemplary embodiments of the aeration device which enable any desired scalability of the aeration device for transition from a smaller to a larger effective reactor volume. Said scalability is achieved on the one hand by varying the number of gas outlet openings  36  in the ring sparger  3  and on the other hand by the number and area of the segment-shaped openings  17  of the aeration ring  14 , in which the porous, gas-permeable material is located. The aeration ring  14  preferably comprises one gas passage opening  36  per 10 liters of effective reactor volume, while the area of the segment-shaped openings  17  comprising porous material preferably amounts to 2 to 2.5 cm2 per 10 liters of effective reactor volume. 
       FIG. 6  shows by way of example a bioreactor  25 , which for example takes the form of a flexible pouch for single use and comprises a stirrer  26 , which may be driven from outside, with stirrer blades  27 . The bioreactor  25  comprises an interior  30 , on the bottom  29  of which is arranged a stirrer flange  31 . The stirrer shaft  28  is mounted rotatably in the stirrer flange. The aeration device  1  is pushed with its central opening  32  onto a shoulder  33  of the stirrer flange  31 . Gas is supplied via a first inflow line  34  to the first inflow  21  and via a second inflow line  35  to the second inflow  23 , which gas emerges from the aeration device  1  and forms bubbles in the liquid medium  37  in the interior  30 . 
     Further inflows and outflows and open- and closed-loop control devices are not shown. 
     In a preferred embodiment, the dimensioning ratio between the diameter of the aeration device  1  and the diameter of the bioreactor  25  preferably amounts to between 0.1 and 0.5, particularly preferably to 0.240. The dimensioning ratio between the aeration device  1  and the diameter of the stirrer blades  27  amounts to between 0.4 and 0.7, preferably to 0.622. 
     In one preferred design of the aeration device, the upper and lower part of the aeration device is manufactured from a plastics material sterilizable with gamma radiation, preferably polycarbonate, while the porous material in the segment-shaped openings  17  consists of polyethene. 
     In further embodiments according to  FIGS. 7 and 8 , the aeration device  1  may be fastened, optionally using sealing elements, via a screw, bayonet, latch, clamp, adhesive or clip connection on the lower part  5  of the aeration device  1  in a circular opening in the lower part of the bioreactor  25  and optionally replaced after use. In these embodiments, the lower part  5  comprises a continuous, circular bottom ( 9 ′). The bottom  9 ′ may be firmly connected to the bottom  9  or, instead of the annular bottom  9  shown in  FIGS. 2 and 3 , may form the bottom of the lower part  5 . For the purpose of inserting the aeration direction into the lower part of the bioreactor, it is advantageous for at least part of the bottom  29  of the bioreactor  25  around the circular opening to be manufactured from a rigid material. The aeration device  1  is fastened in fluid-tight manner in the bioreactor bottom  29  by latching via the peripheral latching lug  38  or screwing via the thread  41  of the central piece  39 ,  40  of the aeration device  1  with the clamping part  41 ,  42 . This embodiment permits flexible insertion and replacement of the aeration device in both single- and multiple-use bioreactors.