Apparatus and method for magnetically coupling bioreactor drive heads

Abstract

A vessel includes an interior volume configured to contain a liquid and a magnetically driven impeller (20) located within the interior volume. The impeller includes a rotatable base portion (22) with blades (28), a rotatable shaft (26), and a ferruginous connector (24). The impeller may be coupled to an external motor and rotated via a magnetic coupling between the iron connector and a selectively magnetizable drive head connector of the external motor to agitate the liquid in the internal volume. The iron connector is not a permanent magnet.

Description

Technical Field

[0001] Embodiments of the present invention generally relate to bioreactor systems and methods, and more particularly, to an apparatus and method for selectively magnetically coupling a drive head to an impeller in stirred tank bioreactor and mixer systems. Background Art

[0002] In the biopharmaceutical industry, single-use or disposable containers are increasingly used. Such containers can be flexible or collapsible plastic vessels or bags supported by external rigid structures (such as stainless steel shells or shells). The use of sterile disposable bags eliminates the time-consuming steps of cleaning the shell and reduces the chance of contamination. The bag can be positioned in a rigid shell and filled with the desired fluid for mixing. The agitator assembly arranged in the bag is used to mix the fluid. Existing agitators are top-driven (with a shaft extending downward into the bag, one or more impellers are mounted on the shaft) or bottom-driven (with an impeller arranged in the bottom of the bag, which is driven by a magnetic drive system or motor positioned outside the bag and / or vessel). Most magnetic agitator systems include a drive motor having a rotating magnetic drive head outside the bag and a rotating magnetic agitator (also referred to as "impeller" in this context) inside the bag. The movement of the magnetic drive head realizes torque transmission, and therefore the rotation of the magnetic agitator, thereby allowing the agitator to mix the fluid in the vessel.

[0003] However, in current designs, the impeller containing the expensive permanent magnets is located within a disposable bag and is discarded with the bag after a single use. In addition, in known systems, there is a gap between the magnets of the drive head and the permanent magnets of the impeller to accommodate design tolerances. This magnetic gap can reduce the holding torque and speed of the drive motor. In addition, increasing the torque and speed of the known magnetic drive head and impeller is challenging because increasing the number and size of the magnets may not be feasible. The known magnetic drive head requires a multi-component lifting device to couple the drive head with the impeller for use. Finally, the disengagement of the magnets of the drive head and the permanent magnets of the impeller is also a difficult process, requiring considerable force and / or additional equipment.

[0004] In view of the above, a need exists for an impeller and drive head that are selectively magnetically coupleable without requiring an impeller with permanent magnets or expensive lifting equipment and that do not include significant magnetic gaps when coupled. Summary of the invention

[0005] In one embodiment, a vessel includes an interior volume configured to hold a liquid and a magnetically driven impeller located within the interior volume. The impeller includes a rotatable base portion having at least one blade, a rotatable shaft, and at least one ferrous connector. The impeller is connectable to an external motor and rotated via a magnetic coupling between the ferrous connector and a selectively magnetizable drive head connector of the external motor to agitate the liquid in the interior volume. The ferrous connector is not a permanent magnet.

[0006] In another embodiment of the present invention, a method for coupling an impeller of a vessel to a drive motor is provided. The method includes placing a drive head of the drive motor in a demagnetized state near the impeller, the impeller including a ferrous impeller connector, which is located within the interior volume of the vessel. Next, the method includes magnetizing the drive head to create a magnetic coupling between the drive head connector of the drive motor and the ferrous impeller connector.

[0007] In yet another embodiment, a method of agitating a fluid in a vessel is provided. The method includes rotating a drive head of a drive motor to rotate an impeller located within an interior volume of the vessel. Rotation of the impeller is accomplished via a magnetic coupling between a selectively magnetizable drive head connector of the drive motor and a ferrous connector of the impeller.

[0008] In an additional embodiment, a method of disconnecting an impeller of a vessel from a drive motor is provided. The method includes demagnetizing a drive head of the drive motor to remove a magnetic coupling between a drive head connector of the drive motor and a ferrous impeller connector of an impeller located within an interior volume of the vessel. The drive motor can then be moved away from the impeller. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] The present invention will be better understood by reading the following description of non-limiting embodiments with reference to the accompanying drawings, in which:

[0010] Figure 1 It is a front elevation view of the bioreactor system.

[0011] Figure 2 shows the Figure 1 A front elevation view of a prior art impeller compatible with a bioreactor system.

[0012] FIG. 3 is a side cross-sectional view of the prior art impeller of FIG. 2 .

[0013] 4 is an enlarged side cross-sectional view of the portion of the prior art impeller of FIG. 2 within rectangle A. FIG.

[0014] Figure 5 It is an exploded elevation view of an impeller, an iron connector and a drive head connector according to an embodiment of the present invention.

[0015] Figure 6 According to an embodiment of the present invention Figure 5Exploded elevation view of a device in which the impeller, iron connector and drive head connector are depicted in dotted lines.

[0016] Figure 7 According to an embodiment of the present invention Figure 5 and Figure 6 A side cross-sectional view of the impeller, iron connector and drive head connector.

[0017] Figure 8 According to an embodiment of the present invention Figure 7 The impeller, iron connector and the part of the drive head within rectangle B that are in the magnetized state.

[0018] Fig. 9 According to an embodiment of the present invention Figure 7 The impeller, iron connector and the portion of the drive head within rectangle B that is in a demagnetized state. DETAILED DESCRIPTION

[0019] Reference will now be made in detail to exemplary embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numerals are used throughout the drawings to refer to the same or like parts.

[0020] As used herein, the terms "flexible" or "collapsible" refer to structures or materials that are pliable or capable of bending without breaking, and may also refer to compressible or expandable materials. An example of a flexible structure is a bag formed from a polyethylene film. The terms "rigid" and "semi-rigid" are used interchangeably herein to describe "non-collapsible" structures, that is, structures that do not fold, collapse, or otherwise deform to significantly reduce their elongated dimensions under normal forces. Depending on the context, "semi-rigid" may also refer to structures that are more flexible than "rigid" elements, such as bendable tubes or catheters, but are still structures that do not collapse longitudinally under normal conditions and forces.

[0021] "Vessel" as the term is used herein means a flexible bag, a flexible container, a semi-rigid container, or a rigid container, as the case may be. The term "vessel" as used herein is intended to include bioreactor vessels having flexible or semi-rigid walls or wall portions, single-use flexible bags, and other containers or conduits typically used in biological or biochemical processes, including, for example, cell culture / purification systems, mixing systems, media / buffer preparation systems, and filtration / purification systems.

[0022] As used herein, the term "bag" means a flexible or semi-rigid container or vessel that is used, for example, as a bioreactor or mixer for the contents inside. In this regard, embodiments of the present invention are suitable for use with bioreactors, mixers, and other devices or systems having an impeller inside the vessel and an external drive motor.

[0023] Reference Figure 1 , a bioreactor system 10 suitable for use with embodiments of the present invention is shown. The bioreactor system 10 includes a generally rigid bioreactor housing 12 mounted on top of a base 14 having a plurality of legs 16. The housing 12 may be formed of, for example, stainless steel, polymers, composite materials, glass, or other metals, and may be cylindrical in shape, although other shapes may be utilized without departing from the broader aspects of the present invention. In certain embodiments, the housing 12 may be a substantially rectangular mixer housing.

[0024] As shown, a single-use flexible vessel or bag 15 is disposed within the housing 12. As mentioned, the housing 12 can be any size (or shape) as long as it is capable of supporting the single-use flexible bioreactor bag 15. For example, according to one embodiment, the housing 12 is capable of accepting and supporting a 10-2000L flexible or collapsible bioprocessing bag assembly 20.

[0025] 2 and 3, a known impeller 100 is depicted that is commonly used with a bioreactor system 10. A flexible bag 15 houses the impeller 100, which is attached to a magnetic hub 110 at the bottom of the interior of the bag. The impeller 100 and the hub 110 (and in some embodiments, the impeller plate) together form an impeller assembly 120. A magnetic drive 130 external to the housing 12 provides the motive force for rotating the magnetic hub 110 and the impeller 100 to agitate the contents of the flexible bag 15. The magnetic hub 110 has a permanent impeller magnet 112, and the magnetic drive 130 includes a permanent drive magnet 132.

[0026] These known impellers 100 are limited because they require permanent magnets in both the magnetic hub 110 and the magnetic drive 130, which leads to several potential design problems. First, in certain applications, the number and size of the required permanent magnets may not be sufficient to support the required torque and impeller agitation speed. For example, due to size or cost constraints, increasing the number or size of permanent magnets may not be feasible. Second, the known drive head is connected and disconnected with the impeller 100 using a lifting device that requires considerable force and includes many parts, which contributes to the high cost of the magnetic drive 130. Third, the permanent magnets 112 in the magnetic hub 110 are discarded along with other consumables. As will be appreciated, the replacement cost of these permanent magnets 112 is high, and the cost of proper disposal can be high. Fourth, the vertical movement of the drive head requires a significant gap G (as depicted in Figures 3 and 4) between the magnets 112 of the magnetic hub 110 and the magnets 132 of the magnetic drive 130. The gap G is necessary to accommodate the tolerances of the structural elements that house and surround the magnets 112, 132 within the magnetic hub 110 and the magnetic driver 130, respectively.

[0027] Refer back Figure 1, the bag 15 includes an interior volume configured to contain a liquid and a magnetically driven impeller 20 located within the interior volume. Figure 5 and Figure 6 As shown in FIG. 1 , the impeller 20 includes a rotatable base portion 22 with at least one blade 28, a rotatable shaft 26, and at least one ferrous connector 24. The impeller 20 can be coupled to an external drive motor and rotated to agitate the liquid in the internal volume via a magnetic coupling between the ferrous connector 24 of the impeller 20 and the ferrous connector 34 of the selectively magnetizable drive head 30 of the drive motor. In an embodiment, the ferrous connectors 24, 34 are not permanent magnets.

[0028] exist Figure 5-9 In the embodiments depicted in FIG. 1 , the impeller 20 does not contain any permanent magnets. In these embodiments, the impeller 20 includes a plurality of ferrous connectors 24 in the base portion 22 of the impeller 20. The ferrous connectors 24 are spaced around a central aperture that accommodates the rotating shaft 26. Figure 5-9 , six (6) ferrous connectors 24 are equally spaced about the rotational axis 26. A different number and / or different arrangement of ferrous connectors 24 does not depart from the invention disclosed herein. In one embodiment, the ferrous connectors 24 are made of steel, but other ferromagnetic materials including, but not limited to, iron, cobalt, nickel, and alloys thereof do not depart from the scope of the present invention. In alternative embodiments, in addition to the ferrous connectors 24, the impeller 20 may include one or more permanent magnets (ideally fewer than in known impellers).

[0029] exist Figure 5-9 In the embodiment depicted in FIG. 1 , the impeller 20 includes three blades 28. However, as will be readily appreciated, the impeller 20 may include more or less than three blades. In certain embodiments, it may be feasible for the impeller 20 to include multiple layers or rows of blades. The blades 28 may have a variety of sizes, shapes, positions, and angles without departing from the present invention.

[0030] In an embodiment, the impeller 20 is configured for use with a drive head that may be selectively magnetizable. Such a drive head may be mechanically magnetizable, such as Figure 5-9 The drive head 30 depicted in FIG. 1 and described below, or in other embodiments, may utilize an electromagnet.

[0031] In certain embodiments, one or more electromagnets (not shown) may be employed in the selectively magnetizable drive head 30 in place of or in addition to permanent magnets. The electromagnet may include one or more solenoids having a ferromagnetic core that is substantially aligned with at least one ferrous connector 24 of the magnetically driven impeller 20. The flow of current to the solenoid may be terminated to turn off the magnet for coupling / disengagement, and then reopened to use the impeller. As will be appreciated, the current may be DC or AC, and the power source may be a battery or an outlet. The intensity of the current may vary depending on the agitation torque / RPM requirements of the vessel. In an embodiment, the electromagnet may be located within the drive head surrounding a rotatable drive shaft. In use, the drive head and shaft will rotate to rotate the impeller.

[0032] Refer back Figure 5 , the exemplary drive head 30 includes a first base portion 32 and a second base portion 38 that are rotatable about a drive shaft 36. In an embodiment, the base portions 32, 38 are made of a non-magnetic material, such as plastic or a non-magnetic metal. Although the drive head 30 and the impeller 20 are shown as having a substantially annular profile, other shapes, sizes, and proportions are possible without departing from the scope of the present invention.

[0033] As shown, the first base portion 32 and the second base portion 38 each have a plurality of ferrous connectors 34 equidistantly surrounding an aperture 31, 41 that receives the drive shaft 36. Each of the first base portion 32 and the second base portion 38 also includes a permanent magnet 40 extending radially from the drive shaft 36 to each ferrous connector 34. As described in more detail below, the base portions 32, 38 can be rotated relative to each other to magnetize / demagnetize the ferrous connectors 34.

[0034] Rotation of the base portions 32, 38 relative to each other aligns the ferrous connector 34 to generate a magnetic field through the ferrous connector 34 and the permanent magnet 40. More specifically, as Fig. 9 , rotating the first and second base portions 32, 38 of the drive head 30 such that the ferrous connectors 34 are aligned but the magnets 40 are oriented in opposite directions demagnetizes the drive head 30 by confining the magnetic field within the drive head 30. Thus, there is no longer a magnetic force pulling the ferrous connector 24 of the impeller 20 toward the ferrous connector 34 of the drive head 30, thereby allowing the impeller 20 to be removed.

[0035] This is accomplished by having adjacent magnets 40 within each of the first base portion 32 and the second base portion 38 having polarities arranged in opposite directions. In the depicted embodiment, half of the magnets 40 are aligned with the positive polarity end adjacent to the aperture that receives the ferrous connector 34 (see FIG. Fig. 9), and one half of the magnet is aligned with the positive polarity end adjacent to the aperture that receives the drive shaft 36 (see Fig. 9 40).

[0036] This arrangement of the polarity of the magnets 40 allows the user to adjust the position of the first base portion 32 whenever the ferrous connectors 34 are aligned as the first base portion 32 is rotated relative to the second base portion 38. Figure 8 and Fig. 9 In the depicted embodiment, each time the first base portion 32 is rotated approximately 60° relative to the second base portion 38, the ferrous connector 34 is aligned.

[0037] exist Figure 5-9 , the drive shaft 36 is retained within the central aperture 41 of the second base portion 38, and the drive shaft 36 is received in the central aperture 31 of the first base portion 32. The drive shaft 36 aligns the first base portion 32 and the second base portion 38 while also allowing rotation about the longitudinal axis of the drive shaft 36. In some embodiments, the material of the shafts 26, 36 is ferromagnetic, thereby allowing the shafts 26, 36 to facilitate a magnetic field generated therein.

[0038] In a particular embodiment, the shaft 36 is ferromagnetic and is held in place within the apertures 31, 41 via magnets 40. As will be appreciated, the shaft 36 is held with sufficient force to allow the base portions 32, 38 to rotate with the shaft 36 when the shaft 36 is rotated via the drive motor, while allowing the first base portion 32 to rotate around the second base portion 38 to selectively magnetize the drive head 30 for impeller coupling / disengagement. In certain embodiments, the central aperture 41 of the second base portion 38 may be a blind hole that terminates in a wall or surface that provides a stopper for the lower end of the shaft 36 to contact. Alternatively, the aperture 41 may include a non-magnetic surface or structure that contacts the lower end of the shaft 36. Similarly, the first base portion 32 may have a blind hole or a non-magnetic surface or structure that contacts the upper end of the shaft 36 to prevent vertical movement.

[0039] In use, the drive head 30 in a demagnetized state can be moved to a position below the impeller 20 via horizontal movement, as opposed to being lifted into place via a lifting device. The drive head 30 can then be magnetized to couple the drive head to the impeller. At this point, the motor can be actuated to rotate the shaft 36, which rotates the base portions 32, 38 of the drive head and in turn rotates the magnetically coupled impeller 20 to agitate the fluid in the vessel. Once agitation is complete, the motor is turned off and the drive head 30 is demagnetized by rotating the first base portion 32 relative to the second base portion 38. The drive motor can then be moved away from the impeller 20.

[0040] In an embodiment, the rotation of the first base portion 32 can be accomplished by hand by inserting a tool (e.g., a rod, etc.) into the circumferential aperture 42 of the first base portion 32, and then pushing the first base portion 32 to rotate (e.g., about 60 degrees) around the axis 36 until the drive head is in a demagnetized state. In other embodiments, the rotation of the first base portion 32 can be accomplished by a motor or a lever.

[0041] Refer again Figure 5-7 In some embodiments, the base portions 32, 38 also include additional alignment guide features in the form of an alignment receiver 33 and a slotted alignment guide 37 including a track 39. The alignment receiver 33 extends from the outer circumferential surface of the first base portion 32 and provides an aperture for receiving a fastener such as a bolt or pin (not shown) that extends through the aperture and into the track 39 of the alignment guide 37.

[0042] As shown, the alignment guide 37 extends from the outer circumferential surface of the second base portion 38 and defines a track 39 that receives the fastener while also allowing rotational movement of the fastener about the longitudinal axis of the drive shaft 36. The track 39 limits the rotational movement of the fastener to an operating angle A. In the depicted embodiment, the operating angle A is between approximately 60° and 120°, which is measured about the longitudinal axis of the drive shaft 36. In other words, the fastener, the alignment receiver 33, and the alignment guide 37 limit the rotational movement of the first base portion 32 relative to the second base portion 38 to an operating angle to magnetize or demagnetize the drive head.

[0043] exist Figure 5 and Figure 6 In the embodiment depicted in FIG, the first base portion 32 has two alignment receivers 33 disposed on opposite sides, and the second base portion 38 has two complementary alignment guides 37 disposed on opposite sides. However, as will be appreciated, embodiments may include more or fewer receivers 33 and guides 37 without departing from the scope of the present invention.

[0044] In another embodiment of the present invention, a method for coupling an impeller 20 of a vessel to a drive motor 30 is provided. The method includes placing a drive head 30 of the drive motor near the impeller 20, which is located within the interior volume of the bag 15. Figure 8 As shown in FIG. 1 , the drive head 30 is in a demagnetized state and the impeller 20 includes a ferrous impeller connector 24. Next, the method includes magnetizing the drive head 30 to create a magnetic connection between the drive head connector 34 of the drive motor and the ferrous impeller connector 24, such as Fig. 9 The demagnetized state of the drive head 30 prevents the magnetic field from radiating externally by closing the circuit within the drive head 30. In an embodiment, the ferrous connector 34 is not a permanent magnet.

[0045] In one embodiment, a drive head structure capable of rotatable magnetization may be used. Figure 8 The magnetization state moves to Fig. 9 The demagnetized state requires that the first base portion 32 be rotated relative to the second base portion 38 so that the ferrous connectors 34 in each base portion are aligned with each other about the drive shaft 36 and the magnets 40 in the first base portion 32 and the second base portion 38 are oriented in the same direction. When the ferrous connectors 34 in the first base portion 32 and the second base portion 38 are aligned and the polarities of the magnets 40 are oriented in the same direction, as shown in FIG. Figure 8 As shown in FIG. 1 , the iron connector 34 generates a magnetic force to pull the iron connector 24 of the impeller 20 toward the drive head 30. When the drive head 30 is in Figure 8 , the impeller 20 rotates with the drive head 30. In the depicted embodiment, the first base portion 32 and the second base portion 38 each have six (6) magnets 40. Alternative numbers or arrangements of magnets 40 within the drive head 30 do not depart from the scope of the present invention.

[0046] In other embodiments, it may be feasible to utilize other non-rotatable magnetization mechanisms, such as a slidable device. In still other embodiments, and as described above, an electromagnet may be used to selectively magnetize the drive head. In such embodiments, current would be applied to a solenoid within the base portion to selectively magnetize or remove the drive head for coupling / discoupling with the impeller.

[0047] In yet another embodiment of the present invention, a method of agitating a fluid in a bag 15 is provided. The method includes rotating a drive head 30 of a drive motor to rotate an impeller 20 located within an interior volume of a vessel. Rotation of the impeller 20 is accomplished via a magnetic coupling between a selectively magnetizable drive head connector 34 of the drive motor and a ferrous connector 24 of the impeller 20. In an embodiment, the connectors 24, 34 are not permanent magnets.

[0048] In an additional embodiment, a method of disconnecting an impeller of a vessel from a drive motor is provided. The method includes demagnetizing a drive head 30 of the drive motor via, for example, rotation of a first base portion 32 as described above to remove the magnetic coupling between a drive head connector 34 of the drive motor and an iron impeller connector 24 of an impeller 20 located within the interior volume of the vessel.

[0049] Compared to the existing impeller 100, the embodiments of the impeller 20 and the drive head 30 provide many benefits. First, the drive head 30 provides the opportunity to increase the holding torque by increasing the number of magnets 40 in the drive head 30. Therefore, the drive head 30 has an increased holding torque and can accommodate increased rpms beyond those known in the art. Next, the impeller 20 and the drive head 30 have relatively few and simple components, thereby reducing the cost and associated maintenance of the hardware required to contact the impeller with the drive head. In addition, the ferrous connector 24 in the impeller 20 is less expensive than a permanent magnet. This results in a cheaper replacement of the impeller 20. Finally, there is no vertical motion in the drive head 30 or the impeller 20. Therefore, a tight gap between the ferrous connector 24 and the ferrous connector 34 can be achieved, thereby further increasing torque and speed compared to known drive heads / impellers.

[0050] As used herein, an element or step recited in the singular and preceded by the word "one" or "an" should be understood as not excluding a plurality of said elements or steps, unless such exclusion is expressly indicated. In addition, reference to "one embodiment" of the present invention is not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the features of the narration. In addition, unless expressly indicated to the contrary, embodiments that "comprise," "include," or "have" an element or multiple elements having a particular property may include additional such elements that do not have that property.

[0051] This written description uses examples to disclose several embodiments of the invention (including the best mode), and also to enable those skilled in the art to practice the embodiments of the invention (including making and using any device or system and performing any incorporated method). The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. These other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements that are not significantly different from the literal language of the claims.

Claims

1. A vessel comprising: an internal volume configured to contain a liquid; a magnetically driven impeller within the interior volume, the impeller comprising a rotatable base portion having at least one blade, a rotatable shaft, and at least one ferrous connector; and wherein the impeller is coupleable to the external motor and rotated via a magnetic coupling between the at least one ferrous connector and a selectively magnetizable drive head connector of the external motor to agitate liquid in the internal volume; as well as Wherein the at least one ferrous connector is not a permanent magnet.

2. The vessel according to claim 1, wherein The magnetically driven impeller does not contain any permanent magnets.

3. The vessel according to claim 1 or 2, wherein: The at least one ferrous connector is a plurality of ferrous connectors formed in a base portion of the impeller, the ferrous connectors being spaced apart around the rotation axis.

4. The vessel according to any one of claims 1 to 3, wherein: The at least one ferrous connector is a steel connector or a plurality of steel cylinders.

5. The vessel according to any one of claims 1 to 4, wherein: The vessel is a bioreactor bag.

6. A method for coupling an impeller of a vessel to a drive motor, comprising: placing a drive head of the drive motor proximate an impeller located within the interior volume of the vessel, the drive head being in a demagnetized state and the impeller including at least one ferrous impeller connector; as well as The drive head is magnetized to create a magnetic coupling between a drive head connector of the drive motor and a ferrous impeller connector.

7. The method according to claim 6, wherein: The ferrous impeller connector is not a permanent magnet.

8. The method according to claim 6 or 7, further comprising: Demagnetizing the drive head so that there is no longer a magnetic connection between the drive head connector and the ferrous impeller connector; as well as Remove the drive motor from the impeller.

9. The method according to any one of claims 6 to 8, further comprising: The drive head is rotated to rotate the impeller via a magnetic coupling between the drive head connector and the ferrous impeller connector.

10. The method according to any one of claims 6 to 9, wherein: The impeller does not contain any permanent magnets.

11. The method according to any one of claims 6 to 10, wherein: The at least one ferrous impeller connector is a steel connector, and wherein the vessel is a bioreactor bag.

12. A method for agitating a fluid in a vessel, comprising: rotating a drive head of a drive motor to rotate an impeller within the interior volume of the vessel; as well as The rotation of the impeller is achieved via a magnetic coupling between a selectively magnetizable drive head connector of the drive motor and a ferrous connector of the impeller.

13. The method according to claim 12, wherein: The ferrous connector is not a permanent magnet.

14. The method according to claim 12 or 13, wherein: The impeller does not contain any permanent magnets.

15. The method according to any one of claims 12 to 14, wherein: The ferrous connector is a steel connector and the vessel is a bioreactor bag.

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