GB2178971A - Floating magnetic stirrer for culture medium - Google Patents

Abstract

A stirrer apparatus for stirring culture medium has a flask 12 with a lid 20, a floating magnetic stirrer 22 responsive to a moving magnetic field, and a moving field generator including poles 16 and coils 18. A guide system is provided for the stirrer including a rod 30 which extends upwardly from the stirrer and a tube 40 which extends through the lid, the rod extending into and being rotatable in the tube; the tube has a closed upper end. In a second embodiment, Figure 6 (not shown), the guide system includes a rod which depends from the lid and extends into a tube sealed to the stirrer. <IMAGE>

Description

SPECIFICATION Magnetic stirrer apparatus with improved stirring action Field of invention The present invention relates to magnetically driven stirrer apparatus wherein the stirrer is buoyant.

Background to the invention US Patent No. 4,465,377 discloses apparatus for stirring liquid material, specifically culture medium. As therein noted, liquid culture medium provides for the growth of cells from nutrients which are contained in the medium. The stirring action which is to be imparted to such liquid culture medium is not a violent stirring, but is a gentle stirring, having as goals not only the stirring of the liquid culture medium and exposure of all cells to the gas above the liquid suface, but the avoidance of damage to the cells, such as would be occasioned by violent agitation, or by crushing of cells, as between two relatively moving parts.In that patent, there is disclosed a flask, with a buoyant, magnetically actuable stirrer within the flask, and a guide rod or shaft extending generally axially of the flask from top to bottom, the stirrer being movable along the guide rod or shaft as the liquid level is varied within the flask. The floating stirrer in some embodiments comprises a magnetic element, and on the exterior of the flask there is provided means for generating a rotating magnetic field to cause rotation of the magnetic element and the buoyant stirrer of which if forms a part. In some embodiments, a guide rod, supported in a lid of the flask, extends to the bottom of the flask, and passes through the buoyant stirrer.In another embodiment, a rotatable drive shaft is supported from the lid, and has a floating stirrer drivingly connected to it for rotation with it, the driving connection permitting movement of the stirrer along the drive shaft as the liquid level changes.

The structure disclosed in the aforementioned patent specification while generally providing for satisfactory operation, has been found to be capable of improvement. For example, although the described structure is constructed so that there is reduced danger of the crushing of cells as between relatively movable elements, the construction has not proven as free of risk as is desirable. In that construction, for example, the engagement between the structure of the floating stirrer and the guide rod or shaft was above the level of the liquid. While this construction minimised the risk of cell damage by liquid entering between the rod or shaft, on the one hand, and the floating stirrer on the other hand, the risk of crushing the cells was not completely eliminated.

A further improvement which is desirable is in connection with the flow of the liquid in the flask.

Preferably rotation of the stirrer effects a "Thomson Secondary Flow", causing liquid to be directed generally outwardly by the stirrer, the liquid then striking the walls of the flask and travelling downwardly towards the bottom and then spiralling upwardly along and about the axis of the flask to the stirrer, thereby providing for circulation and stirring of substantially all of the liquid culture medium in the flask. This is important since it is highly desirable that all of the cells, or as a high proportion of the cells as possible, be exposed to the gaseous atmosphere which exists at the gas-liquid interface in the flask.

Where the stirrer or impeller has a gas at or near its axis of rotation as in the aforementioned patent specification, it has been now recognised that this interferes with the generation of the relatively ideal circulation described above to the possible detriment of the cell proliferation.

Summary of the invention The present invention provides a magnetic stirrer apparatus which includes a flask, a floating magnetic stirrer, means for causing rotation of the stirrer such as means for generating a moving magnetic field, and, further, provides for guiding of the buoyant stirrer so that it rotates about an axis extending through the flask, generally perpendicularly to the liquid surface, and is able to move along that axis, with change in liquid level. The guiding is effected by a guide structure which includes, in a preferred embodiment, a guide rod extending only upwardly from the buoyant stirrer, and into a tube carried by the flask, particularly by a lid on the flask.The tube carried by the flask has its lower end positioned sufficiently above the highest level of the liquid in the flask so that there is no significant risk that liquid, including cells, will ever engage cooperating surfaces of the guide rod and guide tube. In this embodiment, there is no structure extending below the buoyant stirrer and stirrer extends without a gap across the axis of rotation.

In an alternate embodiment the buoyant stirrer is provided with a central depending tube, closed at its lower end so that the tube has no liquid within it. The lower end of the tube is substantially above, the bottom of the flask. A guide rod is fixed to the flask, preferably to the lid of the flask, and extends downwardly, entering the guide tube. Stirrers without gaps extend adjacent the depending tube.

Among the objects of the present invention is the provision of a magnetic stirrer apparatus having bearing surfaces of guide means located so that there is no substantial risk of cells becoming crushed between the bearing surfaces.

Another object of the present invention is the provision of such a stirrer apparatus which provides for enhanced, substantially idealistic liquid circulation.

Still another object of the present invention is to provide a stirrer apparatus with a buoyant magnetic stirrer which will provide for enhanced fluid flow, without disturbance of the natural circulation pattern of a floating rotating stirrer.

The invention will now be described by way of example with reference to and as illustrated in the accompanying drawings.

Figure 1 is a perspective view of a magnetic stirrer apparatus in accordance with the present invention, Figure 2 is a cross-sectional view taken on the line 2-2 of Figure 1, Figure 3 is a cross-sectional view taken on the line 3-3 of Figure 2, Figure 4 is a cross-sectional view taken on the line 4-4 of Figure 2, Figure 5 is a cross-sectional view, with parts broken away, taken on the line 5-5 of Figure 4, and Figure 6 is a cross-sectional view, with parts broken away, showing an alternate embodiment of the apparatus.

Detailed description of drawings Referring now to the drawings, wherein like or corresponding reference numerals are used for like or corresponding parts throughout the several views, there is shown in Figure 1 a magnetic stirrer apparatus 10 including a flask 12 and a lid 20. A support base 14 is provided for the flask 12, and a plurality of poles 16 are provided, the poles being made of magnetisable material, and each having a coil 18 near the bottom thereof. The coils 18 are connected to electric circuitry in known manner to create a rotating magnetic field which extends into the flask 12. The poles 16 may have horizontal portions 16a which extend beneath the support base 14, as shown in Figure 2.

Also shown in Figure 2 is the flask 12, which is of generally cylindrical configuration, having a bottom 12a, and a peripherally extending lip 12b. On the lip 12b, there may be seen the lid 20.

A floating magnetic stirrer 22 is provided, which includes a generally cylindrical hollow member 24 to which is attached a magnetic bar 26.

A guide rod 30 extends upwardly from the upper surface of the member 24. As shown in Figure 3, the member 24 is cylindrical, and the guide rod 30 is placed on and extends along the axis of cylindrical hollow member 24. As shown in Figure 2, the guide rod 30 is attached to cylindrical hollow member 24 by means 32, which may be welding, when the cylindrical hollow member 24 and the guide rod 30 are of, for example, stainless steel.

Referring again to Figure 4, it will be seen that the bar magnet 26 extends diametrically across the lower surface of the cylindrical hollow member 24.

The bar magnet 26 functions as a stirrer or impeller and is continuous from end to end thereof, having no gap at the axis of rotation.

The lid 20 has a central aperture 34 therein, and a guide tube 40 extends through the lid 20, being secured to it by the attachment means 42, which may be welding, solder, adhesive, etc., depending upon the materials of which lid 20 and guide tube 40 are made.

Guide tube 40 is closed at its upper end 44, its lower end 46 being at a location which is above the upper surface of the cylindrical hollow member 24 and the attaching means 32 at the highest level to which the liquid L in flask 12 will be permitted to rise. As is well known, the flask is partially but not completely filled, and after stirring, a small part of the liquid culture medium may be withdrawn, and replaced by a substantially equal amount of liquid: hence, the liquid level varies somewhat, but within a limited range, such as approximately the middle third of flask 12.

As shown in Figure 3, the guide rod 30 extends into the guide tube 40 with some smali clearance. This permits the guide rod 30 to move axially within guide tube 40, and also permits the guide rod 30 to rotate within the guide tube 40. Guide tube 40 may be of stainless steel, plastic, etc., and if it is of plastic, may be either clear or opaque.

As shown in Figure 5, the magnetic bar 26 is of known construction, being magnetised steel of octagonal cross-sectional shape. It is provided with a TeflonR sheath 26a which is coated with a silicone layer 26b, the latter being adhered by adhesive 28 to the bottom surface of the cylindrical hollow member 24.

In operation, the floating stirrer 22 and liquid L are provided in the flask 12, after which the lid 20 is positioned above the upper end of guide rod 20 and lowered so that the guide rod 30 extends into the guide tube 40, lid 20 engaging the lip 1 2b of flask 12.

The rotating field generating means including poles 16 and coils 18 is energised, to produce a rotating magnetic field which causes the magnet 26 to rotate.

Magnet 26, which functions as an impeller and which is the lowest part of the buoyant stirrer 22, causes stirring of the liquid L within the flask 12 in the manner above discussed, that is, by impelling the liquid outwardly to the walls of flask 12 and then downwardly to the bottom 1 2a and then upwardly, generally along and about the axis of flask 12. As is apparent, the portion of guide rod 30 and guide tube 40 which are axially coextensive are remote from the upper surface of the liquid L so that there is no significant risk of liquid culture medium L entering between such surfaces, thereby avoiding any possibility of crushing of cells in the liquid L.Additionally, since there is no structure below the magnetic-impeller 26, and since it is continuous and with a gap, there is no obstruction to axial upward flow, so tha the flow of the liquid culture medium is ideal or close to ideal.

Consequently, all or substantially all of the cells in the liquid culture medium rise to the surface of the liquid, which defines the interface between the liquid L and the gaseous medium above it and are there exposed to the gaseous medium.

In Figure 6 there is shown a portion of an alternate embodiment of a stirrer apparatus 50, the flask 1 2 being shown broken away, and the poles 16 and coils 18 being omitted for clarity. In the apparatus 50, a buoyant stirrer 52 is provided, comprising a cylindrical hollow member 54 having a guide tube extending there through, preferably along the axis there of. The upper end 62 of guide tube 60 is at the upper surface of the cylindrical hollow member 54, guide tube 60 having a closed lower end 64, and being in sealing engagement with the upper wall 54a and the lower wall 54b of the cylindrical hollow member 54. The cylindrical hollow member 24 is thereby hermetically sealed, providing a float, and the guide tube 60 is not subject to having any of the liquid L enter into it. To the bottom of the hollow cylindrical member 54 there are secured a pair of substantially parallel, spaced bar magnets 26, which serve as both magnetic field driven members and as impellers. Bar magnets 26 are each continuous, and are closely adjacent the guide tube 60.

The lower end 64 of guide tube 60 is substantially above the bottom 1 2a of flask 12, so that, as in the first embodiment, there is unobstructed flow of liquid in the region along and about the axis of the flask which extends upwardly from the bottom 12a. This unobstructed region changes length with changes in liquid level, but is of substantial extent even at the lowest level of liquid L, so that the circulatory flow is at or close to ideal, providing exposure of substantially all cells to the gaseous medium.

A lid 20' is provided, having a guide rod 70 extending downwardly from the central part thereof, and into the guide tube 60.

In operation, the stirring apparatus 50 functions similarly to the stirrer apparatus 10. The buoyant stirrer 52 is caused to rotate the magnet impellers 26 causing the above-noted outward flow of fluid to the walls of the flask 12 from closely adjacent the axis of rotation.

Because of the provision of the region of unobstructed flow above the bottom 1 2a on the flask axis and the impellers without gaps, the circulatory stirring motion will be at most minimally disrupted from the ideal or close to ideal pattern achieved by the apparatus 10.

Apparatus 50 even with depending tube 60 nevertheless provides for substantial circulation so that substantially all of the cells in the liquid L are exposed to the gaseous medium above the surface thereof.

Guidance of the buoyant stirrer 52 is provided by the guide rod 70 entering into the guide tube 60.

To summarise, the construction of the first embodiment provides that all of the guide structure is in the gaseous atmosphere above the liquid and the flask, and is above the floating magnetic stirrer; the impeller is continuous being without a gap at the axis of rotation. There is thereby achieved ideal or close to ideal fluid stirring and circulation and no practical risk of crushing of cells of a liquid culture medium.

In the second embodiment, a guide structure is provided which extends less than the full distance between the floating magnetic stirrer and the bottom of the flask, leaving an unobstructed fluid flow region along the axis above the bottom of the flask, and has a pair of continuous impellers so that improved stirring and liquid circulation is achieved in comparison to prior art devices, and there is only a low risk of cell damage, as by crushing between surfaces of the guide elements.

Claims (29)

1. Apparatus for stirring liquid such as a culture medium comprising: a flask, buoyant magnetically attractable stirrer means for stirring liquid medium in said flask, drive means for rotating said stirrer means, and guide means for guiding said stirrer means for rotation about an axis as said stirrer is rotated by said rotating means said guide means being wholly above the liquid level in said flask.

2. Stirring apparatus as claimed in claim 1, wherein the guide means comprises first and second guide elements, one said guide element being attached to and extending upwardly from said stirrer means.

3. Stirring apparatus as claimed in claim 2, further comprising support means carried by said flask for supporting the second guide element.

4. Stirring apparatus as claimed in claim 3, wherein the flask comprises a vessel having a lip defining an opening and the guide element supporting means engages said lip.

5. Stirring apparatus as claimed in claim 4, wherein the flask has a lid and the second guide element is carried by the lid.

6. Stirring apparatus as claimed in claim 4, wherein said first guide element comprises a rod and said second guide element comprises tubular means for slidable receiving said rod therein, and means for supporting said tubular means is provided on said flask.

7. Stirring apparatus as claimed in claim 6 wherein the tubular means rotatably receives the rod therein.

8. Stirring apparatus as claimed in claim 2, wherein the first guide element comprises a rod, the second guide element comprises tubular means for rotatably and slidably receiving at least a part of said rod therein, and support means for supporting said tubular means is provided on said flask.

9. Stirring apparatus as claimed in claim 8, wherein the support means comprises a lid engaging said flask.

10. Stirring apparatus as claimed in claim 9, wherein the tubular means extends through said lid.

11. Stirring apparatus as claimed in claim 8, wherein the tubular means has a closed upper end.

12. Stirring apparatus as claimed in claim 1, wherein the stirrer means comprises a continuous impeller.

13. Stirring apparatus as claimed in any of claims 1 to 12 wherein there is provided fluid path means for permitting an unobstructed flow of liquid in a region along the axis of the flask extending upwardly from the bottom thereof.

14. Stirring apparatus as claimed in claim 13, wherein said guiding means comprises a guide rod and a guide tube and means for connecting one of said guide elements to said buoyant stirrer and the other of said guide elements to said flask.

15. Stirring apparatus as claimed in claim 13, wherein the fluid path means comprises the lowest part of said buoyant stirrer means and the guide means is spaced from the bottom of said flask.

16. Stirring apparatus as claimed in claim 13, wherein said buoyant stirrer means comprises a continuous impeller extending outwardly from the axis of rotation.

17. Stirring apparatus as claimed in claim 16, wherein said connecting means connects said guide rod to said buoyant stirrer means.

18. Stirring apparatus as claimed in claim 15, wherein said connecting means connects said guide tube to said buoyant stirrer means and the lowest part of said stirrer means comprises the lower end of said guide tube.

19. Stirring apparatus as claimed in any of claims 1 to 12 wherein the stirrer comprises only continuous impeller means extending outwardly from the rotational axis of the stirrer for causing movement of liquid in the flask.

20. Stirring apparatus as claimed in claim 19, wherein said apparatus includes a guide structure extending only above the stirrer which comprises a rod extending upwardly from said stirrer.

21. Stirring apparatus as claimed in claim 20, wherein said guide structure further comprises tubular means carried by said flask and receiving said rod therein.

22. Stirring apparatus as claimed in claim 21, further comprising a lid on said flask wherein said tubular means is carried by said lid.

23. Stirring apparatus as claimed in claim 22, wherein said tubular means extends through said lid.

24. Stirring apparatus as claimed in claim 23, wherein said tubular means comprises a tube having a closed upper end.

25. Stirring apparatus as claimed in claim 24, further comprising means for joining said tube to said lid.

26. Stirring apparatus as claimed in claim 22, wherein said tubular means comprises a tube having a closed upper end.

27. Stirring apparatus as claimed in claim 26, wherein the lid is hermetically joined to said tube.

28. Stirring apparatus as claimed in claim 19, wherein the impeller means consists of a single impeller.

29. Stirring apparatus as claimed in claim 19, wherein the impeller means consists of a pair of spaced, parallel impellers.