Agitating – Stirrer within stationary mixing chamber – Magnetic stirrer
Reexamination Certificate
1998-10-13
2001-01-23
Popovics, Robert (Department: 1723)
Agitating
Stirrer within stationary mixing chamber
Magnetic stirrer
C422S105000, C435S288400
Reexamination Certificate
active
06176609
ABSTRACT:
BACKGROUND
1. Field of Invention
This invention provides a method, devices and machines to uniformly and simultaneously mix in vessels. The purpose is to provide a robust method, economical devices and very simple machines to uniformly stir the contents of one vessel or thousands of vessels or microplate wells (6 well, 12 well, 24 well, 48 well, 96 well, 384 well, 864 well, 1536 well, 10,000 well and the deep well, “U” bottom, “V” bottom, PCR and other versions of those microplates) at the same time.
2. Description of Prior Art
Suspending particulates in liquids, breaking up aggregates, aeration of gases in liquids, dissolving solids in liquids, emulsifying two liquids or mixing liquids together has usually been accomplished in large vessels, bottles, flasks and test tubes by magnetic horizontal spin stirring, orbital shakers, vortexing, rocking platforms, bubblers or vibrators. In an effort to miniaturize many of the operations that were done in bottles, flasks and test tubes, scientists have shifted to multi well microplates (6, 12, 24, 48, 48 deep well, 96, 96 deep well, 384, 864, 1536 and 10,000 wells/microplate). Microplates are now commonly used in a wide variety of scientific applications to act as mini-reaction vessels for liquid assays. However because of the combination of the small well diameter, the tall height of the column of liquid and the significant attraction of liquid surface tension forces to the walls of small diameter wells (especially in the 48, 96, 384, 864, 1536 and 10,000 well microplates) it is not possible to adequately resuspend particulates, stimulate the growth of microorganisms, break up aggregates, break open cells, aerate gases in to liquids, emulsify two liquids, mix two liquid reagents, or to dissolve a solid in a liquid by simple agitation on an orbital shaker, vortexer, rocker platform, bubbler or by vibration without generating a force so violent that it would throw the liquids out of the miniature vessels. Magnetic horizontal spin stirring has been adapted to 96 well microplates by VARIOMAG-USA. They put spinning permanent magnet stirrers into the wells of a 96 well microplate and place the 96 well microplate on a magnetic stirring system with an individual modulated (driving) electromagnetic stir point engineered under the center of each well. The placement of the wells exactly over a stir point is critical so the spinning stirrers don't hit the well walls and lose synchronization with the driving electromagnetic field, causing them to vibrate in the wells. If they hit the well wall the whole stirrer has to be stopped repositioned and slowly started spinning again. Often when the stir point system is rapidly spinning, the stir magnets in individual wells get out of synchronization with the driving electromagnetic field for no apparent reason or due to the vibration of the stirring action moving the plate. Part of this sensitivity phenomena is due to the physics of the interaction of the magnetic fields of the driving electromagnet and the spinning magnetic stirrer which line up parallel to each other, thus resulting in a weaker magnetic coupling than if the poles were directly opposed to each other. This weak magnetic coupling also is demonstrated if there is a differential viscosity between the liquids of different wells of the same microplate, as this will slow the stirrers in those wells and throw those magnetic stirrers out of sync. The cost of this magnetic stir point system is $2,400.00 for each 96 well plate and the cost of the individual stirring magnets for each well is $2.45 thus bringing the total cost to stir each plate to $2,635.00. Furthermore a unique stir point configuration (6, 12, 24, 48, 96, 384, 1536, and 10000 wells) is required for each well configuration of the microplate well format used. Because of these technical and cost considerations this system has not been widely used. Another way to provide adequate mixing in microplates is by pipetting the contents of each well up and down. This can be done manually or by robotic work stations. There are several robotic work stations that will do this pipet mixing operation but they will just mix 4 to 12 wells at a time and the pipets must be washed or changed between wells. Recently Robbins Scientific introduced the “Hydra” work station which will pipet and mix 96 wells at a time but it costs ~$30,000 and is still laborious as the pipets must be washed between wells. Furthermore it would be economically impossible to do continuous mixing of multiple microplates simultaneously by pipetting. In addition it would be difficult to place a large robotic workstation in an incubator if microorganisms were the objects being mixed while culturing. Thus the miniaturization of continuous mixing processes on a large number of microplates remains impractical up til now.
SUMMARY OF THE INVENTION
Objects and Advantages
The present invention provides a method of mixing the contents of each of a two-dimensional array of vessels, each vessel having a vertical axis as defined when the vessel is disposed for the mixing of said contents, the method comprising the steps of:
(a) placing magnetic stirrers within said vessels; and
(b) when the vessels are disposed for the mixing of said contents, rotating a permanent magnet about a non-vertical axis of rotation that is so disposed adjacent the array that said rotation of the magnet provides magnetic flux lines that rotate through 360 degrees within a non-horizontal plane within each of the vessels to thereby cause the magnetic stirrers therein to tumble in at least one direction that is other than about the vertical axis of each vessel;
whereby the contents of each vessel containing a said magnetic stirrer are mixed by the tumbling of said magnetic stirrer.
The present invention also provides a system for mixing the contents of each of a two-dimensional array of vessels, each vessel having a vertical axis as defined when the vessel is disposed for the mixing of said contents, the system comprising: means for receiving an array of vessels in a disposition for the mixing of said contents; a permanent magnet disposed in relation to the receiving means for rotation about a non-vertical axis of rotation that is so disposed adjacent the array that said rotation of the magnet provides magnetic flux lines that rotate through 360 degrees within a non-horizontal plane within each of the vessels to thereby cause magnetic stirrers therein to tumble in at least one direction that is other than about the vertical axis of each vessel; and means for so rotating the permanent magnet; whereby the contents of each vessel containing a said magnetic stirrer are mixed by the tumbling of said magnetic stirrer.
Thus it is the object of the method, devices and machines to provide a very simple process of uniformly mixing the contents of thousands of vessels and microplate wells (6 well, 12 well, 24 well, 48 well, 48 deep well, 96 well, 384 well, 864 well, 1536 well, 10,000 well and the deep well, “U” bottom, “V” bottom, PCR and other versions of those microplates) at the same time. We have made stainless steel magnetic stir discs, bars and dowels of different dimensions, shapes and with magnetic field orientations through the long axis so that they will fit into any vessel and provide a vigorous stirring action when they are tumbled end over end through the long axis in a vertical magnetic field(s). By making the magnetic stirrers nearly the same diameter or length as the diameter of the vessel they are stirring or by putting multiple magnetic stirrers into a single vessel a very significant stirring action is effected when they tumble through the magnetic axis. We have discovered that while stainless steel is commonly thought to be non-magnetic, several stainless steels that have been “hardened”, “spring tempered” or “cold worked” are magnetic. Because stainless steel is corrosion resistant, it maybe used as a magnetic stirrer without any protective coating like teflon thus making stainless steel magnetic stirrers very inexpensive.
Magnetic tumbling or stirring i
Cleveland Patrick H.
Markle John R.
Callan Edward W.
Popovics Robert
V & P Scientific, Inc.
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