Patent Application
20070019502
1. Field of the Invention
The invention relates to an improved system and method for stirring suspended solids in a liquid media.
2. Description of the Related Art
Many medical diagnoses require that a fluid sample, such as a blood sample, be taken from a patient, cultured in a growth medium, and then examined for the presence of a pathogen believed to be causing the patient's illness. The growth medium provides nutrients that allow the pathogen, such as bacteria, virus, mycobacteria, mammalian cells or the like, to multiply to a sufficient number so that their presence can be detected.
In some cases, the pathogen can multiply to a large enough number so that it can be detected visually. For example, a portion of the culture can be placed on a microscope slide, and visually examined to detect for the presence of a pathogen of interest.
Alternatively, the presence of a pathogen or other organism can be detected indirectly by detecting for the presence of byproducts given off by the microorganism during its growth. For example, certain microorganisms such as mammalian cells, insect cells, bacteria, viruses, mycobacteria and fungi consume oxygen during their growth and life cycle. As the number of microorganisms increases in the sample culture, they naturally consume more oxygen. Furthermore, these oxygen consuming organisms typically release carbon dioxide as a metabolic byproduct. Accordingly, as the number of organisms present increases, the volume of carbon dioxide that they collectively release likewise increases.
Alternatively, instead of measuring the presence of carbon dioxide to detect the presence of an oxygen consuming microorganism, it is possible to measure a depletion in the concentration of oxygen in the sample of interest. The presence of oxygen consuming organisms can also be detected by measuring a change in the pressure in a sealed sample vial containing the sample of interest. That is, as oxygen in a closed sample vial is depleted by oxygen consuming organisms, the pressure in the sealed sample vial will change. The pressure will further change in the sample vial as the organisms emit carbon dioxide. Therefore, the presence of such organisms can be detected by monitoring for changes in pressure in the closed sample vial.
Several methods exist for measuring the increase of carbon dioxide in a sample to determine whether organisms are present in the sample. For example, an instrument known as the Bactec® 9050 manufactured by Becton Dickinson and Company detects changes in the color of an indicator to determine whether carbon dioxide is present in a sample. That is, each sample is collected in a respective sample vial containing an indicator medium having a chemical that reacts in the presence of carbon dioxide to change color. A light sensor then detects the color of the indicator medium in the sample vial when the sample vial is loaded into the instrument. If the sample contains an organism which emits carbon dioxide as a function of growth and/or metabolic activity, the reflected or fluorescent intensity of the indicator medium will change in response to the presence of carbon dioxide. The light sensor will therefore detect this change in intensity, and the instrument will thus indicate to an operator that an organism is present in the sample contained in the sample vial. Other examples of instruments for detecting the presence of organisms in a sample by measuring the changes in carbon dioxide in the sample are described in U.S. Pat. Nos. 4,945,060, 5,164,796, 5,094,955 and 5,217,876, the entire content of each of these patents being incorporated herein by reference.
An instrument employing an oxygen detecting technique is described in U.S. Pat. No. 5.567,598, the entire content of which is incorporated herein by reference. Instruments that are capable of detecting changes in the pressure in the sample vial are described in U.S. Pat. Nos. 4,152,213, 5,310,658, 5,856,175 and 5,863,752, the entire content of each of these patents being incorporated herein by reference. In addition, an instrument capable of detecting changes in carbon dioxide concentrations, changes in oxygen concentrations, and changes in pressures in the vessel is described in a U.S. patent application of Nicholas R. Bachur et al. entitled “System and Method for Optically Monitoring the Concentration of a Gas, or the Pressure, in a Sample Vial to Detect Sample Growth”, Ser. No. 09/892,061, filed on Jun. 26, 2001, and another instrument capable of detecting changes in carbon dioxide concentrations or changes in oxygen concentrations in the vessel is described in a U.S. Pat. No. 6,709,857, the entire contents of both being incorporated herein by reference.
It is noted that the results obtained by the organism detection techniques described above can be improved if the growth of the organism is enhanced to cause a greater production of carbon dioxide, a greater depletion of oxygen, or a greater change in pressure in the vessel. It is known that the biological activity of a solid sample in a liquid media can be enhanced by maintaining the solid sample in a suspended state. This can be accomplished by continuously stirring the solid-liquid mixture, which improves nutrient, waste and gas exchanges in the mixture.
Examples of stirring techniques are described in U.S. Pat. Nos. 5,586,823, 4,483,623 and 4,040,605, the entire content of each of these patents being incorporated herein by reference. Each of these techniques employs a magnetic stirrer that is placed in the vessel containing the sample and manipulated by a magnet to stir the sample in the vessel.
Although these stirring techniques may be somewhat effective in enhancing sample growth, a need exists for an improved system and method for stirring suspended solids in a liquid media to enhance sample growth and thus improve sample detection results.
In one embodiment, a system comprising one or more sample vessels is provided, the sample vessels comprising a liquid growth medium and a stirrer element, the stirrer element capable of being influenced by a magnetic force, and an incubation and measurement module comprising one or more openings for holding the one or more sample vessels. The incubation and measurement module further comprises at least two drive magnets associated with each of the sample vessels, and a magnet driver adapted to repeatedly move each of the at least two drive magnets toward and away from the surface of the associated sample vessel. The openings are configured to hold the sample vessels such that the longitudinal axis of the vessels are at an angle of less than 90° with the horizontal.
In another embodiment, a system comprising one or more sample vessels is provided, the sample vessels comprising a liquid growth medium and a stirrer element, the stirrer element capable of being influenced by a magnetic force, and an incubation and measurement module comprising one or more openings for holding the sample vessels. The incubation and measurement module further comprises at least two drive magnets associated with each of the one or more sample vessels and a magnet driver comprising a magnet shaft assembly that comprises a shaft and a plurality of the drive magnets. The drive magnets are coupled to the shaft in -pairs, and the magnet driver is adapted to repeatedly move each of the at least two drive magnets toward and away from the surface of the associated sample vessel.
In a further embodiment, a method for stirring a sample is provided, comprising the steps of providing a sample vessel comprising a liquid and a stirrer element capable of being influenced by a magnetic force, tilting the vessel such that the longitudinal axis of the vessel is at an angle of less than 90° with the horizontal, and providing at least two drive magnets configured to repeatedly impose a magnetic influence on the stirrer element.
Identical and like reference numerals refer to identical and like parts, components and structures.
Each panel 106 includes a plurality of openings 110, each of which is adapted to receive a sample vessel 102. As discussed in more detail below, each vessel 102 includes a sample suspended in a liquid media, and a stirrer element. The openings 110 are tilted with respect to the horizontal so that the sample vessels 102 received in the openings 110 are also tilted. Generally, the openings are configured to hold the vessels such that the longitudinal axis of the vessels are at an angle of less than 90° with the horizontal 200 (see, e.g.,
The openings 110 are arranged in a plurality of rows and columns as shown, and each panel 106 can have any practical number of openings. For example, the openings 110 can be arranged in ten rows and nine columns, thus totaling 90 openings 110 per panel 106. The incubation and measurement module 100 further includes one or more doors (not shown) for closing the housing 104 after the panels 106 have been received in the housing 104.
When a sample culture is to be analyzed by the incubation and measurement module 100, the sample culture is placed in a sample vessel 102, and the sample vessel 102 is loaded into a respective opening 110 in a respective panel 106 in the incubation and measurement module 100. The sample vessel 102 is a closed sample vial in this example. The incubation and measurement module 100 can further include a keyboard 112, a barcode reader (not shown), or any other suitable interface that enables a technician to enter information pertaining to the sample into a database stored in a memory in the incubation and measurement module 100, or in a computer (not shown) which is remote from the module 100 and controls the operation of the module 100. The information can include, for example, patient information, sample type, the row and column of the opening 110 into which the sample vessel 102 is being loaded, and so on. The module 100 can include the type of detecting devices as described in U.S. patent application Ser. No. 09/892,061 and U.S. Pat. No. 6,709,857 referenced above.
As shown in
As shown in detail in
In this embodiment, each of the shaft driving pulleys 122 is coupled to a respective magnet shaft assembly 116. (See, e.g.,
In the embodiment shown in
In the embodiment shown in
The positioning of the drive magnets 155 ensures that two drive magnets engage each opening 110 at alternate periods. As shown in greater detail in
In this embodiment, the drive magnet pairs 153-n are coupled to the shaft 148 such that each drive magnet 155-1 and 155-2 of each pair 153 extends from opposite sides of the shaft 148 (e.g., 180° from one another), and at an angle from the longitudinal axis of the shaft 148. A useful angle is approximately 30 degrees from the longitudinal axis. Each drive magnet pair 153-n is typically coupled at the same angle along the shaft 148.
In
This embodiment reflects use of two magnets per opening/vessel, but any plurality of magnets will provide similar stirring advantages. In addition, the plurality of magnets associated with each opening/vessel may be attached to the shaft in any manner that provides the desired influence on the magnetic stirrer within the vessel. For example, instead of drive magnet pairs that extend from a shaft 148 at opposite sides of the shaft, it is possible to use magnet pairs 156-1, 156-2 that extend from the same side of the shaft, e.g. a first magnet 156-1 of a first drive magnet assembly 160-1 extending at an angle of 30° from the shaft, and a second magnet 156-2 extending at an angle of 150° of the drive magnet assembly. In such a case, the magnets 156-1 and 156-2 of an adjacent drive magnet assembly 160-2, will typically extend from an opposite side of the shaft 148. See, e.g.,
As shown in
The motor 130 can be rotated at a speed of, for example, 150 rotations per minute, which causes the stirrer element 162 to travel through the stirring path described above up to 150 times per minute. However, the motor 130 can be controlled to rotate at any practical speed to achieve the desired stirring action.
The stirrer element 162 is typically a magnetic, ferrous metal-filled polymer. The term “magnetic” as used herein refers to a type of ferrous metal, such as magnetic stainless steel, that responds to the magnetic fields of a drive magnet. The ferrous material employed in the stirrer element does not itself have to be a magnet, nor does it have to be magnetized. The stirrer element can be rod shaped or cylindrical as shown, or have any other suitable shape. The stirrer element can be cylindrical with an overall length of about 0.500 inches to 0.750 inches, and an overall diameter of about 0.120 to about 0.220 inches, typically with rounded ends.
By increasing the ferrous fill content of the stirrer element 162, the magnetic influence that the drive magnet 154 has on the stirrer element 162 will increase. Likewise, by decreasing the ferrous fill content of the stirrer element 162, the magnetic influence that the drive magnet 154 has on the stirrer element 162 will decrease. Accordingly, the intensity of the stirring can be varied by simply replacing stirrer element 162 with a stirrer having a different ferrous fill content. Furthermore, the size and shape of the stirrer element 162 need not be changed. Also, by magnetizing the stirrer element 162, the magnetic influence that the drive magnet 154 has on the stirrer element 162 can be adjusted still further. Accordingly, the intensity of the stirring can be varied by simply replacing stirrer element 162 with a stirrer element having a different degree of magnetization.
In each embodiment, the drive magnets 154 and 155 can be provided having various magnetic intensities and magnetic orientation, for example, up to 10,000 Gauss or more. Each can also be provided alone, or in a plurality, and have various sizes and shapes, as magnetic and rare earth magnets are capable of being sintered or cast into different configurations. The drive magnets can act on each opening alone, or as an array or plurality. Different physical motions of the stirrer element can therefore be provided, including alternative rotations, lateral, vertical, and so forth. Each drive magnet can also be provided having different rates of oscillation, i.e., tens, hundreds, or even thousands of rotations per minute.
As reflected in
In accordance with an embodiment of the invention, the stirrer elements 162, 162a, 162b, 162c can comprise about 20% to about 80% of polymer by weight, with the remaining 80% to 20% of the weight being ferrous metal or other magnetic or magnetizable materials. However, any ratio of polymer to ferrous metal can be used as long as it provides sufficient cohesiveness to hold the stirrer element together and to allow sufficient responsiveness to the drive magnet 154. The polymer material is preferably a biologically inert polymer, such as nylon or polypropylene, which reduces the overall surface hardness of the stirrer element, and thus reduces potential damage to the solid sample 158 in the suspension as well as to the sample vessel 102. In one embodiment of the invention, the ferrous material is stainless steel, but can be any suitable material that can respond to magnetic influence from the drive magnet 154. The stirrer element can be further color coded with colors such as blue, gray, red, green, orange, and so on, to provide an indication of the type and percentage content of the polymer and ferrous material. The stirrer element can be provided in the sample vessel 110, or can be added to the sample vessel 110 prior to or after adding the solid sample 158 and liquid media 160 to the sample vessel 110.
The stirrer element can be made from a material that can be magnetized to move in response to the rotation of the permanent magnets of the drive magnet assemblies to induce a continuous or pulsing movement sufficient to provide a stirring motion to the liquid reagent in each vessel. Typically, the stirrer element has a substantially cylindrical shape with a length and diameter sufficient to induce the desired movement to the liquid reagent. The stirrer element generally has a length of about 15-25 mm and diameter of about 2-6 mm. In one preferred embodiment the stirring bar has length of about 20 mm (0.75 inches) and diameter of about 5 mm (0.22 inches). Typically, the stirrer elements have slightly rounded ends
In a preferred embodiment, the stirrer element is produced from a mixture of a moldable polymer or copolymer and a magnetizable material. An example of a suitable polymer includes a styrene-ethylene-butylene-styrene (SEBS) copolymer, as this copolymer is biologically inert and easily molded to the desired shape and size. In other embodiments, the polymer component of the stirrer element is selected from the group consisting of polyethylene, polypropylene, polybutylene, and polystyrene. Typically, the polymer component is a flexible thermoplastic polymer or copolymer. The polymer or copolymer is typically included in an amount of about 20 wt % to about 40 wt % and preferably about 30 wt % based on the total weight of the finished stirrer element.
The magnetizable material is typically included in the amount of about 60 wt % to about 80 wt % and preferable about 70 wt % based on the total weight of the finished stirrer element. The magnetizable material is generally a ferrite compound that can be magnetized to a suitable power to provide the necessary stirring effect. Examples of magnetizable ferrites include Group II metal ferrites and particularly strontium ferrite. The magnetic or magnetizable component can be selected from the group consisting of iron, stainless steel, and ferrite alloys. One preferred embodiment is a mixture of 30 wt % styrene-ethylene-butylene-styrene copolymer and 70 wt % strontium ferrite. The components are mixed together and molded by melting and extruding as a cylindrical member and cutting to length. Alternatively the mixture of polymer and strontium ferrite particles can be compression molded into the desired shape, or heated and injection molded into the desired shape. As noted above, a particularly preferred embodiment of the invention, the stirrer element can comprise a mixture of about 70 wt % strontium ferrite with 30 wt % SEBS polymer, and molded into an approximately 20 mm (0.75 inches) long cylinder, approximately 5 mm (0.220 inches) in diameter, and with rounded ends. The stirrer element can be further magnetized to saturation at approximately 300 Gauss, with two poles aligned diametrically as shown in
In some embodiments, the stirrer elements are formed and then magnetized to the desired power to provide the proper stirring effect. The stirrer elements are magnetized to a power of about 200 Gauss to about 400 Gauss using standard magnetizing procedures. In one preferred embodiment the stirring magnet is magnetized to a power of about 300 Gauss. The ferrite material, such as strontium ferrite, is able to provide a moderate magnetization with persistent strength for the intended life of the stirrer element.
Multiple poles can be patterned within the shape of the stirrer element, and poles can be axially oriented, radially oriented, circularly oriented, or designed in many other configurations to impart the desired attractive or repellent geometry to the stirrer. Such various magnetic pole geometries can further achieve diverse motion of the stirrer element within the liquid and thereby produce desired effects. In preferred embodiments of the invention, the magnetic stirrer element is produced with the opposite poles oriented diametrically around the circumference of the stirrer element. In one embodiment, a stirrer element 162a is formed with a north pole at a first end, and a south pole at a second end f the stirrer element as shown in
The diametrically and axially oriented poles can induce a random, 3-dimensional movement of the stirrer element in response to the movement of the drive magnets. The drive magnets generally move in an orbital path with respect to the culture vessel in a sweeping motion in a plane parallel to the longitudinal axis of the culture vessel. The axis of the circular path of the drive magnets is such that the drive magnets move toward and then away from the culture vessel and the stirrer element so that the stirrer element may exhibit an erratic and pulsating motion. The circular motion of the drive magnets in a generally sweeping path induces a random motion to the stirrer element. The diametrically and axially oriented poles of the stirrer element cause the stirrer element to rotate about its longitudinal axis and simultaneously move and rotate about an axis generally perpendicular to the longitudinal axis of the stirrer element thereby experiencing an analemma-like motion to provide the stirring effect.
As shown in
The increase in availability of many different magnetic materials and thermoplastic polymers with a wide range of properties in recent years has made the molding or extrusion of such complex stirrer element shapes described above possible. Extensive adjustments, therefore, can be made to both the design of the stirrer element and the drive magnets, as described in greater detail below, in order to finely control the degree of motion imparted to the liquid. Also, the magnetization of ferrite filled stirrer elements as described above is easily achieved using high strength permanent magnet fixtures, rather than electromagnetic discharge. Therefore, permanent magnet fixtures with energy directors easily meet production volume requirements for producing stirrer elements.
To adjust the fill ratio of magnetic material in the above embodiments, the magnetic material that is molded with a polymeric matrix into the stirrer element shape can have different percentage volumes (percent fill) and can be chosen from different materials. A higher percentage volume fill of magnetic material will tend to make the stirrer element more massive when the other ingredients used in the element's manufacture are lightweight polymers. The more mass that the stirrer element has, the more influence and effect on stirring the force of gravity will have for the same viscosity or viscoelasticity of the liquid being stirred, and becomes more of a factor in its motion.
In addition to percent volume adjustments, the type of material can be varied to adjust mass and to adjust magnetic coercivity. For example, if the powdered metal fill in the stirrer element is a martensitic stainless steel, it will have a much lower magnetic moment than an element with the same percentage fill but having a higher coercivity, such as strontium ferrite.
Not only can the type of material be selected for magnetic force, but also for nontoxicity, such as required in the case of using the stirrer element in biological samples. Also, the oxidation potential for the material can be selected to suit the application. For example, rust forming in an optically interrogated sampler container could severely impact performance.
To adjust the polymer fill in the above embodiments, the percent volume or mass and the type of polymer used to manufacture the stirrer element can be selectable. A higher percentage of polymer fill can alter the stirrer physical properties for different application environments. For instance, if the polymer has a low durometer value (meaning it is soft) and its percentage increased, the amount of impact force applied to the solids suspended in the liquid media can be decreased. As the polymer volume becomes less and the magnetic fill becomes greater, the element's hardness typically increases and its apparent collision damage to suspended solids may increase.
Selecting different types of polymer can also enhance other performance attributes. If the desired compliance of the material is known, the inherent compatibility with the stirred, contents becomes paramount. Some polymers are known to be toxic to metabolic processes, and some are known to be relatively inert. In the case of selecting a nontoxic polymer, a choice of PTFE instead of polyurethane could determine the element's ultimate effect on stability of the stirred liquid's contents. In certain cases, the selection of a polymer that is chemically active, absorptive, or destructive to agents that harm the liquid's contents may be desirable. Including these detrimental or alternatively, beneficial polymers in the stirrer element can be used to adjust the performance of the container's contents.
Various embodiments of the invention provide several advantages over the conventional stirring devices. For example, because the tilted openings I 10 maintain the sample vessel 102 at an with respect to the horizontal, the embodiments facilitate maximum exposure of liquid phase to gas phase. This therefore, provides an improved dissolved gas exchange as a function of the angle. Furthermore, the angled orientation of the sample vessel 102 increases the probability that the drive magnets will maintain magnetic influence over the stirrer elements. Also, the stirring action can be gentler than in conventional methods since the path of the stirrer element is constrained by the wall 166 of the sample vessel. All of these improved characteristics of the stirring system enhances the growth of the sample in the liquid media 160 and thus increases the overall carbon dioxide production, oxygen depletion and pressure variation in the sample vessel, thereby improving sample detection results.
Those skilled in the art will appreciate that modifications are possible in the embodiments described herein without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims.
This application claims priority to U.S. Provisional Patent Application Ser. No. 60/665,692, filed Mar. 28, 2005.
| Number | Date | Country | |
|---|---|---|---|
| 60665692 | Mar 2005 | US |
