Patent Publication Number: US-2021190403-A1

Title: Method and Apparatus for Freezing Dispensed Droplets of Liquid

Description:
FIELD OF THE DISCLOSURE 
     This disclosure relates to apparatuses and methods for freezing dispensed droplets of liquid in a fluid chamber. 
     BACKGROUND 
     Analytical processes of biological fluids, such as blood, typically combine the analyzed fluid with one or more reagents to trigger the occurrence of a detectable property that corresponds to a measured parameter of the analytical process. One example includes combining blood plasma with a reagent to undergo a reaction that changes the color or the visibility of the detectable property, which may be measured by processing equipment. The processing equipment may be supplied with a biological sample and one or more lyophilized reagent pellets that may be reconstituted during the analytical process. 
     One known method for producing lyophilized reagents includes the step of dispensing liquid reagent droplets of precise volume into a freezing liquid bath in which the liquid droplets freeze and sink to the bottom of the bath. After sinking to the bottom of the bath, the known method includes removing the frozen droplets from the bath and lyophilizing the frozen droplets. In some instances, however, other factors, such as surface tension at the top surface of the freezing liquid, hinder the frozen droplets of liquid reagent from sinking to the bottom of the bath such that the droplets of liquid reagent tend to float near the surface of the freezing liquid. Consequently, subsequent dispensed liquid reagent droplets may combine with the floating droplet, thus resulting in an inaccurate reagent dosage for the combined droplet. Thus, there is a need for improved apparatuses and methods that promote dispensed droplets of liquid to sink to the bottom of a freezing liquid bath. 
     SUMMARY 
     The following presents a simplified summary in order to provide a basic understanding of some aspects described herein. This summary is not an extensive overview of the subject matter disclosed herein. It is intended to neither identify key or critical elements of the claimed subject matter nor delineate the scope thereof. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later. 
     The present disclosure includes various examples of an apparatus for freezing liquid droplets. In accordance with one example, the apparatus comprises a fluid chamber containing a fluid, a liquid dispenser, a gas injector, and a transporter. The liquid dispenser is configured to dispense a droplet of liquid into the fluid chamber. The gas injector is configured to inject a stream of gas transversely to a surface of the fluid contained in the fluid chamber. The transporter is configured to transport at least one of the fluid chamber, the liquid dispenser, and the gas injector relative to each other such that the liquid dispenser dispenses the droplet of liquid on the surface of the fluid contained in the fluid chamber, and the gas injector injects the stream of gas at about where the dispensed droplet of the liquid is located along the surface of the fluid contained in the fluid chamber. 
     In some examples, the transporter is configured to transport the fluid chamber between a first position below the liquid dispenser and a second position below the gas injector. The liquid dispenser is configured to dispense a droplet of liquid into the fluid chamber when the fluid chamber is in the first position. The gas injector is configured to inject the gas stream transversely to the surface of the fluid contained in the fluid chamber when the fluid chamber is in the second position. 
     In some examples, the fluid contained in the fluid chamber is a cryogenic liquid configured to freeze the dispensed droplet of liquid to a frozen droplet. In some examples, the cryogenic liquid is liquid nitrogen. In some examples, the transporter comprises a carousel configured to move the fluid chamber about an axis of rotation between the first position and the second position. In some examples, the carousel comprises a drum, and the fluid chamber is disposed within the drum. In some examples, the carousel comprises a spindle configured to rotate about the axis of rotation, and the spindle is coupled to the drum such that the drum is configured to rotate with the spindle about the axis of rotation. In some examples, the carousel comprises a lid coupled to a top end of the drum. In some examples, the lid is removable from the top end of the drum. In some examples, the fluid chamber is disposed beneath the lid, and the lid comprises an opening aligned with the fluid chamber. In some examples, the fluid chamber is removable from the drum. In some examples, the drum is comprised of stainless steel. In some examples, the carousel comprises an insulation layer disposed between the drum and the fluid chamber. In some examples, the insulation layer comprises air. 
     In some examples, the apparatus comprises multiple fluid chambers, in which the transporter is configured to transport each fluid chamber between the first position below the liquid dispenser and the second position below the gas injector. In some examples, the apparatus comprises multiple liquid dispensers, in which the transporter is configured to transport each fluid chamber to the first position below a respective one of the liquid dispensers. In some examples, the apparatus comprises multiple gas injectors, in which the transporter is configured to transport each fluid chamber to the second position below a respective one of the gas injectors. In some examples, the gas injector comprises a nozzle disposed above the fluid chamber, in which the nozzle is configured to inject the gas stream transversely to the surface of the fluid contained in the fluid chamber. In some examples, the gas injector is configured to inject the gas stream transversely to the surface of the fluid contained in the fluid chamber only when the fluid chamber is in the second position. 
     In some examples, the apparatus comprises a solenoid valve controlling gas flow to the nozzle and configured to switch between a closed position to shut-off the gas stream from reaching the nozzle and an open position to permit the gas stream to reach the nozzle. In some examples, the apparatus comprises a sensor configured to generate a signal relating to a position of the transporter and a control unit in electrical communication with the sensor and the solenoid valve, in which the control unit is configured to receive the signal from the sensor and transmit a command to the solenoid valve to switch between the open and closed positions based on the signal. In some examples, the transporter is configured to transport the liquid chamber from the first position to the second position at a predetermined dwell time so that the droplet of liquid freezes to the frozen droplet before the gas injector injects the stream of gas transversely to the surface of the fluid contained in the fluid chamber. 
     In some examples, the liquid dispenser comprises a nozzle, in which the nozzle is configured to dispense the droplet of liquid into the fluid chamber. In some examples, the nozzle of the liquid dispenser comprises a tip located above the surface of the fluid contained in the fluid chamber at a predetermined distance. In some examples, the predetermined distance between the tip of the nozzle of the liquid dispenser and the surface of the fluid contained in the fluid chamber is set from about ¾ of an inch to about 2 inches. 
     In another example, a method for freezing liquid droplets comprises a step (a) of dispensing a droplet of liquid into a fluid chamber containing a freezing fluid, a step (b) of allowing the droplet of liquid to dwell in the freezing fluid for at least a predetermined dwell time so that the droplet of liquid freezes to a frozen droplet, and a step (c) of injecting a stream of gas transversely to a surface of the freezing fluid at about where the frozen droplet is located along the surface of the freezing fluid so that frozen droplet sinks in the freezing fluid. In some examples, step (a) further comprises using a liquid dispenser to dispense the droplet of liquid into the fluid chamber containing the freezing fluid. In some examples, step (c) further comprises using a gas injector to inject the stream of gas transversely to the surface of the freezing liquid. 
     In some examples, step (c) further comprises monitoring the predetermined dwell time and automatically injecting the stream of gas transversely to the surface of the freezing fluid after the predetermined dwell time. In some examples, the method further comprises the step of transporting the fluid chamber by a transporter from a first position below a liquid dispenser to a second position below a gas injector. In some examples, the method comprises the steps of monitoring a position of the transporter and automatically injecting the stream of gas when the fluid chamber is at a position beneath the gas injector. In some examples, the method further comprises the step of transporting the fluid chamber by the transporter from the second position below the gas injector back to the first positon below the liquid dispenser. In some examples, the method further comprises, after the step of returning the fluid chamber back to the first position, the step of dispensing a second droplet of liquid into the liquid chamber. 
     In some examples, the fluid chamber is integrally attached to the transporter. In some examples, the fluid chamber is removably coupled to the transporter. In some examples, the transporter comprises a carousel, and the step of transporting further comprising rotating, by the carousel, the fluid chamber about an axis of rotation from the first position to the second position. In some examples, the carousel comprises a drum and the liquid chamber is disposed within the drum. In some examples, the carousel comprises a lid coupled to a top end of the drum. In some examples, the lid is removable from the top end of the drum. 
     In some examples, the method comprises, before step (a), moving a liquid dispenser over the fluid chamber to align the liquid dispenser with a target zone located along the surface of the freezing fluid contained in the fluid chamber. In some examples, step (a) further comprises dispensing, by the liquid dispenser, the droplet of liquid at the target zone. In some examples, the method comprises, after step (a) and before step (c), moving a gas injector over the fluid chamber to align the gas injector with the target zone located along the surface of the freezing fluid contained in the fluid chamber. In some examples, step (c) further comprises injecting, by the gas injector, the stream of gas at the target zone. In some examples, the fluid chamber comprises a stationary bath containing the freezing fluid. 
     In some examples, the method further comprises after step (c), collecting, by a retainer basket, the frozen droplet sinking toward a bottom of the fluid chamber. In some examples, the method further comprises after the step of collecting the frozen droplet, drying the frozen droplet. In some examples, the step of drying the frozen droplet comprises lyophilizing the frozen droplet. 
     In accordance with another example, the apparatus comprises a fluid chamber containing a fluid, a liquid dispenser, and a gas injector. The liquid dispenser is configured to move relative to the fluid chamber so that the liquid dispenser is aligned above a target zone located along the surface of the fluid contained in the fluid chamber. The liquid dispenser is configured to dispense a droplet of liquid into the fluid chamber at the target zone. The gas injector is configured to move relative to the fluid chamber so that the gas injector is aligned above the target zone located along the surface of the fluid contained in the fluid chamber. The gas injector is configured to inject a gas stream transversely to the surface of the fluid contained in the fluid chamber at the target zone. 
     In some examples, the fluid chamber comprises a stationary bath containing the fluid. In some examples, the liquid dispenser is configured to move in a longitudinal direction along the bath and dispense multiple droplets of liquid at multiple target zones arranged in the longitudinal direction along the surface of the fluid contained in the bath. In some examples, the liquid dispenser is configured to move in a lateral direction along the bath and dispense multiple droplets of liquid at multiple target zones arranged in the lateral direction along the surface of the fluid contained in the bath. In some examples, the gas injector is configured to move in a longitudinal direction along the bath and inject multiple streams of gas transversely to the surface of the fluid contained in the bath at multiple target zones arranged in the longitudinal direction along the surface of the fluid contained in the bath. In some examples, the gas injector is configured to move in a lateral direction along the bath and inject multiple streams of gas transversely to the surface of the fluid contained in the bath at multiple target zones arranged in the lateral direction along the surface of the fluid contained in the bath. In some examples, the gas injector is configured to wait for at least a predetermined dwell time after the liquid dispenser dispenses the droplet of liquid at the target zone before injecting the stream of gas at the target zone. 
     Other features and characteristics of the subject matter of this disclosure, as well as the methods of operation, functions of related elements of structure and the combination of parts, and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various embodiments of the subject matter of this disclosure. In the drawings, like reference numbers indicate identical or functionally similar elements. 
         FIG. 1  is a schematic drawing of an exemplary process for freezing liquid droplets. 
         FIG. 2  is a flow chart of an exemplary method for freezing liquid droplets. 
         FIG. 3  is a top perspective view of an exemplary apparatus for freezing liquid droplets comprising fluid chambers, a transporter, a liquid dispenser, and a gas injector. 
         FIG. 4  is a front view of the apparatus  FIG. 3 . 
         FIG. 5  is a top plan view of an insulated drum of the apparatus including a plurality of fluid chamber openings. 
         FIG. 6  is a close-up, partial perspective view of the gas injector and a portion of the top of the drum. 
         FIG. 7  is a bottom perspective view of the drum. 
         FIG. 8  is a schematic drawing of a system for delivering and controlling gas flow to a gas injector. 
         FIG. 9  is a schematic drawing of a fluid chamber and a strainer basket for retrieving frozen reagent spheres from the fluid chamber. 
     
    
    
     DETAILED DESCRIPTION 
     While aspects of the subject matter of the present disclosure may be embodied in a variety of forms, the following description and accompanying drawings are merely intended to disclose some of these forms as specific examples of the subject matter. Accordingly, the subject matter of this disclosure is not intended to be limited to the forms or embodiments so described and illustrated. 
     Unless defined otherwise, all terms of art, notations and other technical terms or terminology used herein have the same meaning as is commonly understood by one of ordinary skill in the art to which this disclosure belongs. All patents, applications, published applications and other publications referred to herein are incorporated by reference in their entirety. If a definition set forth in this section is contrary to or otherwise inconsistent with a definition set forth in the patents, applications, published applications, and other publications that are herein incorporated by reference, the definition set forth in this section prevails over the definition that is incorporated herein by reference. 
     Unless otherwise indicated or the context suggests otherwise, as used herein, “a” or “an” means “at least one” or “one or more.” 
     This description may use relative spatial and/or orientation terms in describing the position and/or orientation of a component, apparatus, location, feature, or a portion thereof. Unless specifically stated, or otherwise dictated by the context of the description, such terms, including, without limitation, top, bottom, above, below, under, on top of, upper, lower, left of, right of, in front of, behind, next to, adjacent, between, horizontal, vertical, diagonal, longitudinal, transverse, radial, axial, etc., are used for convenience in referring to such component, apparatus, location, feature, or a portion thereof in the drawings and are not intended to be limiting. 
     Furthermore, unless otherwise stated, any specific dimensions mentioned in this description are merely representative of an exemplary implementation of a device embodying aspects of the disclosure and are not intended to be limiting. 
     The use of the term “about” applies to all numeric values specified herein, whether or not explicitly indicated. This term generally refers to a range of numbers that one of ordinary skill in the art would consider as a reasonable amount of deviation to the recited numeric values (i.e., having the equivalent function or result) in the context of the present disclosure. For example, and not intended to be limiting, this term can be construed as including a deviation of ±10 percent of the given numeric value provided such a deviation does not alter the end function or result of the value. Therefore, under some circumstances as would be appreciated by one of ordinary skill in the art a value of about 1% can be construed to be a range from 0.9% to 1.1%. 
     As used herein, the term “group” refers to a collection of one or more objects. Thus, for example, a group of objects can include a single object or multiple objects. Objects of a group also can be referred to as members of the group. Objects of a group can be the same or different. In some instances, objects of a group can share one or more common properties. 
     As used herein, the term “adjacent” refers to being near or adjoining. Adjacent objects can be spaced apart from one another or can be in actual or direct contact with one another. In some instances, adjacent objects can be coupled to one another or can be formed integrally with one another. 
     As used herein, the terms “substantially” and “substantial” refer to a considerable degree or extent. When used in conjunction with, for example, an event, circumstance, characteristic, or property, the terms can refer to instances in which the event, circumstance, characteristic, or property occurs precisely as well as instances in which the event, circumstance, characteristic, or property occurs to a close approximation, such as accounting for typical tolerance levels or variability of the embodiments described herein. 
     As used herein, the terms “optional” and “optionally” mean that the subsequently described, component, structure, element, event, circumstance, characteristic, property, etc. may or may not be included or occur and that the description includes instances where the component, structure, element, event, circumstance, characteristic, property, etc. is included or occurs and instances in which it is not or does not. 
     The term “reagent” means one or more reagents or components necessary or desirable for use in one or more reactions or processes, for example, one or more components that in any way affect how a desired reaction can proceed. The reagent can comprise a reactive component. However, it is not necessary that the reagent participate in the reaction. The reagent can comprise a non-reactive component. The reagent can comprise a promoter, accelerant, or retardant that is not necessary for a reaction but affects the reaction, for example, affects the rate of the reaction. The reagent can comprise one or more of a solid reagent for reaction and a fluid reagent for reaction. 
     The term “fluid communication” means either direct fluid communication, for example, two regions can be in fluid communication with each other via an unobstructed fluid processing passageway connecting the two regions or can be capable of being in fluid communication, for example, two regions can be capable of fluid communication with each other when they are connected via a fluid processing passageway that can comprise a valve disposed therein, wherein fluid communication can be established between the two regions upon actuating the valve, for example, by dissolving a dissolvable valve disposed in the fluid processing passageway. 
     The term “cryogenic liquid” refers to a liquefied gas that keeps its liquid state at substantially low temperatures. In one example, the term “cryogenic liquid” refers to a liquefied gas having a normal boiling point below about −75° C. In another example, the term “cryogenic liquid” refers to a liquefied gas having a normal boiling point below about −150° C. Examples of cryogens include argon (Ar), helium (He), hydrogen gas (H 2 ), nitrogen gas (N 2 ), oxygen (O 2 ), methane (CH 4 ), and carbon monoxide (CO). 
     The term “lyophilization” refers to a dehydration process that is typically used to preserve a perishable material and/or facilitate transport thereof. Conditions for lyophilization may include subjecting a liquid material and/or a vessel containing the liquid material to freezing conditions while reducing the surrounding pressure to allow the frozen water within the material to sublimate directly from the solid phase to the gas phase. Such freezing conditions may include cooling the material below the lowest temperature at which the solid and liquid phases thereof can coexist (known in the art as the “triple point”). Usually, the freezing temperatures are between −50° C. and −80° C., however, one of skill in the art can determine the appropriate freezing temperature to lyophilize the reagent for use in the automated biochemical assay. 
       FIGS. 1 and 2  illustrate a method  50  for freezing liquid droplets in a fluid chamber  10  containing a freezing liquid  12  according to an example. The method  50  includes a step, or process,  51  of dispensing a droplet of liquid  13  into the fluid chamber  10  containing the freezing fluid  12  having a surface  18 . In one example, the freezing fluid  12  is a cryogenic liquid, such as liquid nitrogen, and the droplet  13  is dispensed by a liquid dispenser  14 . The liquid dispenser  14  is configured to drop individual liquid droplets of reagent solution, whereby each droplet is of substantially uniform size. 
     Once the droplet of liquid is received on the surface  18  of the freezing fluid  12 , the method  50  includes a step  52  of allowing the droplet of liquid  13  to dwell in the freezing fluid  12  for at least a predetermined dwell time ΔT so that the droplet of liquid  13  freezes to a frozen droplet  15 . In some non-limiting examples, the predetermined dwell time ΔT includes at least the period of time between when the dispensed liquid droplet  13  initially contacts the surface of the freezing fluid  12  and when the dispensed liquid droplet  13  fully submerges under the surface of the freezing fluid  12 . In some examples, the predetermined dwell time ΔT is calculated from a number of parameters, including the composition of liquid solution dispensed from the liquid dispenser  14 , the mass and volume of the liquid droplet  13 , the composition of the freezing fluid  12 , the temperature of the freezing fluid  12 , and the pressure of the fluid chamber  10 . The predetermined dwell time ΔT may be extended to account for possible air bubbles trapped inside of the dispensed liquid droplet  13 , interaction between the dispensed liquid droplet  13  and the surface of the freezing fluid  12 , and temperature differentials between the dispensed liquid droplet  13  and the temperature of the freezing fluid  12 . Accordingly, the predetermined dwell time ΔT may vary based on the composition selected for the liquid dispensed into the fluid chamber, the composition selected for the freezing fluid contained in the fluid chamber, and the interaction between the dispensed liquid droplet  13  and the freezing fluid  12 . In some examples, the predetermined dwell time ΔT is one minute or less. 
     After allowing the droplet of liquid  13  to dwell in the freezing fluid  12  for at least the predetermined dwell time ΔT so that the droplet of liquid  13  freezes, the method  50  includes a step  53  of injecting, by a gas injector  17 , a stream of gas  16  transversely to the surface  18  of the freezing fluid  12  at about where the frozen droplet is located along the surface of the freezing fluid  12 . The impulse of the gas stream  16  contacting the frozen droplet  15  breaks the surface tension between the freezing fluid  12  and the frozen droplet  15  so that the frozen droplet  15  sinks in the freezing fluid  12 . Preferably, the stream of gas  16  is injected substantially orthogonally to the surface of the freezing fluid  12 . Thus, step  53  of the method  50  ensures that the dispensed droplet of liquid  13  freezes completely to a frozen droplet  15  and that the frozen droplet  15  sinks to the bottom of the fluid chamber  10 . 
     During the method  50 , in some examples, the fluid chamber  10  may move with respect to the liquid dispenser  14  and the gas injector  17 , as indicated by arrow A in  FIG. 1 . In some examples, the liquid dispenser  14  and the gas injector  17  may move with respect to the fluid chamber  10 , as indicated by arrow B in  FIG. 1 . In one example, the method  50  includes holding the fluid chamber  10  at the same position during all three steps  51 ,  52 , and  53  of the method  50  whereby the liquid dispenser  14  is positioned above the fluid chamber  10  in step  51  and the gas injector  17  is then positioned above the fluid chamber  10  in step  53 . In one example, the method  50  may be automated such that step  53  further includes monitoring the predetermined dwell time ΔT and automatically injecting the stream of gas  16  transversely to the surface of the freezing fluid  12  after the predetermined dwell time ΔT. 
     In another example, the method includes the step of transporting the fluid chamber  10  by a transporter from a first position below the liquid dispenser  14  to a second position below the gas injector  17 . In one example, the fluid chamber  10  may be transported from the first positon to the second position during the step  52  of allowing the droplet of liquid  13  to dwell in the freezing fluid  12  for at least the predetermined dwell time ΔT. In one example, the method  50  may be automated such that step  53  includes monitoring a position of the transporter and the steps of automatically injecting the droplet  13  when the fluid chamber  10  is at the first position beneath the liquid dispenser  14  and automatically injecting the stream of gas  16  when the fluid chamber  10  is at the second position beneath the gas injector  17 . In one example, the method  50  includes a control unit and a sensor to monitor the positon of the transporter and command the gas injector  17  to inject the stream of gas  16 . 
     In one example, after the step  53  of injecting the stream of gas  16  transversely to the surface of the freezing fluid, the method  50  further includes the step of transporting the fluid chamber  10  by the transporter from the second position below the gas injector  17  back to the first position below the liquid dispenser  14  so that another droplet of liquid  13  may be dispensed into the fluid chamber  10 . 
     In other examples, the fluid chamber  10  comprises a bath (not shown) of freezing fluid  12 . In some examples, the bath extends in a longitudinal direction from a first end to a second end and a lateral direction from a first side to a second side. In some examples, step  51  of method  50  further comprises moving the liquid dispenser  14  over the bath of freezing fluid  12  in the longitudinal direction such that multiple droplets of liquid  13  are dispensed into the bath of the freezing fluid  12  at multiple target zones (not shown) spatially arranged along the bath of freezing fluid  12  in the longitudinal direction. In some examples, step  53  of method  50  further comprises moving the gas injector  17  in the longitudinal direction such that a gas stream  16  is injected transversely to the surface  18  of the freezing fluid  12  at about each target zone. In some examples, step  51  of method  50  further comprises moving the liquid dispenser  14  over the bath of freezing fluid  12  in a lateral direction such that multiple droplets of liquid  13  are dispensed into the bath of the freezing fluid  12  at multiple target zones spatially arranged along the bath of freezing fluid  12  in the lateral direction. In some examples, step  53  of method  50  further comprises moving the gas injector  17  in the lateral direction such that a gas stream  16  is injected transversely to the surface  18  of the freezing fluid  12  at about each target zone. In some examples, step  51  further comprises moving the liquid dispenser  14  in a longitudinal direction after dispensing multiple droplets of liquid  13  in the lateral direction along the bath of freezing fluid  12  such that multiple rows of target zones are arranged along the bath of freezing fluid. In some examples, step  53  further comprises moving the gas injector  17  in a longitudinal direction after injecting multiple streams of gas  16  transversely to the surface  18  of the freezing fluid  12  in the lateral direction such that a stream of gas  16  is injected at about each target zone. 
     In some other examples, the method  50  includes dispensing and freezing multiple droplets of liquid  15  simultaneously in the bath of the freezing fluid  12 . In some examples, step  51  further comprises dispensing multiple droplets of liquid  13  simultaneously at multiple target zones with multiple liquid dispensers  14  arranged along the bath of freezing fluid  12  in the longitudinal direction. In some other examples, step  53  further comprises injecting multiple gas streams  16  transversely to the surface  18  of the freezing fluid  12  at about each target zone with multiple gas injectors  17  arranged along the bath of freezing fluid  12  in the longitudinal direction. 
     In some examples, the method  50  further comprises the step of collecting the frozen droplets  15  that sink towards the bottom of the fluid chamber  10 . In some examples, the frozen droplets  15  are collected by providing a retainer basket ( FIG. 9 ) disposed in the fluid chamber  10 . In some examples, the retainer basket is configured to receive and hold the sunken frozen droplets  15  without retaining frozen fluid  12 . In some examples, the step of collecting the frozen droplets  15  includes removing the retainer basket holding the frozen droplets  15  from the fluid chamber  10 . 
     In some examples, the method  50  further comprises the step of drying the frozen droplet  15  after the step of collecting the frozen droplets  15  such that reagent material stored in the frozen droplet  15  is preserved and portable. The step of drying the frozen droplets may include any process to dehydrate the moisture content of the frozen droplets. In some examples, the step of drying the frozen droplets comprises lyophilizing the frozen droplet. 
     Referring to  FIGS. 3 and 4 , an example of the apparatus for implementing the process described with respect to  FIGS. 1 and 2  is indicated by reference number  1000  and includes a transporter  100 , a liquid dispenser  200 , a gas injector  300 , and one or more fluid chambers  126  (openings to the fluid chambers  126  are shown in  FIG. 3 ). In general, each fluid chamber  126  contains a freezing fluid, such as a cryogenic liquid (e.g., liquid nitrogen), and the transporter  100  is configured to transport each fluid chamber between a first position below the liquid dispenser  200  and a second position below the gas injector  300 . The liquid dispenser  200  is configured to dispense a droplet of liquid into a respective fluid chamber  126  when the respective fluid chamber  126  is in the first position. The gas injector  300  is configured to inject a gas stream transversely to a surface of the freezing fluid contained in the respective fluid chamber  126  when the respective fluid chamber  126  is in the second position. 
     In one example, the transporter  100  comprises a carousel configured to move each fluid chamber  126  about an axis of rotation between the first position and the second position. As shown in  FIGS. 3 and 4 , the carousel may comprise a drum  110 , a lid cover  120  enclosing an upper end of the insulated drum  110 , and a base  130  enclosing a bottom end of the insulated drum  110 . In some examples, the drum  110  is comprised of stainless steel and houses the fluid chambers  126 . In some examples, the lid cover  120  is removably coupled to the drum  110 . Referring to  FIGS. 4 and 7 , the carousel further comprises a spindle  132  projecting through the base  130  and aligned with a central opening  122  of the lid cover  120 . As shown in  FIG. 4 , the apparatus  1000  comprises a motor  150  disposed underneath the base  130  and coupled to the spindle  132  such that the axis of rotation of the carousel extends through the spindle  132 . The motor  150  is configured to drive rotation of the spindle  132 , thereby triggering rotation of the carousel such that the base  130 , the drum  110 , and the lid cover  120  rotate about the axis of rotation. In one example, the motor  150  is configured to rotate the carousel at a rate about 1.5 revolutions per minute (RPM). 
     In some examples, the fluid chambers  126  are disposed in the drum  110  and arranged around the central opening  122  and the spindle  132 . In some examples, the carousel comprises an insulation layer (not shown) disposed between the drum  110  and the fluid chambers  126  to minimize heat transfer between the freezing fluid and the ambient air outside the drum  110 . The insulation layer may be comprised of air, a noble gas (e.g., argon), or a material having a low thermal conductivity (e.g., polymeric foam). In one example, each fluid chamber  126  comprises a tube disposed beneath the lid cover  120 . In another example, each fluid chamber  126  comprises a cylindrical wall integrally fixed to a lower surface of the lid cover  120 . As shown in  FIGS. 3 and 5 , the lid cover  120  includes an opening for each fluid chamber  126  spaced around the central opening  122 , in which each opening is aligned with a respective fluid chamber  126  to provide access to the respective fluid chamber. In the illustrative example, the openings are shaped as circles having one inch diameters. In other examples, the openings may have other shapes or different sizes to accommodate for dispensed liquid droplets of various sizes. 
     Referring to  FIG. 5 , in one example, the openings of the fluid chambers  126  may be arranged in groups. As shown in  FIG. 5 , one group of openings  126  is indicated by annotated box A-A shown in  FIG. 5  and includes four openings of fluid chambers  126 . In the illustrative example, each opening is displaced from the center of the lid cover  120  by a different radius r 1 , r 2 , r 3 , or r 4 , in which each respective radius r 1 , r 2 , r 3 , and r 4  is measured from the center of the central opening  122  to the center of the respective opening of the fluid chamber  126 . In the illustrative example shown in  FIG. 5 , an edge of one of the openings in the group closest to the central opening  122  is set such that the edge is separated from the center of the central opening  122  at a first predetermined radius, and an edge of another one of the openings in the group furthest from the central opening  122  is set such that the edge is separated from the center of the central opening at a second predetermined radius. Accordingly, all the openings of the group are located between the first predetermined radius and second predetermined radius. In one example, the first predetermined radius defined from the edge of the opening closest to the central opening  122  to the center of the central opening is set at about 2 inches, and the second predetermined radius defined from the edge of the opening furthest from the central opening  122  to the center of the central opening  122  is set at about 5 inches. 
     In some examples, the transporter  100  further comprises a pellet collector disposed in the drum  110 , whereby the pellet collector is configured to receive the frozen droplets that sink toward the bottom of the fluid chambers  126 . In some examples, the pellet collector comprises a strainer basket that includes a plurality of holes to permit freezing fluid to pass through the strainer basket while retaining the sunken frozen droplets. In one example, as shown in  FIGS. 3 and 4 , the pellet collector may comprise a handle rod  140  extending through the central opening  122  of the lid cover  120 . The handle rod  140  is configured to be grasped so that the pellet collector may be removed from the drum  110  to collect the sunken frozen droplets. In some examples, the strainer basket is disposed in the fluid chamber  126  and extends along the interior surface of the fluid chamber  126  to receive frozen droplets. In some examples, the strainer basket is disposed in the drum  110  and beneath the fluid chambers  126  such that a bottom of each fluid chamber  126  opens into the strainer basket to receive frozen droplets. 
     Freezing fluid is supplied to each fluid chamber  126  such that the surface level of the freezing fluid remains within a predetermined distance from the lid cover  120 . In some examples, the predetermined distance between the surface level of the freezing fluid and the lid cover  120  is set between about ⅛ of an inch to one inch. In some examples, the surface level of freezing fluid in each fluid chamber  126  is monitored to account for the volatility of the freezing fluid. Accordingly, if the surface level of freezing fluid lowers due to evaporation, more freezing fluid is supplied to the freezing fluid chambers  126 . 
     Referring to  FIGS. 3 and 4 , in one example, the liquid dispenser  200  is mounted to a mounting post  220  arranged along a side of the transporter  100 . The gas injector  300  is mounted to a mounting post  320  arranged along the side of the transporter  100  and spatially separated from the mounting post  220 . In one example, mounting post  220  comprises an upright post  210  fixed to a mounting base  212 , a lateral bracket  222  connected to an end of the upright post  210 , and a nozzle bracket  224  extending laterally from a free end of the lateral bracket  222 . In one example, mounting post  320  comprises an upright post  310  fixed to a mounting base  312 , a lateral bracket  322  connected to an end of the upright post  320 , and a nozzle bracket  324  extending laterally from a free end of the lateral bracket  322 . 
     As shown in  FIG. 3 , the liquid dispenser  200  includes one or more dispenser nozzles  230  extending through retention holes formed in the nozzle bracket  224 . In some examples, each dispenser nozzle  230  is positioned above the lid cover  120  at a radius r 1 , r 2 , r 3 , or r 4  corresponding to the positions of the openings to the fluid chambers  126  such that each nozzle  230  is aligned with a center of a respective fluid chamber  126  when fluid chamber  126  is set at the first position. In other examples, the dispenser nozzles  230  may be located above the lid cover  120  whereby each dispenser nozzle  230  is aligned with any position within the diameter of the hole of a respective fluid chamber  126  when set at the first position. As shown in  FIGS. 3 and 6 , the gas injector  300  includes one or more injector nozzles  330  extending through retention holes formed in the nozzle bracket  324 . In some examples, each injector nozzle  330  is positioned above the lid cover  120  at a radius r 1 , r 2 , r 3 , or r 4  corresponding to the positions of the openings to the fluid chambers  126  such that the each nozzle  330  is aligned with a center of the opening of a respective fluid chamber  126  when the fluid chamber is set at the second position. In other examples, the injector nozzles  330  may be located above the lid cover  120  whereby each injector nozzle  330  is aligned with any position within the diameter of the hole of a respective fluid chamber  126  when set at the second position. 
     In one example, the dispenser nozzles  230  and injector nozzles  330  are disposed within the respective nozzle bracket  224 ,  324  in an arrangement corresponding to the arrangement of the openings of fluid chambers  126  as shown in box A-A of  FIG. 5 . Referring to  FIG. 3 , the liquid dispenser  200  comprises a set of four dispenser nozzles  230  aligned with a respective group of openings of fluid chambers  126  that is positioned beneath the nozzle bracket  224 . Referring to  FIGS. 3 and 6 , the gas injector  300  comprises a set of four dispenser nozzles  330  aligned with another respective group of openings of fluid chambers  126  that is positioned underneath the nozzle bracket  324 . Accordingly, as the transporter  100  rotates, a first group of openings of the fluid chambers  126  becomes aligned with the set of dispenser nozzles  230  when positioned beneath the nozzle bracket  224 , and a second group of openings of the fluid chambers  126  becomes aligned with the set of injector nozzles  330  when positioned beneath the nozzle bracket  324 . In other examples, the dispenser nozzles  230 , the injector nozzles  330 , and the openings of the fluid chambers  126  may be set in other arrangements that simultaneously allow a set of dispenser nozzles  230  to dispense fluid into a first group of openings of fluid chambers  126  and a set of injector nozzles  330  to inject gas into a second group of openings of fluid chambers  126 . 
     The liquid dispenser  200  includes a liquid feed line  240  (e.g., hoses, tubes, etc.) connecting each dispenser nozzle  230  to a liquid reservoir (not shown). The gas injector  300  includes a gas feed line  340  (e.g., hoses, tubes, etc.) connecting each injector nozzle  330  to a source of compressed gas (not shown). 
     In some examples, the liquid reservoir contains an aqueous solution of reagents, and the liquid dispenser  200  includes a pump system (not shown) that conveys the liquid reagent from the liquid reservoir to the liquid dispenser through the associated liquid feed line. The pump system allows the liquid dispenser  200  to control the flow rate of liquid reagent passing through the liquid feed line  240  and the frequency of liquid droplets dispensed into the fluid chambers. The liquid dispenser  200  is configured to dispense individual drops of liquid reagent from the dispenser nozzle  230  into the openings of the fluid chambers  126 . The dispenser nozzle  230  includes an orifice (not shown) that is configured to provide substantially uniform drop size. A variety of dispenser nozzles  230  may be used so long as sufficient uniformity of drop size is provided. The dispenser nozzles  230  may be made of Trifluoroethylene or some other polymer with equivalent rigidity and surface characteristics. The size of the orifice in the dispenser nozzle  230  will depend upon the composition of the liquid reagent and the operating pressure used to pump the reagent. In one example, the dispenser nozzle  230  is tapered, and a wall thickness of the dispenser nozzle  230  may vary based on the properties of the liquid reagent being dispensed. 
     The tip of the dispenser nozzle  230  is preferably located a sufficient distance above the surface of the freezing fluid contained in the fluid chamber to permit the dispensed liquid droplet to form a sphere before landing on the surface of the freezing fluid. However, spacing the tip of the dispenser nozzle  230  too great a distance above the surface of the freezing fluid surface permits the dispensed liquid droplet to break up into multiple droplets prior to contacting the freezing fluid. Furthermore, if the tip of the dispenser nozzle  230  is too close to the surface of the freezing fluid, then the dispensed liquid droplet freezes too rapidly once contacting the freezing fluid or promotes splashing of the freezing fluid. Accordingly, in some examples, the tip of the dispenser nozzle  230  is positioned between about ¾ of an inch and about 2 inches above the surface of the freezing fluid. The precise distance between the tip of the dispenser nozzle  230  used will depend upon the particular design of the apparatus, the design of the dispenser nozzle  230  used, and characteristics of the liquid to be dispensed. This distance can be determined by minimal experimentation once other design variables are specified. In some examples, the tips of the liquid dispenser nozzle  230  and the injector nozzle  330  are located about ½ inch above the lid cover  120  having a thickness about ¼ of an inch, whereby the surface of the freezing fluid is set about ⅛ of an inch to about 1 inch below a bottom surface of the lid cover  120 . 
       FIG. 8  illustrates a schematic diagram of a gas delivery and control system  400  according to one example. The system  400  comprises an injector nozzle  410 , a source of compressed gas (e.g., a tank or a compressor)  420 , and a feed line  430  connecting the injector nozzle  410  to the source of compressed gas  420 . The source of compressed gas  420  is configured to generate a stream of gas that is conveyed via the feed line  430  to the nozzle  410 . The system  400  may include an isolation valve  440  (e.g., ball valve) disposed along the feed line  430  and configured to selectively stop the stream of gas along the feed line  430  (e.g., for maintenance purposes or detection of a leak). The system  400  may include a pressure regulator  450  disposed along the feed line  430  and downstream of the isolation valve  440 . The pressure regulator  450  is configured to control the pressure of the gas flow along the feed line  430 . The system  400  may include a solenoid valve  460  disposed along the feed line  430  and upstream of the pressure regulator  450 . The solenoid valve  460  is configured to control the gas flow to the nozzle  410  by switching between a closed position to shut-off the gas stream from reaching the nozzle  410  and an open position to permit the gas stream to reach the nozzle  410 . The system  400  may include a flow valve  470  disposed along the feed line  430  and upstream of the solenoid valve  460  and configured to control the flow rate of the gas stream reaching the injector nozzle  410 . The combination of the pressure regulator  450  and flow valve  470  allow the control of supply pressure at the injector nozzle  410 . The supply pressure to the injector nozzle  410  is regulated to inject a stream of gas with enough pressure to adequately disturb the surface tension of the freezing fluid. The supply pressure to the injector nozzle  410  is further regulated to limit the pressure such that the stream of gas does not promote splashing of the freezing fluid. In one example, the injector nozzle  410  is configured to inject a stream of gas at a supply pressure range of about 10 to 40 pounds per square inch (PSI). In some preferred examples, the injector nozzle  410  is configured to inject a stream of gas a supply pressure range of about 20 to 30 PSI. 
     The delivery and control system  400  may allow the injector nozzle  410  to inject gas into a fluid chamber in short bursts only when the fluid chamber is positioned beneath the injector nozzle  410  or may allow the injector nozzle  410  to dispense a constant stream of gas, whereby the fluid chambers move in and out of the stream of gas by relative movement between the fluid chamber and the injector nozzle  410 . Referring to  FIG. 8 , in some examples, the delivery and control system  400  comprises a control unit  480  in communication with the solenoid valve  460  to control operation of the solenoid valve  460 . In one example, the system  400  is configured to inject gas only when a fluid chamber is disposed beneath the injector nozzle  410 , so the control unit  480  is configured to open the solenoid valve  460  based on a detected position of the injector nozzle  410  with respect to a fluid chamber. In one example, the system  400  may include a sensor  490  that monitors the position of the transporter  100  and communicates to the control unit  480  to open the solenoid valve  460  when the transporter  100  is in a position placing a fluid chamber  126  beneath the nozzle  410 . 
     In one example, the control unit  480  includes one or more processors, computer storage media (e.g., volatile and non-volatile memory), and one or more connectors, receivers, transmitters, and transceivers linked to the sensor  490  and the solenoid valve  460 . The control unit  480  is in electrical communication with the sensor  490  and is configured to receive the signal from the sensor  480 . The control unit  480  is configured to determine the rotation rate or the angular position of the transporter  100  (e.g., the base  130  or drum  110 ) based on the received signal. The control unit  480  is in electrical communication with the solenoid valve  460  and configured to transmit a command to the solenoid valve  460  to switch between the open and closed positions based on the rotation rate or angular position of the transporter  100 . Accordingly, the control unit  480  allows the gas injector  400  to selectively inject the gas stream based on the rotation rate or angular positon of the transporter  100 . 
     In one example, the control unit  480  controls the gas injector  400  to inject the gas stream transversely to the surface of freezing fluid contained in a respective fluid chamber only when the respective fluid chamber is in the second position. In one example, the gas injector  400  starts injecting the stream of gas once a leading edge of the fluid chamber is positioned below the injector nozzle  410  and continues injecting the stream of gas until a trailing edge of the fluid chamber is positioned below the injector nozzle  410 , such that the stream of gas strikes the surface of the freezing fluid transversely along the entire diameter of the fluid chamber. After the trailing edge of the fluid chamber moves away from the injector nozzle  410 , the control unit  480  commands the solenoid valve  460  to switch to the closed position, thereby terminating the gas flow until a leading edge of another fluid chamber is positioned underneath the injector nozzle  410 . In other examples, the gas injector  400  is configured to inject the gas stream continuously while the carousel is moving each fluid chamber between the first and second positions. 
     In one example, the sensor  490  is an optical sensor disposed beneath the base  130  of the transporter  100  and comprises a transmitter ( 492 ) configured to transmit a light beam  494  and a receiver ( 496 ) configured to receive the light beam. Interference of the received light beam triggers the sensor  490  to generate a signal. In one example, as shown in  FIG. 7 , the transporter  100  includes a plurality of projections  134  spatially arranged along a perimeter of the base  130 , whereby each respective projection  134  is configured to rotate between the transmitter  492  and the receiver  496  of the sensor  490 , thereby triggering the sensor  490  to generate a signal when one of the projections  134  blocks the light beam  494 . The sensor  490  is configured to generate a signal that indicates the angular position of the transporter  100 . In one example, the angular separation between the projections  134  along the perimeter of the base  130  corresponds to the angular separation between each group of openings of the fluid chambers  126  (e.g., as shown in box A-A of  FIG. 5 ) along the lid cover  120  such that each projection  134  corresponds to a respective group of openings of fluid chambers  126 . Accordingly, each projection  134  is configured to trigger the sensor  490  when a respective group of openings of fluid chambers  126  is aligned with a set of injector nozzles  330  and another respective group of openings of fluid chambers  126  is aligned with a set of dispenser nozzles  230 . In another example, the angular displacement between each pair of projections  134  corresponds to a respective group of openings of fluid chambers  126  such that detection of one of the projections  134  by the sensor  490  triggers the dispenser nozzle  230  to stop dispensing liquid droplets and the injector nozzle  330  to stop injecting a stream of gas. 
     Process for Preparation of Frozen Reagent Spheres 
     A non-limiting exemplary process for producing and collecting frozen reagent spheres is described herein. In some non-limiting examples, the method  50  and apparatus  1000  described above may be implemented for the exemplary process of producing and collecting frozen reagent spheres, as described herein. In one example, a bulk liquid reagent may be prepared in a bulk reagent bottle. The bulk liquid reagent was dispensed in aliquots (e.g., 24 μL sample size) by a liquid dispenser, such as the liquid dispenser  200  shown in  FIGS. 3 and 4 , into a freezing fluid (e.g., cryogenic liquid). The bulk liquid reagent may be supplied to the liquid dispenser by a pump (e.g., an IVEK™ pump). In one example, the pump comprises four separate feed lines that are each configured to independently transfer an aliquot of the bulk reagent through a liquid dispenser nozzle, such as the liquid dispenser nozzle  230  shown in  FIGS. 3 and 4 , and into a fluid chamber, such as the fluid chamber  126  shown in  FIG. 3 , containing liquid nitrogen (LN2). The dispensing rate of aliquots may vary based on several factors, such as the configuration of the LN2 bath, the physical parameters of the droplet, and the rotation speed of the fluid chambers. In one example, an aliquot of liquid may be dispensed at a rate of about every 3.2 seconds. 
     The LN2 may be held in a stainless steel drum enclosed with a lid cover, such as the drum  110  and cover  120  shown in  FIGS. 3 and 4 . The drum may comprise a bath (e.g., 50 gallon bath) configured to hold the LN2. The lid cover may comprise a plurality of bored holes, which form the fluid chambers. The plurality of fluid chambers may be arranged in groups of four fluid chambers, such as the group of fluid chambers  126  shown in  FIG. 5 , whereby each respective fluid chamber in the group is aligned with a respective liquid dispenser nozzle when the group of fluid chambers is set in a first position. To increase throughput, the fluid chambers and the LN2 bath may be rotated by rotating the drum about a spindle so that the first group of fluid chambers each receive a first dispensed aliquot of liquid reagent. Sometimes, the dispensed aliquot of liquid reagent may float on the surface of the LN2 before sinking to the bottom of the LN2 filled bath. To ensure that the first dispensed aliquot of liquid reagent sinks below the surface of the LN2 before dispensing a second aliquot of liquid reagent, the first group of fluid chambers may be rotated from the first position to a second position, in which the first group of fluid chambers are disposed under a set of gas injector nozzles. As the first group of fluid chambers move toward the second position, a second group of fluid chambers are moved to be aligned with the liquid dispense nozzles. Accordingly, a second aliquot of liquid reagent may then be dispensed into the second group of fluid chambers. The second group of fluid chambers may then be rotated to the second position such that the fluid chambers of the second group are disposed underneath the gas injector nozzles. The cycle of dispensing aliquot of liquid reagent into fluid chambers of a respective group and transporting the fluid chambers of the respective group to a second position may be repeated to prepare a batch of frozen liquid reagent spheres. 
     The rotational rate of the drum and the dispensing rate of the pump may be coordinated by providing projections attached to the base of the drum, such as the base  130  shown in  FIG. 7 , a transmitter, and a sensor, such as the sensor  490  shown in  FIG. 4 . In some examples, the lid cover is connected to the drum, such as the lid cover  120  and drum  110  shown in  FIG. 3 , so that the lid cover may rotate with the drum about the axis of rotation defined by the spindle. Coordinating the lid cover rotation rate with the pump dispenser rate ensures that the dispensed aliquot of liquid reagent drops into the fluid chambers. In some examples, a motor, such as the motor  150  shown in  FIG. 4 , is coupled to the base of the drum by the spindle so that the rotational rate of the drum may be controlled by controlling the speed of the motor. 
     The lid cover may rotate at a rate of about 1.5 RPM. The rotational rate may be selected based on a radius defined between the fluid chambers and a central point of the lid cover. Because the average dwell time of the dispensed liquid reagent in the freezing fluid is calculated to be about 10 seconds in some examples, the rotational speed (e.g., RPM) of the motor is selected to provide adequate time for most of the dispensed aliquots of liquid reagent to fall below the surface of the LN2 before the fluid chamber rotates back to the first position under the liquid dispense nozzle and receives a second aliquot of liquid reagent. 
     However, for a number of reasons, not all dispensed aliquots of liquid reagents will sink below the surface of the LN2 within a single revolution. Accordingly, in some examples, a gas injector, such as the gas injector  300  shown in  FIG. 3 , is disposed adjacent to the drum, and the gas injector comprises plurality of gas injector nozzles arranged to align with each group of fluid chambers when set at the second position. In some examples, the gas injector comprises a tank containing pressurized oxygen, four gas feed lines, and an injector nozzle connected to each gas feed line, such as the gas delivery system shown in  FIG. 8 . The gas injector nozzles may be placed to inject a stream of air transverse to a surface of the fluid contained in the fluid chamber at about 10 seconds after the fluid chamber initially rotates away from the first position under the liquid dispense nozzle. In some examples, the time interval between when the fluid chamber initially rotates away from the first position to the second position and when the gas injector injects a stream of gas is set to be longer than the average dwell time. The gas injector may be configured to deliver a burst of air when the fluid chamber reaches the second position, in which the fluid chamber is aligned with the nozzle of the gas injector. In some examples, the gas delivery system further comprises a pressure gauge, pressure regulator, solenoid and flow valves, and a control unit, such as the gas delivery system shown in  FIG. 8 , to ensure that the injection of air from the gas injector is properly timed with the positioning of the fluid chamber. 
     In some examples, the plurality of gas injector nozzles are each configured to inject a stream of air transversely to the surface of the fluid contained in the fluid chamber to disrupt the surface tension of the LN2. Accordingly, any aliquot of liquid reagent floating on the surface of the LN2 will sink into the LN2 before the fluid chamber returns to the first position under the fluid dispense nozzle to receive a second dispensed aliquot of liquid reagent. 
     Following a number of cycles, the liquid and air burst dispensing may be stopped, and the rotation of the drum and the lid cover may be stopped. The fluid contained in the fluid chambers freeze the aliquots of dispensed liquid reagents into frozen spheres, which sink toward the bottom of the fluid chamber. To recover the frozen spheres, a strainer basket may be disposed along a bottom interior of the drum. For example, as shown in  FIG. 9 , a strainer basket  142  disposed within drum  110  may be attached to a basket recovery shaft that extends through a central opening of the lid cover, such as the handle rod  140  (also shown in  FIG. 3 ). Accordingly, frozen reagent spheres  15  captured by the strainer basket  142  may be collected by grasping and pulling the handle rod  140  such that the strainer basket  142  is removed from the drum  110 . Once removed from the LN2, the frozen reagent spheres  15  may be transferred to a lyophilization tray to undergo a lyophilization process. 
     In the appended claims, the term “including” is used as the plain-English equivalent of the respective term “comprising.” The terms “comprising” and “including” are intended herein to be open-ended, including not only the recited elements, but further encompassing any additional elements. Moreover, in the following claims, the terms “first,” “second,” and “third,” etc. are used merely as labels, and are not intended to impose numerical requirements on their objects. Further, the limitations of the following claims are not written in means-plus-function format and are not intended to be interpreted based on 35 U.S.C. § 112(b), unless and until such claim limitations expressly use the phrase “means for” followed by a statement of function void of further structure. 
     While the subject matter of this disclosure has been described and shown in considerable detail with reference to certain illustrative embodiments, including various combinations and sub-combinations of features, those skilled in the art will readily appreciate other embodiments and variations and modifications thereof as encompassed within the scope of the present disclosure. Moreover, the descriptions of such embodiments, combinations, and sub-combinations is not intended to convey that the claimed subject matter requires features or combinations of features other than those expressly recited in the claims. Accordingly, the scope of this disclosure is intended to include all modifications and variations encompassed within the spirit and scope of the following appended claims.