Patent Publication Number: US-2022228954-A1

Title: Sampling system with a replaceable cassette assembly and methods of using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application No. 62/844,688, filed on May 7, 2019, which is incorporated by reference herein. 
    
    
     FIELD 
     The present disclosure is directed to a sampling system and methods of obtaining samples from containers, such as bioreactors. 
     BACKGROUND 
     Obtaining samples from containers or other systems that support biologically and/or chemically active environments can require complex and careful sampling procedures to avoid contamination of the containers or the environment itself, which can in some circumstances be a safety hazard. To reduce the risk of contamination within such systems, conventional sampling techniques generally require operators to perform multiple, labor-intensive steps. As such, improvements to such systems and methods are desirable. 
     SUMMARY 
     Various embodiments are disclosed herein of a sampling system, including a cassette assembly and a station base that can receive the cassette assembly, and methods of using the sampling system. 
     In some embodiments, sampling system includes a station base with a cassette-receiving surface and a plurality of actuators, and a cassette assembly received on the cassette-receiving surface. The cassette assembly can include a cassette base with a sample inlet, a reservoir for receiving a sample from the sample inlet, a sample outlet, and a fluid flow path extending between the sample inlet, the reservoir, and the sample outlet. The cassette assembly can also include a cassette top that has a plurality of movable members in engagement with respective ones of the plurality of actuators. The cassette assembly can also include an elastomer membrane disposed between the cassette base and the cassette top. One of the movable members can be in contact with the elastomer membrane to provide a sample inlet valve that can be opened and closed by a movement of one of the actuators, and the another one of the movable members can be in contact with the elastomer membrane to provide a sample outlet valve that can be opened and closed by a movement of another actuator. 
     In some embodiments, the elastomer membrane can extend over the reservoir and provides a pump membrane that is movable to vary a volume of the reservoir. The station base can include a pump member and the cassette top includes an air inlet disposed over a location of the reservoir that is in engagement with the pump member to vary a pressure at the pump membrane. 
     In some embodiments, the cassette base further comprises a sanitizing fluid inlet and a gas inlet and movable members that are in engagement with these inlets and additional actuators. 
     In some embodiment, the plurality of moveable members can comprise rocker valves that include a rocker arm in engagement with a respective one of the plurality of actuators and a ball that is in contact with the elastomer membrane. The rocker arms can be movable from a first position in which the respective valve is closed and a second position in which the respective valve is open, and each of the rocker arms can have a first end in engagement with a respective one of the plurality of actuators and a second end that is in contact with a spring member that biases the rocker arm to the first position. 
     In other embodiments, a cassette assembly is provided that includes a cassette base comprising a sample inlet, a reservoir for receiving a sample from the sample inlet, a sample outlet, and a fluid flow path extending between the sample inlet, the reservoir, and the sample outlet; a cassette top comprising a plurality of movable members including at least a first movable member and a second movable member; and an elastomer membrane disposed between the cassette base and the cassette top. The first movable member can be in contact with the elastomer membrane to provide a sample inlet valve that can be opened and closed by a movement of the first movable member, and the second movable member can be in contact with the elastomer membrane to provide a sample outlet valve that can be opened and closed by a movement of the second movable member. A plurality of openings in the cassette assembly can extend from respective ones of the plurality of movable members through the elastomer membrane and the cassette base to receive a plurality of actuators therethrough. In some embodiments, the elastomer membrane comprises silicone, EPDM, Viton, or CFLEX. 
     In another embodiment a method of collecting a fluid sample from an enclosed container is provided. The method can include securing a cassette assembly to a station base, positioning a plurality of actuators of the station base in engagement with respective ones of the plurality of movable members, actuating one of the plurality of actuators to engage with the third movable member to open the sample inlet valve and direct the fluid sample to the reservoir, applying a pressure to the elastomer membrane above the reservoir to cause the elastomer membrane to move into the reservoir and direct the fluid sample from the reservoir to the sample outlet, actuating another one of the plurality of actuators to engage with the fourth movable member to open the sample outlet valve and direct the fluid sample out of the sample outlet, removing the first cassette assembly from the station base, and securing another cassette assembly to the station base to replace the first one. 
     In some embodiments, the plurality of actuators comprise pneumatic air cylinders, and the pneumatic air cylinders are coupled to the station base, which is connected to a gas source and a sanitizing fluid source. Alternatively, the plurality of actuators can be electric actuators. 
     In other embodiments, the cassette assembly can contain all of the wetting components of the fluid sample collection and the station base is not directly exposed to the fluid sample. In other embodiments, portions of the station base can be exposed to the fluid sample, such as at a line out. 
     The foregoing and other objects, features, and advantages of the invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exemplary sampling system for obtaining a sample from a bioreactor or other similar containers or systems that support biologically and/or chemically active environments. 
         FIGS. 2A-2D  are schematic representations of an exemplary operation of the sampling system of  FIG. 1 . 
         FIG. 3  illustrates an exemplary cassette assembly for a sampling system. 
         FIG. 4  shows a side view of a cassette assembly coupled to a station base. 
         FIG. 5  shows an exploded view of the cassette assembly and station base. 
         FIG. 6  shows the exploded view of  FIG. 5  from a lower perspective. 
         FIG. 7  shows a cross-sectional view of the sampling system to illustrate the operation of the actuators and cassette rockers. 
         FIG. 8  shows another cross-sectional view of the sampling system to illustrate the operation of the actuators and cassette rockers. 
         FIG. 9  shows a top perspective view of an exemplary cassette base. 
         FIG. 10  shows a bottom perspective view of an exemplary cassette base. 
         FIG. 11  shows a top view of an exemplary cassette base. 
         FIG. 12  shows an exemplary elastomer membrane for use with a cassette assembly. 
         FIG. 13  shows a top view of a lower portion of a cassette top. 
         FIG. 14  shows a bottom view of the lower portion of the cassette top of  FIG. 13 . 
         FIG. 15  shows a bottom view of an upper portion of the cassette top. 
         FIG. 16  shows a bottom perspective view of the upper portion of the cassette top with a plurality of cassette rockers and balls positioned therein. 
         FIG. 17  shows a bottom view of the upper portion of the cassette assembly shown in  FIG. 16 . 
         FIG. 18  shows a perspective view of an exemplary station base. 
         FIG. 19  shows a perspective view of a cassette assembly secured to the station base of  FIG. 18 . 
         FIG. 20  shows a cassette assembly with another exemplary station base. 
     
    
    
     DETAILED DESCRIPTION 
     The systems and methods described herein, and individual components thereof, should not be construed as being limited to the particular uses or systems described herein in any way. Instead, this disclosure is directed toward all novel and non-obvious features and aspects of the various disclosed embodiments, alone and in various combinations and subcombinations with one another. For example, any features or aspects of the disclosed embodiments can be used in various combinations and subcombinations with one another, as will be recognized by an ordinarily skilled artisan in the relevant field(s) in view of the information disclosed herein. In addition, the disclosed systems, methods, and components thereof are not limited to any specific aspect or feature or combinations thereof, nor do the disclosed things and methods require that any one or more specific advantages be present or problems be solved. 
     As used in this application the singular forms “a,” “an,” and “the” include the plural forms unless the context clearly dictates otherwise. Additionally, the term “includes” means “comprises.” Further, the term “coupled” or “secured” encompasses mechanical and chemical couplings, as well as other practical ways of coupling or linking items together, and does not exclude the presence of intermediate elements between the coupled items unless otherwise indicated, such as by referring to elements, or surfaces thereof, being “directly” coupled or secured. Furthermore, as used herein, the term “and/or” means any one item or combination of items in the phrase. 
     As used herein, the term “exemplary” means serving as a non-limiting example, instance, or illustration. As used herein, the terms “e.g.,” and “for example,” introduce a list of one or more non-limiting embodiments, examples, instances, and/or illustrations. 
     The terms “upstream” and “downstream” are not absolute terms; instead, those terms refer to the direction of flow of fluids within a channel or pathway. Thus, with regard to a structure through which a fluid flows, a first area is “upstream” of a second area if the fluid flows from the first area to the second area. Likewise, the second area can be considered “downstream” of the first area. 
     Unless otherwise indicated, all numbers expressing quantities of ingredients, properties such as molecular weight, percentages, measurements, distances, ratios, and so forth, as used in the specification or claims are to be understood as being modified by the term “about.” Accordingly, unless otherwise indicated, implicitly or explicitly, the numerical parameters set forth are approximations that may depend on the desired properties sought and/or limits of detection under standard test conditions/methods. When directly and explicitly distinguishing embodiments from discussed prior art, the embodiment numbers are not approximates unless the word “about” is recited. 
     Although the operations of some of the disclosed methods are described in a particular, sequential order for convenient presentation, it should be understood that this manner of description encompasses rearrangement, unless a particular ordering is required by specific language set forth below. For example, operations described sequentially may in some cases be rearranged or performed concurrently. Moreover, for the sake of simplicity, the attached figures may not show the various ways in which the disclosed things and methods can be used in conjunction with other things and methods. Additionally, the description sometimes uses terms like “provide” and “produce” to describe the disclosed methods. These terms are high-level descriptions of the actual operations that are performed. The actual operations that correspond to these terms will vary depending on the particular implementation and are readily discernible by one of ordinary skill in the art having the benefit of this disclosure. 
     Unless explained otherwise, all technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and not intended to be limiting. Other features of the disclosure are apparent from the detailed description, claims, abstract, and drawings. 
       FIG. 1  illustrates a sampling system  100  for obtaining a sample from a bioreactor  102  or other similar containers or systems that support biologically and/or chemically active environments. Sampling system  100  includes a sample collection valve  104  that can open to allow a sample to enter a fluid flow path  106 . The sample can be delivered along the flow path  106  to an outlet valve  108 . Outlet valve  108  can open or close to allow or restrict, respectively, the flow of samples through outlet valve  108 . After the sample exits outlet valve  108 , the sample can be directed into an isolated chamber or container  110  for analysis, processing, and/or delivery to another system for analysis and/or processing. For example, the sample can be directed from chamber  110  to an automated analyzer  112 , such as a bioprofile analyzer available from Nova Biomedical of Waltham, Mass. 
     The samples that are dispensed from outlet  108  for analysis or processing are desirably representative of the materials in bioreactor  102  at the time the sample was taken. To reduce the risk of contamination, dilution, or alteration of the composition of the samples taken from sample collection valve  104  and delivered through flow path  106 , a sanitizing fluid can be delivered through a portion of flow path  106  that comes into contact with the samples. 
     To introduce the sanitizing fluid into flow path  106 , a sanitizing fluid inlet valve, such as valve  114  or  116 , is provided upstream of sample collection valve  104 . The sanitizing fluid inlet valve  114 ,  116  is operable between a closed position that restricts fluid flow through sanitizing fluid inlet valve and an open position that allows fluid flow through sanitizing fluid inlet valve. In some embodiments, some or all of the valves can be biased closed. 
     As used here, a “sanitizing fluid” is any fluid that can sanitize, disinfect, or sterilize the valve. The sanitizing fluid can be a liquid, a gas, or a combination thereof. Sanitizing fluids include steam, ethylene oxide, glutaraldehyde, formaldehyde, formalin, chlorine gas, hypochlorite, bromine, hypobromite, iodine, hypoiodite, bromine chloride, chlorine dioxide, ozone, hydrogen peroxide, monochloramine, dichloramine, trichloramine, quatinary ammonium salts, ethanol, 70% ethanol/water, isopropanol, 70% isopropanol/water, peroxyacetic acid, and peracetic acid. In one embodiment, the sanitizing fluid is steam. In another embodiment, the sanitizing fluid is ethylene oxide. In another embodiment, the sanitizing fluid is glutaraldehyde. 
     A gas inlet valve, such as valve  114  or  116  (whichever is not used as the sanitizing fluid inlet valve) can also be provided upstream of sample collection valve  104  to deliver a gas through flow path  106 . The gas can eliminate and/or reduce the amount of sanitizing fluid remaining within flow path  106  after flow path  106  is exposed to the sanitizing fluid. The sanitizing fluid can clean the path and/or remove any material from previous samples in the area contacted by the sanitizing fluid. The gas inlet valve is operable between a closed position that restricts the flow of gas through the gas inlet valve and an open position that allows the flow of gas through the gas inlet valve. In one embodiment, the gas comprises compressed air. 
     To draw a sample from bioreactor  102 , a variable volume reservoir  118  can be provided downstream of sample collection valve  104 . Variable volume reservoir  118  can be moveable between a first position and a second position to draw a sample through sample collection valve  104  and into flow path  106 . The sample can be drawn into at least a portion of variable volume reservoir  118  along a first portion of flow path  106  and discharged from variable volume reservoir  118  along a second portion of flow path  106 . Variable volume reservoir  118  can comprise a diaphragm pump as shown in  FIG. 1 , which can draw in a sample using a vacuum generated on the pump side. 
     As shown by dotted lines in  FIG. 1 , at least a portion of sampling system  100  can comprise a unitary structure  120 . Thus, for example, unitary structure  120  can comprise sample collection valve  104 , sanitizing fluid inlet valve and gas inlet valve  114 ,  116 , outlet valve  108 , and at least a portion of the fluid flow path. Preferably, the entire flow path between the sanitizing fluid inlet valve  114  and the outlet valve  108  is internal to the unitary structure  120 . 
     If desired, one or more filters  122  (e.g., a sterile air filter) can be provided upstream of gas inlet valve, sanitizing fluid inlet valve  114 ,  116  to ensure that the gas or sanitizing fluid that enters flow path  106  is substantially free of impurities and/or contaminants. 
       FIGS. 2A-2D  are schematic representations of the operation of sampling system  100 . As described in more detail below, sampling system  100  can be coupled to bioreactor  102  and can operate to sanitize or sterilize a flow path from the sanitizing fluid inlet valve  114 ,  116  through through the closed pathway of flow path  106 , including sample collection valve  104 , reservoir  118  (e.g., a diaphragm pump), and outlet valve  108 . By being able to sanitize or sterilize the flow path in this manner, the possibility of contaminating bioreactor  102  and/or the samples captured from bioreactor  102  is reduced. 
       FIG. 2A  illustrates a sanitizing procedure in which a sanitizing fluid  124  (e.g., steam) is directed into flow path  106  through an open sanitizing fluid inlet valve  114  (in this embodiment). As shown in  FIG. 2A , sanitizing fluid  124  is directed along flow path  106 , including along the portions of flow path  106  that are in contact with a sample drawn from bioreactor  102  and dispensed along the flow path  106 . For example, sanitizing fluid  124  is directed along flow path  106  past sample collection valve  104 , through variable volume reservoir  118 , and out outlet valve  108 . As sanitizing fluid  124  comes into contact with the internal surfaces that define flow path  106 , those surfaces are sanitized or sterilized. 
     Referring now to  FIG. 2B , sanitizing fluid inlet valve  114  (in this embodiment) is closed and gas inlet valve  116  (in this embodiment) is opened to allow a gas  126  (e.g., air) to enter flow path  106 . As shown in  FIG. 2B , gas  126  can also be directed along flow path  106 , including along the portions of flow path  106  that sanitizing fluid  124  contacts. In this manner, any remaining sanitizing fluid  124  can be purged from flow path  106 . 
       FIG. 2C  illustrates the operation of variable volume reservoir  118  to draw a sample  128  from bioreactor  102  through open sample collection valve  104 . As shown in  FIG. 2C , variable volume reservoir  118  comprises a diaphragm pump that moves from a first volume to a second, larger volume as illustrated by arrow  132 . The enlargement of the volume of variable volume reservoir  118  draws a sample through open sample collection valve  104  and into flow path  106 . Variable volume reservoir  118  has an inlet  134  and an outlet  136 . After sample  128  is drawn into variable volume reservoir  118 , the diaphragm pump moves from the second, larger volume back to a smaller volume as illustrated by arrow  132  in  FIG. 2D . The reduction of the volume of variable volume reservoir  118  discharges sample  128  through outlet  136  of variable volume reservoir  118 . Sample  128  is then discharged through outlet valve  108  to be captured for analysis and/or further processing. 
     Referring again to  FIG. 1 , as sample  128  is discharged through outlet valve  108 , it can be delivered to chamber  110 . To facilitate delivery of sample  128  to chamber  110 , a valve  138  can be provided downstream of outlet valve  108 . Valve  138  can be closed to cause sample  128  to be directed into chamber  110 . Valve  138  can be configured to open to allow the discharge of waste. The discharged waste can include, for example, sanitizing fluid and purging gas that has traveled along the flow path  106  to sanitize and purge excess sample materials from flow path  106 . 
     The sampling systems described herein can include systems that have a reusable component that does not require sterilization between operations and a single-use component that is replaced between operations. The station base can contain all the required mechanical actuators (such as the pneumatic air cylinders or electric actuators, and variable volume pump components) and can be connected (e.g., plumbed) to the control system and purge air and sanitant sources. 
       FIG. 3  illustrates the replaceable component (e.g., the unitary structure  120 ) of the sampling system as a cassette assembly. To provide reusability of the other components described herein (e.g., the station base with actuators), the cassette assembly can include all of the wetting components of the sampling system that come into direct contact with fluid. As used herein, the term “wetting component” as used herein means a component that comes in direct contact with a fluid (gas and/or liquid) and are typically include, for example, reservoirs, conduits, filters, and combinations thereof. 
     The term “cassette” as used herein means a cartridge or other structure capable of fitting and/or connecting to a sample inlet and one or more other fluid connections. The cassette can be a replaceable and/or disposable self-contained unit (e.g., a unitary structure) containing all wetting components of a sampling system of the type described herein. As used herein, the terms “disposable” refer to an element, component, and/or structure that may be disposed with and/or replaced after no more than 10 uses, preferably no more than 5 uses, preferably no more than 2 uses, most preferably no more than 1 use. As used herein, the term “single use” refers to a system that is used once. The term “uses or use,” as used herein, means a sampling procedure that includes receiving a first type or kind of sample before changing to receive a different kind or type of sample. 
     An example of a single use of a cassette would be a situation where a bioreactor is set up, the cassette is connected and used through an entire bioreactor run, in the same manner as a single-use probe or single-use fitting the usage of which is well-known in the industry. After the bioreactor run is completed, the cassette can be removed and replaced. 
     In particular,  FIG. 3  illustrates a cassette assembly  200  that includes a cassette base  202 , a cassette top  204 , and an elastomer membrane  206  disposed (e.g., fitted or assembles) between the cassette base  202  and cassette top  204 . A plurality of valve ports are provided in the cassette base and each can be coupled to a tube or other conduit for coupling with other components of the sampling system. For example,  FIG. 3  illustrates a first tube  208 , which can be coupled to a gas source for delivering a gas to purge sanitizing fluid from the flow path  106 , and a second tube  210 , which can be coupled to a sanitizing fluid source to deliver sanitizing fluid to the flow path  106 . A third tube  212  can be coupled to the bioreactor at sample outlet  205  to receive a sample. The elastomer membrane can be formed of any suitable elastomeric materials (such as, for example, silicone, ethylene propylene diene monomers (EPDM), Viton, and CFLEX) that can serve as a sealing surface for the plurality of valve ports and also as a pump membrane for the variable volume reservoir as described in detail below. 
     As shown in  FIGS. 4-6 , the cassette assembly  200  can be coupled to a station base  214 . Station base  214  can engage with the cassette assembly  200  so that a plurality of pneumatic air cylinders (or other actuators, such as electric actuators) can engage with a plurality of cassette rockers (or rocker arms) to open and close a plurality of valve ports in the cassette assembly  200 . As used herein the term “cassette rocker” or “rocker arm” refers to a structure that can pivot and/or move between at least two positions when a force is applied at one or both ends. 
     The pneumatic air cylinders, therefore, are actuators that are in engagement with the cassette rockers, which are movable members that can move from a first position to a second position causing the elastomer membrane to move and open and close the valve defined by an opening and the elastomer membrane (e.g., a sample inlet valve, sample outlet valve, sanitizing fluid inlet valve, and/or gas inlet valve). As used herein, the term “in engagement” refers to an actuator or actuating member that is positioned so that it can engage with another structure to cause it to move. Therefore, a component can be “engaged” with an actuator even if the two are not in direct contact, so long as the actuator is in position so that it can cause the movement of the other component. 
     For example, in the embodiment shown in  FIGS. 4-6 , pneumatic air cylinders  216 ,  218 ,  220 ,  222  are coupled to station base  214  and engage with respective cassette rockers  226 ,  228 ,  230 ,  232  retained in cassette top  204 . As shown in  FIG. 5 , cassette rockers  226 ,  228 ,  230 ,  232  are retained within a respective rocker guides in a lower portion  234  of cassette top  204 . Upper portion  236  encloses the rocker guides and has a plurality of extending portions  238  (e.g., fingers) that engage with openings that extend through the cassette assembly to align and secure the respective components of the cassette assembly  200  in a desired orientation. For example, a first extension member  240  extends through an opening  242  in lower portion  234 , an opening  244  in elastomer membrane  206 , and an opening  246  in cassette base  202 . Although not shown in  FIG. 5 , first extension member  240  can also extend though a cassette tube retaining member  248  (shown in  FIG. 3 ). 
     Conventional fasteners can be used in place of some or all of the extending portions, or in other different locations in combination with some or all of the extending portions described in this embodiment. 
     Referring again to  FIG. 5 , each cassette rocker can be biased to a closed position by a spring member  250 , which can be retained by a respective spring retaining well  252  (as shown in  FIG. 6 .).  FIGS. 7 and 8  illustrate the operation of the pneumatic air cylinders and cassette rockers. 
     As shown in  FIGS. 7 and 8 , each cassette rocker engages with a ball  254  to provide a rocker valve that can engage with the elastomer membrane  206  to open and close a respective valve port.  FIG. 7  illustrates a rocker valve  258  in a closed state, and  FIG. 7  illustrates the same valve in an open state. In the closed state ( FIG. 7 ), an actuator nose  256  of pneumatic air cylinder  216  does not engage with the cassette rocker  226  of rocker valve  258 . Instead, spring member  250  biases the cassette rocker  226  into engagement with ball  254 , with ball  254  forcing a portion of the elastomer membrane  206  into engagement with the valve port  260 . 
     In  FIG. 8 , the pneumatic air cylinder  216  has been actuated and the actuator nose  256  extends into contact with an end  262  of cassette rocker  226 . The tilting of the cassette rocker  226  causes the spring member  250  to compress and reduces the force of the cassette rocker  226  on the ball  254 . As the force on the ball  254  by the cassette rocker reduces, the force of the ball  254  on the elastomer membrane  206  likewise reduces, causing the valve port  260  to open and permit bi-directional flow therethrough. 
       FIGS. 9-11  show additional details of a cassette base  302 . As discussed above, the cassette base includes a plurality of valve ports that can be coupled to a tube or other conduit for coupling with other components of the sampling system, and opened and closed by a respective rocker valve. 
     As shown in  FIG. 9 , the plurality of valve ports can include a sample collection port  304 , a sanitizing fluid inlet port  314 , a gas inlet port  316 , and a cavity  315  that, in part, defines reservoir  318 . The reservoir  318  is also defined by the respective cavity of the lower portion  334  of the cassette top, as shown in  FIG. 14 . The volume of the reservoir  318  can vary depending on the position of the elastomer membrane as shown in  FIGS. 2A-2D . 
     When the sample collection port  304  is opened, a sample can enter the fluid flow path  306  and be delivered to the reservoir  318  as shown in  FIG. 2C . To deliver the sample from of the reservoir  318 , the elastomer membrane is caused to move into the reservoir where the sample is located and force the sample out of the reservoir as shown in  FIG. 2D . As the sample leaves the reservoir, it exit the outlet port  305 , which has been moved into the open state or position. 
       FIG. 10  shows a bottom view of cassette base  302 , which shows respective openings in fluid connection with the valve ports of the cassette base. These openings can receive and couple to respective tubes or conduits. For example, coupling members  360 ,  362 ,  364 , and  366  can receive tubes or conduits in fluid connection with sample collection port  304 , a sanitizing fluid inlet port  314 , a gas inlet port  316 , and outlet port  305 , respectively. 
       FIG. 11  illustrates a top view of the cassette base  302 . This view clearly shows a plurality of openings  370  in the cassette base  302  for the actuators (e.g., pneumatic air cylinders), which pass through the cassette base to engage with the cassette rockers in the cassette top  204 . In addition, a plurality of alignment openings  372  are shown. These alignment openings  372  receive the extending portions  238  (fingers) of the upper portion  236  of the cassette top  204 .  FIG. 11  also shows an air flow opening  374 . Opening  374  is in fluid connection with an area above the elastomer membrane to allow the reservoir to change its volume (i.e., to operate as a diaphragm pump). Air flow opening permits in the cassette base allows for the pump to be connected to a lower surface of the cassette base, which can be advantageous. 
       FIG. 12  shows the elastomer membrane  206 . As with the cassette base, the elastomer membrane has a plurality of openings  370  for the pneumatic air cylinders, a plurality of alignment openings  372 , and an air flow opening  374 . 
       FIGS. 13 and 14  illustrate the lower portion  234  of the cassette top  204 .  FIG. 13  shows a top view and  FIG. 14  shows a bottom view. As with the cassette base, the lower portion  234  of the cassette top  204  has a plurality of openings  370  for the pneumatic air cylinders, a plurality of alignment openings  372 , and an air flow opening  374 . In addition, as shown in  FIG. 13 , a channel  376  is provided in the top surface of the lower portion  234 . This channel extends from air flow opening  374  to another opening  378  which is in fluid connection with a portion of the reservoir above the elastomer membrane. The channel  376  and openings  374 ,  378  cooperate to allow air from the pump to be delivered through the cassette assembly to a location in the reservoir and above the elastomer membrane. 
       FIGS. 13 and 14  also show the respective ball-receiving openings  380 , which are sized to receive the balls  254 , so that they can move downward to engage with the elastomer membrane and close a respective valve port, and upward to disengage with the elastomer membrane and open a respective valve port.  FIG. 13  also shows the rocker guides (e.g., channels) which receive the cassette rockers. 
       FIGS. 15-17  show the upper portion  236  of cassette top  204 , with the rocker valves ( FIGS. 16 and 17 ) and without ( FIG. 15 ). As discussed above, upper portion  236  encloses the rocker guides and has a plurality of extending portions  238  (e.g., fingers) that engage with openings that extend through the cassette assembly to align and secure the respective components of the cassette assembly  200  in a desired orientation.  FIG. 15  also indicates a recess  278  that receives an O-ring  280  ( FIGS. 16 and 17 ) that provides a sealing surface for the channel  376  in lower portion  234 . 
     As shown in  FIGS. 16 and 17 , the respective cassette rockers  226 ,  228 ,  230 ,  232  are retained within a respective rocker guides in a lower portion  234  (not shown in these figures for convenience) and biased away from the upper portion  236  of the cassette top  204  by a spring member  250 . Each cassette rocker can have a receiving surface  282  that engages with a respective actuator nose of a pneumatic air cylinder. 
     The cassette assemblies described herein can be coupled and secured to a station base in a variety of manners. For example,  FIG. 18  illustrates one exemplary station base  214  on which a cassette assembly can be received.  FIG. 19  illustrates the same station base  214  with a cassette assembly received on a surface of the station base  214  and secured thereto with a plurality of gripping members  284 , such as spring-loaded clamps. 
       FIG. 20  illustrates another exemplary station base and attachment means. In particular, as shown in  FIG. 20 , a cassette assembly  200  can be received on a surface of station base  214 . Station base  214  comprises the plurality of pneumatic air cylinders  216 ,  218 ,  220 ,  222 , which engage with the cassette rockers as described above. After receiving the cassette assembly  200  on the station base  214 , the tubes  208 ,  210 ,  212  of the cassette assembly  200  can be coupled additional tubing (e.g., using quick-connect fittings) to deliver and/or receive fluids from and to other areas of the system as discussed herein. 
     Thus, the sample can flow out outlet valve  108  ( FIG. 1 ) and transition to the station base  214  via a seal (e.g., an o-ring seal) between the cassette assembly  200  and station base  214  at coupling  366  ( FIG. 10 ). 
     In  FIG. 20 , the coupling of the cassette assembly  200  and base station  214  is achieved by a clamp member  290 , which has a handle  292  (e.g., a lever) and a cassette-engaging member  294  (e.g., a clamping plate or surface). Of course, various other mechanisms can be provided to facilitate loading of a cassette assembly onto a station base. For example, in some embodiments, the loading and unloading of a cassette assembly can comprise a spring-loaded system that ejects an old cassette assembly and, upon receipt of a new cassette assembly, automatically closes to load the new cassette assembly on the station base. 
     The cassette assemblies described herein can be disposable (or “single-use” components) to allow for quick transitions from a first sampling procedure to a second sampling procedure (either with the same or a different type of sample), while the station base and related components (e.g., pneumatic air cylinders, clamping members) can be used without requiring sterilization. Thus, in contrast to conventional equipment which requires all components to be sterilized each time, only a portion of the sampling system requires sterilization. 
     The single-use cassette assembly can be readily sterilized, such as by gamma and/or autoclave sterilization. In some embodiments, the cassette assembly can be gamma compatible and pre-attached to other sterile sampling system components, such as bioreactor bags or pre-formed bioreactor vessels, prior to gamma sterilization, thereby eliminating the need to make an aseptic connection during setup. 
     Thus, for example, referring to the unitary structure  120  shown in  FIG. 1 , the entire structure  120  can be sterilized by, for example, gamma radiation, autoclave, or another approach, and connected to bioreactor  102  in a sterile fashion (such as sterile tube welding or a sterile single use connector). Alternatively, without separate sterilization of the structure  120 , the structure  120  would need to be connected to bioreactor  102  and the entire assembly sterilized (gamma radiation, autoclave, etc.). 
     In addition to providing an easily replaceable wetting component, the cassette assemblies described herein also reduce the number of moving parts and connections that can be potential sources of sample contamination. Instead, the valve ports engage with a single diaphragm member (e.g., the elastomer membrane), thereby reducing sliding interfaces and other sources of potential contamination. 
     The sampling systems described herein can be easily scaled up and down in size as desired. In some embodiments, the pump volume of the sampling system is less than 20 mL, less than 10 mL, less than 5 mL, less than 3 mL, and, in other embodiments, less than 2 mL, such as about 1 mL. Thus, the sampling system can draw samples in relatively small increments from a dip tube or other sterile connector. 
     In view of the many possible embodiments to which the principles of the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the following claims. We therefore claim as our invention all that comes within the scope and spirit of these claims.