Patent Publication Number: US-11660600-B2

Title: Microfluidic device with reservoir interface

Description:
TECHNICAL FIELD 
     Example embodiments generally relate to microfluid technology and, in particular, relate to a microfluidic device including an improved reservoir interface. 
     BACKGROUND 
     Microfluidic technologies are used in many scientific, laboratory, and industrial applications. In particular, devices that leverage the operation of microfluidic channels have proven to be very useful for imaging and mixing substances in a variety of fields including cell biology, genetics, fluid dynamics, tissue engineering, fertility testing, synthesis of chemicals and proteins, and the like. Such devices leverage the principles of microfluidics, which involves the study of fluids in amounts smaller than a droplet. To form such small amounts, many devices use microfluidic channels that have a width that is submicron to a few millimeters. These microfluidic channels may be formed in a device that is referred to as a microfluidic chip. The microfluidic channels of the chip permit processing (e.g., mixing, chemical reactions, physical reactions, or the like), as well as, visualization and imaging of such processing. The fluid or fluids applied to the microfluidic chip may include any type of particles including biologic material, such as proteins and other types of cells, chemicals, or the like. 
     However, despite their high utility in a number of contexts, many microfluidic systems can be cumbersome to maintain and operate particularly when applications demand high processing throughput rates. In such applications, issues relating to, for example, cross-contamination between processing operations must be avoided. For example, in medical diagnostics and biomolecular forensics, cross-contamination can lead to inaccurate results and serious ramifications due to false positives. In these cases, any residual fluids from previous processing can generate such false results and invalidate the utility of the later processing. As such, any material or devices that come into contact with the fluids of a particular processing run must either be discarded or thoroughly cleaned. This required cleaning process often involves taking the microfluidic system offline so that components of the system can be removed, cleaned, and verified as having been sufficiently cleaned. In particular, tubing, manifold components, and the like can require such cumbersome cleaning efforts or disposal resulting in high system downtimes and added cost of operation. As such, it would be beneficial to develop microfluidic devices that can minimize or eliminate the post-process cleaning and one-time use peripheral components. 
     BRIEF SUMMARY OF SOME EXAMPLES 
     According to some example embodiments, a microfluidic assembly is provided. The microfluidic assembly may comprise a device source pressure port, a device relief pressure port, a microfluidic chip operably coupled to the device source pressure port and the device relief pressure port, a first input reservoir and a second input reservoir, an output reservoir, and a reservoir interface. The microfluidic chip may comprise a microfluidic circuit configured to support a fluid flow through the microfluidic circuit. The fluid flow may comprise a gas flow and a liquid flow within the microfluidic circuit. The reservoir interface may be configured to operably couple the first input reservoir and the second input reservoir to the microfluidic circuit. The device source pressure port may be configured to receive a source pressure to generate a fluid flow between the device relief pressure port and the device source pressure port and through the microfluidic circuit. The fluid flow may cause a mixing of a first liquid in the first input reservoir with a second liquid in the second input reservoir at a mixing junction of the microfluidic circuit within the microfluidic chip to form an output liquid for delivery to the output reservoir via the fluid flow. The first liquid, the second liquid, and the output liquid need not contact the device source pressure port or the device relief pressure port during the mixing. 
     According to some example embodiments, a microfluidic reservoir interface is provided. The microfluidic reservoir interface may comprise a liquid pipe configured to extend into a liquid within a reservoir, a gas interface, and an interface base configured to support the liquid pipe and the gas interface. The liquid pipe may be configured to be operable coupled to a liquid channel portion of a microfluidic circuit of a microfluidic chip and the gas interface may be configured to be operably coupled to a gas channel portion of a microfluidic device. The liquid pipe may be configured to transport the liquid between the reservoir and the liquid channel portion in response to a fluid flow through the liquid pipe and the gas interface. 
     According to some example embodiments, a method for performing a mixing of liquids is provided. The method may comprise receiving a source pressure applied at a device source pressure port of a microfluidic device, generating a pressure differential and a fluid flow between a device relief pressure port and the device source pressure port through the microfluidic circuit due to receiving the source pressure, and transporting a first liquid from a first input reservoir into the microfluidic circuit due to the fluid flow through the microfluidic circuit. The method may further comprise transporting a second liquid from a second input reservoir into the microfluidic circuit due to the fluid flow through the microfluidic circuit, causing a mixing of the first liquid with the second liquid at a mixing junction of the microfluidic circuit to form an output liquid, and transporting the output liquid to an output reservoir due to the fluid flow through the microfluidic circuit. The first liquid, the second liquid, and the output liquid need not contact the device source pressure port or the device relief pressure port during the mixing. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S) 
       Having thus described some example embodiments in general terms, reference will now be made to the accompanying drawings, which are not necessarily drawn to scale, and wherein: 
         FIG.  1 A  illustrates an example microfluidic device and a fluid flow through the microfluidic device according to some example embodiments; 
         FIG.  1 B  illustrates another example microfluidic device and a fluid flow through the microfluidic device according to some example embodiments; 
         FIG.  2    illustrates an example microfluidic assembly comprising a microfluidic device and a processing control system according to some example embodiments; 
         FIG.  3 A  illustrates an example input portion of a reservoir interface according to some example embodiments; 
         FIG.  3 B  illustrates the example output portion of a reservoir interface according to some example embodiments; 
         FIG.  4    illustrates an example system microfluidic device having a microfluidic circuit according to some example embodiments; 
         FIG.  5    illustrates an example a top view of the microfluidic device of  FIG.  4    and the microfluidic circuit according to some example embodiments; 
         FIG.  6    illustrates a microfluidic device and reservoir tray process according to some example embodiments; 
         FIG.  7    illustrates another example microfluidic device having a microfluidic circuit and a separated output reservoir according to some example embodiments; 
         FIG.  8    illustrates a microfluidic device with an array of individual reservoir interfaces involved in a reservoir tray process according to some example embodiments; and 
         FIG.  9    illustrates a flowchart of an example method for operating a microfluidic assembly according to some example embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Some example embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all example embodiments are shown. Indeed, the examples described and pictured herein should not be construed as being limiting as to the scope, applicability or configuration of the present disclosure. Rather, these example embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like reference numerals refer to like elements throughout. As used herein, operable coupling should be understood to relate to direct or indirect connection that, in either case, enables functional interconnection of components that are operably coupled to each other. 
     According to some example embodiments, a microfluidic device is described that comprises a microfluidic chip and a reservoir interface configured to operably couple input and output reservoirs to the microfluidic chip. The microfluidic device may operate to create microfluidic mixtures from input fluids, where the fluid flow within the device that operates to form the mixture is controlled by application of external gas pressures thereby avoiding liquid contact interactions with any components external to the microfluidic device. Such external gas pressures (e.g., positive or negative pressures) may be applied at the device source pressure port, in controlled manner, to generate a pressure differential and an associated fluid flow between the device source pressure port and a device relief pressure port. Based on whether the applied source provides a positive pressure or a negative pressure, the source may be applied, relative to the direction of the fluid flow, in an upstream position for a positive pressure source or a downstream position for a negative pressure source. As such, a given port of the microfluidic device may be defined as a device source pressure port or device relief pressure port based upon whether the source is a positive pressure source or a negative pressure source. In either case, an example microfluidic device may have a device pressure source port and a device pressure relief port that form the external interfaces to an external processing control system. These ports may operate as gas pressure interfaces that do not come into contact with any liquids that are involved in the microfluidic processing. 
     Additionally, these gas pressure interfaces can operate to force the liquids into a microfluidic circuit that is disposed, at least partially, within a microfluidic chip to perform an operation, such as a mixing operation. The microfluidic chip, according to some example embodiments, may be a transparent block of material with internal microfluidic channels and a mixing junction of the microfluidic circuit for transporting, combining, and manipulating liquids, where the channels are tens to hundreds of microns in diameter. Accordingly, a fluid flow (i.e., a gas and/or liquid flow) through the microfluidic chip can be formed within the microfluidic circuit without the fluid flow causing liquid contact with components external to the microfluidic device. As such, according to some example embodiments, after a microfluid mixture is formed using the microfluidic device, only the device itself is contaminated by the mixing process and therefore the microfluidic device may simply be replaced within an external mixture control system to conduct a subsequent mixture process, without having to clean or replace interface tubing, interface manifolds, or other interface components to an external processing control system. Additionally, once the results of a mixture process are removed from the reservoirs, microfluidic device and the reservoirs may be disposed. However, according to some example embodiments, the microfluidic device may be cleaned and reused in, for example, a separate, offline process that does not affect throughput at processing control stations. 
     As such, a microfluidic assembly, according to some example embodiments, may comprise a microfluidic device and an external processing control system. The microfluidic device, according to some example embodiments, may comprise a microfluidic chip having a microfluidic circuit, a reservoir interface configured to operate as an operational interface between the microfluidic chip and one or more reservoirs from which an input liquid may be extracted or an output liquid may be delivered, and a processing control interface which may comprise the device source pressure port and the device relief pressure port. The microfluidic circuit of the microfluidic chip may be operably coupled to reservoirs via the reservoir interface and the microfluidic device may be operably coupled to a processing control system via at least the device source pressure port, and also, possibly the device relief pressure port. The reservoir interface may therefore support liquid and gas flows into and out of the reservoirs to support the fluid flow through the microfluidic circuit. 
     Further, according to some example embodiments, the microfluidic device may comprise a source pressure gas portion operably coupled to the device source pressure port and a relief pressure gas portion operably coupled to the device relief pressure port. A liquid channel portion of the microfluidic chip may be disposed between the source pressure gas portion and the relief pressure gas portion. These gas portions may operate as contaminant barriers to the liquid channel portion with respect to external components of, for example, the processing control system. Moreover, the source pressure gas portion and the relief pressure gas portion may operate as contamination barriers that bracket the liquid channel portion because, according to some example embodiments, only liquid flows in the liquid channel portion of the microfluidic circuit and only non-contaminant gases (e.g., air) flow in the source pressure gas portion and the relief pressure gas portion. In this manner, according to some example embodiments, cross-contamination between microfluidic processing runs can be avoided without requiring cleaning and/or disposal of some or all components external to the microfluidic device. 
     Now referring to  FIG.  1 A , example microfluidic device  10  is shown in combination with reservoirs  50 . The description of the microfluidic device  10  is provided in the context of a vacuum or negative source, such that the source components and elements are located in downstream positions and the relief components and elements are in upstream positions relative to the fluid flow  12 . However, one of ordinary skill in the art would appreciate that the references to source and relief components and elements may simply be exchanged in the context of a positive pressure source that would be placed in an upstream position relative to the fluid flow  12 . 
     The microfluidic device  10  may comprise a microfluidic chip  20  and a reservoir interface  40 . The microfluidic chip  20  may be constructed from a solid substance formed as, for example a block, and may be transparent or sufficiently translucent to allow for visualization and imaging of the operations performed within the microfluidic chip  20 . In this regard, the microfluidic chip  20  may be constructed of, for example, glass or a PDMS (Polydimethylsiloxane) substance, which may also be known as dimethylpolysiloxane or dimethicone. According to some example embodiments, the microfluidic chip  20  may be constructed of polymetric organosilicon compounds or silicon-based organic compounds, which are commonly referred to as silicones. Further, according to some example embodiments, the microfluidic chip  20  may be created via an injection molding process. 
     The reservoir interface  40  may operate as a coupling device between the microfluidic chip  20  and the reservoirs  50 . The reservoir interface  40  may operate to provide the microfluidic chip  20  and, more specifically, the microfluidic circuit  30  access to the reservoirs  50  to facilitate removal of fluids from, or delivering fluids to, the reservoirs  50 . The reservoirs  50  may include a number of containment devices, such as cups, that are configured to hold a liquid. The reservoirs  50  may include one or more input reservoirs that hold input liquids for processing (e.g., for mixing). The reservoirs  50  may also include one or more output reservoirs that receive a processed liquid (e.g., a liquid mixture). The liquids that are held by the reservoirs  50  for processing may include aqueous liquids, oils, water, or the like. 
     As mentioned above, the microfluidic chip  20  may include a microfluidic circuit  30 . According to some example embodiments, the microfluidic circuit  30  may include portions that are within the microfluidic chip  20  and portions that are external to the microfluidic chip  20  (e.g., portions that flow through the reservoirs  50 ). The microfluidic circuit  30  may comprise a number of interconnected channels within the microfluidic chip  20  with at least some of the channels being microfluidic channels. According to some example embodiments, some or all of the microfluidic channels of the microfluidic circuit  30  may be formed on a common plane of the microfluidic chip  20 . According to some example embodiments, the channels may operate to transport fluids in the form of gases or liquids. The microfluidic channels of the microfluidic circuit  30  that transport fluids may have diameters in the tens to hundreds of microns range. The microfluidic circuit  30  may also comprise a number of ports. According to some example embodiments, a device source pressure port  22  of the microfluidic circuit  30  may be disposed on a first side of the microfluidic chip  20  to facilitate interfacing with external components of, for example, a processing control system including a vacuum or negative pressure source. According to some example embodiments, a device relief pressure port  24  of the microfluidic circuit  30  may be disposed on a second side of the microfluidic chip  20 . In some example embodiments, the device relief pressure port  24  may also be configured to interface with external components of, for example, of a processing control system. 
     Additionally, according to some example embodiments, reservoir ports of the microfluidic chip  20 , for at least some of the reservoirs  50  (e.g., input reservoirs), may be disposed on a third side of the microfluidic chip  20 . According to some example embodiments, the reservoir ports may be holes in the third side of the microfluidic chip  20  that, for example, receive or interface with liquid or gas pipes of the reservoir interface. In this regard, a reservoir of reservoirs  50  may be operably coupled to a respective reservoir port, where a reservoir port comprises a liquid opening and a gas opening. According to some example embodiments, the third side of the microfluidic chip  20  may be a bottom side of the microfluidic chip  20  such that gravity maintains the fluids in the reservoirs  50  until acted upon. The first and second sides of the microfluidic chip  20  may be substantially parallel to each other, and the third side may be substantially perpendicular to both the first side and the second side. According to some example embodiments, the microfluidic channels of the microfluidic circuit  30  may be formed on a common plane through the microfluidic chip  20  with reservoir ports extending from the common plane operably coupled to the reservoir interface  40 . 
     According to some example embodiments, the microfluidic circuit  30  may be comprised of three portions, where at least some of the portions are disposed within the microfluidic chip  20 . According to some example embodiments, the microfluidic circuit  30  may comprise a source pressure gas portion  32 , a liquid channel portion  34 , and a relief pressure gas portion  36 . With respect to the construction of the microfluidic circuit  30 , the device source pressure port  22  may be operably coupled to the source pressure gas portion  32 , and the source pressure gas portion  32  may be operably coupled to the liquid channel portion  34 . The liquid channel portion  34  may be operably coupled to the relief pressure gas portion  36 , and the relief pressure gas portion  36  may be operably coupled to the device relief pressure port  24 . The source pressure gas portion  32  and the relief pressure gas portion  36  may be subjected to gas pressures. The liquid channel portion  34  may be subjected to liquid pressures. 
     In operation, according to some example embodiments, an initial gas pressure may be applied at the device source pressure port  22  by an external source. The applied gas pressure may be a negative pressure. In example embodiments of  FIG.  1 A , a negative pressure (e.g., generated by a vacuum source) is applied at the device source pressure port  22 . The application of the negative gas pressure at the device source pressure port  22  may create a fluid flow  12  through the microfluidic circuit  30  traveling from the device relief pressure port  24  to the device source pressure port  22 . Because the reservoirs  50  are gas-tight sealed to the reservoir interface  40 , the fluid flow  12  transitions between being a gas flow and a liquid flow through the microfluidic circuit  30  and through the reservoirs  50 . In this regard, due to the negative pressure applied at the device source pressure port  22 , gas (e.g., air) may be pulled into the relief pressure gas portion  36  of the microfluidic circuit  30  through relief pressure port  24 . It is again noted that a positive pressure source placed at an upstream position would operate in a similar manner to push gas (e.g., air) into the microfluidic circuit  30  in the same direction. Due to the fluid flow  12 , the gas may be forced into the reservoirs  50 , through the reservoir interface  40 , that hold an input liquid as indicated by white arrow  52 . The gas pressure may create a pressure differential within the reservoirs  50  with the input liquids and pressure may therefore be applied to the input liquids in the reservoirs  50 , which may operate to force the input liquids into the liquid channel portion  34  of the microfluidic circuit  30 , as indicated by the black arrows  53  and  54 , through the reservoir interface  40 . Still being subjected to the fluid flow  12 , the input liquids may be mixed within the liquid channel portion  34  at a mixing junction and transported as an output liquid to an output reservoir of the reservoirs  50 , as indicated by the black arrow  55 , through the reservoir interface  40 . Finally, gas may be forced from the output reservoir of the reservoirs  50  and into the source pressure gas portion  32 , via the reservoir interface  40 , as indicated by the white arrow  51 , which may be pulled from the microfluidic chip  20  via the device source pressure port  22 . 
     As such, the process of moving fluids through the microfluidic circuit  30  involves the flow of gases at the external interfaces, regardless of whether a positive pressure source is applied at an upstream position or a negative pressure is applied at a downstream position. Therefore, no liquids are transported into or out of the device source pressure port  22  or the device relief pressure port  24  during processing, in this case mixing, of the fluids. The fluid flow  12  converts between being a gas flow within the relief pressure gas portion  36 , to a liquid flow in the liquid channel portion  34 , to a gas flow in the source pressure gas portion  32 . Because gas flows are relied upon at the ends of the processing, contamination of component external to the microfluidic device  10  and the reservoirs  50  is avoided. In this regard, the relief pressure gas portion  36  forms a first anti-contamination barrier  35  for the liquid channel portion  34  and source pressure gas portion  32  forms a second anti-contamination barrier  33  for the liquid channel portion  34  due to the gas/liquid and liquid/gas pressure transitions. 
     The microfluidic device  10  of  FIG.  1 A  illustrates example embodiments where both the device source pressure port  22  and the device relief pressure port  24  are disposed on or within the microfluidic chip  20 . However, according to some example embodiments, a microfluidic device may have one or both of the device source pressure port  22  or the device relief pressure port  24  disposed external to the microfluidic chip  20  as described with respect to  FIG.  1 B , as well as with respect to  FIG.  7   . The microfluidic device  11  of  FIG.  1 B  illustrates example embodiments where, for example, the device source pressure port  22  is disposed external to the microfluidic chip  21 . In this regard, for example, the output liquid may exit the microfluidic chip  21  via a tube or other conduit as shown at black arrow  55  into an output reservoir of the reservoirs  50 . Despite the difference in the fluid flow  12  relative to the microfluidic chip  21 , the source pressure gas portion  32  still operates to provide the second anti-contamination barrier  33  for the liquid channel portion  34  due to the gas/liquid and liquid/gas pressure transitions. 
     Having described some of the structural and functional features of some example embodiments of a microfluidic device, reference will now be made to  FIG.  2   , which illustrates a microfluidic assembly  100 . The microfluidic assembly  100  may comprise a microfluidic device  110  and a processing control system  101 . The microfluidic device  110  may be structured and function the same or similar as the microfluidic device  10 , possibly with modifications as described below and otherwise herein. 
     The microfluidic device  110  may comprise a microfluidic chip  112  and a reservoir interface  120 . The microfluidic chip  112  may be structured and function the same or similar as the microfluidic chip  20 , possibly with modifications as described below and otherwise herein. Also, the reservoir interface  120  may be structured and function the same or similar as the reservoir interface  40 , possibly with modifications as described below and otherwise herein. In this regard, the reservoir interface  120  may operate as a coupling device between the microfluidic chip  112  and the reservoirs  132 ,  134 ,  136 , and  138 . The reservoirs  132 ,  134 ,  136 , and  138  may be same or similar to reservoirs  50 . Further, the reservoirs  132 ,  134 ,  136 , and  138  may be, for example, formed as individual cups or canisters made of non-reactive plastic or the like. The reservoirs  132 ,  134 , and  136  may be input reservoirs and may contain an input liquid. As such, reservoirs  132 ,  134 , and  136  may contain input liquids  133 ,  135 , and  137 , respectively. The reservoir  138  may be an output reservoir for receiving an output liquid  139 , which may be a combination of the input liquids  133 ,  135 , and  137 . Accordingly, the reservoir interface  120  may be configured to interface reservoir ports of the microfluidic circuit  114  of the microfluidic chip  112  with the internal cavity of the reservoirs  132 ,  134 ,  136 , and  138  to support either removal of the liquid therein or delivery of a liquid thereto. 
     The microfluidic circuit  114  may be may be structured and function the same or similar as the microfluidic circuit  30 , possibly with modifications as described below and otherwise herein. In this regard, the microfluidic circuit  114  may include a device source pressure port  116  and a device relief pressure port  118 . With respect to functionality, the microfluidic circuit  114  may be configured to support the propagation of a fluid flow through the microfluidic circuit  114 . In some example embodiments, the fluid flow may be a gas/liquid/gas flow travelling in a direction from the device relief pressure port  118  to the device source pressure port  116 , where a negative pressure (e.g., vacuum) is applied at the device source pressure port  116  Alternatively, in some example embodiments, the fluid flow may be a gas/liquid/gas flow travelling in a direction from the device source pressure port  116  to the device relief pressure port  118 , where a positive pressure (e.g., blower) is applied at the device source pressure port  116 . Due to the fluid flow, the input fluids  133 ,  135 , and  137  may be forced from the input reservoirs  132 ,  134 , and  136  into channels of the microfluidic circuit  114  to be combined at a mixing junction. The mixture of liquids may exit the junction, as a result of the fluid flow, as the output fluid  139  for delivery to the output reservoir  138 . 
     The processing control system  101  may be configured to control the processing of liquids by controlling the fluid flow through a microfluidic chip  112  of the microfluidic device  110 . In this regard, the processing control system  101  may comprise a camera  102 , a controller  104 , and a pressure source  106 . The controller  104  may be configured to communicate with and control the operation of camera  102  and the pressure source  106 . In some example embodiments, the controller  104  may comprise a hardware configured processing device (e.g., an application specific integrated circuit (ASIC), field programmable logic array (FPGA)) that is specifically configured to execute the functionalities of the controller  104  described herein. According to some example embodiments, the controller  104  may comprise a software configured processor that is specially configured via the execution of software commands to execute the functionalities of the controller  104  described herein. Accordingly, the controller  104  may include a non-transitory memory device that is configured to store data and instructions for accessing by the processing device to support the execution of the functionalities described with respect to the controller  104  herein. 
     The camera  102  may be optical sensor or other imaging device that is configured to capture still images or video of the microfluidic chip  112 , and more specifically, the microfluidic circuit  114 . In this regard, because the microfluidic chip  112  may be formed of a transparent or translucent substance, and at least the fluid channels of the microfluidic circuit  114  may be disposed on a common plane within the microfluidic chip  112 , images of the fluid processing may be captured by the camera  102 . The captured images may be transmitted to the controller  104  for analysis. 
     The pressure source  106  may be any type of device that is configured to generate a positive or negative pressure, via, for example, a rotating fan. For example, if the pressure source  106  is negative pressure device, the pressure source  106  may be a vacuum device. Alternatively, if the pressure source  106  is positive pressure device, the pressure source  106  may be a blower device. According to some example embodiments, the pressure source  106  may be operably coupled to the microfluidic circuit  114  via connector  107  to the device source pressure port  116 . Because the pressure source  106  does not, according to some example embodiments, come into contact with fluids during processing through the microfluidic chip  112 , the pressure source  106  may be considered a non-contaminated pressure source. Alternatively, if the pressure source  106  were a positive pressure source, the pressure source  106  may be applied at  118 , which may then be referred to as the device source pressure port  118 . 
     The operation of the pressure source  106  may be controlled by the controller  104 . In this regard, the controller  104  may be configured to control a pressure created by the pressure source  106  that generates a fluid flow through the microfluidic circuit  114 . According to some example embodiments, the controller  104  may be configured to maintain the pressure generated by the pressure source  106  at a constant value for a controlled time period of a processing run (e.g., a mixing process). According to some example embodiments, the controller  104  may be configured to change the pressure generated by the pressure source  106  over the time period of a processing run. In this regard, the controller  104  may be configured to evaluate the image captures and associated image data provided by the camera  102  and control the pressure generated by the pressure source  106  based on the image data. In this way, the camera  102  may contribute a feedback loop for the controller  104  to control the operation of the pressure source  106 . 
     According to some example embodiments, a filter  108  may be operably coupled to the device relief pressure port  118 . The filter  108  may be a component of the microfluidic device  110  or the microfluidic assembly  101 . The filter  108  may operate to capture foreign particles to avoid introducing contaminates into the microfluidic circuit  114  by the fluid flow. As such, the device relief pressure port  118  may be considered a non-contaminated filtered gas input to the microfluidic circuit  114 . According to some example embodiments, the filter  108  may be operably coupled to the device relief pressure port  118  via a connection  109 . 
     Additionally, because the fluids being processed in the microfluidic circuit  114  do not come into contact with the connections  107  and  109 , the filter  108  and the pressure source  106  may be reusable between processing runs of different microfluidic devices without having to clean or replace the filter  108  or the pressure source  106 . Further, the connections  107  and  109  (which may be, for example, tubing, portions of a manifold, or the like) of the processing control system  101  may also be reused in subsequent processing runs, because the connections  107  and  109  also do not come into contact with any fluids and therefore do not need to be cleaned or replaced to avoid cross-contamination. 
     Now referencing  FIGS.  3 A and  3 B , a description of portions of a reservoir interface (e.g., reservoir interface  120 ) with respect to an input reservoir and an output reservoir are provided. In this regard, with respect to  FIG.  3 A , an input reservoir interface  210  is shown. The input reservoir interface  210  may comprise a reservoir interface base  212 , a liquid pipe  214 , a gas pipe  216 , and a gasket  218 . The input reservoir interface  210  is shown as being operably coupled to an input reservoir  220  having an input liquid  222  therein. 
     The reservoir interface base  212  may configured to provide structural stability to the input reservoir interface  210 , and the reservoir interface base  212  may be extend across a number of interfaces with respective reservoirs. The reservoir interface base  212  may therefore be a rigid structure that includes openings that align with the reservoir ports of a microfluidic circuit  114  as described herein. In this regard, the reservoir interface base  212  may include an opening for receiving and holding the liquid pipe  214  and an opening for receiving and holding a gas pipe  216 . The liquid pipe  214  may be one example of a liquid interface to the reservoir  220  that is configured to transport the liquid  222  from the reservoir  220  to the liquid channel portion of the microfluidic circuit due to a liquid flow in the liquid channel portion that causes a pressure differential within the reservoir  220 . As described herein, it is understood that the liquid interface to a reservoir need not include a liquid pipe, but rather any means for delivering a liquid pressure to the internal cavity of the reservoir  220 . Similarly, the gas pipe  216  may be one example of a gas interface to the reservoir  220 . In this regard, the gas interface may be configured to transport gas from the relief pressure gas portion into the reservoir  220  due to a gas flow in the relief pressure gas portion causing a pressure differential within the reservoir  220 . 
     The liquid pipe  214  may be hollow tube formed of, for example, glass, plastic, etc. that extends from a liquid opening of an input reservoir port of a microfluidic circuit into the reservoir  220 . As shown in  FIG.  3 A , according to some example embodiments, the liquid pipe  214  may extend above a top surface of the reservoir interface base  212  to facilitate alignment and insertion of the liquid pipe  214  into the liquid opening of the input reservoir port. The liquid pipe  214  may extend to the bottom or adjacent to the bottom of the reservoir  220  to ensure that the liquid pipe  214  is able to access all of the input liquid  222  that is held in the reservoir  220 . According to some example embodiments, the liquid pipe  214  may have a beveled tip to facilitate retrieval of liquid at the bottom of the reservoir  220 . 
     The gas pipe  216  may also be a hollow tube formed of, for example, glass, plastic, etc. that extends from a gas opening of an input reservoir port of a microfluidic circuit into the reservoir  220 . As shown in  FIG.  3 A , according to some example embodiments, the gas pipe  216  may extend above a top surface of the reservoir interface base  212  to facilitate alignment and insertion of the gas pipe  216  into the gas opening of the input reservoir port of the microfluidic circuit. The gas pipe  216  may extend to a shallow depth into the reservoir  220  to limit or avoid contact with the input liquid  222 . 
     The gasket  218  of the input reservoir interface  210  may operate to form a gas-tight seal between the internal cavity of the reservoir  220  and the input reservoir interface  210 . More particularly, the seal is formed around a lip of the reservoir to ensure that the liquid interface and the gas interface are the only openings into the internal cavity of the reservoir  220  to ensure proper fluid flow through the internal cavity of the reservoir  220 . 
     In operation, due to a negative liquid pressure, input liquid  222  may travel through the liquid pipe  214  as indicated by arrow  202 . The negative liquid pressure may be associated with a fluid flow through a microfluidic circuit and may force an amount of the input liquid  222  into the liquid pipe  214  for transport through a liquid opening in an input reservoir port of the microfluidic circuit. In relation with the negative liquid pressure and the exiting of the input liquid  222 , a gas flow through the gas pipe  216  indicated by arrow  204  occurs. 
     In some example embodiments, rather than a negative liquid pressure being applied, a positive gas pressure may be applied to the gas pipe  216  as indicated by arrow  204 . The positive gas pressure may be associated with a fluid flow through a microfluidic circuit and cause an amount of the input liquid  222  to be forced (e.g., pushed) into the liquid pipe  214  for transport through a liquid opening in an input reservoir port of the microfluidic circuit. The seal formed by the gasket  218  may prevent release of gas pressure in the internal cavity to ensure proper pressure control on the input fluid  222 . 
     Now referring to  FIG.  3 B , a portion of a reservoir interface in the form of an output reservoir interface  260  is shown. The output reservoir interface  260  may be structured in the same manner as input reservoir interface  210 . The output reservoir interface  260  may therefore comprise a reservoir interface base  212 , a liquid pipe  214 , a gas pipe  216 , and a gasket  218  (e.g., an output gasket) that operate in the same or similar manner, however, with respect to the output reservoir  270  that receives the output liquid  272 . In this context, the liquid pipe  214  may be operably coupled to the liquid channel portion of a microfluidic circuit and the output gas interface (e.g., the gas pipe  216 ) may be connected to a source pressure gas portion of a microfluidic circuit. 
     In operation, a negative gas pressure may be applied to the gas pipe  216  as indicated by arrow  254 . The negative gas pressure may be associated with a fluid flow through a microfluidic circuit and may pull an amount of gas out of the internal cavity of the reservoir  270 . This negative gas pressure within the internal cavity (maintained by the seal formed by the gasket  218 ) may cause a negative liquid pressure in the liquid pipe  214  to pull an amount of output liquid  272  from the liquid opening of the output reservoir port of the microfluidic circuit and into the reservoir  270  as indicated by the arrow  252 . 
     Alternatively, in some example embodiments, a positive liquid pressure may be applied to the liquid pipe  214  as indicated by arrow  252 . The positive liquid pressure may be associated with a fluid flow through a microfluidic circuit and cause an amount of the output liquid  272  to be pushed into the liquid pipe  214  from a liquid opening in an output reservoir port of a microfluidic circuit. To relieve the pressure in the internal cavity, a gas flow through the gas pipe  216  indicated by arrow  254  occurs. 
     As such, the liquid pipe  214  may be configured to transport the output liquid  272  into the reservoir  270  from a liquid channel portion in a microfluidic circuit due to a liquid flow in the liquid channel portion causing a pressure differential within the reservoir  270 . The output gas interface, in the form of the gas pipe  216 , may therefore be configured to transport gas from the source pressure gas portion into the reservoir  270  due to the gas flow in the source pressure gas portion causing the pressure differential within the reservoir  270 . Further, the gasket  218  may be configured to form a gas-tight seal between an internal space of the reservoir  270 , a liquid channel portion of a microfluidic circuit, and a source pressure gas portion of a microfluidic circuit. 
     Reference will now be made to  FIG.  4    to describe a microfluidic device  300  that may be a component of a microfluidic assembly. Additionally, an example architecture of a microfluidic circuit  320  of the microfluidic device  300  is provided that extends between a device source pressure port  312  and a device relief pressure port  314 . The microfluidic device  300  may be constructed and function in the same or similar manner as the microfluidic device  10 , the microfluidic device  110 , and as otherwise described herein. Similarly, the microfluidic device  300  may comprise a microfluidic chip  310  and a reservoir interface  330 . As described herein, the reservoir interface  330  may be configured to be a coupling device between the reservoirs  360 ,  362 , and  364 , and the microfluidic circuit  320 . 
     The reservoir interface  330  may comprise a reservoir interface base  332  that secures liquid pipes  334 ,  340 , and  346 , and gas pipes  336 ,  342 , and  350 . The liquid pipes  334 ,  340 , and  346 , and the gas pipes  336 ,  342 , and  350  may extend from openings in the microfluidic chip  310  leading to the microfluidic circuit  320  into the internal cavity of a respective reservoirs  360 ,  362 , and  364 . The reservoirs  360 ,  362 , and  364  may, according to some example embodiments, be gas-tight sealed to the reservoir interface base  332  via respective gaskets  338 ,  344 , and  348 . 
     The microfluidic circuit  320  of the microfluidic chip  310  may be configured to mix two input liquids from the reservoirs  360  and  362  to form an output liquid to be delivered into reservoir  364 . The microfluidic circuit  320  may comprise a number of channels that support a fluid flow in the form of a gas flow or a liquid flow through the microfluidic chip  310 . The microfluidic circuit  320  may comprise ports to external components and devices. In this regard, the microfluidic circuit  320  may include a device source pressure port  312  and a device relief pressure port  314 . The microfluidic circuit  320  may be formed to support a fluid flow between the device source pressure port  312  and the device relief pressure port  314 . 
     According to some example embodiments, the microfluidic circuit  320  may comprise three portions, namely, a source pressure gas portion  322 , a liquid channel portion  324 , and a relief pressure gas portion  326 . As described herein, the source pressure gas portion  322  and the relief pressure gas portion  326  may support gas flows, while the liquid channel portion  324  may support a liquid flow. As can be seen in  FIG.  4   , which provides a conceptual diagram of the microfluidic circuit  320 , the source pressure gas portion  322  may comprise a channel operably coupled between the gas pipe  350  and the device source pressure port  312 . Similarly, the relief pressure gas portion  326  may comprise one or more channels that connect between each gas pipe  336  and  342 , and the device relief pressure port  314 . Finally, the liquid channel portion  324  may comprise a number of channels that lead from the liquid pipes  334  and  340  to a mixing junction  325 . The mixing junction  325  may be an intersection of some or all of the channels of the liquid channel portion  324  to perform a mixing operation at the mixing junction  325 . The mixing junction  325  may have one or more output channels that lead to liquid pipes, such as liquid pipe  346 . 
     According to some example embodiments, at least some of the channels of the liquid channel portion may have different lengths (i.e., distances from a respective reservoir port to the mixing junction  325 ). The length of a channel within the liquid channel portion may be considered in the design of the microfluidic chip  310 , since the length of the channel may have an impact on an amount of liquid delivered to the mixing junction  325 . According to some example embodiments, the length of one or more of the channels may be determined as a design parameter based on a desired liquid flow rate for a given applied pressure. In this regard, according to some example embodiments, a channel may be designed to be longer or shorter depending the desired liquid flow rate at a given pressure. Additionally or alternatively, a cross-sectional area or perimeter of a channel may also be a design parameter for obtaining a desired liquid flow rate at a given pressure. 
     As can be seen from the arrows indicated by the channels of the microfluidic circuit  320 , as fluid flow through the microfluidic circuit  320  may be generated. As described herein, a source pressure to generate a fluid flow between the device source pressure port  312  and the device relief pressure port  314  may be applied to, for example, the device source pressure port  312 . According to some example embodiments, a negative pressure may be generated at the device source pressure port  312 . In doing so, a gas flow may be formed through the channel of the source pressure gas portion  322 . This gas flow may create a negative pressure in the internal cavity of the reservoir  364  (i.e., the output reservoir), which may cause a liquid pressure in liquid pipe  346  (e.g., once the microfluidic circuit  320  is primed). In this regard, the microfluidic circuit  320  may be initially filled only with, for example, air. In order to arrive at a steady fluid flow, pressure may be applied to begin the flow of liquid within the microfluidic circuit  320 . The microfluidic circuit  320  may be ready for steady operation or primed when the output liquid begins to fill the reservoir  364 . 
     Additionally, the liquid pressure in liquid pipe  346  may pull liquids through the liquid pipes  334  and  340 , into the microfluidic circuit  320  and into the mixing junction  325 . As such, the fluid flow may cause a mixing of a first liquid in the input reservoir  360  with a second liquid in the input reservoir  362  at a mixing junction  325  of the microfluidic circuit  320  within the microfluidic chip  310  to form an output liquid. Because the liquids are being pulled from the otherwise sealed reservoirs  360  and  362 , a negative gas pressure may be formed in the internal cavities of the reservoirs  360  and  362 , which may be relieved by the entry of gas through the gas pipes  336  and  342  due to a gas flow from the device relief pressure port  314  through the relief pressure gas portion  326 . The output liquid may therefore be delivered to the output reservoir  364  via the fluid flow through the microfluidic circuit  320 . Additionally, the first liquid from the first input reservoir  360 , the second liquid from the second input reservoir  362 , and the output liquid delivered to the output reservoir  364  do not contact the device source pressure port  312  or the device relief pressure port  314  during the mixing. 
     Now referring to  FIG.  5   , top view of an example embodiment of the microfluidic circuit  320  is shown. As mentioned herein, the microfluidic chip  310  may be formed of a transparent or translucent substance, and the channels of the microfluidic circuit  320  may be disposed on a common plane within the microfluidic chip  310 . Accordingly, as provided by the top view of the microfluidic chip  310 , the channels of the microfluidic circuit  320  and the contents of the channels can be visible, and can therefore be imaged, for example, by a camera (e.g., camera  102 ). 
     Following from the description of the microfluidic circuit  320  as shown in  FIG.  4   , the microfluidic circuit  320  as now shown in  FIG.  5    includes the device source pressure port  312  operably coupled to the source pressure gas portion  322 . The source pressure gas portion  322  may be operably coupled, through the reservoir  364 , to the liquid channel portion  324 . The liquid channel portion  324  may be operably coupled, in parallel through the reservoirs  360  and  362 , to the relief pressure gas portion  326 . In turn, the relief pressure gas portion  326  may be operably coupled to the device relief pressure port  314 . 
     In this regard, a gas channel  370  may extend from the device source pressure port  312  to the gas pipe  350 . Similarly, gas channels  392  and  394  may extend from gas pipes  336  and  342 , respective to a common gas channel  390  that is operably coupled to the device relief pressure port  314 . According to some example embodiments, the gas channels associated with the input reservoirs (e.g., reservoirs  360  and  362 ) may be separate channels that do not meet and connect to the device relief pressure port  314 . Rather, the gas channels associated with the input reservoir extend to separate relief pressure ports that may be disposed elsewhere (e.g., on another side surface or even the top surface of the microfluidic circuit  320 ), but still provide a relief function to support a fluid flow through the microfluidic circuit  320 . According to some example embodiments, the input reservoirs need not have gas-tight seals to allow for relief venting, and, as such, the gaskets  338  and  344  may be omitted or replaced with structure that includes relief vent holes. 
     With respect to the liquid channel portion  324 , the liquid channels may be microfluidic channels that operate to propagate a fluid through the microfluidic circuit  320 . In the example embodiment of microfluidic circuit  320 , a liquid channel  380  extends from the liquid pipe  346  to the mixing junction  325  and operates as an output channel for the mixing junction  325 . Liquid channel  384  extends from liquid pipe  334  to mixing junction  325  and operates as an input channel to the mixing junction  325 . Similarly, liquid channel  382  extends from liquid pipe  340  to mixing junction  325  and also operates as an input channel to the mixing junction  325 . 
     According to some example embodiments, the liquid channels (e.g., liquid channels  380 ,  382 ,  384 ) within the microfluidic circuit  320  may have cross-sectional areas (or diameters for circular-shaped cross-sections), that are defined based on a desired flow rate of liquid through the liquid channels. In this regard, according to some example embodiments, the cross-sectional areas of the liquid channels may be sized based on the viscosity of the liquid that is intended to be transported by the liquid channels. Further, some liquid channels may have different cross-sectional areas from other liquid channels. The different cross-sectional areas may be utilized to create different ratios of liquids in a resultant output mixture, even when leveraging a common pressure source. 
     Referring now to  FIG.  6   , an assembly operation for the microfluidic device  300  is shown. In this regard, due to the unitary aspects of the microfluidic device  300 , the microfluidic device  300  may be inserted into a tray  406  of reservoirs, such as reservoirs  360 ,  362 , and  364 . In this regard, the reservoirs  360 ,  362 , and  364  may be affixed or secured in the tray  406  in a manner that prevents relative movement between the reservoirs  360 ,  362 , and  364 . As such, the complementary structured microfluidic device  300  may be coupled to the reservoirs  360 ,  362 , and  364 , and possibly the tray itself to form a cartridge. Such a cartridge may be configured to be installed in a processing control system (e.g., processing control system  101 ) as described herein. Moreover, the microfluidic chip  310 , the reservoirs  360 ,  362 , and  364 , and the reservoir interface  330  may be combined to form a replaceable cartridge that is configured to be installed into and removed from a control apparatus. 
     According to some example embodiments, the assembly process of coupling the microfluidic device  300  to the reservoirs  360 ,  362 , and  364 , and the tray  406  may include movement of the tray  406  in a direction  420  towards the microfluidic device  300 , or movement of the microfluidic device  300  in a direction  410  towards the reservoirs  360 ,  362 , and  364 , and the tray  406 . According to some example embodiments, such movements may be performed by a robot, for example, comprising a robotic arm. While movement of the microfluidic device  300  or the tray may be performed by a robot, the assembly process depicted in  FIG.  6    involves a robotic arm  402  of a robot  400  interfacing with the microfluidic device  300  to cause the movement. In this regard, the robotic arm  402  may comprise a temporary coupling device  404  that attaches the microfluidic device  300  to the robotic arm  402 . The temporary coupling device  404  may be embodied in a number of ways, such as, a suction holding device that creates a vacuum between the device  404  and the top surface of the microfluidic chip  310  to affix the microfluidic device  300  to the robot arm  402  to support movement. As such, according to some example embodiments, the manipulation needed to assemble the microfluidic device  300  to the reservoirs  360 ,  362 , and  364  may be minimal, which simplifies the assembly process thereby saving time and reducing potential errors. Further, the assembly to form cartridges that are prepared for processing at a later time may be performed offline in mass quantities to further streamline processing of the liquids and maximize utilization of the processing control stations. Also, because the assembled cartridges may include sealed reservoirs, spills, contamination, and cross-contamination may be prevented when handling outside of the processing control stations. 
     According to some example embodiments, prior to assembly as described above, the reservoirs  360 ,  362 , and  364 , disposed within the tray  406 , may be accessible to deposit fluids into the reservoirs  360 ,  362 , and  364 . In this regard, a pipetting robot may interface with the open reservoirs (i.e., the input reservoirs) to add fluids prior to assembling the microfluidic device  300  with the reservoirs  360  and  362 . Similarly, after mixing, a disassembly process may be undertaken to make the output reservoir  364  accessible for pipet removal of the output fluid from the output reservoir  364  (or other output reservoirs within the tray  406 ). The accessibility of the reservoirs in the manner may facilitate improvements in throughput, process traceability, error reduction, and reduction of cross contamination. 
     Now referring to  FIG.  7   , a variation of the microfluidic device  300  is provided as microfluidic device  500  where the microfluidic circuit extends beyond the microfluidic chip. In general, the microfluidic device  500  operates similar to the microfluidic device  300 , but has some structural differences. In this regard, the reservoir port of the output reservoir  364  is operably coupled to the microfluidic chip  311  via tubing. In this regard, tubing  339  may be operably coupled between an output port  337  of the microfluidic chip  311  and the liquid pipe  346 . The output port  337  may lead to an output of the mixing junction  325 . Further, a second tube  341  may be operably coupled between the gas tube  350  and the device source pressure port  312 . As such, the source pressure gas portion  322  of the microfluidic circuit  320  may be disposed within the second tube  341 . Additionally, the reservoir interface  330  may have a separated reservoir interface base with a first base portion  333  supporting an interface between the input reservoirs  360  and  362  and the microfluidic chip  311 , and a second base portion  335  supporting an interface between the output reservoir  364  and the tubes  339  and  322 . 
     The input reservoirs  360  and  362  may be secured in a tray  406 . In this regard, the tray  406  may operate as an interface between the reservoirs  360  and  362  and the heater  510  and/or the agitator  511 . The heater  510 , which may be controlled by, for example, the controller  104 , may be configured to control the temperature of the input liquids within the input reservoirs  360  and  362 . Additionally, the agitator  511 , which may be controlled by, for example, the controller  104 , may be configured to agitate the input liquids within the input reservoirs  360  and  362  via movement such as vibration. According to some example embodiments, the heater  510  and agitator  511  may be components of, for example, a heated microplate shaker. 
     Additionally, according to some example embodiments, micro beads  520  may be included with input liquids in the input reservoirs  360  and  362 . When processing with micro beads  520  (e.g., gel beads, streptavidin beads, magnetic beads, or the like) techniques can be employed to avoid aggregation of the beads into clusters, for example, due to interactions between surfaces or molecules bound to surfaces of the input liquids (e.g., DNA). Heating (to reduce molecular bonding) via the heater  510  and agitating via the agitator  511  (to disrupt clusters and to reduce gravitational settling) may performed to improve uniformity of the distribution of the micro beads  520  during processing. 
     However, according to some example embodiments, heating and/or agitation of the output liquid may be not be desirable. As such, the output reservoir  364  may be mechanically separated from the input reservoirs  360  and  362  via the tubes  339  and  322  of the microfluidic device  500 . For example, when the output liquid is a droplet emulsion mixed in the microfluidic chip  311 , agitation may degrade the emulsion. As such, the output reservoir  364  may be mechanically separated and disposed in a non-heated and/or non-shaken mount. According to some example embodiments, flexible tubing may allow for the mechanical separation for the output reservoir  364 , while maintaining the fluid flow connection to the input reservoirs  360  and  362 . The input reservoirs  360  and  362  may be disposed in a heated and/or agitated mount. For example, the input reservoirs  360  and  362  may be disposed in a heated microplate shaker. 
     As shown in  FIG.  8   , an assembly process, according to some example embodiments, may involve a microfluidic device  500  that comprises a number of subunits forming an array of individual reservoir interfaces. In this regard, for example, the microfluidic device  500  may comprise subunits  502 ,  504 ,  506 , and  508  which may have respective microfluidic circuits or a common microfluidic circuit. Again, the microfluidic device  500  may be configured to interface with a tray  520  having an array of reservoirs including the reservoir  522 . The assembly process may be conducted by an individual or a robot to move the microfluidic device  500  towards the tray  520  in the direction  532  or the tray  520  toward the microfluidic device  500  in the direction  530 . 
     Now referencing  FIG.  9   , an example method of operating a microfluidic assembly, such as those described above, is provided. In this regard, according to some example embodiments, the example method  800  may comprise, at  810 , receiving a source pressure applied at a device source pressure port of a microfluidic device, and, at  820 , generating a pressure differential and a fluid flow between a device relief pressure port and the device source pressure port through the microfluidic circuit due to receiving the source pressure. The example method may further comprise, at  830 , transporting a first liquid from a first input reservoir into the microfluidic circuit due to the fluid flow through the microfluidic circuit, and, at  840 , transporting a second liquid from a second input reservoir into the microfluidic circuit due to the fluid flow through the microfluidic circuit. The example method may also comprise, at  850 , causing a mixing of the first liquid with the second liquid at a mixing junction of the microfluidic circuit to form an output liquid. The example method may further comprise, at  860 , transporting the output liquid to an output reservoir due to the fluid flow through the microfluidic circuit. In this regard, the first liquid, the second liquid, and the output liquid do not contact the device source pressure port or the device relief pressure port during the mixing or transporting. 
     Additionally, according to some example embodiments, generating the fluid flow between the device relief pressure port and the device source pressure port may comprise generating a source gas flow through a source pressure gas portion of the microfluidic device that is operably coupled to the device source pressure port, generating a liquid flow through a liquid channel portion of the microfluidic circuit that is operably coupled to the source pressure gas portion through the output reservoir, and generating a relief gas flow through a relief pressure gas portion of the microfluidic circuit that is operably coupled to the device relief pressure port and to the liquid channel portion through the first input reservoir and the second input reservoir. 
     Additionally or alternatively, according to some example embodiments, generating the relief gas flow through the relief pressure gas portion may further comprise generating the relief gas flow through a filter operably coupled to the device relief pressure port. Additionally or alternatively, according to some example embodiments, transporting the first liquid may comprise transporting the first liquid through a liquid pipe that extends into the first input reservoir and into the first liquid. Additionally or alternatively, according to some example embodiments, transporting the first liquid from the first input reservoir may further comprise transporting gas into the first input reservoir via a first gas interface to the microfluidic circuit. 
     The embodiments present herein are provided as examples and therefore the associated inventions are not to be limited to the specific embodiments disclosed. Modifications and other embodiments are intended to be included within the scope of the appended claims. Moreover, although the foregoing descriptions and the associated drawings describe example embodiments in the context of certain example combinations of elements and/or functions, different combinations of elements and/or functions may be used to form alternative embodiments. In this regard, for example, different combinations of elements and/or functions other than those explicitly described above are also contemplated. In cases where advantages, benefits or solutions to problems are described herein, it should be appreciated that such advantages, benefits and/or solutions may be applicable to some example embodiments, but not necessarily all example embodiments. Thus, any advantages, benefits or solutions described herein should not be thought of as being critical, required or essential to all embodiments.