Patent Publication Number: US-2021170408-A1

Title: Microfluidic valves

Description:
BACKGROUND 
     Microfluidics technology has found many applications in the biomedical field, cell biology, protein crystallization and other areas. Such microfluidic technology may include microfluidic valves that control the passage of liquid through a conduit. The scale of microfluidics presents many design challenges with respect to such microfluidic valves. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top sectional view of portions of an example microfluidic valve. 
         FIG. 2  is a side sectional view of portions of the example microfluidic valve of  FIG. 1 . 
         FIG. 3  is a flow diagram of an example liquid flow control method for operating a microfluidic valve. 
         FIG. 4A  is a top sectional view of portions of an example microfluidic valve in a closed state. 
         FIG. 4B  is a side sectional view of portions of the example microfluidic valve of  FIG. 4A . 
         FIG. 5A  is a top sectional view of portions of the microfluidic valve of  FIG. 4A  during opening of the valve. 
         FIG. 5B  is a side sectional view of portions of the example microfluidic valve of  FIG. 5A . 
         FIG. 6A  is a top sectional view of portions of the microfluidic valve of  FIG. 4A  in an open state. 
         FIG. 6B  is a side sectional view of portions of the example microfluidic valve of  FIG. 6A . 
         FIG. 7A  is a top sectional view of portions of an example microfluidic valve in a closed state. 
         FIG. 7B  is a side sectional view of portions of the example microfluidic valve of  FIG. 7A  taken along line  7 B- 7 B 
         FIG. 8A  is a top sectional view of portions of the example microfluidic valve of  FIG. 7A  during opening of the valve. 
         FIG. 8B  is a side sectional view of portions of the example microfluidic valve of  FIG. 8A  taken along line  8 B- 8 B. 
         FIG. 9A  is a top sectional view of portions of the example microfluidic valve of  FIG. 7A  in an open state. 
         FIG. 9B  is a side sectional view of portions of the example microfluidic valve of  FIG. 9A  taken along line  9 B- 9 B. 
         FIG. 10A  is a top sectional view of portions of an example microfluidic valve in a closed state. 
         FIG. 10B  is a side sectional view of the microfluidic valve of  FIG. 10A  taken along line  10 B- 10 B. 
         FIG. 11A  is a top sectional view of portions of an example microfluidic valve in a closed state. 
         FIG. 11B  is a side sectional view of the microfluidic valve of  FIG. 11A  taken along line  11 B- 11 B. 
         FIG. 12A  is a top sectional view of portions of an example microfluidic valve in a closed state. 
         FIG. 12B  is a side sectional view of the microfluidic valve of  FIG. 12A  taken along line  12 B- 12 B. 
         FIG. 12C  is a side view of the microfluidic valve of  FIG. 12B  taken along line  12 C- 12 C. 
         FIG. 13  is a flow diagram of an example liquid flow control method. 
         FIG. 14A  is a side sectional view of an example microfluidic valve. 
         FIG. 14B  is a top sectional view of the example microfluidic valve of  FIG. 14A . 
         FIG. 15A  is a side sectional view of an example microfluidic valve. 
         FIG. 15B  is a top sectional view of the example microfluidic valve of  FIG. 15A . 
         FIG. 16A  is a side sectional view of an example microfluidic valve. 
         FIG. 16B  is a top sectional view of the example microfluidic valve of  FIG. 16A . 
         FIG. 17A  is a side sectional view of an example microfluidic valve. 
         FIG. 17B  is a top sectional view of the example microfluidic valve of  FIG. 17A . 
         FIG. 18  is a top sectional view of portions of an example microfluidic valve. 
         FIG. 19  is a side sectional view of the microfluidic valve of  FIG. 18  taken along line  19 - 19 . 
         FIG. 20  is a top sectional view of portions of an example microfluidic valve. 
         FIG. 21  is a side sectional view of the microfluidic valve of  FIG. 20  taken along line  21 - 21   
         FIG. 22  is a top sectional view of portions of an example microfluidic valve. 
         FIG. 23  is a side sectional view of the microfluidic valve of  FIG. 22  taken along line  23 - 23 . 
     
    
    
     Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements. The figures are not necessarily to scale, and the size of some parts may be exaggerated to more clearly illustrate the example shown. Moreover, the drawings provide examples and/or implementations consistent with the description; however, the description is not limited to the examples and/or implementations provided in the drawings. 
     DETAILED DESCRIPTION OF EXAMPLES 
     Disclosed herein are various example microfluidic valves that avoid much of the reliability issues and fabrication complexities found in many existing microfluidic valves. The disclosed microfluidic valves utilize a constriction in a conduit at an interface of a fluid and a liquid such that a capillary meniscus forms between the fluid and the liquid. For purposes of this disclosure, the term “fluid” refers to a gas or a second liquid that is immiscible with respect to the liquid. For example, in one implementation, the liquid may comprise water while the fluid comprises a second immiscible liquid in the form of an oil. The disclosed microfluidic valves further reduce liquid creep through and across a meniscus which might otherwise result in the valve being unintentionally opened. As a result, the disclosed microfluidic valves may resist greater liquid pressures prior to the meniscus being broken and the valve being opened. 
     In one implementation, the constriction of the example microfluidic valves includes a ceiling edge, wherein the ceiling edge increases strength of the meniscus, increasing the amount of liquid pressure that the valve may resist before the meniscus is broken. In another implementation, the disclosed microfluidic valves include a liquid phobic surface in the fluid portion of the conduit and extending from or proximate to the constriction and the formed meniscus. The liquid phobic surface resists liquid creep along edges of the formed meniscus, increasing the strength of the resistance provided by the meniscus, and thereby increasing the strength of the microfluidic valve. In one implementation, the constriction of the microfluidic valve has a floor edge that increases strength of the meniscus, wherein the meniscus may be selectively broken using a fluid actuator. 
     In some implementations, the valve is actuatable to an open state by a meniscus breaker that breaks the menisci extending across the constriction. Breaking of the menisci across the constriction allows liquid to flow and establish a continuous string or stream of liquid through the conduit. In one implementation, the meniscus breaker may comprise a fluid actuator that displaces fluid to increase fluid pressure on at least one of the menisci so as to break the meniscus. In another implementation, the meniscus breaker may comprise a device that produces sufficient vibration to break at least one of the menisci. 
     In some implementations, strength and robustness of the formed meniscus that closes the microfluidic valve is further enhanced by providing the constriction at the end of a spout. The spout projects into the portion of the conduit containing fluid. In some implementations, reliability of the microfluidic valve is further enhanced by providing a series of constrictions, wherein different menisci are formed in series across the series of constrictions. Opening of the valve involves breaking each of the sequentially formed menisci. 
     In some implementations, the liquid conduit comprises a microfluidic passage. Microfluidic passages may be formed by performing etching, microfabrication (e.g., photolithography), micromachining processes, or any combination thereof in a substrate of a fluidic die in which the liquid conduit may be disposed. Some example substrates may include silicon-based substrates, glass-based substrates, gallium arsenide-based substrates, and/or other such suitable types of substrates for microfabricated devices and structures. Accordingly, microfluidic channels, passages, chambers, orifices, and/or other such features may be defined by surfaces fabricated in the substrate of the fluidic die. Furthermore, as used herein a microfluidic channel or passage may correspond to a channel of sufficiently small size (e.g., of nanometer sized scale, micrometer sized scale, millimeter sized scale, etc.) to facilitate conveyance of small volumes of fluid (e.g., picoliter scale, nanoliter scale, microliter scale, milliliter scale, etc.). 
       FIGS. 1 and 2  schematically illustrate portions of an example microfluidic valve  20 . Microfluidic valve  20  comprises a device for controlling the passage of a liquid through a conduit.  FIGS. 1 and 2  illustrate microfluidic valve  20  in a closed state in which fluid flow through the valve  20  is obstructed or stopped by a capillary meniscus. Microfluidic valve  20  comprises liquid conduit  24 . 
     Conduit  24  comprises a body or structure having an interior along which liquid is to flow when valve  20  is open. Conduit  24  comprises a first interior or a first portion  30  that is to contain a fluid  32  and a second interior or second portion  34  that is supplied with or is to contain a liquid  36 . As shown by  FIG. 1 , portions  30  and  34  are joined or connected to one another at a constriction  40 . A constriction is an interface where a conduit undergoes dimensional changes from a larger flow passage to a smaller flow passage. 
     Constriction  40  provides a structure at which a capillary meniscus may form. Because the constriction  40  is formed between or along a gas-liquid or immiscible fluid/liquid interface between the two portions  30 ,  34  of conduit  24 , capillary meniscus  44  may form across constriction  40 . In particular, portions  34  and  36  are sized such that the liquid  36  within first portion  34  forms the capillary meniscus  44  along the fluid-liquid interface of the two portions. This capillary meniscus  44  serves as a valve to stop liquid flow through conduit  24 . Actuation or opening of this valve provided by capillary meniscus  44  may occur through breaking of the capillary meniscus  44 . 
     As shown by  FIG. 1  constriction  40  comprises a pair of opposite side corners or edges  50 . Edges  50  facilitate the formation of meniscus  44 . However, in some implementations, edges  50 , alone, may not reliably maintain the meniscus  44  over time or in response to pressure increases. As shown by  FIG. 2 , constriction  44  additionally comprises a ceiling corner or edge  52 . Ceiling edge  52  occurs at a juncture where the shorter vertical height of first portion  34  meets the taller or larger vertical height of second portion  30 . Ceiling edge  52  increases the strength of the formed meniscus  44 , increasing the liquid pressure that the capillary meniscus  44  may resist prior to being broken. As a result, ceiling edge  52  increases the strength of microfluidic valve  20 . 
     In the example illustrated, ceiling edge  52  comprises a sharp or relatively sharp corner. The relatively sharp corner providing ceiling edge  52  provides enhanced meniscus strength. Although possibly offering a less robust meniscus, ceiling edge  52  may be curved or rounded in other implementations. 
       FIG. 3  is a flow diagram of an example method  100  for operating a microfluidic valve. Method  100  facilitates the control over the flow of fluid through a conduit in a microfluidic device with enhanced reliability and with a valve that may have fewer fabrication complexities. Although method  100  is described as being carried out with microfluidic valve  20  described above, it should be appreciated that method  100  may likewise be carried out with any of the microfluidic valves described hereafter or with other similar microfluidic valve constructions. 
     As indicated by block  104 , a conduit  24  is provided. The conduit has a first portion  34  and a second portion  30  filled with a fluid and separated by a constriction  40  having a ceiling edge  52  and side edges  50 . As indicated by block  108 , liquid is supplied to the second portion at a pressure so as to form a capillary meniscus  44  across the constriction  40 . The exact value of the pressure of the liquid being supplied to form meniscus  44  may vary depending upon the dimensions, size and shape of constriction  40 , the liquid phobic/liquid philic properties of the surfaces forming the interior portion of conduit  24 , and the properties of the liquid  36  itself. The meniscus  44  stops liquid flow along conduit  24 . As a result, a microfluidic valve in a closed state is formed. 
     As indicated by broken lines and block  112 , liquid flow across valve  20  and through conduit  24  may be established by opening the microfluidic valve. To open the microfluidic valve, a pressure pulse may be applied to the liquid  36  to break the meniscus  44  and establish liquid flow through the conduit  24 . In one implementation, pressure pulse may be generated by a meniscus breaker. In one implementation, the meniscus breaker may comprise a fluid actuator that displaces fluid. In one implementation, the meniscus breaker may comprise a vibration generating mechanism. 
       FIGS. 4A and 4B  illustrate top sectional and side sectional views, respectively, of portions of an example microfluidic valve  220  in a closed state, stopping the flow of liquid through or across the microfluidic valve  220 .  FIGS. 5A and 5B  illustrate microfluidic valve  220  in the process of being opened.  FIGS. 6A and 6B  illustrate microfluidic valve  220  after being opened, with liquid flowing through microfluidic valve  220 . 
     Microfluidic valve  220  is similar to microfluidic valve  20  described above except that microfluidic valve  220  additionally comprises meniscus breaker  260  and controller  264 . For ease of illustration, controller  264  is not illustrated in  FIG. 5A, 5B, 6A or 6B . Those components of microfluidic valve  220  that correspond to components of microfluidic valve  20  are numbered similarly. 
     Meniscus breaker  260  comprises a device that, upon being actuated by controller  264 , breaks the capillary meniscus  44  extending across constriction  40  and maintaining valve  220  in a closed state. In one implementation, meniscus breaker  260  may comprise a liquid pump, such as an inertial pump that increases the pressure of the adjacent liquid to a sufficient extent so as to break the corresponding meniscus extending across constriction  40 . In one implementation, meniscus breaker  260  comprises a fluid actuator that displaces fluid to create a pressure pulse in liquid  36 . Examples of such a fluid actuator that may be utilized include, but are not limited to, thermal actuators, piezo-membrane-based actuators, electrostatic membrane actuators, mechanical/impact driven membrane actuators, magnetostrictive drive actuators, electrochemical actuators, other such microdevices, or any combination thereof. In one implementation, meniscus breaker  260  comprises a thermal resistor that vaporizes the adjacent fluid to create a bubble that displaces adjacent liquid to break the corresponding meniscus. In other implementations, meniscus breaker  260  may comprise micro-electromechanical systems that vibrate to a sufficient extent so as to break the adjacent meniscus. 
     Controller  264  controls actuation of meniscus breaker  260 . In one implementation, controller  264  comprises a processing unit that follows instructions contained in a non-transitory computer-readable medium. In another implementation, controller  264  comprises an integrated circuit, such as an application-specific integrated circuit (ASIC). Controller  264  outputs control signals that initiate, terminate or adjust operation of meniscus breaker  260 . 
     In one implementation, meniscus breaker  260  comprises an electrically driven device, such as an electrically driven fluid actuator or electrically driven vibrator contained in the same substrate or layer/collection of layers that form and define conduit  24 . For example, meniscus breaker  260  and conduit  24  may be formed as part of a single microfluidic circuit chip or die. In such an implementation, the single microfluidic circuit chip or die may comprise switches in the form of transistors which are actuated in response to signals from controller  264 . In one implementation, controller  264  may also be formed or provided upon the single microfluidic circuit chip or die that also supports meniscus breaker  260  and defines conduit  24 . In yet another implementation, controller  264  may be remote from the circuit chip or die including meniscus breaker  260  and conduit  24 , wherein a communication interface, such as a contact pad, port or other connector, is provided on the circuit chip or die for connection to the remote controller  264 . 
     In operation, liquid flow through microfluidic valve  220  is initially controlled and stopped by initially supplying liquid  36  to portion  34  of conduit  24  at a pressure chosen so as to form meniscus  44  across constriction  40 , stopping liquid flow along conduit  24 . As discussed above, the ceiling edge  52  increases the reliability and robustness of the formed meniscus  44  to reduce the likelihood of accidental breakage of meniscus  44  and accidental opening of microfluidic valve  220 . 
     As shown by  FIGS. 5A and 5B , when microfluidic valve  220  is to be opened, controller  264  outputs control signals actuating meniscus breaker  260 . In one implementation, meniscus breaker  260  applies a pressure pulse to the liquid  36  in portion  34 . As discussed above, the pressure pulse may be created by displacing fluid, for example by vaporizing a portion of liquid, or vibrating the fluid  36  within portion  34  of conduit  24 . This pressure pulse results in meniscus  44  expanding into portion  30  as shown in  FIGS. 5A and 5B , eventually breaking to establish liquid flow through conduit  24  as indicated by arrows  266  in  FIGS. 6A and 6B . 
       FIGS. 7A and 7B  illustrate top sectional and side sectional views, respectively, of portions of an example microfluidic valve  320  in a closed state, stopping the flow of liquid through or across the microfluidic valve  320 .  FIGS. 8A and 8B  illustrate microfluidic valve  320  in the process of being opened.  FIGS. 9A and 9B  illustrate microfluidic valve  320  after being opened, with liquid flowing through microfluidic valve  320 . 
     Microfluidic valve  320  is similar to microfluidic valve  220  described above except that microfluidic valve  320  comprises conduit  324  having a constriction  340  with floor edge  352 . Those components of microfluidic valve  320  that correspond to components of microfluidic valve  220  are numbered similarly. For ease of illustration, controller  264  is not illustrated in  FIG. 8A, 8B, 9A or 9B . 
     Floor edge  352  occurs at a juncture where the floor of first portion  34  meets the deeper vertical height of second portion  30 . Floor edge  352  increases the strength of the formed meniscus  44 , increasing the liquid pressure that the capillary meniscus  44  may resist prior to being broken. As a result, floor edge  352  increases the strength of microfluidic valve  20 . 
     In the example illustrated, floor edge  352  comprises a sharp or relatively sharp corner. The relatively sharp corner of floor edge  352  provides enhanced capillary meniscus strength. Although possibly offering a less robust capillary meniscus, floor edge  352  may be curved or rounded in other implementations. 
     In operation, liquid flow through microfluidic valve  320  is initially controlled and stopped by initially supplying liquid  36  to portion  34  of conduit  324  at a pressure chosen so as to form meniscus  44  across constriction  340 , stopping liquid flow along conduit  324 . The exact value of the pressure of the liquid being supplied to form meniscus  44  may vary depending upon the dimensions, size and shape of constriction  40 , the liquid phobic/hydrophilic properties of the surfaces forming the interior portion of conduit  324  and the properties of the liquid  36  itself. As discussed above, the floor edge  352  increases the reliability and robustness of the formed meniscus  44  to reduce the likelihood of accidental breakage of capillary meniscus  44  and accidental opening of microfluidic valve  320 . 
     As shown by  FIGS. 8A and 8B , when microfluidic valve  320  is to be opened, controller  264  outputs control signals actuating meniscus breaker  260 . In one implementation, meniscus breaker  260  applies a pressure pulse to the liquid  36  in portion  34 . As discussed above, the pressure pulse may be created by displacing fluid or vibrating the fluid  36  within portion  34  of conduit  324 . This pressure pulse results in meniscus  44  expanding into portion  30  as shown in  FIGS. 8A and 8B , eventually breaking to establish liquid flow through conduit  324  as indicated by arrows  266  in  FIGS. 9A and 9B . 
       FIGS. 10A and 10B  illustrate top sectional and side sectional views, respectively, of portions of an example microfluidic valve  420  in a closed state, stopping the flow of liquid through or across the microfluidic valve  420 . Microfluidic valve  420  is similar to microfluidic valves  220  and  320  described above in that microfluidic valve  420  comprises a constriction  440  having both a ceiling edge  52  and floor edge  352 . Those components of microfluidic valve  420  that correspond to components of microfluidic valves  220  and  320  are numbered similarly. Although the ceiling edge  52  and floor edge  352  are illustrated as having equal heights, in other implementations, the ceiling edge  52  and the floor edge  352  may have different heights. 
     Ceiling edge  50  and floor edge  352 , combined with side edges  50 , provide a continuous edge or corner about the juncture interface between portions  30  and  34 . This continuous edge provides an even more robust and stronger meniscus  44  that is less likely to accidental breakage which might result in accidental opening of microfluidic valve  420 . As with microfluidic valves  220  and  320 , microfluidic valve  420  may be selectively opened through the output of control signals from controller  264  to meniscus breaker  260 , causing meniscus breaker  260  to apply a pressure pulse to liquid  36  to break the meniscus  44  and establish liquid flow through conduit  424 . 
       FIGS. 11A and 11B  illustrate top sectional and side sectional views, respectively, of portions of an example microfluidic valve  520  in a closed state, stopping the flow of liquid through or across the microfluidic valve  520 .  FIGS. 11A and 11B  illustrate microfluidic valve  520  in a closed state in which fluid flow through the valve  520  is obstructed or stopped by a capillary meniscus  44 . Microfluidic valve  520  comprises liquid conduit  524 . 
     Conduit  524  comprises a body or structure having an interior along which liquid is to flow when valve  520  is open. Conduit  524  comprises a first interior or a first portion  530  that is to contain a fluid  32  and a second interior or second portion  534  that is supplied with or is to contain a liquid  36 . Portions  530  and  534  are joined or connected to one another at a constriction  540 . A constriction is an interface where a conduit undergoes dimensional changes from a larger flow passage to a smaller flow passage. 
     Constriction  540  provides a structure at which a capillary meniscus may form. Because the constriction  540  is formed between or along a fluid-liquid interface between the two portions  530 ,  534  of conduit  524 , capillary meniscus  44  may form across constriction  540 . In particular, portions  534  and  536  are sized such that the liquid  36  within first portion  534  forms the capillary meniscus  44  along the fluid-liquid interface of the two portions. This capillary meniscus  44  serves as a valve to stop liquid flow through conduit  524 . Actuation or opening of this valve provided by capillary meniscus  44  may occur through breaking of the capillary meniscus  44 . 
     As shown by  FIG. 11A , constriction  540  comprises a pair of opposite side corners or edges  50 . Edges  50  facilitate the formation of meniscus  44 . However, in some implementations, edges  50 , alone, may not reliably maintain the meniscus  44  over time or in response to pressure increases. As shown by  FIG. 11B , microfluidic valve  520  additionally comprises liquid phobic surfaces  570 A,  570 B (collectively referred to as surfaces  570 ). Liquid phobic surfaces  570  extend along interior surfaces of portion  530  of conduit  524 . Liquid phobic surface  570 A extends along the ceiling of portion  530  while liquid phobic surface  570 B extends along the floor of portion  530 . Liquid phobic surfaces  570  extend from constriction  540 , away from constriction  540  or from regions in close proximity to constriction  540  away from constriction  540  in portion  530 . Liquid phobic surfaces  570  repel liquid  36  to inhibit the creep of liquid  36  past constriction  540  and onto the floor or ceiling of portion  530 . 
     In one implementation, liquid phobic surfaces  570  are formed from a hydrophobic material such as polytetrafluoroethylene. In other implementations, liquid phobic surface  570  may be formed from other liquid phobic materials, materials that are phobic to (that repel) the liquid to be supplied to portion  534  of conduit  524 . In one implementation, liquid phobic surfaces  570  are formed by a thin film or coating deposited upon the floor and ceiling of portion  530 , wherein the thin film or coating slightly project below the floor and ceiling, respectively, of portion  534  at constriction  540 . In another implementation, liquid phobic surfaces  570  are formed by layers of liquid phobic material slightly recessed into the floor and ceiling of portion  540  such that the interior most surfaces of liquid phobic surface  570  are flush with or slightly recessed from the floor and ceiling of portion  534  at constriction  540 . In some implementations, one of liquid phobic surfaces  570 A,  570 B may be omitted. 
     In one implementation, constriction  540  has a smallest opening dimension (the smallest dimension of the height or width of the opening forming constriction  540 ). In such an implementation, each of liquid phobic surfaces  570  extend away from constriction  540  by a distance of at least 1 times the smallest opening dimension and no greater than 10 times the smallest opening dimension. In one implementation, each of the liquid phobic surfaces  570  extends away from constriction  540  by a distance of at least three times the smallest opening dimension and no greater than 10 times the smallest opening dimension. In such an implementation, the minimum distance by which liquid phobic surfaces  570  extend away constriction  540  facilitates the formation of a sufficiently robust meniscus  44 . In such an implementation, the maximum distance by which liquid phobic surfaces  570  may extend away from constriction  540  facilitates reliable opening of microfluidic valve  520  by meniscus breaker  260  in response to control signals from controller  264 . 
       FIGS. 12A and 12B  illustrate top sectional and side sectional views, respectively, of portions of an example microfluidic valve  620  in a closed state, stopping the flow of liquid through or across the microfluidic valve  620 . Microfluidic valve  620  is similar to microfluidic valve  420  described above in that microfluidic valve  620  comprises a constriction  440  having side edges  50 , ceiling edge  52  and floor edge  352 . Unlike microfluidic valve  420 , microfluidic valve  620  additionally comprises liquid phobic surfaces  670  (shown with an enlarged thickness for purposes of illustration). Those components of microfluidic valve  620  that correspond to components of microfluidic valves  220 ,  320 , and  420  are numbered similarly. 
       FIG. 12C  illustrates . . . As shown by  FIG. 12C , portion  530  of conduit  424  has a face  632  terminating at side edges  50 , ceiling edge  52  and floor edge  352  of constriction  440  to define the mouth or opening between portions  530  and  34  of conduit  424 . Liquid phobic surfaces  670  extend along face  632  about constriction  440 , about the mouth or opening. Liquid phobic surfaces  670  reduce a likelihood of liquid within portion  34  from creeping past constriction  440  and onto face  632 . 
     In one implementation, liquid phobic surfaces  670  are formed from a hydrophobic material such as polytetrafluoroethylene. In other implementations, liquid phobic surface  670  may be formed from other liquid phobic materials or materials that are phobic to (tending to repel) the liquid  36  to be supplied through portion  34  of conduit  424 . In one implementation, liquid phobic surfaces  670  are formed by a thin film or coating deposited upon face  632 . In another implementation, liquid phobic surfaces  670  are formed by layers of liquid phobic material slightly recessed into the face  632 . 
     In the example illustrated, liquid phobic surfaces  670  do not cover an entirety of face  632 , but a limited area of face  632  outwardly extending from edges  50 ,  52 ,  352 . In other implementations, surfaces  670  may cover an entirety of face  632 . Although surfaces  670  are illustrated as continuously extending about the opening defined by edges  50 ,  52 ,  352 , in other implementations, surfaces  670  may comprise multiple spaced patches of liquid philic material or coatings about the opening defined by edges  50 ,  52 ,  352 . In some implementations, the internal floor, ceiling and/or outer internal sides of portion  530  extending away from the mouth in the direction indicated by arrow  673  may additionally or alternatively be covered or at least partially covered by a liquid filling material. 
       FIG. 13  is a flow diagram of an example method  700  for providing and controlling a microfluidic valve to control the flow of a liquid. As indicated by block  704 , a conduit is provided, wherein the conduit has a first portion and a second portion filled with a fluid and separated by a constriction. As indicated by block  708 , a hydrophobic surface is provided proximate the constriction in the first portion of the conduit. As indicated by block  712 , fluid is supplied to the second portion of the conduit at a pressure so as to form a meniscus across the constriction. The meniscus and the hydrophobic surface impede liquid flow into the first portion. 
       FIGS. 14A and 14B  are side and top sectional views, respectively, illustrating an example microfluidic valve  820 . Microfluidic valve  820  comprises substrate  822 , chamber layer  823 , floor layer  825 , ceiling layer  827 , meniscus breaker  860 , flow sensor  862  and controller  864 . Substrate  822  comprises a base layer upon which the remaining components of microfluidic valve  820  are formed. In one implementation, substrate  822  forms part of a microfluidic chip having microfluidic passages. Such microfluidic passages may be formed by performing etching, microfabrication (e.g., photolithography), micromachining processes, or any combination thereof in a substrate of a fluidic die. Some example substrates  822  may include silicon-based substrates, glass based substrates, gallium arsenide based substrates, and/or other such suitable types of substrates for microfabricated devices and structures. Accordingly, microfluidic channels, passages, chambers, orifices, and/or other such features may be defined by surfaces fabricated in the substrate of the fluidic die. Furthermore, as used herein a microfluidic channel or passage may correspond to a channel of sufficiently small size (e.g., of nanometer sized scale, micrometer sized scale, millimeter sized scale, etc.) to facilitate conveyance of small volumes of fluid (e.g., picoliter scale, nanoliter scale, microliter scale, milliliter scale, etc.). 
     Chamber layer  823  comprise a layer of material patterned upon substrate  822 . In one implementation, chamber layer  823  extends on top of floor layer  825 . In other implementations, chamber layer  823  extends around side portions of floor layer  825 . Chamber lay  823  defines a liquid passage  826  comprising a liquid supply portion  828  and a liquid receiving portion  830  connected by a tapering portion  834 . Tapering portion  834  narrows as it approaches receiving portion  830 . Tapering portion  834  is joined to receiving portion  830  at a constriction  840 . Chamber layer  823  forms side edges  850  which form opposite sides of constriction  840 . In one implementation, chamber layer  823  comprises a layer of patterned material such as SU8, polyimide, polydimethylsiloxane (PDMS), etc. 
     Floor layer  825  comprises a layer of material extending below tapering portion  834 . In the example illustrated, floor layer  825  additionally extends below supply portion  828 . As shown by  FIG. 14A , floor layer  825  rises above substrate  822 , forming a floor edge  852  at constriction  840 . In one implementation, floor layer  825  comprise a layer of an epoxy, such as SU8. 
     Ceiling layer  827  comprises a layer of material formed on top of chamber layer  823  and forming a ceiling of each of portions  828 ,  830  and  834 . In one implementation, ceiling layer  827  comprises a layer of material such as a resist material, such as SU8, a polyimide, a PDMS, a glass, a cyclic olefin copolymer (COC), etc. In one implementation, ceiling layer  827  is formed by depositing a layer on top of the sacrificial material filling each of portions  828 ,  830  and  834 , wherein upon hardening or solidification of the top at layer  827 , the sacrificial material is removed. The completed combination of layers  822 ,  824 ,  827  and  830  forms a microfluidic valve having a constriction across which a capillary meniscus  844  may be formed when fluid is supplied under an appropriate pressure into portions  828  and  834 . The meniscus inhibits liquid within portions  828  and  834  from flowing into or through receiving portion  830 . 
     Meniscus breaker  860  is similar to meniscus breaker  260  described above. In one implementation, breaker  860  is formed upon substrate  822  and projects through a patterned opening in floor layer  825 . In one implementation, meniscus breaker  860  may comprise a thermal resistor connected to electric conductive traces and transistors provided on substrate  822 . 
     Sensor  862  comprises a component that senses the presence and/or flow of liquid within and through receiving portion  830  of passage  826 . In one implementation, sensor  862  may comprise a wet-dry sensor. For example, in one implementation, sensor  862  may comprise spaced electrodes of a circuit, wherein the circuit completed within a liquid extending across and contacting the spaced electrodes. In such an implementation, a dry state may indicate that valve  820  is presently closed, that meniscus is intact and that no liquid is flowing through valve  820 . A wet state would indicate the presence of liquid across sensor  862 , indicating that meniscus  844  has been broken and that valve  820  has been opened. In another implementation, sensor  862  may comprise an electrical impedance sensor. In yet other implementations, sensor  862  may comprise an optical sensor. Signals from sensor  862  are communicated to controller  864 . 
     Controller  864  is similar to controller  264  described above. Controller  864  controls actuation of meniscus breaker  860 . In the example illustrated controller  864  controls actuation of meniscus breaker  860  based at least in part upon signals received from sensor  862 . Such signals may indicate when the application of pressure pulses should be ceased by meniscus breaker  860 . In some implementations, meniscus breaker  860  may further be utilized to pump fluid along passage  826 . For example, in one implementation, meniscus breaker  860  may be formed as an inertial pump using the fluid actuator. In such an implementation, bumping provided by meniscus breaker  860  may be controlled by controller  864  based upon signals from sensor  862  to provide a selected flow rate of liquid or a selected flow rate of particles, cells or other objects carried by the flowing liquid. In one implementation, controller  864  comprises a processing unit that follows instructions contained in a non-transitory computer-readable medium. In another implementation, controller  864  comprises an integrated circuit, such as an application-specific integrated circuit (ASIC). 
     In one implementation, meniscus breaker  860  comprises an electrically driven device, such as an electrically driven fluid actuator or electrically driven vibrator contained in or on substrate layer  822 . For example, meniscus breaker  860  and passage  826  may be formed as part of a single microfluidic circuit chip or die. In such an implementation, the single microfluidic circuit chip or die may comprise switches in the form of transistors which are actuated in response to signals from controller  864 . In one implementation, controller  864  may also be formed or provided upon the single microfluidic circuit chip or die that also supports meniscus breaker  860  and defines liquid passage  826 . In yet another implementation, controller  864  may be remote from the circuit chip or die including meniscus breaker  860  and liquid passage  866 , wherein a communication interface, such as a contact pad, port or other connector is provided on the circuit chip or die or connection to the remote controller  864 . 
       FIGS. 15A and 15B  are side and top sectional views, respectively, illustrating an example microfluidic valve  920 . Microfluidic valve  920  is similar to microfluidic valve  820  described above except that microfluidic valve  920  additionally comprises liquid phobic surfaces  970 ,  972 . Those remaining components of microfluidic valve  920  that correspond to components of microfluidic valve  820  are numbered similarly. 
     Liquid phobic surface  970  is similar to liquid phobic surface  570 A described above. As shown by  FIG. 15A , liquid phobic surface  970  extends along a ceiling of portion  830 , extending away from constriction  840 . As shown by  FIG. 15B , liquid phobic surface  972  is additionally provided on face  932  extending from opposite sides of constriction  940 . Liquid phobic surfaces  970 ,  972  reduce a likelihood of liquid within portion  834  from creeping past constriction  840  and into portion  830 . 
       FIGS. 16A and 16B  are side and top sectional views, respectively, illustrating portions of an example microfluidic valve  1020 . Microfluidic valve  1020  is similar to microfluidic valve  820  except that microfluidic valve  1020  comprises overhead layer  1025  in place of floor layer  825 . Those remaining components of microfluidic valve  1020  that correspond to components of microfluidic valve  820  are numbered similarly. 
     Overhead layer  1027  comprises a layer of material suspended from top at layer  827  and/or resting upon sides of chamber layer  823 . Overhead layer  1027  extends above at least portions of portion  834  proximate to constriction  840 . Overhead layer  1027  forms a ceiling edge  1052  which cooperates with side edges  850  to form constriction  1040 . Ceiling edge  1052  facilitates the formation of a more robust meniscus  1044  across constriction  1040  to stop liquid flow from chamber  834  from portion  834  into portion  830 . As discussed above, the formed meniscus is broken by meniscus breaker  860  in response to control signals from controller  864  which may be based at least in part upon signals from sensor  862 . Breaking of the meniscus  1044  opens microfluidic valve  1020 , permitting liquid to flow through and along portion  830  of passage  826 . 
       FIGS. 17A and 17B  are top and side sectional views, respectively, illustrating portions of an example microfluidic valve  1120 . Microfluidic valve  1120  is similar to microfluidic valves  820 ,  920  and  1020 . Those components of microfluidic valve  1120  that correspond to components of valves  820 ,  920  and  1020  are numbered similarly. Similar to microfluidic valve  820 , microfluidic valve  1120  comprises floor layer  825  providing floor edge  852 . Similar to microfluidic valve  920 , microfluidic valve  1120  comprises liquid phobic surfaces  972  along face  932 . Similar to microfluidic valve  1020 , microfluidic valve  1120  comprises overhead layer  1025 , forming ceiling edge  1052 . Side edges  850 , floor edge  852  and ceiling edge  1052  form constriction  1140  which is completely surrounded by such edges along face  932 . Liquid phobic surfaces  972  additionally inhibit accidental creep of liquid through constriction  1140 . As a result, microfluidic valve  1120  provides a robust capillary meniscus  1144  when liquid flow is to be stopped. As in the above implementations, microfluidic valve  1120  may be opened by breaking the meniscus  1144  using pressure pulses or other stimuli provided by meniscus breaker  860  in response to signals from controller  864  which may be based at least in part upon signals from sensor  862 . 
       FIGS. 18 and 19  are sectional views illustrating portions of an example microfluidic valve  1220 .  FIG. 18  is a top sectional view of microfluidic valve  1220  while  FIG. 19  is a side sectional view of microfluidic valve  1220 . Microfluidic valve  1220  comprises conduit  1224  having a fluid passage  1226 , meniscus breaker  1260 , sensor  1262 , sensor  1263  and controller  1264 . 
     Conduit  1224  comprises at least one layer of material forming fluid passage  1226 . Fluid passage  1226  projects or extends off of a fluid supply passage or slot  1265 . The fluid passage  1226  of conduit  1224  comprises liquid receiving portion  1230 , spout  1232  and liquid supplying portion  1234 . Spout  1232  is formed in the body of conduit  1224  and projects into portion  1230 . Portion  1234  extends through spout  1232 , where it is connected to portion  1230  at a constriction  1240 . As shown by  FIGS. 18 and 19 , constriction  1240  is completely surrounded by corners or edges. As shown by  FIG. 18 , constriction  1240  comprises side corners or edges  1250 . As shown by  FIG. 19 , constriction  1240  comprises ceiling edge  1252  and a floor edge  1253 . The continuous edge of constriction  1240  formed at the end of spout  1232  provides a robust capillary meniscus  1244 . Although the ceiling edge  1252  and floor edge  1253  are illustrated as having equal heights, in other implementations, the ceiling edge  1252  and the floor edge  1253  may have different heights. 
     In the example illustrated, spout  1232  comprises tapering sides  1255  that provide edges  1250  with an acute profile. This acute profile further inhibits creep of liquid beyond constriction  1240 . In other implementations, spout  1232  may have other shapes at its end. 
     Meniscus breaker  1260  is similar to meniscus breaker  860  described above. Meniscus breaker  1260  is formed in portion  1234  and upon actuation, creates pressure pulses or other stimuli so as to controllably break the meniscus  1244 . Meniscus breaker  1260  operates under the control of controller  1264 . 
     Sensors  1262 ,  1263  comprise sensing devices that output signals from which controller  1264  may determine the state of valve  1220 . In one implementation, sensors  1262 ,  1263  comprise sensing devices that output signals from which controller  1264  may determine whether meniscus  1244  exists or has been broken, or whether liquid is flowing through constriction  1240 , i.e. the valve is open. 
     Sensor  1262  is located within portion  1230  of conduit  1224 . In one implementation, sensor  1262  is located flush or along a floor, ceiling or sidewall of portion  1230  of conduit  1224  to reduce obstruction of flow when valve  1220  is opened. In one implementation, sensor  1262  may comprise a wet-dry sensor that senses the presence or absence of liquid. For example, in one implementation, sensor  1262  may comprise spaced electrodes of a circuit, wherein the circuit is completed when a liquid extends across and contacts the spaced electrodes. In such an implementation, a dry state may indicate that valve  1220  is presently closed, that meniscus is intact, and that no liquid is flowing through valve  1220 . A wet state would indicate the presence of liquid across sensor  1262 , indicating that meniscus  1244  has been broken and that valve  1220  has been opened. In other implementations, sensor  1262  may comprise other sensing devices, such as a flow sensor which senses the rate at which fluid or liquid is flowing across sensor  1262 . 
     Sensor  1263  is located within portion  1234  of conduit  1224 , upstream of portion  1230 , on an opposite side of meniscus  1244  when valve  1220  is closed. In one implementation, sensor  1263  is located flush or along a floor, ceiling or sidewall of portion  1234  of conduit  1224  to reduce obstruction of flow when valve  1220  is opened. In one implementation, sensor  1263  is located proximate to constriction  1240  so as to detect the flow of liquid through constriction  1240 . In one implementation, sensor  1263  may comprise a flow sensor that senses whether liquid is flowing or moving within portion  1234  of conduit  1224 . In some implementations, sensor may comprise an electrical impedance sensor that senses the presence of liquid within portion  1234 . In some implementations, sensor  1263  may have dual functions: sensing the flow of liquid through portion  1234  and sensing the number or count of cells or particles flowing through portion  1234  of conduit  1224  or the rate at which cells or particles carried in the liquid are flowing through portion  1234  of conduit  1224 . In such implementations, sensor  1263  (schematically illustrated) may extend across the width of conduit  1234  such that particles or cells cannot flow around such a sensor without being counted. 
     Although sensors  1262 ,  1263  are depicted in the illustrated locations, sensor  1262 ,  1263  may be provided at other locations in the respective portions  1230  and  1234  of conduit  1224 . In some implementations, portion  1230  may contain multiple spaced sensors  1262 . In some implementations, portion  1234  may contain multiple spaced sensors  1263 . In some implementations, one or both of sensors  1262 ,  1263  may be omitted. 
       FIGS. 20 and 21  illustrate portions of an example microfluidic valve  1320 . Valve  1320  is similar to valve  1220  described above except that valve  1320  comprises spout  1332  in place of spout  1232 . Those remaining components of valve  1320  that correspond to components of valve  1220  are numbered similarly. 
     As shown by  FIG. 21 , spout  1332  is tapered about all sides so as to form a continuous acute edge about a junction of portion  1230  and  1234 . In one implementation, edges  1250 ,  1252  and  1253  form a continuous edge that is circular. In another implementation, edges  1250 ,  1252  and  1253  form a continuous edge that is polygonal. 
       FIGS. 22 and 23  are sectional views schematically illustrating portions of an example microfluidic valve  1420 . Microfluidic valve  1420  is similar to microfluidic valve  620  described above except that microfluidic valve  1420  additionally comprises sensor  1262  (described above) and constrictions  1440 A,  1440 B,  1440 C (collectively referred to as constrictions  1440 ) and sensors  1448 A,  1448 B and  1448 C (collectively referred to as sensors  1448 ). Those remaining components of microfluidic valve  1420  that correspond to components of microfluidic valve  620  are numbered similarly. 
     Constrictions  1440  comprise narrowing regions arranged in series within portion  34 . Constrictions  1340  provide multiple successive regions where the capillary meniscus may be formed at a liquid-fluid interface along portion  34 , closing valve  1420 . In one implementation, constrictions  1440  comprise a series of opposing teeth or annular rings spaced along portion  34 , wherein the teeth continuously extend about the interior of portion  34  on both sides, the top and the bottom of portion  34 . In one implementation, such multiple constrictions  1440 , arranged in series, assist in reducing the likelihood of accidental or inadvertent opening of valve  1420  due to pressure fluctuations or variations in either of portions  30  or  34 . 
     In one implementation, a liquid-fluid interface is formed at constriction  1440 A, forming a capillary meniscus across constriction  1440 A, wherein the capillary menisci across constriction  1440 A closes valve  1420 . In the event of inadvertent breaking or bursting of the capillary meniscus across constriction  1440 A, liquid may flow through constriction  1440 A and form a second capillary meniscus across constriction  1440 B, once again closing valve  1420 . In the event of inadvertent breaking or bursting of the capillary missed is across constriction  1440 B, liquid may flow through constriction  1440 B and form a third capillary meniscus across constriction  1440 C, once again closing valve  1420  and inhibiting the flow of liquid into portion  30 . 
     In the example illustrated, each of such constrictions  1440  has a width of less than or equal to 20 μm in one implementation, less than or equal to 10 μm. Although constriction  1440  are illustrated as being similar in size such that the capillary menisci formed across such constrictions have substantially similar burst pressure thresholds, the pressure at which such capillary menisci would break, in other implementations, constrictions  1440  may be differently shaped or differently sized such that the different constrictions  1440  result in different capillary menisci having different bursts or break pressure thresholds. For example, in one implementation, the different restrictions  1440  may be differently shaped or differently sized so as to provide capillary menisci having ever-increasing burst pressure thresholds as the constrictions  1440  approach portion  30 . Although valve  1420  is illustrated as comprising three such constriction  1440  in portion  34 , in other implementations, about 920 may have a greater or fewer of such supplemental constrictions  1440 . 
     In the example illustrated, meniscus breaker  262  is situated sufficiently close to each of such constrictions  1440  so as to create pressure burst or pressure pulses in the liquid that are near the liquid-fluid interface so as to burst each capillary meniscus that forms across the different constrictions  1440 . In one implementation, meniscus breaker  262  may be sequentially fired or actuated multiple times, once for each constriction  1440  and its associated capillary meniscus. In other implementations, meniscus breaker  262  may be fired or actuated a single time for a sufficient duration so as to break each of the capillary menisci that sequentially form across the constrictions  1440  or inhibit the formation of such capillary menisci once the initial capillary meniscus has been broken. 
     Sensors  1448  are similar to sensor  1262  described above. In the example illustrated, sensor  1448 A is located within or along portion  34  between constrictions  1440 A and  1440 B. Sensor  1448 B is located within or along portion  34  between constrictions  1440 B and  1440 C. Constriction  1448 C is located within or along portion  34  between constrictions  1440 D and  440 . Each of such sensors  1448  output signals that facilitate the determination of the state of liquid flow in a particular volume by controller  264 . 
     Based upon signals from sensor  1448 A, controller  264  may determine whether a capillary meniscus is present at constriction  1440 A. For example, in implementations where sensor  1448 A comprise a wet-dry sensor, a dry state indicated by sensor  1448 A may indicate the presence of a capillary meniscus at constriction  1440 A, whereas a wet state may indicate that any such capillary meniscus previously extending across constriction  1340 A has been broken. Based upon signals from sensors  1448 A and  1448 B, controller  264  may determine whether the capillary meniscus is present across constriction  1440 B. Based upon signals from sensors  1448 A,  1448 B and  1448 C, controller  264  may determine whether a capillary meniscus is present across constriction  1448 C. Based upon signals from such sensors  1448 , controller  264  may ascertain the risk of microfluidic valve  1420  being accidentally opened. Based upon signals from sensors  1448 , controller  264  may determine whether meniscus breaker  262  should be actuated additional times or should be actuated to provide greater pulse pressure so as to break all of the capillary menisci and completely open valve  1420 . 
     Although the present disclosure has been described with reference to example implementations, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the claimed subject matter. For example, although different example implementations may have been described as including features providing one or more benefits, it is contemplated that the described features may be interchanged with one another or alternatively be combined with one another in the described example implementations or in other alternative implementations. Because the technology of the present disclosure is relatively complex, not all changes in the technology are foreseeable. The present disclosure described with reference to the example implementations and set forth in the following claims is manifestly intended to be as broad as possible. For example, unless specifically otherwise noted, the claims reciting a single particular element also encompass a plurality of such particular elements. The terms “first”, “second”, “third” and so on in the claims merely distinguish different elements and, unless otherwise stated, are not to be specifically associated with a particular order or particular numbering of elements in the disclosure.