Microfluidic devices, systems and methods

Abstract

A microfluid valve that is operable via capillary action to close a fluid path in a primary channel and then to re-open the fluid path passively via capillary action. Various embodiments and circuits operable to perform the functions of the valve are disclosed, each comprising at least one control channel that receives a control liquid to close the valve and withdrawal sub-circuit that can passively withdraw control liquid from the same or another control channel to re-open the valve.

Description

[0001] MICROFLUIDIC DEVICES, SYSTEMS AND METHODS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to microfluidic valves, microfluidic circuits or devices incorporating valves, and other associated devices, systems, methods, and components thereof.

[0004] BACKGROUND TO THE INVENTION

[0005] Microfluidic devices are miniaturised liquid handling systems typically embedded in small chips. Their size makes them suitable for use in biological, chemical, and clinical applications due to their low volume demands, low cost, and disposability.

[0006] 'Point-of-care' (POC) devices are a key application for microfluidics. In general, POC devices can reduce instrumentation complexity of measurement or diagnostics devices to transfer complex laboratory procedures into broad applications for untrained personnel outside the laboratory environment. In medicine, the ability to carry out an instantaneous test, and act on the results as fast as possible can be critical. In a triage situation, medical intervention can be delayed by minutes to hours because of the time taken to transport a patient to the hospital. In this situation, POC devices would allow a paramedic to test, a doctor to remotely diagnose a patient, and immediate care to be given. Beyond triage, POC devices also have the potential to positively influence equality in access to medical care. The typical medical care pipeline (consultation, testing, diagnosis, and treatment) often takes place over multiple appointments with a medical professional. For many low socio-economic groups, multiple appointments with a doctor are not financially feasible, and as a result many individuals do not present for diagnosis and miss out on required medical care. Therefore, POC devices can allow timely access to medical treatment for low- income groups and similar groups. Accordingly, there are major societal, ethical, and commercial interests in improving POC devices or providing alternatives.

[0007] Some of the key challenges for POC devices are reducing cost, improving high- volume manufacturing capabilities, and ease of use. Capillaries is an emerging field within microfluidics in which capillary systems are connected to circuit-like structures to enable and / or improve functionality of a microfluidic circuit. Such systems are driven purely by capillary pressure, utilising surface tension effects that are determined by surface geometry and surface chemistry to automate or pre-set flow control within a microfluidic chip. As such they do not require peripheral elements to enable autonomous sampling and laboratory operations like mixing and analysis on chips. The use of self-driven capillary circuits appears to be one of the most promising approaches for POC diagnostic devices as they do not require electrical accessories and can be pre-programmed through their geometry.

[0008] One fundamental requirement for the fully autonomous operation of capillary circuits continues to be the availability of basic valving operations that do not need any external power source. Two-level trigger valves or externally controlled valves are examples of devices that can perform such valving operations. PCT patent application PCT / IB2021 / 051153, the contents of which are hereby incorporated by reference, discloses recent developments in this technology space including various microfluidic valve designs and circuits that can be utilised to enable the design of complex circuitry with integrated logic and valving, without the need for external control. The operating principle behind the disclosed valves and circuits is a capillary action transistor valve structure that comprises a main channel for conveying a liquid via capillary action, and that is triggerable via a capillary pressure input to close the valve. Closing of the valve occurs based on inflation of an occluding air bubble into the main channel by the applied capillary pressure, thus preventing further flow through the main channel.

[0009] While trapped bubbles have been used for various applications in actively-driven microfluidics, including to alter flow dynamics and mixing and to realise hydraulic capacitors, they have not yet been extensively used in capillaries. To fill this gap, the abovementioned transistor valve structure demonstrates autonomous capillaryaction fluidic valving, with no need for external instrumentation, and a variety of fundamental valving operations, including use to provide feedback, metering, and logic operations.

[0010] One of the challenges associated with the abovementioned transistor valve structure is it is only operable to close the valve, and the automated re-opening or reversible actuation of the valve is not possible. In the context of a capillary test, reversable actuation may allow progress of a test to be automatically halted by the transistor valve structure, and then to be resumed after a certain condition is met. This condition could be a predetermined time period during which reagents may be allowed to react. Accordingly, there is a need to provide a capillary action transistor valve that reversibly actuatable, and / or to provide microfluidic circuits or systems incorporating such a valve. In this specification where reference has been made to patent specifications, other external documents, or other sources of information, this is generally for the purpose of providing a context for discussing the features of the invention. Unless specifically stated otherwise, reference to such external documents is not to be construed as an admission that such documents, or such sources of information, in any jurisdiction, are prior art, or form part of the common general knowledge in the art.

[0011] It is an object of the present invention to provide an alternative microfluidic capillary valve, circuit or device that can be closed and then reversibly actuated to open again, and to provide associated systems and methods thereof, or to at least provide the public with a useful choice.

[0012] SUMMARY OF THE INVENTION

[0013] In a first general aspect, the invention may broadly be said to consist of a microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; at least one capillary control channel, each capillary control channel being separately fluidly connected to the void volume and having inlet for receiving a corresponding control liquid and conveying the control liquid toward the void volume via capillary action, wherein at least one of the capillary control channel(s) is configured as a trigger channel that drives a corresponding control liquid ("trigger liquid") toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; and a withdrawal subcircuit fluidly connected to an outlet of at least one of the capillary control channel(s), to drive the flow of the corresponding control liquid received within the respective control channel(s) through the corresponding outlet and away from the void volume, thereby substantially increasing or re-permitting the flow of the primary liquid through the primary channel. In a second general aspect, the invention may broadly be said to consist of a microfluidic device comprising: a main channel for conveying a primary liquid, and the microfluidic valve of the first aspect wherein the primary channel of the first microfluidic valve is connected in series to the main channel.

[0014] In a third general aspect, the invention may broadly be said to consist of a method for operating the microfluidic valve of the first aspect comprising the steps of: driving, through capillary action, a volume of trigger liquid through the trigger channel toward the void volume to generate a first capillary force that causes a meniscus restrained at the first port to expand from the first port into the primary channel, to inhibit or reduce a flow of primary liquid in the primary channel.

[0015] The method may further comprise the step of triggering a flow of the volume of control liquid contained in the control channel connected to withdrawal sub-circuit away from the void volume to generate a second capillary force that causes the meniscus to retract from the primary channel toward the void volume, to re-permit or increase the flow of primary liquid in the primary channel.

[0016] In a fourth general aspect, the invention may broadly be said to consist of a microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; a first capillary trigger channel ("first trigger channel") fluidly connected to the void volume, and configured to convey a trigger liquid toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; a second capillary withdrawal channel ("second withdrawal channel") fluidly connected to the void volume and configured to convey a withdrawal liquid away from the void volume to substantially permit or increase a flow of the primary liquid through the primary channel. In a fifth general aspect, the invention may broadly be said to consist of a microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; a capillary trigger channel fluidly connected to the void volume and configured to convey first trigger liquid toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; one or more second capillary withdrawal channel(s) ("second withdrawal channel(s)") fluidly connected to the void volume and configured to convey second withdrawal liquid(s) away from the void volume to substantially increase or permit a flow of the primary liquid through the primary channel.

[0017] In a sixth general aspect, the invention may broadly be said to consist of a microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; multiple capillary control channels, each capillary control channel being separately fluidly connected to the void volume and having inlet for receiving a corresponding control liquid and conveying the control liquid toward the void volume via capillary action, wherein at least one of the capillary control channel(s) is configured as a trigger channel that drives a corresponding control liquid ("trigger liquid") toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; and a withdrawal subcircuit for each of a plurality of the control channels, each withdrawal subcircuit being fluidly connected to an outlet of the respective capillary control channel, to drive the flow of the corresponding control liquid received within the respective control channel(s) through the corresponding outlet and away from the void volume, thereby substantially increasing the flow of the primary liquid through the primary channel.

[0018] In a seventh general aspect, the invention may broadly be said to consist of a microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; at least one capillary control channel fluidly connected to the void volume, and configured to convey a control liquid toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel, each capillary control channel having an inlet for receiving a flow of a corresponding control liquid into the channel; and a withdrawal subcircuit fluidly connected to an outlet of at least one of the control channel(s) and configured to trigger and drive the flow of the control liquid contained within the control channel through the outlet of the control channel to substantially increase or re-permit the flow of the primary liquid through the primary channel.

[0019] In an eighth general aspect, the invention may broadly be said to consist of a microfluidic device comprising: a main channel for conveying a primary liquid, a first microfluidic valve as per the microfluidic valve of any one of the preceding aspects; and wherein the primary channel of the first microfluidic valve is connected in series to the main channel.

[0020] In a ninth general aspect, the invention may broadly be said to consist of a method for operating a microfluidic valve as per any one of the preceding aspects comprising the steps of: pre-filling the second withdrawal channel with a volume of second withdrawal liquid; conveying a volume of first trigger liquid through the first trigger channel toward the void volume to generate a first capillary force that causes a meniscus restrained at the first port to expand from the first port into the primary channel, to inhibit or reduce a flow of primary liquid in the primary channel.

[0021] The phrase "capillary action" as used herein refers to the surface tension-driven phenomenon that causes a liquid to flow through narrow channels due to the adhesive and cohesive forces between the liquid molecules and the channel walls. This results in motion of the liquid without the need for external pressure or mechanical pumping. Related terms and phrases such as "capillaric" or "capillary force" are to be interpreted in a similar manner.

[0022] The term "microfluidic" as used herein refers to the manipulation, control, or processing of fluids at a microscale, typically within channels or structures with dimensions ranging from tens to hundreds of micro-meters. Capillary-based microfluidic systems leverage the phenomena of capillary action and surface tension to achieve fluid control, enabling applications in diagnostics, chemical analysis, biological assays, and other fields requiring miniaturised fluid handling.

[0023] The term "meniscus" as used in this specification refers to the curved surface of a liquid, typically formed at the interface between the liquid-gas phase, and a solid surface or within a narrow channel, which plays a primary role in controlling the flow of liquid in microfluidic devices through capillary action.

[0024] The term "comprising" as used in this specification and claims means "consisting at least in part of". When interpreting each statement in this specification and claims that includes the term "comprising", features other than that or those prefaced by the term may also be present. Related terms such as "comprise" and "comprises" are to be interpreted in the same manner.

[0025] It is intended that reference to a range of numbers disclosed herein (for example, 1 to 10) also incorporates reference to all rational numbers within that range (for example, 1, 1.1, 2, 3, 3.9, 4, 5, 6, 6.5, 7, 8, 9 and 10) and also any range of rational numbers within that range (for example, 2 to 8, 1.5 to 5.5 and 3.1 to 4.7) and, therefore, all sub-ranges of all ranges expressly disclosed herein are hereby expressly disclosed. These are only examples of what is specifically intended and all possible combinations of numerical values between the lowest value and the highest value enumerated are to be expressly stated in this application in a similar manner. As used herein the term "and / or" means "and" or "or", or both. When used as part of a list, the term "and / or" means any combination of one or more of the items in the list, unless stated otherwise.

[0026] As used herein "(s)" following a noun means the plural and / or singular forms of the noun.

[0027] The invention consists in the foregoing and envisages constructions of which the following gives examples only.

[0028] BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Preferred embodiments of the invention will be described by way of example only and with reference to the drawings, in which:

[0030] Fig. 1 is a schematic of a first embodiment capillary valve;

[0031] Figs. 2A-2E are schematics showing various stages of operation of the first embodiment microfluidic valve;

[0032] Fig. 3A is a flow diagram of an embodiment of a method for operating the first or second embodiment microfluidic valve;

[0033] Fig. 3B is a flow diagram of an embodiment of a method for prefilling a withdrawal channel of the first or second embodiment microfluidic valve;

[0034] Fig. 3C is a flow diagram of an embodiment of a method for reopening the first or second embodiment microfluidic valve;

[0035] Fig. 4 is a schematic of a second embodiment microfluidic valve;

[0036] Figs. 5A-5C are schematics of the second embodiment microfluidic valve during various stages of operation;

[0037] Fig. 6 is a simplified circuit diagram of a first embodiment microfluidic circuit incorporating the first or second embodiment microfluidic valve;

[0038] Fig. 7A is a circuit diagram of a second embodiment microfluidic circuit incorporating the first or second embodiment microfluidic valve;

[0039] Fig. 7B is a schematic of the second embodiment microfluidic circuit implemented on a substrate material; Figs. 8A-8D show diagrams of four stages of operation of the second embodiment microfluidic circuit of Fig. 7;

[0040] Fig. 9 is a flow diagram of a third embodiment method for operating the first or second embodiment microfluidic circuit;

[0041] Figs. 10A and 10B are schematics of a two-level capillary trigger valve incorporated in the second embodiment microfluidic circuit;

[0042] Fig. 11 is a schematic of a prior art microfluidic valve that is not reversibly actuatable;

[0043] Fig. 12 is a schematic of the microfluidic valve of Fig. 1 incorporating a liquid modifier in the withdrawal channel of the valve;

[0044] Fig. 13 is a schematic of an alternative microfluidic circuit embodiment incorporating a microfluidic valve having multiple withdrawal channels;

[0045] Fig. 14 is a flow diagram of a method of operating the valve of Fig. 13;

[0046] Fig. 15 is a flow diagram of a method of operating the circuit of Fig. 13;

[0047] Figs. 16A-16C are schematics showing various stages of operation of further embodiment of a microfluidic valve;

[0048] Fig. 17 is a schematic showing the microfluidic valve of Fig. 16 implemented in a microfluidic device; and

[0049] Fig. 18 is a flow diagram of a method of operation of the microfluidic valve of Fig. 16 or microfluidic device of Fig. 17.

[0050] DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0051] In the following detailed description, reference is made to specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. It is to be understood that the various embodiments of the invention, although different, are not necessarily mutually exclusive. Furthermore, a particular feature, structure, or characteristic described herein in connection with one embodiment may be implemented within other embodiments without departing from the scope of the invention as defined by the accompanying claims. In addition, it is to be understood that the location or arrangement of individual elements within each disclosed embodiment may be modified without departing from the scope of the invention as defined by the accompanying claims. The following detailed description is, therefore, not to be taken in a limiting sense.

[0052] The word "exemplary" is used herein to mean "serving as an example, instance, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Likewise, the terms "embodiment(s) of the invention", "alternative embodiment(s)", and "exemplary embodiment(s)" do not require that all embodiments of the method(s) or apparatus include the discussed feature, advantage or mode of operation. The following description of preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or use.

[0053] Referring to Fig. 1 a schematic of a first embodiment microfluidic valve 100 of the invention is shown, configured and operable to regulate the flow of liquid within a microfluidic channel. The valve 100 enables both opening and closing of a liquid flow path through the channel (or increasing and decreasing the flow of liquid) and is triggerable into each one of these states. For instance, the valve 100 can be considered as being reversibly operable in that it allows closing or partially closing of the liquid flow path through the channel, and then the subsequent further opening of the liquid flow path.

[0054] The microfluid valve 100 is operable using capillary action, eliminating the need for external devices or systems and minimising operator intervention. Accordingly, it may be considered a passively operated valve 100 that leverages capillary forces to control fluid flow required for the valve's operations. This type of valve relies on inherent physical properties, such as surface tension, wettability and geometrical design to control fluid movement. External inputs, other than a user introducing liquids to the valve or associated circuit, or active mechanisms are preferably not utilised for its operation. This enhances its applicability in compact, low-cost and autonomous systems, such as in diagnostic assays and lab-on-chip or POC devices. In contrast, an actively operated capillary valve may integrate external stimuli, such as electrical, thermal or mechanical forces to influence capillary force or liquid flow. The valve may be operable in conjunction with such components in certain embodiments. Although, the configuration described herein allows for entirely passive operation (other than a user or other external system introducing the liquids into the valve or associated circuit). The valve 100 comprises a primary capillary channel 101 (herein referred to as "primary channel") for conveying a primary liquid in use. A void volume 102 is fluidly connected to the primary channel 101 via a first port 103 of the void volume 102. A first capillary trigger channel 104 (herein referred to as the "trigger channel") is fluidly connected to the void volume 102 and configured to convey a trigger liquid in use. A second capillary withdrawal channel 105 (herein referred to as the "withdrawal channel") is also fluidly connected to the void volume 102 and configured to convey a withdrawal liquid in use. The primary channel 101 may form a section of a channel of a microfluidic circuit which is intended to fluidly connect to the valve 100 for opening and closing the microfluidic circuit channel. Alternatively, the primary channel 101 may be fluidly connectable or fluidly connected in series to a channel of a microfluidic circuit to enable opening and closing of the connected channel, in use.

[0055] The withdrawal channel 105 can be pre-filled with a withdrawal liquid to prime the valve 100. During operation, a flow of liquid within the trigger channel 104 towards the void volume triggers the valve into a closed or partially closed state, where liquid flow through the primary channel 101 past the first port 103 is at least partially inhibited. To-reopen the valve 100 and increase the flow of liquid through the primary channel 101 past the first port 103, the withdrawal liquid in the pre-filled withdrawal channel 105 is driven out of the withdrawal channel 105 and away from the void volume 102. The flow of liquid into the trigger channel 104 and the flow of liquid out of the withdrawal channel 105 are both preferably driven by capillary forces, to effectuate the closing and opening of the valve 100. This results in flow regulation while minimising the need for external intervention.

[0056] The first port 103 comprises a geometry that inhibits the primary liquid in the primary channel from flowing through the first port 103 into the void volume 102 during operation. This results in a meniscus of the primary liquid being restrained at the first port 103 when the primary liquid is flowing through the primary channel 101.

[0057] In this specification, the term "geometry" of a physical element of the valve refers to the shape and / or dimensions of that element, as well the orientation and / or position of that elements or components of the valve. For instance, a geometry of the first port 103 may include an angle 103a between a region of an inner peripheral wall 102A of the void volume 102 located at or adjacent the first port 103 and an imaginary plane 110 spanning across the first port 103. This angle is configured to inhibit flow of liquid from the primary channel 101 through the first port and into the void volume 102. Preferably, the angle 103a is approximately 180 degrees or greater relative to the imaginary plane 110 to provide enhanced stability in inhibiting flow. However, in some embodiments, the angle may be less than 180 degrees provided it is sufficient to inhibit liquid flow into the void volume 102 from the primary channel 101.

[0058] The geometry of the first port 103 is further configured such that liquid is inhibited from flowing into the void volume 102 through first port 103 from the primary channel 101 in both open and closed states of the valve 100. In this embodiment, the first port 103 is laterally positioned relative to the primary channel 101, such that it is located to the side of the channel 101 or branches from it, rather than the imaginary plane 110 being in-line with / across the primary flow path of the primary channel 101. Other embodiments may comprise alternative geometric configurations of the first port 103 to perform the intended function of inhibiting flow of liquid from the primary channel 101 into the void volume 102 through the first port 103, in both the open and closed states of the valve 100.

[0059] Referring also to Figs. 2A-2E, the trigger channel 104 is configured to enable a trigger liquid 104A to flow into the trigger channel 104 via a trigger channel inlet 106, toward the void volume 102. The inlet 106 may be configured to fluidly connect with any suitable fluid source. For instance, the inlet 106 may be configured to fluidly connect to the primary channel 101 downstream of the first port 103. Alternatively, the inlet 106 may be configured to fluidly connect to another liquid source of a microfluidic circuit incorporating the valve 100. This flow of trigger liquid 104A into the trigger channel 104 generates a first capillary force Fl that causes an occluding air bubble 108 to be pushed out from the void volume 102, beyond the first port 103, and into the primary channel 101 to effectively inhibit or at least reduce the flow of the primary liquid 101A in the primary channel 101 past the first port 103. For the trigger liquid to generate a sufficient force to move the occluding bubble 108, the valve 100 is preferably configured such that an absolute magnitude of a first capillary pressure attributed to the trigger liquid 104A flowing in the trigger channel 104 is substantially greater than an absolute magnitude of a capillary pressure attributed to the primary liquid 101A flowing in the primary channel 101 at the first port, during operation. The valve 100 may be configured in this manner by configurating the relative geometries of the trigger channel 104 and primary channel 101, which can affect the capillary pressure of liquids flowing through the respective channels, and / or by configuring the type of liquids flowing through the channels and their surface tensions for instance, as is known in the art of capillary microfluidics.

[0060] A substantially higher capillary pressure in the trigger channel 104 compared to the first port 103 of the primary channel 101 during operation, enables the inflation of a bubble into the primary channel 101 and this bubble restricts the flow of liquid in the primary channel 101, and in a preferred implementation eventually fully closes the channel 101 for flow.

[0061] In this specification and claims, the phrase "capillary pressure" with respect to a capillary channel or a liquid within the channel means a Laplace pressure, created by the liquid's meniscus as interacts with the respective channel walls, which in turn applies the driving pressure for the liquid within the respective channel. The Laplace pressure exerted by a meniscus can be calculated using the Young-Laplace Equation (1) where P_cap is the capillary pressure, and R_horizontal and R_vertical are the primary radii of the meniscus in the horizontal and vertical direction respectively. A capillary pressure attributed to a liquid refers to the capillary pressure associated with the meniscus of a liquid as it interacts with its respective channel.

[0062] The direction and rate of flow of a liquid within a channel is dependent on the pressure gradient exhibited across the liquid. The capillary pressure created by a liquid's meniscus as it interacts with the respective channel walls can induce a gradient in pressure across the liquid. A liquid having two opposing meniscuses with two opposing capillary pressures will ultimately flow in a direction and rate that is based on the difference / g radient between these two opposing capillary pressures. The rate of flow will further be based on the ratio of the pressure gradient across the liquid to the fluidic resistance (2) where Q is the volumetric flow rate, AR is the pressure gradient vector, and R is the fluidic resistance between the two menisci. It is possible for the pressure gradient to be influenced by other factors than the capillary pressure, such as the gravitational pressure acting on liquid in an inlet. However, it is expected in a capillary microfluidic system that capillary pressures are significant compared to other external pressures and hence substantially govern the flow of the liquids within the system.

[0063] As mentioned, it would be desirable to configure the valve 100 to close, and then to re-open in an automated or self-driving manner. This would mean that flow of primary liquid in the primary channel 101 could be stopped and started in stages, as may be required for an analytical test. This may be useful for capillary circuit designs which either heavily rely on transistor valve components, or ones which use a capillary pump that cannot be easily controlled (paper pumps in a lateral flow test, for example).

[0064] In this exemplary embodiment, the valve 100 comprises a secondary, withdrawal channel 105 for manipulating the occluding bubble and re-opening the valve 100. The withdrawal channel 105 is connected to the void volume 102 at a separate connection 114 to the trigger channel 104 connection 111 with the void volume 102 (in other words not through the trigger channel 104). The manner in which the trigger channel 104 and the withdrawal channel 105 are connected to the void volume 102 can be likened to a parallel connection in an electronic circuit for instance, rather than a series connection. Further, the withdrawal channel 105 is configured to be pre-filled with a withdrawal liquid before the valve 100 is triggered into the closed state. The pre-filling may be before filling of the trigger channel 104 to close the valve 100.

[0065] In this specification, and unless stated otherwise, the cross-sectional area of a channel is intended to refer to the area of the channel along an imaginary plane that is substantially orthogonal to the longitudinal axis of the channel. This could be an imaginary plane that is parallel to plane 109A, for instance, for trigger channel 104, or a plane that is parallel to plane 109B for withdrawal channel 105. The cross- sectional area is typically the cross-sectional area that is perpendicular to the direction of flow of liquid within the channel.

[0066] In this specification, and unless stated otherwise, the depth of a channel is intended to mean the linear distance between opposing surfaces of the channel along an axis that is substantially orthogonal to both the longitudinal axis of the channel and the width of the channel. For example, in the trigger channel 104, the depth is measured along an axis perpendicular to the plane 109A and perpendicular to the width of the channel within that plane. Similarly, for the withdrawal channel 105, the depth is measured along an axis perpendicular to the plane 109B and perpendicular to the width of the channel within that plane.

[0067] As shown in Fig. 2B, the withdrawal channel 105 is configured to contain a withdrawal liquid 105A for priming the valve 100. The withdrawal channel 105 comprises an inlet 107 for receiving and pre-filling the withdrawal channel 105 with the withdrawal liquid 105A. This inlet 107 may be configured to fluidly connect to any suitable liquid source. For instance, the inlet 107 may be configured to fluidly connect to the primary channel 101 upstream of the first port 103, in the intended direction of flow of the liquid in the primary channel 101. Alternatively, it may be configured to fluidly connect to another liquid source or inlet of a microfluidic circuit incorporating the device 100.

[0068] In use, after priming the withdrawal channel 105, and subsequently, after a trigger liquid has been introduced into trigger channel 104 to close the valve (as shown in Figs. 2C and 2D), driving the withdrawal liquid 105A away from the void volume 102 will generate a second capillary force F2 that promotes retraction of the occluding air bubble 108 from the primary channel 101 toward the void volume 102, to effectively permit or increase the flow of primary liquid 101A in the primary channel 101 past the first port 103 (as shown in Fig. 2E) and re-open the valve 100.

[0069] In one implementation, the valve 100 may be configured such that an absolute magnitude of a first capillary pressure attributed to the trigger liquid 104A contained within the trigger channel is substantially greater than an absolute magnitude of a second capillary pressure attributed to the withdrawal liquid 105A contained in the withdrawal channel 105 (when liquid is not being withdrawn or drive out of the withdrawal channel 105 away from the void volume connection 114). This configuration reduces the capillary pressure required to defl ate / retract the occluding bubble, compared to a withdrawal channel with a relatively high, second capillary pressure attributed to it (e.g., a second capillary pressure that is substantially the same or greater than the first capillary of the trigger channel). This may reduce the complexity in designing the withdrawal sub-circuit or component that is connected to the withdrawal channel and configured to drive liquid out of the withdrawal channel via capillary action. A capillary pump connected to the withdrawal channel, for the purposes of driving the withdrawal liquid out of the withdrawal channel, can be configured to have a capillary pressure sufficient to overcome the second capillary pressure and withdrawal the liquid, for instance. This may be simpler than configuring the capillary pump to drive liquid out of the trigger channel to deflate / retract the occluding bubble in some applications for instance. However, in other implementations, the absolute magnitude of the first capillary pressure may be substantially the same or lower than the absolute magnitude of the second capillary pressure and having a separate withdrawal channel to the trigger channel may still provide other benefits such as improved reliability or manufacturability, compared to having a single channel for both triggering the valve into the closed state and reopening the valve as will be explained in relation to the embodiment shown in Fig. 16.

[0070] The target relative capillary pressures can be preconfigured for the trigger channel 104 and the withdrawal channel 105.

[0071] In this exemplary implementation, an absolute magnitude of the first capillary pressure attributed to the trigger liquid 104A may be at least 10% greater than an absolute magnitude of the second capillary pressure attributed to the withdrawal liquid 105A, or at least 25% greater, or at least 50% greater, when liquid is not being withdrawn or driven out of the withdrawal channel 105. This is application dependent, and other relative magnitudes of the first and second capillary pressures are not intended to be excluded from the scope of protection.

[0072] The valve 100 may be configured so that the absolute magnitude of the second capillary pressure attributed to withdrawal liquid 105A in the withdrawal channel 105 is substantially greater than an absolute magnitude of a third capillary pressure attributed to primary liquid 101 contained in the primary channel 101 at the first port 103 during operation. In this manner, the flow of trigger liquid in the trigger channel will more likely cause an occluding bubble to be generated at the first port 103, pushing air into the primary channel 101 to close of the valve 200, rather than air being pushed into the withdrawal channel. This can simplify the manner in which the valve 100 is designed to enable closing of the primary channel during operation. For instance, the withdrawal channel volume or length can be minimised as it does need to account for a relatively large volume of air being pushed into the withdrawal channel during closing. In other implementations however, the valve may be configured such that the absolute magnitude of the second capillary pressure may be the same or lower than the absolute magnitude of the third capillary pressure and the valve may still be operable to effectively close the valve 100 during operation, potentially with some of the air being pushed into the withdrawal channel. The withdrawal channel may be effectively designed to account for this additional volume of air without compromising on the overall functionality of the valve as described herein.

[0073] During operation, when the withdrawal channel is pre-filled with a withdrawal liquid, the withdrawal liquid 105A has a pressure acting towards the void volume from the meniscus at or adjacent junction 114. This pressure is acting against reopening of the valve 100. Accordingly, the valve 100 further comprises a withdrawal sub-circuit or other component or device (not shown) configured to connect the withdrawal liquid 105A in the withdrawal channel 105 to a withdrawal pressure that is in an opposing direction and greater than the pressure of the withdrawal liquid 105A acting towards the void volume. This pressure difference enables re-opening of the valve during operation. In one exemplary implementation described in further detail below, a trigger valve may be connected to the withdrawal channel 105 and can be activated to connect the liquid 105A in the withdrawal channel 105 with a capillary pump or other withdrawal device, for instance. The capillary pump may include a channel that generates a relatively higher capillary pressure of an opposing meniscus to that within the withdrawal channel and facing the void volume. This relatively higher capillary pressure is sufficient to withdraw the liquid in 105A from the channel 105, thereby re-opening the valve 100.

[0074] As shown in Figs. 2A to Fig. 2E, the valve 100 is operable in or between a first closed state (hereinafter referred to as the "closed state") and a second open state (hereinafter referred to as the "open state"). The "closed state" in relation to the valve 100 may mean a substantially fully closed state, as shown in Fig. 2D, in which liquid flow through the primary channel 101 is substantially fully inhibited or fully obstructed. The valve may be alternatively or additionally operable to partially close or partially obstruct the flow path in the primary channel 101, such as to the extent shown in Fig. 2C. Accordingly, reference to a "closed state", unless stated otherwise, could mean triggering or transitioning the valve into a more obstructed state relative to a previous state. In this scenario, liquid flow through the primary channel 101 may be further restricted or decreased. Similarly, the "open state" may mean a substantially fully open state, in which liquid flow through the primary channel 101 is substantially fully unobstructed, such as shown in FIG 2A. But it could also refer to a state where the flow path in primary channel 101 is less obstructed relative to a previous state, such that liquid flow through the primary channel 101 is further permitted or increased (e.g., as shown in Fig. 2E). The extent to which the valve opens in the open state and / or closes, in the closed state, may be controlled by adjusting a volume of the trigger channel 104 relative to the volumes of the withdrawal and primary channels 105, 101. This may be achieved by altering the length and / or cross-sectional area of the trigger channel 104, for instance. The valve 100 is therefore configured to regulate the flow of primary liquid through the primary channel 101 to allow for a decrease in flow, and subsequently an increase in flow.

[0075] In one implementation, the valve 100 may be a binary valve that is only operable in one of two distinct states; a first closed state and a second open state. In other words, the valve 100 is configured such that it is operable to maintain a steady state in the closed state or the open state only. In this implementation, the valve 100 may comprise or be connected to a circuit configured to introduce a first volume of liquid into the trigger channel 104 for closing the valve 100, and withdraw a second volume of liquid from the withdrawal channel 105 for re-opening the valve 100 to the substantially same extent as before it was closed. In other implementations, the valve 100 is operable to maintain one or more other steady states between the first closed state and the second open state. In one such implementation, the valve 100 may comprise or be connected to a circuit configured to introduce varying volumes of liquid into the trigger channel 104 and maintain the varying volumes for a steady state period of time to provide varying degrees of closure of the valve 100. In other words, the valve 100 may be operable to incrementally and / or gradually decrease the flow of primary liquid 101A through the primary channel 101 between the second open state and the first closed state. Additionally, or alternatively, the circuit may be configured to withdraw varying volumes of the liquid from the withdrawal channel 105 and maintain the liquid within the withdrawal channel for a steady state period to allow for varying degrees of re-opening of the valve 100. In other words, the valve 100 may be operable to incrementally and / or gradually increase the flow of primary liquid 101A through the primary channel 101 between the first closed state and the second closed state. Accordingly, the valve 100 may operate as a flow control valve 100 having higher sensitivity or control overflow than a binary flow control valve.

[0076] The primary liquid 101A flow influenced by the operational states of valve 100 is the flow passing through the valve 100 and across the first port 103. An increase or decrease in flow of primary liquid 101A with respect to the operational states may mean an increase or decrease in the flow rate of the primary liquid crossing the first port 103, for instance. The valve 100 is operable to transition from the open state to the closed state and / or transition into a decreased-flow state (e.g., as shown from Fig. 2A to Fig. 2D), and is reversibly operable to transition from the closed state (e.g., as shown in Fig. 2D) back to the open state and / or an increased-flow state (e.g., as shown in Fig. 2A via the state shown in Fig. 2E). During operation, the valve 100 may transition from the open / increased-flow state, which may be a partially open state, but preferably a fully open state, toward the closed / decreased-flow state, which may be a partially, but preferably a fully closed state, when a trigger liquid 104A flows into the trigger channel 104 via inlet 106, toward the void volume 102. The valve 100 is configured to transition from the open state to the second closed state, even when a minimum volume of withdrawal liquid 105A is contained in the withdrawal channel 105.

[0077] As mentioned, to facilitate the above operation, the valve 100 is configured such that desired capillary pressures are exhibited and attributed to the liquids flowing in the trigger channel, and into and out of withdrawal channel during priming, opening and closing of the valve 100. The valve 100 may be configured and operable to generate these capillary pressures by configuring any combination of one or more of: the geometries of the trigger channel, the primary channel and / or the withdrawal channel, the withdrawal liquid supply circuit or channels and / or the trigger liquid supply circuit or channels, the withdrawal liquid withdrawal circuit or device, and / or the type or material properties of withdrawal liquid and / or trigger liquid being used for instance.

[0078] In an implementation, the target relative magnitudes of the capillary pressures attributed to the trigger liquid in the trigger channel and withdrawal liquid in the withdrawal channel (prior to re-opening the valve), are at least partly attributable to distinct first and second geometries of the trigger channel 104 and the withdrawal channel 105. For example, as shown in Fig. 1, the trigger channel 104 may comprise a substantially smaller cross-sectional area relative to the cross-sectional area of the withdrawal channel 105, at least at or adjacent the connection of each channel 104, 105 with the void volume 102 and for a predefined length of each of the channels 104, 105 to achieve a relatively higher capillary pressure in the trigger channel relative to the withdrawal channel as per some of the abovementioned implementations. The first and second distinct geometries of the first trigger channel 104 and the second withdrawal channel 105 may alternatively, or in addition, comprise distinct depths, at least at or adjacent the connections of the respective channels 104, 105 with the void volume 102. For example, the withdrawal channel 105 may comprise a substantially greater depth than the trigger channel 104 to achieve a relatively higher capillary pressure in the trigger channel relative to the withdrawal channel. The first and second distinct geometries of the first trigger channel 104 and the second withdrawal channel 105 may alternatively, or in addition, comprise other distinct geometries, such inner wall angles, for achieving target relative capillary pressure magnitudes.

[0079] In yet another implementation, the valve 100 may comprise or be configured to connect to one or more liquid modifiers connected to the trigger channel 104 and / or to the withdrawal channel 105 for modifying one or more properties of the trigger liquid 104A (such as the surface tension) and / or one or more properties of the withdrawal liquid 105A (such as the surface tension), to achieve the target difference in absolute magnitude(s) between the first capillary pressure and / or second capillary pressure. An exemplary implementation is shown in Fig. 12 where the withdrawal channel further comprises a liquid modifier 180 located within the channel 105. The liquid modifier 180 is located proximal to the connection 114 but may alternatively be located anywhere between the outlet 112 and connection 114. The liquid modifier 180 may be a dried surfactant added within the channel 105. The dried surfactant may reduce the surface tension at or adjacent the connection 114 associated with channel 105, once the liquid has filled the withdrawal channel. This may make it easier to withdrawal liquid from the channel 105, which means that the geometry requirements on the withdrawal channel can be partially alleviated, and / or the valve 100 may be operable to re-open quicker. Alternatively, or in addition, a liquid modifier may be implemented in the trigger channel 104 to increase the surface tension of the trigger liquid 104A at or adjacent the connection 111.

[0080] In an implementation, liquids of differing material properties may be used for the trigger liquid and the withdrawal liquid to achieve the desired relative magnitudes of the capillary pressures attributed to the trigger liquid and withdrawal liquid in the trigger channel and withdrawal channel respectively. For example, a sample liquid may be retained in one of the trigger or withdrawal channels, and a reagent liquid may be retained in the other of the channels. These may have different material properties, such as contact angles and / or surface tensions, that result in varying capillary pressures within the respective channels for the same channel dimensions. Reagents could include enzyme mixtures or buffer solutions for instance. Whereas sample liquids may include: wine, whole blood, blood plasma, or river water or wastewater. Other liquids may be used in the respective channels, and this is application dependent.

[0081] Any combination of two or more of the abovementioned implementations may be incorporated or combined in the valve 100 to achieve the target relative magnitudes between the first capillary pressure and the second capillary pressure as would be understood by the person skilled in the art.

[0082] Referring back to Figs. 1 and 2A-2E, the valve 100 is configured to transition from the closed / decreased-flow state (e.g., as shown in Fig. 2D) toward the open / increased-flow state (which may be a partially or fully open state, e.g., as shown in Fig. 2A) when withdrawal liquid 105A contained in the withdrawal channel 105 flows away from the void volume 102, as shown in Fig. 2E. The valve 100 is configured to operate in this manner even when a volume of trigger liquid 104A is contained in the trigger channel 104.

[0083] As previously mentioned, in one implementation, the valve 100 may be configured such that an absolute magnitude of a second capillary pressure attributed to the withdrawal liquid 105A flowing or contained in the withdrawal channel 105 is substantially greater than an absolute magnitude of a capillary pressure attributed to the primary liquid 101A contained in the primary channel 101 at the first port 103. Relative geometries and / or liquid material properties relating to the withdrawal channel and primary channel may be preconfigured to achieve the target relative capillary pressures attributed to the liquids within these channels as described above with regards to the trigger channel and withdrawal channel.

[0084] In some implementations, a flow resistance of the withdrawal channel 105 at or adjacent the connection with the void volume 102 may be substantially greater than a flow resistance of the primary channel 101 at or adjacent the first port 103.

[0085] During a re-opening stage of operation of the valve 100, the valve 100 (or a circuit connected to the valve 100) is configured to generate a pressure gradient across the withdrawal liquid in the withdrawal channel 105 that drives the withdrawal liquid 105A in the withdrawal channel 105 away from the void volume 102 or connection 114. This may be achieved by connecting the withdrawal channel to a capillary pump that draws liquid away from the void volume 102 and connection 114 using capillary action. The capillary pump utilises capillary action to transport and regulate the movement of the withdrawal liquid without the need for mechanical pumping components. The capillary pump may comprise a channel or channel network connected to a vent and / or a porous structure or wick material that induces fluid flow through intermolecular adhesive and cohesive forces, enabling passive transport of the withdrawal liquid.

[0086] The capillary pump preferably comprises a geometry that generates an opposing capillary pressure that is substantially greater than the capillary pressure of the meniscus located at or adjacent the connection 114. The relative geometries, including relative dimensions, of the capillary pump and the withdrawal channel may be preconfigured to achieve this difference in respective capillary pressure magnitudes as described above in relation to the trigger channel and withdrawal channel for instance. In this manner, the pressure gradient across the withdrawal liquid, when the withdrawal channel is fluidly connected to the capillary pump, drives the withdrawal liquid away from the void volume 102, causing the occluding bubble to retract back towards the void volume 102 and reopen the valve 100.

[0087] As will be explained in further detail below, the valve 100 may be triggerable to initiate flow of the withdrawal liquid 105A contained in the withdrawal channel 105 away from the void volume 102 / connection 114. The trigger may be the opening of a fluid connection between the withdrawal channel 105 and a capillary pump, for instance. The trigger may be related to a predetermined trigger condition, such as a time or sequence-related trigger condition. For example, the withdrawal channel 105 may be triggered to initiate flow of the withdrawal liquid 105A contained in the channel 105, when a predetermined period has elapsed since closing the valve 100 or when a state of operation of a circuit (requiring closure of the valve / decreased flow) is complete. As mentioned in the background section, in the context of a capillary test, the predetermined period and / or sequence-related condition may correspond reagents reacting while the valve is closed, before flow of the primary liquid may be resumed again and / or before the rate of flow of the primary liquid is actively increased again.

[0088] The trigger channel 104 and the withdrawal channel 105 may broadly be referred to as control channels 104, 105, both configured to receive a flow or volume of a control liquid (i.e., the trigger liquid or the withdrawal liquid). At least one of these control channels (e.g., 104) is configured to generate sufficient capillary force to close the valve, when the flow of control liquid is received within the channel, and at least one of the control channels (e.g., 105) is configured to fluidly connect to a withdrawal sub-circuit that is configured to trigger and drive a flow of the control liquid within the control channel out of the channel, to at least partially re-open the valve 100. As will be described further below with reference to alternative implementations (valve 100A and circuit / device 400A) there may be one control channel that is controllable to perform both functions of closing and re-opening the valve, or there may be multiple channels that can are individually or collectively controllable to perform both functions of closing and re-opening the valve. The valve 100 may be implemented in a device or system configured to perform a multistep chemistry process. For example, Loop-mediated isothermal amplification (LAMP) or Polymerase chain reaction (PCR) assays may have defined heating times and multiple cycles (e.g., 60°C for 45 seconds). Using valve 100, reagents could be held in an actively heated reaction chamber for a predefined period of time, while the valve 100 is maintained in a closed sate, before being moved into another chamber after the appropriate time by reopening the valve 100.

[0089] In a sandwich Enzyme-Linked Immunosorbent Assay (ELISA) test, the valve 100 may be utilised to enable reaction, incubation, and washing steps carried out in series. For the incubation step, it is typically necessary to keep the same sample in contact with a functionalised surface for a period of time, which can occur when the valve is in the closed state. Reopening the valve 100 may then allow the sample to proceed to the washing step.

[0090] The valve 100 may be implemented in systems or devices of other multi-stage chemistry applications as would be apparent to the skilled person.

[0091] Referring back to Fig. 1, in a preferred implementation of the valve 100, a geometry of the trigger channel 104 at a fluid connection between the trigger channel 104 and the void volume 102 is configured to inhibit liquid in the trigger channel 104 from flowing into the void volume 102 in both the open and closed states of the valve. For instance, a geometry of the trigger channel 104 may include an angle Illa between a region of the inner peripheral wall 102B of the void volume 102, located at or adjacent a fluid connection 111 with the trigger channel 104, and an imaginary plane 109A extending across the fluid connection with the trigger channel 104. The angle Illa is preferably sufficient to inhibit liquid from flowing into the void volume 102, in use. Preferably, the angle Illa is approximately 180 degrees or greater relative to the imaginary plane 109A to provide enhanced stability in inhibiting flow. However, in some embodiments, the angle may be less than 180 degrees provided it is sufficient to inhibit liquid flow into the void volume 102 from the trigger channel 104. The geometry of the trigger channel 104 is further configured such that liquid is inhibited from flowing into the void volume 102 through connection 111 in both open and closed states of the valve 100. Similarly, a geometry of the withdrawal channel 105 at a fluid connection between the withdrawal channel 105 and the void volume 102 is configured to inhibit liquid in the withdrawal channel 105 from flowing into the void volume 102 in both the open and closed states of the valve. For instance, a geometry of the withdrawal channel 105 may include an angle 114a between a region of the inner peripheral wall 102C of the void volume 102, located at or adjacent a fluid connection 114 with the withdrawal channel 105, and an imaginary plane 109B extending across the fluid connection with the withdrawal channel 105. The angle is preferably sufficient to inhibit liquid from flowing into the void volume 102, in use. Preferably, the angle 114a is approximately 180 degrees or greater relative to the imaginary plane 109B to provide enhanced stability in inhibiting flow. However, in some embodiments, the angle may be less than 180 degrees provided it is sufficient to inhibit liquid flow into the void volume 102 from the withdrawal channel 105. The geometry of the withdrawal channel 105 is further configured such that liquid is inhibited from flowing into the void volume 102 through connection 114 in both open and closed states of the valve 100.

[0092] In a preferred implementation, a cross-sectional area, or a depth, or both, of the trigger channel 104 at a fluid connection between the trigger channel 104 and the void volume 102 is substantially equal to a cross-sectional area, or a depth, or both, of the trigger channel 104 along an intermediate length of the channel 104. The trigger channel 104 preferably comprises a substantially uniform cross-sectional area, or a substantially uniform depth, or both, along a substantial length between an inlet 106 and a fluid connection 111 between the trigger channel 104 and the void volume 102. In this manner, the trigger channel 104 comprises substantially consistent dimensions leading up to the connection with the void volume 102, making the capillary pressure and other fluid dynamics associated with the channel 104 more consistent and predictable.

[0093] Similarly, a cross-sectional area, or a depth, or both of the withdrawal channel 105 at a fluid connection 114 between the withdrawal channel 105 and the void volume 102 is substantially equal to a cross-sectional area, or a depth, or both, of the withdrawal channel 105 along an intermediate length of the channel 105. Preferably, the withdrawal channel 105 comprises a substantially uniform cross-sectional area, or a substantially uniform depth, or both, along a substantially length between an inlet 107 and an outlet 112 of the withdrawal channel. In this manner, the withdrawal channel 105 comprises substantially consistent dimensions leading up to the connection 114 with the void volume 102, making the capillary pressure and other fluid dynamics associated with the channel 105more consistent and predictable.

[0094] In this exemplary implementation of the valve 100, the valve 100 further comprises a microfluidic sub-circuit or microfluidic element fluidly connected to the withdrawal channel 105 and configured to control a prefilling of the withdrawal channel 105 with withdrawal liquid, during operation. For instance, the inlet 107 of the withdrawal channel 105 may be fluidly connected to, or configured to fluidly connect to, a valve sub-circuit that is operative to allow the flow of a liquid through the inlet 107 to prime the valve, and to substantially inhibit the flow of withdrawal liquid through the inlet 107 after priming. The pre-filling sub-circuit may be operable to inhibit further flow of withdrawal liquid into the withdrawal channel 105 through the inlet 107, when the withdrawal channel receives a predetermined volume of the withdrawal liquid via the inlet 107. Alternatively, or in addition, the closing of the valve sub-circuit may be associated with a time-related or other sequence-related condition. Alternatively, the prefilling sub-circuit or element may comprise an inlet fluidly connected to the withdrawal channel and that may be isolated from the withdrawal channel by external action rather than capillary action.

[0095] Referring back to Figs. 2A-2E, and also to Fig. 3A a preferred method 300 of operating the self-driven capillary valve 100 of the invention will now be described. Figs 2A and 2B show the state of the valve 100 before it has been closed. The withdrawal channel 105 have been pre-filled with a withdrawal liquid and the primary channel 101 has a primary liquid 101 flowing therethrough past the valve. Accordingly, the method of operation 300 comprises the initial step of pre-filling the withdrawal channel 105 with a volume of withdrawal liquid (step 320) via inlet 107 to prime the valve 100. Before, after or even during this step 320, flow of primary liquid is enabled through the primary channel 101 past the first port 103 to generate and restrain a meniscus at the first port 103 (step 310). Steps 310 and 320 may be performed in any order without departing from the scope of the invention. The flow of primary liquid through the primary channel 101 may be generated using a capillary pump in some implementation. Fig. 2C shows the valve 100 during closing. During this stage (step 330 of method 300) a volume of trigger liquid 104A is conveyed through the trigger channel 104 via the inlet 106 toward the connection 111 with void volume 102. When this happens, air is displaced out of the trigger channel 104 into the void volume 102. This displaced air approximately exclusively inflates the occluding bubble in the primary channel 101, as shown. The flow of trigger liquid into the trigger channel 104 thereby generates a first capillary force, Fl, that causes the meniscus restrained at the first port 103 to expand from the first port 103 into the primary channel 101. In an implementation, the force Fl is sufficient to cause the occluding bubble to substantially fully close the primary channel 101 as shown in Fig. 2D.

[0096] The step 330 of conveying the trigger liquid through the trigger channel 104 may comprise directing a flow of the primary liquid in the primary channel 101 into the trigger channel 104. The redirected flow of the primary liquid is preferably downstream of the first port 103 in such an implementation. Alternatively, the trigger liquid may be provided via an alternative fluid source.

[0097] Fig. 2E shows the effects of step 340 of method 300 comprising re-opening the valve 100. In this step 340, a volume of withdrawal liquid contained in the withdrawal channel 105 is withdrawn away from the void volume 102 toward outlet 112 to generate a second capillary force, F2, that causes the meniscus to retract from the primary channel 101 back toward the void volume 102 and into the withdrawal channel 105. In other words, as liquid is removed from the withdrawal channel 105, the bubble deflates and re-opens the valve 100. This action re-permits or increases the flow of primary liquid in the primary channel 101. In an implementation, the withdrawing of liquid from channel 105 is sufficient to fully re-open the valve 100 into the state shown in Fig. 2A. being the fully open state. The outlet 112 of the withdrawal channel 105 may be fluidly connected or configured to fluidly connect to a capillary pump in some implementations to drive the flow of withdrawal liquid 105A out of the withdrawal channel 105.

[0098] Referring to Fig. 3B, the step 320 of prefilling the withdrawal channel 105 with a volume of withdrawal liquid is shown in more detail. The step comprises initially drawing and retaining the volume of withdrawal liquid in the withdrawal channel 105 (sub-step 321). Preferably this volume is sufficient to enable subsequent re-opening of the valve via withdrawing the volume of liquid. The flow of withdrawal liquid into the withdrawal channel 105 may terminate when a predetermined volume of liquid is drawn into the withdrawal channel 105 (step 322). This may be determined based on a volume of liquid provided by a user via a corresponding inlet, or based on a selfclosing mechanism connected to the inlet 107, or via any other suitable method that would be apparent to the person skilled in the art. In one implementation, the step 321 of pre-filling the withdrawal channel 105 comprises directing a flow of primary liquid from the primary channel 101 into the withdrawal channel 105. This redirected flow is preferably upstream of the first port 103. Alternatively, the withdrawal liquid may be provided via an alternative fluid source. A self-closing mechanism may isolate the inlet 107 from the source of withdrawal liquid (e.g., the primary channel or other source) when a sufficient volume flows through the inlet 107.

[0099] Referring to Fig. 3C, the stage 340 of opening the valve 100 is shown in more detail. This step comprises the sub-set of triggering the volume of withdrawal liquid contained in the withdrawal channel 105 to flow through an outlet 112 of the withdrawal channel (sub-step 341), away from the void volume 102 / connection 114. This flow is then maintained until the target opened state is achieved (sub-step 342). In an implementation, the flow of liquid in withdrawal channel 105 through the outlet

[0100] 112 is maintained using a high pressure, low resistance capillary pump connected to the outlet 112. The flow of the volume of withdrawal liquid through the outlet 112 may be triggered via a flow of a liquid connected to the capillary pump.

[0101] Referring to Figs. 4, and 5A-5C, in one implementation the microfluidic valve 100 may further comprise a vent 113 fluidly connected to the withdrawal channel 105 for enabling quicker opening of the valve 100 from the closed state. The vent 113 may be directly open to atmosphere or a significantly larger volume of air, for instance. The vent 113 is fluidly connected at an intermediate position along a length of the withdrawal channel 105, between the connection 114 with the void volume 102 and the outlet 112. This may be between the inlet 107 and the connection 114 with the void volume 102 in some implementations. The fluid connection between the vent

[0102] 113 and the withdrawal channel 105 preferably comprises a configuration that prevents liquid from flowing from the withdrawal channel 105 into the vent 113. For example, a geometry of the withdrawal channel at this fluid connection prevents liquid from flowing into the vent 113 as described for the connections 114 and 111, for instance.

[0103] As shown in Fig. 5B, the vent 113 is preferably connected to the withdrawal channel 105 at a position along the length of the withdrawal channel that results in the predetermined volume of withdrawal liquid prefilling past this position (e.g., at step 320 of method 300). Accordingly, during operation, when the volume of withdrawal liquid is triggered to flow through the outlet 112 (e.g., at step 340), the withdrawal liquid will flow back past the vent 113, in turn exposing the vent 113 to the void volume 102. As shown in Fig. 5C, this allows the occluding bubble to retract and air to escape via the vent 113 (rather than being drawn out via the remaining flow of the withdrawal liquid).

[0104] A benefit to this implementation and method of opening the valve 100 is that it could potentially operate faster to open the valve 100. The implementation and method may be less controllable however, making it more suitably for a binary actuation of the valve 100, for instance.

[0105] Referring to Fig. 6, a schematic of a microfluid circuit 150 incorporating the capillary valve 100 is shown. A primary liquid inlet 152 of the circuit 150 fluidly connects to the primary channel 101 of the valve 100 to enable the flow of primary liquid 101A through the primary channel. A user may provide a volume of the primary liquid 101A through the inlet 152 and the liquid may flow through the primary channel 101 through capillary action. A trigger liquid inlet 153 fluidly connects to the trigger channel 104 via the channel inlet to enable the flow of trigger liquid into the trigger channel 104 and trigger the valve 100 into the closed position. A user may provide a volume of the trigger liquid 104A through the inlet 153 and the liquid may flow through the trigger channel 104 through capillary action to close / decrease flow through the valve 100. A withdrawal liquid inlet 154 fluidly connects to the withdrawal channel to prefill the channel and prime the valve 100. A user may provide a volume of the withdrawal liquid 105A through the inlet 154 prior to closing the valve 100 and the liquid may flow through the withdrawal channel 105 through capillary action. Any two or more of the inlets 152, 153, 154 may be a common inlet or fluidly connected to the same fluid source, with the filling of the respective channels being controlled through other circuit elements that appropriately sequence the filling of / flow through each respective channel 101, 104, 105.

[0106] In this exemplary embodiment, the capillary valve 100 is fluidly connected to a retraction pump 151 via an outlet 112 of the withdrawal channel 105 to enable the withdrawal of liquid to reopen the valve 100 after it has been closed. In this implementation, the retraction pump 151 may be a capillary pump configured to enable the flow of the withdrawal liquid 105A through the pump via capillary action. The retraction pump 151 may be operable to trigger flow of the withdrawal liquid 105A out of the channel 105 and through the pump 151 using an appropriate triggering sub-circuit (not shown in this figure) as will be described in further detail below with regards to device 400. Triggering the flow of the withdrawal liquid 105A out of the withdrawal channel outlet 112 causes the valve 100 to reopen / increase flow after the valve has been closed as previously mentioned.

[0107] Referring to Figs. 7A and 7B, a more detailed implementation of a microfluidic device 400 comprising a circuit used to manage the ordered filling of the channels 101, 104 and 105, and of activation of the withdrawal of liquid from withdrawal channel 105 will now be described.

[0108] The microfluidic device 400 comprises a substrate 450 on which microfluidic channels and components are formed. This substrate 450 facilitates the creation of microfluidic pathways and is constructed from suitable materials as is known in the art including glass, polymers, or silicon-based materials.

[0109] The device 400 may be implemented as a microfluidic chip. The chip may be portable and usable in a point-of-care (POC) setting. Such a device may sometimes be referred to as a lab-on-chip (LOC) device, where measurement or analysis of substances is transferred from a complex laboratory setting to relatively untrained personnel outside of a laboratory environment.

[0110] The device 400 comprises a microfluidic based circuit including capillaric components such as capillary channels to self-pump liquids within the device 400 and automate the various stages of functionality. The device 400 is configured to function with little to no requirement for external instrumentation and minimal intervention by a user, in use. In this manner, the device 400 may be considered a passively operated capillary device as described in relation to valve 100. Various capillary components may be used, including, but not limited to flow resistors, capillary pumps, reservoirs, transistor valves, and trigger valves to achieve the passive functionality and desired circuit programming described herein.

[0111] Within the substrate 450, a main channel 401 is formed to convey the primary liquid through the device 400. This main channel 401 serves as a central channel that enables flow of a primary liquid between different regions and sub-circuits of the microfluidic device 400. The main channel 401 is fluidly connected to a liquid source, being a source of the primary liquid to be conveyed through the device 400. The liquid source may comprise an inlet 402 (402A in Fig. 7A), such as an intake pad formed in the substrate 450 for receiving the primary liquid (e.g., by a user to initiate flow of the primary liquid within channel 401). The main channel 401 may be fluidly connected to a subcircuit or element, such as a capillary pump 405, for controlling the flow rate of primary liquid through the channel 401. The capillary pump 405 comprises a flow resistance path or section 406 that significantly contributes or determines the overall volume of the pump 405. The path 406 may be a serpentine or meandering flow resistance section. The pump 405 is configured to control a capillary pressure and flow rate of the primary liquid through the main channel 401 when the valve 100 is in an open / increased flow state. The pump 405 terminates in a release chamber or reservoir 407 where the primary liquid may be dispensed.

[0112] The microfluidic valve 100 may be fluidly connected with the main channel 401, to control opening and closing of the main channel 401 as described above. In particular, the primary channel 101 of the valve 100 may be fluidly connected in series to the main channel 401 for controlling the flow of primary liquid within the main channel 401. The valve 100 is fluidly connected in series between the fluid source or intake 402 and the capillary pump 405 in this implementation.

[0113] The trigger channel 104 of the valve 100 is fluidly connected to the main channel 401 and primary channel 101, and the valve 100 is configured to transition into a closed state when the primary liquid flows through the primary channel 101 and into the trigger channel 101 via the trigger channel inlet 106. In alternative configurations, the trigger channel inlet 106 may be fluidly connected to another trigger liquid source (labelled 402B in Fig. 7A) which may be an intake pad for instance for a user to input a trigger liquid and initiate closing of the valve 100 for instance. The device 400 may further comprise microfluidic circuitry or element(s) for controlling the flow of the trigger fluid into the trigger channel 104. The microfluidic circuitry or element may control the timing or sequence of intake of trigger liquid in the trigger channel 104, and accordingly the timing or sequence for closing the valve 100. The timing or sequence may be relative to when the primary liquid is received at the inlet 402, for instance.

[0114] In this implementation, for instance, the device 400 further comprises flow resistance path 403 fluidly connected upstream of the valve 100, between the valve 100 and the intake 401 for controlling a time delay between the intake of primary liquid via 401 and closing of the valve 100. The flow resistance path 403 is situated in series with the main channel 401, upstream of the first port 103 and trigger channel inlet 106 of the valve 100. The path 403 may be a serpentine or meandering flow resistance section. In the same or other implementations, one or more valves or other flow controlling elements may be implemented between the trigger liquid source and the trigger channel inlet 104 for enabling temporal control of closing of the valve 100. This control may be autonomous as in this implementation, or human activated for instance, depending on the particular application.

[0115] The microfluidic circuit 100 further comprises a fill subcircuit 410 formed in the substrate 100 for controlling the prefilling of the withdrawal channel 105 of the valve 100 with a predetermined volume of withdrawal liquid. The inlet 107 of the withdrawal channel 105 is thereby fluidly connected to the fill subcircuit 410, facilitating controlled introduction of a predetermined volume of withdrawal liquid into the withdrawal channel 105. The inlet 107 of the withdrawal channel 105 of the valve 100 is preferably fluidly connected to an outlet 412 of the fill subcircuit 410. Once the predetermined volume is achieved, the fill subcircuit 410, serving as a smart valve, suspends further liquid entry into the inlet 107.

[0116] The fill subcircuit 410 is fluidly connected to and receives its liquid supply from a fluid source, facilitating controlled volume control of withdrawal liquid introduced into the withdrawal channel 105. An inlet 411 of the fill subcircuit is fluidly connected to the fluid source of the withdrawal liquid. This fluid source may be the same source 402 as the primary liquid in main channel 401. Accordingly, the inlet 411 may be fluidly connected to the main channel 401 upstream of the valve 100 / first port 103. Alternatively, the inlet 411 may be connected to another fluid source of the device 400, such as a liquid pad or inlet for receiving liquid from a user to initiate filling of the withdrawal channel with a withdrawal liquid.

[0117] The fill subcircuit 410 further comprises microfluidic circuitry or a microfluidic element 413 fluidly connected between the inlet 411 and outlet 412 for regulating the volume of withdrawal liquid received within withdrawal channel 105 during operation. In particular, the microfluidic circuitry or element 413 is configured to terminate a flow of withdrawal liquid into inlet 107 of the valve 100 when a predetermined volume of the withdrawal liquid flows into the channel 105 from the fluid source.

[0118] In one exemplary implementation, the fill subcircuit 410 comprises a valve 413 fluidly connected between the inlet 411 and the outlet 412 of the fill subcircuit 410 to control the flow of withdrawal liquid into the withdrawal channel 105 during the filling of the channel 105. The valve 413 may be a valve technology, as described in the Applicant's PCT patent application PCT / IB2021 / 051153, the contents of which are hereby incorporated by reference. These valves assist in the initiation and termination of flow of a liquid through the valve as described in the above reference patent application. The structure of this valve is described in more detail under the transistor valve section of this specification. In summary, the valve 413 comprises a primary channel connected the inlet 411 and outlet 412, and a void volume connected to the primary channel via the port. The port comprises a geometry that inhibits the flow of liquid from the primary channel into the void volume. For example, a region of an inner peripheral wall of the void volume located at or adjacent the port is preferably angled at approximately 180 degrees or greater relative to an imaginary plane extending across the first port. A trigger channel is fluidly connected to the void volume, for receiving a liquid therethrough and subsequently closing the valve 413 by forcing an occluding bubble to extend across the primary channel. The trigger channel is fluidly connected to the withdrawal channel 105, preferably via a flow resistance path 414 of the sub-circuit 410. The trigger channel may comprise the flow resistance path 414. The trigger channel fluidly connects to the withdrawal channel 105 between the inlet 107 and the connection between the channel 105 and with the void volume 102, preferably at a position that is substantially indicative of the target predetermined volume for prefilling the channel 105 with withdrawal liquid. For instance, the trigger channel may fluidly connect the withdrawal channel 105 at or adjacent the fluid connection between the channel 105 and the void volume 102 of valve 100. The flow resistance path 414 comprises a predetermined flow resistance indicative of a target rate of closing of the valve 410.

[0119] During operation, when the valve 413 is the open / increased flow state, prior to filling of the withdrawal channel 105 with the predetermined volume of withdrawal liquid, the primary channel between the inlet 411 and outlet 412 is open allowing for the primary liquid to flow via capillary action into the withdrawal channel 105. When the withdrawal liquid reaches the predetermined volume defined by the position of the connection between the withdrawal channel 105 and the trigger channel, the withdrawal liquid will flow into the trigger channel via the flow resistance path 414. When a sufficient volume of liquid flows through the trigger channel, a capillary force generated by the liquid will cause an occluding bubble to be pushed out of the void volume into the primary channel of the valve 413, to substantially seal / close or decrease the flow within the flow path between the inlet 411 and outlet 412 of the fill subcircuit 410 and terminate the flow of withdrawal liquid into the withdrawal channel 105.

[0120] The microfluidic device 400 further comprises a withdrawal subcircuit 420 operatively and fluidly connected to valve 100 for controlling the withdrawal and discharge of the withdrawal liquid from the withdrawal channel 105 to open the valve 100. The outlet 112 of the withdrawal channel 105 is thereby fluidly connected to the withdrawal subcircuit 420. The withdrawal subcircuit 420 is configured to activate and control the flow of withdrawal liquid contained within the withdrawal channel 105 through the outlet 112. It achieves this by applying an opposing capillary pressure to the withdrawal channel (compared to the pressure of the meniscus facing the void volume 102) that is sufficient to drive the withdrawal liquid 105A away from the void volume and out of the outlet 112.

[0121] In an exemplary implementation the withdrawal subcircuit is configured to control the timing or sequence of activation of flow of the withdrawal liquid through outlet 112. Accordingly, the withdrawal subcircuit 420 comprises triggering circuitry 422 for appropriately timing / sequencing the activation of flow of the withdrawal liquid through the outlet 112.

[0122] In an exemplary implementation the withdrawal subcircuit 420 is further configured to control a flow rate of the withdrawal liquid out of the withdrawal channel 105, once activated. In this implementation, a capillary pump 423 fluidly connects to the withdrawal channel outlet 112 to control the flow rate of withdrawal liquid through the outlet 112, once triggered. The capillary pump 423 comprises a channel / flow path 424. The flow path 424 may be in the form of a serpentine or meandering flow resistance section to control the flow rate, for instance. The capillary pump terminates in a release chamber or reservoir where the withdrawal liquid may be dispensed. This may be the same chamber or reservoir 407 as the pump 405 or a different one. The capillary pump is configured such that a sum of capillary forces acting on the liquid in the withdrawal channel 105 causes the liquid to move away from the void volume 102. The pump 423 thereby comprises a capillary pressure sufficient to drive the withdrawal liquid 105A in the withdrawal channel 105 away from the void volume 102 and is configured to generate a pressure gradient across the withdrawal liquid 105A that drives the withdrawal liquid 105A out of the outlet 112 and away from the void volume 102 of the valve 100. The channel 424 of the capillary pump generates an absolute capillary pressure sufficient to create a pressure gradient across the withdrawal liquid, driving its flow through the outlet 112. The capillary pump channel may comprise a distinct geometry relative to the withdrawal channel geometry (at or adjacent the void volume) to create the pressure gradient. For instance, the capillary pump channel 424 may comprises a cross-sectional area that is substantially smaller than the cross-sectional area of the second withdrawal channel (at or adjacent the void volume), and / or a depth of the capillary pump channel 424 may be substantially smaller than a depth of the withdrawal channel at or adjacent the void volume. Other methods known in the art of Capillaries may be used for achieving a target capillary pressure within the channel 424 sufficient to generate the target pressure gradient.

[0123] The triggering circuitry 421 of the withdrawal subcircuit 420 is fluidly connected to the outlet 112 of the withdrawal channel 105 and comprises a capillary trigger valve 425, operative to substantially inhibit flow of withdrawal liquid in a closed or off state and substantially permit flow of withdrawal liquid in an open or on state of the valve

[0124] 425. The trigger valve 425 is operative based on the flow of a trigger fluid through the valve 425 and is accordingly fluidly connected via a trigger channel 426 to a trigger fluid source 427. Configurations of suitable trigger valves which may be incorporated in the device 400 as valve 425 are described under the "trigger valve" section of this specification. The fluid source may be an inlet or intake pad 427 for a user to initiate opening of the valve 100 by inputting a trigger liquid therein, for instance. In this implementation, the trigger channel 426 is also fluidly connected to a capillary pump, being the capillary pump 423 (although this could also be a different pump), to control the rate of flow of the trigger liquid through the trigger channel

[0125] 426. One or more other capillaric components may be utilised to control the timing of the flow of trigger fluid through the trigger channel 426, such as flow resistance paths and / or other valves.

[0126] The triggering circuitry 422 optionally comprises a sealing transistor valve 428 fluidly connected in series to the trigger channel 426 to control the flow of trigger liquid past the trigger valve 425. A structure of the transistor valve 428 is described in further detail in the "transistor valves" section of the specification. The transistor valve 428 may comprise a similar structure to the valve 413 of the fill subcircuit 410, for instance, and be configured to operate in an open state in which liquid flow through the trigger channel 426 (past the valve 428) is substantially permitted and in a closed state in which liquid flow through the trigger channel 426 (past the valve 428) is substantially inhibited. A trigger channel 429 of the valve 428 is fluidly connected to the trigger channel 426 (or alternatively another fluid source) to provide the trigger for closing the valve 428 once a sufficient volume of trigger liquid has traversed downstream of the valve 428. The sufficient volume of trigger liquid being predefined to enable triggering of the trigger valve 425. In this manner, the triggering circuitry is operable to receive a trigger liquid, convey a trigger liquid to trigger the flow of withdrawal liquid through the outlet 112, and then to terminate flow of the trigger liquid after flow of the withdrawal liquid has been activated. Once the flow of withdrawal liquid is activated, the capillary pump 423 acts to maintain the flow and comprises a sufficient and predefined volume to maintain flow that corresponds to at least the volume of flow required to reopen valve 100.

[0127] The device 400 may be fabricated by CNC micro-milling channels into a substrate sheet 450 formed from any suitable material, such as Poly-(Methyl-Methacrylate) PMMA, glass, silicon, polymers and hybrid structures made from multiple materials. A micro milling machine may be used for this purpose. The choice of material will affect the surface wettability / contact angles of the respective capillary channels in the circuit, and accordingly should be selected based on the desired contact angle for a particular liquid / substance being used. Some materials, such as Polydimethylsiloxane (PDMS) and polymethylmethacrylate (PMMA) may have contact angles greater than 60 degrees, e.g., close to 90 degrees. Surface treatment may be desirable for such materials to obtain wettable surfaces that provide sufficient capillary pressure. One technique for rendering a capillary circuit hydrophilic is gas phase treatments. Another commonly used hydrophilization technique is vacuum based or solution-based surface grafting of silanes with hydrophilic end groups, including notably polyethylene glycol (PEG) silanes with anti-fouling properties. The substrate could additionally or alternatively be coated with a hydrophilic material.

[0128] One or more surface coatings may be applied to the substrate and one or more of the formed channels to achieve a desired surface property for the channels. Remaining solvent after surface coating may be removed by drying the substrate.

[0129] The invention is not intended to be limited to this device fabrication example. The device 400 may be fabricated from any suitable material known in the art including glass, plastics materials, polymers, silicon, metals, and the like. Transparent materials are desired for at least the transducing sub-circuit to enable visual observation by a user. The fabrication process or technique may include any suitable method including surface micromachining, bulk micromachining, moulding, embossing, and conventional machining with micro-cutters, for instance.

[0130] Dimensions for the capillaric channels may be 50-250 m wide channels. Depths of channels depend on their function but may be selected to be approximately 50-250 pm deep and for chambers or voids this may be 5-500 pm. Channels and reservoirs may have any cross-sectional shape as desired by the application, including annular or rectangular cross-section. Other sizes and shapes are envisaged without departing from the scope of the invention.

[0131] The various elements including microfluidic channels, valves, reservoirs, chambers, and flow resistors may be formed separately from other elements and connected thereto, or as exemplified, the device 400 is formed as a single integral component.

[0132] While the embodiments have been described herein with relation to a flow of liquids through the various components, the term 'liquid' preferably encompasses at least any aqueous solution. Although the valve 100 and device 400 may be operable using other liquids.

[0133] Referring to Figs. 8A-8D and 9, an implementation of a method 350 comprising the stages of operation of the device 400 will now be described. As shown in Fig. 8A, the method 350 comprises inputting or receiving a withdrawal liquid 105A to prefill the withdrawal channel 105 (step 351). In the device 400 this is achieved by inputting / receiving a primary liquid 401A into / from inlet pad 402, and then diverting a flow of the primary liquid 401A toward the fill subcircuit inlet, the diverted flow becoming the withdrawal liquid 105A. It will be appreciated that in alternative implementations, the withdrawal liquid may be separate to the primary liquid and comprise a separate inlet as shown in Fig. 7A for instance. Flow of the primary / withdrawal liquids is by self-driven capillary action through the respective capillary channels.

[0134] The withdrawal liquid 105A will continue to fill channel 105 until the transistor valve 413 is triggered to terminate flow of withdrawal liquid 105A into the channel 105 (step 352). This is exhibited when the withdrawal channel is filled with the predetermined volume of withdrawal liquid as shown in Fig. 8A. The predetermined volume may be the volume of withdrawal channel 105 between outlet 112 and fluid connection 114 for instance. At the termination of this stage, the trigger valve 425 prevents the withdrawal liquid from immediately filling the pump 423, while the transistor valve 413 isolates the withdrawal channel from the fill inlet 107.

[0135] As shown in Fig. 8B, sometime after filling the withdrawal channel 105, the valve 100 may be triggered into a closed state. This may be an event that occurs some period of time after the primary liquid 401A is introduced into the device 400. This time period may be governed by the flow resistance path 403, which may be configured to delay closing of the valve 100 until after sufficient time has passed to allow for prefilling of the withdrawal channel 105. As shown in Fig. 8B as primary liquid 401A flows through the valve 100, a part of the liquid is diverted into the trigger channel 104 of the valve, causing the valve 100 to transition into the closed state (step 353). It will be appreciated that in some embodiments, the triggering of the valve 100 into the closed state may occur based on an input from a user, such as by inputting a trigger liquid into the trigger channel at a desired time / sequence stage (rather than diverting a flow of the primary liquid using preconfigured circuitry) or elsewise triggered by other flows. The relatively higher capillary pressure in the trigger channel 104 compared to capillary pressure in the withdrawal channel 105 allows for the closing of the valve 100, even when the withdrawal channel is prefilled with liquid as per steps 351 and 352.

[0136] As shown in Fig. 8C, the circuit 400 may be actuated to re-open the valve 100, by opening the trigger valve fluidly connecting the outlet 112 and the capillary pump 423. Opening of the trigger valve may be achieved by introducing a trigger liquid 426A into the trigger channel 426 of the triggering circuitry (step 354). This trigger liquid may be introduced via an input pad / inlet 427, or alternatively, it may be via a delayed flow of another liquid source of the circuit 400 (e.g., the primary liquid source) into the trigger channel 426. As the trigger liquid 426A flows past the trigger valve 425, it opens the valve 425 and the fluid connection between the withdrawal channel outlet 112 and the capillary pump 423. After triggering flow of the withdrawal liquid out of the outlet 112, the source of trigger liquid 426A may be isolated from the pump 423, so that the pump continues to withdrawal the liquid 105A from the withdrawal channel consistently and predictably.

[0137] As shown in Fig. 8D, the flow of the predetermined volume of withdrawal liquid out of withdrawal channel 105 continues until the valve 100 reaches the target open state (step 355). This results in an increased air gap between the withdrawal liquid and the fluid connection 114 with the void volume 102. The capillary pump 423 governs the flow rate of the withdrawal liquid in this stage. The flow of withdrawal liquid away from the void volume 102 may terminate when the pump 423 is full. Accordingly, the volume of the pump 423 may be pre-configured to reach a desired open state, such as a partially open state or a fully open state of the valve 100.

[0138] In one configuration, the geometry of the withdrawal channel 105 may be preconfigured such that the pump 423 stops withdrawing liquid from the channel before it is filled. Referring to Fig. 13, alternative embodiments of a valve 200 and a circuit 500 incorporating the valve 200 are shown. The valve 200 comprises the same or similar features as valve 100 and only those that differ will be described in detail herein. All other features of any of the embodiments relating to valve 100. The valve 200 comprises multiple withdrawal channels 205-1 - 205-n (where n is an integer greater than one) connected to the void volume 102. The withdrawal channels 205- 1 - 205-n are similar to withdrawal channel 105 of valve 100 but may comprise of a smaller volume such that the collective volume of all withdrawal channels 205-1 - 205-n is the same or similar to withdrawal channel 105. Each withdrawal channel 205-1 - 205-n are preferably directly connected to the void volume 203 (not shown) as per the withdrawal channel 105. The multiple withdrawal channels 205-1 - 205-n may be fluidly connected to separate or a common fluid source for prefilling the channels with predetermined volumes of withdrawal liquid, as described in relation to valve 100.

[0139] The valve 200 is configured to separately actuate flow of withdrawal liquid out of each withdrawal channel 205-1 - 205-n. In this manner, after the valve 100 has transitioned into the closed state by introducing trigger liquid into the trigger channel 204, flow of withdrawal liquid out of each withdrawal channel can be actuated separately. The valve 200 can be configured such that the withdrawal of a volume of liquid from each withdrawal channel 205-1 - 205-n would partially re-open the valve 100. In this manner, the valve 100 may be operable to maintain multiple steady open states between the valve's fully closed state and fully open state, when liquid is withdrawn from each withdrawal channel 205-1 - 205-n sequentially. This results in an incremental increase in flow of primary liquid through the valve as each withdrawal channel 205-1 - 205-n is sequentially activated.

[0140] In an implementation, the trigger channel 204 and the withdrawal channels 205-1 - 205-n may be configured such that an absolute magnitude of the collective capillary pressures attributed to the trigger liquid flowing in the respective trigger channel 204 is substantially greater than an absolute magnitude of the collective capillary pressures attributed to the withdrawal liquids contained in the respective withdrawal channels 205-1 - 205-n, when the withdrawal liquids contained in the withdrawal channels 205-1 - 205-n have not been fluidly connected to (or flow of the withdrawal liquids out of the channels 205-1 - 205n has not yet been activated based on) any higher capillary pressure flow path (such as a higher pressure capillary pump). Any one of the implementations described in the preceding paragraphs for controlling the capillary pressure in the first trigger channel 104 and second withdrawal channel 105 of valve 100 may be incorporated in this implementation to control the magnitude of collective capillary pressures in the trigger channel 204 and withdrawal channels 205- 1 - 205-n.

[0141] In the same, or another implementation, the valve 200 may be configured such that an absolute magnitude of a collective capillary pressure attributed to the withdrawal liquid(s) flowing or contained in the withdrawal channel(s) 205-1 - 205-n is substantially greater than an absolute magnitude of a third capillary pressure attributed to the primary liquid contained in the primary channel 201, at least during the closed state of the valve 200. Further, an absolute magnitude of the collective capillary pressures attributed to the withdrawal liquid(s) flowing in the withdrawal channels 205-1 - 205-n may be increased to be substantially greater than an absolute magnitude of the collective capillary pressures attributed to the trigger liquids contained in the trigger channel 204, when the valve 200 is triggered to transition from the closed state to the open state.

[0142] Referring to Fig. 14, a method of operation 360 of the valve 200 may comprise the steps of generating a flow of primary liquid through the primary channel 201 past the first port (not shown but similar to first port 103) to generate and restrain a meniscus at the first port (step 361), and pre-filling each withdrawal channel 205-1 - 205-n with a volume of withdrawal liquid (step 361) via respective inlet(s). Steps 361 and 362 may be performed in any order without departing from the scope of the invention.

[0143] At step 363, the valve 200 is further operable to close when a volume of trigger liquid is conveyed through the trigger channel 204 via the inlet 106 toward the void volume (also not shown, but similar to void volume 102), as described for step 330 in method 300. When this happens, air is displaced out of the trigger channel 204 into the void volume, inflating the occluding bubble in the primary channel 201. At step 364, the valve 200 may be re-opened in multiple stages. In this step 364, liquid may be withdrawn from each channel 205-1 - 205-n sequentially to incrementally re-open / increase flow of primary liquid through the valve 200. The volume of withdrawal liquid contained in each withdrawal channel 205-1 - 205n may be withdrawn away from the void volume toward the respective withdrawal channel outlets to generate capillary force, which causes the meniscus to partially retract from the primary channel 201 back toward the void volume and into the respective withdrawal channel. In other words, as liquid is removed from each withdrawal channel 205-1 - 205-n, the bubble partially deflates and partially re-opens the valve 200. When this action is repeated sequentially for each withdrawal channel 205-1 - 205-n, the valve 100 can be re-opened incrementally. In an exemplary implementation, the withdrawing of liquid from all channels 205-1 - 205-n is sufficient to fully re-open the valve 200 into the state shown in Fig. 2A. being the fully open state.

[0144] Referring back to Fig. 13, an embodiment of a microfluidic device 500 incorporating the multi-withdrawal-channel valve 200 is shown. The device 500 comprises all of the features of any of the embodiments described in relation to valve 400 and only features that differ will be described in detail. The device 500 comprises multiple fill sub-circuits 510-1 - 510-n and multiple triggering circuits 522-1 - 522-n, each similar to the sub-circuits 410 and 422 as described in relation to device 400. Each filling and triggering subcircuit pair 510-1, 522-1 - 510-1, 522-n fluidly connect to a respective withdrawal channel 205-1 - 205-n of the valve 200, as per the circuits 410, 422 to channel 105 of device 400. The filling subcircuits 510-1 - 510-n are each configured to fill each of the withdrawal channels with predetermined volumes of withdrawal liquid from a primary liquid source 502 and the triggering sub-circuits 522-1 - 522-n are each configured to individually actuate flow of the withdrawal liquids out of their respective withdrawal channels 205-1 - 205-n. In the embodiment shown, one or more the triggering circuits may be connected to a separate input 527- 1 - 527-n, and wherein a liquid received through an input 527-1 - 527-n triggers the actuation of flow of the withdrawal liquid from the associated withdrawal channel 205-1 - 205-n (in a similar manner to triggering flow out of withdrawal channel 105 via input 427 in device 400). In this manner, a user may control the actuation of flow of withdrawal liquid out of each withdrawal channel, and accordingly the reopening of the valve 200. In an alternative embodiment, the triggering circuit 522-1 may be connected to a liquid source and the remaining triggering sub-circuits may be connected to the first triggering sub-circuit 522-1 and to one another in series such that they are sequentially controlled to actuate flow of withdrawal liquid out of the respective withdrawal channels when a liquid is received by the first sub-circuit from the liquid source. The circuit 500 may comprise a flow resistance path between each of the trigger circuits to control the timing of actuation of flow of withdrawal liquid out of the respective withdrawal channels. In either embodiment, the device 500 is operable to actuate flow of withdrawal liquid through the respective withdrawal channels sequentially, resulting in the incremental reopening of valve 200.

[0145] Referring to Fig. 15, a method 370 of operating the device 500 may thereby comprise inputting or receiving withdrawal liquids to prefill the withdrawal channels 205-1 - 205-n (step 371). The withdrawal liquid continues to fill each channel 205-1 - 205- n until the transistor valve in each of the fill subcircuits 510-1 - 510-n is triggered to terminate flow of withdrawal liquid into the respective channel 205-1 - 205-n (step 372). This is exhibited when the withdrawal channel is filled with the predetermined volume of withdrawal liquid. Sometime after filling the withdrawal channels 205-1 - 205-n are filled, the valve 200 may be triggered into a closed state. This may be a sequenced event that occurs some period of time after the primary liquid is introduced into the device 500 via inlet 502 which may be preprogrammed or controlled by a user. Liquid is conveyed into the trigger channel 504 of the valve 100 to cause the valve 100 to transition into the closed state (step 373). The circuit 500 is then actuated to re-open the valve 200 incrementally, by opening the trigger valve of each trigger circuit 522-1 - 522-n sequentially (step 373).

[0146] Referring now to Figs. 16A-16C and 17 alternative implementations of a valve 100A and microfluidic circuit or device 400A are shown comprising a single, common channel 124 configured to function as both the trigger channel and the withdrawal channel for closing and re-opening the valve 100. The valve 100A and the circuit or device 400A are both respectively similar to the implementations described with regards to valve 100 and the circuit or device 400. The only difference being that the valve 100A does not comprise separate trigger and withdrawal channels connected to the void volume 102. Instead, a common control channel 124 is connected to the void volume 102 and the fill sub-circuitry (402B, 413) and withdrawal sub-circuitry (425, 423) are fluidly connected to this control channel 124, (in the same manner in which they are fluidly connected to withdrawal channel 105 for valve 100). The fill sub-circuitry is configured to drive liquid into the control channel 124 through capillary action to trigger the valve 100A into the closed state shown in Fig. 16B, and the withdrawal sub-circuitry is configured to drive the liquid out of the control channel 124 to re-open the valve as shown in Fig. 16C.

[0147] The control channel 124 may be the same or similar to the trigger channel 104 described in relation to the valve 100. In other words, the control channel 124 is configured to enable a liquid 124A to flow into the control channel 124 via a control channel inlet 106, toward the void volume 102. This flow of liquid 124A into the control channel 124 generates a first capillary force Fl that causes an occluding air bubble 108 to be pushed out from the void volume 102, beyond the first port 103, and into the primary channel 101 to effectively inhibit or at least reduce the flow of the primary liquid 101A in the primary channel 101 past the first port 103. For the liquid to generate a sufficient force to move the occluding bubble 108, the valve 100A is preferably configured such that an absolute magnitude of a capillary pressure attributed to the liquid 124A flowing in the control channel 124 is substantially greater than an absolute magnitude of a capillary pressure attributed to the primary liquid 101A flowing in the primary channel 101 at the first port 103. In other words, the pressure in the control channel 124 is greater than the pressure at the first port 103. The valve 100A may be configured in this manner by configuring the relative geometries of the control channel 124 and the primary channel 101 and / or the first port 103, and / or or by configuring the type of liquids flowing through the channels and their surface tensions as described in relation to trigger channel 104 and primary channel 101 of valve 100 for instance.

[0148] A substantially higher capillary pressure in the control channel 124 compared to the first port 103 of the primary channel 101 during operation, enables the inflation of a bubble into the primary channel 101 and this bubble restricts the flow of liquid in the primary channel 101, and in a preferred implementation eventually fully closes the channel 101 for flow as shown in Fig. 16B.

[0149] The control channel 124 is connected to fill sub-circuitry at inlet 107 that may be the same or similar to the fill sub-circuitry connected to the withdrawal channel 105 of valve 100, for instance. The source of liquid may be the primary channel 101, upstream of port 103 or a different liquid source as described in relation to valve 100 for both the trigger and withdrawal channels 104 and 105.

[0150] The withdrawal sub-circuitry (or other withdrawal component or device) connected to the outlet of the control channel 124 may be the same or similar to the withdrawal sub-circuitry (or withdrawal device or component) described in relation to the withdrawal channel 105 of valve 100. In this implementation, the withdrawal subcircuit or other component or device is configured to connect the control liquid 124A in the control channel 124 to a withdrawal pressure that is in an opposing direction and greater than the pressure of the control liquid 124A acting towards the void volume. This pressure difference enables re-opening of the valve 100A during operation. A trigger valve 425 connected to the control channel 124 and can be activated to connect the liquid 124A in the control channel 124 with a capillary pump 423, for instance. The capillary pump 423 in this implementation being configured to generate a relatively higher capillary pressure of an opposing meniscus to that within the control channel 124 and facing the void volume 102, when liquid 423A is flowing through the capillary pump 423. This relatively higher capillary pressure being sufficient to withdraw the control liquid in 124A from the channel 124, thereby creating a retraction force F2 that retracts the bubble back towards the first port 103 and re-opens the valve 100A as shown in Fig. 16C.

[0151] The capillary pump preferably comprises a geometry that generates an opposing capillary pressure that is substantially greater than the capillary pressure of the meniscus located at or adjacent the connection 114 between the control channel 124 and the void volume 102, when liquid 423A flows through the capillary pump. The relative geometries, including relative dimensions, of the capillary pump and the control channel may be preconfigured to achieve this difference in respective capillary pressure magnitudes as described above in relation to the capillary pump and withdrawal channel of the valve 100, for instance. In this manner, the pressure gradient across the control liquid, when the control channel is fluidly connected to the capillary pump, drives the control liquid away from the void volume 102, causing the occluding bubble to retract back towards the void volume 102 and reopen the valve 100.

[0152] In this implementation, the same control channel 124 is being used to inflate the occluding bubble and thus close the valve 100A, and defl ate / retract the occluding bubble and thus re-open the valve 100A. The degree to which the valve 100A can be closed and then subsequently re-open may be configured for a particular application. For instance, it may be configured to fully close and fully open the flow path in primary channel 101, or only partially close and / or partially open the flow path in primary channel 101. Referring to Fig. 18, a method 380 of operating the valve 100A comprises driving a flow of control liquid 124A into the control channel 124 to close the valve 100A. Reopening the valve comprises triggering the flow of the control liquid 124A through the outlet and driving flow through the capillary pump until the valve 100A re-opens.

[0153] Other features of the valve 100A are as described in relation to valve 100 and thus have been given like reference numerals. These features and their various implementations have not been described again with reference to this implementation for the sake of brevity.

[0154] Another implementation of valve 100A and circuit or device 400A may be similar to that described in relation to device 500, where there may be multiple control channels 124-1 - 124-n connected separately to the void volume 102, and a fill sub-circuit connected to each of these channels 124-1 - 124-n for driving a flow of control liquid into each channel. To close the valve, all control channels 124-1 - 124-n (or at least a number of the channels) are filled with the control liquid. The collective pressures of these channels displace a sufficient volume of air in the void volume 102 to inflate the bubble 108 and close the valve 100A. Each channel may be connected to a separate withdrawal sub-circuit or to a withdrawal sub-circuit that sequences the triggering of withdrawal of the control liquid from each of the control channels 124- 1 - 124-n. This arrangement allows for the incremental re-opening of the valve in stages as described in relation to the device 500.

[0155] Capillary channels and capillary pumps

[0156] As described, the embodiments relating to any one of the valve 100, the valve 100A, the valve 200, the microfluidic circuit 150, and the microfluidic devices 400, 400A, and 500, include capillary channels and capillary pumps. These channels and pumps operate based on the creation of a Laplace pressure, created by a liquid's meniscus which in turn applies the driving pressure for the fluid within the channel. The Laplace pressure exerted by a meniscus can be calculated using the Young-Laplace Equation (1) where P_cap is the capillary pressure, and R_horizontal and R_vertical are the primary radii of the meniscus in the horizontal and vertical direction respectively. These radii are dependent on the height and width of the channel as well as the top, bottom, left, and right contact angles of liquid with the corresponding four microchannel walls and the surface tension of the liquid. A contact angle smaller than 90 degrees is preferred for the left, right and bottom microchannel walls, as the capillary pressure becomes insignificant when approaching 90 degrees, and a single imperfection in the microchannel can lead to local changes in contact angle that could disrupt circuit functionality. Surfaces that have a contact angle of less than or equal to 60 degrees are more preferred for a sufficient capillary pressure for self-powered operation in the preferred embodiment.

[0157] This pressure can be preselected for each of the channels and for the pumps, and the geometries of the capillary channels and capillary pumps of the device 400 may be designed accordingly to suit a particular application / implementation. Valves

[0158] The trigger valve 425 fluidly connecting the trigger channel 426 and the outlet 112 of the withdrawal channel 105 (or control channel 124) is preferably a passive, nonmechanical valve that utilises interfacial surface tension to block or restrict flow in a channel. The valve 425 is a capillary valve operating without moving parts. Such a valve comprises an abrupt change in geometry or hydrophobicity in a surface carrying the withdrawal liquid at the outlet 112 to stop the withdrawal liquid (or control liquid) at the outlet 112 in the closed or off state of the valve. A flow of trigger liquid past the outlet 112 breaks this tension to then permit flow of the withdrawal liquid (or control liquid) past outlet 112 and into the capillary pump channel.

[0159] Referring to Figs. 10A and 10B, a close up of the trigger valve that may be used for trigger valve 425 is shown, to illustrate the basic principle of operation of this valve. A local change in geometry disrupts the flow of liquid which can prevent further flow of the liquid along the capillary channel. Capillary stop valves are used to stop flow in a channel using a sudden divergence of the channel cross-section. This divergence usually means a constriction in the channel followed by a sudden enlargement, or in other words an abrupt enlargement in the cross-sectional area of a capillary channel. The valve may be a one-level or two-level trigger valve, for instance.

[0160] Referring to Fig. 10A, a schematic of a capillary stop valve is shown to illustrate this basic principle of operation. A local change in geometry can disrupt the flow of liquid along the capillary channel. Capillary stop valves are used to stop flow in a channel using a sudden divergence of the channel cross-section. This divergence usually means a constriction in the channel followed by a sudden enlargement, or in other words an abrupt enlargement in the cross-sectional area of a capillary channel.

[0161] As shown in Fig. 10A, the trigger valve works by creating an abrupt increase in the cross-sectional area via two dimensions, the width, w, and depth, d, of the channel. In other words, there is an increase in the cross-sectional area at the intersection between the primary channel (liquid 1) and the trigger channel (liquid 2) that is achieved by a widening of the trigger channel (relative to the primary channel) but also by increasing the depth of the trigger channel relative to the primary channel). In addition, in the two-level trigger valve, the primary channel and the trigger channel are preferably oriented at approximately 90 degrees to one another (or the main axes of liquid flow in the channels are angled 90 degrees to one another).

[0162] Referring to Fig. 10B, the geometry of an outlet 61 of the primary channel 62 is configured to inhibit liquid in the primary channel 61 from passing into the trigger channel 63. More specifically, an inner peripheral wall 64 of the trigger channel 63 located at or adjacent the outlet 61 of the primary channel 62 is angled at about 180 degrees or more relative to an imaginary plane extending across the outlet, as can be seen in Figure 10B. This geometry is shown across the width, w, dimension, and a similar geometry is exhibited in the depth, d, dimension. In the device 400, this angle for the width, w, dimension is >180 degrees for valve 425 to increase the reliability of the valve in the un-triggered state (by increasing the respective Laplace pressure). It will be appreciated that this angle can be designed as required by the intended application.

[0163] This angle constraint ensures that a meniscus moved by a flow of liquid passing through the trigger channel 4, in the direction C, 'pins' at the imaginary plane 65 due to surface tension effects, whereas an angle less than 180 degrees may allow the capillary forces driving the liquid flow to overcome surface tension effects, causing the meniscus, and therefore the liquid, to pass through the outlet 61 into the trigger channel 63. However, angles that are less than 180 degrees (but greater than 0 degrees) may still provide an effective valve and are not intended to be excluded as possible implementations. Although they may be potentially less stable designs.

[0164] For valve 425, the withdrawal channel 105 (or control channel 124) act as the primary liquid channel, and the channel 426 acts as the trigger channel. In some embodiments, a one level trigger valve may be used instead of one or more of the above-mentioned valves to achieve the same or similar functionality as described herein.

[0165] Sealing Transistor Valves

[0166] The device 400 or 400A comprises multiple transistor valves, e.g., 413, 428 and modified transistor valve 100 or 100A. The construction and various embodiments of such valves is described in detail in PCT patent application PCT / IB2021 / 051153 which is hereby incorporated by reference. The following description outlines the construction and functionality of this type of valve in some detail and such constructions may be implemented for any of the transistor valves 413, 428, 100 and 100A described herein.

[0167] As shown in Fig. 11 the transistor valve comprises a main channel 2 and a trigger channel 4 having an inlet and an outlet 6. The trigger channel 4 allows for liquid 30 communication between the trigger channel 4 and the main channel 2, via the inlet of the trigger channel 4 that provides a connection therebetween.

[0168] The inlet of the trigger channel 4 provides a connection between the trigger channel 4 and the main channel 2. Further, the outlet 6 of the trigger channel 4 provides a connection between the trigger channel 4 and the main channel 2 through a void volume 7. The void volume 7 therefore facilitates that connection between the trigger channel 4 and the main channel 2 via a first port 8 that connects the void volume 7 to the main channel 2. The first port 8 has a geometry that inhibits liquid present in the main channel 2 from flowing through the first port 8 into the void volume 7. More specifically, as can be seen in Figure 11, an inner peripheral wall 12 of the void volume 7 located at or adjacent the first port 8 may be angled at about 180 degrees or more relative to an imaginary plane 13 extending across the first port 8.

[0169] This angle constraint ensures that a meniscus 9 moved by a flow of liquid passing through the main channel 2, in the direction A, 'pins' at the imaginary plane 13 due to surface tension effects, whereas an angle less than 180 degrees may allow the capillary forces driving the liquid flow to overcome surface tension effects, causing the meniscus 9, and therefore the liquid to pass through the first port 8 into the void volume 7. However, angles that are less than 180 degrees (but greater than 0 degrees) may still provide an effective valve and are not intended to be excluded as possible implementations. Although they may be potentially less stable designs. Likewise, the geometry of the outlet 6 of the trigger channel 4 is configured to inhibit liquid in the trigger channel 4 from passing into the void volume 7. More specifically, an inner peripheral wall 14 of the void volume 7 located at or adjacent the outlet 6 of the trigger channel 4 may be angled at about 180 degrees or more relative to an imaginary plane 15 extending across the outlet 6, as can be seen in Figure 11.

[0170] This angle constraint ensures that a meniscus moved by a flow of liquid passing through the trigger channel 4, in the direction B, 'pins' at the imaginary plane 15 due to surface tension effects, whereas an angle less than 180 degrees may allow the capillary forces driving the liquid flow to overcome surface tension effects, causing the meniscus, and therefore the liquid, to pass through the outlet 6 into the void volume 7. However, angles that are less than 180 degrees (but greater than 0 degrees) may still provide an effective valve and are not intended to be excluded as possible implementations. Although they may be potentially less stable designs.

[0171] By contrast, the connection between the inlet of the trigger channel 4 and source of trigger fluid has a geometry that permits liquid in source channel to flow into the trigger channel 4 through the inlet. Therefore, the configuration of the outlet 6 into the void volume 7, as well as the configuration of the first port 8 out of the void volume 7, prevent any liquid from flowing into the void volume 7, whether that liquid is present in the main channel 2 or the trigger channel 4. Thus, a meniscus 9 moved by a flow of liquid in the main channel 2 will 'pin', or be restrained, at the first port 8, while the flow of liquid continues downstream through the main channel 2.

[0172] A cross-sectional area of the first port 8 is configured to be substantially larger than a cross-sectional area of the trigger channel 4. In some configurations, a cross- sectional area of the outlet 6 of the trigger channel 4 may be equal to the cross- sectional area of the trigger channel 4. As a result of the relative sizes of the cross- sectional areas of these various features, a capillary force, generated by the flow of liquid through the trigger channel 4 causes the meniscus restrained at the first port 8 to expand from the first port 8 into the main channel 2.

[0173] This forms a gaseous bubble which acts to inhibit flow of liquid in the main channel 2 past the first port 8. Depending on the extent to which the gaseous bubble extends into the main channel 2, in some configurations the gaseous bubble may act to inhibit, but allow, some flow of liquid in the main channel 2 past the first port 8. In some other configurations, as in the valves of the preferred embodiment, the gaseous bubble may act to completely prevent liquid in the main channel 2 from flowing past the first port 8.

[0174] In some embodiments, the length of the trigger channel 4 partly determines the volume of gas therein displaced by the capillary force generated by the flow of liquid therethrough, and thus may determine the extent to which the gaseous bubble, or meniscus, extends or expands into the primary channel. Therefore, a length of the trigger channel 4 determines the extent to which the meniscus restrained at the first port 8 expands from the first port 8 into the main channel 2 upon generation of the capillary force by the flow of liquid through the trigger channel 4. Thus, the length of the trigger channel 4 may be configured so that the microfluidic valve 1 may provide a desired flow resistance through the main channel 2 upon activation thereof.

[0175] Therefore, the microfluidic valve 1 acts to inhibit flow of liquid in the main channel 2 past the first port 8 when triggered by a flow of liquid through the trigger channel 4. The trigger channel source may be the main channel itself, or it may be a different source. In the former instance, when the inlet 5 of the trigger channel 4 is connected to the main channel 2, the microfluidic valve 1 can be described as a 'self-sealing' valve, in that the flow of liquid through the main channel 2 which triggers its operation, is also the same flow of liquid that is inhibited as a result of its operation.

[0176] However, in the latter case, the microfluidic valve is 'non-self-sealing', as the flow of liquid through the trigger channel that triggers its operation is not necessarily the same flow of liquid in the main channel that is inhibited as a result of its operation.

[0177] Advantages and applications

[0178] The microfluid valve implementations and the related circuits and devices described provide microfluidic structures operable by capillary action (with or without human intervention) to re-open a transistor valve after it has been closed. This enables the automation of more complex multi-step chemistry processes as described above. Another advantage of the microfluid valve 100 or valve 100A for instance when multiple withdrawal channels 105-1 105-n or control channels 124-1 - 124-n are incorporated, is its capability to be implemented in an analogue actuation manner, meaning that the valve 100 can be actuated to states in-between fully closed and fully open. This feature allows for precise control over the flow rate of the liquid in the primary channel, enabling the fine-tuning of test conditions and the optimization of assay performance. In a medical diagnostic application, for instance, the analogue actuation could be used to modulate the flow of a sample through a detection chamber, ensuring optimal contact between the sample and the detection reagents, ultimately leading to more accurate and sensitive test results.

[0179] Furthermore, the microfluid valve 100 or valve 100A can be integrated into existing microfluidic devices, offering a cost-effective and straightforward solution for enhancing the performance and functionality of current capillary test systems. Its compact design and compatibility with various materials, such as glass, plastic, or silicon, make it a versatile and adaptable component for a wide range of applications.

[0180] The valve 100 or 100A and related circuits and devices 400 or 400A can be utilised in various industries, including medical diagnostics, chemical analysis, and industrial quality control, where rapid and accurate testing is important. In the medical field, for instance, the valve 100 or 100A and the related devices 400 or 400A can be employed in point-of-care testing devices for blood glucose monitoring, infectious disease detection, and other critical diagnostic applications, enabling faster and more efficient patient care.

[0181] One or more of the components and functions illustrated in the figures may be rearranged and / or combined into a single component or embodied in several components without departing from the invention. Additional elements or components may also be added without departing from the scope of the invention.

[0182] The present disclosure may thus relate to further aspects and embodiments as defined in the following numbered clauses.

[0183] 1. A microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; at least one capillary control channel, each capillary control channel being separately fluidly connected to the void volume and having inlet for receiving a corresponding control liquid and conveying the control liquid toward the void volume via capillary action, wherein at least one of the capillary control channel(s) is configured as a trigger channel that drives a corresponding control liquid ("trigger liquid") toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; and a withdrawal subcircuit fluidly connected to an outlet of at least one of the capillary control channel(s), to drive the flow of the corresponding control liquid received within the respective control channel(s) through the corresponding outlet and away from the void volume, thereby substantially increasing or re-permitting the flow of the primary liquid through the primary channel.

[0184] 2. The microfluidic valve of clause 1 wherein the microfluidic valve comprises a single control channel, the single control channel being configured as the trigger channel and being fluidly connected at the outlet of the control channel to the withdrawal subcircuit.

[0185] 3. The microfluidic valve of clause 1 wherein the microfluidic valve comprises a first control channel configured as the trigger channel and a second control channel fluidly connect at the outlet of the second control channel to the withdrawal subcircuit.

[0186] 4. The microfluidic valve of any one of clause 1 to clause 3 wherein the valve is configured to operate between a first state and a second state, wherein in the first state, a flow of the primary liquid through the primary channel is substantially restricted or reduced relative to the second state.

[0187] 5. The microfluidic valve of clause 4 wherein the valve is configured to be reversibly operable between the first state and the second state.

[0188] 6. The microfluidic valve of clause 4 or clause 5 wherein the first state is a fully closed state in which the flow of primary liquid in the primary channel past the first port is substantially inhibited.

[0189] 7. The microfluidic valve of clause 6 wherein the second state is a partially open, or a fully open state, in which the flow of primary liquid in the primary channel past the first port is substantially permitted or increased relative to the first state.

[0190] 8. The microfluidic valve of any one of clause 4 to clause 7 wherein the valve is configured and operable to transition from the first state to the second state when the withdrawal subcircuit drives the flow of the control liquid in at least one of the connected control channel(s) through the corresponding outlet of the channel and away from the void volume, during operation.

[0191] 9. The microfluidic valve of clause 8 wherein the valve is configured and operable to transition from the first state toward the second state when the withdrawal subcircuit generates a pressure gradient across the control liquid in at least one of the connected control channel(s) sufficient to drive flow of the control away from the void volume.

[0192] 10. The microfluidic valve of clause 9 wherein the withdrawal subcircuit is configured to generate the pressure gradient by driving a flow of liquid past the outlet of the corresponding control channel via capillary action.

[0193] 11. The microfluidic valve of any one of clause 4 to clause 10 wherein the valve is configured such that, in the first state, the trigger liquid in the trigger channel exhibits a first absolute capillary pressure that is distinct to a second absolute capillary pressure of a control liquid in another control channel ("second control channel").

[0194] 12. The microfluidic valve of clause 11 wherein the first absolute capillary pressure is greater than the second absolute capillary pressure.

[0195] 13. The microfluidic valve of clause 11 or clause 12 wherein the first trigger channel comprises a first geometry, and the second control channel comprises a second geometry that is distinct from the first geometry, and wherein the first and second absolute capillary pressures are at least partly attributable to the distinct first and second geometries.

[0196] 14. The microfluidic valve of any one of clause 11 to clause 13 wherein the valve further comprises one or more first channel networks fluidly connected to the first trigger channel, and / or one or more channel networks fluidly connected to the second control channel, and wherein the first and second distinct absolute capillary pressures are at least partly attributable to the first channel network and / or the second channel network.

[0197] 15. The microfluidic valve of any one of clause 11 to clause 14 further comprising a first liquid modifier contained or connected to the first trigger channel for modifying a property of the first trigger liquid, and / or a second liquid modifier contained or connected to the second control channel for modifying a property of the second control liquid, and wherein the distinct first and second absolute capillary pressures are at least partly attributable to the first liquid modifier and / or the second liquid modifier.

[0198] 16. The microfluidic valve of any one of clause 4 to clause 15 wherein the valve comprises two or more control channel(s) fluidly connected to the void volume and to a corresponding withdrawal sub-circuit at the outlet of the control channel.

[0199] 17. The microfluidic valve of clause 16 wherein the valve is configured to operate in one or more other states between the first state and the second state.

[0200] 18. The microfluidic valve of clause 17 wherein the valve is operable to incrementally increase the flow of the primary liquid in the primary channel by sequentially driving flow of the control liquids out of the respective control channels via their corresponding withdrawal sub-circuits.

[0201] 19. The microfluidic valve of any one of clause 1 to clause 18 wherein the valve comprises two or more trigger channel(s) fluidly connected to the void volume.

[0202] 20. The microfluidic valve of clause 19 wherein the valve is operable to incrementally decrease the flow of the primary liquid in the primary channel by sequentially driving the flow of the trigger liquids into the respective trigger channel(s) toward the void volume.

[0203] 21. The microfluidic valve of any one of clause 4 to clause 20 wherein the valve is configured such that, in the first state, a first absolute capillary pressure exhibited by the trigger liquid in the trigger channel is substantially greater than a third absolute capillary pressure exhibited by the primary liquid at the first port, when the trigger liquid and the primary liquid are contained in the trigger channel and the primary channel respectively.

[0204] 22. The microfluidic valve of clause 21 wherein the trigger channel and the primary channel comprise distinct geometries, and the distinct first and third absolute capillary pressures are at least partially attributed to the distinct geometries of the trigger channel and the primary channel.

[0205] 23. The microfluidic valve of clause 21 or clause 22 further comprising one or more channel networks connected to the trigger channel and / or the primary channel and the distinct first and third absolute capillary pressures are at least partially attributed to the one or more channel networks.

[0206] 24. The microfluidic valve of any one of clause 21 to clause 23 further comprising one or more liquid modifiers connected or contained within the trigger channel and / or the primary channel, and wherein the distinct first and third absolute capillary pressures are at least partially attributed to the one or more liquid modifiers.

[0207] 25. The microfluidic valve of any one of clause 4 to clause 24 wherein the valve is configured such that, in the first state, a second absolute capillary pressure exhibited by the control liquid in the control channel connected to the withdrawal sub-circuit is substantially greater than a third absolute capillary pressure exhibited by the primary liquid in the primary channel at the first port, when the control liquid and the primary liquid are contained in the control channel and the primary channel respectively.

[0208] 26. The microfluidic valve of clause 25 wherein the control channel and the primary channel comprise distinct geometries, and the distinct second and third absolute capillary pressures are at least partially attributed to the distinct geometries of the second withdrawal channel and the primary channel.

[0209] 27. The microfluidic valve of clause 25 or clause 26 further comprising one or more channel networks connected to the control channel and / or the primary channel and the distinct second and third absolute capillary pressures are at least partially attributed to the one or more channel networks.

[0210] 28. The microfluidic valve of any one of clause 25 to clause 27 further comprising one or more liquid modifiers connected or contained within the control channel and / or the primary channel, and wherein the distinct second and third absolute capillary pressures are at least partially attributed to the one or more liquid modifiers.

[0211] 29. The microfluidic valve of any one of clause 1 to clause 29 wherein the valve is configured such that, during operation, a trigger liquid flowing into the trigger channel toward the void volume generates a first capillary force that causes an occluding air bubble to move beyond the first port into the primary channel, to inhibit or reduce a flow of primary liquid in the primary channel past the first port. 30. The microfluidic valve of clause 29 wherein the valve is configured such that, during operation, a control liquid flowing in a control channel away from the void volume generates a second capillary force that causes the occluding air bubble to retract from the primary channel toward the void volume to permit or increase the flow of liquid in the primary channel past the first port.

[0212] 31. The microfluidic valve of any one of the preceding clauses wherein the trigger channel comprises a cross-sectional area at or adjacent the void volume, that is substantially smaller than the cross-sectional area of another control channel at or adjacent the void volume.

[0213] 32. The microfluidic valve of any one of the preceding clauses wherein a first depth of the trigger channel is substantially smaller than a second depth of the other control channel.

[0214] 33. The microfluidic valve of any one of the preceding clauses wherein a flow resistance of the trigger channel is substantially greater than a flow resistance of the other control channel.

[0215] 34. The microfluidic valve of any one of the preceding clauses wherein a flow resistance of the trigger channel is substantially greater than a flow resistance of the primary channel.

[0216] 35. The microfluidic valve of any one of the preceding clauses wherein a flow resistance of a control channel connected to the withdrawal sub-circuit is substantially greater than a flow resistance of the primary channel.

[0217] 36. The microfluidic valve of any one of the preceding clauses wherein a geometry of the trigger channel at a fluid connection between the first trigger channel and the void volume is configured to inhibit liquid in the trigger channel from flowing into the void volume.

[0218] 37. The microfluidic valve of any one of the preceding clauses wherein a geometry of each control channel at a fluid connection between the control channel and the void volume is configured to inhibit liquid in the control channel from flowing into the void volume.

[0219] 38. The microfluidic valve of any one of the preceding clauses wherein a cross- sectional area, or a depth, or both, of the trigger channel at a fluid connection between the first trigger channel and the void volume is substantially equal to a cross-sectional area, or a depth, or both, of the trigger channel along an intermediate length of the channel.

[0220] 39. The microfluidic valve of any one of the preceding clauses wherein a cross- sectional area, or a depth, or both of each control channel at a fluid connection between the control channel and the void volume is substantially equal to a cross- sectional area, or a depth, or both, of the control channel along an intermediate length of the channel.

[0221] 40. The microfluidic valve of any one of the preceding clauses wherein the trigger channel comprises a substantially uniform cross-sectional area, or a substantially uniform depth, or both, along a substantial length between an inlet and an outlet of the trigger channel.

[0222] 41. The microfluidic valve of any one of the preceding clauses wherein each control channel comprises a substantially uniform cross-sectional area, or a substantially uniform depth, or both, along a substantially length between an inlet and an outlet of the control channel.

[0223] 42. The microfluidic valve of any one of the preceding clauses wherein an inner peripheral wall of the void volume located at or adjacent the first port is angled at approximately 180 degrees or greater relative to an imaginary plane extending across the first port.

[0224] 43. The microfluidic valve of any one of the preceding clauses wherein an inner peripheral wall of the void volume located at or adjacent a fluid connection with the trigger channel is angled at approximately 180 degrees or greater relative to an imaginary plane extending across the fluid connection with the trigger channel.

[0225] 44. The microfluidic valve of any one of the preceding clauses wherein an inner peripheral wall of the void volume located at or adjacent a fluid connection with each control channel connected to the withdrawal sub-circuit is angled at about 180 degrees or more relative to an imaginary plane extending across the fluid connection with the control channel. 45. The microfluidic valve of any one of the preceding clauses wherein an inlet of the trigger channel is fluidly connected to the primary channel downstream of the first port.

[0226] 46. The microfluidic valve of any one of the preceding clauses wherein an inlet of at least one control channel connected to the withdrawal sub-circuit is fluidly connected to the primary channel upstream of the first port.

[0227] 47. The microfluidic valve of any one of the preceding clauses further comprising a vent fluidly connected to at least one control channel that is connected to the withdrawal sub-circuit.

[0228] 48. The microfluidic valve of clause 47, wherein the vent is fluidly connected at an intermediate position along a length of the respective control channel.

[0229] 49. The microfluidic valve of any one of the preceding clauses the withdrawal subcircuit is configured to trigger and drive the flow of control liquid through the outlet of each connected control channel.

[0230] 50. The microfluidic valve of any one of clause 1 to clause 49 wherein the withdrawal subcircuit is configured to control the flow of withdrawal liquid contained within the connected control channel through the outlet of the control channel.

[0231] 51. The microfluidic valve of clause 50 wherein the withdrawal subcircuit is configured to control a rate of flow of control liquid contained within the control channel through the outlet of the control channel.

[0232] 52. The microfluidic valve of clause 50 or clause 51 wherein the withdrawal subcircuit comprises a capillary pump configured to control the flow of control liquid through the outlet of the connected control channel.

[0233] 53. The microfluidic valve of clause 52 wherein the capillary pump comprises a channel for liquid to flow through the channel, and during operation, a fourth absolute capillary pressure attributed to the liquid flowing through the capillary channel generates a pressure gradient across the control liquid of the connected control channel sufficient to drive the flow of the control liquid through the outlet and away from the void volume. 54. The microfluidic valve of clause 53 wherein the capillary pump channel comprises a distinct geometry relative to the connected control channel geometry.

[0234] 55. The microfluidic valve of clause 54, wherein the capillary pump channel comprises a cross-sectional area that is substantially smaller than the cross-sectional area of the connected control channel.

[0235] 56. The microfluidic valve of either one of clause 53 or clause 54 wherein a depth of the capillary pump channel is substantially smaller than a depth of the connected control channel.

[0236] 57. The microfluidic valve of any one of clause 1 to clause 56 wherein the withdrawal subcircuit is configured to trigger the flow of control liquid through the outlet of the connected control channel.

[0237] 58. The microfluidic valve of clause 57 wherein the withdrawal subcircuit comprises a withdrawal trigger channel fluidly connected to the outlet of the connected control channel, and wherein a flow of liquid through the withdrawal trigger channel triggers the flow of control liquid through the outlet of the connected control channel.

[0238] 59. The microfluidic valve of clause 58 wherein the withdrawal subcircuit comprises a capillary valve fluidly connected between the outlet of the connected control channel and the withdrawal trigger channel of the withdrawal subcircuit.

[0239] 60. The microfluidic valve of clause 59 wherein the capillary valve is configured to inhibit flow of control liquid through the outlet of the connected control channel in a closed operative state of the capillary valve, and permit the flow of control liquid through the outlet of the connected control channel in an open operative state of the capillary valve.

[0240] 61. The microfluidic valve of clause 60 wherein the capillary valve is a capillary trigger valve configured to trigger from the closed operative state into the open operative state when a liquid flows through the withdrawal trigger channel past the outlet of the connected control channel.

[0241] 62. The microfluidic valve of any one of clause 57 to clause 61 wherein an inlet of the withdrawal trigger channel comprises an inlet for connected with a second liquid source upstream of the connection with the outlet of the respective control channel. 63. The microfluidic valve of any one of clause 1 to clause 62 wherein the withdrawal subcircuit comprises a first capillary pump fluidly connected to an outlet of the connected control channel.

[0242] 64. The microfluidic valve of clause 63 wherein the first capillary pump comprises a flow path connected to a vent, chamber or reservoir downstream of the outlet of the connected control channel.

[0243] 65. The microfluidic valve of either one of clause 63 to clause 64, when dependent on any one of clause 58 to clause 62, wherein the first capillary pump of the withdrawal sub-circuit is fluidly connected to the withdrawal trigger channel downstream of the connection with the outlet of the connected control channel.

[0244] 66. A microfluidic device comprising: a main channel for conveying a primary liquid, and the microfluidic valve of any one of the preceding clauses ("first microfluidic valve"), wherein the primary channel of the first microfluidic valve is connected in series to the main channel.

[0245] 67. The microfluidic device of clause 66 wherein an inlet of the control channel of the first microfluidic valve is fluidly connected to a fill subcircuit configured to control filling of a respective control channel connected to the withdrawal sub-circuit with a predetermined volume of control liquid.

[0246] 68. The microfluidic device of clause 67 wherein the fill subcircuit is configured to substantially fluidly isolate the inlet of the control channel connected to the withdrawal sub-circuit from the control channel when the predetermined volume of control liquid is driven into the control channel to inhibit further flow of control liquid into the control channel.

[0247] 69. The microfluidic device of clause 67 or clause 68 wherein an inlet of the fill subcircuit is fluidly connected to a first fluid source.

[0248] 70. The microfluidic device of any one of clause 67 to clause 69 wherein an inlet of the fill subcircuit is fluidly connected to the main channel upstream of the first port of the first microfluidic valve. 71. The microfluidic device of any one of clause 67 to clause 70 wherein an outlet of the fill subcircuit is fluidly connected to the inlet of the control channel connected to the withdrawal sub-circuit of the first microfluidic valve.

[0249] 72. The microfluidic device of any one of clause 67 to clause 71 wherein the fill subcircuit further comprises a second microfluidic valve fluidly connected between an inlet and an outlet of the fill subcircuit, to inhibit flow of liquid into an inlet of the control channel when a predetermined volume of control liquid flows into the control channel via the inlet.

[0250] 73. The microfluidic device of any one of clause 66 to clause 72 wherein the withdrawal subcircuit further comprises a third microfluidic valve fluidly connected to the main capillary channel upstream of the connection with the outlet of the connected control channel of the first microfluidic valve.

[0251] 74. The microfluidic device of clause 73 wherein the third microfluidic valve is configured to permit the flow of liquid through the withdrawal trigger channel past the connection with the outlet of the connected control channel in an open operative state, and inhibit the flow of liquid through the main capillary channel past the connection with the outlet of the connected control channel in a closed operative state.

[0252] 75. The microfluidic device of clause 74 wherein the third microfluidic valve is configured to trigger from the open operative state to the closed operative state when predetermined volume of liquid flows through the third microfluidic valve.

[0253] 76. The microfluidic device of any one of clause 66 to clause 75 wherein the valve comprises multiple control channels and multiple withdrawal sub-circuits connected to each of the respective control channel.

[0254] 77. The microfluidic device of clause 76 wherein the device comprises multiple fill subcircuits fluidly connected to each of the control channels connected to withdrawal sub-circuits.

[0255] 78. The microfluidic device of any one of clause 66 to clause 77 further comprising a flow path connected in series to the main channel upstream of the first port of the first microfluidic valve. 79. The microfluidic device of clause 78 wherein the flow path is connected in series to the main channel downstream of a connection from the main channel to an inlet of the control channel connected to the withdrawal sub-circuit of the first microfluidic valve.

[0256] 80. The microfluidic device of any one of clause 66 to clause 79 wherein the main channel is fluidly connected to a second capillary pump downstream the first port of the first microfluidic valve.

[0257] 81. The microfluidic device of clause 80 wherein the second capillary pump comprises a flow path fluidly connected to a vent, chamber or reservoir.

[0258] 82. The microfluidic device of any one of clause 66 to clause 81 wherein the trigger channel of the first microfluidic valve is fluidly connected to the main channel downstream of the first port.

[0259] 83. A method for operating the microfluidic valve of any one of clause 1 to clause 65 comprising the steps of: driving, through capillary action, a volume of trigger liquid through the trigger channel toward the void volume to generate a first capillary force that causes a meniscus restrained at the first port to expand from the first port into the primary channel, to inhibit or reduce a flow of primary liquid in the primary channel.

[0260] 84. The method of clause 83 further comprising the step of triggering a flow of the volume of control liquid contained in the control channel connected to withdrawal sub-circuit away from the void volume to generate a second capillary force that causes the meniscus to retract from the primary channel toward the void volume, to re-permit or increase the flow of primary liquid in the primary channel.

[0261] 85. The method of clause 84 wherein the step of triggering the flow of the volume of control liquid away from the void volume comprises triggering flow of the volume of control liquid through an outlet of the respective control channel.

[0262] 86. The method of clause 85 wherein the flow of the volume of control liquid through the outlet is triggered via a flow of liquid through a capillary channel of the withdrawal sub-circuit, fluidly connected to the outlet. 87. The method of any one of clause 83 to clause 86 comprising the step of driving, through capillary action, a flow of control liquid into the control channel connected to the withdrawal sub-circuit.

[0263] 88. The method of clause 87 wherein microfluidic device comprises a single control channel and driving the control liquid into the control channel connected to the withdrawal sub-circuit occurs by driving the trigger liquid into the trigger channel.

[0264] 89. The method of clause 87 wherein microfluidic device comprises multiple control channels and driving the control liquid into the control channel connected to the withdrawal sub-circuit occurs prior to driving the trigger liquid into the trigger channel.

[0265] 90. The method of any one of clause 87 to clause 88 wherein the step of driving the control liquid into the control channel comprises retaining a volume of the control liquid in the control channel.

[0266] 91. The method of any one of clause 87 to clause 90 wherein the step of driving the control liquid into the control channel connected to the withdrawal sub-circuit comprises directing a flow of primary liquid from the primary channel into the control channel.

[0267] 92. The method of clause 91 wherein the step of driving the control liquid into the control channel connected to the withdrawal sub-circuit comprises directing a flow of primary liquid from the primary channel upstream of the first port.

[0268] 93. The method of any one of clause 87 to clause 92 wherein the step of driving the control liquid into the control channel connected to the withdrawal sub-circuit comprises terminating a flow of control liquid into the control channel when a predetermined volume of liquid is drawn into the control channel.

[0269] 94. The method of any one of clause 83 to clause 93 wherein the step of driving the trigger liquid into the trigger channel comprises directly a flow of the primary liquid into the trigger channel.

[0270] 95. The method of clause 94 wherein the step of driving the trigger liquid into the trigger channel comprises directly a flow of the primary liquid downstream of the first port. 96. The method of any one of clause 83 to clause 95 further comprising the step of generating flow of primary liquid through the primary channel using a capillary pump.

[0271] 97. The method of any one of clause 83 to clause 96 further comprising driving control liquid into multiple control channels each fluidly connected to a respective withdrawal sub-circuit.

[0272] 98. The method of clause 97 wherein the method further comprises sequentially withdrawing control liquid from the multiple control channels, away from the void volume, to cause a meniscus to incrementally retract from the primary channel toward the void volume, and incrementally re-permit or increase the flow of primary liquid in the primary channel.

[0273] 99. A microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; a first capillary trigger channel ("first trigger channel") fluidly connected to the void volume, and configured to convey a trigger liquid toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; a second capillary withdrawal channel ("second withdrawal channel") fluidly connected to the void volume and configured to convey a withdrawal liquid away from the void volume to substantially permit or increase a flow of the primary liquid through the primary channel.

[0274] 100. The microfluidic valve of clause 99 further comprising any one or more of the implementations of clause 2 to clause 65.

[0275] 101. A microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; a capillary trigger channel fluidly connected to the void volume and configured to convey first trigger liquid toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; one or more second capillary withdrawal channel(s) ("second withdrawal channel(s)") fluidly connected to the void volume and configured to convey second withdrawal liquid(s) away from the void volume to substantially increase or permit a flow of the primary liquid through the primary channel.

[0276] 102. The microfluidic valve of clause 101 further comprising any one or more of the implementations of clause 2 to clause 65.

[0277] 103. A microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; multiple capillary control channels, each capillary control channel being separately fluidly connected to the void volume and having inlet for receiving a corresponding control liquid and conveying the control liquid toward the void volume via capillary action, wherein at least one of the capillary control channel(s) is configured as a trigger channel that drives a corresponding control liquid ("trigger liquid") toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; and a withdrawal subcircuit for each of a plurality of the control channels, each withdrawal subcircuit being fluidly connected to an outlet of the respective capillary control channel, to drive the flow of the corresponding control liquid received within the respective control channel(s) through the corresponding outlet and away from the void volume, thereby substantially increasing the flow of the primary liquid through the primary channel.

[0278] 104. The microfluidic valve of clause 103 further comprising any one or more of the implementations of clause 2 to clause 65.

[0279] 105. A microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; at least one capillary control channel fluidly connected to the void volume, and configured to convey a control liquid toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel, each capillary control channel having an inlet for receiving a flow of a corresponding control liquid into the channel; and a withdrawal subcircuit fluidly connected to an outlet of at least one of the control channel(s) and configured to trigger and drive the flow of the control liquid contained within the control channel through the outlet of the control channel to substantially increase or re-permit the flow of the primary liquid through the primary channel.

[0280] 100. The microfluidic valve of clause 105 further comprising any one or more of the implementations of clause 2 to clause 65.

[0281] Further modifications may be made thereto without departing from the scope of the invention as defined by the accompanying claims.

Claims

CLAIMS1. A microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; at least one capillary control channel, each capillary control channel being separately fluidly connected to the void volume and having inlet for receiving a corresponding control liquid and conveying the control liquid toward the void volume via capillary action, wherein at least one of the capillary control channel(s) is configured as a trigger channel that drives a corresponding control liquid ("trigger liquid") toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; and a withdrawal subcircuit fluidly connected to an outlet of at least one of the capillary control channel(s), to drive the flow of the corresponding control liquid received within the respective control channel(s) through the corresponding outlet and away from the void volume, thereby substantially increasing or re-permitting the flow of the primary liquid through the primary channel.

2. A microfluidic valve as claimed in claim 1 wherein the microfluidic valve comprises a single control channel, the single control channel being configured as the trigger channel and being fluidly connected at the outlet of the control channel to the withdrawal subcircuit.

3. A microfluidic valve as claimed in claim 1 wherein the microfluidic valve comprises a first control channel configured as the trigger channel and a second control channel fluidly connect at the outlet of the second control channel to the withdrawal subcircuit.

4. A microfluidic valve as claimed in any one of claim 1 to claim 3 wherein the valve is configured to operate between a first state and a second state, wherein in the first state, a flow of the primary liquid through the primary channel is substantially restricted or reduced relative to the second state.

5. A microfluidic valve as claimed in claim 4 wherein the valve is configured to be reversibly operable between the first state and the second state.

6. A microfluidic valve as claimed in claim 4 or claim 5 wherein the first state is a fully closed state in which the flow of primary liquid in the primary channel past the first port is substantially inhibited.

7. A microfluidic valve as claimed in claim 6 wherein the second state is a partially open, or a fully open state, in which the flow of primary liquid in the primary channel past the first port is substantially permitted or increased relative to the first state.

8. A microfluidic valve as claimed in any one of claim 4 to claim 7 wherein the valve is configured and operable to transition from the first state to the second state when the withdrawal subcircuit drives the flow of the control liquid in at least one of the connected control channel(s) through the corresponding outlet of the channel and away from the void volume, during operation.

9. A microfluidic valve as claimed in claim 8 wherein the valve is configured and operable to transition from the first state toward the second state when the withdrawal subcircuit generates a pressure gradient across the control liquid in at least one of the connected control channel(s) sufficient to drive flow of the control away from the void volume.

10. A microfluid valve as claimed in claim 9 wherein the withdrawal subcircuit is configured to generate the pressure gradient by driving a flow of liquid past the outlet of the corresponding control channel via capillary action.

11. A microfluid valve as claimed in any one of claim 4 to claim 10 wherein the valve is configured such that, in the first state, the trigger liquid in the trigger channel exhibits a first absolute capillary pressure that is distinct to a second absolute capillary pressure of a control liquid in another control channel ("second control channel").

12. A microfluidic valve as claimed in claim 11 wherein the first absolute capillary pressure is greater than the second absolute capillary pressure.

13. A microfluidic valve as claimed in claim 11 or claim 12 wherein the first trigger channel comprises a first geometry, and the second control channel comprises asecond geometry that is distinct from the first geometry, and wherein the first and second absolute capillary pressures are at least partly attributable to the distinct first and second geometries.

14. A microfluidic valve as claimed in any one of claim 11 to claim 13 wherein the valve further comprises one or more first channel networks fluidly connected to the first trigger channel, and / or one or more channel networks fluidly connected to the second control channel, and wherein the first and second distinct absolute capillary pressures are at least partly attributable to the first channel network and / or the second channel network.

15. A microfluidic valve as claimed in any one of claim 11 to claim 14 further comprising a first liquid modifier contained or connected to the first trigger channel for modifying a property of the first trigger liquid, and / or a second liquid modifier contained or connected to the second control channel for modifying a property of the second control liquid, and wherein the distinct first and second absolute capillary pressures are at least partly attributable to the first liquid modifier and / or the second liquid modifier.

16. A microfluidic valve as claimed in any one of claim 4 to claim 15 wherein the valve comprises two or more control channel(s) fluidly connected to the void volume and to a corresponding withdrawal sub-circuit at the outlet of the control channel.

17. A microfluidic valve as claimed in claim 16 wherein the valve is configured to operate in one or more other states between the first state and the second state.

18. A microfluidic valve as claimed in claim 17 wherein the valve is operable to incrementally increase the flow of the primary liquid in the primary channel by sequentially driving flow of the control liquids out of the respective control channels via their corresponding withdrawal sub-circuits.

19. A microfluidic valve as claimed in any one of claim 1 to claim 18 wherein the valve comprises two or more trigger channel(s) fluidly connected to the void volume.

20. A microfluidic valve as claimed in claim 19 wherein the valve is operable to incrementally decrease the flow of the primary liquid in the primary channel by sequentially driving the flow of the trigger liquids into the respective trigger channel(s) toward the void volume.

21. A microfluidic valve as claimed in any one of claim 4 to claim 20 wherein the valve is configured such that, in the first state, a first absolute capillary pressure exhibited by the trigger liquid in the trigger channel is substantially greater than a third absolute capillary pressure exhibited by the primary liquid at the first port, when the trigger liquid and the primary liquid are contained in the trigger channel and the primary channel respectively.

22. A microfluidic valve as claimed in claim 21 wherein the trigger channel and the primary channel comprise distinct geometries, and the distinct first and third absolute capillary pressures are at least partially attributed to the distinct geometries of the trigger channel and the primary channel.

23. A microfluidic valve as claimed in claim 21 or claim 22 further comprising one or more channel networks connected to the trigger channel and / or the primary channel and the distinct first and third absolute capillary pressures are at least partially attributed to the one or more channel networks.

24. A microfluidic valve as claimed in any one of claim 21 to claim 23 further comprising one or more liquid modifiers connected or contained within the trigger channel and / or the primary channel, and wherein the distinct first and third absolute capillary pressures are at least partially attributed to the one or more liquid modifiers.

25. A microfluidic valve as claimed in any one of claim 4 to claim 24 wherein the valve is configured such that, in the first state, a second absolute capillary pressure exhibited by the control liquid in the control channel connected to the withdrawal sub-circuit is substantially greater than a third absolute capillary pressure exhibited by the primary liquid in the primary channel at the first port, when the control liquid and the primary liquid are contained in the control channel and the primary channel respectively.

26. A microfluidic valve as claimed in claim 25 wherein the control channel and the primary channel comprise distinct geometries, and the distinct second and third absolute capillary pressures are at least partially attributed to the distinct geometries of the second withdrawal channel and the primary channel.

27. A microfluidic valve as claimed in claim 25 or claim 26 further comprising one or more channel networks connected to the control channel and / or the primarychannel and the distinct second and third absolute capillary pressures are at least partially attributed to the one or more channel networks.

28. A microfluidic valve as claimed in any one of claim 25 to claim 27 further comprising one or more liquid modifiers connected or contained within the control channel and / or the primary channel, and wherein the distinct second and third absolute capillary pressures are at least partially attributed to the one or more liquid modifiers.

29. A microfluidic valve as claimed in any one of claim 1 to claim 29 wherein the valve is configured such that, during operation, a trigger liquid flowing into the trigger channel toward the void volume generates a first capillary force that causes an occluding air bubble to move beyond the first port into the primary channel, to inhibit or reduce a flow of primary liquid in the primary channel past the first port.

30. A microfluidic valve as claimed in claim 29 wherein the valve is configured such that, during operation, a control liquid flowing in a control channel away from the void volume generates a second capillary force that causes the occluding air bubble to retract from the primary channel toward the void volume to permit or increase the flow of liquid in the primary channel past the first port.

31. A microfluidic valve as claimed in any one of the preceding claims wherein the trigger channel comprises a cross-sectional area at or adjacent the void volume, that is substantially smaller than the cross-sectional area of another control channel at or adjacent the void volume.

32. A microfluidic valve as claimed in any one of the preceding claims wherein a first depth of the trigger channel is substantially smaller than a second depth of the other control channel.

33. A microfluidic valve as claimed in any one of the preceding claims wherein a flow resistance of the trigger channel is substantially greater than a flow resistance of the other control channel.

34. A microfluidic valve as claimed in any one of the preceding claims wherein a flow resistance of the trigger channel is substantially greater than a flow resistance of the primary channel.

35. A microfluidic valve as claimed in any one of the preceding claims wherein a flow resistance of a control channel connected to the withdrawal sub-circuit is substantially greater than a flow resistance of the primary channel.

36. A microfluidic valve as claimed in any one of the preceding claims wherein a geometry of the trigger channel at a fluid connection between the first trigger channel and the void volume is configured to inhibit liquid in the trigger channel from flowing into the void volume.

37. A microfluidic valve as claimed in any one of the preceding claims wherein a geometry of each control channel at a fluid connection between the control channel and the void volume is configured to inhibit liquid in the control channel from flowing into the void volume.

38. A microfluidic valve as claimed in any one of the preceding claims wherein a cross-sectional area, or a depth, or both, of the trigger channel at a fluid connection between the first trigger channel and the void volume is substantially equal to a cross-sectional area, or a depth, or both, of the trigger channel along an intermediate length of the channel.

39. A microfluidic valve as claimed in any one of the preceding claims wherein a cross-sectional area, or a depth, or both of each control channel at a fluid connection between the control channel and the void volume is substantially equal to a cross- sectional area, or a depth, or both, of the control channel along an intermediate length of the channel.

40. A microfluidic valve as claimed in any one of the preceding claims wherein the trigger channel comprises a substantially uniform cross-sectional area, or a substantially uniform depth, or both, along a substantial length between an inlet and an outlet of the trigger channel.

41. A microfluidic valve as claimed in any one of the preceding claims wherein the each control channel comprises a substantially uniform cross-sectional area, or a substantially uniform depth, or both, along a substantially length between an inlet and an outlet of the control channel.

42. A microfluidic valve as claimed in any one of the preceding claims wherein an inner peripheral wall of the void volume located at or adjacent the first port is angledat approximately 180 degrees or greater relative to an imaginary plane extending across the first port.

43. A microfluidic valve as claimed in any one of the preceding claims wherein an inner peripheral wall of the void volume located at or adjacent a fluid connection with the trigger channel is angled at approximately 180 degrees or greater relative to an imaginary plane extending across the fluid connection with the trigger channel.

44. A microfluidic valve as claimed in any one of the preceding claims wherein an inner peripheral wall of the void volume located at or adjacent a fluid connection with each control channel connected to the withdrawal sub-circuit is angled at about 180 degrees or more relative to an imaginary plane extending across the fluid connection with the control channel.

45. A microfluidic valve as claimed in any one of the preceding claims wherein an inlet of the trigger channel is fluidly connected to the primary channel downstream of the first port.

46. A microfluidic valve as claimed in any one of the preceding claims wherein an inlet of at least one control channel connected to the withdrawal sub-circuit is fluidly connected to the primary channel upstream of the first port.

47. A microfluidic valve as claimed in any one of the preceding claims further comprising a vent fluidly connected to at least one control channel that is connected to the withdrawal sub-circuit.

48. A microfluidic valve as claimed in claim 47, wherein the vent is fluidly connected at an intermediate position along a length of the respective control channel.

49. A microfluidic valve as claimed in any one of the preceding claims wherein the withdrawal sub-circuit is configured to trigger and drive the flow of control liquid through the outlet of each connected control channel.

50. A microfluidic valve as claimed in any one of claim 1 to claim 49 wherein the withdrawal subcircuit is configured to control the flow of withdrawal liquid contained within the connected control channel through the outlet of the control channel.

51. A microfluidic valve as claimed in claim 50 wherein the withdrawal subcircuit is configured to control a rate of flow of control liquid contained within the control channel through the outlet of the control channel.

52. A microfluidic valve as claimed in claim 50 or claim 51 wherein the withdrawal subcircuit comprises a capillary pump configured to control the flow of control liquid through the outlet of the connected control channel.

53. A microfluidic valve as claimed in claim 52 wherein the capillary pump comprises a channel for liquid to flow through the channel, and during operation, a fourth absolute capillary pressure attributed to the liquid flowing through the capillary channel generates a pressure gradient across the control liquid of the connected control channel sufficient to drive the flow of the control liquid through the outlet and away from the void volume.

54. A microfluidic valve as claimed in claim 53 wherein the capillary pump channel comprises a distinct geometry relative to the connected control channel geometry.

55. A microfluidic valve as claimed in claim 54, wherein the capillary pump channel comprises a cross-sectional area that is substantially smaller than the cross- sectional area of the connected control channel.

56. A microfluidic valve as claimed in either one of claim 53 or claim 54 wherein a depth of the capillary pump channel is substantially smaller than a depth of the connected control channel.

57. A microfluidic valve as claimed in any one of claim 1 to claim 56 wherein the withdrawal subcircuit is configured to trigger the flow of control liquid through the outlet of the connected control channel.

58. A microfluidic valve as claimed in claim 57 wherein the withdrawal subcircuit comprises a withdrawal trigger channel fluidly connected to the outlet of the connected control channel, and wherein a flow of liquid through the withdrawal trigger channel triggers the flow of control liquid through the outlet of the connected control channel.

59. A microfluidic valve as claimed in claim 58 wherein the withdrawal subcircuit comprises a capillary valve fluidly connected between the outlet of the connected control channel and the withdrawal trigger channel of the withdrawal subcircuit.

60. A microfluidic valve as claimed in claim 59 wherein the capillary valve is configured to inhibit flow of control liquid through the outlet of the connected control channel in a closed operative state of the capillary valve, and permit the flow of control liquid through the outlet of the connected control channel in an open operative state of the capillary valve.

61. A microfluid valve as claimed in claim 60 wherein the capillary valve is a capillary trigger valve configured to trigger from the closed operative state into the open operative state when a liquid flows through the withdrawal trigger channel past the outlet of the connected control channel.

62. A microfluidic valve as claimed in any one of claim 57 to claim 61 wherein an inlet of the withdrawal trigger channel comprises an inlet for connected with a second liquid source upstream of the connection with the outlet of the respective control channel.

63. A microfluidic valve as claimed in any one of claim 1 to claim 62 wherein the withdrawal subcircuit comprises a first capillary pump fluidly connected to an outlet of the connected control channel.

64. A microfluidic valve as claimed in claim 63 wherein the first capillary pump comprises a flow path connected to a vent, chamber or reservoir downstream of the outlet of the connected control channel.

65. A microfluidic valve as claimed in either one of claim 63 to claim 64, when dependent on any one of claim 58 to claim 62, wherein the first capillary pump of the withdrawal sub-circuit is fluidly connected to the withdrawal trigger channel downstream of the connection with the outlet of the connected control channel.

66. A microfluidic device comprising: a main channel for conveying a primary liquid, and the microfluidic valve of any one of the preceding claims ("first microfluidic valve"), wherein the primary channel of the first microfluidic valve is connected in series to the main channel.

67. The microfluidic device of clause 66 wherein an inlet of the control channel of the first microfluidic valve is fluidly connected to a fill subcircuit configured to controlfilling of a respective control channel connected to the withdrawal sub-circuit with a predetermined volume of control liquid.

68. The microfluidic device of clause 67 wherein the fill subcircuit is configured to substantially fluidly isolate the inlet of the control channel connected to the withdrawal sub-circuit from the control channel when the predetermined volume of control liquid is driven into the control channel to inhibit further flow of control liquid into the control channel.

69. The microfluidic device of clause 67 or claim 68 wherein an inlet of the fill subcircuit is fluidly connected to a first fluid source.

70. The microfluidic device of any one of clause 67 to claim 69 wherein an inlet of the fill subcircuit is fluidly connected to the main channel upstream of the first port of the first microfluidic valve.

71. The microfluidic device of any one of clause 67 to claim 70 wherein an outlet of the fill subcircuit is fluidly connected to the inlet of the control channel connected to the withdrawal sub-circuit of the first microfluidic valve.

72. The microfluidic device of any one of clause 67 to claim 71 wherein the fill subcircuit further comprises a second microfluidic valve fluidly connected between an inlet and an outlet of the fill subcircuit, to inhibit flow of liquid into an inlet of the control channel when a predetermined volume of control liquid flows into the control channel via the inlet.

73. The microfluidic device of any one of clause 66 to claim 72 wherein the withdrawal subcircuit further comprises a third microfluidic valve fluidly connected to the main capillary channel upstream of the connection with the outlet of the connected control channel of the first microfluidic valve.

74. The microfluidic device of clause 73 wherein the third microfluidic valve is configured to permit the flow of liquid through the withdrawal trigger channel past the connection with the outlet of the connected control channel in an open operative state, and inhibit the flow of liquid through the main capillary channel past the connection with the outlet of the connected control channel in a closed operative state.

75. The microfluidic device of clause 74 wherein the third microfluidic valve is configured to trigger from the open operative state to the closed operative state when predetermined volume of liquid flows through the third microfluidic valve.

76. The microfluidic device of any one of clause 66 to claim 75 wherein the valve comprises multiple control channels and multiple withdrawal sub-circuits connected to each of the respective control channel.

77. The microfluidic device of clause 76 wherein the device comprises multiple fill subcircuits fluidly connected to each of the control channels connected to withdrawal sub-circuits.

78. The microfluidic device of any one of clause 66 to claim 77 further comprising a flow path connected in series to the main channel upstream of the first port of the first microfluidic valve.

79. The microfluidic device of clause 78 wherein the flow path is connected in series to the main channel downstream of a connection from the main channel to an inlet of the control channel connected to the withdrawal sub-circuit of the first microfluidic valve.

80. The microfluidic device of any one of clause 66 to claim 79 wherein the main channel is fluidly connected to a second capillary pump downstream the first port of the first microfluidic valve.

81. The microfluidic device of clause 80 wherein the second capillary pump comprises a flow path fluidly connected to a vent, chamber or reservoir.

82. The microfluidic device of any one of clause 66 to claim 81 wherein the trigger channel of the first microfluidic valve is fluidly connected to the main channel downstream of the first port.

83. A method for operating a microfluidic valve as claimed in any one of claim 1 to claim 65 comprising the steps of: driving, through capillary action, a volume of trigger liquid through the trigger channel toward the void volume to generate a first capillary force that causes a meniscus restrained at the first port to expand from the first port into the primary channel, to inhibit or reduce a flow of primary liquid in the primary channel.

84. A method as claimed in claim 83 further comprising the step of triggering a flow of the volume of control liquid contained in the control channel connected to withdrawal sub-circuit away from the void volume to generate a second capillary force that causes the meniscus to retract from the primary channel toward the void volume, to re-permit or increase the flow of primary liquid in the primary channel.

85. A method as claimed in claim 84 wherein the step of triggering the flow of the volume of control liquid away from the void volume comprises triggering flow of the volume of control liquid through an outlet of the respective control channel.

86. A method as claimed in claim 85 wherein the flow of the volume of control liquid through the outlet is triggered via a flow of liquid through a capillary channel of the withdrawal sub-circuit, fluidly connected to the outlet.

87. A method as claimed in any one of claim 83 to claim 86 comprising the step of driving, through capillary action, a flow of control liquid into the control channel connected to the withdrawal sub-circuit.

88. A method as claimed in claim 87 wherein microfluidic device comprises a single control channel and driving the control liquid into the control channel connected to the withdrawal sub-circuit occurs by driving the trigger liquid into the trigger channel.

89. A method as claimed in claim 87 wherein microfluidic device comprises multiple control channels and driving the control liquid into the control channel connected to the withdrawal sub-circuit occurs prior to driving the trigger liquid into the trigger channel.

90. A method as claimed in any one of claim 87 to claim 88 wherein the step of driving the control liquid into the control channel comprises retaining a volume of the control liquid in the control channel.

91. A method as claimed in any one of claim 87 to claim 90 wherein the step of driving the control liquid into the control channel connected to the withdrawal subcircuit comprises directing a flow of primary liquid from the primary channel into the control channel.

92. A method as claimed in claim 91 wherein the step of driving the control liquid into the control channel connected to the withdrawal sub-circuit comprises directing a flow of primary liquid from the primary channel upstream of the first port.

93. A method as claimed in any one of claim 87 to claim 92 wherein the step of driving the control liquid into the control channel connected to the withdrawal subcircuit comprises terminating a flow of control liquid into the control channel when a predetermined volume of liquid is drawn into the control channel.

94. A method as claimed in any one of claim 83 to claim 93 wherein the step of driving the trigger liquid into the trigger channel comprises directly a flow of the primary liquid into the trigger channel.

95. A method as claimed in claim 94 wherein the step of driving the trigger liquid into the trigger channel comprises directly a flow of the primary liquid downstream of the first port.

96. A method as claimed in any one of claim 83 to claim 95 further comprising the step of generating flow of primary liquid through the primary channel using a capillary pump.

97. A method as claimed in any one of claim 83 to claim 96 further comprising driving control liquid into multiple control channels each fluidly connected to a respective withdrawal sub-circuit.

98. A method as claimed in claim 97 wherein the method further comprises sequentially withdrawing control liquid from the multiple control channels, away from the void volume, to cause a meniscus to incrementally retract from the primary channel toward the void volume, and incrementally re-permit or increase the flow of primary liquid in the primary channel.

99. A microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that ameniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; a first capillary trigger channel ("first trigger channel") fluidly connected to the void volume, and configured to convey a trigger liquid toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; a second capillary withdrawal channel ("second withdrawal channel") fluidly connected to the void volume and configured to convey a withdrawal liquid away from the void volume to substantially permit or increase a flow of the primary liquid through the primary channel.

100. A microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; a capillary trigger channel fluidly connected to the void volume and configured to convey first trigger liquid toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; one or more second capillary withdrawal channel(s) ("second withdrawal channel(s)") fluidly connected to the void volume and configured to convey second withdrawal liquid(s) away from the void volume to substantially increase or permit a flow of the primary liquid through the primary channel.

101. A microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel;multiple capillary control channels, each capillary control channel being separately fluidly connected to the void volume and having inlet for receiving a corresponding control liquid and conveying the control liquid toward the void volume via capillary action, wherein at least one of the capillary control channel(s) is configured as a trigger channel that drives a corresponding control liquid ("trigger liquid") toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel; and a withdrawal subcircuit for each of a plurality of the control channels, each withdrawal subcircuit being fluidly connected to an outlet of the respective capillary control channel, to drive the flow of the corresponding control liquid received within the respective control channel(s) through the corresponding outlet and away from the void volume, thereby substantially increasing the flow of the primary liquid through the primary channel.

102. A microfluid valve comprising: a primary capillary channel ("primary channel") for conveying a primary liquid; a void volume having a first port connecting the void volume to the primary channel, the first port having a geometry that inhibits the primary liquid in the primary channel from flowing through the first port into the void volume such that a meniscus of the primary liquid is restrained at the first port when the primary liquid is flowing through the primary channel; at least one capillary control channel fluidly connected to the void volume, and configured to convey a control liquid toward the void volume to substantially reduce or inhibit a flow of the primary liquid through the primary channel, each capillary control channel having an inlet for receiving a flow of a corresponding control liquid into the channel; and a withdrawal subcircuit fluidly connected to an outlet of at least one of the control channel(s) and configured to trigger and drive the flow of the control liquid contained within the control channel through the outlet of the control channel to substantially increase or re-permit the flow of the primary liquid through the primary channel.

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