EP4735175A1

EP4735175A1 - Timed valve

Info

Publication number: EP4735175A1
Application number: EP24735654.6A
Authority: EP
Inventors: Jeroen Lammertyn; Dries VLOEMANS; Francesco DAL DOSSO
Original assignee: Katholieke Universiteit Leuven
Current assignee: Katholieke Universiteit Leuven
Priority date: 2023-06-29
Filing date: 2024-06-28
Publication date: 2026-05-06
Also published as: WO2025003467A1

Abstract

The present invention relates to a microfluidic device comprising (i) a vent [104], which opens upon dissolution of an air-impermeable and water-soluble membrane [102] and (ii) means [105] for increasing hydraulic resistance to liquid flow located upstream of said vent [104]. The invention further relates to use of the device of the invention to partition a volume of liquid and to a method to partition a volume of liquid.

Description

TIMED VALVE

FIELD OF THE INVENTION

The present invention relates to a microfluidic device comprising a vent, which opens upon dissolution of an air-impermeable and water-soluble membrane. The invention further relates to the use of the device of the invention for liquid partitioning.

BACKGROUND OF THE INVENTION

When displacing liquid within a microfluidic device, it is often necessary and desirable to isolate fluidically a subset of the liquid from a larger volume of liquid in a manner where the ability to displace the isolated liquid independently from the larger volume is retained without requiring an additional user intervention (e.g., transfer to another independent fluid container). This need is further illustrated by current practice in blood sampling. Currently, the blood collection step and the further manipulation and analysis of the sample are decoupled and require user intervention/actuation at several time points. Hereto, the sample first has to be collected from the patient after which it is transferred to the device (i.e., cartridge, cassette, paper strip) which is then used to perform further downstream liquid processes such as storage, sample preparation or (bio)chemical analysis. When the same device is used to both collect the sample (e.g., via microneedles) directly from a living organism (e.g., human body, animal or plant) and further process it downstream in the system, it is necessary to decouple the extracted sample liquid from the unlimited sample source (e.g., represented by the body bloodstream) in the living organism. Another relevant example is where it is desired to decouple the filtered and unfiltered liquid sample fractions (e.g., plasma and blood cell fractions during plasmapheresis) to avoid contamination. To achieve this decoupling, various types of microfluidic valving methods such as mechanical valves with moving elements, valving via heating and the like exist. However, most of these valves are very complex which make them too expensive for usage in disposable microfluidic systems and/or require user intervention to decouple fluidically the isolated volume of liquid from the larger liquid volume it is isolated from.

US2016/279634 discloses a microfluidic device comprising an inlet and a capillary channel, i.e., fluid conduit, in connection therewith. A dissolvable valve is provided comprising a dissolvable membrane having a first side oriented towards the capillary channel, and capillary means connected to the second side of the dissolvable membrane such that when the membrane is dissolved by the liquid, liquid is transported through the valve to the second side of the membrane by capillary action.

AU2014280043 discloses a microfluidic device comprising a sacrificial valve, e.g., water-soluble membrane, whose opening is triggered by the opening of a second valve, causing a retraction of a fluid spacer thus bringing liquid into contact with the dissolvable valve membrane.

There is thus a need for a valving system that would allow to combine in a single step that does not require user actuation, the isolation of a smaller volume of liquid from a larger volume in a manner allowing further manipulation of the isolated liquid (e.g., by aspiration force).

SUMMARY

The present invention relates to a microfluidic device comprising, a. an inlet for liquid; b. a fluid conduit in fluid connection with the inlet; c. a first air-impermeable and water-soluble membrane that (i) is closing a first opening in a wall of the fluid conduit, (ii) is positioned to dissolve upon circulation of liquid through the fluid conduit, and (iii) has a first side oriented toward an inside of the fluid conduit; d. a vent that is in fluid connection with the other side of the first air-impermeable and water-soluble membrane and wherein said vent comprises means to prevent liquid flow through the first opening, while allowing circulation of air therethrough; e. means for increasing hydraulic resistance to liquid flow, located downstream of the inlet and upstream of the first opening; and, f. an outlet, located downstream of the opening, and in fluid connection therewith.

In one embodiment, the device of the invention further comprises, a pump, downstream of, and in fluid connection with, the outlet..

In one embodiment, the microfluidic device comprises, a. an inlet for liquid; b. a fluid conduit in fluid connection with the inlet; c. a first air-impermeable and water-soluble membrane that (i) is closing a first opening in the wall of the fluid conduit, (ii) is positioned to dissolve upon circulation of liquid through the fluid conduit, and (iii) has a first side oriented toward the inside of the fluid conduit; d. a vent that is in fluid connection with the other side of the first air-impermeable and water-soluble membrane so that when the first membrane is opened by dissolution in liquid flowing through the fluid conduit, air can flow through the vent inside the fluid conduit and wherein said vent comprises means to prevent liquid flow through the first opening, while allowing circulation of air therethrough; e. means for increasing hydraulic resistance to liquid flow, located downstream of the inlet and upstream of the first opening, and configured so that when the first membrane is open, the intake of air from the vent can overcome the surface tension of the liquid passing through the fluid conduit and thereby partition said liquid; and, f. a pump configured to draw in liquid through the fluid conduit.

In one embodiment, said walls of the fluid conduit define said inside.

In one embodiment, the means for increasing hydraulic resistance to liquid flow comprises, a geometric flow resistance, a porous filtration element, a thermal expansion valve, a hydrogel swelling valve, a hydrophobic flow resistance, a plunger valve, a rotating valve, a pressure valve or a combination thereof.

In one embodiment, the means for increasing hydraulic resistance to liquid flow comprise, or consist of, a geometric flow resistance, a porous filtration element, a thermal expansion valve, a hydrogel swelling valve, a hydrophobic flow resistance or a combination thereof.

In one embodiment, the means for increasing hydraulic resistance to liquid flow, comprise a filter. In one embodiment, said filter is a plasma separation membrane.

In one embodiment, the means for increasing hydraulic resistance to liquid flow, comprise a single, or an array of, hollow microneedle(s). In one embodiment, the means to prevent liquid flow through the first opening, while allowing circulation of air therethrough, comprise, or consists of, hydrophobic porous material.

In one embodiment, the means for increasing hydraulic resistance to liquid flow comprise: a. a first chamber in fluid connection with the inlet and with the fluid conduit; b. a second air-impermeable and water-soluble membrane that (i) is closing an opening in a wall of the first chamber, (ii) is positioned to dissolve upon circulation of liquid through the first chamber, and (iii) has a first side oriented toward an inside of the first chamber; c. a second chamber that (i) is filled with a hydrophilic porous material, (ii) is in fluid connection with the other side of the second membrane and, (iii) comprises a trapped volume of gas in the pore of the hydrophilic porous material, and, d. a geometric restriction in the fluid connections upstream and downstream of the first chamber.

Preferably, the dissolution speed (e.g., in water) of said second membrane is adjusted to avoid fluid communication between the first chamber and second chamber before opening of the first membrane.

In one embodiment, the means for increasing hydraulic resistance to liquid flow comprise: a. a first chamber in fluid connection with the inlet [106] and with the fluid conduit; b. a second air-impermeable and water-soluble membrane that (i) is closing an opening in a wall of the first chamber, (ii) is positioned to dissolve upon circulation of liquid through the first chamber, and (iii) has a first side oriented toward an inside of the first chamber; c. a second chamber that (i) is filled with a hydrophilic porous material, (ii) is in fluid connection with the other side of the second membrane so that when the second membrane is opened by dissolution in liquid flowing through the first chamber, part of that liquid is absorbed by the hydrophilic porous material, expelling the trapped volume of gas in the pores of the hydrophilic porous material towards the first chamber [114] resulting the formation of a gas bubble therein; and, d. a geometric restriction in the fluid connections upstream and downstream of the first chamber configured to trap into said first chamber the gas bubble formed by capillary filling of the second chamber after opening of the second membrane; and wherein the dissolution speed of said second membrane is adjusted to avoid fluid communication between the first chamber and second chamber before opening of the first membrane.

In one embodiment, the pump is a capillary pump.

The present invention further relates to the use of the microfluidic device of the invention, to partition a volume of aqueous liquid.

The invention also relates to a method to partition a volume of aqueous liquid comprising the steps of a. drawing in aqueous liquid through the fluid conduit of the microfluidic device according to the invention; and, b. partitioning said aqueous liquid.

In one embodiment of the method of the invention the step of partitioning the aqueous liquid does not require any user intervention to open and/or close valves nor the use of valves fitted with actuators.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1. panel A is a drawing of an exemplary embodiment of the fluid conduit [101], Panel B is a drawing of an exemplary embodiment of the microfluidic device.

FIG. 2 illustrates fluid flows in exemplary embodiments of the device and fluid conduit shown in FIG. 1 during operation, before (panels A, i and ii) and after (panels B, iii and iv) the opening of the membrane [102], Solid arrows represent liquid flows. Dashed arrows represent air flows. Solid T- shaped lines shows blocking of fluid flows. References to individual elements of the device and fluid conduit are identical to that in FIG. 1.

FIG. 3. Panels i to vii are drawings illustrating fluid flows in an exemplary embodiment of a device and fluid conduit comprising a plasma separation membrane [107] during operation. Solid arrows represent liquid flows. Dashed arrows represent air flows. Solid T-shaped lines shows blocking of fluid flows.

FIG. 4. Panels i to v are drawings illustrating fluid flows in an exemplary embodiment of a device and fluid conduit wherein an array of hollow microneedles [111] is used. Solid arrows represent liquid flows. Dashed arrows represent air flows. Solid T-shaped lines shows blocking of fluid flows.

FIG. 5. Panels i to ix are drawings illustrating fluid flows in an exemplary embodiment of a device and fluid conduit wherein the second valve of the invention is used as a mean [105] for increasing hydraulic resistance to liquid flow during operation. Solid arrows represent liquid flows. Dashed arrows represent air flows. Solid T-shaped lines shows blocking of fluid flows.

DETAILED DESCRIPTION

Here the inventors have developed a first valve comprising a dissolvable membrane separating a liquid conduit from a vent. The first valve, when incorporated within a microfluidic device comprising, upstream of said valve, means for increasing hydraulic resistance to liquid flow, allows to split off a discrete liquid volume from an upstream liquid source.

The present invention relates to a microfluidic device. The microfluidic device comprises a fluid conduit [101] with an opening [112] in the wall of said fluid conduit [101], The fluid conduit [101] may comprise walls that define an inner compartment or inside. In one embodiment, the fluid conduit [101] is selected from the group consisting of a channel, a duct, a chamber and combinations thereof. The fluid conduit (e.g., a chamber, a channel and/or a duct) comprises two parts defined by the location of the opening [112], the upstream part [101a] and the downstream part [101b], In one embodiment, the microfluidic device comprises a vent [104], In one embodiment, the vent [104] is in fluid connection with the opening [112], When the opening [112] is open, both the upstream part [101a] and the downstream part [101b] of the fluid conduit [112] are connected via the vent [104] to the outside environment. In other words, when the opening [112] is open, air can circulate between the inside of the fluid conduit [101] and the outside environment via the opening [112] and the vent [104], The inside of the fluid conduit [101] and the vent [104] are separated by an air-impermeable water-dissolvable membrane [102], In one embodiment, the air-impermeable water-dissolvable membrane [102] is closing the opening [112] in the wall of the fluid conduit [101], In one embodiment, the air-impermeable water-dissolvable membrane [102] is positioned to dissolve upon circulation of (aqueous) liquid through the fluid conduit [101], In one embodiment, the air- impermeable water-dissolvable membrane [102] has a first side oriented toward the inside of the fluid conduit [101], In one embodiment, the other side of the membrane [102] is connected to the outside environment of the device through the vent [104], In other words, the vent [104] is in fluid connection with the other side of the air-impermeable water-dissolvable membrane [102], When the first membrane [102] is opened by dissolution in aqueous liquid flowing through the fluid conduit, air can flow through the vent [104] inside the fluid conduit. In one embodiment, the vent [104] comprises, between the outside environment and the membrane [102], (e.g., flanking the side of the membrane [102] oriented toward the vent [104]) means to prevent liquid outflow through the opening [112], while allowing circulation of air therethrough, such as an air-permeable, hydrophobic porous material [103], In one embodiment said means to prevent liquid outflow through the opening [112], while allowing circulation of air therethrough is an air-permeable liquid barrier. Example of air-permeable liquid barrier that may be used in the context of the invention include, without being limited to, porous material configured to prevent entry of liquid therein, geometric restriction, surface coating and combinations thereof. FIG. 1A illustrates an exemplary embodiment of such a fluid conduit.

The device further comprises, upstream of the opening [112] and/or in fluid connection therewith, means [105] for increasing hydraulic resistance to liquid flow and an inlet [106] for liquid. In one embodiment, the means [105] for increasing hydraulic resistance to liquid flow are located between the inlet [106] and the opening [112], In one embodiment, the device comprises downstream of the opening and/or in fluid connection therewith, an outlet [119], Downstream of the opening [112], the fluid conduit [101] may be connected via the outlet [119], to further means for liquid processing (e.g., volume metering, sample dilution, sample incubation, sample splitting, readout, among many more) and/or to a pump [108], acting as driving source for the liquid manipulation inside the microfluidic device. In one embodiment, the pump [108] is downstream of and/or in fluid connection with the outlet. In one embodiment, the pump is configured to draw in liquid through the fluid conduit. This pump [108] can either be active (e.g., peristaltic pump, pressure pump, syringe pump, ...) or, preferably, passive in nature (e.g., capillary pump). FIG. IB illustrates an exemplary embodiment of such a device.

The terms “upstream” and “downstream” are used herein in reference to position along the liquid flow from the inlet to towards the outlet of the microfluidic device of the invention. Herein, A being “upstream” with respect to B typically means that A is, along the liquid flow, closer to the inlet than B. A being “downstream” with respect to B typically means that A is, along the liquid flow, closer to the outlet than B. Before dissolution of the membrane [102], liquid flows from the upstream part of the fluid conduit [101a] towards and in the downstream part of the fluid conduit [101b] when a downstream negative pressure gradient (APpump) is applied (e.g., using the pump [108]). During this process, the membrane [102] dissolves into the sample liquid [109], The dissolution time of the membrane [102] can be tuned by adjusting the thickness (e.g., a couple of pm to several hundreds of pm), material type (e.g., polyvinyl alcohol) and composition (e.g., mixture percentage of used chemicals, molecular weight of used chemicals) of the membrane. After opening of the membrane by dissolution, the intake of air through the vent [104], the opening [112] and subsequently, the downstream part of the fluid conduit [101b] splits the sample liquid into an upstream [109a] and downstream [109b] fraction. To allow the entrance of air into the fluid conduit [101] and consequently break up the liquid flow, the hydraulic flow resistance Rc generated by the means [105] for increasing hydraulic resistance to liquid flow in the upstream part of the microfluidic device, must be large enough to force air flow being pulled from the ambient environment through the vent [104], the opening [112] and then into the fluid conduit [101], and thus overcome the liquid cohesion originating from the surface tension of the sample liquid [109] in the fluid conduit [101], More specifically, the pressure drop ( c) generated by the means [105] for increasing the hydraulic resistance to liquid flow in the upstream part of the microfluidic device, must be large enough to force the intake of air from the ambient environment through the vent [104], the opening [112] and then into the fluid conduit [101], and thus overcome the liquid cohesion originating from the surface tension (APv) of the sample liquid [109] in the fluid conduit [101], jzis equal to the pressure difference over the liquid-air interface of the sample liquid [109] at the opening [112] in the main conduit and may be calculated using the Young- Laplace equation (Eq. (1)) below: where, APv, is the pressure difference over the liquid surface, y, the surface tension of the liquid and R_x and R_y, the radii of curvature in each of the axes that are parallel to the liquid surface.

The pressure drop (APc) generated by the means [105] for increasing the hydraulic resistance to liquid flow in the upstream part of the microfluidic network can be calculated using the electronic analogy for fluidic systems (Eq. (2)): where, Rc, resembles the hydraulic resistance to liquid flow for a given flow rate, Q, of the sample liquid [109] through the microfluidic channel. It is within the reach of the skilled artisan to tune (e.g., by changing the channel geometry, surface properties, etc.) the means [105] for increasing the hydraulic resistance so that APc > APv- Consequently, upon opening of the membrane [102] by dissolution, the intake of air from the ambient environment is favored over the intake of additional liquid from the upstream microfluidic network. This results in the splitting of the sample liquid [109] in the main fluidic conduit [101] into an upstream [109a] and downstream liquid fraction [109b], Once separated, the downstream sample liquid fraction [109b] can be further manipulated in the downstream part of the microfluidic device, where depending on the application, additional fluid operations may be performed (e.g., volume metering, sample dilution, sample incubation, sample splitting, readout, among many more). This is particularly interesting in applications where it is desired to separate a discrete sample volume (e.g., blood, interstitial fluid) from a large or unlimited (continuous) sample source (i.e., human body) and/or where it is desired to fluidically decouple the downstream microfluidic system from the upstream part of the microfluidic network connected to a sample source. Applications of interest can be (micro-) sampling and point-of-care diagnostics. FIG. 2A-B illustrates an exemplary embodiment of a microfluidic device before (panel A) and after (panel B) dissolution of the membrane [102],

In one embodiment, the microfluidic device comprises, a. an inlet [106] for liquid; b. a fluid conduit [101] in fluid connection with the inlet [106]; c. a first air-impermeable and water-soluble membrane [102] that (i) is closing a first opening [112] in the wall of the fluid conduit [101], (ii) is positioned to dissolve upon circulation of liquid through the fluid conduit [101], and (iii) has a first side oriented toward the inside of the fluid conduit [101]; d. a vent [104] that is in fluid connection with the other side of the first membrane [102] so that when the first membrane [102] is opened by dissolution in liquid flowing through the fluid conduit [101], air can flow through the vent [104] inside the fluid conduit [101] and wherein said vent [104] comprises means to prevent liquid flow through the first opening [112], while allowing circulation of air therethrough; e. means [105] for increasing hydraulic resistance to liquid flow, located downstream of the inlet [106] and upstream of the first opening [112], and configured so that when the first membrane [102] is open, the intake of air from the vent [104] can overcome the surface tension of the liquid passing through the fluid conduit [101] and thereby partition said liquid; and, f. a pump [108] configured to draw in liquid through the fluid conduit [101],

In one embodiment, the microfluidic device comprises a. an inlet [106] for liquid; b. a fluid conduit [101] in fluid connection with the inlet [106], preferably a fluid conduit [101] in fluid connection with the inlet [106] and wherein said fluid conduit [101] comprises walls that define an inside; c. a first air-impermeable and water-soluble membrane [102] that (i) is closing a first opening [112] in the wall of the fluid conduit [101], (ii) is positioned to dissolve upon circulation of liquid through the fluid conduit [101], and (iii) has a first side oriented toward the inside of the fluid conduit [101]; d. a vent [104] that is in fluid connection with the other side of the first air-impermeable and water-soluble membrane [102] and wherein said vent [104] comprises means to prevent liquid flow through the first opening [112], while allowing circulation of air therethrough; e. means [105] for increasing hydraulic resistance to liquid flow, located downstream of the inlet [106] and upstream of the first opening [112]; f. an outlet [119], located downstream of the opening [112] and in fluid connection therewith; and, g. a pump [108], downstream of, and in fluid connection with, the outlet [119], Preferably, the pump is configured to draw in liquid through the fluid conduit [101],

A detailed description of the different steps of the working principle are illustrated using an exemplary embodiment of the microfluidic device in FIG. 2 i to iv: (i) Sample liquid [109] located in the upstream part is displaced (e.g., by aspiration using a pump) into the fluid conduit [101], Upon filling of the fluid conduit [101] with sample liquid [109], the dissolvable membrane [102] begins to reconstitute in the sample liquid [109],

(ii) As long as the dissolvable membrane [102] forms a physical barrier between the fluid conduit [101] and the vent [104], the sample liquid [109] will be able to flow cohesively towards and in the downstream part of the fluid conduit [101b],

(iii) From the moment the dissolvable membrane [102] is open, the means to prevent liquid flow through the opening [112], while allowing circulation of air therethrough (such as a liquid barrier formed by air-permeable, hydrophobic porous material [103]) prevents outflow of the sample liquid [109] outside of the microfluidic device through the vent [104], The opening of the membrane [102] establishes a gas-permeable fluidic connection between the fluid conduit [101] and the vent [104] and the hydraulic resistance generated by the means [105] for increasing hydraulic resistance to liquid flow in the upstream part of the microfluidic device forces the intake of air from the vent [104] into the fluid conduit [101], In particular, the introduced flow resistance allows to break up the cohesive forces (i.e., surface tension) that keep the sample liquid [109] in the fluid conduit [101] together. As a consequence, the sample liquid [109] is separated in two liquid plugs.

(iv) From this moment, it is fluidically favorable (i.e., path with least resistance) to pull in air from the environment via the vent [104] instead of pulling sample liquid [109] from the part of the microfluidic device upstream of the opening [112], Consequently, the sample liquid in the downstream part of the fluid conduit [101b] can be further manipulated, independently of liquid [109a] remaining upstream of the opening [112],

The volume of sample liquid [109] entering the downstream part of the fluid conduit [101b] before splitting can be adjusted by tuning the dissolution speed (i.e., by adjusting film thickness, material type and composition) of the membrane [102] and/or the volumetric flow rate at which the sample liquid [109] is manipulated through the fluidic conduit [101],

The microfluidic device of the invention comprises means [105] for increasing hydraulic resistance to liquid flow, located upstream of the opening [112], In one embodiment, said means [105] for increasing hydraulic resistance to liquid flow are configured so that when the membrane [102] is open, the intake of air from the vent [104] can overcome the surface tension of the liquid passing through the fluid conduit [101] and thereby partition said liquid. In other words, the means [105] for increasing hydraulic resistance to liquid flow is configured so as to generate upstream of the opening [112], a pressure drop ( Pc) superior to the surface tension (zl/Y) of the liquid [109, 110b] in the fluid conduit [101],

Examples of means [105] for increasing hydraulic resistance to liquid flow include, without being limited to, plunger valves, rotating valves, pressure valves and thermal expansion valves, hydrogel swelling valves, geometric flow resistors (i.e., channel restriction, microneedles), hydrophobic flow resistors and porous filtration elements (i.e., filter). As explained hereinabove, it is within the reach of the skilled artisan to select and tune the means [105] for increasing the hydraulic flow resistance accounting notably for the properties (e.g., viscosity and surface tension) of the used liquid and flow behavior (e.g., flow rate) inside the microfluidic device.

In one embodiment, the means [105] for increasing hydraulic resistance to liquid flow comprise, or consist of, a geometric flow resistance (e.g., hollow microneedles), a porous filtration element (e.g., a plasma separation membrane), a thermal expansion valve, a hydrogel swelling valve, a hydrophobic flow resistance, a plunger valve, a rotating valve, a pressure valve or a combination thereof. In one embodiment, the means [105] for increasing hydraulic resistance to liquid flow comprise, or consist of, a geometric flow resistance (e.g., hollow microneedles), a porous filtration element (e.g., a plasma separation membrane), a thermal expansion valve, a hydrogel swelling valve, a hydrophobic flow resistance or a combination thereof.

In one embodiment, the means [105] for increasing hydraulic resistance to liquid flow comprise, or consist of, a filter. In one embodiment, said filter is a plasma separation membrane [107], In one embodiment, wherein a plasma separation membrane is used, the dissolution speed of the membrane [102] is configured to avoid the entry of blood cells in the downstream part of the fluid conduit [101b],

Examples of plasma separation membrane include without being limited to Whatman Fusion 5, Whatman MFI, Vivid™ GF, Vivid™ GX, Vivid™ GR.

In one embodiment, the means [105] for increasing hydraulic resistance to liquid flow, comprise, or consist of, a single, or an array of, hollow microneedles [111], In this embodiment, the inlet [106] is the opening(s) of the single, or array of, hollow microneedle(s) [111].

The present invention also relates to a second valve that may be used in the microfluidic device of the invention as a mean [105] for increasing hydraulic resistance to liquid flow. In one embodiment, the second valve comprises, a. first chamber [114] comprising an inlet for liquid and an outlet for liquid; b. an air-impermeable and water-soluble membrane [118] that (i) is closing an opening [115] in the wall of the first chamber [114], (ii) is positioned to dissolve upon circulation of liquid through the first chamber [114], and (iii) has a first side oriented toward the inside of the first chamber [114]; c. a second chamber [116] that (i) is filled with a hydrophilic porous material [117], (ii) is in fluid connection with the other side of the second membrane [118] and/or (iii) comprises a trapped volume of gas in the pores of the hydrophilic porous material; and, d. a geometric restriction at the inlet and at the outlet of the first chamber [114],

In one embodiment, the first chamber [114] comprises walls defining an inside.

In one embodiment, the second chamber is configured so that when the second membrane [118] is opened by dissolution in liquid flowing through the first chamber [114], part of the liquid is absorbed by the hydrophilic porous material [117], The trapped volume of gas in the pores of the hydrophilic porous material [117] is thereby expelled toward the first chamber [114], resulting in the formation of a gas bubble therein.

In one embodiment, the geometric restriction at the inlet and at the outlet of the first chamber [114] are configured to trap into said first chamber [114] the gas volume, or bubble, formed by capillary filling of the second chamber [116] after opening of the second air-impermeable and water-soluble membrane [118],

In one embodiment, the dissolution speed of the second air-impermeable and water-soluble membrane [118] is adjusted to avoid fluid communication between the first chamber [114] and second chamber [116] before opening of the first air-impermeable and water-soluble membrane [102],

FIG. 5i illustrates an exemplary embodiment of a microfluidic device comprising such a second valve. It is to be understood that the second chamber [116] is configured to trap gas in the pores of the hydrophilic porous material [117] before the opening of the second membrane [118], In other words, the second chamber [116] comprises a trapped volume of gas in the pores of the hydrophilic porous material [117],

When the second valve of the invention is used as a mean [105] for increasing hydraulic resistance to liquid flow in the microfluidic device of the invention, the dissolution speed of the membrane [118] is adjusted to avoid fluid communication between the first chamber [114] and second chamber [116] before air circulation between the vent [104] and the fluid conduit [101] becomes possible (i.e. opening of the first membrane [102]).

The volume of gas trapped in the hydrophilic porous material [117] is configured to form in the first chamber [114] a gas bubble sufficiently large to be trapped by the geometric restrictions at the inlet and outlet of the first chamber [114],

Examples of hydrophilic porous material that may be used in the context of the invention include without being limited to, (nitro)cellulose paper, glass-fiber paper and capillary microstructures (e.g., array of micropillars).

The microfluidic device of the invention comprises means to prevent liquid flow through the opening [112], while allowing circulation of air therethrough.

In one embodiment, the means to prevent liquid outflow through the opening [112], while allowing circulation of air therethrough is an air-permeable liquid barrier. In one embodiment, the means to prevent liquid outflow through the opening [112] and/or the air-permeable liquid barrier is selected from the group consisting of, porous material configured to prevent entry of liquid therein (such as hydrophobic porous material), geometric restriction, surface coating and combinations thereof. In one embodiment, the means to prevent liquid flow through the opening [112], while allowing circulation of air therethrough, comprise, or consist of, hydrophobic porous material [103],

Examples of hydrophobic porous material that may be used in the context of the invention include, without being limited to filter paper with inherent hydrophobic properties or filter paper that is treated hydrophobically, hydrophobic polymer membranes (e.g., comprising or composed of, polytetrafluorethylene, polyvinylidene fluoride, and/or polypropylene). The microfluidic device of the invention comprises an air-impermeable and water soluble membrane [102] and, in embodiment wherein the microfluidic device comprises the second valve of the invention, a second air-impermeable and water-soluble membrane [118],

The air-impermeable and water-soluble membrane(s) may be dissolved by aqueous liquid, including, without being limited to (aqueous) biological fluids such as (whole) blood, serum or plasma.

Examples of material that can be used in the context of the invention for the air-impermeable and water-soluble membrane(s) include, without being limited to, polyvinyl alcohol (PVA), dissolvable polysaccharides, gelatin and the like.

In embodiments, the air-impermeable and water-soluble membrane(s) comprise a substance to be released into the liquid circulating in the fluid conduit [101], Example of material that may be included in the air-impermeable and water-soluble membrane(s) of the invention include, without being limited to blood anticoagulant reagents, (such as Ethylenediaminetetraacetic acid, heparin, sodium citrate, citrate, sodium fluoride), DNA and/or RNA stabilizing reagents, cell lysis and viral inactivation reagents, assay reagents, micro and/or nanoparticles and compounds to be used as internal control and/or calibration means.

The present invention further relates to the use of the microfluidic device of the invention to partition a volume of aqueous liquid.

The present invention also relates to a method to partition a volume of aqueous liquid comprising the steps of: a. drawing in aqueous liquid through the fluid conduit [101] of the microfluidic device of the invention; and, b. partitioning said volume of liquid.

In one embodiment, step b of the method of the invention does not require any user intervention to open and/or close valves nor the use of valves fitted with actuators.

In embodiments, the use and/or the method of the invention exclude substantial physical interventions on the human or animal body which require professional medical expertise to be carried out and/or which entail a substantial health risk and/or do not necessitate the presence of a human or animal body. List of references used

[101] fluid conduit

[101a] part of the fluid conduit [101] upstream of the first opening [112]

[101b] part of the fluid conduit [101] downstream of the first opening [112]

[102] first membrane

[103] hydrophobic porous material

[104] vent

[105] means for increasing resistance to liquid flow

[106] inlet

[107] plasma separation membrane

[108] pump

[109] sample liquid

[109a] upstream plug of sample liquid

[109b] downstream plug of sample liquid

[110] whole blood sample

[110a] blood cell fraction

[110b] plasma fraction

[111] hollow microneedle(s)

[112] first opening

[113] lumen of the hollow microneedle(s) [111]

[114] first chamber

[115] second opening

[116] second chamber

[117] hydrophilic porous material

[118] second membrane

[119] outlet EXAMPLES

The present invention is further illustrated by the following examples.

Example 1: Device with a filtration membrane

In this example, the means [105] for increasing hydraulic resistance to liquid flow comprises a porous filter that is integrated into the upstream part of the microfluidic device. Such microfluidic devices with an integrated filter are, in particular, interesting for applications that require the separation/removal of specific compounds such as cells, cell debris, nucleic acids, proteins and other contaminating (bio)chemicals from the sample liquid which can induce unwanted bias in downstream (bio)analytical processes. This typically requires the sample to be sent through a filter, typically, consisting of a porous substrate (e.g., untreated/treated nitrocellulose, glass fiber, asymmetric polysulfone, . . .) or packed column with microparti cles/beads. When flowing the sample through, the filter introduces a hydraulic resistance, which in combination with the downstream vent allows to split off a discrete liquid plug from the filtered sample liquid.

An example of such a microfluidic device is illustrated in FIG. 3, where a plasma separation membrane is being used to retain blood cells from whole blood and only allows the plasma fraction to be sent to the downstream part of the microfluidic device.

A detailed description of the different steps of operation is given in FIG. 3 i to vii:

(i) A volume of whole blood [110] is applied to the inlet [106] of the microfluidic device, which is in fluid communication with the plasma separation membrane [107], This can be a venous blood sample stabilized with anticoagulants (i.e., heparin, K2EDTA, K3EDTA, sodium citrate, among others), a stabilized capillary blood sample with anticoagulants or a nonstabilized capillary blood sample.

(ii) When making contact with the plasma separation membrane, the blood sample is absorbed through capillary forces. During the wicking process, the blood cells are retained in the upstream part of the porous substrate (top part in case of vertical filtration membranes) of the plasma separation membrane [107] resulting in the separation of blood cells [110a] and plasma fraction [110b], The separation of the blood cells [110a] and plasma fractions [110b] inside the plasma separation membrane [107] can be driven solely through capillary forces or an additional external pressure gradient can be used to pull the whole blood sample through the porous membrane and drive the plasma separation. (iii-iv) Once the plasma separation membrane [107] is fully saturated, the plasma fraction is aspirated into the fluid conduit [101]and the dissolvable membrane [102] begins to reconstitute in the plasma fraction [110b],

(v) As long as the dissolvable membrane [102] forms a physical barrier between the fluid conduit [101] and the vent [104], the plasma fraction [110b] will be able to flow cohesively from the upstream part [101a] to the downstream part [101b] of the fluid conduit [101],

(vi) From the moment the dissolvable membrane [102] is open, the hydrophobic porous material [103] prevents outflow of the plasma fraction [110b] outside of the microfluidic device through the vent [104], The opening of the membrane [102] establishes the connection between the fluid conduit [101] and the vent [104] after which the hydraulic resistance of the plasma separation membrane [107] in the upstream part of the microfluidic device forces the intake of air from the vent [104] into the fluid conduit [101], In particular, the introduced flow resistance by the upstream plasma separation membrane [107] allows to break up the cohesive forces that keep the plasma fraction [110b] in the fluid conduit [101] together. As a consequence, the plasma fraction [110b] located in the downstream part of the fluid conduit [101b] becomes a discrete plasma fraction volume that is completely separated from the upstream part.

(vii) From this moment, it is fluidically favorable (i.e., path with least resistance) to pull in air from the environment via the vent [104] instead of pulling the plasma fraction [110b] in the part of the microfluidic device upstream of the vent [104], Consequently, the plasma volume in the downstream part of the fluid conduit [101b] can be further manipulated independently of that remaining upstream of the vent [104],

In this example, the dissolution speed of the dissolvable membrane [102] is preferably configured to avoid passage of blood cells in the downstream part of the fluid conduit [101b],

Example 2: Device with hollow microneedle

In this example, the means [105] for increasing hydraulic resistance to liquid flow comprises a single or multiple hollow microneedle(s) [111]. Such microfluidic device with one or multiple integrated hollow microneedle(s) are, in particular, interesting for applications where it is desired to extract a sample liquid (e.g., capillary blood, interstitial fluid) [109] directly from a living organism (e.g., human body, animal or plant) and further process it in the device. To enable processing of the sample (e.g., storage, preparation, analysis) in the microfluidic device, a discrete sample volume is required and, therefore, it is necessary to decouple the extracted sample liquid from the unlimited sample source (e.g., represented by the body bloodstream) in the patient. The small diameter of the lumen [113] inside the hollow microneedle(s) [111] induces a hydraulic flow resistance, which in combination with the vent [104] allows to split off a discrete liquid plug and then decouple fluidically the microfluidic device from the sample source. Such a device is illustrated by panel A in FIG. 4.

A detailed description of all the different steps of the operation of a device with integrated hollow microneedles as means [105] for increasing hydraulic resistance to liquid flow is illustrated in FIG.

4 i to v:

(i) After piercing the skin with the hollow microneedles, the sample liquid (e.g., capillary blood or interstitial fluid) [109] is aspirated from the sample source, through the inlet [106] and lumen of the hollow microneedles, into the fluid conduit [101] of the microfluidic device by a microfluidic pump.

(ii) The dissolvable membrane [102] begins to reconstitute in the sample liquid [109],

(iii) As long as the dissolvable membrane [102] forms a physical barrier between the fluid conduit [101] and the hydrophobic porous material [103], the sample liquid [109] will be able to flow cohesively from the upstream to the downstream microfluidic network.

(iv) From the moment the dissolvable membrane [102] is open, the hydrophobic porous material [103] prevents outflow of the sample liquid [109] outside of the microfluidic device through the vent [104], The opening of the membrane [102] establishes the air connection between the fluid conduit [101] and the vent [104] after which the hydraulic resistance of the hollow microneedle(s) [111] in the upstream part of the microfluidic device forces the intake of air from the vent [104] into the fluid conduit [101], In particular, the introduced flow resistance by the upstream hollow microneedle(s) [111] allows to break up the cohesive forces that keep the sample liquid [109] in the fluid conduit [101] together. As a consequence, the sample liquid [109b] located in the downstream part of the fluid conduit [101b] becomes a discrete sample liquid volume that is completely separated from the upstream part [109a],

(v) From this moment, it is fluidically favorable (i.e., path with least resistance) to pull in air from the environment via the vent [104] instead of pulling sample liquid from the part of the microfluidic device upstream of the vent [104], Consequently, the discrete sample liquid volume can be further manipulated in the downstream microfluidic network, independently of the upstream one.

Example 3: Device with a trapped-sas valve

In this example, the means [105] for increasing hydraulic resistance to liquid flow comprises a valve comprising a chamber containing trapped gas behind a dissolvable membrane that, after letting through a certain amount of liquid, will increase the hydraulic flow resistance by entrapping a gas bubble in the liquid path.

The valve is located upstream vent [104] and downstream of the inlet [106] and comprises a first chamber [114], in fluid connection with the (upstream) inlet [106] and the (downstream) fluid conduit [101], The first chamber [114] is separated from an adjacent second chamber [116] containing porous hydrophilic material [117] (e.g., filter paper) by another dissolvable membrane [118], When sample liquid [109] is manipulated through the first chamber [114], the dissolvable membrane [118] dissolves by reconstituting into the sample liquid [109], The dissolution time of the dissolvable membrane [118] can be tuned by adjusting the thickness (e.g., a couple of pm to several hundreds of pm), material type (i.e., polyvinyl alcohol) and composition (i.e., mixture percentage of used chemicals, molecular weight of used chemicals) of the used membrane. Once the dissolvable membrane [118] is open, part of the sample liquid [109] is absorbed by the hydrophilic porous substrate [117], expelling the air out of the pores of hydrophilic porous substrate [117] and leading to the formation of an air bubble in the first chamber [114], This air bubble is then trapped in between geometric restrictions that flank the first chamber [114] thereby leading to an increased hydraulic flow resistance. Consequently, the valve is able to increase the flow resistance within the microfluidic device after a certain time - determined by the second membrane [118] dissolution speed and/or the volumetric flow rate of the liquid, without the need for user intervention. This is particularly interesting in microfluidic systems, where no upstream hydraulic resistance is present.

A detailed description of the different steps of the working principle is shown in FIG. 5 i to ix

(i) Sample liquid [109] is aspirated toward the first chamber [114] (e.g. by a microfluidic pump).

(ii) Upon filling of the first chamber [114] with the sample liquid [109], the dissolvable membrane [118] reconstitutes in the sample liquid [109],

(iii) As long as the dissolvable membrane [118] forms a physical barrier between the first chamber [114] and the second chamber [116] containing a hydrophilic porous substrate [117], the sample liquid [109] will be able to flow toward the fluid conduit [101], Upon filling of the fluid conduit [101] with the sample liquid [109], the dissolvable membrane [102] reconstitutes in the sample liquid [109], The dissolving time of the dissolvable membranes [118, 102] can be customized to specific windows by adjusting the thickness (e.g., a couple of pm to several hundreds of pm), material type (i.e., polyvinyl alcohol) and composition (z.e., mixture percentage of used chemicals, molecular weight of used chemicals) of the used membrane.

(iv) As long as the dissolvable membranes [118] and [102] form intact physical barriers, the sample liquid [109] will be able to flow into the downstream part of the fluid conduit [101b],

(v) Meanwhile, before the fluidic connection between the first [114] and second chamber [116] is established, liquid circulating within the fluid conduit [101] has opened the first membrane [102], However, as insufficient hydraulic flow resistance is generated upstream of the vent [104] to overcome the surface tension of liquid circulating with the fluid conduit, no air is pulled from the environment

(vi-vii) However, from the moment the dissolvable membrane [118] is open, the first chamber [114] and second chamber [116] become fluidically connected. As a consequence, the sample liquid [109] within the first chamber [114] will be absorbed by the hydrophilic porous substrate [117] in the second chamber [116], Upon wicking of the sample liquid [109] in the hydrophilic porous substrate [117], the gas within the pores of the hydrophilic porous substrate [117] will be pushed out toward the first chamber [114], forming an air bubble therein.

(viii) Only once a gas bubble is trapped within the first chamber [114], sufficient hydraulic resistance is present in the part of the device upstream of the vent [104], forcing the intake of air into the fluid conduit. In particular, the introduced flow resistance by the entrapped air bubble allows to break up the cohesive forces that keep the sample liquid [109] in the fluid conduit [101] together. As a consequence, the sample liquid located in the downstream part of the fluid conduit [101b] becomes a discrete sample liquid volume that is completely separated from the upstream part.

(ix) From this moment, it is fluidically favorable (i.e. path with least resistance) to pull in air from the environment via the vent [104] instead of pulling sample liquid [109] from the part of the microfluidic device upstream of the opening. Consequently, the sample liquid volume in the downstream part of the fluid conduit [101b] can be further manipulated independently of that remaining upstream of the opening [112],

Claims

1. A microfluidic device comprising, a. an inlet [106] for liquid; b. a fluid conduit [101] in fluid connection with the inlet [106]; c. a first air-impermeable and water-soluble membrane [102] that (i) is closing a first opening [112] in a wall of the fluid conduit [101], (ii) is positioned to dissolve upon circulation of liquid through the fluid conduit [101], and (iii) has a first side oriented toward an inside of the fluid conduit [101]; d. a vent [104] that is in fluid connection with the other side of the first air-impermeable and water-soluble membrane [102] and wherein said vent [104] comprises means to prevent liquid flow through the first opening [112], while allowing circulation of air therethrough; e. means [105] for increasing hydraulic resistance to liquid flow, located downstream of the inlet [106] and upstream of the first opening [112]; f. an outlet [119], located downstream of the opening [112], and in fluid connection therewith.

2. The microfluidic device according to claim 1, wherein said means [105] for increasing hydraulic resistance to liquid flow comprise, a geometric flow resistance, a porous filtration element, a thermal expansion valve, a hydrogel swelling valve, a hydrophobic flow resistance, a plunger valve, a rotating valve, a pressure valve or a combination thereof.

3. The microfluidic device according to claim 1 or 2, wherein said means [105] for increasing hydraulic resistance to liquid flow comprise, a geometric flow resistance, a porous filtration element, a thermal expansion valve, a hydrogel swelling valve, a hydrophobic flow resistance, or a combination thereof.

4. The microfluidic device according to any one of claims 1 to 3, wherein said means [105] for increasing hydraulic resistance to liquid flow, comprise a filter.

5. The microfluidic device according to claim 4, wherein said filter is a plasma separation membrane [107],

6. The microfluidic device according to any one of claims 1 to 5, wherein said means [105] for increasing hydraulic resistance to liquid flow, comprise a single, or an array of, hollow microneedle(s) [111].

7. The microfluidic device according to any one of claims 1 to 6, wherein said means to prevent liquid flow through the first opening [112], while allowing circulation of air therethrough, comprise, or consist of, hydrophobic porous material [103],

8. The microfluidic device according to any one of claims 1 to 7, wherein said means [105] for increasing hydraulic resistance to liquid flow comprise: a. a first chamber [ 114] in fluid connection with the inlet [ 106] and with the fluid conduit [101]; b. a second air-impermeable and water-soluble membrane [118] that (i) is closing an opening [115] in a wall of the first chamber [114], (ii) is positioned to dissolve upon circulation of liquid through the first chamber [114], and (iii) has a first side oriented toward an inside of the first chamber [114]; c. a second chamber [116] that (i) is filled with a hydrophilic porous material [117], (ii) is in fluid connection with the other side of the second membrane [118] and (iii) comprises a trapped volume of gas in the pore of the hydrophilic porous material; and, d. a geometric restriction in the fluid connections upstream and downstream of the first chamber [114] .

9. The microfluidic device according to any one of claims 1 to 8, wherein said device further comprises a pump [108], downstream of, and in fluid connection with, the outlet [119],

10. The microfluidic device according to claim 9, wherein said pump [108] is a capillary pump.

11. Use of the microfluidic device according to any one of claims 1 to 10, to partition a volume of aqueous liquid.

12. A method to partition a volume of aqueous liquid comprising the steps of a. drawing in aqueous liquid through the fluid conduit [101] of the microfluidic device according to any one of claim 1 to 10; and, b. partitioning said aqueous liquid.

13. The method of claim 12, wherein step b does not require any user intervention to open and/or close valves nor the use of valves fitted with actuators.