阅读说明：本技术 用于将小滴注射在微流体系统中的系统和设备 (System and device for injecting droplets in a microfluidic system ) 是由 埃里克·卡雷尔 查洛特·莱格 皮埃尔-安托伊内·丘尼阿塞 埃利安·马廷 于 2020-04-07 设计创作，主要内容包括：本发明公开了一种用于将第一流体(F1)的小滴递送到第二流体(F2)的小滴的微流体设备,其包括：主通道(10),其具有携载所述第二流体的小滴的载体流体(FC)；辅助通道(20),其在第一相交点(T1)处通过第一孔口(41)及第一流体界面(31)且在所述第一相交点下游的第二相交点(T2)处通过第二孔口(42)及第二流体界面(32)流体地联接到所述主通道,其中所述载体流体的流动诱发所述第一孔口和所述第二孔口之间的压力差,所述压力差产生平衡条件,使得所述第二流体界面的弯月面在所述第二孔口附近维持在所述辅助通道中,其中平衡偏差触发所述第一流体的体积从所述第二流体界面到所述主通道中的释放。(The present invention discloses a microfluidic device for delivering a droplet of a first fluid (F1) to a droplet of a second fluid (F2), comprising: a main channel (10) with a carrier Fluid (FC) carrying droplets of the second fluid; an auxiliary channel (20) fluidly coupled to the main channel at a first intersection point (T1) through a first orifice (41) and a first fluid interface (31) and at a second intersection point (T2) downstream of the first intersection point through a second orifice (42) and a second fluid interface (32), wherein a flow of the carrier fluid induces a pressure difference between the first orifice and the second orifice that creates an equilibrium condition such that a meniscus of the second fluid interface is maintained in the auxiliary channel near the second orifice, wherein an equilibrium deviation triggers a release of a volume of the first fluid from the second fluid interface into the main channel.)

1. A microfluidic device with a controlled system for delivering a volume of a first fluid (F1) and one or more releases of one or more droplets of a second fluid (F2), comprising:

-a main channel (10) provided with a carrier Fluid (FC) having a flow direction (FW), the carrier fluid carrying one or more droplets of the second fluid immersed in the carrier Fluid (FC);

-a secondary channel (20) formed as a reservoir having a predefined closed volume (V1), fluidly coupled to the primary channel at two points of intersection, wherein the secondary channel:

connect to a first intersection point (T1) through a first aperture (41) configured to create a first fluid interface (31) between the carrier fluid and the first fluid in the auxiliary channel;

connect to a second intersection point (T2) downstream of the first intersection point through a second aperture (42) configured to create a second fluid interface (32) between the carrier fluid and the first fluid;

wherein the flow of the carrier fluid induces a pressure differential between the first and second orifices, the pressure differential creating an equilibrium condition such that the meniscus of the second fluid interface is maintained in the auxiliary channel in the vicinity of the second orifice;

wherein an equilibrium deviation from the equilibrium condition greater than a predefined threshold triggers a release of the volume of the first fluid from the second fluid interface into the primary channel.

2. The microfluidic device according to claim 1, wherein the equilibrium deviation at the second fluid interface (32) with respect to the equilibrium condition is caused by at least one droplet of the second fluid passing in the main channel between the first intersection point and the second intersection point, thereby increasing a pressure drop and triggering a release of the volume of the first fluid from the second fluid interface.

3. The microfluidic device according to any of claims 1 to 2, wherein the equilibrium deviation at the second fluid interface relative to the equilibrium condition is generated by an actuator (16) allowing release of the volume of the first fluid from the second fluid interface.

4. Micro-fluidic device according to claim 3, characterized in that the actuator is a piezoelectric actuator (17) interacting directly or indirectly with the auxiliary channel, preferably with ultrasonic vibrations.

5. A microfluidic device according to claim 3, wherein the actuator acts on a deformable membrane arranged in the auxiliary channel, which deformable membrane triggers the release of a droplet from the second fluidic interface when pressed.

6. The microfluidic device according to any one of the preceding claims, wherein one or more pairs of electrodes (18) are positioned along the main channel at or downstream of the second intersection point to generate an electric field inside the main channel and cause coalescence of droplets of the first fluid with droplets of the second fluid.

7. The microfluidic device of claim 1, wherein when no droplet circulates in the main channel, the first fluid interface having a first radius of curvature and a second radius of curvature and the second fluid interface having a third radius of curvature and a fourth radius of curvature are sized to follow the formula:

wherein:

q corresponds to the flow rate in the main channel;

R_La linear hydraulic resistance corresponding to the main channel;

L_ABcorresponding to a distance between the first intersection point and the second intersection point;

γ corresponds to the interfacial tension between the first fluid and the carrier fluid;

h' corresponds to the first radius of curvature of the first fluid interface;

w' corresponds to the second radius of curvature of the first fluid interface;

h corresponds to the third radius of curvature of the second fluid interface;

w corresponds to the fourth radius of curvature of the second fluid interface.

8. The microfluidic device of any one of the preceding claims, wherein the first and second radii of curvature of the first and second fluid interfaces with third and fourth radii of curvature are sized to follow the formula when one or more droplets are circulating between the first and second intersection points:

wherein:

q corresponds to the flow rate in the main channel;

R_La linear hydraulic resistance corresponding to the main channel;

L_ABcorresponding to a distance between the first intersection point and the second intersection point;

α corresponds to a constant;

n corresponds to the number of droplets of the third fluid circulating between the first intersection point and the second intersection point;

L_dropa length corresponding to a droplet of the third fluid circulating between the first intersection point and the second intersection point;

γ corresponds to the interfacial tension between the first fluid and the carrier fluid;

h' corresponds to the first radius of curvature of the first fluid interface;

w' corresponds to the second radius of curvature of the first fluid interface;

h corresponds to the third radius of curvature of the second fluid interface;

w corresponds to the fourth radius of curvature of the second fluid interface.

9. The microfluidic device according to any one of the preceding claims, wherein the pressure drop in the main channel between the first and second intersection points is increased by a cross-sectional definition (80) of the main channel arranged between the first and second intersection points, preferably just upstream of the second orifice.

10. The microfluidic device according to any of the preceding claims, wherein the auxiliary channel has a funnel shape (50) arranged near and converging towards the second orifice.

11. Microfluidic device according to anyone of the preceding claims, wherein a reduced section (60) is provided next to the first aperture at the entrance of the auxiliary channel.

12. A microfluidic device according to any one of the preceding claims wherein one monitoring element tracks at least one droplet circulating between the first intersection point and the second intersection point.

13. A microfluidic device as claimed in any one of the preceding claims wherein a surfactant compound is provided in the carrier fluid and/or in the droplets of the second fluid.

14. The microfluidic device of claim 1, further comprising one or more additional secondary channels, each secondary channel formed as an additional reservoir having a predefined enclosed volume, fluidly coupled to the main channel at two additional intersections, wherein the secondary channels are connected to the main channel.

15. The microfluidic device according to any of the preceding claims, wherein the second fluid (F2) is a urine sample to be analyzed, wherein the carrier fluid is an oil, and wherein the first fluid is a reagent configured to detect an analyte contained in the second fluid.

Background

This document relates to the handling of fluids in microfluidic and millifluidic systems, and more precisely in so-called droplet systems-droplet microfluidics (droplet microfluidics), which are used in e.g. biochemical and biological analysis applications. This document addresses mixing several fluids in a controlled manner.

More specifically, the present application is directed to two-phase flow in a microchannel in which droplets of a second fluid are transported by a carrier fluid. This microchannel system allows the release of a controlled volume of a first fluid into the main channel when a droplet of a second fluid passes through the intersection between the main channel and the auxiliary channel.

The principle of a pico-syringe delivering droplets of a first fluid into droplets of a second fluid in the range from picoliters to microliters has been investigated.

Such a pico-injector as shown in fig. 1 is disclosed in document US 2016194225. Droplets are injected from the side reservoir into the main channel by means of the activation electrodes.

However, such micro-injectors require very fine pressure control in the side reservoir to operate properly. Such accurate absolute pressure control requires the use of expensive components.

The present inventors have endeavored to propose a more cost-effective solution to deliver droplets of a first fluid into droplets of a second fluid in the range of picoliters to microliters.

Disclosure of Invention

This document proposes a microfluidic device with a controlled system for delivering a volume of a first fluid and one or more releases of one or more droplets of a second fluid, comprising:

a main channel provided with a carrier fluid having a flow direction, the carrier fluid carrying one or more droplets of a second fluid submerged in the carrier fluid,

-a secondary channel formed as a reservoir having a predefined closed volume, fluidly coupled to the primary channel at two intersections, wherein the secondary channel:

connected to the first intersection point by a first orifice configured to create a first fluidic interface between the carrier fluid and the first fluid in the auxiliary channel;

connecting to a second intersection point downstream of the first intersection point through a second orifice configured to create a second fluid interface between the carrier fluid and the first fluid;

wherein the flow of the carrier fluid induces a pressure difference between the first and second orifices, the pressure difference creating an equilibrium condition such that a meniscus of the second fluid interface is maintained in the auxiliary channel in the vicinity of the second orifice;

wherein an equilibrium deviation from an equilibrium condition greater than a predefined threshold triggers a release of the volume of the first fluid from the second fluid interface into the primary channel.

Thus, no fine pressure control is required in such devices. Instead, the relative pressure drop is used to create the above-mentioned equilibrium conditions, which is less costly than using a high accuracy pump. The size of the microfluidic chip is thus optimized and scalable. This microfluidic device is also an advantageous solution from the point of view of power consumption.

We note here that the so-called "balance bias" can be any type of phenomenon and be generated by any type of actuator.

Under the expression "release of volume" it should be understood as release of one droplet, but it is not limited to droplet release. This said volume can also be released directly into one droplet circulating into the main channel.

The equilibrium condition means that the microfluidic device is arranged in such a way that this microfluidic chip is in a stable situation which becomes unstable in the presence of small disturbances. When the situation is unstable, a balance deviation occurs.

Such devices, which may be referred to as "mini-syringes," are controllable, reproducible, and specific. In practice, the system is controllable, since it can be decided whether to release the volume of the first fluid or not. Furthermore, the system is reproducible, since the release volume is always the same for a given protocol, which is determined, inter alia, by a given flow rate, a fixed size of the droplet, a given auxiliary channel and a given size of the channel. Finally, the system is specific, since the release is precise.

Furthermore, due to the reliable stabilization of the second fluidic interface, the microfluidic chip is reusable even if the operation of the microfluidic device is stopped.

According to one option, a deviation of the equilibrium at the second fluid interface with respect to the equilibrium condition may be generated by at least one droplet of the second fluid passing in the main channel between the first intersection point and the second intersection point, thereby increasing the pressure drop and triggering a release of the volume of the first fluid from the second fluid interface.

The transfer of a drop between the first intersection point and the second intersection point creates a disturbance, which means that the system has moved away from the equilibrium condition. Under conditions where the disturbance is sufficiently large, a volume (e.g., a droplet) of the first fluid is released into the main channel.

This microfluidic device makes it possible to define a balanced/unbalanced condition such that the perturbation induced by the transfer of a droplet between the first and second orifices is sufficient to trigger the release of the volume of the first fluid into the main channel. Thus, the operation is purely passive, involving no active components. Thus, such systems are very cost effective.

According to one option, a balance deviation at the second fluid interface from an equilibrium condition may be generated by the actuator, thereby allowing release of the volume of the first fluid from the second fluid interface.

Thus, the release is controlled by selective activation of the actuator, which may be generated by software. Thus, a reliable and conditional control is possible.

According to one option, the actuator may be a piezoelectric actuator interacting directly or indirectly with the secondary channel, preferably with the ultrasonic vibrations.

Such piezoelectric actuators are easy to control and are efficient. Such piezoelectric actuators may be integrated directly on the substrate in a microchip configuration.

According to one option, the actuator may act on a deformable membrane arranged in the auxiliary channel, which upon being pressed triggers the release of the droplet from the second fluid interface.

According to one option, one or more pairs of electrodes may be positioned along the main channel at or downstream of the second intersection point to generate an electric field inside the main channel and cause coalescence of droplets of the first fluid with droplets of the second fluid.

The electrodes are easy to position and control. Coalescence is selectively triggered by activation of the electrodes.

According to one aspect, when no droplet can circulate in the main channel, a first fluid interface having a first radius of curvature and a second fluid interface having a third radius of curvature and a fourth radius of curvature are sized to follow the formula:

wherein:

q corresponds to the flow rate in the main channel;

R_La linear hydraulic resistance corresponding to the main channel;

L_ABcorresponding to the first phaseA distance between the intersection point and the second intersection point;

γ corresponds to the interfacial tension between the first fluid and the carrier fluid;

h' corresponds to a first radius of curvature of the first fluid interface;

w' corresponds to a second radius of curvature of the first fluid interface;

h corresponds to a third radius of curvature of the second fluid interface;

w corresponds to a fourth radius of curvature of the second fluid interface.

Due to this geometry, the system is stable when no droplets of the second fluid circulate in the main channel.

According to one aspect, when one or more droplets may circulate between a first intersection point and a second intersection point, a first fluid interface having a first radius of curvature and a second fluid interface having a third radius of curvature and a fourth radius of curvature are sized to follow the formula:

wherein:

q corresponds to the flow rate in the main channel;

R_La linear hydraulic resistance corresponding to the main channel;

L_ABcorresponding to the distance between the first intersection point and the second intersection point;

α corresponds to a constant;

n corresponds to the number of drops of the third fluid circulating between the first intersection point and the second intersection point;

L_drioa length corresponding to a drop of the third fluid circulating between the first intersection point and the second intersection point;

γ corresponds to the interfacial tension between the first fluid and the carrier fluid;

h' corresponds to a first radius of curvature of the first fluid interface;

w' corresponds to a second radius of curvature of the first fluid interface;

h corresponds to a third radius of curvature of the second fluid interface;

w corresponds to a fourth radius of curvature of the second fluid interface.

When the fluid is circulated in a two-branch configuration, the flow ratio between the two branches is set by the ratio between the resistances of each branch to the fluid flow. Setting the geometry of each channel can change the flow ratio between the two channels. If a second fluid immiscible with the first fluid is present in one branch, the two menisci will separate the second fluid from the first fluid. Each meniscus is capable of sustaining a voltage drop. By setting the size of each meniscus with the channel geometry parameters it is possible to create a stable situation which stops the flow in the second channel. It is possible to set the parameters such that the situation is stable and becomes unstable (flow occurs in the second channel) with little disturbance.

The above inequality determines an equilibrium condition for not releasing the volume of the first fluid into the main channel when one or more droplets of the second fluid are transferred between the first intersection point and the second intersection point. In such a situation, an actuator is necessary in order to release the volume of the first fluid into the main channel.

According to one aspect, when a deviation in equilibrium at the second fluid interface with respect to the equilibrium condition may be generated by a droplet of the second fluid passing in the main channel between the first intersection point and the second intersection point, thereby increasing the pressure drop and triggering a release of the volume of the first fluid from the second fluid interface, then a droplet may be circulated between the first intersection point and the second intersection point, and the first fluid interface having the first radius of curvature and the second fluid interface having the third radius of curvature and the fourth radius of curvature are sized to follow the formula:

when the actuator is not used, the above inequality determines the equilibrium condition to be followed for releasing the volume of the first fluid into the main channel when one or more droplets pass the second intersection point.

According to one option, the pressure drop in the main channel between the first and second intersection points may be increased by a cross-sectional definition of the main channel arranged between the first and second intersection points, preferably just upstream of the second orifice.

The cross-sectional definition of the main channel creates an overpressure (i.e. increases the pressure drop) and this allows droplets to pass in the main channel at the cross-sectional definition to reliably trigger the release of the desired volume from the second fluid interface. Whenever the cross-sectional definition approaches the second intersection point, a droplet of the first fluid delivered from the second interface will travel with a droplet of the second fluid in the main channel. The cross-sectional definition of the main channel also allows tracking of droplets of the main channel by monitoring the pressure at a location between the first intersection point and the second intersection point.

According to one option, wherein the secondary channel has a funnel shape arranged near the second aperture and converging towards the second aperture.

When operation of the microfluidic device is stopped, the pressure between the first and second ports equalizes. Due to the funnel shape, the second fluid interface remains near the second intersection point and does not move substantially backwards. The funnel shape is such that the first and second radii of curvature at the first fluid interface will assume the same magnitude as the third and fourth radii of curvature at the second fluid interface.

Furthermore, when the microfluidic device is operated again, a pressure gradient will be created which will again advance the third radius of curvature and the fourth radius of curvature in order to again equalize the pressure at the second orifice.

The funnel shape may have an aperture angle between 40 ° and 160 °.

According to one option, a reduced section may be provided at the entrance of the secondary channel immediately adjacent the first aperture.

The reduced section at the inlet of the secondary channel prevents one or more droplets of the second fluid passing through the primary channel from entering the secondary channel. Only the carrier fluid may enter the secondary channel.

It is necessary to have some carrier fluid in the reduction section. It is also necessary to have first and second large radii of curvature at the first fluid interface. Thus, if the first fluid rises to the level of the second orifice, this must not rise to the reduced section. Eventually, the resistance at the secondary channel will change as the first fluid will be emptied. If the resistance at the first orifice is extremely large compared to the resistance of the secondary channel, the change in resistance will be limited. An injection that is reproducible throughout the life of the product would be preferred.

Due to the arranged cross-sectional definition of the main channel, the funnel shape of the second aperture and the reduced section next to the first aperture, the rate of fluid injection at the second aperture is dependent on the ratio of the resistances between the first and second apertures through the main channel and between the first and second apertures through the auxiliary channel. This particular geometry makes it possible to manage the hydraulic resistance of the auxiliary channel and to balance this ratio.

According to one option, a monitoring element may track at least one droplet circulating between the first intersection point and the second intersection point.

In the case of the use of such monitoring elements, the latter allow to know exactly when to activate the actuator. It also allows for control of smooth operation of the microsyringe.

According to one option, the monitoring element may be formed as a pressure sensor for measuring a pressure present at a location between the first and second intersection points for controlling the operation of the device.

According to one option, the monitoring element may be formed as a capacitive sensor for determining the passage of a droplet in the main channel between the first and second intersection points for controlling the operation of the device.

According to one option, the surfactant compound may be provided in a carrier fluid and/or in droplets of a second fluid.

The surfactant compound changes the interfacial tension between the second fluid interface and the first fluid interface when the surfactant compound is injected in the carrier fluid. Which allows to adjust the operating range of the system and the release of the volume of the first fluid into the main channel.

According to one option, one or more further secondary channels may be provided, each secondary channel being formed as a further reservoir having a predefined closed volume, fluidly coupled to the primary channel at two further points of intersection, wherein the secondary channels are connected to the primary channel.

The serial configuration of the micro-injectors allows for the injection of several products and the release of controlled volumes of different fluids into the main channel.

According to one option, the carrier fluid may be an oil, such as mineral oil. The first fluid may be a reagent configured to detect an analyte contained in the second fluid. The second fluid may be a urine sample to be analysed.

The present disclosure further proposes a method of releasing one or more droplets of a first fluid and one or more droplets of a second fluid within a microfluidic device, wherein the method comprises:

-providing a main channel carrying one or more droplets of a second fluid immersed in a carrier fluid,

-providing a secondary channel formed as a reservoir having a predefined closed volume, fluidly coupled to the primary channel at two intersection points, fluidly coupled to the first intersection point by a face first orifice configured to create a first fluid interface between the carrier fluid and the first fluid in the secondary channel, and fluidly coupled to a second intersection point downstream of the first intersection point by a second orifice configured to create a second fluid interface between the carrier fluid and the first fluid,

-imparting a flow of carrier fluid into the main channel, thereby inducing a pressure difference between the first and second orifices from the flow of carrier fluid, the pressure difference creating an equilibrium condition such that the meniscus of the second fluid interface is maintained in the auxiliary channel in the vicinity of the second orifice;

-generating an equilibrium deviation from the equilibrium condition greater than a predefined threshold, thereby triggering a release of the volume of the first fluid from the second interface into the main channel.

Drawings

FIG. 1 shows a micro-injector according to the prior art;

FIG. 2 shows a mini-injector according to the invention;

FIG. 3 shows a pico-injector with an actuator and electrodes according to the invention;

FIG. 4 shows a mini-injector according to a second embodiment;

FIG. 5 shows a system of serially connected mini-syringes according to the invention;

fig. 6 shows the evolution of the hydraulic resistance of the main channel according to the invention with respect to time.

Fig. 7 shows an enlarged view of the microfluidic system.

Fig. 8 and 9 show a first fluid interface and a second fluid interface, respectively, where the meniscus occurs.

Fig. 10 shows an enlarged view of a modified microfluidic system with a deformable membrane and a sensor.

Detailed Description

This document provides a device for delivering a controlled volume of a first fluid and one or more releases of one or more droplets of a second fluid into a main channel in the micrometer to millimeter range by using a microfluidic device having a microchannel. The microchannels are treated so as to be hydrophobic. Where the carrier fluid is hydrophobic, the microchannels need to be hydrophobic. However, the carrier fluid may also be hydrophilic, and in such cases, the microchannels are hydrophilic. The microfluidic device may operate at ambient temperature or at another temperature.

Such asFIG. 7Here it is shown that one or two pumps PC1, PC2 are provided to circulate a carrier fluid, designated FC, into the main channel, designated 10. In addition, a pump P2 is provided to release drops of the second fluid F2 into the main channel 10. The system consisting of pumps PC1 and P2 is typically flow-focused geometry. This flow focusing is an example of generating droplets. In another embodiment, this flow focusing may be replaced by a T-junction, a co-flow, or another system. The flow focusing geometry allows for the creation of a toolA droplet of a second fluid having a smaller size and a small spacing between two consecutive droplets. The two elongated channels 101, 102, 110 increase the hydraulic resistance of each channel by extending the length of each channel. Therefore, the change in hydraulic resistance when forming a droplet of the second fluid is negligible. Pump PC2 and channel 103 allow two consecutive droplets of second fluid F2 to be spaced apart and the flow rate to be increased by injecting an amount of carrier fluid into the main channel.

The second fluid F2 is immiscible with the carrier fluid FC and, therefore, the second fluid F2 is maintained as droplets along its path within the laminar flow of the carrier fluid. In the example shown, the carrier fluid is an oil, such as a mineral oil. The second fluid F2 is, for example, a body fluid. Here, we particularly consider the situation where the second fluid is a urine sample of a human individual. However, the second fluid may be a urine sample from an animal (veterinary use). Further, the second fluid may be lymph, fresh blood, saliva, sweat or any type of body fluid.

Basically, the provided arrangement can be used for any biological analysis. Furthermore, the provided arrangement can be used in any framework of any chemical process that requires precise injection of a compound/species into another compound/species.

Such asFIGS. 2 and 7Shown therein, the mini-injector device 9 comprises the above-mentioned main channel 10 in which a carrier fluid FC having a flow direction FW circulates, and an auxiliary channel 20 which will be discussed later.

In the main channel, the flow velocity is between 0,001mm/s and 10mm/s, preferably between 0,02mm/s and 1 mm/s. Conditions are such that the flow is laminar.

The main channel and all other channels described herein may be micro-machined conduits implemented in a substrate. Alternatively, the main channel and all other channels described herein may be silicon microchip systems.

The nominal cross-section of the main channel may be between 10 μm²And 1 mm.

In the example shown, the transverse cross-section exhibits a rectangular shape (with width and height). However, a circular shaped transverse cross-section or any other basic transverse cross-sectional shape is also encompassed within the present disclosure.

The carrier fluid carries one or more droplets of the second fluid F2. The mini-syringe 9 also comprises an auxiliary channel 20 formed as a reservoir containing a pre-defined closed volume V1 of a first fluid F1.

The first fluid F1 may be a reactant intended for a chemical reaction when a specific compound contained in the second fluid F2 is present. This first fluid F1 is immiscible with the carrier fluid FC. This first fluid F1 may be all types of reagents capable of interacting and detecting glucose, proteins, ketones or hormones such as LH and HCG contained in the second fluid F2.

This secondary channel 20 is fluidly coupled to the primary channel at two intersection points T1, T2. More precisely, the auxiliary channel 20 is connected to the first intersection point T1 through the first orifice 41. Within the auxiliary channel, immediately adjacent to the first orifice or at a certain distance D1 of the first orifice 41 (according to the gradual consumption of the first fluid over time), we find the first fluid interface 31 between the carrier fluid FC and the first fluid F1.

The auxiliary passage is also connected to a second intersection point T2 downstream of the first intersection point by a second orifice 42. Within the secondary channel, next to the second orifice 42, we find the second fluid interface 32 between the carrier fluid and the first fluid. Here we note that when the pump PC1 and/or PC2 is stopped, the second fluid interface 32 remains near the second orifice 42 for reasons explained further below.

The auxiliary channel is U-shaped as a whole, and the first intersection point and the second intersection point are positioned on the same side of the main channel. However, it is possible to have a first intersection point on one side of the main channel and a second intersection point on the other side of the main channel. In this case, the auxiliary channel does not exhibit a U-shape. Furthermore, the second orifice 42 has a funnel shape 50 in the auxiliary channel converging towards the second orifice.

Here we note that the influence of gravity is negligible.

When the microfluidic device is in operation, the second fluid interface 32 is pressure balanced atThe proximity of both orifices is maintained in the auxiliary channel, which is allowed due to the particular geometry of the system. In effect, the flow of the carrier fluid induces a pressure difference (P) between the first and second orifices_A-P_B) The pressure differential creates an equilibrium condition.

The amount of the first fluid in the reservoir formed by the auxiliary channel gradually decreases after a plurality of releases of the volume of the first fluid; the volumetric loss of the first fluid is to some extent proportional to the effective operation of the device.

Due to the provided arrangement, the volume loss causes a movement of the meniscus at the first fluid interface 31. More precisely, said first fluidic interface is moved away from the first orifice 41, equivalent to said volume loss. However, the meniscus at the second fluid interface 32 remains substantially near the second orifice. In other words, distance D1 multiplied by the cross-sectional area of the secondary channel represents the volume loss.

Under nominal operation, i.e. when the carrier fluid circulates in the main channel, this pressure difference (P)_A-P_B) Pushing the first fluid interface 31 away from the main channel.

When operation of the microfluidic device is stopped, the respective pressures at the first and second orifices are equalized.

At the second orifice 42 a funnel shape 50 is provided in the secondary channel, said funnel shape converging towards the second orifice.

Advantageously, the first and second radii of curvature R1 and R2 at the first fluid interface will assume the same magnitude as the third and fourth radii of curvature R3 and R4 at the second fluid interface.

Furthermore, when the microfluidic device is operated again (pump PC1 and/or PC2 activated), a pressure gradient is created as mentioned before, which causes the third and fourth radii of curvature to change again in order to again equalize the pressure at the second orifice.

The conditions are defined below such that the second fluid interface of the first fluid is maintained at the level of the main channel without leakage.

First, a condition without a droplet of the second fluid F2, i.e., only the carrier fluid FC flowing through the main channel 10, was investigated.

In one aspect, the pressure drop in a channel in which fluid circulates at a flow rate Q is equal to the hydraulic resistance of the channel R multiplied by the flow rate: Δ ═ Q × R.

The hydraulic resistance of a microfluidic channel depends on its dimensions, as well as on the viscosity η of the fluid flowing there. For example, for a rectangular cross-section channel having a height h and a width w, the linear hydraulic resistance can be estimated by the following equation:

in the pico-injector shown in fig. 2, there is a pressure drop between the first and second intersection points:

P_A-P_B＝Q×R_L×L_AB

wherein:

P_Acorresponding to a pressure at the first intersection;

P_Bcorresponding to the pressure at the second intersection;

q corresponds to the flow rate in the main channel;

R_La linear hydraulic resistance corresponding to the main channel;

L_ABcorresponding to the distance between the first and second intersection points.

On the other hand, typically, there is a pressure difference at the intersection of the interface between the two fluids. This is the laplace pressure, expressed by the surface tension coefficient γ (n.m)^-1) And the main curvatures R1 and R2 of the surface give:

as shown in fig. 2, there are two interfaces between the first fluid and the carrier fluid. In the case of a rectangular cross-section, R1 cannot be less than half the height H1 of the channel, while R2 cannot be less than half the width W1, as shown in fig. 8. Thus, considering the two radius of curvature constraints, the pressure at the first intersection, the second intersection and within the first fluid are related by the following relationship:

and P_A-P_B＝Q*R_L*L_AB，

Wherein:

P_Ccorresponding to the pressure in the auxiliary channel within the first fluid;

γ corresponds to the interfacial tension between the first fluid and the carrier fluid;

h' corresponds to a first radius of curvature R1 of the first fluid interface;

w' corresponds to a second radius of curvature R2 of the first fluid interface;

h a third radius of curvature R3 corresponding to the height H2 of the second fluid interface relative to the channel, as shown in fig. 9;

w corresponds to a fourth radius of curvature R4 of the second fluid interface relative to the width W2, as shown in fig. 9;

therefore, the first fluid does not leak in the main passage if the following conditions are satisfied:

the volume of the first fluid is released from the second fluid interface into the main channel only when there is an equilibrium deviation from the equilibrium condition.

In one embodiment, the deviation of the equilibrium at the second fluid interface with respect to the equilibrium condition is generated by at least one droplet of the second fluid F2 passing in the main channel between the first intersection point and the second intersection point.

According to one example, the volume is released before the at least one droplet is delivered in the vicinity of the second intersection point and when this at least one droplet is between the first intersection point and the second intersection point.

According to another example, the volume is released during the transfer of the at least one droplet at the level of the second intersection point.

According to another example, the volume is released when the at least one droplet is positioned just downstream of the second intersection point, just after the at least one droplet passes in the vicinity of the second intersection point.

The conditions that allow the second fluid interface to advance as the droplet passes into the second intersection point are explained below.

In the case of a two-phase flow, as shown in fig. 6, the resistance between the first and second intersection points is no longer constant: the transfer of the droplet creates an overpressure.

In effect, the hydraulic resistance of the main passage between the first and second intersection points varies over time. In a first time a, only carrier fluid is present between the first and second intersection points: the pressure drop is minimized and the third and fourth radii of curvature of the second fluid interface are relatively high. In a second time b, the droplet of the second fluid reaches the first intersection point, the hydraulic resistance of the channel increases, causing an increase in the pressure drop between the first and second intersection points: the second fluid interface advances in the secondary channel and deforms to assume a smaller radius of curvature. In a third time c, the droplet of the second fluid is completely between the first intersection point and the second intersection point. During a fourth time d, a droplet of the second fluid passes at the level of the second orifice: this is the moment when the volume of the first fluid is released from the second fluid interface into the main channel. The release of the volume of the first fluid from the second fluid interface into the main channel can thus be modified by varying the flow rate, size or frequency of the droplets of the second fluid.

A monitoring element 96, such as a pressure sensor or a capacitive sensor, may be used to track at least one droplet circulating between the first intersection point and the second intersection point. A pressure sensor may be placed along the main channel. The capacitive sensor may be positioned to face the main channel and measure a change in volume that determines when at least one droplet of the second fluid traverses the second orifice. Other sensors may also be used to track at least one droplet circulating between the first intersection point and the second intersection point.

A good approximation of the pressure drop in the main channel when passing droplets is as follows:

ΔP_drop＝Q*R_L*[L_AB+(α-1)*n*L_drop]

wherein:

L_dropis that the droplet of the second fluid is strictly below L_ABLength of (d);

n is the number of droplets between the first intersection point and the second intersection point;

alpha is between 1 and 10.

Thus, the second fluid interface proceeds without leakage of the first fluid in the main channel, provided that:

in other words, at the level of the second orifice, there is a confined meniscus. That is, geometrically, from the moment the diameter of the meniscus is equal to the diameter of the second orifice, if the pushing continues instead of continuing to decrease, the meniscus size starts to increase: beyond the limit point. The system is used so as not to be far from this limit point but to remain stable. To remain stable, this means that it does not continue until the diameter of the meniscus starts to increase again, which corresponds to the moment when the system transitions from a stable system to an unstable system. The system is just set in this balanced condition called the unbalanced distance.

As shown in fig. 2, the operating range of a pico-injector depends on the size of the microfluidic channel and on the properties of the fluid used. Thus, the selection made may correspond to a wide range of flow rates for which the system is operating. This solution is suitable for microsystems, i.e. having characteristic dimensions of about 1 μm to 1mm, and a flow velocity of about 1 μm/s to 1cm/s, i.e. a flow rate of about several fL/s to several mL/s. Below this range, it is not possible to release the volume of the first fluid in the main channel. Above this range, the microfluidic protocol is exited.

In the absence of a droplet of the second fluid, the hydraulic resistance between a and B is equal to:

therefore, in order for the system to be stable and not leak the second fluid in the absence of droplets of the second fluid, the flow rate Q must be:

now consider that a droplet of the second fluid circulates in the main channel, having an L of 100 μm_dropLength and are spaced apart by more than 300 μm. Thus, at most a single droplet is present between the first and second intersection points. Considering α -5, the hydraulic resistance between the first intersection point and the second intersection point is equal to:

therefore, in order to make the system stable and not leak the second fluid when the drop is delivered, we must have:

in another embodiment, as shown in fig. 3, an actuator 16 is added near the secondary channel. This actuator acts as a deformable membrane arranged in the auxiliary channel.

As shown in fig. 10, a side pocket 95 is provided in fluid communication with the secondary channel at a location upstream of the first fluid interface. The side pocket is secured directly to the auxiliary passage in an airtight manner by an aperture 98.

In addition, a deformable membrane 97 formed as one flexible side wall of the side recess is provided. Side pocket 95 is filled with carrier fluid FC.

The amount of carrier fluid inside side pocket 95 that can be pushed out of the side pocket when the side pocket is pressed is between 0.1pL and 10 μ L.

In another embodiment, the side pocket 95 may also be positioned directly in the secondary channel between the first and second fluid interfaces. In such a case, side pocket 95 is filled with first fluid F1.

It should be noted that the side pocket may have different shapes: cube, or sphere, or another form.

The material from which the deformable membrane is constructed is flexible and allows the membrane to reduce the volume of the side recess 95 or auxiliary channel when pressed. The thickness of the film is between 1 μm and 50 mm.

When the deformable membrane is pressed by actuating the actuator 99, a portion of the fluid contained in the side recess 95 or the secondary channel is pushed out of the cavity or the secondary channel, causing a volume of the first fluid to be released into the primary channel at the second orifice.

Monitoring element 96 allows for tracking of at least one droplet between the first and second orifices. When this monitoring element notices a droplet reaching the second orifice, the deformable membrane is pressed to release the volume of the first fluid into the main channel.

This actuator may also be a piezoelectric actuator 17 interacting directly or indirectly with the secondary channel, preferably with ultrasonic vibrations. This ultrasonic vibration creates a radiation pressure that disturbs the second fluid interface.

When the actuator is activated, release of the droplet from the second fluidic interface is allowed/triggered. This actuator is another way to create a deviation in balance from a balanced condition.

Thus, a pico injector may be passive or require an external system such as an actuator.

According to one option, an electrode 18 is provided which is positioned along the main channel just downstream of the second intersection point. The electrodes are used to generate an electric field inside the main channel and cause coalescence of droplets of the first fluid with droplets of the second fluid.

Depending on the nature of the fluids F1, F2 to be brought together, the coalescence may occur passively, i.e. without any actuation of an electric field, by only bringing droplets of the first fluid into effective contact with droplets of the second fluid. Surfactants present in the carrier fluid may aid this passive coalescence.

In another embodiment, e.g.FIG. 4As shown therein, the cross-sectional definition 80 of the main channel is arranged between the first and second intersection points, preferably only upstream of the second orifice. Further, a reduced section 60 is provided at the entrance of the secondary channel immediately adjacent the first aperture.

The cross-sectional confinement 80 of the main channel creates an overpressure and this allows droplets of the main channel passing at the second intersection point to travel with droplets released from the first fluidic interface. This cross-sectional definition of the main channel also allows tracking of droplets of the main channel.

The reduced section 60 at the entrance of the secondary channel, i.e. at the first orifice 41, prevents one or more droplets passing through the primary channel from entering the secondary channel. Only the carrier fluid FC passes through the reduced section 60.

Whenever this condition may occur, the reducing section 60 may also prevent some of the first fluid from flowing back into the main channel.

The hydraulic resistance of the reducing section 60, which is independent of the value of D1, is independent of the position of the meniscus at the first fluid interface, which remains constant along the volume loss of the first fluid.

In another embodiment, as shown in fig. 5, the microfluidic device may further comprise at least a further auxiliary channel 92 similar to the first auxiliary channel 9. The microfluidic device may have more than two auxiliary channels, for example three auxiliary channels as shown in fig. 5. Each auxiliary channel 9, 92, 93 is formed as a reservoir with a predefined closed volume, fluidly coupled to the main channel at two intersection points, downstream of the second intersection point of the first auxiliary channel and connected to the main channel.

The second auxiliary channel 92 contains a third fluid F3; the third auxiliary passage 93 receives a fourth fluid F4.

Such microfluidic devices can be used to inject several products in a serial configuration in order to release controlled volumes of different fluids. However, the different auxiliary channels may also be arranged in a parallel configuration. The secondary channel may be as shown in fig. 5, or a combination of a pico-injector as shown in fig. 2 and/or a pico-injector as shown in fig. 3 and/or a pico-injector as shown in fig. 4.

The surfactant compound may be added in the carrier fluid and/or in droplets of the second fluid. By modifying the interfacial tension, it facilitates customization and utilization of conditions that have a second fluid interface near the second orifice without leaking into the primary channel. Various types of surfactants are possible: span 80, Tween 20 or Tween 80. Other classical surfactants not mentioned are also possible.

It should be noted that although the carrier fluid above is an oil and the second fluid is an aqueous solution, the opposite configuration is also contemplated, i.e., an aqueous solution as the carrier fluid and an oily solution as the second fluid.

The height of the secondary channels may be different from the height of the primary channels. For example, the secondary channels may be larger to allow for storage of larger amounts of fluid and thus increase, for example, the duration of use of the system.

Gravity has no effect on the above, and hydrostatic pressure can be neglected relative to other physical quantities such as capillary action and head losses.