Patent ID: 12239985

DETAILED DESCRIPTION

The present document promotes a device for delivering one or more release of a controlled volume of a first fluid with one or more droplets of a second fluid into a main channel with the use of a microfluidic device having micro-channels at a range from micrometer to millimeter. The micro-channels are treated in order to be hydrophobic. The micro-channels need to be hydrophobic when the carrier fluid is hydrophobic. However, the carrier fluid can also be hydrophilic and in such case, the micro-channels are hydrophilic. H This microfluidic device can work at ambient temperature or at another temperature.

As shown atFIG.7, there is provided one or two pumps PC1, PC2to circulate a carrier fluid denoted FC into a main channel denoted10. Further, there is provided one pump P2to release drop of a second fluid F2into the main channel10. The system composed of the pumps PC1and P2is classically a flow focusing geometry. This flow focusing is an example of generation of droplets. In another embodiment, this flow focusing could be replaced by a T junction, a co flow or another system. This flow focusing geometry allows to create droplets of the second fluid with small size and small spacing between two consecutive droplets. Two lengthening channels101,102,110increase hydraulic resistance of each channel by extending the length of each channel. Thus, the change in hydraulic resistance when a droplet of the second fluid is formed is negligible. The pump PC2and the channel103allow to space two consecutive droplets of the second fluid F2and increase the flow rate by injecting a quantity of carrier fluid into the main channel.

The second fluid F2is non-miscible with carrier fluid FC, therefore the second fluid F2remains as droplets along their path within the laminar flow of the carrier fluid. In the illustrated example the carrier fluid is an oil, for instance mineral oil. The second fluid F2is for example a body fluid. Here we consider in particular the case where the second fluid is a urine sample of a human individual. However, the second fluid can be a urine sample of an animal (veterinary usage). Also, the second fluid can be lymph, fresh blood, saliva, sweat, or any type of body fluids.

Basically, the promoted arrangement can be used for any biological analysis. Besides, the promoted arrangement can be used for any frame of any chemical process requiring a precise injection of a compound/species in another compound/species.

As illustrated inFIGS.2and7, the pico-injector device9comprises the abovementioned main channel10in which circulates a carrier fluid FC having a flow direction FW and an auxiliary channel20that will be discussed later on.

Within the main channel, the flow velocity is comprised between 0.001 mm/s and 10 mm/s, preferably between, 0.2 mm/s and 1 mm/s. The conditions are such that the flow is laminar.

The main channel and all other channels described herein can be micro-machined conduits realized in a substrate. Alternately, the main channel and all other channels described herein can be part of a silicon miniature system-on-a-chip.

Nominal cross section of the main channel can be comprised between 10 μm2and 1 mm.

The transverse section exhibits in the illustrated example a rectangle shape (with width and height). However, a rounded shaped transverse section or any other basic transverse sectional shape is also encompassed within the present disclosure.

The carrier fluid carries one or more droplets of the second fluid F2. The pico-injector9also comprises an auxiliary channel20formed as a reservoir containing a predefined closed volume V1of a first fluid F1.

The first fluid F1can be a reactant intended for a chemical reaction when brought in presence of a particular compound contained in the second fluid F2. This first fluid F1is non miscible with the carrier fluid FC. This first fluid F1can be all type of reagent able to interact and detect glucose, proteins, ketones or hormones such as LH and HCG contained in the second fluid F2.

This auxiliary channel20is fluidly coupled to the main channel at two intersections T1,T2. More precisely, the auxiliary channel20is connected to a first intersection T1via a first orifice41. Within the auxiliary channel, at immediate vicinity of the first orifice or at a certain distance D1of the first orifice41(according to the progressive consumption of the first fluid along time), we find a first fluid interface31between the carrier fluid FC and the first fluid F1.

The auxiliary channel is also connected to a second intersection T2downstream to the first intersection, via a second orifice42. Within the auxiliary channel, at immediate vicinity of the second orifice42, we find a second fluid interface32between the carrier fluid and the first fluid. We note here that when pump PC1and/or PC2stops, the second fluid interface32remains at vicinity of the second orifice42for reasons explained further below.

The auxiliary channel has an overall U shape and the first and second intersection are in the same side of the main channel. However, it is possible to have the first intersection on one side of the main channel and the second intersection on the other side of the main channel. In this case, the auxiliary channel does not exhibit a U shape. Besides, the second orifice42has a funnel shape50in the auxiliary channel, converging toward the second orifice.

We note here that influence of gravity is negligible.

When the microfluidic device is operating, the second fluid interface32is maintained in the auxiliary channel, at the vicinity of the second orifice by pressure balance, which is allowed thanks to the particular geometry of the system. Indeed, a flow of the carrier fluid induces a difference of pressure (PA−PB) between the first and second orifice generating a balance condition.

The quantity of the first fluid in the reservoir formed by auxiliary channel decreases gradually after multiple releases of a volume of the first fluid; the loss of volume of the first fluid is somewhat proportional to the effective operation of the device.

Thanks to the promoted arrangement, the loss of volume provokes a move of the meniscus at the first fluid interface31. More precisely, said first fluid interface moves away from the first orifice41tantamount the said loss of volume. But the meniscus at the second fluid interface32stays substantially at the vicinity of the second orifice. In other words, the distance D1multiplied by the cross sectional area of the auxiliary channel represents the loss of volume.

Under nominal operation, i.e. when carrier fluid circulates in the main channel, this difference of pressure (PA−PB) pushes the first fluid interface31away from the main channel.

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

A funnel shape50is provided in the auxiliary channel, at the second orifice42, the funnel shape converging towards the second orifice.

Advantageously, the first and second radii of curvature R1,R2at the first fluid interface come to take the same size as the third and fourth radii of curvature R3,R4at the second fluid interface.

Furthermore, when the microfluidic device is put back into operation (activation of pump PC1and/or PC2), a pressure gradient is generated as mentioned before, which causes the third and fourth radii of curvature to change again so as to balance again the pressures at the second orifice.

The condition so that the second fluid interface of the first fluid remains at the level of the main channel without leakage is determined below.

First, the case without droplets of the second fluid F2, i.e. only the carrier fluid FC flows through the main channel10, is studied.

On the one hand, the pressure drop in a channel where a 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 section channel of height h and width w, the linear hydraulic resistance can be approximated by:

RL=12*η[1-0.63*(hw)]*h3*w

In the pico-injector illustrated inFIG.2, there is a pressure drop between the first intersection and the second intersection:
PA−PB=Q×RL×LAB
wherein:PAcorresponds to the pressure at the first intersection;PBcorresponds to the pressure at the second intersection;Q corresponds to the flow rate in the main channel;RLcorresponds to a lineic hydraulic resistance of the main channel;LABcorresponds to a distance between the first intersection and the second intersection.

On the other hand, classically, there is a pressure difference at the crossing of an interface between two fluids. This is the Laplace pressure, the expression of which is given by the surface tension coefficient γ (N·m−1) and the main curvatures of the surface R1and R2:

Δ⁢P=γ(1R1+1R2)

As illustrated inFIG.2, there are two interfaces between the first fluid and the carrier fluid. In the case of a rectangular section, R1cannot be less than half of the height H1of the channel while R2cannot be less than half of the width W1, as illustrated inFIG.8. Thus, considering the limit case for the two radii of curvature, the pressures at the first intersection, the second intersection and within the first fluid are linked by the relations:

(PC-PB)max=2⁢γ*(1h+1w),(PC-PA)max=2⁢γ*(1h′+1w′)⁢⁢andPA-PB=Q*RL*LAB,
wherein:PCcorresponds to the pressure within the first fluid, in the auxiliary channel;γ corresponds to the interfacial tension between the first fluid and the carrier fluid;h′ corresponds to a first radius of curvature R1of the first fluid interface;w′ corresponds to a second radius of curvature R2of the first fluid interface;h corresponds to a third radius of curvature R3of the second fluid interface with regard the height H2of the channel, as illustrated inFIG.9;w corresponds to a forth radius of curvature R4of the second fluid interface with regard the width W2, as illustrated inFIG.9;

Consequently, the first fluid does not leak in the main channel if the following condition is satisfied:

Q*RL*LAB<2⁢γ*(1h+1w-1h′-1w′)

A volume of the first fluid from the second fluid interface into the main channel is released only when a balance deviation prevails with regard to the balance condition.

In one embodiment, the balance deviation with regard the balance condition at the second fluid interface is generated by at least one droplet of the second fluid F2passing in the main channel between the first intersection and the second intersection.

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

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

According to another example, the volume is released just after the passage of the at least one droplet at the vicinity of the second intersection, when the at least one droplet is localized just downstream to the second intersection.

The conditions allowing the progression of the second fluid interface when a droplet passes into the second intersection, is explained below.

In the case of a two-phase flow, as illustrated inFIG.6, the resistance between the first intersection and the second intersection is no longer constant: the passage of a droplet producing an overpressure.

Indeed, the hydraulic resistance of the main channel between the first intersection and the second intersection is varying as a function of time. In a first time a, there is only carrier fluid between the first intersection and the second intersection: the pressure drop is minimized, the third and fourth radii of curvature of the second fluid interface are relatively high. In a second time b, a droplet of the second fluid arrives at the first intersection, the hydraulic resistance of the channel increases causing an increase in the pressure drop between the first intersection and the second intersection: the second fluid interface progress in the auxiliary channel and deforms to take a smaller radius of curvature. In a third time c, the droplet of the second fluid is entirely between the first intersection and the second intersection. In a fourth time d, the droplet of the second fluid passes at the level of the second orifice: it is the moment of a release of a volume of the first fluid from the second fluid interface into the main channel. The release of volume of the first fluid from the second fluid interface into the main channel can thus be modified by varying the flow rate, the size or the frequency of the droplets of the second fluid. A monitoring element96such as a pressure sensor or a capacitive sensor can be used to track at least one droplet circulating between the first intersection and the second intersection. The pressure sensor can be placed along the main channel. The capacitive sensor can be placed facing the main channel and measured the variation of the capacity determining when at least one droplet of the second fluid cross the second orifice. Other sensors can also be used to track the at least one droplet circulating between the first intersection and the second intersection.

A good approximation of the pressure drop in the main channel when passing a droplet is as follows:
ΔPdrop=Q*RL*[LAB+(α−1)*n*Ldrop]
wherein:Ldropis the length of a droplet of the second fluid which is strictly inferior to LAB;n is the number of droplets between the first intersection and the second intersection;α is comprises between 1 and 10.

Thus, the second fluid interface progress without the leaking of the first fluid in the main channel provided that:

[LAB+(α-1)*n*Ldrop]*Q*RL<2⁢γ*(1h+1w-1h′-1w′).

In other words, at the level of the second orifice, there is a limiting meniscus. That is to say that geometrically, from the moment the diameter of the meniscus is equal to the diameter of the second orifice, if one continues to push, instead of continuing to decrease, the meniscus size begins to increase: a limit point is crossed. The system is used in order to be not far from this limit point but to remain stable. To remain stable, it implies not to go until the diameter of the meniscus begins to increase again, corresponding to the moment when the system passes from a stable system to an unstable one. The system is set up just below this balance condition, called distance to imbalance.

The operating range of a pico-injector, as illustrated inFIG.2, depends on the dimensions of the microfluidic channels, and on the nature of the fluids used. Thus, the choices made can correspond to a wide range of flow rates for which the system operates. This solution works for a micro-system, that is to say with characteristic dimensions of the order of 1 μm to 1 mm, with flow velocities of the order of 1 μm/s to 1 cm/s, i.e. flow rates of the order of a few fL/s to a few mL/s. Below this range, the release of a volume of the first fluid in the main channel is impossible. Above this range, the microfluidic regime is exited.

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

R=1⁢2*1⁢0*1⁢0-3*5⁢0⁢0*1⁢0-6[1-0.63*(50*10-660*10-6)]*(5⁢0*1⁢0-6)3*6⁢0*1⁢0-6=1.0*1⁢01⁢3⁢⁢Pa·s·m-3.

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

Q<2*2⁢0*1⁢0-3*(15⁢0*1⁢0-6+12⁢5*1⁢0-6-15⁢0*1⁢0-6-11⁢5⁢0*1⁢0-6)1.0*1⁢01⁢3=1.3*1⁢0-1⁢0⁢⁢m3·s-1=130⁢⁢nL·s-1

It is now considered that droplets of the second fluid circulate in the main channel, that they have a Ldroplength of 100 μm and that they are spaced more than 300 μm. Thus, there is at most a single droplet between the first intersection and the second intersection. Considering that α=5, the hydraulic resistance between the first intersection and the second intersection is equal to:

R=(3⁢0⁢0-1⁢0⁢0)*1⁢0-63⁢0⁢0*1⁢0-6*1.0*1⁢01⁢3+1⁢0⁢0*1⁢0-63⁢0⁢0*1⁢0-6*5*1.0*1⁢01⁢3=2.3*1⁢01⁢3⁢⁢Pa·s·m-3

Thus, for the system to be stable and the second fluid not to leak when a drop passes, we must have:

Q<2*2⁢0*1⁢0-3*(15⁢0*1⁢0-6+12⁢5*1⁢0-6-15⁢0*1⁢0-6-11⁢5⁢0*1⁢0-6)2.3*1⁢01⁢3=5.7*1⁢0-1⁢1⁢⁢m3·s-1=57⁢⁢nL·s-1

In another embodiment, as illustrated inFIG.3, an actuator16is added at the vicinity of the auxiliary channel. This actuator is acting as a deformable membrane arranged in the auxiliary channel.

As illustrated inFIG.10, there is provided a side pocket95in fluid communication with the auxiliary channel at a position upstream of the first fluid interface. The side pocket is directly fixed to the auxiliary channel in an hermetic manner through the orifice98.

Further, there is provided deformable membrane97formed as one flexible side wall of the side pocket. The side pocket95is filled with carrier fluid FC.

The volume of the carrier fluid inside the side pocket95that can be pushed out of the side pocket when the side pocket is pressed is comprised between 0.1 μL and 10 μL.

In another embodiment, the side pocket95could also be localized directly in the auxiliary channel between the first fluid interface and the second fluid interface. In such case, the side pocket95is filled by the first fluid F1.

In should be noted that the side pocket can have different shapes: either a cube, or a ball, or another form.

The material constituting the deformable membrane is flexible and allows the membrane to reduce the volume of the side pocket95or the auxiliary channel when pressed. The thickness of the membrane is comprised between 1 μm and 50 mm.

When the deformable membrane is pressed by actuating an actuator99, a portion of the fluid contained in the side pocket95or the auxiliary channel is pushed out of the cavity or the auxiliary channel provoking the release of a volume of the first fluid at the second orifice, into the main channel.

The monitoring element96allows the tracking of at least one droplet between the first orifice and second orifice. When this monitoring element notice that one droplet arriving to the second orifice, the deformable membrane is pressed to release a volume of the first fluid into the main channel.

This actuator can also be a piezoelectric actuator17interacting directly or indirectly with the auxiliary channel, preferably with ultrasonic vibrations. This ultrasonic vibrations generates radiation pressure disturbing the second fluid interface.

When the actuator is activated, a release of a droplet from the second fluid interface is allowed/triggered. This actuator is another manner to generate a balance deviation with regard the balance condition.

Therefore, the pico-injector can either be passive, or requiring an external system such as an actuator.

According to one option, there are provide electrodes18positioned along the main channel, just downstream to the second intersection The electrodes are used to create an electric field inside the main channel and provoke a coalescence of a droplet of the first fluid with a droplet of the second fluid.

Depending on the nature of fluids F1,F2to be brought together, the coalescence may happen passively, i.e. without any electric field actuation, just by bringing a droplet of the first fluid at effective contact with a droplet of the second fluid. A surfactant present in the carrier fluid can help this passive coalescence.

In another embodiment, as illustrated inFIG.4, a cross-section restriction80of the main channel is arranged between the first intersection and the second intersection, preferably just upstream the second orifice. Besides, next to the first orifice, a reduced section60at the entrance of the auxiliary channel is provided.

The cross-section restriction80of the main channel generates an overpressure and this allows the droplet of the main channel passing at the second intersection and the droplet released from the first fluid interface to travel together. This cross section restriction of the main channel also allows to realize a tracking of the droplet of the main channel.

The reduced section60at the entrance of the auxiliary channel, i.e. at the first orifice41, prevents one or more droplet passing through the main channel from entering the auxiliary channel. Only the carrier fluid FC passes through reduced section60.

The reduced section60can also prevent some first fluid to flow back to the main channel, whenever this condition could occur.

The hydraulic resistance of the reduced section60does not depend on the position of the meniscus at the first fluid interface, this hydraulic resistance is irrespective of D1value, it remains steady along the loss of volume of the first fluid.

In another embodiment, as illustrated inFIG.5, the microfluidic apparatus can further comprises at least a further auxiliary channel92, similar to the first auxiliary channel9. It can have more than two auxiliary channel, for instance three as illustrated inFIG.5. Each auxiliary channel9,92,93are formed as a reservoir having a predefined closed volume, fluidly coupled to the main channel at two intersections, downstream to the second intersection of the first auxiliary channel and connected to the main channel.

The second auxiliary channel92houses a third fluid F3; the third auxiliary channel93houses a fourth fluid F4.

Such microfluidic apparatus can be used to inject several products in serial configuration in order to release a controlled volume of different fluids. However, the different auxiliary channel can be arranged in parallel configuration also. The auxiliary channels can be as illustrated inFIG.5or being a composition of a pico-injector as illustrated inFIG.2and/or a pico-injector as illustrated inFIG.3, and/or a pico-injector as illustrated inFIG.4.

A surfactant compound can be added in the carrier fluid and/or in the droplets of the second fluid. By modifying the interfacial tension, it helps on customizing and playing on the conditions for having the second fluid interface at the vicinity of the second orifice without leaking into the main channel. Various types of surfactants are possible: Span® 80 (a nonionic surfactant) Tween® 20 (a polyethylene glycol sorbitan monolaurate) or Tween® 80 (a polyethylene glycol sorbitan monooleate). 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 an aqueous solution, the converse configuration is also contemplated, namely an aqueous solution as carrier fluid and an oily solution as second fluid.

The height of the auxiliary channel can be different from that of the main channel. For instance, the auxiliary channel can be larger to allow to store a larger volume of fluid and thus increase the duration of use of the system, for example.

There is no influence of gravity on what is described above, the hydrostatic pressure can be neglected with regard the other physical quantities such as capillarity and loss of hydraulic head.