Synchronization of capillary flow in parallel microchannels using passive microfluidic valves

Abstract

The present invention relates to a trigger valve integrated with the stop valve to synchronize the flow in parallel microchannels. A stop valve is made by introducing a step on three sides of the microchannel. A step is a 90° divergence along the path of any side of the microchannel. The step is introduced on both the side walls and the bottom wall. Since there is no modification on the top valve, the liquid can move on the top wall freely. A trigger valve is a modified version of the stop valve, where the channel is slowly converging in a curved manner with a pointed tip. Both valves have the same height and width work based on the Laplace pressure change at the meniscus of the flowing fluid. The valves act as pressure barriers to the fluid flow enables synchronizing the flow in parallel microchannels with one single inlet.

Description

[0001] TITLE OF THE INVENTION

[0002] SYNCHRONIZATION OF CAPILLARY FLOW IN PARALLEL MICROCHANNELS USING PASSIVE MICROFLUIDIC VALVES

[0003] FIELD OF THE INVENTION

[0004] The present invention relates to a microfluidic device with passive valves which have a potential impact on point-of-care diagnostic devices. More specifically, relates to synchronization of capillary flow in parallel microchannels using passive microfluidic valves.

[0005] BACKGROUND OF THE INVENTION

[0006] Capillary microfluidics is widely being used in point of care diagnostic applications due to ease of use. Microfluidics often need valves to control and manipulate the flow. A lot of active valves are developed which need external stimuli such as electric, magnetic, pneumatic or thermal signals to control the fluid flow. These involves complexity and adds cost to the overall system. The use of passive microfluidic valves helps in decreasing the complexity of the device and also helps in easy implementation in disposable point-of-care diagnostic devices. The passive valves can be developed by controlling the Laplace pressure which is governing the capillary flow. Laplace pressure at the interface depends only on the surface tension, contact angle and the channel shape. Depending on the valve’s design and function, the valves are categorized into different types. A few types are stop valves, Trigger valves, retention valves and burst valves.

[0007] There are a few types of trigger valves which only depend on the modification of the surface properties. Modification of surface properties add additional functionalization steps which takes more time. Moreover, many of these functionalization steps involved will degrade with time and cannot be efficiently used for a longer period of time. OBJECT OF THE INVENTION

[0008] An object of the invention, the present invention relates to a microfluidic device with passive valves which have a potential impact on point-of-care diagnostic devices.

[0009] Another object of the present invention relates to the development of a new type of trigger valve. This trigger valve when integrated with the stop valve can be used to synchronize the flow in parallel microchannels.

[0010] SUMMARY OF THE INVENTION

[0011] The present invention relates to a microfluidic device with passive valves which have a potential impact on point-of-care diagnostic devices. The present invention develops a new type of trigger valve. This trigger valve when integrated with the stop valve can be used to synchronize the flow in parallel microchannels.

[0012] In one embodiment, the present invention describes about two different types of valves. The first one is a stop valve and the second one is a trigger valve. The microfluidic channels connecting these valves have the same width and height. Apart from the design of the valves, a combination of both valves is used to synchronise the flow in a circuit of capillary microchannels. A stop valve is made by introducing a step on three sides of the microchannel. A step is considered as a 90° divergence along the path of any side of the microchannel. The step is introduced on both the side walls and the bottom wall. Since there is no modification on the top valve, the liquid can move on the top wall freely. A trigger valve is a modified version of the stop valve which can help the flow happen in a channel having the same dimensions as the stop valve. The trigger valve is fabricated in such a way that the channel is slowly converging in a curved manner so that the end of the channel has a pointed tip. In another embodiment, the present invention illustrates the synchronisation of flow in a circuit of parallel microchannels with one single inlet using trigger valve integrated with the stop valve. Both valves work based on the Laplace pressure change at the meniscus of the flowing fluid. The valves act as pressure barriers to the fluid flow. When the fluid is flowing inside a straight microchannel, the Laplace pressure is constant, and the fluid flows inside the microchannel with a characteristic angle which is equal to the contact angle (9S) between the Fluid-Solid-Gas interface. A concave radius of curvature of the meniscus says that the Laplace pressure is positive. When the meniscus encounters the stop valve, there is a sudden decrease in the Laplace pressure at the interface. At this stage the meniscus adjusts to the shape of the valve. The meniscus changes its shape from concave to convex, which in turn, describes that there is a decrease in pressure. The trigger valve has the same height and width as the stop valve, but the end of the channel is slowly converging. When the meniscus encounters any valve, it adjusts itself to the shape of the valve. In the case of the stop valve, the meniscus changes its shape from concave to convex. This causes a change in the overall radius of curvature from negative to positive. This causes a sudden fall in the Laplace pressure. But in the case of the trigger valve, since the valve is fabricated in a concave shape when the meniscus encounters the trigger valve, the body remains concave, indicating that the overall radius of curvature is still positive. During this process, there is an increase in the radius of curvature. The approximation of the shape of the meniscus when moving after the trigger valve. The offset G plays a significant role in the determination of the flow condition when a trigger valve is encountered. If the value of G increases, the probability of flow happening at the trigger valve increases. The likelihood of flow happening when increasing G at the trigger valve.

[0013] Other aspects of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learnt by the practice of the invention.

[0014] BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 shows (a)stop valve (1), (b)trigger valve (2).

[0016] Figure 2 Meniscus dynamics when encountered a stop valve (1) (a) Side View (b) Top View. Figure 3 Regime plot (stop Valve).

[0017] Figure 4 Meniscus dynamics at the trigger valve (2) (a)Top View (b) Isometric view. Figure 5 (d)>(c)>(b)>(a)- Decreasing order of Probability for flow to happen, where G1<G2<G3<G4.

[0018] Figure 6 Parallel Microchannel Device (a) Top View (b) Isometric View.

[0019] Figure 7 Parallel Microchannel Designs with only one trigger valve.

[0020] Referring to the drawings, the embodiments of the present invention are further described. The figures are not necessarily drawn to scale, and in some instances the drawings have been exaggerated or simplified for illustrative purposes only. One of ordinary skill in the art may appreciate the many possible applications and variations of the present invention based on the following examples of possible embodiments of the present invention.

[0021] DETAILED DESCRIPTION OF THE INVENTION

[0022] The following description is presented to enable any person skilled in the art to make and use the embodiments, and is provided in the context of a particular application and its requirements. Various modifications to the disclosed embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other embodiments and applications without departing from the scope of the present invention. Thus, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein.

[0023] The present invention describes about two different types of valves. The first one is a stop valve (1) and the second one is a trigger valve (2). The microfluidic channels connecting these valves have the same width and height. Apart from the design of the valves, a combination of both valves is used to synchronise the flow in a circuit of capillary microchannels. Figure la shows the construction of the stop valve. A stop valve is made by introducing a step on three sides of the microchannel. A step is considered as a 90° divergence along the path of any side of the microchannel. The step is introduced on both the side walls and the bottom wall. Since there is no modification on the top valve, the liquid can move on the top wall freely. A trigger valve is a modified version of the stop valve which can help the flow happen in a channel having the same dimensions as the stop valve. A graphical image of the trigger valve is shown in Figure lb. The trigger valve is fabricated in such a way that the channel is slowly converging in a curved manner so that the end of the channel has a pointed tip. of the Stop Valve

[0024] Both valves work based on the Laplace pressure change at the meniscus of the flowing fluid. The valves act as pressure barriers to the fluid flow. When the fluid is flowing inside a straight microchannel, the Laplace pressure is constant, and the fluid flows inside the microchannel with a characteristic angle which is equal to the contact angle (9S) between the Fluid-Solid-Gas interface. A concave radius of curvature of the meniscus says that the Laplace pressure is positive. When the meniscus encounters the stop valve, there is a sudden decrease in the Laplace pressure at the interface. At this stage the meniscus adjusts to the shape of the valve. The meniscus changes its shape from concave to convex, which in turn, describes that there is a decrease in pressure. The side view and top view of the meniscus dynamics when encountering the step are shown in Figure 2. When the meniscus encounters the step, the contact angle on the top wall remains the same as 9Ssince there is no pressure barrier on the top wall. But on the bottom wall, the effective angle changes from 9S The process of the meniscus readjusting itself to the shape of the step can also be referred as pinning. During the process of pinning, the Laplace pressure at the meniscus decreases. If the Laplace pressure goes to zero, the meniscus stops at the step. This principle is used in the case of a stop valve. Since the meniscus is free to spread on the top wall, it tends to spread on the side walls due to top wall effect. This effect can also be referred to as the corner filling effect. The corner filling effect can be seen in Figure 2b along the top wall.

[0025] However, the functionality of the valve depends on different parameters such as the width of the channel before step (wi), the height of the channel before step (hi), the width of the channel after step (wi), the height of the channel after the step (I12), contact angle (0S) and Surface tension (y). To find the dependency of these parameters on the flow conditions, experiments are performed by varying all the depending parameters. Different devices of varying aspect ratios are fabricated to determine the flow and No-Flow conditions. The channel width before the step(wi) is varied from 200 pm to 400pm, and the height (hi) is varied from 100pm to 800pm to vary the aspect ratio from 0.25 to 2. Similarly, the width of the channel after step (W2) is varied from 600 pm to 1600 pm. The step height (h2-hi) is tested at 100 pm and 200 pm. The step is fixed between 10mm to 20mm away from the inlet reservoir for all the geometries. The Flow / Conditions are evaluated by visualizing the meniscus position under the microscope. Ethanol / water mixture is used to vary the contact angle. The contact angle varies from 77° to 33°. Figure 3 describes the flow and no-flow conditions when encountering a stop valve. of the trigger valve

[0026] The trigger valve has the same height and width as the stop valve, but the end of the channel is slowly converging, as shown in Figure lb. When the meniscus encounters any valve, it adjusts itself to the shape of the valve. In the case of the stop valve, the meniscus changes its shape from concave to convex. This causes a change in the overall radius of curvature from negative to positive. This causes a sudden fall in the Laplace pressure. But in the case of the trigger valve, since the valve is fabricated in a concave shape when the meniscus encounters the trigger valve, the body remains concave, indicating that the overall radius of curvature is still positive. During this process, there is an increase in the radius of curvature. The approximation of the shape of the meniscus when moving after the trigger valve is shown in Figure 4. It is seen that the offset G shown in Figure lb plays a significant role in the determination of the flow condition when a trigger valve is encountered. If the value of G increases, the probability of flow happening at the trigger valve increases. The likelihood of flow happening when increasing length G at the trigger valve is shown in Figure 5. Synchronization of Flow in a circuit of parallel microchannels

[0027] The present invention demonstrates the flow synchronization in parallel microchannels with one single inlet. This kind of design is often used in Rapid test kits where there is no need for external intervention during the test. The design of the circuit is shown in Figure 6. Application of this type of passive microfluidic valve is in designing of Point of Care diagnostic devices similar to rapid test kits where capillary forces / hydrostatic forces are used to drive the flow in the devices. These types of valves can also be used in some of the active microfluidic techniques with low Reynold’s number flows where synchronization or even distribution of flow is needed throughout the reservoirs / chambers. These valves can also be used in horizontal layering of multiple immiscible fluids along the microchannel using a step valve.

[0028] It may be appreciated by those skilled in the art that the foregoing drawings, examples and experimental evidences are merely illustrative and are not to be taken as limitations upon the scope of the invention.

Claims

We Claim:

1. A device for synchronizing the capillary flow in parallel microchannel with passive microfluidic valves comprises, a stop valve (1) made by introducing a step on three sides of the microchannel; a trigger valve (2) is curved with a pointed tip at the end of the channel to provide a slow convergence; characterized in that, the stop valve and trigger valve are of same width and height and work based on the Laplace pressure which changes at the meniscus of the flowing fluid to synchronize the fluid flow in parallel microchannels with one single inlet.

2. The device as claimed in claim 1, wherein the step is considered as a 90° divergence along the path of any side of the microchannel.

3. The device as claimed in claim 1, wherein the meniscus changes its shape from concave to convex.

4. The device as claimed in claim 1, wherein the Laplace pressure decreases at the interface, when the meniscus encounters the stop valve.

5. The device as claimed in claim 1, wherein the functionality of the valves depends on different parameters including the width of the channel before step (wl), the height of the channel before step (hl), the width of the channel after step (wl), the height of the channel after the step (h2), contact angle (0S) and Surface tension (y).

6. The device as claimed in claim 1, wherein the channel width before the step(wl) is between 200pm to 500pm, and the height (hl) is varied from 100pm to 800pm to vary the aspect ratio from 0.25 to 2.

7. The device as claimed in claim 1, wherein the width of the channel after step (w2) is varied from 600 pm to 1600 pm and the height (h2-hl) is tested between 100 pm and 400 pm.

8. The device as claimed in claim 1, wherein the step is between 10 mm to 20mm away from the inlet reservoir for all the geometries.

9. The device as claimed in claim 1, wherein the radius of curvature increases when the meniscus encounters the trigger valve.

10. The device as claimed in claim 1, wherein the value of G increases, the probability of flow happening at the trigger valve increases.

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