Patent Application
20190201890
This application claims priority to EPC Application No. 17210837.5, filed on 28 Dec. 2017, and to EPC Application No. 18156738.9, filed on 14 Feb. 2018, each of which is incorporated herein by reference in its entirety.
The invention relates to the field of microfluidic devices. More specifically it relates to a device allowing microfluidic pumping using wetting control.
Medical devices for analysis usually deal with very small amounts of fluid, and transportation of these small amounts of fluid is often required for inducing reactions and for analysis. Pumps are used for this transportation. Nevertheless, traditional pumps are typically large and bulky in comparison with a microfluidic channel, and they have moving parts which makes integration, such as integration on a chip, difficult or non viable. For this reason, pumps usually are not integrated.
Pumping systems thus need to be scaled down and be compact for pumping fluids in microchannels. Micro pumps have typically dimensions ranging within millimeters, and have the ability to pump fluids at volume flow rates ranging from fractions of a milliliter up to a several milliliters per minute. The wide availability of relatively cheap micro-machining techniques enables such devices to be viable, both technically and commercially. Portable dialysis machines and intravenous drug delivery (for instance, insulin) are examples of medical devices which comprise these micro pumps. In the developing field of micro-fluidics, so-called lab-on-a-chip devices exploit the laminar flow characteristics of small cross-section liquid channels to perform transport in a variety of chemical reactions and controlled mixing and liquid analysis, using very small volumes of liquids. These devices are finding increasing numbers of applications in bio-medical research. Such devices would benefit from the availability of a suitable and compatible micro pump either as a stand-alone or integrated component.
Micro pumps are often based on reciprocating diaphragms and make use of valves based for example on flexible flaps or diaphragms. Micro-pumps are generally only capable to induce very limited flow rates. Such flow rates are too low to be useful for some particular applications, for example in point-of-care medical devices in which speed and parallelization of analysis is important. Examples of existing micropumps are described in Abhari et al., Int. J. Electrochem. Sci. 7 (2012) 9765-9780, Chen et al., J. Micromech. Microeng. 18 (2008) 013001 (22pp), and Iverson et al. Microfluid Nanofluid 5 (2008) 145-174.
Another requirement for micro-pumps is high energy efficiency. This is important for mobile applications, particularly those in which power is supplied by batteries. It is desirable to minimize the power consumption and to maximize the time that the device can run on the battery.
Jamming of moving parts is another potential source of problems. Some applications use fluids that can cause moving parts to become jammed if the system is used for longer time. Examples would be the pumping of blood, insulin, etc. due to clotting and sedimentation. Micropumps featuring actuators with sliding surfaces, for instance between cylinders and pistons, and valves featuring contacting surfaces, such as flap or reed valves can suffer from reliability problems due to sticking and thus blocking of these sub-systems. Moreover, mechanical features typically do not scale down well. For example, flaps in microfluidic devices are unreliable, because Van der Waals forces have an important influence at microscopic level. In addition, sliding and moving surfaces can damage the fluid being pumped in the case of biological fluids. Rupturing of cell membranes due to moving parts, due to excessively high shear rates or due to pulsed pressure is an undesirable effect associated with displacement pumps and mechanical pumps. It would therefore be desirable to provide a compact pump, suitable for point-of-care medical devices. Advantageously such pumps also show a low power usage, are able to produce a flow of fluid that is responsive to the demands of the system in terms of flow rate and also do not introduce the cyclical pressure pulses that are usually associated with positive displacement pumps.
It is an object of embodiments of the present invention to provide a reliable and compact microfluidic pumping system. It is an advantage of embodiments of the present invention that pumps are provided with reduced or no back-flow. It is an advantage of embodiments of the present invention that pumps are provided having no need for mechanical moving parts.
The present invention relates to a microfluidic pumping system for providing continuous or pulsed pumping action of a sample fluid along a microfluidic channel of a microfluidic device, the pumping system comprising:
the at least one microfluidic rectification system being laid out in or along the microfluidic channel, and the at least one actuator being adapted for creating a pressure in the microfluidic channel, the system thus being adapted for providing continuous or pulsed fluid movement of the sample fluid in a predetermined direction along the microfluidic channel when actuation of the pumping fluid in the actuator channel takes place and further not providing substantial sample fluid movement when no actuation takes place. The at least one actuator may be adapted for providing sample fluid immobilization when no actuation takes place. The actuator may be adapted for providing continuous or pulsed unidirectional fluid movement of the sample fluid. It is an advantage of embodiments of the present invention that fluid can be provided in a predetermined direction while the pumping action is performed, and fluid movement or diffusion, such as back-diffusion, is reduced or even completely avoided when no pumping action is performed. Where in embodiments of the present invention, reference is made to a rectification system, reference is made to any system allowing flow in one or some directions and reducing the flow in at least one other direction. The rectification system may be embodied in different ways, such as for example based on diode like devices or devices directing fluids in one direction using the wettability properties of the walls.
The at least one actuator may branch out of the microfluidic channel, the branched-out actuator comprising a polarizer adapted to change, e.g. increase, wettability when active, the actuator further comprising surfaces adapted to decrease wettability when polarizers are inactive, thus adapted for providing a movement of fluid for creating a varying pressure in the microfluidic channel. It is an advantage of embodiments of the present invention that the pumped fluid itself creates pressure on the microfluidic channel, reducing the amount of fluid in contact with the pumping fluid and/or the amount of fluid that needs to enter in the actuator.
The at least one actuator may be a loop shaped actuator, part of the actuator channel having a common region with the microfluidic channel, the at least one actuator being adapted for pumping the pumping liquid around the loop such that during said pumping, sample fluid is flowing in between the pumping liquid flow. The polarizer may be localized in the loop or may be localized in the common region. The sample fluid flowing in between the pumping liquid, may be flowing in the loop or in the common region.
The rectification system may comprise a shaped junction of the microfluidic channel and the actuator channel providing reducing the flow of a pumping fluid in the microfluidic channel and of the sample fluid in the actuator channel, and wherein the actuator comprises electrodes for generating fluid motion. It is an advantage of embodiments of the present invention that continuous or pulsed pumping is obtained with a compact design without mechanical pieces, providing separation between pumped fluid and pumping fluid via design of the outlet taking into account contact angles of the fluids, preventing back flow and contamination.
The shaped junction may provide hydrophilic surface properties in the microfluidic channel that is intended to receive the sample fluid, and hydrophobic surface properties in the actuator loop to direct both fluids into their designated channel.
The pumping fluid and sample fluid may have different properties. The polarizer may be adapted for generating fluid motion by polarization across the interface between the pumping fluid and the sample fluid. It is an advantage of embodiments of the present invention that fluid can be provided in a predetermined direction while the pumping action is performed, and fluid movement or diffusion, such as back-diffusion, is reduced or even completely avoided when no pumping action is performed.
The actuator may be adapted to provide a back- and forth-movement of a predetermined volume, the actuator further being connected to the microchannel by a channel characterized by a volume being equal to or longer than the predetermined volume of the back- and forth-movement induced by the actuator. It is an advantage of embodiments of the present invention that the pumping fluid, such as oil or air, is distant from the microfluidic channel, reducing the chances of contamination of the pumped fluid.
At least one microfluidic rectification system may comprise at least one fluidic diode. It is an advantage of embodiments of the present invention that the pumping system is easy to produce, by etching for example, and it does not require moving parts, and ensures unidirectional flow.
At least one microfluidic rectification system may comprise at least one fluidic valve, e.g. at least one fluidic one-way valve. It is an advantage of embodiments of the present invention that, by not powering the fluidic valve, no backflow of the pumped fluid takes place, and further, if combined with a branched actuator, high control of the fluid direction is obtained.
The polarizer may comprise two electrode layers in different walls of the actuator channel, e.g. opposite walls of the actuator channel. It is an advantage of embodiments of the present invention that electrodes can be provided by known methods of deposition in integrated microfluidic systems.
The surface of the actuator may comprise at least one dielectric layer. It is an advantage of embodiments of the present invention that control via EWOD (electrowetting-on-dielectric) can be provided, and more flexibility of fluid is obtained, because fluid does not need to be electrically conductive.
The present invention also relates to a microfluidic system comprising at least one fluidic channel and one or more fluidic pumping systems as described above. It is an advantage of embodiments of the present invention that a resilient system without mechanical pumps can still provide fluidic pumping without the need of external pumps, increasing integrability and portability.
The microfluidic system may comprise a number N parallel pumping systems actuating with a 360°/N phase shift, for providing continuous or pulsed flow in a predetermined direction of a microfluidic system. It is an advantage of embodiments of the present invention that a unidirectional, very smooth continuous flow can be obtained. The microfluidic system may comprise two parallel pumping systems actuating with a 180° phase shift, for providing continuous flow in a predetermined direction of a microfluidic system.
The microfluidic system further may combine any or all of open-ended shaped or loop-shaped microfluidic channels for providing fluid rectification and/or pumping, branched-out actuators for providing pressure in the microfluidic channels, microfluidic diodes or one-way valves for fluid rectification, and portions of the microfluidic channel with a length and/or section adapted for increasing locally the fluid pressure and/or the volumetric flow rate. It is an advantage of embodiments of the present invention that highly integrated, complex microfluidic systems can be obtained without the need of bulky external or internal pumps, mechanical valves or pieces. The present invention also relates to a diagnostic device comprising at least one fluidic channel and one or more fluidic pumping systems according to any of the previous claims for pumping a sample fluid through the fluidic channel to an analyzer for analyzing the sample.
Particular and preferred aspects of the invention are set out in the accompanying independent and dependent claims. Features from the dependent claims may be combined with features of the independent claims and with features of other dependent claims as appropriate and not merely as explicitly set out in the claims.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiment(s) described hereinafter.
The drawings are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes.
Any reference signs in the claims shall not be construed as limiting the scope.
In the different drawings, the same reference signs refer to the same or analogous elements.
The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. The dimensions and the relative dimensions do not correspond to actual reductions to practice of the invention.
Furthermore, the terms first, second and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequence, either temporally, spatially, in ranking or in any other manner. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.
Moreover, the terms top, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein.
It is to be noticed that the term “comprising”, used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression “a device comprising means A and B” should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.
Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.
Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.
Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.
In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.
Where in embodiments of the present invention reference is made to “integrated”, reference is made to any type of integration in a substrate, such as for example monolithically integrated, heterogeneously integrated or even hybridly integrated.
Where in embodiments of the present invention reference is made to the pumped fluid, reference is made to the fluid that one wishes to propagate in the microfluidic device. Where in embodiments of the present invention reference is made to the pumping fluid, reference is made to the fluid that is used to generate the pumping action. This fluid is thus not of interest for analyzing or further use in the microfluidic system, but is introduced for inducing pumping action. Where in embodiments of the present invention reference is made to “fluid rectifier”, reference is made to a feature or device adapted to facilitate the flow of a fluid in one predetermined direction in a microfluidic device, while reducing or impeding the flow in other directions, thus obtaining a unidirectional current of fluid. For example, fixed geometries such as nozzles, diffusers, and the like provided along a microchannel qualify as rectifiers, because they facilitate flow in one direction and reduce or impede flow in the opposite.
Where in embodiments of the present invention reference is made to “wetting”, reference is made to the tendency of a fluid to cover a surface.
Where in embodiments of the present invention reference is made to interface energy or surface energy, reference is made to energy (per unit area) of an interface.
Where in embodiments of the present invention reference is made to a contact angle, the contact angle is defined as follows : In general a system will want to rearrange itself such that the total of all energies is as small as possible. In a three-phase system where only the interface energies play a role (=other energies such as the gravitional energy can be neglected), then at equilibrium the interface line between the two fluid phases will position itself at a certain angle with respect to the solid surface. This angle, measured through the liquid of interest, is called the contact angle (θ). In a solid-liquid-vapor system it depends on the interface energies as follows:
γsl+γlv cos θ−γsv=0 or cos θ=(γsv−γsl)/γlv
where γ is the interface energy, and the subscripts I, s, v refer to solid, liquid, vapor. More generally, in a solid-fluid 1-fluid 2 system, the contact angle θ1 with respect to fluid 1 is given by
γsf
and one could similarly define a contact angle θ2 with respect to fluid 2. The sum of these is then θ1+θ2=180°.
Where in embodiments of the present invention reference is made to capillary force, reference is made to the tendency of the interface between the three phases to move and minize the total energy. The energy gained when the interface moves over a distance is equal to the product of the capillary force and said distance.
Where in embodiments of the present invention reference is made to a hydrophilic surface, reference is made to a surface where the watery fluid tends to spread out. This corresponds to a contact angle θwatery fluid<90°.
Where in embodiments of the present invention reference is made to a hydrophobic surface, reference is made to a surface where the watery fluid tends to contract. This corresponds to a contact angle θwatery fluid>90°.
Where in embodiments of the present invention reference is made to electrowetting, reference is made to the following effect : In embodiments of the present invention typically one of the fluids interacts strongly with electric fields e.g. because of dissolved ions (these can even be background ions, such as CO2 dissolved in water forming carbonic acid H2CO3 and forming H+, HCO3
In a first aspect, the present invention thus relates to a microfluidic pumping system for providing continuous or pulsed pumping action of a sample fluid along a microfluidic channel of a microfluidic device. The pumping system comprises at least one actuator comprising an actuator channel and a polarizer. The polarizer and the surfaces of the actuator channel are adapted for generating pumping fluid motion by alternate variation of the wetting properties in the actuator channel. The pumping system also comprises at least one microfluidic rectification system for facilitating the flow of a sample fluid in a predetermined direction and reducing the flow in another direction. The at least one microfluidic rectification system is being laid out in or along the microfluidic channel, and the at least one actuator is adapted for creating a pressure in the microfluidic channel, the system thus being adapted for providing continuous or pulsed fluid movement of the sample fluid in a predetermined direction along the microfluidic channel when actuation of the pumping fluid in the actuator channel takes place and further not providing substantial sample fluid movement when no actuation takes place. The at least one actuator may be adapted for providing sample fluid immobilization when no actuation takes place. The actuator may be adapted for providing continuous or pulsed unidirectional fluid movement of the sample fluid.
In embodiments of the present invention, movement of a fluid in a microfluidic channel is thus obtained by changing the wetting characteristics of the surface of an actuator for liquids. The liquid interface position is altered by changing the wetting properties of the surfaces, e.g. by applying an electric field or an electric potential. By appropriately controlling the hydrophilic or hydrophobic characteristics, the fluid can be moved through the microfluidic channel. To prevent fluid to flow in an unwanted direction, fluid rectifiers can be used which allow the flow only in one direction of the channel.
In the following, two exemplary embodiments of the present invention are shown. Different pumping methods are described, one making use of back-and-forth fluid motion in combination with fluid rectifiers, one by using an actuator that circulates a pumping fluid and that pulls the sample fluid further during the circulation of the pumping fluid.
In the embodiment of
The pumping fluid 213 must be chosen in accordance with the application of the device so it is immiscible with the pumped fluid 203. The pumping fluid 213 must in addition also have different electrowetting properties than the pumped fluid 203. The ring 305 is almost completely filled with the pumping fluid 213. If the fluid to be pumped is water-based, the pumping fluid in the ring may be oil. By th movement of the pumping fluid 213, a gradient of pressure is generated, the pumped liquid 203 advances and eventually leaves through the outlet 303, thus providing actuation using the loop and a unidirectional stream of pumped liquid 203 through the channel.
By way of illustration,
The width of the channel 301 used may depend on the fluid to be analysed. A narrow channel provides the advantage of a better control (lower electric fields, . . . ) and enables more actuate measurements of molecular properties. However, capillary forces of the liquid in those narrow channel can be too high. The average radius of the loop may advantageously be selected such that it is larger than 40 times the width of the channel. The microfluidic channel connected to the inlet and the one connected to the outlet may be tangential to the loop, and may even be colinear. By way of illustration, embodiments of the present invention not being limited thereto, a number of different outlet configurations 303b and 303c are shown in
Other rectifier and actuator may be provided. For example, fluidic diodes are fluidic devices or channel features that allow flow preferentially in one direction. These features cause that flow resistance for forward motion to be small, while providing large flow resistance for backward motion. In some embodiments of the present invention, a fluidic diode may comprise a set of cavities along the channel, with geometric shapes which give the effect of unidirectionality of a diode. A single geometric formation may be enough, but in the case of diodes, it is preferred a set comprising a plurality of these geometric formations or shapes, because efficiency increases, so less amount of liquid flows back. The present examples are not limiting, and the present invention can work with any other fluidic diode as well. By way of illustration, the principles of operation of an exemplary bead-based diode are shown in
In the embodiment of
The length L of the reservoir of the actuator 405, and/or of the connection 406 between the actuator 405 and the microchannel, can be made long enough to act as a buffer, preventing leaks of the pumping fluid 213 into the channel. For example, if oil is used, contamination of the fluid due to oil entering the microchannel can be avoided by providing long connections or actuators. Presence of bubbles in the microchannels, which may clog the channels, can be avoided also if the second fluid 213 is gaseous (e.g. air) by use of a sufficiently long actuator 405 and/or actuator connection 406.
Powering the electrodes on the ring 305 of the pump of
The exemplary embodiment of
Other types of diodes may be used as well. Another type of static-geometry, passive diode is the Tesla valve. Gamboa et al., Journal of Fluids Engineering 127, 339-346 (2005) have shown that this diode can operate in the laminar flow regime, with a similar lack of rectification at Re<200. Many other types of diodes can be used. Examples of diodes that do work at very low Reynolds numbers are micro-check valves and bead-based diodes.
Combinations of features may be provided. For example, a couple of triangular cavities 404 as in
In embodiments of the present invention, external pressure is not essential for the operation of the pump. If needed, it can be applied only to provide a first filling of the microchannel, and in particular of the actuator, but during the rest of operation pressure is provided by the actuators. Electrical contacts (or any other means to vary wetting and/or provide an alternate fluid movement) are needed only in the actuators. Thus, contacts are not needed in the places where the fluid is required and liquid can be sent to parts of the system distanced from the actuators. The fact that the actuation is produced in a branch channel means that the interface between the fluids (e.g. the interface between water-based pumped fluid and oil or air), necessary for creating unbalance in the energy and produce forces, may be distant from the microchannel. This means that the fluid may be continuously pumped or pumped in a pulsed manner in the present invention, in contrast to pumping of droplets along a channel. Pumping of droplets may be locally present, as shown by the droplets 223 inside of loop-shaped pumps like in
In a second aspect of the present invention, a fluidic system comprising a pumping system according to embodiments of the first aspect is described. Some embodiments of the present invention are conceptually similar to an electric rectifier circuit in which electric potential can be identified with fluid pressure, and charge flow or electric current can be identified with liquid flow, or an electric charge pump circuit. By extension and analogy, all translations of electrical rectifiers and charge pumps into a fluidic analogy are included as well. For example, an external actuator can be seen as an alternate voltage source, a microfluidic diode as an electrical diode, or a ring pump as a transistor. Some embodiments are discussed in the following paragraphs, the present invention not being limited to these examples.
The upper right drawing 510 shows a fluidic analogy of an “electrical rectifier”. In this configuration, parallel branches are operated out of phase by a couple of actuators 405, 415. This particular configuration provides a continuous or pulsed flow, much smoother than in the previous configuration 500, if both actuators are operated 180° out of phase, so the actuator 405 is pushing fluid upwards via the upper fluidic diode 403 of the actuator branch, while the opposite actuator 415 is pulling (or drawing) fluid through its lower fluidic diode 412 in one cycle, and in the following cycle, the actuator 405 is sucking fluid upwards via the upper fluidic diode 402 of the actuator branch, while the opposite actuator 415 is pushing fluid through its upper fluidic diode 413. The lower drawing 520 shows a plurality of modules, increasing the distance at which fluid can be provided by increasing locally the pressure along the microchannel. Intermediate fluid rectifiers such as (micro)fluidic diodes 521 may be optionally included, but are not essential.
Alternatively, the embodiment of a pump shown in
Valves can also be combined with other configurations, such as the rectifier configuration 510 of
As an example of possible configurations and combinations thereof, various microfluidic circuits schemes 700, 710, 720, 730 are shown in
In embodiments using actuation via energization of electrodes and capacitance, using air as the low-s fluid is advantageously easy to implement. Typically, air is provided in the “free connection” (analogous to “ground potential” in an electric circuit) opposite to the connection to the microfluidic channel where pumping action is required. In such embodiments, since air is highly compressible, including in series a plurality of actuators usually does not result in addition of pressures. In the configurations with a linear actuator, the “free connection” of the actuator is typically at atmospheric pressure. It is possible to put “repeater” pumps after a predetermined channel length, as shown in the left configuration 700 and bottom configuration 730. This additional portion, indicated by a resistor symbol 701 of
The microchannels, pumps and other elements of the microfluidic system may be provided in a material that is not completely opaque. This allows optical monitoring of the process. For example, they may be provided in a transparent or translucent substrate and covered by a transparent cap.
In a third aspect of the present invention, a method of fabrication of a system according to the first or second aspect is provided. A combination of several known techniques and industrial routes can be used for manufacturing such systems and structures. For example, two microfabricated wafers are bonded together with enclosed microchannels and electrowetting-controlled fluidic devices in between. The electrodes and electrical contacts are fabricated on the bottom wafer with fluidic input/output ports drilled through, for example a glass layer, or any other type of suitable material such as a composite, polymer, ceramic, a semiconductor wafer, a 6-inch-diameter silicon wafer, etc. Semiconductor wafers have the advantage that well known routes of processing are already industrially implemented. The 4-inch-diameter top wafer can be made of any suitable material, preferably transparent, for example Pyrex, which allows for optical observation of the liquids in the m icrochannels.
For the preparation of the bottom wafer, a 2-μm-thick layer of SiO2 is deposited by plasma-enhanced chemical vapor deposition (PECVD). Next, the electrode layer is formed by depositing and patterning a 300-nm-thick layer of aluminum. Any other suitable conductor, such as a metal (gold, platinum, copper, etc.) can be used. The electrode layer may comprise connections for an electrical source. A layer of SiO2 is then deposited and polished by chemical mechanical planarization (CMP) to a thickness of 2 μm. After CMP, the electrical-contact-pad openings are patterned and wet-etched in hydrofluoric acid. The microchannel layer is then formed by a 11-μm-thick patterned SU-8 photoresist. Next, a hydrophobic, amorphous fluoropolymer layer (aFP) film is spun on the wafer so that the aFP covers the top of the SU-8, including the channel side and bottom walls. The spun solution may comprise 3% aFP suspended in a perfluorinated solvent. After spinning, the wafer is baked at 90° C. for 30 s to evaporate the remaining solvent, resulting in a 200-nm-thick film. This layer is further hardened by vacuum baking at 150° C. for 1 min. In the final process step, an ultrasonic drill creates 2-mm-diameter fluidic ports through the wafer. A thick photoresist layer protects the aFP layer from damage during the drilling and is removed with acetone after drilling.
For the preparation of the top wafer, the microchannel layer is formed by a 11-μm-thick patterned SU-8 photoresist. Next, a transparent 100 nm layer of ITO is sputtered onto the wafer. This provides an electrode, and may be connectable to a source or to ground. Finally, 2% aFP is spun on the wafer and baked. The aFP application process is the same as that used for the bottom wafer, except in this case the film is only 80 nm thick. The actuator may comprise an width of around 100 microns, while the height (d) may be much smaller, for example 10 microns, or have two different sizes. The actuator may comprise two regions, one region A (with a distance d1 of 22 microns between the upper and lower wall) connected to the microfluidic channel and filled with aqueous solution, and another stout region B (with a distance d2 of 11 microns) mainly comprising oil or air, separated by a step or a slope. A high energization and pulling force of fluid from the tall region into the stout region is provided, thereby providing in the tall region a lower capacitance than that of the stout region.
The microfluidic layer may comprise also fluidic diodes, by providing shapes, cavities, neckings or other geometrical features, by known methods such as etching. These may have few microns, for example a single cavity 404 of
The final microfluidic structure is formed by thermally bonding the aFP surfaces of the two wafers. The bond is formed by applying pressure to the top of the Pyrex wafer at 150° C. After bonding, liquid connections are made with port assemblies, which are adhered (e.g. with glue such as epoxy) to the bottom of the silicon wafer. The ports can be a threaded component that allows for standard-size tubing to be conveniently connected. For example, 1-mm-diameter Teflon tubing can be used. Other tubings can be used, or no tubings, thus providing the liquid through open ports by pipetting, injection, etc.
In a fourth aspect, a diagnostic device is provided comprising fluidic channels.
| Number | Date | Country | Kind |
|---|---|---|---|
| 17210837.5 | Dec 2017 | EP | regional |
| 18156738.9 | Feb 2018 | EP | regional |
