Background

[0001] Digital microfluidic (DMF) devices may be used to perform operations on volumes of fluid, such as the manipulation of fluid droplets to facilitate handling and testing of various fluids on a small scale. Such devices may be used in the medical industry, for example to analyze proteins, analyze deoxyribonucleic acid (DNA), detect pathogens, perform clinical diagnostic testing, and/or for synthetic chemistry, among other types of industries and/or for other purposes.

Brief Description of the Drawings

[0002] FIGs. 1A-1 E illustrate example digital microfluidic (DMF) devices, in accordance with examples of the present disclosure.

[0003] FIG. 2 illustrates another example DMF device, in accordance with examples of the present disclosure.

[0004] FIG. 3 illustrates an example apparatus including a DMF device and coupled circuitry, in accordance with examples of the present disclosure.

[0005] FIGs. 4A-4C illustrate different example pressure regulators of a DMF device, in accordance with examples of the present disclosure.

[0006] FIG. 5 illustrates an example operation of a DMF device, in accordance with examples of the present disclosure.

[0007] FIG. 6 illustrates an example method for generating fluid droplets of reaction fluids in a DMF device, in accordance with examples of the present disclosure. Detailed Description

[0008] In the following detailed description, reference is made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific examples in which the disclosure may be practiced. It is to be understood that other examples may be utilized and structural or logical changes may be made without departing from the scope of the present disclosure. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present disclosure is defined by the appended claims. It is to be understood that features of the various examples described herein may be combined, in part or whole, with each other, unless specifically noted otherwise.

[0009] Digital microfluidic (DMF) devices may be used to perform chemical processing operations on different fluids in parallel by providing digitized movement of reaction fluids throughout the DMF device. The digitized movement of reaction fluids may be achieved using a plurality of electrodes that form part of or are coupled to the DMF device, and which provide an electric field to drive the flow of reaction fluids as fluid droplets within an interconnected chamber. The electrodes may be arranged in a two-dimensional array and may be individually addressed by circuitry, sometimes herein referred to as “selective actuation”, to provide the digitized and controlled flow of picoliter to microliter sized fluid droplets of reaction fluids by drawing the fluid droplets toward an addressed electrode. As the respective electrode is addressed, the addressed electrode provides an electric field within the DMF device and/or onto the reaction fluid, and due to a charge of the reaction fluid, a fluid droplet of the reaction fluid is directed along a microfluidic path. For example, respective ones of the plurality of electrodes may be sequentially actuated to draw the fluid droplet of the reaction fluid along a respective microfluidic path. The movement of the fluids within the DMF device may be used to move, mix, and/or split fluid droplets of reaction fluids into two respective smaller fluid droplets, among other uses, and to drive a chemical processing operation thereon.

[0010] DMF devices may operate using a multiphase flow comprising a chemical component in a continuous phase and another chemical component in a droplet phase. For example, a carrier fluid may be in a continuous phase and used to generate and carry a fluid droplet of the reaction fluid, e.g., in a droplet phase, throughout the DMF device and to drive chemical processing operations on the fluid droplet of the reaction fluid. In various examples, the DMF device includes the interconnected chamber connected to a plurality reaction fluid wells. The carrier fluid may fill the interconnected chamber and the reaction fluid wells. The reaction fluids may be inserted into the plurality of reaction fluid wells and carried through at least one of a plurality of microfluidic paths defined by the interconnected chamber via the carrier fluid. Electrodes of the array may be disposed proximal to the reaction fluid well to move the reaction fluids along the reaction fluid well to the interconnected chamber. As the reaction fluids are moved into the interconnected chamber, individual fluid droplets of the reaction fluids may be separated from each other, with the carrier fluid being interposed between and/or generally surrounding the fluid droplets of the reaction fluids. Interior surfaces of the DMF device associated with fluid flow may be coated with a hydrophobic coating to assist with the fluid flow.

[0011] In various implementations, the selective actuation of electrodes may not result in a fluid droplet of the reaction fluid separating and flowing into the interconnected chamber due to back pressure of the carrier fluid within the reaction fluid wells. For example, the reaction fluid may need to overcome the back pressure of the carrier fluid to advance to the interconnected chamber. In some implementations, the fluid droplets of reaction fluids may be generated with back pressure present by adding surfactants to the reaction fluids to assist with movement or by adjusting the design of the DMF device, such as the roll off angle of the hydrophobic coating on interior surfaces of the DMF device. However, adding surfactants may impact the chemical processing or analysis performed and the design may be adjusted for each specific use, which may increase time and cost in manufacturing the DMF devices.

[0012] Examples of the disclosure are directed to a DMF device which includes a pressure regulator to adjust a pressure of the carrier fluid and thereby reduce the driving force for moving fluid droplets of reaction fluids from the reaction fluid wells into the interconnected chamber for chemical processing. The adjusted pressure of the carrier fluid may be timed with selective actuation of electrodes associated with the reaction fluid wells to synchronize the adjusted pressure with the fluid droplet formation. After fluid droplets of the reaction fluids enter the interconnected chamber, the pressure regulator may return the pressure of the carrier fluid back to the normal state, which may be associated with a higher pressure than the adjusted pressure. A normal state of the DMF device or normal pressure, as used herein, includes a state of the DMF device associated with and/or including the pressure of the carrier fluid being non-adjusted or actuated by the pressure regulator. The selective and timed adjustment of the pressure of the carrier fluid is sometimes herein referred to as “pressure pulsing.” By performing pressure pulsing, fluid droplets of the reaction fluids may be generated and moved into the interconnected chamber using lower driving force applied by the select electrodes as compared to keeping the pressure of the carrier fluid at normal state (e.g., first pressure). For example, the lower the back pressure of the carrier fluid, the lower a driving force applied in order to advance the fluid droplets of the reaction fluids. Furthermore, the fluid droplets of the reaction fluids may be generated using the variable carrier fluid pressure without modifying the reaction fluid with surfactant additives, or adjusting other DMF features, such as adjusting the hydrophobic coating quality, or well or electrode design.

[0013] An example DMF device comprises a housing including an interconnected chamber and with a two-dimensional array of electrodes couplable to the interconnected chamber, a plurality of reaction fluid wells fluidically coupled to the interconnected chamber and to contain a plurality of reaction fluids, and a carrier fluid reservoir fluidically coupled to the interconnected chamber and the plurality of reaction fluid wells, the carrier fluid reservoir to contain a carrier fluid. The example DMF device further comprises a pressure regulator coupled to the carrier fluid reservoir.

[0014] In some examples, the DMF device further includes circuitry communicatively coupled to the two-dimensional array of electrodes and the pressure regulator to selectively actuate select electrodes of the two- dimensional array and the pressure regulator to cause movement of fluidic droplets of the plurality of reaction fluids into the interconnected chamber from the plurality of reaction fluid wells.

[0015] In some examples, the circuitry is to actuate the pressure regulator such that the pressure regulator moves a component of the pressure regulator to adjust pressure of the carrier fluid within the plurality of reaction fluid wells between a first state of the DMF device at a first pressure and a second state of the DMF device at a second pressure below the first pressure. For example, the first state may include a normal state associated with a first pressure and the second state may be associated with the second pressure that is lower than the first pressure.

[0016] In some examples, the DMF device includes a fluidic inlet fluidically coupled to the carrier fluid reservoir and to the interconnected chamber. In such examples, the carrier fluid reservoir is disposed outside the housing and fluidically coupled to the fluidic inlet, and the pressure regulator is disposed outside the housing and includes a linear actuator to change an elevation of the carrier fluid reservoir. The changed elevation may cause a change in hydraulic head of the carrier fluid, which results in the second pressure below the first pressure.

[0017] In some examples, the pressure regulator includes a piston disposed in the carrier fluid reservoir, wherein the piston is to move between a first position and a second position within the carrier fluid reservoir.

[0018] In some examples, the pressure regulator includes a membrane and an electromagnetic coil or piezo-electric component disposed within the carrier fluid reservoir, wherein the electromagnetic coil or piezo-electric component is coupled to the membrane to move the membrane between a first position and a second position within the carrier fluid reservoir.

[0019] In some examples, the DMF device further includes a pressure sensor disposed with the carrier fluid reservoir.

[0020] In some examples, the housing further includes a base substrate and a top substrate, the interconnected chamber including a bottom surface defined by the base substrate and a top surface defined by the top substrate and the two-dimensional array of electrodes being couplable to the base substrate. And, the carrier fluid is contained within the interconnected chamber, the plurality of reaction fluid wells, and the carrier fluid reservoir.

[0021] Some examples are directed to an apparatus comprising a DMF device, a two-dimensional array of electrodes, and circuitry. The DMF device including a housing that defines an interconnected chamber, a plurality of reaction fluid wells fluidically coupled to the interconnected chamber, the plurality of reaction fluid wells to contain a plurality of reaction fluids, a carrier fluid reservoir fluidically coupled to the interconnected chamber and the plurality of reaction fluid wells, the carrier fluid reservoir to contain a carrier fluid, and a pressure regulator coupled to the carrier fluid reservoir to adjust a pressure within the plurality of reaction fluid wells. The apparatus further includes a two-dimensional array of electrodes coupled to and disposed along the interconnected chamber, and circuitry communicatively coupled to the two-dimensional array of electrodes and the pressure regulator to selectively actuate electrodes of the two-dimensional array of electrodes and the pressure regulator to adjust a pressure of the carrier fluid within the plurality of reaction fluid wells and to drive movement of fluid droplets of the plurality of reaction fluids into the interconnected chamber from the plurality of reaction fluid wells.

[0022] In some examples, the apparatus further includes a driving instrument including the circuitry and the two-dimensional array of electrodes, the driving instrument to receive the DMF device.

[0023] In some examples, the circuitry is to selectively actuate the electrodes of the two-dimensional array of electrodes to form the fluid droplets of the plurality of reaction fluids as surrounded by the carrier fluid, and actuate the pressure regulator to adjust the pressure of the carrier fluid within the plurality of reaction fluid wells and to drive the movement of the fluid droplets of the plurality of reaction fluids into the interconnected chamber.

[0024] In some examples, the circuitry is to actuate the pressure regulator to adjust the pressure of the carrier fluid between a first pressure and a second pressure, wherein the pressure regulator is a mechanical mechanism coupled to or disposed within the carrier fluid reservoir. [0025] Some examples are directed to a method of operating the DMF device and/or apparatus. An example method comprises selectively actuating respective electrodes of a two-dimensional array of electrodes of a DMF device to form fluid droplets of a plurality of reaction fluids disposed in a plurality of reaction fluid wells of the DMF device, wherein the fluid droplets of the plurality of reaction fluids are surrounded by a carrier fluid, and selectively actuating a pressure regulator coupled to a carrier fluid reservoir of the DMF device, thereby causing a pressure of the carrier fluid within the plurality of reaction fluid wells to adjust from a first pressure to a second pressure. The method further includes, in response to the selective actuation of the respective electrodes and the pressure regulator, causing the fluid droplets of the plurality of reaction fluids to move into an interconnected chamber of the DMF device from the plurality of reaction fluid wells.

[0026] In some examples, the method further includes synchronizing the selective actuating of the respective electrodes with the selective actuating of the pressure regulator, such that the pressure of the carrier fluid adjusts to the second pressure in response to or concurrently with the formation of the fluid droplets of the plurality of reaction fluids.

[0027] In some examples, the method further includes causing the pressure of the carrier fluid to adjust back toward the first pressure in response to the fluid droplets of the plurality of reaction fluids moving into the interconnected chamber of the DMF device.

[0028] As used herein, a chamber refers to or includes an enclosed and/or semienclosed region of the DMF device, which may be formed of an etched or micromachined portion (e.g., negative space forming a conduit in a substrate or substrates) and which may be used to perform chemical processing on fluids therein. An interconnected chamber refers to or includes a chamber that is couplable to an array of electrodes to define a plurality of microfluidic paths which may kept discrete or may overlap via the selective actuation of the electrodes. In some examples, the fluid droplet of a reaction fluid may include a volume of about 1 microliter (pL) or less, such as a volume of between about 0.1 pL and about 1 pL, about 0.25 pL and about 1 pL, about 0.5 pL and about 1 pL, about 0.5 pL and about 0.75 pL, about 0.25 pL and about 0.75 pL, or about 0.1 pL and about 0.5 pL, among other ranges. In some examples, the fluid droplet may be larger, such as on a nanoliter (nL) scale or between about 0.1 nL and about 0.5 nL. A channel refers to or includes a path through which a fluid or semi-fluid may pass, which may allow for transport of volumes of fluid on the order of pL, nanoliters, picoliters, or femtoliters. A well, such as a reaction fluid well, refers to or includes a column capable of storing a volume of fluid. In some examples, the well may store a volume of fluid that includes more than one droplet of fluid, such as at least two fluid droplets of a reaction fluid. In some example, a well may store a volume of fluid in a range between about 1 pL and about several milliliters (mL) of fluid. In some examples, the well may store a volume of fluid between about 1 pL and about 1 mL, about 1 pL and about 500 pL, about 1 pL and about 50 pL, about 1 pL and about 10 pL, or about 1 pL and about 5 pL, among other volume ranges. A reservoir refers to or includes a column where fluid collects, such as the carrier fluid. In some examples, a reservoir may collect a larger volume of fluid than a well may store.

[0029] A reaction fluid refers to or includes fluid containing substances, molecules, mixtures, and/or other components used to drive a biochemical reaction. A fluid droplet of a reaction fluid, as used herein, refers to or includes a discrete portion of fluid (e.g., a liquid), which may be surrounded by a carrier fluid. A carrier fluid refers to or includes fluid that flows through portions of the DMF device and which carries solid and/or fluid particles, such as fluid droplets of the reaction fluids. As an example of a fluid droplet of the reaction fluid, an immiscible fluid, such as an aqueous solution, is surrounded by an oil phase. Fluid droplets of reaction fluids may be formed from a fluid packet of the reaction fluid. A fluid packet of the reaction fluid refers to or includes a volume of fluid that is larger than a fluid droplet of the reaction fluid.

[0030] Turning now to the figures, FIGs. 1 A-1 E illustrate example DMF devices, in accordance with examples of the present disclosure.

[0031] As shown in FIG. 1A, an example DMF device 100 comprises a housing 102 including an interconnected chamber 104 and with a two-dimensional (2D) array of electrodes 106 couplable to the interconnected chamber 104. The housing 102 may include substrates, with the interconnected chamber 104, among other components, formed by and/or between the substrates as etched or micromachined portions. The etched or micromachined portions forming the interconnected chamber 104, and optionally additional chambers, wells, reservoirs, and/or channels may be a height in the range of about 10 micrometer (pm) to about 2 millimeter (mm). Each substrate, such as the top and base substrates 102-1 , 102-2 illustrated by FIG. 1 B, may be formed of a plurality of different materials which are in layers, as further described herein. Referring back to FIG. 1A, the interconnected chamber 104, and optionally other chambers, wells, reservoirs, and channels, may be formed by etching or micromachining processes in a substrate to form the various etched or micromachined portions. As such, the chamber(s), wells, reservoirs and/or channels may be defined by surfaces fabricated in the substrate(s) of the DMF device 100.

[0032] The 2D array of electrodes 106 are couplable to the housing 102 and may be disposed proximal to the interconnected chamber 104. As used herein, a 2D array of electrodes refers or includes to a plurality of electrodes which are arranged in an array in at least two directions. The interconnected chamber 104 may define a plurality of microfluidic paths via use of the 2D array of electrodes 106. For example, the interconnected chamber 104 may be used to provide the plurality of different microfluidic paths via selective actuation of respective electrodes of the 2D array of electrodes 106. In some examples, the 2D array of electrodes 106 are positioned along and/or exposed to the interconnected chamber 104. In other examples, the 2D array of electrodes 106 are coupled to the housing 102, as further described herein. Proximal, as used herein (e.g., proximal to the interconnected chamber 104), refers to or includes being disposed in line with a portion of the DMF device 100, such as being positioned along, above, below, and/or exposed to the portion of the DMF device 100.

[0033] As further described herein, electrodes of the 2D array of electrodes 106 are to actuate to selectively move a plurality of reaction fluids along respective microfluidic paths within the interconnected chamber 104. Example electrodes include transparent electrodes, ring electrodes, linear electrodes, almost continuous electrodes, ground electrodes, and/or actuating electrodes, among others. The electrodes of the 2D array of electrodes 106 may be the same size or different sizes. The electrodes may be formed of a conductive material, such as metal, conductive polymers, indium tin oxide (ITO), transparent conductive oxides, carbon nanotube, among other material.

[0034] As used herein, a transparent electrode refers to or includes an electrode that is transparent or semi-transparent. Use of transparent electrodes, along with a transparent lid, as further described below, may allow for a user to visually view fluid flow within the DMF device 100 while chemical operations are being performed by the DMF device 100 and/or to verify proper fluid processing is occurring. A ring electrode refers to or includes an electrode which is annulus shaped. The ring electrode(s) may be shaped to extend around a portion of the DMF device 100, such as a portion of the interconnected chamber 104. A linear electrode refers to or includes an electrode which extends in a straight line and for a portion of the DMF device 100. A plurality of linear electrodes may be placed in the 2D array along a portion of the DMF device 100, and may provide greater control of fluid flow, as compared to an almost continuous electrode, due to known electrode positions and localized resolution. An almost continuous electrode refers to or includes an electrode which extends along a portion of the DMF device 100, such as along the bottom surface or top surface of the interconnected chamber 104 (e.g., see electrode 106-5 of FIG. 1 B). An almost continuous electrode may reduce manufacturing costs, as compared to an array of linear electrodes.

[0035] A ground electrode refers to or includes an electrode that provides or establishes a connection to ground. An actuating electrode refers to or includes an electrode that is actuated (e.g., a voltage is applied thereto by coupled circuitry), and in response, generates an electric field based on a differential between the actuating electrode (e.g., the applied voltage) and ground. In some examples, ground may be provided by a ground electrode, and in other examples, ground is provided by fluid within the DMF device 100. Use of a ground electrode may provide greater control of fluid flow and/or formation of a fluid droplet of the reaction fluids as compared to use of fluid within the interconnected chamber 104 as ground. Using fluid as ground may reduce manufacturing costs.

[0036] The DMF device 100 further includes a plurality of reaction fluid wells 108 fluidically coupled to the interconnected chamber 104 and to contain a plurality of reaction fluids. The plurality of reaction fluid wells 108 may be disposed within the housing 102, such as between the substrates (e.g., between the top substrate 102-2 and the base substrate 102-1 illustrated by FIG. 1 B). As further described herein, a user may insert the plurality of reaction fluids into the plurality of reaction fluid wells 108 via fluidic inlets, such as fluidic inlets 111 -1 , 111 -2, 111 -3, 111 -4, 111 -5, 111 -6, 111 -7, 111 -8 as illustrated by FIG. 1 C.

[0037] Referring to FIG. 1A, the DMF device 100 includes a carrier fluid reservoir 110 and a pressure regulator 112. The carrier fluid reservoir 110 is fluidically coupled to the interconnected chamber 104 and the plurality of reaction fluid wells 108. The carrier fluid reservoir 110 contains a carrier fluid used as a carrier to move fluid droplets of the reaction fluids through the DMF device 100. The carrier fluid may be inserted to the carrier fluid reservoir 110, in some examples, via a fluidic inlet, such as one of fluidic inlets 111 -1 , 111 -2, 111 -3, 111 -4, 111 -5, 111 -6, 111 -7, 111 -8 illustrated by FIG. 1 C.

[0038] Referring to FIG. 1 A, the pressure regulator 112 is coupled to the carrier fluid reservoir 110. The pressure regulator 112 may be used to provide a variable carrier fluid pressure. As used herein, a pressure regulator refers to or includes circuitry and/or a physical structure that causes adjustment in pressure of the carrier fluid, such as when the carrier fluid is contain within the interconnected chamber 104, the plurality of reaction fluid wells 108, and the carrier fluid reservoir 110. Example pressure regulators include a linear actuator, such as a lift or stage, a robotic arm, a gantry, and/or a pulley system that moves the carrier fluid reservoir 110 or a portion thereof in a vertical axis, a piston disposed in the carrier fluid reservoir 110, and a membrane and an electromagnetic coil or piezo-electric component disposed within the carrier fluid reservoir 110, among other regulators. Example pressure regulators are further illustrated by FIGs. 4A-4C. [0039] Although the carrier fluid reservoir 1 10 and the pressure regulator 112 are illustrated by FIG. 1 A as being disposed in the housing 102 of DMF device 100, examples are not so limited. In some examples, the carrier fluid reservoir 1 10 and the pressure regulator 112 are disposed outside the housing 102 and are coupled thereto. In some examples, the carrier fluid reservoir 1 10 may include a first portion disposed within the housing 102 and a second portion disposed outside the housing 102, such as illustrated by FIGs. 4A-4C.

[0040] The DMF device 100 illustrated by FIG. 1 A may include variations, some of which are illustrated by FIGs. 1 B-1 E. Example variations include, but are not limited to, top and base substrates forming the interconnected chamber, electrodes disposed on the top and/or base substrates of the interconnected chamber, and electrodes disposed on an additional substrate couplable to the housing, among other variations. Each DMF device of FIGs. 1 B-1 E includes an implementation of the DMF device 100 of FIG. 1 A, including at least some of the same features and components, as illustrated by the common numbering. The common features and components are not repeated for ease of reference.

[0041] FIGs. 1 B-1 E illustrate an example implementation of the DMF device 100 of FIG. 1 A. FIG. 1 B is a cross-sectional view of the interconnected chamber 104 of the example implementation of the DMF device 100 (from line A of FIG. 1 C). FIG. 1 C is a top view of the example implementation, and FIG. 1 D is another cross-sectional view of the example implementation (from line B of FIG. 1 C). As shown, the housing 102-1 , 102-2 of the DMF device 100 includes a base substrate 102-1 and a top substrate 102-2. In some examples, the top substrate 102-2 may form or include a lid of the DMF device 100. In some examples, the top substrate 102-2, or a portion thereof, may be transparent. In some examples, the top substrate 102-2 may be transparent, and, in other examples, both the top and base substrates 102-1 , 102-2 are transparent. A transparent substrate(s) (and optionally electrodes) may allow for optical monitoring of fluid flow and/or chemical operations within the DMF device 100 by a user, which may be used to visually verify the DMF device 100 is functioning properly.

[0042] In some examples, the interconnected chamber 104 includes a bottom surface 109 defined by the base substrate 102-1 and a top surface 107 defined by the top substrate 102-2. As used herein, a bottom surface of the interconnected chamber refers to or includes a floor or lower surface of the chamber with respect to gravity. A top surface of the interconnected chamber refers to or includes a ceiling or overhead surface of the chamber with respect to gravity. The carrier fluid 114 may be contained within the interconnected chamber 104, the plurality of reaction fluid wells (e.g., well 108-1 ), and the carrier fluid reservoir (e.g., carrier fluid reservoir 110 illustrated by FIG. 1 D). [0043] The plurality of electrodes 106-1 , 106-2, 106-3, 106-4, 106-5 of the DMF device 100 may be arranged in a 2D array (herein generally referred to as “the 2D array of electrodes 106” for ease of reference) and are coupleable to the base substrate 102-1 . In some examples, and as shown by FIG. 1 B, the 2D array of electrodes 106 are disposed on or within the base substrate 102-1 . In some examples, the 2D array of the plurality of electrodes 106 may extend level with or extrude above the bottom surface 109 of the chamber 104 as defined by the base substrate 102-1 , such that the electrodes may be in contact with fluids 114, 115-1 , 115-2 contained in the interconnected chamber 104. However, examples are not so limited, and the 2D array of electrodes 106 may be disposed within the base substrate 102-1 and may not be exposed to fluids in the interconnected chamber 104, or may include a coating disposed on the 2D array of electrodes 106 and/or may be disposed in another substrate, such as substrate 121 illustrated by FIG. 1 E.

[0044] Referring to FIG. 1 B, in some examples, the electrodes of the 2D array of electrodes 106 include actuating electrodes 106-1 , 106-2, 106-3, 106-4 and a ground electrode 106-5. The actuating electrodes 106-1 , 106-2, 106-3, 106-4 may be disposed on or within the base substrate 102-1 and the ground electrode 106-5 may be disposed on or within the top substrate 102-2. Use of a ground electrode 106-5 with plurality of actuating electrodes 106-1 , 106-2, 106- 3, 106-4 may allow for greater control of fluid flow and/or formation of fluid droplets of the reaction fluids as compared to using fluid control without the ground electrode 106-5. For example, to provide flow, the charge from the actuating electrodes 106-1 , 106-2, 106-3, 106-4 may go to ground. Without the use of the ground electrode 106-5, a stray charge may accumulate in the DMF device 100, which produces an electric field and causes forces on fluid therein. [0045] Although FIG. 1 B illustrates the ground electrode 106-5 as a single electrode (e.g., an almost continuous electrode), examples are not so limited. In some examples, a plurality of ground electrodes may be disposed on or within the top substrate 102-2. In other examples, all of the electrodes of the 2D array of electrodes 106 are actuating, and no ground electrodes are used. In some examples, at different points in time, respective electrodes of the 2D array of electrodes 106 may be floating or set at ground, such as when the respective electrodes are not being used to draw the fluid along the microfluidic path. [0046] FIG. 1 B illustrates a side view of the DMF device 100, from the perspective of cross-sectional A as illustrated by FIG. 1 C. As illustrated by and referring to FIG. 2, the DMF device 200 may include a plurality of fluidic inlets 211 -1 , 211 -2, 211 -3, 211 -4, 211 -5. The plurality of fluidic inlets 211 -1 , 211 -2, 211 -3, 211 -4, 211 -5 may fluidically couple to the plurality of reaction fluid wells 208-1 , 208-2, 208-3, 208-4 and the carrier fluid reservoir 210. The reaction fluids and the carrier fluid may be input into the reaction fluid wells 208-1 , 208-2, 208-3, 208-4 and the carrier fluid reservoir 210 via the fluidic inlets 211 -1 , 211 -2, 211 -3, 211 -4, 211 -5, such as by pipetting or other sources, e.g., robotics, coupled blister packs, among others.

[0047] The plurality of reaction fluid wells 208-1 , 208-2, 208-3, 208-4 may be disposed within the housing 202, such as between the substrates (e.g., between top substrate 102-2 and base substrate 102-1 illustrated by FIG. 1 B). For example and referring back to FIG. 1 B, FIG. 1 B illustrates a respective reaction fluid well 108-1 that is disposed between the top substrate 102-2 and the base substrate 102-1 . The plurality of reaction fluid wells may fluidically couple to the interconnected chamber 104, as illustrated by the reaction fluid well 108-1 fluidically coupling to the interconnected chamber 104 and the fluidic inlet 111 -1. [0048] As shown by FIG. 1 B, a carrier fluid 114 may be contained between the bottom surface 109 and the top surface 107 of the chamber 104 of the DMF device 100. The carrier fluid 114 may be used to flow the plurality of reaction fluids, as fluid droplets, through the interconnected chamber 104. [0049] In some examples, the plurality of reaction fluids, as illustrated by the respective reaction fluid 115-1 , 115-2, may include aqueous fluids and the carrier fluid 114 may include an oil fluid. For example, the carrier fluid 114 may include an oil. In some examples, the carrier fluid 114 may include a silicon oil or fluorinated oil, such as FC-40 or FC-3283. Non-limiting examples of the carrier fluid 114 include FC-40, FC-43, FC-77, fluorophoroheptane (FC-84), FC- 3283, perfluoro-n-octane, perfluorodecalin, perfluorophenanthrene, perfluorohexyloctane, octofluoropropane, decafluorobutane, perfluoropentane, perfluorohexane, perfluorooctane, decafluoropentane, perfluoro(2-methyl-3- pentaone), perfluoro-15-crown-5-ether, bis-(perfluorobutyl) ethane, perfluorobutyl tetrahydrofuran, bi-perfluorohexyl ethane, perfluoro-n-hexane, perfluorooctyl bromide, perfluorotributylamine, perfluorotripentylamine, and perfluorotripropylamine, among others. In some examples, the carrier fluid 114 may include a non-fluorinated oil, such as polyphenylmehtylsiloxane, polydimethylsiloxane, hexadecane, tetradecane, octadecane, dodecane, mineral oil, isopar, or squalene. However examples are not so limited and may include other types of carrier fluids and reaction fluids that are immiscible.

[0050] The reaction fluids may include a variety of types of fluids used to drive biochemical processes. Example reaction fluids include a sample fluid, buffer fluids, and other reagents in fluids. Buffer fluids refer to or include fluids which assist in maintaining a pH within the fluids, such as mitigating or resting pH changes and/or maintaining the pH within a range. Example buffer fluids include a solution with a weak base or acid, such as a solution containing citrate, acetate, or phosphate salts. The sample fluid may include an aqueous solution or fluid containing a sample, in solid or fluid form, and/or reagents. A sample fluid, as used herein, refers to or includes any material, collected from a subject, such as biologic material and carried in a fluid. Examples are not so limited and may include a variety of fluids which contain reagents.

[0051] In some examples, the DMF device 100 may further include or be coupled to circuitry 103. The circuitry 103 may be communicatively coupled to the 2D array of electrodes 106 and the pressure regulator 112 to selectively actuate electrodes of the 2D array of electrodes 106 and the pressure regulator 112 to cause movement of fluidic droplets of the plurality of reaction fluids into the interconnected chamber 104 from the plurality of reaction fluid wells. In some examples, the circuitry 103 may be supported by the housing 102-1 , 102- 2. In other examples, the circuitry 103 may be supported by another device and is couplable to the DMF device 100. For example, the circuitry 103 may be external to the housing 102-1 , 102-2 and/or the DMF device 100.

[0052] In some examples, the circuitry 103 is to actuate the pressure regulator 112 such that the pressure regulator 112 moves a component to adjust pressure of the carrier fluid 114 within the plurality of reaction fluid wells (e.g., 108-1 ) between a first state of the DMF device 100 at a first pressure and a second state of the DMF device 100 at a second pressure below the first pressure. The actuation of the pressure regulator 112 may be synchronized with the actuation of the electrodes of the 2D array of electrodes 106 associated with the reaction fluid wells to generate and advance fluid droplets of reaction fluids into the interconnected chamber 104. An example of the fluid droplet generation is further illustrated herein, at least by FIG. 5. The change in pressure between the first pressure and the second pressure may be associated with between about 1 mm to about 1 centimeter, or no more than 1 centimeter of carrier fluid. [0053] Example circuitry includes a processor and memory, as further described below. In other examples, the circuitry 103 includes an anisotropic conductive layer (e.g., an anisotropically decoupling layer 103-1 and the 2D array of electrodes 106 illustrated by FIG. 1 E) of the DMF device 100 which may conduct electricity in one direction and is coupled to the 2D array of electrodes 106 and is couplable to external circuitry, such as an external processor and/or memory. Using a conductive layer on the DMF device 100 may reduce costs of the DMF device 100, which may be disposable. Use of processor and/or memory may allow for greater control of fluid flow as compared to use of external processor and/or memory.

[0054] FIG. 1 C illustrates a top view of the DMF device 100. In some examples, as shown by FIG. 1 B and 1 C, the plurality of fluidic inlets 111 -1 , 111 -2, 111 -3, 111 -4, 111 -5, 111 -6, 111 -7, 111 -8 are disposed on and through the top substrate 102-2. In some examples, as previously described and referring to FIG. 1 B, the top substrate 102-2 may be a lid with the ground electrode 106-5 disposed thereon. In some examples, the lid and ground electrode 106-5 may be transparent to allow for viewing of fluid flow and/or chemical operations within the DMF device 100.

[0055] FIG. 1 D illustrates another side view of the DMF device 100, from the perspective of cross-sectional B as illustrated by FIG. 1 C, and which shows the carrier fluid reservoir 110. As shown by FIG. 1 D, the DMF device 100 includes the top substrate 102-2 coupled to the base substrate 102-1 . The top substrate 102-2 has gaps for fluid manipulation which form the interconnected chamber (e.g., 104 illustrated by FIG. 1 B), the reaction fluid wells (e.g., 108-1 illustrated by FIG. 1 B), and the carrier fluid reservoir 110 which is coupled to the pressure regulator 112. The carrier fluid may be inserted into a fluidic inlet 111 -8 that is coupled to the carrier fluid reservoir 110 for fluidic processing.

[0056] Referring back to FIG. 1 B, the circuitry 103 may be communicatively coupled to the 2D array of electrodes 106 to selectively actuate electrodes of the 2D array of electrodes 106 and the pressure regulator 112, and in response, to cause application of electrowetting forces on the plurality of reaction fluids to form fluid droplets of the plurality of reaction fluids and to drive the selective fluid flow of the fluid droplets of the reaction fluids within the interconnected chamber 104. In some examples, fluid droplets of the plurality of reaction fluids may be formed by drawing fluid from the reaction fluid wells into the interconnected chamber 104. The actuation of the pressure regulator 112 may cause a pressure of the carrier fluid 114 within or on the reaction fluid wells to adjust from a first pressure to a second pressure that is below the first pressure. The pressure adjustment may be synchronized with the actuation of select electrodes to reduce a driving force to generate and drive movement of the fluid droplets of the reaction fluids into the interconnected chamber 104 as compared to a driving force used when the carrier fluid 114 is the first (higher) pressure. [0057] Accordingly, in some examples, the circuitry 103 is to actuate the pressure regulator 112 to move a component of the pressure regulator 112 to adjust pressure of the carrier fluid 114 (e.g., back pressure) within the plurality of reaction fluid wells (e.g., 108-1 ) between a first state of the DMF device 100 at a first pressure and a second state of the DMF device 100 at a second pressure below the first pressure. The first pressure may be associated with a first state of the DMF device 100 in which the DMF device 100 is operating at a normal or non-adjusted pressure of the carrier fluid 114, e.g., the first pressure. In the first state, the carrier fluid 114 may apply back pressure on the reaction fluid wells, which may be overcome by the driving force of the electrodes to drive the fluid droplets of the reaction fluids into the interconnected chamber 104. The second pressure may be associated with a second state of the DMF device 100 in which the DMF device 100 is operating at an adjusted pressure due to the actuation of the pressure regulator 112. In the second state, the back pressure of the carrier fluid 114 is removed or reduced as compared to the first state, such that the driving force of the electrodes to drive the fluid droplets of the reaction fluids into the interconnected chamber 104 may be reduced as compared to the first state.

[0058] FIG. 1 B illustrates a respective reaction fluid well 108-1 fluidically coupled to the fluidic inlet 111 -1 and is used to describe an example operation for forming a fluid droplet 115-2 of the reaction fluid 115-1 , 115-2. The reaction fluid 115-1 , 115-2 may be inserted to the DMF device 100 and forms a fluid packet 115-1 , which comprises a finite number of separate fluid droplets of the reaction fluid 115-1 , 115-2, and which may be moved together within the reaction fluid well 108-1 . Respective electrodes 106-1 , 106-2, 106-5 of the 2D array of electrodes 106 may be located in the reaction fluid well 108-1 and used to form the fluid droplet 115-2 of the respective reaction fluid 115-1 ,115-2 from the fluid packet 115-1. In some examples, the reaction fluids may be inserted to the reaction fluid wells via a pipette or other object containing a volume of the reaction fluid and via the plurality of fluidic inlets. For example, the reaction fluid 115-1 , 115-2 is inserted into the fluidic inlet 111 -1 and, in response, the fluid packet 115-1 of the reaction fluid 115-1 , 115-2 forms in the reaction fluid well 108-1 . Electrowetting forces split the fluid packet 115-1 into the fluid droplet 115-2 of the reaction fluid 115-1 , 115-2. The electrowetting forces are generated by applying an electric field via the electrodes 106, and which cause individual fluid droplets of the reaction fluid 115-1 , 115-2 to pull off from the fluid packet 115-1. The electric field may cause a change in conductivity and permittivity at the interface between the reaction fluid 115-1 , 115-2 and carrier fluid 114, and produces an electric force on the interface. The electric force may cause stress on the interface, which may be referred to as a Maxwell stress, or when integrated over the area of the interface, this may be referred to as the Maxwell force. By pulling on the portion of the reaction fluid 115-1 , 115-2, while the rest of fluid is held back by other forces, such as capillary forces, the fluid droplet 115-2 of the reaction fluid 115-1 , 115-2 is broken off from the fluid packet 115-1 of the reaction fluid 115-1 , 115-2.

[0059] In various examples, concurrently with generating the electrowetting forces to split the split the fluid packet 115-1 into the fluid droplet 115-2 of the reaction fluid 115-1 , 115-2, the pressure of the carrier fluid 114 is adjusted (e.g., reduced) via actuation of the pressure regulator 112 to reduce the amount of electrowetting forces used to split the fluid packet 115-1 , as described above. [0060] The following provides a specific example of forming fluid droplets from the respective reaction fluid 115-1 , 115-2 illustrated by FIG. 1 B. The reaction fluid 115-1 , 115-2, as a fluid packet 115-1 , may be pulled into a shape that contains a neck 117 via electrowetting forces, and then pulled further by the electrowetting forces and as synchronized with the adjustment of the pressure of the carrier fluid 114, with the neck 117 breaking off to form a fluid droplet 115- 2 of the reaction fluid 115-1 , 115-2. Concurrently with pulling the fluid packet 115-1 into the shape containing the neck 117, the pressure of the carrier fluid 114 is reduced from a first pressure to a second pressure. In some examples, at least two of the electrodes of the reaction fluid well 108-1 may provide electrowetting forces on the fluid packet 115-1 of the reaction fluid 115-1 , 115-2 to form the neck 117 and break off the neck 117 to form the fluid droplet 115-2 of the reaction fluid 115-1 , 115-2 that is smaller than the fluid packet 115-1. [0061] Once fluid droplets are formed, the circuitry 103 may selectively actuate other electrodes of the 2D array of electrodes 106 and the components of the array to provide additional electrowetting forces and other forces on fluids within or proximal to respective microfluidic paths of the interconnected chamber 104 and to draw the fluids along the respective microfluidic paths for further chemical processing. Additionally, the circuitry 103 may cause the pressure of the carrier fluid 114 to revert back to the first pressure via further or removal of the actuation of the pressure regulator 112.

[0062] In some examples, as shown by FIG. 1 D, the DMF device 100 may include a pressure sensor 118 disposed with the carrier fluid reservoir 110. The pressure sensor 118 may be used to monitor the pressure of the carrier fluid and adjust the pressure. For example, the feedback from the pressure sensor 118 may include a sensor signal used to control or adjust the pressure of the carrier fluid. In some examples, the sensor signal may indicate a position of the pressure regulator 112 and is used to adjust the position of the pressure regulator 112 to mitigate or reduce errors in the actuation of pressure control. As a specific example, for a linear actuator used as the pressure regulator 112, the sensor signal may indicate a position of the linear actuator and an amount of (e.g., additional) movement to position the carrier fluid reservoir 110 to achieve the second pressure.

[0063] As noted above, in some examples, the 2D array of electrodes 106 may not be disposed on the base substrate 102-1 of the DMF device 100. FIG. 1 E illustrates an example implementation of any of the DMF devices 100 of FIGs. 1 A-D. More particularly, FIG. 1 E is a partial view of the interconnected chamber 104 of the DMF device 100 and does not illustrate all components of the DMF device 100. As illustrated by FIG. 1 E, in some examples, the electrodes 106-1 , 106-2, 106-3 of the 2D array of electrodes 106 are disposed on or within another substrate 121 which is couplable to the base substrate 102-1 . The other substrate 121 may form part of another device 127 which includes the circuitry 103-2. For example, the other device 127 may include a driving instrument that the DMF device 100 is inserted into and which couples the 2D array of electrodes 106 and the circuitry 103-2 to the DMF device 100 via circuitry 103-1 of the DMF device 100. In various examples, the DMF device 100 may be a consumable device which may be used once and then discarded. Having the 2D array of electrodes 106 and (external) circuitry 103-2 separate from and couplable to the DMF device 100 may reduce manufacturing costs. As shown by FIG. 1 E, in some examples, the circuitry 103-1 of the DMF device 100 includes an anisotropically decoupling layer which couples the 2D array of electrodes 106 and external circuitry 103-2 (e.g., a processor and/or memory) to the DMF device 100 to move fluid droplets of the reaction fluids along microfluidic paths of the DMF device 100.

[0064] FIG. 2 illustrates another example DMF device, in accordance with examples of the present disclosure. The DMF device 200 of FIG. 2 may comprise at least some of substantially the same features and components as DMF device 100 as illustrated by any of FIGs. 1 A-1 E, as shown by the similar numbering. For example, the DMF device 200 includes a housing 202, an interconnected chamber 204, a plurality of fluidic inlet 21 1 -1 , 21 1 -2, 21 1 -3, 211 - 4, 21 1 -5 (herein generally referred to as the “fluidic inlets 21 1 ” for ease of reference), a plurality of reaction fluid wells 208-1 , 208-2, 208-3, 208-4 (herein generally referred to as “the reaction fluid wells”), a carrier fluid reservoir 210, and a pressure regulator 212. The housing 202 of the DMF device 200 may include a lid and the fluidic inlets 21 1 are disposed in and through the lid. The common features and components are not repeated for ease of reference.

[0065] As previously described, the DMF device 200 includes reaction fluid wells 208 and a carrier fluid reservoir 210 which fluidically couple to the fluidic inlets 21 1 and to the interconnected chamber 204. The reaction fluid wells 208 contain or store the plurality of reaction fluids 220-1 , 220-2, 220-3, 220-4 (herein generally referred to as “the reaction fluids”). The carrier fluid reservoir 210 contains or stores the carrier fluid 214. Each of the fluidic inlets 21 1 may fluidically couple to a different reaction fluid well 208 or to the carrier fluid reservoir 210, with each of the reaction fluid wells 208 and the carrier fluid reservoir 210 being fluidically coupled to the interconnected chamber 204. Respective fluids are inserted into the reaction fluid wells 208 and carrier fluid reservoir 210 via the fluidic inlets 21 1 , for example, via pipette or other sources. [0066] As shown by FIG. 2, a plurality of electrodes may be arranged in a 2D array, which may be used to provide localized resolution of the electric field to provide fluid droplet formation, thermal zones, and/or selective control of fluid flow of fluid droplets of the reaction fluids. In the example illustrated by FIG. 2, the 2D array of electrodes 206 are arranged in an array that includes rows and columns of electrodes forming a rectangular shape. However, examples are not so limited and other shaped arrays may be formed that include electrodes in two dimensions. For example, the 2D array of electrodes 206 may have a variety of different arrangements and sizes and may include more or less electrodes than illustrated.

[0067] FIG. 3 illustrates an example apparatus including a DMF device and coupled circuitry, in accordance with examples of the present disclosure. The apparatus 330 comprises a DMF device 200, a 2D array of electrodes 206, and circuitry 203.

[0068] The DMF device 200 may include the DMF device illustrated by FIG. 2, and may comprise an example implementation of, or comprise at least some of substantially the same features and components as any one of the examples DMF devices 100, 200 as described in association with any of FIGs. 1 A-2.

[0069] For example, the DMF device 200 includes a housing 202 that defines an interconnected chamber 204, reaction fluid wells 208 fluidically coupled to the interconnected chamber 204 and to contain reaction fluids 220, a carrier fluid reservoir 210 fluidically coupled to the interconnected chamber 204 and the reaction fluid wells 208, the carrier fluid reservoir 210 to contain a carrier fluid 214, and a pressure regulator 212 coupled to the carrier fluid reservoir 210 to adjust a pressure of the carrier fluid 214 within the reaction fluid wells 208. The details of the common features and components are not repeated for ease of reference.

[0070] The apparatus 330 further includes a 2D array of electrodes 206. As previously described, the 2D array of electrodes 206 are coupled to and disposed along the interconnected chamber 204. In some examples, the 2D array of electrodes 206 are disposed within or on a substrate of the housing 202. In other examples, the 2D array of electrodes 206 may form part of another device, such as a driving instrument containing the 2D array of electrodes 206 and circuitry 203, that the DMF device 200 is inserted into.

[0071] The apparatus 330 further includes circuitry 203. The circuitry 203 may be coupled to or forms part of the DMF device 200, and may track and/or control operation of the plurality of electrodes 206 and the pressure regulator 112. In some examples, the circuitry 203 forms part of a driving instrument. The operations may comprise activation or actuation, deactivation, and other settings, e.g., setting to ground or floating and timings associated with the same. [0072] For example, the circuitry 203 may coordinate operations of the DMF device 200 including the flow of fluid and/or electrowetting-caused manipulation of fluid droplets of the reaction fluids 220 within the DMF device 200, such as moving, merging, and/or splitting, respectively. Such manipulation may include causing fluid droplets of the reaction fluids 220 to into and move along the interconnected chamber 204 within the DMF device 200. The various examples operations of the circuitry 203 may be operated interdependently and/or in coordination with each other, in at least some examples.

[0073] The circuitry 203 may be communicatively coupled to the 2D array of electrodes 206 and the pressure regulator 212 to selectively actuate electrodes of the 2D array of electrodes 206 and the pressure regulator 212 to adjust a pressure of the carrier fluid 214 within the reaction fluid wells 208 and to drive movement of fluid droplets of the plurality of reaction fluids 220 into the interconnected chamber 204 from the reaction fluid wells 208. As previously described, the interconnected chamber 204 and the reaction fluid wells 208 may contain the carrier fluid 214, and the circuitry 203 is to selectively actuate electrodes of the 2D array of electrodes 206 as synchronized with the actuation of the pressure regulator 212 to form the fluid droplets of the reaction fluids 220 as surrounded by the carrier fluid 214. For example, the circuitry 203 may actuate the pressure regulator 212 to adjust the pressure of the carrier fluid 214 within the reaction fluid wells 208 and to drive the movement of the fluid droplets of the reaction fluids 220 into the interconnected chamber 204.

[0074] As previously described, in some examples, the circuitry 203 is to actuate the pressure regulator 212 to adjust the pressure of the carrier fluid 214 between a first pressure and a second pressure. For example, and as further illustrated by FIGs. 4A-4C, the pressure regulator 212 may be or include a mechanical mechanism coupled to or disposed within the carrier fluid reservoir 210 or a portion thereof. [0075] In some examples, the apparatus 330 further comprises a driving instrument 337 including the circuitry 203 and/or the 2D array of electrodes 206. The driving instrument 337 may receive the DMF device 200 and may arrange or place the DMF device 200 such that the electrodes of the 2D array of electrodes 206 are disposed in contact with or proximal to the interconnected chamber 204. In various examples, the driving instrument 337 may include movable or switchable magnets, thermal zones (e.g., heated or cooled zones), and/or optical sensing components, such as micro imaging optics and/or fluorimetery optics, such as a fluorescence detector.

[0076] Example DMF devices and/or apparatuses may include variations from that illustrated by FIGs. 1A-3. As noted above, such variations may include, but are not limited to, the number of fluidic inlets and/or fluidic inlets, the number of electrodes, and/or arrangement of electrodes, among others.

[0077] FIGs. 4A-4C illustrate different example pressure regulators of a DMF device, in accordance with examples of the present disclosure. Any of the example pressure regulators 412-A, 412-B, 412-C of FIGs. 4A-4C may be implemented in any of the DMF devices 100, 200 or apparatus 330 illustrated by FIGs. 1 A-3. More particularly, FIGs. 4A-4C illustrate parts of example DMF devices which include the pressure regulators 412-A, 412-B, 412-C. The DMF device 400 illustrated by any of FIGs. 4A-4C may comprise an example implementation of, or comprise at least some of substantially the same features and components as any one of the examples DMF device described in association with any of FIGs. 1 A-3, as shown by the common numbering. The common features and components are not repeated for ease of reference. [0078] In some examples, as illustrated by FIGs. 4A-4C, the carrier fluid reservoir or a portion thereof may be disposed outside the housing 402-1 , 402-2 of the DMF device 400 and fluidically coupled to a fluidic inlet 411 -8 and to the interconnected chamber (not illustrated by FIGs. 4A-4C). For example, the carrier fluid reservoir may include a first carrier fluid reservoir portion 410-1 that is disposed outside the housing 402-1 , 402-1 and a second carrier fluid reservoir portion 410-2 that is disposed within the housing 402-1 , 402-2. The first carrier fluid reservoir portion 410-1 may be coupled to the second carrier fluid reservoir portion 410-2 via channel 434, such as tubing. In some examples, the first carrier fluid reservoir portion 410-1 may include a container and the second carrier fluid reservoir portion 410-2 may include a well or reservoir located in the housing 402-1 , 402-2.

[0079] FIG. 4A shows an example pressure regulator 412-A which includes a linear actuator 433. The linear actuator 433 may change an elevation of the carrier fluid reservoir, e.g., the first carrier fluid reservoir portion 410-1 , to adjust a back pressure of the carrier fluid 414. Example linear actuators include a lift or stage, a robotic arm, a gantry, and/or a pulley system, among other actuators, that move the carrier fluid reservoir, e.g., the first carrier fluid reservoir portion 410-1 , in a vertical axis or direction. In some examples, the linear actuator 433 includes a motor driven screw coupled to a stage or lift that holds the first carrier fluid reservoir portion 410-1 .

[0080] More particularly, at 430, FIG. 4A shows the DMF device 400 in a first state in which the pressure of the carrier fluid 414 is at a first pressure. The first pressure may include a non-adjusted or normal pressure, and which may result in back pressure applied to the reaction fluid wells by the carrier fluid 414. At 432, FIG. 4A shows the DMF device 400 in a second state in which the pressure of the carrier fluid 414 is at a second pressure. The second pressure may include a lower pressure than the first pressure. The second pressure of the carrier fluid 414 may be generated by actuating the pressure regulator 412- A, which in response moves from a first position P1 associated with the first state of the DMF device 400, as illustrated at 430, to a second position P2 associated with the second state of the DMF device 400, as illustrated at 432. The first position P1 may include the carrier fluid reservoir, e.g., the first carrier fluid reservoir portion 410-1 , being at a first elevation as illustrated by H1 . The second position P2 may include the carrier fluid reservoir, e.g., the first carrier fluid reservoir portion 410-1 , being at a second elevation illustrated by H2, which is lower than H1 . The lower second elevation H2 may cause an adjustment to the hydraulic head of the carrier fluid 414, which lowers the pressure of the carrier fluid 414 to the second pressure. Hydraulic head refers to or includes a measurement of fluid pressure as a potential at a measurement point. In some examples, using the linear actuator 433 may allow for greater pressure changes as compared to other pressure regulators.

[0081] FIG. 4B shows an example pressure regulator 412-B which includes a piston 437. The piston 437 may be disposed in the carrier fluid reservoir, e.g., in the first carrier fluid reservoir portion 410-1 . The piston 437 may change positions to adjust a back pressure of the carrier fluid 414. For example, the piston 437 is to move between a first position P1 and a second position P2 within the carrier fluid reservoir, e.g., first carrier fluid reservoir portion 410-1 , and, in response, to adjust a back pressure of the carrier fluid 414. The piston 437 may include or act as a syringe pump.

[0082] More particularly, at 436, FIG. 4B shows the DMF device 400 in a first state in which the pressure of the carrier fluid 414 is at a first pressure. The first pressure may include a non-adjusted or normal pressure, and which may result in back pressure applied to the reaction fluid wells by the carrier fluid 414. At 438, FIG. 4B shows the DMF device 400 in a second state in which the pressure of the carrier fluid 414 is at a second pressure. The second pressure may include a lower pressure than the first pressure. The second pressure of the carrier fluid 414 may be generated by actuating the pressure regulator 412- B, e.g., the piston 437, which in response moves from a first position P1 associated with the first state of the DMF device 400, as illustrated at 436, to a second position P2 associated with the second state of the DMF device 400, as illustrated at 438. The first position P1 may include the piston 437 being a first distance D1 from the bottom of the carrier fluid reservoir, e.g., the first carrier fluid reservoir portion 410-1 . The second position P2 may include the piston 437 being a second distance D2 from the bottom of carrier fluid reservoir, e.g., the first carrier fluid reservoir portion 410-1 , where D2 is greater than D1 . The greater distance D2 may lower the pressure of the carrier fluid 414 to the second pressure. Use of the piston 437 may allow for the pressure regulator 412-B to be disposed within the housing 402-1 , 402-2, and/or for the carrier fluid 414 to be enclosed such contamination and/or spilling of the carrier fluid 414 is mitigated or prevented. Using the piston 437 may allow for less changes to be made to the DMF device 400 as compared to other pressure regulators. [0083] FIG. 4C shows an example pressure regulator 412-C which includes a membrane 444 and coil or piezo-electric component 442. The membrane 444 and coil or piezo-electric component 442 may be disposed in the carrier fluid reservoir, e.g., in the first carrier fluid reservoir portion 410-1 . The membrane 444 may change positions to adjust a back pressure of the carrier fluid 414. For example, the electromagnetic coil or piezo-electric component 442 may be coupled to the membrane 444 to move the membrane 444 between a first position P1 and a second position P2 within the carrier fluid reservoir, e.g., in the first carrier fluid reservoir portion 410-1 , and, in response, to adjust a back pressure of the carrier fluid 414. The membrane 444 may be formed of a flexible material and may flex in response mechanical or electrical pushing or pulling forces provided by coil or the piezo-electric component 442.

[0084] More particularly, at 439, FIG. 4C shows the DMF device 400 in a first state in which the pressure of the carrier fluid 414 is at a first pressure. The first pressure may include a non-adjusted or normal pressure, and which may result in back pressure applied to the reaction fluid wells by the carrier fluid 414. At 440, FIG. 4C shows the DMF device 400 in a second state in which the pressure of the carrier fluid 414 is at a second pressure. The second pressure may include a lower pressure than the first pressure. The second pressure of the carrier fluid 414 may be generated by actuating the pressure regulator 412- B, e.g., coil or piezo-electric component 442, which in response causes the membrane 444 to flex and moves from a first position P1 associated with the first state of the DMF device 400, as illustrated at 439, to a second position P2 associated with the second state of the DMF device 400, as illustrated at 440. The first position P1 may include the membrane 444 being relaxed and with the whole membrane 444 being a first distance D1 from the bottom of the carrier fluid reservoir, e.g., the first carrier fluid reservoir portion 410-1 . The second position P2 may include the membrane 444 flexing via interaction with the coil or piezo-electric component 442 and with at least a portion of the membrane 444 being second distance D2 from the bottom of carrier fluid reservoir, e.g., the first carrier fluid reservoir portion 410-1 , where D2 is greater than D1 . The greater distance D2 may lower the pressure of the carrier fluid 414 to the second pressure.

[0085] Use of membrane 444 and coil or piezo-electric component 442 may allow for the pressure regulator 412-C to be disposed within the housing 402-1 , 402-2 and/or may provide for greater speed of the pressure adjustment and/or reduced size as compared to other pressure regulators. For example, speed of pressure actuation may be given by the ratio of the distance from the membrane 444 to the carrier fluid reservoir, e.g., the first carrier fluid reservoir portion 410- 1 , and the speed of sound in the carrier fluid 414 (e.g., about 1500 meter/second). In some examples, the speed of pressure actuation may be on the order of 50 microsecond (ps).

[0086] Although FIGs. 4A-4C illustrate pressure regulator 412-A, 412-B, 412-C being disposed outside the housing 402-1 , 402-2 of the DMF device 400, examples are not so limited. For example, the piston 437 of FIG. 4B may be disposed within the second carrier fluid reservoir portion 410-2, with the DMF device 400 not including the first carrier fluid reservoir portion 410-1 . In other examples, membrane 444 and coil or piezo-electric component 442 of the FIG. 4C may be disposed within the second carrier fluid reservoir portion 410-2, with the DMF device 400 not including the first carrier fluid reservoir portion 410-1 . [0087] FIG. 5 illustrates an example operation of a DMF device, in accordance with examples of the present disclosure. More particularly, FIG. 5 illustrates a close-up view of a reaction fluid well 508-1 of a DMF device and respective electrodes 551 of a 2D array of electrodes which are arranged proximal to the reaction fluid well 508-1 . The DMF device is filled with the carrier fluid 514, such that the carrier fluid 514 fills the reaction fluid well 508-1 . At 550, the reaction fluid is dispensed into the reaction fluid well 508-1 via the fluidic inlet 511 -1 , and the reaction fluid forms into a fluid packet 515-1 . At 552, the first electrode 506-1 is actuated followed by actuation of the second electrode 506-2 and the third electrode 506-3 to draw the fluid packet 515-1 of the reaction fluid toward the interconnected chamber 504. At 554, the pressure regulator is actuated to reduce the back pressure of the carrier fluid 514 as synchronized with actuation of the fourth electrode 506-4 followed by the fifth electrode 506-5, which results in the fluid packet 515-1 being pulled into a shape that contains a neck 517-1 via electrowetting forces. At 558, the neck 517-1 of the fluid packet 515-1 breaks off to form a fluid droplet 515-2 of the reaction fluid, and respective electrodes 553 of the 2D array associated with the interconnected chamber 504, and which are proximal to the entry to the interconnected chamber 504, are actuated to provide electrowetting forces on the fluid droplet 515-2 of the reaction fluid to form another neck 517-2 and break off the neck 517-2 to form a second fluid droplet 515-3 of the reaction fluid that is smaller than the fluid droplet 515-2 of the reaction fluid and which is in the interconnected chamber 504. Also at 558, the pressure of the carrier fluid 514 may be brought back to the normal state (e.g., the first pressure).

[0088] FIG. 6 illustrates an example method for generating fluid droplets of reaction fluids in a DMF device, in accordance with examples of the present disclosure. The method 680 may be implemented using any of the abovedescribed DMF devices and/or apparatuses.

[0089] At 682, the method 680 includes selectively actuating respective electrodes of a 2D array of electrodes of a DMF device to form fluid droplets of a plurality of reaction fluids disposed in a plurality of reaction fluid wells of the DMF device, wherein the fluid droplets of the plurality of reaction fluids are surrounded by a carrier fluid. At 684, the method 680 includes selectively actuating a pressure regulator coupled to a carrier fluid reservoir of the DMF device, thereby causing a pressure of the carrier fluid within the plurality of reaction fluid wells to adjust from a first pressure to a second pressure. At 686, the method 680 includes, in response to the selective actuation of the respective electrodes and the pressure regulator, causing the fluid droplets of the plurality of reaction fluids to move into an interconnected chamber of the DMF device from the plurality of reaction fluid wells.

[0090] As previously described, the method 680 may include synchronizing the selective actuating of the respective electrodes with the selective actuating of the pressure regulator, such that the pressure of the carrier fluid adjusts to the second pressure in response to or concurrently with the formation of the fluid droplets of the plurality of reaction fluids. The synchronization may include concurrent or timed actuation which may result in a reduction of back pressure of the carrier fluid on the reaction fluids and may allow for reduced driving force to generate the fluid droplets of the reaction fluids and to advance to fluid droplets of the reaction fluids into the interconnected chamber for performing various chemical processing thereon.

[0091] In some examples, the method 680 includes causing the pressure of the carrier fluid to adjust back toward the first pressure in response to the fluid droplets of the plurality of reaction fluids moving into the interconnected chamber of the DMF device. The reduction of the pressure of the carrier fluid to the second pressure may be temporary, such that the reduced pressure has minimal or no impact on further processes performed by the DMF device. By using the variable carrier pressure, the reduced carrier pressure may be synchronized with actuation of select electrodes to improve fluid droplet formation and advancement from the reaction fluid wells to the interconnected chamber as compared to a steady pressure state, and while minimizing flow impacts for further processing. The improvement of fluid droplet formation and advancement may be achieved without use of a surfactant to reduce surface tension, with reduced driving force, and with use of simplified well and electrode design, and/or reduced demand on hydrophobicity as compared to the steady pressure state. The second pressure is lower than the first pressure, associated with the normal state of the DMF device, and may be a negative pressure in some examples.

[0092] Examples are not limited to methods as described by FIG. 6. In some examples, other methods may be directed to forming or manufacturing a DMF device and/or an apparatus as described herein. An example method of manufacturing may include forming a housing defining the interconnected chamber, the reaction fluid wells, and the carrier fluid reservoir, and to support a plurality of electrodes of a 2D array and a pressure regulator, and disposing the plurality of electrodes along the chamber. In some examples, the method may further include including positioning circuitry for support by the housing for actuating the plurality of electrodes and/or the pressure regulator. [0093] Any of the described DMF devices may be formed of a variety of material formed in a stack. For example, a housing may formed of a plurality of different materials which are in layers, e.g., layers of substrates, in a stack. The different material layers may include a top (transparent) substrate material layer and/or a base substrate material layer, with etched or micromachined portions between that form the reaction fluid wells, the carrier fluid reservoir and the interconnected chamber, among other components. In some examples, at least one of the substrate layers may have electrodes formed thereof.

[0094] In some examples, the top (transparent) substrate material and/or the base substrate layer may have a low energy coating (e.g., a polytetrafluoroethylene (PTFE), such as Teflon™, fluorosilane, a polyamide, such as Kapton® FN, fluoroalkylsilane, 1 H,1 H,2H,2H- Perfluorodecyltriethoxysilane, trichloro(1 H,1 H,2H,2H-perfluorooctyl)silane)) proximal to and/or in contact with the chambers, wells, reservoirs and/or channels of the DMF device and the electrodes, and/or a dielectric coating (e.g., a polyimide, such as Kapton®, Ethylene tetrafluoroethylene (ETFE), paralyne, alumina, silica, silicon nitride, aluminum nitride, aluminum oxide) proximal and/or in contact with the electrodes and/or the low energy coating. As used herein, a low energy coating refers to or includes a layer formed of a material having surface free energy less than 30 milliNewton/meter (mN/m). In some examples, the low energy coating may have a free energy of 20 mN/m, and/or may provide a contact angle hysteresis of less than about 10 degrees.

[0095] The stack may additionally include a planarization layer with a thickness that is proportional to the electrodes, which may be formed of SU-8, paralyne, Polydimethylsiloxane (PDMS), acrylates, among other materials. For example, the planarization layer may have a thickness between the same thickness as the electrodes (e.g., in wells and/or chamber) to plus 100 percent of the thickness of the electrodes (e.g., two times the thickness of the electrodes). In some examples, the planarization layer has a thickness of between the same thickness as the electrodes and plus 10 percent of the thickness of the electrodes, or the same thickness of the electrodes and plus 50 percent of the thickness of the electrodes, among other ranges. The carrier fluid (e.g., an inert filler fluid) may be filled in the chambers, wells, reservoirs, and/or channels of the DMF device. The chambers, wells, reservoirs, and/or channels may be a height in the range of about 10 gm to about 2 mm. The various electrodes may be a length of about 40 gm to about 3 mm.

[0096] In some examples, the low energy coating is formed of PTFE. In some examples, the dielectric coating may be formed of a polyimide (e.g., Kapton®) for ease of deposition. In other examples, the dielectric coating may be formed of silicon nitride. In some examples, the planarization layer may be formed of the same material as the dielectric coating, such as a polyimide, and which may reduce the number of fabrication steps. In some specific examples, the stack may include a low energy coating formed of PTFE, a dielectric coating formed of a polyimide (e.g., Kapton®), and a planarization layer formed of the polyimide (e.g., Kapton®).

[0097] Although the above examples describe the flow of fluid within the chamber via electrowetting forces applied via the plurality of electrodes, examples are not so limited. In some examples, the control the flow of fluid within the wells and/or the interconnected chamber of any of the described DMF devices may be provided via ion emitters of the DMF device, instead of and/or by the electrodes. In some examples, a charge applicator may be brought into charging relation to a plate of the DMF device, whereby the charge applicator is to apply (e.g., deposit) charges onto the plate to cause an electric field which induces electrowetting movement of fluid within and through the DMF device. In some examples, the charge applicator is an addressable airborne charge depositing unit which may be brought into charging relation to the plate of the DMF device to deposit airborne charges onto the plate. In some examples, the charge applicator may be brought into releasable contact with, and charging relation to, the plate. The charge applicator may generate and apply the charges having a first polarity and/or an opposite second polarity, depending on whether the charge applicator is to build charges on anisotropic decoupling layer of the DMF device or is to neutralize charges. The first polarity may be positive or negative depending on the particular goals, while the second polarity is the opposite of the first polarity. Via such arrangements and in some examples, the DMF device may omit the electrodes, which would otherwise be used to cause microfluidic operations such as moving, merging, and/or splitting droplets within the DMF device. “Charges”, as used herein, refers to or includes ions (+/-) or free electrons.

[0098] Any of the above described device and/or substrates may include an anisotropic decoupling layer (e.g., 103-1 of FIG. 1 E). The anisotropic decoupling layer may decouple the working areas of the DMF device (e.g., the chamber) from electronics of the DMF device, such as the plurality of electrodes and/or the pressure regulator. For example, the anisotropic decoupling layer and the electrodes may be referred to as an anisotropic conductive layer, which facilitates migration of charges across the base substrate by providing lower resistivity across or through the base substrate and a higher lateral resistivity along the plane through which the base substrate extends. The decoupling may allow for the working areas of the of the DMF device, which contain fluids, to be inexpensive and consumable. The anisotropic decoupling layer may be formed of metal microparticles or nanoparticles aligned to form chains in one direction and encased in a polymer matrix (e.g., polymethylacrylate).

[0099] The various ranges provided herein include the stated range and any value or sub-range within the stated range. Furthermore, when “about” is utilized to describe a value, this includes, refers to or includes variations (up to +/— 10%) from the stated value.

[00100] Circuitry, such as the circuitry 103, 203 of FIGs. 1 B and 2, may include a processor and a memory. Circuitry may comprise a processor and associated memories, and optionally communication circuitry. Example circuitry includes a processor electrically coupled to, and in communication with, memory to generate control signals to direct operation of a DMF device, as well as the particular portions, components, operations, instructions, and/or methods, as described herein. Example control signals include instructions stored in memory to direct and manage microfluidic operations. The circuitry may be referred to as being programmed to perform the above-identified actions, functions, etc. In other examples, as described above, the circuitry 103, 203 may include an anisotropic conductive layer, such as the above-described anisotropic decoupling layer and a plurality of electrodes which are used to provide a plurality of microfluidic paths, which couples to electrodes of an external device. [00101] In response to or based on commands received and/or via machine readable instructions, the circuitry generates control signals as described above. The circuitry may be embodied in a general purpose computing device and/or incorporated into or associated with at least some of the example DMF devices, as well as the particular portions, components, electrodes, fluid actuators, operations, instructions, and/or methods, etc. as described herein.

[00102] Processor refers to or includes a presently developed or future developed processor that executes machine readable instructions contained in a memory or that includes circuitry to perform computations. Execution of the machine readable instructions, such as those provided via memory of the circuitry, may cause the processor to perform the above-identified actions, such as circuitry to implement operations via the various examples. The machine readable instructions may be loaded in a random access memory (RAM) for execution by the processor from their stored location in a read only memory (ROM), a mass storage device, or some other persistent storage (e.g., non- transitory tangible medium or non-volatile tangible medium), as represented by memory. The machine readable instructions may include a sequence of instructions, a processor-executable machine learning model, or the like. In some examples, memory comprises a computer readable tangible medium providing non-volatile storage of the machine readable instructions executable by a processor of circuitry. In some examples, the machine readable tangible medium may be referred to as, and/or comprise at least a portion of, a computer program product. In other examples, hard wired circuitry may be used in place of or in combination with machine readable instructions to implement the functions described. For example, circuitry may be embodied as part of at least one application-specific integrated circuit (ASIC), at least one field- programmable gate array (FPGA), and/or the like. In some examples, the circuitry not limited to any specific combination of hardware circuitry and machine readable instructions, nor limited to any particular source for the machine readable instructions executed by the circuitry. [00103] In some examples, the circuitry may be implemented within or by a stand-alone device, such as a microprocessor. In some examples, the circuitry may be partially implemented in interface devices and partially implemented in a computing resource separate from, and independent of, the example interface devices but in communication with the example interface devices. For instance, the circuitry may be implemented via a server accessible via the cloud and/or other network pathways. In some examples, the circuitry may be distributed or apportioned among multiple devices or resources.

[00104] Although specific examples have been illustrated and described herein, a variety of alternate and/or equivalent implementations may be substituted for the specific examples shown and described without departing from the scope of the present disclosure. This application is intended to cover any adaptations or variations of the specific examples discussed herein. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.