VIA CELLULAR FLUIDICS

CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a PCT International Application and claims priority of United States Patent Application No. 16/549,543, filed on August 23, 2019. The entire disclosure of the above application is incorporated herein by reference.

STATEMENT OF GOVERNMENT RIGHTS [0002] The United States Government has rights in this invention pursuant to Contract No. DE-AC52-07NA27344 between the U.S. Department of Energy and Lawrence Livermore National Security, LLC, for the operation of Lawrence Livermore National Laboratory.

FIELD

[0003] The present disclosure relates generally to microfluidics, and more particularly to systems and methods for facilitating open cell lattices for engineering transport phenomena and chemical reactions, which provide desired flow properties.

BACKGROUND

[0004] The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.

[0005] A growing area of importance in the field of microfluidics involves is obtaining even greater levels of control over chemical reactions at interfaces with a structure, as well as obtaining even greater control over heat and mass transport at interfaces within a structure. Obtaining greater levels of control at interfaces may be important for chemical reactions, as well as heat and mass transport, in various types of devices such as electrochemical devices, thermochemical devices, bio-reactor devices, batteries, fuel cells, etc., which often involve the application of micro-fluidics. Conventional microfluidics are typically limited to actively-pumped fluid transport in enclosed microchannels, and typically are limited to structures having in a planar configuration. More advanced microfluidic structures which enable degrees of control over chemical reactions, as well as heat and mass transfer, at interfaces within the structure, would potentially open up new possibilities in chemical/process engineering applications.

SUMMARY

[0006] This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.

[0007] In one aspect the present disclosure relates to an engineered cellular fluidics structure. The structure may comprise a plurality of tessellated cells formed from a plurality of interconnected elements, with the interconnected elements formed from a curable resin. The interconnected elements form voids within each cell. The voids communicate with one another, and the elements are formed such that the voids have a non-uniform dimension to create a varying porosity within the structure.

[0008] In another aspect the present disclosure relates to an engineered cellular fluidics structure. The structure may comprise a plurality of tessellated cells formed from a plurality of interconnected struts, with the interconnected struts formed from a curable resin. The interconnecting struts form voids within each cell, with the struts being formed such that the voids have a non-uniform dimension and communicate with one another to create a varying porosity within the structure. The structure is constructed using a material which forms a catalyst to create solid-liquid- gas interfaces at each of the voids within the structure.

[0009] In still another aspect the present disclosure relates to a method for forming an engineered cellular fluidics structure. The method may comprise using a substrate material to form a plurality of tessellated cells, the cells being defined in part by a plurality of interconnected struts. The method may further include forming the plurality of tessellated cells such that the interconnected struts define a plurality of voids in the plurality of tessellated cells, with the voids being in flow communication with one another. The method may further include forming the plurality of tessellated cells such that at least a subplurality of the voids have different dimensions, to create a varying porosity within the structure.

[0010] Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.

[0012] Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.

[0013] Figure 1 is a perspective view of a single plane splitter lattice structure in accordance with one embodiment of the present disclosure;

[0014] Figure 2 is a simplified diagrammatic representation of a 3D channel splitter lattice structure;

[0015] Figure 3 is a an illustration of a plan (top) view of the 3D structure shown in Figure 2, with fluid flowing through capillary action in two orthogonal planes into the lattice structure;

[0016] Figure 4 is a side view of the lattice structure in Figure 3 taken in accordance with section line 4-4 in Figure 3 further illustrating the splitting of the capillary flow through the lattice structure;

[0017] Figure 5 is a perspective diagrammatic illustration of a 3D spiral flow pattern that may be created in a lattice structure using the teachings of the present disclosure;

[0018] Figure 6 is a plan (top) view of a lattice structure in accordance with the present disclosure created to provide the 3D spiral flow pattern shown in Figure 5;

[0019] Figure 7a is a side view of a portion of a lattice structure in accordance with the present disclosure, illustrating how the size of the voids (i.e., pores) in each cell of the structure strongly influences the capillary flow characteristics within the structure;

[0020] Figure 7b shows a side view of a portion of a lattice structure similar to that shown in Figure 7a, but with the columns further spaced apart from one another, which limits bleed-through of fluid to adjacent columns; and

[0021] Figure 8 shows various embodiments of different forms of lattice structures in accordance with the present disclosure, along with structures that have been carbonized to produce electrically conductive lattices. DETAILED DESCRIPTION

[0022] Example embodiments will now be described more fully with reference to the accompanying drawings.

[0023] The present disclosure relates broadly to the design, fabrication and use of open cell lattices for facilitating engineering transport phenomena and chemical reactions. Such structures may also be understood as “engineered cellular fluidic structures”, as they are designed with the intent of controlling fluid flow, gas flow, or a combination of fluid/gas flow, through capillary action. The architecture of the structures constructed using the teachings presented herein are “engineered” in the sense that the fluidic structures are constructed in a highly defined manner in accordance with a CAD construction, and typically with a curable resin, to optimize important performance characteristics. Such performance characteristics may include control over porosity of the structure and capillary forces to provide desired flow properties including one or more desired capillary flow channels, as well as control over multi-phase interfaces and other functionalities that are important with microfluidic structures or devices.

[0024] The cellular fluidic structures of the present disclosure can be produced by additive manufacturing methods, for example and without limitation, via projection microstereolithography or two photon lithography. The use of additive manufacturing techniques to form the lattice structures of the various embodiments disclosed herein may be combined with other fabrication and processing techniques including, without limitation, fabrication techniques relating to surface functionalization, catalyst deposition, thermal treatment, removal of sacrificial material, etc. The foregoing manufacturing techniques may be used singly or in combination to achieve desired functionalities. Such desired functionalities may include one of, or combinations of, for example, a desired electric conductivity, a desired thermal conductivity, desired mechanical properties, a desired catalytic activity, or a desired stability, just to name a few important functionalities. By using engineered cellular fluidics, a fluid can be distributed either passively (by capillary action alone) or actively (e.g., by pumping) in an open, three-dimensional configuration. These features offer significant potential for generating new microfluidic devices and related technologies in the field of chemical/process engineering and related devices (e.g., chemical/electrochemical reactors, packed beds, bubble columns, etc.). [0025] Figure 1 shows an engineered cellular fluidic structure 10 in accordance with one embodiment of the present disclosure. For convenience, the engineered cellular fluidic structure 10 will be referred to simply as the “lattice” structure 10 throughout the following discussion.

[0026] The lattice structure 10 in this example forms a single plane channel splitter which is able to split a fluid flow into several desired paths within a single plane. The lattice structure 10 includes flow defining paths 12 and voids 14 having dimensions which, in this example, are engineered to provide the multi-flow path split seen occurring in the lattice structure 10. The fluid flow is injected or released at one end 16 of the lattice structure 10 and flows through capillary action along path 18 until branching into flows 20, which then propagate in three parallel paths 22 through a length of the lattice structure 10 before being channeled in flows 24 toward a center of the structure, and then re-combined into a single flow channel 26. Accordingly, the various flow channels are all presented within a single plane in this example. The dimensions of the fluid defining paths 12 and the voids 14 are controlled to provide the capillary action that creates these flow paths. While three parallel flow paths 22 are shown, together with one re-combined flow channel 26, it will be appreciated that a greater or lesser number of the flow paths 22 could be created, along with more than one re-combined flow channel 26.

[0027] Figure 2 shows a diagrammatic perspective view of a 3D lattice splitter structure 100 design where the fluid flow through the splitter structure occurs in two distinct planes 102 and 104 arranged orthogonal to one another (i.e., in a 3D space). Figure 3 shows the 3D lattice splitter structure 100 from a plan (top) view, illustrating the intersecting orthogonal flow planes 102 and 104. Figure 4 shows a side view taken in accordance with section line 4-4 in Figure 3 showing the plane 102. The plane 102 can be seen to be formed by two parallel paths 102a and 102b.

[0028] While the lattice splitter structure 100 is shown with only two orthogonally arranged flow planes 102 and 104, it will be appreciated that a 3D lattice structure with more than two orthogonal flow planes could just as easily be formed. For example, a lattice structure with three distinct non-perpendicular flow planes angularly arranged at 120 degrees from another (from a plan view perspective) could be provided.

[0029] Figures 5 and 6 show yet another 3D lattice structure 200 in accordance with another embodiment of the present disclosure. In this example the lattice structure 200 is engineered to provide a spiral, pyramid flow path 202 as indicated in the simplified diagrammatic drawing of Figure 5. Figure 6 shows a plan view (top view looking down) onto the lattice structure 200 to further illustrate the spiral, pyramid flow path 202.

[0030] Figure 7a shows a portion of a lattice structure 300 constructed in accordance with one embodiment of the present disclosure to illustrate how the manufacture of the lattice structure 300 controls the capillary flow through cells of the structure. The lattice structure 300 is designed by tessellating one or more types of 3D unit cells in space. In this example the lattice structure 300 includes pluralities of unit cells 302a-302h formed by interconnecting struts 306, which form voids 302a1- 302h1 in each unit cell. Unit cells 302a are disposed adjacent one another to form one column, while unit cells 302b-302h are also disposed in a like manner to form a plurality of closely adjacently positioned columns. In this example the unit cells 302a each have centrally formed voids 302a1 , while unit cells 10b-1 Oh each have voids 302b1-302h1 , respectively. The voids 302a1 can be seen to be the largest in cross sectional area. The voids 302b1 are smaller in cross sectional area than the voids 302a1 , voids 302c1 are smaller than the voids 302b1 , and so forth, with the voids 302h1 being the smallest. Note also that the spacing between adjacent columns of cells decreases from left to right across the lattice structure 300, such that the columns formed by the cells 302a and 302b are spaced farther apart than columns formed by the unit cells 302g and 302h. Figure 7b shows a similar lattice structure 300’ but with the columns 302a’-302g’ spaced even further apart, which prevents “bleed through” of liquid between adjacent columns. Accordingly, the spacing of the columns of the structures 300 and 300’ can also be used to help control the capillary flow of fluid through the lattice structures.

[0031] The porosity of the lattice structure 10 can further be controlled by changing one or more parameters, for example, changing the unit cell size of each unit cell 302a-302h shown in Figure 7a in one or more of the X, Y and/or Z dimensions, or changing the material used to construct the one or more of the unit cells 302a-302h. Porosity can also be changed by changing dimensions of the struts 306 that are used to form the cells 302a-302g so as to change the dimensions of the voids 302a1-302h1. In this example it will be noted that the struts 306 used to form the column of cells 302a are considerably thinner than those used to form column of cells 302h. The voids 302a1-302h1 (i.e., the empty space) in each unit cell 302a- 302h influences the capillary flow of the liquid front, and can remain constant or change shape throughout the lattice structure 300. Curve 308 indicates how the porosity of the lattice structure 300 increases as the pore size (dimensions of the voids 302a1-302h1) creases.

[0032] The lattice structure 300 may also contain one or more additional features such as solid walls and surfaces, or selectively located inlets and outlets for fluid flow to enable connecting to microfluidic pumps and other components or devices. The final design of the lattice structure 300, or any of the other embodiments discussed herein, may be generated as a CAD (computer aided design) file.

[0033] When the physical lattice 10, 100, 200 or 300 is fabricated from the CAD file, such fabrication may be accomplished, in one example, by additive manufacturing methods such as projection microstereolithography (PuSL) or two photon lithography (2PL), in which a light source is used to selectively polymerize a pattern onto a surface of a photosensitive resin. The process is repeated layer-by- layer for each digital slice of the CAD file (microns to tens of microns in thickness). The photosensitive resin may contain (but is not limited to) one of more of the following components: (1) one or more monomer or polymer species, typically those undergoing light-initiated free radical polymerization (e.g., acrylates, thiolenes), (2) a photoinitiator, (3) a photoabsorber, (4) stabilizers or inhibitors (e.g., 4-methoxyphenol), (5) salts or solid fillers (e.g., catalyst material, sacrificial material, pore formers, nanoparticles for improved mechanical properties), (6) solvents or diluents, (7) other additives (e.g., surfactants, thermal initiators, sintering aids, adhesion promoters, etc.). The fabrication process may also include multiple resins (e.g., a hydrophilic and a hydrophobic polymer) that are selectively cured, as well as a rinsing step between swapping resins, for example by delivering water or solvents to the printed body, or dipping the printed body into a bath.

[0034] The fabricated lattice 10/100/200/300 may be cleaned using chemical or physical methods, for example through the use of solvents or through sonication, and may be post-cured. Post-curing may be carried out, for example, by using a UV chamber or similar light source, or by thermal treatment, and further functionalized (e.g., UV/ozone and oxygen plasma treatment).

[0035] Referring to Figures 8, examples of lattice structures 400, 500 and 600 which have been carbonized to form carbonized lattice structures 400’, 500’ and 600’, respectively. In practice, one will be able to carbonize virtually any structure in order to make it electrically conductive. However, there is a fair amount of shrinkage during the carbonization process, as evident from the illustrations shown in Figure 8, so this is an important factor that needs to be taken into account when designing the structure and the sizes of the cells/pores. The carbonized lattice structures 400’-600’ are carbonized by thermally treating an underlying lattice structure to reduce the structure to a carbon-based structure which then has conductivity as one of its functionalities. The carbonized lattice structure 400’ can be seen to include a substantially larger central void 400a’, while carbonized lattice structure 500’ includes a plurality of smaller voids 500a’. Carbonized lattice structure 600’ differs still further by including a base portion 602’ with a plurality of spaced apart columns 604’ that project outwardly from the base portion. A principal feature of the structures shown in Figure 8 is that due to capillary forces, the liquid will be contained in the tiny pores of the lattices and not bleed out into the larger voids 400a’ of 400’, 500a’ of 500’ and the spaces between columns 604’.

[0036] One or more catalyst materials or functional coatings may also be applied to any of the lattice structures 10, 100, 200, 400-600 or 400’-600’ by methods including, but not limited, to: (1) electroplating, for example using copper, gold or silver, (2) electroless plating, for example using nickel phosphide, copper, or gold, (3) atomic layer deposition, (4) chemical vapor deposition, and (5) liquid flow and evaporation, such as by flowing a solution containing a solvent through the lattice structure 100-400, followed by evaporation of the solvent.

[0037] Catalyst-coated lattice structures may also be deployed as active electrodes in electrochemical reactors or fuel cells. This use can include incorporation into standard H-cell reactor configurations, liquid-fed, vapor-fed, and liquid/vapor-fed flow cells, or as gas diffusion electrodes (GDEs). A typical use case is the electrochemical reduction of carbon dioxide (C02) into useful products. One example of a possible GDE setup using a lattice fluidic device may involve: (1) a cathode consisting of a lattice coated with a metallic catalyst (e.g., copper), (2) a liquid electrolyte (e.g., a hydroxide or salt solution) contained or flowing through the smaller capillary pores of the lattice, (3) the reactant gas (C02) flowing through larger pores in the lattice, (4) a counter electrode (e.g., a similar lattice of a "mirrored" structure), (5) an anion exchange membrane, and (6) other electrochemical cell elements (e.g., reference electrode, O-rings/gaskets, tubing, electrode connections to external instrumentation, etc.). The use of lattice structures 400-600 constructed with solid- liquid-gas interfaces (catalyst-electrolyte-C02) are expected to have especially significant commercial interest and activity.

[0038] The use of the engineered lattice structures 10/100/200/300/40075007600’ thus provides the ability to optimize the lattice structure by maximizing the occurrence of these triple-phase interfaces. Lattice structures 100- 600 further enable shifting the overall reactor design space from a planar to a three- dimensional configuration, thereby even further increasing productivity per unit volume.

[0039] Other example implementations/applications for the lattice structures 10-600 disclosed herein include (but are not limited to): 1) A lattice fluidic device for evaporative mass transport, in which the occurrence of liquid-gas interfaces is optimized for transport of species from the liquid to the gas phase; 2) a lattice fluidic device for CO2 or other gas capture, in which the occurrence of liquid-gas interfaces is optimized for efficient dissolution of the gas molecules into the liquid phase; 3) a lattice fluidic liquid-liquid extraction device, in which two liquids are brought into contact without mixing, and the species of interest is transported by chemical potential driven diffusion from one phase to the other, at maximum occurrences of liquid- liquid interfaces; 4) a lattice fluidic heat exchanger, in which two immiscible fluids of different temperatures are brought into contact within the lattice to facilitate heat transfer; 5) a lattice fluidic thermal element, in which the lattice is made of a thermally conductive material and provides heating or cooling of the fluid selectively and efficiently; or 6) as printheads for ink delivery.

[0040] Electrowetting is another application of the structures described herein. Electrowetting is the modification of the wetting properties of a surface with an applied electric field. A cellular fluidics device such as that described herein can be directly fabricated from, or coated with, an electrically conductive material (e.g., metal). The surface of the conductive material can be treated with a thin layer of an electric insulator (e.g., a ceramic). One or multiple liquids can be fed into the cellular fluidics device, either passively (spontaneous uptake by capillary force) or actively (e.g., by pumping). By applying an electrical potential to the conductive material, the wetting properties (contact angle) of the liquid-solid interface change (typically from hydrophobic to hydrophilic). The combination of the adhesion force due to surface wetting and the architecture of the cellular fluidics structure enables control over the flow of the liquid through the structure. Control of fluid flow can even be exerted either in the presence or absence of gravity, making such structures especially useful in space applications.

[0041] Bubble flow management is still another application for the subject matter the various embodiments of the structure 10 disclosed herein. Many devices (e.g., reactors, bubble columns, etc.) involve multiphase flow of one or more gases being transported in a liquid phase. Gas bubbles can be fed into one of the embodiments of the structure of the present disclosure, or can be generated from a gas-evolving reaction in the liquid phase. Cellular fluidics can be employed to spatially and temporally direct the flow paths and frequencies or spacings of bubbles, by using architecture design, material properties, flow rates, etc. or a combination thereof. Applications include but are not limited to bubble columns, gas fed reactors, bubble-induced fluid agitation for mass transport improvement and gas product forming.

[0042] Still another application for the present application is in connection with transpiration cooling. Transpiration cooling relies on heat transfer from a solid phase to a fluid that evaporates after absorbing that heat. In a heat pipe, the liquid is typically flown through a porous layer adjacent to the hot surface where it vaporizes, and is then condensed at a cold interface and recirculated back into the plow path. With cellular fluidics structures such as those described herein, the porous media can be designed as a deterministic ordered structure, facilitating the control over flow, thermal conductivity, heat transfer rates, point of phase change, etc., by using the architecture and choice of material. Applications of these concepts include but are not limited to: spacecrafts, jet and rocket engines, computer cooling systems, etc.

[0043] Still another application of the subject matter of the present disclosure is in connection with engineered living materials. For example, cellular fluidics can be used as scaffolds that provide transport of gases, liquids, and nutrients to living cells. Such cellular fluidic structures as described herein may be used to manipulate cells by serving as extracellular matrices (ECMs) in order to guide the growth, environmental responsiveness, or for the self-healing of hybrid cooperative materials with multicellular hierarchy. The structures described herein can be designed and functionalized to promote growth and functioning of a variety of cells, including but not limited to yeasts, fungi, embryonic plant cells, mammalian cells. In one example, a cellular fluidics device such as disclosed herein can be designed and fabricated to contain channels of higher density unit cells (i.e., smaller effective pore size). This allows flowing solutions of biopolymers such as fibronectin only through these prescribed smaller pore size channels, allowing three-dimensional patterning with the biopolymer. The biopolymer, e.g. fibronectin, promotes adhesion to the ECM, i.e. the lattice structure. Hence, the cellular fluidics device/structure can be deterministically patterned with cells. Another example may involve a cellular fluidics structure such as described herein encapsulating embryonic plant cells (seeds). Because the structure of the device is porous, gases, liquids, and dissolved nutrients can be continuously transported to the seeds, allowing growth, for example seeds growing on a tree-like cellular fluidics device.

[0044] Cellular fluidics structures such as those described herein can also be used to control the size and shapes of cell spheroids, providing advantages to common techniques such as hanging drop methods, in which the spheroids often end up mis-shaped or merge with adjacent cells. The cellular fluid structures described herein can thus be applied to a variety of cells, tissues, and other biological systems to provide scaffolding, vasculature, respiration and hydration, etc.

[0045] The systems and methods disclosed herein are therefore expected to find utility in a wide range of devices. Such devices may include devices in which chemical reactions, heat and mass transport at interfaces are important, such as electrochemical devices, thermochemical devices, bio-reactor devices, batteries, fuel cells, or a wide range of other applications as noted herein. Specific applications may include, but are not limited to, electrochemical reaction catalysis at gas-liquid-solid interfaces, liquid-liquid interface extraction, microfluidic heat transfer, sensing platforms, controlled evaporation devices, and selective coating technologies.

[0046] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

[0047] Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.

[0048] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms “comprises,” “comprising,” “including,” and “having,” are inclusive and therefore specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. The method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed.

[0049] When an element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another element or layer, it may be directly on, engaged, connected or coupled to the other element or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.). As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items.

[0050] Although the terms first, second, third, etc. may be used herein to describe various elements, components, regions, layers and/or sections, these elements, components, regions, layers and/or sections should not be limited by these terms. These terms may be only used to distinguish one element, component, region, layer or section from another region, layer or section. Terms such as “first,” “second,” and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first element, component, region, layer or section discussed below could be termed a second element, component, region, layer or section without departing from the teachings of the example embodiments.

[0051] Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.