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1. (US20160109467) Microfluidic devices and methods for performing serum separation and blood cross-matching
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BACKGROUND

      Technical Field
      This invention generally pertains to devices, apparatus, and methods for separation of serum from whole blood and potentiation of agglutination reactions in microfluidic devices. Agglutination reactions involving antigen:antibody reactions are useful in cross-matching for blood transfusion.
      Description of the Related Art
      Analysis of blood prior to transfusion or for clinical assessments relies on diagnostic devices, such as cross-matching or blood-typing devices, and blood chemistry monitors that measure metabolites such as glucose or cholesterol. Such devices must frequently use serum, the uncolored fluid portion of the blood containing analytes of interest to clinicians. Serum samples are separated from whole blood before analysis to remove red blood cells and clotting factors, which have the potential to interfere with cross-match agglutination reactions, colorimetric tests, as well as contribute to hematocrit-dependent variations amongst samples. Therefore, prior to testing, a preprocessing operation is required in which the blood sample is separated into a serum and a clot containing red blood cells.
      In the conventional method of serum separation, a whole blood sample is placed in a blood collection tube, allowed to clot, and subjected to centrifugal separation, which enables collection of the serum fraction. However, there has been a dramatic transition in diagnostic analysis from the macroscale to the microscale, with specimen volume requirements decreasing from milliliters to microliters, thereby reducing assay times from hours to minutes. The conventional method of serum separation, requiring sample centrifugation, is obviously not amenable to microscale adaptation. As the engineering of microfluidic diagnostic devices continues to be the focus of competitive research, there is a neglected need for improvements in the preparation of samples for analysis. In adapting these devices for clinical diagnosis, special features are needed to provide serum separated from red blood cells and clotting factors.
      Administration of blood in the form of packed erythrocytes or whole blood is often critical in the treatment of trauma, hypovolemic shock, anemia and clotting disorders. Blood transfusion typically requires characterization of the donor blood so as to match the ABO blood type of the donor and recipient, or, more generally, requires a cross-match analysis. This is done to avoid a hemolytic transfusion reaction in which red cells having a major incompatibility antigen are inadvertently administered to a recipient having an antibody to that antigen, and also to avoid the minor side reaction in which a red cell antigen in the recipient's blood is attacked by antibodies in the plasma of the donor. Serious consequences such as kidney failure or splenic rupture can result from a transfusion of mismatched blood.
      Currently, medical technicians in the field do not have access to a simple and accurate means of evaluating a donor and recipient pair for possible transfusion reactions during emergency medical treatment, for example, during military operations. Tube agglutination assays are currently used prior to blood transfusion, however these assays are cumbersome and involve erythrocyte preparation and long incubation times. These assays may not always lead to consistent results depending upon the experience of the technician. Additionally, some technicians do not have access to a laboratory qualified to perform agglutination assays. Therefore, there is a strong need in the art for a blood cross-matching device that is quick and simple to use and thus amenable for evaluation of donor and recipient transfusion compatibility during emergency medical care. The present invention fulfills these needs and provides further related advantages.

BRIEF SUMMARY

      In one aspect, the present invention provides a microfluidic device having utility in any number of applications, such as for separating a serum fraction from a whole blood sample. In one embodiment, the microfluidic device includes: a) a microfluidic channel having a first end and a second end; b) a sample inlet fluidly connected to the first end of the microfluidic channel configured for receiving a blood sample; and c) a composite membrane interposed between the sample inlet and the first end of the microfluidic channel, wherein the composite membrane is capable of activating blood coagulation and removing selected particles from the blood; and d) an optional on-device pump fluidly connected to the second end of the microfluidic channel. In certain embodiments the optional on-device pump is present. In another embodiment, the composite membrane of the microfluidic device includes at least two membranes. In another embodiment, the composite membrane includes a glass fiber filter. In another embodiment, the composite membrane includes a glass fiber filter and a porous membrane. In another embodiment, the composite membrane also includes an activator of blood coagulation.
      In another aspect, the present invention provides microfluidic cartridges and devices which may be used for a number of different assays, including for cross-match assessment of a blood donor and a blood recipient. In one embodiment, the microfluidic cartridge or device includes: a) a fluid separation subcircuit that includes: i) a microfluidic channel having a first end and a second end; ii) a sample inlet fluidly connected to the first end of the microfluidic channel configured for receiving a blood sample; iii) a composite membrane interposed between the sample inlet and the first end of the microfluidic channel, wherein the composite membrane is capable of activating blood coagulation and removing selected particles from the blood; and iv) an optional on-device pump fluidly connected to the second end of the microfluidic channel; and b) a solute mixing subcircuit that includes: i) a serpentine mixing channel, said mixing channel having a first end and a second end and having a critical length for enabling solute mixture by diffusion; ii) a first and second intake channel fluidly joined to said first end of said mixing channel at a staging union; said first intake channel for conveying a first fluid and said second channel for conveying a second fluid; wherein said staging union is configured with a micro-passive valve for simultaneously releasing said first and second fluids into said mixing channel; iii) a downstream channel fluidly joined to the second end of said mixing channel, wherein the downstream channel has a width greater than the width of the mixing channel; iv) a pump for controlledly initiating fluid flow across said micro-passive valve, wherein said pump is fluidly connected to said downstream channel, and initiates flow by a suction stroke; and v) a vent terminating said downstream channel. In certain embodiments the optional on-device pump is present. In another embodiment, the microfluidic cartridge further includes a third intake channel fluidly joined to the first end of the mixing channel at the staging union; the third intake channel for conveying a third fluid to said staging area. In yet another embodiment of the microfluidic cartridge, the fluid separation subcircuit and solute mixing subcircuits are fluidly connected. In another embodiment of the invention, the composite membrane includes at least two membranes. In another embodiment of the invention, the composite membrane includes a glass filter. In another embodiment of the invention, the composite membrane includes a glass filter and a porous membrane. In another embodiment of the invention, the composite membrane includes an activator of blood coagulation.
      Methods for using the microfluidic devices for separation of serum from blood samples and for cross-matching donor and recipient samples are also provided.

BRIEF DESCRIPTION OF THE DRAWINGS

       FIG. 1 is a schematic view illustrating the operation of a first embodiment of a microfluidic device in accordance with aspects of the present invention.
       FIGS. 2A-B are cross-sectional views illustrating the operation of a second and third embodiment of a microfluidic device in accordance with aspects of the present invention.
       FIG. 3 is a schematic view illustrating the operation of a fourth embodiment of a microfluidic device in accordance with aspects of the present invention.
       FIG. 4 is a schematic view of representative microfluidic assay circuits of the present invention.
       FIG. 5 is a schematic of a second embodiment of the microfluidic assay circuits of the present invention.
       FIG. 6 shows results of cross-match reactions between different donors and recipients using a microfluidic device of the present invention.

DETAILED DESCRIPTION

      In one aspect, the present invention provides a microfluidic device configured to prepare a serum sample for analysis and methods for use of the same. The device is capable of promoting blood coagulation and manipulating the flow of the fluid sample in order to prepare a separated serum sample. The device employs a composite membrane that is capable of providing a matrix to hold a blood sample in place while promoting coagulation. Various embodiments of the device further utilize a plurality of microfluidic channels, inlets, valves, pumps, and other elements arranged in various configurations.
      In another aspect, the present invention provides microfluidic cartridges and devices configured to conduct cross-match assessments of blood samples from a donor and a recipient and methods for use of the same. Whole blood from the intended recipient is initially applied to a fluid subcircuit that comprises a composite filter designed to promote on-cartridge coagulation and particle separation, thereby providing an isolated serum sample for cross-match assessment. Packed red cells or whole blood from a donor unit and the separated serum from the intended recipient are added to separate intake channels of the mixing subcircuit of the microfluidic cartridge of the present invention. The donor and recipient samples are contacted in a side-by-side diffusion interface created in a serpentine channel of the mixing subcircuit. Diffusion of solutes between samples in the mixing channel leads to immune binding and visible agglutination reactions if the donor and recipient blood types are not compatible. A downstream flow control channel, with a dimension greater than that of the serpentine mixing channel, modulates and prolongs the liquid flow rate, thereby potentiating immune binding and agglutination reactions. In reactions run for up to ten minutes, agglutination due to incompatibility between blood donor and recipient was easily visually detectable using the microfluidic cartridges of the present invention. If no agglutination was observed, then the blood donor and the recipient are compatible.

1. Definitions

      These definitions are provided as an aid in interpreting the claims and specification herein. Where works are cited by reference, and definitions contained therein are inconsistent with those supplied here, the definition used therein shall apply only to the work cited and not to this disclosure.
      Microfluidic cartridge: a “device”, “card”, or “chip” with internal fluid-handling mesostructures by convention having at least one dimension less than 500 μm. These fluidic structures may include microfluidic channels, chambers, valves, vents, vias, pumps, inlets, nipples, and detection means, for example.
      Microfluidic channel: as used here, is an enclosed conduit or passage for a fluid having a z-dimension of less than 500 μm, more preferably less than or about 250 μm, and most preferably about or less than 100 μm (about 4 mils), and a cross-sectional area that is broader than deep. The most narrow dimension, also termed the “critical dimension”, of a channel has the most profound effect on flow, Reynolds Number, pressure drop, and in the devices described here, the most narrow dimension is typically the z-dimension or diameter.
      Microfluidic channels with generally rectangular cross-sections are characterized by x-, y- and z-dimensions. The x-dimension is taken as the length “L” of the channel along the axis of flow, the y-dimension as the width and the z-dimension as the depth. When formed by injection molding, the channel roof and walls are typically joined by a radius. Some microfluidic channels have a circular cross-section and are characterized by a diameter. Other shapes are also possible.
      It will be recognized that the words “top”, “bottom”, “upper”, “lower”, “side”, “roof”, “floor”, “base” and “horizontal” as used here are relative terms and do not necessarily describe the orientation of the device or device components in relation to the plane of the earth's surface unless explicitly stated to be so. The use of the devices flat on the surface of a table is not intended to be limiting and the z-axis is generally chosen to be perpendicular to the major plane of the device body only as a matter of convenience in explanation and manufacture.
      Finger (Bellows) Pump: is a device formed as a cavity, often cylindrical in shape, covered by a flexible, distensible diaphragm, and with an upstream microfluidic channel inlet and a downstream outlet fluidly connected to the cavity. In operation, by placing a vent as the outlet, the diaphragm can be pressed down without generating a differential pressure in the cavity, but by then covering the vent and releasing the elastic diaphragm, a suction pressure pulse is generated that finds use in drawing fluid through the inlet microfluidic channel. In the devices of the present invention, a suction pulse of this kind serves to initiate the assay by initiating fluid flow through a capillary stop; the suction pulse, however, is not required or desired for sustaining fluid flow, which is driven by passive flow capillarity once the upstream microfluidic channel is wetted.
      Surfactants: are amphiphilic molecules that lower the surface and interfacial tensions of a liquid by collecting at the interface, allowing easier spreading on a solid surface and reducing the contact angle. Anionic, cationic, zwitterionic, nonionic, and fluorophilic surfactants are contemplated. Anionic surfactants include sodium dioctyl sulfosuccinate (e.g., Aerosol OT-75) marketed by CYTEC Industries. Non-ionic surfactants include polysorbates (e.g., polysorbate 80), polyoxyethylene lauryl ether, n-lauryl-ß-D-maltopyranoside (LM), cetyl ether, stearyl ether, and nonylphenyl ether, Tween® 80, Triton® X-100, and other surfactants. As nonionic surfactants, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, polyoxyethylene-polyoxypropylene condensate, acyl polyoxyethylene sorbitan ester, alkyl polyoxyethylene ether, n-dodecyl-ß-D-maltoside, sucrose monolaurate, polyoxyethylene lauryl ether, polyoxyethylene alkylene phenyl ether, polyoxyethylene alkylene tribenzyl phenyl ether, polyoxyethylene glycol p-t-octyl phenyl ether, polyoxyethylene higher alcohol ether, polyoxyethylene fatty acid ester, polyoxyethylene sorbitan fatty acid ester, sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, polyoxyethylene alkylamine, glycerol fatty acid ester, n-octyl-ß-D-thioglycoside, cetyl ether (C16), lauryl ether (C12), oleyl ether, behenyl ether (C20), polyoxyethylene monolaurate and the like are used. Commercially available nonionic surfactants of this type include Igepal® CO-610 marketed by the GAF Corporation; and Triton® CF-12, X-45, X-114, X-100 and X-102, all marketed by the Dow Chemical Company; Tergitol®15-S-9 marketed by the Union Carbide Corporation; PLURAFAC® RA-40 marketed by BASF Corp; Neodol® 23-6.5 marketed by the Shell Chemical Company and Kyro EOB marketed by the Procter & Gamble Company. Amphoteric or zwitterionic surfactants are also useful in providing detergency, emulsification, wetting and conditioning properties. Representative amphoteric surfactants include fatty acid amides of amino acids (such as Amisoft® LS-11 and HS-21 made by Ajinomoto), N-coco-3-aminopropionic acid and acid salts, N-tallow-3-iminodiproprionate salts. As well as N-lauryl-3-iminodiproprionate disodium salt, N-carboxymethyl-N-cocoalkyl-N-dimethylammonium hydroxide, N-carboxymethyl-N-dimethyl-N-(9-octadecenyl)ammonium hydroxide, (1-carboxyheptadecyl)-trimethylammonium hydroxide, (1-carboxyundecyl) trimethylammonium hydroxide, N-cocoamidoethyl-N-hydroxyethylglycine sodium salt, N-hydroxyethyl-N-stearamidoglycine sodium salt, N-hydroxyethyl-N-lauramido-ß-alanine sodium salt, N-cocoamido-N-hydroxyethyl-ß-alanine sodium salt, as well as mixed alicyclic amines, and their ethoxylated and sulfated sodium salts, 2-alkyl-1-carboxymethyl-1-hydroxyethyl-2-imidazolinium hydroxide sodium salt or free acid wherein the alkyl group may be nonyl, undecyl, or heptadecyl. Also useful are 1,1-bis(carboxymethyl)-2-undecyl-2-imidazolinium hydroxide disodium salt and oleic acid-ethylenediamine condensate, propoxylated and sulfated sodium salt. Amine oxide amphoteric surfactants are also useful. This list is by no means exclusive or limiting.
      Surfactants can be added to a reagent to modify the surface tension of the reagent or added to a solid substrate to modify the interfacial tension of the substrate. During molding of a plastic article with a surfactant additive, a sufficient number of surfactant molecules migrate to the surface of the substrate, a process called “blooming”, so as to yield a low contact angle surface. The process is described in US Patent Application 2008/0145280 to Bookbinder, which is incorporated herein by reference in its entirety.
      Surfactants useful as admixtures with plastics to provide hydrophilic surface properties include polyethylene oxide, polypropylene oxide, nonylphenol ethyoxylate and polyalkylenyeneoxide modified heptamethyltrisiloxane, sodium or ammonium salts of nonyl phenol ethoxyl sulfonic acid, sodium lauryl sulfate, sodium 2-ethylhexyl sulfate and sodium dioctylsulfo succinate, and ionic salts of 2-acrylamido-2-methyl propanesulfonic acid, N-vinyl caprolactam, caprolactone acrylate, N-vinyl pyrrolidone, and sulfate and acrylic monomers, for example.
      “Low HLB (hydrophilic-lipophilic balance) wetting agents” are a subclass of surfactants preferred in the present invention for coating plastic surfaces to decrease contact angle and wet-out time. A low HLB wetting agent of the invention can be an anionic, a cationic, a zwitterionic or a non-ionic wetting agent, the latter being preferred. HLB numbers less than or equal to 6 are preferred; wetting agents of this type, when first dried to a surface, are essentially not solubilized when exposed to an aqueous reagent, but can be applied with alcohols, for example. The wetting agent of the invention can also be a mixture of two or more wetting agents. Candidates include, C12-C20 fatty acid esters of sucrose or xylose, glycerides of sucrose, fatty acid esters of polyoxyethylene, esters of fatty alcohols and polyoxyethylene, esters of sorbitan, esters of polyoxyethylene sorbitan, alcohol-polyglycide esters, and glyceride-polyglycides, also including for example Pluronic® L121, Pluronic® L122, PEO(2) cetyl ether (Brij® 52), PEO(2) stearyl ether (Brij® 72), Sorbitol mono-oleate (Span.® 20), Sorbitol tristearate (Span® 65), PEO(200) di-oleate (Maypeg® 200) sorbitol mono-stearate, glycerol mono-stearate, sucrose esters, alkyl naphthalene sodium sulfonate (Alkanol® B), N-octadecyl-disodium sulfosuccinamate (Aerosol® 18), polyoxyalkylene fatty ester (Nonisol® 250), dimethyl octynediol (Surfynol® 102), dimethyl hexynediol and the like.
      Capillary pressure or “capillary action” describes a pressure or a movement of a liquid under that pressure respectively, also termed “capillarity”, and refers to the tendency of a liquid in a microfluidic channel to advance or recede in a channel so as to minimize the overall surface free energy of the liquid/channel/vapor system. For example, a liquid with a low surface tension will advance to “wet out” a channel made from a material with a high surface energy such as glass. When injected in a microfluidic channel, liquids displaying a concave meniscus will tend to advance in the channel, and liquids displaying a convex meniscus will tend to recede. Thus capillarity is a vectored force resulting in wetting and passive flow of an aqueous liquid in a hydrophilic microfluidic channel.
      “Wetout” time: refers to a measurement of the time required for a liquid to advance a standardized length in a microfluidic channel of a given geometry and surface characteristics (generally in mm/s). “Wetout” rate refers to an instantaneous rate of advance of a liquid front in a microfluidic channel in units of volume per unit time (μL/μsec) and can be modulated by surface treatments and by controlling channel geometry. Passive flow driven by downstream wetout can be used to control upstream flow velocity.
      Herein, where a “means for a function” is claimed, it should be understood that the scope of the invention is not limited to the mode or modes illustrated in the drawings alone, but also encompasses all means for performing the function that are described in this specification and any equivalent means.
      Means for Fabrication: Fabrication methods include laser stenciling, lamination, embossing, stamping, injection molding, masking, etching, photocatalyzed stereolithography, soft lithography, and so forth, or any combination of the above. Each cartridge can be formed of a pair of members or layers glued or fused together, or of a plurality of layers glued or fused together. The term “layer” refers to any of one or more generally planar solid substrate members or glue layers comprising a cartridge; “layers” also includes individual sheets, roll stock, and any molded body members formed as generally planar members. Layers may be joined with pressure sensitive adhesive (PSA) or thermal adhesive. Alternatively, they may be fused under pressure with heat, solvent, or by ultrasonic welding. The number of layers in the device will be dependent on the required functionalities and the fabrication process is chosen.
      Plastic is a preferred material for building microfluidic devices of the present invention. Plastics which may be used include olefins, cyclic polyolefins, cyclic olefin copolymers, polyesters, polyethylene terephthalate, polybutylene terephthalate, polystyrenes, polycarbonates, polypropylene, polyethylene, polyurethane, polyether sulfone, polyvinyl chloride, polyvinyl acetate, polyamides, polyimides, polyacrylate, polymethylmethacrylate (PMMA), polytetrafluoroethylenes, polydimethylsiloxane (PDMS), polysilane, cellulose triacetate, thermoplastics in general, and so forth. Composites and copolymers are also frequently used. The knowledge to select plastics or other solid substrates and conventional adhesives is widely known in related arts.
      “Conventional” is a term designating that which is known in the prior art to which this invention relates.
      “About” and “generally” are broadening expressions of inexactitude, describing a condition of being “more or less”, “approximately”, or “almost” in the sense of “just about”, where variation would be insignificant, obvious, or of equivalent utility or function, and further indicating the existence of obvious minor exceptions to a norm, rule or limit. For example, in various embodiments the foregoing terms refer to a quantity within 20%, 10%, 5%, 1% or 0.1% of the value which follows the term.
      Unless the context requires otherwise, throughout the specification and claims which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense—that is as “including, but not limited to”.

2. Features and Methods of Use for Microfluidic Cartridges and Devices for Serum Separation

      Exemplary embodiments of the invention can be better understood in reference to the attached figures. However, it is to be understood that the illustrated embodiments do not limit the scope of the invention and certain non-illustrated embodiments are also included.
       FIG. 1 is a schematic view of the device 110 illustrating the operation of a first embodiment of the invention. As shown in FIG. 1, a microfluidic device 110 comprises a microfluidic channel 120 having a first end 122 and a second end 124. As illustrated, device 110 is in the form of a cartridge, however, the form of device 110 is not essential to the present invention and persons of ordinary skill in the art can readily select a suitable form for a given application. The microfluidic devices of the present invention, such as device 110, may be constructed from a material, such as plastic, mylar or latex, using a method such as injection molding or lamination.
      As further shown in FIG. 1, device 110 comprises a sample inlet 130 fluidly connected to first end 122 of microfluidic channel 120 for receiving a liquid sample and a composite membrane 140 interposed between sample inlet 130 and first end 122 of microfluidic channel 120. As used herein, the term “membrane” refers to any planar material with a Z-dimension, including filters, which are porous membranes. Composite membrane 140 is capable of providing a matrix to hold a blood sample in place and, importantly, promoting coagulation of the blood sample. Composite membrane 140 is also capable of selectively retaining the clotted components of the blood sample and other selected particles, such as white blood cells, red blood cells, polymeric beads, such as polystyrene or latex beads with sizes from 1-100 μm, and bacteria cells, such as E. coli, from the liquid sample. Composite membrane 140 may comprise a plurality of filters or membranes or a single filter or membrane comprising a plurality of different fibers types. An optional finger pump 150 having a vent hole 152 is fluidly connected to the second end 124 of microfluidic channel 120.
      During operation, a liquid blood sample is placed into sample inlet 130 (as shown in FIG. 1) whereupon the liquid blood is absorbed by membrane 140, which promotes the coagulation of the blood sample. Finger pump 150 is depressed, either manually by a user or mechanically by an external device, vent hole 152 is substantially sealed, such as by covering vent hole 152, and finger pump 150 is subsequently released. During depression of finger pump 150, vent hole 152 remains uncovered so that air in finger pump 150 may be expelled through vent hole 152. Upon release of finger pump 150, a negative fluid pressure is created in microfluidic channel 120 and a liquid serum sample is drawn through membrane 140 into, and through, microfluidic channel 120 into the sample collection well 170. In contrast, the clotted constituents as well as particles of the sample are retained by composite membrane 140 and do no enter sample collection well 170. In various embodiments, the negative pressure is provided by means other than the finger pump (e.g., an associated pneumatic instrument or other means) or the fluid moves under force of gravity.
       FIGS. 2A-B depict cross-sectional views of alternative embodiments of composite membrane 140. As shown in FIG. 2A, the composite membrane may comprise two membranes, membranes 142 and 144. Membranes 142 and 144 may comprise the same or different materials. In one embodiment, the membrane 142 comprises a material that activates blood coagulation, such as glass fibers. In one embodiment, the second membrane 144 may be selected to provide particle-separation functions. In this embodiment, membrane 144 may comprise a filter with a pore size of around 1-2 μm in order to selectively remove red blood cells and white blood cells from the liquid sample. Such membranes may include, but are not limited, to asymmetric and non-asymmetric membranes comprising polysulfone (manufactured by PALL, Inc.). The two or more membranes may be stacked one on top of the other in device 110.
      In operation, a blood sample is placed in sample inlet 130. When a drop of whole blood is applied to the device 110, the blood sample is drawn into membrane 142, which causes the blood to clot. Under negative pressure, the clotted sample is further drawn into second membrane 144, which retains the clotted and particulate matter while the liquid serum sample passes through the membrane into voids 182 and 184. The volume of voids 182 and 184 is sufficiently small such that the separated serum sample moves by capillary flow into the first end 122 of the microfluidic channel.
      An alternative embodiment of the composite filter is shown in FIG. 2B. As depicted, composite filter 146 comprises a single membrane comprising a plurality of different fiber types, at least one of which promotes the coagulation of unclotted blood. Fibers selected for the composite filter medium include, but are not limited to, cotton linter fibers, glass microfibers, polyester (PET) staple fibers, and lower melting polyester binder fibers. Polyester staple fibers of about 1.5 denier (wherein “denier” is a term of art that refers to a unit that describes the thickness and length of a fiber) and about 0.25-in length may be the backbone of the filter to provide the gross structure of the membrane. Optionally, cotton linter fibers may be used to provide a readily wettable capillary network to passively draw the blood through the filter. Glass microfibers of about 0.40 μm mean fiber diameter may produce the fine pore structure needed for cell and particle separation. Fibers may be joined by woven or nonwoven means. Nonwoven filters may be constructed by wetlaid, spunbonded, or meltblown means. To increase strength, polyester binder fibers may optionally be added to the composite membrane.
      As an alternative embodiment of the present invention, the composite membranes of FIGS. 2A-B may further contain one or more accelerators of blood coagulation. Blood coagulation activators known in the art include, but are not limited to, thrombin, snake venoms, such as Russells viper venom, platelet activating factor (PAF or ß-Acetyl-y-O-alkyl-L-∂-phosphatidylcholine), collagen, materials bearing multiple negative charges on their surfaces, such as borosilicate flakes or hallow beads, and aluminum-silicate mineral clays, such as kaolin.
       FIG. 3 is a schematic view of the device 110 illustrating the operation of one embodiment of the invention. Sample collection well 170 may be sealed with adhesive membrane 190. During operation, device 110 is supplied with sample collection well 170 sealed from the environment by adhesive membrane 190. In one embodiment of the present invention, adhesive membrane 190 is a pressure sensitive, removable tape. A liquid blood sample is placed into sample inlet 130 whereupon the liquid blood is absorbed by filter 140, which promotes the coagulation of the blood sample. Finger pump 150 is depressed, either manually by a user or mechanically by an external device, vent hole 152 is substantially sealed, such as by covering vent hole 152, and finger pump 150 is then released. During depression of finger pump 150, vent hole 152 remains uncovered so that air in finger pump 150 may be expelled through vent hole 152. Upon release of finger pump 150, a negative fluid pressure is created in microfluidic channel 120 and a liquid serum sample is drawn through membrane 140 into, and through, microfluidic channel 120 into the sample collection well 170. Adhesive membrane 190 is removed from device 110 by user manipulation of tab 195 to enable removal of a separated serum sample for further analysis. As noted above, the finger pump is not a required feature of all embodiments and fluid movement may be initiated and/or maintained by other means.
      Methods for separation of serum from whole blood samples by use of the microfluidic devices are also provided. For example, in some embodiments, such methods comprise introducing the blood sample into the sample inlet of any of the disclosed microfluidic devices and contacting the blood sample with the composite membrane therein. The separated serum may then be isolated by the user and employed in further analyses, for example cross-matching analyses by contacting the isolated serum with a blood sample (e.g., a recipient blood sample) and observing the presence or absence of an agglutination reaction.

3. Features and Methods of Use for Microfluidic Cartridges and Devices for Blood Cross-Match Analysis

      Embodiments of the microfluidic devices of the present invention are planar, disposable cartridges that are generally credit card-sized. Most on-cartridge fluid handling and structural elements have internal dimensions ranging in size from less than 100 μm to a few mm in size and are designed to handle fluid volumes from a few microliters to a milliliter or two.
       FIG. 4 is a schematic view of a microfluidic device 100 illustrating the operation of another embodiment of the invention. As illustrated, device 100 is in the form of a cartridge, however, the form of device 100 is not essential to the present invention and persons of ordinary skill in the art can readily select a suitable form for a given application. The microfluidic devices of the present invention, such as device 100, may be constructed from a material, such as transparent plastic, mylar or latex, using a method such as injection molding or lamination.
      As shown in FIG. 4, the microfluidic device 100 comprises a fluid subcircuit 110 for serum separation. Subcircuit 110 comprises a microfluidic channel 120 having a first end 122 and a second end 124. Fluid subcircuit 110 further comprises a sample inlet 130 fluidly connected to first end 122 of microfluidic channel 120 for receiving a liquid sample and a composite membrane 140 interposed between sample inlet 130 and first end 122 of microfluidic channel 120. As used herein, the term “membrane” refers to any planar material with a Z-dimension, including filters, which are porous membranes. Composite membrane 140 is capable of providing a matrix to hold a blood sample in place and, importantly, promoting coagulation of the blood sample. Composite membrane 140 is also capable of selectively retaining the clotted components of the blood sample and other selected particles, such as white blood cells, red blood cells, polymeric beads, such as polystyrene or latex beads with sizes from 1-100 μm, and bacteria cells, such as E. coli, from the liquid sample. Composite membrane 140 may be comprised of a plurality of filters or membranes or a single filter or membrane comprised of a plurality of different fibers types. A finger pump 150 having a vent hole 152 is fluidly connected to the second end 124 of microfluidic channel 120. Although illustrated with a finger pump, the finger pump is not a required feature of all embodiments and fluid movement may be initiated and/or maintained by other means.
      During operation, a liquid blood sample is placed into sample inlet 130 (as shown in FIG. 4) whereupon the liquid blood is absorbed by membrane 140, which promotes the coagulation of the blood sample. Finger pump 150 is depressed, either manually by a user or mechanically by an external device, vent hole 152 is substantially sealed, such as by covering vent hole 152, and finger pump 150 is subsequently released. During depression of finger pump 150, vent hole 152 remains uncovered so that air in finger pump 150 may be expelled through vent hold 152. Upon release of finger pump 150, a negative air pressure is created in microfluidic channel 120 and a liquid serum sample is drawn through membrane 140 into, and through, microfluidic channel 120 into the sample collection well 170. In contrast, the clotted constituents of the sample are retained by composite membrane 140 and do no enter sample collection well 170. Separated serum is to be removed manually by the user for further cross-match analysis as described below.
      The cartridge of body member 100 further comprises a mixing subcircuit for the mixing of solutes between two or more liquid samples. As exemplified by the microfluidic device of FIG. 4, three intake channels 212, 214, and 216, generally with inlet wells 222, 224, and 226, are joined at a staging union 230. A liquid sample is introduced into a first inlet well and another sample or reagent liquid is introduced into a second inlet well. Optionally, a third liquid sample is introduced into a third well. One sample or reagent will include a particulate suspension of red blood cells. A second sample or reagent will include separated serum. A third, optional, sample or reagent may include a diluent, as described in greater detail below.
      The microfluidic device includes micro-passive valves interposed between the intake channels 212, 214, and 216 and the staging union 230 and are configured to form a dual fluid stop. The fluid stops illustrate the general principal that an aqueous liquid will not cross a surface energy barrier without an additional force. Thus a meniscus forms where the channel geometry expands sharply and or a hydrophobic barrier surface is formed. When energy is provided, for example as a suction pulse applied downstream by finger pump 260 or other means to start the assay, all fluids will simultaneously cross the micro-passive valves and enter the common serpentine mixing channel 240. Fluids flow into serpentine mixing channel 240 by capillary action and solutes in the fluids mix together by diffusion as the liquids pass through the serpentine mixing channel. The serpentine turns of the mixing channel increase the overall length of the mixing channel, and thus the distance travelled by the liquids. Importantly, increasing the time that the liquids reside in the mixing channel through the serpentine configuration also increases the time for solutes in the liquid streams to mix by diffusion. When the particulate suspension of red blood cells is contacted with serum in the second sample, antibodies present in the second sample will cause an agglutination reaction to occur if there is no cross-match between the two samples, demonstrating they are not compatible for blood transfusion. In contrast, no agglutination reaction occurs if the first and second samples are compatible for blood transfusion. Agglutination reactions are observed by the user by the appearance of dynamically moving particle aggregates or “clumps” in the serpentine mixer 240 and the downstream channel 250 of the microfluidic device. The length of the serpentine channel is selected such that the time the flowing liquids reside in the serpentine channel is sufficient for the liquids to mix and an agglutination reaction to occur if there is no cross-match. A length which allows for sufficient mixing to enable an agglutination reaction is referred to as the “critical length.”
      The bottom surfaces of the inlet wells 222, 224, 226, intake channels 212, 214, 216, serpentine mixer 240, and tailpipe 250 may be coated with a surfactant to make the surfaces hydrophilic and promote the capillary flow of liquid sample through the microfluidic circuit. Agglutination reactions may be observed by the user through visual detection of moving particle aggregates or “clumps” dynamically passing through the serpentine mixer 240 and into the downstream channel 250. The downstream channel is configured such that it has a greater width than the width of the mixing channel. Due to the greater width of the downstream channel which increases the cross-sectional volume of the channel thereby reduces the velocity of the liquid front, however the flow rate of the liquid streams in the mixing channel remain the same, thereby increasing the amount of sample to be mixed in the channel.
      In an alternative embodiment of the microfluidic devices of the present invention cartridge body member 100, has two intake channels 212 and 216, generally with inlet wells 222 and 226, joined at a staging union 230. A liquid sample containing a particulate suspension of red blood cells is introduced into channel 212; a second liquid sample containing separated serum is introduced into channel 216. In this embodiment of the invention, dilution of the particulate blood sample may be performed off-cartridge, prior to loading of the blood sample into inlet well 222 of the microfluidic device of FIG. 4. A red blood cell diluent may be included to achieve any of the following advantages: reduction of the concentration of agglutinins in the donor blood that may participate in an auto-immune reaction with the donor red bloods cells and induce hemolysis or agglutination as a side-reaction; reduction of the Zeta potential (negative surface charge) on the donor red blood cells, which inhibits cellular aggregation; reduction in the density of red blood cells in the detection window, such that aggregates of cells are more easily viewed; or prevention of complement-mediated steric hindrance of antibody-antigen binding that might contribute to a false negative reaction (e.g., a cross-match). Exemplary diluents include but are not limited to isotonic saline solutions that may or may not include EDTA to prevent clotting of donor blood prior to cross-match analysis. When the particulate blood sample and diluent are contacted with serum in the second sample, antibodies present in the second sample will cause an agglutination reaction to occur if there is no cross-match between the red blood cell and serum samples, indicating and they are not compatible for a blood transfusion. In contrast, no agglutination reaction will occur if the particulate and serum samples are compatible for a blood transfusion. Agglutination reactions are observed by the user by the appearance of dynamically moving particle aggregates or “clumps” in the serpentine mixer 240 and the downstream channel 250.
      Another alternative embodiment of the microfluidic devices of the present invention is shown in FIG. 5. In this embodiment, microfluidic device 105 comprises a fluid subcircuit 115 for serum separation that is fluidly connected to intake channel 216. Serum separation is performed as described above; however, in this embodiment of the invention, the serum collection chamber 175 functions as sample inlet well 226 of the embodiment of FIG. 4. The principles of operating microfluidic device 105 of this embodiment of the invention are similar to those of microfluidic device 100, except that operation of microfluidic device 105 does not require that the user manually apply a serum sample to a sample inlet well.
      Methods for use of any of the foregoing microfluidic devices in cross-matching of two different blood samples, such as cross match of a donor blood sample and a recipient blood sample, are also provided. For example, the methods may be for performing a cross match of a donor blood sample and a recipient blood sample. In one of these embodiments, the method comprises:
      a) contacting the donor blood sample with the composite membrane of any of the foregoing microfluidic devices;
      b) isolating serum from the donor blood sample;
      c) contacting the isolated serum with the recipient blood sample; and
      d) observing the presence or absence of an agglutination reaction.
      Advantageously, certain embodiments of the methods are performed using microfluidic devices in which a fluid subcircuit for serum separation is fluidly connected to a sample inlet and mixing channel (e.g., as described with respect to FIG. 5). In embodiments of these methods, serum separation is performed, and the separated serum is contacted with a whole blood sample on the same microfluidic device. For example, in some embodiments the cross matching methods comprise:
      a) introducing a donor blood sample into a serum separation subcircuit of a microfluidic device having fluidly connected serum separation subcircuits and solute mixing subcircuits (e.g., as described above in reference to FIG. 5) and contacting the donor blood sample with a composite membrane in the serum separation subcircuit to separate donor serum from the donor blood sample;
      b) contacting the donor serum with a recipient blood sample in a mixing channel of the solute mixing subcircuit; and
      c) observing the presence or absence of an agglutination reaction.

EXAMPLES

Example 1: Assessment of Glass Fiber Filters in Promoting Blood Coagulation

      This example demonstrates that glass fiber filters promote blood coagulation on a microfluidic device.
      Various borosilicate glass fiber filters as set forth in Table 1 were stacked with the Pall Vivid GR membrane and laminated into “cartridges” (i.e., into a microfluidic device) using standard construction methods known in the art. For testing, 100 μL of fresh, whole blood was applied to the filter and allowed to clot for up to 15 minutes. Liquid sample was pulled by vacuum into a collection chamber. Performance of the filters was evaluated based on the volume of serum obtained in one minute and on the color of the serum. As shown in Table I, several of the glass fiber filters tested enabled on-card serum separation. Pink serum indicates that some degree of hemolysis has occurred. These results indicate that serum separation can, surprisingly, be achieved on-card (i.e., within a microfluidic device) by incorporation of a glass fiber filter into the design of the device. Interestingly, not all glass fiber filters displayed identical properties in this assessment. The function of the Porex glass fiber filter was superior to the others in that it did not promote hemolysis, but rather generated a clear serum sample. Pore size or filter thickness of the glass fiber filters tested varied, but no correlation was observed with performance.
      Thus, this unique composite filter design, which introduces a borosilicate glass fiber filter, displays superior functionality over prior art filtering devices. While the prior art blood filters are limited to performing particle separation, the composite filters of the present invention can further promote blood coagulation, thereby removing inhibitory clotting factors and providing serum for further diagnostic analysis.
      
[TABLE-US-00001]
TABLE 1
 
Borosilicate glass fiber filters tested in serum separation
Brand   Pores Thickness Volume  
(Glass fiber) Grade (microns) (microns) (μL) Color
 
Porex D 2.7 640 20 Clear
Pall A/D 3.1 580-740 20 Pink
Whatman GF/D 2.7 675 20 Pink
Macherey MN 85/90 BF 0.5 400 20 Pink
Nagel
 

Example 2: Design of a Microfluidic Subcircuit for Serum Separation

      This example demonstrates serum separation by a microfluidic device incorporating a glass fiber, composite filter.
      A microfluidic subcircuit with a collection chamber and a port was designed to separate serum from a whole blood sample. Fresh, whole finger-stick collected blood (approximately 200 μL) was applied to a composite filter as described above and allowed to clot. In operation, the user's index finger compresses a finger pump, while a second finger covers the vent holes. The vacuum generated when the index finger is removed pulls the sample through the filters into the collection chamber. The filtered sample was collected using a mechanical pipettor with a disposable tip. The recovered material was characterized as serum by measurement of the residual fibrinogen content. Plasma contains fibrinogen, while serum is depleted of this protein due to activation of the clotting cascade, during which fibrinogen is converted into insoluble fibrin to create the blood clot. The blood clot is retained in the composite filter, while the liquid serum passes through the filter and into the collection chamber.
      A fibrinogen ELISA kit (manufactured by Alpco Diagnostics, Salem, N.H.) was used to measure fibrinogen content of the samples. Samples recovered from the serum separation subcircuit were compared to serum generated by the conventional protocol of blood clotting and centrifugation in vacucontainers. Plasma collected in vacutainers containing sodium citrate as an anticoagulant was also assayed. Four different plasma samples were found to contain from 2.9 to 4.2 mg/mL fibrinogen, while serum samples generated by centrifugation were found to be mostly depleted of fibrinogen, containing from 0 to 300 ng/mL fibrinogen (approximately 10,000 fold less than plasma). Surprisingly, as shown in FIG. 6, the amount of fibrinogen detected in each of the eleven samples of material obtained from the serum separation subcircuit was also negligible (from 0 to 3000 ng/mL fibrinogen). These results demonstrate the successful design of a serum separation subcircuit into a microfluidic device through use of a glass fiber, composite filter. The microfluidic devices disclosed herein offer significant advantages over conventional serum separation protocols, which require large, heavy, and costly laboratory equipment to practice.
      The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, including but not limited to U.S. Patent Application Nos. 61/820,576; 61/820,585 and 61/820,579; each filed May 7, 2013, are incorporated herein by reference, in their entirety. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.