Patent Application
20070272309
Microfluidic systems, that is, systems or devices having channels or chambers that are fabricated on the micron or submicron scale, are used to perform a multitude of chemical and physical processes on a micro-scale. Individual components of the microfluidic systems can be used alone or together, for example, to control or measure the transport of fluid inside microchannels. Typical applications for microfluidic systems include analytical and medical instrumentation, industrial process control equipment, and liquid and gas phase chromatography. In these systems, methods to reliably aliquot volumes of sample from one conduit into a second conduit are important for performing the analysis. In some cases, sample volumes as small as 1 nL are required for analysis, which is a volume too small to be reliably dispensed by known macroscale methods employing conventional valves or pipettes. It would be advantageous to have a microfluidic system that could be used with a wide range of processes and process liquids and that could be fabricated on a microchip platform. It would also be advantageous to have a device with a fast response time and precise control over small sample volumes and flows.
Microfluidic control devices, such as microvalves manufactured from silicon or elastomers, including devices fabricated from hydrogels, soft elastomers with control lines embossed in a substrate, and devices fabricated with structures that are free to move within microchannels are currently known. More information on these devices can be found in Shoji and Esashi, J., Micromech. Microeng., 4, 157-171, 1994; Beebe et al., Nature, 404, 588-59O, April 2000; Unger et al., Science, 288, 113-116, April 2000; Rehm et al., uTAS 2001, 227-229, October 2001; and U.S. Pat. App. No. 2004/0123658. However, these devices suffer from one or more of the disadvantages of not being easily integrated into microchip platforms, having excess dead volume, high power requirements, slow response times, are difficult and costly to manufacture and to assemble, are able to withstand only modest pressure differentials, are restricted to a narrow range of processes and process liquids, are subject to solvent-induced deformation effects, uneven (or unpredictable) performance due to minor variations in material properties, have problems associated with degradation associated with silanated micro channel coatings, and/or respond poorly to solvent-induced shrinkage and swelling.
Therefore, there is a need for a microfluidic control device that has a fast response time, precise control over small gas and liquid flows, and precise control over small gas and liquid volumes in the channels and chambers of microfluidic systems. There is also a need for a microfluidic control device that can be integrated into a microchip platform and is compatible with a wide range of chemicals and solvents that are used in microfluidic systems.
According to the present invention, a device for microfluidic control is provided. The device comprises a conduit having a first end and a second end, a first path in fluid flow contact with the conduit, a second path in fluid flow contact with the conduit, and a regulator that is moveable in the conduit. The regulator has an outer dimension that is larger than the first end and the second end so the regulator cannot pass out of the conduit and is comprised of a substantially elastic material having a structural component, which can be a composite polymer formed from a composite mixture comprising a polymerizable precursor and a particulate filler. The composite mixture can additionally comprise a surfactant, photo-initiator, and/or two or more polymerizable precursors, and/or two or more particulate fillers. Optionally, the device can have a plurality of paths, such as first, second, and third paths, where each path is in fluid flow contact with the conduit, and/or a plurality of regulators that are movable in a conduit. The regulator can be substantially incompressible, have specific optical properties, and/or have a substantially stable volume when exposed to a fluid. Further, the regulator can be formed from a composite mixture in the conduit by the in situ polymerization of the composite mixture with an energy source. The composite mixture can additionally comprise a photo-initiator and the energy source can be a radiating light source. The regulator can also be substantially cylindrically shaped and moveable in a back and forth motion or reciprocating motion within the conduit. Alternately, the regulator can be substantially toothed wheel shaped and rotationally moveable within the conduit. The device can additionally comprise a substrate where the conduit, and/or a plurality of conduits are in the substrate. Optionally, the substrate can have an axle and the regulator can be substantially toothed wheel shaped and rotationally moveable around the axle.
A system for microfluidic control comprising a plurality of conduits is also provided, where each conduit has a first end and a second end, a first path in fluid flow contact with one or more conduit, a second path in fluid flow contact with one or more conduit, and a plurality of regulators, each regulator being independently moveable in a separate conduit. Each regulator has an outer diameter that is larger than the first end and the second end so each regulator cannot pass out of the conduit, and is comprised of a substantially elastic material having a structural component.
The device can be fabricated by combining a polymerizable precursor and a particulate filler to form a composite mixture, introducing the composite mixture into a conduit, and exposing the conduit to an energy source to polymerize the composite mixture in situ thereby forming a regulator. Preferably, the composite mixture comprises one or more polymerizable precursor and one or more particulate fillers. More preferably, the polymerizable precursors can be one or more fluorinated acrylate or fluorinated methacrylate, where most preferably, at least one polymerizable precursor is a perfluoropolyether acrylate, or methacrylate admixed with monomers (polymerizable precursors that are mono- or multi-functional in terms of polymerizable moiety. The foregoing mixture can optionally contain a fluorescent monomer. Preferably, the particulate filler is a surface treated particulate filler, and/or a polyhedral oligomeric silsesquioxane.
The composite mixture can additionally comprise a surfactant, and/or a photo-initiator and the conduit can be exposed to a radiating light source through a mask to form the regulator. Preferably, the photo-initiator is fluorinated and/or an aromatic ketone.
Additionally, the finished device can have two or more regulators within each conduit, with unpolymerized composite mixture being removed from the conduit. Optionally, a substrate having a plurality of conduits can be selected and the composite mixture can be introduced into each conduit, thereby forming a plurality of regulators. The substrate can have three or more conduits and the composite mixture can be introduced into three or more conduits to form three or more regulators on the same substrate. One or more of the conduits can be exposed to a radiating light to form one or more substantially cylindrically shaped regulators and each substantially cylindrically shaped regulator can be moveable in a back and forth motion within the conduit. Alternately, one or more of the conduits can be exposed to a radiating light to form one or more substantially toothed wheel shaped regulators and each substantially toothed wheel shaped regulator can be rotationally moveable within the conduit. The substrate can additionally have an axle and the conduit can be exposed to a radiating light to form a substantially toothed wheel shaped regulator around the axle.
The device can be used for determining a fluid flow rate in a microfluidic device by moving a fluid of a given viscosity past a regulator, thereby moving the regulator at the fluid flow rate. A radiating light is directed to a portion of the regulator such that the radiating light is reflected or transmitted to a detector and the reflected or transmitted light is measured a periodic signal in time. Then, the signal is processed and the frequency of the signal is determined, followed by relating the signal frequency to the fluid flow rate. The radiating light can be reflected or transmitted to a plurality of detectors. Also, a plurality of radiating lights can be directed to the regulator and the radiating lights can be reflected or transmitted to a plurality of detectors. A device for microfluidic control as described above having a substantially toothed wheel shaped regulator can be used to determine fluid flow rate and the radiating light can be directed to a toothed portion of the regulator such that the radiating light is reflected or transmitted to the detector.
These and other features, aspects and advantages of the present invention will become better understood from the following description, appended claims, and accompanying drawings where:
According to one embodiment of the present invention, there is provided a device for microfluidic control. The device comprises a regulator that is moveable in a conduit and is formed from a composite mixture comprising a polymerizable precursor and a particulate filler. The use of a particulate filler in the regulator confers a wide range of desirable properties to the regulator, such as, a range of rigidity versus flexibility, additional tensile and compressive strength, optical properties, and dimensional stability. The regulator can operate under high pressure, such as thousands of pounds per square inch (psi), and the addition of the particulate filler to the regulator provides substantial advantages in reduced compressibility. Further, the microfluidic control device of the present invention has a fast response time and precise control over small gas and liquid flows and small gas and liquid volumes in the channels and chambers of the microfluidic system. Further, the microfluidic control device can be integrated into a substrate, such as a microchip platform.
The microfluidic control device of the present invention can include interconnecting conduits that can be filled with fluids. These devices can be used for analytical procedures such as the analysis of chemical and biological substances. Examples of such devices include high-performance liquid chromatography (HPLC) and flow-injection analysis (FIA).
In certain preferred embodiments, a coated or surface-treated particulate filler is used in the composite mixture to form the regulator. By utilizing surface treated particulate filler (for example hydrophobically treated fumed silica) particles in the composite polymer mixture formulation, as opposed to silanated micro channel coatings, such as those described in U.S. Pat. App. No. 2004/0052929, the problems associated with the degradation of the silane film, which are known in the art to occur over time, can be overcome. Silane films form multilayers (under most reaction and hydrolysis conditions) and as a result are inhomogeneous in nature. The silane films, which are covalently bound to the hydrophilic silica (silanol) surfaces of the micro channels, over time and under varying solution conditions (pH, salts, proteins, etc.) degrade and will be washed away. In microvalve, injector/pipettor, and diverter applications, the mobile monolith polymer element is repeatedly actuated. The mechanical nature of this repeated motion causes wear and degradation of the surface coating, which can contaminated an integrated micro-total analysis system (HPLC for example). By incorporating surface treated particulate filler micro particles within the composite matrix, the composite polymer element can have added advantages of low wear and friction without the associated problems of system contamination when samples are being processed.
As used in this disclosure, the following terms have the specified meanings.
The term “composite polymer” means a material obtained by the polymerization of a mixture of a particulate filler and one or more polymerizable precursors.
The term “conduit” means any of various channels or networks of channels including capillaries and tubing.
The term “elastic material” means a material that recovers its original shape partially or completely after a deforming force has been removed.
The term “fluid” means any of various liquids, gasses, or loose solid materials in bulk.
The term “micro-scale” means a micron or submicron scale, that is, having at least one cross-sectional dimension in the range from about 0.1 am to about 500 μm.
The term “microfluidic” means a system or device having channels or chambers that are on the micro-scale.
The term “monolithic polymer” means a polymerized polymerizable precursor without a particulate filler.
The term “regulator” means any of various devices by which a fluid flow can be started, stopped, or adjusted by a movable part that opens, shuts, or partially obstructs one or more openings.
The term “structural component” means a particle or a part affecting the structure, composition, physical make-up, or nature of a substance.
The term “substrate” means a chip with lithographically fabricated microchannels or conduits, and includes other conduit and channel networks such as capillaries and tubing.
The term “comprise” and variations of the term, such as “comprising” and “comprises,” are not intended to exclude other additives, components, integers or steps.
All dimensions specified in this disclosure are by way of example only and are not intended to be limiting. Further, the proportions shown in these Figures are not necessarily to scale. As will be understood by those with skill in the art with reference to this disclosure, the actual dimensions of any device or part of a device disclosed in this disclosure will be determined by the intended use.
All amounts disclosed herein as a percentage is a weight percent of the total weight of the composition.
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The device 10 can additionally comprise an interconnecting conduit 18 that provides a route for fluid to be redirected around the regulator 16 when the regulator 16 is seated against the conduit second end 13, as shown in
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In a preferred but not required embodiment, the regulator 52, 53, and 54 is a composite polymer obtained by photoinitiated polymerization of a mixture of particulate filler and one or more polymerizable precursors.
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A second detector can be added to the device shown in
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In one embodiment, the regulator is a substantially elastic material containing a structural component. The regulator can be a composite polymer formed from the polymerization of a composite mixture comprising a polymerizable precursor and a particulate filler. The regulator is movable in the conduit, that is, the regulator will not bond to the surrounding conduit walls or surrounding structures and is free to move or rotate inside the conduit. The regulator is also confined within regions of the conduit, as defined by specific features in the device geometry. In a preferred but not required embodiment, the regulator is formed by the in situ polymerization of the composite mixture in the conduit. In a more preferred but not required embodiment, the in situ polymerization is effected by light exposure or heating. In a most preferred but not required embodiment, the composite mixture is polymerized by the in situ photo-initiated and lithographically defined polymerization of a polymerizable precursor and a particulate filler in the conduit. According to this embodiment, the composite mixture is polymerized in situ in the shape defined by a mask by exposing a region of the conduit to a radiating light through the mask. The use of a mask allows fabrication of regulators with irregular and arbitrary geometry inside the channel. Furthermore, since the regulators do not bond to the surrounding conduit walls or surrounding structures, the regulators are moveable in the conduit. For example, the regulator can move in a back and forth motion within the conduit, or the regulator can be rotationally movable in the conduit. When the regulator is formed by photo-initiated polymerization of the composite mixture in situ, optical access to the composite mixture in the conduit region of polymerization is provided. When the regulator is formed by in situ polymerization by thermal or other radiative means, optical access is not necessarily provided.
The composite mixture is comprised of one or more polymerizable precursor and a particulate filler and can additionally comprise a polymerization initiator, such as a photo-initiator, and one or more solvents. The composite mixture can be in the form of a slurry, that is, a liquid containing a particulate filler that may not necessarily be suspended, such as with a particulate filler having a particle size of between about 100 nm and about 100 μm; a colloidal suspension, such as with a particulate filler having a particle size range of between about 1 nm and 100 nm; and a free-flowing liquid. However, the composite mixture can have other forms as will be understood by those of skill in the art with reference to this disclosure.
The polymerizable precursor can be any of various monomer materials, such as butanediol diacrylate, diethylene glycol diacrylate, divinyl benzene, ethylene glycol diacrylate, hexanediol diacrylate, neopentyl glycol diacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, propylene glycol diacrylate, trimethylolpropane triacrylate, halogenated acrylates, such as heptafluorobutyl acrylate and trifluoroethylacrylate, methacrylates, halogenated methacrylates, and combinations of the preceding monomers. Preferred polymerizable precursors are able to impart (in polymerized form) desirable characteristics to the regulator including hydrophobicity, chemical stability, low toxicity, inertness to a variety of solvents, limited shrinkage/swelling (in HPLC solvents), resistance to weathering, release properties, low coefficient of friction and wear resistance, high tensile modulus, low surface energy, water impermeability (due to the hydrophobic nature). In a preferred but not required embodiment, the polymerizable precursor is a halogenated acrylate or halogenated methacrylate, including halogenated monomers of mono and multifunctional (di-, tri-, or tetra-functional) alkyl, cycloalkyl and/or aryl acrylates and methacrylates, with fluorinated moieties being able to impart (in polymerized form) more desirable properties. Examples of such halogenated polymerizable precursors include but are not limited to perfluoropolyether diacrylate, fluorinated acrylate oligomers, fluorinated tetraethylene glycol diacrylate, 1H,1H,6H,6H-perfluorohexylenediacrylate, 1H, 1H,2H,2H-perfluoro-1,6-hexylenedimethacrylate, 2,2,3,3-tetrafluoro-1,4-butylenediacrylate, 2,2,3,3-tetrafluoro-1,4-butanediol diacrylate, 1H,1H,7H-dodecafluoroheptyl acrylate, 1H,1H,7H-dodecafluoroheptyl methacrylate, 1H, 1H-heptafluorobutyl acrylate, 1H, 1H-heptafluoro-n-butyl methacrylate, 1H,1H,3H-hexafluorobutyl acrylate, 1H,1H,3H-hexafluorobutyl acrylate, 3-perfluorohexyl-2-hydroxypropyl acrylate, 3-perfluorohexyl-2-hydroxypropylmethacrylate, 2,2,3,3-tetrafluoropropyl acrylate, 2,2,3,3-tetrafluoropropyl methacrylate, chlorinated acrylate oligomers, 3-chloro-2-hydroxypropyl methacrylate, 2,4,6-tribromophenyl methacrylate, pentabromophenyl acrylate, pentabromophenyl methacrylate, isobornyl acrylate, isobornyl methacrylate, and combinations thereof. Most preferably, the polymerizable precusor is a combination of perfluoropolyether diacrylate and 1H,1H,6H,6H-perfluorohexylenediacrylate. However, other polymerizable precursors including other halogenated compounds that are mono-, di-, tri-, and tetra functional that are capable of forming a composite polymer can be used according to the present invention, as will be understood by those of skill in the art with reference to this disclosure. Further information on fluorinated polymerizable precursors can be found in Rolland, et al., JACS, 126, 2322 (2004); Priola, et al., Macromolecular Chemistry and Physics, 198, 6, 1983 (1997); and Tonelli, et al., J. Applied Polymer Science, 59, 311 (1996).
The particulate filler can be in the form of a particle, bead, powder, fumed ceramic, fiber, floc, or other structural material, or a combination of the preceding particulate fillers. The particulate filler can be encapsulated, that is, chemically non-bonded with the surrounding polymer. Alternately, the particulate filler can bond directly to the surrounding polymer. In a preferred, but not required embodiment, the particulate filler is a surface treated particulate filler. Surface treating the particulate filler facilitates the release of the composite polymer regulator from the surrounding conduit when the regulator is formed in situ. Composite polymer regulators can have an initial frictional resistance that must be overcome before the regulator can be made mobile. For example, a regulator made up of a composite polymer element having an untreated particulate filler can require application of pressures up to several thousand psi before the composite polymer element releases from the surrounding conduit walls and becomes mobile. In contrast, incorporating a surface treated particulate filler into a composite polymer regulator can lower the sliding resistance between the regulator and the wall of the conduit. Such a regulator can be moved at lower pressure, typically at several times lower pressure. The size of the particulate filler is selected to be less than the smallest dimension of the conduit and can be as small as several nanometers.
The composition of the particulate filler can be glass, silica particles (coated or uncoated), coated beads, ceramic, metals and metal oxides, polymers, carbon black, and combinations of the preceding fillers. The particulate filler can also include a surface treated particulate filler. Examples of preferred particulate fillers include silica (SiO2), titania (TiO2), alumina (Al2O3), zirconia (ZrO2), magnetically permeable materials, such as colloidal iron and iron-nickel alloys, mica, glass, and polymers, such as poly(tetrafluoroethylene), poly(methyl methacrylate), latex, poly(styrene), and combinations of the preceding fillers. Other preferred particulate fillers include carbon blacks (Degussa Corp., Hopewell, Va.; and Cabot Corp., Boston, Mass.). In a certain preferred, but not required embodiment, three different grades of carbon black were added to a monomer solution (80 wt % perfluoropolyether diacrylate, 20 wt % methylene chloride, 0.5 wt % 2,2-dimethoxy-2-phenyl acetophenone) and successfully polymerized.
According to another embodiment of the present invention, the particulate filler is selected such that the composite polymer regulator is substantially incompressible as compared to a monolithic polymer regulator. The particulate filler can occupy a substantial fraction of the volume of the regulator and the particulate filler can be selected such that the particulate filler is selected to have a higher modulus of elasticity than that of a monolithic polymer. According to the present invention, when the composite polymer regulator is under compression, the compaction of the regulator is limited to a value greater than the filler volume fraction, thereby resulting in increased durability of the regulator under high compressive forces. In a preferred but not required embodiment, a composite polymer regulator win not exceed the bulk polymer elastic limit of the polymer and the composite polymer regulator will be substantially resistant to creep when a compressive force is applied to the composite polymer regulator. In a more preferred embodiment, a polyhedral oligomeric silsequioxane (POSS) is incorporated into the composite polymer. The incorporation of a polyhedral oligomeric silsesquioxane (POSS) provides nanoscale reinforcement of the composite mixture. POSS nanoparticles provide a robust Si—O core surrounded by organic groups, which can be functionalized, thus providing an inorganic core that is compatible with the organic matrix with complete molecular level dispersion. High levels are attainable without adversely affecting the material's physical properties, such as viscosity, optical properties, etc., whereas there is a dramatic increase in mechanical and thermal properties (such as Tg, Young's modulus, bending modulus, etc.). Furthermore, the organic groups can be functionalized to be reactive (as opposed to non reactive, as above). This hybrid inorganic-organic molecule can be utilized as a POSS monomer, which can be polymerized into the composite polymer. By varying the functionality of the reactive group (to a methacrylate, for example), multifunctional POSS monomers can be utilized as cross linkers in conjunction with standard organic monomers (as in this application). Examples of preferred, but not required, polyhedral oligomeric silsesquioxanes (POSS) include alcohol POSS, phenol POSS, amine POSS, silane POSS, chlorosilane POSS, silanol POSS, fluoroalkyl POSS, epoxide POSS, methacrylate POSS, acrylate POSS, phosphine POSS, ester POSS, and thiol POSS, all which can be obtained from Hybrid Plastics, Fountain Valley, Calif. Other polyhedral oligomeric silsesquioxanes (POSS) that can be incorporated into the composite polymer as a filler to provide hybrid organic-inorganic nanocomposites that are able to impart improved structural integrity can also be used according to the present invention, such as those described in U.S. Pat. App. Nos. 2003/0055193, and 2002/0198282, as well as other forms, sizes, and compositions of the particulate fillers, as will be understood by those of skill in the art with reference to this disclosure.
In certain preferred embodiments, the surface of the particulate is modified to control hydrophobicity, reactivity, etc., for example an acrylate-modified silica. Surface treated particulate filler materials are desirable for the added integrity these materials provide to the composite polymer. Care must be taken to ensure that a high enough shear rate is used to properly disperse the particulate filler (i.e., nanoparticles), which tend to agglomerate in the bulk and in unlike solvent. Examples of surface treated particulate filler materials include treated fumed silica that is hydrophobically modified, such as hexamethyldisilazane (HMDS) (Degussa Corp., Hopewell, Va.; and Cabot Corp., Boston, Mass.), dimethyldichlorosilane (Degussa Corp., Hopewell, Va.; and Cabot Corp., Boston, Mass.), and dimethyl silicone (Degussa Corp., Hopewell, Va.; and Cabot Corp., Boston, Mass.); structurally modified and methracrylsilane-treated fumed silica (Degussa Corp., Hopewell, Va.); and fumed silica that is surface modified with fluorinated silanes, such as tridecafluoro-1,1,2,2-tetrahydrooctyl-triethoxysilane (Gelest Inc., Morrisville, Pa.), and heptadecafluoro 1,1,2,2-tetrahydrodecyl-triethoxysilane (Gelest Inc., Morrisville, Pa.). However, other silylated materials can be used according to the present invention, such as those prepared by the silanization techniques described in U.S. Pat. App. No. 2004/0052929, as will be understood by those of skill in the art with reference to this disclosure.
Micro-scale polymer devices can become significantly less visible when immersed in a liquid. According to another embodiment, the particulate filler, polymeric precursor, or other additives, such as dyes, etc., can be selected to add specific optical properties to a composite polymer regulator. The use of a particulate filler in the composite mixture results in a composite polymer regulator that can exhibit amplified light refraction, scattering and/or light-absorbing and/or fluorescent properties as compared to a monolithic polymer. When a regulator with an optical property is desired, a particulate filler can be selected that is naturally colored and/or that has a refractive index substantially different than that of the bulk polymer and/or that is fluorescent. For example, light reflected, absorbed, or emitted from a regulator can be used as a diagnostic to obtain information on the location or orientation or motion of the regulator. Regulators having optical properties can be used in a sensing system, such as with a microfluidic control device that is used as a flow meter. According to the present invention, the particulate filler can be varied to modify other properties of the composite polymer. For example, the volume and type of particulate filler can be varied to modify the friction coefficient of the regulator, and the volume and type of filler can be varied to improve the polymerization resolution of the regulator. There are a variety of fluorescent monomers that can also be incorporated into the composite mixture. Examples of fluorescent monomers include fluorescein dimethacrylates, such as 3′,6′-dimethacryloxyspirobenzo[c]-furan [1,9′] xanthen-3-one (Polysciences, Inc., Warrington, Pa.); and fluorescein O,O′-diacrylates, such as 3″,6′-diacryloxyspirobenzo[c]-furan[1,9″]xanthen-3-one (Sigma-Aldrich, St. Louis, Mo.) which can make visible and track the movement of the composite polymer—creating a micro scale sensor that measures flow (as in a flow meter) or measures viscosity. These fluorescent monomers are provided merely as examples and other fluorescent monomers can be used according to the present invention as will be understood by those of skill in the art with reference to this disclosure.
According to another embodiment of the present invention, a particulate filler can be selected such that the composite polymer has a substantially stable volume when exposed to various fluid compositions, that is, the composite polymer will have reduced or no dimensional change in response to variations in fluid composition, as compared to a monolithic polymer. Micro-scale polymer devices that are immersed in liquid can undergo dimensional changes due to interaction with the liquid, that is, the shape and size of the polymer can change with exposure to liquids of different polarity. This behavior can limit the practical usefulness of polymer devices to perform reliable mechanical functions. According to the present invention, an amount and a composition of a particulate filler can be selected and added to the composite mixture, prior to polymerization, such that the composite polymer containing the selected particulate filler will have reduced or no dimensional change in response to variations in fluid composition.
According to another embodiment of the present invention, a solvent can be combined with the polymerizable precursor and the particulate filler. The solvent component can be any of various solvents capable of being suitably combined with the selected polymerizable precursor and particulate filler, such as water and organic solvents. By understanding the intermolecular interactions involving the polymerizable precursor and the particulate filler, a judicious choice of solvent can be made to ensure that the overall solvent-polymer/monomer-filler system chemistry is optimized. In a preferred but not required embodiment, the solvent is selected from the group consisting of C1-C6 alcohols, C4-C8 ethers, C3-C6 esters, C1-C4 carboxylic acids, halocarbons, dimethyl sulfoxide, dimethylsulfone, sulfolane, and N-methyl pyrrolidone, and combinations of the preceding solvents. In a more preferred but not required embodiment, the solvent is selected from the group consisting of highly fluorinated ethers (3M, St. Paul, Minn.), Fomblin™s (Solvay; and Solexis, Thorofare, N.J.), Fluorinert™s (3M, St. Paul, Minn.), methylene chloride (Sigma-Aldrich, St. Louis, Mo.), chloroform (Sigma-Aldrich, St. Louis, Mo.), and tert-butanol (Sigma-Aldrich, St. Louis, Mo.). However, other solvents can be used according to the present invention, as will be understood by those of skill in the art with reference to this disclosure.
According to another embodiment of the present invention, a polymerizing element (e.g., a polymerization catalyst) can be combined with the polymerizable precursor and the particulate filler. Preferably, the polymerizing element will induce polymerization of the polymerizable precursor admixed with a particulate filler in a short time, such as less than 100 seconds. In addition, preferred polymerizing elements afford clear materials/films that do not yellow upon radiation and when varying their content in the in the polymerizable composite mixture from about 0.01 wt % to about 10 wt %. The polymerizing element can include any of various common polymerization initiators, such as azobisisobutyronitrile; azobisdihydrochloride; benzoyl peroxide; lauroyl peroxide; potassium persulfate; aromatic ketones; such as benzophenone, 2,2-dimethoxy-2-phenyl acetophenone, benzoin, benzoin ethyl ether, and benzoin isopropyl ether, Irgacures (Ciba Specialty Chemicals, Tarrytown, N.Y.), such as Irgacure 184-1-hydroxy-cyclohexyl-phenyl-ketone, Irgacure 651-benzodimethyl ketal, Irgacure 907-2-methyl-1-[4-methylthio-phenyl]-morpholino-propan1-one, Irgacure 369—2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, Irgacure 500—a mixture of 50 wt % 1-hydroxy-cyclohexyl-phenyl-ketone and 50 wt % benzophenone, and Irgacure 819—phosphine oxide, phenyl bis(2,4,6-trimethyl benzoyl); Darocures (Ciba Specialty Chemicals, Tarrytown, N.Y.), such as Darocur 1173-2-hydroxy-2-methyl-1-phenyl-propan-1-one, and Darocur 2959-1-[4-(2-hydroxyethoxy) phenyl]-2-hydroxy-2-methyl-propan-1-one; Sarcures (Sartomer Company, Inc., Exton, Pa.), such as Sarcure SR1135—a mixture of 2,4,6 trimethylbenzoyldiphenyl phosphine oxide, 2, 4, 6-trimethylbenzophenone, 4-methylbenzophenone, oligo (2-hydroxy-2-methyl-1-(4-(1-methylvinyl)phenyl)propanone); and fluorinated photo-initiators that are based on the aromatic ketone type and structure, such as those described in U.S. Pat. No. 5,391,587. In a preferred embodiment, the polymerizing element is a photo-initiator. In a more preferred embodiment, the polymerizing element is an aromatic ketone or aromatic ketone derivative. More preferably, the polymerizing element is a halogenated photo-initiator (with fluorinated photoinitiators being most preferable) that appropriately matches the chemical nature of the polymerizable precursor, particulate filler, and solvent mixture. Halogenated photo-initiators are generally more soluble and thus less likely to result in the photoinitiator becoming a plasticizer. The use of halogenated photo-initiators can overall result in a smaller quantity of photo-initiator that is used (e.g., less than about 1 wt %), and an overall more efficient photo polymerization of the composite (monomer/solvent/filler) mixture. Other polymerizable precursors, such as azobisisobutyronitrile (AIBN) can also be used as a thermal initiator, or photo-initiator. However, AIBN is typically slower to induce polymerization and the photo-initiation process requires a larger amount of photo-initiator (e.g., about between 2-5 wt %). Also, excess un-utilized photo-initiator can behave as a plasticizer and compromises the structural integrity of the composite polymer.
According to another embodiment of the present invention, a surfactant can be combined with the composite mixture, including the polymerizable precursor, the particulate filler, and the polymerizing element. The addition of a surfactant to the composite mixture as an additive can stabilize the dispersion of the particulate filler in the composite mixture. Examples of suitable surfactants include but are not limited to non-ionic surfactants; long chain alcohols (such as n-decanol and dodecanol), poly(ethylene oxide)s (such as, Brij™ series, Sigma-Aldrich Corp, St. Louis, Mo.), polyglycols (such as, DOWFAX™ series, Dow Chemical Co., Houston, Tex.), poly(propylene oxide)-poly(ethylene oxide) copolymers (such as, Pluronic™ series, BASF Corp., Mount Olive, N.J.), polyoxyethylene, polyoxyethylene alkylphenols, polyoxyethylene alcohols, polyoxyethylene esters, polyoxyethylene mercaptans, polyoxyethylene alkylamines, polyol esters, Triton-X series (Dow Chemical Co., Houston, Tex.), Tween™ series (Sigma-Aldrich Corp, St. Louis, Mo.), ionic surfactants (including anionic, cationic, and zwitterionic), and sodium dodecyl sulfate (SDS), sodium di(2-ethylhexyl) sulfosuccinate (AOT), and cetyltrimethylammoniumbromide (CTAB). However, as will be understood by those of skill in the art with reference to this disclosure, other surfactants according to the present invention can be used. Further, as will be understood by those of skill in the art with reference to this disclosure, the stabilizing moiety can be optimized so as to give excellent steric stabililization in a given external phase, and different surfactants can be selected depending on the external phase. If the system incorporates charged particles, electrostatic repulsion may be the driving force to induce stability in the dispersion. On the other hand, van der Waals interactions, hydrophobic, steric and bridging forces can also be taken into account when attempting to create a stable dispersion.
According to another embodiment of the present invention is a method of making a device for microfluidic control. The method comprises combining a polymerizable precursor and a particulate filler to form a composite mixture. Then, the composite mixture is introduced into the conduit. Next, the conduit is exposed to an energy source to polymerize the composite mixture in situ, thereby forming a regulator, where the regulator is movable in the conduit, and the conduit is sized so the regulator cannot pass out of the conduit. In a preferred but not required embodiment, the composite mixture additionally comprises a photo-initiator. In a more preferred but not required embodiment, the conduit is exposed to a radiating light source through a mask to form the regulator.
Now referring to
In a preferred but not required embodiment, the method comprises premixing the particulate filler and the polymerizable precursor to form the composite mixture. In a more preferred but not required embodiment, the method additionally comprises forming the composite mixture by combining the particulate filler with a premixed mixture of one or more polymerizable precursors, photo-initiators, and solvents. However, the composite mixture can be combined by other methods, such as combining the composite mixture in situ, as will be understood by those of skill in the art with reference to this disclosure.
In another preferred but not required embodiment, the composite mixture is introduced into a conduit that is an existing microchannel structure or a conduit formed within a substrate. In a more preferred embodiment, the composite mixture is introduced into a conduit by injecting the composite mixture into the conduit.
In a preferred but not required embodiment, the above-described methods for making a device for microfluidic control can be used to fabricate a regulator in a conduit where the conduit can be actuated by pressure. In another preferred embodiment, the above-described methods for making a device for microfluidic control can be used to fabricate fluidic components such as a valve and a flow meter inside a network of microfluidic channels. The method of making a device for microfluidic control can be used to fabricate composite polymer gears inside a conduit. This can be accomplished by fabricating a gear around a center point, which can be a pin or axle formed in the substrate. However, the above described methods for making a device for microfluidic control can be used to fabricate other components for microfluidic control as will be understood by those of skill in the art with reference to this disclosure.
In another embodiment, the present invention is a method for microfluidic control. The method comprises selecting a device for microfluidic control, where the device comprises a conduit having a first path and a second path that are in fluid flow contact with the conduit, and a regulator, where the regulator is movable in the conduit and the conduit is sized so the regulator cannot pass out of the conduit. Then, fluid is placed into the conduit. Next, the regulator is moved by the application of a pressurizing force to direct or stop the fluid flow.
In a preferred but not required embodiment, the fluid is placed in the conduit by injecting the fluid into the conduit. According to the present invention, the initial state of operation of the device is a load state. In the load state, a fluid fills an open conduit between the first path, which is a fluid inlet, and a second path, which is a fluid outlet. The injection can be performed from this initial load state. However, the injection can be performed by other methods, such as with the fluid inlet and fluid outlet at varying pressures, as will be understood by those of skill in the art with reference to this disclosure.
In another preferred but not required embodiment, the method comprises a method for microfluidic control where the device delivers a sample to an apparatus, such as an analysis column. Now referring again to
In a preferred but not required embodiment, as shown in
In another embodiment, the pressure in the analysis column 59 can be the highest pressure in the system at that time, leading to the outlet check valve 403 closing immediately after the injection state is terminated. This procedure leads to an alternate method of filling the sample chamber and achieving the load state. Now referring again to
Now referring to
A composite mixture was formed from the substances listed in Table IA.
The composite mixture was prepared by mixing the ethoxylated trimethylolpropane triacrylate, SR454 (Sartomer Company, Inc., Exton, Pa.) and the trifluoroethylacrylate, 2,2,2 TFEA (Sigma-Aldrich Corp., St. Louis, Mo.) to form a monomer mixture. Then, the photo-initiator, 2,2′-azobisisobutyronitrile, AIBN, (5 mg) (Sigma-Aldrich Corp., St. Louis, Mo.) was added to the monomer mixture. A solvent mixture was prepared by combining the dioxane (Sigma-Aldrich Corp., St. Louis, Mo.) and the 2-methoxyethanol (Sigma-Aldrich Corp., St. Louis, Mo.). The monomer mixture and solvent mixture were then mixed in a 8:2 volume:volume ratio, that is, 800 L of the monomer mixture was mixed with 200 L of the solvent mixture. A particulate filler of 1 m diameter, non-porous silica particles (10 wt %) (Sigma-Aldrich Corp., St. Louis, Mo.) was then added to the monomer mixture and solvent mixture to create a suspension/slurry of monomer, solvent, and particles.
A composite mixture was formed from the substances listed in Table IB.
The composite mixture was prepared by mixing the perfluoropolyether diacrylate
(Sartomer Company, Inc., Exton, Pa.), 1H,1H,6H,6H-Perfluorohexyldiacrylate (Oakwood Products, Inc., West Columbia, S.C.), and methylene chloride (Sigma-Aldrich Corp., St. Louis, Mo.) to form a monomer/solvent mixture. Then, the photo-initiator, 5 mg of 2,2-dimethoxy-2-phenyl acetophenone (Sigma-Aldrich Corp., St. Louis, Mo.) was added to the monomer/solvent mixture. The monomer mixture and solvent mixture were then mixed in a 8:2 volume:volume ratio, that is, 800 L of the monomer mixture was mixed with 200 L of the solvent mixture. A particulate filler of 16 nm diameter, hydrophobic treated fumed silica (5 wt %) (Degussa Corp., Hopewell, Va.) was then added to the monomer/solvent/PT mixture to create a suspension/slurry of monomer, solvent, PI, and particles.
A particulate filler was selected such that the composite polymer regulator was substantially incompressible, as compared to a monolithic polymer regulator. As a comparative example, a regulator comprising a monolithic polymer was substantially extruded through a fine passage when the regulator was subjected to a 10,000 psi high compressive force. Whereas, a regulator comprising a composite polymer containing a 50% silica particulate filler, prepared according to the present invention, compressed to about 50% of the initial volume. This degree of compression did not exceed the bulk polymer elastic limit of the polymer and the regulator part was substantially resistant to extrusion.
As a further example, the compressive strength of Nylon 6,6 and compared to the compressive strength of a composite polymer prepared with Nylon 6,6 according to the present invention. The compressive strength of Nylon 6,6 was tested and at 10% compression, the compressive strength was about 12,000 psi. Whereas, a composite polymer prepared according to the present invention with 30% glass-filled Nylon 6,6 was tested and the compressive strength at 10% compression was about 39,000 psi.
A particulate filler was selected such that the composite polymer had a substantially stable volume when exposed to various fluid compositions, that is, the composite polymer had reduced or no dimensional change in response to variations in fluid composition, as compared to a monolithic polymer. As a comparative example, a monomer mixture containing ethoxylated trimethylolpropane triacrylate and trifluoroethylacrylate in an 80:20 volume:volume ratio was mixed with methoxyethanol in a 50:50 volume:volume ratio. Trace amounts of azobisisobutyronitrile, a photoinitiator, was added and the mixture was photopolymerized. When the resulting monolithic polymer was placed in water, the element shrank to 55% of its original volume. Whereas, following the same procedure, and adding 7 wt % of particles of colloidal antimony pentoxide, with an outer diameter of 7-11 nm, to the mixture, the polymerized composite polymer shrank by only 20% of its original volume.
A regulator that was used as a composite piston was formed by introducing the composite mixture from Example IA into a 150 m inner diameter optically transparent silica capillary by injecting the composite mixture into the capillary with a syringe. A 2 mm length of the capillary was then exposed to broadband ultraviolet radiation, peaking at around 365 nm with total energy flux of 40 mW/cm2, for 30 seconds. Upon exposure to the ultraviolet radiation, a composite particle-filled solid polymer piston with a length dimension of 2 mm and a width dimension that is approximately equal to the inner diameter of the surrounding capillary was formed. The composite piston did not bond to the surrounding capillary and was thus free floating. The piston was mobilized by applying between about 1 psi to about 5 psi of pressure to one terminal end of this first capillary. An adjoining second capillary, having a 25 m inner diameter, was connected to the second terminal of the first capillary. The composite piston within the first capillary was pushed against the adjoining capillary and put under pressure in excess of 2000 psi with little to no damage or permanent distortion to the composite piston. Ejecting the composite piston from the first capillary and examining the composite piston under a microscope confirmed the geometry of the composite piston. The composite piston was iteratively exposed to acetonitrile, methanol, isopropanol, water, and aqueous buffers with pH ranging from between about 2 to about 12. The swelling and shrinking of the composite piston was observed between exposures to these liquids and the swelling and shrinking of the composite piston was less than 10% of its original diameter in all cases.
A regulator that was used as a composite piston was formed by introducing the composite mixture from Example IB into a 150 m inner diameter optically transparent silica capillary by injecting the composite mixture into the capillary with a syringe. A 2 mm length of the capillary wpas then exposed to broadband ultraviolet radiation, peaking at around 365 nm with total energy flux of 2500 mW/cm2, for 35 seconds. Upon exposure to the ultraviolet radiation, a composite particle-filled solid polymer piston with a length dimension of 2 mm and a width dimension that is approximately equal to the inner diameter of the surrounding capillary was formed. The composite piston bonded to the surrounding capillary and was mobilized by applying between about 1000 psi to about 1500 psi of pressure to one terminal end of the capillary. The composite piston was ejected onto a cleaned microscope slide with no damage to the composite piston. Ejecting the composite piston from the capillary and examining the composite piston under a microscope confirmed the geometry of the composite piston. The composite piston was iteratively exposed to acetonitrile, methanol, ethanol, isopropanol, water, and aqueous buffers with pH ranging from between about 2 to about 12. The swelling and shrinking of the composite piston was observed between exposures to these liquids using a microfabricated ruler and the swelling and shrinking of the composite piston was less than 2% of its original diameter in all cases.
Although the present invention has been discussed in considerable detail with reference to certain preferred embodiments, these preferred embodiments are understood not to be required embodiments, and other embodiments are possible. Therefore, the scope of the appended claims should not be limited to the description of preferred embodiments contained herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10666466 | Sep 2003 | US | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US04/30202 | 9/15/2004 | WO | 2/6/2007 |
