Abstract:
A fluid conveyance system includes a flow passage and a cavity adjacent a side of the flow passage. A wall of the passage includes a flexible section that separates the cavity from the flow passage. The cavity contains a ferrofluidic material. The system further includes at least one magnetic field source positioned adjacent the flow channel. The magnetic field source is operable to move the ferrofluidic material in the cavity to exert a pressure on the flexible section and displace the flexible section into the flow passage to alter the flow of material through the passage. A method of collecting components from a sample volume includes the steps of distributing magnetic particles into the sample volume, capturing the components from the sample volume, and applying a magnetic field to the sample volume to control directional flow of the sample volume.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority under 35 U.S.C. §119 to U.S. Provisional Application No. 61/479,581, filed Apr. 27, 2011, the content of which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to fluid transport systems, and more specifically to fluid flow control systems that are driven by a ferrofluid and magnetic fields. 
       BACKGROUND OF THE INVENTION 
       [0003]    Microfluidic devices are applied in various fields, including biotechnology, chemical analysis and clinical chemistry. A microfluidic system features a network of conduits, channels or hollows formed on a base plate of plastic, glass or silicon substrate. The sizes of the channels are very small, and the transport of microfluids can be affected by the surface tension of the fluid and the wettability of the wall surfaces. 
         [0004]    Current microfluidic systems utilize pneumatic, mechanical, and electromechanical or MEMS-based techniques to operate valves and perform mixing, directional flow, fluid transport and pumping functions. These techniques require relatively large pieces of equipment with various hose connections to provide the control and drive functions. Large pieces of equipment and hose assemblies are undesirable because they can consume large amounts of energy and occupy a significant amount of workspace, among other reasons. 
         [0005]    Conventional pneumatic, mechanical, and electromechanical systems for pumping fluids have additional drawbacks when used in certain medical applications. For example, cardiopulmonary bypass machines (or heart-lung machines) typically utilize a peristaltic or roller pump to circulate blood through the body during surgery or other event when the heart and lungs do not function. Red blood cells are very sensitive to mechanical pressure, however, and can be destroyed by excessive pressure on the tubing. Conventional peristaltic pumps used with heart machines compress and constrict tubing that carries the blood cells, creating a risk of damage to the blood cells. 
         [0006]    Some pneumatic, mechanical, and electromechanical transport systems allow pump or valve components to contact the fluid being pumped. Some fluid products chemically react with materials used in pumps and valves, making conventional pumps and valves inadequate. 
         [0007]    Conventional heat transfer systems, like heat pipes that circulate water, ethanol, acetone, sodium, or mercury, suffer drawbacks because they require expensive materials and have limited application. 
         [0008]    In view of the foregoing drawbacks, there is a need to improve existing systems and methods for mixing and transporting fluids, including both gases and liquids. There is also a need to improve existing microfluid transport systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The foregoing summary and detailed description that follows will be more clearly understood when read in conjunction with the drawing figures, wherein: 
           [0010]      FIG. 1  is a truncated cross-sectional view of a microfluidic system in accordance with one embodiment of the invention, shown in a first mode of operation; 
           [0011]      FIG. 2  is a truncated cross-sectional view of the microfluidic system of  FIG. 1 , shown in a second mode of operation; 
           [0012]      FIG. 3  is a truncated cross-sectional view of a microfluidic system in accordance with another embodiment of the invention, shown in a first mode of operation; 
           [0013]      FIG. 4  is a truncated cross-sectional view of the microfluidic system of  FIG. 3 , shown in a second mode of operation; 
           [0014]      FIG. 5  is a truncated cross-sectional view of the microfluidic system of  FIG. 3 , shown in a third mode of operation; 
           [0015]      FIG. 6  is a cross-sectional view of a fluid transport system in accordance with another embodiment of the invention; 
           [0016]      FIG. 7  is a cross-sectional view of a fluid transport system in accordance with another embodiment of the invention; 
           [0017]      FIG. 8  is a truncated cross-sectional view of a flow control system in accordance with another embodiment of the invention, shown in a first mode of operation; and 
           [0018]      FIG. 9  is a truncated cross-sectional view of a flow control system in accordance with another embodiment of the invention, shown in a second mode of operation. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    Although the invention is illustrated and described herein with reference to specific embodiments and examples, the invention is not intended to be limited to the details shown. Rather, various modifications may be made in the details within the scope and range of equivalents of the claims and without departing from the invention. 
         [0020]    The drawbacks of conventional fluid transport systems, including conventional microfluidic systems, are resolved in many respects by utilizing ferrofluids in accordance with apparatuses, systems and processes of the invention. Apparatuses, systems and processes in accordance with the invention utilize ferrofluids and magnetic fields to perform various functions for fluid flow control, and are applicable to both microfluidic systems and conventional fluid transport systems. 
         [0021]    Ferrofluids are comprised of nanoparticles of a ferric compound such as Fe 2 0 3  that are suspended in a liquid in such a way that they stay in relatively homogeneous suspension. The ferric particles are coated with a surfactant, such as a sodium hydroxide, to reduce the surface tension between the particles and the liquid. The base of the fluid may be a moderate to low viscosity oil, such as mineral oil. When formulated correctly, the ferrofluid rapidly responds to the presence of a magnetic field by altering its shape to correspond to the magnetic field lines. This results in a fluid that can quickly and repeatedly change its shape, and even flow against gravity as it moves along the field lines. 
       Fluid Membrane Valves and Pumps 
       [0022]    In one intended application, the magnetic properties of ferrofluids are utilized to generate pressure on microfluidic channels and structures to control flow and provide pumping pressure to gases or fluids in adjoining microchannels.  FIGS. 1 and 2  schematically illustrate a ferrofluidic valve  100  in accordance with one embodiment of the invention. Valve  100  is positioned adjacent a microfluid conduit  150  formed in a substrate  151 . Conduit  150  includes a micro flow channel  152  that carries a liquid L. Valve  100  includes a reservoir  110  containing a ferrofluid  120 . Flow channel  152  is separated from the reservoir  110  by a flexible membrane  112  on a first side  114  of the reservoir. Valve  100  also includes a magnetic field source  130 . Embodiments of the invention may feature various magnetic field sources and arrangements, including arrangements that utilize electromagnets or permanent magnets that are movable with mechanical control. Magnetic field source  130  includes an electromagnet  132 , positioned on a second side  116  of reservoir  110 , opposite first side  114 . 
         [0023]    Valve  100  is operable between an open mode, shown in  FIG. 1 , and a closed mode, shown in  FIG. 2 . Electromagnet  132  is configured to apply a magnetic field through reservoir  110  and displace ferrofluid  120  against flexible membrane  112 . This is achieved by selecting a proper pole orientation and magnetic field strength that cause the ferrofluid  120  to push against the membrane  112  and distort the membrane so that it expands into the microfluidic channel. In this manner, it is possible to use the ferrofluid  120  to apply sufficient pressure to the membrane  112  to reduce or completely cut off the flow of liquid L in micro flow channel  152 . 
         [0024]    The thickness and elasticity of membrane  112  allow the membrane to flex in response to fluid pressure exerted by the ferric particles  122  in the magnetic field. At full power, the electromagnet  132  displaces the ferrofluid and creates sufficient pressure behind membrane  112  to expand the membrane into flow channel  152  until a section of the membrane contacts a wall section across from the membrane, as shown in  FIG. 2 . In this closed condition, membrane occupies and obstructs the cross sectional area of flow channel  152 , preventing further flow of liquid L. Flow of liquid L is restored by cutting power to the electromagnet  152 . When power to the electromagnet  152  is cut, the elasticity of membrane  112 , and the stored energy resulting from the membrane&#39;s expansion, return the membrane to the unexpanded or open state shown in  FIG. 1 , allowing flow to resume. 
         [0025]    Ferrofluid driven systems in accordance with the invention can also be used in pumping applications. In a preferred embodiment, multiple electromagnets are driven by an electrical signal generator such that the timing of the pressure being applied by the ferrofluid to the microfluidic channel occurs in a staggered timing sequence from one end of the ferrofluidic cavity to the other. In this manner, the compression of the microfluidic channel by the cascading row of electromagnets generates a preferred direction of pressure applied to the fluid in the microfluidic channel and generates a peristaltic pumping function. This architecture can also be used to perform a negative pressure pumping function by driving the entire length of the ferrofluidic channel to close the microfluidic channel over a length and then releasing the magnetic hold in sequence over the channel length. This will generate an increasing volume in the microfluidic channel as it expands to its normal dimensions, producing a pulling or negative pressure force on the fluid in the microfluidic channel. By incorporating both positive and negative pressure functions, a linear electromagnetic pump can generate significant pumping force within the microfluidic channel. 
         [0026]    When using magnetic material such as materials used in magnetic core memories, it is possible to maintain a magnetic field between times where current is applied to an electromagnet. Electromagnetic field formation can be generated by placing a coil of conductive material around a volume of ferrofluid. Alternatively, a core made of ferric or similar material can be provided in specific locations in a flow system to concentrate the electromagnetic field and produce localized zones with significantly high field strength. 
         [0027]      FIGS. 3-5  schematically illustrate one example of a ferrofluid driven pump  200  in accordance with the invention. Pump  200  is positioned adjacent a microfluid conduit  250  formed in a substrate  251  surrounding a micro flow channel  252 . Flow channel  252  carries a liquid L. Pump  200  includes a reservoir  210  containing a ferrofluid  220 . Flow channel  252  is separated from the reservoir  210  by a flexible membrane  212  on a first side  214  of the reservoir. Pump  200  also includes a magnetic field source  230 . Magnetic field source  230  includes a series of electromagnets  232 A-D arranged in a row along reservoir  210 . Electromagnets  232 A-D are positioned on a second side  216  of reservoir  210 , opposite first side  214 . 
         [0028]    Pump  200  is operable to move fluid L along flow channel  252 . Electromagnets  232 A-D are activated individually and in a synchronized pattern to displace fluid L.  FIG. 3  shows pump  200  in an off setting, with none of the electromagnets  232 A-D activated. In  FIG. 4 , pump  200  is shown as it would appear after electromagnet  232 A is activated, followed shortly after by electromagnet  232 B. In this state, ferrofluid  220  displaces membrane  212  to create an occlusion  213  in flow channel  252 . Membrane  212  is displaced from left to right in the figure, in response to the sequential activation of electromagnet  232 A followed by electromagnet  232 B. This sequential activation displaces liquid L in the direction represented by arrow A.  FIG. 5  shows pump  200  with electromagnets  232 A and  232 B deactivated, and electromagnet  232 C activated. Electromagnet  232 C is activated shortly after activation of electromagnet  232 B, resulting in a wave or ripple effect in flexible membrane  212 . This ripple effect causes occlusion  213  to move along the flow channel in a continuous wave and displace liquid L in the direction represented by arrow A. 
         [0029]    Occlusion  213  is schematically shown as completely obstructing flow channel  252 . It will be understood that occlusion  213  need not fill or occupy the entire flow channel  252  to displace liquid L in the channel. The magnetic field and pressure behind membrane  212  may be adjusted so that the membrane only extends partially but not completely across flow channel  252 . This option may be desirable where liquid L contains red blood cells or other components that are sensitive to mechanical pressure. Where red blood cells are transported in liquid L, a reduced pressure behind membrane  212  will ensure that blood cells are not crushed between the membrane and the wall of the flow channel. 
         [0030]    Pump  200  is schematically shown with electromagnets in a linear arrangement. Pumps in accordance with the invention can also feature electromagnets arranged around a rotor arrangement, with a flow conduit arranged around the rotor, similar to a mechanical peristaltic pump. 
       Sample Collection 
       [0031]    Ferric nanoparticles with appropriate surfactants and sample bonding agents can be distributed within a sample volume to collect specific components of a sample for study, analysis, concentration or collection. Recovery of the particles with the bonded sample agents can be achieved using a magnetic field, and the sample can be manipulated within the sample analysis/storage architecture of a system via the ferrofluidic characteristic imparted to the sample. 
         [0032]    In one embodiment of the invention, ferrite particles are treated to have a pseudo porous surface. Alternatively, the ferrite particles are coated with a protein that can then be coated with a trapping agent suitable for attaching to the component to be collected. These particles are much smaller than commercially available coated ferrite particles, allowing the particles to stay in suspension in gas as well as liquids. 
         [0033]    After the ferrite particles have trapped the components to be collected, the ferrite particles are maintained in the sample volume to allow the flow direction of sample material to be controlled. That is, the sample material takes on the characteristics of a ferrofluid that can be precisely guided as it passes into the sample processing and analysis sections of a microfluid analysis or imaging system. 
         [0034]    Electrostatic traps or electromagnetic bars can be employed to collect all the particles. By flowing fluid down the bars or adjusting the flow direction and applying alternate direction magnetic fields, the trapped sample component with the ferrite particles is driven to a collection/analysis point. The mass of each particle increases after the particle attaches to a trapped element. The trapped elements will have different masses from one particle to another. Flow speed and directional shifting are then used to separate the particles in gas (air) or liquids based on differences in mass and size so that components of different masses can be selectively collected and concentrated at different points. 
         [0035]    Particles may also be separated by mass and collected for analysis using a ferromagnetic mass separator. The particles are dispersed in a microfluid and passed through a varying strength magnetic field or a curved pathway. The speed of each particle is dependent on its mass. Particles of different mass travel in different adjacent pathways and are separated such that they can be collected at different locations. The collected particles can be analyzed separately, or separated for additional processing. By using magnetic fields to impact the flow so as to separate the particles by mass, a continuous sample flow can be utilized and continuous separation can be provided. This has particular application for large samples, long term analysis/monitoring, and continuous processing applications. 
         [0036]    The following section discusses different applications of ferrofluid control systems in accordance with the invention. 
       EXAMPLES 
     Example 1 
     Fluid Driven Membrane Pump and Valve 
       [0037]    Referring to  FIG. 6 , a fluid driven pump  300  is shown in accordance with another embodiment of the invention. Pump  300  includes a cluster of flexible conduits  310  placed around a central flexible tube  320  containing a ferrofluid  322 . An electromagnet  350  is placed externally to the flow conduits  310  and flexible tube  320 . Electromagnet  350  is ring shaped and surrounds a section of the length of the conduits  310 . A magnetic field is applied through the conduits  310  to interact with the ferrofluid  322 . The magnetic field properties are selected through known techniques to pull ferric particles  324  in the ferrofluid in a radial outward direction. This creates a circular pressurized “wave” of ferrofluid that exerts radial outward pressure on the wall  321  of flexible tube  320 . The pressure is sufficient to constrict the diameters of each of the flexible conduits  310  and displace fluid in the conduits. 
         [0038]    Fluid is transported through the conduits in a chosen direction (for example, in a direction normal to the cross section shown in the Figure) by moving the magnetic field and ferrofluid wave in the chosen direction. The magnetic field is moved along the length of the conduit cluster and tube in the chosen direction to drive the ferrofluid wave and displace a volume of fluid in the flexible conduits in the chosen direction. The ferrofluid wave is driven by a series of electromagnets placed along the length of the conduit cluster, which are activated in a synchronized manner as discussed above to move the wave in the chosen direction. Repeated application of the magnetic field creates a fluid driven positive displacement pump. As opposed to mechanical displacement pumps that use rollers or shoes to compress the flow channel, fluid driven pumps in accordance with the invention can displace fluid under a precisely controlled pressure that does not damage pressure-sensitive components in the fluid. 
         [0039]    Fluid driven membrane pumps in accordance with the invention are scaleable to any size and can be designed to accommodate various pumping capacities. Although a single cluster is shown in  FIG. 6 , the present invention also includes pumps that utilize multiple clusters grouped together in a contiguous assembly. In a preferred embodiment, clusters are bundled together to generate greater flow. Multiple clusters can be mounted together to create pumps of any capacity. Pumps in accordance with the invention can be driven in a synchronized manner so that all the pumping elements operate together, creating a peristaltic or pulsed flow. Alternatively, pumps in accordance with the invention can be driven out of sync, for example in phase steps, so that the flow is less forceful but continuous with little or no detectable pulsation. These pumps can be utilized in many applications ranging from medical applications (e.g. heart pumps) to marine uses (e.g. trolling motors, and bow/stern thrusters). 
       Example 2 
     Fluid Driven Membrane Pump and Valve 
       [0040]      FIG. 7  shows a pump and valve system  400  similar to Example 1, except that the system uses a flexible tube  410  surrounded by a single pipe  420 . Flexible tube  410  contains a ferrofluid  412 , and pipe  420  is filled with a gas or liquid  422 . A source of magnetic field in the form of an electromagnet  450  is positioned around the exterior of pipe  420 . Electromagnet  450  is ring shaped and surrounds a section of the length of pipe  420 . A magnetic field is applied through pipe  420  to interact with ferrofluid  412 . The magnetic field properties are selected through known techniques to pull ferric particles in the ferrofluid in a radial outward direction. This creates a circular wave of ferrofluid that exerts a radially outward pressure on the wall of flexible tube  410 . The outward pressure on tube  410  expands the tube wall  411 , constricting and reducing the surrounding area in pipe  420 . The ferrofluid wave is driven in a given axial direction along the axis of the pipe  420  by a series of electromagnets placed along the length of pipe  420 . 
       Example 3 
     Pressure Surge Control 
       [0041]    In another embodiment of the invention, a fluidic driven membrane is used for pressure surge control. The pressure surge control system has essentially the same arrangement and function as that shown in  FIG. 1 , except the flexible membrane expands into the flow channel in response to pressure surges that are detected in the system. A control system regulates the degree to which the membrane expands into the flow channel, the expansion being regulated as a function of pressure conditions or other variables. The system reduces or negates pressure surges by actively and dynamically altering the flow dimensions and shape of the flow in the pipe. 
       Example 4 
     Ferrofluid Valve 
       [0042]      FIGS. 8 and 9  show a ferrofluid valve  500  having a “balloon” like membrane  510  filled with ferrofluid  520 . Membrane  510  is connected to a side wall of a flow channel. Valve  500  is mounted inside a “T” intersection between two pipes  530  and  540 , with membrane  510  anchored above an opening  550  where pipe  530  enters pipe  540 . An electromagnet  560  is mounted on the pipe intersection adjacent membrane  510 . 
         [0043]    As magnetic force is applied by electromagnet  560 , the ferrofluid  520  is driven toward one region of the balloon. With enough magnetic force, ferrofluid  520  exerts sufficient pressure inside membrane  510  to expand the membrane toward pipe  530  and obstruct opening  550 , thereby blocking flow. Valve  500  provides extremely precise adjustment of flow and can change flow nearly instantaneously, much faster than mechanical valves. Without any mechanical surfaces, the ferrofluid valve  500  does not have any mechanical parts to wear out or leak. Membranes enclosed with ferrofluid in accordance with the invention can be used to regulate the flow of gases or liquids in a pipe. 
         [0044]    By utilizing membranes filled with ferrofluids and magnetic force patterning, simple non-mechanical systems can be created that have a wide range of applications. Ferrofluid driven systems in accordance with the invention eliminate the drawbacks of conventional fluid transport systems. For example, ferrofluid driven pumps and valves require no external openings to access the components of the pump or valve, and only require a magnetic field source positioned outside of the membrane. Ferrofluidic membrane devices in accordance with the invention can provide higher reliability, lower cost, faster operation, and cover a wider range of functionality than conventional fluid transport systems. In addition, ferrofluidic membrane devices in accordance with the invention can be leveraged with diaphragm based regulators and similar devices that can be used to generate a wide range of functional capabilities. 
         [0045]    While preferred embodiments of the invention have been shown and described herein, it will be understood that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the spirit of the invention. Accordingly, it is intended that the appended claims cover all such variations as fall within the spirit and scope of the invention.