Patent Application
20120275929
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.
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.
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.
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.
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.
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.
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.
The foregoing summary and detailed description that follows will be more clearly understood when read in conjunction with the drawing figures, wherein:
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.
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.
Ferrofluids are comprised of nanoparticles of a ferric compound such as Fe203 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.
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.
Valve 100 is operable between an open mode, shown in
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
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.
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.
Pump 200 is operable to move fluid L along flow channel 252. Electromagnets 232A-D are activated individually and in a synchronized pattern to displace fluid L.
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.
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.
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.
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.
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.
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.
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.
The following section discusses different applications of ferrofluid control systems in accordance with the invention.
Referring to
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.
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
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
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.
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.
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.
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.
| Number | Date | Country | |
|---|---|---|---|
| 61479581 | Apr 2011 | US |
