Micro-fluidic valve with a colloidal particle element

Details Micro-fluidic valve with a colloidal particle element Micro-fluidic valve with a colloidal particle element

2002-05-03

2004-10-12

Yu, Justine R. (Department: 3746)

Valves and valve actuation

Electrically actuated valve

Freely rotatable ball valve

C251S129010

Reexamination Certificate

active

06802489

ABSTRACT:

FIELD OF THE INVENTION
The present invention is directed to the use of colloidal-size particles to realize microfluidic and photonic devices.
BACKGROUND OF THE INVENTION
The “lab-on-a-chip” concept, in which three-dimensional microfabrication techniques borrowed from the integrated circuit industry are employed to create electrical circuits that interface with chemical or biological systems upon micropatterned substrates, has gained significant research interest in recent years, and has been heralded as the next silicon revolution. The drastic reduction in length scales from conventional techniques to microelectrical-mechanical systems (MEMS) will allow tasks to be performed more rapidly, efficiently, and on smaller sample volumes than ever before. Functional systems fabricated to exploit this microscale fluid motility possess great promise to significantly streamline processes for fundamental research and medical applications in areas such as bioanalysis, medical diagnostics and therapeutics. Such developments will enable a large-scale shift from centralized laboratories to remote point-of-care and benchtop diagnostic facilities.
Initially, single devices such as pumps, valves, mixers, filters, and sensors have been developed to perform individual tasks on microfluidic samples. Seamlessly integrating individual devices capable of single operations will finally bring to fruition the promise of micro total analysis systems (&mgr;TAS) as portable laboratories, chemical production facilities, remediation units, health monitors and countless other applications which would benefit from miniaturization. In order to construct such devices, however, a common platform must be developed which allows for complete control of heterogeneous or complex fluids as well as specifically targeted sensing and feedback actuation.
Generally, the utility, speed and performance of microfluidic chips increases as the overall device size decreases, particularly for devices that are ultimately designed for human implantation. The need to mix, administer and separate fluids at these length scales has long been a limiting factor in such devices. Specifically, the ultimate size of microfluidic devices has been restricted by the size of the actuator, which can be classified as either those micromachined specifically for microfluidic application or conventional actuators that have been miniaturized for integration with microfluidic devices. Examples of the latter include electromagnetic plungers connected to pneumatic systems, miniature piezoelectrics and memory alloys. Such actuators function well, but must be affixed to the microfluidic chip as additional hardware with epoxy resin. Actuators that may be micromachined, such as electrostatic, thermopneumatic, electromagnetic and bimetallic actuators consume significantly less space than conventional actuators but often require difficult etching procedures.
Microfluidic flow controllers, such as chip-top valves and pumps, have also historically been plagued by size limitations imposed by actuators. The first microvalve consisted of a silicon seat with a nickel diaphragm actuated by a solenoid plunger and measured approximately 3 mm. Subsequently, as piezoelectric stacks, electromagnetic alloys and thermopneumatics became fashionable, microvalves and reciprocating micropumps became smaller, but continue to dwarf the scale of microchannels and other chip-top features. More recently, electroosmosis, which requires no moving parts and overcomes some of these limitations, has experienced success as a viable means of microfluidic flow generation and control. This technique is quite efficient at transporting and separating ionic liquids and relies upon the principle of electrophoresis, the migration of ions in an electric field, and the resulting osmotic pressure gradient to induce the flow of bulk fluids.
While some current microfluid handling devices and techniques enable functional devices at microscales, they may also impose significant constraints upon potential device capability, flexibility and performance. For instance, electroosmotically driven flow requires complex circuitry, a high-voltage power supply and is dependent upon the ionic properties of the solution and has the potential to separate components of the solution from the bulk. While molecular separation by electrophoresis has been exploited for particular applications such as nucleic acid sequencing and the development of protein targeted chemotherapy, the complications discussed here are generally considered obstacles to &mgr;TAS intended for applications with heterogeneous fluids such as blood or urine. Additionally, the scale of flow controllers, such as pumps and valves, has not kept pace with the miniaturization of flow channels themselves, thus limiting the ultimate size at which practical devices may be created. Recent efforts have made strides to overcome the limitations of traditional materials and techniques; for example, a first-generation pumping and valving system fabricated completely from elastomeric materials allows for in situ fluids control on length scales below 100 &mgr;m. While functionally simple and conceptually elegant, the pneumatic actuation scheme still hinders the ultimate utility of these devices through the need for interfacing to external equipment. To completely integrate fluidic processes upon a single chip, the current paradigms of microfluids handling must be abandoned in favor of units that are of equivalent size to the process into which they are being imbedded. An attempt to achieve these ends has been made using “smart” hydrogel structures fabricated directly within microfluidic networks (&mgr;FNs). These structures, while only tens of microns in size and very efficient at measuring and responding to specific environmental conditions, such as pH and temperature, are quite limited in their sensing capabilities and ability to produce a broad range of feedback options. Additionally, these structures have demonstrated only the ability to regulate flow, not initiate it. Integrating simultaneous microscale fluid pumping and valving completely on the microscale is a key component to the development of &mgr;TAS.
Microscale devices designed to accomplish specific tasks have repeatedly demonstrated superiority over their macroscale analogues and in many cases have proven capable of performing functions not possible on the macroscale. The advantages of such devices are due largely to unique transport properties resulting from low Reynolds number flows (Re<1) and vastly increased surface to volume ratios. Additionally, microfluidic processes may be easily parallelized for high throughput and require vastly smaller sample volumes; a significant benefit for applications in which reagents or analytes are either hazardous or at a premium. In general, the utility, speed and performance of Microsystems increase as the overall device size decreases. The need to mix, pump, and direct fluids at very small length scales, however, has long been the limiting factor in the development of microscale systems, thus generating a tremendous amount of interest in the burgeoning field of microfluidics. As improved actuation techniques have become available, conventional valving and pumping schemes have been miniaturized yet continue to dwarf microchannels and other chip-top features. Recently, several approaches conceived explicitly for the microscale have been developed including platforms based upon electrohydrodynamics, electroosmosis, interfacial phenomena, conjugated materials, magnetic materials and multilayer soft lithography. While these microfluid handling techniques enable functional devices on microscopic length scales, they also impose unique constraints upon potential device capability, flexibility and performance. To fully integrate multiple fluidic processes within a single microsystem, methods for microfluid handling must be developed which are accommodating to fluids of complex and dynamic composition and are of comparable size to the processes into which they are being

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