Abstract:
A latching microregulator for regulating liquid flow on micro-scale levels comprises a substrate having an inlet port and an outlet port, a valve element defining a valve chamber for opening and closing the inlet port, and an actuator assembly for actuating the valve element. The valve chamber is configured to contain a volume of fluid, and the inlet port and the outlet port are in fluid communication with the valve chamber to provide a liquid flow path through the chamber. The actuator assembly comprises a cantilever beam for moving the valve element between an open position and a closed position, an actuator, such as a piezoelectric element, for moving the cantilever beam, and a latch, such as a permanent magnet, for securing the cantilever beam in the closed position. A flow regulation system comprises a plurality of fluid channels of varied flow conductance and a plurality of latching microregulators for selectively blocking or allowing flow through each of the fluid channels.

Description:
RELATED APPLICATION 
     The present invention is a divisional application of U.S. patent application Ser. No. 10/179,537 filed Jun. 24, 2002 now U.S. Pat. No. 6,981,518 entitled “Latching Micro-Regulator” which, in turn, claims priority to U.S. Provisional Patent Application No. 60/364,803 filed Mar. 15, 2002 entitled “Latching Micro-Regulator”, the contents of which are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a micro-regulator and a bi-stable latching valve for regulating fluid flow on micro-scale dimensions. 
     BACKGROUND OF THE INVENTION 
     In the chemical, biomedical, bioscience and pharmaceutical industries, it has become increasingly desirable to perform large numbers of chemical operations, such as reactions, separations and subsequent detection steps, in a highly parallel fashion. The high throughput synthesis, screening and analysis of (bio)chemical compounds, enables the economic discovery of new drugs and drug candidates, and the implementation of sophisticated medical diagnostic equipment. Of key importance for the improvement of the chemical operations required in these applications are an increased speed, enhanced reproducibility, decreased consumption of expensive samples and reagents, and the reduction of waste materials. 
     Microfluidic devices and systems provide improved methods of performing chemical, biochemical and biological analysis and synthesis. Microfluidic devices and systems allow for the performance of multi-step, multi-species chemical operations in chip-based micro chemical analysis systems. Chip-based microfluidic systems generally comprise conventional ‘microfluidic’ elements, particularly capable of handling and analyzing chemical and biological specimens. Typically, the term microfluidic in the art refers to systems or devices having a network of processing nodes, chambers and reservoirs connected by channels, in which the channels have typical cross-sectional dimensions in the range between about 1.0 μm and about 500 μm. In the art, channels having these cross-sectional dimensions are referred to as ‘microchannels’. 
     By performing the chemical operations in a microfluidic system, potentially a number of the above-mentioned desirable improvements can be realized. Downscaling dimensions allows for diffusional processes, such as heating, cooling and passive transport of species (diffusional mass-transport), to proceed faster. One example is the thermal processing of liquids, which is typically a required step in chemical synthesis and analysis. In comparison with the heating and cooling of liquids in beakers as performed in a conventional laboratory setting, the thermal processing of liquids is accelerated in a microchannel due to reduced diffusional distances. Another example of the efficiency of microfluidic systems is the mixing of dissolved species in a liquid, a process that is also diffusion limited. Downscaling the typical dimensions of the mixing chamber thereby reduces the typical distance to be overcome by diffusional mass-transport, and consequently results in a reduction of mixing times. Like thermal processing, the mixing of dissolved chemical species, such as reagents, with a sample or precursors for a synthesis step, is an operation that is required in virtually all chemical synthesis and analysis processes. Therefore, the ability to reduce the time involved in mixing provides significant advantages to most chemical synthesis and analysis processes. 
     Another aspect of the reduction of dimensions is the reduction of required volumes of sample, reagents, precursors and other often very expensive chemical substances. Milliliter-sized systems typically require milliliter volumes of these substances, while microliter sized microfluidic systems only require microliter volumes. The ability to perform these processes using smaller volumes results in significant cost savings, allowing the economic operation of chemical synthesis and analysis operations. As a consequence of the reduced volume requirement, the amount of chemical waste produced during the chemical operations is correspondingly reduced. 
     In microfluidic systems, regulation of minute fluid flows through a microchannel is of prime importance, as the processes performed in these systems highly depend on the delivery and movement of various liquids such as sample and reagents. A flow control device may be used to regulate, allow or halt the flow of liquid through a microchannel, either manually or automatically. Regulation includes control of flow rate, impeding of flow, switching of flows between various input channels and output channels, as well as volumetric dosing. It is generally desirable that flow control devices, such as valves, precisely and accurately regulates fluid flow, while being economical to manufacture. 
     SUMMARY OF THE INVENTION 
     The present invention provides a latching micro-regulator for regulating liquid flow on micro-scale levels. The latching micro-regulator provides binary addressable flow control using digital latching. The latching micro-regulator includes a bi-stable latching valve comprising a substrate having an inlet port and an outlet port, a valve seat defining a valve chamber for opening and closing the inlet port, and an actuator assembly for actuating the valve element. The valve chamber is configured to contain a volume of fluid, and the inlet port and the outlet port are in fluid communication with the valve chamber to provide a liquid flow path through the chamber. The actuator assembly comprises a cantilever beam for moving the valve seat between an open position and a closed position, an actuator, such as a piezoelectric element, for moving the cantilever beam, and a latch, such as a permanent magnet, for securing the cantilever beam in the closed position. 
     According to a first aspect of the invention, a bi-stable latching valve for controlling fluid flow through a channel is provided. The bi-stable latching valve comprises a substrate defining an inlet port and an outlet port in communication with the channel, a valve seat, an actuator assembly for selectively moving the valve seat between the open position and the closed position and a latching mechanism. The valve seat defines a valve chamber in communication with the inlet port and the outlet port for containing a volume of fluid and the valve seat moves between a closed position wherein the valve seat blocks one of said inlet port and said outlet port and an open position to allow fluid flow through the valve chamber to regulate fluid flow through the chamber. The latching mechanism latches the valve seat in one of said open position and closed position. 
     According to another aspect, a flow regulating system is provided. The flow regulating system comprises a first flow channel for conveying liquids having a first flow resistance, a first bi-stable valve in communication with the first flow channel for selectively blocking liquid flow through the first flow channel, a second flow channel for conveying liquids having a second flow resistance and a second bi-stable valve in communication with the second flow channel for selectively blocking liquid flow through the second flow channel. 
     According to yet another aspect, a flow regulating system is provided. The flow regulating system comprises a first flow channel for conveying liquids having a first flow resistance, a first bi-stable latching valve in communication with the first flow channel for selectively blocking liquid flow through the first flow channel, a second flow channel for conveying liquids having a second flow resistance and a second bi-stable latching valve in communication with the second flow channel for selectively blocking liquid flow through the second flow channel. The first and second bi-stable latching valve each comprise a piezoelectric actuator for selectively opening and blocking the flow channel, and a magnetic latch for locking the valve in a closed position. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  is a cross-sectional side view of an embodiment of the bi-stable latching valve of the present invention. 
         FIG. 2   a  is a detailed side view of the bi-stable latching valve of  FIG. 1  in an open position. 
         FIG. 2   b  is a top view of the bi-stable latching valve of  FIG. 2   a.    
         FIGS. 3   a  and  3   b  illustrate the bi-stable latching valve switching from a closed position to an open position. 
         FIGS. 4   a  and  4   b  illustrate the bi-stable latching valve switching from an open position to a closed position. 
         FIG. 5  is a schematic diagram of a flow regulating system for a microfluidic system implementing a plurality of bi-stable latching valves according to an illustrative embodiment of the invention to provide variable control of fluid flow. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a digital latching micro-regulator including a bi-stable latching valve for accurately controlling fluid flow on demand. The present invention will be described below relative to an illustrative embodiment. Those skilled in the art will appreciate that the present invention may be implemented in a number of different applications and embodiments and is not specifically limited in its application to the particular embodiments depicted herein. 
     The present invention provides a bi-stable latching valve for selectively blocking fluid flow through a channel. The valve is positioned in a channel to selectively block liquid flow through the channel. As shown in  FIG. 1 , the bi-stable latching valve  10  of the present invention comprises a substrate  20  having an inlet port  22  and an outlet port  24  formed therein in fluid communication with a channel through which liquid flows. The substrate  20  is preferably formed of glass or plastic, though other materials may be used. The bi-stable latching valve  10  further includes a valve seat  30  cooperating with the substrate to define a valve chamber  26  in communication with the inlet port  22  and the outlet port  24  for containing a volume of fluid. The valve seat  30  selectively blocks the inlet port  22  to regulate the flow of fluid into the chamber  26 . The position of the valve seat  30  controls the fluid flow into the chamber  26 . The position of the valve seat  30  is controlled by an actuator assembly  50 . The actuator assembly can comprise any suitable structure for selectively operating or moving the valve seat  30  to block the inlet port  22  or the outlet port  24 . According to one embodiment, the actuator assembly includes a cantilever beam  40  hinged to the substrate  20 , an actuator  52 , and a latching mechanism  60 . 
     The position of the valve seat  30  is determined by the position of the cantilever beam  40 . The valve seat  30  is connected to the cantilever beam  40 , which is in turn connected to the actuator  52 . The actuator  52  can comprise any suitable structure for moving the valve seat  30  between an open position for allowing fluid to enter or exit the chamber, and a closed position. Examples of suitable actuators include mechanical, electrical, electromechanical, and magnetic devices. According to a preferred embodiment, the actuator  52  is a piezoelectric element. The cantilever beam  40  is hinged at a first end  41  to the glass substrate  20  and rotates about the fixed hinge under the control of the actuator  52  to move the valve seat  30  between the open and closed positions. When the cantilever beam  40  is lowered, the beam pushes the valve seat  30  into a closed position, thereby blocking the inlet port and preventing fluid flow into the chamber. When the cantilever beam  40  is raised, the valve  30  is moved to an open position to allow fluid flow through the chamber  26 . The cantilever beam  40  is driven by the piezoelectric element  52 , which selectively applies a driving force to the beam  40 . 
     The bi-stable latching valve  10  further includes a latching mechanism  60  for selectively latching or holding the beam  40  in a selected position. The latching mechanism can include any suitable mechanical, electrical, electromechanical or magnetic structure suitable for latching the beam  40 . The latching mechanism  60 , according to a preferred embodiment, comprises a permanent magnet  62  and a permalloy element  46  disposed on a free end  44  of the beam  40 . The permanent magnet  62  is attached to the glass substrate  20  opposite the permalloy element  46  and is configured to attract the permalloy element  46 . The magnetic attraction between the permanent magnet and the permalloy element is effective to latch, i.e. to retain, the valve element in a closed position to prevent fluid flow through the bi-stable latching valve  10 . 
     As shown in  FIGS. 2   a  and  2   b , the valve seat  30  is cylindrical in shape and includes a rim  38  about the circumference of the valve seat  30 , which defines the valve chamber  26 . The rim  38  cooperates with the glass substrate  20  to fluidly seal the valve chamber  26 . The valve chamber communicates with the inlet port  22  and the outlet port  24 . The valve seat  30  is preferably formed of a flexible material, such as silicone rubber, though one skilled the art will recognize that alternate materials may be used. The valve seat  30  further comprises a membrane portion  32 , a first protrusion  34  for contacting the cantilever beam  40  and second protrusion  36  for selectively blocking the inlet port  22  to prevent the flow of fluid through the valve chamber  26 , thereby blocking fluid flow through the associated channel. The second protrusion blocks the inlet port  22  when the cantilever beam depresses the valve seat  30  by pushing on the first protrusion  34 . One skilled in the art will recognize that the valve seat  30  is not limited to a cylindrical shape, and that any suitable shape may be utilized. 
     The operation of the bi-stable latching valve  10  is illustrated in  FIGS. 3   a – 3   b  and  FIGS. 4   a – 4   b . The bi-stable latching valve  10  switches between two stable states: an ON state, which allows the flow of liquid through the valve chamber and an OFF state, which prevents the flow of liquid through the valve chamber. The state of the bi-stable latching valve  10  is controlled by the driving force on the cantilever beam  40  by the actuator  52  and the magnetic latching force created by the permanent magnet  62  on the beam free end. According to the illustrative embodiment, the bi-stable latching valve only requires power to switch between the two stable states and does not otherwise require power to operate. 
       FIG. 3   a  illustrates the bi-stable latching valve  10  in an OFF state, where the second protrusion  36  of the valve seat  30  blocks the inlet port  22  so that fluid is prevented from flowing through the valve chamber  26 . In the OFF state, the latching mechanism  60  latches the cantilever beam  40  in the closed position by securing the permalloy element  46  to the permanent magnet  60 . As shown, when the attractive force of the magnet pulls the cantilever beam towards the magnet, causing the cantilever beam to push the valve into the closed position, such that the first protrusion blocks the inlet port. The valve maintains the closed position until activated. 
     To open the bi-stable latching valve and allow fluid flow, a voltage is applied to the piezoelectric element  52  using a controller (not shown). The applied voltage causes the piezoelectric element to compress, applying an opposite force on the cantilever beam in the direction away from the magnet. If the force generated is sufficient to overcome the magnetic attraction between the magnet and the permalloy, the magnet releases the permalloy element and the cantilever beam raises, pulling the valve seat  30  clear of the inlet port  22 . As shown in  FIG. 3   b , fluid flows through unobstructed inlet port  22  into the valve chamber and out of the valve chamber via the outlet port. 
     The bi-stable latching valve  10  remains in the ON state, as shown in  FIG. 4   a , until the controller subsequently actuates the piezoelectric element  52  by applying a second voltage. The second voltage causes the piezoelectric element to expand, which applies a driving force on the cantilever beam  40 , pushing the beam towards the magnet  60 . The lowered beam in turn applies a force to the valve seat  30 , which shifts into a closed position, blocking the inlet port. When the permalloy element  46  is brought close to the magnet  62 , a magnetic latching force generated by the magnet latches the beam  40  into the closed position until a subsequent actuation of the piezoelectric element  52 . 
     The bi-stable latching valve  10  may be employed in a valve architecture to provide binary addressable flow control using digital latching. As shown in  FIG. 5 , multiple bi-stable latching valves may be connected to channels  550  of specific flow conductance that vary according to a pre-determined ratio to provide a micro-regulator  500 . Each bi-stable latching valve  10  can be set to an on or off state as described previously, allowing or blocking flow through its associated flow channel  550 . The bi-stable latching valves are selectively activated in various combinations to provide a number of discrete flow conductance states through the micro-regulator  500 . The net flow through the micro-regulator is therefore determined by the sum of the flows through the open bi-stable latching valves  10 . The number of discrete flow conductance states is determined by the number of bi-stable latching valves in the system and the flow conductance ratios between the channels. 
     A typical example of a 4-bit micro-regulator system is illustrated in  FIG. 5 . The individual channels  550   a ,  550   b ,  550   c  and  550   d  in the system have flow conductance ratios of 1:2:4:8, thus providing 16 discrete net flow conductance states. For example, a first flow conductance state may be provided by opening all of the bi-stable latching valves  10   a – 10   d  to allow flow through all of the channels  550   a ,  550   b ,  550   c  and  550   d . A second flow conductance state is achieved by closing the first bi-stable latching valve  10   a , while leaving the remaining bi-stable latching valves  10   b ,  10   c ,  10   d  open, allowing fluid flow through the channels  550   b ,  550   c  and  550   d  only. A third conductance state is achieved by closing the first and second bi-stable latching valves  10   a ,  10   b  while leaving the remaining bi-stable latching valves  10   c ,  10   d  to allow flow through the associated channels  550   c  and  550   d , and so on. This allows flow rates to be controlled to a 6.67% precision. Higher precision can be obtained by increasing the number of bits in the system—for example an 8-bit system has 128 discrete states, achieving less than 1% precision in the flow rate control. 
     One skilled in the art will recognize that any suitable bi-stable valve for selectively blocking liquid flow through a channel may be used in the flow regulating system  500  of  FIG. 5  to provide variable flow resistance. The micro-regulator  500  may have any suitable number of channels arranged in any suitable configuration and having any suitable flow resistance to achieve a system having variable flow resistance, wherein the flow resistance depends on the state of the bi-stable valves. 
     The manufacturing process for the bi-stable latching valve  10  of an illustrative embodiment of the present invention is efficient, economical and simplified. The valve seat  30  may be formed by surface micromachining of a substrate, followed by deposition of silicone rubber, the permalloy element  46  and polysilicon. The substrate  20  is etched to form a channel and then drilled to form the inlet port  22  and the outlet port  24 . The cantilever beam  40  may be attached and hinged to the glass substrate through means known in the art. The permalloy element may be bonded to the beam and the permanent magnet  62  may be bonded to the substrate through means known in the art. The piezoelectric element  52  or other actuator for driving the cantilever beam  40  may be attached to the beam through any suitable means. 
     The present invention has been described relative to an illustrative embodiment. Since certain changes may be made in the above constructions without departing from the scope of the invention, it is intended that all matter contained in the above description or shown in the accompanying drawings be interpreted as illustrative and not in a limiting sense. 
     It is also to be understood that the following claims are to cover all generic and specific features of the invention described herein, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.