Abstract:
A valve for use in microfluidic structures. The valve uses a spherical member, such as a ball bearing, to depress an elastomeric member to selectively open and close a microfluidic channel. The valve may be operated manually or by use of an internal force generated to shift the spherical member to its activated position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This patent application claims benefit from U.S. Provisional Patent Application Serial No. 60/213,865, filed Jun. 23, 2000, which application is incorporated herein by reference. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    This invention relates generally to microscale devices for performing analytical testing and, in particular, to a valve for use in laminated plastic microfluidic structures.  
           [0004]    2. Description of the Prior Art  
           [0005]    Microfluidic devices have recently become popular for performing analytical testing. Using tools developed by the semiconductor industry to miniaturize electronics, it has become possible to fabricate intricate fluid systems which can be inexpensively mass produced. Systems have been developed to perform a variety of analytical techniques for the acquisition of information for the medical field.  
           [0006]    Microfluidic devices may be constructed in a multi-layer laminated structure where each layer has channels and structures fabricated from a laminate material to form microscale voids or channels where fluids flow. A microscale channel is generally defined as a fluid passage which has at least one internal cross-sectional dimension that is less than 100 μm and typically between about 0.1 μm and about 500 μm. The control and pumping of fluids through these channels is affected by either external pressurized fluid forced into the laminate, or by structures located within the laminate.  
           [0007]    Many different types of valves for use in controlling fluids in microscale devices have been developed. U.S. Pat. No. 4,895,500, which issued on Jan. 23, 1990, describes a silicon micromechanical non-reverse valve which consists of a cantilever beam extending over a cavity and integrally formed with the silicon wafer such that the beam can be shifted to control flow within channels of the microfluidic structure.  
           [0008]    U.S. Pat. No. 5,443,890, which issued Aug. 22, 1995 to Pharmacia Biosensor AB, describes a sealing device in a microfluidic channel assembly having first and second flat surface members which when pressed against each other define at least part of a microfluidic channel system between them.  
           [0009]    U.S. Pat. No. 5,593,130, which issued on Jan. 14, 1997 to Pharmacia Biosensor AB, describes a valve for use in microfluidic structures in which the material fatigue of the flexible valve membrane and the valve seat is minimized by a two-step seat construction and the fact that both the membrane and the seat are constructed from elastic material.  
           [0010]    U.S. Pat. No. 5,932,799, which issued Aug. 3, 1999 to YSI Incorporated, teaches a microfluidic analyzer module having a plurality of channel forming laminate layers which are directly bonded together without adhesives, with a valve containing layer directly adhesivelessly bonded over the channel containing layers and a flexible valve member integral with the valve layer to open and close communication between feed and sensor channels of the network.  
           [0011]    U.S. Pat. No. 5,962,081, which issued Oct. 5, 1999 to Pharmacia Biotech AB, describes a method for the manufacturer of polymer membrane-containing microstructures such as valves by combining polymer spin deposition methods with semiconductor manufacturing techniques.  
           [0012]    U.S. Pat. No. 5,977,355, which issued on Oct. 26, 1999 to Xerox Corporation, describes a valve array system for microdevices based on microelectro mechanical systems (MEMS) technology consisting of a dielectric material forming a laminate which is embedded within multiple laminate layers.  
           [0013]    U.S. Pat. No. 6,068,751, which issued on May 30, 2000, describes a microfluidic delivery system using elongated capillaries that are enclosed along one surface by a layer of malleable material which is shifted by a valve having a electrically-powered actuator.  
           [0014]    U.S. patent application Ser. No. 09/677,250, filed Oct. 2, 2000, and assigned to the assignee of the present invention describes a one way check valve for use in laminated plastic microfluidic structures. This valve allows one way flow through microfluidic channels for use in mixing, dilution, particulate suspension and other techniques necessary for flow control in analytical devices.  
           [0015]    Several types of valves are commonly used for fluid management in flow systems. Flap valves, ball-in-socket valves, and tapered wedge valves are a few of the valve types existing in the macroscale domain of fluid control. However, in the microscale field, where flow channels are often the size of a human hair (approximately 100 microns in diameter), there are special needs and uses for valves which are unique to microscale systems, especially microfluidic devices incorporating fluids with various concentrations of particulate in suspension. Special challenges involve mixing, dilution, fluidic circuit isolation, and anti-sediment techniques when employing microscale channels within a device. The incorporation of a simple compact valve within microscale devices addresses these potential problems while maintaining high density of fluidic structure within the device.  
         SUMMARY OF THE INVENTION  
         [0016]    It is therefore an object of the present invention to provide an efficient and reliable valve suitable for use in a microfluidic system.  
           [0017]    It is a further object of the present invention is to provide a microfluidic valve which can be integrated into a cartridge constructed of multi-layer laminates.  
           [0018]    It is a further object of the present invention is to provide an array of microfluidic valves that can be integrated into a cartridge constructed of multi-layer laminates.  
           [0019]    These and other objects of the present invention will be more readily apparent in the description and drawings that follow. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    [0020]FIG. 1 is a fragmentary cross-sectional view of a microfluidic device containing a basic ball bearing valve according to the present invention;  
         [0021]    [0021]FIG. 2 is a fragmentary cross-sectional view of the valve of FIG. 1 shown in its activated position;  
         [0022]    [0022]FIG. 3 is a fragmentary cross-sectional view of another embodiment of a ball bearing valve according to the present invention; and  
         [0023]    [0023]FIG. 4 is a perspective view of a microfluidic array which uses a plurality of ball bearing valves according to the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0024]    Referring now to FIG. 1, there is shown a microfluidic valve assembly, generally indicated at  10 , which contains a valve constructed according to the present invention. Assembly  10  includes a spherical member or ball bearing  12  which is located within a channel  14  formed between a rigid top layer  16  and a rigid interior layer  18  within assembly  10 . Layer  16  and layer  18  each contain a cutout area  20  and  22  respectively within which ball bearing  12  is contained in channel  14 . Rigid layers  16 ,  18  may be constructed from a material such as MYLAR. Spherical member  12  may be constructed from metal, hard plastic, or any other similar material.  
         [0025]    A membrane  24  constructed of a flexible material is located adjacent layer  18  opposite channel  14 . Membrane  24 , which is preferably made from a thin elastomeric material, completely isolates channel  14  from a channel  26  by spanning across cutout area  22 . One suitable material that may be used for membrane  24  is polyvinylidene chloride (PVDC) which is the material commonly used as SARAN WRAP® film. Channel  26  is capable of carrying fluids within  10  assembly  10 , and in the present embodiment is formed by a narrow section  26   a  and a wider section  26   b . Channel section  26   b  is formed by layer  18  along with adjacent membrane  24 , and a rigid bottom layer  28 , while section  26   a  is located within membrane  24  and an additional rigid layer  30  adjacent bottom layer  28 .  
         [0026]    In operation, the flow of a fluid traveling within channel  26  can be controlled within assembly  10  by spherical member  10 . Referring now to FIG. 2, member  12  is shifted by a sufficient force in the direction shown by arrow A. This force may be applied manually using the finger of a human operator, or by any suitable mechanical means as known in the art. This movement causes flexible membrane  24  to contact bottom layer  28 , closing channel  26  to any fluid movement between channel section  26   a  and section  26   b . Note that layer  18  acts to aid in centering member  12  in the process of activating valve assembly  10 , as member  12  is essentially captured within cutout area  22  of layer  18 . When the operating force is removed from member  12 , said member is shifted back to its unactuated position as shown in FIG. 1 by virtue of the elastomeric property of membrane  24 .  
         [0027]    [0027]FIG. 3 illustrates a second embodiment of a valve assembly constructed according to the present invention. It will be understood that similar parts will be given the same index numerals. Referring now to FIG. 3, there is shown a valve assembly  10   a  having a spherical member  12  located within a channel  14  which is formed between a layer  18  and an elastomeric layer  16   a.    
         [0028]    Elastomeric membrane  24  is located adjacent layer  18  opposite channel  14 , while spherical member  12  is situated in cutout section  22  within layer  18  and contacts member  24  at this location, as was previously shown in FIG. 1. Channel  26 , which consists of a narrow section  26   a  and a wider section  26   b , is formed between membrane  24  and bottom layer  28 , and is capable of carrying fluids within a microfluidic circuit.  
         [0029]    An upper channel  36  is formed within assembly  10   a  between layer  16   a  and a rigid upper layer  38 . Channel  36  contains a fluid which is capable of providing a force capable of activating valve assembly  10   a . As can be clearly seen in FIG. 3, fluid flowing in the direction of arrow B will flow over spherical member  12 , which is located beneath layer  16   a.    
         [0030]    To operate valve assembly  10   a , if the force generated by a fluid flowing in direction B within channel  36 , the fluid will force membrane  24  downwardly in the direction of arrow A, causing member  12  to shift and causing membrane  24  to contact layer  28 , closing channel  26  to any fluid movement between channel  26   a  and  26   b . When the flow of the fluid within channel  36  is reduced such that the force acting upon member  12  is less than that force exerted by membrane  24  on the lower part of member  12 , member  12  will return to the position shown in FIG. 3, and thus allowing fluid flow within channel  26 .  
         [0031]    The valve assembly of the present invention can also be used to control a microfluidic array. Referring now to FIG. 4, there is shown a microfluidic array, generally indicated at  50 . Array  50  consists of a lower array section  52  and an upper array section  54 . Section  52  contains a plurality of spaced apart indentations  56  which are sized to contain a plurality of spherical members  12  as taught in FIGS.  1 - 3 . Also within section  52 , there is contained a microfluidic circuit (not shown) which is constructed having channels similar to that shown in FIG. 3. This circuit may be designed to perform many functions which are familiar to those skilled in the art of microfluidic circuitry design.  
         [0032]    Section  54  may be constructed similar to the valve circuitry shown in FIG. 3 in that the lower surface is constructed for a elastomeric material which is deformed by spherical members  12  when the valves are in the inactive position. The control of the operation of the valves may be done using fluidic channels, similar to channel  36  in FIG. 3, or operation of the valves may also be accomplished using common electrical, magnetic, or pneumatic means, as is well known in the art.  
         [0033]    The control of the operation of array  50  is accomplished by use of external control means  60  which is coupled to section  54  via a cable  62 . Control means  60  may be a computer or programmable control or the like, or any device familiar to those skilled in the art. Or, alternatively, array  50  could be inserted as a cartridge into a separate machine which would control operation of the valves within the array.  
         [0034]    While the present invention has been shown and described in terms of several preferred embodiments thereof, it will be understood that this invention is not limited to these particular embodiments and that many changes and modifications may be made without departing from the true spirit and scope of the invention as defined in the appended claims.