Mobile monolithic polymer elements for flow control in microfluidic devices

Abstract

A cast-in-place and lithographically shaped mobile, monolithic polymer element for fluid flow control in microfluidic devices and method of manufacture. Microfluid flow control devices, or microvalves that provide for control of fluid or ionic current flow can be made incorporating a cast-in-place, mobile monolithic polymer element, disposed within a microchannel, and driven by either fluid or gas pressure against a retaining or sealing surface. The polymer elements are made by the application of lithographic methods to monomer mixtures formulated in such a way that the polymer will not bond to microchannel walls. The polymer elements can seal against pressures greater than 5000 psi, and have a response time on the order of milliseconds. By the use of energetic radiation it is possible to depolymerize selected regions of the polymer element to form shapes that cannot be produced by conventional lithographic patterning and would be impossible to machine.

1 - 4 . (cancelled)  
     
     
         5 . A method for making a mobile, monolithic polymer element in a microchannel, comprising; 
 a) injecting a monomer mixture dissolved in a solvent into the microchannel, wherein the composition of the monomer mixture is such that the polymer formed by polymerizing the monomer does not bond to the microchannel wall;    b) polymerizing the monomer by application of radiation; and    c) flushing unpolymerized monomer mixture from the microchannel.    
     
     
         6 . The method of  claim 5 , wherein the radiation is UV, visible, or thermal radiation.  
     
     
         7 . A method for making a monolithic polymer element in a microchannel such that the polymer element conforms to the configuration of the microchannel and does not bond to the microchannel wall, comprising the steps of: 
 preparing a monomer mixture by mixing together    a) one or more cross-linking agents selected from the group including ethylene glycol diacrylate, diethylene glycol diacrylate, propylene glycol diacrylate, butanediol diacrylate, neopentyl glycol diacrylate, hexanediol diacrylate, pentaerythritol triacrylate, pentaerythritol tetracrylate, trimethylolpropane triacrylate, or divinyl benzene,    b) tetrahydrofurfuryl acrylate,    c) at least one nonpolar monomer selected from the group branched or straight chain C 1 -C 12  alkyl acrylates, or styrene, and    d) at least one monomer capable of carrying a charge at a pH of between about 2 and 12 selected from the group including C 1 -C 12  alkyl or aryl acrylates substituted with sulfonate, phosphate, boronate, carboxylate, amine, or ammonium;    adding the monomer mixture to a solvent, comprising;    a) water containing up to 100 mM buffer salts, and    b) at least one of the group including C 1 -C 6  alcohols, C 4 -C 8  ethers, C 3 -C 6  esters, C 1 -C 4  esters, C 1 -C 4  carboxylic acids, methyl sulfoxide, sulfolane, or N-methyl pyrrolidone, and    a polymerization initiator, wherein the monomer/solvent mixture forms a single phase mixture at a temperature below about 40° C.;    loading the combined mixture into a capillary tube;    applying a mask to the surface of the capillary tube, wherein the mask defines the shape of the polymer monolith to be produced;    polymerizing the combined mixture by exposing the monomer mixture to radiation through the mask; and    flushing unpolymerized monomer from the microchannel.    
     
     
         8 . The method of  claim 7 , wherein the radiation includes thermal, visible, or UV radiation.  
     
     
         9 . The method of  claim 8 , wherein wavelength of the radiation is greater than about 257 nm.  
     
     
         10 . A mobile polymer monolith disposed in a microchannel and made by the method of  claim 7 .  
     
     
         11 - 17 . (cancelled)  
     
     
         18 . A method for shaping a monolithic polymer element disposed within a microchannel, comprising: 
 exposing the surface of the polymer element to energetic radiation to remove a portion of the surface and thereby shape the polymer element; and    flushing the microchannel with a liquid to remove depolymerized material.    
     
     
         19 . The method of  claim 18 , wherein the source of energetic radiation is a laser.  
     
     
         20 . The method of  claim 19 , wherein the laser is a frequency doubled Argon-ion laser operating at 257 nm.  
     
     
         21 . (cancelled)  
     
     
         22 . A method of making a mobile, monolith polymer element in a microchannel, comprising: 
 a) preparing a monomer mixture by mixing together 1,3-butanedioldiacrylate, tetrahydrofurfuryl alcohol, hexyl alcohol, acryloyloxyethyltrimethylammonium methyl sulfate, and a photoinitiator;    b) preparing a solvent mixture by mixing together acetonitrile, methoxyethanol, and phosphate buffer;    c) mixing together the monomer and solvent mixtures in the ratio of 60:40 by volume;    d) loading the combined mixture into a capillary tube;    e) polymerizing the combined mixture by exposure to UV radiation; and.    f) flushing unreacted monomer from the microchannel.    
     
     
         23 . A mobile monolithic polymer element disposed within a microchannel and made by the method of  claim 22 .  
     
     
         24 . A device for controlling fluid flow in a microchannel, comprising 
 a mobile monolithic polymer element disposed in the microchannel, wherein said polymer element is made by the method of  claim 22;     at least one retaining means disposed in the microchannel; and means for applying a displacing force to the either end of the microchannel.    
     
     
         25 . (cancelled)