Microfluidic systems including three-dimensionally arrayed channel networks

Abstract

The present invention provides, in certain embodiments, improved microfluidic systems and methods for fabricating improved microfluidic systems, which contain one or more levels of microfluidic channels. The inventive methods can provide a convenient route to topologically complex and improved microfluidic systems. The microfluidic systems provided according to the invention can include three-dimensionally arrayed networks of fluid flow paths therein including channels that cross over or under other channels of the network without physical intersection at the points of cross over. The microfluidic networks of the invention can be fabricated via replica molding processes, also provided by the invention, utilizing mold masters including surfaces having topological features formed by photolithography. The microfluidic networks of the invention are, in some cases, comprised of a single replica molded layer, and, in other cases, are comprised of two, three, or more replica molded layers that have been assembled to form the overall microfluidic network structure. The present invention also describes various novel applications for using the microfluidic network structures provided by the invention.

1 . A method for forming a microfluidic network structure comprising:
 providing at least one mold substrate;   forming at least one topological feature on a surface of the mold substrate to form a first mold master, where at least one of said at least one topological feature is a two-level topological feature characterized by a first portion having a first depth or height with respect to a region of the surface adjacent to the feature and a second portion, integrally connected to the first portion, having a second depth or height with respect to the region of the surface adjacent to the feature, which is greater than the first depth or height;   contacting the surface with a first hardenable liquid;   hardening the liquid thereby creating a first molded replica of the surface;   removing the first molded replica from the first mold master; and assembling the first molded replica into a structure comprising a microfluidic network having at least a one fluid flow path comprising a series of interconnected channels within the structure, the series of interconnected channels including at least one first channel disposed within a first level of the structure, at least one second channel disposed within a second level of the structure, and at least one connecting channel fluidically interconnecting the first channel and the second channel, where at least one of which channels has a cross-sectional dimension not exceeding about 500 μm and where the structure includes at least one channel disposed within the first level of the structure that is non-parallel to at least one channel disposed within the second level of the structure.   
     
     
         2 . The method for forming a microfluidic network structure as in  claim 1 , wherein the topological features comprise protrusions from the surface of the first mold master, and wherein the first portion of the at least one two-level topological feature has a first height with respect to the region of the surface adjacent to the two-level topological feature and the second portion has a second height with respect to the region of the surface adjacent to the feature, which is greater than the first height. 
     
     
         3 . The method for forming a microfluidic network structure as in  claim 2 , wherein the first molded replica formed by the hardening step and removing step includes a first surface forming the first level of the microfluidic network formed in the assembling step, and wherein the at least one first channel disposed in the first level is molded by the first portion of the at least one two-level topological feature. 
     
     
         4 . The method for forming a microfluidic network structure as in  claim 3 , wherein the first molded replica formed by the hardening step and removing step further includes the at least one connecting channel of the microfluidic network formed in the assembling step, and wherein the connecting channel is molded, at least in part, by the second portion of the at least one two-level topological feature. 
     
     
         5 . The method for forming a microfluidic network structure as in  claim 2 , wherein the contacting step comprises:
 creating a layer of the first hardenable liquid on the surface of the first mold master, the layer having a depth exceeding the first height but not exceeding the second height.   
     
     
         6 . The method for forming a microfluidic network structure as in  claim 5 , wherein the creating step further comprises the step of:
 bringing a surface of a second mold substrate into contact with a surface of the second portion of the at least one two-level topological feature in the surface of the first mold master.   
     
     
         7 . The method for forming a microfluidic network structure as in  claim 6 , wherein the surface of the second mold substrate is an essentially planar, featureless surface. 
     
     
         8 . The method for forming a microfluidic network structure as in  claim 6 , wherein the second mold substrate comprises a second mold master and wherein the surface of the second mold master includes at least one topological feature formed thereon. 
     
     
         9 . The method for forming a microfluidic network structure as in  claim 8 , wherein at least one topological feature in the surface of the second mold master is formed by a photolithography process. 
     
     
         10 . The method for forming a microfluidic network structure as in  claim 8 , wherein the surface of the second mold master comprises a molded replica of another surface including at least one topological feature thereon. 
     
     
         11 . The method for forming a microfluidic network structure as in  claim 10 , wherein the second mold master is formed from an elastomeric material. 
     
     
         12 . The method for forming a microfluidic network structure as in  claim 8 , wherein the at least one topological feature in the surface of the second mold master comprises a protrusion from the surface. 
     
     
         13 . The method for forming a microfluidic network structure as in  claim 12 , wherein the first molded replica formed by the hardening step and removing step includes a second surface forming the second level of the microfluidic network formed in the assembling step, and wherein the at least one second channel disposed in the second level is molded by the at least one topological feature in the surface of the second mold master. 
     
     
         14 . The method for forming a microfluidic network structure as in  claim 12 , wherein the surface of the second mold master includes at least one two-level topological feature thereon, which two-level topological feature is characterized by a first portion having a first height with respect to a region of the surface adjacent to the feature and a second portion, integrally connected to the first portion, having a second height with respect to the region of the surface adjacent to the feature, which is greater than the first height. 
     
     
         15 . The method for forming a microfluidic network structure as in  claim 14 , wherein at least a portion of the second portion of the two-level topological feature of the second mold master is shaped and positioned to mate with at least a portion of the second portion of a two-level topological feature of the first mold master when the mold masters are brought together in the bringing step. 
     
     
         16 . The method for forming a microfluidic network structure as in  claim 15 , wherein at least a portion of the second portion of the two-level topological feature of the second mold master is shaped and positioned to interdigitate with at least a portion of the second portion of a two-level topological feature of the first mold master when the mold masters are brought together in the bringing step. 
     
     
         17 . The method for forming a microfluidic network structure as in  claim 15 , wherein the first molded replica formed during the hardening step and removing step further includes the at least one connecting channel of the microfluidic network formed in the assembling step, and wherein the connecting channel is molded, at least in part, by the second portion of the at least one two-level topological feature of the second mold master. 
     
     
         18 . The method for forming a microfluidic network structure as in  claim 8 , wherein at least one topological feature on the surface of the first mold master comprises a first alignment element and wherein at least one topological feature on the second mold master comprises a second alignment element, the second alignment element shaped to be matable with the first alignment element. 
     
     
         19 . The method for forming a microfluidic network structure as in  claim 18 , wherein both of the first and second alignment elements comprise topological features that do not mold, during the contacting and hardening steps, channels in fluid communication with the at least one fluid flow path in the microfluidic network structure. 
     
     
         20 . The method for forming a microfluidic network structure as in  claim 18 , wherein the first and second alignment elements comprise topological features that mate together during the bringing step, and wherein at least a portion of at least one connecting channel of the microfluidic network structure is molded, at least in part, from at least a portion of the mated topological features. 
     
     
         21 . The method for forming a microfluidic network structure as in  claim 8 , wherein the contacting step comprises:
 bringing the surface of the first mold master into at least partial contact with the surface of the second mold master;   aligning the at least one topological feature of the first mold master and the at least one topological feature of the second mold master with respect to each other to yield a desired alignment of features;   applying the first hardenable liquid in contact with a periphery of the interface between the first and second mold masters; and   allowing the first hardenable liquid to flow into interstices between the first and the second mold masters by capillary action.   
     
     
         22 . The method for forming a microfluidic network structure as in  claim 8 , wherein the contacting step comprises:
 forming a layer of the first hardenable liquid on the surface of the first mold master;   bringing the surface of the second mold master into at least partial contact with the surface of the first mold master; and   aligning the at least one topological feature of the first mold master and the at least one topological feature of the second mold master with respect to each other to yield a desired alignment of features.   
     
     
         23 . The method for forming a microfluidic network structure as in  claim 21  or  22 , further comprising:
 interdigitating at least a portion of the at least one topological feature of the first mold master and at least a portion of the at least one topological feature of the second mold master.   
     
     
         24 . The method for forming a microfluidic network structure as in  claim 8 , wherein the removing step comprises:
 applying a force to at least one of the first and the second mold masters tending to separate the masters from each other;   removing the first molded replica from the surface of the first mold master while leaving the first molded replica in contact with and supported by the surface of the second mold master; and   removing the second mold master from the first molded replica.   
     
     
         25 . The method for forming a microfluidic network structure as in  claim 24 , further comprising after the step of removing the first molded replica from the surface of the first mold master while leaving the first molded replica in contact with and supported by the surface of the second mold master, and before the step of removing the second mold master from the first molded replica, the step of:
 contacting the first molded replica with a support surface.   
     
     
         26 . The method for forming a microfluidic network structure as in  claim 1 , wherein the first hardenable liquid comprises a liquid able to solidify to form a solid polymeric material. 
     
     
         27 . The method for forming a microfluidic network structure as in  claim 26 , wherein the first hardenable liquid comprises a curable prepolymer of an elastomeric polymer. 
     
     
         28 . The method for forming a microfluidic network structure as in  claim 27 , wherein the first hardenable liquid comprises a curable prepolymer of poly(dimethylsiloxane). 
     
     
         29 . The method for forming a microfluidic network structure as in  claim 26 , wherein the hardening step comprises applying heat to the first hardenable liquid. 
     
     
         30 . The method for forming a microfluidic network structure as in  claim 26 , wherein the hardening step comprises applying ultraviolet radiation to the first hardenable liquid. 
     
     
         31 . The method for forming a microfluidic network structure as in  claim 1 , wherein the assembling step comprises:
 providing a first support substrate having at least one oxidizable surface;   oxidizing the oxidizable surface of the first support substrate and the first molded replica;   bringing the surface of the first support substrate into conformal contact with at least a portion of a first surface of the first molded replica; and   sealing the first molded replica to the first support substrate via chemical reaction between the surfaces.   
     
     
         32 . The method for forming a microfluidic network structure as in  claim 31 , wherein the oxidizable surface of the first support substrate is essentially planar having essentially no features disposed thereon. 
     
     
         33 . The method for forming a microfluidic network structure as in  claim 32 , wherein the first support substrate is formed of a different material than the material forming the first molded replica. 
     
     
         34 . The method for forming a microfluidic network structure as in  claim 32 , wherein the first support substrate is formed of a material that is the same as that forming the first molded replica. 
     
     
         35 . The method for forming a microfluidic network structure as in  claim 31 , wherein the first support substrate comprises a second molded replica. 
     
     
         36 . The method for forming a microfluidic network structure as in  claim 35 , further comprising before the oxidizing step the steps of:
 bringing at least a portion of the first surface of the first molded replica into contact with at least a portion of a surface of the second molded replica;   aligning molded features of the first molded replica with molded features of the second molded replica to yield a desired alignment of features; and   separating the surfaces of the first molded replica and the second molded replica from each other without disrupting the desired alignment of features.   
     
     
         37 . The method for forming a microfluidic network structure as in  claim 35 , further comprising after the oxidizing step and before the bringing step the steps of:
 placing a liquid that is essentially non-reactive with the surfaces oxidized in the oxidizing step in contact with at least one of the surfaces oxidized in the oxidizing step;   disposing the first surface of the first molded replica and a surface of the second molded replica adjacent to each other such that they are separated from each other by a continuous layer of the liquid that is essentially non-reactive with the surfaces oxidized in the oxidizing step;   aligning molded features of the first molded replica with molded features of the second molded replica to yield a desired alignment of features; and   removing the liquid that is essentially non-reactive with the surfaces oxidized in the oxidizing step from between the surfaces.   
     
     
         38 . The method for forming a microfluidic network structure as in  claim 37 , wherein the step comprising removing the liquid that is essentially non-reactive with the surfaces oxidized in the oxidizing step from between the surfaces and the bringing step comprise a single step. 
     
     
         39 . The method for forming a microfluidic network structure as in  claim 37 , wherein the liquid that is essentially non-reactive with the surfaces oxidized in the oxidizing step is removed from between the surfaces by evaporation. 
     
     
         40 . The method for forming a microfluidic network structure as in  claim 31 , wherein the assembling step further comprises:
 providing a second support substrate having at least one oxidizable surface;   oxidizing the oxidizable surface of the second support substrate and the first molded replica;   bringing the surface of the second support substrate into conformal contact with at least a portion of a second surface of the first molded replica; and   sealing the first molded replica to the second support substrate via chemical reaction between the surfaces.   
     
     
         41 . The method for forming a microfluidic network structure as in  claim 40 , wherein the oxidizable surface of the second support substrate is essentially planar having essentially no features disposed thereon. 
     
     
         42 . The method for forming a microfluidic network structure as in  claim 41 , wherein the second support substrate is formed of a different material than the material forming the first molded replica. 
     
     
         43 . The method for forming a microfluidic network structure as in  claim 41 , wherein the second support substrate is formed of a material that is the same as that forming the first molded replica. 
     
     
         44 . The method for forming a microfluidic network structure as in  claim 40 , wherein the second support substrate comprises a second molded replica. 
     
     
         45 . The method for forming a microfluidic network structure as in  claim 1 , further comprising after the assembling step the steps of:
 at least partially filling the at least one fluid flow path of the microfluidic network with a second hardenable liquid;   solidifying the second hardenable liquid into a molded article having a structure conforming to the flow path of the microfluidic network; and   removing the microfluidic network structure surrounding the molded article.   
     
     
         46 . A method for forming a molded structure comprising:
 providing at least one mold substrate;   forming at least one two-level topological feature having at least one cross-sectional dimension not exceeding about 500 μm on a surface of the substrate to form a mold master, which two-level topological feature is characterized by a first portion having a first depth or height with respect to a region of the surface adjacent to the feature and a second portion, integrally connected to the first portion, having a second depth or height with respect to the region of the surface adjacent to the feature, which is greater than the first depth or height;   contacting the surface with a hardenable liquid;   hardening the liquid thereby creating a molded replica of the surface; and   removing the molded replica from the mold master.   
     
     
         47 . The method for forming a molded structure as in  claim 46 , wherein the molded replica formed by the hardening step and removing step includes a first surface with at least one channel disposed therein that is molded by the first portion of the at least one two-level topological feature and further includes at least one connecting channel fluidically interconnected to and oriented essentially perpendicularly to the channel disposed in the first surface of the molded replica, which connecting channel is molded by the second portion of the two-level topological feature. 
     
     
         48 . The method for forming a molded structure as in  claim 46 , wherein the mold substrate comprises a silicon wafer. 
     
     
         49 . The method for forming a molded structure as in  claim 48 , wherein at least one surface of the silicon wafer is coated with at least a first layer of photoresist having a surface forming a surface of the substrate on which the at least one topological feature is formed in the forming step. 
     
     
         50 . The method for forming a molded structure as in  claim 49 , wherein the photoresist comprises a positive photoresist. 
     
     
         51 . The method for forming a molded structure as in  claim 49 , wherein the photoresist comprises a negative photoresist. 
     
     
         52 . The method for forming a molded structure as in  claim 49 , wherein the forming step comprises:
 providing a first photo mask defining a first pattern;   exposing the surface of the first layer of photoresist to radiation through the first photo mask;   coating the surface of the first layer of photoresist with a second layer of photoresist;   providing a second photo mask defining a second pattern; and   exposing a surface of the second layer of photoresist to radiation through the second photo mask.   
     
     
         53 . The method for forming a molded structure as in  claim 52 , wherein the first and second photomasks comprise printed transparencies. 
     
     
         54 . The method for forming a molded structure as in  claim 53 , wherein the first and second patterns are designed by a computer assisted design program and are printed onto the transparencies with a high resolution printer. 
     
     
         55 . The method for forming a molded structure as in  claim 52 , further comprising after each of the exposing steps, the step of:
 developing the photoresist layer with a developing agent that selectively removes photoresist material based on whether the photoresist material has been exposed to radiation through the photomask to yield a positive relief pattern in photoresist with topological features corresponding to the pattern of the photo mask.   
     
     
         56 . The method for forming a molded structure as in  claim 52 , further comprising after the second exposing step, the step of:
 developing the first and second photoresist layers with a developing agent that selectively removes photoresist material based on whether the photoresist material has been exposed to radiation through either of the first or second photomasks to yield a positive relief pattern in photoresist with topological features corresponding to the first and second patterns of the first and second photo masks.   
     
     
         57 . The method for forming a molded structure as in  claim 52 , further comprising after the step for providing the second photo mask and before the second exposing step, the step of:
 aligning the second photo mask so that the second pattern has a desired orientation and position with respect to a prior orientation and position of the first pattern of the first photo mask.   
     
     
         58 . The method for forming a molded structure as in  claim 57 , wherein features of the first pattern of the first photo mask correspond to first portions of the at least one two-level topological feature and wherein features of the second pattern of the second photo mask correspond to second portions of the at least one two-level topological feature. 
     
     
         59 . A method for forming a molded structure comprising:
 providing a first mold master having a surface formed of an elastomeric material and including at least one topological feature with at least one cross-sectional dimension not exceeding about 500 μm thereon;   providing a second mold master having a surface including at least one topological feature with at least one cross-sectional dimension not exceeding about 500 μm thereon;   placing a hardenable liquid in contact with the surface of at least one of the first and second mold master;   bringing the surface of the first mold master into at least partial contact with the surface of the second mold master;   hardening the liquid thereby creating a molded replica of the surface of the first mold master and the surface of the second mold master; and   removing the molded replica from at least one of the mold masters.   
     
     
         60 . A method for forming a molded structure comprising:
 providing a first mold master having a surface including at least a first topological feature with at least one cross-sectional dimension not exceeding about 500 μm thereon and at least a second topological feature comprising a first alignment element;   providing a second mold master having a surface including at least a first topological feature with at least one cross-sectional dimension not exceeding about 500 μm thereon and at least a second topological feature comprising a second alignment element having a shape that is matable to the shape of the first alignment element;   placing a hardenable liquid in contact with the surface of at least one of the first and second mold master;   bringing the surface of the first mold master into at least partial contact with the surface of the second mold master;   aligning the first topological features of the first and second mold masters with respect to each other by adjusting a position of the first mold master with respect to a position of the second mold master until the first alignment element matingly engages the second alignment element;   hardening the liquid thereby creating a molded replica of the surface of the first mold master and the surface of the second mold master; and   removing the molded replica from at least one of the mold masters.   
     
     
         61 . The method for forming a microfluidic network structure as in  claim 60 , wherein both of the first and second alignment elements comprise topological features that do not mold, during the hardening step, any features of the final molded structure. 
     
     
         62 . The method for forming a microfluidic network structure as in  claim 60 , wherein the first and second alignment elements comprise topological features that together mold, during the hardening step, at least a portion of at least one feature of the final molded structure. 
     
     
         63 . The method for forming a molded structure as in  claim 60 , wherein at least one of the first mold master and the second mold master is formed of an elastomeric material. 
     
     
         64 . A method for molding an article comprising:
 providing a first mold master having a surface with a first set of surface properties;   providing a second mold master having a surface with a second set of surface properties, wherein the surface of at least the first mold master is formed of an elastomeric material, and wherein at least one of the first and second mold master has a surface including at least one topological feature with at least one cross-sectional dimension not exceeding about 500 μm thereon;   placing a hardenable liquid in contact with the surface of at least one of the first and second mold master;   bringing the surface of the first mold master into at least partial contact with the surface of the second mold master;   hardening the liquid thereby creating a molded replica of the surface of the first mold master and the surface of the second mold master;   separating the masters from each other; and   removing the molded replica from the surface of the first mold master while leaving the molded replica in contact with and supported by the surface of the second mold master.   
     
     
         65 . The method for molding an article as in  claim 64 , wherein the separating step comprises applying a peeling force to at least one of the first and second mold masters. 
     
     
         66 . The method for molding an article as in  claim 64 , wherein the surface of at least one of the first and second mold masters has been silanized. 
     
     
         67 . The method for molding an article as in  claim 64 , wherein the elastomeric material comprises a silicone polymer. 
     
     
         68 . The method for molding an article as in  claim 67 , wherein the silicone polymer comprises poly(dimethylsiloxane). 
     
     
         69 . The method for molding an article as in  claim 68 , wherein the molded replica is formed of poly(dimethylsiloxane). 
     
     
         70 . The method for molding an article as in claim  71 , wherein the surface of the second mold master is formed of a material other than poly(dimethylsiloxane).