Abstract:
A method of forming a polymer-based microfluidic system platform using network building blocks selected from a set of interconnectable network building blocks, such as wire, pins, blocks, and interconnects. The selected building blocks are interconnectably assembled and fixedly positioned in precise positions in a mold cavity of a mold frame to construct a three-dimensional model construction of a microfluidic flow path network preferably having meso-scale dimensions. A hardenable liquid, such as poly (dimethylsiloxane) is then introduced into the mold cavity and hardened to form a platform structure as well as to mold the microfluidic flow path network having channels, reservoirs and ports. Pre-fabricated elbows, T&#39;s and other joints are used to interconnect various building block elements together. After hardening the liquid the building blocks are removed from the platform structure to make available the channels, cavities and ports within the platform structure. Microdevices may be embedded within the cast polymer-based platform, or bonded to the platform structure subsequent to molding, to create an integrated microfluidic system. In this manner, the new microfluidic platform is versatile and capable of quickly generating prototype systems, and could easily be adapted to a manufacturing setting.

Description:
RELATED APPLICATION 
     This application claims priority in provisional application filed on Mar. 26, 2001, entitled “Polymer-Based Platform for Microfluidic Systems” serial No. 60/278,864, by inventor(s) William J. Benett, Peter Krulevitch, Mariam N. Maghribi, Julie Hamilton, Klint A. Rose, and Amy W. Wang. 
    
    
     The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG-46 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to microfluidic systems and methods for fabricating such systems. More particularly, the present invention relates to a polymer-based microfluidic system platform, and a method and system for forming the platform capable of integrating of various microdevices together with microfluidic circuits in a single compact unit. 
     BACKGROUND OF THE INVENTION 
     There is a growing need to develop portable instrumentation for field-based detection and analysis of chemical or biological warfare agents, as well as for medical diagnostics, drug discovery, chemical synthesis, and environmental and industrial monitoring applications. Microfluidic systems incorporating micromachined devices play a key role in these new instruments, combining sample collection, preparation, and analysis all in a compact package, as well as enabling automated operation. More than just miniaturized versions of larger components manufactured using traditional methods, these fluidic devices and systems exploit unique physical phenomena and advantageous scaling laws which occur at the micro-scale, such as laminar flow and surface tension effects. 
     Producing truly integrated microfluidic systems, however, has proven to be a challenge in the past because many of the system components are made from different, incompatible materials, or are too complex to integrate on a single substrate. And while a great deal of work has focused on the fabrication and function of microdevices, such as micropumps, valves, etc., comparatively little has been developed in the packaging of microfluidic systems for the combined operation of such microdevices. The integration of different devices into single compact units thus presents one of the key challenges existing today to realizing robust microfluidic systems which provide highly efficient interfacing between devices or with the external environment. 
     It would therefore be advantageous to have a platform construction using a simple yet effective packaging process and system which enables integration of multiple microfluidic components, such as valves, pumps, filters, reservoirs, mixers, separators, power sources, connectors, electronics, optical elements (e.g. optical fibers, lasers, LEDs, other light sources, filters, and lenses) and sensors, along with microfluidic circuits into single compact units. The platform, system and technique should be flexible enough to address the unique packaging requirements in forming prototype microfluidic systems, but which is also cost-effective to easily adapt to mass production. To this end, the use of pre-fabricated building blocks for assembling the variably complex network configurations would enable rapid prototyping of microfluidic circuits in a wide range of possible configurations. 
     SUMMARY OF THE INVENTION 
     One aspect of the invention includes a method of forming a microfluidic system platform comprising the steps of: providing a mold frame having frame walls surrounding a mold cavity; providing a set of mold forms for use in molding hollow microfluidic features, the set of mold forms comprising elongated mold forms for use in molding microfluidic channels, and block mold forms for use in molding microfluidic cavities; constructing a three-dimensional model construction of a microfluidic flow path network in the mold cavity by interconnecting mold forms selected from the set of mold forms and suspending the model construction in the mold cavity via the frame walls; introducing a hardenable liquid into the mold cavity to immerse the model construction thereby; hardening the liquid to form (1) a platform structure having a shape of the mold cavity and (2) the microfluidic flow path network in the platform structure having a seamless shape of the model construction and including at least two access ports for enabling fluidic communication with the formed microfluidic flow path network; and removing the model construction from the platform structure through the at least two access ports so as to avail the formed microfluidic flow path network. Preferably, the hardenable liquid is a polymeric material, such as an elastomeric silicone polymer such as poly (dimethylsiloxane). 
     Another aspect of the present invention includes a method of forming an integrated microfluidic system comprising the steps of: providing a mold frame having frame walls surrounding a mold cavity; providing a set of mold forms for use in molding hollow microfluidic features, the set of mold forms comprising elongated mold forms for use in molding microfluidic channels, and block mold forms for use in molding microfluidic cavities; constructing a three-dimensional model construction of a microfluidic flow path network in the mold cavity by interconnecting mold forms selected from the set of mold forms and suspending the model construction in the mold cavity via the frame walls; introducing a hardenable liquid into the mold cavity to immerse the model construction thereby; hardening the liquid to form (1) a platform structure having a shape of the mold cavity and (2) the microfluidic flow path network in the platform structure having a seamless shape of the model construction and including at least two access ports for enabling fluidic communication with the formed microfluidic flow path network; removing the model construction from the platform structure through the at least two access ports so as to avail the formed microfluidic flow path network; and connecting a pre-formed microdevice to the platform structure so that fluidic communication is established with the formed microfluidic flow path network via at least one of the at least two access ports of the platform structure. 
     Still another aspect of the present invention is a system for mold-forming a microfluidic system platform, the system comprising: a mold frame having frame walls surrounding a mold cavity; a set of interconnectable mold forms for use in molding hollow microfluidic features, the set of mold forms comprising elongated mold forms for use in molding microfluidic channels, and block mold forms for use in molding microfluidic cavities; and a three-dimensional model construction of a microfluidic flow path network suspended in the mold cavity via the frame walls and comprising releasably interconnected mold forms selected from the set of interconnectable mold forms, wherein, upon introducing and hardening a hardenable liquid in the mold cavity, a platform structure may be mold-formed having a shape of the mold cavity, and the microfluidic flow path network may be mold-formed in the platform structure having a shape of the model construction and having at least two access ports through which the model construction may be removed. 
     Another aspect of the present invention is a microfluidic system platform comprising: a molded structure having a seamless three-dimensional microfluidic flow path network molded therein, the microfluidic flow path network including at least two molded access ports for enabling fluidic communication with the microfluidic flow path network. 
     And another aspect of the present invention is an integrated microfluidic system comprising: a molded structure having a seamless three-dimensional microfluidic flow path network molded therein, the microfluidic flow path network including at least two molded access ports for enabling fluidic communication with the microfluidic flow path network; and at least one pre-formed microdevice externally connected to the molded structure to establish fluidic communication with the microfluidic flow path network through at least one of the access ports. 
     One advantage of the microfluidic system platform of the present invention is that it can integrate many functions into one system, including pumping, mixing, diluting, separating, filtering, sensing, etc. In this way, sample processing and analysis can be performed on just one chip/module, which were formerly performed as separate functions on different modules so that the analysis took much more time. This significantly overcomes the difficulty of connecting multiple components and feeding a sample fluid efficiently from component to component. Additionally, further advantages of the present invention&#39;s hybrid method to integrating microdevices into systems include: incorporates and uses optimized custom and off-the-shelf components; improves device yields; facilitates maintenance; and makes it possible to isolate disposables from more expensive, reusable system components, thus reducing operations costs. The present invention also enables rapid prototyping and/or commercial mass-production. These advantages of the present invention add value to the general advantages of miniaturization and integration, such as reduction in the use of expensive chemical reagents to a minimum, minimal test sample volume requirements, and ability to maintain system calibration and produce a constant flow of accurate measuring-data without being affected by external influences such as temperature or aging. In this way, hand-held or palm-top chemical/biological laboratories can be built for portability. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated into and form a part of the disclosure, are as follows: 
         FIG. 1  is an exploded view of an exemplary mold frame of the present invention; 
         FIG. 2  is a perspective view of four exemplary mold forms used in constructing the model construction of the microfluidic flow path network; 
         FIG. 3A  is a cross-sectional view taken along line  3 A of  FIG. 2 , illustrating the exemplary interconnection feature of a cylindrical mold form; 
         FIG. 3B  is a cross-sectional view taken along line  3 B of  FIG. 2 , illustrating the exemplary hollow core of the connector pin mold form. 
         FIG. 4  is a perspective view of a mold frame with the cover plate wall removed, illustrating a model construction of an exemplary microfluidic flow path network. 
         FIG. 5  is a perspective view of an exemplary molded platform structure molded from the model construction of  FIG. 4 . 
         FIG. 6  is a perspective view of two exemplary interconnect mold forms having T and L-shape configurations. 
         FIG. 7  is a cross-sectional view of an exemplary mounting and interconnection of a mold form in the mold cavity. 
         FIG. 8  is a perspective view of an exemplary base wall having micro-scale topographic features. 
         FIG. 9  is a cross-sectional view of an illustrative model construction arrangement in surface-to-surface contact with the micro-scale topographic features of  FIG. 8 . 
         FIG. 10  is a cross-sectional view of a molded platform structure formed from the model construction of  FIG. 9 . 
         FIG. 11  is a cross-section view following  FIG. 10  subsequent to the bonding of a substrate cover to enclose the micro-scale cavities and thereby form a micro-scale microfluidic flow path network. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is directed to methods of forming polymer-based microfluidic system platform structures and integrated microfluidic systems utilizing such platform structures. As used herein and in the claims, the term “microfluidic system,” as well as “microfluidic network” and “microfluidic flow path network,” generally refer to both micro-scale fluidic systems (micron range dimensions), and meso-scale fluidic systems (greater than micron range dimensions). It is appreciated that in both micro- and meso-scales, fluid volumes transferred through microfluidic systems are typically in the order of microliters to milliliters. Furthermore, meso-scale is understood to be the intermediate level between macro and micro-scales. Thus meso-scale features serve as an interface between macro and micro mediums to enable direct exchange and interaction with a user, e.g. receiving fluid samples via pipette. 
     The polymer-based microfluidic system platform of the present invention serves two main functions: (1) as an integrated platform for incorporating and packaging microdevices and components, such as commercially-available micro-pumps and valves, sensors, mixers, separators, glass and silicon microfluidic chips, PC boards and electronics including integrated circuit ships, and optical elements (e.g. optical fibers, lasers, LEDs, other light sources, filters, and lenses), along with microfluidic circuits (e.g. flow channels and reservoirs) into a single compact unit, and (2) as an interface between macro and micro-scale mediums to provide integrally formed channels and volumes preferably having meso-scale dimensions for handling relatively large volumes of test sample fluid for subsequent channeling into smaller micro-scale processing and analyzing regions and/or components. In regards to the integration function, it is notable that the method of the present invention serves to hybrid integrate various microdevices without compromising functionality of any of the microdevices. In contrast, device functionality is often compromised in monolithically integrated microfluidic systems. Hybrid integration strategies such as that of the present invention are more flexible and allow for optimization and testing of the various components before integration. 
     Additionally, the method and system of the present invention enables the rapid prototyping of an essentially infinite number of possible microfluidic circuits and systems. Rapid formation is possible due to the use of pre-fabricated building blocks or mold forms in constructing a model construction representing the desired configuration of microfluidic flow path network. Various microfluidic and electronic chips and other components can also be directly incorporated to the formed platform to produce complete microfluidic systems. Furthermore, rapid formation is possible due to the complete and seamless formation of the entire microfluidic flow path network in a single molding step without the need for further steps, such as the sandwiching of two cavity halves. The method and system of the present invention enables the rapid prototyping fabrication of microfluidic systems having various complexities including various size ranges due to the simple interconnecting assembly of the component building blocks, and provisions for their easy removal from the molded platform structure. 
     Generally, the microfluidic system platform is mold-formed in a casting process involving a mold frame having a mold cavity, and a model construction assembled in the mold cavity representing a desired configuration of a microfluidic flow path network. The term “microfluidic flow path network” is used herein and in the claims to define a continuous network of hollow cavities and channels formed within a single platform structure and having a seamless shape of the model construction. The model construction is assembled utilizing mold forms selected from a set of pre-formed interconnectable mold forms having various network shapes. Upon introducing and hardening a molding liquid, a platform structure is formed having the microfluidic flow path network mold-formed therein with such hollow network features as microfluidic channels and reservoirs. The resulting platform structure can be completely self-contained, or can interface to external components such as electronics, power sources, and detection instrumentation. 
     Turning now to the drawings,  FIGS. 1 and 4  show an exemplary mold frame, generally indicated at reference character  10 , used to fabricate a microfluidic system platform, such as the exemplary platform structure  37  in  FIG. 5 . The mold frame  10  generally has a three-dimensional construction comprising frame walls surrounding a mold cavity ( 15  in  FIG. 4 ). The frame walls shown in  FIG. 1  include sidewalls  11  (four shown), a lower wall or base  13  and an upper wall or cover  12 . The shape of the mold cavity  15  is determined by the particular arrangement of the frame walls surrounding the mold cavity  15 . It is appreciated that while the mold frame  10  is shown in  FIG. 1  as an assembly of three component parts, alternative structures and configurations may be utilized, such as where the base  13  and the sidewalls  11  are integrally joined, with only the cover  12  being removable. In certain embodiments, the mold cavity  15  may be completely enclosed by the frame walls. For such embodiments, two ports (not shown) may be used to fill the mold cavity: a fill port and a vent port. Upon injecting a molding liquid into the fill port, air escapes through the vent port. Preferably the frame walls have throughbores  14  which are bored, mold-formed, or otherwise produced thereon to communicate with the mold cavity  15 . The throughbores  14  may be pre-formed in a generic pattern, or custom formed for a pre-determined network configuration. In any event, it is appreciated that the throughbores  14  are not limited to any pattern or location on the frame walls. And the mold frame  10  may be constructed from any rigid material composition, e.g. a polymeric material such as acrylic, which is non-reactive with the types of molding liquids used in the present invention. 
       FIG. 2  shows an exemplary set of pre-fabricated building blocks or mold forms for use in constructing a model construction (such as  31  in  FIG. 4 ) outlining and spatially representing a desired microfluidic flow path network (such as  32  in  FIG. 5 ). The set of available mold forms serves to mold hollow microfluidic features having particular shapes, and generally include at least elongated mold forms and block mold forms. The elongated mold forms, e.g.  17  and  18 , are for use in molding microfluidic channels, and the block mold forms are for use in molding microfluidic cavities. For example, a wire mold form  17 , having an elongated narrow construction, is provided for use in molding a microfluidic channel. It is notable however that other elongated mold forms may be utilized to form microfluidic channels, such as tubing. 
     A connector pin  18  is also provided having a configuration used to position and fixedly secure the wire mold form  17  to the mold frame  10 . As shown in  FIG. 3B , a cross-sectional view of the connector pin  18  is shown, with the connector pin  18  having a head portion  19 , a middle shank portion  20  and a leading end portion  21 . Additionally, a hollow core  22  extends through the connector pin  18  from the head to the leading end  21 . The hollow core  22  is dimensioned to extend a wire mold form  17  or tubing therethrough in a close-tolerance manner such as to prevent leakage of a molding fluid therebetween. It is notable that plastic tubing has been evidenced to form a better seal with the hollow pin. As shown in  FIG. 4 , the middle shank portion  20  of the connector pin  18  is dimensioned to be seated in the throughbores  14  of the mold frame  10  also in a close-tolerance manner. The connector pin  18  serves to position and align the wire mold form  17  within the mold cavity  15 . It is notable that variations of the connector pin  18  are possible, such at the connector pin  50  shown in  FIG. 9  having a leading end with a conical tip to form a seal when pressed to contact a surface. It is also notable that the wire or otherwise elongated mold forms need not be linear; bending of the elongated mold forms to a curvilinear or angular shape can produce molded microchannels having configurations of even greater complexity. 
     Block mold forms also comprise the set of available mold forms, and are used to mold cavities and volumes. In  FIG. 2 , two illustrative embodiments of the block mold form are provided: a cylindrical block mold form  23 , and a rectangular block mold form  24 . Each of the block mold forms  23 ,  24  preferably have a threaded bore or bores  25  used for fixedly mounting and immobilizing the block mold form to the mold frame  10 . As shown in  FIGS. 7 and 9 , mounting screws  30  may be engaged in the threaded bores  25  to secure the block mold form, e.g.  23 , in the mold cavity  15 . Furthermore, the mounting screws  30  may also serve to produce surface-to-surface contact between a face of the block mold form with an inner surface  16  of the frame walls. The block mold forms may additionally have connector holes  26  for interconnectably seating an end of a wire mold form  17  (see  FIG. 7 ), such that the wire mold form may be removed at a later time. It is appreciated, however, that the interconnection of mold forms may be achieved by other suitable means, such that in any case, continuity is preserved between the later mold-formed hollow features to allow fluidic communication therebetween. 
     Interconnect mold forms, such as  27 ,  28  shown in  FIG. 6 , may additionally be provided in the set of mold forms available for constructing the model construction of a microfluidic flow path network. The interconnect mold forms preferably have a hollow configuration, with connector ports  29  enabling access to the hollow core. For each interconnect mold form, at least two connector ports  29  are provided which are in fluidic communication with each other. In  FIG. 6 , interconnect mold forms having T and L-shaped configurations are shown, indicated at reference characters  27  and  28 , respectively. It is appreciated, however, that other suitable two- or three-dimensional shapes and configurations may be employed to produce complex three-dimensional network configurations. The interconnect mold forms may be fabricated from any suitable rigid or semi-rigid material, such as a polymer, capable of insertably receiving a wire mold form. Preferably, however, the interconnect mold forms are pre-formed from the same material as that used for molding the platform structure. In a preferred embodiment, the material composition is a polymeric material. Moreover, an elastomeric silicone polymer such as poly (dimethylsiloxane), herein after “PDMS,” is preferably utilized. In any case, the interconnect mold forms are preferably used in conjunction with the elongated mold forms, such as the wire mold form  17 . In particular, the interconnect mold forms are configured to snugly receive the ends of one or more wire mold forms  17  in a manner supporting removal at a later time. It is notable that the interconnect mold forms are preferably not removed from the final structure, instead remaining embedded in the platform structure. In contrast, the connector pins  18  and the block mold forms are in most cases removed, as will be discussed in detail below. 
     In  FIG. 4 , an assembled model construction  31  is shown suspended in the mold cavity  15  via the frame walls. The assembly  31  has connector pins  18  insertably positioned in throughbores  14  to thereby position and extend wire mold forms  17  in the mold cavity  15 . And interconnect mold forms  27 ,  28  are further used to interconnect and position the wire mold forms  17  in various directions. Three cylindrical block mold forms  23  are also shown interconnected with wire mold forms  17 . While the model construction  31  shown in  FIG. 4  is suspended only from the four frame sidewalls  11 , it is appreciated that the base wall  13  and opposing cover or top wall ( 12  in  FIG. 1 ) may also be employed to extend additional mold forms therefrom and into the mold cavity  15 . The connector pins  18  are seated in the throughbores  14  such that they may be removed in an outward direction subsequent to molding. Additionally, the wire mold forms  17  extending through the connector pins  18  may also be removed through the throughbores  14 . As shown in  FIG. 4 , the wire mold forms  17  and the cylindrical mold forms  23  are suspended in the mold cavity  15 , with only the connector pins  18  contacting the mold frame  10 . However, as can be seen in  FIG. 7 , block mold forms, such as cylindrical mold form  23  may also contact and be directly secured to the frame walls. It is notable that the mounting screw  30  may be used to either push away or draw in the cylindrical mold form  23  into pressing surface-to-surface contact with one of a pair of opposing inner surfaces. A mounting screw  30  is used in  FIG. 7  to draw in the cylindrical mold form  23  so as to press an upper surface of the cylindrical mold form into surface-to-surface contact with an upper inner surface  16  of a frame wall. While not shown in the drawings, the assembly of the model construction  31  may additionally include the interconnection of pre-formed microdevices to the model construction  31  within the mold cavity  15  prior to molding. Such pre-mold interconnection of a microdevice serves to embed the microdevice in the resulting molded platform, and, upon removing the model construction from the molded platform, the microdevice is in fluidic communication with the microfluidic flow path network. 
     In this manner, the model construction  31  is constructed having a configuration associated with and spatially demarcating the microfluidic flow path network  32  shown in broken lines in  FIG. 5 . The model construction  31  shown in  FIGS. 4 and 5  illustrate an exemplary construction of a simple mixing system, where two fluid types are separately deposited into the platform  37  for mixing. It is appreciated, however, that many other assemblies may be constructed for performing different functions for different applications. Common to all model constructions, however, is the creation of a three-dimensional configuration utilizing any number and combination of mold forms. It is appreciated that the three-dimensional configurations which are possible with the present invention include the non-intersecting overlap of two or more orthogonal channels at different levels, i.e. having channels which cross over or under other channels without physical intersection at the points of cross over. 
     Once the mold construction  31  is constructed and suspended in the mold cavity  15 , a hardenable liquid is introduced into the mold cavity  15  to immerse the mold construction  31 . The hardenable liquid may be poured into the mold cavity  15  through an open end of an open mold frame, or as discussed previously, injected into an enclosed mold cavity via an inlet port and a vent port (not shown). The hardenable liquid used for molding may comprise essentially any liquid that can be solidified into a solid capable of containing and transporting fluids in a microfluidic flow path network. In a preferred embodiment, the hardenable liquid comprises a polymeric or polymer-containing material, hereinafter “polymeric material”. And preferably still, the polymeric material is an elastomeric silicone polymer, such as PDMS. Silicone polymers, for example poly (dimethylsiloxane) or PDMS, are especially preferred because they may be cured with heat, such as by exposure of the polymeric liquid to temperatures of about 65 degrees Celsius to about 75 degrees Celsius for exposure times of about, for example, 1 hour. PDMS is a silicone rubber that can be spun onto a substrate or poured into a mold while in its liquid precursor state. Micron-scale features patterned on the mold may be replicated in the cured PDMS. Additionally, room temperature bonding to silicon, glass, or other PDMS substrates can be achieved simply by oxidizing the surface in an O 2  plasma and pressing the two substrates together. These techniques may be employed to create sealed microchannels, which have been previously fabricated for such applications as electro-phoretic separation and cell cytometry. 
     In any case, the introduction of PDMS or other molding liquid serves to completely immerse the model construction  31 , such that all exposed surfaces of the model construction is contacted by the molding liquid. Introduction of the hardenable liquid also serves to fill the mold cavity  15  such that the liquid is molded in the shape of the mold cavity. It is important that the model construction  31  be completely immersed in the liquid such that all exposed surfaces of the model construction are in contact with the liquid. Non-exposed surfaces of the model construction  31 , however, are excepted from liquid contact so that access ports, such as  34 ,  34 ′ in  FIG. 5 , may be formed allowing entry into the formed microfluidic flow path network. The non-exposed surfaces include those surfaces in contact with the mold frame. As shown in  FIG. 7 , the contact may be along a surface-to-surface contact area  16 ′ between a block mold form  23  and an inner surface  16  of one of the frame walls. Additionally, non-exposed surfaces also include those surfaces of mold forms, for example the connector pins  18 , which are seated in the throughbores  14  of the mold frame  10 . 
     After introducing the hardenable liquid into the mold cavity  15 , the liquid is hardened as discussed above to produce a platform structure, such as the platform structure  37  shown in  FIG. 5  having a shape of the mold cavity  15 . Additionally, hardening the liquid mold-forms the microfluidic flow path network  32  within the platform structure  37 , with the microfluidic flow path network  32  having a seamless shape patterned after the model construction. It is appreciated that the seamless shape of the microfluidic flow path network is formed in a single molding step such that the microfluidic flow path network is a unitary whole encased by the monolithic configuration of the platform structure. Furthermore, the microfluidic flow path network  32  includes at least two access ports, each enabling fluidic communication with the microfluidic flow path network from beyond the platform structure. In  FIG. 5 , six access ports  34 ,  34 ′ are shown which were formed from the non-exposed contact surfaces between the mold forms and the frame walls. In particular, the access ports  34 ,  34 ′ in  FIG. 5  were formed due to the seating of the connector pins  18  through the throughbores  14  of the mold frame  10  in  FIG. 4 . It is notable that the seating arrangement of the connector ports  18  in the throughbores  14  serve also to align the formed access ports with throughbores  14 , such that some of the mold forms of the model construction may be removed through the throughbore subsequent to final formation. 
     Next, the model construction  31  is removed from the platform structure  37  to avail the interconnected cavities, channels, ports, etc. of the microfluidic flow path network  32  shown in  FIG. 5 . Removal of the mold forms is typically by disassembling the mold forms and removing at least some of them through the access ports  34 ,  34 ′. It is notable that the removal of block mold forms which are in surface-to-surface contact with an inner surface  16  of the mold frame  10  requires the initial removable of one of the frame walls from the mold frame  10 . As can be seen in  FIGS. 4 and 5 , the removable of mold forms through the access ports  34 ,  34 ′ may cause inevitable circuit breaches in the platform structure which were necessary for suspending the model construction in the mold cavity. These extra access ports are occluded to enclose the microfluidic system and circuit. As shown in  FIG. 5 , the hollow channels  17 ′ and the access ports  34 ′ on opposite ends of the platform must be sealably filled. The remaining access ports  34 , however, are used to access the microfluidic flow path network. It is notable that removal of the model construction is typically through the throughbores of the mold frame, and therefore prior to removing the molded platform structure from the mold frame. However, it is appreciated that other means for suspending the model construction in the mold cavity may support removal of the platform structure prior to removal of the model construction therefrom. It is also notable that not all mold forms used to construct the model construction is to be removed. Preferably, the interconnect mold forms are left embedded in the platform structure, but both the connector pins  18  and the block mold forms  23  are removed. 
     The microfluidic system platform, such as  37  in  FIG. 5 , created in this manner will have a seamless microfluidic flow path network integrally formed within the platform structure. Furthermore, the network will have at least two access ports to enable fluidic communication with the flow path network. At least two access ports is necessary to enable fluidic transport into and out of the formed platform. And due to the suspension of the model construction in the mold cavity, the model construction is completely encased by the hardened liquid after molding. Thus, the fluid flow path network will have a seamless configuration with at least one channel having a closed cross-section encased by the molded platform structure. 
     Subsequent to the removal of the model construction from the molded platform structure  37 , a microdevice may be further integrated with the platform structure  37  to produce a hybrid integrated microfluidic system for combined operation in a single compact unit. The term “microdevice”, is used herein and in the claims as a pre-formed discrete device or component for performing a specific function in a microsystem, with many of the microdevices being commercially available. Thus, the term “microdevice” includes but is not limited to valves, pumps, filters, reservoirs, mixers, separators, power sources, connectors, electronics, optical elements (e.g. optical fibers, lasers, LEDs, other light sources, filters, and lenses) and sensors. It is also notable that microdevices comprise fluidic devices, such as micropumps and valves, as well as non-fluidic devices, such as optical or electrical devices (e.g. optical fibers, detectors, filters, integrated circuits, etc.) And the term “hybrid integration” is used herein to define the combination of these pre-formed without modifying or otherwise compromising functionality thereof. 
     Pre-formed microdevices may be connected to the platform structure to establish fluidic communication with the microfluidic flow path network via the access ports. The manner of connection may be by direct bonding of the microdevice to the platform structure, such as by oxidation bonding as discussed above. In this case, an enlarged docking cavity (not shown) may be molded into the platform structure to bond the microdevice therein so that fluidic communication is established with at least one access port. Alternatively, at least one of the access ports may be a docking port  34  enabling docking connection with pre-formed microdevices, such as the micropumps  41  and  42  in  FIG. 5 . The docking ports  34  are adapted to captively seat the microdevice therein. The use of PDMS for modeling the platform structure enables snug friction-fit seating and docking of external devices, due primarily to its elastomeric composition and properties. It is appreciated that the formation of the access ports and/or docking ports is carried out for connection with a particular type of microdevice. It is also notable that the microdevice(s) are preferably removably connected to the platform structure, such that the microdevice may be plugged into and out of a docking port. The elastomeric properties of the preferred PDMS composition of the platform structure enable captive seating of a microdevice, such as, for example the micropumps  41 ,  42  in  FIG. 5 . In this manner, worn, damaged or single-use microdevices may be easily replaced without discarding the platform structure and other microdevices also connected thereto. 
     In another embodiment of the present invention, the formed platform structure may comprise both meso-scale features and micro-scale features, with the meso-scale features interfacing macro and micro-scale mediums. As shown in  FIG. 8 , a base wall  13  has an inner surface  16  having micro-scale topographical features  43 ,  44 ,  45  formed thereon, typically by a conventional process such as by photolithography. The exemplary micro-scale topographic features shown in  FIG. 8  include a positively-relieved microchannel mold form  43  having micro-scale dimensions, e.g. between about 1-100 microns width and height. The microchannel mold form  43  is shown integrally connected to a first raised surface  44  and a second raised surface  45 . Preferably, the raised surfaces  44  and  45  have a footprint the same or similar to in area as a corresponding meso-scale mold form used in the construction of a meso-scale model construction. Meso-scale features are mold-formed into the platform structure by utilizing meso-scale mold forms selected from a set of meso-scale mold forms. Meso-scale mold forms provided in the set of interconnectable mold forms have larger dimensions than the micro-scale features, typically in the range of 1-10 mm diameters. As shown in  FIG. 9 , a meso-scale cylindrical block mold form  23  is placed in contact with the first raised surface  44  along a contact area  46 . Additionally, a connector pin  50  having a threaded shank portion and a preferably smooth leading end portion is threadedly secured to the cover  12  of the mold frame and pressed against the second raised surface  45 . As can be seen in  FIG. 9 , the connector pin  50  has a conical tip which is in flush mating contact with a conical cavity  47  formed on the second raised surface  45 . The mating contact serves to produce sealed contact between the connector pin  50  and the second raised surface  45 . Upon introducing PDMS or other molding liquid into the mold cavity  15  and hardening or otherwise solidifying the PDMS, a molded platform structure  37  is formed, shown in  FIG. 10 , having the meso-scale features, such as the reservoir  47 , in fluidic communication with the formed microchannel  48  formed from the micro-scale microchannel mold form  43 . As can be seen in  FIG. 10 , the microchannel  48  is formed along one surface of the resulting platform structure  37 . 
     Various microfluidic platform structures formed according to the present invention may be formed for subsequent bonding with other platform structures to form larger microfluidic systems. Each platform structure may comprise a complete, self-contained system, or serve to accomplish a specific function of a larger fluidic system. In the case of specialized modules, alignment of the various platforms structures is required so as to establish fluidic communication between respective access ports. This may be accomplished using alignment features molded into the platforms using alignment mold forms provided in the set of mold forms. Such alignment mold forms are typically not used in conjunction with other selected mold forms for construction the model construction. Exemplary alignment features, e.g. cavities  36 , are shown in FIG.  1 , such that protrusions from a second platform structure (not shown may be matably inserted therein in stacking combination. 
     While particular operational sequences, materials, temperatures, parameters, and particular embodiments have been described and or illustrated, such are not intended to be limiting. Modifications and changes may become apparent to those skilled in the art, and it is intended that the invention be limited only by the scope of the appended claims.