Abstract:
The various embodiments described herein relate to fabricating and using open microfluidic networks according to methods, systems, and devices that can be used in applications ranging from home-testing, diagnosis, and research laboratories. Open microfluidic networks allow the input, handling, and extraction of fluids or components of the fluid into or out of the open microfluidic network. Fluids can be inserted into an open microfluidic channel by using open sections of the open microfluidic network. Passive valves can be created in the microfluidic network, allowing the creation of logic circuits and conditional flow and volume valves. The fluid can be presented via the microfluidic network to diagnostic and analysis components. Fluids and components of the fluid can be extracted from the open microfluidic network via functional open sections that are easily interfaced with other microfluidic networks or common laboratory tools.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority from U.S. Provisional Application 61/674,415, filed Jul. 23, 2012, and entitled “Methods, Systems, and Devices Relating to Open Microfluidic Channels,” which is hereby incorporated herein by reference in its entirety. 
     
    
     FIELD 
       [0002]    The present technology relates to various methods, systems, and devices regarding fluid handling for medical devices, and in particular, interfacing bodily fluids with a microfluidic network and the subsequent handling of the fluid in order to direct it towards diagnostic sensing or biomarker analysis components. 
       BACKGROUND 
       [0003]    An open microchannel is defined as a microfluidic channel whose cross-section is composed of solid walls as well as at least one section with open liquid-air interface. Open microchannels present advantageous properties linked to their reliability, function, and manufacturability. Open microchannels solve a problem related to air bubbles, as the gas can escape through the open face of the channel, thus creating a device that is more reliable in comparison to traditional closed channel setups. However, prior to the inventions described herein, flow in open microfluidic channels was not well understood, and the few existing methods demonstrated until now have had limited functionality, namely transporting fluid for a short distance in a straight line, as described in the filed patents Ser. Nos. 11/470,021 and 09/943,080. A second problem in existing technology relating to open microfluidic channels was the lack of ability to control the flow of fluid, thus preventing the creation of advanced fluid handling platforms designed entirely or in large part based on that technology. Thirdly, there was, prior to the inventions described herein, a lack of tools allowing for the insertion of fluid into, or removal of fluid from, the open channel. All of the known methods relied on dipping a single device into the liquid of interest in order to sample a small amount, rather than having the ability to create networks in which fluid can be inserted at precise locations and at different times. Further, no known method prior to the inventions described herein provides for the removal of fluid from these channels. Thus, there is a need in the art for improved open microfluidic channels and related systems, devices, and methods. 
       SUMMARY 
       [0004]    The basis of this invention is centered around the benefits in the manufacturing of shallow open microchannels, as this can be performed in one single molding or embossing step as it does not require bonding to enclose the channel, enabling large scale manufacturing of complex networks at low costs. These advantages make open microchannel networks particularly well suited for disposable diagnostic devices for which fluids require precise handling with low manufacturing costs. This document describes a set of methods and embodiments that facilitate new methods for handling fluid or bodily samples and enable the interfacing with microfluidic networks in new ways. The preferred embodiment of the approaches described is for use in medical devices, at-home diagnostic devices, and laboratory analysis platforms. 
         [0005]    The ability to create flow in open microfluidic channels is a required condition for creating functional open microfluidic networks. As open microfluidic channels contain open liquid-air interfaces, pressure sources are not the preferred method to drive fluid flow; rather spontaneous capillary flow offers a reliable, scalable driving force for fluid flow. The use of capillary-driven flow to manipulate fluids in complex open microfluidic networks is a novel feature previously unused in open microfluidic channels. In order to insure that spontaneous capillary flow (SCF) occur in a channel containing any number of open liquid-air interfaces in its cross-section, an analysis of capillary force was developed, to define a design guideline ensuring that the capillary force provided by the walls of the microfluidic channel overcomes the resistance created by the open sections of the microfluidic channel. The result of the analysis is written in a SCF relation stating that the ratio of the free perimeter (p f ), defined by the length of the cross-section open to air or another medium, and the wetted perimeter (p w ), defined by the length of the cross-section made up of solid hydrophilic material must be less than the cosine of the contact angle (θ) of the fluid with the channel walls. When the SCF relation is satisfied, the channel will drive the flow through the microfluidic network by capillary forces. Importantly, the SCF relation extends to most channel configurations containing open liquid-air and wetted sections. Further, the open liquid-air sections do not have to be continuous or contiguous. Thus the SCF relation still holds for complex channel geometries containing open “windows” on the channel (e.g. a circular aperture in the wall of a channel) as well channels containing multiple open liquid-air interfaces at the same point in the channel (e.g. a fluid completely suspended between two rails in a channel devoid of ceiling and floor). Open microfluidic channels verifying the SCF relation also have the benefit of not being constrained to rectangular cross-sections. The SCF relation can be written in equation (1): 
         [0000]        p   j   /p   v &lt;cos(0)  (1)
 
         [0006]    Equation (1) represents the fundamental physical background for the development of the building blocks for the handling of fluids in open microfluidic networks described in the patent following. Importantly, open microfluidic methods eliminate the problem inherent in microfluidics of bubble formation being catastrophic within a microchannel, and enable simplified manufacturing due to no required bonding to seal the channel. We have developed fluid manipulation techniques based on open channel concepts, which are the building blocks to create a microfluidic fluid handling network amenable to human bodily fluid collection and analysis. The two aspects covered by this invention pertain to (1) handling fluid into and out of the microfluidic network and (2) handling techniques within the microfluidic network. The development of an analytical model for describing conditions of flow in open microfluidic channels has lead to the establishment of an equation detailing the geometrical conditions for flow in open microfluidic networks and precise design guidelines that enable a dramatic expansion of the functionalities of open microfluidic systems. One of the enabling aspects of such a development is the ability to flow fluids in shallow open microfluidic grooves, open microfluidic grooves with non-rectangular cross-sections, non-planar and angled open microfluidic grooves, as well as open microfluidic systems with more than one open interface (e.g. no channel ceiling nor floor). 
         [0007]    The open microfluidic handling methods developed enable novel mechanisms to bring fluid into and out of the microfluidic network, and can incorporate methods including extracting fluid from a pool or droplet on a surface, such as human skin, from a reservoir, or from another open microfluidic channel. The design rules developed, made explicit by the SCF relation described in equation (1), allow the creation of open capillary networks amenable to capturing blood pooling on the surface of the skin (as is the case for many diagnostic applications) and transferring it into an open fluidic network. Additionally, it enables the design of open interconnection features allowing the transfer of fluids from one open microfluidic network to another. The possibility of extracting and exchanging fluids from one open microfluidic channel to another enables the use of open microfluidic devices to create complex assays by assembling pre-fabricated standard building blocks or by leveraging  3 D geometries simply by placing one open microfluidic network on top of another, while allowing fluidic contacts from one network to the other. Importantly, these methods can operate regardless of air bubble formation, as there is at least one open liquid-air interface present in the channel, such as in a channel with a U-shaped cross-section containing no ceiling atop the microfluidic channel. Further, open microfluidic networks can leverage the open interface area to insert immiscible fluids or gases to sever the fluid present in the channel in two sections. The ability of separating fluids in sections allows the creation of user actuated open microfluidic valves that are the basis of advanced control over fluid flows in open microfluidic networks. 
         [0008]    Shallow open microfluidic methods also enable the creation of fluidic networks that can be readily interfaces with traditional pipetting systems in order to perform robotic interfacing with the microfluidic network. The design guidelines developed also enable the creation of microfluidic grooves that have the ability to drive the flow of fluid using only a subset of the walls of the channel and not the totality of the walls of the channel, such that the flow can be propelled around edges that would usually cause pinning. The flow pas pinning edges and lines further enables the creation of non-planar channels that flow around concave and convex angles, or onto a new plane branching off of the main microfluidic channel. The design rules developed also allow the capillary flow of a fluid over heterogeneous patches on the wall or floor of the microfluidic groove. Such patches can include absorbent pads for capture of blood, reaction sites for detection of blood analytes, translucent materials for optical analysis of the blood, or open apertures for physical access to the blood in the microfluidic groove. Particularly, open apertures can be used to add or remove substance from the channel, connected to a substance-specific removal area (e.g. an organic solvent for chemical extraction, antibody-laden hydrogel for detection, magnet for magnetic bead removal), or a large, set volume opening for contact with another open fluid or extraction method. 
         [0009]    The other important aspects of the open microfluidic handling methods pertain to handling techniques of fluid within the microfluidic network. Because a specific set of design constraints can be used to create flow within a microfluidic network, they can also be leveraged to create unique functionality within the open microfluidic network that otherwise could not be achieved with closed microfluidic systems or other open microfluidic systems. The first general method enabled by open microfluidic systems pertain to the unique ability to pin a fluid in a channel devoid of a ceiling. The design guideline provides precise geometrical rules for describing the conditions of flow in an open microfluidic channel, and by corollary the conditions for which flow cannot occur in an open microfluidic groove. Thus a channel can be designed such that at a certain location the conditions for flow are conditionally met based on a user-actuated system. The second general set of methods pertains to manipulating the channel walls or creating unique flow environments within the open microfluidic network. These methods can include flowing the fluid over an aperture in the floor of the channel such that the fluid does not pin at this surface, placing a dried substance on the walls of the channel such that a fluid flows therein and incorporates the substance into the fluid, creating a mechanism for capillary pulling of fluid from one of the open channel to the other, directing fluid to multiple planes at any angle, or a mechanism for allowing asynchronous fluids from various channels to incorporate into a larger channel or chamber without air bubble formation or dissipation. The latter method is enabled by the open microfluidic environment as two fluids present in the channel at any location will not provoke the entrapment of an air bubble, as gas will be able to escape through the open liquid-air section, thus the two fluids coming from either input channel in the branching area can merge without risking catastrophic failure of the microfluidic system. Additionally, the open microfluidic approach enables the connection of multiple networks together without risking the entrapment of air bubbles that prevent further use of the microfluidic network. 
         [0010]    All of these methods can be used to create complex fluidic networks that could be useful in a variety of applications, either in simple point-of-care devices (incorporating a dried or lyophilized sample into the channel, combining multiple channels to a central location) or for more complex fluid networks, which can be interfaced with liquid handling systems. Open networks are enabling for the reliability of these complex fluid networks, and further enhance the ability to fabricate channels in high throughput, as no bonding is necessary to complete device fabrication. 
         [0011]    Certain examples shall now be described. 
         [0012]    In Example 1, a microfluidic device comprises a first microscaled channel configured to allow flow of fluids by capillary action, wherein the channel has at least one portion of the channel comprising a first cross-section. The first cross-section comprises a wetted surface comprising hydrophilic material and a free interface comprising an open air-liquid interface. The wetted surface contacts fluid flowing through the channel. The ratio of a cross-sectional length of the free interface and a cross-sectional length of the wetted surface is less than the cosine of the contact angle, thereby permitting spontaneous capillary flow. 
         [0013]    Example 2 relates to the microfluidic device according to Example 1, wherein the first cross-section further comprises at least two wetted surfaces, and an interface with a high contact angle, a hydrophobic area, or a second free liquid-air interface. 
         [0014]    Example 3 relates to the microfluidic device according to Example 2, wherein the first cross-section comprises a rectangular or trapezoidal shape, wherein the free interface comprises a first free interface defined in a top portion of the first cross-section and a second free interface defined in a bottom portion of the first cross-section. 
         [0015]    Example 4 relates to the microfluidic device according to Example 1, wherein the free interface is defined in a bottom portion of the device such that the free interface can be brought into contact with a volume of fluid pooling on a surface, thereby causing capture of at least a portion of the volume and flow of the volume into the groove. 
         [0016]    Example 5 relates to the microfluidic device according to Example 1, wherein the first microscale channel further comprises a second free interface comprising an open air-liquid interface or an insert of optically transparent material, wherein the first channel is configured to allow flow of fluid over the second free interface, and wherein the second free interface defines a light path configured to allow light to strike the fluid in the groove in order to perform a fluorescence or spectrometry analysis of the fluid. 
         [0017]    Example 6 relates to the microfluidic device according to Example 1, wherein the open air-liquid interface is configured to provide access for the removal of a fluid sample from the channel or any component of that fluid sample. 
         [0018]    Example 7 relates to the microfluidic device according to Example 6, wherein the open air-liquid interface is configured to receive a second capillary channel, thereby allowing the fluid flow into a second fluidic network. 
         [0019]    Example 8 relates to the microfluidic device according to Example 1, wherein the first channel further comprises a second cross-section that comprises a first configuration and a second configuration. The first configuration has a ratio of a cross-sectional length of a free interface and a cross-sectional length of a wetted surface that is greater than the cosine of the contact angle, thereby preventing spontaneous capillary flow. The second configuration has a ratio of the cross-sectional length of the free interface and a cross-sectional length of the wetted surface that is less than the cosine of the contact angle. 
         [0020]    Example 9 relates to the microfluidic device according to Example 8, further comprising a conversion mechanism configured to convert the second cross-section from the first configuration to the second configuration and from the second configuration to the first configuration. 
         [0021]    Example 10 relates to the microfluidic device according to Example 9, wherein the conversion mechanism comprises a presence or absence of an immiscible fluid over at least part of the open air-liquid interface of the second cross-section, such that the immiscible fluid constitutes a portion of the wetted surface. 
         [0022]    Example 11 relates to the microfluidic device according to Example 11, wherein the conversion mechanism comprises a solid material configured to move between a position non-adjacent to the first channel and a position coupled with the first channel, such that the material constitutes a portion of the wetted surface. 
         [0023]    Example 12 relates to the microfluidic device according to Example 9, wherein the conversion mechanism comprises movement of the walls of the first channel between the first configuration and the second configuration. 
         [0024]    Example 13 relates to the microfluidic device according to Example 1, wherein the channel comprises a material configured to remove at least a portion of the fluid. 
         [0025]    Example 14 relates to the microfluidic device according to Example 13, wherein the channel comprises an aperture defined in the channel, wherein the aperture provides fluid access to an external environment. 
         [0026]    Example 15 relates to the microfluidic device according to Example 13, wherein the material comprises a hydrogel, paper, or another liquid-absorbent material. 
         [0027]    Example 16 relates to the microfluidic device according to Example 13, wherein the material comprises an inorganic phase, an organic solvent, an antibody-laden hydrogel or another analyte-extracting material. 
         [0028]    Example 17 relates to the microfluidic device according to Example 1, wherein the channel is configured to enable flow at any angle relative to horizontal. 
         [0029]    Example 18 relates to the microfluidic device according to Example 1, wherein the channel is defined along a surface of a needle. 
         [0030]    Example 19 relates to the microfluidic device according to Example 18, wherein the first channel is coupleable to a second microscale channel on a surface of a base that is coupleable to the needle. 
         [0031]    Example 20 relates to the microfluidic device according to Example 1, wherein a ratio of the cross-sectional length of the free interface to the cross-sectional length of the wetted surface decreases along a length of the first channel, whereby a droplet of fluid added to an inlet of the channel is self-propelled along the length of the first channel. 
         [0032]    Example 21 relates to the microfluidic device according to Example 1, further comprising a second cross-section and a transition between the first and second cross-sections. The second cross-section is greater in size in comparison to the first cross-section. The transition causes pinning of the flow of fluids, such that the flow is only enabled when liquid is provided downstream of the geometry change. 
         [0033]    Example 22 relates to the microfluidic device according to Example 1, wherein the first channel is in fluid communication with a common area, wherein at least one additional channel is also in fluid communication with the a common area, thereby allowing device filling independent of synchronized fluid additions. 
         [0034]    Example 23 relates to the microfluidic device according to Example 1, wherein the first channel comprises material positioned on a surface of the first channel, whereby the material is configured to incorporate into solution when a fluid flows through the first channel. 
         [0035]    In Example 24, a method for using a microscale channel comprises providing fluid to or removing fluid from a first microscale channel. The first channel comprises a first cross-section that comprises a wetted surface comprising hydrophilic material and a free interface comprising an open air-liquid interface. The wetted surface contacts fluid flowing through the channel. The ratio of a cross-sectional length of the free interface and a cross-sectional length of the wetted surface is less than the cosine of the contact angle, thereby permitting spontaneous capillary flow. 
         [0036]    Example 25 relates to the method according to Example 24, wherein the providing fluid to the first microscale channel comprises inserting the fluid in the first channel with an automated fluid dispensing system. 
         [0037]    Example 26 relates to the method according to Example 25, wherein the automated fluid dispensing system is a manual or automated pipettor. 
         [0038]    Example 27 relates to the method according to Example 24, wherein the providing fluid to the first microscale channel comprises contacting the first channel with a fluid pooling on a surface, thereby drawing the fluid into the first channel. 
         [0039]    Example 28 relates to the method according to Example 27, wherein the fluid is blood and the surface is the surface of the skin. 
         [0040]    Example 29 relates to the method according to Example 24, wherein the removing the fluid from the first microscale channel comprises placing the first channel in fluid communication with a second channel, wherein the second channel has a second cross-section with a ratio of a cross-sectional length of a free interface to a cross-sectional length of a wetted surface that is smaller than the ratio of the first cross-section. 
         [0041]    Example 30 relates to the method according to Example 24, wherein the providing fluid to the first microscale channel comprises placing an end of the first channel into a second channel, wherein the second channel has a second cross-section with a ratio of a cross-sectional length of a free interface to a cross-sectional length of a wetted surface that is greater than the ratio of the first cross-section. 
         [0042]    Example 31 relates to the method according to Example 24, wherein the removing the fluid from the first microscale channel comprises removing a substance from the fluid through an open air-liquid interface window defined in the channel. 
         [0043]    Example 32 relates to the method according to Example 31, wherein the removing the substance from the fluid comprises removing magnetic beads by applying a magnetic force at the window. 
         [0044]    Example 33 relates to the method according to Example 32, wherein the removing the magnetic beads comprises trapping the beads on a solid surface by placing the solid surface in substantially proximity with or in contact with the surface of the liquid at the window. 
         [0045]    Example 34 relates to the method according to Example 31, wherein the removing the substance from the fluid comprises extracting particles from the fluid by contacting the fluid with an immiscible fluid at the window. 
         [0046]    Example 35 relates to the method according to Example 31, wherein removing the substance from the fluid comprises removing particles by trapping the particles on a material placed in contact with the fluid interface at the window, wherein the material comprises compounds configured to bind the particles. 
         [0047]    In Example 36, a method for using a microscale channel comprises moving fluid within a first microscale channel. The first channel comprises a first cross-section that comprises a wetted surface comprising hydrophilic material and a free interface comprising an open air-liquid interface. The wetted surface contacts fluid flowing through the channel. The ratio of a cross-sectional length of the free interface and a cross-sectional length of the wetted surface is less than the cosine of the contact angle, thereby permitting spontaneous capillary flow. 
         [0048]    Example 37 relates to the method according to Example 36, wherein the moving fluid within the first channel comprises urging fluid through the first channel and at least one other channel into a common channel or holding chamber, wherein flow within each of the first channel and the at least one other channel are independent, thereby allowing a combination of different flows without air bubble formation. 
         [0049]    Example 38 relates to the method according to Example 36, wherein the first channel comprises a flow control location comprising a flow control cross-section comprising a ratio of free interface to wetted surface that is greater than the cosine of the contact angle, the method further comprising reducing the ratio of the flow control cross-section to a value smaller than the cosine of the contact angle. 
         [0050]    Example 39 relates to the method according to Example 38, wherein the reducing the ratio of the flow control cross-section further comprises adding an immiscible fluid to the channel such that the immiscible fluid spans a portion of the free interface of the first channel. 
         [0051]    Example 40 relates to the method according to Example 38, wherein the reducing the ratio of the flow control cross-section further comprises displacing a material that covers a portion of the free interface of the first channel. 
         [0052]    Example 41 relates to the method according to Example 38, wherein the reducing the ratio of the flow control cross-section further comprises displacing at least one wall of the first channel, thereby reducing a length of the free interface. 
         [0053]    Example 42 relates to the method according to Example 36, wherein the moving the fluid within the first channel further comprises causing the fluid to flow on a first plane oriented at any angle, and causing the fluid to traverse to a second plane with a connector oriented at any angle relative to the first plane. 
         [0054]    Example 43 relates to the method according to Example 42, wherein the connector comprises an open microfluidic channel having only two wetted surfaces. 
         [0055]    Example 44 relates to the method according to Example 36, wherein the moving the fluid within the first channel further comprises causing the fluid to flow over a heterogeneous area disposed on a wall of the first channel. 
         [0056]    Example 45 relates to the method according to Example 44, wherein the area is an open liquid-air interface. 
         [0057]    Example 46 relates to the method according to Example 44, wherein the area is an absorbent material, thereby causing the absorption of a defined fluid volume. 
         [0058]    Example 47 relates to the method according to Example 44, wherein the area is a second immiscible fluid. 
         [0059]    Example 48 relates to the method according to Example 36, wherein the moving the fluid within the first channel further comprises causing the fluid to flow over an opening in a bottom portion of the first channel such that the fluid is in fluid communication with ambient air on a top portion and the bottom portion of the first channel. 
         [0060]    Example 49 relates to the method according to Example 36, wherein the moving the fluid within the first channel further comprises applying a reagent in dried form on the surface of the first channel such that the reagent dissolves into the fluid as the fluid is moved through the channel. 
         [0061]    Example 50 relates to the method according to Example 36, wherein the moving the fluid within the first channel further comprises coating at least a portion of at least one wall of the first channel with a reagent, wherein the reagent comprises particles of interest. 
         [0062]    While multiple embodiments are disclosed, still other embodiments of the present invention will become apparent to those skilled in the art from the following detailed description, which shows and describes illustrative embodiments of the invention. As will be realized, the invention is capable of modifications in various obvious aspects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and detailed description are to be regarded as illustrative in nature and not restrictive. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0063]      FIG. 1A  is a perspective view of an exemplary embodiment of a microchannel containing an open interface. 
           [0064]      FIG. 1B  is a perspective view of an exemplary embodiment of a microchannel containing an open interface. 
           [0065]      FIG. 1C  is a perspective view of an exemplary embodiment of a microchannel containing an open interface. 
           [0066]      FIG. 1D  is a perspective view of an exemplary embodiment of a microchannel containing an open interface. 
           [0067]      FIG. 1E  is a sidelong view of an exemplary embodiment of a microchannel containing an open interface. 
           [0068]      FIG. 1F  is a sidelong view of an exemplary embodiment of a microchannel containing an open interface. 
           [0069]      FIG. 1G  is a sidelong view of an exemplary embodiment of a microchannel containing an open interface. 
           [0070]      FIG. 1H  is a perspective view of an exemplary embodiment of a microchannel containing an open interface. 
           [0071]      FIG. 2A  is a perspective view of an exemplary embodiment of a microfluidic channel used to collect fluid pooling on a surface. 
           [0072]      FIG. 2B  is a perspective view of an exemplary embodiment of a microfluidic channel used to collect fluid pooling on a surface. 
           [0073]      FIG. 2C  is a perspective view of an exemplary embodiment of a microfluidic channel used to collect fluid pooling on a surface. 
           [0074]      FIG. 2D  is a underside perspective view of a microfluidic channel used to collect fluid pooling on a surface according to an exemplary embodiment. 
           [0075]      FIG. 3A  is a perspective view of an open microfluidic channel with an open interface used to extract particles in fluid or a portion of the fluid itself from the channel according to one exemplary embodiment. 
           [0076]      FIG. 3B  is a perspective view of an open microfluidic channel with an open interface used to extract particles in fluid or a portion of the fluid itself from the channel according to one exemplary embodiment. 
           [0077]      FIG. 3C  is a perspective view of an open microfluidic channel with an open interface used to extract particles in fluid or a portion of the fluid itself from the channel according to one exemplary embodiment. 
           [0078]      FIG. 3D  is a perspective view of an open microfluidic channel with an open interface used to extract particles in fluid or a portion of the fluid itself from the channel according to one exemplary embodiment. 
           [0079]      FIG. 4A  is a perspective view of liquid in an open microfluidic channel, the liquid flowing over a heterogenous patch in the wall of the channel, according to certain exemplary embodiments. 
           [0080]      FIG. 4B  is a perspective view of liquid in an open microfluidic channel, the liquid flowing over a heterogenous patch in the wall of the channel, according to certain exemplary embodiments. 
           [0081]      FIG. 4C  is a cross-sectional view of liquid in an open microfluidic channel, the liquid flowing over a heterogenous patch in the wall of the channel, according to certain exemplary embodiments. 
           [0082]      FIG. 4D  is a cross-sectional view of liquid in an open microfluidic channel, the liquid flowing over a heterogenous patch in the wall of the channel, according to certain exemplary embodiments. 
           [0083]      FIG. 4E  is a cross-sectional view of liquid in an open microfluidic channel, the liquid flowing over a heterogenous patch in the wall of the channel, according to certain exemplary embodiments. 
           [0084]      FIG. 5A  is a perspective view of an open microfluidic channel in which a material is either placed in contact with the open interface section of the microfluidic channel or distant of it, allowing the controllable flow through the microchannel, according to one embodiment. 
           [0085]      FIG. 5B  is a perspective view of an open microfluidic channel in which a material is either placed in contact with the open interface section of the microfluidic channel or distant of it, allowing the controllable flow through the microchannel, according to one embodiment. 
           [0086]      FIG. 5C  is a perspective view of an open microfluidic channel in which a force applied to the channel can reduce or increase the free perimeter at a certain location, thereby enabling or preventing the flow of a fluid in the channel, respectively, according to one embodiment. 
           [0087]      FIG. 5D  is a perspective view of an open microfluidic channel in which a force applied to the channel can reduce or increase the free perimeter at a certain location, thereby enabling or preventing the flow of a fluid in the channel, respectively, according to one embodiment. 
           [0088]      FIG. 6A  is a perspective view of a liquid flowing in an open microfluidic channel starting at one plane and bringing the fluid in an open microfluidic channel on a second plane, according to certain exemplary embodiments. 
           [0089]      FIG. 6B  is a perspective view of a liquid flowing in an open microfluidic channel starting at one plane and bringing the fluid in an open microfluidic channel on a second plane, according to certain exemplary embodiments. 
           [0090]      FIG. 6C  is a cross-sectional view of a liquid flowing in an open microfluidic channel starting at one plane and bringing the fluid in an open microfluidic channel on a second plane, according to certain exemplary embodiments. 
           [0091]      FIG. 7A  is a perspective view of an open microchannel defined in a needle that connects into a second open microfluidic channel at the base of the needle, according to one exemplary embodiment. 
           [0092]      FIG. 7B  is a perspective view of an open microchannel defined in a needle that connects into a second open microfluidic channel at the base of the needle, according to the exemplary embodiment of  FIG. 7A . 
           [0093]      FIG. 8A  is a perspective view of an exemplary embodiment of an open microfluidic channel with cross-sections that progressively narrow, according to an exemplary embodiment. 
           [0094]      FIG. 8B  is a perspective view of an exemplary embodiment of an open microfluidic channel with cross-sections that progressively narrow, according to an exemplary embodiment. 
           [0095]      FIG. 8C  is a perspective view of an exemplary embodiment of an open microfluidic channel with cross-sections that progressively narrow, according to an exemplary embodiment. 
           [0096]      FIG. 8D  is a perspective view of an exemplary embodiment of an open microfluidic channel with cross-sections that progressively narrow, according to an exemplary embodiment. 
           [0097]      FIG. 8E  is a perspective view of an exemplary embodiment of an open microfluidic channel with cross-sections that progressively narrow, according to an exemplary embodiment. 
           [0098]      FIG. 8F  is a perspective view of an exemplary embodiment of an open microfluidic channel with cross-sections that progressively narrow, according to an exemplary embodiment. 
           [0099]      FIG. 8G  is a perspective view of an exemplary embodiment of an open microfluidic channel with cross-sections that progressively narrow, according to an exemplary embodiment. 
           [0100]      FIG. 9A  is a perspective view of an open microfluidic channel with cross-sections that abruptly narrow, thereby enabling the creation of a capillary valve that does not require an air outlet to prevent the formation of air bubbles to operate, according to certain exemplary embodiments. 
           [0101]      FIG. 9B  is a perspective view of an open microfluidic channel with cross-sections that abruptly narrow, thereby enabling the creation of a capillary valve that does not require an air outlet to prevent the formation of air bubbles to operate, according to certain exemplary embodiments. 
           [0102]      FIG. 9C  is a perspective view of an open microfluidic channel with cross-sections that abruptly narrow, thereby enabling the creation of a capillary valve that does not require an air outlet to prevent the formation of air bubbles to operate, according to certain exemplary embodiments. 
           [0103]      FIG. 10A  is a perspective view of a Y channel allowing two sources of fluid to join and in which one branch can be filled before the other branch without the risk of creating an air bubble, according to an exemplary embodiment. 
           [0104]      FIG. 10B  is a perspective view of a Y channel allowing two sources of fluid to join and in which one branch can be filled before the other branch without the risk of creating an air bubble, according to an exemplary embodiment. 
           [0105]      FIG. 10C  is a perspective view of a Y channel allowing two sources of fluid to join and in which one branch can be filled before the other branch without the risk of creating an air bubble, according to an exemplary embodiment. 
           [0106]      FIG. 10D  is a perspective view of a Y channel allowing two sources of fluid to join and in which one branch can be filled before the other branch without the risk of creating an air bubble, according to an exemplary embodiment. 
           [0107]      FIG. 10E  is a perspective view of a Y channel allowing two sources of fluid to be routed into two other channels, in which one source branch can be filled before the other source branch without the risk of creating an air bubble, according to an exemplary embodiment. 
           [0108]      FIG. 10F  is a perspective view of a Y channel allowing two sources of fluid to join and in which one branch can be filled before the other branch without the risk of creating an air bubble, according to an exemplary embodiment. 
           [0109]      FIG. 10G  is a perspective view of a Y channel allowing two sources of fluid to join and in which one branch can be filled before the other branch without the risk of creating an air bubble, according to an exemplary embodiment. 
           [0110]      FIG. 11A  is a perspective view of a method enabling the flow of fluids from one open microfluidic channel to another, according to one embodiment. 
           [0111]      FIG. 11B  is a perspective view of an open microfluidic network built inside a larger open microfluidic network, according to one embodiment. 
           [0112]      FIG. 11C  is a perspective view of an open microfluidic network built inside a larger open microfluidic network, according to one embodiment. 
           [0113]      FIG. 11D  is a perspective view of the embodiment of  FIG. 11C  showing fluid flow. 
           [0114]      FIG. 11E  is a perspective view of an alternate embodiment of the system which enables the flow of fluid from one open microfluidic channel to another in an approach that allows the building of open microfluidic networks. 
           [0115]      FIG. 11F  is a perspective view of the embodiment of  FIG. 11E  showing fluid flow. 
           [0116]      FIG. 12A  is a perspective view of an alternative embodiment of the system facilitating the flow of fluids from one open microfluidic channel into a larger volume reservoir in an approach that allows the filling of an open microfluidic reservoir of variable volumes that is accessible from at least one opening. 
           [0117]      FIG. 12B  is a perspective view of the embodiment of  FIG. 12A  showing fluid flow. 
           [0118]      FIG. 12C  is a perspective view of the embodiment of  FIG. 12A , again showing fluid flow. 
           [0119]      FIG. 13A  is a side view of an exemplary embodiment of the system enabling the capture of excess fluid on a surface through open microfluidic channels to dry or remove liquids from a surface. 
           [0120]      FIG. 13B  is a side view of another exemplary embodiment of the system enabling the capture of excess fluid on a surface through open microfluidic channels to dry or remove liquids from a surface. 
           [0121]      FIG. 14A  is a perspective view of an exemplary embodiment of the system enabling the application of a substance to an open microfluidic channel or reservoir to apply treatments to a contained fluid. 
           [0122]      FIG. 14B  is a perspective view of the embodiment of  FIG. 14A , showing the substance applied to the fluid. 
           [0123]      FIG. 14C  is a perspective view an alternative exemplary embodiment of the system enabling the application of a substance to an open microfluidic channel or reservoir to apply treatments to a contained fluid. 
           [0124]      FIG. 14D  is a perspective view of the embodiment of  FIG. 14C , showing the substance applied to the fluid. 
       
    
    
     DETAILED DESCRIPTION 
       [0125]    The various systems and devices disclosed herein relate to devices for use in medical procedures and systems. More specifically, various embodiments relate to various medical devices, including open devices, methods and systems relating to a microfluidic network. 
         [0126]    It is understood that the various embodiments of the devices and related methods and systems disclosed herein can be incorporated into or used with any other known medical devices, systems, and methods. For example, the various embodiments disclosed herein may be incorporated into or used with any of the medical devices and systems disclosed in copending U.S. Application No. 61/590,644, dated Jan. 25, 2012, entitled “Handheld Device for Drawing, Collecting, and Analyzing Bodily Fluid,” and U.S. application Ser. No. 13/750,526, dated Jan. 25, 2013, entitled “Handheld Device for Drawing, Collecting, and Analyzing Bodily Fluid,” all of which are hereby incorporated herein by reference in their entireties. 
         [0127]    Referring generally to the figures, an “open microfluidic groove” is defined as a channel with a cross-section containing one or more sections for which the fluid spans over an open air-liquid interface and one or more sections for which the fluid contacts a hydrophilic material. The open microfluidic groove will also be referred to herein as an open microfluidic groove, an open microfluidic network, an open microfluidic channel, a microfluidic channel, a microfluidic groove, or more generally as a channel or a groove. It is understood that one or more grooves or channels can make up a network. At each point in the microfluidic groove, the length of the section of the cross-section contacting hydrophilic material is called the wetted perimeter, and the length of the remaining section is called the free perimeter. Further, the SCF relation, determining whether spontaneous capillary flow occurs in the open microfluidic channel, states that the ratio of the free perimeter and the wetted perimeter of the microfluidic groove must be less than the cosine of the contact angle of the fluid on the hydrophilic material constituting the walls of the microfluidic groove. A microfluidic groove designed for performing a specific function or assembled with other microfluidic components is called an open microfluidic network. 
         [0128]    Leveraging the open aspect of the microfluidic groove as well as surface tension phenomena, a variety of fluidic components can be developed allowing the control of the flow through the microfluidic groove and the creation of larger open microfluidic networks. The design rule stating that the ratio of the free perimeter and the wetted perimeter of the microfluidic groove is less than the cosine of the contact angle of the fluid, allows the design of microfluidic channels containing several open liquid-air interfaces, or channels that do not require the totality of the wetted perimeter to operate (and thus can still flow if partly blocked by an air bubble or a ridge in the fabrication). Open microfluidic channel or microfluidic grooves can be designed as a channel with a U-shaped cross-section devoid of a ceiling, or a channel with a rectangular cross-section devoid of a ceiling and floor for example. Another example is a channel with a rectangular cross-section devoid of a ceiling and containing circular apertures in its floor. Certain other embodiments include channels with a V-shaped cross-section, trapezoidal cross-sections, rounded or multi-indented cross-sections. These channel embodiments enable the design of channels that allow straightforward access for inserting or removing substances from the microfluidic network. 
         [0129]    Typical microfluidic approaches contain several inherent challenges that limit their reliability and ease-of-use for diagnostic, handheld, and analysis applications. One of these challenges is the difficulty of fabricating fully enclosed microfluidic channels, often requiring a bonding step. Open microfluidic channels resolve this issue, as they allow the creation of microfluidic networks that can be fabricated in one simple embossing step. A second challenge of typical microfluidic networks is the formation and entrapment of air bubbles, often synonymous of a critical failure of the whole microfluidic system. A common workaround involves the placement of air escapes to allow trapped air bubbles to escape, thus maintaining the fluidic connection within the microfluidic channel. Open microfluidic networks solve these prior art limitations by allowing at all locations air bubbles to escape. 
         [0130]    A third challenge in microfluidic systems is the interconnection between the microscale channel and the macroscale real world. In most traditional microfluidic systems, the fabrication of a usable device relies on establishing a water- or air-tight connection between a tube leading into the microfluidic device and the device itself. Open microfluidic channels allow the input and output of fluid into and from a channel by simply putting a drop of fluid in contact with the channel or inserting a second open microfluidic network in a first one. Further, open microfluidic channels enable the removal of particles from the fluid contained in the open microfluidic channel by leveraging the open interfaces for extraction by means of magnetic, diffusion, physical, or other interaction forces. 
         [0131]    Referring now to the figures, the devices, systems and methods pertaining to the use of an open microfluidic network will be described in detail.  FIG. 1A-FIG .  1 D are perspective views of various exemplary embodiments of open microfluidic channels  11 . These open microfluidic channels  11  typically involve at least one free surface  12  and at least one wetted surface  13 . In certain exemplary embodiments, the cross-section of the microfluidic channel  11  verifies the SCF relation stating that the ratio of the length of the cross-section spanning over the at-least one free surface  12  to the length of the cross-section spanning over the at-least one wetted surface  13  is less than the cosine of the contact angle of the fluid  14  on the wetted surface  13 , ensuring that fluid  14  spontaneously flows by capillary force along channel  11 . 
         [0132]    The depicted embodiments are of a fluidic channel with one open interface in a channel with a rectangular cross-section  15  (as shown in  FIG. 1A ), of a fluidic channel in a parallel rail embodiment  16  (as shown in  FIG. 1B ), of a fluidic channel with various free and wetted surfaces  17  (as shown in  FIG. 1C ), of a fluidic channel with a curved surface  18  and a second contacting surface  19  (as shown in  FIG. 1D ), all of which allow fluid to freely flow within the channel  11 . However, other embodiments involving free surfaces  12  and wetted surfaces  13  can be enabled using this technique and can involve wedge channels, channels with apertures, channels with a V-shaped cross-section  20  (as shown in  FIG. 1E ), channels with a U-shaped cross-section  21  (as shown in  FIG. 1F ), and channels with a round cross section  22  (as shown in  FIG. 1G ), among others. Furthermore, the V-shaped cross-section depicted in  FIG. 1E  allows the creation of open microfluidic grooves that allow the capillary flow of fluids even with part of the wetted perimeter impaired by factors such as an air bubble, a fabrication defect, or a local hydrophilic treatment defect. 
         [0133]    In the exemplary embodiment depicted in FIG.  1 H., the walls  23   a  of an open microfluidic channel  11  validate the design criteria alone such that they enable the flow over a ridge or fabrication defect  24   a , that would otherwise have caused the pinning of the fluid at that location and thus the blockage of the channel. Other embodiments are possible. 
         [0134]      FIGS. 2A-2D  are perspective views of an open microfluidic channel  11  that comes into contact with a pooling liquid  22  that exists on a surface  23 . The pooling liquid  22  can be blood, and the liquid can be pooling on a surface  23  such as the skin. By way of example, and as depicted in  FIG. 2A , the open microfluidic channel  11  may contain a capture region  24  and a channel region  25  that are connected and can allow the fluid  22  to flow into the channel. The open microfluidic channel  11  is composed of free surfaces  12  and wetted surfaces  13  satisfying the SCF relation, stating that the ratio of the length of the cross-section of channel  11  spanning over the at-least one free surface  12  to the length of the cross-section of channel  11  spanning over the at-least one wetted surface  13  is less than the cosine of the contact angle of the fluid  14  on the wetted surface  13 . 
         [0135]    The device embodiments described in  FIGS. 2A-2C  can be used, for example, by placing the capture region  24  of the open microfluidic channel  11  in contact with the pooling liquid  22  on a surface  23 , allowing fluid to freely pull into the microfluidic channel  11 . Upon completely removing the fluid, or when the user desires, the channel  11  is disconnected from fluid  22  and the flow of fluid in the channel ceases. In the embodiment described in  FIG. 2D , an expanded open area  26  is designed at the capture region  24  to facilitate the contact of the open microfluidic network with the blood pooling on the surface. 
         [0136]    In  FIG. 2A , the capture region  24  and the channel region  25  are represented by an open channel devoid of a ceiling or top portion, the extremity of which can contact a fluid  22 . The capture region  24  is wider than the channel region  25  in order to facilitate broad capture of a pooling fluid. In alternative embodiments the walls of the capture region  24  can be raised or extended to allow the creation of a wider caption region  24 . 
         [0137]    In the alternate embodiment described in  FIG. 2B , the capture region  24  is open near the surface  23  (or “bottom”) in order to facilitate the capture of a pooling fluid  22 . The channel region  25  is open away from the surface  23  (or “top”) in order to prevent the exposure of fluid to the surface  23 . The transition from the capture region  24  and the channel region  25  may be comprised of a small section of channel open both to the top and the bottom, by an immediate transition from open to the top to open to the bottom, or by an overlapping region in which the channel  11  is both closed on top and on bottom. 
         [0138]    In the alternate embodiment described in  FIG. 2C , the capture region  24  is open to both the top and the bottom relative to the surface  23 , thus allowing the capture of fluid  22 , and connection to the channel region  25  open only at the top, in order to prevent exposure of the fluid to the surface  23 . These embodiments may be developed with cross-sectional geometries of the channel  11 , the channel region  25 , or the capture region  24 , so as to provide a higher wetted surface  13 . By way of example, such embodiments may include V-shaped, trapezoidal-shaped, or crenated-shaped cross-sections. 
         [0139]      FIGS. 3A-3D  are various perspective views of certain embodiments of the open microfluidic channel  11  for use for removing fluid or components of those substances from within an open microfluidic platform.  FIG. 3A  illustrates an open microfluidic channel  11  with apertures  27  open to another environment, such as a solvent, an oil, a gas, a hydrogel, or another substance. The open microfluidic channel  11  follows the SCF relation such that the ratio of the length of the cross-section of the channel  11 —spanning over the at least one free surface  12 , including the opening of the aperture  27 —to the length of the cross-section of channel  11 —spanning over the at-least one wetted surface  13 —is less than the cosine of the contact angle of the fluid  14  on the wetted surface  13 . These embodiments allow any analytes present in the liquid  14  flowing in the microfluidic groove to flow over the aperture  27 , so that they may be extracted from, or viewed in the fluid  14  through the apertures  27 . 
         [0140]      FIG. 3B . is a perspective view of an embodiment of the open microfluidic channel  11  further comprising a pad  28  in the center of the channel  11  such that analyte  22  or fluid  14  is extracted through the bottom of the channel as fluid  14  passes over the pad  28 . It is understood that capillary flow occurs over the channel  11  (even in the absence of the pad  28 ), thereby ensuring a reliable connection between the fluid  14  in the groove  11  and the pad  28 . 
         [0141]      FIG. 3C  depicts a suspended channel  11  dipping into an open reservoir  29  such that a fluid  14  is extracted from the reservoir  29  into the open microfluidic network  11 . 
         [0142]      FIG. 3D  shows an alternate exemplary embodiment wherein a first open channel  11  is placed within a second open channel  30 , thus allowing fluid flowing down the first channel  11  to contact the second channel  30  and flow along that second channel  30 . Other embodiments facilitating the exchange of fluid between a first open microfluidic network and a second microfluidic network can be devised. One concept is to have the wetted surfaces of the second microfluidic network extend over the free surfaces of the first microfluidic network, such that the fluid can be driven by spontaneous capillary flow in contact with the surfaces of the second network and subsequently the fluid can be flowed along the second fluidic network. The latter embodiment can be achieved using interdigitated open microfluidic networks for instance. 
         [0143]      FIG. 4A  is a perspective view of an exemplary embodiment showing a liquid  14  entering the open microfluidic channel  11  and flowing over a heterogeneous area  31  in the wall  13  of the microfluidic channel  11 , which in various embodiments can be an open interface, an absorbent pad, or an immiscible fluid. In these embodiments, the open microfluidic channel  11  is designed to allow a wetted surface  13  that can operate without a floor  32 , thus allowing fluid  14  to flow over the heterogeneous patch  31 . An analyte  33  can be extracted from the fluid  14  through contact with the heterogeneous patch by means of a capture mechanism which could be a hydrogel laden with a capture substance, a pad containing a capture substance, a magnet, or another solid-phase capture system. The heterogeneous patch could also be a transparent material allowing optical access to the analyte  33  dissolved in the fluid  14 . 
         [0144]      FIG. 4B  is a perspective view of an embodiment of the heterogeneous patch described in relation to  FIG. 4A . In these exemplary embodiments, an aperture  34  connects the fluid  14  flowing in the channel  11  to another fluidic or gaseous environment  35 . This second fluidic environment  35  can be a specific liquid or gaseous phase to extract a chemical component contained in the fluid  14  or a fraction of the fluid  14 , as desired. 
         [0145]      FIG. 4C  is a cross-sectional view of the embodiment in  FIG. 4B . Illustrating the open microfluidic channel  11  with wetted surface  13  and two free surfaces  12 , including the aperture  34 . The fluid  14  is able to flow over the aperture  34  as the channel validated the SCF relation stating that the ratio of the length of the cross-section of channel  11  spanning over the at-least one free surface  12 , including the opening of the aperture  34 , to the length of the cross-section of channel  11  spanning over the at-least one wetted surface  13  is less than the cosine of the contact angle of the fluid  14  on the wetted surface  13 . 
         [0146]    In the alternate embodiment depicted in  FIG. 4D , magnetic beads in the fluid  37 —used to bind an analyte of interest—are carried by the liquid  14  and extracted  38  into the environment outside of the channel by means of a magnetic force, as created by a magnet  37  for instance. Once extracted from the microfluidic groove, the beads out of the liquid  38  can be placed into a diagnostic device or equipment for chemical or molecular analysis. Other means of bead extraction are well-known by those of skill in the art and can be incorporated into the device. 
         [0147]    In the embodiment depicted in  FIG. 4E , a fluid  14  flows over an immiscible fluid  39 , at the location of the aperture  34 . The contact of the two fluids allows the extraction of beads  38  through diffusion or other electrical forces, of an analyte  37  carried by the fluid  14 . Once in the immiscible phase, the analyte  33  can be removed from the microfluidic network for subsequent analysis or flowed to an analysis region or component. 
         [0148]      FIGS. 5A-5B  are perspective views of an exemplary embodiment comprising an open microfluidic channel  11  controllably allowing fluid flow along its length depending on the position of a material closing part of a free interface in the cross-section of channel  11 . An open microfluidic channel, or network  11 , with a U-shape cross-section with hydrophilic walls  13  and an open liquid-air interface  12  on the ceiling validates the design criteria stating that the ratio of the length of the cross-section of channel  11  spanning over the at-least one free surface  12 , including the opening of the aperture  27 , to the length of the cross-section of channel  11  spanning over the at-least one wetted surface  13  is less than the cosine of the contact angle of the fluid  14  on the wetted surface  13 , allows a fluid to flow along its length. At a certain point in the length of the microfluidic channel the cross-section is changed such that it does not validate the SCF relation anymore. The change can be gradual or abrupt, such that the fluid stops advancing at a specific location along the channel  11 . In the case of an abrupt change, a ridge  50  causes the pinning of the advancing fluid  14  at a defined location. A displaceable material is allowed to move from a position  51  non-contiguous to the open microfluidic groove, displayed in  FIG. 5A , to a position  52  contiguous to the microfluidic groove, displayed in  FIG. 5B . When the material is moved from the open position  51  to the closed position  52 , through the instruction of a user or an electronic circuit, it is allowed to be in contact with the fluid  14  flowing in the microfluidic groove, thus adding to the wetted perimeter of the microfluidic groove and causing a variation of the ratio of the free perimeter to the wetted perimeter. The system can be designed such that this ratio varies from a first value less than the cosine of the contact angle of the fluid to a second value higher than the cosine of the contact angle of the fluid, thus enabling spontaneous capillary flow. Finally, the fluid  14 , flowing in the open microfluidic groove, originally blocked in the channel when the material is positioned in the open position  51 , can flow over the material when it is positioned in the closed position  52 , and continue along the open microfluidic groove  11 . The material used to perform the switching from a geometry not validating the SCF relation condition to a geometry validating the SCF relation and thus allowing spontaneous capillary flow can be either a solid plastic, a hydrogel, or another miscible or immiscible fluid. 
         [0149]    An alternative embodiment is shown in  FIGS. 5C and 5D , in which the fluid  14  is stopped at a specific location  53  in the microfluidic channel wherein the geometry of the open microfluidic channel does not validate the SCF relation, which states that the ratio of the length of the cross-section of the channel  11 —spanning over the at-least one free surface  12 , including the opening of the aperture  27 —to the length of the cross-section of the channel  11 —spanning over the at-least one wetted surface  13 —is less than the cosine of the contact angle of the fluid  14  on the wetted surface  13 . When a user actuated force  53  is imparted on the open microfluidic groove, displayed in  FIG. 5C , causing the displacement of the walls  54  of the microfluidic channel  11 , displayed in  FIG. 5D , the aforementioned ratio is decreased to a value less than the cosine of the contact angle of the fluid in the microfluidic channel, and the flow is allowed to continue along the length of the channel  11 . 
         [0150]      FIG. 6A  is a perspective view of a fluid  14  flowing in an open microfluidic channel  11  starting at a first plane  60  and flowing around an angle or curved plane into a continuation of the microfluidic groove on a new plane  61  different from the first plane  60 . Importantly in these embodiments the angle of the two planes is less than 180 degrees. In this embodiment, the open microfluidic channel needs to satisfy the SCF relation, which states that the ratio of the length of the cross-section of the channel  11  spanning over the at-least one free surface  12 , including the opening of the aperture  27 , to the length of the cross-section of the channel  11  spanning over the at-least one wetted surface  13  is less than the cosine of the contact angle of the fluid  14  on the wetted surface  13 . 
         [0151]    In the embodiment shown in  FIG. 6B , the angle between the first plane  60  and the second plane  61  is more than 180 degrees. Specifically, this embodiment prevents the pinning of fluid at the curvature line  62  by ensuring that the microfluidic channel  11  meets a more stringent SCF relation equivalent to that used for an open microfluidic channel devoid of both a ceiling and a wall or floor. Essentially, these embodiments allow the fluid  14  to flow past the curvature line  62  by the capillary force provided by the walls of the channel alone. 
         [0152]    In the embodiment depicted in  FIG. 6C , a microfluidic channel  11  open on top is defined on a planar surface  63 , and is designed according to the aforementioned SCF relation, thus ensuring the flow of fluid in the microfluidic channel. At a certain location in the first channel  11 , a second microfluidic channel  64  build in a plane  65  intersects the channel  11 . The SCF relation allows the creation of a junction between the first  11  and second channels  64  such that fluid can flow both through the first channel  11  and along the second channel  64 . In order to achieve this, the second channel  64  extends into the first channel  11  using, at least in part, a channel that is devoid of both ceiling and floor, such that the fluid can flow by capillary flow using the two side walls  66 ,  67 . This system allows splitting the fluid flowing in the microfluidic network between a microfluidic network with a certain function and a second microfluidic network stacked on top of the first one and connected to it through a vertical open connector system. 
         [0153]      FIGS. 7A-7B  are perspective views of various exemplary embodiments comprising an open microchannel  11 , which again validates the SCF relation—stating that the ratio of the free perimeter to the wetted perimeter is lower than the cosine of the contact angle, placed along a needle  70  that is designed to penetrate a membrane  71 , such as the skin of a user or a membrane covering a reservoir of fluid. When the needle (originally non-contacting the membrane  71  as depicted in  FIG. 7A ), pierces the membrane  71  and accesses a fluid  14 , such as blood or a reagent, the fluid  14  is able to flow into the microfluidic channel  11  along the side of the needle  70 , as depicted in  FIG. 7B . At the base  72  of the needle  70 , the needle contacts a surface  73  containing an open microfluidic groove  74 . These embodiments also validate the SCF relation for the given fluid  14 . The open microfluidic groove  11  in the needle contact the open microfluidic groove  74  in the base surface in the same plane or at an angled junction such that a fluid  14  can flow along from the microfluidic groove  11  into the microfluidic groove  74 . The microfluidic network thus allows drawing fluid from a source protected by a membrane, through a tailored needle, and into an open microfluidic network containing other analysis, chemistry, or diagnostic fluidic components. Furthermore, such a system allows the constant drawing of a fluid  14  into a microfluidic network that may have active or passive analysis components. 
         [0154]      FIGS. 8A-8B  are perspective views of an open microfluidic channel  11  with a cross-section of the wetted surface  13  that progressively narrows from a wide configuration  80  to a narrow configuration  81 , as shown in  FIG. 8A . At all points, however, the free surface cross sectional area  12  to the wetted surface cross sectional area  13  is less than the cosine of the contact angle between the fluid to be flowed in the channel and the wetted surface  13 . As shown in  FIG. 8B , when a droplet of fluid  82  is placed in the microfluidic channel  11 , a first side of the droplet (or “leading edge”)  83 , facing towards the narrow end  81  of the microfluidic groove  11 , experiences a ratio of the free cross-section to the wetted cross section less than the second side of the droplet (or “the trailing edge”)  84 , facing the wider end  80  of the groove  11 . In such a system, a droplet of fluid  82 , containing at least one open liquid-air interface, will self-propel through the microfluidic channel  11 , from the wider end  80  to the narrower end  81 . Furthermore, in these embodiments this can be achieved with one or more open interfaces, such as channels devoid of a ceiling, a ceiling and a floor, or channels devoid of a ceiling and containing apertures in the floor, as would be apparent to one of skill in the art. 
         [0155]    In the embodiment depicted in  FIGS. 8C-8D , the change of geometry along the channel length is not gradual, rather it contains finite geometrical steps  85 . In these exemplary embodiments, a droplet of fluid  82  inserted in the channel will equally flow along the channel  11 , towards the narrower end  81 , provided that the geometries of the channel are designed in such a way so as to allow the volume of the fluid to span from a step in the channel to the next step in the channel. 
         [0156]    In  FIGS. 8E-8G , another embodiment is depicted which allows the creation of open volume controlled valves that only permit fluid flow along a channel provided a sufficient amount of volume is inserted. In  FIG. 8E , a fluid droplet  82  is inserted into the microfluidic groove  11 , and through the mechanism described previously, it is able to self-propel forward as long as the ratio of free to wetted perimeter at the leading edge  83  is smaller than the ratio of free to wetted perimeter at the trailing edge  84 . When the trailing edge  84  reaches an abrupt change in geometry  86 , if the leading edge does not validate the condition described, the droplet  82  stops. 
         [0157]      FIG. 8F . depicts the addition of an additional fluid  87  consisting of an aqueous fluid of similar surface energy, an aqueous fluid of lower surface energy, or an immiscible fluid may be inserted into the channel and will itself flow down the channel  11  in a similar way as the first droplet  82 . The open aspect of the channel will prevent air bubble formation in the channel as air can escape between the two fluids  82  and  87  in the area  88 . 
         [0158]    As shown in  FIG. 8G , if the additional fluid  87  is miscible with the droplet  82  and contacts the original droplet  82 , the volume of the additional fluid adds to that of droplet and the increased droplet  89  may contain the sufficient volume to contact a subsequent geometrical change  90 . If the additional fluid  87  is immiscible with the droplet  82  and contacts the original droplet  82 , the two droplets connect but do not mix, and the fluid  87  propels the fluid  82  beyond the constriction. With this method of self-microfluidic propulsion, a channel  11  can be devoid of specialized geometries; so long as the immiscible back fluid  87  surface energy is less than the original fluid  82 . Once the droplet  89  contacts the geometrical change  90 , the whole droplet is able to flow forward into the microfluidic network. 
         [0159]      FIGS. 9A-9E  are perspective views of embodiments of an first open microfluidic channel  11  with a cross-sectional wetted surface  13  that expands abruptly to a second channel  91  having a wetted perimeter  92 , creating a pinning line  93 . Importantly, the two wetted perimeters  13  and  91  must be of different width and height, and both channels  11  and  91  must validate the SCF relation that the ratio of the free surface cross sectional area  12  to the wetted surface cross sectional area  13  as less than the cosine of the contact angle between the fluid  14  and the wetted surface  13 . 
         [0160]    As shown in  FIG. 9A , when a fluid  14  enters the first channel  11 , the change in geometry causes fluid pinning on the plane  93 . A fluid  94  inserted in the second channel  91  flows in direction of the first channel  11 , as the air can escape from the open interfaces  95  of the microfluidic channel, as shown in  FIGS. 9B-9C . Upon contact of the fluids  14  and  94 , the pinning on line  93  is released and the fluid can then flow according to the natural pressure gradient generated by capillary force or any other pressure source, as depicted in  FIGS. 9D-9E . Reversibly, if the first fluid to enter the network is fluid  94  in the channel  91 , no pinning will be observed as the geometry is narrowing instead of increasing. 
         [0161]    In the embodiment of  FIGS. 9D-9E , a controllable open capillary valve is described. Similarly, a fluid  14  flowing down an open microfluidic channel  11  reaches an abrupt expansion in geometry, causing pinning of the fluid  14  at device plane  93 , as depicted in  FIG. 9D . An open area  96  allowing the manual or electronically controlled deposition of fluid is placed immediately after the plane  93 . When a fluid is added in the area  96 , it removes the pinning of liquid  14  on plane  93  and allows the flow  97  to pursue along the channel according to the natural pressure gradient, as shown in  FIG. 9E . Conversely, when fluid  14  is removed from area  96 , a fluid from the open microfluidic channel  11  can once again pin at the plane  93 . 
         [0162]      FIGS. 10A and 10B  are perspective views of embodiments comprising an open microfluidic network  98  further comprising first and second open microfluidic channels  99 , 100  combining into a single combinatorial area, in this case a third channel  101 . Each of the channels  99 ,  100 ,  101  further validate the SCF relation that the ratio of the free surface cross sectional area  12  to the wetted surface cross sectional area  13  as less than the cosine of the contact angle between the fluid  14  and the wetted surface  13  such that spontaneous capillary flow can occur. In these exemplary embodiments, a fluid  102  entering the first channel  99  can flow down the channel, reaches the intersection point between the channels  99 ,  100 ,  101 , and is able to flow down the third channel  101 . In certain embodiments, a capillary valve such as is depicted in  FIG. 9A  can be added to prevent flow down the second channel  100 . 
         [0163]    In exemplary embodiments, a second fluid  103  can be added to the second channel  100 , flow down the channel, without risk of trapping an air bubble as gas can escape through the open interfaces, as depicted in  FIG. 10B . Once connected to the fluid  102  in the first channel  99 , the fluid  103  can combine volume to the volume of fluid  102  flowing into the third channel  101  and create a resulting flow  104  comprised of both fluids  102 ,  103 . These embodiments enable the creation of a device combining the fluid from multiple sources that may not deliver fluid synchronously, without the risk of creating air bubbles, so as to combine the liquids delivered by both sources. These embodiments can have applications in mixing fluids in microfluidic networks or for more efficient human bodily fluid collection from multiple sources. 
         [0164]      FIGS. 10C-10E  describe alternate embodiments in which the connection geometry  105  between the first  99  and second channels  100  is rounded in order to increase the ability of the first fluid  102  to fill the combinatorial area/third channel  101 . Similarly  FIGS. 10E-10G  describe an embodiment using open microfluidic channels that have different profiles, such as the X-shaped cross section of  FIG. 10E . By way of example, and as depicted in  FIGS. 10E-10G , a V-shaped cross-section  106  allows more reliable connection of the fluids flowing down the first  99  and second channels  100  into the third channel  101 . The bottom edge  107  of the V-shaped cross-section enhances the capillary pull along both the connection of the first channel  99  to the third channel  101 , and the connection of the second channel  100  to the third channel  101 , as the fluid can follow the same single line connecting all these channels together. This method can allow fluid to flow into any third channel area  101 , including an open microchannel, a pad, a reservoir, or any other general area for fluid to congregate. 
         [0165]      FIG. 11A-11B  are perspective views of an alternate embodiment enabling the flow of fluids from one open microfluidic channel to another and reversibly in an approach that allows the building of open microfluidic networks by assembling standardized open microfluidic components. In this method, the open microfluidic channel  11  is ended at an extremity  108  which would stop the flow of fluid due to pinning. In these embodiments, a second open microfluidic channel  109  is placed in close proximity to the first channel  11  and fluid transfer from one channel to the other is enabled through the addition of a structure  110  connected to the second channel  109  and overreaching into channel  11 . As fluid is flowing by capillary force along the first channel  11 , it is brought in contact with the structure  110 , which allows the fluid to bridge over the gap  111  and contact the wetted surfaces of channel  109 . Reversibly, the structure  110  will enhance the ability of fluid flowing along channel  109  to contact the walls of the first channel  11 . 
         [0166]      FIG. 11B  is a perspective view of yet another alternate embodiment open microfluidic network inside a larger open microfluidic network. The first channel  11  validated the SCF relation such that fluid  14  is able to flow along its length by capillary force. The first channel  11  is built inside a surface of a second open microfluidic channel  112 , which also validates the SCF relation, allowing fluid  113  to flow along the length of channel  112 . In these embodiments, a first fluid can be flown into the microfluidic network and be reacted, incubated, or acted upon, and a second carrier fluid or dilution fluid can be flown subsequently. Application of these embodiments may include the dilution a fluid sample of interest such as blood, the insertion of a chemical reagent to react with the fluid sample of interest, or the deposition on the surfaces of a microchannel of a chemical treatment that will react with a fluid sample of interest inserted in the larger channel. In the latter example chemical reagents, such as lysis buffers or anti-clot factors, or sensing/capture materials, such as functionalized hydrogels or magnetic beads, can be deposited. 
         [0167]      FIGS. 11C-11D  are perspective views of an embodiment which enables the flow of fluids from one open microfluidic channel to another in an approach that allows the building of open microfluidic networks that can be easily assembled and separated by standard open microfluidic components. In this method the open microfluidic channel  11  is ended at an extremity  114  which would stop the flow of fluid due to pinning. A second open microfluidic channel or part of a channel  115  is placed in close proximity to the channel  11  and fluid transfer from one channel to the other is enabled through the contact of the part of a channel  115  interior to the extremity  114 . As fluid is flowing by capillary force along channel  11 , it is brought into contact with the structure  115 , which allows fluid  113  to flow from channel  11  into channel  116 , enhanced by the contacting surface area of the channel or parts of a channel  115 . 
         [0168]      FIGS. 11E-11F  are perspective views of an alternate embodiment which enables the flow of fluid  113  from one open microfluidic channel to another in an approach that allows the building of open microfluidic networks that can be easily assembled and separated by standard open microfluidic components. In this method the open microfluidic channel  11  terminates at an extremity  117  which would stop the flow of the fluid  113  due to pinning. This extremity  117  would have two openings positioned directly across from each other in the channel  11 . A part of a second microfluidic channel  118  is placed directly through these two openings within channel  11  and fluid transfer from one channel to the other is enabled through the contact of the part of a channel, which is an interior structure  118  to the extremity  117 . As the fluid  113  flows by capillary force along channel  11 , it is brought into contact with the interior structure  118 , which allows fluid to flow from channel  11  into channel  119 , enhanced by the depth of the structure  118  interior to the extremity  117 . 
         [0169]      FIG. 12A-12C  are perspective views of various alternative embodiments facilitating the flow of fluids from one open microfluidic channel into a larger volume reservoir in an approach that allows the filling of an open microfluidic reservoir of variable volumes that is accessible from at least one opening. In these embodiments, the open microfluidic channel  11  enters a reservoir  120  that contains fluid contact ridges  121  that enhance the surface area of the reservoir  120 . These fluid contact ridges  121  may be spaced such that the fluid contact ridges  121  would allow the fluid  113  to transfer from the open microfluidic channel  11  into the reservoir  120  and capillary forces would maintain the fluid in the reservoir  120  enhanced by fluid contact ridge number and surface area  121 . 
         [0170]      FIG. 13A-13B  are a perspective views of a embodiments of a method enabling the capture of excess fluid  113  on a surface  122  through open microfluidic channels  123  to dry or remove liquids in a simple way from a surface  122 . In this method the open microfluidic channels  123  come into close proximity with the surface  122  such that the fluid  113  on the surface  122  will come into contact with the channels  123  and be pulled into the channels  123  and away from the surface  122 . 
         [0171]      FIGS. 14A-14B  are perspective views of various embodiments of a method enabling the application of a substance  124  to an open microfluidic channel  11  or reservoir  120  as a simple method to apply treatments to a contained fluid. This substance  124  may be dried or otherwise immobilized to a surface  125  that would comprise paper, plastic, rubber, or another material and would be placed on the channel  11  or reservoir  120  bottom. In this method the substance  124  would be transferred to the channel  11  or reservoir  120  when fluid enters the area, allowing the substance to dissolve into the fluid. In another embodiment, FIGS.  14 BC and  14 D depict the embodiments in which the substance  124  is dried or otherwise immobilized to a surface  125  that would comprise paper, plastic, rubber, or another material and would be placed on the top of the channel  11  or reservoir  120 . In these embodiments, the substance  124  would be transferred to the channel  11  or reservoir  120  when fluid is already contained in the area when the surface  125  contacts the fluid within the channel  11  or reservoir  120 . 
         [0172]    While certain embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims. 
         [0173]    The embodiments, illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms ‘comprising,’ ‘including,’ ‘containing,’ etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claimed technology. 
         [0174]    The present disclosure is not to be limited in terms of the particular embodiments described in this application, which are intended as illustrations of various aspects. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent compositions, apparatuses, and methods within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds compositions or biological systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. 
         [0175]    Other embodiments are set forth in the following claims.