Microfluidic device

A microfluidic device includes a substrate, first and second capillary inlets, a microfluidic channel unit, an outlet disposed downstream of the microfluidic channel unit, and a suction member disposed downstream of the outlet. A first liquid is drawn into a first sub-channel and a main channel of the microfluidic channel unit through the first capillary inlet. A second liquid is drawn into a second sub-channel of the microfluidic channel unit through the second capillary inlet. The suction member provides a predetermined suction force to permit the second liquid to penetrate into the first liquid and to break up into droplets in the first liquid, thereby generating monodisperse emulsions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority from Taiwanese application no. 104142028, filed on Dec. 15, 2015.

BACKGROUND

Technical Field

The disclosure relates to a microfluidic device, more particularly to a microfluidic device for generating monodisperse emulsions.

Background Information

Conventionally, for generating monodisperse emulsions, a microfluidic device as shown inFIG. 1may be used. The microfluidic device includes a main channel90and two sub-channels91,92. An aqueous liquid901is delivered to the main channel90, and an oily liquid902is delivered to the two sub-channels91,92. Both the aqueous liquid901and the oily liquid902are driven by a positive pressure supplied by syringe pumps (not shown). Droplets903are formed at a place where the aqueous liquid901and the oily liquid902meet, and are driven by the syringe pumps to an observation zone (not shown) of the microfluidic device for observation. For driving the aqueous liquid901and the oily liquid902, the main channel90and the sub-channels91,92are respectively connected to the syringe pumps by three narrow tubes (not shown). Therefore, it is relatively complicated to connect the microfluidic device with the syringe pumps.

In addition, if the aqueous liquid901and the oily liquid902are driven by a negative pressure applied at a location downstream of the main channel90and the sub-channels91,92, it is necessary to supply the amount of pressure needed to drive901and902simultaneously to thereby generate monodisperse emulsions. Besides, the microfluidic device using a negative pressure still needs to be connected to a syringe pump (not shown). Therefore, most researchers would prefer not to use a negative pressure to generate monodisperse emulsions.

One of the inventors of this application has proposed, in US patent application publication no. 2011/0247707 A1, a microfluidic chip device in which a fluid is driven by a negative pressure. However, the microfluidic chip device is not intended to generate monodisperse emulsions.

SUMMARY

Therefore, an object of the disclosure is to provide a microfluidic device with a suction member. With the provision of the suction member, a predetermined suction force (i.e., a negative pressure) is produced to drive movements of first and second liquids to thereby generate monodisperse emulsions. In addition, the microfluidic device and the suction member are portable and can be easily assembled.

According to the disclosure, a microfluidic device includes a substrate, a first capillary inlet, a second capillary inlet, a microfluidic channel unit, an outlet, and a suction member. The substrate has upper and lower surfaces, and defines an emulsion forming zone. The first capillary inlet is formed in the upper surface of the substrate for passage of a first liquid therethrough. The second capillary inlet is formed in the upper surface of the substrate for passage of a second liquid therethrough. The second liquid is immiscible with the first liquid. The microfluidic channel unit is formed in the substrate and has a high affinity for the first liquid. The microfluidic channel unit includes a main channel, a first sub-channel, and a second sub-channel. The main channel extends through the emulsion forming zone to terminate at a proximal end and a distal end disposed downstream of the proximal end. The first sub-channel is disposed downstream of the first capillary inlet and upstream of the proximal end of the main channel such that the first liquid is drawn into the first sub-channel through the first capillary inlet by virtue of capillary action of the first liquid, and is further drawn into the main channel by the affinity between the first liquid and the microfluidic channel unit. The second sub-channel is disposed downstream of the second capillary inlet and upstream of the proximal end of the main channel so as to permit the second liquid to be drawn into the second sub-channel through the second capillary inlet by virtue of a capillary action of the second liquid. The outlet is formed in the lower surface of the substrate and is disposed downstream of the distal end of the main channel. The suction member is made from a shape memory polymer, and is disposed downstream of the outlet. The suction member is configured to provide a predetermined suction force such that the second liquid in the second sub-channel is permitted to penetrate into the first liquid in the main channel so as to break up into droplets in the first liquid, thereby generating monodisperse emulsions in the emulsion forming zone.

DETAILED DESCRIPTION

With reference toFIGS. 2 and 3, a microfluidic device for generating monodisperse emulsions includes a substrate1, a first capillary inlet21, a second capillary inlet22, a microfluidic channel unit2, an outlet26, and a suction member3.

The substrate1has upper and lower surfaces101,102, and defines an emulsion forming zone103for observation purposes.

The first capillary inlet21is formed in the upper surface101of the substrate1for passage of a first liquid201therethrough.

The second capillary inlet22is formed in the upper surface101of the substrate1for passage of a second liquid202therethrough. The second liquid202is immiscible with the first liquid201.

The microfluidic channel unit2is formed in the substrate1and has a high affinity to the first liquid201. The microfluidic channel unit2includes a main channel23, a first sub-channel24, and a second sub-channel25.

The main channel23extends through the emulsion forming zone103to terminate at a proximal end231and a distal end232disposed downstream of the proximal end231. In this embodiment, the main channel23is meander-shaped and includes a plurality of enlarged regions230which are parallel to each other.

The first sub-channel24is disposed downstream of the first capillary inlet21and upstream of the proximal end231of the main channel23such that the first liquid201is first drawn into the first sub-channel24through the first capillary inlet21by virtue of capillary action of the first liquid201, and is further drawn into the main channel23by the affinity of the first liquid201with the microfluidic channel unit2(seeFIG. 3(a)).

The second sub-channel25is disposed downstream of the second capillary inlet22and upstream of the proximal end231of the main channel23so as to permit the second liquid202to be drawn into the second sub-channel25through the second capillary inlet22by virtue of a capillary action of the second liquid202(seeFIG. 3(a)).

In this embodiment, as shown inFIG. 2, the first and second liquids201,202are respectively stored in first and second reservoirs211,221. Once inner spaces of the first and second reservoirs211,221are respectively in fluid communication with the first and second capillary inlets21,22, the first and second liquids201,202stored in the first and second reservoirs211,221are respectively drawn into the first sub-channel24and the second sub-channel25.

The outlet26is formed in the lower surface102of the substrate1and is disposed downstream of the distal end232of the main channel23. The lower surface102of the substrate1has an attaching region104configured to surround the outlet26.

In this embodiment, the substrate1is a laminate including upper and lower layers11,12, and the upper layer11is made from a transparent material. The microfluidic channel unit2is disposed between the upper and lower layers11,12. The first and second capillary inlets21,22extend through the upper layer11and are in fluid communication with the first and second sub-channels24,25, respectively. The outlet26extends through the lower layer102and is in fluid communication with the distal end232of the main channel23.

The suction member3is made from a shape memory polymer (SMP), and is disposed downstream of the outlet26. The suction member3is configured to provide a predetermined suction force (i.e., a predetermined negative pressure) such that the second liquid202in the second sub-channel25is permitted to penetrate into the first liquid201in the main channel23so as to break up into droplets203in the first liquid201, thereby generating monodisperse emulsions in the emulsion forming zone103(seeFIG. 3(b)).

In this embodiment, the microfluidic channel unit2has a lipophilic affinity, the first liquid201is an oily liquid, and the second liquid202is an aqueous liquid.

In addition, the suction member3has a top surface30and is transformable between a permanent state (FIG. 4(a)) and a temporary state (FIG. 4(b)) when subjected to an external stimulus, such as heat, electricity, light, etc. The top surface30includes an attachment region32and a cavity31that is surrounded by the attachment region32and that extends downward to terminate at a bottom region301. In the permanent state, the attachment region32is higher than the bottom region301by a predetermined height. In the temporary state, the bottom region301is flush with the attachment region32. The attachment region32is configured to mate with the attaching region104such that when the attachment region32of the suction member3in the temporary state is brought into fluid-tight engagement with the attaching region104to thereby bring the outlet26into register with the bottom region301(seeFIG. 2), the predetermined suction force is generated in response to transformation of the suction member3from the temporary state to the permanent state. In this embodiment, heat energy is used to trigger transformation of the suction member3. When the suction member3in the permanent state is hot-pressed at a temperature higher than a glass transition temperature (Tg) of the shape memory polymer (SMP), it is deformed to the temporary state. If the suction member3in the temporary state is cooled down to a temperature lower than the Tg of the SMP, the suction member3is maintained in the temporary state until the suction member3is heated to a temperature higher than the Tg of the SMP again. At this point, the suction member3is transformed to the permanent state.

In this embodiment, the suction member3is a modular structure such that the cavity31has a standardized volume for generating the predetermined suction force when the suction member3is transformed from the temporary state to the permanent state.

As shown inFIG. 5, an adhesive layer33is disposed on the attachment region32of the suction member3, and a releasable layer34covers the adhesive layer33. Before the suction member3is attached to the lower surface102of the substrate1, the releasable layer34is removed from the adhesive layer3so as to permit the attachment region32of the suction member3in the temporary state to be brought into fluid-tight engagement with the attaching region104by virtue of the adhesive layer33(seeFIG. 2).

In this embodiment, a monomer composition is polymerized to form the shape memory polymer (SMP), i.e., the suction member3. The SMP formed from the monomer composition may fall into one of the following four categories: an SMP composed of a covalently cross-linked glassy thermoset network, an SMP composed of a covalently cross-linked semi-crystalline network, an SMP composed of a physically cross-linked glassy copolymer, and an SMP composed of a physically cross-linked semi-crystalline block copolymer. As the monomer composition may include various types of monomers which are well-known in the art and which can be selected based on requirements, details of the monomers are omitted herein for the sake of brevity.

In this embodiment, the monomer composition includes a monomer, a cross-linker, and an initiator. The monomer is selected from the group consisting of methyl methacrylate (MMA) and butyl methacrylate (BMA). The cross-linker may be ethylene glycol dimethacrylate (EGDMA) or tetraethylene glycol dimethacrylate (TEGDMA). The initiator may be 2,2-azobisisobutyronitrile (AIBN) or 1,1-azobiscyclohexanecarbonitrile (ABCN). In addition, to facilitate the transformation of the suction member3, the monomer composition may further include a heat transferring material in an amount ranging from 1 wt % to 5 wt % based on the total weight of the monomer composition. The heat transferring material is selected from the group consisting of nanocarbon materials and boron nitride.

FIGS. 6 and 7show a mold assembly4for making a plurality of the suction members3simultaneously. The mold assembly4includes a base mold41, a middle mold42, and a cover43.

The base mold41includes a lower segment411, an upper segment412, a plurality of mold pieces413, and a plurality of protrusions414. The lower segment411has an upward surface4111on which the upper segment412is disposed. The upper segment412has a flat surface4121with a dimension smaller than that of the upward surface4111. The mold pieces413are disposed on the flat surface4121and arranged in an array. Each of the protrusions414extends upwardly from a corresponding one of the mold pieces413. The mold pieces413and the protrusions414are different in dimensions and may have a circular or square cross-section. In this embodiment, the mold pieces413and the protrusions414are in cylindrical form.

The middle mold42is configured to be matingly engaged with the base mold41, and includes a plurality of through holes423. When the base mold41and the middle mold42are assembled, each of the through holes423, a corresponding one of the mold pieces413, and a corresponding one of the protrusions414cooperatively define a molding space424.

The cover43is disposed to cover the middle mold42. The cover43and the middle mold42are provided with an interengageable mechanism. In this embodiment, the middle mold42has an upper portion421provided with a guiding groove422and the cover43has a marginal edge431configured to engage the guiding groove4211such that the cover43is slidably and fittingly engageable with the middle mold42. To make the suction members3, the monomer composition is poured into the molding spaces424defined between the base mold41and the middle mold42, and the cover43is disposed on and engaged with the middle mold42to close the molding spaces424. After polymerization, the cover43and the middle mold42are removed, and the suction members3can be removed from the middle mold42. To facilitate the removal of the suction members3from the mold assembly4, each of the base mold41, the middle mold42, and the cover43may have an outer coating layer made of Teflon.

During polymerization of the monomer composition, although a pressure in each of the molding spaces424may increase, as the base mold41, the middle mold42, and the cover43are matingly engaged with one another, the monomer composition is not likely to leak out from the molding spaces424.