Method of fabricating valve unit in a microfluidic device

Provided are a valve unit, a microfluidic device including the same, and a method of fabricating the valve unit. The method includes: forming a lower substrate including a channel including a first region and a second region which is deeper than the first region and is adjacent to one side of the first region; forming an upper substrate comprising a valve material chamber which extends only partially through the upper substrate; filling the valve material chamber with a valve material and curing the valve material in the valve material chamber; attaching a surface of the upper substrate in which the valve material chamber is formed to a surface of the lower substrate in which the channel is formed, so that the valve material chamber overlaps an overlapped portion of the first region, and does not overlap a non-overlapped portion of the first region; melting the valve material accommodated in the valve material chamber to flow the valve material into the non-overlapped portion of the first region; and curing the valve material flowed into the non-overlapped portion to close the first region.

CROSS-REFERENCE TO RELATED PATENT APPLICATION

This application claims priority from Korean Patent Application No. 10-2008-0044728, filed on May 14, 2008 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

One or more embodiments relate to microfluidics, and more particularly, to a valve unit controlling fluid flow, a microfluidic device including the same, and a method of fabricating the valve unit.

2. Description of the Related Art

In general, microfluidic devices are used to perform biological or chemical reactions by manipulating small amounts of fluid. Microfluidic devices include microfluidic structures arranged in a platform in various forms, such as chips, disks, or the like. Such a microfluidic structure includes a chamber that can accommodate a fluid, a channel through which the fluid can flow, and a valve that can control the flow of the fluid. The chamber, channel, and valve may be disposed in the platform in a variety of configurations.

A biochip is such a microfluidic structure that is arranged in a small-sized chip platform in order to perform tests including biochemical reactions. In particular, a device that is manufactured to perform multi-step processing and manipulation on a single chip, is referred to as a lab-on-a chip.

To transfer a fluid in a microfluidic structure, an operating pressure is needed. A capillary pressure or a pressure applied by a separate pump is used as the operating pressure. Recently, centrifugal force-based microfluidic devices in which a microfluidic structure is arranged in a compact disk (CD)-shaped platform have been proposed. These devices are also referred to as Lab CD or Lab-on a CD.

An example of a valve unit included in a microfluidic device is disclosed in U.S. Patent Application Publication No. 2008/0042096. The valve unit includes an injection hole for injecting a phase transition material into the microfluidic device. To form the injection hole in the microfluidic device, which is an injection product, a protrusion corresponding to the injection hole has to be formed in a mold. A resin injected into the mold is separated from each other by the protrusion and then rejoined, which can cause a so-called weld-line formed in the injection product after the resin is cured. The weld-line deteriorates the rigidity of the microfluidic device, resulting in defects. In addition, it is difficult to smoothly polish the mold due to the protrusion formed in the mold. Thus, a surface of the injection product becomes rough and the smoothness thereof deteriorates. In addition, a process of closing the injection hole is further needed after forming the valve unit, and thus the manufacturing costs increase. Moreover, due to a draft angle formed in the protrusion in order to easily separate the injection product from the mold, an inclination is formed in an inner circumferential surface of the injection hole. As a result, the injection product has a step difference such that when the valve is operated by applying energy, such as electromagnetic waves, the step difference of the injection hole may cause diffusion of light. Thus, an operation of the valve unit may be interfered with and malfunction.

SUMMARY

One or more embodiments provide a valve unit that does not include an inlet for injecting a valve material to an inside of a microfluidic device, and thus can be manufactured relatively inexpensively.

One or more embodiments also provide a microfluidic device including the valve unit.

One or more embodiments also provide a method of fabricating the valve unit.

According to an aspect of one or more embodiments, there is provided a valve unit comprising: a first region formed in a lower substrate; a second region formed in the lower substrate to be deeper than the first region and be adjacent to one side of the first region; a third region formed in the lower substrate to be deeper than the first region and be adjacent to the other side of the first region; a valve material chamber formed in an upper substrate attached to the lower substrate, overlapping with a portion of the first region, constituting an overlapped portion, and not overlapping with the remaining portion of the first region, constituting a non-overlapped portion; and a valve material that is cured in the non-overlapped portion of the first region to close the first region, whereupon energy is applied to the valve material cured in the non-overlapped portion, such that the valve material is removed from the first region, resulting in opening of the first region.

According to another aspect of one or more embodiments, there is provided a microfluidic device comprising: a platform having a lower substrate, and an upper substrate attached to a top surface of the lower substrate; a channel, formed in the platform, providing a path of fluid flow; and the valve unit controlling the fluid flow via the channel.

According to another aspect of one or more embodiments, there is provided a method of fabricating a valve unit, the method comprising: forming a lower substrate comprising a first region, a second region formed to be deeper than the first region and be adjacent to one side of the first region, and a third region formed to be deeper than the first region and be adjacent to the other side of the first region; forming an upper substrate comprising a valve material chamber; injecting a valve material into the valve material chamber and curing the valve material; attaching a surface of the upper substrate in which the valve material chamber is formed to a surface of the lower substrate in which the first through third regions are formed, such that the valve material chamber overlaps with a portion of the first region, constituting an overlapped portion, and does not overlap with the remaining portion of the first region, constituting a non-overlapped portion; melting the valve material accommodated in the valve material chamber to flow the valve material into the non-overlapped portion of the first region; and recurring the valve material flowed into the non-overlapped portion to close the first region.

When the first region is opened, the valve unit may allow a fluid to flow from the second region to the third region, and the non-overlapped portion may be disposed closer to the second region than the overlapped portion.

Each of the lower substrate and the upper substrate may comprise a thermoplastic resin.

The valve material may comprise a phase transition material that is in a solid state at room temperature and melted when the phase transition material absorbs energy.

The valve material may comprise a plurality of micro heating particles, dispersed in the phase transition material, generating heat when the micro heating particles absorb electromagnetic wave energy.

The micro heating particles may comprise metal oxide particles.

The phase transition material may comprise a wax, a gel, or a thermoplastic resin.

The second region and the third region may be formed in the channel of the microfluidic device.

The microfluidic device may further comprise a chamber connected to one side of the channel, accommodating a fluid, wherein the second region or the third region is formed in the chamber.

The platform may be configured to be rotatable by using a motor.

DETAILED DESCRIPTION

Hereinafter, exemplary embodiments of a valve unit, a microfluidic device including the same, and a method of fabricating the valve unit will be described more fully with reference to the accompanying drawings.

FIG. 1is a perspective view illustrating a microfluidic device10according to an embodiment. Referring toFIG. 1, the microfluidic device10includes a platform11that is disk-shaped and rotatable. The platform11includes a lower substrate15and an upper substrate20bonded to the lower substrate15. Each of the lower substrate15and the upper substrate20may be formed of a thermoplastic resin.

The microfluidic device10includes a plurality of chambers35for accommodating a fluid therein, a channel31that is connected to the chambers35and provides a path for fluid flow, and valve units100and150for controlling the fluid flow via the channel31. In addition, the microfluidic device10may engage with a spindle motor (not shown) which can rotate the platform11at high speed. An installation hole39is formed at a center portion of the microfluidic device10so as to accommodate the spindle motor. Due to rotation of the platform11by the spindle motor, fluid in the chambers35or channel31of the microfluidic device10is pressurized in a radial direction towards an outer circumferential portion of the platform11.

In the microfluidic device10, the arrangement of the chambers35, the channel31, and the valve units100and150is determined by specific biochemical applications, such as centrifugal separation of a fluid sample, an immune serum reaction, gene analysis, or the like. That is, the embodiments are not limited to the arrangement of the chambers35, the channel31and valve units100and150of the microfluidic device10as illustrated inFIG. 1, and the microfluidic device10can have a variety of structures according to the use thereof.

FIG. 2is a perspective view illustrating one of the valve units100of the microfluidic device10ofFIG. 1, according to an embodiment.FIG. 3is a perspective view illustrating one of the valve units150of the microfluidic device10ofFIG. 1, according to another embodiment. The valve units100may be disposed in the channel31of the microfluidic device10ofFIG. 1. The valve units150may be disposed adjacent to the chambers35of the microfluidic device10ofFIG. 1, respectively.

Referring toFIG. 2, the valve unit100includes a first region101, a second region107, and a third region105that are formed in the channel31. The first region101is formed downward from a top surface of the lower substrate15. The second region107is formed downward from a top surface of the lower substrate15, is deeper than the first region101and is adjacent to one side of the first region101with a step. The third region105is formed downward from a top surface of the lower substrate15, is deeper than the first region101and is adjacent to the other side of the first region101with a step. Referring toFIG. 4A, the second region107and the third region105have the same depth D2, and the first region101has a depth D1which is less than the depth D2of the second region107and the third region105. Thus, the first region101is a stepped region which protrudes upward from a bottom surface of the channel31.

In addition, the valve unit100includes a valve material chamber or cavity109that is formed upward from a bottom surface of the upper substrate20and extends only partially through the upper substrate20. The valve material chamber109partially overlaps with the first region101. A portion of the first region101overlapped with the valve material chamber109is referred to as an overlapped portion102, and the remaining portion of the first region101, which is not overlapped with the valve material chamber109, is referred to as a non-overlapped portion103. A valve material V is initially accommodated in the valve material chamber109in a cured form. The valve material V accommodated in the valve material chamber109is melted so that it flows into the non-overlapped portion103of the first region101. The valve material V is then cured again to close the first region101. The non-overlapped portion103is adjacent to the third region105and the overlapped portion102is adjacent to the second region107.

The valve material V includes a phase transition material that melts when heated, and a plurality of micro heating particles P (refer toFIG. 4A) that are dispersed in the phase transition material and generate heat by absorbing electromagnetic wave energy. For example, the phase transition material may be a wax. When the wax is heated, it is melted into a liquid state and a volume of the wax expands. Examples of the wax may include paraffin wax, microcrystalline wax, synthetic wax, natural wax, and the like.

Alternatively, the phase transition material may be a gel or a thermoplastic resin. The gel may be one selected from the group consisting of polyacrylamide, polyacrylates, polymethacrylates, and polyvinylamides. The thermoplastic resin may be one selected from the group consisting of cyclic olefin copolymer (COC), polymethylmethacrylate (PMMA), polycarbonate (PC), polystyrene (PS), polyoxymethylene (POM), perfluoralkoxy (PFA), polyvinylchloride (PVC), polypropylene (PP), polyethylene terephthalate (PET), polyetheretherketone (PEEK), polyamide (PA), polysulfone (PSU), and polyvinylidene fluoride (PVDF).

The micro heating particles P may be uniformly dispersed throughout the wax and may have a diameter of 1 nm to 100 μm in order to freely pass through the channel31. When electromagnetic wave energy is supplied, for example, by radiation of a laser L emitted from a laser light source5, the temperature of the micro heating particles P is rapidly increased by the energy such that the micro heating particles P generate heat. Each of the micro heating particles P can include a core comprising a metal component and a hydrophobic surface on the core. For example, each of the micro heating particles P can have a molecular structure including a iron (Fe) core and a plurality of surfactants coupled to the Fe core and surrounding the Fe core.

In general, the micro heating particles P may be stored by dispersing them in carrier oil. The carrier oil may be hydrophobic so as to allow the micro heating particles P with the hydrophobic surface to be dispersed uniformly. The valve material V may be formed by adding carrier oil in which the micro heating particles P are dispersed to a melted phase transition material and mixing them together.

In the above description, the micro heating particles P have a polymer type particle structure. However, the embodiments are not limited thereto, and the micro heating particles P can have various other particle structures, such as a quantum dot or a magnetic bead structure. Further, the micro heating particles P can include a metal oxide, such as Al2O3, TiO2, Ta2O3, Fe2O3, Fe3O4, or HfO2. Alternatively, the valve material V may not necessarily include the micro heating particles P, and may include only the phase transition material without the micro heating particles P.

The valve unit100is a normally closed valve in which the channel31, which is closed, is opened by irradiating electromagnetic wave energy to the valve material V. The laser light source5is an example of an energy source for irradiating electromagnetic waves to the valve material V, and provides energy to the valve material V by irradiating electromagnetic waves, for example, radiation of the laser L to the valve material V. The laser light source5may include a laser diode (LD).

FIGS. 4A and 4Bare cross-sectional views sequentially illustrating a process of operating the valve unit100ofFIG. 2, according to an embodiment. Referring toFIG. 4A, a fluid F is intended to flow from the third region105to the second region107via the channel31. However, the valve material V cured in the non-overlapped portion103closes the first region101, and thus the fluid F cannot flow. In this regard, when the laser L is irradiated to the valve material V by using the laser light source5for a period of time, the micro heating particles P included in the valve material V are rapidly heated, and thus the phase transition material is rapidly heated. As a result, the valve material V is rapidly melted, and accordingly, the first region101is opened, and the fluid F can flow from the third region105to the second region107, as illustrated inFIG. 4B.

Referring toFIG. 3, the valve unit150includes a first region151, a second region157and a third region155. The first region151and the second region157are formed in the channel31, while the third region155is formed in the chamber35. The first region151is formed downward from a top surface of the lower substrate15. The second region157is formed downward from a top surface of the lower substrate15, is deeper than the first region151and is adjacent to one side of the first region151with a step. The third region155is formed downward from a top surface of the lower substrate15, is deeper than the first region151and is adjacent to the other side of the first region151with a step.

In addition, the valve unit150includes a valve material chamber159that is formed upward from a bottom surface of the upper substrate20. The valve material chamber159also overlaps with an overlapped portion152of the first region151and does not overlap with a non-overlapped portion153of the first region151, similar to the valve material chamber109of the valve unit100ofFIG. 2. The non-overlapped portion153is adjacent to the third region155and the overlapped portion152is adjacent to the second region157. A valve material V is initially accommodated in the valve material chamber159in a cured form. The valve material V accommodated in the valve material chamber159is melted so that it flows into the non-overlapped portion153of the first region151. The valve material V is then cured again to close the first region151.

The valve unit150is also a normally closed valve that opens the channel31when the valve material V is irradiated by the laser light L emitted from the laser light source5, similar to the valve unit100ofFIG. 2. The valve material V ofFIG. 3is the same as the valve material V of the valve unit100ofFIG. 2, and thus a description thereof is not repeated here.

FIGS. 5A through 5Dare cross-sectional views sequentially illustrating a method of fabricating the valve unit ofFIG. 2, according to an embodiment.

Referring toFIG. 5A, to fabricate the valve unit100ofFIG. 2, first, the lower substrate15is prepared. The lower substrate15includes the channel31having the first region101formed to a first depth D1, the second region107formed to a second depth D2greater than the first depth D1and adjacent to one side of the first region101with a step, and the third region105formed to the second depth D2and adjacent to the other side of the first region101with a step. The lower substrate15may be prepared by injection molding a thermoplastic resin.

Referring toFIG. 5B, to fabricate the valve unit100, the upper substrate20is prepared. The upper substrate20may be thinner than the lower substrate15, and includes the valve material chamber109. The upper substrate20may also be prepared by injection molding the thermoplastic resin. The upper substrate20does not include an inlet for injecting the valve material to the microfluidic device10, and thus a so-called weld line is not formed in the injection molding process. Thus, a possibility of a rigidity defect of the upper substrate20decreases. In addition, a process of closing the inlet is unnecessary, and thus the manufacturing costs can be reduced.

A melted valve material V is injected into the valve material chamber109by using a means, for example, a dispenser3, and then cured. The valve material V is prepared by mixing a phase transition material with a plurality of micro heating particles P, as described above, and when the valve material V is cured, it is adhered to the valve material chamber109.

Referring toFIG. 5C, the surface of the upper substrate20in which the valve material chamber109is formed is bonded to a surface of the lower substrate15in which the first, second and third regions101,107and105are formed. The upper substrate20and the lower substrate15are bonded to each other using, for example, an ultraviolet (UV) adhesive method or an ultrasonic welding method. The upper and lower substrates20and15are bonded to each other such that the valve material chamber109is disposed to partially overlap with a portion of the first region101. In addition, the non-overlapped portion103of the first region101, which is not overlapped with the valve material chamber109, is disposed to be adjacent to the third region105and the overlapped portion102of the first region101, which is overlapped with the valve material chamber109, is disposed to be adjacent to the second region107.

Then, the lower substrate15and the upper substrate20are heated, or the valve material V is supplied with energy E by irradiating laser beams thereto, thereby melting the valve material V. Referring toFIG. 5D, some of the melted valve material V flows into the non-overlapped portion103of the first region101by a capillary phenomenon and remains there The valve material V in the non-overlapped portion103is cured again at room temperature, thereby closing the non-overlapped portion103of the first region101. As a result, the manufacture of the valve unit100ofFIG. 2is completed.

Since it is difficult to accurately measure the valve material V, a small amount of the valve material V may flow over a boundary of the valve material chamber109when the valve material V is injected to the valve material chamber109. Due to the overflow of the valve material V, when the upper substrate20is bonded to the lower substrate15, portions of the upper substrate20and the lower substrate15adjacent to the valve material chamber109may not be rigidly attached to each other. However, the non-overlapped portion103closed by the valve material V is formed upstream to the valve material chamber109in terms of the flow direction of the fluid F illustrated inFIG. 4A, and thus the leakage of the fluid F can be prevented. Indeed, through an experiment in which a plurality of valve units the same as the valve unit100ofFIG. 2were formed in a platform and the platform was rotated at 4000 rpm for 5 minutes, no leakage of fluid in any of the valve units occurred.

While exemplary embodiments has been particularly shown and described, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the inventive concept as defined by the following claims.