US 20050241815 A1
A microfluidic device includes a formed sheet of glass or glass ceramic material formed to have one or more first micro channels on a first surface thereof and one or more second micro channels on a second surface opposite the first. The second channels are complementary to the first channels and the first channels are substantially closed by a first sheet of glass or glass ceramic material bonded to the first surface of the formed sheet. The second channels may be substantially closed by a second sheet of a glass or glass ceramic material bonded to the second surface. The first and second sheets may also be formed sheets. The device may be formed by vacuum-forming the formed sheet against a single surface mold, then bonding a plate to one or both sides of the formed sheet.
1. A microfluidic device comprising a molded sheet of a glass or glass ceramic material bonded to at least one sheet of a glass or glass ceramic material so as to form micro channels.
2. The microfluidic device as recited in
3. The microfluidic device of
4. The microfluidic device of
5. The microfluidic device of
6. The microfluidic device of
7. The microfluidic device of
8. The microfluidic device of
9. The microfluidic device of any one of claims 1 wherein said at least one sheet comprises a second molded sheet.
10. A method of forming a microfluidic device, the method comprising:
providing a mold;
positioning a softened sheet of glass or ceramicizable glass over said mold;
applying a differential gas pressure to said sheet to conform said sheet to said mold, thereby forming micro channels on at least one surface of said sheet;
substantially closing said micro channels on said at least one surface of said sheet by bonding a sheet of glass or ceramicizable glass over said mold.
11. The method of
12. The method of
13. The method of
14. The method
15. The method of
This application claims the benefit of priority under 35 U.S.C. § 119 of European Patent Application Serial No. EP04291114.9 filed on Apr. 30, 2004.
1. Field of the Invention
The present invention relates generally to microfluidic devices and methods for producing such devices, and particularly to high-thermal-efficiency glass, glass-ceramic, or ceramic microchannel or microfludic devices and methods for producing such devices.
2. Technical Background
Microchannel or microfluidic devices are generally understood as devices containing fluid passages having a characteristic dimension that generally lies in the range of 10 micrometers (μm) to 1000 μm in which fluids are directed and processed in various ways. Such devices have been recognized as holding great promise for enabling revolutionary changes in chemical and biological process technology, in particular because heat and mass transfer rates in microfluidic devices may be increased by orders of magnitude over rates achievable in conventional chemical processing systems.
Fluidic microcircuits in glass or glass-ceramic have the advantage of generally superior chemical resistance. But glass and glass-ceramics are relatively poor conductors of heat, and thermal exchange is a key feature in most chemical synthesis. Accurate and safe local heat management generally allows chemical processing at relatively higher concentrations, pressures and temperatures, leading in most cases to better yields and higher efficiency.
The present invention provides a device having microfluidic channels formed of thin glass, glass-ceramic or ceramic sheet material possessing good surface characteristics and good strength, and provides a process for reliably and efficiently producing such devices and channels. The thin-walled microchannels allow efficient heat exchange while offering superior chemical durability and heat resistance. The inventive forming process provides a simplified and reliable manufacturing process while providing a resulting device that maximizes thermal exchange.
According to one embodiment of the present invention, a microfluidic device includes a formed sheet of glass or glass ceramic material. The formed sheet is formed to have one or more first micro channels on a first surface thereof and one or more second micro channels on a second surface opposite the first. The second channels are complementary to the first channels. The first channels are substantially closed by a first sheet of glass or glass ceramic material bonded to the first surface of the formed sheet, and the second channels may be substantially closed by a second sheet of a glass or glass ceramic material bonded to the second surface. The first or second sheet may also be a formed sheet if desired.
According to another embodiment of the present invention, a method is provided for forming a microfluidic device. The method includes providing a single-surface mold, positioning a sheet of glass or ceramicizable glass on the mold, heating the mold and the sheet, and applying a differential gas pressure to the sheet to conform the sheet to the mold. The result is the formation of micro channels on at least one surface of the sheet, generally on both surfaces. Microchannels are then substantially closed or enclosed by bonding a plate of glass or ceramicizable glass over at least one surface of the sheet that includes microchannels.
According to yet another embodiment of the present invention, a method is provided for forming a microfluidic device, the method including the step of rolling out a first soft glass sheet over a moving mold, the first sheet having a first surface opposite the mold and a second surface opposite the first surface and resting on said mold; the method further including vacuum forming said soft glass sheet to conform said sheet to said mold, forming thereby a conformed sheet having micro channels on both the first and second surfaces thereof; the method further including rolling out a second soft glass sheet onto said first surface of said conformed sheet, thereby bonding said second soft glass sheet to said conformed sheet and substantially closing said micro channels on said first surface; the method further including releasing said conformed sheet from said mold. The method may additionally include rolling out a third soft glass sheet onto said second surface of said conformed sheet, thereby bonding said second soft glass sheet to said conformed sheet and substantially closing said micro channels on said second surface.
It is to be understood that both the foregoing general description and the following detailed description present embodiments of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the invention and, together with the description, serve to explain the principles and operations of the invention.
The present invention provides a device having microfluidic channels formed of thin glass, glass-ceramic or ceramic sheet material possessing good surface characteristics and good strength, and provides a process for reliably and efficiently producing such devices and channels. The method of the present invention employs forming by means of differential gas pressure to achieve the desired thin-walled, high-surface quality microchannels of glass, glass-ceramic, or ceramic. The resulting thin-walled microchannels allow efficient heat exchange while offering superior chemical durability and heat resistance. The inventive forming process provides a simplified and reliable manufacturing process while providing a resulting device that maximizes thermal exchange.
According to the present invention, micro channels are created by a process that includes closing a three dimensional glass, glass ceramic or ceramic shape, and not solely by stacking micro-structured plates. An exemplary process constituting one aspect of the present invention will be described below with reference to
Prior to use, the mold 20 is coated with a suitable release agent, such as calcium hydroxide (Alcohol+Disperbick 190 at 0.5% suspension, for example). Disperbick 190 is readily available from BYK-Chemie Gmbh, Abelstr. 14 D-46483 Wesel, Gemany.) The relief agent is desirably sprayed uniformly over the entire surface of the mold 20.
As shown in
The sheet 30 and the mold 20 are then heated together to a point above the annealing point of the glass material, and desirably near but below the softening point thereof. In the case of Corning 1737® which has an annealing point of about 721° C. and a softening point of about 925° C., for example, the mold and sheet may be heated to about 870° C. over a period of about 20 minutes.
Vacuum is then applied to the vacuum box 24 for a sufficient time to cause the sheet 30 to conform to the profile of the mold 20, resulting in formed sheet 32 as represented in
The vacuum forming, in addition to reshaping the thin sheet 30 into a formed sheet 32, also has the effect of redrawing (“vacuum redrawing”) the sheet 30, resulting a formed sheet 32 that is generally thinner than the originally thin sheet 30, particularly in the areas where material was drawn into the mold. This vacuum forming process thus allows reliable, repeatable formation of wall structures as thin as 0.3 mm or less, desirably in the range of about 0.2 mm to about 0.7 mm or less. On the other hand, using suitably thick starting sheets, wall structures of greater thicknesses may also be formed using this process, including thicknesses in the range of about 0.7 mm to about 3 mm, which thicknesses may be useful in for use in high pressure or very high pressure applications.
After vacuum forming, the mold 20 and formed sheet 32 are cooled to a temperature sufficiently low to allow the formed sheet 32 to retain its formed shape, but desirably sufficiently high to allow easy removal from the mold 20. For Corning 1737®, for example, the sheet 30 may be cooled to about 750° C. over a 2 minute period. A light air pressure is then applied to the vacuum channels 22 to remove the formed sheet 32 from the mold 20. The release agent significantly facilitates this step. The resulting formed sheet 32 is depicted in cross section in
Next, top and bottom plates 34 and 36 are positioned against the formed sheet 32 as shown in the cross section of
The assembly 38 is then bonded to form a microfluidic device 50 having closed or enclosed microchannels or passages 40, as shown in
The above-described example of the inventive process is capable of forming, in the same process step, twin circuits separated by a thin glass layer. Starting from a 0.5 mm thick sheet, for example, the thickness of the sidewalls 58 may range from 0.4 to 0.3 mm, offering little barrier to heat exchange. The sidewalls may be thicker if desired, by starting with a 0.7 mm or a 1 mm thick sheet.
Standard fluid connectors 52, shown in
Since the forming process described above easily produces twin complementary channel patterns on the upper and lower surfaces of the formed sheet 32, one natural application for microfluidic devices formed in this manner is heat exchange. Channels one side of the formed sheet 32 may contain a first fluid F1, while channels on the other side of the formed sheet 32 may contain a second fluid F2, as shown in
Microchannel arrangements created by the processes described herein need not be limited to alternating, non-communicating channel arrangements such as those shown in
For example, if desired, the mold on which the formed sheet 32 is formed may be designed to minimize the channel size of some or all channels on one side of the formed sheet 32, resulting, in minimized channels 60 interspersed with regular channels 40, such as shown in the microfluidic device 50 of
An embodiment of a device according to the present invention having minimized channel size on one side of the formed sheet is shown in plan view in
In another alternative embodiment of microfluidic devices of the present invention, openings for fluid communication may be established, as desired, between the fluid channels on one side of the formed sheet 32 and the complementary fluid channels on the other side, by removing selected portions of the channel walls within the formed sheet 32. For example, removal (by grinding, drilling, or other suitable process) from the formed sheet 32 of the material within the dashed perimeter 41 shown in
Microfluidic devices of the present invention have been successfully produced using various glass compositions, including Corning 0211, Corning 7059, Corning 1737, available from Corning Incorporated, Corning, N.Y., USA, and Glaverbel D 263, available from Glaverbel Group, 1170 Brussels, Belgium. Of these, Corning 1737 offers the smallest coefficient of thermal expansion of about 37.6×10−7 C. A microfluidic device formed of Corning 1737 is suitable for use with fluid temperatures of up to 650° C. Alumino-boro-silicate glasses, such as Kerablack, (available from Keraglass, 77 Bagneau sur Loing, France) may also be used. After the microfluidic device is formed as above, then Kerablack would by ceramicized into vitroceram, providing an ultra-low coefficient of thermal expansion of about to −2.10−7.
As yet another embodiment of the present invention, two glass materials having reasonably close coefficients of thermal expansion may be used to form a single microfluidic device. For example, the formed sheet 32 may be formed of Corning 1737 while the top and bottom sheets 34 and 36 used to close the passages in the device 50 may be formed of Pyrex 7740 (see
Preferred Manufacturing Process
The isothermal process described above has been demonstrated for prototype building and may be suitable for very small-scale manufacture. One embodiment of a more cost-effective and efficient industrial process is described below with reference to
As shown in
For forming 7740 Pyrex, for example, desirable thermal conditions are 1350° C. glass delivery onto 650° C. heated rollers and mold. The release agent is desirably carbon black from acetylene cracking. The thinner the glass sheet, the higher the roller temperature should be. 0.8 mm rolled and vacuum formed sheets have been demonstrated, offering less than 0.2 mm thick glass at the bottom of the formed shape.
Microfluidic devices of the present invention and produced by the process of the present invention need not be limited to designs with near-vertical channel walls.
The process and method of the present invention allow repeatable and reliable formation of very thin-walled glass microchannels. The resulting microfluidic devices of the present invention are particularly suited to high-throughput microfluidic heat exchange.
In comparison with other methods of forming microfluidic devices, the current invention also allows for the provision of increased wall surface area between adjacent channels relative to the cross-sectional area of the channels. The large wall surface area is mainly attributable to the relatively high channel aspect ratios (ratios of channel height to channel width) achievable with the disclosed method, as high as 2:1 or more.