Patent Publication Number: US-6655924-B2

Title: Peristaltic bubble pump

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The described invention relates to microfluidic structures. More specifically, it relates to the pumping of microfluidic structures using a peristaltic bubble pump. 
     2. Description of Related Art 
     Micro-electromechanical systems (MEMS) provide a technology that enables the miniaturization of electrical and mechanical structures. MEMS is a field created primarily in the silicon area, where the mechanical properties of silicon (or other materials such as aluminum, gold, etc.) are used to create miniature moving components. MEMS can also be applied to GaAs, quartz, glass and ceramic substrates. 
     An example of a MEMS device could be a small mechanical chamber where two liquids (biofluids, drugs, chemicals, etc.) are mixed and a sensor interprets the result. MEMS could also be integrated with logic functionalities i.e. having a CMOS circuit to perform some algorithm with the data provided by the sensor. The CMOS circuit could then have circuit elements that transport the results of the algorithm and the sensor input to another device. 
     One of the mechanical processes typically performed by MEMS is transporting small amounts of fluids through channels. One way to do this is through the use of a variety of mechanical and non-mechanical pumps. 
     Mechanical pumps include piezo-electric pumps and thermo pneumatic peristaltic pumps. These pumps typically use a membrane which, when pressure is exerted on the membrane, restricts or allows fluid flow as desired. These pump structures with membranes, however, are relatively complex to manufacture. 
     Non-mechanical pumps include electrokinetic pumps. Electrokinetic pumps use an ionic fluid and a current imposed at one end of the channel and collected at the other end of the channel. This current in the ionic fluid impels the ionic fluid towards the collection pad of the electrokinetic pump. 
     Another type of non-mechanical pump uses a thermal bubble to pump fluids through a microchannel. FIGS. 1A and 1B show a prior art example of a thermal bubble pump used to pump a fluid. A controllable heater (not shown) above the pump chamber  1  causes a bubble  4  to expand or shrink. A nozzle-shaped inlet  2  and a nozzle-shaped outlet  3  create a net flow from the inlet  2  to the outlet  3 . FIG. 1A shows an example in which an expanding bubble  4  causes a net flow out of the main chamber  1  through the outlet  3 . FIG. 1B shows an example in which a shrinking bubble  4  causes a net flow into the main chamber  1  through the inlet  2 . The shape of the nozzle-shaped inlet  2  and outlet  3  bias the direction of fluid flow; however, the efficiency of the bubble pump is fairly low as a backflow through both the inlet  2  and outlet  3  occurs. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B show a prior art example of a thermal bubble used to pump a fluid. 
     FIG. 2A is a block diagram showing one embodiment of a bubble peristaltic pump. 
     FIGS. 2B-2H show an example of pumping fluid through the structure of FIG. 2A by generating bubbles with heating elements. 
     FIGS. 3A-3H show an example of using a structure having more than two heating elements to pump fluid from an inlet to an outlet. 
     FIG. 4 is a schematic diagram that shows another embodiment of a pump that uses multiple heating elements to pump fluid from an inlet through a pump chamber and out through an outlet. 
     FIG. 5 is a 3-D diagram that shows an example bubble pump. 
    
    
     DETAILED DESCRIPTION 
     A method and apparatus for using a bubble peristaltic pump is described. The bubble peristaltic pump uses heating elements to regulate flow of fluid through a pump chamber by selectively blocking one or more inlets and/or outlets of the chamber. 
     FIG. 2A is a block diagram showing one embodiment of a bubble peristaltic pump. The pump comprises a chamber  5  having an inlet  10  and an outlet  20 . A first heating element  12  is located in proximity with the inlet  10 , and a second heating element  22  is located in proximity with the outlet  20 . The pump chamber  5  is filled with a fluid. The first and second heating elements  12 ,  22  are not active initially. 
     FIGS. 2B-2F show an example of pumping fluid through the structure of FIG. 2A by generating bubbles with the heating elements  12 ,  22 . FIG. 2B shows a first bubble  14  generated within the fluid by the first heating element  12  heating up. Fluid flows out both the inlet  10  and outlet  20  until the bubble  14  becomes large enough to block the inlet  10 . 
     FIG. 2C shows the first bubble  14  expanded larger than just blocking the inlet  10 . After the inlet  10  is blocked, as the first bubble  14  increases in size by the first heating element  12  continuing to heat the fluid, the fluid is expelled from the chamber  5  through the outlet  20 . 
     FIG. 2D shows the first bubble  14  being held approximately constant in size. This may be achieved by keeping the temperature of the heating element  12  at a fairly constant temperature. In one embodiment, a feedback mechanism may be employed to monitor the size of the bubble  14  or the flow of fluid through the chamber  5  and may adjust the heating elements accordingly. As the second heating element  22  heats up, a second bubble  24  is generated. 
     FIG. 2E shows the first bubble  14  still blocking the inlet  10 , and a second bubble  24  expanding as the second heating element  22  heats up the fluid. As the second bubble  24  expands in size, fluid moves out of the chamber  5  through the outlet  20  until the second bubble  24  blocks the outlet  20 . 
     FIG. 2F shows the second bubble  24  still blocking the outlet  20 , as the first bubble  14  is reduced in size by allowing the first heating element  12  to cool. Fluid is pulled in through the inlet to fill the void left from the shrinking first bubble  14 . 
     FIG. 2G shows the second bubble  24  still blocking the outlet  20 . The first bubble  14  is eliminated by allowing the first heating element  12  to continue to cool. Fluid is pulled in through the inlet  10  to fill the void left from the shrinking first bubble  14  (no longer shown). 
     FIG. 2H shows a bubble  34  generated by the first heating element  12 , and the bubble  24  (from FIG. 2G) is reduced in size or eliminated by allowing the second heating element  22  to cool. The bubble  34  expands to block the inlet  10 , and the bubble  24  is reduced in size or eliminated to no longer block the outlet  20 . As the bubble  34  expands, fluid is expelled from the chamber through the outlet  20 . In one embodiment, bubble  34  is the same as the first bubble  14  which was never completely eliminated. In another embodiment, the first bubble  14  is completely eliminated after the first heating element  12  cools off, and a new bubble  34  is generated when the first heating element  12  heats up again. Similarly, bubble  24  may alternatively be reduced in size but not eliminated or vice versa. Additionally, it should be noted that a bubble formed by one element may combine with other bubbles formed by other heating elements, and the combined bubble may act in a similar fashion as that described with respect to the single bubbles associated with particular heating elements. 
     The process of expelling fluid from the chamber (described with respect to FIGS. 2C,  2 D,  2 E) and then refilling the chamber with new fluid (described with respect to FIGS. 2F,  2 G) are then continually repeated to pump fluid through the chamber  5 . 
     FIGS. 3A-3H show an example of using a structure having more than two heating elements to pump fluid from an inlet  110  to an outlet  120 . 
     FIG. 3A shows a chamber  105  that is filled with fluid. Within the chamber, there are three heating elements  112 ,  122 ,  132 . A first heating element  112  is located in proximity of the inlet  110 , a third heating element  122  is located in proximity of the outlet  120 , and a second heating element is located between the first heating element  112  and the third heating element  132 . 
     FIG. 3B shows a first bubble  114  generated by the first heating element  112 . The first bubble  114  expands to block the inlet  110 . 
     FIG. 3C shows the first bubble  114  expanding further, which expels fluid from the chamber  105  through the outlet  120 . FIG. 3C also shows a second bubble  124  generated by a second heating element  122 . As the bubble expands, fluid is expelled from the pump chamber  105 . In one embodiment, the second heating element is calibrated to expand the second bubble  124  until the bubble  124  touches multiple walls of the chamber  105 . 
     FIG. 3D shows the first bubble  114  and the second bubble  124  fully expanded. A third bubble  134  is generated by the third heating element  132  heating up. Fluid continues to be expelled as the bubbles  124 ,  134  continue to expand. 
     FIG. 3E shows the third bubble  134  blocking the outlet  120 . Fluid is expelled from the pump chamber  105  until the third bubble  134  blocks the outlet  120 . 
     FIG. 3F shows the second and third bubbles  124 ,  134  being held at a relatively constant size, as the first bubble  114  is reduced in size or eliminated by allowing the first heating element  112  to cool. In one embodiment, the second and third bubbles  124 ,  134  are held at approximately the same size by keeping the temperature of the heating elements  122 ,  132  at a fairly constant temperature. In one embodiment, a feedback mechanism may be employed to monitor the size of the bubbles  124 ,  134  or the flow of fluid through the chamber and may adjust the heating elements accordingly. 
     FIG. 3G shows the third bubble  134  being held at a relatively constant size, as the second bubble  124  is eliminated or reduced in size by allowing the second heating element  122  to cool. 
     FIG. 3H shows a bubble  144  generated by the first heating element  112  heating up, as the third bubble  134  is eliminated or reduced in size by allowing the third heating element  132  to cool. The bubble  144  blocks the inlet  110  and further expansion of bubble  144  expels fluid through the outlet  120 . 
     The process of expelling fluid from the chamber  105  (described with respect to FIGS. 3C,  3 D,  3 E) and then refilling the chamber  105  with new fluid (described with respect to FIGS. 3F,  3 G) are then continually repeated to pump fluid through the chamber  105 . 
     FIG. 4 is a schematic diagram that shows another embodiment of a pump that uses multiple heating elements  212 ,  222 ,  232  to pump fluid from an inlet  210  through a pump chamber  205  and out through an outlet  220 . An inlet heating element  212  is located in proximity to the inlet  210  and forms an inlet bubble valve, and an outlet heating element  232  is located in proximity to the outlet  210  and forms an outlet bubble valve. Fluid can be pumped through the structure of FIG. 4 in a similar fashion as described with respect to FIGS. 3A-3H. The inlet heating element  212  and the outlet heating element  232  of FIG. 4 are smaller than the similar heating elements  112 ,  132  of FIGS. 3A-3H. The smaller heating elements  212 ,  232  are able to open and close the bubble valve faster than larger heating elements, i.e., heat up to form a bubble to block fluid flow and cool off to allow fluid flow, respectively. The smaller heating elements  212 ,  232  also use less energy than larger heating elements. 
     FIG. 5 is a 3-D diagram that shows an example bubble pump. In one embodiment, the chamber  305 , inlet  310 , and outlet  320 , are formed in a substrate  300 . The substrate may be made from any of materials such as glass, ceramic, plastic, or silicon. In one embodiment, the chamber  305  may be milled, etched, or molded into the desired shape. 
     In one embodiment, a cover  330  is formed over the chamber  305 , inlet  310 , and outlet  320 . Two or more heating elements  340  are used to create the bubbles. In one embodiment, the heating elements  340  comprise serpentine aluminum; however, various other metals may be used to heat the fluid. The heating element is appropriately picked to provide a heated temperature that exceeds the boiling point of the fluid to be pumped, in order to produce the previously described bubbles. 
     In one embodiment, the cover  330  is a pyrex glass that can accommodate the high temperature of the heating elements  340 . Other materials such as silicon, or ceramic may alternatively be used as a cover  330 . 
     In one embodiment, one or more through-holes  350  in the substrate  300  allow electrical connectivity to contacts  352  of the heating elements  340 . In one embodiment, a controller coupled to the heating element  340  is calibrated to generate the appropriate sized bubble to accomplish the above described pumping. If a transparent cover  330  is used, then the controller can be visually calibrated to generate the appropriate sized bubbles. 
     Thus, a bubble peristaltic pump and method of using the same is disclosed. However, the specific embodiments and methods described herein are merely illustrative. For example, although the pump chamber was described with respect to a single inlet and outlet, the concepts described are easily extendable to a pump chamber having multiple inlets and outlets. Numerous modifications in form and detail may be made without departing from the scope of the invention as claimed below. The invention is limited only by the scope of the appended claims.