Hydrogel-driven micropump

[0001] 1. Field of the Invention

[0002] The present invention relates to a hydrogel-driven micropump, particularly to a hydrogel-driven micropump.

[0003] 2. Description of Related Art

[0004] A small-scale fluid system mainly comprises a micropump, a microvalve, a flow rate meter, a microchannel, and a fluid mixing device. Using a micromechanical process and technique (MEMS), various small-scale fluid driving chips are produced for applications in biotechnology, for portable environmental detection devices, precise flow control or fluid driving systems, following a tendency to ever smaller dimensions. Micropumps are important components of small-scale fluid systems for driving fluid and have been used in conjunction with micro total analysis systems (TAS), lab-on-chips, medicine dosers and biochip systems.

[0005] For producing micropumps, various novel materials and working techniques have been tried and have led to a large variety of designs, such as electromagnetic, electrostatic, piezoelectric, form-remembering alloy and double-metal micropumps. Table 1 shows properties of these designs.

TABLE 1
				Maximum
	Flow rate	Volatagepower	consumption	pressure
Type	(l/min)	(V)	(mW)	(kpa)
piezoelectric	1300	160		90
piezoelectric	40	100		15
electrostatic	850	200	1	31
Warm flow	34	6	2000	4
electromagnetic	20	3	900
double metal	43	16
Memory alloy	50		630	0.52

[0006] Each of the various designs for micropumps have shortcomings, such as high working voltage or high power consumption. A high working voltage requires a complicated power supply, which does not fit into a portable device, making control and detection applications hard to implement, so that applications are limited.

[0007] The present invention provides a micropump which works at low voltage and low power consumption and is thus easily combined with any device, following the tendency to low-voltage, low-power, portable devices with a high degree of safety.

[0008] The present invention uses expansion and contraction of hydrogel for driving fluid. Volume changes of expanding and contracting hydrogel drive fluid in a chamber via a membrane. Electrophoretic fluid is driven by an electric field, causing hydrogel to expand and shrink. Electrophoresis is a mature technology, used for separating and analyzing substances, like proteins. Originally, to carry out electrophoresis a voltage of several hundred volts was needed. Due to miniaturization, however, which reduces distances between positive and negative terminals, required voltages have been reduced considerably along with reaction times. Thus the present invention works at low voltage and at low power.

[0009] Manufacturing of the hydrogel-driven micropump of the present invention is done by a micromechanical working process (MEMS), combining a semiconductor manufacturing process and precise mechanics for producing small structural parts for microsystems. Employing a micromechanical working process has the following advantages: (1) Production of thousands or hundreds of samples on a single chip, reducing production cost; (2) producing tiny and precise components; (3) manufacturing of mechanical and electronic devices being combinable on a single chip. All components of micropumps are produced using bulk micromachining, so that combining with microvalves, flow rate meters, microchannels and fluid mixing devices is readily possible.

[0010] The hydrogel-driven micropump of the present invention comprises: two fluid chambers; a fluid channel, connecting the two fluid chambers; a first substrate plate and a second substrate plate, which are glass wafers produced by micromechanical working, each having accommodating spaces which are placed next to the two fluid chambers and connected by inward extending bridges, with electric terminals leading to the accommodating spaces; a middle substrate, sandwiched between the first and second substrate plates and made by a bulk micromachining process, having separated accommodating spaces close to ends thereof. A separating block is placed between the accommodating spaces. The middle substrate between the first and second substrate plates forms a micropump body. All of the substrates are separated by membranes. The accommodating spaces for electrophoretic fluid are located between the membranes and the first and second substrate plates, respectively, and insulating material. An electrophoretic fluid channel is left between the membranes and the bridges. The fluid channel is placed within the middle substrate between the membranes. The first substrate plate has through holes from outside to the two fluid chambers, allowing fluid to be injected.

[0011] The main object of the present invention is to provide a hydrogel-driven micropump operating at low voltage and with low power consumption, suitable for portable, safe devices.

[0012] Another object of the present invention is to provide a hydrogel-driven micropump operated by expanding and contracting of hydrogel, deforming membranes and thus driving a fluid.

[0013] A further object of the present invention is to provide a hydrogel-driven micropump, with hydrogel being expanded and contracted by electrophoresis, wherein applying voltage shifts an electrophoretic fluid, changing liquid absorption of the hydrogel, thus deforming the hydrogel, while operating voltage and power consumption are low.

[0014] A further object of the present invention is to provide a hydrogel-driven micropump produced by a micromechanical working process using bulk micromachining for separately manufacturing each component and assembling the components with adding membranes and hydrogel, attaining good system integration.

[0015] The present invention can be more fully understood by reference to the following description and accompanying drawings.

[0016] FIGS. 1a and 1b are schematic illustrations of the hydrogel-driven micropump of the present invention.

[0017] FIGS. 2a and 2b are schematic illustrations of the bulk micromachining process for producing the hydrogel-driven micropump of the present invention.

[0018] Hydrogel is a polymeric material having a fine net-like structure and being able quickly to absorb a quantity of liquid of dozens of the original mass. Having absorbed water, hydrogel expands, and after having released water, hydrogel shrinks. Therefore, by varying the quantity of absorbed water, the volume of a piece of hydrogel is changeable. Hydrogel is made of polyacrylamide-co-acrylic acid. Absorption of water until saturation and subsequent volume change happen very fast. The fastest rate is absorption of a 70-fold mass of water within one minute, accompanied by a volume increase of 100% per second.

[0019] Electrophorese usually needs application of several hundred volts for allowing ions to separate by a sufficient distance between electric terminals. For example, for separating hemo-proteins, a distance of several centimeters to several tens of centimeters is required.

[0020] When electrophorese is performed, positive ions are by an applied electric field moved towards a negative terminal, taking along molecules of the solvent at the following velocity: $v=\frac{E}{4}$

[0021] where v denotes the velocity of the solution, denotes the dielectric constant, denotes the electromotive force, E denotes the electric field strength, and denotes the coefficient of viscosity of the solution. As above formula shows, the velocity of the solution is proportional to the electric field strength. If the distance between the electric terminals is reduced to several tens of micrometers, being {fraction (1/1000)} of the distant used for conventional electrophoresis, the required voltage is reduced accordingly to several hundreds of mV, while traveling time of an ion from one terminal to the opposite terminal is reduced from a second to several milliseconds. Increasing of the voltage further reduces the traveling time. The electrophoretic fluid contains phosphate, thus fast expanding of the hydrogel and fast flow of the electrophoretic fluid lead to a high operating frequency of the micropump, so that a high flow rate of over 1000 ml/min is achieved.

[0022] As shown in FIGS. 1a and 1b, the hydrogel-driven micropump of the present invention mainly comprises: two fluid chambers 11, 12; a fluid channel 13, connecting the two fluid chambers 11, 12; a first substrate plate 21 and a second substrate plate 22, which are glass wafers produced by micromechanical working, each having accommodating spaces 31, 32 which are placed next to the two fluid chambers 11, 12 and connected by inward extending bridges 211, 221, with electric terminals 41, 42 leading to the accommodating spaces 31, 32; a middle substrate 23, sandwiched between the first and second substrate plates 21, 22 and made by a semiconductor manufacturing process, having ends 231, 232 located next to the two fluid chambers 11, 12, respectively. A separating block 233 is placed between the two fluid chambers 11, 12. The middle substrate 23 between the first and second substrate plates forms a micropump body. All of the substrates are separated by membranes 5. The accommodating spaces 31, 32 for hydrogel and electrophoretic fluid are located between the membranes 5 and the first and second substrate plates 21, 22, respectively, and insulating material 24. An electrophoretic fluid channel 33 is left between the membranes 5 and the bridges 211, 221. The fluid channel 13 is placed between the membranes 5 and the middle substrate 23. The first substrate 21 plate has through holes 212, 213 from outside to the two fluid chambers, allowing fluid to be injected. The insulating material 24 is sediment material, like SiO₂ or Si₃N₄ or photoresist material, like SU8.

[0023] More than two fluid chambers are alternatively used, with a fluid chamber being located between each two neighboring fluid chambers.

[0024] Furthermore, alternatively the lower half of the micropump shown in FIG. 1a, consisting of the middle substrate 23, the separating plate 233, the insulating material 24, the electric terminals 41, 42 and the second substrate plate 22 is replaced by a substrate plate having a depression directly accommodating the fluid chambers 11, 12.

[0025] The electric terminals 41, 42 are made by platinum galvanization. As hydrogel polyacrylamide-co-acrylic acid is used, which absorbs water rapidly and within a short reaction time. Phosphate is employed as electrophoretic fluid. The membranes 5 are made of polymerized silicon acid amide. Silicon has excellent flexibility and biochemical stability, acid amide has good chemical and thermal characteristics.

[0026] The present invention works by expanding and contracting of hydrogel. Volume change of the hydrogel deforms the membranes 5, driving fluid in the fluid chambers 11, 12. Electrophorese causes electrophoretic fluid to flow to one end of the micropump, varying the quantity of fluid absorbed by hydrogel and causing hydrogel to expand or contract.

[0027] As shown in FIG. 1a, the hydrogel-driven micropump of the present invention is operated applying an electric voltage between the electric terminals 41 and 42. With the electric terminal 41 being positively charged and the electric terminal 42 being negatively charged, electrophoretic fluid flows from the accommodation chamber 31 through the electrophoretic fluid channel 33 into the accommodation chamber 32. Then hydrogel in the accommodation chamber 31 is depleted of fluid and shrinks, while hydrogel in the accommodation chamber 32 is filled with fluid and expands. The membranes 5 consequently deform, with the volume of the fluid chamber 11 being enlarged and the volume of the fluid chamber 12 being reduced, so that fluid is pressed outward through the through hole 213 and sucked inward through the through hole 212.

[0028] Referring to FIG. 1b, after switching polarity, so that the electric terminal 41 is negatively charged and the electric terminal 42 is positively charged, electrophoretic fluid flows from the accommodation chamber 32 through the electrophoretic fluid channel 33 into the accommodation chamber 31. Then hydrogel in the accommodation chamber 32 is depleted of fluid and shrinks, while hydrogel in the accommodation chamber 31 is filled with fluid and expands. The membranes 5 consequently deform, with the volume of the fluid chamber 12 being enlarged and the volume of the fluid chamber 11 being reduced, so that fluid in the fluid chamber 11 is pressed through the fluid channel 13 into the fluid chamber 12.

[0029] After this, the above step of expanding the fluid chamber 11 is repeated, so that fluid is sucked in through the through hole 212. Following this, the fluid chamber 11 shrinks, and the fluid chamber 12 expands, causing fluid to flow from the fluid chamber 11 through the fluid channel 13 into the fluid chamber 12. Then the fluid chamber 12 is contracted, pushing out fluid through the through hole 213.

[0030] The present invention allows for bi-directional flow of fluid. By installing microvalves and blocking valves, bi-directional operation is achieved. Adding of other structural parts, like microdetectors or microtubes generates a complete microsystem.

[0031] A micromachining process combines a semiconductor manufacturing process with micromechanical working for manufacturing complete microsystems. Bulk micromachining has already been widely used. The hydrogel-driven micropump of the present invention is manufactured by bulk micromachining. As shown in FIG. 2a, manufacturing of the first and second substrate plates 21, 22 comprises the following steps:

[0032] 1. Coating two ends of a glass wafer 80 with separated platinum layers 81 to serve as electric terminals.

[0033] 2. Placing a photoresist layer of SU8 on the glass wafer 80 to form a first photoresist layer 82.

[0034] 3. Placing a photoresist layer of SU8 on the first insulating layer 82 to form a second photoresist layer inside containing the accommodating spaces for hydrogel.

[0035] 4. Putting a SiO₂ membrane 84 on top and boring through holes.

[0036] As shown in FIG. 2b, manufacturing of the micropump body comprises the following steps:

[0037] 1. Taking a (100)-cut Si wafer as a base.

[0038] 2. Placing SiN₂ layers 101 on two ends of the Si wafer to form etching openings.

[0039] 3. Using basic fluid, performing anisotropic etching down to a preset depth.

[0040] 4. Placing a SiN₂ layer 102 on a middle section of the Si wafer.

[0041] 5. Coating the two ends of the Si wafer with SiN₂ layers 103.

[0042] 6. Using basic fluid, performing anisotropic etching of holes and (111)-inclinations in the Si wafer.

[0043] 7. Putting a SiO₂ membrane 104 on top, forming fluid chambers.

[0044] While the invention has been described with reference to a preferred embodiment thereof, it is to be understood that modifications or variations may be easily made without departing from the spirit of this invention which is defined by the appended claims.