May 15, 2005 - Sung Rae Hwang', Woo Young Sim', Do Han Jeon1, Geun Young Kim',. Sang Sik Yang' and James Jungho Pak2. School of Electronics Eng., ...
Proceedings of the 3', Annual International IEEE EMBS Special Topic Conference on Microtechnologies in Medicine and Biology Kahuku, Oahu, Hawaii 6 12 - 15 May 2005
Fabrication and Test of a Submicroliter-level Thermopneumatic Micropump for Transdermal Drug Delivery Sung Rae
Hwang', Woo Young Sim', Do Han Jeon1, Geun Young Kim', Sang Sik Yang' and James Jungho Pak2
School of Electronics Eng., Ajou University, Suwon, Korea E-mail: ssvan(?_aiou.ac.kr, Tel. +82-31-219-2481, Fax +82-31-212-9531 Department of Electrical Eng., Korea University, Seoul, Korea Abstract- This paper presents the fabrication and test of a thermnopneumatic micropump without membrane for transdermal drug delivery systems (DDS). A micropump consists of two air chambers, a microchannel and a stop valve. The air chambers have ohmic heaters on the Pyrex glass substrate. They can be achieved by the precise control of the drug delivery amount. The micropump is fabricated by the spin-coating process, the lithograph process, the molding process and etc. The total size of micropump and the resistance of the micro heater are 13 x 9 mm2 and 690 Q, respectively. The meniscus motion in the microchannel is ovserved with a high speed camera and discharge volume of the micropump is calculated through the frame analysis of the recorded video data. Each discharge volumes are 0.1 Al/for 3 sec at 15 V and 0.1 /i/for 1.8 sec at 20 V.
The total dimension of the micropump is 13 x 9 x 0.9 mm3 and the heater resistance is 690 Q. The dimensions of the heater, the chamber, and the channels of the micropump are determined to meet the desired discharge volume. The fabrication process of the micropump is shown in Figure 2. First, the Cr/Au (500/1000 A) layer is deposited and patterned on the Pyrex glass substrate, which becomes the micro heater. The negative thickphotoresist (SU-8-2100) forms the microchannel and the two air chambers on the glass substrate after the photolithography process. The SEM photograph of the patterned channel is shown Figure 3. Finally we applied heat and pressure to bond the glass substrate with the oxidized silicon substrate. The photograph of fabricated micropump is shown in Figure 4.
Keywords - Micropump, DDS, Thermopneumatic, Inject
1. INTRODUCTION Recently, various micro fluidic devices have been developed for applications in DDS. The important objectives of DDS are the reduction of side-effects due to the excessive dosage and the enhancement of the treatment effectiveness. They can be achieved by the precise control of the drug delivery amount. Several groups have made liquid dispensing actuators especially designed for DDS [1, 2]. They focused on the pump-like structures that can deliver drug continuously or measure the flow rate for the accurate drug delivery at the expense of the complication. In order to reduce the cost and simplify the structure without losing the accurateness, we have made a drug delivery micropump that injects a proper amount of drug by means of a bubble generated by electric heating.
Figure 1. The structure of the micropump.
The upper part
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(a) Cr/Au depositon and patterning
11. STRUCTURE AND FABRICATION The schematic diagram of the micropump structure is shown in Figure 1. A micropump consists of two air chambers, a microchannel and a stop valve. The air chambers have ohmic heaters on the Pyrex glass substrate. A microchannel connects the chambers and the inlet and the outlet ports. The stop valve near the outlet port region is to control the drug amount [3].
0-7803-8711-2/05/$20.00©2005 IEEE
The bottom part
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(b) Electro-discharge machining
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Figure 2. The fabrication process of the micropump (A-A')
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Figure 3. The channel and chambers.
Figure 5. Schematic illustration of measurement setup.
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Figure 4. The photograph of the fabricated micropump.
111. MEASUREMENT AND RESULTS
Figure 6. Time sequence of micorpump activation under input voltage 10 V. ((a) t=7 sec, (b) t-43 sec. (c) t=50 sec (d) t=56 sec)
The measurement setup of micropump is shown in Figure 5. To determine the characteristics of micropump, we performed the test for various input voltages (5 30 V). Figure 6 shows the sequential capture images of the micropump during the operation when the input voltage is 10 V. The one cycle of the operation includes drug filling by the capillary force, the bubble expansion by heating, and the drug discharge through the outlet port. It takes one minute to eject the liquid. This result means that the input energy is not enough to eject the liquid. The fabricated micropump operates properly when the input voltage higher than ISV is applied. Figure 7 shows the sequential capture images of the micropump during the operation when the input voltage is 20 V. The bubble pushes the liquid mainly to the outlet port rather than to the inlet port during the ejection period. When the input is off after the ejection, the channel is refilled with the liquid by the capillary force and the negative pressure of the air in the channel due to the natural cooling. It takes about one minute to refill the channel. -
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Figure 7. Time sequence of micorpump activation under input voltage 20 V. ((a) t=0 sec, (b) t=0. 4 sec. (c) t 0.6 sec (d) t-=l .8 sec)
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[2] D. Maillefer, S. Gamper, B. Frehner, P. Balmer, H. Van Lintel, and P. Renaud,"A high-performance silicon micropump for disposable drug delivery systems," The 14th IEEE international conference on MEMS, pp. 413417, Jan. 2001. [3] T. S. Leu, P. Y. Chang, "Pressure barrier of -capillary stop valves in micro sample separators," Sensors and Actuators A, 1 15, pp 508-515, 2004.
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Input voltage (V) Figure 8. The peak flow velocity vs. the input voltage.
The discharge volume of the micropump is calculated from the meniscus movement in the microchannel observed with a high speed video camera. The micropump discharges 0.1 microliter for 3 seconds when the input voltage is 15 V and the same amount for 1.8 seconds when the input voltage is 20 V. Figure 8 shows the peak flow velocity in the channel near the outlet port during the discharge for various input voltages applied to the heater. The discharge volume of the micropump does not depend on the input voltage. The discharge time decreases as the input voltage increases.
IV. CONCLUSIONS We have demonstrated a thermopneumatic micropump with microneedles for trans-dermal drug delivery systems (DDS). Each discharge volumes are 0.1 tL/for 3 sec at 15 V and 0.1 tL/for 1.8 sec at 20 V. The experimental results show that the fabricated micropump is feasible for the submicroliter-level drug delivery systems.
ACKNOWLEDGMENT This research has been supported by the Intelligent Microsystem Center (IMC), which carries out one of the 21st century's Frontier R&D Projects sponsored by the Korea Ministry of Commerce, Industry and Energy.
REFERENCES [I] D. A. L. Van, T. McGuire, and R. Langer, "Smallscale systems for in vivo drug delivery," Nature biotechnology, vol 21, no. 10, pp. 1184-1191, Oct.
2003.
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