1. In this poster, a reconfigurable microvalve array for BioMEMS lab-on-a-chip application is proposed. The device is connected to one inlet port and multiple outlet ports. Hydrogel thermal actuation is used to control the ON and OFF state of each outlet valve. At the entrance of each outlet port, a hydrogel blocker (PNIPAM (N-isopropylacrylamid)) is deposited. Correspondingly, a thermal resistor is embedded beneath the hydrogel actuator. Each thermal resistor can be individually addressed and controlled by a circuit. By default, there is a small gap between the hydrogel blocker and the outlet port entrance. Hence the hydrogel valve is turned ON. In order to turn off a valve, a voltage is applied to the corresponding thermal resistor to generate Joule heat to heat up the temperature of the hydrogel blocker. Hence the hydrogel block expands and blocks the entrance of the outlet port, and the valve is turned OFF. Since each thermal resistor can be individually addressed, the microvalve can be reconfigured to any combination of states. This offers the flexibility in controlling the flow of microfludics in BioMEMS lab-on-a-chip device. The working principle of the microvalve device is analyzed. Based on analysis, an optimized microvalve design is suggested. ANSYS simulation is used to verify the effectiveness of the microvalve. The proposed microvalve can be used for various BioMEMS applications. Abstract The structure design of the proposed reconfigurable microvalve array is shown in Fig. 2. As shown in the figure, the round microchannel is connected to one inlet and four outlets. At the entrance of each outlet, there is a hydrogel controlled microvalve to regulate the microfluid flow, as shown in Figure 3. Heating resistors are embedded in the hydrogel chambers of the microvalve and each of them can be individually controlled. In room temperature, the hydrogel expands to press the membrane blocker, so that the entrance of the outlets are all blocked, hence the microvalves are all in “off” state. As a result, the liquid flow from inlet can only circulate around the round channel and no liquid can flow out from outlets. If we want to direct the input liquid flow to any outlet, we just need to apply a voltage to the heating resistor of the corresponding valve. The heating current will generate Joule heat hence increase the temperature of the chamber beyond the threshold temperature of the hydrogel. As a result, the hydrogel shrinks and the membrane blocker moves back. The microvalve is open and the liquid flow can flow out to that individual outlet. Since the resistor heater of each microvavle is individually controllable, the microvalve array can be reconfigured so that input liquid flow can be directed to any outlet or multiple outlets. This offers great flexibility in regulating the liquid flow for Lab-on-a-Chip device. Reconfigurable Microvalve Array for BioMEMS Lab-on-a-Chip Application Huaning Zhao, Shiang-Yu Lin, Advisor: Prof. Xingguo Xiong, Prof. Prabir K. Patra Department of Biomedical, University of Bridgeport, Bridgeport, CT 06604 Department of Electrical and Computer Engineering, University of Bridgeport, Bridgeport, CT 06604 Structure Design of MicroValve Introduction ANSYS Simulation The fabrication flow of the proposed microvalve is shown in Fig. 9. The bottom silicon microchannels and the top part (valves, heating resistors, hydrogel) are fabricated separately. The bottom silicon microchannels are made by photolithography and KOH etching. The top part is made by micromolding technique. Both parts are then aligned and bonded together. BioMEMS lab-on-a-chip (LoC) devices have been widely used for disease diagnosis applications. Using a tiny drop of blood sample, it can simultaneously diagnose multiple diseases, and give the results within minutes. This greatly reduces the cost and improve the efficiency in medical lab tests. In BioMEMS LoC devices, microvalves are needed to regulate the flow of microfluid sample. Various microvalve designs have been reported. In this project, we proposed a reconfigurable microvalve device based on thermal electrical effect of hydrogel material. Conclusions and Future Work Length (μm)Width (μm)Height (μm) INLET CHANNEL88----- OUTLET CHANNEL85----- ROUND CHANNEL (OPEN)888 ROUND CNANNEL (CLOSED)886 FLASK882 HYDROGEL CHAMBER8810 Fig. 7 Contour plot of membrane deflection ANSYS FEM simulation is used to verify the function of the microvalve. The 3D ANSYS model of the microvalve is shown in Fig. 5. The cross-section view of the simulated membrane deflection is shown in Fig. 6. The contour plot of the membrane deflection is shown in Fig. 7. As shown in the figures, the largest deflection of the membrane occurs in the central area. The displacement can reaches 12μm, which is large enough to maintain the microvalve in the “off” state. Hand calculation result indicates the volume change of Hydrogel can be more than 4 times of its regular volume. In this poster, we proposed a reconfigurable microvalve array based on hydrogel thermal actuation. The microvavle has one inlet and three outlet ports. The entrance of each outlet is controlled by a hydrogel valve. Thermal actuation is used to control the ON and OFF state of each outlet valve. The working principle of the microvavle is analyzed. ANSYS simulation is used to verify the function of the microvalve. The fabrication process of the microvalve is also suggested. The proposed microvavle can be used for bioMEMS Lab-on-a-chip application. In the future, we will actually implement the device and measure its performance. For the membrane blocker, the relationship between pressure and resulted deflection is listed as below: P=8z max 3 Et/[3(1-v 2 )R 4 ] [2] in it, P is the pressure, z is the membrane deflection, E is Young‘s modulus of membrane material, t is the membrane thickness, v is Piossion's ratio, and R is the diameter of the membrane. The relationship between pressure and membrane deflection is shown in Fig. 4. Based on the curve, we can find out the required pressure from hydrogel in order to maintain the valve to be in default “off” state. This in turn can guide us in the device design. Based on the analysis, the design parameters of the microvavle is listed in Table 1. VOLTAGE (V)RESPOND TIME (s) 150.36 2100,09 3150.04 4200.0225 5250.0144 6300.0136 Results and Discussion 1. Outlets (“on” state, liquid flows out); 2. Sliding blocker ; 3. Hydrogel (PNIPAM); 4. Heating resistor; 5. PDMS membrane; 6. Inlet; 7. Inlet flow direction 8. Outlets (“off” state, no liquid flowing out). The respond time measures how fast the microvalve can switch between “on” and “off” states. When voltage is applied to the heating resistor, resulted Joule heat is accumulated inside the hydrogel chamber and eventually heats up the temperature of PNIPAM to exceed the threshold value (T c ). Hence the hydrogel blocker shrinks and the microvalve is turned on. Based on theoretical analysis, we estimate the relationship between heating voltage and the response time of the microvalve. The results are shown in Table 2 and Fig. 8. As we can see, if the voltage is too small ( 25V), the respond time eventually approach a saturation value. Generally, we may set the operation voltage to be 15~25V, with the respond time of the microvalve as 0.0144~0.04 sec. 1. A Richter, et al., “Electronically controllable microvalves based on smart hydrogels: magnitudes and potential applications,” J. of Microelectromechanical Systems, Vol.12, No.5, pp. 748- 753, Oct. 2003. 2. R.H. Liu, et al., “Fabrication and characterization of hydrogel-based microvalves,” J. of MEMS, Vol.11, No.1, pp.45-53, Feb. 2002 3. M.W.A. Ibrahim, et al., “Hydrogel microvalve device modeling and simulation,” Proc. Of 2005 Intl. Conf. on MEMS, NANO and Smart Systems, Vol., No., pp. 221- 222, July 24-27, 2005. Fig.1 Hydrogel swelling v.s. temperature [1] Table 1 Design parameters of microvalve Table 2 Voltage and respond time Fig. 8 Relationship of voltag and respond time Fig.4 Relationship between membrane deflection and pressure Tc=32°C Device Analysis and Optimization Fabrication Flow Fig. 6 Cross-section view of the membrane deflection simulation Fig. 2 Top View of the Micro Valve outlet (off) outlet (on) outlet (off) flow direction thermal resister outlet (on) off on Reference Some thermal sensitive hydrogel material such as PNIPAM (N-isopropylacrylamid) demonstrates interesting reversible thermal swelling effect. As shown in Fig. 1, the hydrogel is swallen at or below room temperature. However, if the hydrogel is heated above a threshold temperature (T c =32ºC in this case), the hydrogel switches from a hydrophilic, swollen state to a hydrophobic, collapsed state and rapidly shrinks its volume. This interesting phenomenon is utilized in our microvalve design. Fig. 3 Hydrogel valve design Fig. 5 3D ANSYS model of microvavle Fig. 9 Fabrication flow of the microvalve (cross-sectional view)