Transcript Reconfigurable Microvalve Array for BioMEMS Lab-on-a

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
Table 1 Design parameters of microvalve
Length (μm)
Width (μm)
Abstract
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.
Introduction
Height (μm)
INLET CHANNEL
8
8
-----
OUTLET CHANNEL
8
5
-----
ROUND CHANNEL (OPEN)
8
8
8
ROUND CNANNEL (CLOSED)
8
8
6
FLASK
8
8
2
HYDROGEL CHAMBER
8
8
10
ANSYS Simulation
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.
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.
Some thermal sensitive hydrogel material such
Fig. 5 3D ANSYS model of microvavle
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
Fig. 6 Cross-section view of the membrane
Fig. 7 Contour plot of membrane deflection
hydrogel is heated above a threshold
deflection simulation
temperature (Tc=32ºC in this case), the hydrogel
switches from a hydrophilic, swollen state to a
Tc=32°C
hydrophobic, collapsed state and rapidly shrinks
The respond time measures how fast the microvalve can switch between “on” and “off”
its volume. This interesting phenomenon is
states. When voltage is applied to the heating resistor, resulted Joule heat is
Fig.1 Hydrogel swelling v.s. temperature[1] accumulated inside the hydrogel chamber and eventually heats up the temperature of
utilized in our microvalve design.
PNIPAM to exceed the threshold value (Tc). 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
The structure design of the proposed reconfigurable microvalve array is shown in Fig. 2.
results are shown in Table 2 and Fig. 8. As we can see, if the voltage is too small
As shown in the figure, the round microchannel is connected to one inlet and four outlets.
(<15V), the Joule heat is weak and heat accumulation inside the chamber is very slow.
At the entrance of each outlet, there is a hydrogel controlled microvalve to regulate the
Thus the respond time increases rapidly. As voltage increases, heat accumulation
microfluid flow, as shown in Figure 3. Heating resistors are embedded in the hydrogel
becomes faster and the respond time decreases. While if the voltage is too larger
chambers of the microvalve and each of them can be individually controlled. In room
(>25V), the respond time eventually approach a saturation value. Generally, we may
temperature, the hydrogel expands to press the membrane blocker, so that the entrance
set the operation voltage to be 15~25V, with the respond time of the microvalve as
of the outlets are all blocked, hence the microvalves are all in “off” state. As a result, the
0.0144~0.04 sec.
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
Table 2 Voltage and respond time
apply a voltage to the heating resistor of the corresponding valve. The heating current will
VOLTAGE (V) RESPOND TIME (s)
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
1
5
0.36
moves back. The microvalve is open and the liquid flow can flow out to that individual
2
10
0,09
outlet. Since the resistor heater of each microvavle is individually controllable, the
3
15
0.04
microvalve array can be reconfigured so that input liquid flow can be directed to any outlet
4
20
0.0225
or multiple outlets. This offers great flexibility in regulating the liquid flow for Lab-on-a-Chip
device.
5
25
0.0144
1. Outlets (“on” state, liquid flows out);
2. Sliding blocker ;
6
30
0.0136
Fig. 8 Relationship of voltag and respond time
3. Hydrogel (PNIPAM);
outlet (off)
4. Heating resistor;
thermal resister
5. PDMS membrane;
The fabrication flow of the proposed microvalve is shown in Fig. 9. The bottom silicon
6. Inlet; 7. Inlet flow direction
microchannels and the top part (valves, heating resistors, hydrogel) are fabricated
8. Outlets (“off” state, no liquid flowing out).
separately. The bottom silicon microchannels are made by photolithography and KOH
off
outlet (on)
etching. The top part is made by micromolding technique. Both parts are then aligned
on
on
and bonded together.
Results and Discussion
Structure Design of MicroValve
Fabrication Flow
outlet (on)
off
flow
direction
outlet (off)
Fig. 2 Top View of the Micro Valve
Fig. 3 Hydrogel valve design
Device Analysis and Optimization
For the membrane blocker, the relationship between
pressure and resulted deflection is listed as below:
P=8zmax3Et/[3(1-v2)R4] [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.
Fig. 9 Fabrication flow of the microvalve (cross-sectional view)
Conclusions and Future Work
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.
Reference
Fig.4 Relationship between
membrane deflection and pressure
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.