Development of Microsensor and Microactuator Using the Swelling and Shrinking Properties of Hydrogel
Date Issued
2014
Date
2014
Author(s)
Kuo, Jui-Chang
Abstract
This work presents the development of micro sensing and actuating devices by adopting the swelling and shrinking properties of hydrogel. The developed devices include an inertial switch and a microgripper. The passive inertial switch employs multiwall carbon nanotube (MWCNT) hydrogel composites integrated with an inductor/capacitor (L-C) resonator. The device consists of a polydimethylsiloxane (PDMS) micro-fluidic chip containing MWCNT-hydrogel composite and water droplet, and a glass substrate with a capacitor plate and an inductor coil. When the acceleration exceeds the designed threshold-level, the water passes through the channel to the hydrogel cavity. The hydrogel swells and changes the capacitance of the integrated L-C resonator, which in turn changes the resonant frequency that can be remotely detected. Each sensor unit does not require on-board power and circuitry for operation, so the proposed device is disposable, and is suitable for low-cost applications. All PDMS structures were fabricated using soft lithography. The L-C resonator was fabricated using a lift-off process to pattern metal layers on a glass substrate. The response time of the device is considerably reduced by introducing MWCNTs into the hydrogel composites. The characterization of the proposed device was also demonstrated. The threshold g-values, which differ for various applications, were strongly affected by the channel widths. The phase-dip measurement shows that the resonant frequencies shift from 164 MHz to approximately 148 MHz when the device is activated by acceleration. Also, we proposed a magnetic hydrogel-based microgripper that can be wirelessly manipulated using magnetic fields. The proposed device can move freely in liquids when driven by direct current (dc) magnetic fields, and perform a gripping motion by using alternating current (ac) magnetic fields. The device is fabricated from a biocompatible hydrogel material that can be employed for intravascular applications. The actuation mechanism for gripping motions is realized by controlling the exposure dose on the hydrogel composite during the lithography process. The preliminary characterization of the device is also presented. The measurement results show that the gripping motion reached a full stroke at approximately 38oC. By dispersing multiwall carbon nanotubes (MWCNT) into the material, the overall response timeof the gripping motion decreases by approximately 2-fold. Device manipulations such as the gripping motion, translational motion, and rotational motion are also successfully demonstrated on a polyvinylchloride (PVC) tube and in a polydimethylsiloxane (PDMS) microfluidic channel.
Subjects
Hydrogel
Inertial switch
L-C resonator
MEMS device
Magnetic driving system
Microgripper
Type
thesis
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