Hydrogel-based microdevices

Summary form only given. This talk presents two hydrogel-based devices: a microgripper that can be wirelessly manipulated using magnetic fields, and a passive inertial switch using MWCNT-hydrogel composite integrated with an inductor/capacitor (L-C) resonator. The proposed microgripper 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 38 ^o C. By dispersing multiwall carbon nanotubes (MWCNT) into the material, the overall response time of 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 polyvinyl chloride (PVC) tube and in a polydimethylsiloxane (PDMS) microfluidic channel. The passive inertial switch consists of a 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 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.