UBC Theses and Dissertations
Wireless MEMS drug delivery device enabled by a micromachined Nitinol actuator as a pumping mechanism Fong, Jeffrey Chun Kit
Traditional drug delivery methods utilize systemic administration where the medication is circulated through the entire body. These methods require a high dosage at the point of entry in order to reach the therapeutic level at the targeted location and can result in serious side effects. Implantable drug delivery devices can be used to increase efficacy by targeting specific regions in the body and by safely using higher drug concentrations. Microfabrication allows for the creation of these minimally invasive devices to treat conditions not previously possible due to the limited amount of space surrounding the target area. Devices with passive releasing mechanisms have been commercialized but ones with active mechanisms are still in the works. In this thesis, a shape memory alloy (SMA) actuator is micromachined into a rectangular, planar coil to perform cantilever-like actuation. The SMA-coil actuator forms a passive resonant circuit that functions as a wireless heat source activated using external radio-frequency (RF) electromagnetic fields. SiO₂ stress layers are selectively patterned on the Nitinol SMA structure to manipulate the cantilever profile at the nominal cold state. RF radiation with varying field frequencies showed strong frequency dependence of wireless heating, actuation displacement, and force generation by several actuators with resonant frequencies of 170-245 MHz. When excited at resonance, these actuators exhibited maximum out-of-plane displacement and force of 215 µm and 71 mN, respectively. The actuator was integrated into a 10.0×10.5×2.1 mm³ polyimide-packaged chip containing a micromachined Parylene-C pump chamber to force the release of the drug from the reservoir by wirelessly activating the actuator. Experimental operation of the prototypes showed successful release of the test agents from devices placed in liquid and excited by radiating tuned RF fields with an output power of 1.1 W. These tests revealed a single release volume of 219 nL, suggesting that the device’s capacity of 76 µL is equivalent to ~350 individual ejections. Thermal behavior of the activated device is also reported in detail. This proof-of-concept prototype validates the effectiveness of wireless RF pumping for fully controlled, long-lasting drug delivery, a key step towards enabling patient-tailored, targeted local drug delivery through highly miniaturized implants.
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Attribution-NonCommercial-NoDerivs 2.5 Canada