UBC Theses and Dissertations
Remotely controlled drug delivery systems Zaher, Amir
Implantable drug delivery is becoming an increasingly important field of research, providing great potential for a wide range of flexible and low cost solutions for localized treatment of chronically debilitating diseases. This dissertation presents work that encompasses several approaches for the remote triggering, powering, and control of micro drug delivery devices and systems, designed with remote-controllability, minimal power requirements, biocompatibility, and the potential for minimally invasive implantation in mind. The control mechanisms used rely on microtechnology, nanotechnology, and electromagnetic power transfer to magnetic nanoparticles and magnetic nanowires, for the heating and actuation of thermoresponsive Poly(N-isopropylacrylamide) hydrogels (PNIPAm) in the form of nanoparticles in membranes and stand-alone microdroplets, and actuation of flexible membranes for drug pumping. Thermoresponsive PNIPAm, in any form such as nanoparticles, microdroplets, or mezzo scale bulk material shapes, has the property of swelling with water in its hydrophilic state below a critical temperature. At higher temperatures, a sharp change occurs, the polymer network becomes hydrophilic, and the water molecules in the network is expelled, causing the overall material to shrink in size, while the released water or aqueous solution is left free to flow around or away from the material. When embedded in membrane matrices used as drug delivery gates, PNIPAm nanoparticles act as diffusion and flow blockers below the critical temperature. When PNIPAm surpasses the critical temperature, induced by heat from local magnetic iron oxide nanoparticles (exposed to a 62 mT, 450 kHz magnetic field), it shrinks in size and increases the drug flow through membrane pathways. The combination of this membrane design with osmotic pumping and methods for tailoring the drug release profile is reported. Simulation supports experimental results while describing interactions between the osmotic pump and the thermoresponsive membranes. A sensitivity analysis based on a fluidic circuit analogy gives insight into the contributions of the components of the device, in particular those of membranes affecting the displacement of fluid. PNIPAm microdroplets, spherical microparticles larger than the PNIPAm nanoparticles discussed above, are fabricated with embedded magnetic iron oxide nanoparticles or magnetic iron nanowires and pre-loaded with an aqueous drug. Upon magnetic heating, these microdroplets shrink in size and expel the drug. Magnetic nanowires have much lower power requirements when compared with widely-used iron oxide magnetic nanoparticles for triggering PNIPAm, due to their ability to generate losses via physical vibration within the microdroplets. A model is used to corroborate the experimentally observed low power (1 mT, 20 kHz magnetic field) required to induce PNIPAm microdroplet shrinkage. This model for nanowire loaded microdroplet design is compared with the well-established theory for power generation from magnetic iron oxide nanoparticles, and associated experiments (using a 72 mT, 600 kHz magnetic field) in order to confirm the validity of the calculated power generated by iron nanowires. The findings in this work offer several flexible options for the application of PNIPAm as a remotely triggerable drug delivery controller or carrier, using relatively simple fabrication methods, permitting several degrees of customization of the delivery rate or profile by adjusting the PNIPAm material, its magnetic content, and the applied magnetic field, all the while demonstrating the use of magnetic nanowires as a more efficient power transfer material when compared to traditionally used magnetic nanoparticles. The findings associated with the efficient triggering of PNIPAm microdroplets can be implemented in a more power-friendly design of magnetic, remotely triggered membranes which, although implemented in conjunction with osmotic pumps here, can be coupled with other pressure sources.
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