RESUMEN
On-demand drug delivery systems are promising for a wide range of therapeutic applications. When combined with wireless implants for controlled drug delivery, they can reduce overall dosage and side effects. Here, we demonstrate release of fluorescein from a novel on-demand release system for negatively charged compounds. The release system is based on a modified electroresponsive polypyrrole nanoparticulate film designed to minimize ion exchange with the stored compound - a major passive leakage mechanism. We further designed an ultrasonically powered mm-sized implant to electronically control the on-demand drug delivery system in vivo. Release kinetics are characterized both in vitro and in vivo in mice using fluorescein as a model drug, demonstrating the feasibility of wireless, controllable drug release using an ultrasonically powered implant.
RESUMEN
Efficient ultrasonic power transfer to implantable devices requires precise transmitter beamforming to the receiver and can quickly degrade with small changes in implant location. Ultrasound localization can be used to find and track implants in the body to maintain an efficient link. We present a framework to calculate localization accuracy showing that sub-mm accuracy is obtainable using only three receive channels. A harmonic backscatter approach, which passively provides contrast in the frequency domain without active load modulation is compared to active uplink from the implant. The localization accuracy using both active uplink and harmonic backscatter from the implant power receiver is characterized using a linear array probe. The measured location standard deviation is nearly two orders of magnitude smaller than the half-power beamwidth of the array focal spot. Finally, beamforming using the measured location information increases the available power by over 20 × compared to an unfocused beam.
RESUMEN
Miniaturized ultrasonic receivers are designed for efficient powering of implantable medical devices with reconfigurable power loads. Design parameters that affect the efficiency of these receivers under highly variable load conditions, including piezoelectric material, geometry, and operation frequency, are investigated. Measurements were performed to characterize electrical impedance and acoustic-to-electrical efficiency of ultrasonic receivers for off-resonance operation. Finally, we propose, analyze, and demonstrate adaptive matching and frequency tuning techniques using two different reconfigurable matching networks for typical implant loads from 10 [Formula: see text] to 1 mW. Both simulations and measurements show a significant increase in total implant efficiency (up to 50 percentage points) over this load power range when operating off-resonance with the proposed matching networks.