Polyelectrolyte multilayer microchamber-arrays for in-situ cargo release: Low frequency vs. medical frequency range ultrasound

An implantable ultrasound triggered controlled release micro-chamber (MC) array based on polylactic acid (PLA) sealed polyelectrolyte multilayers (PEM) is presented. In this work Rhodamine B (RhB) nano-precipitates are loaded as model cargo and sealed water tight within micro-air bubbles. Cargo release at low frequency (LFUS (37 kHz)) and high frequency ultrasound (HFUS (2 MHz, medical range)) is compared. The release speed and mechanism varies significantly between both ultrasound frequencies, allowing for a 60 times faster MC opening at HFUS. LFUS MC opening is based on material fatigue combined with thermo-acoustic effects while strong thermo-acoustic effects are responsible for MC opening at HFUS. The slower MC opening at LFUS allows for controlling the release amount and enables multiple release pulses compared to HFUS. Not PLA coated and no air bubble entrapping PEM thin films are in case of HFUS destroyed, while no interaction is determined at LFUS.