Controlled rupture of magnetic LbL polyelectrolyte capsules and subsequent release of contents employing high intensity focused ultrasound

Microcapsules consisting of 12 layers of poly(allylamine hydrochloride)/poly (styrene sulfonate) pairs were produced employing the Layer by Layer method with Fe₃O₄ super paramagnetic nanoparticles incorporated. BSA labelled RBITC was contained within the capsule core. Capsules implanted into a gel matrix were exposed to HIFU. Two sizes of samples were tested to see the range of focused ultrasound impact. Treatment conditions examined: ultrasonic intensities of 35W, 70W, 105W, irradiation periods of 1 s, 2 s, 4 s. Capsules with iron oxide in the 6th layer appear most stable in terms of capsule rupture, protein labelled dye release and iron leakage. Capsules with the iron oxide nanoparticles on the 4th or the 10th layer are easily ruptured allowing for protein labelled dye release with increased sonication time and increased applied ultrasonic power. This is thought to be due to the high levels of internal heat generated within capsules on sonication propagation. In the 4th and 10th layers an imbalance of heat dissipation is thought to occur resulting in enhanced capsule rupture. In the case of BSV samples these exhibited a greater amount of rupture than expected suggesting a wider impact of ultrasound suggesting a greater propagation through the tissue gel mimic.