Large diameter microbubbles produced by a catheter-sized microfluidic device for sonothrombolysis applications

Abstract

Therapeutic approaches that enhance thrombolysis by combining tissue plasminogen activator (tPA), ultrasound (US), and/or microbubbles (MBs) are known generally as sonothrombolysis techniques. To date, sonothrombolysis clinical trials and experimental investigations have primarily utilized commercially available MB formulations (or derivatives thereof) with MB diameters generally in the range 1 – 4 µm. The restriction on MB diameter is due to a risk of gas emboli formation, which has left MBs outside of this diameter range virtually unexplored for sonothrombolysis applications. However, it is broadly understood that large MBs confer larger bioeffects when excited acoustically, as has been shown in sonoporation, blood brain barrier disruption, and sonothrombolysis applications. In support of the hypothesis that large MBs confer enhanced therapeutic effects, we demonstrate that MBs with diameters between 10 – 20 µm achieve a 4.5-fold increase in in vitro sonothrombolysis rates compared to MBs with diameters between 1 – 4 µm. In addition, we present the development of a catheter (1.5 mm diameter) containing a flow-focusing microfluidic device (FFMD) capable of producing large-diameter MBs suitable for catheter-directed sonothrombolysis applications. The microfluidically-produced MBs are comprised of N2 gas and a weak albumin/dextrose shell, which confers short MB half-lives and reduces the risk of gas emboli formation. Finally, we present the results of administering microfluidically produced MBs directly into the rat brain to demonstrate that large MBs with short lifetimes are safe for in vivo deployment.