Characterisation of an almost ‘off the shelf’ nanodroplet formulation for pre-clinical research

Abstract: In recent years, ultrasound-responsive nanodroplets have been investigated for their potential benefits over conventional microbubble ultrasound contrast agents. In particular, their submicron scale may offer enhanced stability, while their nanoscale size may allow extravasation and improved access to interstitial spaces. Upon reaching a target site, such nanodroplets can be forced to undergo acoustic droplet vaporization (ADV) into microbubbles when exposed to ultrasound at pressures above a certain threshold, inferring potential imaging and therapeutic function. Nanodroplets can be fabricated directly via in-house methods or derived from some commercial microbubble preparations. As a means to aid comparison across studies seeking to advance our understanding of nanodroplets and their potential uses, we investigate nanodroplets fabricated from the commercial contrast agent, MicroMarker (Fujifilm). To better understand their acoustic behaviors, single cavitation is assessed, and acoustic signals are analyzed using computational software (MATLAB). Nanodroplet stability is also evaluated by comparing the size of microbubbles under frozen conditions (-8°C) after one week of storage post preparation.MicroMarker microbubbles were condensed into stable MicroMarker nanodroplets that persisted for several days at 5°C (185.6 ±2.5 nm), the size of MicroMarker nanodroplets remained stable over 1 week in frozen storage at -8°C (189.9 ±1.3 nm) without a significant difference in size, while single nanodroplet conversion to microbubbles was observed at pressures as low as 220 kPa. Higher pressures led to increased asymmetry in microbubble oscillations and fragmentation.