Optimising the manufacture of perfluorocarbon nanodroplets through varying sonication parameters

Perfluorocarbon nanodroplets (PFC-NDs) are promising ultrasound-responsive theranostic agents with applications in both diagnostic imaging and drug delivery. The acoustic vaporisation threshold, extravasation potential, and stability of PFC-NDs are all affected by their size. However, methods to ensure reproducible size and concentration during production by sonication are lacking. To address this need, we examined the effect of temperature, sonication time, sonication intensity, PFC concentration and sonicator tip height on ND characteristics. PFC-NDs with a perfluoro-n-pentane (PFP) core and a phospholipid shell were manufactured by probe-sonication. Pulsed sonication was used to maintain the sample temperature below the boiling point of PFP. Median particle diameter was measured using nanoparticle tracking analysis. PFC-ND diameter increased with increasing PFP concentration, with a stronger relationship as sonicator tip height increased. Above 5% v/v PFP, there was a qualitative increase in the number of particles visible by light microscopy. Increasing the sonication duration did not yield a significant change in ND size. A minimum amplitude of 60% was required for mixing to occur, with amplitudes of 80% and 100% resulting in foam production. Sonicator power output was linear with respect to time but differed depending on sample volume, composition, and vessel geometry. This study indicates that controlling the processing parameters can facilitate reproducible manufacturing of PFC-NDs.