Optimizing the composition and size of perfluorocarbon nanodroplets to balance their acoustic activation and blood...

Phase-change perfluorocarbon nanodroplets (PCND) are nanoscale carriers that can be vaporized acoustically to form echogenic microbubbles. This enables ultrasound-triggered imaging and therapy to extend beyond the intravascular space. Despite being extensively studied, their in vivo pharmacokinetics have been reported inconsistently and direct comparisons between formulations are lacking. This limits rational formulation design and translation. Thus, we developed a formulation-property-function framework by systematically decoupling core volatility, shell composition and particle size of protein- and lipid-coated PCND with C₅F₁₂ or C₆F₁₄ cores and mean diameters of ∼200 and ∼ 300 nm. Across formulations, physicochemical properties, including stability, mechanical deformability and acoustic vaporization threshold, were found to be formulation dependent. These properties, in turn, influence acoustic vaporization, tolerated dose and in vivo pharmacokinetics. Notably, larger or protein-coated PCND exhibited lower acoustic vaporization thresholds, but had lower tolerated doses, shorter circulation half-lives and reduced tumor accumulation. Conversely, smaller or lipid-coated PCND demonstrated improved tolerability, prolonged circulation and greater tumor retention, though they required higher acoustic pressures for vaporization. Additionally, shell mechanics governed PCND deformability, likely influencing their circulation and ability to traverse microvascular constrictions. Tumor accumulation was therefore shaped by both formulation properties and tumor vascular architecture. Formulations with greater stability, deformability, and prolonged circulation accumulated even in less permissive vasculature, whereas formulations with lower stability and shorter circulation required higher vascular permeability for detectable delivery. Overall, we provide a mechanistic framework for PCND design that links formulation parameters to their pharmacological profile and balances vaporization efficiency with in vivo performance and dose tolerability.