Phase Change Ultrasound Contrast Agents with a Photopolymerized Diacetylene Shell

Abstract

Phase change contrast agents for ultrasound (US) imaging consist of nanodroplets (NDs) with a perfluorocarbon (PFC) liquid core stabilized with a lipid or a polymer shell. Liquid ↔ gas transition, occurring in the core, can be triggered by US to produce acoustically active microbubbles (MBs) in a process named acoustic droplet vaporization (ADV). MB shells containing polymerized diacetylene moiety were considered as a good trade off between the lipid MBs, showing optimal attenuation, and the polymeric ones, displaying enhanced stability. This work reports on novel perfluoropentane and perfluorobutane NDs stabilized with a monolayer of an amphiphilic fatty acid, i.e. 10,12-pentacosadiynoic acid (PCDA), cured with ultraviolet (UV) irradiation. The photopolymerization of the diacetylene groups, evidenced by the appearance of a blue color due to the conjugation of ene-yne sequences, exhibits a chromatic transition from the nonfluorescent blue color to a fluorescent red color when the NDs are heated or the pH of the suspension is basic. An estimate of the molecular weights reached by the polymerized PCDA in the shell, poly­(PCDA), has been obtained using gel permeation chromatography and MALDI-TOF mass spectrometry. The poly­(PCDA)/PFC NDs show good biocompatibility with fibroblast cells. ADV efficiency and acoustic properties before and after the transition were tested using a 1 MHz probe, revealing a resonance frequency between 1 and 2 MHz similar to other lipidic MBs. The surface of PCDA shelled NDs can be easily modified without influencing the stability and the acoustic performances of droplets. As a proof of concept we report on the conjugation of cyclic RGD and PEG chains of the particles to support targeting ability toward endothelial cells.

Proton range verification with ultrasound imaging using injectable radiation sensitive nanodroplets: a feasibility study

“…Theoretical considerations and experimental observations support the assumption of a negligible surface tension. Indeed, the nanodroplets employed in this study have an outstanding in-vial stability (Toumia et al 2019), while models predict a fast dissolution of nanodroplets with a positive surface tension (Mountford and Borden 2016). Additionally, it has been described that perfluorocarbons can decrease the overall surface tension of droplets (Unger and Matsunaga 2010).…”

“…nanodroplets employed in this study are comprised of a perfluorobutane (C4F10, boiling point of -2°C) liquid core encapsulated by a polymerizable fatty acid monolayer of 10,12-pentacosadiynoic acid (PCDA). The complete nanodroplet synthesis is described elsewhere (Toumia et al 2019) and can be performed with standard laboratory equipment. Moreover, feasibility of production was observed to be reproducible and laboratory-independent, as nanodroplets were initially developed in the University of Rome Tor Vergata, and subsequently prepared in the KU Leuven campus KULAK.…”

“…2.2.2 Nanodroplet size and concentration. The size distribution of the nanodroplets was measured by Dynamic Light Scattering (DLS), as described in (Toumia et al 2019). The median diameter of the nanodroplets (intensity-weighted) was found to be 842 nm ± 12 nm (n=4) and the polydispersity index was 0.25 ± 0.02.…”

“…Additionally, the shell can be functionalized to target tissues of interest, making them suitable for molecular imaging and targeted therapy (Deshpande et al 2010). Localized nanodroplet vaporization can be achieved with ultrasound waves at moderate to high intensities , Toumia et al 2019 or through laser heating (Dove et al 2014), yielding micrometer-sized echogenic bubbles readily imaged with Contrast Enhanced Ultrasound Imaging (CEUS). In order to minimize potential tissue damage from cavitation or heating, droplet vaporization should be achieved with moderate levels of acoustic or thermal energy (Sheeran et al 2011).…”

Advances in Targeted Tumor Diagnosis and Therapy Based on Ultrasound-Responsive Nanodroplets

“…A pentapeptide, which includes the RGD sequence followed by a D-Phe-Lys moiety to close the cyclic structure, i.e. cyclo (Arg-Gly-Asp-D-Phe-Lys) or cRGD, has been chosen to tether onto the surface of the poly (10,12-pentacosadiynoic acid) NDs [34]. With cRGD conjugated to the surface via PEG spacer, the bioadhesion of NDs with HUVEC cells is significantly enhanced…”