Preparation of Phase-Change Nanodroplets and an Experimental Study

Abstract

To investigate the vaporization threshold of perfluoropentane encapsulated lipids nanodroplets and their feasibilities in assessing radio-frequency ablation margins in vitro. The nanodroplets with lipids shell and perfluoropentane (PFP) kemel was prepared by a Homogenization/emulsion method of which the size and zeta potential were measured by dynamic light scattering instrument (DLS). The phase change of perfluoropentane (PFP) nanodroplets (PFPNDs) stimulated by temperature rise was observed with the inverted optical microscope and ultrasonography. Echo intensity of bubbles generation from nanodroplets was calculated at different temperature points to plot the temperature-intensity curve. The temperature at the margins of hyperechogenicity zones generated from radiofrequency ablation (RFA) under ultrasonic guidance in tissue-mimicking phantom were measured with a thermocouple probe. The mean diameter of PFPNDs was 479.9±18.8nm. A few bubbles were observed at 50°C for PFPNDs with the inverted optical microscope, while a mass of bubbles generated rapidly from PFPNDs at 60°C, partly coalesced and ruptured ,and most of them ruptured at a higher temperature. No bubbles were observed in the Control group. With the ultrasonography, weak echo intensity of bubbles generated from PFPND at 50°C was detected. And when temperature rose to 60°C for PFPNDs or higher, the echo intensity reached peak value. Echo intensity in the Control group was not enhanced. The hyperechogenicity zones in the tissue-mimicking phantom dispersed with PFPNDs presented as elliptic shape along with the RFA needle, and the mean temperature at margin was 60.4°C. Little hyperechogenicity zones irregularly occurred in the Control group. The prepared PFPNDs can vaporize at given temperature. PFPNDs, with the vaporization threshold closed to the temperature threshold of tissues coagulative necrosis caused by RFA, is potential to assess the radiofrequency ablation margins in real time.