Ultrasound Characterization of Mechanical Properties of Nanometric Contrast Agents with PLGA Shell in Suspension
Résumé
Dispersion and absorption are examined for dilute suspensions of Ultrasound Contrast Agents of nanometric size (nACUs), with typical radii around 100 nm. This new generation of contrast agents is designed for targeted delivery of drugs. Compared to standard contrast agents used for imaging, particles are of smaller size to pass the endothelial barrier, their shell made up of biocompatible polymer (PLGA) is stiffer to undergo a longer time life and they have a liquid (PFOB) instead of a gaseous core. Ultrasound propagation in dilute suspension of nACUs is modelled by combining i) a dilatational mode of oscillation assuming an incompressible shell with a visco-elastic behaviour of Maxwell type (relaxation), and ii) a translational mode of oscillation induced by visco-inertial interaction with the ambient fluid. Experimental measurements of the dispersion and absorption properties of nACUs solutions over the 1-100 MHz frequency range are performed for various temperatures and concentrations. They allow to fit with good accuracy three unknown parameters of the nACUs shell: the thickness, the Young modulus and the viscosity (or equivalently the relaxation frequency). Obtained values are compatible with literature data and offer insight into the behaviour of PLGA shells in suspension [Work supported by programme Emergence-UPMC].
Domaines
Acoustique [physics.class-ph]
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