Nanomaterials as Ultrasound Theragnostic Tools for Heart Disease Treatment/Diagnosis

Abstract

A variety of different nanomaterials (NMs) such as microbubbles (MBs), nanobubbles (NBs), nanodroplets (NDs), and silica hollow meso-structures have been tested as ultrasound contrast agents for the detection of heart diseases. The inner part of these NMs is made gaseous to yield an ultrasound contrast, which arises from the difference in acoustic impedance between the interior and exterior of such a structure. Furthermore, to specifically achieve a contrast in the diseased heart region (DHR), NMs can be designed to target this region in essentially three different ways (i.e., passively when NMs are small enough to diffuse through the holes of the vessels supplying the DHR, actively by being associated with a ligand that recognizes a receptor of the DHR, or magnetically by applying a magnetic field orientated in the direction of the DHR on a NM responding to such stimulus). The localization and resolution of ultrasound imaging can be further improved by applying ultrasounds in the DHR, by increasing the ultrasound frequency, or by using harmonic, sub-harmonic, or super-resolution imaging. Local imaging can be achieved with other non-gaseous NMs of metallic composition (i.e., essentially made of Au) by using photoacoustic imaging, thus widening the range of NMs usable for cardiac applications. These contrast agents may also have a therapeutic efficacy by carrying/activating/releasing a heart disease drug, by triggering ultrasound targeted microbubble destruction or enhanced cavitation in the DHR, for example, resulting in thrombolysis or helping to prevent heart transplant rejection.