Study of a novel ultrasonically triggered drug vehicle with magnetic resonance properties

We developed a novel ultrasonically triggered drug vehicle with magnetic resonance (MR) properties by encapsulating superparamagnetic iron oxide (SPIO) nanoparticles in hydroxyapatite (HA)-coated liposomes. The effects of HA coating on the background leakage, ultrasound response and MR signal were investigated. HA coating of liposomes significantly reduced the background leakage of liposome. It also enhanced their sensitivity to ultrasound regardless of HA thickness or ultrasound frequency, even under sonication conditions of high frequency (1 and 3 MHz) and low power density (0.2–0.4 W cm−2) used for diagnosis. However, it was found that the ultrasonically triggered vehicle could exhibit T2 contrast in MR images by encapsulating SPIO. However, HA coating reduced the r2 value of SPIO encapsulated in liposomes, but had no significant effect on the r2∗ value, implying that MR images of HA-coated liposomes encapsulating SPIO could be probed by the T2∗ signal. Most importantly, the r2∗–r2 value of HA-coated liposomes encapsulating SPIO decreased after sonication, suggesting that the proposed vehicle could be used not only as a MR-guided drug vehicle capable of ultrasonically triggered release but also as a MR reporter to probe ultrasonic triggering.