(a) Still frame images illustrating the formation of a bubble cloud from the tail of perfluorohexane (PFH)-loaded microbullet (MB) upon firing of an ultrasound (US) pulse signal. (b) The trajectory (dotted arrow) of a (right) PFH-loaded microbullet is imaged 55 µs after an (left) US pulse signal. A dotted circle accents the emerging vaporized PFH while boxes highlight the location of the MB. (c) A MB incubated with PFH emulsion but not conjugated with cysteamine displays no emulsion expansion nor movement after a US pulse signal. Inset images show the (a) PFH-loaded MB and the (c) control MB (i.e., without cysteamine) while the US icon represents a US-triggered pulse signal (44 µsec, 1.6 MPa). Images obtained at a frame rate of 18,000 fps using a 40X objective. Scale bar, 40 µm (a, c) and 120 µm (b).