  Manipulation of micro/nano particles has been well studied and demonstrated
by optical, electromagnetic, and acoustic approaches, or their combinations.
Manipulation of internal structure of droplet/particle is rarely explored and
remains challenging due to its complicated nature. Here we demonstrated the
manipulation of internal structure of disk-in-sphere endoskeletal droplets
using acoustic wave for the first time. We developed a model to investigate the
physical mechanisms behind this novel phenomenon. Theoretical analysis of the
acoustic interactions indicated that these assembly dynamics arise from a
balance of the primary and secondary radiation forces. Additionally, the disk
orientation was found to change with acoustic driving frequency, which allowed
on-demand, reversible adjusting disk orientations with respect to the
substrate. This novel dynamic behavior leads to unique reversible arrangements
of the endoskeletal droplets and their internal architecture, which may provide
a new avenue for directed assembly of novel hierarchical colloidal
architectures and intracellular organelles or intra-organoid structures.
