  One of the most important potential applications of self-propelled nano- and
microdevices is targeted drug delivery. To realize this, biocompatible
particles that can be guided collectively towards a target inside a patient's
body are required. Acoustically propelled nano- and microparticles constitute a
promising candidate for such biocompatible, artificial motile particles. The
main remaining obstacle to targeted drug delivery by self-propelled nano- and
microdevices is to also achieve a reliable and biocompatible method for guiding
them collectively to their target. Here, we propose such a method. As we
confirm by computer simulations, it allows for the remote guiding of large
numbers of acoustically propelled particles to a prescribed target by combining
a space- and time-dependent acoustic field and a time-dependent magnetic field.
The method works without detailed knowledge about the particle positions and
for arbitrary initial particle distributions. With these features, it paves the
way for the future application of self-propelled particles as vehicles for
targeted drug delivery in nanomedicine.
