  As society paves its way towards device miniaturization and precision
medicine, micro-scale actuation and guided transport become increasingly
prominent research fields with high impact in both technological and clinical
contexts. In order to accomplish directed motion of micron-sized objects
towards specific target sites, active biohybrid transport systems, such as
motile living cells that act as smart biochemically-powered micro-carriers,
have been suggested as an alternative to synthetic micro-robots. Inspired by
the motility of leukocytes, we propose the amoeboid crawling of eukaryotic
cells as a promising mechanism for transport of micron-sized cargoes and
present an in-depth study of this novel type of composite active matter. Its
transport properties result from the interactions of an active element (cell)
and a passive one (cargo) and reveal an optimal cargo size that enhances the
locomotion of the load-carrying cells, even exceeding their motility in the
absence of cargo. The experimental findings are rationalized in terms of a
biohybrid active matter theory that explains the emergent cell-cargo dynamics
and enables us to derive the long-time transport properties of amoeboid
micro-carries. As amoeboid locomotion is commonly observed for mammalian cells
such as leukocytes, our results lay the foundations for the study of transport
performance of other medically relevant cell types and for extending our
findings to more advanced transport tasks in complex environments, such as
tissues.
