  The integration of motile cells into biohybrid microrobots offers unique
properties such as sensitive responses to external stimuli, resilience, and
intrinsic energy supply. Here we study biohybrid microtransporters that are
driven by amoeboid Dictyostelium discoideum cells and explore how the speed of
transport and the resulting viscous drag force scales with increasing radius of
the spherical cargo particle. Using a simplified geometrical model of the
cell-cargo interaction, we extrapolate our findings towards larger cargo sizes
that are not accessible with our experimental setup and predict a maximal cargo
size beyond which active cell-driven transport will stall. The active forces
exerted by the cells to move a cargo show mechanoresponsive adaptation and
increase dramatically when challenged by an external pulling force, a mechanism
that may become relevant when navigating cargo through complex heterogeneous
environments.
