  We propose and study a simple, physical model for phagocytosis, i.e. the
active, actin-mediated uptake of micron-sized particles by biological cells.
The cell is described by the phase field method and the driving mechanisms of
uptake are actin ratcheting, modeled by a dynamic vector field, as well as
cell-particle adhesion due to receptor-ligand binding. We first test the
modeling framework for the symmetric situation of a spherical cell engulfing a
fixed spherical particle. We then exemplify its versatility by studying various
asymmetric situations like different particle shapes and orientations, as well
as the simultaneous uptake of two particles. In addition, we perform a
perturbation theory of a slightly modified model version in the symmetric
setting, allowing to derive a reduced model, shedding light on the effective
driving forces and being easier to solve. This work is meant as a first step in
describing phagocytosis and we discuss several effects that are amenable to
future modeling within the same framework.
