Volume-filling and quorum-sensing in models for chemosensitive movement

Chemotaxis is one of many mechanisms used
by cells and organisms to navigate through the environment,
and has been found on scales varying from the microscopic to
the macroscopic. Chemotactic movement has also attracted
a great deal of computational and modelling attention. Some
of the continuum models are unstable in the sense that they
can lead to finite time blow-up, or “overcrowding” scenarios.
Cell overcrowding is unrealistic from a biological context, as it
ignores the finite size of individual cells and the behaviour of
cells at higher densities. We have previously presented a mathematical
model of chemotaxis incorporating density dependence
that precludes blow-up from occurring, [19]. In this paper, we
consider a number of approaches by which such equations can
arise based on biologically realistic mechanisms, including the
finite size of individual cells - “volume filling” and the employment
of cell density sensing mechanisms - “quorum-sensing”.
We show the existence of nontrivial steady states and we study
the traveling wave problem for these models. A comprehensive
numerical exploration of the model reveals a wide variety of
interesting pattern forming properties. Finally we turn our attention
to the robustness of patterning under domain growth,
and discuss some potential applications of the model.