Rheological properties of cellular aggregates formed by pilus mediated interactions

Aggregates of living cells are an example of active materials with unconventional material properties. The rheological properties of cellular aggregates can, therefore, be markedly different from those exhibited by passive soft systems. Motivated by colonies of Neisseria gonorrhoeae bacteria, we develop a continuum theory to study cellular aggregates formed by attractive pulis mediated intercellular interactions. We find that the formation of cellular aggregates is an active phase separation process and we discuss the activity-induced viscoelastic properties of such aggregates. By studying the behaviour of aggregates under oscillatory shear, we can link the loss and storage moduli of the aggregates to the dynamics of the active intercellular forces. Due to the turnover of pili, the aggregates show a liquid-like behaviour at large times and strong shear-thinning effect under the large amplitude oscillatory shear. Our theory provides an important insight on how pilus mediated intercellular forces in cellular aggregates govern their material properties which in the future could be tested experimentally.