The mechanical response of biological tissues is essential for their function, and therefore we would like to better understand how single cells control global tissue properties such as tissue fluidity. A confluent tissue fluidizes when cells are able to diffuse by executing a series of cell rearrangements, which are called T1 transitions in 2D.  In a 2D model for disordered confluent tissues, it has been shown that the tissue fluidizes when the T1 energy barriers disappear as the target shape index approaches a critical value (3.81). In disordered systems, the linear response becomes fluidlike (i.e. the shear modulus vanishes) at this same critical point. However, it has been shown that the ordered ground states of 2D vertex models become linearly unstable at a lower value of the target shape index (3.72).  Therefore, an interesting open question is whether the ground states of the 2D vertex model are fluid-like or solid-like between 3.72 and 3.81. Using four-cell and many-cell numerical simulations, we demonstrate that for a hexagonal ground state, T1 energy barriers only vanish at 3.81, indicating that ordered systems have the same critical point as disordered systems and that ordered tissues are only fluid-like above this critical point.

Modeling solid-fluid transitions of biological tissues

2019 Spring National Meeting

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