Bursts and cavity formation in Hydra cells aggregates: experiments and simulations

We present experimental results and a simulation in two dimensions of the expansion and bursting of aggregates of Hydra cells formed from an initially disordered mixture. In the experiments, after cell sorting, the aggregate rounds and swells until violent bursts occur, forcibly expelling internal fluid and loose cells. We use Monte Carlo techniques to simulate the bursts in two dimensions. Initially, we consider a ring made of a monolayer of cells enveloping an internal fluid. Each cell and the internal medium have their areas controlled by target area size. Increasing the target area of the internal cavity causes the aggregate to swell. We observe that aggregates of cells with higher surface tension generate higher internal pressure. In the simulations the cell ring bursts when it is too thin to endure fluctuations in the cellular membranes. The process is relevant to embryonic development.