# From individual-based mechanical models of multicellular systems to free-boundary problems

## TL;DR

This paper develops a mechanical model for two interacting cell populations, deriving a free-boundary continuum model, proving its mathematical properties, and validating it through numerical simulations that align well with individual-based models.

## Contribution

It introduces a novel link between discrete cell models and continuum free-boundary problems, including mathematical analysis and validation.

## Key findings

- Continuum model accurately describes cell population dynamics.
- Mathematical proof of existence and traveling-wave solutions.
- Numerical results agree with individual-based simulations.

## Abstract

In this paper we present an individual-based mechanical model that describes the dynamics of two contiguous cell populations with different proliferative and mechanical characteristics. An off-lattice modelling approach is considered whereby: (i) every cell is identified by the position of its centre; (ii) mechanical interactions between cells are described via generic nonlinear force laws; and (iii) cell proliferation is contact inhibited. We formally show that the continuum counterpart of this discrete model is given by a free-boundary problem for the cell densities. The results of the derivation demonstrate how the parameters of continuum mechanical models of multicellular systems can be related to biophysical cell properties. We prove an existence result for the free-boundary problem and construct travelling-wave solutions. Numerical simulations are performed in the case where the cellular interaction forces are described by the celebrated Johnson-Kendall-Roberts model of elastic contact, which has been previously used to model cell-cell interactions. The results obtained indicate excellent agreement between the simulation results for the individual-based model, the numerical solutions of the corresponding free-boundary problem and the travelling-wave analysis.