MecaCell: an Open-source Efficient Cellular Physics Engine

We present an open source physics engine specialised for multi-cellular artificial organisms simulations. It is computationally efficient in comparison to gas-based and finite element models and more realistic than standard mass-springdamper systems. Introduction Morphogenetic engineering can often make good use of some biologically plausible improvements. Mechanics, in particular, are quite important to a certain group of bioinspired artificial life experiments. The usual tradeoff in cell simulation being between accuracy and computational efficiency, we have developed a model specialised in cellular physics which aims to stay efficient while precise enough for most artificial life applications. It is based on an improved mass-spring-damper (MSD) system, the use of which is widespread in the literature, mainly because of its computational efficiency. The main limitation in MSD systems is the difficulty they have when taking into account uneven adhesive forces and global tensegrity of a simulated biological system while allowing the simulation of freely moving cellular clusters in a 3D environment (Joachimczak et al. (2013)). We improved on this model by adding adhesion and collision springs, and we took inspiration from Euler-Bernouilli beam theory to account for flexure, torsion and shear, which are only possible with standard MSD system (which natively only handle compression) by using complex topologies. Physics model In our current cellular model, a cell is represented by a 3D position, an orientation and an implicit surface. Each cell also has a mass, a radius, a stiffness and an adhesive strength (influencing connection length, resistance to traction, flexure, torsion and shear). Cells are linked two by two by a simplified elastic beam modeled by one compression spring that embeds two tendons per cells. One is used to simulate the flexure relative to the compression spring and the other the torsion. These forces allow for the development of linear structures with interesting tensegrity characteristics. Mass Mass Implicit surface Implicit surface Cell A Cell B