Numerical modelling of the normal adhesive elastic-plastic interaction of a bacterium

Bacteria are a widespread group of organisms. On the microscale, bacteria colonies are of discrete nature. Looking from the mechanical point of view the suspension containing the bacteria may be considered as a system of living active ultrafine particles (size: 0.1-10 mu m). In order to understand the mechanical behaviour of the bacteria system it is important to understand the behaviour of a single bacterium. The present paper proposes an adhesive interaction model for the simulation of bacteria cells, which can be also applied for the interaction for other biological cells. The main attention is given to describe and numericaly simulate the interaction of a bacterium with a flat surface within a liquid medium. In the simulations an adhesive force is taken into account. Adhesion plays a significant role, because it can keep a bacterium on the surface. It is described by the attractive van der Waals force. In order to achieve the stick of adhesive particles, additionally developed adhesive-dissipative models are presented. The bacterium interaction is described by an elastic-plastic model; these results are thereafter compared with results from an elastic model. Different known models such as Derjaguin, Muller and Toporov (DMT) and Derjaguin, Landau, Verwey, Overbeek (DLVO) models are considered. Obtained results show the approach and deformation process of an adhesive-dissipative bacterium by presenting force displacement diagrams. The bacterium-surface interaction model is developed in the framework of the discrete element method (DEM). The numerical experiments confirm that force-displacement plots exhibit a hysteresis similar to those observed in Atomic Force Microscopy (AFM) experiments. The proposed model can be applied for the numerical simulation of the interaction process of bacteria with a surface, as well as simulations of the sticking process. (C) 2015 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.