Studying the Internal Stress Heterogeneity of the Growing Biofilm by the Micropillar Deformation of the Growing Substrate

Abstract

The bacterial biofilm is a microbial community in which bacteria are embedded in the extracellular matrix and can also be used as a solid composite. It was found that internal stresses are generated during pellicle growth, which exists between the air and the liquid. But we do not know if there is the internal stress in the biofilm, which exists between the air and the solid, and how does the internal stress evolve and distribute in the growing biofilm. So, in this paper, we make the growing substrate into the micropillar array to grow biofilms, each micropillar has the deformation due to the growing heterogeneity of the biofilm around the micropillar, and we can get the internal stress by measuring each micropillar’s deformation. First, we find that the direction of the internal stress is approximately along the biofilm expansion at the early time, colonies are formed in the biofilm at the later time, which cause the internal stress locally along the expansion of the colony. Second, the internal stress is proportional to the biofilm thickness. Finally, we find that the matrix producing cells contribute more the internal stress, and the internal stress evolving is closely related to the secretion of the extracellular matrix. Form our work, we obtain the distribution of the internal stress direction, we also can use the biofilm thickness, which is easy to measure, express the internal stress approximately, by doing so, we can further study other phenomena of biofilms, such as self-healing and mechanical resistance.

Analysis of biofilm expansion rate on agar substrates with different stiffness under limited nutrition

“…However, due to the heterogeneity of bio lm growth, there exists the internal stress along the cluster radial expansion direction locally. The internal stress direction is getting more uniform with the bio lm growth, as the cell density and the extracellular matrix increase [21].…”

“…According to previous studies [21] the correlation between the bio lm thickness and the internal stress magnitude can be expressed in the following equation:…”