Spatially confined rigid membranes reorganize their morphology in response to the imposed constraints. A crumpled elastic sheet presents a complex pattern of random folds focusing the deformation energy 1 , whereas compressing a membrane resting on a soft foundation creates a regular pattern of sinusoidal wrinkles with a broad distribution of energy [2][3][4][5][6][7][8] . Here, we study the energy distribution for highly confined membranes and show the emergence of a new morphological instability triggered by a period-doubling bifurcation. A periodic selforganized focalization of the deformation energy is observed provided that an up-down symmetry breaking, induced by the intrinsic nonlinearity of the elasticity equations, occurs. The physical model, exhibiting an analogy with parametric resonance in a nonlinear oscillator, is a new theoretical toolkit to understand the morphology of various confined systems, such as coated materials or living tissues, for example wrinkled skin Several theoretical approaches have been proposed to describe the wrinkling instability for very small compression ratio, that is, near the instability threshold 2,3,7 . However, the large-compression domain remains largely unexplored, with the notable exception of the wrinkle-to-fold transition observed in ref. 8 for an elastic membrane on liquid and the self-similar wrinkling patterns in skins 14 . In the former case, the deformation of the membrane is progressively focalized into a single fold, concentrating all the bending energy. In contrast, for thin rigid membranes on elastomers, large compression induces perturbations of the initial wrinkles but the elasticity of the soft foundation maintains a regular periodic pattern whose complexity increases with the compression ratio.A polydimethylsiloxane (PDMS) film, stretched and then cured with ultraviolet radiation-ozone, or a thin polymer film bound to an elastomer foundation, remains initially flat. Under a slight compression, δ = (L 0 − L)/L 0 , these systems instantaneously form regular (sinusoidal) wrinkles with a well-defined wavelength, λ 0 . Increasing δ generates a continuous increase of the amplitude of the wrinkles and a continuous shift to lower wavelength (λ = λ 0 (1 − δ); see Fig. 1g). By further compression of the sheet, more complex patterns emerge. Above some threshold, δ > δ 2 0.2, we observe a dramatic change in the morphology leading to a pitchfork bifurcation: one wrinkle grows in amplitude at the expense of its neighbours (Fig. 1). The profile of the membrane is no longer described by a single cosinusoid but requires a combination of two periodic functions, cos(2π x/λ) and cos(2π x/2λ). The amplitude of the 2λ mode increases with the compression ratio, whereas the λ mode vanishes. This effect is similar to period-doubling bifurcations in dynamical systems 15,16 observed in Rayleigh-Bernard convections 17 , dynamics of the heart tissue 18-20 , oscillated granular matter 21,22 or bouncing droplets on soap film 23 . In contrast to previous works, we describe here a sp...
Wrinkled morphology is a distinctive phenotype observed in mature biofilms produced by a great number of bacteria. Here we study the formation of macroscopic structures (wrinkles and folds) observed during the maturation of Bacillus subtilis pellicles in relation to their mechanical response. We show how the mechanical buckling instability can explain their formation. By performing simple tests, we highlight the role of confining geometry and growth in determining the symmetry of wrinkles. We also experimentally demonstrate that the pellicles are soft elastic materials for small deformations induced by a tensile device. The wrinkled structures are then described by using the equations of elastic plates, which include the growth process as a simple parameter representing biomass production. This growth controls buckling instability, which triggers the formation of wrinkles. We also describe how the structure of ripples is modified when capillary effects are dominant. Finally, the experiments performed on a mutant strain indicate that the presence of an extracellular matrix is required to maintain a connective and elastic pellicle.biofilm elasticity | biofilm growth | wrinkles formation B acterial biofilms most often refer to communities that self-assemble into a cohesive extracellular matrix on solid surfaces or as pellicles floating on top of liquids. Bacteria self-organize in a collective behavior, giving a large-scale coherence to the system. Biofilms thus represent a protected life mode allowing bacteria to survive in hostile environments and from where they can disperse to colonize new niches (1, 2). A primary characteristic of biofilm formation is the production of exopolymeric substances by some cells. These substances mostly consists of exopolysaccharides (EPS), a few specific proteins, and nucleic acids (3-5), but their exact composition depends on the strain of the bacterium and the type of nutrients present in the culture medium (6, 7). When studied in a laboratory, wild-type strains of Bacillus subtilis are known to produce floating pellicles of rich and complex multiscale architectures (8, 9). The vertical structures range from the local 50-μm-scale "fruiting bodies" (10) to the extended macroscopic patterns illustrated in Fig. 1. As recently suggested in ref. 11, multiscale roughness could play a role in increasing the defense capability of B. subtilis against vapor and liquid antimicrobial agents.This study centers on the physical forces acting on biofilm and determining their morphologies at the macroscopic scale. To proceed, we restrict our experimental approach to the simplified case where macroscopic pellicles stand on rich static media. We primarily focus on the pellicles formed by the wild-type strain NCIB 3610, but present some features measured on another wildtype strain DV1 to obtain a more complete picture of existing morphologies. Of course the phenotypes are even more complex in nature given the possible multistrain and species coassembly and the diversity of settings and environments.T...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.