School of Biomedical Sciences, University of Leeds, Leeds, UK.
School of Engineering, Newcastle University, Newcastle Upon Tyne, UK.
NPJ Biofilms Microbiomes. 2020 Apr 14;6(1):19. doi: 10.1038/s41522-020-0126-1.
Bacterial biofilms in natural and artificial environments perform a wide array of beneficial or detrimental functions and exhibit resistance to physical as well as chemical perturbations. In dynamic environments, where periodic or aperiodic flows over surfaces are involved, biofilms can be subjected to large shear forces. The ability to withstand these forces, which is often attributed to the resilience of the extracellular matrix. This attribute of the extracellular matrix is referred to as viscoelasticity and is a result of self-assembly and cross-linking of multiple polymeric components that are secreted by the microbes. We aim to understand the viscoelastic characteristic of biofilms subjected to large shear forces by performing Large Amplitude Oscillatory Shear (LAOS) experiments on four species of bacterial biofilms: Bacillus subtilis, Comamonas denitrificans, Pseudomonas fluorescens and Pseudomonas aeruginosa. We find that nonlinear viscoelastic measures such as intracycle strain stiffening and intracycle shear thickening for each of the tested species, exhibit subtle or distinct differences in the plot of strain amplitude versus frequency (Pipkin diagram). The biofilms also exhibit variability in the onset of nonlinear behaviour and energy dissipation characteristics, which could be a result of heterogeneity of the extracellular matrix constituents of the different biofilms. The results provide insight into the nonlinear rheological behaviour of biofilms as they are subjected to large strains or strain rates; a situation that is commonly encountered in nature, but rarely investigated.
在自然和人工环境中，细菌生物膜具有广泛的有益或有害功能，并表现出对物理和化学干扰的抵抗力。在涉及表面周期性或非周期性流动的动态环境中，生物膜可能会受到较大的剪切力。这种抵抗能力通常归因于细胞外基质的弹性，细胞外基质的这一属性被称为粘弹性，是由微生物分泌的多种聚合物成分的自组装和交联形成的。我们的目标是通过对枯草芽孢杆菌、脱氮假单胞菌、荧光假单胞菌和铜绿假单胞菌这四种细菌生物膜进行大振幅振荡剪切（LAOS）实验，来了解在大剪切力作用下生物膜的粘弹性特征。我们发现，对于每种测试的生物膜，非线性粘弹性测量指标，如循环内应变硬化和循环内剪切增稠，在应变幅度与频率的关系图（皮普金图）中表现出细微或明显的差异。生物膜在非线性行为的开始和能量耗散特性方面也表现出可变性，这可能是不同生物膜的细胞外基质成分异质性的结果。这些结果提供了对生物膜在受到大应变或应变速率时的非线性流变行为的深入了解；这种情况在自然界中很常见，但很少被研究。
