University of Ljubljana, Faculty of Mechanical Engineering, Aškerčeva cesta 6, Ljubljana, Slovenia.
University of Ljubljana, Faculty of Mechanical Engineering, Aškerčeva cesta 6, Ljubljana, Slovenia.
Ultrason Sonochem. 2022 Jun;87:106053. doi: 10.1016/j.ultsonch.2022.106053. Epub 2022 Jun 2.
Numerous studies have already shown that the process of cavitation can be successfully used for water treatment and eradication of bacteria. However, most of the relevant studies are being conducted on a macro scale, so the understanding of the processes at a fundamental level remains poor. In attempt to further elucidate the process of cavitation-assisted water treatment on a scale of a single bubble, the present paper numerically addresses interaction between a collapsing microbubble and a nearby compliant structure, that mechanically and structurally resembles a bacterial cell. A fluid-structure interaction methodology is employed, where compressible multiphase flow is considered and the bacterial cell wall is modeled as a multi-layered shell structure. Simulations are performed for two selected model structures, each resembling the main structural features of Gram-negative and Gram-positive bacterial cell envelopes. The contribution of two independent dimensionless geometric parameters is investigated, namely the bubble-cell distance δ and their size ratio ς. Three characteristic modes of bubble collapse dynamics and four modes of spatiotemporal occurrence of peak local stresses in the bacterial cell membrane are identified throughout the parameter space considered. The former range from the development of a weak and thin jet away from the cell to spherical bubble collapses. The results show that local stresses arising from bubble-induced loads can exceed poration thresholds of cell membranes and that bacterial cell damage could be explained solely by mechanical effects in absence of thermal and chemical ones. Based on this, the damage potential of a single microbubble for bacteria eradication is estimated, showing a higher resistance of the Gram-positive model organism to the nearby bubble collapse. Microstreaming is identified as the primary mechanical mechanism of bacterial cell damage, which in certain cases may be enhanced by the occurrence of shock waves during bubble collapse. The results are also discussed in the scope of bacteria eradication by cavitation treatment on a macro scale, where processes of hydrodynamic and ultrasonic cavitation are being employed.
大量研究已经表明，空化过程可成功地用于水处理和细菌消除。然而，大多数相关研究都是在宏观尺度上进行的，因此对基本层面上的过程理解仍然较差。为了进一步阐明在单个气泡尺度上的空化辅助水处理过程，本文数值研究了在机械和结构上类似于细菌细胞的可变形结构附近的微气泡溃灭过程。采用流固耦合方法，其中考虑可压缩多相流，细菌细胞壁建模为多层壳结构。对两种选定的模型结构进行了模拟，每种结构都模拟了革兰氏阴性和革兰氏阳性细菌细胞包膜的主要结构特征。研究了两个独立的无量纲几何参数的贡献，即气泡-细胞距离δ和它们的尺寸比ς。在考虑的参数空间内，确定了三种微气泡溃灭动力学的特征模式和四种细菌细胞膜中峰值局部应力的时空发生模式。前三种模式包括从细胞上形成的弱薄射流到球形气泡溃灭的发展。结果表明，由气泡引起的负载产生的局部应力可能超过细胞膜的穿孔阈值，并且在没有热和化学效应的情况下，细菌细胞损伤可以仅通过机械效应来解释。基于此，估算了单个微气泡对细菌消除的破坏潜力，显示革兰氏阳性模型生物对附近气泡溃灭具有更高的抵抗力。微流被确定为细菌细胞损伤的主要机械机制，在某些情况下，在气泡溃灭期间可能会增强冲击波的发生。还在宏观尺度上通过空化处理进行细菌消除的范围内讨论了结果，其中正在使用流体动力和超声空化过程。
