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Marques Mendes Almeida da Rosa Leal, Catarina
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- Rheology of living cellsPublication . Portela, R.; Franco, Jose M.; Almeida, Pedro L.; Patricio, Pedro; Sobral, Rita; R. Leal, CatarinaThe mechanical behavior of living cells, during planktonic growth, has been thoroughly explored combining common biological techniques with rheology and rheo-imaging measurements. Under a shear flow, bacterial cultures of Staphylococcus aureus revealed a complex and rich rheological behavior not usually accessed in biological studies. In particular, in stationary shear flow, the viscosity increased during the exponential phase and returned close to its initial value at the late phase of growth, accompanied by the stabilization of the bacterial population. In oscillatory flow, the elastic and viscous moduli exhibited power-law behaviors whose exponents are dependent on the bacteria growth stage, and can be associated to a Soft Glassy Material behavior. These behaviors were framed in a microscopic model that suggests the formation of a dynamic web-like structure, where specific aggregation phenomena may occur, depending on growth stage and cell density. Furthermore, systematic measurements combining optical density and dry weight techniques presented new evidences, which confirmed that the observed cell aggregation patterns developed during growth, under shear, can not only be cell density dependent.
- Cell necklaces behave as a soft glassy materialPublication . Franco, Jose M.; Patricio, Pedro; Almeida, Pedro L.; Portela, Raquel; Sobral, Rita; R. Leal, CatarinaPreviously we have reported a complex and rich viscoelastic behavior observed during the Planktonic growth of S. aureus strain COL1. In particular, in stationary shear flow, the viscosity Keeps increasing during the exponential phase and returns close to its initial value for the late phase of growth, where the bactéria population stabilizes. In oscillatory flow, the elastic and viscous moduli exhibit power--‐law behaviors whose exponentes are dependente on the bacteria growth stage. These power--‐law dependencies of G’ and G’’ match a Soft Glassy Material behavior. To describe this observed behavior, we have hypothesized a microscopic model considering the formation of a dynamic web--‐like structure, where percolation phenomena can occur, depending on growth stage and cell density. In this communication we describe the formation of these web--‐like structures, resembling cell necklaces at a specific time interval during bacterial growth. These findings were obtained by combining the previous data with new measurements performed in a rheometer with real--‐time image acquisition.