What is it about?

Critical shear stresses for bacterial biofilms from dental unit waterlines are studied with microfluidics. The effect of elevated Mg2+ are investigated, providing a new perspective on the non-Newtonian nature of some biofilms and their treatment.

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Why is it important?

Because of the protective and adaptive nature of bacterial biofilms they are a very potent vector for virulent infections as wall as an engineering challenge for most civil and industrial water systems. Limiting their growth required the application of significant antimicrobial agents and general maintenance. Our results show that in a low ionic environment, the studied strain (Pseudomonas aeruginosa, PPF-1) produces ejected biofilm material nearly continuously, which can result in increased downstream colonization of engineered flow systems. Introducing magnesium salt increased mechanical stability, which resulted in elevated tolerances to shear stresses. However, the enhanced magnesium seemed also to place the PPF-1 biofilm into a viscoplastic mechanical state, which resulted in signature responses to critical shear stresses, such as catastrophic sloughing involving abrupt tearing that produced clean edges at the fracture boundary, indicating that the biofilm had become brittle. The biofilm removal in this state was complete except for the channel corners.


We remain intrigued by the complex mechanical behaviours of bacterial biofilms which can change in space and time and literally respond to external challenges as they arise. There are very few examples of bacterial biofilms displaying viscoplatic mechanical properties. We wonder if transforming them to a viscoplastic state might be a promising approach to tearing them our of water conduits, without using aggressive antibacterial chemicals.

Jesse Greener

Read the Original

This page is a summary of: Critical shear stresses of Pseudomonas aeruginosa biofilms from dental unit waterlines studied using microfluidics and additional magnesium ions, Physics of Fluids, February 2022, American Institute of Physics, DOI: 10.1063/5.0076737.
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