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The quantification of biofilm mechanical properties canserve asa basis for understanding biofilm resilience and for developing biofilmcontrol strategies. One aspect of tensile testing that is likely tobe important for a viscoelastic material such as bacterial biofilm,but unfortunately is often overlooked (i.e., not controlled or reported),is the strain rate used during testing. Thus, we performed tensiletesting on intact S. epidermidisbiofilms using themicrocantilever method at 12 strain rate values ranging over approximately3 orders of magnitude (0.013–9.07 s–1). Ultimateor cohesive strength, elastic modulus, and toughness increased withincreasing strain rate and approached a plateau at approximately 1.3s–1. Failure strain, on the other hand, did notexhibit any trend with strain rate. Given that the mean values ofsome parameters increased by as much as 1 order of magnitude overthe strain rate range used in this work, we suggest that the strainrate during tensile testing should be carefully controlled and reportedto facilitate comparisons among different studies. Furthermore, thequantitative expressions developed in this work that relate mechanicalproperty values with strain rate may be useful for modeling the deformationof bacterial biofilms under applied loads. [ABSTRACT FROM AUTHOR]

Biofilms possess unique mechanical properties that are vital to their stability and function. Biofilms are made of extracellular polymeric substances (EPS) secreted by microorganisms and comprise polysaccharides, proteins, extracellular DNA (eDNA), and lipids. EPS is the primary contributor and driver of the biofilm structure and mechanical properties such as stiffness, cohesion, and adhesion. EPS enhances the elasticity and viscosity of biofilms, allowing them to withstand mechanical stresses, shear forces, and deformation. Therefore, biofilms are notoriously difficult to remove and can result in billions of dollars in losses for various industries due to their adverse effects, such as contamination, pressure loss, and corrosion. As a result, it is essential to comprehend the mechanical properties of biofilms to control or remove them in various scenarios. We undertook a fundamental study to determine the relationship between individual EPS components and biofilm mechanical properties. In this study, a CDC biofilm reactor was used to grow pure culture biofilms (Staphylococcus epidermidis) which were treated with six EPS modifier agents (Ca 2+ , Mg 2+ , periodic acid, protease K, lipase, and DNAase I) to modify or cleave specific EPS components. The mechanical properties (Young's Modulus) of treated biofilms were subsequently tested using atomic force microscopy (AFM), the biofilm EPS functional groups were measured via the Fourier transform infrared (FTIR) spectroscopy, and biofilm structural characteristics using confocal imaging. The FTIR results showed that EPS modifier agents successfully reduced their target EPS components. Similarly, the confocal microscopic analysis results showed that most of these modifier agents (except lipase) significantly reduced (P-value <0.05) the biovolume and thickness of treated biofilms. Conversely, most of these modifier agents (except protease K) significantly increased (P-value <0.05) the roughness coefficient of the biofilms. Finally, data from AFM showed that biofilm mechanical properties (Young's modulus) significantly (P-value <0.05) changed with their EPS composition. These results have significant ramifications for biofilm management and control in myriad scenarios., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Srijan Aggarwal reports financial support was provided by NSF, (Copyright © 2024 Elsevier B.V. All rights reserved.)

Bacterial biofilms are highly resistant to common antibacterial treatments, and several physiological explanations have been offered to explain the recalcitrant nature of bacterial biofilms. Herein, a biophysical aspect of biofilm recalcitrance is being reported on. While engineering structures are often overdesigned with a factor of safety (FOS) usually under 10, experimental measurements of biofilm cohesive strength suggest that the FOS is on the order of thousands. In other words, bacterial biofilms appear to be designed to withstand extreme forces rather than typical or average loads. In scenarios requiring the removal or control of unwanted biofilms, this emphasizes the importance of considering strategies for structurally weakening the biofilms in conjunction with bacterial inactivation.