Remote Magnetic Actuation of Micrometric Probes for <em>in situ</em> 3D Mapping of Bacterial Biofilm Physical Properties

Abstract

Bacterial adhesion and growth on interfaces lead to the formation of three-dimensional heterogeneous structures so-called biofilms. The cells dwelling in these structures are held together by physical interactions mediated by a network of extracellular polymeric substances. Bacterial biofilms impact many human activities and the understanding of their properties is crucial for a better control of their development - maintenance or eradication - depending on their adverse or beneficial outcome. This paper describes a novel methodology aiming to measure in situ the local physical properties of the biofilm that had been, until now, examined only from a macroscopic and homogeneous material perspective. The experiment described here involves introducing magnetic particles into a growing biofilm to seed local probes that can be remotely actuated without disturbing the structural properties of the biofilm. Dedicated magnetic tweezers were developed to exert a defined force on each particle embedded in the biofilm. The setup is mounted on the stage of a microscope to enable the recording of time-lapse images of the particle-pulling period. The particle trajectories are then extracted from the pulling sequence and the local viscoelastic parameters are derived from each particle displacement curve, thereby providing the 3D-spatial distribution of the parameters. Gaining insights into the biofilm mechanical profile is essential from an engineer's point of view for biofilm control purposes but also from a fundamental perspective to clarify the relationship between the architectural properties and the specific biology of these structures.

Spatial distribution of mechanical properties in Pseudomonas aeruginosa biofilms, and their potential impacts on biofilm deformation

“…Around 10–15 particles in the field of view were analyzed. A more visual description of the procedure can be found in Galy et al (2014).…”

“…In recent years, novel microrheological techniques have been developed (Birjiniuk et al, 2014;Cao et al, 2016;Galy et al, 2012;Karampatzakis et al, 2017;Thomen et al, 2017). In particular, magnetic actuation with magnetic tweezers, coupled with magnetic microparticles, may be ideal (Galy et al, 2012(Galy et al, , 2014Zrelli et al, 2013). This technique can overcome the limitations of other microscale techniques by using strong forces and in situ measurements.…”

Spatial distribution of mechanical properties in Pseudomonas aeruginosa biofilms, and their potential impacts on biofilm deformation

“…About 10-15 particles were analyzed per field. A more visual description of the procedure can also be found in Galy et al (2014).…”

“…In recent years, novel microrheological techniques have been developed (Birjiniuk et al, 2014;Cao et al, 2016;Galy et al, 2012;Karampatzakis et al, 2017;Thomen et al, 2017). In particular, magnetic actuation with magnetic tweezers, coupled with magnetic microparticles, may be ideal (Galy et al, 2014;Galy et al, 2012;Zrelli et al, 2013). This technique can overcome the limitations of other microscale techniques by using strong forces and in-situ measurements.…”