(625ab) Decoupling Adhesion From Cohesion In Biofilm-Substrate Composites

Biofilm formation is enhanced by bacteria through their production extracellular polymeric substances (EPS).  Therefore, the mechanical properties, particularly the elastic modulus and the failure stress of these biocomposites, coupled with the adhesion energy between the biofilm and substrate are important in quantitative prediction of microbe fate in environmental applications.

Recently, we introduced a technique allowing fabrication and characterization of freestanding asymmetric membranes at fluid-fluid interfaces.   Using this technique, biofilms of the Escherichia coli mutant D21g were synthesized by adsorption and complex formation of bacteria at the air-water interface of a pendant drop.  By comparing the shape of the drop during dilation of its surface with continuum models, the elasticity (i.e cohesive interactions) in the biofilm can be quantified.

For biofilms grown on an elastic solid substrate, the problem break-up and release is a more complex balance between cohesive interactions in the film and the adhesion energy between the film and substrate.  By measuring planar biaxial deformation characteristics of the composite biofilm-substrate system, the adhesion between biofilm and substrate can be decoupled from the elastic contributions of each.  Here, we present biaxial mechanical data, ie.e force-displacement and digital image correlation, for d21g biofilms grown on polydimethylsiloxane (PDMS).  Although biofilm intrinsic elasticity (cohesion) depends on age, growth phase, and other environmental conditions, the data show that interfacial effects (i.e. adhesion) dominate the composite system deformation in most cases studied.  More importantly, this work describes how adhesion energy can be decoupled from cohesive interactions and gives the basis for a technique which can be used to study the impact of cleaning agents or therapies design to mitigate biofilm adhesion.