Dependence of Hydrogel-Glass Energy of Adhesion and Kinetics of Delamination on Hydrogel Concentration

Pseudomonas aeruginosa bacteria move collectively at viscous interfaces via twitching motility¹, which plays an important role in biofilm formation and subsequent infection. This phenomenon is studied by forcing the bacteria to twitch at the interface of a glass microscope slide and a hydrogel such as agar. The expanding bacterial colony needs to break the adhesive bond between the glass and the agar. Although the pulling force generated by the type-IV-pilus² and the stiffness of the agar hydrogel³ have been measured, the adhesive interaction between the glass and the agar is not well characterized. We have used micropipette deflection experiments to measure the increase in the adhesive shear strength with increasing agar concentration: 120 ± 60 N/m² for 1.0% w/v agar, and 260 ± 110 N/m² for 1.5% w/v agar. To more accurately mimic the breaking of the adhesive bond by the bacterial cells, we have developed a confined blister test that measures the energy of adhesion and the kinetics of delamination of agar-glass interfaces. I will describe the results of our measurements performed for different agar concentrations.
1 Semmler, Whitchurch, Mattick (1999) Microbiology 145:2863
2 Maier (2013) Soft Matter 9:5667
3 Sharma, Bhattacharya (2014) Journal of Food Engineering 141:93