PhD Thesis Presentation: Micropipette Deflection and Constrained Blister Measurements of Agar-Glass Adhesion

PhD Candidate

Richard Parg

Abstract

We have studied the adhesion between agar hydrogels and glass substrates using micropipette deflection and constrained blister experiments. This work was motivated by observations of changes in the twitching motility of P. aeruginosa bacterial colonies at an agar-glass interface, characterized by transitions in the average bacterial colony edge speed and the average width of fingers that characterized the advancing colonies, as well as the local agar concentration near the agar-solid surface, as the agar concentration C was increased above 1.6% w/v. We observed a similar transition in the peak shear stress required to break the agar-glass interface in the micropipette deflection experiment. We further explored the dependence of the agar-glass adhesion on the agar concentration C by designing and constructing a constrained blister experiment, which more closely mimicked the delamination caused by twitching bacterial colonies. In the constrained blister experiment, the delamination of thin agar layers was produced by creating and growing a blister in the centre of the agar through the application of a small pressure P, with the deformation of the agar layer limited to 500 nm. We analyzed video sequences of the blister growth to measure the equivalent circular radius for both the outer ring (\(r_o\), delamination front) and inner ring (\(r_i\), constrained region) of blisters that were formed at constant pressures P ranging from 0.59 kPa to 1.93 kPa for agar concentrations C between 1.0% w/v and 1.9% w/v. In our experiment’s, the difference between \(r_i\) and \(r_o\) was constant for stable blister growth. The blister radius \(r_i\) increased linearly with time for all values of P at each agar concentration C. Additionally, at each agar concentration C, blister growth rate \(r_i\) increased linearly with increased pressure P. We extrapolated the pressure dependence of the blister growth rate to the minimum pressure required to observe blister growth, for each agar concentration C, which allowed us to determine the energies of adhesion \(E_{adh}\). These measurements revealed an agar concentration dependence of \(E_{adh}\) that was consistent with transitions near C= 1.6% w/v observed in the bacterial twitching and micropipette deflection experiments. Taken together, the micropipette deflection and constrained blister experiments allow a general strategy for characterization of hydrogel adhesion on a variety of substrates.

Examination Committee

• Dr. Hermann Eberl, Chair
• Dr. John Dutcher, Advisor Dr. Manjusri Misra, Advisory Committee
• Dr. Michael Massa, Graduate Faculty
• Dr. Christopher Murray, External Examiner (Lakehead University)