  A method combining video imaging in parallel microchannels with a
semi-empirical mathematical model provides non-intrusive, high-throughput
measurements of time-varying biofilm viscosity. The approach is demonstrated
for early growth Pseudomonas sp. biofilms exposed to constant flow streams of
nutrient solutions with different ionic strengths. The ability to measure
viscosities at early growth stages, without inducing a shear-thickening
response, enabled measurements that are among the lowest reported to date. In
addition, good time resolution enabled the detection of a rapid thickening
phase, which occurred at different times after the exponential growth phase
finished, depending on the ionic strength. The technique opens the way for a
combinatorial approach to beter understand the complex dynamical response of
biofilm mechanical properties under well-controlled physical, chemical and
biological growth conditions and time-limited perturbations.
