Affiliation: Department of Chemical and Biochemical Engineering, University of Iowa 

Abstract: Biofilms formed on medical implants remain a major clinical challenge due to their resistance to antibiotics and the host immune system. Conventional treatments often fail, leaving residual bacteria that persist and re-establish infection. Thermal shock, applied as localized heating of implant surfaces, has emerged as a promising strategy to eradicate biofilms. Even before applying thermal shock, planktonic bacteria disperse continuously from mature biofilms, and this process can be strongly influenced by local stimuli such as temperature. The underlying mode of this phenomenon remains unclear, as bacterial reduction may result either from in-situ death within the biofilm or from dispersion of live cells responding to thermal stress. Dispersed bacteria, however, pose a risk of entering the bloodstream. 

This study investigates P. aeruginosa PAO1 biofilms under in-vitro conditions with and without thermal shock. We quantified bacterial departure into surrounding media and tissue mimics. Results show that dispersion into liquid media reached equilibrium within one minute, indicating rapid dynamic exchange between biofilm and planktonic population. Flow-cell experiments with minimized chance of re-adhesion showed that residual biofilm populations persisted, highlighting the resilience of attached bacteria. 

In tissue mimics, bacterial penetration followed an active transport mode rather than passive diffusion, with dispersion coefficients comparable to small molecules but extending deeper than expected. Application of thermal shocks (50–80 °C, 1–20 min) enhanced dispersion into deeper PVA layers, with bacteria detectable up to 12 mm at sub-lethal exposures (60–70 °C). Notably, an 80 °C shock for 3 minutes eradicated both surface biofilms and dispersed populations, preventing regrowth during subsequent incubation—even in the presence of tobramycin. By contrast, milder treatments promoted dispersal, leading to biofilm regrowth within one day. 

Authors: Hossein Zare and Eric Nuxoll