Influence of particle size, shape, and magnetic properties on torque-driven biofilm removal using anisotropic magnetic particles

Biofilms are structured communities of bacteria embedded within an extracellular polymeric substance (EPS) matrix, which forms a protective barrier that restricts drug penetration and increases antibiotic tolerance, making their complete elimination particularly challenging. Here, we investigate a magneto-mechanical approach using rotating magnetic fields (RMFs) to deliver controlled mechanical stress to Enterococcus faecalis biofilms via anisotropic magnetic particles (AMPs). Microrods, nanochains, and nanorods with distinct sizes and magnetic properties were actuated under identical RMF conditions on implant-relevant titanium substrates. Micron-scale magnetic microrods generate sufficient magnetic torque to mechanically disrupt the EPS matrix and detach biofilm structures, significantly increasing suspended bacterial cells without marked bactericidal effects. In contrast, nanoscale AMPs do not induce biofilm detachment but cause membrane damage, increasing the proportion of injured cells. These findings demonstrate a size-dependent transition between microscale biofilm detachment and nanoscale membrane interactions, identifying particle size as the dominant parameter governing magneto-mechanical biofilm disruption.