Learning from bacterial locomotion in complex media for robotic design and medical devices

The ability of bacteria to navigate complex media underlies infection, biofilm formation, and immune evasion. Research on bacterial locomotion informs the engineering of targeted micro-robotic systems, inspiring a new generation of drug delivery vehicles. Although the hydrodynamics of bacterial swimming has been well-studied in Newtonian fluids, the real-world biological environment, such as mucus layers, polymeric gels, and extracellular matrices, exhibits non-Newtonian properties (shear thinning, viscoelasticity, yield stress, etc.) that profoundly reshape bacterial locomotion. There are at least three key questions that complicate the study of bacterial locomotion in complex media. First, how do confined geometry and viscoelastic environments affect the propulsion strategies of bacteria? Second, beyond passive rheological influences, how does bacterial activity remodel their surroundings through interfacial physics, including but not limited to capillary flows, Marangoni-like instabilities, and surface buckling? Third, beyond single-cell dynamics, how do pairwise interactions and large-scale collective movement produce emergent structures, such as branched swarms, rotating clusters, metastable jams, that reflect a delicate balance of propulsion, fluid memory, and confinement? This review first examines the operation mechanisms of single bacterial locomotion and how they inspire the design of microrobots, including biologically inspired synthetic microrobots to replicate the function of bacteria and biologically hybrid approaches that incorporate living bacteria for cargo delivery. We also review studies on how bacteria–surface interactions facilitate the design of biomedical devices. We then review recent experimental progress on bacterial locomotion in complex media, highlighting how bacterial strategies to overcome viscoelastic drag, confinement, and mechanical heterogeneity can inform the next generation of microrobotic design. Finally, we review recent advances in computational modeling approaches, including various squirmer frameworks and flagella-based approaches to model bacteria, different types of viscoelastic fluid models, and computational algorithms. These simulations can not only account for various modes of locomotion in complex environments but also reveal emergent behaviors and design principles that are difficult to capture experimentally. Together, these efforts provide a roadmap for developing environment-aware microrobots capable of efficient propulsion and task execution in complex biological settings.