The influence of bodily fluid rheology on biofilm formation: known facts and open questions.

Biofilms-microbial communities encased in a self-produced extracellular matrix-pose a significant challenge in clinical settings due to their association with chronic infections and antibiotic resistance. Their formation in the human body is governed by a complex interplay of biological and environmental factors, including the biochemical composition of bodily fluids, fluid dynamics, and cell-cell and cell-surface interactions. Improving therapeutic strategies requires a deeper understanding of how host-specific conditions shape biofilm development. Despite efforts to replicate in vivo conditions, in vitro models are often insufficient for capturing the complex dynamics of biofilm formation within the host. This limitation hinders the translation of experimental findings into clinical applications and slows the development of targeted therapies. In this review, we examine the role of fluid dynamics within the human body, with a particular focus on how the biochemical composition, rheological properties of bodily fluids and local flow conditions influence surface colonization and biofilm formation. We survey the current state of the field and outline key open challenges, intending to inform and inspire the development of next-generation experimental models that more closely reflect physiological reality.This article is part of the theme issue 'Biological fluid dynamics: emerging directions'.