| Fluids play an important role in a wide range of biological processes. They facilitate cellular activities, protect us from infection and propagate nutrients throughout the body, to name a few. In each case, the properties of the fluid are finely tuned to the task at hand, and understanding those properties can afford a deeper understanding of the underlying biology. Furthermore, knowing how disease or environmental factors alter the properties of these fluids can provide a means to interpret, and forecast, downstream deleterious effects.;To this end, microrheology is an increasingly popular means of investigating biological fluids. This technique, whereby tracer particles are embedded in the fluid of interest and their diffusive movements are used to infer the viscous and elastic moduli of the surrounding fluid, offers insight into properties of the fluid at a spatial and temporal resolution unmatched by traditional macrorheology approaches.;Despite its benefits, the wider application of microrheology has been limited by the presence of two, frequently encountered, phenomena: the existence of an active driving force coupled to the stochastic movement of the tracer particles, and the presence of spatial, or temporal, heterogeneity in the fluid under investigation. This work proposes best practices for addressing each of these phenomena and demonstrates how they may be coupled to diffusion models to more accurately describe, and predict, the movement of micro- and nano-scale particles through biological fluids. We apply the methodology developed herein to the analysis of bronchoalveolar lavage fluid from a pediatric cystic fibrosis cohort as part of an ongoing effort to characterize pulmonary manifestations of the disease. |
