Swimming cells, including bacteria, sperm, and plankton, play integral roles in processes ranging from human reproduction to ecosystem dynamics to bioremediation in soil. In particular, swimming cells ubiquitously live in dynamic fluid environments that are characterized by complex porous microstructure. In this talk, we will examine the physical mechanisms underlying the transport of motile bacteria in a model microfluidic porous medium, which is used to precisely control both microstructure and flow. We show that such confined flows generate striking heterogeneity in the spatial distribution of motile bacteria due to interactions between cell shape and fluid flow. Unlike passive Brownian particulates, the effective diffusion of actively swimming `run-and-tumble' bacteria is significantly hindered in flow. In the case of magnetotactic bacteria - which use earth's magnetic field for navigation - we demonstrate that porous media flows can entirely halt their directed motility, locally trapping cells in the porous microstructure. This work illustrates how the physical environment impacts fundamental survival strategies of swimming cells and carries potential implications for biofilm formation and resource competition biomes.

Presbyopia is the most common vision disorder, resulting in compromised near vision for nearly all individuals over the age of 50. The mechanism(s) by which the eye becomes presbyopic remain poorly understood, though most indications point to natural aging processes in the lens, including growth, remodeling, and stiffening. These changes, which occur in parallel, result in an altered balance of residual stresses between the lens and its capsule in the accommodated state. However, their respective contributions to presbyopia are as yet unknown. Our lab is currently combining biochemical/biomechanical experiments, mechanobiological experiments, and multi-scale modeling for elucidating which of these factors is most important with a long-term goal of reversing or preventing these changes.