Mechanical confinement affects cells via two main mechanisms: shielding from environmental stimuli and providing mechanical resistance against cell deformation. I begin with a theoretical investigation of multicellular spheroids in microfluidic conditions. I discuss the asymmetries in nutrient gradients stemming from fluid flow and the partial confinement provided by the chamber substrate and how the latter limits the capacity of fluid flow to let spheroids grow to their ideal diffusion-limited size. Simulating mechanical forcing by an oscillatory flow shows that spheroid poroelasticity induces inward compressive-stress gradients, which could contribute to overcoming diffusion-limited growth. I then present an experimental investigation of bacterial aggregates, or flocs, intercepted in constrictions. Flocs are taken from saturated batch cultures of fluorescent Bacillus subtilis and injected into microchannels with funnel-shaped constrictions (smallest width 10 μm). I present the novel observation that intercepted aggregates supplied with nutrient-rich medium actively escape from the constrictions. This behaviour begins with a multiple-fold outward expansion of the aggregates (strain rate 0.5-1% min-1), which lasts ~3 hours at room temperature and is characterised by chain-like bacterial morphology and reduced biomass growth. Once the aggregates have reached a sufficiently low cell density, around half the cells separate from the floc and leave the funnel. After that, biomass grows from the remaining floc kernel, with negligible floc deformation. This "escape" mode requires both interception, which compresses aggregates, and a nutrientrich medium to occur. Its kinetics suggest that enzymatic degradation could be occurring and be triggered by the bacteria mechanically sensing confinement.
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