Fig. 1

3D porous media for direct visualization of bacteria motion. a Schematic of 3D porous media made by jammed packings of hydrogel particles, shown as gray circles, swollen in liquid LB medium. E. coli, shown in green, are dispersed at a low concentration within the pores between the particles. The packing is transparent, enabling imaging within the 3D pore space; inset shows a micrograph of a GFP-labeled bacterium. Scale bar represents 2 μm. b Time-projection of a 200 nm fluorescent tracer particle as it diffuses through the pore space, showing tortuous channels, each composed of a series of randomly-oriented, directed paths. Scale bar represents 5 μm. c Complementary cumulative distribution function 1-CDF of the smallest confining pore size a measured using tracer particle diffusion for four different porous media with four different hydrogel particle packing densities. Percentage indicates the mass fraction of dry hydrogel granules used to prepare each medium. Dashed line indicates cell body length of E. coli as a reference. Distributions are exponential, as indicated by straight lines on log-lin axes