Figure 1. Orientation of the WT E. coli cells attached on top of PDMS line patterns at 24 h after inoculation.

(a) Schematic description of PDMS line patterns used in this study. Pattern Length (L) and Height (H) were fixed at 4 mm and 5 μm, respectively, while pattern width (W) and inter-pattern distance (D) were varied. (b) Definition of cell orientation. Cells attached to both the top and side of line patterns and in the grooves, but only the cells attached on top of line patterns were compared for cell orientation. (c) Representative fluorescence images of WT E. coli cells attached on top of 5 μm (c1), 10 μm (c2), or 20 μm (c3) wide face-up line patterns after 24 h biofilm growth, 5 μm (c4) wide face-up line patterns at 2 h after initial attachment, and 5 μm (c5) wide face-down line patterns after 24 h biofilm growth (Bar = 10 μm). Cells were also found attached on the side of protruding line patterns and in the grooves between topographic line patterns. These cells are covered with white lines to more clearly show the cells on top of the line patterns (the focus of this study). (d) Distribution of cell orientation on top of face-up narrow (5 μm wide), medium (10 μm wide), or wide (20 μm wide) PDMS line patterns after 24 h biofilm growth, face-up narrow patterns at 2 h after initial attachment, and face-down narrow line patterns after 24 h biofilm growth with 3 μm inter-pattern distance (mean ± standard error shown; at least three biological replicates were tested for each sample). Smooth PDMS was included as control.