(a-i) Schematic of the microtrichia on smooth and 10 × 10 × 2 µm microstructured surface (ridges and grooves, 10 µm in width, and grooves, 2 µm deep) (shown to scale). (a-ii) On smooth glass, microtrichia made tip contact (seen as black dots under interference reflection microscopy [IRM]). Outer fringe layer (fl) is outside the seal (arrowheads). (a-iii) On 10 × 10 × 2 µm substrates, contact from microtrichia and fl was similar to the contact on the smooth surface. (b-i and b-ii) On 3 × 3 × 2 µm substrates, the microtrichia made tip contact on the ridges, as well as in the grooves, as seen in (b-iii). However, fewer microtrichia made contact within the narrow grooves compared to the 10 × 10 × 2 µm surface. Note that (b-ii) and (b-iii) differ only in the focus height. (c-i to c-iii) On 3 × 3 × 4 µm substrates, microtrichia made close contact on the ridges, but inside the deep grooves there was no contact. (d-i) Schematic of microtrichia coming into tip contact on smooth glass (inset: contact area observed under IRM). (d-ii) Schematic representing a hypothetical scenario that was not observed where the microtrichia tips bend and make side contacts. Scale bars: 3 µm for all microscopy images.