Fig. 2.

Fabrication techniques and resulting PA structures. (a–e) The fabrication process starts by either (a) dropping freshly dissolved PA for microtextures with randomly oriented nanofibers, or (b) dragging an aged PA solution for microtextures with aligned nanofibers on a silica substrate. (c) Then, a PDMS mold was used to cover the PA solution while allowing it to conform to the mold, self-assemble into nanofibers, and gel by exposure to ammonium hydroxide (NH₄OH). The PA gel was then polymerized under UV irradiation and released from the mold to realize the PA microtextures. The process in (a, c) was used to achieve well-defined three-dimensional (3D) PA structures with (d) randomly oriented nanofibers including (f) removable layers with microtextures or (g) pores and surface microtextures such as (g) channels, (i) holes, (j) posts, and (k) two-level topographies with features down to 5 μm in size. On the other hand, following the process in (b, c), microtextures with (l, m) channels and holes were also achieved but with aligned nanofibers (inset in m).