Unraveling the Mechanisms Governing Anisotropy in Accordion‐Shaped Honeycomb Microlattice Fabricated by Two‐Photon Polymerization

Abstract

High‐resolution printing afforded by two‐photon polymerization (2PP) has opened up vast design space, spanning over four orders of magnitude (sub‐μm to cm), unleashing the opportunity to fabricate architected materials with intriguing mechanical characteristics. This study seeks to exploit direct laser writing to print accordion‐shaped honeycomb lattices constituted of slender micro‐membranes to achieve in‐plane mechanical anisotropy. The deformation mechanisms governing orientation‐sensitive mechanical properties of the lattice are examined by in situ investigations in a scanning electron microscope. The microlattice displays greater flexibility, compliance, and strain hardening during in‐plane compression, whereas it is highly stiff and resistant to fatigue in the out‐of‐plane orientation. The high aspect ratio of accordion‐shaped cells imparts prominent in‐plane anisotropy, with longitudinal stiffness twice the transverse stiffness. Folding, interlocking, and compaction of micro‐walls are the major deformation mechanisms, inducing brilliant energy dissipation ability, with up to 87% mechanical work‐absorption. Digital image correlation analysis reveals that strain re‐distribution facilitated by hinges dictates the recoverability of the microlattice. This work provides useful mechanistic insights at the micrometer length scale for tuning the orientation‐sensitive mechanical response of mesostructures printed by 2PP.