Spatially architected PLA honeycombs inspired by beetle elytra for integrated fire safety and mechanical integrity

Polylactic acid (PLA) is attractive for fused deposition modeling (FDM), yet its structural use is constrained by the coupled challenges of flammability, additive-induced embrittlement, and printed-part reliability. Herein, a material–structure integrated strategy is proposed by coupling a biomass-derived phosphorus–carbon flame-retardant formulation with multi-material FDM and beetle elytra-inspired cellular design. Epoxidized soybean oil-modified orange peel powder (EOP) was combined with ammonium polyphosphate (APP) to construct a synergistic flame-retardant PLA system, in which the optimized A20E10 formulation containing 20 wt% APP and 10 wt% EOP achieved an LOI of 34%, a UL-94 V-0 rating, and a reduced THR of approximately 30 MJ m −2 through APP-catalyzed carbonization and EOP-assisted compact char formation. To decouple fire protection from load-bearing function, A20E10 was extruded into flame-retardant PLA (fr-PLA) filament and spatially printed with neat PLA into a beetle elytra-inspired fr-PLA/PLA/fr-PLA sandwich honeycomb architecture. The resulting biomimetic structure spatially positions flame-retardant fr-PLA in the outer protective regions while retaining neat PLA as the mechanically supportive core, with the honeycomb geometry contributing to heat-transfer regulation and load dispersion. In this manner, the intrinsic flame-retardant function of A20E10 is deployed at the structural level without uniformly incorporating flame-retardant additives throughout the entire component. This work establishes a sustainable additive-manufacturing route for lightweight fire-safe PLA components with spatially programmed material functions.