Fig. 1. Transversal composition gradients in olive cuticles and cuticle-inspired artificial membranes.

a Cross-section of an olive cuticle imaged with TEM. b, c Schematics (not to scale) of the graded architecture in the b olive cuticle and c SBS/CNC membranes. d ATR-IR spectra of SBS, CNCs, and an SBS/CNC composite at the top and bottom side of the membrane. Signals marked with dot and star correspond to the CNCs’ –OH and C–O/C–C vibrations. e Box plot showing the relative concentration of CNCs (RCC) as a function of transversal position (n = 5 in each position) in a SBS/CNC membrane determined by Raman microscopy. The RCC was calculated from the intensities (I) of the CNCs’ C–O (1096 cm⁻¹) and SBS’ CH₂ (1437 cm⁻¹) vibration bands. Whiskers extend to min and max values, box edges show 25–75 percentiles, center line represents median, and hollow square represents mean. The dashed line and gray band are the mean ± s.d. (n = 3 in each position) of the RCC of the SBS reference. f, g SEM images of the cross-section of f SBS and g SBS/CNC membranes. All composite membranes shown here were ~33 μm and contained 10 wt% CNCs.