Figure 1: Soft, deterministic network composites in designs inspired by non-mineralized biological materials.

(a) Optical images and an exploded view schematic illustration (lower left inset) of a skin-like composite that consists of a lithographically defined wavy filamentary network of polyimide, analogous to a collagen/elastin structure, embedded in a soft breathable elastomer, analogous to a biological ground substance. The image shows this material wrapped onto the tip of the thumb. (b) Optical image of a similar material partially peeled away from the skin of the forearm. (c) Optical image of the polyimide network during removal from a PMMA-coated silicon wafer. (d) Schematic illustration of a wavy network constructed from a collection of ‘horseshoe’ building blocks configured into a triangular array; the inset at the bottom right provides the key geometrical parameters of the building block. (e) Experimental (denoted by line) and computational (FEA; denoted by line plus square symbol) results for the stress–strain response of this type of network (triangular lattice geometry with θ=180°, R=400 μm, w*=0.15 and thickness=55 μm). Blue and green colours represent the soft materials with and without network mesh, respectively. The three regimes of behavior are analogous to those that occur in biological materials. The network responds primarily by bending and stretching in regimes of small (toe) and large (linear) strain, respectively. The intermediate regime (heel) marks the transition. (f) Optical images with overlaid FEA results for the composite shown in (a) evaluated at different tensile strains. The polyimide network is in a lattice geometry as in (d). The colour in e,f denotes the magnitude of maximum principal strain. All scale bars are 1 cm.