Engineering 3D Hierarchical Structures with Bio-Mimetic Solid Fraction Gradient

We present a versatile method to create 3-D surfaces with complex hierarchical microstructures that mimic the patterns found on springtail skin. Our method innovatively merges two fixed-spacing patterns at different scales to create patterns with varying spacing but does not require precise alignment. The key is to utilize localized stretching strain when gradually laminating a thin microstructured elastomer layer onto a wavy substrate. To demonstrate this new fabrication process, we laminated a micro-pillar thin polydimethylsiloxane (PDMS) film on a wavy PDMS substrate with millimeter-scale inverted pyramidal holes. This resulted in hierarchical surface micropillars that display varying spacings along the peaks and the valleys of the wavy substrate. To our best knowledge, this is the first report to generate controllable micro-patterns with a gradient spacing from fixed-spacing patterns. Our new process overcomes one of the major challenges in producing bio-inspired patterns with diverse variations for studies of biomimicry and biomutualism.