3D printing of micro/nano-hierarchical structures with various structural stiffness for controlling friction and deformation

Micro/nano-hierarchical structures are the building blocks of textured functional surfaces. Having control over the 3D shapes of these building blocks will lead to better control over their friction and deformation when in contact with other surfaces, paving the way for better-engineered surfaces. In this study, a high-resolution twophoton lithography additive manufacturing technique was utilized to produce micro/nano-hierarchical structures composed of nanohairs on top of micropillars. Varying the tapering angle of the micropillar and the length of the nanohairs enabled control over the effective stiffness of the micro/nano-hierarchical structures. Individual micro/nano-hierarchical structures were subjected to normal and tangential loading inside a scanning electron microscope, which enabled in-situ monitoring of the structural deformation in addition to their frictional response. This study revealed that changes in the structure stiffness by varying the tapering angle resulted in changes in the onset of sliding motion, friction force, and coupling between the deformation of the nanohair and the micropillar, thereby providing a new direction for friction and deformation control by tailoring structure stiffness through 3D printing.