Shear force measurement of actuated, gecko-inspired adhesion elements with hierarchical polydimethylsiloxane pattern

The transfer of systems from nature to technical schemes is still a challenge as the fabrication of such complex systems in a cost efficient way while keeping the intended technical functionality requires appropriate materials and fabrication techniques. Here the multi-scale hierarchy of the gecko foot was transferred into membrane-actuated gecko-inspired adhesion elements (AE) to study the adhesion to surfaces. Therefore, a three level hierarchical polydimethylsiloxane (PDMS) structure comprising a membrane for actuating and the micron-patterned AE were mould from a microtechnical fabricated master into PDMS by thermal and UV curing. The micron-patterned AE consist of dot or line micron patterns on top of cuboid posts with 15 µm height that representing the second hierarchical level. For master fabrication lithographic masking, wet and dry etching as well as SU8 3D lithography was applied. The adhesion of such AE on smooth, rough and chemically modified glass surfaces was measured by determining the shear force for several different AE designs and PDMS materials. A slip of the micron sized PDMS AEs at the adhesion test sample surface was measured. This slip of the PDMS elements being in contact to the surface can enhance the accepted shear force and the measured anisotropy of the shear force for linear AEs. The results found can contribute to the optimization of PDMS AE for technical surfaces with chemically and topographically inhomogeneous properties.