Fibrillar Elastomeric Micropatterns Create Tunable Adhesion Even to Rough Surfaces

Acknowledgements V.B., N.K.G., and E.A. contributed with conception and experimental design. V.B. performed the experiments. V.B., R.H., A.G., and R.M.M. carried out analysis and interpretation of data. V.B., R.H., A.G., and E.A. wrote the manuscript. V.B. and R.H. contributed equally to this work. V.B. acknowledges funding by SPP 1420 of the German Science Foundation DFG. E.A., N.K.G., and R.H. acknowledge funding from the European Research Council under the European Union/ERC Advanced Grant “Switch2Stick,” Agreement No. 340929.Peer reviewedPublisher PD

Fibrillar elastomeric micropatterns create tunable adhesion even to rough surfaces

Biologically inspired, fibrillar dry adhesives continue to attract much attention as they are instrumental for emerging applications and technologies. To date, the adhesion of micropatterned gecko-inspired surfaces has predominantly been tested on stiff, smooth substrates. However, all natural and almost all artificial surfaces have roughnesses on one or more different length scales. In the present approach, micropillar-patterned PDMS surfaces with superior adhesion to glass substrates with different roughnesses are designed and analyzed. The results reveal for the first time adhesive and nonadhesive states depending on the micropillar geometry relative to the surface roughness profile. The data obtained further demonstrate that, in the adhesive regime, fibrillar gecko-inspired adhesive structures can be used with advantage on rough surfaces; this finding may open up new applications in the fields of robotics, biomedicine, and space exploration

Precipitant-Free Crystallization of Protein Molecules Induced by Incision on Substrate

Nucleation of protein crystals has been shown to be facilitated by substrates decorated with both nano- to micro-scale hierarchical undulations and spatially varying surface potential. In fact, on such surfaces, several proteins were found to crystallize without having to use any precipitant in contrast to all other homogeneous and heterogeneous systems in which precipitant is an essential ingredient for nucleation. While these surfaces were so patterned whole through the area that was brought in contact with the protein solution, it was not clear exactly to what extent the surfaces were required to be patterned to trigger nucleation without use of any precipitant. Here we show that a simple incision may be enough on an otherwise smooth surface for this purpose. In particular, the substrate used here is a smooth silicone film with its surface plasma oxidized to create a thin crust of silica. An incision is then generated on this surface using a sharp razor blade. The silica crust being brittle leads to random nano-microscopic undulations at the vicinity of the incision. These undulations along with surface charge can induce protein crystal nucleation without precipitant

Precipitantless Crystallization of Protein Molecules Induced by High Surface Potential

In the context of protein crystallization, surface decorated with heterogeneous topographical features decreases the energy barrier for nucleation, thereby facilitating crystallization; a precipitant is, nevertheless, required to be used. Here we eliminate the need of such precipitant by using a combined effect of nanoscopic surface undulations and charges on a substrate. Using surface instabilities as a tool for generating such features on polymeric materials, we show that intrinsic curvature of nanofeatures (<10 nm) coupled with surface charges lead to spatial gradient in potential as high as 140 V·μm^–1, where curvature gets maximum. These surfaces show remarkable ability to induce nucleation not achieved by any other conventional process. They induce precipitantless nucleation of proteins, directed crystallization of a specific protein from a mixture of two or more species, and even simultaneous crystallization from a mixture of proteins. These results signify large scale molecular ordering at the bulk by effects initiated at the surface