Enhanced fabrication and characterization of gecko-inspired mushroom-tipped microfiber adhesives

Abstract

Geckos exhibit a unique ability to adhere repeatedly and reversibly to a variety of surfaces. Considerable scientific and engineering efforts over the last decade have produced gecko-inspired adhesives which can outperform the gecko in some regards. However, the best results come from adhesives which are difficult to mass-produce, or degrade through repeated use. Here, we propose a method for fabricating micrometer-scale, gecko-inspired adhesive structures with mushroom tips in densely packed arrays using deep reactive ion etching (DRIE) and soft mold replication. We use xenon difluoride etching to release the cured polymer structures from the DRIE-processed silicon wafer, and soft mold replication to avoid surface fluorination in the final adhesive patches. The patterned adhesives exhibit more than an order of magnitude increase in pull-off force compared to an unstructured, flat control sample. More importantly, the adhesives’ structures retain 80% of their original attachment strength through repeated use, even after 1000 contact cycles. To investigate the importance of three parameters described in theoretical works, we characterize the effect of boundary conditions on friction, the effect of backing layer on pull-off force, and the effect of retraction speed on pull-off force. Our fabrication approach could be used to mass produce wafer-size patches of structured adhesive that exhibit higher repeatability and the utilized experimental adhesive characterization methods will allow better optimization of future gecko-inspired adhesive designs.