Rose Pistil Stigma: Hierarchical Superhydrophobic Surfaces with Hydrophilic Microtips for Microdroplet Manipulation.

Finger-like radial hierarchical micropillars with folded tips are observed on the surface of the rose pistil stigma (RPS). Impressively, a water droplet on the surface of the RPS presents a spherical shape and it still hangs on the surface even when the RPS is turned over. Superhydrophobicity and high adhesion to water are demonstrated on the RPS, which is beneficial for the RPS to remain clean and fresh. The special wetting behavior of the RPS is highly related to its hierarchical microstructures and surface chemistry. Finger-like hierarchical micropillars with a high aspect ratio are capable of retaining air to support superhydrophobicity while the microgap between the micropillars and on the hydrophilic tips enables the RPS to retain a high adhesion to water. These findings about the unique wetting behaviors of the RPS may provide inspiration for the design and fabrication of functional wetting surfaces for diverse applications such as microdroplet manipulation, three-dimensional cell culture, and microfluidics.