Exploring the Role of Habitat on the Wettability of Cicada Wings.

Evolutionary pressure has pushed many extant species to develop micro/nanostructures that can significantly affect wettability and enable functionalities such as droplet jumping, self-cleaning, antifogging, antimicrobial, and antireflectivity. In particular, significant effort is underway to understand the insect wing surface structure to establish rational design tools for the development of novel engineered materials. Most studies, however, have focused on superhydrophobic wings obtained from a single insect species, in particular, the Psaltoda claripennis cicada. Here, we investigate the relationship between the spatially dependent wing wettability, topology, and droplet jumping behavior of multiple cicada species and their habitat, lifecycle, and interspecies relatedness. We focus on cicada wings of four different species: Neotibicen pruinosus, N. tibicen, Megatibicen dorsatus, and Magicicada septendecim and take a comparative approach. Using spatially resolved microgoniometry, scanning electron microscopy, atomic force microscopy, and high speed optical microscopy, we show that within cicada species, the wettability of wings is spatially homogeneous across wing cells. All four species were shown to have truncated conical pillars with widely varying length scales ranging from 50 to 400 nm in height. Comparison of the wettability revealed three cicada species with wings that are superhydrophobic (>150°) with low contact angle hysteresis (<5°), resulting in stable droplet jumping behavior. The fourth, more distantly related species (Ma. septendecim) showed only moderate hydrophobic behavior, eliminating some of the beneficial surface functional aspects for this cicada. Correlation between cicada habitat and wing wettability yielded little connection as wetter, swampy environments do not necessarily equate to higher measured wing hydrophobicity. The results, however, do point to species relatedness and reproductive strategy as a closer proxy for predicting wettability and surface structure and resultant enhanced wing surface functionality. This work not only elucidates the differences between inter- and intraspecies cicada wing topology, wettability, and water shedding behavior but also enables the development of rational design tools for the manufacture of artificial surfaces for energy and water applications.

Ca2+-dependent intracellular drug delivery system developed with "raspberry-type" particles-on-a-particle comprising mesoporous silica core and α-synuclein-coated gold nanoparticles.

For the development of an intracellular cargo release system with mesoporous silica nanoparticles (MSN), gold nanoparticles coated with an amyloidogenic protein of α-synuclein were employed to prepare a protein-mediated nanocomposite into the "raspberry-type" particles-on-a-particle (PoP). The PoPs were successfully fabricated only at pH 4.4 by yielding the MSN coverage to 75.3% with 5 nm gold nanoparticles covalently coated with a mutant form of α-synuclein containing a cysteine residue at the C-terminus. The entrapped cargo of rhodamine 6G was shown to be selectively released from PoPs upon exposure to divalent cations including the α-synuclein-specific pathophysiological ligand of Ca(2+). Intracellular uptake of the PoPs preloaded with doxorubicin as an anticancer drug and its subsequent Ca(2+)-dependent release were demonstrated with HeLa cells in the presence of intracellular Ca(2+)-regulating agents. Therefore, the fabrication of PoPs with the self-interactive protein of α-synuclein is expected to serve as a platform technology for preparation of diversified nanocomposites with various nanoparticles and/or bioactive molecules for eventual applications in the areas of theranostics.