Smart surfaces with tunable wettability have aroused much attention in the past few years. However, to obtain a surface that can reversibly transit between the lotus-leaf-like superhydrophobic isotropic and rice-leaf-like superhydrophobic anisotropic wettings is still a challenge. This paper, by mimicking microstructures on both lotus and rice leaves, reports such a surface that is prepared by creating micro/nanostructured arrays on the shape memory polymer. On the surface, the microstructure shapes can be reversibly changed between the lotus-leaf-like random state and the rice-leaf-like 1D ordered state. Accordingly, repeated switch between the superhydrophobic isotropic and anisotropic wettings can be displayed. Research results indicate that the smart controllability is ascribed to the excellent shape memory effect of the polymer, which endows the surface with special ability in memorizing different microstructure shapes and wetting properties. Meanwhile, based on the smart wetting performances, the surface is further used as a rewritable functional platform, on which various droplet transportation programmes are designed and demonstrated. This work reports a superhydrophobic surface with switchable isotropic/anisotropic wettings, which not only provides a novel functional material but also opens a new avenue for application in controlled droplet transportation.

BackgroundComparison of major histocompatibility complex (MHC) genes across vertebrate species can reveal molecular mechanisms underlying the evolution of adaptive immunity-related proteins. As the first terrestrial tetrapods, amphibians deserve special attention because of their exposure to probably increased spectrum of microorganisms compared with ancestral aquatic fishes. Knowledge regarding the evolutionary patterns and mechanisms associated with amphibian MHC genes remains limited. The goal of the present study was to isolate MHC class I genes from two Rhacophoridae species (Rhacophorus omeimontis and Polypedates megacephalus) and examine their evolution.ResultsWe identified 27 MHC class I alleles spanning the region from exon 2 to 4 in 38 tree frogs. The available evidence suggests that these 27 sequences all belong to classical MHC class I (MHC Ia) genes. Although several anuran species only display one MHC class Ia locus, at least two or three loci were observed in P. megacephalus and R. omeimontis, indicating that the number of MHC class Ia loci varies among anuran species. Recombination events, which mainly involve the entire exons, played an important role in shaping the genetic diversity of the 27 MHC class Ia alleles. In addition, signals of positive selection were found in Rhacophoridae MHC class Ia genes. Amino acid sites strongly suggested by program to be under positive selection basically accorded with the putative antigen binding sites deduced from crystal structure of human HLA. Phylogenetic relationships among MHC class I alleles revealed the presence of trans-species polymorphisms.ConclusionsIn the two Rhacophoridae species (1) there are two or three MHC class Ia loci; (2) recombination mainly occurs between the entire exons of MHC class Ia genes; (3) balancing selection, gene duplication and recombination all contribute to the diversity of MHC class Ia genes. These findings broaden our knowledge on the evolution of amphibian MHC systems.

Controllable manipulation of microdroplets is significant for the microfluidics, biomedical areas, microreactors, and so on; however, until now, reports about no-loss and selective capture/release of different microdroplets are still rare. Herein, we report a new superhydrophobic shape memory adhesive surface that can solve this problem. The surface is prepared by sticking a pillar-structured superhydrophobic polyurethane layer onto a shape memory polyurethane−cellulose nanofiber (PU−CNF) layer. Because of the good shape memory performance of the PU−CNF layer, the obtained surface can memorize and display various microstructure arrangements during the stretching/releasing process. Meanwhile, multiple superhydrophobic adhesive states from low-adhesive rolling performance to highadhesive pinning performance can be observed on the surface, and all these adhesive states can be reversibly controlled between each other. Based on the smart shape memory ability in surface adhesion, not only traditional in situ capture/release of one microdroplet but also selective capture and release of different microdroplets can be realized. This work reports a new superhydrophobic shape memory adhesive surface; it is envisioned that this smart surface would be a powerful platform for microfluidics systems, complex droplet transportation, biological analysis, and so on.

The PU/CNF nanocomposites display water-triggered fast shape memory ability, such as curling and unfolding, demonstrating tailored shape memory performance.

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