Surface topography plays a key role in the colonization of substrata by the colonizing stages of marine fouling organisms. For the innovation of marine antifouling coatings, it is essential to understand how topographic cues affect the settlement of these organisms. In this study, tapered, spiked microstructures and discrete honeycombs of varying feature dimensions were designed and fabricated in order to examine the influence of topography on the attachment of zoospores of the green macroalga Ulva linza and cells of the diatom (microalga) Navicula incerta. Contrasting results were obtained with these two species of algae. Indeed, the preferred location of cells of N. incerta was dominated by attachment point theory, which suggested a positive correlation between the density of cells adhering and the amount of available attachment points, while the settlement of spores of U. linza was mainly regulated by both Wenzel roughness and local binding geometry.

We introduce actively tunable diffractive optical elements fabricated from shape-memory polymers (SMPs). By utilizing the shape-memory effect of the polymer, at least one crucial attribute of the diffractive optical element (DOE) is tunable and adjustable subsequent to the completed fabrication process. A thermoplastic, transparent, thermoresponsive polyurethane SMP was structured with diverse diffractive microstructures via hot embossing. The tunability was enabled by programming a second, temporary shape into the diffractive optical element by mechanical deformation, either by stretching or a second embossing cycle at low temperatures. Upon exposure to the stimulus heat, the structures change continuously and controllable in a predefined way. We establish the novel concept of shape-memory diffractive optical elements by illustrating their capabilities, with regard to tunability, by displaying the morphing diffractive pattern of a height tunable and a period tunable structure, respectively. A sample where an arbitrary structure is transformed to a second, disparate one is illustrated as well. To prove the applicability of our tunable shape-memory diffractive optical elements, we verified their long-term stability and demonstrated the precise adjustability with a detailed analysis of the recovery dynamics, in terms of temperature dependence and spatially resolved, time-dependent recovery.

Bioinspired nanofur, covered by a dense layer of randomly distributed high aspect ratio nano- and microhairs, possesses superhydrophobic and air-retaining properties. Nanofur is fabricated using a highly scalable hot pulling method in which softened polymer is elongated with a heated sandblasted plate. Here we investigate the stability of the underwater air layer retained by the irregular nanofur topography by applying hydraulic pressure to the nanofur kept underwater, and evaluate the gradual changes in the air-covered area. Furthermore, the drag reduction resulting from the nanofur air retention is characterized by measuring the pressure drop across channels with and without nanofur.

The exceptionally adhesive foot of the gecko remains clean in dirty environments by shedding contaminants with each step. Synthetic gecko-inspired adhesives have achieved similar attachment strengths to the gecko on smooth surfaces, but the process of contact self-cleaning has yet to be effectively demonstrated. Here, we present the first gecko-inspired adhesive that has matched both the attachment strength and the contact self-cleaning performance of the gecko's foot on a smooth surface. Contact self-cleaning experiments were performed with three different sizes of mushroom-shaped elastomer microfibres and five different sizes of spherical silica contaminants. Using a load-drag-unload dry contact cleaning process similar to the loads acting on the gecko foot during locomotion, our fully contaminated synthetic gecko adhesives could recover lost adhesion at a rate comparable to that of the gecko. We observed that the relative size of contaminants to the characteristic size of the microfibres in the synthetic adhesive strongly determined how and to what degree the adhesive recovered from contamination. Our approximate model and experimental results show that the dominant mechanism of contact self-cleaning is particle rolling during the drag process. Embedding of particles between adjacent fibres was observed for particles with diameter smaller than the fibre tips, and further studied as a temporary cleaning mechanism. By incorporating contact self-cleaning capabilities, real-world applications of synthetic gecko adhesives, such as reusable tapes, clothing closures and medical adhesives, would become feasible.

Many plants and insects possess multi‐functional surfaces covered by dense nanohair. Such a nanofur is of high interest for various biomimetic applications like self‐healing, air retention, and oil/water separation. Here, we introduce a highly scalable and competitive molding technique for the fabrication of biomimetic nanofur. With this method, we pull nanofur out of flat polycarbonate and tune its wettability from hydrophilic to superhydrophobic. By mechanically structuring these samples we create various devices suitable for microfluidics. The nanofur can be also used for the fabrication of self‐healing surfaces inspired by pitcher plants as well as for air‐retaining surfaces mimicking the water fern Salvinia minima. Finally, we utilize the nanofur for oil/water separation and the cleaning of oil spills.

Nanofur is produced by hot pulling, a highly scalable molding technique for the fabrication of biomimetic surfaces densely covered with nanohair. This nanofur can be used for various biomimetic applications, such as self-healing, air retention, and oil-water separation as demonstrated by H. Hölscher and co-workers in article 1300083. The SEM image shows the fractal surface topography of nanofur fabricated from polycarbonate.

Hot embossing and pulling techniques are presented allowing the fabrication of hierarchical micro- and nano-structures. By utilizing demolding forces we replicate nanopillars with high aspect ratio (AR of 10) and small diameters (200 nm). Furthermore, we draw a dense nanofur either with defined or random design. Introducing a electromechanical sensor system we subsequently fabricated a threefold hierarchical structure. Using these replication techniques tiny hairs for bio-inspired designs can be realized with short cycle times and high scalability.

Hot embossing allows for low cost fabrication of nanostructures with highest aspect ratios on large surfaces and is commonly based on a large variety of polymers. The widespread use of nanostructured materials, however, poses environmental challenges. Here, we show that biodegradable wood from renewable resources can be structured on the nano-scale and that surface characteristics can be imprinted and three-dimensionally formed. In particular, we show that so-called liquid wood made out of lignin can be structured with feature sizes down to 100-200 nm and three dimensionally shaped by microthermoforming. We demonstrate optical active surfaces by diffractive elements, the change of hydrophobic to super-hydrophobic behavior and the fabrication of super-hydrophobic microfluidic channels. Based on these results we anticipate new applications in the nano-and micro-range, particularly for use in sensitive environments without posing a risk to nature. The new compound material will allow for a substitution of conventional polymers used as material in one way applications of e. g. the consumer, the food or the disposable medical industry.

Applying 3D direct laser writing, artificial hierarchical gecko-type structures are designed and fabricated down to nanometer dimensions. In this way, the elastic modulus and the length scale of the gecko's setae are very closely matched. Direct laser writing is a very flexible rapid prototyping method allowing the fabrication of arbitrary nanostructures. Since the parameters of the structures can be easily changed, this technique is perfect for design studies of dry adhesives. Measuring the adhesional forces by atomic force microscopy, the influence of several design parameters like density, aspect ratio, and tip-shape on dry adhesion performance are systematically examined. In this way, it is revealed that hierarchy is favorable for artificial gecko-inspired dry adhesives made of stiff materials on the nanometer scale.

Among different surface cues, the settlement of cells and larvae of marine macrofouling organisms has been found to be strongly influenced by surface microtopographies. In this article, the settlement of zoospores of the green alga Ulva linza on a surface topographic gradient has been investigated. "Honeycomb" gradient structures with feature sizes ranging from 1 to 10 μm were prepared by hot embossing, and the effect on the density of spores that attached in settlement assays was quantified. The highest density of spores was found when the size of the microstructures was similar to or larger than the size of the spores. With decreasing size of the structures, spore settlement density decreased. Interestingly, spore settlement density correlated with the Wenzel roughness of the surfaces. "Kink sites" on the surface played an important role and resembled preferred attachment positions. Furthermore, the gradients allowed the minimum pit size that the spores were able to squeeze into to be determined.

Adhesion of geckos, like this Tokay gecko, is based on the complex formation of delicate hairs covering their toes. 3D direct laser writing is the perfect tool to study such structures, as described by M. Rohrig, H. Holscher and co-workers on page 3009. Fabrication using 3D direct laser writing takes advantage of multiphoton absorption to create arbitrary micro- and nanostructures. The high flexibility of this rapid prototyping technique is exemplified with the presented “Small” logo: the width of the “l” in the logo is only 2.5 μm. Images copyright Eric Isselee, fivespots, KIT, 2012. Used under license from Shutterstock.com.