This paper is part of The EvansAbstract. The cuticle is the main interface between plants and their environment. It covers the epidermis of all aerial primary parts of plant organs as a continuous extracellular matrix. This hydrophobic natural composite consists mainly of the biopolymer, cutin, and cuticular lipids collectively called waxes, with a high degree of variability in composition and structure. The cuticle and cuticular waxes exhibit a multitude of functions that enable plant life in many different terrestrial habitats and play important roles in interfacial interactions. This review highlights structure-function relationships that are the subjects of current research activities. The surface waxes often form complex crystalline microstructures that originate from self-assembly processes. The concepts and results of the analysis of model structures and the influence of template effects are critically discussed. Recent investigations of surface waxes by electron and X-ray diffraction revealed that these could be assigned to three crystal symmetry classes, while the background layer is not amorphous, but has an orthorhombic order. In addition, advantages of the characterisation of formation of model wax types on a molecular scale are presented. Epicuticular wax crystals may cause extreme water repellency and, in addition, a striking self-cleaning property. The principles of wetting and upto-date concepts of the transfer of plant surface properties to biomimetic technical applications are reviewed. Finally, biomechanical studies have demonstrated that the cuticle is a mechanically important structure, whose properties are dynamically modified by the plant in response to internal and external stimuli. Thus, the cuticle combines many aspects attributed to smart materials.

The control of growth rate and the mechanical integrity of the tomato (Lycopersicon esculentum Mill.) fruit has been attributed to the exocarp. This study focused on the biomechanics of the fruit skin (FS) comprising cuticle, epidermis and a few subdermal cell layers, and the enzymatically isolated cuticular membrane (CM) during fruit growth and ripening. Morphology and mechanical properties of the FS and the CM of three cultivars were analysed separately at three distinct ripening stages by scanning electron microscopy (SEM) and one-dimensional tension testing, respectively. Both were subject to significant cultivar-specific changes. Thickness of the CM increased during ripening from 7.8-8.6 to 9.9-15.7 microm and exceeded by far that of the epidermal cell wall. The mechanical properties, such as modulus of elasticity, strength, and failure strain, were highest in the FS for all cultivars at any stage, with only one exception; however, the cuticle largely mirrored these properties throughout fruit maturation. Stiffness of both isolated CM and FS increased from immature to fully ripe fruits for all cultivars, while failure stress and failure strain displayed a tendency to decrease for two of them. Stress-strain behaviour of the CM could be described as strain softening, mostly linear elastic throughout, and strain hardening, and was subject to growth-related changes. The FS displayed strain hardening throughout. The results indicate evidence for the cuticle to become increasingly important as a structural component for the integrity of the tomato fruit in addition to the epidermis. A supplementary putative model for tomato fruit growth is proposed.

Nanomaterials show extraordinary properties and, among them, polymeric nanofibers are of high interest for several applications. Here, the applicability of a high throughput production system is investigated by combining solution-based electrospinning with centrifugal spinning. Ultrathin nanofibers were generated with diameters in the tens of nanometer regime using polyethylene glycol and polylactic acid, and the productivity of the highly interconnected nanofiber nonwoven meshes was orders of magnitude faster compared to that of materials made with traditional electrospinning methods. Such a manufactured layer of nanofibers shows great potential for filter applications, for example.

Nature reveals a great variety of inorganic-organic composite materials exhibiting good mechanical properties, high thermal and chemical stability, and good barrier properties. One class of natural bio-nanocomposites, e.g. found in mussel shells, comprises protein matrices with layered inorganic fillers. Inspired by such natural bio-nanocomposites, the cationic recombinant spider silk protein eADF4(κ16) was processed together with the synthetic layered silicate sodium hectorite in an all-aqueous setup. Drop-casting of this bio-nanocomposite resulted in a thermally and chemically stable film reflecting a one-dimensional crystal. Surprisingly, this bio-nanocomposite coating was, though produced in an all-aqueous process, completely water insoluble. Analyzing the structural details showed a low inner free volume due to the well-oriented self-assembly/alignment of the spider silk proteins on the nanoclay surface, yielding high oxygen and water vapor barrier properties. The here demonstrated properties in combination with good biocompatibility qualify this new bio-nanocomposite to be used in packaging applications.

Drug delivery systems allow tissue/cell specific targeting of drugs in order to reduce total drug amounts administered to an organism and potential side effects upon systemic drug delivery. Most drug delivery systems are polymer-based, but the number of possible materials is limited since many commercially available polymers induce allergic or inflammatory responses or lack either biodegradability or the necessary stability in vivo. Spider silk proteins represent a new class of (bio)polymers that can be used as drug depots or drug delivery systems. The recombinant spider silk protein eADF4(C16), which can be processed into different morphologies such as particles, films, or hydrogels, has been shown to fulfil most criteria necessary for its use as biomaterial. Further, eADF4(C16) particles have been shown to be well-suited for drug delivery. Here, a new method was established for particle production to reduce particle size and size distribution. Importantly, cellular uptake of these particles was shown to be poor in HeLa cells. Therefore, variants of eADF4(C16) with inversed net charge or incorporated cell penetrating peptides and receptor interacting motifs were tested, showing much better cellular uptake. Interestingly, uptake of all silk variant particles was mainly achieved by clathrin-mediated endocytosis.

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Proteins are ubiquitous biopolymers that adopt distinct three-dimensional structures and fulfil a multitude of elementary functions in organisms. Recent systematic studies in molecular biology and biotechnology have improved the understanding of basic functional and architectural principles of proteins, making them attractive candidates as concept generators for technological development in material science, particularly in biomedicine and nano(bio)technology. This paper highlights the potential of molecular biomimetics in mimicking high-performance proteins and provides concepts for applications in four case studies, i.e. spider silk, antifreeze proteins, blue mussel adhesive proteins and viral ion channels.