Cuticle-mimetic Layered Polymeric Materials
Livia Bast, University of Strathclyde/University of Fribourg
Prof. Nico Bruns, University of Strathclyde
The objectives of this research project are to synthesise polymer-based layered composite structures consisting of alternating layers of polymers and guest compounds such as natural and synthetic waxes, nanoparticles and the reflection protein reflectin, to design polymeric materials which release cargo in a controlled way to their surface, e.g. to regenerate a lubricating film, and to create layered polymer/protein hybrid materials with stimuli-responsive optical properties. This project will result in a deeper understanding of the function and structure-property relationships of plant cuticles by creating model systems which allow us to precisely fine-tune parameters such as lamellar thickness and composition. Further to this, stimuli-responsive materials which self-impregnate or self-lubricate their surface by a controlled release of waxes and lubricants, or that show tuneable structural colours will be created. Design principles for multi-layered composite polymers with a gradient of composition will be elaborated, which can be transferred to many other multi-layered hybrid materials and therefore open pathways to a plethora of new bio-inspired materials.

Insect Repellent Wrinkly Colloids
Johannes Bergmann, University of Fribourg
Prof. Ullrich Steiner, University of Fribourg
The objectives of this research project are to develop a scalable route for the manufacture of cellulose-based colloids which mimic the topographic domains of Litchi chinensis, to study the behaviour of spray-coating of these colloids onto various surfaces with the aim to optimize their adhesion and mechanical properties, and to study the efficacy of these surfaces in terms of insect repellency. Fundamentally, this project will increase our understanding of wrinkle formation on the surface of spheres, from a physical and biological point of view. Our synthesis effort will result in the biomimetic creation of wrinkly colloids. The design and manufacture criterial will in turn provide input into T1 and T2. On the applied side, we will create insect repellent surfaces that can be sprayed on from a suspension of wrinkly colloids. The aim is to create a proof of principle for an agricultural deployment by the end of the funding period.

Hairy Surfaces – From Plants to Novel Technical Materials
Ha-Neul Chae, University of Freiburg
Prof. Jürgen Rühe, University of Freiburg
The objectives of this research project are to develop a method for the preparation of hairy polymer surfaces where the hairs are generated through combining micro-replication of a porous structure with a (mechanical) cold drawing process, to explore the mechanism of the process and study what different structures can be formed by using this process, to study how the material properties of the substrate are altered through coverage with the hairs (wetting, heat loss) and compare this to hairy plant surfaces, and, finally, to embed the hairs into a responsive layer which acts like the cuticle of plants in order to allow the hairs to stand up or lay down in response to external stimuli. In preliminary results, we have shown that the generation of hairs with aspect ratios of >>100 is possible. We expect this project to elucidate the mechanism of hair formation in detail (extension of the polymer as a function of applied force and adhesion to the porous template/dimension of the porous template). The results will allow us a better understanding about which polymers can be used for the hair generation and which templates are suitable. We hope to obtain materials where the surface properties are significantly altered by the addition of the hairy structures to the surfaces.

Industrially Producible Structurally Coloured materials
Benjamin Droguet, University of Cambridge
Prof. Silvia Vignolini, University of Cambridge
Originally, the objective of this research project was to develop structural coloured coatings for the industrial partner Mars. The withdrawal of Mars from the consortium, and its replacement by L’Oréal, shifted the focus of this task from edible structurally coloured materials to industrially producible structurally coloured materials based on cellulose nanocrystals, with the aim to readily use them in cosmetic applications. The aim of this task is therefore to provide a method for fabrication of a range of multiple and uniform hues of unprecedented dimensions, produced under industrially relevant conditions from the self-assembly of cellulose nanocrystals. The fabrication of cellulose-based structural colours is based on an industrial printing technique enabling a commercially viable scaling-up production of nanocellulose-based photonic films. Various sizes have been successfully obtained and a patent is being filed.

Regulation of Cuticle Patterning
Jordan Ferria, University of Cambridge
Prof. Beverley Glover, University of Cambridge
The objectives of this research project are to explore genetic regulation of cuticular patterning, and to test the hypothesis that mechanically induced buckling generates cuticular patterning. The combined approaches adopted by Jordan will provide the first analysis of surface patterning in any organism. These analyses will feed into the work of our colleagues by providing plants with varied surface properties for optical analysis (Silvia Vignolini, Ullrich Steiner), analysis of insect interactions (Thomas Speck), and biomimetic inspiration for the materials groups. The insights into the regulation of cuticle patterning will inform design principles for all groups.

Leaf-cuticle Inspired Membranes
Aristotelis Kamtsikakis, University of Fribourg
Prof. Christoph Weder, University of Fribourg
Upon their transition from an aquatic to a drier terrestrial environment, plants developed a thin protective layer known as cuticle functioning primarily as a water transport barrier to avoid dehydration. From a material science point of view, cuticles are multi-component membranes consisting of polymers (mainly cutin and polysaccarides) and waxes, regulating mass transport at the plant-air interface. It has been previously speculated that asymmetric water transport properties may be present in some plant cuticles, however this aspect has hardly been explored. Driven by these properties, we set out to investigate the water transport characteristics and cuticular architecture of astomatous plant membranes isolated from olive (Olea europaea) and ivy (Hedera helix) leaves. Inspired by the asymmetric water transport properties and the compositionally-graded architecture of these biological membranes, we developed artificial polymer-based nanocomposites displaying similar structural gradients and tunable asymmetric water transport characteristics by using a hydrophobic polymer and nanocellulose. We further explored the effect of surface chemistry and aspect-ratio of nanocellulose on the water and ethanol transport properties of these artificial membranes as potential candidates for liquid-liquid separation processes.

Tuning Hierarchical Topographical and Chemical Surface Patterns
Konstantinos Roumpos, University of Freiburg
Prof. Günter Reiter, University of Freiburg
The objectives of this research project are to generate and study the evolution of hierarchical topographical patterns in thin polymer films governed by film instabilities and the release of elastic energy stored in these films and to explore the physical and rheological properties of supported and freely standing thin polymer films. More specifically, the interactions of thin polymer layers with fiber network-decorated surfaces (contact mechanics, adhesion forces, crack formation) have been studied, with the outlook of generating plant-inspired topographies. Key parameters, such as the temperature, the thicknesses of the polymer films, their thermal history and preparation conditions, have been varied in order to tune the emerging patterns. Moreover, the rheological behavior of thin films on patterned substrates has been studied. We were successful in transferring the pattern of the substrate on the polymer film by means of dewetting and in quantifying the forces acting on the film during this process. The resulting patterns have been compared with patterns found on plant surfaces, like the surface cell layer on plant leaves.

Design Spaces of Wrinkled Cuticle Surfaces
Venkata A. Surapaneni, University of Freiburg
Prof. Thomas Speck, University of Freiburg
The objectives of this research project are to study the robustness of properties against changes in geometrical configurations of the structures like height, width and distance of cuticular folds. This will not only allow us to identify the point(s) in ontogeny at which plant surfaces gain (and maybe lose again) their full functionality but also to define the "design space" for the development of biomimetic structures. The experimental results which describe the relationship between geometrical configuration and function of cuticular folds and will serve as basis for the development of materials with responsive properties that are tuneable e.g. by selective swelling.

Wrinkled Cellulose Surfaces for Structural Colours
Gea van de Kerkhof, University of Cambridge
Prof. Silvia Vignolini, University of Cambridge
The objectives of this research project are to design and fabricate structurally coloured surfaces based on “disordered diffraction gratings” using stress-induced wrinkling of cellulose thin films that contain cellulose nano-crystals, and to correlate the amount of disorder with the photophysical properties of these materials. Through this project, we expect to obtain bio-compatible structurally coloured films with ultimate control of the optical appearance which can find application as bio-compatible coloured surfaces obtained with sustainable materials. These results will allow scalable fabrication of materials that can find application in packaging.