How much biology is in the product? Role and relevance of biological evolution and function for bio-inspired design

The Plant Leaf: A Biomimetic Resource for Multifunctional and Economic Design

As organs of photosynthesis, leaves are of vital importance for plants and a source of inspiration for biomimetic developments. Leaves are composed of interconnected functional elements that evolved in concert under high selective pressure, directed toward strategies for improving productivity with limited resources. In this paper, selected basic components of the leaf are described together with biomimetic examples derived from them. The epidermis (the "skin" of leaves) protects the leaf from uncontrolled desiccation and carries functional surface structures such as wax crystals and hairs. The epidermis is pierced by micropore apparatuses, stomata, which allow for regulated gas exchange. Photosynthesis takes place in the internal leaf tissue, while the venation system supplies the leaf with water and nutrients and exports the products of photosynthesis. Identifying the selective forces as well as functional limitations of the single components requires understanding the leaf as an integrated system that was shaped by evolution to maximize carbon gain from limited resource availability. These economic aspects of leaf function manifest themselves as trade-off solutions. Biomimetics is expected to benefit from a more holistic perspective on adaptive strategies and functional contexts of leaf structures.

Straight roads into nowhere - obvious and not-so-obvious biological models for ferrophobic surfaces

There are currently efforts to improve strategies for biomimetic approaches, to identify pitfalls and to provide recommendations for a successful biomimetic work flow. In this contribution, a case study of a concrete biomimetic project is described that started with a posed technical problem for which seemingly obvious biological models exist. The technical problem was to devise a ferrophobic surface that prevents the contact between the copper surface of a tuyère (a water cooled aeration pipe within a blast furnace) and liquid iron. Therefore, biological external surfaces that strongly repel liquids appeared to be suitable, particularly the hair cover of the water fern Salvinia molesta and the surface of Collembola (an arthropod group). It turned out, however, that it was not feasible to realise the functional structures of both biological models for the tuyère problem. Instead, a seemingly not obvious biological model was identified, namely micropores within the cell walls of water-transporting conduits of plants that connect the conduits to a three-dimensional flow network. These specially shaped pores are assumed to be able to create stable air bodies, which support the refilling of embolised conduits. By adopting the shape of these micropores, a successful prototype for a ferrophobic copper surface repelling liquid iron could be devised. This case study illustrates that straight road maps from technical problems to obvious biological models are no guarantee for success, and that it is difficult to arrive at a formalised biomimetic working scheme. Rather, a broad understanding of biological function and its complexity is beneficial.