Plants as concept generators for biomimetic light-weight structures with variable stiffness and self-repair mechanisms

Plants possess many structural and functional properties that have a high potential to serve as concept generators for the production of biomimetic technical materials and structures. We present data on two features of plants (variable stiffness due to pressure changes in cellular structures and rapid self-repair functions) that may be used as models for biomimetic projects.

Self-Repairing Membranes for Inflatable Structures Inspired by a Rapid Wound Sealing Process of Climbing Plants

A new self-repairing membrane for inflatable light weight structures such as rubber boats or Tensairity constructions is presented. Inspired by rapid self-sealing processes in plants, a thin soft cellular polyurethane foam coating is applied on the inside of a fabric substrate, which closes the fissure if the membrane is punctured with a spike. Experimental tests are carried out with a purpose built setup by measuring the air mass flow through a leak in a damaged membrane sample. It is shown that the weight per unit area of the self-repairing foam as well as the curing of the two component PU-foam under an overpressure influence the repair efficiency. Curing the foam under overpressure affects the relative density as well as the microstructure of the foam coatings. Maximal median repair efficiencies of 0.999 have been obtained with 0.16 g.cm 2 foam cured at 1 bar overpressure. These results suggest that the bio-inspired technique has the potential to extend the functional integrity of injured inflatable structures dramatically.

The structural basis of oscillation damping in plant stems-biomechanics and biomimetics

Oscillations and their damping were investigated for plant stems of Cyperus alternifolius L., Equisetum hyemale L., Equisetum fluviatile L., Juncus effuses L., Stipa gigantea Link, and Thamnocalamus spathaceus (Franch.) Soderstr. With the exception of T. spathaceus, mechanical damping of the oscillation of individual plant stems, even without side organs, leaves or inflorescences, is quite effective. Our experiments support the hypothesis that embedding stiff sclerenchymatous elements in a more compliant parenchymatous matrix provides the structural basis for the dissipation of mechanical energy in the plant stem. As an application the naturally occurring structures were mimicked in a compound material made from hemp fabrics em- bedded in polyurethane foam, cured under pressure. Like its natural model it shows plastic deformability and viscoelastic be- haviour. In particular the material is characterized by a remarkably high shock absorption capacity even for high impact loads.

Bio-inspiration as a Concept for Sustainable Constructions Illustrated on Graded Concrete

The building industry is one of the main contributors to worldwide resource consumption and anthropogenic climate change.Therefore,sustainable solutions in construction are particularly urgent.Inspired by the success principles of living nature,biologists and engineers present here an interdisciplinary work:The sustainability assessment of a bio-inspired material technology called graded concrete,which was developed at ILEK.Gradient structural materials can be found in plants on different hierarchical levels,providing a multitude of creative solutions for technology.Graded concrete applies this biological concept of structural optimization to the interior structure of concrete components to minimize material and resource expenditure.To evaluate the sustainability of this innovation,a newly developed quantitative Bio-inspired Sustainability Assessment(BiSA)method is applied.It focuses on the relationship of environmental,social and economic functions and the corresponding burdens quantified basing on life cycle assessment.The BiSA of graded concrete slabs shows significant improvements over conventional concrete for the applied use case.While an overall reduction of environmental burdens by 13%is expected,economic burdens can be reduced by up to 40%and social burdens by 35.7%.The assessment of the graded concrete technology identifies its potential with regard to sustainable construction.The presented work provides a blueprint for the interdisciplinary,integrative work on sustainable,bio-inspired innovations.It shows that the synergies of bio-inspiration and BiSA within technical product development can be fruitful.