Abstract: Silks spun by arthropods exhibit a set of unique properties that have emerged as the
result of over four hundred million years of evolution. Silks show the most optimized combination
of tensile strength and deformation at breaking, yielding the highest work of fracture of any known
material. These outstanding features have thrust an increasing interest in reproducing or even
improving the properties of natural silks. However, the advances in the field are hampered by an
incomplete knowledge on the relation between microstructure and mechanical properties as well as
by uncertainties related to the influence of processing in the performance of the fiber. In this work
we present some of the most significant contributions of our groups to the field, stressing the
possibility of controlling the tensile properties of silks and the contribution of this basic knowledge
to the production of artificial regenerated fibers. Spider silk shows a large variability that it is
thought to allow the spider to adapt the fibers to its immediate requirements, but represents a major
drawback for its study or application. The development of the wet stretching process has allowed
the modification of silk fibers in a controlled and reproducible way for the first time. Besides,
recent improvements in the spinning of regenerated silkworm silk fibers have led to artificial fibers
with properties that approach those of natural silks. These progresses allow envisaging the
production of bioinspired fibers in a not too distant future.
Abstract: In this article I discuss the backgrounds, some technical insights, and the novel
developments of a bioengineering approach to semi-synthetic minimal cells that is currently
pursued within the EU project SYNTHCELLS. Originally developed by Pier Luigi Luisi and
coworkers at the Swiss Federal Institute of Technology (ETH, Zurich), the project aims to the
construction of liposome-based bioreactors, which display living properties, although at a minor
Abstract: A butterfly's fore- and hindwings act as one low aspect ratio wing. The variation in the
feathering angle is not as large as that of other insects such as a dragonfly and a damselfly. A butterfly
varies the lead-lag angle of the forewing and the angle between the thorax and the abdomen at
take-off. This implies the possibility that the insect moves all parts of its body to fly. This is an
advantage that an insect has over a conventional aircraft. Moreover, a new method to investigate an
insect’s flight control ability is introduced. An attached plate disturbs the insect, and a remarkable
flight pattern can be observed. The flight control ability of the insect can be elucidated by analyzing
the insect’s flight pattern.
Abstract: Myliobatidae is a family of large pelagic rays including cownose, eagle and manta rays.
They are extremely efficient swimmers, can cruise at high speeds and can perform turn-on-a-dime
maneuvering, making these fishes excellent inspiration for an autonomous underwater vehicle.
Myliobatoids have been studied extensively from a biological perspective; however the fluid
mechanisms that produce thrust for their large-amplitude oscillatory-style pectoral fin flapping are
unknown. An experimental robotic flapping wing has been developed that closely matches the
camber and planform shapes of myliobatoids. The wing can produce significant spanwise
curvature, phase delays down the span, and oscillating frequencies of up to 1 Hz, capturing the
dominant kinematic modes of flapping for myliobatoids. This paper uses dye flow visualization to
qualitatively characterize the fluid mechanisms at work during steady-state oscillation. It is shown
that oscillatory swimming uses fundamentally different fluid mechanisms than undulatory
swimming by the generation of leading-edge vortices. Lessons are distilled from studying the fluid
dynamics of myliobatoids that can be applied to the design of biomimetic underwater vehicles using
morphing wing technology.
Abstract: The deployment of leaves with plane surface and straight parallel folds, as observed in
leaves of hornbeam and beech, was investigated by using numerical methods. In both species the
veins are angled at 30° to 50° from the midrib, when the leaves are outstretched. Although a higher
angle allows the leaf to be folded more compactly within the bud, it has very small leaf area in the
early stage of unfolding. The midrib of leaf grows very slowly at first and then it does with an
almost constant speed. From the numerical simulation, it was found that the midrib grows with the
minimum unfolding energy. The deployment of flowers was also investigated from mechanical
point of view. A potato flower has five or six petals with triangle gussets between petals. The bud
volume becomes largest when the number of petals, N, is five. However, the energy for unfolding
of the model with N = 5 or 6 is smaller than those of other models, if the energy can be represented
by the total kinetic energy during unfolding.
Abstract: A bat-like aircraft is proposed, using a smart joint mechanism to actuate the morphing
of the wings. The smart joint stays in its deformed shape after cooling, which can be up to 5% of
25 mm length joint. The morphing of the wing shapes of three different bat species is evaluated
using a planar lifting line analysis. The morphing improves the lift coefficient over 1000% and the
lift to drag ratio over 300% at an angle of attack of 0.6°. The results compare well with what is
expected from the type of flight and morphology that has been documented for the bats.
Abstract: Compliant mechanisms fulfil a desired force and displacement characteristic. The
development of such structures having a defined kinematical motion and subjected to several
constraints, like deformability, stiffness and activation force is highly challenging. The present
work deals with a methodology for analysing compliant mechanisms considering geometrically
nonlinear deformations. By assembling pre-calculated nonlinear beam elements a new beam truss
approach is introduced. The accuracy and quality of the mechanical model are verified by selected
examples and compared to existing methods.
Abstract: Many biological materials exhibit a hierarchical structure over more than one length
scale. Understanding how hierarchy affects their mechanical properties emerges as a primary
concern, since it can guide the synthesis of new materials to be tailored for specific applications. In
this paper the strength and stiffness of hierarchical materials are investigated by means of a fractal
approach. A new model is proposed, based both on geometric and material considerations and
involving simple recursive formulas.