Inspired by phenomena in the plant world, a
meteoro-sensitive rotational actuator is developed. The design
uses a hygro-active shell, whose water-based swelling is restricted
at selective locations to form a helicoid structure. The influence
of geometrical parameters on the performance is investigated
using a numerical analysis of various geometries, by looking at
resulting rotation and torque during this rotation. Prototypes
are built of five key geometries in the design space, to validate
the simulations and to investigate the real-life behaviour
of the design. These prototypes are submerged in water to
investigate their deformation, after which they are placed in
a torsion machine to investigate the torque during rotation.
The experiments result in similar rotations and torques as the
simulations. The designed Hygromorphic Rotational Actuator is
capable of passively rotating its own structure, thereby expanding
the possibilities of engineers and designers when designing passive
autonomous systems.

The mechanisms that move plants can serve as biological role models for engineers, designers and architects. This practice is slowly being implemented in various engineering fields, with architects often being pioneers. Various methodologies have been written about the subject, but often only from an architectural point of view.
The classification presented in this paper provides a different perspective on the
subject. It is structured like a toolbox, containing a clear classification of the technical working principles that plants use to generate motion. With the working principles abstracted, it is no longer necessary to dive deep into the inner workings of plants.
The Scopus and Web of Science databases have been systematically searched for
compliant plant movements. Plants mainly move by reallocating water, either actively via osmosis or passively via hygroscopic tissue. In compliant plant mechanisms, these basic movement initiators bring about deformations of plant parts. These movements are classified according to their goal: does the plant move quasi-static or dynamic? And does the plant only use a mechanism or does it rely on the gradual storage and fast release of elastic energy as well? Quasi-static movements are often only mechanical and reversible, while dynamic movements rely on energy storage and are often irreversible due to their failure-based release. A bilayer structure in one form or another is present in almost all mechanisms, proving its large adaptability to various circumstances. This
adaptability is achieved by the various configurations of the two layers, including
fibre-orientation and cellular set-up.
Existing bio-inspired devices are classified according to the same system. This
enables identification of plant mechanisms that are already suited for implementation and exposes plant movements that are not yet used in the human world. Additionally, a lot could be gained from copying mechanisms on a cellular level rather than on a macroscopic level. Most importantly, a change in mindset needs to happen in order to fully benefit the intricate mechanisms that the plant world has to offer.