MotorSkins—a bio-inspired design approach towards an interactive soft-robotic exosuit

The work presents a bio-inspired design approach to a soft-robotic solution for assisting the knee-bending in users with reduced mobility in lower limbs. Exosuits and fluid-driven actuators are fabric-based devices that are gaining increasing relevance as alternatives assistive technologies that can provide simpler, more flexible solutions in comparison with the rigid exoskeletons. These devices, however, commonly require an external energy supply or a pressurized-fluid reservoir, which considerably constrain the autonomy of such solutions. In this work, we introduce an event-based energy cycle (EBEC) design concept, that can harvest, store, and release the required energy for assisting the knee-bending, in a synchronised interaction with the user and the environment, thus eliminating any need for external energy or control input. Ice-plant hydro-actuation system served as the source of inspiration to address the specific requirements of such interactive exosuit through a fluid-driven material system. Based on the EBEC design concepts and the abstracted bio-inspired principles, a series of (material and process driven) design experimentations helped to address the challenges of realising various functionalities of the harvest, storage, actuation and control instances within a closed hydraulic circuit. Sealing and defining various areas of water-tight seam made out of thermoplastic elastomers provided the base material system to program various chambers, channels, flow-check valves etc of such EBEC system. The resulting fluid-driven EBEC-skin served as a proof of concept for such active exosuit, that brings these functionalities into an integrated ‘sense-acting’ material system, realising an auto-synchronised energy and information cycles. The proposed design concept can serve as a model for development of similar fluid-driven EBEC soft-machines for further applications. On the more general scheme, the work presents an interdisciplinary design-science approach to bio-inspiration and showcases how biological material solutions can be looked at from a design/designer perspective to bridge the bottom–up and top–down approach to bio-inspiration.Deutsche Forschungsgemeinschafthttps://doi.org/10.13039/501100001659Peer Reviewe

Special issue: bioinspired architectural and architected materials

Peer Reviewe

The filter‐house of the larvacean Oikopleura dioica. A complex extracellular architecture: From fiber production to rudimentary state to inflated house

While cellulose is the most abundant macromolecule in the biosphere, most animals are unable to produce cellulose with the exception of tunicates. Some tunicates have evolved the ability to secrete a complex house containing cellulosic fibers, yet little is known about the early stages of the house building process. Here, we investigate the rudimentary house of Oikopleura dioica for the first time using complementary light and electron microscopic techniques. In addition, we digitally modeled the arrangement of chambers, nets, and filters of the functional, expanded house in three dimensions based on life-video-imaging. Combining 3D-reconstructions based on serial histological semithin-sections, confocal laser scanning microscopy, transmission electron microscopy, scanning electron microscopy (SEM), and focused ion beam (FIB)-SEM, we were able to elucidate the arrangement of structural components, including cellulosic fibers, of the rudimentary house with a focus on the food concentration filter. We developed a model for the arrangement of folded structures in the house rudiment and show it is a precisely preformed structure with identifiable components intricately correlated with specific cells. Moreover, we demonstrate that structural details of the apical surfaces of Nasse cells provide the exact locations and shapes to produce the fibers of the house and interact among each other, with Giant Fol cells, and with the fibers to arrange them in the precise positions necessary for expansion of the house rudiment into the functional state. The presented data and hypotheses advance our knowledge about the interrelation of structure and function on different biological levels and prompt investigations into this astonishing biological object.Deutsche Forschungsgemeinschaft http://dx.doi.org/10.13039/501100001659Peer Reviewe

Rethinking filter: An interdisciplinary inquiry into typology and concept of filter, towards an active filter model

This work aims to re-investigate different aspects of a variety of filters and filtration processes within diverse realms of knowledge from an interdisciplinary point of view, and develops a comprehensive Active Model of Filter that accommodates the phenomena in its entire diversity and complexity. The Active Filter Model proposes to take Filter-from various fields and scales operating at material and symbolic level-not as mere objects, but as difference-producing phenomena that need to be addressed as complex active systems within event-based boundaries. The model underlines a systemic, operative, performative, and negentropic nature to the phenomena that invites one to; recognize various elements and intra-actions within a filter system; follow chains of operations and processes that render the activity; take the performative and ecology building aspect of the filter activity into consideration; and acknowledge the negentropic, order-producing nature of filtering phenomena. The Active Filter Model is meant to serve as a foundation for further analysis and synthesis in various fields dealing with Filter, and the research approach is put forward as a paradigm for how seemingly disciplinary concepts such as Filter can be rethought through interdisciplinary methods, and mutually complement research questions within active matter, biology, information philosophy, data science and sustainability discourses.Ethics & Philosophy of Technolog

Honeycomb Actuators Inspired by the Unfolding of Ice Plant Seed Capsules

Plant hydro-actuated systems provide a rich source of inspiration for designing autonomously morphing devices. One such example, the pentagonal ice plant seed capsule, achieves complex mechanical actuation which is critically dependent on its hierarchical organization. The functional core of this actuation system involves the controlled expansion of a highly swellable cellulosic layer, which is surrounded by a non-swellable honeycomb framework. In this work, we extract the design principles behind the unfolding of the ice plant seed capsules, and use two different approaches to develop autonomously deforming honeycomb devices as a proof of concept. By combining swelling experiments with analytical and finite element modelling, we elucidate the role of each design parameter on the actuation of the prototypes. Through these approaches, we demonstrate potential pathways to design/develop/construct autonomously morphing systems by tailoring and amplifying the initial material’s response to external stimuli through simple geometric design of the system at two different length scales

Ice plant hydro-actuation mechanism.

<p>Top: (A) The seed capsules of the ice plant, <i>Delosperma nakurense</i> are shown in dry (closed) and wet (open) state. The five seed containing compartments are closed and covered by a protective valve (each measuring ca. 3mm in length) in the dry state and open upon wetting. (B) Two hygroscopic keels halves responsible for unfolding/folding of the seed capsule; the keels are bent inward in the dry state and bend outward upon hydration. (C) Each keel consists of a network of ellipsoid/hexagonal shape cells (confocal microscopy images of the transverse cell cross-section -field diameter: ca. 0.4 mm). (D) A highly swellable cellulosic inner layer filling up the lumen of the cells is responsible for the unidirectional opening of the cells and the reversible anisotropic expansion/contraction of the cell-network upon wetting/drying cycles (FCA stained cells cross section with lignified cell wall stained in red and the cellulosic inner layer in blue- field diameter: ca. 100 μm). (E) Cryo-SEM micrograph of the cellulosic inner layer (field diameter: ca. 20μm). (redrawn after [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0163506#pone.0163506.ref008" target="_blank">8</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0163506#pone.0163506.ref020" target="_blank">20</a>]). Bottom: Abstraction of the actuation principles from lower to higher lengthscale; (5) volume change of a highly swellable material inside a circular confinement induces an isotropic volume change of the cell; (4) Tailoring the geometry of such cell enables an anisotropic deformation upon swelling/shrinkage cycles; (3) Through periodic arrangement of the cells, the cooperative anisotropic deformation of individual cells results in a unidirectional expansion/contraction of the cellular structure at a larger length scale,(2,1) which can be translated into bending of the whole honeycomb structure when the deformation is restricted at one side (re-sketched after [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0163506#pone.0163506.ref020" target="_blank">20</a>]).</p

Passive hydro-actuation of bio-inspired bilayer-honeycomb device.

<p>Initial (left) and final actuated state (right) of the passive hydro-actuation upon changing the relative humidity from 50 to 95% are depicted at different levels of the design; (a) A bilayer made up of spruce veneer (active layer) glued to a thick paper (passive layer), bends upon anisotropic swelling of the spruce veneer in the direction perpendicular to the cellulose fibrils orientation. (b) Two of such bilayers attached together, constructs a cell-like structure that can open/closes upon changes in the relative humidity. (c) Scaling up the bilayer-cell concept into a hydro-actuated honeycomb prototype that expands up to 5 fold upon actuation (sequential images after 0, 2, 4 and 16 hours of exposure to 95%RH) [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0163506#pone.0163506.ref020" target="_blank">20</a>].</p

Finite element simulation of bilayer and bilayer cell.

<p>Left: single bilayer in initial (a) and actuated state (c); Right: Bilayer-cell in initial (b) and actuated (d) configuration.</p

Equilibrium curvature of the actuated bilayer and bilayer-cell upon exposure to 95% relative humidity and wetting with liquid water.

<p>Equilibrium curvature of the actuated bilayer and bilayer-cell upon exposure to 95% relative humidity and wetting with liquid water.</p