Passive Hydro-actuated Unfolding of Ice Plant Seed Capsules as a Concept Generator for Autonomously Deforming Devices

In der Natur und ihren biologischen Systemen existieren zahlreiche Beispiele für gerichtete Bewegung durch spezifische Reaktion auf externe Stimuli. Diese potentiellen Quellen der Inspiration dienen oft als Vorbilder für energieeffiziente "Smart" Technologien. Vom Wasser getriebenen schnellen Zuschnappen der Venusfliegenfalle bis zum einfacheren ebenso hydroresponsiven Biegen der Weizengrannen, viele Pflanzen haben im Laufe der Evolution verschiedene Mechanismen entwickelt, um Wasser als Triebkraft ihrer Aktoren-Gewebe zu nutzen, die für spezifische und gerichtete Bewegung sowie die gewünschte Verformung sorgen. Das ist diesen Pflanzen möglich durch die Organisation ihrer Gewebe in ausgereiften, komplexen und hierarchisch organisierten Architekturen auf verschiedensten Skalen. Einige Arten der Familie Aizoaceae, auch bekannt als Mittagsblumen oder Ice plant, zeigen ein geniales Beispiel für solche passiven Betätigungssysteme, da sie einen "intelligenten" Mechanismus entwickelt haben, um ihre Schutzsamenkapseln öffnen zu lassen und die Samen nur in Anwesenheit von flüssigem Wasser (Regen) freizugeben. Schwerpunkt der ersten Phase dieser Arbeit war die Untersuchung der zu Grunde liegenden Mechanismen und der strukturellen und kompositorischen Basis von Wasser-getriebenen Bewegungen der Samenkapseln von Ice plant (Delosperma nakurense) auf ihren verschiedenen hierarchischen Ebenen. Fünf hygroskopische Kiele erwiesen sich als aktive "Muskeln", die zu einer reversiblen origamiartigen Entfaltung der Samenkapsel führen, wenn diese mit Wasser benetzt wird. Jeder Kiel besteht aus zwei wabenartigen Geweben, die aus hochgradig schwellfähigen und elliptisch-sechseckig geformten Zellen zusammengesetzt sind, die entlang einem inerten Träger organisiert sind. Als Hauptmotor der Aktuation wurde die signifikante Schwellung von hochgradig schwellfähigen zellulosereichen Innenschichten (CIL) im Lumen der Zellen identifiziert. Die Morphologie der CIL und deren physikochemische Reaktion auf Wasser wurde unter Verwendung einer Vielzahl von Techniken untersucht und damit gezeigt, dass der Entropiegewinn während der Wasserabsorption die Hauptantriebskraft für die Schwellung der Zellen ist. Die Umsetzung dieser relativ kleinen Energiebeiträge in eine konzertierte und komplexe makroskopische Bewegung, wurde durch ein optimiertes Design auf den verschiedenen Ebenen der hierarchischen Organisation des Systems erläutert. Das kooperative anisotropische Anschwellen der Zellen des hygroskopischen Gewebes führt durch das Timoschenko Doppelschicht-Biegeprinzip zu einer Umsetzung in eine Biegebewegung der Strukturen und letztlich zur Entfaltung der Samenkapseln. Inspiriert von den zugrunde liegenden Mechanismen in Ice plants, wurden zwei unterschiedliche Strategien entwickelt, um durch kleine Dehnungen im mikroskopischen Bereich eine vorprogrammierte Makro-Bewegung einer Wabenstruktur zu ermöglichen. Durch eine geschickte Anwendung dieses einfachen Prinzips, kann eine Mimik des biologischen Vorbilds im weiteren technischen Sinne zu zahlreichen Anwendungsbeispielen führen, wie als passive Schalter und Aktoren in der Biomedizin, Landschaftsgestaltung oder der Architektur.Numerous examples of actuated-movements with specific responses of the structure to external stimuli can be found in biological systems, which can be a potential source of inspiration for the design of energy-efficient "smart" devices. From the hydro-driven rapid snapping of the Venus fly trap leaves to simple hydro-responsive bending of wheat awns, various plants have evolved different mechanisms to utilize water as an actuator to undergo a desired deformation via sophisticated architecture at different hierarchical levels of their systems. Some species of the family Aizoaceae, also known as ice plants, show an ingenious example of such passive actuation systems, as they evolved a smart mechanism to open their protective seed capsules and release their seeds only in the presence of liquid water (rain). The scope of the first phase of the thesis was to investigate the underlying mechanism and the structural and compositional basis of the hydro-actuated movement of the ice plant seed capsules (Delosperma nakurense) at several hierarchical levels. Five hygroscopic keels were found to be the active muscles responsible for the reversible origami-like unfolding of the seed capsule upon wetting. Each keel consists of two honeycomb-like tissues made up of highly swellable hexagonal/elliptical shape cells running along an inert backing tissue. The significant swelling of a highly swellable cellulosic inner layer (CIL) inside the lumen of these cells was found to be the main engine of the actuation. The morphology and physicochemical response of the CIL to water was studied using a variety of techniques and it was shown that the entropic changes during water absorption were the main driving force for swelling of the cells. The translation of such relatively small available energy to the complex movement at a macro scale was explained by an optimized design at different hierarchical levels of the system. The cooperative anisotropic swelling of the cells in the hygroscopic tissue is translated into a flexing movement of the structure via simple Timoshenko’s bilayer bending principle, which then results in an unfolding of the seed capsules. Inspired by the underlying mechanism in ice plant, two different strategies were developed to translate small strains at micro scale into a pre-programmed macro movement of a honeycomb structure. Through a clever application of the same simple concepts, one can "mimic" the biological model system in a broader engineering sense, with potential applications of such passive switches in biomedicine, agricultural engineering or architectural design

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 modelled 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 amongst 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

Evaluation of neutron spectra and dose equivalent from a Varian 2100C/D Medical Linear Accelerator: Monte Carlo simulation and a literature review

In this study was carried out a review according to experimental and Monte Carlo studies in the literature on the neutron production from 18 MV, Varian 2100C/D linac. The effects of these neutrons were investigated on the total fluence, the energy spectra, and the dose equivalent. These factors were calculated as a function of depth and the radiation field size by simulation of linac head using of MCNPX2.6.0 code. The neutron strength was found equal to 1.23 × 1012 nGy−1.The results showed that with increasing the field size from 5 × 5 to 40 × 40 cm2, the neutron fluence and dose equivalent in the water phantom rose to the maximum value for 25 × 25 cm2 field (3.05 × 107 ncm−2Gy−1 and 3.14 mSvGy−1 respectively) and then decreased with increasing the field size. According to the results, the magnetite-steel, ordinary, and limonite-steel concrete walls significantly increased the neutron dose equivalent for about 27.4%, 17.2%, and 13.5%, respectively

Pressurized honeycombs as soft-actuators: a theoretical study

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Programing stimuli-responsiveness of gelatin with electron beams: basic effects and development of a hydration-controlled biocompatible demonstrator

Abstract Biomimetic materials with programmable stimuli responsiveness constitute a highly attractive material class for building bioactuators, sensors and active control elements in future biomedical applications. With this background, we demonstrate how energetic electron beams can be utilized to construct tailored stimuli responsive actuators for biomedical applications. Composed of collagen-derived gelatin, they reveal a mechanical response to hydration and changes in pH-value and ion concentration, while maintaining their excellent biocompatibility and biodegradability. While this is explicitly demonstrated by systematic characterizing an electron-beam synthesized gelatin-based actuator of cantilever geometry, the underlying materials processes are also discussed, based on the fundamental physical and chemical principles. When applied within classical electron beam lithography systems, these findings pave the way for a novel class of highly versatile integrated bioactuators from micro- to macroscales