The complex structure of Fomes fomentarius represents an architectural design for high-performance ultralightweight materials

We thank C. Li from the Max Planck Institute of Colloids and Interfaces in Potsdam, Germany, for help during synchrotron measurements at the μSpot beamline at BESSY at the Helmholtz-Zentrum Berlin für Materialien und Energie in Berlin, Germany. We acknowledge the provision of facilities and technical support by Aalto University at the OtaNano Nanomicroscopy Center (Aalto-NMC). This work was supported by the Academy of Finland project 348628, the Jenny and Antti Wihuri Foundation (Centre for Young Synbio Scientists), and the Academy of Finland Center of Excellence Program (2022–2029) in Life-Inspired Hybrid Materials (LIBER) project number 346106, and by internal funding from the VTT Technical Research Center of Finland Ltd. We also acknowledge the Dutch Research Council (NWO, domain Applied and Engineering Sciences: MYCOAT project number 18425) and the Horizon 2020 programs of the European Union (FUNGAR; project 58132 and iNEXT-Discovery, project 871037) for NMR studies. Furthermore, the high-field NMR experiments were supported by uNMR-NL, the National Roadmap Large-Scale NMR Facility of the Netherlands (NWO grant 184.032.207), and the uNMR-NL grid (NWO grant 184.035.002).High strength, hardness, and fracture toughness are mechanical properties that are not commonly associated with the fleshy body of a fungus. Here, we show with detailed structural, chemical, and mechanical characterization that Fomes fomentarius is an exception, and its architectural design is a source of inspiration for an emerging class of ultralightweight high-performance materials. Our findings reveal that F. fomentarius is a functionally graded material with three distinct layers that undergo multiscale hierarchical self-assembly. Mycelium is the primary component in all layers. However, in each layer, mycelium exhibits a very distinct microstructure with unique preferential orientation, aspect ratio, density, and branch length. We also show that an extracellular matrix acts as a reinforcing adhesive that differs in each layer in terms of quantity, polymeric content, and interconnectivity. These findings demonstrate how the synergistic interplay of the aforementioned features results in distinct mechanical properties for each layer.Peer reviewe

Additive and Subtractive Modification of Butterfly Wing Structural Colors

The modification of photonic nanoarchitectures occurring in butterfly wing scales with different nanostructures was investigated experimentally and by modeling. Single crystalline, polycrystalline, simple thin film, and pepper-pot-type photonic nanoarchitectures in the wing scales of different butterflies were investigated. By atomic layer deposition (ALD) (additive) the color of all nanoarchitectures was red shifted and by plasma etching (subtractive) the color of all nanoarchitectures was blue shifted in a controllable way. Langmuir-Blodgett multilayers of silica nanospheres were used as physical models. ALD produced color shifts similar to those for butterfly wings. In the case of a simple thin film, a theoretical calculation reproduced the spectral alterations well. For the more complex photonic nanoarchitectures, the general trends of the modifications were well reproduced by more sophisticated models, but differences in the magnitude of the alterations were found, attributed to the complex, random porous structures of the pepper-pot-type structures

MANIPULATION OF NANOSCALE WRINKLES ON TRANSPARNET AND FLEXILBE FILMS FOR MULTI-MODAL STRUCTURL COLORATION

Department of Mechanical EngineeringMost materials and devices with structurally switchable color features responsive to external stimuli can actively and flexibly display various colors. However, realizing covert???overt transformation behavior, especially switching between transparent and colored states, is more challenging. Current stimulus-response pattern hiding and displaying technology responds to numerous external stimuli (temperature, light, mechanical stimulation, etc.) and causes a change in dye properties and in the spacing of nanostructures. In this phase change method, it is difficult to completely hide information because patterns are easily expressed due to limited viewing angles or irregular external conditions. Therefore, there is a need for a method of controlling a transparent nanoscale surface that can completely hide information. Thus, we introduce a method of forming traditional buckling-type corrugations using bilayer-like or trilayer film. In addition, the photonic structure is fabricated using an inkjet printing method and completely laminated into the film. Moreover, in this dissertation , we study the principle of structural color in which living organisms have color by a nanostructure without pigment and the characteristics of the nanostructured photonic crystal hidden in it and design a color-changing nanostructure for single and complex structural colors. Nanoscale wrinkles are generated on the ductile top surface of various multilayered substrates by external stimuli, and their geometrical and optical features are determined by the material and structural properties of the laminated films. First, we develop a bilayer-like laminated film with a rigid SiO2-nanoparticle (NP)-encapsulated poly(dimethylsiloxane) (PDMS) composite structure surrounded by soft PDMS as a multidimensional structural color platform. Owing to the similarity in the optical properties of PDMS and SiO2 NPs, this device is fully transparent in the normal state. However, as their mechanical strengths differ considerably, upon compressive loading, buckling-type instability arises on the surface of the laminate, leading to the generation of 1D or 2D wrinkled patterns in the form of gratings. As a result, we demonstrate an application of the device in which quick response codes are displayed or hidden as covert???overt convertible-colored patterns for optical encryption/decryption, showing their remarkable potential for anti-counterfeiting applications. Second, we describe a thin trilayer film that can generate various wrinkles on transparent and flexible films in the presence of external mechanical bending. In particular, the wrinkle wavelength can be controlled on a tens of nanometer scale by modulating the material properties of each layer. This active modulation plays a critical role in determining resulting structural color spectra. In other words, the wrinkles function as a diffraction grating so that the film displays bright structural colors under bending conditions. After the bending stress is released, the wrinkles disappear and the film becomes transparent again. Lastly, we demonstrate that the material and structural patterning technique shows remarkable potential for structural coloration applications such as multimodal displays and novel barcode-based anti-counterfeiting techniques.ope

Application and Development of Mechanoresponsive Polymer Structures

Mechanoresponsive Systeme antworten auf mechanische Reize mit einer Eigenschaftsänderung. Diese Dissertation umfasst die Arbeiten mit zwei mechanoresponsiven Systemen, die optisch auf mechanische Reize antworten. Sie basieren auf polymeren Strukturen, einer Polymerbürste und einem Hydrogelnetzwerk. Ihr optischer Antwortmechanismus ermöglicht die Beobachtung wirkender Kräfte als ein Ansatz zur in situ-Kraftmessung. Im ersten Teil wird ein existierendes, mechanoresponsives System zur Anwendung gebracht, das auf einer mit Fluoreszenzfarbstoff markierten Polyelektrolytbürste basiert. Die Ladungen des Polyelektrolyts können die Fluoreszenz des Farbstoffs unterdrücken, sodass lokale Kompression und Zugspannung über die Fluoreszenzintensität unterschieden werden können. Die mechanoresponsive Polymerbürste wurde als mechanosensitive Oberflächenbeschichtung angewandt, um Unterschiede in der Kontaktspannungsverteilung von Gecko-inspirierten adhäsiven Mikrostempelstrukturen aufzuklären. Die erarbeiteten Ergebnisse und daraus abgeleiteten Ablösemechanismen der Mikrostempeltypen deckten sich qualitativ mit Vorhersagen aus theoretischen Ansätzen. Aufgrund geometrischer Einschränkungen einer planaren Oberflächenbeschichtung zielt der zweite Teil darauf ab, dieses mechanoresponsive Prinzip in ein dreidimensionales Netzwerk zu überführen und ein mechanoresponsives Hydrogelnetzwerk als Plattform zur Kraftmessung zu entwickeln. Konzeptionell besitzt ein homogenes Netzwerk vorhersagbare mechanische Eigenschaften, sodass lokale optische Antworten auf mechanische Kräfte ermöglichen könnten, die wirkenden Kräfte zu lokalisieren und quantifizieren. Basierend auf einer Gestaltung nach der Flory-Rehner-Theorie wurden Präkursoren mit vordefinierter Größe und Architektur für die Hydrogelherstellung eingesetzt, um auf ein homogenes Netzwerk abzuzielen. Zu diesem Zweck wurde das Mischungsvolumen durch Tropfenmikrofluidik reduziert. Für den optischen Antwortmechanismus wurden die Hydrogelnetzwerk-Präkursoren mit zwei verschiedenen Fluorophoren markiert, die sich durch abstandsabhängige Emission über Förster-Resonanzenergietransfer auszeichnen. Die Funktionalität des optischen Antwortmechanismus wurde auf globaler Ebene durch Kollabieren und kontrolliertes Quellen des Netzwerks, dann auf lokalisierter Ebene durch definierte mechanische Belastung mit Rasterkraftmikroskopie gezeigt. Durch ihre Anpassbarkeit könnte die Hydrogelplattform zukünftig verschiedenste Anwendungen im Bereich intrisischer Kraftmessung weicher Materie bedienen.Mechanoresponsive systems respond to mechanical triggers by changes in a certain property. This thesis covers the work conducted with two mechanoresponsive systems that respond optically to mechanical triggers. These two systems are based on polymer structures, a polymer brush and a hydrogel network. Thus, the optical response mechanism allows observing acting forces as an approach to force sensing in situ. In the first part, an existing mechanoresponsive system based on a polyelectrolyte brush labeled with a fluorescent dye is engaged in application. The charges of the polyelectrolyte are able to quench the fluorescence of the dye so that local compression or tension can be distinguished from the local fluorescence intensity. The mechanoresponsive polymer brush was applied as mechanosensitive surface coating to elucidate differences in the contact stress distributions of gecko-inspired adhesive micropillar structures. The determined results and the derived detachment mechanisms of the micropillar types were in qualitative accordance with predictions from theoretical approaches. Overcoming the geometrical limitations of a planar surface coating, the second part aims at translating the mechanoresponse principle to a three-dimensional network and developing a mechanoresponsive hydrogel as a platform for force sensing. Conceptually, a homogeneous network allows to predict mechanical properties so that localized optical mechanoresponses could enable locating and quantifying acting forces. Based on network design principles from the Flory-Rehner theory, precursors with predefined size and architecture were utilized in hydrogel preparation, aiming for a homogeneous network. Further in this regard, the mixing volume was reduced by employing droplet microfluidics. As optical response mechanism, the hydrogel network precursors were labeled with two kinds of fluorophore, featuring distance-dependent emission from Förster Resonance Energy Transfer. The functionality of the optical response mechanism was demonstrated on global level by collapsing and controlled swelling of the network, and on a localized level by defined mechanical stress, applied with Atomic Force Microscopy. Owing to its adjustability, the hydrogel platform might be employed in various applications that require intrinsic force sensing of soft matter in future

The genetics and evolution of iridescent structural colour in Heliconius butterflies

The study of colouration has been essential in developing key concepts in evolutionary biology. The Heliconius butterflies are well-studied for their diverse aposematic and mimetic colour patterns, and these pigment colour patterns are largely controlled by a small number of homologous genes. Some Heliconius species also produce bright, highly reflective structural colours, but unlike pigment colour, little is known about the genetic basis of structural colouration in any species. In this thesis, I aim to explore the genetic basis of iridescent structural colour in two mimetic species, and investigate its adaptive function. Using experimental crosses between iridescent and non-iridescent subspecies of Heliconius erato and Heliconius melpomene, I show that iridescent colour is a quantitative trait by measuring colour variation in offspring. I then use a Quantitative Trait Locus (QTL) mapping approach to identify loci controlling the trait in the co-mimics, finding that the genetic basis is not the same in the two species. In H. erato, the colour is strongly sex-linked, while in H. melpomene, we find a large effect locus on chromosome 3, plus a number of putative small effect loci in each species. Therefore, iridescence in Heliconius is not an example of repeated gene reuse. I then show that both iridescent colour and pigment colour are sexually dimorphic in H. erato and H. sara, pointing to differing selection pressures on the sexes. Structural colour, and to a lesser extent pigment colour, are condition dependent, suggesting the trait could be used as a signal of condition in mate choice. Together this work provides an understanding of the evolution of structural colour in Heliconius, in terms of its genetic control and its function as a signal and mimetic warning pattern

DEVELOPMENT OF FUNCTIONAL NANOCOMPOSITE MATERIALS TOWARDS BIODEGRADABLE SOFT ROBOTICS AND FLEXIBLE ELECTRONICS

World population is continuously growing, as well as the influence we have on the ecosystem\u2019s natural equilibrium. Moreover, such growth is not homogeneous and it results in an overall increase of older people. Humanity\u2019s activity, growth and aging leads to many challenging issues to address: among them, there are the spread of suddenly and/or chronic diseases, malnutrition, resource pressure and environmental pollution. Research in the novel field of biodegradable soft robotics and electronics can help dealing with these issues. In fact, to face the aging of the population, it is necessary an improvement in rehabilitation technologies, physiological and continuous monitoring, as well as personalized care and therapy. Also in the agricultural sector, an accurate and efficient direct measure of the plants health conditions would be of help especially in the less-developed countries. But since living beings, such as humans and plants, are constituted by soft tissues that continuously change their size and shapes, today\u2019s traditional technologies, based on rigid materials, may not be able to provide an efficient interaction necessary to satisfy these needs: the mechanical mismatch is too prohibitive. Instead, soft robotic systems and devices can be designed to combine active functionalities with soft mechanical properties that can allow them to efficiently and safely interact with soft living tissues. Soft implantable biomedical devices, smart rehabilitation devices and compliant sensors for plants are all applications that can be achieved with soft technologies. The development of sophisticated autonomous soft systems needs the integration on a unique soft body or platform of many functionalities (such as mechanical actuation, energy harvesting, storage and delivery, sensing capabilities). A great research interest is recently arising on this topic, but yet not so many groups are focusing their efforts in the use of natural-derived and biodegradable raw materials. In fact, resource pressure and environmental pollution are becoming more and more critical problems. It should be completely avoided the use of in exhaustion, pollutant, toxic and non-degradable resources, such as lithium, petroleum derivatives, halogenated compounds and organic solvents. So-obtained biodegradable soft systems and devices could then be manufactured in high number and deployed in the environment to fulfil their duties without the need to recover them, since they can safely degrade in the environment. The aim of the current Ph.D. project is the use of natural-derived and biodegradable polymers and substances as building blocks for the development of smart composite materials that could operate as functional elements in a soft robotic system or device. Soft mechanical properties and electronic/ionic conductive properties are here combined together within smart nanocomposite materials. The use of supersonic cluster beam deposition (SCBD) technique enabled the fabrication of cluster-assembled Au electrodes that can partially penetrate into the surface of soft materials, providing an efficient solution to the challenge of coupling conductive metallic layers and soft deformable polymeric substrates. In this work, cellulose derivatives and poly(3-hydroxybutyrate) bioplastic are used as building blocks for the development of both underwater and in-air soft electromechanical actuators that are characterized and tested. A cellulosic matrix is blended with natural-derived ionic liquids to design and manufacture completely biodegradable supercapacitors, extremely interesting energy storage devices. Lastly, ultrathin Au electrodes are here deposited on biodegradable cellulose acetate sheets, in order to develop transparent flexible electronics as well as bidirectional resistive-type strain sensors. The results obtained in this work can be regarded as a preliminary study towards the realization of full natural-derived and biodegradable soft robotic and electronic systems and devices

Advances in Hydrogels

Hydrogels are a class of soft materials with crosslinked network structures. They show good biocompatibility, biodegradability, hydrophilicity, and mechanical properties similar to those of tissue, so they have a wide range of applications. In recent years, a variety of multifunctional hydrogels with excellent performance have been developed, greatly expanding the depth and breadth of their applications. This book is the reprint of the Special Issue “Advances in Hydrogels”, which focused on the recent advances regarding hydrogels, aiming to provide reference for researchers in related fields. This book included one editorial, thirteen original research articles, and three valuable reviews from thirteen different countries including Canada, China, Thailand, Mexico, India, Saudi Arabia, Chile, Germany, the Czech Republic, Colombia, Romania, Israel, and the USA