Bioinspired supramolecular fibers drawn from a multiphase self-assembled hydrogel.

Inspired by biological systems, we report a supramolecular polymer-colloidal hydrogel (SPCH) composed of 98 wt % water that can be readily drawn into uniform ([Formula: see text]6-[Formula: see text]m thick) "supramolecular fibers" at room temperature. Functionalized polymer-grafted silica nanoparticles, a semicrystalline hydroxyethyl cellulose derivative, and cucurbit[8]uril undergo aqueous self-assembly at multiple length scales to form the SPCH facilitated by host-guest interactions at the molecular level and nanofibril formation at colloidal-length scale. The fibers exhibit a unique combination of stiffness and high damping capacity (60-70%), the latter exceeding that of even biological silks and cellulose-based viscose rayon. The remarkable damping performance of the hierarchically structured fibers is proposed to arise from the complex combination and interactions of "hard" and "soft" phases within the SPCH and its constituents. SPCH represents a class of hybrid supramolecular composites, opening a window into fiber technology through low-energy manufacturing.

Chemical composition of processed bamboo for structural applications.

Natural materials are a focus for development of low carbon products for a variety of applications. To utilise these materials, processing is required to meet acceptable industry standards. Laminated bamboo is a commercial product that is currently being explored for structural applications, however there is a gap in knowledge about the effects of commercial processing on the chemical composition. The present study utilised interdisciplinary methods of analysis to investigate the effects of processing on the composition of bamboo. Two common commercial processing methods were investigated: bleaching (chemical treatment) and caramelisation (hygrothermal treatment). The study indicated that the bleaching process results in a more pronounced degradation of the lignin in comparison to the caramelised bamboo. This augments previous research, which has shown that the processing method (strip size) and treatment may affect the mechanical properties of the material in the form of overall strength, failure modes and crack propagation. The study provides additional understanding of the effects of processing on the properties of bamboo.

The strength of plants: theory and experimental methods to measure the mechanical properties of stems.

From the stems of agricultural crops to the structural trunks of trees, studying the mechanical behaviour of plant stems is critical for both commerce and science. Plant scientists are also increasingly relying on mechanical test data for plant phenotyping. Yet there are neither standardized methods nor systematic reviews of current methods for the testing of herbaceous stems. We discuss the architecture of plant stems and highlight important micro- and macrostructural parameters that need to be controlled and accounted for when designing test methodologies, or that need to be understood in order to explain observed mechanical behaviour. Then, we critically evaluate various methods to test structural properties of stems, including flexural bending (two-, three-, and four-point bending) and axial loading (tensile, compressive, and buckling) tests. Recommendations are made on best practices. This review is relevant to fundamental studies exploring plant biomechanics, mechanical phenotyping of plants, and the determinants of mechanical properties in cell walls, as well as to application-focused studies, such as in agro-breeding and forest management projects, aiming to understand deformation processes of stem structures. The methods explored here can also be extended to other elongated, rod-shaped organs (e.g. petioles, midribs, and even roots).

Comparison of kink-band structures and specificities of cell wall polysaccharides in modern and ancient flax fibres.

Flax (Linum usitatissimum L.) is a plant of industrial importance, its fibres being presently used for high-value textile applications, composite reinforcements as well as natural actuators. Human interest in this fibre-rich plant dates back several millennia, including to Ancient Egypt where flax was used extensively in various quotidian items. While the recent technical developments of flax fibres continue to diversify through scientific research, the historical use of flax also has rich lessons for today. Through careful examination of ancient Egyptian and modern flax fibres, this study aims to conduct a multi-scale characterization from the yarn to the fibre cell wall scale, linking differences in structure and polysaccharide content to the mechanical performance and durability of flax. Here, a multi-scale biochemical study is enriched by scanning electron microscopy and nanomechanical investigations. A key finding is the similarity of cellulose features, crystallinity index and local mechanical performances between ancient and modern fibres. Biochemically speaking, monosaccharides analysis, deep-UV and NMR investigations demonstrate that ancient fibres exhibit less pectins but a similar hemicellulosic content, especially through uronic acids and galactose, suggesting the sensitivity of these non-crystalline components.

Recent Developments in Shape Memory Elastomers for Biotechnology Applications.

Shape memory elastomers have revolutionised the world since their introduction in the 20th century. The ability to tailor chemical structures to produce a family of materials in wide-ranging forms with versatile properties has propelled them to be ubiquitous. Recent challenges in the end-of-life management of polymeric materials should prompt us to ask, 'what innovations in polymeric materials can make a strong case for their use as efficient materials?' The development of smart elastomers that can acquire, convey, or process a stimulus (such as temperature, pressure, electromagnetic field, moisture, and chemical signals) and reply by creating a useful effect, specifically a reversible change in shape, is one such innovation. Here, we present a brief overview of shape memory elastomers (SMEs) and thereafter a review of recent advances in their development. We discuss the complex processing of structure-property relations and how they differ for a range of stimuli-responsive SMEs, self-healing SMEs, thermoplastic SMEs, and antibacterial and antifouling SMEs. Following innovations in SEMs, the SMEs are forecast to have significant potential in biotechnology based on their tailorable physical properties that are suited to a range of different external stimuli.

Facile, Energy-Efficient Microscale Fibrillation of Polyacrylamides under Ambient Conditions.

Insight into fiber formation can provide new rationale for the design and preparation of fibers with programmed mechanical properties. While synthetic bioinspired fibers have shown impressive tensile properties, the fiber formation process remains poorly understood. Moreover, these systems are highly complex and their formation is environmentally and economically costly. Controlled fiber formation under ambient conditions from polyacrylamide solutions with properties comparable to natural fibers such as wool and coir is demonstrated. Photopolymerization and subsequent microscale fibrillation of different acrylamides in water/ethanol mixtures yield a simple and energy-efficient route to fiber formation. This strategy reduces required processing energy by two-to-three orders of magnitude. Through extensive experimental elucidation, insight into precise fiber forming conditions of polymeric solutions is achieved. Ethanol is utilized as a chain transfer agent to control the molecular weight of the polyacrylamides, and the entanglement regimes of the solutions are determined through rheological characterization showing fiber formation above the entanglement concentration. Unique from previously reported hydrogel microfibers, it is shown that fibers with good mechanical properties can be obtained without the need for composites or crosslinkers. The reported approach offers a platform for fiber formation under ambient conditions with molecular-level understanding of their assembly.

Social media enables people-centric climate action in the hard-to-decarbonise building sector.

The building and construction sector accounts for around 39% of global carbon dioxide emissions and remains a hard-to-abate sector. We use a data-driven analysis of global high-level climate action on emissions reduction in the building sector using 256,717 English-language tweets across a 13-year time frame (2009-2021). Using natural language processing and network analysis, we show that public sentiments and emotions on social media are reactive to these climate policy actions. Between 2009-2012, discussions around green building-led emission reduction efforts were highly influential in shaping the online public perceptions of climate action. From 2013 to 2016, communication around low-carbon construction and energy efficiency significantly influenced the online narrative. More significant interactions on net-zero transition, climate tech, circular economy, mass timber housing and climate justice in 2017-2021 shaped the online climate action discourse. We find positive sentiments are more prominent and recurrent and comprise a larger share of the social media conversation. However, we also see a rise in negative sentiment by 30-40% following popular policy events like the IPCC report launches, the Paris Agreement and the EU Green Deal. With greater online engagement and information diffusion, social and environmental justice topics emerge in the online discourse. Continuing such shifts in online climate discourse is pivotal to a more just and people-centric transition in such hard-to-decarbonise sectors.

Beyond What Meets the Eye: Imaging and Imagining Wood Mechanical-Structural Properties.

Wood presents a hierarchical structure, containing features at all length scales: from the tracheids or vessels that make up its cellular structure, through to the microfibrils within the cell walls, down to the molecular architecture of the cellulose, lignin, and hemicelluloses that comprise its chemical makeup. This structure renders it with high mechanical (e.g., modulus and strength) and interesting physical (e.g., optical) properties. A better understanding of this structure, and how it plays a role in governing mechanical and other physical parameters, will help to better exploit this sustainable resource. Here, recent developments on the use of advanced imaging techniques for studying the structural properties of wood in relation to its mechanical properties are explored. The focus is on synchrotron nuclear magnetic resonance spectroscopy, X-ray diffraction, X-ray tomographical imaging, Raman and infrared spectroscopies, confocal microscopy, electron microscopy, and atomic force microscopy. Critical discussion on the role of imaging techniques and how fields are developing rapidly to incorporate both spatial and temporal ranges of analysis is presented.

Investigations by AFM of Ageing Mechanisms in PLA-Flax Fibre Composites during Garden Composting.

PLA-flax non-woven composites are promising materials, coupling high performance and possible degradation at their end of life. To explore their ageing mechanisms during garden composting, microstructural investigations were carried out through scanning electron microscopy (SEM) and atomic force microscopy (AFM). We observe that flax fibres preferentially degrade 'inwards' from the edge to the core of the composite. In addition, progressive erosion of the cell walls occurs within the fibres themselves, 'outwards' from the central lumen to the periphery primary wall. This preferential degradation is reflected in the decrease in indentation modulus from around 23 GPa for fibres located in the preserved core of the composite to 3-4 GPa for the remaining outer-most cell wall crowns located at the edge of the sample that is in contact with the compost. Ageing of the PLA matrix is less drastic with a relatively stable indentation modulus. Nevertheless, a change in the PLA morphology, a significant decrease in its roughness and increase of porosity, can be observed towards the edge of the sample, in comparison to the core. This work highlights the important role of intrinsic fibre porosity, called lumen, which is suspected to be a major variable of the compost ageing process, providing pathways of entry for moisture and microorganisms that are involved in cell wall degradation.

Curved-crease origami face shields for infection control.

The COVID-19 pandemic has created enormous global demand for personal protective equipment (PPE). Face shields are an important component of PPE for front-line workers in the context of the COVID-19 pandemic, providing protection of the face from splashes and sprays of virus-containing fluids. Existing face shield designs and manufacturing procedures may not allow for production and distribution of face shields in sufficient volume to meet global demand, particularly in Low and Middle-Income countries. This paper presents a simple, fast, and cost-effective curved-crease origami technique for transforming flat sheets of flexible plastic material into face shields for infection control. It is further shown that the design could be produced using a variety of manufacturing methods, ranging from manual techniques to high-volume die-cutting and creasing. This demonstrates the potential for the design to be applied in a variety of contexts depending on available materials, manufacturing capabilities and labour. An easily implemented and flexible physical-digital parametric design methodology for rapidly exploring and refining variations on the design is presented, potentially allowing others to adapt the design to accommodate a wide range of ergonomic and protection requirements.

Lessons on textile history and fibre durability from a 4,000-year-old Egyptian flax yarn.

Flax has a long and fascinating history. This plant was domesticated around 8,000 BCE1 in the Fertile Crescent area2, first for its seeds and then for its fibres1,3. Although its uses existed long before domestication, residues of flax yarn dated 30,000 years ago have been found in the Caucasus area4. However, Ancient Egypt laid the foundations for the cultivation of flax as a textile fibre crop5. Today flax fibres are used in high-value textiles and in natural actuators6 or reinforcements in composite materials7. Flax is therefore a bridge between ages and civilizations. For several decades, the development of non- or micro-destructive analysis techniques has led to numerous works on the conservation of ancient textiles. Non-destructive methods, such as optical microscopy8 or vibrational techniques9,10, have been largely used to investigate archaeological textiles, principally to evaluate their degradation mechanisms and state of conservation. Vibrational spectroscopy studies can now benefit from synchrotron radiation11 and X-ray diffraction measurement in the archaeometric study of historical textiles12,13. Conservation of mechanical performance and the ultrastructural differences between ancient and modern flax varieties have not been examined thus far. Here we examine the morphological, ultrastructural and mechanical characteristics of a yarn from an Egyptian mortuary linen dating from the early Middle Kingdom (Eleventh Dynasty, ca. 2033-1963 BCE) and compare them with a modern flax yarn to assess the quality and durability of ancient flax fibres and relate these to their processing methods. Advanced microscopy techniques, such as nano-tomography, multiphoton excitation microscopy and atomic force microscopy were used. Our findings reveal the cultural know-how of this ancient civilization in producing high-fineness fibres, as well as the exceptional durability of flax, which is sometimes questioned, demonstrating their potential as reinforcements in high-technology composites.

Mechanical Properties of Flax Tape-Reinforced Thermoset Composites.

Three thermoset resin systems-bio-epoxy, epoxy, and polyester-with 30 v% flax fiber reinforcement have been studied to identify the optimal fiber-resin combination in a typical composite structure. Tensile, interface and interlaminar shear strength together with flexural and impact damage tolerance were compared in this study. The results revealed that mechanical and interfacial properties were not significantly affected by the different resin systems. Microscopy studies reveal that epoxy laminates predominantly fail by fibre linear breakage, polyester laminates by fiber pull-out, and bio-epoxy laminates by a combination of the two. The higher failure strains and pull-out mechanism may explain the better impact damage tolerance of polyester composites. Flow experiments were also conducted, revealing faster impregnation and lower void content with polyester resin, followed by bio-epoxy, due to their lower viscosities. Overall, bio-epoxy resin demonstrates comparable performance to epoxy and polyester resins for use in (semi-)structural bio-composites.

Recent Progress in Processing Functionally Graded Polymer Foams.

Polymer foams are an important class of engineering material that are finding diverse applications, including as structural parts in automotive industry, insulation in construction, core materials for sandwich composites, and cushioning in mattresses. The vast majority of these manufactured foams are homogeneous with respect to porosity and structural properties. In contrast, while cellular materials are also ubiquitous in nature, nature mostly fabricates heterogeneous foams, e.g., cellulosic plant stems like bamboo, or a human femur bone. Foams with such engineered porosity distribution (graded density structure) have useful property gradients and are referred to as functionally graded foams. Functionally graded polymer foams are one of the key emerging innovations in polymer foam technology. They allow enhancement in properties such as energy absorption, more efficient use of material, and better design for specific applications, such as helmets and tissue restorative scaffolds. Here, following an overview of key processing parameters for polymer foams, we explore recent developments in processing functionally graded polymer foams and their emerging structures and properties. Processes can be as simple as utilizing different surface materials from which the foam forms, to as complex as using microfluidics. We also highlight principal challenges that need addressing in future research, the key one being development of viable generic processes that allow (complete) control and tailoring of porosity distribution on an application-by-application basis.

A Review of Permeability and Flow Simulation for Liquid Composite Moulding of Plant Fibre Composites.

Liquid composite moulding (LCM) of plant fibre composites has gained much attention for the development of structural biobased composites. To produce quality composites, better understanding of the resin impregnation process and flow behaviour in plant fibre reinforcements is vital. By reviewing the literature, we aim to identify key plant fibre reinforcement-specific factors that influence, if not govern, the mould filling stage during LCM of plant fibre composites. In particular, the differences in structure (physical and biochemical) for plant and synthetic fibres, their semi-products (i.e., yarns and rovings), and their mats and textiles are shown to have a perceptible effect on their compaction, in-plane permeability, and processing via LCM. In addition to examining the effects of dual-scale flow, resin absorption, (subsequent) fibre swelling, capillarity, and time-dependent saturated and unsaturated permeability that are specific to plant fibre reinforcements, we also review the various models utilised to predict and simulate resin impregnation during LCM of plant fibre composites.

Mapping thermal conductivity across bamboo cell walls with scanning thermal microscopy.

Scanning thermal microscopy is a powerful tool for investigating biological materials and structures like bamboo and its cell walls. Alongside nanoscale topographical information, the technique reveals local variations in thermal conductivity of this elegant natural material. We observe that at the tissue scale, fibre cells in the scattered vascular tissue would offer preferential pathways for heat transport due to their higher conductivities in both anatomical directions, in comparison to parenchymatic cells in ground tissue. In addition, the transverse orientation offers more resistance to heat flow. Furthermore, we observe each fibre cell to compose of up to ten layers, with alternating thick and thin lamellae in the secondary wall. Notably, we find the thin lamellae to have relatively lower conductivity than the thick lamellae in the fibre direction. This is due to the distinct orientation of cellulose microfibrils within the cell wall layers, and that cellulose microfibrils are highly anisotropic and have higher conductivity along their lengths. Microfibrils in the thick lamellae are oriented almost parallel to the fibre cell axis, while microfibrils in the thin lamellae are oriented almost perpendicular to the cell axis. Bamboo grasses have evolved to rapidly deposit this combination of thick and thin layers, like a polymer composite laminate or cross-laminated timber, for combination of axial and transverse stiffness and strength. However, this architecture is found to have interesting implications on thermal transport in bamboo, which is relevant for the application of engineered bamboo in buildings. We further conclude that scanning thermal microscopy may be a useful technique in plant science research, including for phenotyping studies.

Biomimetic Supramolecular Fibers Exhibit Water-Induced Supercontraction.

Spider silk is a fascinating material, combining high strength and elasticity that outperforms most synthetic fibers. Another intriguing feature of spider silk is its ability to "supercontract," shrinking up to 50% when exposed to water. This is likely on account of the entropy-driven recoiling of secondary structured proteins when water penetrates the spider silk. In contrast, humidity-driven contraction in synthetic fibers is difficult to achieve. Here, inspired by the spider silk model, a supercontractile fiber (SCF), which contracts up to 50% of its original length at high humidity, comparable to spider silk, is reported. The fiber exhibits up to 300% uptake of water by volume, confirmed via environmental scanning electron microscopy. Interestingly, the SCF exhibits tunable mechanical properties by varying humidity, which is reflected by the prolonged failure strain and the reversible damping capacity. This smart supramolecular fiber material provides a new opportunity of fabricating biomimetic muscle for diverse applications.

Observation of interfacial damage in a silk-epoxy composite, using a simple mechanoresponsive fluorescent probe.

Polymer composite materials are found throughout the world both natural and artificial in origin. In the vast majority of applications in these arenas, composites serve as structural support or reinforcement. Demand for lightweight tough composites is growing in multiple application spaces such as aerospace, biomaterials, and infrastructure with physical properties as diverse as the applications. The unifying component in all composites is the presence of the interphase. Many measurement techniques and measurement tools have been developed for the study of this crucial region in composite materials. Many of these methods are great for the measurement and study of bulk properties or model systems. However, development of tools that permit the direct observation of interactions at the interphase during applied stress are needed. Here we employ fluorescence lifetime imaging and hyperspectral imaging to observe activation of a fluorogenic dye at the composite interface as a result of applied stress. The advantages of this system include commercial availability of the dye precursor, and simple one-pot functionalization. The attachment of the dye at the interface is easily monitored through emission wavelength shifts or fluorescence lifetime. Interfacial mechano-responsive dyes have potential for both fundamental studies as well as industrial use as a structural health monitoring tool.

The biocomposite tube of a chaetopterid marine worm constructed with highly-controlled orientation of nanofilaments.

The ultrastructure of the self-constructed tube housing of the bioluminescent marine worm, Chaetopterus sp. reveals that the bio-nanocomposite tube comprises of multiple non-woven plies of multi-axially oriented organic nanofilaments (ø 50-1100nm) cemented together by an unstructured organic matrix binder. The thin-walled, impermeable tubes are bio-inspirational for conventional pipe technology. Orientation distribution analyses revealed that the dominant orientation angles of nanofilaments in the tube were 0°, ±45° and ±65°, which correlate well with optimal winding angles for 'man-made' fibre reinforced composite pipes subjected to specific loading conditions. Such a use of high aspect ratio nanofilaments in multi-axial laminates would impart toughness and flexibility to the tube structure, and facilitate rapid tube growth. While the tube production mechanism is not entirely known at this stage, our time-lapse studies show that, contrary to generic assumptions in literature, the worm actively, rapidly and sporadically produces and expands the tube.

Housing tubes from the marine worm Chaetopterus sp.: biomaterials with exceptionally broad thermomechanical properties.

The housing tube material of the marine worm Chaetopterus sp. exhibits thermal stability up to 250°C, similar to other biological materials such as mulberry silkworm cocoons. Interestingly, however, dynamic mechanical thermal analysis conducted in both air and water elucidated the lack of a glass transition in the organic tube wall material. In fact, the viscoelastic properties of the anhydrous and undried tube were remarkably stable (i.e. constant and reversible) between -75°C and 200°C in air, and 5°C and 75°C in water, respectively. Moreover, it was found that hydration and associated-water plasticization were key to the rubber-like flexible properties of the tube; dehydration transformed the material behaviour to glass-like. The tube is made of bionanocomposite fibrils in highly oriented arrangement, which we argue favours the biomaterial to be highly crystalline or cross-linked, with extensive hydrogen and/or covalent bonds. Mechanical property characterization in the longitudinal and transverse directions ascertained that the tubes were not quasi-isotropic structures. In general, the higher stiffness and strength in the transverse direction implied that there were more nanofibrils orientated at ± 45° and ± 65° than at 0° to the tube axis. The order of the mechanical properties of the soft-tough tubes was similar to synthetic rubber-like elastomers and even some viscid silks. The complex structure-property relations observed indicated that the worm has evolved to produce a tubular housing structure which can (i) function stably over a broad range of temperatures, (ii) endure mechanical stresses from specific planes/axes, and (iii) facilitate rapid growth or repair.