Explore the vast range of titles available.

This paper provides an overview of recent progress made in the area of cellulose nanofibre-based nanocomposites. An introduction into the methods used to isolate cellulose nanofibres (nanowhiskers, nanofibrils) is given, with details of their structure. Following this, the article is split into sections dealing with processing and characterisation of cellulose nanocomposites and new developments in the area, with particular emphasis on applications. The types of cellulose nanofibres covered are those extracted from plants by acid hydrolysis (nanowhiskers), mechanical treatment and those that occur naturally (tunicate nanowhiskers) or under culturing conditions (bacterial cellulose nanofibrils). Research highlighted in the article are the use of cellulose nanowhiskers for shape memory nanocomposites, analysis of the interfacial properties of cellulose nanowhisker and nanofibril-based composites using Raman spectroscopy, switchable interfaces that mimic sea cucumbers, polymerisation from the surface of cellulose nanowhiskers by atom transfer radical polymerisation and ring opening polymerisation, and methods to analyse the dispersion of nanowhiskers. The applications and new advances covered in this review are the use of cellulose nanofibres to reinforce adhesives, to make optically transparent paper for electronic displays, to create DNA-hybrid materials, to generate hierarchical composites and for use in foams, aerogels and starch nanocomposites and the use of all-cellulose nanocomposites for enhanced coupling between matrix and fibre. A comprehensive coverage of the literature is given and some suggestions on where the field is likely to advance in the future are discussed.

Microfibrillated cellulose (MFC) is a fascinating material with an obvious potential for composite reinforcement due to its excellent mechanics together with high specific surface area. However, in order to use this potential, commercially viable solutions to important technological challenges have to be found. Notably, the distinct hydrophilicity of MFC prevents efficient drying without loss in specific surface area, necessitating storage and processing in wet condition. This greatly hinders compounding with important technical polymers immiscible with water. Differently from cellulose, the chemistry of the major wood polymers lignin and hemicellulose is much more diverse in terms of functional groups. Specifically, the aromatic moieties present in lignin and acetyl groups in hemicellulose provide distinctly less polar surface-chemical functionality compared to hydroxyl groups which dominate the surface-chemical character of cellulose. It is shown that considerable advantages in the production of MFC-filled poly(lactic acid) filaments for three-dimensional printing can be obtained through the use of MFC containing residual lignin and hemicellulose due to their advantageous surface-chemical characteristics. Specifically, considerably reduced agglomerations of MFC in the filaments in combination with improved printability and improved toughness of printed objects are achieved. This article is part of a discussion meeting issue ‘New horizons for cellulose nanotechnology’.

Golf tees with a plastic head and wooden shaft were prepared by back injection moulding of a beech wood (Fagus sylvatica) shaft with different polymers (i.e. ionomer, polypropylene, and polyamide). In order to facilitate adhesion between the polymer melt and the wood surface, the wooden shafts were pre-treated with different primer substances, including a commercially available primer for ABS edges, a 10% solution of alkyl ketene dimer (AKD) in toluene and tumbling lacquer. The mechanical strength of the wood-plastic interphase was characterized by applying a pull-out test. Bond strength values of more than 9 N/mm² were observed for polyamide, whereas ionomer and polypropylene specimens achieved values between 0.7 and 3.8 N/mm². Surprisingly, the used primers failed to improve interfacial adhesion with the exception of the ionomer sample pre-treated with the commercial ABS-primer. Although light microscopy and SEM revealed some differences in the penetration behaviour of the different polymers as well as in the extent of plastic wood deformation imposed during injection moulding, the chemical nature of the polymer seems to be the most important determinant for the bond strength of wood-plastic hybrid components.

Recent studies provide strong evidence that single myosin class V molecules transport vesicles and organelles processively along F-actin, taking several 36-nm steps, 'hand over hand', for each diffusional encounter. The mechanisms regulating myosin-V's processivity remain unknown. Here, we have used an optical-tweezers-based transducer to measure the effect of load on the mechanical interactions between rabbit skeletal F-actin and a single head of mouse brain myosin-V, which produces its working stroke in two phases. We found that the lifetimes of the first phase of the working stroke changed exponentially and about 10-fold over a range of pushing and pulling forces of ± 1.5 pN. Stiffness measurements suggest that intramolecular forces could approach 3.6 pN when both heads are bound to F-actin, in which case extrapolation would predict the detachment kinetics of the front head to slow down 50-fold and the kinetics of the rear head to accelerate respectively. This synchronizing effect on the chemo-mechanical cycles of the heads increases the probability of the trail head detaching first and causes a strong increase in the number of forward steps per diffusional encounter over a system with no strain dependence.

The ability to coordinate the timing of motor protein activation lies at the center of a wide range of cellular motile processes including endocytosis, cell division, and cancer cell migration. We show that calcium dramatically alters the conformation and activity of the myosin-VI motor implicated in pivotal steps of these processes. We resolved the change in motor conformation and in structural flexibility using single particle analysis of electron microscopic data and identified interacting domains using fluorescence spectroscopy. We discovered that calcium binding to calmodulin increases the binding affinity by a factor of 2,500 for a bipartite binding site on myosin-VI. The ability of calcium-calmodulin to seek out and bridge between binding site components directs a major rearrangement of the motor from a compact dormant state into a cargo binding primed state that is nonmotile. The lack of motility at high calcium is due to calmodulin switching to a higher affinity binding site, which leaves the original IQ-motif exposed, thereby destabilizing the lever arm. The return to low calcium can either restabilize the lever arm, required for translocating the cargo-bound motors toward the center of the cell, or refold the cargo-free motors into an inactive state ready for the next cellular calcium flux.

Key Points Single-molecule approaches for studying the dynamic properties of motor proteins have come of age. Recent technical developments allow us to see more details of molecular motions and of the forces that molecules generate. Atomic force microscopy provides the highest available resolution, of about one nanometre, for imaging soft and dynamic motor proteins in action. Recently, significant progress has been made in imaging fragile samples and in high-speed imaging, with rates of up to 25 frames per second being achieved; for example, it is possible to image kinesin motors on top of microtubules with low forces while still being able to resolve single domains of the motor proteins. Fluorescence microscopy is unbeaten in achieving molecular specificity of imaging. Progress has been rapid, especially in single-molecule fluorescence methods. Detectors, which are mostly charged coupled device cameras, are constantly getting more efficient and less noisy. Methods for restricting the sample volume to suppress background noise are becoming increasingly sophisticated. Last, but not least, chemical fluorophores, genetically encoded fluorescent proteins and fluorescent nanoparticles are becoming more versatile, bright and stable. Single-molecule fluorescence experiments in cells remain challenging. Crowding and background fluorescence are difficult to avoid. High hopes are resting on newly developed bright and stable dyes, as well as on fluorescent nanoparticles, especially in the near-infrared spectral range, where cellular background fluorescence is minimal. Optical trapping has been firmly established as a tool of choice when measuring steps or power strokes of motor proteins as well as forces generated by single motors. Optical trapping is being implemented in increasingly sophisticated and powerful ways. The resolution of sub-nanometre steps is possible, time resolution can be as good as microseconds, and controlled forces of piconewtons can be exerted on single molecules in well-controlled geometries. It remains a challenge to apply optical tweezers in cells. Specificity of trapping, as opposed to indiscriminate trapping of various intracellular objects, is hard to achieve, and it is difficult to calibrate force and displacement measurements in cells. Promising developments include the trapping of distinct high-index cellular components, such as lipid droplets, and the use of externally introduced high-index particles, such as gold nanobeads, as well as the exploration of resonantly enhanced trapping. Single-molecule techniques, such as atomic force microscopy, single-molecule fluorescence microscopy and optical tweezers, have helped resolve the mechanisms behind the power strokes, processive steps and forces of cytoskeletal motors. Such techniques might also reveal how motors are integrated into composite mechanical machines to generate complex functions in cells. Much has been learned in the past decades about molecular force generation. Single-molecule techniques, such as atomic force microscopy, single-molecule fluorescence microscopy and optical tweezers, have been key in resolving the mechanisms behind the power strokes, 'processive' steps and forces of cytoskeletal motors. However, it remains unclear how single force generators are integrated into composite mechanical machines in cells to generate complex functions such as mitosis, locomotion, intracellular transport or mechanical sensory transduction. Using dynamic single-molecule techniques to track, manipulate and probe cytoskeletal motor proteins will be crucial in providing new insights.

Motor proteins such as myosin use the energy from ATP to drive a conformational change that generates mechanical force, or power stroke. Using a single-molecule, optical-trap setup, the reverse movement could be observed for myosin-V heads bound to actin when external load is applied, which has implications for myosin's mechanochemical cycle. Complex forms of cellular motility, including cell division, organelle trafficking or signal amplification in the auditory system, require strong coordination of the myosin motors involved. The most basic mechanism of coordination is via direct mechanical interactions of individual motor heads leading to modification of their mechanochemical cycles. Here we used an optical trap–based assay to investigate the reversibility of the force-generating conformational change (power stroke) of single myosin-Va motor heads. By applying load to the head shortly after binding to actin, we found that, at a certain load, the power stroke could be reversed, and the head fluctuated between an actin-bound pre– and a post–power stroke conformation. This load-dependent mechanical instability might be critical to coordinate the heads of processive, dimeric myosin-Va. Nonlinear response to load leading to coordination or oscillations amongst motors might be relevant for many cellular functions.

Floods cause average annual losses of more than US$30 billion in the US and are estimated to significantly increase due to global change. Flood resilience, which currently differs strongly between socio‐economic groups, needs to be substantially improved by proactive adaptive measures, such as timely purchase of flood insurance. Yet, knowledge about the state and uptake of private adaptation and its drivers is so far scarce and fragmented. Based on interpretable machine learning and large insurance and socio‐economic open data sets covering the whole continental US we reveal that flood insurance purchase is characterized by reactive behavior after severe flood events. However, we observe that the Community Rating System helps overcome this behavior by effectively fostering proactive insurance purchase, irrespective of socio‐economic backgrounds in the communities. Thus, we recommend developing additional targeted measures to help overcome existing inequalities, for example, by providing special incentives to the most vulnerable and exposed communities. Plain Language Summary Flood resilience of individuals and communities can be improved by bottom‐up strategies, such as insurance purchase, or top‐down measures like the US National Flood Insurance Program's Community Rating System (CRS). Our interpretable machine learning approach shows that flood insurances are mostly purchased reactively, after the occurrence of a flood event. Yet, reactive behaviors are ill‐suited as more extreme events are expected under future climate, also in areas that were not previously flooded. The CRS counteracts this behavior by fostering proactive adaptation across a widespread range of socio‐economic backgrounds. Future risk management including the CRS should support and motivate individuals' proactive adaptation with a particular focus on highly vulnerable social groups to overcome existing inequalities in flood risk. Key Points Flood insurance purchase in the US is dominated by reactive behavior after severe floods The Community Rating System (CRS) fosters proactive insurance adoption irrespective of socio‐economic background The CRS should further balance existing inequalities by targeting specific population segments

Oil palm trunk (OPT) is an inexpensive, abundantly available by-product of palm oil production which is typically not put to material use. Due to its comparably high cellulose content, OPT represents a suitable raw material for the preparation of cellulose nanofibrils (CNFs). Aiming for full utilization of the raw material and minimized energy demand, non-delignified and partially delignified (alkali-pretreated) OPT was subjected to mechanical fibrillation in the present study. As compared to CNFs from fully delignified OPT, the lignin-rich microfibrils obtained by this approach generally showed higher average fibril diameters, lower thermal stability as well as lower viscosity, and higher sedimentation rate in suspension. However, the combination of alkali-pretreatment and fibrillation by disc-grinding and subsequent high-pressure homogenization resulted in fibrils with properties similar to those of CNFs from fully delignified OPT. As proven by IR-spectroscopy, thermogravimetry and chemical composition analysis, alkali-treated OPT fibrils still contained substantial amounts of residual lignin which could, for instance, act as a natural coupling agent or binder in composite applications. Moreover, the facile delignification process applied herein requires far less chemicals and energy than conventional pulping and is thus beneficial from both the economic and ecological perspective.