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Shape memory polymer (SMP) sheets patterned with black ink hinges change shape in response to external stimuli, such as absorbed thermal energy from an infrared (IR) light. The geometry of these hinges, including size, orientation, and location, and the applied thermal loads significantly influence the final folded shape of the sheet, but these variables have not been fully investigated. We perform a systematic study on SMP sheets to fundamentally understand the effects of single and double hinge geometries, hinge orientation and spacing, initial temperature, heat flux intensity, and pattern width on the folding behavior. We have developed thermo-viscoelastic finite element models to characterize and quantify the stresses, strains, and temperatures as they relate to SMP shape changes. Our predictions indicate that hinge orientation can be used to reduce the total bending angle, which is the angle traversed by the folding face of the sheet. Two parallel hinges increase the total bending angle, and heat conduction between the hinges affects the transient folding response. IR intensity and initial temperatures can also influence the transient folding behavior. These results can provide guidelines to optimize the transient folding response and the three-dimensional folded structure obtained from self-folding polymer origami sheets that can be applied for myriad applications. [ABSTRACT FROM AUTHOR]

We developed a new equation of state (EOS) for nanocarbons in the thermodynamic range of high explosives detonation products (up to 50GPa and 4000K). This EOS was fitted to an extensive database of thermodynamic properties computed by molecular dynamics simulations of nanodiamonds and nano-onions with the LCBOPII potential. We reproduced the detonation properties of a variety of high explosives with the CARTE thermochemical code, including carbon-poor and carbon-rich explosives, with excellent accuracy. [ABSTRACT FROM AUTHOR]

We consider the question of the amorphization of metallic alloys by melt quenching, as predicted by molecular dynamics simulations with semi-empirical potentials. The parametrization of the potentials is discussed on the example of the ternary Cu-Ti-Zr transition metals alloy, using the ab-initio simulation as a reference. The pair structure in the amorphous state is computed from a potential of the Stillinger-Weber form. The transferability of the parameters during the quench is investigated using two parametrizations: from solid state data, as usual and from a new parametrization on the liquid structure. When the adjustment is made on the pair structure of the liquid, a satisfactory transferability is found between the pure components and their alloys. The liquid structure predicted in this way agrees well with experiment, in contrast with the one obtained using the adjustment on the solid. The final structure, after quenches down to the amorphous state, determined with the new set of parameters is shown to be very close to the ab-initio one, the latter being in excellent agreement with recent X-rays diffraction experiments. The corresponding critical temperature of the glass transition is estimated from the behavior of the heat capacity. Discussion on the consistency between the structures predicted using semi-empirical potentials and ab-initio simulation, and comparison of different experimental data underlines the question of the dependence of the final structure on the thermodynamic path followed to reach the amorphous state. [ABSTRACT FROM AUTHOR]

We report the nanomechanical unfolding of individual self-folded graphene flakes on a flat substrate by using atomic force microscopy techniques. The nanomechanical measurements and molecular dynamics simulations reveal the detailed unfolding process that turns a z-shaped self-folded graphene segment into a flat membrane. A reversible sliding phenomenon in the adhered graphene region during the unfolding process is observed. The findings are useful to better understand the reversible folding properties of graphene and in pursuit of reversible and morphing graphene origami. [ABSTRACT FROM AUTHOR]

This paper presents the fabrication of self-folding devices with minimal human intervention. The devices utilize two easily obtainable and commercially available materials, namely, PVC shrink wrap (contraction layer) and copper foil tape (structural layer). The selffolding structure uses predefined crease patterns to create mountain and valley folds when subjected to a temperature change (67 °C to 91 °C). A unique crease pattern is designed through defined gap widths to act as hinges. The fabrication technique involves a rapid prototyping methodology that employs low-cost materials. The rapid and efficient manufacturing of the self-folding assembly has an advantage over other fabrication techniques that require numerous layers and complex manufacturing steps. As a result, the self-folding technology in this study achieves the 3D transformation of a cubic and pyramid structure from a 2D framework. [ABSTRACT FROM AUTHOR]

Soft deformable materials are needed for applications such as stretchable electronics, smart textiles, or soft biomedical devices. However, the design of a durable, cost-effective, or biologically compatible version of such a material remains challenging. Living animal cells routinely cope with extreme deformations by unfolding preformed membrane reservoirs available in the form of microvilli or membrane folds. We synthetically mimicked this behavior by creating nanofibrous liquid-infused tissues that spontaneously form similar reservoirs through capillarity-induced folding. By understanding the physics of membrane buckling within the liquid film, we developed proof-of-concept conformable chemical surface treatments and stretchable basic electronic circuits. [ABSTRACT FROM AUTHOR]

Continuous fiber reinforced thermoset composites are highly important in a variety of industrial applications because of their ultrahigh specific strength. However, conventional shaping techniques for such materials can hardly achieve very sophisticated shapes. In this paper, we present an unconventional method to enable complex shapes for continuous fiber reinforced thermoset epoxy composites that provided a capability of topology change due to the dynamic ester bonds. Thus, the corresponding composites providing largely enhanced mechanical strength can be endowed with complex permanent shapes via folding. At lower temperatures, the exchange reaction was frozen and the epoxy networks provided ideal shape memory behavior. Accordingly, the composites with complex permanent shapes enabled a self-folding shape recovery process. In addition, a laser half-cutting technique was applied to build controllable defects within the composites. As a result, more complex folding geometries which were extremely challenging for handwork can be easily fabricated. [ABSTRACT FROM AUTHOR]

In our study, we investigated the additive manufacturing (AM) of ceramic-based functionally graded materials (FGM) by the direct AM technology thermoplastic 3D printing (T3DP). Zirconia components with varying microstructures were additively manufactured by using thermoplastic suspensions with different contents of pore-forming agents (PFA), which were co-sintered defect-free. Different materials were investigated concerning their suitability as PFA for the T3DP process. Diverse zirconia-based suspensions were prepared and used for the AM of singleand multi-material test components. All of the samples were sintered defect-free and in the end, we could realize a brick wall-like component consisting of dense (<1% porosity) and porous (approx. 5% porosity) zirconia areas to combine different properties in one component. T3DP opens the door to the AM of further ceramic-based 4D components, such as multi-color, multi-material, or especially, multi-functional components. [ABSTRACT FROM AUTHOR]

The paper deals with the methodology of film growth simulations using classical molecular dynamics and an empirical interaction potential. We focus on the effect of the cut-off distance (rC) of the short-range part of the potential. On the one hand, we find thatrCdoes not affect the qualitative conclusions of the simulations and that its quantitative effect is in the logical direction (better crystallinity at higherrC). On the other hand, we show that the aforementioned quantitative effect is very strong, and clearly underestimated in the literature. The film crystallinity is affected by (non-)neglecting of as seemingly low energies as several meV per bond. The results are important for the design of growth simulations of crystalline films and for the correct interpretation of their results. [ABSTRACT FROM AUTHOR]

Optically transparent poly(methyl methacrylate) (PMMA)-based blends with significantly enhanced mechanical and shape memory properties have been successfully prepared via in-situ formation of micro-scale polylactide stereocomplex crystallites (sc-PLA) in the PMMA matrix in this work. To achieve this goal, a certain content of poly( l -lactide) (PLLA) was firstly melt-blended with PMMA to obtain completely miscible PMMA/PLLA blends, and then an equimolar poly( d -lactide) (PDLA) was incorporated into the blends, giving rise to the in-situ formation of sc-PLA between PLLA and PDLA. In this way, the micro-scale sc-PLA particles were successfully fabricated and homogeneously dispersed in the PMMA matrix. Consequently, these resultant PMMA/sc-PLA blends possess extremely superior optical transparency, even when the content of sc-PLA reaches up to 12 wt%. A further increase in the content of sc-PLA would lead to the formation of sc-PLA network and aggregation, resulting in the deterioration of optical transparency. Moreover, the incorporation of sc-PLA micro-particles significantly enhances the mechanical property of PMMA and the maximum (≈103 MPa) of these blends demonstrates 50% increase than that (≈70 MPa) of PMMA. More importantly, it has been found that the shape recovery performance of PMMA could be effectively improved by the incorporation of sc-PLA. The optimal shape recovery ratio (86%) and high shape fixing ratio (almost 100%) can be obtained for the PMMA/sc12 blend which exhibits excellent optical transparency. It is reasonable to believe that these optically transparent blends with largely enhanced mechanical and shape memory properties possess great application potential in advanced shape memory fields. [ABSTRACT FROM AUTHOR]

Motivated by the self-assembly of natural systems, researchers have investigated the stimulusresponsive curving of thin-shell structures, which is also known as self-folding. Self-folding strategies not only offer possibilities to realize complicated shapes but also promise actuation at small length scales. Biaxial mismatch strain driven self-folding bilayers demonstrate bifurcation of equilibrium shapes (from quasi-axisymmetric doubly curved to approximately singly curved) during their stimulus-responsive morphing behavior. Being a structurally instable, bifurcation could be used to tune the self-folding behavior, and hence, a detailed understanding of this phenomenon is appealing from both fundamental and practical perspectives. In this work, we investigated the bifurcation behavior of self-folding bilayer polygons. For the mechanistic understanding, we developed finite element models of planar bilayers (consisting of a stimulus-responsive and a passive layer of material) that transform into 3D curved configurations. Our experiments with crosslinked Polydimethylsiloxane samples that change shapes in organic solvents confirmed our model predictions. Finally, we explored a design scheme to generate gripper-like architectures by avoiding the bifurcation of stimulus-responsive bilayers. Our research contributes to the broad field of self-assembly as the findings could motivate functional devices across multiple disciplines such as robotics, artificial muscles, therapeutic cargos, and reconfigurable biomedical devices. [ABSTRACT FROM AUTHOR]

ABSTRACT The thermo-mechanical response of heat activated shape memory polymers (SMPs) has been investigated using a thermo-viscoelastic finite element analysis that accounts for external and internal heat sources. SMPs can be thermally stimulated by external heat sources, such as temperature and surface heat flux, or from internal viscous heating. Viscous heating can significantly affect the response of SMP sheets by increasing the temperature during pre-strain, which accelerates stress relaxation. This stress relaxation results in a slower shrinking rate when the SMP is reheated. Viscous heating also causes an increase in temperatures during unconstrained recovery. The predicted results elucidate how the coupled thermo-mechanical loading conditions affect folding and unfolding of SMP sheets in response to localized heating in a hinged region. A parametric study of sheet thickness, hinge width, degree of pre-strain, and hinge surface temperature is also conducted. The validated results can provide guidelines for the design of functional, self-folding structures. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1207-1219 [ABSTRACT FROM AUTHOR]

Traditional origami structures fold along predefined hinges, and the neighboring facets of the hinges are folded to transform planar surfaces into three-dimensional (3D) shapes. In this study, we present a new self-folding design and fabrication approach that has no folding hinges and can build 3D structures with smooth curved surfaces. This four-dimensional (4D) printing method uses a thermal-response control mechanism, where a thermo shrink film is used as the active material and a photocurable material is used as the constraint material for the film. When the structure is heated, the two sides of the film will shrink differently due to the distribution of the constraint material on the film. Consequently, the structure will deform over time to a 3D surface that has no folding hinges. By properly designing the coated constraint patterns, the film can be self-folded into different shapes. The relationship between the constraint patterns and their correspondingly self-folded surfaces has been studied in the paper. Our 4D printing method presents a simple approach to quickly fabricate a 3D shell structure with smooth curved surfaces by fabricating a structure with accordingly designed material distribution. [ABSTRACT FROM AUTHOR]

Multiple biological processes involve the stretching of nucleic acids (NAs). Stretching forces induce local changes in the molecule structure, inhibiting or promoting the binding of proteins, which ultimately affects their functionality. Understanding how a force induces changes in the structure of NAs at the atomic level is a challenge. Here, we use all-atom, microsecond-long molecular dynamics to simulate the structure of dsDNA and dsRNA subjected to stretching forces up to 20 pN. We determine all of the elastic constants of dsDNA and dsRNA and provide an explanation for three striking differences in the mechanical response of these two molecules: the threefold softer stretching constant obtained for dsRNA, the opposite twist-stretch coupling, and its nontrivial force dependence. The lower dsRNA stretching resistance is linked to itsmore open structure,whereas the opposite twist-stretch coupling of both molecules is due to the very different evolution of molecule's interstrand distance with the stretching force. A reduction of this distance leads to overwinding in dsDNA. In contrast, dsRNA is not able to reduce its interstrand distance and can only elongate by unwinding. Interstrand distance is directly correlated with the slide base-pair parameter and its different behavior in dsDNA and dsRNA traced down to changes in the sugar pucker angle of these NAs. [ABSTRACT FROM AUTHOR]

Purpose This paper aims to provide an experimental evaluation of geometric errors on the edges of parts manufactured by the fused deposition modeling (FDM) process.Design/methodology/approach An experimental plan was conducted by building parts in ABS thermoplastic resin on a commercially available machine with given combinations of the three geometric variables (inclination, included and incidence angle) defined in the first part of the paper. Edges on built parts were inspected on a two-dimensional non-contact profilometer to measure position and form errors.Findings The analysis of measurement results revealed that the edge-related variables have significant influences on the geometric errors. The interpretation of error variations with respect to the different angles confirmed the actual occurrence of the previously discussed error causes. As an additional result, quantitative predictions of the errors were provided as a function of angle values.Research limitations/implications The experimental results refer to fixed process settings (material, FDM machine, layer thickness, build parameters, scan strategies).Originality/value The two-part paper is apparently the first to have studied the edges of additively manufactured parts with respect to geometric accuracy, a widely studied topic for surface features. [ABSTRACT FROM AUTHOR]

Self-folding origami is of great interest in current research on functional materials and structures, but there is still a challenge to develop a simple method to create freestanding, reversible, and complex origami structures. This communication provides a feasible solution to this challenge by developing a method based on the digit light processing technique and desolvation-induced self-folding. In this new method, flat polymer sheets can be cured by a light field from a commercial projector with varying intensity, and the self-folding process is triggered by desolvation in water. Folded origami structures can be recovered once immersed in the swelling medium. The self-folding process is investigated both experimentally and theoretically. Diverse 3D origami shapes are demonstrated. This method can be used for responsive actuators and the fabrication of 3D electronic devices. [ABSTRACT FROM AUTHOR]

Water-responsive biopolymer thin films with engineered matrix characteristics can accomplish desirable shape changing properties such as self-folding. Self-folding response of chitosan film is experimentally characterized by its total folding time and rate of folding. Here, atomistic simulation is employed to investigate the molecular mechanism responsible for modified self-folding behavior observed in nanoparticle reinforced chitosan films. The nanocomposite system is solvated with water content varying from 10% to 100% of total mass of the system. The free volume available for diffusion of water molecules is affected by the flexibility of glycosidic linkages present in chitosan chains. The increase in mobility of water molecules with increase in water content decides the rate of folding. A separate molecular system is modeled with confined region between nanoparticles densified with chitosan chains and water molecules. The thickness of confined region is determined from the critical distance of influence of nanoparticles on water molecules. The adsorption of water on nanoparticle surface and relaxation of chitosan chains are responsible for increased total folding time with nanoparticle concentration. This simulation study, complemented with experimental observations provides a useful insight into the designing of actuators and sensors based on the phenomenon of hygromorphism. [ABSTRACT FROM AUTHOR]

Water flow inside polyamide (PA) reverse osmosis (RO) membranes is studied by steady state nonequilibrium molecular dynamics (NEMD) simulations in this work. The PA RO membrane is constructed with the all-atom model, and the density and average pore size obtained thereby are consistent with the latest experimental results. To obtain the time-independent water flux, a steady state NEMD method is used under various pressure drops. The water flux in our simulations, which is calculated under higher pressure drops, is in a linear relation with the pressure drops. Hence, the water flux in lower pressure drops can be reliably estimated, which could be compared with the experimental results. The molecular details of water flowing inside the membrane are considered. The radial distribution function and residence time of water around various groups of polyamide are introduced to analyze the water velocities around these groups, and we find that water molecules flow faster around benzene rings than around carboxyl or amino groups in the membrane, which implies that the main resistance of mass transport of water molecules comes from the carboxyl or amino groups inside the membranes. This finding is in good consistency with experimental results and suggests that less free carboxyl or amino groups should be generated inside RO membranes to enhance water permeance. [ABSTRACT FROM AUTHOR]

Recently bilayer smart hydrogel beams are widely used in various applications such as sensors, actuators, self-folding structures and switches. Developing a strong tool for designing these bilayer smart hydrogel beams is necessary. In this article, we developed an analytical method to solve the swelling induced bending of bilayer beams made of a pH-sensitive layer attached to an inert elastomer layer. A total deformation gradient tensor, without assuming any intermediary virtual state, is defined to map the initial configuration to the deformed state. An exponential function with four constants is employed to describe the deformation of the pH-sensitive gel layer. The proposed method leads to a system of equations with six unknowns that can be simply solved via numerical techniques. As a case study, this method is implemented to solve the swelling induced bending of several bilayer beams with various parameters. The outcomes of the analytical solution are in excellent agreement with the finite element method results, thus confirming the strength of the presented method. [ABSTRACT FROM AUTHOR]

Biomolecular transport systems based on cytoskeletal filaments and motor proteins have become promising tools for a wide range of nanotechnological applications. In this paper, we report control of such transport systems using substrates with switchable shape. We demonstrate this approach on the example of microtubules gliding on surfaces of self-folding polymer bilayers with adsorbed kinesin motors. The polymer bilayers are able to undergo reversible transitions between flat and tube-like shapes that allow the externally controlled retention and release of gliding microtubules. The demonstrated approach, based on surfaces with reconfigurable topography, opens broad perspectives to control biomolecular transport systems for bioanalytical and sensing applications, as well as for the construction of subcellular compartments in the field of synthetic biology. [ABSTRACT FROM AUTHOR]

Control of higher-order polymer structures attracts a great deal of interest for many researchers when they lead to the development of materials having various advanced functions. Among them, conjugated polymers that are useful as starting materials in the design of molecular wires are particularly attractive. However, an equilibrium existing between isolated chains and bundled aggregates is inevitable and has made their physical properties very complicated. As an attempt to simplify this situation, we previously reported that a polymer chain of a water-soluble polythiophene could be isolated through complexation with a helix-forming polysaccharide. More recently, a covalently self-threading polythiophene was reported, the main chain of which was physically protected from self-folding and chain-chain π-stacking. In this report, we wish to report a new strategy to isolate a water-soluble polythiophene and to control its higher-order structure by a supramolecular approach: that is, among a few bile acids, lithocholate can form stoichiometric complexes with cationic polythiophene to isolate the polymer chain, and the higher-order structure is changeable by the molar ratio. The optical and morphological studies have been thoroughly performed, and the resultant complex has been applied to the selective recognition of two AMP structural isomers. [ABSTRACT FROM AUTHOR]

Urea and poly(ethylene glycol) (PEG)-functionalized amphiphilic random copolymers served as self-folding polymers in both water and chloroform via hydrophobic and/or hydrogen-bonding interactions. For this, a urea-bearing methacrylate (BPUMA) was newly designed as a trigger monomer. Various random, gradient, and block copolymers were synthesized by living radical copolymerization of PEG methyl ether methacrylate (PEGMA) and BPUMA to systematically survey folding/association properties. Importantly, self-folding in both water and chloroform requires the random incorporation of BPUMA along a chain and the control of its composition, while gradient or block counterparts tend to induce multichain aggregation. Typically, 30-40 mol % BPUMA random copolymers effectively fold in water to form compact globular unimer micelles with hydrophobic/hydrogen-bonding core covered by multiple PEG arm chains. The dual functionalization of polymers with hydrophilic PEG and hydrophobic/hydrogen-bonding urea units afforded single-chain compartmentalized polymers in both aqueous and organic media. [ABSTRACT FROM AUTHOR]

Oriented polystyrene (PS) has attracted attention due to its capability of sequential self-folding behaviors by infrared (IR) light heating. It has been seen that temporal changes of the shape and properties of PS are affected by its pre-defined molecular structure. In this study, full atomistic molecular dynamics (MD) simulations are carried out to study the effect of initially applied strain on the thermoelastic properties and shape recovery behaviors of the oriented PS. The shape memory creation procedure (SMCP) is described by long-time simulation and initial strains between 15% and 100% are applied by in-plane tensile loadings. As the extent of pre-stretching increases, the anisotropy of elastic modulus and linear coefficient of thermal expansion (CTE) increase primarily due to the molecular alignment. The shape fixity ratio increases by up to 24% and the recovery ratio decreases by up to 32% by increasing the initial strain. In particular, the shape recovery ratio is mainly affected by the orientational order parameter of the oriented PS. The rate of the recoveries of the thermomechanical properties and shape reduce for a more pre-stretched PS. The retardation of conformational transformation comes from a reduction in the sizes of free volume elements. The results demonstrate a microstructure-property relationship which is important in designing the self-folding behaviors of oriented PS. [ABSTRACT FROM AUTHOR]

Magnetic shape memory (MSM) alloys are a new class of smart materials with extraordinary strains up to 12% and frequencies in the range of 1 to 2 kHz. The MSM actuator is a potential device which can achieve high performance electromagnetic actuation by using the properties of MSM alloys. However, significant non-linear hysteresis behavior is a significant barrier to control the MSM actuator. In this paper, the Preisach model was used, by capturing experiments from different input signals and output responses, to model the hysteresis of MSM actuator, and the inverse Preisach model, as a feedforward control, provided compensational signals to the MSM actuator to linearize the hysteresis non-linearity. The control strategy for path tracking combined the hysteresis compensator and the modified fuzzy sliding mode control (MFSMC) which served as a path controller. Based on the experimental results, it was verified that a tracking error in the order of micrometers was achieved. [ABSTRACT FROM AUTHOR]

Folding planar sheets to make 3D shapes from is an ancient practice with many new applications, ranging from personal fabrication of customized items to design of surgical instruments for minimally invasive surgery in self-folding machines. Given a polyhedral mesh, unfolding is an operation of cutting and flattening the mesh. The flattened polyhedral nets are then cut out of planar materials and folded back to 3D. Unfolding a polyhedral mesh into planar nets usually require segmentation. Either used as a preprocessing step to simplify the mesh and provide semantics or as the result of unfolding to avoid overlapping, the segmentation and the unfolding operations are decoupled. Consequently, segmented components may not be unfoldable and unfolded nets usually provide no semantic meaning and make folding difficult. In this paper, we propose a strategy that tightly couples unfolding and segmentation. We show that the proposed method produces unfoldable segmentation that resembles carefully designed paper craft. The key idea that enables this capability is an algorithm that learns from failed unfoldings. [ABSTRACT FROM AUTHOR]

A simple and effective method has been developed for the synthesis of previously unknown cyclopenta- and cyclohexa[4',5']thieno-[2',3':4,5]pyrimido[1,6- b][1,2,4]triazines in a single step by reaction of 4-hydrazinocyclopenta- and 4-hydrazinocyclohexa[4,5]thieno-[2,3- d]pyrimidines with sodium salts of methyl 4-aryl(heteryl)-2,4-dioxobutanoates. It was shown that the determining factor in the formation of tetracyclic products was isomerization by intramolecular recyclization with mechanism analogous to the Dimroth rearrangement. [ABSTRACT FROM AUTHOR]

This paper makes a comparative study about the structural performances of the consolidated AM (additive manufacturing) parts and the multi-piece assemblies. Generally, it is recognised that AM part consolidation can improve the structural performance compared to the traditional multi-piece assembly. However, this may not be true given that the AM materials are directionally weakened, especially in the build direction (BD). Hence, the comparative study performed in this work will provide some conclusions and at the same time, these conclusions could be valuable guidelines for designing AM part consolidation. For implementation details, the level set topology optimisation method will be applied to optimising the multi-piece assembly with rigid joints and the AM part with weakened material properties; and the same design domain will be shared in order to make a fair comparison. A set of different joint positions and material weakening levels will be studied in order to get comprehensive conclusions. [ABSTRACT FROM PUBLISHER]

A generalized hydrodynamic fluctuation model is proposed to simplify the calculation of the dynamic structure factor S(ω, k) of non-ideal plasmas using the fluctuation-dissipation theorem. In this model, the kinetic and correlation effects are both included in hydrodynamic coefficients, which are considered as functions of the coupling strength (Г) and collision parameter (kλei), where λei is the electron-ion mean free path. A particle-particle particle-mesh molecular dynamics simulation code is also developed to simulate the dynamic structure factors, which are used to benchmark the calculation of our model. A good agreement between the two different approaches confirms the reliability of our model. [ABSTRACT FROM AUTHOR]

The collective modes of a familiar two-dimensional one-component-plasma with the repulsive logarithmic interaction between the particles are analysed using the quasi-crystalline approximation (QCA) combined with the molecular dynamic simulation of the equilibrium structural properties. It is found that the dispersion curves in the strongly coupled regime are virtually independent of the coupling strength. Arguments based on the excluded volume consideration for the radial distribution function allow us to derive very simple expressions for the dispersion relations, which show excellent agreement with the exact QCA dispersion over the entire domain of wavelengths. Comparison with the results of the conventional fluid analysis is performed, and the difference is explained. [ABSTRACT FROM AUTHOR]

Selective Laser Melting (SLM) is a laser-based powder bed Additive Manufacturing process that can produce near net shape products with metallic powders according to Computer-Aided Design models. In this paper, a useful analytical model of SLM is proposed by investigating the energy requirement of the process. Results from the experiments on SLM of pure nickel and pure tin are reported. By compiling process parameter data from various literatures and experiments, this model has shown to enable predictions of the energy input required to process different metallic materials to an order of magnitude despite the many assumptions made. Possible explanations for the deviation in predictions and actual energy inputs are also discussed. [ABSTRACT FROM PUBLISHER]

Additive manufacturing (AM) offers numerous benefits for innovative design solutions. However, engineers are currently not supported in identifying and incorporating these potentials systematically in their design solutions. In this paper, previous Design for Additive Manufacturing (DfAM) approaches are first reviewed comprehensively and classified into distinct categories according to their main purpose and application. They are then analysed further by being related to conventional design methodologies like VDI 2221. Since previous DfAM approaches only provide selective assistance at single steps in the product development process, a new framework for DfAM is proposed. Existing methods and tools, both from DfAM and from general design methodologies, are integrated into the modular framework structure. A concept for using the framework is presented to provide design engineers with continuous support in all product development phases, thereby fostering the complete exploitation of AM potentials and the development of AM-conformal designs. [ABSTRACT FROM PUBLISHER]

The self-folding behavior in response to external stimuli observed in hydrogels is potentially used in biomedical applications. However, the use of hydrogels is limited because of its reduced mechanical properties. These properties are enhanced when the hydrogels are cross-linked and reinforced with nanoparticles. In this work, molecular dynamics (MD) simulation is applied to perform uniaxial tension and pull out tests to understand the mechanism contributing towards the enhanced mechanical properties. Also, nanomechanical characterization is performed using quasi static nanoindentation experiments to determine the Young's modulus of hydrogels in the presence of nanoparticles. The stress–strain responses for chitosan (CS), chitosan reinforced with hydroxyapatite (HAP) and cross-linked chitosan are obtained from uniaxial tension test. It is observed that the Young's modulus and maximum stress increase as the HAP content increases and also with cross-linking process. Load displacement plot from pullout test is compared for uncross-linked and cross-linked chitosan chains on hydroxyapatite surface. MD simulation reveals that the variation in the dihedral conformation of chitosan chains and the evolution of internal structural variables are associated with mechanical properties. Additional results reveal that the formation of hydrogen bonds and electrostatic interactions is responsible for the above variations in different systems. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of surface steps naturally created by the glide of dislocations subjected to cyclic loading is examined using molecular dynamics simulations. Three face centred cubic metals, Al, Cu and Ag are analysed. An atomistic reconstruction phenomenon is observed at these surface steps which can induce strong irreversibility. Three different mechanisms of reconstruction are defined. They induce different reconstruction rates and various relief evolutions depending on the temperature. Surface slip irreversibility under cyclic loading is analysed. All surface steps are intrinsically irreversible under usual fatigue laboratory loading amplitude without the arrival of opposite sign dislocations. A surface step is reversible only when an opposite sign dislocation subsequently glides on a nearby atomic plane. Steps created by opposite sign dislocation glides on non neighbouring planes are irreversible. The irreversibility cumulates cycle by cycle and a micro-notch is produced whose depth increases cyclically. A rough estimation of surface irreversibility is carried out for pure edge dislocations in persistent slip bands in wavy materials. This gives an irreversibility fraction between 0.5 and 0.75 in copper. An analysis coupling surface mechanisms with the classical bulk slip irreversibility model proposed by Differt, Essmann and Mughrabi in 1986 and applied to pure screw dislocations gives an irreversibility fraction of 0.62 in copper. Similar estimations in nickel give irreversibility fractions around 0.6 and 0.8 for pure edge and screw dislocations respectively. These values are in agreement with recent atomic force microscopy measurements. [ABSTRACT FROM AUTHOR]

This study demonstrates a new approach to autonomous folding for the body of a 3D robot from a 2D sheet, using heat. We approach this challenge by folding a 0.27-mm sheetlike material into a structure. We utilize the thermal deformation of a contractive sheet sandwiched by rigid structural layers. During this baking process, the heat applied on the entire sheet induces contraction of the contracting layer and thus forms an instructed bend in the sheet. To attain the targeted folding angles, the V-fold spans method is used. The targeted angle ϑout can be kinematically encoded into crease geometry. The realization of this angle in the folded structure can be approximately controlled by a contraction angle ϑ in. The process is non-reversible, is reliable, and is relatively fast. Our method can be applied simultaneously to all the folds in multi-crease origami structures. We demonstrate the use of this method to create a lightweight mobile robot. [ABSTRACT FROM AUTHOR]

The article focuses on the significance of 3-dimensional (3D) bioprinting in medical care. It is stated that 3D bioprinting enables to produce complex designs from a computer-aided file and makes it possible to generate identical copies of patient tissues and organs within 3D space. It is noted that an extrusion-based 3D printer has been used to print a porcine aortic valve structure by using 2 types of hydrogel scaffolds for root and the leaflets.

Cellulose is a pervasive polymer, displaying hierarchical lengthscales and exceptional strength and stiffness. Cellulose's complex organization, however, also hinders the detailed understanding of the assembly, mesoscopic properties, and structure of individual cellulose building blocks. This study combines nanolithography with atomic force microscopy to unveil the properties and structure of single cellulose nanofibrils under weak geometrical confinement. By statistical analysis of the fibril morphology, it emerges that confinement induces both orientational ordering and self‐folding of the fibrils. Excluded volume simulations reveal that this effect does not arise from a fibril population bias applied by the confining slit, but rather that the fibril conformation itself changes under confinement, with self‐folding favoring fibril's free volume entropy. Moreover, a nonstochastics angular bending probability of the fibril kinks is measured, ruling out alternating amorphous–crystalline regions. These findings push forward the understanding of cellulose nanofibrils and may inspire the design of functional materials based on fibrous templates. The combination of nanolithography with atomic force microscopy allows the detailed study of single cellulose nanofibrils under weak confinement. Statistical analysis shows confinement‐induced ordering and self‐folding of the nanofibrils, and a nonstochastic kink bending probability. These results push forward the understanding of the properties and structure of nanocellulose. [ABSTRACT FROM AUTHOR]

An approach to build a chemomechatronic system inspired by self‐folding robots is described. This system, which comprises a protein‐based hydrogel bound to a low‐profile laminate, responds to different aqueous environments by undergoing geometric transformations. This response is dependent on the thickness and stiffness of the templating hydrogel, which directly regulates the diffusion of water into and out of the platform to initiate its reversible shape changes. When modified to include more complex geometries, these controllable shape changes can also be used to selectively trigger multiple folding events, illustrating a new platform for chemically initiated mechatronic devices. Together, these data show how compositionally discrete components are physically, chemically, and mechanically coupled together to generate a new actuator for biohybrid self‐folding systems. A protein‐based hydrogel is coupled to a hinged metal scaffold, creating a new biohybrid self‐folding system. The folding behavior of the system is tracked and characterized using a lumped capacitance model to elucidate the effects that hydrogel dimensions, cross‐linking, and water diffusion have on the self‐folding behavior. [ABSTRACT FROM AUTHOR]

3D printing is recognized as a powerful tool to develop complex geometries for a variety of materials including nanocellulose. Herein, a one‐pot synthesis of 3D printable hydrogel ink containing zeolitic imidazolate frameworks (ZIF‐8) anchored on anionic 2,2,6,6‐tetramethylpiperidine‐1‐oxylradical‐mediated oxidized cellulose nanofibers (TOCNF) is presented. The synthesis approach of ZIF‐8@TOCNF (CelloZIF8) hybrid inks is simple, fast (≈30 min), environmentally friendly, takes place at room temperature, and allows easy encapsulation of guest molecules such as curcumin. Shear thinning properties of the hybrid hydrogel inks facilitate the 3D printing of porous scaffolds with excellent shape fidelity. The scaffolds show pH controlled curcumin release. The synthesis route offers a general approach for metal–organic frameworks (MOF) processing and is successfully applied to other types of MOFs such as MIL‐100 (Fe) and other guest molecules as methylene blue. This study may open new venues for MOFs processing and its large‐scale applications. One‐pot synthesis of Cello‐MOF, a 3D printable hydrogel ink containing metal–organic frameworks anchored on anionic cellulose nanofibers, is presented. The synthesis approach allows easy encapsulation of drugs such as curcumin and methylene blue into CelloMOF. The stimuli‐responsive release of drugs from the 3D printed porous scaffold is demonstrated. [ABSTRACT FROM AUTHOR]

Matrix solid phase dispersion (MSPD) has proven to be an efficient sample preparation method for solid, semi-solid, and viscous samples. Applications of MSPD have covered biological, food, and environmental samples, including both organic and inorganic analytes. This review presents an update on the development of MSPD in the period 2015~June 2018. In the first part of this review, we focus on the latest development in MSPD sorbent, including molecularly imprinted polymers, and carbon-based nanomaterials etc. The second part presents the miniaturization of MSPD, discussing the progress in both micro-MSPD and mini-MSPD. The on-line/in-line techniques for improving the automation and sample throughput are also discussed. The final part summarizes the success in the modification of original MSPD procedures. [ABSTRACT FROM AUTHOR]

The reliability of a QSAR classification model depends on its capacity to achieve confident predictions of new compounds not considered in the building of the model. The results of this external validation process show the applicability domain (AD) of the QSAR model and, therefore, the robustness of the model to predict the property/activity of new molecules. In this paper we propose the use of the rivality and modelability indexes for the study of the characteristics of the datasets to be correctly modeled by a QSAR algorithm and to predict the reliability of the built model to prognosticate the property/activity of new molecules. The calculation of these indexes has a very low computational cost, not requiring the building of a model, thus being good tools for the analysis of the datasets in the first stages of the building of QSAR classification models. In our study, we have selected two benchmark datasets with similar number of molecules but with very different modelability and we have corroborated the capacity of the predictability of the rivality and modelability indexes regarding the classification models built using Support Vector Machine and Random Forest algorithms with 5-fold cross-validation and leave-one-out techniques. The results have shown the excellent ability of both indexes to predict outliers and the applicability domain of the QSAR classification models. In all cases, these values accurately predicted the statistic parameters of the QSAR models generated by the algorithms. [ABSTRACT FROM AUTHOR]

This paper proposes a micro self-folding using a self-rolling up deformation. In the fabrication method at micro scale, self-folding is an especially useful method of easily fabricating complex three-dimensional (3D) structures from engineered two-dimensional (2D) sheets. However, most self-folded structures are limited to 3D structures with a hollow region. Therefore, we made 3D structures with a small hollow region by self-rolling up a 2D sheet consisting of SU-8 and a temperature-responsive hybrid hydrogel of poly(N-isopropylacrylamide-co-acrylic acid) (pNIPAM-AAc). The temperature-responsive hydrogel can provide repetitive deformation, which is a good feature for micro soft robots or actuators, using hydrogel shrinking and swelling. Our micro self-rolling up method is a self-folding method for a 3D structure performed by rolling up a 2D flat sheet, like making a croissant, through continuous self-folding. We used our method to fabricate 3D structures with a small hollow region, such as cylindrical, conical, and croissant-like ellipsoidal structures, and 3D structures with a hollow region, such as spiral shapes. All the structures showed repetitive deformation, forward rolling up in 20 °C cold water and backward rolling up in 40 °C hot water. The results demonstrate that self-rolling up deformation can be useful in the field of micro soft devices. [ABSTRACT FROM AUTHOR]

A self-folding structure fabricated by additive manufacturing (AM) can be automatically folded into a demanding three-dimensional (3D) shape by actuation mechanisms such as heating. However, 3D surfaces can only be fabricated by self-folding structures when they are flattenable. Most generally, designed parts are not flattenable. To address the problem, we develop a shape optimization method to modify a nonflattenable surface into flattenable. The shape optimization framework is equipped with topological operators for adding interior/boundary cuts to further improve the flattenability. When inserting cuts, self-intersection is locally prevented on the flattened two-dimensional (2D) pieces. The total length of inserted cuts is also minimized to reduce artifacts on the finally folded 3D shape. [ABSTRACT FROM AUTHOR]