Reformation Of Bonds Research Articles

Superior strength and toughness of graphene/chitosan fibers reinforced by interfacial complexation

Graphene fibers have been fabricated by wet spinning, in which interfacial interactions including hydrogen bond, ionic bond, covalent bond and π-π interaction were usually constructed to achieve effective translation of the extraordinary properties inherent in graphene microscopic building blocks to macroscopic bulk materials. However, the interactions would induce the aggregation of graphene oxide (GO) spinning dope, leading to the local inhomogeneity and deteriorating mobility which was unfavorable for the translation of GO inherent performance. In order to overcome the contradiction, an interfacial polyelectrolyte complexation (IPC) spinning not involving in the usage of organic solvents was proposed to in-situ build a hierarchical assembly structure of well-ordered GO sheets and chitosan molecules by mimicking natural nacre. After partial reduction of GO fibers using HI, strong and tough graphene fibers with tensile strength of 875.5 MPa and toughness of 17.85 MJ/m3 were obtained due to strong ionic bond and hydrogen bond interactions between rGO and chitosan. Molecular dynamics simulation revealed the fracture mechanism of the graphene fibers that was the slippage of rGO sheets and chitosan molecules accompanied by the breaking and reforming of interfacial bonds. Combing the considerable electrical conductivity, the fibers exhibited a promising application potential as wearable electronics and conductors.

Tuning the Mechanical Properties of Metallopolymers via Ligand Interactions: A Combined Experimental and Theoretical Study

Metal–ligand interactions provide a means for modulating the mechanical properties of metallopolymers as well as an avenue toward understanding the connection between cross-link interaction strength and macroscale mechanical properties. In this work, we used nickel carboxylate as the tunable cross-linking interaction in a metallopolymer. Different numbers and types of neutral ligands that coordinate to the metal center are introduced as an easy approach to adjust the strength of the ionic interactions in the nickel carboxylate cross-links, thus allowing macroscale mechanical properties to be tuned. Density functional theory (DFT) calculations, with the external forces explicitly included (EFEI) approach, were used to quantify how the number and type of ligands affect the stiffness, strength, and thermodynamic stability of the nickel carboxylate cross-linking interactions. Interpreting the bulk material properties in the context of these DFT results suggests that the stiffness and strength of the cross-linking interactions primarily control the initial stiffness and yield strength of the metallopolymer, while the mechanical behavior at higher strain is controlled by dynamical bond re-formation and interactions with the polymer environment. The physicochemical insight gained from this work can be used in the rational design of metallopolymers with a wide scope of targeted mechanical properties.

Branched Alkylamine-Reduced Graphene Oxide Hybrids as a Dual Proton-Electron Conductor and Organic-Only Water-Splitting Photocatalyst.

We report multifunctionalities including the solid electrolytic property, electron conductivity (EnC), and photocatalytic water splitting (PWS) ability of organic-only hybrids obtained by intercalating short and branched-chain alkylamines including methylamine (MA), butylamine (BA), pentylamine (PA), and isomethylbytylamine (IMBA) in reduced graphene oxide (rGO). The alkylamine-rGO hybrids were synthesized by a facile solid-state reduction process. Within the series, IMBA-rGO exhibited high proton conductivity (PrC), EnC, and optimized PWS capacity. The PrC of IMBA-rGO was from 10-4 to 10-3 S cm-1, which is only half an order less than that for pristine GO. The EnC was 1.25 μA/V. Though the PWS performances of MA-rGO, BA-rGO, and PA-rGO were comparatively lower, IMBA-rGO could generate about 1.5 times H2 compared with that for R-TiO2. The IR spectra indicate the association of IMBA and GO by chemical bonds. The Raman spectra show the transformation of GO's nonconductive sp3 carbon sites into electron-conductive sp2 carbon centers. The thermogravimetric analysis show improved water adsorbing capacity of IMBA-rGO, which resulted in higher PrC. Doping of the nitrogen atom at the graphitic sp2 system was confirmed from the presence of pyrrolic N in X-ray photoelectron spectroscopy spectra. The resultant N-type semiconducting behavior is majorly responsible for the PWS process. The powder X-ray diffraction analysis indicates a more flexible interlayer space in IMBA-rGO, which facilitates both the reformation of hydrogen bonds during proton conduction and water dynamics during photocatalysis. The material indicates the possibility of devising graphene-based organic-only multifunctional hybrids.

Observation of the Imidazole-Imidazolium Hydrogen Bonds Responsible for Selective Proton Conductance in the Influenza A M2 Channel.

The integral membrane M2 protein is a 97-residue membrane protein that assembles as a tetramer to conduct protons at a slow rate (102-103/s) when activated by low pH. The proton conductance mechanism has been extensively debated in the literature, but it is accepted that the proton conductance is facilitated by hydrogen bonds involving the His37 residues. However, the hydrogen bonding partnership remains unresolved. Here, we report on the measurement of 15N-15N J-couplings of 15N His37-labeled full length M2 (M2FL) protein from Influenza A virus embedded in synthetic liquid crystalline lipid bilayers using two-dimensional J-resolved NMR spectroscopy. We experimentally observed the hydrogen-bond mediated J-couplings between Nδ1 and Nε2 of adjacent His37 imidazole rings, providing direct evidence for the existence of various imidazolium-imidazole hydrogen-bonding geometries in the histidine tetrad at low pH, thus validating the proton conduction mechanism in the M2FL protein by which the proton is transferred through the breaking and reforming of the hydrogen bonds between pairs of His37 residues.

Self-healing, reprocessing and 3D printing of transparent and hydrolysis-resistant silicone elastomers

Various intrinsic self-healing silicone elastomers have been developed by incorporating different dynamic noncovalent or covalent bonds into elastomeric crosslinked networks. However, these self-healable silicone elastomers are either nontransparent or nonresistant to hydrolysis. In this study, a transparent and hydrolysis-resistant silicone elastomer with self-healability, reprocessability and 3D printability is facilely fabricated by successively thiol-ene UV-curing between thiol and vinyl functionalized polysiloxanes, and thermocuring between carboxyl and amido functionalized polysiloxanes. These obtained elastomers show an excellent healing efficiency of 97%, and the healing processes are repeatable for many times. Moreover, these elastomers can be repeatedly reprocessed with a recovery of 90% of virgin mechanical strengths, and the reprocessed elastomers can still repair damages with an efficiency over 90%. These self-healing and reprocessing behaviors mainly derive from the rearrangement of crosslinked networks via reversible breakage and reformation of ionic bonds. Importantly, the silicone elastomers are transparent with a transmittance of over 90% in visible light and hydrolysis-resistant to hydro-thermal treatment. Besides, the silicone elastomers can be fabricated into various self-healable architectures via 3D printing. Therefore, a feasible approach is provided to impart reversible ionic association induced self-healing and reprocessing to 3D printable silicone elastomers.

How methane hydrate recovers at very high pressure the hexagonal ice structure.

Methane hydrate was recently shown, both experimentally and through simulations, to be stable up to the remarkably high pressure of 150 GPa. A new methane hydrate high-pressure (MH-IV) phase, reminiscent of ice at ambient pressure, was described for pressures above approximately 40 GPa. We disentangle here the main contributions to the relative stability of the lower pressure, denoted MH-III, and the high-pressure MH-IV structures. Through several simulation techniques, including metadynamics and path integral molecular dynamics for nuclear quantum effects, we analyze the phase transition mechanism, which implies hydrogen bond breaking and reforming, as well as methane reordering. The transition pathway is far from trivial, and the quantum delocalization of the hydrogen nuclei plays a significant role.

Modification of cysteine residues for mass spectrometry-based proteomic analysis: facts and artifacts

Mass spectrometric proteomic analysis at the sample preparation stage involves the artificial reduction of disulfide bonds in proteins formed between cysteine residues. Such bonds, when preserved in their native state, complicate subsequent enzymatic hydrolysis and interpretation of the research results. To prevent the re-formation of the disulfide bonds, cysteine residues are protected by special groups, most often by alkylation. In this review, we consider the methods used to modify cysteine residues during sample preparation, as well as possible artifacts of this stage. Particularly, adverse reactions of the alkylating agents with other amino acid residues are described. The most common alkylating compound used to protect cysteine residues in mass spectrometric proteomic analysis is iodoacetamide. However, an analysis of the literature in this area indicates that this reagent causes more adverse reactions than other agents used, such as chloroacetamide and acrylamide. The latter can be recommended for wider use. In the review we also discuss the features of the cysteine residue modifications and their influence on the efficiency of the search for post-translational modifications and protein products of single nucleotide substitutions.

Computational insights into O-glycosylation in a CTLA4 Fc-fusion protein linker and its impact on protein quality attributes

The hinge region of immunoglobulin G1 (IgG1) is used as a common linker for Fc-fusion therapeutic proteins. With the advances of high-resolution mass spectrometry and sample treatment strategies, unexpected O-linked glycosylation has been observed in the linker. However, the molecular mechanism involved in this unusual posttranslational modification is unknown. In this study, we applied site-direct mutagenesis, mass spectrometry, analytical chromatography, and computational modeling to investigate O-glycosylation processes in a clinically used CTLA4 Fc-fusion protein and its impacts on protein quality attributes. Surprisingly, O-glycans could be formed at new sites when an initial O-glycosylation site was eliminated, and continued to occur until all potential O-glycosylation sites were nulled. Site-preference of O-glycosylation initiation was attributed to the complex formation between the linker peptide and glycan transferase whereas the O-glycosylating efficiency and the linker flexibility were correlated using molecular modeling and simulations. As predicted, O-glycan-free CTLA4 Fc-fusion proteins were more homogenous for sialylation, and interestingly less prone to protein aggregation. Attenuating protein aggregation was a desirable effect, and could be related to the reduced presence of linker O-glycans that hindered inter-chain disulfide bond reformation. Findings from this study shed light on new therapeutic protein design and development.

On the Strength of Hair across Species

Summary The hair of mammals varies in diameter across species from ∼60 μm in humans to over ∼400 μm in giraffes and elephants. Here, we establish that the tensile strength of hair generally decreases with increasing diameter. Although there is a commonality in the morphology of the hair in such differing species as they all possess a cortex surrounded by cuticles, there are also significant differences in the hierarchical structure that contribute to the observed differences in strength. In this work, the internal structure of the hair from different species is examined, with some unique peculiarities in javelina and capybara hair uncovered. The dimensional dependence of hair strength is compared using Weibull predictions. The good correlation of the strength of hair using such Weibull analysis suggests that the failure strength is dictated by the probability distribution of flaws within the cortex.

Semiconducting SiGeSn high-entropy alloy: A density functional theory study

High-entropy alloys (HEAs), which have been intensely studied due to their excellent mechanical properties, generally refer to alloys with multiple equimolar or nearly equimolar elements. According to this definition, Si-Ge-Sn alloys with equal or comparable concentrations of the three group IV elements belong to the category of HEAs. As a result, the equimolar elements of Si-Ge-Sn alloys likely cause their atomic structures to exhibit the same core effects of metallic HEAs such as lattice distortion. Here, we apply density functional theory (DFT) calculations to show that the SiGeSn HEA indeed exhibits a large local distortion effect. Unlike metallic HEAs, our Monte Carlo and DFT calculations show that the SiGeSn HEA exhibits no chemical short-range order due to the similar electronegativity of the constituent elements, thereby increasing the configurational entropy of the SiGeSn HEA. Hybrid density functional calculations show that the SiGeSn HEA remains semiconducting with a bandgap of 0.38 eV, promising for economical and compatible midinfrared optoelectronic applications. We then study the energetics of neutral single Si, Ge, and Sn vacancies and (expectedly) find wide distributions of vacancy formation energies, similar to those found in metallic HEAs. However, we also find anomalously small lower bounds (e.g., 0.04 eV for a Si vacancy) in the energy distributions, which arise from the bond reformation near the vacancy. Such small vacancy formation energies and their associated bond reformations retain the semiconducting behavior of the SiGeSn HEA, which may be a signature feature of a semiconducting HEA that differentiates from metallic HEAs.

The development of a direct approach to formulate high oil content zein-based emulsion gels using moderate temperatures

The current research presents an effective direct route to obtain high oil content zein-based emulsion gels at moderate temperatures that is feasible for large-scale production. The preparation procedure involved the dissolution of zein in 90% (w/w) aqueous ethanol, followed by addition of glycerol and oil, and finally heating at ~90 °C to induce ethanol evaporation which promotes zein self-assembly and aggregation. The CLSM and cryo-SEM images confirmed the formation of nanoscale spherical zein aggregates organized on the oil droplet interface while excess proteins form a continuous percolating network between the oil droplets. The coiled-coil conformation of zein particles and the role of hydrogen bonds leading to the formation of a zein network through association of spherical zein particles were confirmed using infra-red spectroscopy and temperature-dependent rheology, respectively. Hard gel (4 °C) to soft gel (90 °C) transition was observed in a temperature ramp rheology experiment, indicating strengthening and weakening of hydrogen interactions between the particulate protein aggregates. Similar hydrogen bond breakdown and reformation was observed in a thixotropy experiment while applying high shear and withdrawal, respectively. Stability studies revealed glycerol syneresis, resulting in the deterioration of the gel's mechanical properties due to increase in hardness and decrease in cohesiveness at room temperature. Overall, these results provide important insight into the gelation mechanism and gel characteristics of zein-stabilized emulsion gels prepared by a direct route under moderate temperature conditions, which can be used for various food applications.

Double‐crosslinked reversible redox‐responsive hydrogels based on disulfide–thiol interchange

ABSTRACTWe present novel redox‐responsive hydrogels based on poly(N‐isopropylacrylamide) or poly(acrylamide), consisting of a reversible disulfide crosslinking agent N,N′‐bis(acryloyl)cystamine and a permanent crosslinking agent N,N′‐methylenebisacrylamide for microfluidic applications. The mechanism of swelling/deswelling behavior starts with the cleavage and reformation of disulfide bonds, leading to a change of crosslinking density and crosslinking points. Raman and ultraviolet‐visible spectroscopy confirm that conversion efficiency of thiol–disulfide interchange up to 99%. Rheological analysis reveals that the E modulus of hydrogel is dependent on the crosslinking density and can be repeatedly manipulated between high‐ and low‐stiffness states over at least 5 cycles without significant decrease. Kinetic studies showed that the mechanical strength of the gels changes as the redox reaction proceeds. This process is much faster than the autonomous diffusion in the hydrogel. Moreover, cooperative diffusion coefficient (Dcoop) indicates that the swelling process of the hydrogel is affected by the reduction reaction. Finally, this reversibly switchable redox behavior of bulky hydrogel could be proven in microstructured hydrogel dots through short‐term photopatterning process. These hydrogel dots on glass substrates also showed the desired short response time on cyclic swelling and shrinking processes known from downsized hydrogel shapes. Such stimuli‐responsive hydrogels with redox‐sensitive crosslinkers open a new pathway in exchanging analytes for sensing and separating in microfluidics applications. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019, 57, 2590–2601

Silicone dielectric elastomer with improved actuated strain at low electric field and high self-healing efficiency by constructing supramolecular network

Dielectric elastomers (DE) suffer from cracks and breaks during repeated cycles, thus a DE material with both high actuated strain (SA) and self-healing ability is highly desired. Herein, for the first time we report a self-healable silicone DE (SiR-SN) with large SA under low electric field by constructing supramolecular network assembled by hydrogen bonds and ionic bonds from two components involving carboxyl modified polymethylvinylsiloxane (PMS-g-COOH) and amino terminated polydimethylsiloxane (PDMS-NH2). The results show that as PMS-g-COOH content increases, the dielectric constant (ε′) of SiR-SN increases owing to an increase in dipole content whereas the elastic modulus (Y) decreases because of a decrease in crosslinking density, leading to the significantly increased SA at a given electric field. SiR-SN with 0.2/1 of the mass ratio of PMS-g-COOH to PDMS-NH2 shows much higher ε′ and SA than the commercial silicone DE. Interestingly, self-healing of SiR-SN at 80 °C leads to the re-formation of hydrogen bonds, and thus the recovery of network structure, whereas self-healing at 100 °C can lead to the conversion from hydrogen bonds into ionic ones, and thus the change of network structure. As a result, a self-healing efficiency of 115% in tensile strength and almost 100% in SA at a given electric field can be achieved after self-healing at 80 °C for 5 h, whereas an increase in Y and higher breakdown strength can be achieved after self-healing at 100 °C, which may sustain the repeated stress and prolong the service life. It is promising that this new self-healable silicone dielectric elastomer with large actuated strain under low electric field could be used especially in biological and medical fields.

Editable and bidirectional shape memory chitin hydrogels based on physical/chemical crosslinking

Advances in soft robotics have enabled rapid progress in shape memory hydrogels, including unidirectional, bidirectional and multidirectional shape memory hydrogels. However, shape memory hydrogels with editable feature have hardly been reported. Here, chitin based bilayer hydrogels were prepared based on alkali/urea aqueous system. Due to the different swelling properties of the two layers, namely physical crosslinking layer and chemical crosslinking layer, the hydrogels can bend toward opposite direction in water and ethanol, showing a bidirectional shape memory behavior. Meanwhile, this bidirectional shape memory hydrogels can be programmed to different shapes with external force after immerging in alkali solution as a result of the hydrogen bond breakage and reformation via hydroxyl ion, displaying an editable feature. We believe that the editable and bidirectional shape memory chitin bilayer hydrogels have great potential in soft robotics.

Optimization design on simultaneously strengthening and toughening graphene-based nacre-like materials through noncovalent interaction

Nacre exhibits outstanding mechanical properties due to its hierarchically microstructural features and associated multiscale deformation behaviors, enlightening human to design high-performance graphene-based nacre-like materials (GNMs) in the past decade. However, those GNMs mimicking brick-and-mortar microstructure always cannot give consideration to both strength and toughness because the pullout process of graphene oxide (GO) sheets that amplifies toughness in GNMs is extremely limited compared to natural nacre. Toward this end, a combination of modified shear-lag model and atomic simulations is proposed to investigate the optimal strategy of simultaneously strengthening and toughening for GNMs reinforced by strong noncovalent interfacial interactions. The modified shear-lag model can well couple the interlayer sliding and structural stability to characterize the toughening effect during the pullout process. We demonstrate that the interfacial toughness and shear strength tuned by interlayer noncovalent interactions significantly impact the effective tensile strength of GNMs, while toughness is mainly dominated by the interlayer sliding before strain localization during the pullout process of GO sheets. Melamine molecule is chosen as the representative interlayer crosslink agent owing to the ultrastrong noncovalent interaction between melamine and GO. Our atomic simulations indicate that melamine bound to GO by anomalous hydrogen bonding can greatly improve the interfacial shear stress and maintain the interlayer energy-dissipation efficiency resulting from the breaking and reforming of hydrogen bonds. An optimal range of melamine content and GO oxidation degree is then explored for synchronously superior strength and toughness by balancing the competitions among the reduction of intralayer tensile limit of GO sheets, the improvement of the interlayer shear strength, and the reduction of interfacial toughness. In particular, a scaling law is proposed as the evaluation criterion to correlate the inner inelastic deformation of GNMs and their mechanical properties, revealing why interlayer noncovalent interaction can optimize strength and toughness simultaneously while most other crosslinks usually cannot.

Wood–Moisture Relationships Studied with Molecular Simulations: Methodological Guidelines

This paper aims at providing a methodological framework for investigating wood polymers using atomistic modeling, namely, molecular dynamics (MD) and grand canonical Monte Carlo (GCMC) simulations. Atomistic simulations are used to mimic water adsorption and desorption in amorphous polymers, make observations on swelling, mechanical softening, and on hysteresis. This hygromechanical behavior, as observed in particular from the breaking and reforming of hydrogen bonds, is related to the behavior of more complex polymeric composites. Wood is a hierarchical material, where the origin of wood-moisture relationships lies at the nanoporous material scale. As water molecules are adsorbed into the hydrophilic matrix in the cell walls, the induced fluid–solid interaction forces result in swelling of these cell walls. The interaction of the composite polymeric material, that is the layer S2 of the wood cell wall, with water is known to rearrange its internal material structure, which makes it moisture sensitive, influencing its physical properties. In-depth studies of the coupled effects of water sorption on hygric and mechanical properties of different polymeric components can be performed with atomistic modeling. The paper covers the main components of knowledge and good practice for such simulations.

Intermolecular Dynamics of Water: Suitability of Reactive Interatomic Potential.

Reactive interatomic potentials for water have been developed by researchers based on their ability of bond breaking and formation, which have numerous advantages and applications in different fields. The question that is being addressed in this work is whether these reactive interatomic potentials properly account for the intermolecular dynamics of water that includes both hydrogen bonding as well as librational motions. It should be noted that breaking and reformation of hydrogen bonds occur prior to covalent bond breaking of water molecules (which requires a significant amount of energy), which has numerous applications in absorption as well as solvation problems. Based on correlations with experimental observations, it has been demonstrated that the current forms of the reactive potentials perform poorly in comparison to other well-established empirical interatomic potential models of water, such as TIP4P/2005f, with regard to the intermolecular dynamics of water. Translational and rotational diffusivities, power spectra, and hydrogen-bond lifetime analyses are carried out and compared to available experimental data as well as those obtained from TIP4P/2005f models to arrive at such conclusions.

Reversible Hydrogel Photopatterning: Spatial and Temporal Control over Gel Mechanical Properties Using Visible Light Photoredox Catalysis.

There is a growing interest in being able to control the mechanical properties of hydrogels for applications in materials, medicine, and biology. Primarily, changes in the hydrogel's physical properties, i.e., stiffness, toughness, etc., are achieved by modulating the network cross-linking chemistry. Common cross-linking strategies rely on (i) irreversible network bond degradation and reformation in response to an external stimulus, (ii) using dynamic covalent chemistry, or (iii) isomerization of integrated functional groups (e.g., azobenzene or spiropyran). Many of these strategies are executed using ultraviolet or visible light since the incident photons serve as an external stimulus that affords spatial and temporal control over the mechanical adaptation process. Here, we describe a different type of hydrogel cross-linking strategy that uses a redox-responsive cross-linker, incorporated in poly(hydroxyethyl acrylate)-based hydrogels at three different weight percent loadings, which consists of two viologen subunits tethered by hexaethylene glycol and capped with styrene groups at each terminus. These dicationic viologen subunits (V2+) can be reduced to their monoradical cations (V•+) through a photoinduced electron transfer (PET) process using a visible light-absorbing photocatalyst (tris(bipyridine)ruthenium(II) dichloride) embedded in the hydrogel, resulting in the intramolecular stacking of viologen radical cations, through radical-radical pairing interactions, while losing two positive charges and the corresponding counteranions from the hydrogel. It is shown how this concerted process ultimately leads to collapse of the hydrogel network and significantly (p < 0.05) increases (by nearly a factor of 2) the soft material's stiffness, tensile strength, and percent elongation at break, all of which is easily reversed via oxidation of the viologen subunits and swelling in water. Application of this reversible PET process was demonstrated by photopatterning the same hydrogel multiple times, where the pattern was "erased" each time by turning off the blue light (∼450 nm) source and allowing for oxidation and reswelling in between patterning steps. The areas of the hydrogel that were masked exhibited lower (by 1-2 kPa) shear storage moduli (G') than the areas that were irradiated for 1.5 h. Moreover, because the viologen subunits in the functional cross-linker are electrochromic, it is possible to visualize the regions of the hydrogel that undergo changes in mechanical properties. This visualization process was illustrated by photopatterning a larger hydrogel (∼9.5 cm on its longest side) with a photomask in the design of an array of stars.

Swift heavy ion-irradiated multi-phase calcium borosilicates: implications to molybdenum incorporation, microstructure, and network topology

A series of calcium borosilicate glasses with varying [B2O3], [MoO3], and [CaO] were prepared and subjected to 92 MeV Xe ions used to simulate the damage from long-term α-decay in nuclear waste glasses. Modifications to the solubility of molybdenum, the microstructure of separated phases, and the Si–O–B network topology were investigated following five irradiation experiments that achieved doses between 5 × 1012 and 1.8 × 1014 Xe ions/cm2 in order to test the hypotheses of whether irradiation would induce, propagate, or anneal phase separation. Using electron microscopy, EDS analysis, Raman spectroscopy, and XRD, irradiation was observed to increase the integration of MoO42− by increasing the structural disorder within and between heterogeneous amorphous phases. This occurred through Si/B-O-Si/B bond breakage and reformation of boroxyl and 3/4-membered SiO4 rings. De-mixing of the Si–O–B network concurrently enabled cross directional Ca and Mo diffusion along defect created pathways, which were prevalent along the interface between phases. The initiation and extent of these changes was dependent primarily on the [SiO2]/[B2O3] ratio, with [MoO3] having a secondary effect on influencing the defect population with increasing dose. Microstructurally, these changes to bonding caused a reduction in heterogeneities between amorphous phases by reducing the size and increasing the spatial distribution of immiscible droplets. This general increase in structural disorder prevented crystallization in most cases, but where precipitation was initiated by radiation, it was re-amorphized with increasing dose. These outcomes suggest that internal radiation can alter phase separation tie lines, and can therefore be used as a tool to design certain structural environments for long-term encapsulation of radioisotopes.

Self‐Healable Multifunctional Electronic Tattoos Based on Silk and Graphene

AbstractElectronic tattoos (E‐tattoos), which can be intimately mounted on human skin for noninvasive and high‐fidelity sensing, have attracted the attention of researchers in the field of wearable electronics. However, fabricating E‐tattoos that are capable of self‐healing and sensing multistimuli, similar to the inherent attributes of human skin, is still challenging. Herein, a healable and multifunctional E‐tattoo based on a graphene/silk fibroin/Ca2+ (Gr/SF/Ca2+) combination is reported. The highly flexible E‐tattoos are prepared through printing or writing using Gr/SF/Ca2+ suspension. The graphene flakes distributed in the matrix form an electrically conductive path that is responsive to environmental changes, such as strain, humidity, and temperature variations, endowing the E‐tattoo with high sensitivity to multistimuli. The performance of the E‐tattoo is investigated as a strain, humidity, and temperature sensor that shows high sensitivity, a fast response, and long‐term stability. The E‐tattoo is remarkably healed after damage by water because of the reformation of hydrogen and coordination bonds at the fractured interface. The healing efficiency is 100% in only 0.3 s. Finally, as proof of concept, its applications for monitoring of electrocardiograms, breathing, and temperature are shown. Based on its unique properties and superior performance, the Gr/SF/Ca2+ E‐tattoo may be a promising candidate material for epidermal electronics.