Use of lateral-exit crossed-pin fixation for pediatric supracondylar humeral fractures: a retrospective case series.

Surgeons have been reluctant to perform crossed-pin fixation for displaced pediatric supracondylar humeral (SCH) fractures because it carries a risk of iatrogenic ulnar nerve injury. This study aimed to introduce lateral-exit crossed-pin fixation for displaced pediatric SCH fractures and to evaluate its clinical and radiological outcomes, with a particular focus on iatrogenic ulnar nerve injuries. Children who underwent lateral-exit crossed-pin fixation for displaced SCH fractures between 2010 and 2015 were retrospectively reviewed. Lateral-exit crossed-pin fixation involved the introduction of a medial pin from the medial epicondyle, as in the conventional method, followed by pulling the pin through the lateral skin until the distal and medial aspects of the pin were just under the cortex of the medial epicondyle. The time to union and loss of fixation were assessed. Flynn's clinical criteria (cosmetic and functional factors) and complications including iatrogenic ulnar nerve injury were investigated. A total of 81 children with displaced SCH fractures were treated with lateral-exit crossed-pin fixation. All but one patient achieved union with good alignment, with an average time to union of 7.9 weeks (3.9-10.3 weeks). Only one patient exhibited cubitus varus deformity associated with loss of reduction. All patients recovered to almost their full range of motion. No case of iatrogenic ulnar nerve injury developed; however, iatrogenic radial nerve injury developed in one patient. Lateral-exit crossed-pin fixation provides sufficient stability with a lower risk of iatrogenic ulnar nerve injury in children with displaced SCH fractures. This method is an acceptable technique for crossed-pin fixation.

Atomistic Insights into Interfacial Optimization Mechanism for Achieving Ultralow-Friction Amorphous Carbon Films under Solid-Liquid Composite Conditions.

The combination of fluid lubricants and textured amorphous carbon (a-C) can provide an ultralow friction state, which can improve the reliability and service life of dynamic machinery. However, the coupling effects of the contact pressure and oil content on the friction-reducing efficiency is still lack of study, and the corresponding friction mechanism is also not fully understood, which cannot be achieved by experiment due to the limitation of in situ characterization. In this study, using the reactive molecular dynamics simulation, the insight into the evolution of interfacial structures induced by both contact pressures and oil contents on a-C surface was systematically investigated to explore the fundamental mechanism. In particular, the friction difference between textured and untextured a-C films was evaluated comparatively. Results indicate that the tribological performance strongly depends on the interfacial lubrication state, which is jointly determined by the oil content and contact pressure; the best operating condition to achieve ultralow friction coefficient (0.002) is obtained, and the evolution of friction coefficient with oil content and contact pressure is highly dominated by the lubricant mobility, cross-linking between mating a-C surfaces, or competition/synergy of the H stress state from the lubricant with interfacial passivation. Furthermore, the difference in friction reduction between textured and untextured systems is unveiled; with the increase of contact pressure, the role of texturing a-C surface in antifriction changes from positive to negative effect, which is related to the transformation of interfacial hybridized structure and anomalous flow of lubricant. These results can significantly enhance the understanding of composite lubrication systems through computation and also provide a roadmap for the R&D of the advanced lubrication system according to the working conditions.

Atomic-Scale Understanding on the Tribological Behavior of Amorphous Carbon Films under Different Contact Pressures and Surface Textured Shapes.

The textured design of amorphous carbon (a-C) film can significantly improve the tribological performance and service life of moving mechanical components. However, its friction dependence on different texture shapes, especially under different load conditions, remains unclear. In particular, due to the lack of information regarding the friction interface, the underlying friction mechanism has still not been unveiled. Therefore, the effects of contact pressure and textured shapes on the tribological behavior of a-C films under dry friction conditions were comparatively studied in this work by reactive molecular dynamics simulation. The results show that under low contact pressure, the tribological property of a-C film is sensitive to the textured shape, and the system with a circular textured surface exhibits a lower friction coefficient than that with a rectangular textured surface, which is attributed to the small fraction of unsaturated bonds. However, the increase of contact pressure results in the serious reconstruction and passivation of the friction interface. On the one hand, this induces a growth rate of friction force that is much smaller than that of the normal load, which is followed by a significant decrease in the friction coefficient with contact pressure. On the other hand, the destruction or even disappearance of the textured structure occurs, weakening the difference in the friction coefficient caused by different textured shapes of the a-C surface. These results reveal the friction mechanism of textured a-C film and provide a new way to functionalize the a-C as a protective film for applications in hard disks, MEMS, and NEMS.

Autonomous Interfacial Assembly of Polymer Nanofilms via Surfactant-Regulated Marangoni Instability.

Interfacial polymerization (IP) provides a versatile platform for fabricating defect-free functional nanofilms for various applications, including molecular separation, energy, electronics, and biomedical materials. Unfortunately, coupled with complex natural instability phenomena, the IP mechanism and key parameters underlying the structural evolution of nanofilms, especially in the presence of surfactants as an interface regulator, remain puzzling. Here, we interfacially assembled polymer nanofilm membranes at the free water-oil interface in the presence of differently charged surfactants and comprehensively characterized their structure and properties. Combined with computational simulations, an in situ visualization of interfacial film formation discovered the critical role of Marangoni instability induced by the surfactants via various mechanisms in structurally regulating the nanofilms. Despite their different instability-triggering mechanisms, the delicate control of the surfactants enabled the fabrication of defect-free, ultra-permselective nanofilm membranes. Our study identifies critical IP parameters that allow us to rationally design nanofilms, coatings, and membranes for target applications.

Insights into Superlow Friction and Instability of Hydrogenated Amorphous Carbon/Fluid Nanocomposite Interface.

Hydrogenated amorphous carbon (a-C:H) film exhibits the superlubricity phenomena as rubbed against dry sliding contacts. However, its antifriction stability strongly depends on the working environment. By composting with the fluid lubricant, the friction response and fundamental mechanisms governing the low-friction performance and instability of a-C:H remain unclear, while they are not accessible by experiment due to the complicated interfacial structure and the lack of advanced characterization technique in situ. Here, we addressed this puzzle with respect to the physicochemical interactions of a-C:H/oil/graphene nanocomposite interface at atomic scale. Results reveal that although the friction capacity and stability of system are highly sensitive to the hydrogenated degrees of mated a-C:H surfaces, the optimized H contents of mated a-C:H surfaces are suggested in order to reach the superlow friction or even superlubricity. Interfacial structure analysis indicates that the fundamental friction mechanism attributes to the hydrogenation-induced passivation of friction interface and squeezing effect to fluid lubricant. Most importantly, the opposite diffusion of fluid oil molecules to the sliding direction is observed, resulting in the transformation of the real friction interface from a-C:H/oil interface to oil/oil interface. These outcomes enable an effective manipulation of the superlow friction of carbon-based films and the development of customized solid-fluid lubrication systems for applications.

Correction: Novel two-dimensional tetrahexagonal boron nitride with a sizable band gap and a sign-tunable Poisson's ratio.

Correction for 'Novel two-dimensional tetrahexagonal boron nitride with a sizable band gap and a sign-tunable Poisson's ratio' by Mehmet Emin Kilic et al., Nanoscale, 2021, 13, 9303-9314, DOI: 10.1039/D1NR00734C.

Novel two-dimensional tetrahexagonal boron nitride with a sizable band gap and a sign-tunable Poisson's ratio.

By performing first-principles calculations, a new two-dimensional (2D) boron nitride (th-BN) with perfectly ordered arrangements of tetragonal and hexagonal rings is predicted to be energetically, dynamically, thermally, and mechanically stable. The unique structure endows th-BN with anisotropic mechanical, electronic, and optical properties. Remarkably, th-BN exhibits exceptional mechanical properties such as high in-plane stiffness and sign-tunable Poisson's ratio (PR). The PR of th-BN gradually decreases with the increase of axial strain and even becomes negative at a very small strain (∼2%), which is novel, thereby offering the ability to become non-auxetic, auxetic, and partially auxetic 2D nanomaterials depending on the strain rate and direction. The structure can withstand tensile strain as large as 36%, and shows ultrahigh ideal strength that can even outperform graphene and hexagonal BN. The th-BN is a natural 2D semiconductor with an indirect wide band gap of 4.49 eV. The band gap can be tuned by applying lattice strain and hydrogenation. The full hydrogenated th-BN exhibits an indirect-to-direct band gap transition. The th-BN shows high optical absorption in the ultraviolet region. The optical absorption spectrum is highly direction-dependent and tunable by strain, suitable for high-performance optoelectronic device applications. Furthermore, th-BN can be stacked into two different configurations, and are dynamically stable and exhibit exotic electronic properties. The desirable direct band gap and anisotropic effective mass of the th-C/th-BN heterostructure suggest that th-BN can be a suitable substrate for tetrahexcarbon.

Tailoring the Nanostructure of Graphene as an Oil-Based Additive: toward Synergistic Lubrication with an Amorphous Carbon Film.

Graphene exhibits great potential as a lubricant additive to enhance the antifriction capacity of moving mechanical components in synergism with amorphous carbon (a-C) as a solid lubricant. However, it is particularly challenging for experiments to accurately examine the friction dependence on the physical nanostructure of the graphene additive and the corresponding interfacial reactions because of the inevitable complexity of the graphene structure fabricated in experiments. Here, we address this puzzle regarding the coeffect of the size and content of the graphene additive at the a-C interface using reactive molecular dynamics simulations. Results reveal that the friction-reducing behavior is more sensitive to graphene size than content. For each graphene structure, with increasing content, the friction coefficient always decreases first and then increases, while the friction behavior exhibits significant dependence on the graphene size when the graphene content is fixed. In particular, the optimized size and content of the graphene additive are suggested, in which an excellent antifriction behavior or even superlubricity can be achieved. Analysis of the friction interface indicates that with increasing graphene size, the dominated low-friction mechanism transforms from the high mobilities of the base oil and graphene additive in synergism to the passivation and graphene-induced smoothing of the friction interface. These outcomes disclose the roadmap for developing a robust solid-liquid synergy lubricating system.

Enabling reversible redox reactions in electrochemical cells using protected LiAl intermetallics as lithium metal anodes.

Rechargeable electrochemical cells with metallic anodes are of increasing scientific and technological interest. The complex composition, poorly defined morphology, heterogeneous chemistry, and unpredictable mechanics of interphases formed spontaneously on the anodes are often examined but rarely controlled. Here, we couple computational studies with experimental analysis of well-defined LiAl electrodes in realistic electrochemical environments to design anodes and interphases of known composition. We compare phase behavior, Li binding energies, and activation energy barriers for adatom transport and study their effects on the electrochemical reversibility of battery cells. As an illustration of potential practical benefits of our findings, we create cells in which LiAl anodes protected by Langmuir-Blodgett MoS2 interphases are paired with 4.1 mAh cm-2 LiNi0.8Co0.1Mn0.1O2 cathodes. These studies reveal that small- and larger-format (196 mAh, 294 Wh kg-1, and 513 Wh liter-1) cells based on protected LiAl anodes exhibit high reversibility and support stable Li migration during recharge of the cells.

Role of the carbon source in the transformation of amorphous carbon to graphene during rapid thermal processing.

A fast transfer-free synthesis of a graphene structure can be successfully achieved by Ni-catalysed transformation of amorphous carbon (a-C) during rapid thermal processing, but the role of the a-C structure in the a-C-to-graphene transformation is still unclear. In this paper, the dependence of the transformation of a-C to graphene, the diffusion behaviour of C, and the graphene quality on the a-C structures was comparatively investigated by reactive molecular dynamics simulation and Ni was selected as a catalyst. The results demonstrated that different a-C structures affected the diffusion of C into Ni layers and the re-dissolving behaviour of the grown graphitic structures, and thus dominated the remnant number of C atoms, which played a critical role in the formation and quality of graphene.

Carbon Nitride Phosphorus as an Effective Lithium Polysulfide Adsorbent for Lithium-Sulfur Batteries.

Lithium-sulfur (Li-S) batteries are attracting substantial attention because of their high-energy densities and potential applications in portable electronics. However, an intrinsic property of Li-S systems, that is, the solubility of lithium polysulfides (LiPSs), hinders the commercialization of Li-S batteries. Herein, a new material, that is, carbon nitride phosphorus (CNP), is designed and synthesized as a superior LiPS adsorbent to overcome the issues of Li-S batteries. Both the experimental results and the density functional theory (DFT) calculations confirm that CNP possesses the highest binding energy with LiPS at a P concentration of ∼22% (CNP22). The DFT calculations explain the simultaneous existence of Li-N bonding and P-S coordination in the sulfur cathode when CNP22 interacts with LiPS. By introducing CNP22 into the Li-S systems, a sufficient charging capacity at a low cutoff voltage, that is, 2.45 V, is effectively implemented, to minimize the side reactions, and therefore, to prolong the cycling life of Li-S systems. After 700 cycles, a Li-S cell with CNP22 gives a high discharge capacity of 850 mA h g-1 and a cycling stability with a decay rate of 0.041% cycle-1. The incorporation of CNP22 can achieve high performance in Li-S batteries without concerns regarding the LiPS shuttling phenomenon.

Accelerated Data-Driven Accurate Positioning of the Band Edges of MXenes.

Functionalized MXene has emerged a promising class of two-dimensional materials having more than tens of thousands of compounds, whose uses may range from electronics to energy applications. Other than the band gap, these properties rely on the accurate position of the band edges. Hence, to synthesize MXenes for various applications, a prior knowledge of the accurate position of their band edges at an absolute scale is essential; computing these with conventional methods would take years for all the MXenes. Here, we develop a machine learning model for positioning the band edges with GW level of accuracy having a minimum root-mean-squared error of 0.12 eV. An intuitive model is proposed based on the combination of Perdew-Burke-Ernzerhof band edge and vacuum potential having a correlation of 0.93 with GW band edges. These models can be utilized to identify MXenes for a desired application in an accelerated manner.

Transformation of amorphous carbon to graphene on low-index Ni surfaces during rapid thermal processing: a reactive molecular dynamics study.

The transformation of amorphous carbon to graphene on different Ni surfaces during rapid thermal processing was explored using reactive molecular dynamics simulation. Due to the difference in activation energy, Ni surfaces affected the diffusion behavior of C into Ni and thus modulated the remnant number of C atoms, dominating the formation and quality of graphene, which accorded with the developed empirical equation.

Unexpected Roles of Interstitially Doped Lithium in Blue and Green Light Emitting Y2O3:Bi3+: A Combined Experimental and Computational Study.

To enhance the photoluminescence of lanthanide oxide, a clear understanding of its defect chemistry is necessary. In particular, when yttrium oxide, a widely used phosphor, undergoes doping, several of its atomic structures may be coupled with point defects that are difficult to understand through experimental results alone. Here, we report the strong enhancement of the photoluminescence (PL) of Y2O3:Bi3+ via codoping with Li+ ions and suggest a plausible mechanism for that enhancement using both experimental and computational studies. The codoping of Li+ ions into the Y2O3:Bi3+ phosphor was found to cause significant changes in its structural and optical properties. Interestingly, unlike previous reports on Li+ codoping with several other phosphors, we found that Li+ ions preferentially occupy interstitial sites of the Y2O3:Bi3+ phosphor. Computational insights based on density functional theory calculations also indicate that Li+ is energetically more stable in the interstitial sites than in the substitutional sites. In addition, interstitially doped Li+ was found to favor the vicinity of Bi3+ by an energy difference of 0.40 eV in comparison to isolated sites. The calculated DOS showed the formation of a shallow level directly above the unoccupied 6p orbital of Bi3+ as the result of interstitial Li+ doping, which may be responsible for the enhanced PL. Although the crystallinity of the host materials increased with the addition of Li salts, the degree of increase was minimal when the Li+ content was low (<1 mol %) where major PL enhancement was observed. Therefore, we reason that the enhanced PL mainly results from the shallow levels created by the interstitial Li+.

Monolayer BC2: an ultrahigh capacity anode material for Li ion batteries.

There is great interest in developing promising candidate materials for high-capacity, low cost, environmentally friendly, longer cycle life anodes for lithium ion batteries. Due to better Li adsorption properties than graphene, boron doped graphene has been considered to be an attractive anode material for Li-ion batteries. Using first principles density functional theory calculations, we investigate the effect of increasing boron concentration on the gravimetric capacity of monolayered boron doped carbon sheets. The calculations are performed for uniformly boron doped carbon sheets, BCx (x = 7, 5, 3, 2 and 1) as well as their non-uniformly doped counterparts, which are found to be energetically preferable for x = 5, 2 and 1. Our results indicate pronounced enhancement in gravimetric capacity with increasing concentration of B, up to x = 2. The storage capacity of the uniformly doped BC2 turns out to be the highest ever reported for B doped graphene sheets, which is 1.9 times (1667 mA h g-1) that of the previously reported value for BC3 (J. Phys. Chem. Lett., 2013, 4, 1737-1742). This dramatic increase in the capacity of uniformly doped BC2 occurs because of the availability of significantly more empty states above the Fermi level compared to the other BCx sheets. Moreover, the diffusion energy barriers and open circuit voltage are found to be lower in uniformly doped BC2, leading to better Li kinetics. For x = 1, Li binds very strongly to the uniformly doped BC and higher diffusion energy barriers are found for non-uniformly doped BC, rendering them ineffective as anode materials. Our study reveals that BC2 is the most promising candidate as an anode material for Li ion batteries owing to its high Li storage capacity combined with low diffusion barrier and low open circuit voltage.

Simulation Protocol for Prediction of a Solid-Electrolyte Interphase on the Silicon-based Anodes of a Lithium-Ion Battery: ReaxFF Reactive Force Field.

We propose the ReaxFF reactive force field as a simulation protocol for predicting the evolution of solid-electrolyte interphase (SEI) components such as gases (C2H4, CO, CO2, CH4, and C2H6), and inorganic (Li2CO3, Li2O, and LiF) and organic (ROLi and ROCO2Li: R = -CH3 or -C2H5) products that are generated by the chemical reactions between the anodes and liquid electrolytes. ReaxFF was developed from ab initio results, and a molecular dynamics simulation with ReaxFF realized the prediction of SEI formation under real experimental conditions and with a reasonable computational cost. We report the effects on SEI formation of different kinds of Si anodes (pristine Si and SiOx), of the different types and compositions of various carbonate electrolytes, and of the additives. From the results, we expect that ReaxFF will be very useful for the development of novel electrolytes or additives and for further advances in Li-ion battery technology.

Atomistics of the lithiation of oxidized silicon (SiOx) nanowires in reactive molecular dynamics simulations.

Although silicon oxide (SiOx) nanowires (NWs) are recognized as a promising anode material for lithium-ion batteries (LIBs), a clear understanding of their lithiation mechanism has not been reported yet. We elucidate the lithiation mechanism of SiOx NWs at the atomic scale based on molecular dynamics (MD) simulations employing the ReaxFF reactive force field developed through first-principles calculations. SiOx NWs with crystalline Si (c-Si) core and amorphous SiO2 (a-SiO2) shell structures of ∼1 nm in thickness show smaller volume expansion than pristine Si NWs, as found in previous experiments. Lithiation into SiOx NWs creates two interfaces: c-Si/a-LixSi and a-LixSi/a-LiySiO2. The mobility of the latter, which is located farther toward the outside of the NW, is slower than that of the former, which is one of the reasons why the thin SiO2 layer can suppress the volume expansion of SiOx NWs during lithiation. Another reason can be found from the stress distribution, as the SiOx NWs show stress distribution different from the pristine case. Moreover, the lithiation of SiOx NWs leads to the formation of Li2O and Li4SiO4 compounds in the oxide layer, where several Li atoms (not a majority) in Li4SiO4 can escape from the compound and diffuse into the c-Si, in contrast to the Li2O case. However, Li atoms that pass through the SiO2 layer penetrate into the c-Si preferentially along the 〈110〉 or 〈112〉 direction, similar to the mechanism observed in pristine Si NWs. We expect that our comprehensive understanding of the lithiation mechanism of SiOx NWs will provide helpful guidance for the design of SiOx anodes to obtain better performing LIBs.

Mechanistic Insight into the Chemical Exfoliation and Functionalization of Ti3C2 MXene.

MXene, a two-dimensional layer of transition metal carbides/nitrides, showed great promise for energy storage, sensing, and electronic applications. MXene are chemically exfoliated from the bulk MAX phase; however, mechanistic understanding of exfoliation and subsequent functionalization of these technologically important materials is still lacking. Here, using density-functional theory we show that exfoliation of Ti3C2 MXene proceeds via HF insertion through edges of Ti3AlC2 MAX phase. Spontaneous dissociation of HF and subsequent termination of edge Ti atoms by H/F weakens Al-MXene bonds. Consequent opening of the interlayer gap allows further insertion of HF that leads to the formation of AlF3 and H2, which eventually come out of the MAX, leaving fluorinated MXene behind. Density of state and electron localization function shows robust binding between F/OH and Ti, which makes it very difficult to obtain controlled functionalized or pristine MXene. Analysis of the calculated Gibbs free energy (ΔG) shows fully fluorinated MXene to be lowest in energy, whereas the formation of pristine MXene is thermodynamically least favorable. In the presence of water, mixed functionalized Ti3C2Fx(OH)1-x (x ranges from 0 to 1) MXene can be obtained. The ΔG values for the mixed functionalized MXenes are very close in energy, indicating the random and nonuniform functionalization of MXene. The microscopic understanding gained here unveils the challenges in exfoliation and controlling the functionalization of MXene, which is essential for its practical application.

Functionalization effect on a Pt/carbon nanotube composite catalyst: a first-principles study.

Chemical interactions between Pt and both pristine and defective carbon nanotubes (CNTs) that were functionalized with various surface functional groups, including atomic oxygen (-O), atomic nitrogen (-N), hydroxyl (-OH) and amine (-NH2) groups, were investigated through first-principles calculations. Our calculations suggest that the oxygen or nitrogen of the surface functional group can promote better structural stability of a Pt/CNT complex in terms of the binding energy enhancement between Pt and CNTs. Enhanced binding of the Pt/CNT complex would improve the long-term durability of the complex and thus enhance the catalytic activity of Pt catalysts supported on CNTs. Among the functional groups investigated, atomic nitrogen resulted in the most consistent increase in the Pt binding energies on pristine or defective CNTs. Moreover, atomic nitrogen decoration on the surface of CNTs rather than substitution into the CNTs appears to be more desirable. A d-band centre analysis and H2 adsorption calculations also revealed that the catalytic activity of Pt can be improved via efficient functionalization of the CNT support.

Exosome engineering for efficient intracellular delivery of soluble proteins using optically reversible protein-protein interaction module.

Nanoparticle-mediated delivery of functional macromolecules is a promising method for treating a variety of human diseases. Among nanoparticles, cell-derived exosomes have recently been highlighted as a new therapeutic strategy for the in vivo delivery of nucleotides and chemical drugs. Here we describe a new tool for intracellular delivery of target proteins, named 'exosomes for protein loading via optically reversible protein-protein interactions' (EXPLORs). By integrating a reversible protein-protein interaction module controlled by blue light with the endogenous process of exosome biogenesis, we are able to successfully load cargo proteins into newly generated exosomes. Treatment with protein-loaded EXPLORs is shown to significantly increase intracellular levels of cargo proteins and their function in recipient cells in vitro and in vivo. These results clearly indicate the potential of EXPLORs as a mechanism for the efficient intracellular transfer of protein-based therapeutics into recipient cells and tissues.