Toward the Production of Super Graphene.

The quality requirements of graphene depend on the applications. Some have a high tolerance for graphene quality and even require some defects, while others require graphene as perfect as possible to achieve good performance. So far, synthesis of large-area graphene films by chemical vapor deposition of carbon precursors on metal substrates, especially on Cu, remains the main way to produce high-quality graphene, which has been significantly developed in the past 15 years. However, although many prototypes are demonstrated, their performance is still more or less far from the theoretical property limit of graphene. This review focuses on how to make super graphene, namely graphene with a perfect structure and free of contaminations. More specially, this study focuses on graphene synthesis on Cu substrates. Typical defects in graphene are first discussed together with the formation mechanisms and how they are characterized normally, followed with a brief review of graphene properties and the effects of defects. Then, the synthesis progress of super graphene from the aspects of substrate, grain size, wrinkles, contamination, adlayers, and point defects are reviewed. Graphene transfer is briefly discussed as well. Finally, the challenges to make super graphene are discussed and a strategy is proposed.

Porous Graphene Produced by Carbothermal Shock for Green Electromagnetic Interference Shielding in Both Microwave and Terahertz Bands.

The prospect of graphene-based shielding materials in the form of fillers is limited by the cumbersome preparation of graphene. Herein, defect-tunable porous graphene prepared by carbothermal shock using low-value sucrose as a precursor is proposed as an effective shielding filler. The resultant porous graphene exhibits 32.5 dB shielding efficiency (SE) and 2.5-18 GHz effective bandwidth at a mass loading of 20 wt%, competing with the shielding performance of graphene fillers prepared by other methods. Particularly, defect-rich graphene synthesized by increasing voltage and prolonging time shows increased electromagnetic (EM) wave absorption, echoing the current concept of green shielding. In addition, the strategy of controlling the discharge conditions to improve the absorption by the shield is developed in the terahertz band. The average SE and reflection loss of the samples in the THz band (0.2-1.2 THz) exhibit 40.7 and 15.9 dB at filler loading of 5 wt%, respectively, achieving effective shielding and absorption of THz waves. This work paves a new way for low-cost preparation of graphene for EM interference shielding fillers. Meanwhile, it supplies a reference for the shielding research of the upcoming applications integrating multiple EM bands (such as sixth-generation based integrated sensing and communication).

A time-space conversion method for material synthesis research.

Research on material synthesis is mostly performed through batch by batch testing with each corresponding to a set of parameters and a reaction time. Concurrent experiments that allow for multiple loadings throughout an inhomogeneous reaction zone provide a way to obtain high-throughput results. Here, a time-space conversion method is proposed. By sequentially passing a number of identical objects through a reaction zone, a significant diversity of reactions in one batch can be achieved depending on the spatial distribution and changes with time of the reaction zone. In particular, when the reaction zone is steady, the evolution of a reaction can be associated with the objects at their corresponding reaction stage. This greatly improves the efficiency and accuracy of research on material synthesis kinetics. This method may initiate a new wave of material synthesis research and accelerate the development of material science.

Towards large-scale graphene transfer.

The transfer process is crucial for obtaining high-quality graphene for its large-scale industrial application. In this review, graphene transfer methods are systematically classified along with an analysis of the contamination or impurity of graphene that is introduced during the transfer process. Two key processes are emphasized, the substrate removal process and the direct/indirect transfer of graphene. Based on the efficiency and cost factors of industrial scale production, various transfer methods are summarized and evaluated. Potential transfer technologies and future research directions for industrial application are prospected.

Low-temperature fusion fabrication of Li-Cu alloy anode with in situ formed 3D framework of inert LiCux nanowires for excellent Li storage performance.

The commercialization of rechargeable Li metal batteries is hindered by dendrite growth and volumetric variation. Herein, we report a Li-rich dual-phase Li-Cu alloy with built-in 3D conductive skeleton to replace conventional planar Li anode. The Li-Cu alloy is simply prepared by fusion of Li and Cu metals at a relatively low-temperature of 500 °C, followed by a cooling process where phase-segregation leads to metallic Li phase distributed in the network of LiCux solid solution phase. Different from the common Li alloy, the electrochemical alloying reaction between Li and Cu metals is not observed. Therefore, the lithiophilic LiCux nanowires guides conformal plating of Li and the porous framework provides superior dimensional stability for the anode. This unique ferroconcrete-like structure of Li-Cu alloy enables dendrite-free Li plating for an expanded cycling lifetime. Constructing a new type of Li alloy with in situ formed electrochemically inactive framework is a promising and easily scaled-up strategy toward practical application of Li metal anodes.

Preparation of Ultra-Smooth Cu Surface for High-Quality Graphene Synthesis.

As grown graphene by chemical vapor deposition typically degrades greatly due to the presence of grain boundaries, which limit graphene's excellent properties and integration into advanced applications. It has been demonstrated that there is a strong correlation between substrate morphology and graphene domain density. Here, we investigate how thermal annealing and electro-polishing affects the morphology of Cu foils. Ultra-smooth Cu surfaces can be achieved and maintained at elevated temperatures by electro-polishing after a pre-annealing treatment. This technique has shown to be more effective than just electro-polishing the Cu substrate without pre-annealing. This may be due to the remaining dislocations and point defects within the Cu bulk material moving to the surface when the Cu is heated. Likewise, a pre-annealing step may release them. Graphene grown on annealed electro-polished Cu substrates show a better quality in terms of lower domain density and higher layer uniformity than those grown on Cu substrates with only annealing or only electro-polishing treatment.

A general and simple method for evaluating the electrical transport performance of graphene by the van der Pauw-Hall measurement.

Expected for many promising applications in the field of electronics and optoelectronics, a reliable method for the characterization of graphene electrical transport properties is desired to predict its device performance or provide feedback for its synthesis. However, the commonly used methods of extracting carrier mobility from graphene field effect transistor or Hall-bar is time consuming, expensive, and significantly affected by the device fabrication process other than graphene itself. Here we reported a general and simple method to evaluate the electrical transport performance of graphene by the van der Pauw-Hall measurement. By annealing graphene in vacuum to remove the adsorbed dopants and then exposing it in ambient surroundings, carrier mobility as a function of density can be measured with the increase of carrier density due to the dopant re-adsorption from the surroundings. Further, the relationship between the carrier mobility and density can be simply fitted with a power equation to the first level approximation, with which any pair of measured carrier mobility and density can be normalized to an arbitrary carrier density for comparison. We experimentally demonstrated the reliability of the method, which is much simpler than making devices and may promote the standard making for graphene characterization.

Cellular internalization of rod-like nano hydroxyapatite particles and their size and dose-dependent effects on pre-osteoblasts.

Nano hydroxyapatite particles (n-HA) have been reported to promote osteogenic activities of bone-related cells, while inhibiting tumor cell growth, and the biological effects of n-HA are related with the particle size, dose, culture time and cell type. In this work, we prepared n-HA with a strictly controlled rod-like shape and adjustable sizes without any surface chemical contaminations. Using the prepared n-HA, we investigated the size and dose effect of the nano particles on pre-osteoblasts for up to 7 days. We probed cell proliferation and gene expression in the presence of n-HA, the cellular uptake pathways of n-HA particles, as well as the extracellular and intracellular [Ca2+] ([Ca2+]i) changes caused by the particles, in order to get a better understanding of the biological effects of n-HA of various sizes. The n-HA exhibited size- and dose-dependent impacts on MC3T3-E1 proliferation, intracellular reactive oxygen species (ROS) generation, mitochondrial membrane potential, and osteogenic gene expression. 40 nm n-HA caused the slowest MC3T3-E1 growth, the highest intracellular ROS concentration, the largest mitochondrial membrane potential loss and the lowest level of osteogenic gene expression among the samples. The cytotoxicity of 40 nm n-HA increased with the dose and culture time. 70 nm n-HA showed beneficial effects on MC3T3-E1 growth, but the positive effect disappeared at the highest concentration on day 7. 100 nm n-HA promoted cell growth and the promoting effect increased with the dose. Cells cultured with 100 nm n-HA expressed the highest level of osteogenic gene expression among the experimental groups. We discovered that the presence of n-HA increased [Ca2+]i but did not elevate extracellular [Ca2+]. The [Ca2+]i increased as the n-HA size decreased. We also found that n-HA may enter cells through two pathways and that the amount of engulfed particles depended on the particle size. The internalized n-HA particles located in the cytosol, endosomes, lysosomes and nuclei. The particles dissolved in lysosomes and raised [Ca2+]i, which correlated with the cell death and osteogenic gene expression. In conclusion, the particle size, dose, and culture time influenced the biological effects of n-HA on ME3T3-E1 cells, probably by changing the [Ca2+]i in the cells instead of the extracellular [Ca2+].

Bone mineral density, microarchitectural and mechanical alterations of osteoporotic rat bone under long-term whole-body vibration therapy.

Low-magnitude, high-frequency whole body vibration (WBV) is receiving increasing interest as a non-pharmacological anti-osteoporosis approach. However, the long-term effect of WBV therapy is seldom studied. In this study, the efficacy of 16-week WBV (0.3g, 30 Hz) on bone mineral density (BMD), microarchitectural parameters and mechanical properties of ovariectomized rat femur were examined by in vivo peripheral quantitative computed tomography (pQCT), ex vivo micro-computed tomography (µCT), dynamic mechanical analysis (DMA) and fracture test. To the best of our knowledge, 16 weeks of WBV administration (20 min/day) is currently the longest duration on rodent. The longitudinal BMD change showed that positive effect of WBV on ovariectomized rat femoral neck diminished with prolonged administration duration. In addition, 16-week of WBV treatment was found to cause significantly reduction in the mean BMD, trabecular BMD (Tb.BMD), trabecular bone volume ration (BV/TV), trabecular number (Tb.N) and maximum load in femoral neck of ovariectomized rat. Metaphyseal Tb.BMD and BV/TV were also significantly decreased in WBV treated ovariectomized group than non-treated controls. Whole-femur DMA was demonstrated as a sensitive tool in distinguishing osteoporotic femur from healthy aged-matched controls, in terms of decreased storage modulus (E') and loss factor (tan δ). However, E' and tan δ are not enhanced by 16-week WBV treatment. Together, these findings indicate that administration duration played an important role in the effect of WBV. 16-week WBV may exacerbate trabecular bone loss in ovariectomized rat femur, especially in trabecular-rich femoral neck region. An optimal WBV protocol including administration duration should be established prior to long-term clinical practice.

Administration duration influences the effects of low-magnitude, high-frequency vibration on ovariectomized rat bone.

Low-magnitude, high-frequency vibration (LMHFV) has been proposed as a non-drug anti-osteoporosis treatment. However, the influence of administration duration on its effect is seldom investigated. In this study, the effect of 16-week LMHFV (0.3 g, 30 Hz, 20 min/day) on the bone mineral densities (BMDs), bone mechanical properties, and cellular responses of osteoporotic and healthy rats was examined by in vivo peripheral quantitative computed tomography (pQCT), fracture tests, cell assays, and mRNA quantification. Forty-eight adult rats were equally assigned to sham surgery (SHM), sham surgery with LMHFV (SHM+V), ovariectomy (OVX), and ovariectomy with LMHFV (OVX+V) groups. At week 8, LMHFV ameliorated ovariectomy-induced deterioration of trabecular bone, with a significantly higher tibia trabecular BMD (+11.2%) being noted in OVX+V rats (vs. OVX). However, this positive effect was not observed at later time points. Furthermore, 16 weeks of LMHFV caused significant reductions in the vertebral mean BMD (-13.0%), trabecular BMD (-15.7%), and maximum load (-21.5%) in OVX+V rats (vs. OVX). Osteoblasts derived from osteoporotic rat bone explants showed elevated BSP and OSX mRNA expression induced by LMHFV on day 1. However, no further positive effect on osteoblastic mRNA expression, alkaline phosphatase activity, or calcium deposition was observed with prolonged culture time. A higher ratio of RANKL/OPG induced by LMHFV suggests that osteoclastogenesis may be activated. Together, these results demonstrate that administration duration played an important role in the effect of LMHFV. Early exposure to LMHFV can positively modulate osteoporotic bone and osteoblasts; however, the beneficial effect seems not to persist over time. © 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1147-1157, 2016.

Bone morphogenetic protein Smads signaling in mesenchymal stem cells affected by osteoinductive calcium phosphate ceramics.

Porous calcium phosphate ceramics (CaP ceramics) could induce ectopic bone formation which was regulated by various signal molecules. In this work, bone marrow mesenchymal stem cells (MSCs) were cultured on the surface of osteoinductive hydroxyapatite (HA) and biphasic calcium phosphate (BCP) ceramics in comparison with control (culture plate) for up to 14 days to detect the signal molecules which might be affected by the CaP ceramics. Without adding osteogenic factors, MSCs cultured on HA and BCP both expressed higher Runx2, Osterix, collagen type I, osteopontin, bone sialoprotein, and osteocalcin at various stages compared with control, thus confirmed the osteoblastic differentiation of MSCs. Later study demonstrated the messenger RNA level of bone morphogenetic protein 2 (BMP2) and BMP4 were also significantly enhanced by HA and BCP. Furthermore, Smad1, 4, 5, and Dlx5, the main molecules in the BMP/Smads signaling pathway, were upregulated by HA and BCP. Moreover, the higher expression of Smads and BMP2, 4 in BCP over HA, corresponded to the better performance of BCP in stimulating in vitro osteoblastic differentiation of MSCs. This was in accordance with the better osteoinductivity of BCP over HA in vivo. Altogether, these results implied that the CaP ceramics may initiate the osteoblastic differentiation of MSCs by influencing the expression of molecules in BMP/Smads pathway.

Selective effects of hydroxyapatite nanoparticles on osteosarcoma cells and osteoblasts.

The effects of hydroxyapatite nanoparticles (HA-NPs) on two kinds of cells, human MG63 cells and the normal osteoblasts were investigated. According to the MTT assay and fluorescent staining assay, it was proved that HA-NPs could inhibit the growth of MG63 cells but slightly support proliferation of the osteoblasts. Meanwhile, transmission electron microscopy (TEM) was employed to observe the ultrastructural alterations of both cells. The TEM results showed that HA-NPs had entered the two kinds of cells. Typical apoptosis was observed in the MG63 cells, especially in the group of 250 µg/mL with 5 days culture. While no apoptosis could be found in the normal osteoblasts at any concentration group of HA-NPs. Our results suggested that the HA-NPs had selective effects to different kinds of cells: supporting proliferation to the normal bone cells while causing apoptosis to the osteosarcoma cells.