Polyurethane-Based Stretchable Semiconductor Nanofilms with High Intrinsic Recovery Similar to Conventional Elastomers.

Polymer semiconductors with large elastic recovery (ER) under high strain in thin film state are highly desirable for stretchable electronics. Here we report a type of stretchable semiconductor PU(DPP)x, by copolymerization of oligodiketopyrrolopyrrole-based conjugated block and hydrogenated polybutadiene flexible block via urethane linkage for intermolecular hydrogen bonding. By regulating block ratio, PU(DPP)35 with 35 wt % conjugated block exhibits high intrinsic ER > 80% under 175% strain (ε) in pseudo free-standing thin film state, comparable with commercial elastomers, and crack onset strain (COS) > 300% along with maximum hole mobility of 0.19 cm2 V-1 s-1 in organic thin film transistors to bring it to the best performing block copolymer-type stretchable semiconductors. Enhanced mobility is achieved using PU(DPP)35 as the binder for conjugated polymer PDPPT3. The 25 wt %-PDPPT3 blend displays mobility up to 1.28 cm2 V-1 s-1 along with COS ∼120%, and 10 wt %-PDPPT3 blend exhibits ER of 78% at ε = 150%, COS of ∼230%, modulus of 36.5 MPa, maximum mobility of 0.62 cm2 V-1 s-1 and no obvious degradation of mobility at ε = 150% after 100 cycles of strain. Moreover, the structural similarity enables the blend film uniform and stable microstructure against mechanical and thermal deformation. Notably, PU(DPP)35 and the blend are characterized by high mechanical performance similar to that of commercial elastomers in thin film state, and demonstrate their potential for high performance stretchable electronics.

Complete surface reconstruction of nanoporous gold during CH4 pyrolysis.

The catalytic activity and selectivity of metallic nanocatalysts can be controlled using physical and chemical methods to tune the exposed crystal facets. Nanoporous metals (NPMs) have unique bicontinuous structures, large specific surface areas, and high catalytic activities, and are widely used in the field of heterogeneous catalysis. However, owing to the complex surface topography of NPMs, it is difficult to regulate their exposed crystal facets over a large area. In this study, nanoporous gold (NPG) is successfully prepared with a complete regular surface that exposes the Au {111} and {100} facets through a methane pyrolysis reaction. The results of high-spatial and -temporal resolution in situ experiments and theoretical calculations indicate that C species significantly weaken the interaction between surface Au atoms with low coordination numbers and their surrounding atoms, which results in the migration and recombination of surface atoms. This research fundamentally clarifies the reconstruction mechanism of porous materials during methane pyrolysis and provides a theoretical basis for the targeted regulation of exposed NPM surfaces.

Anomalous detwinning in constrained Cu nanoparticles.

In this work, the detwinning process in a 9 nm graphene-constrained Cu nanoparticle was investigated at 1009 °C via in situ high-resolution transmission electron microscopy. Instead of the expected reverse glide of the twinning dislocations, two new twins were formed; the four twin zones rotated synergistically before vanishing. Furthermore, the twin boundary migration energy and the system energy were increased continuously with detwinning. The increased resistance to twin boundary migration in constrained nanoparticles enriches our understanding of the twinning mechanism and may facilitate the design of high-strength and high-ductility nanomaterials.

Dynamic co-catalysis of Au single atoms and nanoporous Au for methane pyrolysis.

Nanocatalysts and single-atom catalysts are both vital for heterogeneous catalysis. They are recognized as two different categories of catalysts. Nevertheless, recent theoretical works have indicated that Au nanoparticles/clusters release Au single atoms in CO oxidation, and they co-catalyze the oxidation. However, to date, neither experimental evidence for the co-catalysis nor direct observations on any heterogeneous catalysis process of single-atom catalysts are reported. Here, the dynamic process of nanoporous Au to catalyze methane pyrolysis is monitored by in situ transmission electron microscopy with high spatial-temporal resolutions. It demonstrates that nanoporous Au surfaces partially disintegrate, releasing Au single atoms. As demonstrated by DFT calculation, the single atoms could co-catalyze the reaction with nanoporous Au. Moreover, the single atoms dynamically aggregate into nanoparticles, which re-disintegrate back to single atoms. This work manifests that under certain conditions, the heterogeneous catalysis processes of nanocatalysts and single-atom catalysts are not independent, where their dynamic co-catalysis exists.

Vertical Stacking of Copper Sulfide Nanoparticles and Molybdenum Sulfide Nanosheets for Enhanced Nonlinear Absorption.

The construction of p-n junctions is necessitated by applications which require effective charge separation. Here, a novel heterostructure (HS) of molybdenum sulfide (MoS2) and copper sulfide (Cu2-xS) was synthesized by chemical vapor deposition, with Cu2-xS nanoparticles vertically stacked on a MoS2 nanosheet. A well-defined epitaxial relationship between MoS2 and Cu2-xS is established, although the corresponding lattice mismatch is as large as 20%. The band-edge alignment is experimentally determined, indicating that the MoS2-Cu2-xS HS is a type II heterojunction. Photoluminescence quenching indicates effective charge separation in HS. The resultant HS shows enhanced nonlinear absorption in comparison with single-component MoS2 nanosheets and Cu2-xS nanoparticles.

Atomic-scale selectivity of hydrogen for storage sites in Pd nanoparticles at atmospheric pressure.

Hydrogen-storage materials are important carriers for a viable hydrogen economy. Despite palladium being the most studied storage material, the hydrogen-storage mechanism of Pd remains ambiguous owing to the lack of atomic-scale evidence of the diffusion and storage of H atoms in its lattice. In the study reported here, this classical process was investigated on the atomic scale using an in situ transmission electron microscope equipped with an atmospheric-pressure sample holder. The expansion of the Pd interplanar spacings was found to comprise three distinct stages during the diffusion of H atoms. Moreover, the expansion in d-spacing of Pd{111} was markedly different from that of Pd{220}. First-principles calculations indicate that H atoms mainly occupy the centers of the tetrahedral cages in the Pd unit cells during the diffusion stage, and they eventually occupy the octahedral cage centers in the equilibrium state. Moreover, H atoms were detected in substantially high densities in defects such as stacking faults and twin boundaries. These observations on the preferred hydrogen-storage domains can help clarify the hydrogen-storage mechanism and offer guidelines on the future design of higher-capacity hydrogen-storage materials.

Lithium chloride attenuates suppressed differentiation induced by mechanical strain in cementoblasts.

Aim: The purpose of this study was to investigate the influence of mechanical strain on OCCM-30 cementoblast differentiation and Wnt/ß-catenin pathway activity. Materials and Methods: Mechanical tension in the form of 2500-µ strain was applied to the cells using the Forcel four-point bending system, with or without the Wnt signaling activator, lithium chloride. Changes in cell differentiation and the expression of Wnt/ß-catenin pathway components in response to strain and lithium chloride were assessed by real-time PCR, immunofluorescence, and western blotting. Results: The mRNA expression levels of the cementoblastogenesis-related genes alkaline phosphatase, runt-related transcription factor 2, and collagen 1, were decreased with mechanical strain. Similarly, the Wnt signaling pathway component genes LRP5, AXIN2, and LEF1 were decreased. The immunofluorescence assay demonstrated that scant ß-catenin underwent nuclear translocation after the cells were subjected to mechanical strain. Moreover, western blotting showed that the protein levels of both ß-catenin and phosphorylated ß-catenin were increased after mechanical strain. In the presence of lithium chloride, the differentiation that was suppressed by mechanical strain was attenuated. Conclusions: 2500-µ strain mechanical strain inhibited cementoblast differentiation activity in vitro, which could be alleviated by actviating Wnt/ß-catenin signaling using lithium chloride.

A multi-slot coaxial microwave antenna for liver tumor ablation.

This paper presents a multi-slot coaxial antenna with a pi impedance matching network for liver tumor ablation. A multi-slot radiating probe was optimized by using the modified genetic algorithm to produce a near-spherical heating zone with significantly increased possibility of conformal treatment. A pi impedance matching network was designed to match the feeding transmission line and antenna without increasing antenna size. The reflection coefficient, ablation zone shape, specific absorption rate, and temperature were determined by a finite element electromagnetic simulation using COMSOL. Experimental validations were designed to evaluate the proposed antenna. Both simulation and experimental results show that the proposed antenna has the ability for liver tumor ablation, which offers faster heating rates in the heating center and more localized heating distribution than the conventional single-slot antenna.

An effective method for monitoring tissue temperature using low-field MRI system.

This technical note describes an effective method for monitoring temperature based on the minimum curvature surface fitting (MCSF) referenceless proton resonance frequency shift (PRFs) at 0.35 T. Experimental tests on phantom, ex vivo porcine livers and human brain were conducted. A comparison study between the proposed method and a fiber optic temperature probe was conducted for microwave (MW) ablation. Experimental results showed that temperature root mean square error (RMSE) calculated by MCSF model were lower than those computed by high-order polynomial fitting. For ablation experiments, the temperature errors between temperature probe and MCSF method were all less than 2∘C.

Quantitative MR thermometry based on phase-drift correction PRF shift method at 0.35 T.

BACKGROUND: Noninvasive magnetic resonance thermometry (MRT) at low-field using proton resonance frequency shift (PRFS) is a promising technique for monitoring ablation temperature, since low-field MR scanners with open-configuration are more suitable for interventional procedures than closed systems. In this study, phase-drift correction PRFS with first-order polynomial fitting method was proposed to investigate the feasibility and accuracy of quantitative MR thermography during hyperthermia procedures in a 0.35 T open MR scanner. METHODS: Unheated phantom and ex vivo porcine liver experiments were performed to evaluate the optimal polynomial order for phase-drift correction PRFS. The temperature estimation approach was tested in brain temperature experiments of three healthy volunteers at room temperature, and in ex vivo porcine liver microwave ablation experiments. The output power of the microwave generator was set at 40 W for 330 s. In the unheated experiments, the temperature root mean square error (RMSE) in the inner region of interest was calculated to assess the best-fitting order for polynomial fit. For ablation experiments, relative temperature difference profile measured by the phase-drift correction PRFS was compared with the temperature changes recorded by fiber optic temperature probe around the microwave ablation antenna within the target thermal region. RESULTS: The phase-drift correction PRFS using first-order polynomial fitting could achieve the smallest temperature RMSE in unheated phantom, ex vivo porcine liver and in vivo human brain experiments. In the ex vivo porcine liver microwave ablation procedure, the temperature error between MRT and fiber optic probe of all but six temperature points were less than 2 °C. Overall, the RMSE of all temperature points was 1.49 °C. CONCLUSIONS: Both in vivo and ex vivo experiments showed that MR thermometry based on the phase-drift correction PRFS with first-order polynomial fitting could be applied to monitor temperature changes during microwave ablation in a low-field open-configuration whole-body MR scanner.

Comparison of the success rate between self-drilling and self-tapping miniscrews: a systematic review and meta-analysis.

Background: Both the self-drilling and self-tapping miniscrews have been commonly used as anchorage reinforcement devices in orthodontic treatment. Objective: The aim of this study was to compare the success rates of self-drilling and self-tapping miniscrews in orthodontic practice. Search methods: Literature searches were performed by electronic search in database including PubMed, Embase, Cochrane Central Register of Controlled Trials, China National Knowledge Infrastructure and SIGLE, and manual search of relevant journals and reference lists of included studies. Eligibility criteria: Randomized controlled trials, clinical controlled trials and cohort studies comparing the success rates of self-drilling and self-tapping miniscrews as orthodontic anchorage. Data collection and analysis: The data of success rates and root contact rates were extracted by two investigators independently. After evaluating the risk of bias, the odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Subgroup analysis was performed on the basis of study design, follow-ups, participant ages and immediate/delayed loading. Sensitivity analysis was performed to test the stability of the results in meta-analysis. Results: Six studies assessed as high quality were included in the meta-analysis. The meta-analysis results showed no difference between the two types of screws in the success rates. The root contact rates of the two screws were similar, while self-drilling miniscrews displayed higher risk of failure when contacting with a tooth root. Conclusions: Currently available clinical evidence suggests that the success rates of self-tapping and self-drilling miniscrews are similar. Determination of the position and direction of placement should be more precise when self-drilling miniscrews are used in sites with narrow root proximity. Registration: None. Conflict of interest: None.

Periodontal regeneration with stem cells-seeded collagen-hydroxyapatite scaffold.

Re-establishing compromised periodontium to its original structure, properties and function is demanding, but also challenging, for successful orthodontic treatment. In this study, the periodontal regeneration capability of collagen-hydroxyapatite scaffolds, seeded with bone marrow stem cells, was investigated in a canine labial alveolar bone defect model. Bone marrow stem cells were isolated, expanded and characterized. Porous collagen-hydroxyapatite scaffold and cross-linked collagen-hydroxyapatite scaffold were prepared. Attachment, migration, proliferation and morphology of bone marrow stem cells, co-cultured with porous collagen-hydroxyapatite or cross-linked collagen-hydroxyapatite, were evaluated in vitro. The periodontal regeneration capability of collagen-hydroxyapatite scaffold with or without bone marrow stem cells was tested in six beagle dogs, with each dog carrying one sham-operated site as healthy control, and three labial alveolar bone defects untreated to allow natural healing, treated with bone marrow stem cells - collagen-hydroxyapatite scaffold implant or collagen-hydroxyapatite scaffold implant, respectively. Animals were euthanized at 3 and 6 months (3 animals per group) after implantation and the resected maxillary and mandibular segments were examined using micro-computed tomography scan, H&E staining, Masson's staining and histometric evaluation. Bone marrow stem cells were successfully isolated and demonstrated self-renewal and multi-potency in vitro. The porous collagen-hydroxyapatite and cross-linked collagen-hydroxyapatite had average pore sizes of 415 ± 20 µm and 203 ± 18 µm and porosity of 69 ± 0.5% and 50 ± 0.2%, respectively. The attachment, proliferation and migration of bone marrow stem cells were satisfactory on both porous collagen-hydroxyapatite and cross-linked collagen-hydroxyapatite scaffolds. Implantation of bone marrow stem cells - collagen-hydroxyapatite or collagen-hydroxyapatite scaffold in beagle dogs with experimental periodontal defects resulted in significantly enhanced periodontal regeneration characterized by formation of new bone, periodontal ligament and cementum, compared with the untreated defects, as evidenced by histological and micro-computed tomography examinations. The prepared collagen-hydroxyapatite scaffolds possess favorable bio-compatibility. The bone marrow stem cells - collagen-hydroxyapatite and collagen-hydroxyapatite scaffold - induced periodontal regeneration, with no aberrant events complicating the regenerative process. Further research is necessary to improve the bone marrow stem cells behavior in collagen-hydroxyapatite scaffolds after implantation.