Mechanical properties of freestanding few-layer graphene/boron nitride/polymer heterostacks investigated with local and non-local techniques.

van der Waals two-dimensional materials and heterostructures combined with polymer films continue to attract research attention to elucidate their functionality and potential applications. This study presents the fabrication and mechanical testing of 2D material heterostacks, consisting of few-layer boron nitride and graphene heterostructures synthesized via chemical vapor deposition, capped with a polymethyl methacrylate layer and suspended across ∼200 µm wide trenches using a combined wet-dry transfer method. The mechanical characterization of the heterostacks was performed using two independent approaches: (a) non-local testing with a custom-built tensile testing platform and (b) local load-displacement testing employing atomic force microscopy probes, complemented by finite element simulations. Both approaches provided new results, which are in good agreement with each other. Overall, our findings offer new insights into a combined load capacity in complex multi-material two-dimensional systems, and can contribute to advancing micro and nano-scale device designs and implementations.

An extended model for chirality selection in single-walled carbon nanotubes.

The chirality selective production of single-walled carbon nanotubes (SWCNTs) continues to represent one of the most important technological challenges. In this study, an extended model which considers all steps of the SWCNT growth process, including adsorption, decomposition, diffusion, and incorporation, is applied, for the first time, to obtain chirality selection in the SWCNT populations. We show that the dependence of the population distribution on chirality, defined as a product of the nucleation probability and the growth rate, has a volcano-shape. The model is in good agreement with the reported experimental studies and supports the results which show the surplus of near armchair or near zigzag SWCNTs. The present work emphasizes the role of the catalyst in chirality selection via optimization of chemisorption strength between the carbon species and the catalyst surface needed to achieve stable nucleation and fast growth rates. The obtained results can be used in catalyst designs to define the pathways towards the growth of SWCNTs with specific chiralities exhibiting distinguished electronic properties.

In Situ Measurements of Strain Evolution in Graphene/Boron Nitride Heterostructures Using a Non-Destructive Raman Spectroscopy Approach.

The mechanical properties of engineered van der Waals (vdW) 2D materials and heterostructures are critically important for their implementation into practical applications. Using a non-destructive Raman spectroscopy approach, this study investigates the strain evolution of single-layer graphene (SLGr) and few-layered boron nitride/graphene (FLBN/SLGr) heterostructures. The prepared 2D materials are synthesized via chemical vapor deposition (CVD) method and then transferred onto flexible polyethylene terephthalate (PET) substrates for subsequent strain measurements. For this study, a custom-built mechanical device-jig is designed and manufactured in-house to be used as an insert for the 3D piezoelectric stage of the Raman system. In situ investigation of the effects of applied strain in graphene detectable via Raman spectral data in characteristic bonds within SLGr and FLBN/SLGr heterostructures is carried out. The in situ strain evolution of the FLBN/SLGr heterostructures is obtained in the range of (0-0.5%) strain. It is found that, under the same strain, SLG exhibits a higher Raman shift in the 2D band as compared with FLBN/SLGr heterostructures. This research leads to a better understanding of strain dissipation in vertical 2D heterostacks, which could help improve the design and engineering of custom interfaces and, subsequently, control lattice structure and electronic properties. Moreover, this study can provide a new systematic approach for precise in situ strain assessment and measurements of other CVD-grown 2D materials and their heterostructures on a large scale for manufacturing a variety of future micro- and nano-scale devices on flexible substrates.

Controlled Fabrication of Quality ZnO NWs/CNTs and ZnO NWs/Gr Heterostructures via Direct Two-Step CVD Method.

A novel and advanced approach of growing zinc oxide nanowires (ZnO NWs) directly on single-walled carbon nanotubes (SWCNTs) and graphene (Gr) surfaces has been demonstrated through the successful formation of 1D-1D and 1D-2D heterostructure interfaces. The direct two-step chemical vapor deposition (CVD) method was utilized to ensure high-quality materials' synthesis and scalable production of different architectures. Iron-based universal compound molecular ink was used as a catalyst in both processes (a) to form a monolayer of horizontally defined networks of SWCNTs interfaced with vertically oriented ZnO NWs and (b) to grow densely packed ZnO NWs directly on a graphene surface. We show here that our universal compound molecular ink is efficient and selective in the direct synthesis of ZnO NWs/CNTs and ZnO NWs/Gr heterostructures. Heterostructures were also selectively patterned through different fabrication techniques and grown in predefined locations, demonstrating an ability to control materials' placement and morphology. Several characterization tools were employed to interrogate the prepared heterostructures. ZnO NWs were shown to grow uniformly over the network of SWCNTs, and much denser packed vertically oriented ZnO NWs were produced on graphene thin films. Such heterostructures can be used widely in many potential applications, such as photocatalysts, supercapacitors, solar cells, piezoelectric or thermal actuators, as well as chemical or biological sensors.

Hypoxia Modulates Epithelial Permeability via Regulation of Vascular Endothelial Growth Factor in Airway Epithelia.

Hypoxia resulting from occlusion of the sinus ostium is known to be one of the major pathogenic mechanisms of sinusitis. Hypoxia-inducible factor (HIF)-1 is a widely known transcription factor that induces the cellular response to hypoxic conditions and activates the transcription of several genes, including vascular endothelial growth factor (VEGF). We hypothesized that induced permeability caused by hypoxia is a major pathophysiologic mechanism of upper airway diseases, such as sinusitis. The aim of this study was to investigate the mechanism of hypoxia-induced hyperpermeability, which mediates increased paracellular permeability and enhanced microbial invasiveness in the airway epithelium. We show that expression of VEGF mRNA and protein and HIF-1α protein increased as a function of time under hypoxia in normal human nasal epithelial cells. Our results also indicate that VEGF expression was induced by transfection with a mammalian expression vector encoding HIF-1 but down-regulated by transfection with small interfering RNA specific for HIF-1α under hypoxic conditions. Results of a transepithelial permeability assay measuring transepithelial electrical resistance indicated that permeability was increased as a function of time under hypoxia and was rescued by anti-VEGF monoclonal antibody (bevacizumab) and small interfering RNA specific for HIF-1α. We detected up-regulated HIF-1α and VEGF expression in mucosal epithelium samples from patients with sinusitis compared with normal mucosal epithelium using Western blotting and immunohistochemical staining. In conclusion, we suggest that the hypoxia-HIF-1α-VEGF axis plays an important role in hyperpermeability of airway epithelial cells, implying a role in the pathophysiology of upper respiratory tract diseases, such as sinusitis.

Can mitochondrial dysfunction be a predictive factor for oxidative stress in patients with obstructive sleep apnea?

Mitochondrial dysfunction reflects a lifelong cumulative burden of cellular damage, and a decrease in mitochondrial DNA (mtDNA) copy number is associated with oxidative stress and chronic inflammation. The goal of this study was to assess whether mitochondrial dysfunction and a decrease in mtDNA copy number are common features of patients with obstructive sleep apnea syndrome (OSA). We compared mtDNA copy number between 20 healthy volunteers and 20 patients with OSA and investigated whether a significant attenuation of mtDNA copy number was observed in genomic DNA isolated from whole blood of OSA patients. Our observations lead to the hypothesis that mtDNA copy number is lower in whole blood DNA of OSA subjects and might be related to OSA severity, reflecting excessive oxidative stress in patients with OSA.

Tissue-engineered tracheal reconstruction using three-dimensionally printed artificial tracheal graft: preliminary report.

Three-dimensional printing has come into the spotlight in the realm of tissue engineering. We intended to evaluate the plausibility of 3D-printed (3DP) scaffold coated with mesenchymal stem cells (MSCs) seeded in fibrin for the repair of partial tracheal defects. MSCs from rabbit bone marrow were expanded and cultured. A half-pipe-shaped 3DP polycaprolactone scaffold was coated with the MSCs seeded in fibrin. The half-pipe tracheal graft was implanted on a 10 × 10-mm artificial tracheal defect in four rabbits. Four and eight weeks after the operation, the reconstructed sites were evaluated bronchoscopically, radiologically, histologically, and functionally. None of the four rabbits showed any sign of respiratory distress. Endoscopic examination and computed tomography showed successful reconstruction of trachea without any collapse or blockage. The replaced tracheas were completely covered with regenerated respiratory mucosa. Histologic analysis showed that the implanted 3DP tracheal grafts were successfully integrated with the adjacent trachea without disruption or granulation tissue formation. Neo-cartilage formation inside the implanted graft was sufficient to maintain the patency of the reconstructed trachea. Scanning electron microscope examination confirmed the regeneration of the cilia, and beating frequency of regenerated cilia was not different from those of the normal adjacent mucosa. The shape and function of reconstructed trachea using 3DP scaffold coated with MSCs seeded in fibrin were restored successfully without any graft rejection.

Paranasal sinus mucoceles with ophthalmologic manifestations: a 17-year review of 96 cases.

BACKGROUND: The purpose of this study was to assess the characteristics of paranasal sinus mucoceles with ophthalmologic manifestations with a focus on optic neuropathy. METHODS: From January 1993 to May 2010, 96 consecutive patients diagnosed with paranasal sinus mucoceles with ophthalmologic manifestations were investigated. Clinical and therapeutic factors and demographics were reviewed from medical records. Statistical associations between clinical and therapeutic factors and visual outcomes after surgery were also analyzed. RESULTS: A total of 352 patients were diagnosed with paranasal sinus mucoceles and underwent surgical treatment. Ninety-six of them presented with ophthalmologic symptoms, and periorbital swelling and pain were the most common symptoms (36.4%) in those patients. Among the 96 patients with ophthalmologic manifestations, 18 (18.8%) were diagnosed with optic neuropathy based on the deterioration of their visual acuity and unilateral relative afferent papillary defect. Ten of these 18 patients showed improvements in their vision after surgical intervention. The statistical analysis of the association between clinical and therapeutic factors and visual outcomes showed that the presence of infection was the only significant factor (p = 0.023). CONCLUSION: Paranasal sinus mucoceles present various ophthalmologic manifestations. Among them, optic neuropathy may be one of the most devastating conditions. In treating optic neuropathy caused by mucoceles, the presence of infection was the only factor that had any influence on postoperative visual outcomes. Therefore, we conclude that not only surgical drainage and ventilation of the sinus are necessary, but infection control is also a vital factor in treating mucoceles with optic neuropathy.

Treatment outcomes of juvenile nasopharyngeal angiofibroma according to surgical approach.

OBJECTIVE: This is a retrospective study to assess treatment outcomes according to stage and surgical approach in advanced juvenile nasopharyngeal angiofibroma (JNA). METHODS: We retrospectively evaluated 20 JNA patients diagnosed and treated at our hospital. We only enrolled advanced disease with Radkowski stages greater than I and with minimum follow-up of 1 year (range 1-8.5). RESULTS: Recurrence or remnants were observed in 7 patients out of 20 patients (35.0%) who underwent primary surgical resection of advanced JNA and the mean interval to recurrence was 15.6 months (range 6-38). A recurrence rate according to a different stage was as follows: 33.3% in stage IIa, 33.3% in stage IIb, 50.0% in stage IIc and no recurrence in stage III. An endoscopic approach was chosen in 4 patients among these patients, four were classified as stage IIb tumors, one as a stage IIc tumor, with a recurrence rate of 25.0%, but no recurrence found in stage IIa disease. A midfacial degloving approach was used in 7 patients, with a recurrence rate of 42.9% and maxillary swing approach was taken in 3 patients with complete control. Postoperative complications required interventions occurred in 14.8%, more in the invasive maxillary swing or infratemporal fossa approaches. CONCLUSIONS: Although selecting minimal invasive or invasive approaches is equivocal, we recommend using the endoscopic approach or a midfacial degloving approach for the treatment of JNA extended to the pterygopalatine fossa. For stage III, aggressive surgery is preferable to guaranty a complete resection even if postoperative complications are more frequent. For a stage IIc, we could choose between a minimally invasive approach or a more aggressive one balancing between the possibility of salvage surgery in the future and the occurrence of postoperative healing problems.

Endoscopic surgery for inverted papilloma originating from the sphenoid sinus and related clinical characteristics.

CONCLUSIONS: Bony changes on CT imaging of inverted papilloma (IP) are useful for predicting tumor origin and recurrence sites. Because the lateral wall and floor of the sphenoid sinus are the most common origin and recurrence sites, the anterior wall of the sphenoid sinus should be opened as wide as the lateral wall and inferiorly to the level of the floor, especially in deeply pneumatized sphenoid sinuses. OBJECTIVES: The incidence of isolated sphenoid IP is exceedingly low. So far, there have not been studies on the usual origin and recurrence sites of the sphenoid sinus. We sought to identify the sites of origin and recurrence and describe clinical characteristics, radiological features, and proper endoscopic management. PATIENTS AND METHODS: We retrospectively reviewed medical records of patients with IP of the sphenoid sinus. Data collection included clinical presentations, origin and recurrent sites, radiological features, and surgical methods. RESULTS: Seven patients were identified. The most common symptoms were headache and nasal obstruction. Radiological findings showed that most tumors extended into the nasal cavity or ethmoid sinus combined frequently with erosion of the lateral wall or intersinus septum. We noted simultaneous attachment to multiple walls in five subjects, including both lateral wall and floor attachment in three subjects.