Correlation between MWCNT aspect ratio and the mechanical properties of composites of PMMA and MWCNTs

The correlation between MWCNT aspect ratio and the quasi-static and dynamic mechanical properties of composites of MWCNTs and PMMA was studied for relatively long MWCNT lengths, in the range 0.3mm to 5mm (aspect ratios up to 5 x 105) and at low loading (0.15wt%). The height of the MWCNTs prepared were modulated by controlling the amount of water vapour introduced in the reactor limiting Ostwald ripening of the catalyst, the formation of amorphous carbon and any increase in CNT diameter. The Tg of PMMA increased by up to 4 ºC on addition of the longest tubes as they have the ability to form physical junctions with the polymer chains which lead to enhanced PMMA-MWCNTs interactions and increased mechanical properties, Young's modulus by 20% on addition of 5mm long MWCNTs. Predictions of the Young's modulus of the composites of PMMA and MWCNT with the Mori-Tanaka theory show that future micromechanical models should account for MWCNT agglomeration and polymer-nanotube interactions as a function of CNT length

Wear behavior characterization of hydrogels constructs for cartilage tissue replacement

This paper aims to characterize the wear behavior of hydrogel constructs designed for human articular cartilage replacement. To this purpose, poly (ethylene glycol) diacrylate (PEGDA) 10% w/v and gellan gum (GG) 1.5% w/v were used to reproduce the superior (SUP) cartilage layer and PEGDA 15% w/v and GG 1.5% w/v were used to reproduce the deep (DEEP) cartilage layer, with or without graphene oxide (GO). These materials (SUP and DEEP) were analyzed alone and in combination to mimic the zonal architecture of human articular cartilage. The developed constructs were tested using a four-station displacement control knee joint simulator under bovine calf serum. Roughness and micro-computer tomography (µ-CT) measurements evidenced that the hydrogels with 10% w/v of PEGDA showed a worse behavior both in terms of roughness increase and loss of uniformly distributed density than 15% w/v of PEGDA. The simultaneous presence of GO and 15% w/v PEGDA contributed to keeping the hydrogel construct’s characteristics. The Raman spectra of the control samples showed the presence of unreacted C=C bonds in all the hydrogels. The degree of crosslinking increased along the series SUP < DEEP + SUP < DEEP without GO. The Raman spectra of the tested hydrogels showed the loss of diacrylate groups in all the samples, due to the washout of unreacted PEGDA in bovine calf serum aqueous environment. The loss decreased along the series SUP > DEEP + SUP > DEEP, further confirming that the degree of photo-crosslinking of the starting materials plays a key role in determining their wear behavior. µ-CT and Raman spectroscopy proved to be suitable techniques to characterize the structure and composition of hydrogels

Graphene oxide and reduced graphene oxide nanoflakes coated with glycol chitosan, propylene glycol alginate, and polydopamine: Characterization and cytotoxicity in human chondrocytes

Recently, graphene and its derivatives have been extensively investigated for their interest-ing properties in many biomedical fields, including tissue engineering and regenerative medicine. Nonetheless, graphene oxide (GO) and reduced GO (rGO) are still under investigation for improving their dispersibility in aqueous solutions and their safety in different cell types. This work explores the interaction of GO and rGO with different polymeric dispersants, such as glycol chitosan (GC), propylene glycol alginate (PGA), and polydopamine (PDA), and their effects on human chondro-cytes. GO was synthesized using Hummer’s method, followed by a sonication-assisted liquid-phase exfoliation (LPE) process, drying, and thermal reduction to obtain rGO. The flakes of GO and rGO exhibited an average lateral size of 8.8 ± 4.6 and 18.3 ± 8.5 µm, respectively. Their dispersibility and colloidal stability were investigated in the presence of the polymeric surfactants, resulting in an improvement in the suspension stability in terms of average size and polydispersity index over 1 h, in particular for PDA. Furthermore, cytotoxic effects induced by coated and uncoated GO and rGO on human chondrocytes at different concentrations (12.5, 25, 50 and 100 µg/mL) were assessed through LDH assay. Results showed a concentration-dependent response, and the presence of PGA contributed to statistically decreasing the difference in the LDH activity with respect to the control. These results open the way to a potentially safer use of these nanomaterials in the fields of cartilage tissue engineering and regenerative medicine

Graphene Oxide‐Doped Gellan Gum–PEGDA Bilayered Hydrogel Mimicking the Mechanical and Lubrication Properties of Articular Cartilage

Articular cartilage (AC) is a specialized connective tissue able to provide a low-friction gliding surface supporting shock-absorption, reducing stresses, and guaranteeing wear-resistance thanks to its structure and mechanical and lubrication properties. Being an avascular tissue, AC has a limited ability to heal defects. Nowadays, conventional strategies show several limitations, which results in ineffective restoration of chondral defects. Several tissue engineering approaches have been proposed to restore the AC's native properties without reproducing its mechanical and lubrication properties yet. This work reports the fabrication of a bilayered structure made of gellan gum (GG) and poly (ethylene glycol) diacrylate (PEGDA), able to mimic the mechanical and lubrication features of both AC superficial and deep zones. Through appropriate combinations of GG and PEGDA, cartilage Young's modulus is effectively mimicked for both zones. Graphene oxide is used as a dopant agent for the superficial hydrogel layer, demonstrating a lower friction than the nondoped counterpart. The bilayered hydrogel's antiwear properties are confirmed by using a knee simulator, following ISO 14243. Finally, in vitro tests with human chondrocytes confirm the absence of cytotoxicity effects. The results shown in this paper open the way to a multilayered synthetic injectable or surgically implantable filler for restoring AC defects

Optical Properties and Ultrafast Near‐Infrared Localized Surface Plasmon Dynamics in Naturally p‐Type Digenite Films

Copper chalcogenides are materials characterized by intrinsic doping properties, allowing them to display high carrier concentrations due to their defect-heavy structures, independent of the preparation method. Such high doping enables these materials to display plasmonic resonances, tunable by varying their stoichiometry, as shown previously for Cu2-xS, Cu2-xSe, and Cu2-xTe, with 0 1 ns) signal associated with phonon-phonon scattering relaxation. These results confirm the possibility of fabricating Cu9S5 films retaining the plasmonic properties of individual NCs, anticipating integrating these films into heterojunctions with suitable hole acceptor materials to build hot-hole-transfer-based optoelectronic devices

Measures of socioeconomic status and self-reported glaucoma in the UK Biobank cohort

Purpose: To determine ocular, demographic, and socioeconomic associations with self-reported glaucoma in the UK Biobank.Methods: Biobank is a study of UK residents aged 40–69 years registered with the National Health Service. Data were collected on visual acuity, intraocular pressure (IOP), corneal biomechanics, and questionnaire from 112?690 participants. Relationships between ocular, demographic, and socioeconomic variables with reported diagnosis of glaucoma were examined.Results: In all, 1916 (1.7%) people in UK Biobank reported glaucoma diagnosis. Participants reporting glaucoma were more likely to be older (mean 61.4 vs 56.7 years, P<0.001) and male (2.1% vs 1.4%, P=0.001). The rate of reported glaucoma was significantly higher in Black (3.28%, P<0.001) and Asian (2.14%, P=0.009) participants compared with White participants (1.62%, reference). Cases of reported glaucoma had a higher mean IOP (18?mm?Hg both eyes, P<0.001), lower corneal hysteresis (9.96 right eye, 9.89 left eye, P<0.001), and lower visual acuity (0.09 logMAR right eye, 0.08 logMAR left eye, P<0.001) compared with those without (16?mm?Hg both eyes, hysteresis 10.67 right eye, 10.63 left eye, 0.03 logMAR right eye, 0.02 logMAR left eye). The mean Townsend deprivation index was ?0.72 for those reporting glaucoma and ?0.95 for those without (P<0.001), indicating greater relative deprivation in those reporting glaucoma. Multivariable logistic regression showed that people in the lowest income group (<£18?000/year) were significantly more likely to report a diagnosis of glaucoma compared with any other income level (P<0.01). We observed increasing glaucoma risk across the full range of income categories, with highest risk among those of lowest income, and no evidence of a threshold effect.Conclusions: In a large UK cohort, individuals reporting glaucoma had more adverse socioeconomic characteristics. Study of the mechanisms explaining these effects may aid our understanding of health inequality and will help inform public health interventions

CNT synthesis for IC interconnects

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 315-336).Based on their properties, carbon nanotubes (CNTs) have been identified as ideal replacements for copper interconnects in integrated circuits given their higher current density, inertness, and higher resistance to electromigration. Although at the laboratory level CNTs have proven their technical viability as interconnects, fabrication issues such as growing the desired type of CNTs in selected positions, at temperatures compatible with CMOS processing (below 500"C), and with the appropriate electrical connections, remain challenges that are hindering their introduction into industry. The purpose of this study was to develop the processes and understanding needed to establish CNTs as viable replacements for metal-based integrated circuit (IC) interconnects. Through over a thousand synthesis experiments using a dedicated thermal Chemical Vapor Deposition (CVD) system, a systematic approach was developed starting with growth of CNTs on insulating substrates, then moving to conducting substrates, and finally integrating CNT growth into insulating scaffolds with regularly spaced pores. The following results were achieved: Control of the type of carbon nanotubes grown using simple process parameter variations: By focusing on controlling catalyst morphology evolution to obtain dense and tall carpets of vertically-aligned CNTs on insulating substrates, we were able to tune the diameter and number of walls, by simply timing the introduction of a reducing agent (hydrogen) into the thermal process.(cont.) Growth of dense carpets of vertically-aligned CNTs on conductive substrates below 5000C: By focusing on the material properties of the catalyst and underlayer, we discovered important requirements for the underlayer grain structure evolution, as well as by preheating the incoming hydrocarbon gas, growth of dense and vertically aligned carpets of nanotubes on conductive underlayers at growth temperatures below 5000C could be achieved. Electrical characterization showed that we obtained ohmic contact between the CNTs and the substrate. Control of CNT crystallinity via gas preheating : We discovered that the time and temperature of gas preheating was critical for the crystallinity of the resulting CNTs. This was done by comparing the output gases from varying gas preheat treatments to the corresponding CNT structures. This allowed a discussion of the critical gas compounds responsible for growth of crystalline CNTs. Growth of CNTs into periodic insulating scaffolds on conductive substrates: We have grown CNTs on conductive substrates and in regularly-spaced pores of an insulating anodized alumina scaffold. This allowed simulation of an interconnect via system for future measurement of the electrical properties of CNTs. This structure can also serve as a starting point for future development of dense arrays of CNT-based devices.by Gilbert Daniel Nessim.Ph.D

One-Step Synthesis of a Binder-Free, Stable, and High-Performance Electrode; Cu-O|Cu₃P Heterostructure for the Electrocatalytic Methanol Oxidation Reaction (MOR)

Although direct methanol fuel cells (DMFCs) have been spotlighted in the past decade, their commercialization has been hampered by the poor efficiency of the methanol oxidation reaction (MOR) due to the unsatisfactory performance of currently available electrocatalysts. Herein, we developed a binder-free, copper-based, self-supported electrode consisting of a heterostructure of Cu3P and mixed copper oxides, i.e., cuprous–cupric oxide (Cu-O), as a high-performance catalyst for the electro-oxidation of methanol. We synthesized a self-supported electrode composed of Cu-O|Cu3P using a two-furnace atmospheric pressure–chemical vapor deposition (AP-CVD) process. High-resolution transmission electron microscopy analysis revealed the formation of 3D nanocrystals with defects and pores. Cu-O|Cu3P outperformed the MOR activity of individual Cu3P and Cu-O owing to the synergistic interaction between them. Cu3P|Cu-O exhibited a highest anodic current density of 232.5 mAcm−2 at the low potential of 0.65 V vs. Hg/HgO, which is impressive and superior to the electrocatalytic activity of its individual counterparts. The formation of defects, 3D morphology, and the synergistic effect between Cu3P and Cu-O play a crucial role in facilitating the electron transport between electrode and electrolyte to obtain the optimal MOR activity. Cu-O|Cu3P shows outstanding MOR stability for about 3600 s with 100% retention of the current density, which proves its robustness alongside CO intermediate

Natural Laterite as a Catalyst Source for the Growth of Carbon Nanotubes and Nanospheres

Carbon nanotubes (CNTs), the closest structure to ideal one-dimensional (1D) conductors, have stimulated substantial interest in the last decades for many applications in the field of nanotechnology. Unfortunately, the high cost of efficient metal catalysts limits the large-scale exploitation of carbon nanomaterials synthesis processed by chemical vapor deposition (CVD). However, minor or even trace amounts of metal or metal oxides in the ideal form to be used as catalysts can be easily found in almost all-natural materials. Herein we report on the synthesis of carbon nanotubes and nanospheres obtained via CVD from a natural laterite, as a catalyst source. The synthesized nanostructures were carefully analyzed by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), high-resolution transmission electron microscopy (HR-TEM), micro-Raman spectroscopy and thermogravimetric analysis (TGA). In particular, we investigated and discussed the structural properties of the catalyst nanoparticles and of the produced carbon nanomaterials as well as the influence of temperature on the activity of the laterite based catalyst. At 700 \ubaC, mainly CNTs grew while at 800 \ubaC, carbon nanospheres start to form and they become clearly visible in form of continuous networks of spheroidal structures in the samples grown at 900 \ubaC. The obtained yields indicate that it could be possible to scale up the synthesis of CNTs to be used in technological applications, starting from natural mineral oxide sources