142 research outputs found
Wear behavior characterization of hydrogels constructs for cartilage tissue replacement
No full textThis 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
Sol-gel approach to incorporate millimeter-long carbon nanotubes into fabrics for the development of electrical-conductive textiles
No full textIn this paper, a new and versatile approach to obtain a good dispersion in water-based paste of short (ffi 1.5 mm) and long (ffi 3.0 mm) millimeter-sized carbon nanotubes (CNT) for the fabrication of electroconductive textiles is reported. With this aim, N-[3-(triethoxysilyl)propyl]ethylenediamine (EDAES) was used in combination with a waterborne thermo-degradable surfactant to stabilize the dispersion of two different kinds of carbon nanotubes (CNT) in hydroalcoholic solutions. A polyurethane thickener was added to each CNT dispersion to obtain dense pastes that were deposited onto cotton fabrics using the knife-over-roll technique. High magnification images confirm that the nanotubes are well dispersed in both coatings, furthermore appearing homogeneously distributed on the cotton surface. The conductivity of the long CNT-coated fabrics was confirmed by the electrical resistance of 2.61x 104Ω/sq which decreased to 9.46x102Ω/sq for short CNT size. Moreover, after one washing cycle, the electrical conductivity variations of coating containing the shortest nanotubes retain over 99%, demonstrating its adhesion on the fabric. The increase of the textile stiffness was less than 20% for both treated samples compared to the reference, without affecting significantly the fabric samples comfort. The developed cotton fabrics worked well as wearable conductive materials in heart rate monitoring using photoplethysmography
Graphene Oxide and Reduced Graphene Oxide Nanoflakes Coated with Glycol Chitosan, Propylene Glycol Alginate, and Polydopamine: Characterization and Cytotoxicity in Human Chondrocytes
No full textRecently, graphene and its derivatives have been extensively investigated for their interesting 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 chondrocytes. 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
Phase-Dependent Photocatalytic Activity of Bulk and Exfoliated Defect-Controlled Flakes of Layered Copper Sulfides under Simulated Solar Light
No full textSunlight-driven photocatalysis is an environmentally friendly approach to solve ecological issues. The development of simple yet sufficiently stable photocatalytic materials capable of responding to the full-spectrum light remains challenging. Here, we demonstrate the phase transformations of bulk copper sulfides from digenite (Cu9S5) to djurleite (Cu1.97S) and low chalcocite (Cu2S) by the reactive thermal annealing during ambient pressure chemical vapor deposition, followed by their top-down exfoliation. Using multiple techniques, we confirm that monoclinic Cu2S is primarily formed at higher temperatures or greater reaction times and using a reducing atmosphere. We measured the average thickness to be approximately 4 nm for the exfoliated flakes with relatively large lateral sizes of up to 10 μm. We tested the three phases of bulk copper sulfides and their exfoliated forms as photocatalysts for dye degradation under simulated solar light irradiation. Exfoliated Cu2S flakes exhibited superior photocatalytic activity (0.007 min−1), roughly twice higher than that of bulk chalcocite, which could be predominantly attributed to their 2D structure and also 2D planar defects, which could serve as active centers for dye photodegradation. Our study paves the way for developing nextgeneration full-spectrum-responsive 2D copper sulfide photocatalysts for environmental decontamination
2D TiS2 Flakes for Tetracycline Hydrochloride Photodegradation under Solar Light
No full textHere, we report a simple route of synthesizing bulk layered TiS2 via chemical vapor transport (CVT) using non-toxic inorganic precursors, followed by successful isolation of few-layered TiS2 flakes using high-frequency-based liquid-phase exfoliation. Exfoliated TiS2 flakes exhibit significantly enhanced photocatalytic activity towards the degradation of tetracycline hydrochloride (TCH) under simulated solar light irradiation, achieving ~ 95% degradation efficiency with its reaction rate constants six times higher than that of the bulk counterpart. The underlying degradation mechanism can be attributed to the fully exposed reactive sites originating from the well-defined layered structure. Trapping experiments coupled with electron paramagnetic resonance (EPR) measurements confirm the generation of electrons and hydroxyl radicals as major active species. The photodegradation pathway and intermediates of TCH were studied in-depth through liquid chromatography-mass spectrometry (LC-MS). The current work provides new insight into using exfoliated TiS2 for environmental remediation
CNT synthesis for IC interconnects
No full textThesis (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
Graphene Oxide‐Doped Gellan Gum–PEGDA Bilayered Hydrogel Mimicking the Mechanical and Lubrication Properties of Articular Cartilage
No full textArticular 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
Designing of carbon nanotubes/cotton fabric composite for e-textiles: effect of carbon nanotubes-lenght on electroconductive properties
No full textNonfunctionalized carbon nanotubes featuring length over than 500 μm, were mixed with an amino-functionalized sol-gel precursor and a highly volatile solvent in order to obtain a well-dispersed solution. Finally, a thickener was added to the nanotubes dispersion thus obtaining a viscous paste, which was deposited on cotton fabrics through knife-over-roll technique thus achieving a surface coating with high electrical conductivity. The as-prepared conductive cotton fabrics were characterized by different chemical-physical techniques and showed a sheet resistance of about 9.5 • 102 Ω/sq. Developed conductive fabrics can find applications as conductive material or wearable sensors
High performance, binder-free electrodes with single atom catalysts on doped nanocarbons for electrochemical water splitting synthesized using one-step thermally controlled delamination of thin films
No full textDeveloping high performance catalysts for electrochemical water splitting is critical for an efficient and sustainable route to hydrogen production. For this, single-atom catalysts (SACs) are the best candidates, as they offer the highest atom efficiency. However, current methods to produce SACs involve a complex synthesis, often requiring multiple lengthy and expensive steps and yielding an insufficient density of single atoms. Here, we report a one-step chemical vapor deposition (CVD) synthesis to produce free-standing (FS) electrodes with Ni SACs on a matrix of sulfur-doped carbon nanofibers (CNFs), referred to as SACs@nanocarbon. The mechanism is based on a temperature-controlled delamination of thin films, with Au in contact with a SiO2 substrate, leading to the nucleation and growth of SACs@nanocarbon. Advanced characterization methods indicate the presence of Ni and Au single atoms and larger gold aggregates on the CNF matrix surface. These non-platinum group metal (non-PGM) electrodes showed exceptional performance for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). They performed for over 20 000 cycles with negligible change in overpotential at higher currents, with low onset overpotentials of 305 mV at 10 mA cm-2 for the OER and 40 mV at 17 mA cm-2 for the HER. The overpotential decreased to 195 mV at a current density of 100 mA cm-2. Remarkably, the electrode performance improved over cycling, while gold was dissolving in the electrolyte. This novel synthesis yielding SACs@nanocarbon could pave the way for the development of non-PGM, high performance electrodes for many other electrocatalytic applications. Additionally, the new paradigm of temperature-controlled delamination of thin films could be used to synthesize new materials.Developing high performance catalysts for electrochemical water splitting is critical for an efficient and sustainable route to hydrogen production
Aspect Ratio‐Engineered Ru‐Integrated W18O49: Controlled Growth and Enhanced Electrocatalytic Activity
No full textThe sustainable production of renewable fuels and feedstocks is currently constrained by the slow kinetics of anodic oxygen evolution reaction (OER). Precious metal‐based catalysts such as Ir suffer from stability issues as well as high capital cost. To enforce the future of green hydrogen production, this study develops Ru‐integrated W18O49 nanowires (NWs), as an efficient and stable OER electrocatalyst. This study obtains Ru‐W18O49 NWs by a combined physical vapor deposition–chemical vapor deposition approach. It discovers the NWs growth mechanism, characterized by two different growth kinetics. Herein, it finds that the integration of just 3% of Ru in the oxygen‐deficient W18O49 NWs remarkably increases the number of active catalytic sites during OER, showing faster kinetics (60 mV dec−1) and a reduced overpotential of 360 mV at 10 mA cm−2. The electrode's observed catalytic performance and long‐term durability over 36 h (12 h each at 10, 30, and 100 mA cm−2) combined with the versatility of the two‐step synthetic route, are a promising research approach for future industrial applications
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