Orientadores: Alexandre Leite Rodrigues de Oliveira, Eliana Aparecida de Rezende Duek / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Biologia / Made available in DSpace on 2018-08-26T15:35:48Z (GMT). No. of bitstreams: 1 Assaf_Kyl_M.pdf: 4219247 bytes, checksum: 1f0af33b698c2094539d28e23f3f042b (MD5) Previous issue date: 2015 / Resumo: Lesões traumáticas de nervos periféricos podem gerar separação de seus cotos, impossibilitando a neurorrafia término-terminal. Nesses casos, os enxertos autólogos são muito utilizados, mas apresentam algumas desvantagens, como disponibilidade do tecido doador, formação de neuromas dolorosos na área doadora, entre outras. A técnica de tubulização, na qual são empregados tubos para orientar e proteger o nervo durante a regeneração, oferece vantagens como preservação da área doadora e possibilidade de manipulação do ambiente interno do tubo. Muitos aspectos do tubo a ser utilizado para regeneração nervosa devem ser considerados, como sua biocompatibilidade, biodegradabilidade, tempo de degradação, etc. A poli(?-caprolactona) (PCL) é um material que possui tais propriedades. Os nanotubos de carbono (NT1) e o grafeno (NTN) também possuem características que os tornam excelentes dispositivos para implantes neurais e para compor compósitos poliméricos. Neste trabalho, nervos isquiáticos de ratos Lewis foram transeccionados e tubulizados com PCL, PCL com nanotubos de carbono, PCL com óxido de grafeno e PCL com ambas as nanoestruturas. A caracterização dos nanocompósitos mostrou que as nanoestruturas tem boa dispersão, não alteram o grau de cristalinidade do PCL, oferecem reforço na matriz polimérica e provocam alteração na mobilidade molecular na parte amorfa do polímero. Na análise das próteses por microscopia eletrônica de varredura, os tubos NT1, NTN e também os confeccionados com a mistura deles, apresentaram um número importante de células aderidas, quando comparados ao PCL. Todos os materiais também se mostraram biocompatíveis. Na contagem das fibras nervosas e na comparação das áreas dos nervos, a mistura mostrou diferenças estatísticas em relação aos demais grupos experimentais (p<0,05). Porém, nas análises morfométricas não foram observadas diferenças entre os grupos. Ainda, a avaliação funcional dos animais não mostrou uma recuperação significativa da marcha. Contudo, a comparação das massas dos músculos sóleo e tibial anterior e a análise histológica desses, revelaram preservação de massa, sem atrofia das fibras musculares, indicando reinervação bem sucedida / Abstract: Injuries to peripheral nerves generate proximal and distal stumps, usually making end-to-end neurorrhaphy impossible. In such cases, autologous grafts are widely used, but have some disadvantages, such as availability of donor tissue, formation of painful neuromas in the donor area, etc. The tubulization technique, in which tubes are used to guide and protect the nerve during regeneration, offers advantages such as preservation of the donor nerve area and the possibility of manipulating the internal environment of the tube. Many aspects of the conduit to be used for nerve regeneration must be considered as biocompatibility, biodegradability, degradation time, etc. The poly (?-caprolactone) (PCL) is possesses most of these properties. Carbon nanotubes and graphene also have features that make them excellent devices for neural implants and to constitute polymer composites. In this work, sciatic nerves of Lewis rats were transected and tubulized with PCL, PCL with carbon nanotubes (NT1), PCL with graphene oxide (NTN) and PCL with both nanostructures. Nanocomposites characterization showed that nanoparticles have good dispersion, do not alter the degree of PCL crystallinity, provide reinforcement of the polymer matrix and cause changes in the molecular mobility in the amorphous part of the polymer. In the analysis of the prostheses by scanning electron microscopy, NT1, NTN and its mixture showed higher number of adhered cells as compared to the PCL. All materials were also biocompatible. The counting regenerated nerve fibers and comparison of the nerve areas, the mixture showed statistical differences when compared to the other experimental groups (p <0.05). Nevertheless, morphometric analyzes were not different among groups. Furthermore, functional evaluation of the animals showed no significant gait recovery after 8 weeks post surgery. However, comparison of the weigth of the soleus and anterior tibialis and the histological analysis revealed absence of atrophy and preservation of the tissue, indicating a successful reinervation / Mestrado / Biologia Celular / Mestra em Biologia Celular e Estrutural

Thesis (M. Sc. (Physics)) -- University of Limpopo, 2016. / Bilayer graphene and single-walled carbon nanotubes were studied through classical molecular dynamics using Tersoff potential. The Tersoff potential has been the most successful model to replicate much of the semiconducting properties in carbon structures. The simulations were performed within a canonical (NVT) ensemble for structural properties and isothermal–isobaric ensemble (NPT) for thermodynamic properties of both materials. The bilayer graphene consists of two models of 64 and 256 atoms. Single-walled carbon nanotubes consist of three chiral structures of 264 atoms which is cnt(12,10), 260 atoms which is cnt(10,12) and armchair structure of 312 atoms which is cnt(12,12). The structural and thermodynamics properties were investigated in a range of temperature from 300 - 5000 K. It has been found that some of the properties of the graphene and carbon nanotube are similar. Graphene256 was found to be more stable than graphene64 and the armchair cnt(12,12) appears to be more mechanically stable than chiral cnt(12,10). Graphene and single-walled carbon nanotubes were also studied using X-ray diffraction and atomic force microscopy (AFM). The lattice constant for both materials were calculated and they agree well with the computational results. For carbon nanotubes, different solvents were used for characterization using the AFM. Chloroform was the best solvent since we managed to find some bundles of carbon nanotube. For ethanol and toluene solvents we did not managed to get any bundles. The diameter of single-walled carbon nanotube was determined only on a solution that chloroform solvent was used.

Only 2.5% of the water on Earth is fresh water and only less than 1% is accessible to human consumption. Landlocked and desert communities and communities that are not wealthy enough to provide clean drinking water via conventional water treatment technologies are facing severe water shortages and tend to rely on long distance transportation to supply fresh water for their daily use. As a lot of the water-scarce countries have abundant annual solar irradiation and relatively high humidity, this project proposes a technology that harvests water from ambient air using an anhydrate salt and releases it for collection using sunlight. This technology is designed to be potentially deployed in night-day cycles, as the humidity at night is at its peak, and solar irradiation during the day is also at its peak. In this work, a mesoporous silica powder filled with CuCl2 and coated with carbon nanotubes is used. The water capture performance of this material was investigated with different relative humidity environments. Furthermore, the powder agglomeration sizes of this material were also investigated for each relative humidity environment. Water release was investigated under 1 kW/m2 simulated solar light in an in-lab ~60% relative humidity environment. The results show that this mesoporous material was able to capture water at 12% relative humidity conditions, low enough to capture water from the air in the Sahara Desert. At relative humidity of 15% and 35%, the material was able to absorb 0.12 and 0.25 kg/kg of water, respectively, within 100 minutes, which indicates its fast water harvesting kinetics. A fully hydrated sample released 0.26 kg/kg of water in almost half an hour under 1 kW/m2 simulated sunlight. This project sheds more light on utilizing the atmosphere as an alternative water source.

Lithium-sulfur (Li-S) batteries are faced with practical drawbacks of poor cycle life and low charge efficiency which hinder their advancements. Those drawbacks are primarily caused by the intrinsic issues of the cathodes (sulfur) and the anodes (Li metal). In attempt to resolve the issues found on the cathodes, this work discusses the method to prepare a binder-free three-dimensional carbon nanotubes-sulfur (3D CNTs-S) composite cathode by a facile and a scalable approach. Here, the 3D structure of CNTs serves as a conducting network to accommodate high loading amounts of active sulfur material. The efficient electron pathway and the short Li ions (Li+) diffusion length provided by the 3D CNTs offset the insulating properties of sulfur. As a result, high areal and specific capacities of 8.8 mAh cm−2 and 1068 mAh g−1, respectively, with the sulfur loading of 8.33 mg cm−2 are demonstrated; furthermore, the cells operated at a current density of 1.4 mA cm−2 (0.1 C) for up to 150 cycles. To address the issues existing on the anode part of Li-S batteries, this work also covers the novel approach to protect a Li metal anode with a thin layer of two-dimensional molybdenum disulfide (MoS2). With the protective layer of MoS2 preventing the growth of Li dendrites, stable Li electrodeposition is realized at the current density of 10 mA cm−2; also, the MoS2 protected anode demonstrates over 300% longer cycle life than the unprotected counterpart. Moreover, the MoS2 layer prevents polysulfides from corroding the anode while facilitating a reversible utilization of active materials without decomposing the electrolyte. Therefore, the MoS2 protected anode enables a stable cycle life of over 500 cycles at 0.5 C with the high sulfur loading amount of ~7 mg cm−2 (~67 wt% S content in cathode) under the low electrolyte/sulfur (E/S) ratio of 6 μL mg−1. This translates to the specific energy and power densities of ~550 Wh kg-1 and ~300 W kg−1, respectively. Additionally, such values far exceed the electrochemical performance of the current Li-ion batteries. Therefore, the synergetic effect of utilizing the 3D CNT-S cathode and the MoS2 protected Li anode will allow the Li-S batteries to become applicable for the transportation and the large-scale energy grid applications.

Chronic Venous Insufficiency (CVI) is a disease of the lower limbs that affects millions of people in the United States. It is categorized by constant venous hypertension, which can lead to swelling of the legs, pain, skin changes and ulcers. One of the widely known symptoms that can lead to CVI is varicose veins. The main source of the problem of CVI is incompetent venous valves. The purpose of venous valves is to direct blood through the veins to the heart and prevent retrograde flow to the lower limbs. CVI can be caused by leg injury, pregnancy, genetics, age, and prolonged standing. Current treatments of the disease include compression stocking therapy, ablation, vein stripping, and valve reconstruction. CVI has become such a problem for patients, especially those with secondary incompetence in the deep veins, because the current treatments are used to alleviate the symptoms of the disease but do not treat the source of the problem. One solution that has great potential is to create an implantable venous valve that could restore function of the venous system. In the past many prosthetic venous valves have been made, but none are clinically used because of problems with biocompatiblility, thrombogenicity caused by high shear rates, and longterm functionality that has been hindered by leaflet stiffening. The purpose of this research was to create a venous valve that could overcome these difficulties. This was done by designing the valve out of carbon-infiltrated carbon nanotubes (CI-CNTs). This material has been proven to be thrombo-resistant, biocompatible due to its non-reactive properties, and durable. The valve was designed to be initially open and to close with physiological pressures. The shear rate caused by implantation of the valve was minimized to reduce the likelihood of thrombus formation. FEA and CFD analysis was performed to verify the valve would function under physiological conditions and that shear rates would be in the normal range. The final design was tailored for implantation in the common femoral vein. It had a diameter of 12.7 mm, length of approximately 40 mm, and thickness of 0.3 mm. With a hydrostatic pressure of 20 mmHg it fully closed with a maximum stress of 117 MPa, which is below the ultimate strength of CI-CNTs. The CFD analysis demonstrated the valve would cause a maximum shear rate of 225.1 s

This diploma thesis deals with design, implementation and testing of fluorescence microscope intended for carbon nanotubes spectroscopy. Theory of fluorescence resulting from solid state physics and atomic structure of nanotubes is briefly discussed. The basic idea, optical scheme and optical elements used in the fluorescence microscope are described based on requirements resulting from the theory. The thesis mentions the sample preparation procedure and measurements of its optical activity as well. Realized microscope is usable for fluorescence measurements within the supposed range of wavelengths as was proved by testing.

Since the discovery of carbon nanotubes (CNTs), they have gained much interest in many science and engineering fields. The modification of CNTs by introducing different functional groups to their surface is important for CNTs to be tailored to fit the need of specific applications. This dissertation presents several CNT-based systems that can provide biomedical and environmental advantages. In this research, polyethylenimine (PEI) and polyvinyl alcohol (PVA) were used to coat CNTs through hydrogen bonding. The release of doxorubicin (DOX, an anticancer drug) from this system was controlled by temperature. This system represents a promising method for incorporating stimuli triggered polymer-gated CNTs in controlled release applications. To create an acid responsive system CNTs were coated with 1,2-Distearoyl-snglycero- 3-Phosphoethanolamine-N-[Amino(Polyethylene glycol)2000]-(PE-PEG) and Poly(acrylic acid) modified dioleoy lphosphatidyl-ethanolamine (PE-PAA). An acidlabile linker was used to cross-link PAA, forming ALP@CNTs, thus making the system acid sensitive. The release of DOX from ALP@CNTs was found to be higher in an acidic environment. Moreover, near infrared (NIR) light was used to enhance the release of DOX from ALP@CNTs. A CNT-based membrane with controlled diffusion was prepared in the next study. CNTs were used as a component of a cellulose/gel membrane due to their optical property, which allows them to convert NIR light into heat. Poly(Nisopropylacrylamide) (PNIPAm) was used due to its thermo-sensitivity. The properties of both the CNTs and PNIPAm’s were used to control the diffusion of the cargo from the system, under the influence of NIR. CNTs were also used to fabricate an antibacterial agent, for which they were coated with polydopamine (PDA) and decorated with silver particles (Ag). Galactose (Gal) terminated with thiol groups conjugated with the above system was used to strengthen the bacterial targeting ability. The antibacterial activity of Ag/Gal@PDA@CNTs was examined on Escherichia coli. NIR was used to enhance the antibacterial activity of Ag/Gal@PDA@CNTs. Finally, CNTs were used as a support for methyl orange (MO) and palladium catalysts (Pd). MO was used due to its ability to enhance the catalyst activity. Pd@CNTs composites were used to test the reduction rate of nitrite with and without the addition MO. The results showed that over repeated cycles of nitrite reduction, the activity enhancement was lost. In summary, CNTs are promising building blocks for preparation of smart and stimuli responsive systems that have potential for a wide range of applications. The methods presented are simple and can be scaled up for industrial processing purposes.

We investigate the conditions under which electron irradiation of single-walled carbon nanotube (SWCNT) bundles with 2 keV electrons produces an increase in the Raman D peak. We find that an increase in the D peak does not occur when SWCNTs are preheated in situ at 600 C for 1 h in ultrahigh vacuum (UHV) before irradiation is performed. Exposing SWCNTs to air or other gases after preheating in UHV and before irradiation results in an increase in the D peak. Small diameter SWCNTs that are not preheated or preheated and exposed to air show a significant increase in the D and G bands after irradiation. X-ray photoelectron spectroscopy shows no chemical shifts in the C1s peak of SWCNTs that have been irradiated versus SWCNTs that have not been irradiated, suggesting that the increase in the D peak is not due to chemisorption of adsorbates on the nanotubes.

Early and accessible diagnostics are important elements to reducing the negative side-effects of untreated disease. One key advancement in diagnostic monitoring is through the development of highly sensitive sensors that have the capability to detect lower concentrations, while still remaining accessible for point-of-care use. This dissertation characterizes electrochemical sensing platforms that are enhanced by convection and by 3D electrodes made from high surface area, vertically aligned carbon nanotubes (VACNTs). Free-standing VACNTs were patterned into microchannel arrays for flow-through amperometric sensing. Convective mass transfer enhancement was shown to improve sensor performance in amperometric sensing through the use of high surface area to fluid volume structures and concentration boundary layer confinement. Through-flow sensing of hydrogen peroxide produced drastically higher signals than stirred sensing, with over 90% of the hydrogen peroxide being oxidized as it passed through the channels. Non-enzymatic sensing of glucose was achieved by chemical reaction of glucose with methyl viologen to produce on average 3.4 electrons per glucose molecule, significantly higher than that obtained with enzymatic sensing with glucose oxidase. A scaled down sensor enabled detection from 200 μL of glucose by flow injection analysis with a limit of detection of 360 nM and a linear sensing range up to at least 150 μM glucose. Such sensing range offers the potential to measure glucose levels found in saliva. This work demonstrates the utility of high aspect ratio electrodes made of VACNTs. Convection and surface area are shown to enhance the sensitivity of flow-through VACNT amperometric sensors by effectively utilizing the available analyte to increase the measured current density. Advances in nanomaterials, combined with electrochemical impedance spectroscopy, have allowed impedimetric biosensors to have high sensitivity while remaining label-free, pushing towards enabling portable diagnosis at the point-of-care. Porous, 3D VACNT electrodes for impedance-based biosensing were fabricated with different electrode height, gap width, and configuration. Sensitivity was characterized by functionalizing the representative protein streptavidin onto VACNT electrodes for detection of biotin. Tall, closely-spaced VACNT interdigitated electrodes are shown to have the highest electroactive surface area (15x the 2D geometric area) and the highest sensitivity, allowing for a 1 ng/mL limit of detection. Aspect ratio and surface area are shown to be important factors in determining the sensitivity of 3D VACNT interdigitated electrodes for impedimetric sensing of biomolecules bound to electrode surfaces. Although this biosensing platform is shown with streptavidin and biotin, it could be extended to other proteins, antibodies, viruses, and bacteria.

Cette thèse porte sur la catalyse supportée sur nanotubes de carbone. Plusieurs aspects ont été étudiés, électrocatalyse pour la production d'hydrogène à partir d'eau, catalyse pour la synthèse organique et électrocatalyse de la réaction de réduction de l'oxygène. Différents catalyseurs ont été synthétisés à partir d'assemblages supramoléculaires de molécules amphiphiles autour de nanotubes de carbone ou d'adhésion de molécules polyaromatiques à la surface des nanotubes et ont impliqué l'utilisation de catalyseur moléculaire ou nanoparticulaire. L'utilisation de ces catalyseurs pour les différents types de réactions mentionnés plus haut ont abouti à des résultats intéressants. / This PhD thesis deals with the catalysis supported on carbon nanotubes. Several aspects have been studied such as electrocatalysis for hydrogen production form water, catalysis for organic synthesis and electrocatalysis of the oxygen reduction reaction. Many different catalysts have been synthesized based on supramolecular assembly of amphiphilic molecules around carbon nanotubes or assembly of polyaromatic molecules at the surface of the nanotubes. These catalysts are made of metallic complexes or metallic nanoparticles. These catalysts have been successfully used to perform the reactions mentioned above.