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The effects of vapor-grown carbon nanofiber (VGCNF) weight fraction, applied stress, and temperature on the viscoelastic responses (creep strain, creep rate, and creep compliance) of VGCNF/vinyl ester (VE) nanocomposites were studied using a central composite design (CCD). The nanocomposite test articles were fabricated by high shear mixing, casting, curing, and post-curing in an open face mold under a nitrogen environment. Short-term creep/creep recovery experiments were conducted at prescribed combinations of temperatures (23.8 – 69.2 C), applied stresses (30.2 – 49.8 MPa), and VGCNF weight fractions (0.00 – 1.00 parts of VGCNF per hundred parts of resin, phr) determined from the CCD. The response surface models (RSMs) for predicting these viscoelastic responses were developed using the least squares method and an analysis of variance procedure. The response surface estimates indicate that increasing the VGCNF weight fraction decreases the creep resistance of the VGCNF/VE nanocomposites at high temperatures (46.5 – 69.2 C).

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Ph. D. (Department of Chemistry, Faculty of Applied and Computer Sciences), Vaal University of Technology. / A major challenge for this generation is cleaning up heavy metal pollution disposed during industrial, domestic and agricultural activities. So, to obtain clean water resources, new treatment technologies are needed that can be applied to a broad range of highly toxic heavy metals in water. In this study, metal organic frameworks (MOFs) were synthesized from 1,2,4,5-tertabenzene carboxylic acid with metal salts of; cobalt, copper, iron, antimony, strontium and lanthanum through solvothermal method. The synthesized MOFs were reacted with polyvinyl alcohol (PVA) by electrospinning. To the best of our knowledge it is for the first time that such hybrid materials are synthesized and reported. PVA/MOF materials were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry analyzer (TGA). The SEM micrographs of PVA/MOFs materials showed relatively uniform nanofibers that were non-beaded and entangled. Some formed patches, while others were partially cross linked. TGA analysis revealed that PVA/MOF nanofibers exhibited higher decomposition temperature than PVA nanofibres. Thus, it confirmed the interactive force between MOF and PVA nanofibres. FTIR plots also exhibited shifts in critical functional group positions, thus it confirmed that there was a given amount of MOFs embedded in the electrospun fibrous mat. PVA/MOFs materials were used in the adsorption of lead ions in solution to study the effects of temperature, time dependant studies and concentrations. The batch adsorption experiments were performed at five different Pb(II) ion concentrations (20, 40, 60, 80 and 100 mg/L), four different temperatures (25, 40, 60 and 80 oC), time dependent studies ranged from (5, 10, 30 and 60 min) and pH of all Pb(II) solutions were recorded to be 5.05. The results indicated that the uptake performance of PVA and PVA/MOFs nanofibers significantly changed with concentration, temperature and time. The PVA/MOFs nanofiber hybrids demonstrated greater adsorption percentage and adsorption capacity for Pb(II) ions than PVA nanofibers. PVA nanofibers showed moderate adsorption percentage and capacity performance of 25.5 % and 44.13 mg/g (meaning 44.13 mg of Pb(II) per gram of PVA nanofibers) while PVA/MOFs nanofibers showed improved percentage and capacity perfomance (PVA/Cu-MOFs 76.36 % and 152.72 mg/g), (PVA/Co-MOFs 59.41 % and 99.28 mg/g), (PVA/La-MOFs 92.27 % and 184.03 mg/g), (PVA/Cd-MOFs 83.19 % and 165.94 mg/g), (PVA/Sb-MOFs 50.66 % - 91.57 mg/g), (PVA/Sr-MOFs 58.85 % - 124.82 mg/g) and (PVA/Fe-MOFs 56.76 % - 108.82 mg/g). The adsorption data of Pb(II) ions on PVA and all PVA/MOFs nanofibers showed that a pseudo-second order kinetic model was more suitable than a pseudo first order kinetic model. The adsorption rate was much faster on PVA/MOFs nanofibers. This is marked by lower activation energy compared to PVA nanofibers activation energy. The Temkin model did not correlate well with all the adsorption data. On the contrary, Freundlich and Langmuir isotherm models described the adsorption data adequately. All PVA/MOFs nanofibers followed Langmuir isotherm model, only PVA nanofibers followed Freundlich isotherm model. The PVA and PVA/MOFs nanofibers gave negative values of enthalpy change (ΔHo) and negative values of Gibbs free energy change (ΔGo) showing the adsorption processes were exothermic and spontaneous. Moreover, obtained positive entropy changes (ΔSo) on PVA, PVA/Fe-MOF, PVA/Cu-MOF, PVA/Co-MOF and PVA/Sb-MOF nanofibers showed that the sorped Pb(II) ions were not restricted on the electrospun nanofibres and physisorption mechanism was dominant, while negative entropy changes (ΔSo) on PVA/Sr-MOF and PVA/La-MOF nanofibers indicated that chemisorption was more dominant. The influence of ubiquitous cations such as Ca(II) and Mg(II) on the adsorption of Pb(II) ions onto PVA and PVA/MOF nanofibers was also assessed. The results showed that the ubiquitous ions had no significant influence on the sorption of Pb(II) ions. Current investigation provides a method to develop novel PVA/MOFs nanofibers hybrid adsorbents for water purification system. The adsorption capacities and removal achieved with the PVA/MOFs nanofibers sorbent were higher than those for PVA sorbent. The electro spun nanofiber sorbents presents an efficient alternative for pre-treating lead ions in aqueous solutions. Results from this research demonstrated that higher performance novel nanofibers, which possessed higher adsorption percentages and capacity capabilities were obtsained far exceeding some of the commonly used adsorbents, were obtained.

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Mechanical interactions of cells with their immediately surrounding extracellular matrix (ECM) is now known to be critical in pathophysiology. For example, during cancer progression, while uncontrollable cell division leads to tumor formation, the subsequent metastatic migration of cells from the primary tumor site to distant parts of the body causes most cancer-related deaths. The metastatic journey requires cells to be able to adopt different shapes and move persistently through the highly fibrous native ECM, thereby requiring significant spatiotemporal reorganization of the cell cytoskeleton. While numerous studies performed on flat 2-dimensional culture platforms and physiological 3D gels have elucidated cytoskeletal reorganization, our understanding on how cells adapt to natural fibrous microenvironments and regulate their behavior in response to specific ECM biophysical cues including fiber size, spacing, alignment and stiffness remains in infancy. Here, we utilize the non -electrospinning Spinneret tunable engineered parameters (STEP) technique to manufacture ECM mimicking suspended fibrous matrices with precisely controlled fiber diameters, network architecture, inter-fiber spacing and structural stiffness to advance our fundamental understanding of how external cues affect cytoskeleton-based cellular forces in 3-distinct morphological processes of the cell cycle starting from division to spreading and migration. Mechanobiological insights from these studies are implemented to deliver intracellular cargo inside cells using electrical fields. Holistically, we conclude that fibrous environments elicit multiple new cell behaviors never before reported. Specifically, our new findings include (i) design of fiber networks regulates actin networks and cell forces to sculpt nuclei in varying shapes: compressed ovals, tear drop, and invaginations, and drive the nuclear translocation of transcription factors like YAP/TAZ. In all these shapes, nuclei remain rupture-free, thus demonstrating the unique adaptability of cells to fibers, (ii) dense crosshatch networks are fertile environments for persistent 1D migration in 3D shapes of rounded nuclei and low density of actin networks, while sparse fiber networks induce 2D random migration in flattened shapes and well-defined actin stress fibers, (iii) actin retraction fiber-based stability regulates mitotic errors. Cells undergoing mitosis on single fibers exhibit significant 3D movement, and those attached to two fibers can have rotated mitotic machinery, both conditions contributing to erroneous division, and (iv) a bi-phasic force response to electroporation that coincides with actin cytoskeleton remodeling. Cells on suspended fibers can withstand higher electric field abuse, which opens opportunities to deliver cargo of varying sizes inside the cell. Taken altogether, our findings provide new mechanobiological understanding of cell-fiber interactions at high spatiotemporal resolution impacting cell migration, division and nuclear mechanics-key behaviors in the study of pathophysiology. / Doctor of Philosophy / Cancer, one of the major pathophysiological conditions, progresses within the living body through spreading of malignant cells from the primary tumor to distant secondary sites, ultimately leading to life-ending outcomes. Such spreading of cancer also known as cancer metastasis requires mechanical interactions of cells with their immediately surrounding microenvironment or the extracellular matrix (ECM). Cells utilize their cytoskeleton, a dynamic internal network of filamentous proteins, to adopt various morphologies, exert mechanical forces and physically remodel their local environment as they navigate through the highly fibrous native ECM. While previous research has elucidated how biochemical factors and bulk matrix properties regulate such cytoskeletal organization and single cell behavior, our understanding of how cells adapt to fibrous environments and respond to local biophysical cues like fiber diameter, spacing, alignment and stiffness remains in infancy. Here we use the non -electrospinning Spinneret tunable engineered parameters (STEP) to generate suspended nanofiber networks of tunable geometric and mechanical properties to mimic the native cellular environment. We discover that cells elongated within these ECM-mimicking environments utilize a unique cytoskeletal caging structure to regulate the shape and response of their nuclei in a fiber -diameter and organization-dependent manner. Additionally, we demonstrate that these elongated cell morphologies often observed during metastatic cancer cell movements, is achievable not only in aligned fibers but can also be induced by dense networks of fibers in a crossing organization. Specifically, such dense crosshatch networks allow cells to migrate persistently at high speeds while cells on sparsely spaced networks demonstrate slower and random movements. As cells elongated during interphase rounded up to undergo division, we find that the underlying fiber-geometry modulates mitotic dynamics through differential levels of actin retraction fiber-mediated stability, leading to significant alterations in orientation of mitotic machinery and mitotic spindle defects. Finally, we utilize these mechanobiological insights on cytoskeletal organization and cell shape control to optimize intracellular delivery of cargo using high-voltage electric fields. We demonstrate suspended cells are capable of withstanding higher electric fields and identify multistage cell contractility recovery dynamics, which correlate with cytoskeletal disruption and reassembly. Taken altogether, our findings provide a comprehensive understanding of the fibrous ECM-mediated regulation of the cytoskeletal organization and its impact in cell migration, division and nuclear mechanics. Knowledge obtained from this study will improve our understanding of cancer metastasis and provide predictive data for in vivo cellular response, essential for cytoskeleton-targeting cancer therapies.

Tesis por compendio / [EN] The current PhD thesis deals with the development and characterization of novel nanocomposites based on biodegradable poly(mannitol sebacate) (PMS) matrices with tailored properties and shape-memory capabilities for biomedical applications. Two types of fillers -cellulose nanocrystals (CNC) and electrospun poly(lactic acid) nanofibers (NF-PLA)- were used as reinforcement in order to induce and/or enhance the shape-memory properties of PMS matrices. Also, different crosslinking profiles and stoichiometric ratios between mannitol and sebacic acid (1:1 and 1:2) were studied and evaluated to obtain samples with low and high degrees of crosslinking. An appropriate combination of the crosslinking profile and the monomer ratio for PMS matrix, as well as the addition of low content of CNC, allowed the development of PMS/CNC nanocomposites with a wide range of mechanical properties and degradation profiles. On the other hand, highly oriented poly(lactic acid) (PLA) nanofiber mats obtained by electrospinning were embedded in the PMS matrices. An enhancement of up to 53-fold in the Young's modulus was observed for PMS/NF-PLA nanocomposites filled with 15 wt% of PLA nanofibers. The incorporation of fillers (CNC and NF-PLA) allowed the development of thermally active shape-memory nanocomposites with an enhancement of parameters such as recovery stress and shape fixity. The electrospun PLA-reinforced nanocomposites, offered the best balance of mechanical and thermal properties, as well as a greater control of the transition temperature for switching the change of shape, within a useful range of temperatures. Owing to that, these materials may be of interest as smart responsive systems in long-term biomedical applications. / [ES] La presente tesis doctoral, se centra en el desarrollo y caracterización de nuevos nanocompuestos biodegradables, a partir de matrices de poli(mannitol sebacato) (PMS) con propiedades a medida y capacidades de memoria de forma para aplicaciones biomédicas. Dos tipos de cargas -nanocristales de celulosa (CNC) y nanofibras de ácido poliláctico (NF-PLA) obtenidas mediante electrospinning- se han utilizado como refuerzo, con la finalidad de inducir y/o mejorar las propiedades de memoria de forma en matrices de PMS. Se han estudiado y evaluado diferentes tratamientos de curado y ratios de reacción entre el mannitol y ácido sebácico (1:1 y 1:2), con la finalidad de obtener muestras con bajo y alto grado de reticulación. Una combinación adecuada del tratamiento de curado y el ratio entre monómeros del PMS, así como la adición de bajos contenidos de CNC, permitió desarrollar nanocompuestos de PMS/CNC con un amplio rango de propiedades mecánicas y perfiles de degradación. Por otro lado, se han producido mats de nanofibras de ácido poliláctico (PLA) con alta orientación mediante la técnica de electrospinning, para embeberse en matrices de PMS, observándose una mejora de hasta 53 veces en el módulo de Young para nanocompuestos de PMS/NF-PLA con un 15% en peso de nanofibras. La incorporación de cargas (CNC y NF-PLA) permitió el desarrollo de nanocompuestos con memoria de forma activada térmicamente, con una mejora de parámetros tales como la fuerza de recuperación y la capacidad de fijación. Los nanocompuestos reforzados con NF-PLA obtenidas por electrospinning, ofrecieron el mejor balance de propiedades mecánicas y térmicas, así como un mayor control de la temperatura de transición para la activación del cambio de forma en un intervalo útil de temperaturas. Por todo ello, estos materiales pueden resultar de interés como sistemas activos en aplicaciones biomédicas de larga duración. / [CA] La present tesi doctoral se centra en el desenvolupament i caracterització de nous nanocompostos biodegradables a partir de matrius de poli(mannitol sebacato) (PMS) amb propietats a mesura i capacitats de memòria de forma per a aplicacions biomèdiques. Dos tipus de càrregues -nanocristals de cel·lulosa (CNC) i nanofibres d'àcid polilàctic (NF-PLA) obtingudes mitjançant electrospinning- s'han utilitzat com a reforç amb la finalitat d'induir i/o millorar les propietats de memòria de forma en matrius de PMS. S'han estudiat i avaluat diferents tractaments de curat i ràtios de reacció entre el mannitol i àcid sebàcic (1:1 i 1:2) amb la finalitat d'obtenir mostres amb baix i alt grau de reticulació. Una combinació adequada del tractament de curat i el ràtio entre monòmers del PMS, així com l'addició de baixos continguts de CNC, va permetre desenvolupar nanocompostos de PMS/CNC amb un ampli rang de propietats mecàniques i perfils de degradació. D'altra banda, s'han produït mats de nanofibres d'àcid polilàctic (PLA) amb alta orientació mitjançant la tècnica de electrospinning, per embeure's en matrius de PMS, observant-se una millora de fins a 53 vegades en el mòdul de Young per nanocompostos de PMS/NF-PLA amb un 15% en pes de nanofibres. La incorporació de càrregues (CNC i NF-PLA) va permetre el desenvolupament de nanocompostos amb memòria de forma activada tèrmicament, amb una millora de paràmetres tals com la força de recuperació i la capacitat de fixació. Els nanocompostos reforçats amb NF-PLA obtingudes per electrospinning, van oferir el millor balanç de propietats mecàniques i tèrmiques, així com un major control de la temperatura de transició per a l'activació del canvi de forma en un interval útil de temperatures. Per tot això, aquests materials poden resultar d'interés com a sistemes actius en aplicacions biomèdiques de llarga durada. / Sonseca Olalla, A. (2015). DEVELOPMENT OF SHAPE-MEMORY COMPOSITES BASED ON A BIODEGRADABLE POLYESTER ELASTOMER [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/54129 / Compendio