Material Modifications for Improved Performance of Shape Memory Polymer Medical Devices

Shape memory polymers (SMPs) are a class of materials that can be programmed into a secondary, metastable geometry and subsequently stimulated to return to their original geometry. These biocompatible materials enable the delivery and subsequent expansion of multiple catheter-based medical devices, including low density foams for embolic applications. In this work, cold plasma surface modifications and bulk compositional changes were used to address three design limitations of previous SMP systems: controlled foam expansion, controlled foam membrane removal, and inherent x-ray visibility. SMP parameters including glass transition temperature, foam pore size, expansion rate in water, and x-ray contrast can be modified by altering the SMP composition or by using particulate additives to form an SMP composite. However, aggressive changes in bulk material chemistry can also affect properties associated with the surface, such as biocompatibility or hydrophobicity. To address the current limitations of SMP devices, this dissertation investigates the use of cold gas plasma techniques as an additional tool to alter surface material properties independent of bulk material composition. The material modifications imparted by plasma processes or changes in composition were first analyzed on simple film and bulk substrates using techniques such as ellipsometry, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, uniaxial tensile testing, and goniometry. After material characterization, each process was applied to a specific medical device application and characterized based on device performance criteria. Device-specific characteristics, including cell-material interactions, x-ray visibility, fluid permeability, and expansion kinetics, were conducted on device prototypes using confocal microscopy, fluoroscopic imaging, flow system analysis, and isothermal expansion imaging, respectively. Cold plasma film deposition using hydrocarbon gases was proven to influence SMP foam expansion kinetics by modulating the rate of moisture plasticization. Additionally, oxygen and tetrafluoromethane cold plasmas preferentially removed foam membranes to increase the interconnected porosity and fluid permeability of embolic SMP scaffolds with minimal impacts on material toughness. Finally, chemically incorporating triiodobenzene containing monomers not only provided x-ray visibility, but also significantly improved tensile toughness

Material Modifications for Improved Performance of Shape Memory Polymer Medical Devices

Shape memory polymers (SMPs) are a class of materials that can be programmed into a secondary, metastable geometry and subsequently stimulated to return to their original geometry. These biocompatible materials enable the delivery and subsequent expansion of multiple catheter-based medical devices, including low density foams for embolic applications. In this work, cold plasma surface modifications and bulk compositional changes were used to address three design limitations of previous SMP systems: controlled foam expansion, controlled foam membrane removal, and inherent x-ray visibility. SMP parameters including glass transition temperature, foam pore size, expansion rate in water, and x-ray contrast can be modified by altering the SMP composition or by using particulate additives to form an SMP composite. However, aggressive changes in bulk material chemistry can also affect properties associated with the surface, such as biocompatibility or hydrophobicity. To address the current limitations of SMP devices, this dissertation investigates the use of cold gas plasma techniques as an additional tool to alter surface material properties independent of bulk material composition. The material modifications imparted by plasma processes or changes in composition were first analyzed on simple film and bulk substrates using techniques such as ellipsometry, x-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, differential scanning calorimetry, dynamic mechanical analysis, uniaxial tensile testing, and goniometry. After material characterization, each process was applied to a specific medical device application and characterized based on device performance criteria. Device-specific characteristics, including cell-material interactions, x-ray visibility, fluid permeability, and expansion kinetics, were conducted on device prototypes using confocal microscopy, fluoroscopic imaging, flow system analysis, and isothermal expansion imaging, respectively. Cold plasma film deposition using hydrocarbon gases was proven to influence SMP foam expansion kinetics by modulating the rate of moisture plasticization. Additionally, oxygen and tetrafluoromethane cold plasmas preferentially removed foam membranes to increase the interconnected porosity and fluid permeability of embolic SMP scaffolds with minimal impacts on material toughness. Finally, chemically incorporating triiodobenzene containing monomers not only provided x-ray visibility, but also significantly improved tensile toughness

Fractionation and encapsulation of copaiba oleoresin (Copaifera officinalis) using supercritical technologies

Orientadores: Julian Martínez, Carmen Lucia QueirogaTese (doutorado) - Universidade Estadual de Campinas, Faculdade de Engenharia de AlimentosResumo: Este trabalho foi dividido em três etapas. A etapa (I) consistiu na formação de emulsões contendo óleo-resina de copaíba (Copaifera officinalis), usando amidos modificados como agentes estabilizantes. Foram investigados os efeitos da concentração de amido modificado (g/L), concentração de óleo-resina (mg/mL) e proporção óleo-resina/água (%, v/v) no diâmetro médio das gotas formadas. O tempo de sonicação e a potência ultrassônica foram fixados em 6 min e 480 W, respectivamente. A formulação que proporcionou menor diâmetro de gota foi selecionada para um segundo planejamento, variando a potência ultrassônica e o tempo de sonicação. As emulsões que apresentaram maior estabilidade cinética e menor diâmetro da gota foram submetidas à secagem por freeze-drying e spray-drying. Ambas técnicas de secagem produziram partículas amorfas com diferentes tamanhos e baixa umidade. Além disso, conseguiu-se uma elevada eficiência de encapsulação e alta estabilidade contra degradação térmica. A análise morfológica indicou que a natureza dos amidos modificados não afetou sua microestrutura, mas as técnicas de secagem produziram partículas com diferentes microestruturas externas. A análise por CLSM (Microscopia Confocal de Varredura a Laser) confirmou a encapsulação do óleo-resina de copaíba dentro da matriz polimérica. A etapa II foi a encapsulação do óleo-resina de copaíba pela técnica de Extração com Fluido Supercrítico de Emulsões (SFEE), a partir da emulsão selecionada na etapa I (menor diâmetro da gota e maior estabilidade cinética). Inicialmente foram avaliadas a vazão de CO2 e de emulsão, mantendo constantes temperatura, pressão e tempo de extração do solvente. O diâmetro do bocal coaxial utilizado para injetar a emulsão ao sistema SFEE foi de 177,8 ?m. Após selecionar a condição da suspensão com menor concentração residual de acetato de etila, foi realizado outro estudo variando o tempo de extração do solvente, com o intuito de maximizar a taxa de remoção do solvente orgânico da suspensão na SFEE. A suspensão com a menor concentração de acetato de etila foi submetida à secagem. Os resultados obtidos evidenciaram uma redução na concentração de acetato de etila de 79588 (concentração de acetato de etila no início da emulsão) para 1484,5 ppm, atingindo desta forma o nível permitido pela FDA (Food and Drug Administration), que é de 5000 ppm por dia. Além disso, verificou-se que, quanto menor concentração de acetato de etila na suspensão, menor a recuperação de ?-cariofileno e maior perda de óleo-resina no frasco de coleta. O tamanho das partículas suspensas mostrou pouca variação em relação ao tamanho das gotas da emulsão injetada no sistema SFEE. Verificou-se também que as partículas secas apresentaram características semelhantes às das partículas caracterizadas na etapa I. Finalmente, a etapa III consistiu no fracionamento do óleo-resina de copaíba com CO2 supercrítico, com o intuito de concentrar sesquiterpenos e ácidos diterpênicos. Primeiramente foram avaliados os efeitos da pressão e do material adsorvente na composição das frações recuperadas. Posteriormente, com o intuito de recuperar o óleo-resina retido nos materiais adsorventes utilizados no SFF (Fracionamento com Fluido Supercrítico), foi realizada uma extração de Soxhlet empregando acetato de etila seguido de etanol. Os resultados mostraram que a pressão e os materiais adsorventes tiveram efeito nas cinéticas de fracionamento e na composição química das frações. Também foi observada a produção de frações mais purificadas de ?-cariofileno com a zeólita 13X a 9 MPa. Esta condição também permitiu concentrar e purificar o ácido copálico, que permaneceu adsorvido mesmo após a dessorção com CO2 supercrítico, e foi recuperado por extração Soxhlet com acetato de etilaAbstract: This work was divided in three stages. Stage (I) consisted in the formation of emulsions containing oleoresin from copaiba (Copaifera officinalis), using modified starches as stabilizers. The effects of modified starch concentration (g/L), oleoresin concentration (mg/mL) and oleoresin/water ratio (%, v/v) in the average diameter of the droplets were investigated. Sonication time and ultrasonic power were fixed at 6 min and 480 W, respectively. The formulation that provided the lowest droplet diameter was selected for a second planning, varying ultrasonic power and the sonication time. The emulsions with higher kinetic stability and lowest droplet diameter were subjected to drying by freeze-drying and spray-drying. Both drying techniques produced amorphous particles with different sizes and low humidity. Also, high encapsulation efficiency and high stability against thermal degradation were achieved. The morphological analysis indicated that the nature of the modified starches did not affect its microstructure, but drying techniques produced particles with different external microstructures. The CLSM (Confocal Laser Scanning Microscopy) analysis confirmed the encapsulation of copaiba oleoresin within the polymer matrix. Stage II of this work was the encapsulation of copaiba oleoresin by Supercritical Fluid Extraction of Emulsions (SFEE), from the emulsion selected in Stage I (lower droplet diameter and higher kinetic stability). Initially, CO2 and emulsion flow rates were evaluated, maintaining temperature, pressure and solvent extraction time constant. The diameter of the coaxial nozzle used to inject the emulsion into SFEE system was 177.8 ?m. After selecting the condition of suspension with the lowest residual ethyl acetate concentration, another study was carried out, varying the solvent extraction time, to maximize the rate of organic solvent removal from the suspension in SFEE. The suspension with the lowest concentration of ethyl acetate was subjected to drying. The results showed a reduction in the ethyl acetate concentration from 79588 (ethyl acetate concentration at the start of the emulsion) to 1484.5 ppm, thus reaching the level allowed by the FDA (Food and Drug Administration), which is 5000 ppm per day. Also, it was found that the lower the concentration of ethyl acetate in the suspension, the lower the recovery of ?-caryophyllene and the greater the loss of oleoresin in the collection flask. The size of the suspended particles showed little variation from the droplet size of the emulsion injected into the SFEE system. It was also verified that the dried particles showed similar characteristics to the particles characterized in Stage (I). Finally, Stage III of this thesis consisted in the fractionation of copaiba oleoresin with supercritical CO2, to concentrate sesquiterpenes and diterpenic acids. First, the effects of pressure and adsorbent material on the composition of the recovered fractions were evaluated. Next, to recover the oleoresin retained in the adsorbent materials used in SFF (Supercritical Fluid Fractionation), a Soxhlet extraction was performed using ethyl acetate followed by ethanol. The results showed that pressure and adsorbent materials influenced the fractionation kinetics and the chemical composition of the fractions. The production of purified fractions of ?-caryophyllene with zeolite 13X at 9 MPa was verified. This condition also allowed concentrating and purifing copalic acid, which remained adsorbed even after desorption with supercritical CO2 and was recovered by Soxhlet extraction with ethyl acetateDoutoradoEngenharia de AlimentosDoutor em Engenharia de AlimentosCAPE

Synthesis of Micro- and Nanoparticles in Sub- and Supercritical Water: From the Laboratory to Larger Scales

Featured Application This review on hydrothermal particle synthesis is mainly oriented to new researchers or research groups that are attracted by the promising future of this technology. This review gives an interesting overview. The use of micro- and nanoparticles is gaining more and more importance because of their wide range of uses and benefits based on their unique mechanical, physical, electrical, optical, electronic, and magnetic properties. In recent decades, supercritical fluid technologies have strongly emerged as an effective alternative to other numerous particle generation processes, mainly thanks to the peculiar properties exhibited by supercritical fluids. Carbon dioxide and water have so far been two of the most commonly used fluids for particle generation, the former being the fluid par excellence in this field, mainly, because it offers the possibility of precipitating thermolabile particles. Nevertheless, the use of high-pressure and -temperature water opens an innovative and very interesting field of study, especially with regards to the precipitation of particles that could hardly be precipitated when CO(2)is used, such as metal particles with a considerable value in the market. This review describes an innovative method to obtain micro- and nanoparticles: hydrothermal synthesis by means of near and supercritical water. It also describes the differences between this method and other conventional procedures, the most currently active research centers, the types of particles synthesized, the techniques to evaluate the products obtained, the main operating parameters, the types of reactors, and amongst them, the most significant and the most frequently used, the scaling-up studies under progress, and the milestones to be reached in the coming years

Classical and reactive molecular dynamics: Principles and applications in combustion and energy systems

Molecular dynamics (MD) has evolved into a ubiquitous, versatile and powerful computational method for fundamental research in science branches such as biology, chemistry, biomedicine and physics over the past 60 years. Powered by rapidly advanced supercomputing technologies in recent decades, MD has entered the engineering domain as a first-principle predictive method for material properties, physicochemical processes, and even as a design tool. Such developments have far-reaching consequences, and are covered for the first time in the present paper, with a focus on MD for combustion and energy systems encompassing topics like gas/liquid/solid fuel oxidation, pyrolysis, catalytic combustion, heterogeneous combustion, electrochemistry, nanoparticle synthesis, heat transfer, phase change, and fluid mechanics. First, the theoretical framework of the MD methodology is described systemically, covering both classical and reactive MD. The emphasis is on the development of the reactive force field (ReaxFF) MD, which enables chemical reactions to be simulated within the MD framework, utilizing quantum chemistry calculations and/or experimental data for the force field training. Second, details of the numerical methods, boundary conditions, post-processing and computational costs of MD simulations are provided. This is followed by a critical review of selected applications of classical and reactive MD methods in combustion and energy systems. It is demonstrated that the ReaxFF MD has been successfully deployed to gain fundamental insights into pyrolysis and/or oxidation of gas/liquid/solid fuels, revealing detailed energy changes and chemical pathways. Moreover, the complex physico-chemical dynamic processes in catalytic reactions, soot formation, and flame synthesis of nanoparticles are made plainly visible from an atomistic perspective. Flow, heat transfer and phase change phenomena are also scrutinized by MD simulations. Unprecedented details of nanoscale processes such as droplet collision, fuel droplet evaporation, and CO2 capture and storage under subcritical and supercritical conditions are examined at the atomic level. Finally, the outlook for atomistic simulations of combustion and energy systems is discussed in the context of emerging computing platforms, machine learning and multiscale modelling

New generation of continuous hydrothermal flow synthesis materials for environmental applications

The demands for new materials such as carbonaceous nanomaterials and their nanocomposites that are produced in a more efficient, economical, and environmentally friendly manner, as well as the need to integrate them into applications that address global issues, is a current challenge. The focus of this doctoral research project was to develop faster, cleaner synthetic methods to produce materials with superior physical and chemical properties utilising sustainable and/or renewable precursors, ultimately delivering solutions to challenges in environmental applications and beyond. This was accomplished using a continuous hydrothermal flow synthesis approach. Continuous hydrothermal flow synthesis is an unconventional method that uses supercritical water as a reaction environment, and it was designed for the very fast, continuous flow production of high quality and high quantity nanomaterials, with real-time control over the process parameter (temperature, pressure, precursors concentration, pH, and flow rates). For the first time, by developing and applying CHFS methodologies, carbon quantum dots (CQDs) and nitrogen-doped carbon quantum dots (NCQDs) were synthesized. The CHFS CQDs and NCQDs were produced from biomass-related precursors: glucose and citric acid; the synthetic process can be classified not only as green but sustainable too. The reduction of graphene oxide with a non-corrosive and reusable reducing agent (formic acid) was achieved. The reduced graphene oxide with different oxygen content (17.37 at%, 16.82 at% and 13.3 at%) was synthesised. A new CHFS method to produce nano TiO2 (anatase) has been developed to pioneer the one-pot synthesis of carbonaceous nanocomposites of TiO2 with NCQDs and reduced graphene oxide (rGO). All the materials produced in this study have been characterised and tested in environmental-related applications: a) toxic ions sensing (CQDs, NCQDs) with promising limits of detection for hexavalent chromium (LODCQDs= 3.62 ppm and LODNCQDs=0.365 ppm), b) graphene-related membrane-based water treatment with good performances, and photocatalysis where the TiO2 and its carbonaceous nanocomposites were tested for photodegradation of methylene blue with excellent conversions and rates constants (the best photocatalyst, TiO2-NCQDs-rGO(1), showed a conversion of 93.45% and a rate constant of 25.24 x10-5 s-1). This research project designed and engineered new promising carbonaceous materials, expanding the CHFS portfolio to new frontiers. The as-prepared materials exhibited superior physical, chemical, and morphological characteristics demonstrating their potential for environmental applications and beyond

Inhibition of metal dusting corrosion on Fe-based alloy by combined near surface severe plastic deformation (NS-SPD) and thermochemical treatment

Combined NS-SPD and thermochemical treatment has been used to improve the metal dusting corrosion resistance of Incoloy 800. After testing under infinite carbon activity for 20−100 h, carbon was not found in the NS-SPD region while corrosion products formed in the non-NS-SPD region. The improved resistance is a result of the NS-SPD yielding a high density of defects in the deformation zone that developed into an ultra-fine-grained structure near the surface during the subsequent thermochemical treatment. These microstructural changes increase the effective diffusion coefficient for Cr in the alloy, hence promoting the formation of a highly protective oxide scale.publishedVersio

Impregnation of polycarbonate with copper nanoparticles using supercritical CO2

Studio sulla produzione di pellet di polycarbonate caricati con nanoparticelle di rame utilizzando il metodo di impregnazione supercritica. In particolare un metodo di impregnazione a 2 step è stato studiatoope