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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
11

Dissolved oxygen and pH monitoring within cell culture media using a hydrogel microarray sensor

Lee, Seung Joon 15 May 2009 (has links)
Prolonged exposure of humans and experimental animals to microgravity is known to be associated with a variety of physiological and cellular disturbances. With advancements in aerospace technology and prolonged space flights, both organism and cellular level understanding of the effects of microgravity on cells will become increasingly important in order to ensure the safety of prolonged space travel. To understand these effects at the cellular level, on-line sensor technology for the measurement and control of cell culture processes is required. To do this measurement, multiple sensors must be implemented to monitor various parameters of the cell culture medium. The model analytes used in this study were pH and dissolved oxygen which have physiological importance in a bioreactor environment. In most bioprocesses, pH and dissolved oxygen need to be monitored and controlled to maintain ionic strength and avoid hypoxia or hyperoxia. Current techniques used to monitor the value of these parameters within cell culture media are invasive and cannot be used to make on-line measurements in a closed-loop system. In this research, a microfabricated hydrogel microarray sensor was developed to monitor each anlyte. Either a pH or an oxygen sensitive fluorescent agent was immobilized into a hydrogel structure via a soft lithography technique and the intensity image of the sensor varied from the target analyte concentration. A compact detection system was developed to quantify concentration of each analyte based on the fluorescence image of the sensor. The system included a blue LED as an illumination source, coupling optics, interference filters and a compact moisture resistant CCD camera. Various tests were performed for the sensor (sensitivity, reversibility, and temporal/spatial uniformity) and the detection system (temporal/spatial stability for the light source and the detector). The detection system and the sensor were tested with a buffer solution and cell culture media off-line. The standard error of prediction for oxygen and pH detection was 0.7% and 0.1, respectively, and comparable to that of commercial probes, well within the range necessary for cell culture monitoring. Lastly, the system was coupled to a bioreactor and tested over 2 weeks. The sensitivity and stability of the system was affordable to monitor pH and dissolved oxygen and shows potential to be used for monitoring those analytes in cell culture media noninvasively.
12

Electrokinetic concentration enrichment within a microfluidic device integrated with a hydrogel microplug

Dhopeshwarkar, Rahul Rajesh 15 May 2009 (has links)
A simple and efficient technique for the concentration enrichment of charged species within a microfluidic device was developed. The functional component of the system is a hydrogel microplug photopolymerized inside the microfluidic channel. The fundamental properties of the nanoporous hydrogel microplug in modulating the electrokinetic transport during the concentration enrichment were investigated. The physicochemical properties of the hydrogel plug play a key role in determining the mode of concentration enrichment. A neutral hydrogel plug acts as a physical barrier to the electrophoretic transport of charged analytes resulting in size-based concentration enrichment. In contrast, an anionic hydrogel plug introduces concentration polarization effects, facilitating a size and charge-based concentration enrichment. The concentration polarization effects result in redistribution of the local electric field and subsequent lowering of the extent of concentration enrichment. In addition, an electroosmotic flow originating inside the pores of the anionic hydrogel manipulates the location of concentration enrichment. A theoretical model qualitatively consistent with the experimental observations is provided.
13

Preparation of Copolymers of Acrylic Acid and Acrylamide for Copper (II) Capture from Aqueous Solutions

Zhang, Yudong 01 October 2009 (has links)
Cross-linked copolymers of acrylic acid (sodium acrylate) and acrylamide were synthesized by free radical polymerization. The copolymer hydrogel was studied for capture of copper ion from aqueous solution. Effects of macromolecular structure (i.e., content of the acrylic acid, the quantity of the carboxyl groups neutralized with sodium hydroxide, and the degree of cross-linking) on water-sorption and copper ion uptake were investigated. With an increase in the content of acrylic acid (sodium acrylate), the copper sulfate uptake increases, and water sorption decreases quickly and then slowly increases when the acrylic acid content is high enough. The copper ion uptake is accompanied with a release of sodium ions from the copolymer. Increasing the percentage of the carboxyl groups neutralized by sodium hydroxide will increase the uptake of copper sulfate and water. With an increase in the content of the cross-linking agent, both copper sulfate uptake and water sorption decrease. Even though valence of copper ion is two times that of sodium ion, the copper ions sorption and sodium ions release do not follow a simple ion exchange relation because of insertion of acrylamide co-monomers in macromolecular chain. When copper ions interact with carboxyl groups in the copolymer to form chelating complexes, the water sorption decreases substantially. An analysis of adsorption isotherm indicates that at relatively low concentrations of CuSO4 in water, the copper ion sorption into the copolymer follows the Langmuir model. The wide angle X-ray diffraction (WAXD) data reveal that the copper sulfate sorbed in the hydrogel is not in crystalline state.
14

Electrokinetic concentration enrichment within a microfluidic device integrated with a hydrogel microplug

Dhopeshwarkar, Rahul Rajesh 15 May 2009 (has links)
A simple and efficient technique for the concentration enrichment of charged species within a microfluidic device was developed. The functional component of the system is a hydrogel microplug photopolymerized inside the microfluidic channel. The fundamental properties of the nanoporous hydrogel microplug in modulating the electrokinetic transport during the concentration enrichment were investigated. The physicochemical properties of the hydrogel plug play a key role in determining the mode of concentration enrichment. A neutral hydrogel plug acts as a physical barrier to the electrophoretic transport of charged analytes resulting in size-based concentration enrichment. In contrast, an anionic hydrogel plug introduces concentration polarization effects, facilitating a size and charge-based concentration enrichment. The concentration polarization effects result in redistribution of the local electric field and subsequent lowering of the extent of concentration enrichment. In addition, an electroosmotic flow originating inside the pores of the anionic hydrogel manipulates the location of concentration enrichment. A theoretical model qualitatively consistent with the experimental observations is provided.
15

Struktur, Eigenschaften und Reaktionen oxidierter Dextrane

Sowinski, Heike, January 2008 (has links)
Tübingen, Univ., Diss., 2008.
16

Zum Quellungsdruck von polymeren Hydrogelen

Wack, Holger January 2007 (has links)
Zugl.: Kiel, Univ., Diss., 2007
17

Hydrogel nanoparticles and assemblies for bioapplications

Gaulding, Jeffrey Clinton 27 August 2014 (has links)
Hydrogels are cross-linked networks of highly hydrophilic polymer chains. When reduced to colloidal dimensions, particles of this sort are termed “microgels�? and both discrete particles and ensembles have intriguing properties. Microgels can be made to be susceptible to numerous environmental stimuli, such as temperature and pH. The resultant changes in the network hydration lead to characteristic swelling responses which can have great impact on properties of the gel network such as the porosity, hydrophilicity, stiffness, or particle-particle packing. The multitude of responsive stimuli; the architectural versatility of discrete particles; and the variety of particle ensembles have made the study of microgels and their assemblies a very rich field. Primarily due to their physiological softness and the aforementioned versatility, responsive microgels are of great interest as a material to address the daunting challenges facing the next generation of healthcare. This dissertation describes investigations into hydrogel nanoparticles and assemblies thereof, with the goals of expanding their utility in applications such as drug delivery and non-fouling interfaces through the development of novel materials to both extend their synthetic versatility and to probe their underlying properties. Physiologically-relevant degradable cross-linking within microgels is studied, though the incorporation of hydrolytically degradable or reduction-responsive cross-links. More complex structures are demonstrated for both types of cross-linking as synthetic and architectural control enables additional functional microgel designs. Microgel assemblies, particularly thin films, have been demonstrated to have numerous desirable properties for biological applications, such as reduced cell attachment, drug delivery, and self-healing capabilities. This dissertation includes additional fundamental studies of microgel films, both in their synthesis, such as methods for depositing films onto colloidal substrates, and in their application, as investigations into the origins and critical factors for self-healing films. Further, the cell-resistant properties of microgel multilayers are studied and evidence suggests that the viscoelastic or mobile character of the films is likely the main factor that directs cell adhesion. The work in this dissertation serves to both expand our toolset with regard to the functional synthesis of microgels and assemblies and to improve our fundamental understanding of phenomena of interest for a variety of potential applications. Both of these should serve to allow the enormous potential of hydrogel nanoparticles and their assemblies to be more efficiently tapped for a wide range of applications in the field of biomaterials.
18

Nové biodegradovatelné hydrogely / New Biodegradable Hydrogels

Vetrík, Miroslav January 2015 (has links)
The key tool for tissue engineering is the scaffold that supports cells for new tissue growth. Materials used for creating scaffolds are based on polymeric materials, carbon nanofibers, ceramics, and metals and their alloys. In my thesis, I describe the synthesis and characterization of new biodegradable hydrogels containing biodegradable crosslinks and biodegradable nanofibrous materials intended for scaffolds for tissue engineering. I also describe the preparation of macroporous hydrogels intended for neural tissue healing. In the first portion of this thesis, I examine a hydrogel based on a pH- responsive crosslinker. This hydrogel is stable at basic and neutral pHs but is degradable at pH < 7.4. The degradation rate of this hydrogel can be tailored. This hydrogel can be utilized as an esophageal stent or as a targeted drug release system in the stomach. The second portion of this thesis focuses on a biodegradable hydrogel designed for neural tissue repair. This hydrogel is composed of copolymers of N-(2- hydroxypropyl)methacrylamide and a newly synthesized biodegradable crosslinker based on 6,6'-dithiodinicotinic acid. This hydrogel can be stored in a neutral environment without degradation. Its long-term storage capability is another great advantage for clinical applications. During storage,...
19

Použití alternativních surovin pro pěstování okrasných dřevin v kontejnerech

Frlausová, Monika January 2014 (has links)
Was experimentally evaluated the effect of selected nursery growing media development and quality of the crops produced. Added alternative components were observed coir, peat and coconut hydrogel. As a model plant was chosen for the experiment Cotoneaster buxifolius ,Nana', an attempt was one year. Parameters were evaluated: plant height, average length of shoots, number of shoots, root collar diameter, the volume of the root system. The raw material, which should in the future to replace peat in growing nursery substrates showed a positive effect on the quality and quantity of the crops.
20

Desenvolvimento de tecnologia de biofabricação com laser infravermelho para recobrimento de próteses articulares com hidrogel / Development of biofabrication technology with Infrared laser to coating of articular prostheses with hydrogel

Passos, Marcele Fonseca, 1986- 19 August 2018 (has links)
Orientador: Passos, Marcele Fonseca / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Química / Made available in DSpace on 2018-08-19T02:23:46Z (GMT). No. of bitstreams: 1 Passos_MarceleFonseca_M.pdf: 15093576 bytes, checksum: fc209e9f43b60067bf5b99f169881ea4 (MD5) Previous issue date: 2011 / Resumo: Na área dos materiais, um campo em crescente expansão é o desenvolvimento de hidrogéis poliméricos para aplicações biomédicas. Entre a grande classe de hidrogéis poliméricos estudados, o poli 2-hidróxi etil metacrilato (pHEMA) recebe especial atenção, devido a sua biocompatibilidade, alta hidrofilicidade e fácil preparação. Para aplicação como substituinte da cartilagem articular natural em próteses articulares, as quais, normalmente apresentam como principal componente (substrato) o polietileno de ultra alto peso molecular (PEUAPM), a adesão do sistema (hidrogel - substrato) ainda é um parâmetro a ser avaliado. Modificações adequadas no material e considerações de projeto, no entanto, podem melhorar a aderência do conjunto, via embricamento mecânico. Dentro de um grupo multidisciplinar e em ascensão, Instituto Nacional de C&T em Biofabricação - BIOFABRIS, este projeto, teve como objetivo, desenvolver novos biomateriais, usando técnicas de engenharia para obtenção de dispositivos biomédicos (próteses e órteses ortopédicas). Foi desenvolvida uma tecnologia de biofabricação visando melhorar as propriedades mecânicas dos hidrogéis de pHEMA, bem como obter uma adesão adequada entre este polímero e a superfície articular artificial, a fim de minimizar o desgaste sofrido pelos componentes que constituem os dispositivos ortopédicos, um dos principais fatores que geram sua falência. Usando a técnica de biofabricação, foi possível obter hidrogéis de pHEMA desde a simulação do produto até a caracterização final, para aplicações específicas: cartilagem articular artificial, foco principal da dissertação; e, como cartilagem reconstrutiva, atuando como suporte ao crescimento de células (hidrogéis porosos). A avaliação do mecanismo de polimerização e reticulação do pHEMA, o calor específico e a condutividade térmica da solução do 2-hidróxi etil metacrilato (HEMA) foram obtidos via técnica de Calorimetria Exploratória Diferencial. Tais parâmetros serviram de subsídio para a simulação computacional, a qual permitiu estimar os parâmetros do processo de reticulação do pHEMA, como potência do laser a 30 W e tempo reacional de 120 segundos, na temperatura de 399 K. As propriedades térmicas, como temperatura de transição vítrea e degradação, apresentaram valores similares aos dados encontrados na literatura, na faixa de 109 e 118 ºC, e na faixa de 354 e 376 ºC, respectivamente. Os resultados obtidos do coeficiente de atrito do par tribológico PEUAPM-pHEMA apresentaram valores altos, contudo, a tecnologia de biofabricação desenvolvida neste projeto, mostrou-se uma importante ferramenta para a obtenção de biomateriais para aplicações diversificadas / Abstract: In the materials field, a rapidly expanding field is the development of polymeric hydrogels for biomedical applications. Among the large class of polymeric hydrogels studied, poly 2-hydroxy ethyl methacrylate (pHEMA) receives special attention. For application as replacements of natural articular cartilage in articular prostheses, which usually present as a main component (substrate) the polyethylene of ultra high molecular weight (UHMWPE), the adhesion of system (hydrogel - substrate) is still a parameter to be evaluated. Appropriate modifications in the material and design considerations, however, can improve the adhesion of the set by embrication mechanic. Within a multidisciplinary group and on the rise, National Institute of C & T in Biofabrication -BIOFABRIS, this project aims to develop new biomaterials using engineering techniques for obtaining biomedical devices (prostheses and orthoses, orthopedic). It was developed a technology aiming to both improve the mechanical properties of pHEMA hidrogel as well as to obtain proper adhesion between this polymer and the artificial articular surface in order to minimize the wear suffered by the components that constitute the orthopedic devices, one of the main factors that cause bankruptcy. Using the technique of biofabrication was possible to obtain hydrogels pHEMA from the simulation of the product until the final characterization, for specific applications: artificial articular cartilage, the main focus of the dissertation, and as a reconstructive cartilage, acting as a support cell growth (porous hydrogels). The evaluation of the mechanism of polymerization and crosslinking of pHEMA, the specific heat and thermal conductivity of the solution of 2-hydroxy ethyl methacrylate (HEMA) were obtained by the technique of Differential Scanning Calorimetry. These parameters served as input to the computer simulation, which allowed to estimate the process parameters of pHEMA crosslinking, such as laser power 30 W and the reaction time of 120 seconds at a temperature of 399 K. The thermal properties and glass transition temperature and degradation, showed values similar to those found in the literature, to know, in the range of 109 and 118 °C, and in the range of 354 and 376 °C, respectively. The obtained results of the friction coefficient for the tribological pair UHMWPE-pHEMA have demonstrated high values, however, the biofabrication technology developed in this project, was important a tool for obtaining biomaterials for different applications / Mestrado / Desenvolvimento de Processos Químicos / Mestre em Engenharia Química

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