Zugl.: Kiel, Univ., Diss., 2007

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.

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.

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.

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.

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.

Metal-polymer nanocomposites consisting of gold nanorods and temperature-responsive hydrogel nanoparticulates were investigated for use in externally-controlled drug delivery systems. Several different thermo-responsive hydrogels including poly(N-isopropyl acrylamide) (PNIPAAm) and poly(N-isopropryl acrylamide-co-acrylic acid) (P(NIPAAm-co-AA)) nanoparticles were synthesized for these nanocomposites using an aqueous dispersion polymerization method. In addition, nanoparticles of interpenetrating polymer networks (IPN) composed of poly(acrylamide) (PAAm) and poly(acrylic acid) (PAA) were synthesized using a water-in-oil emulsion polymerization. Temperature-responsive equilibrium swelling behavior of nanoparticles with varying crosslinking densities was characterized using dynamic light scattering. IPN systems exhibited a positive swelling response upon heating while PNIPAAm and copolymer systems collapsed upon increase in temperature above the transition point. Nanoparticles were characterized using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) which demonstrated shape and morphology of polymer particles. Gold-polymer nanocomposites were formed by grafting gold nanorods to the surface of the polymer nanoparticles. Amine-functionalized gold nanorods were coupled to polymers using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (Sulfo-NHS) to activate carboxyl groups on the surface of the polymer nanoparticles. TEM confirmed successful formation of the metal-polymer nanocomposites. Loading and release of a model therapeutic were done to assess the potential use of the polymer component of the nanocomposite for drug delivery. Fluorescein, a model for chemotherapeutics, was loaded into P(NIPAAm-co-AA) polymer nanoparticulates. Loading of the compound was shown to be a function of crosslinking density in the polymer network. Maximum loading was achieved using nanoparticles synthesized with a 10 mol% crosslinker feed ratio with entrapment efficiencies of 80.0 % and loading capacities of 12.0 %. Cytotoxicity studies were performed using a NIH/3T3 mouse fibroblast cell model. Cell viabilities in presence of P(NIPAAm-co-AA) nanoparticles were comparable to (not statistically different than) controls at concentrations up to 4 mg/ml. Similarly, gold-polymer composite concentrations up to 0.5 mg/ml caused limited cell death. / text

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.

Tübingen, Univ., Diss., 2008.

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.