Amino-functionalised polystyrene microspheres are promising candidates as delivery systems due to their unique features, tunable surface functionalities, and controllable release of the cargo. Herein several strategies for the conjugation of biologically relevant cargoes to these microspheres and their biological evaluation are described. Firstly, dispersion and suspension polymerisation methods were applied for the synthesis of these devices. Subsequently, these polymeric particles were employed in multistep solid phase synthesis to conjugate a broad range of cargoes. The capability of the resulting constructs to cross the cell membrane and deliver the desired cargo was evaluated by flow cytometry and confocal microscopy. Additionally, the effect of these particles on cell viability was determined. Moreover a chemical strategy for dual fuctionalisation allowed the production of microspheres capable of carrying two cargos simultaneously (e.g. a biologically relevant cargo and a tracking fluorophore). Several strategies were used to transport biomolecules such as peptides and oligonucleotides inside cells. Cell-impermeable peptides with neuroprotective activity were conjugated to microspheres to facilitate their internalisation and they were efficiently delivered into neuroblastom cells (SH-SY5Y) without affecting their therapeutic activity. In addition, several microsphere-mediated oligonucleotide delivery strategies were investigated. As a first approach, siRNA was successfully attached to microspheres via thiol linkage or via electrostatic interaction (by formation of polycationated microspheres-siRNA microplexes). Using both strategies EGFP expression was efficiently down-regulated in cervical cancer cells permanently expressing EGFP (HeLa-EGFP) following beadfection. Additionally embryonic stem (ES) cells were beadfected with siRNA linked to microspheres by amide formation and essential transcription factors implicated in cell renewal and differentiation were successfully silenced, exceeding the silencing capabilities of commercially available lipofection products. Furthermore, a novel approach for the intracellular delivery of plasmid DNA was designed. Following an easy protocol for the linearisation and functionalisation of the plasmid DNA, this was covalently coupled to beads and cells were homogeneously ‘beadfected’. Finally, the coupling of fluorogenic substrates for caspase-3 to microspheres allowed the in situ monitoring and quantification of apoptotic process within cells. In conclusion, these small particles are excellent devices for the efficient intracellular delivery of a broad range of cargoes.

A child, angry at concrete and strip malls, enjoying coffee from too many styrofoam cups.

Interfacial tension provides valuable information about polymer processes such as foaming, particle (pigment) suspension, wetting, and blending. Among the methods commonly used to measure surface tension, drop shape methods entail several advantages such as simplicity and versatility. The profile of the drop, which is determined by the balance between gravity and surface forces, is easily defined. The surface tension is obtained from the profile of the drop. Recent progress in image analysis and data acquisition systems makes it possible to digitalize drop images directly using a video frame grabber with a digital camera. The digital signals are easily analyzed using different algorithms to determine the surface/interfacial tension from the drop profile. This study concentrates on one of the drop methods, the pendant drop method, which involves the determination of a drop profile of one dense liquid suspended in another liquid at mechanical equilibrium. Despite theoretical simplicity of using sessile and pendant drops for determining the surface tension of polymer melts, research in this area is limited because of the experimental difficulty associated with maintaining equilibrium of highly viscous melts. This paper examines the surface tension of polystyrene melts using Axisymmetric Drop Shape Analysis (ADSA) at high temperatures. This thesis focuses on attaining a stable pendant drop during experiments and modifying experimental designs. The method is verified by experiments in the air and nitrogen, where reproducibility tests and statistical analyses are performed. The surface tension of polystyrene (PS) that melts in supercritical carbon dioxide is obtained while the gas solubility is correlated with the surface tension value determined under various conditions. The Sanchez-Lacombe (S-L) equation of state (EOS) is applied to estimate the Pressure-Volume-Temperature (PVT) data of the PS/supercritical-carbon-dioxide mixtures, which gives density data. The relationship between surface tension and density is described by the empirical Macleod equation. To characterize the stability of pendant drops formed by the polymer melt, the Bond number is found to be useful; in particular, a stable pendant drop is obtained when the Bond number is between 0.4 and 0.8. This thesis presents experimental results of the surface tension of polystyrene in supercritical carbon dioxide, together with theoretical calculations for a corresponding system. The surface tension is determined by Axisymmetric Drop Shape Analysis-Profile (ADSA-P), where a high pressure and temperature cell is designed and constructed to facilitate the formation of a pendant drop of polystyrene melt. Self-consistent field theory (SCFT) calculations are applied to simulate the surface tension of a corresponding system, and a good agreement with the experiment is obtained. The physical mechanisms for three main experimental trends are explained using SCFT, and none of the explanations depend on the configurational entropy of the polymer constituents. These calculations therefore rationalize the use of simple liquid models for the quantitative prediction of surface tensions of polymers. As pressure and temperature increase, the surface tension of polystyrene decreases. A linear relationship is found between surface tension and temperature, and between surface tension and pressure; the rate of surface tension change with temperature is dependent on pressure. A linear relationship is found between surface tension and temperature, and between surface tension and pressure within a temperature range of 170-210C and a pressure range of 500-2,000 psi. Two monodisperse polystyrenes of Mw ~ 100,000 and Mw ~400,000 and a polydisperse polystyrene were investigated to show the temperature and pressure effect on the surface tension in supercritical nitrogen. Regardless of the molecular weight and polydispersity, the surface tension of polystyrenes decreases as the pressure and temperature increase. Monodisperse polystyrene of a higher molecular weight has a higher surface tension by 6-9 mJ/m2 at each experimental condition. The surface tension dependence on temperature and on pressure is more significant for the higher molecular weight polystyrene; the surface tension has been varied more in the higher molecular weight polystyrene than in the lower molecular weigh polystyrene. For a polydisperse polystyrene, high surface tension values seem to be determined predominantly by its high molecular weight portion of polystyrene molecules. An empirical equation was generated to relate surface tension to the density difference between the polymer and supercritical nitrogen. This research should have implications in understanding polymer foaming processes and have application in various polymer engineering fields including polymer characterizations, polymer synthesis, and surface modifications.

Interfacial tension provides valuable information about polymer processes such as foaming, particle (pigment) suspension, wetting, and blending. Among the methods commonly used to measure surface tension, drop shape methods entail several advantages such as simplicity and versatility. The profile of the drop, which is determined by the balance between gravity and surface forces, is easily defined. The surface tension is obtained from the profile of the drop. Recent progress in image analysis and data acquisition systems makes it possible to digitalize drop images directly using a video frame grabber with a digital camera. The digital signals are easily analyzed using different algorithms to determine the surface/interfacial tension from the drop profile. This study concentrates on one of the drop methods, the pendant drop method, which involves the determination of a drop profile of one dense liquid suspended in another liquid at mechanical equilibrium. Despite theoretical simplicity of using sessile and pendant drops for determining the surface tension of polymer melts, research in this area is limited because of the experimental difficulty associated with maintaining equilibrium of highly viscous melts. This paper examines the surface tension of polystyrene melts using Axisymmetric Drop Shape Analysis (ADSA) at high temperatures. This thesis focuses on attaining a stable pendant drop during experiments and modifying experimental designs. The method is verified by experiments in the air and nitrogen, where reproducibility tests and statistical analyses are performed. The surface tension of polystyrene (PS) that melts in supercritical carbon dioxide is obtained while the gas solubility is correlated with the surface tension value determined under various conditions. The Sanchez-Lacombe (S-L) equation of state (EOS) is applied to estimate the Pressure-Volume-Temperature (PVT) data of the PS/supercritical-carbon-dioxide mixtures, which gives density data. The relationship between surface tension and density is described by the empirical Macleod equation. To characterize the stability of pendant drops formed by the polymer melt, the Bond number is found to be useful; in particular, a stable pendant drop is obtained when the Bond number is between 0.4 and 0.8. This thesis presents experimental results of the surface tension of polystyrene in supercritical carbon dioxide, together with theoretical calculations for a corresponding system. The surface tension is determined by Axisymmetric Drop Shape Analysis-Profile (ADSA-P), where a high pressure and temperature cell is designed and constructed to facilitate the formation of a pendant drop of polystyrene melt. Self-consistent field theory (SCFT) calculations are applied to simulate the surface tension of a corresponding system, and a good agreement with the experiment is obtained. The physical mechanisms for three main experimental trends are explained using SCFT, and none of the explanations depend on the configurational entropy of the polymer constituents. These calculations therefore rationalize the use of simple liquid models for the quantitative prediction of surface tensions of polymers. As pressure and temperature increase, the surface tension of polystyrene decreases. A linear relationship is found between surface tension and temperature, and between surface tension and pressure; the rate of surface tension change with temperature is dependent on pressure. A linear relationship is found between surface tension and temperature, and between surface tension and pressure within a temperature range of 170-210C and a pressure range of 500-2,000 psi. Two monodisperse polystyrenes of Mw ~ 100,000 and Mw ~400,000 and a polydisperse polystyrene were investigated to show the temperature and pressure effect on the surface tension in supercritical nitrogen. Regardless of the molecular weight and polydispersity, the surface tension of polystyrenes decreases as the pressure and temperature increase. Monodisperse polystyrene of a higher molecular weight has a higher surface tension by 6-9 mJ/m2 at each experimental condition. The surface tension dependence on temperature and on pressure is more significant for the higher molecular weight polystyrene; the surface tension has been varied more in the higher molecular weight polystyrene than in the lower molecular weigh polystyrene. For a polydisperse polystyrene, high surface tension values seem to be determined predominantly by its high molecular weight portion of polystyrene molecules. An empirical equation was generated to relate surface tension to the density difference between the polymer and supercritical nitrogen. This research should have implications in understanding polymer foaming processes and have application in various polymer engineering fields including polymer characterizations, polymer synthesis, and surface modifications.

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Thesis (M.S.)--University of Florida, 2006. / Title from title page of source document. Document formatted into pages; contains 61 pages. Includes vita. Includes bibliographical references.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2003. / Includes bibliographical references (leaves 23). Also available in electronic version. Access restricted to campus users.

Thesis (M.B.A.)--University of Hong Kong, 1984.

Residual stress distributions in injection moulded polystyrene plaques have been computed using various calculation methods based on procedures from the literature. Some of the mathematical procedures have been extended to provide improved analysis of the process. The results have been compared with measured distributions obtained using the layer removal technique. The purpose of this work was to resolve some of the disagreements between the measured residual stress distributions in injection moulded parts and those predicted by computations made in the literature. The calculations are made using the general purpose software "Mathcad". Various temperature, time and pressure dependent material models have been used to calculate the residual stress and they are compared. Special attention has been paid to choosing boundary conditions that match the moulding parameters used in the manufacture of the injection mouldings on which the measurements were made. Similarly, care has been taken to choose boundary conditions that correspond with the different actual storage times before analysis for the samples and also boundary conditions that correspond with the post-moulding conditioning. Measurements of residual stresses distributions were made on mouldings produced under conditions chosen to simplify the modelling requirements. The sensitivity of the calculations to the materials property data and to the boundary conditions used have been examined. The experimental verification includes examination of the postmoulding changes. The predicted residual stress distributions over the entire moulding and post-moulding history have been found to be in generally good agreement with the corresponding experimental results under various processing conditions and post-moulding changes. In particular, kinematic boundary conditions for the moulding conditions and the postmoulding conditions, due to different temperaturesa nd relaxation times of the polymer, have been found to be critical ingredients in the calculation of the residual stress distributions.

Thesis (MSc)--University of Stellenbosch, 2007 / Bibliography. Also available via the Internet.