Alternative methods to control the molecular weight and short chain branching distribution of polyethylene were investigated. The ability to produce polyolefins with multimodal microstructural distributions using single catalyst/single reactor set-up is very attractive and could, in principle, be used to produce polyolefin resins with advanced molecular architecture. In this thesis, resins with controlled microstructures were produced, characterized and properties tested in order to develop a better understanding of polymerization structure-property relationships. Copolymerizations of ethylene and 1-hexene were carried out with an in-situ supported metallocene catalyst. Copolymers were produced with different alkylaluminum activators and the effect on molecular weight and short chain branching distributions was examined. It was found that different activator types produce polymer with unimodal and narrow molecular weight distributions but with very different short chain branching distributions. Each activator exhibits unique comonomer incorporation characteristics to produce bimodal short chain branching distributions with the use of a single activator. By using individual and mixed activator systems, it is possible to control the short chain branching distributions of the resulting copolymers while maintaining narrow molecular weight distributions. To further investigate the capabilities of this in-situ supported catalyst system, an experimental design was carried out to study the effect of polymerization conditions on the catalyst activity and microstructure of poly(ethylene-co-1-octene). The parameters investigated were: polymerization temperature, monomer pressure, chain transfer to hydrogen, comonomer/ethylene feed ratio and concentration of alkylaluminum. The effect of each parameter on the catalyst activity, comonomer incorporation and molecular weight distribution was investigated. The results obtained were not typical of a conventional single-site catalyst. The copolymerization system was sensitive to all of the parameters and many interactions were evident. The most prominent effect was the catalyst response to temperature. As the temperature was decreased, the short chain branching distributions of the copolymers became broad and bimodal. Overall, it was found that a wide range of microstructures could be produced, ranging from copolymers with low and high 1-octene content with unimodal to broad short chain branching distributions, and from low to high molecular weight with narrow to broad molecular weight distributions. To examine the effect of these broad short chain branching distributions on the polymer properties, a series of poly(ethylene-co-1-hexene) resins with very distinct, and in some cases bimodal crystalline distributions, were synthesized. The attractive feature of the resins in this study is that their molecular weight distributions are similar but each possesses a different short chain branching distribution, thus effectively minimizing the effect of molecular weight on the properties investigated. It was found that the tensile properties of a copolymer could be controlled by the ratio of the crystalline species present in the sample. In this study, a balance of stiffness and toughness was exhibited by a copolymer containing a large proportion of crystalline material and a small fraction of material of lower crystallinity. A series of poly(ethylene-co-1-octene) resins with tailored molecular weight and short chain branching distributions were synthesized with a heterogeneous metallocene catalyst in a two-stage polymerization process. Blends of high molecular weight copolymer and low molecular weight homopolymer and reverse blends of low molecular weight copolymer and high molecular weight homopolymer were produced. The physical properties of these resins were tested for their dynamic mechanical (tensile) and rheological properties. Increasing the copolymer content in the blend resulted in a decrease in stiffness. However, the energy dampening properties of these blends benefit from the presence of the copolymer. It was also confirmed that the melt flow properties of polymers mostly depend on their molecular weight distribution. Regardless of the comonomer content, the melt viscosities decreased with the addition of low molecular weight polymer.

Wear of the polyethylene (PE) bearing surface and wear particle-induced osteolysis (bone resorption) can lead to failure of modular total knee replacements and make expensive revision surgery necessary. Gamma-in-air sterilization of the PE insert and having a modular tibial component are both risk factors for excessive backside wear that contribute to osteolysis and implant failure. The overall wear (backside and topside) of modular total knee replacements has been subjected to considerable research in order to avoid such implant failure. The investigations reported in the present thesis evaluated both the clinical and in vitro wear performance of modular total knee replacements. The clinical investigations included damage assessment of retrieved PE inserts. A semi-quantitative grading method was developed and used to assess backside surface damage on 52 PE inserts retrieved from contemporary total knee replacement surgeries. Statistical analyses, such as univariate and multiple linear regression analysis, were performed to identify factors that influence backside damage including implant design features and patient characteristics. The damage features on the retrieved tibial PE inserts were also assessed with surface characterization techniques, such as scanning electron microscopy, energy dispersive X-ray analysis, and surface profilometry. To reduce surface damage and thus wear, PE inserts should be either gas-plasma or ethylene-oxide sterilized, used with polished tibial trays and held in place with a partial-peripheral locking mechanism. Synovial fluid samples were aspirated from a total of twenty patients and some basic biochemical analyses were performed. The total protein concentration, protein constituent fractions, the level of osmolality, and trace element concentrations were measured and compared with the same characteristics of four serum lubricants that were frequently used in simulator wear testing to mimic synovial fluid. In vitro investigations were conducted to explore the effects of some major constituents of the serum lubricants on the wear rate using a knee simulator apparatus. Increased protein constituent degradation led to increased wear. Such findings suggested that a protein layer acted as a boundary lubricant to protect the PE surfaces of knee implants. The protein constituent fractions of alpha calf serum (ACS) were similar to those measured for synovial fluid. These ACS lubricants were used in further wear studies in which hyaluronic acid (HA) and phosphate buffer solution (PBS) were successively added. The PBS was used in place of the distilled water to generate a serum lubricant with a clinically relevant level of osmolality. The thermal stability of the ACS lubricants and synovial fluid were measured. The thermal stability of the ACS lubricant that contained HA and PBS was about the same as that of human synovial fluid. The simulator wear rate of PE was significantly influenced by both HA and PBS. In further investigations, sodium azide, which has been used to inhibit microbial growth in simulator wear testing, was shown to be highly ineffective. Microbial contamination was recognized and the organism responsible was identified using standard microbiological methods. The use of an antibiotic-antimycotic mixture as the microbial inhibitor in the ACS + PBS + HA lubricant created a sterile environment and thus very clinically relevant environment for wear testing. The content of this thesis represents a comprehensive data collection on retrieval analysis and lubricant-specific knee simulator wear testing of modular total knee replacements. A more clinically relevant lubricant composition for simulator wear testing was proposed (U.S. patent Serial number 60/899,894; pending since February 9th, 2007) that improved upon the current guideline from the International Standards Organization for knee simulator wear testing. The present thesis should serve as a guide for the surgeon, researcher and the implant manufacturer to evaluate retrieved implant components and to select lubricant additives for wear testing that closely mimics the in vivo wear conditions.

The synthesis of four homologous anthraquinones (AQ I-IV) bearing increasing lengths of polyethylene glycol (PEG) side chains and their binding to AT- and GC-rich DNA hairpins are reported. The molecules were designed such that the cationic charge is at a constant position and the ethylene glycol units chosen to allow significant increases in size with minimal changes in hydrophobicity. The mode and affinity of binding were assessed using circular dichroism (CD), nuclear magnetic resonance (NMR), surface plasmon resonance (SPR), and isothermal titration calorimetry (ITC). The binding affinity decreased as the AQ chain length increased along the series with both AT- and GC-rich DNA. ITC measurements showed that the thermodynamic parameters of AQ I-IV binding to DNA exhibited significant enthalpy-entropy compensation. The enthalpy became more favorable while the entropy became less favorable. The correlation between enthalpy and entropy may involve not only the side chains, but also changes in the binding of water and associated counterions and hydrogen bonding. The interactions of AQ I-IV with GC-rich DNA have been studied via molecular dynamics (MD) simulations. The geometry, conformation, interactions, and hydration of the complexes were examined. As the side chain lengthened, binding to DNA reduced the conformational space, resulting in an increase in unfavorable entropy. Increased localization of the PEG side chain in the DNA groove, indicating some interaction of the side chain with DNA, also contributed unfavorably to the entropy. The changes in free energy of binding due to entropic considerations (-3.9 to -6.3 kcal/mol) of AQ I-IV were significant. The kinetics of a homologous series of anthraquinone threading intercalators, AQT I-IV with calf thymus DNA was studied using the stopped-flow. The threading mechanisms of the anthraquinones binding to DNA showed sensitivity to their side chain length. Fitting of the kinetic data led to our proposal of a two step mechanism for binding of AQT I, bearing the shortest side chain, and a three step mechanism for binding of the three longer homologs. Binding involves formation of an externally bound anthraquinone-DNA complex, followed by intercalation of the anthraquinone for AQT I-IV, then isomerization to another complex with similar thermodynamic stability for AQT II-IV.

In Lembang, a farming community on western Java, family-sized, plug-flow, polyethylene biogas systems fed with cow dung, are being used as an integrated solution to issues related to energy, agriculture and waste management. Through simple, on-farm research and observation, a number of key problems have been addressed and improvements made to the design. Due to the large supply of cow dung in the area, and the potential to spread the benefits of the technology beyond the homes of dairy farmers, the feasibility of developing a communal, polyethylene biogas system for several households, has been investigated. Experiments on small model-digesters were combined with observations of full-scale biogas systems in use. Measurement equipment and techniques were constructed and developed, in order to measure biogas production and other relevant process parameters. Results indicate that a communal system can be an appropriate choice, but only under a certain set of circumstances.

Alternative methods to control the molecular weight and short chain branching distribution of polyethylene were investigated. The ability to produce polyolefins with multimodal microstructural distributions using single catalyst/single reactor set-up is very attractive and could, in principle, be used to produce polyolefin resins with advanced molecular architecture. In this thesis, resins with controlled microstructures were produced, characterized and properties tested in order to develop a better understanding of polymerization structure-property relationships. Copolymerizations of ethylene and 1-hexene were carried out with an in-situ supported metallocene catalyst. Copolymers were produced with different alkylaluminum activators and the effect on molecular weight and short chain branching distributions was examined. It was found that different activator types produce polymer with unimodal and narrow molecular weight distributions but with very different short chain branching distributions. Each activator exhibits unique comonomer incorporation characteristics to produce bimodal short chain branching distributions with the use of a single activator. By using individual and mixed activator systems, it is possible to control the short chain branching distributions of the resulting copolymers while maintaining narrow molecular weight distributions. To further investigate the capabilities of this in-situ supported catalyst system, an experimental design was carried out to study the effect of polymerization conditions on the catalyst activity and microstructure of poly(ethylene-co-1-octene). The parameters investigated were: polymerization temperature, monomer pressure, chain transfer to hydrogen, comonomer/ethylene feed ratio and concentration of alkylaluminum. The effect of each parameter on the catalyst activity, comonomer incorporation and molecular weight distribution was investigated. The results obtained were not typical of a conventional single-site catalyst. The copolymerization system was sensitive to all of the parameters and many interactions were evident. The most prominent effect was the catalyst response to temperature. As the temperature was decreased, the short chain branching distributions of the copolymers became broad and bimodal. Overall, it was found that a wide range of microstructures could be produced, ranging from copolymers with low and high 1-octene content with unimodal to broad short chain branching distributions, and from low to high molecular weight with narrow to broad molecular weight distributions. To examine the effect of these broad short chain branching distributions on the polymer properties, a series of poly(ethylene-co-1-hexene) resins with very distinct, and in some cases bimodal crystalline distributions, were synthesized. The attractive feature of the resins in this study is that their molecular weight distributions are similar but each possesses a different short chain branching distribution, thus effectively minimizing the effect of molecular weight on the properties investigated. It was found that the tensile properties of a copolymer could be controlled by the ratio of the crystalline species present in the sample. In this study, a balance of stiffness and toughness was exhibited by a copolymer containing a large proportion of crystalline material and a small fraction of material of lower crystallinity. A series of poly(ethylene-co-1-octene) resins with tailored molecular weight and short chain branching distributions were synthesized with a heterogeneous metallocene catalyst in a two-stage polymerization process. Blends of high molecular weight copolymer and low molecular weight homopolymer and reverse blends of low molecular weight copolymer and high molecular weight homopolymer were produced. The physical properties of these resins were tested for their dynamic mechanical (tensile) and rheological properties. Increasing the copolymer content in the blend resulted in a decrease in stiffness. However, the energy dampening properties of these blends benefit from the presence of the copolymer. It was also confirmed that the melt flow properties of polymers mostly depend on their molecular weight distribution. Regardless of the comonomer content, the melt viscosities decreased with the addition of low molecular weight polymer.

Wear of the polyethylene (PE) bearing surface and wear particle-induced osteolysis (bone resorption) can lead to failure of modular total knee replacements and make expensive revision surgery necessary. Gamma-in-air sterilization of the PE insert and having a modular tibial component are both risk factors for excessive backside wear that contribute to osteolysis and implant failure. The overall wear (backside and topside) of modular total knee replacements has been subjected to considerable research in order to avoid such implant failure. The investigations reported in the present thesis evaluated both the clinical and in vitro wear performance of modular total knee replacements. The clinical investigations included damage assessment of retrieved PE inserts. A semi-quantitative grading method was developed and used to assess backside surface damage on 52 PE inserts retrieved from contemporary total knee replacement surgeries. Statistical analyses, such as univariate and multiple linear regression analysis, were performed to identify factors that influence backside damage including implant design features and patient characteristics. The damage features on the retrieved tibial PE inserts were also assessed with surface characterization techniques, such as scanning electron microscopy, energy dispersive X-ray analysis, and surface profilometry. To reduce surface damage and thus wear, PE inserts should be either gas-plasma or ethylene-oxide sterilized, used with polished tibial trays and held in place with a partial-peripheral locking mechanism. Synovial fluid samples were aspirated from a total of twenty patients and some basic biochemical analyses were performed. The total protein concentration, protein constituent fractions, the level of osmolality, and trace element concentrations were measured and compared with the same characteristics of four serum lubricants that were frequently used in simulator wear testing to mimic synovial fluid. In vitro investigations were conducted to explore the effects of some major constituents of the serum lubricants on the wear rate using a knee simulator apparatus. Increased protein constituent degradation led to increased wear. Such findings suggested that a protein layer acted as a boundary lubricant to protect the PE surfaces of knee implants. The protein constituent fractions of alpha calf serum (ACS) were similar to those measured for synovial fluid. These ACS lubricants were used in further wear studies in which hyaluronic acid (HA) and phosphate buffer solution (PBS) were successively added. The PBS was used in place of the distilled water to generate a serum lubricant with a clinically relevant level of osmolality. The thermal stability of the ACS lubricants and synovial fluid were measured. The thermal stability of the ACS lubricant that contained HA and PBS was about the same as that of human synovial fluid. The simulator wear rate of PE was significantly influenced by both HA and PBS. In further investigations, sodium azide, which has been used to inhibit microbial growth in simulator wear testing, was shown to be highly ineffective. Microbial contamination was recognized and the organism responsible was identified using standard microbiological methods. The use of an antibiotic-antimycotic mixture as the microbial inhibitor in the ACS + PBS + HA lubricant created a sterile environment and thus very clinically relevant environment for wear testing. The content of this thesis represents a comprehensive data collection on retrieval analysis and lubricant-specific knee simulator wear testing of modular total knee replacements. A more clinically relevant lubricant composition for simulator wear testing was proposed (U.S. patent Serial number 60/899,894; pending since February 9th, 2007) that improved upon the current guideline from the International Standards Organization for knee simulator wear testing. The present thesis should serve as a guide for the surgeon, researcher and the implant manufacturer to evaluate retrieved implant components and to select lubricant additives for wear testing that closely mimics the in vivo wear conditions.

The compound 2,6-anthracenedicarboxylic acid is used as a comonomer for the synthesis of poly(ethylene terephthalate). The resulting copolymers are characterized and further functionalized by Diels-Alder grafting or crosslinking through the anthracenate unit. Diels-Alder reaction is used to graft small molecules and oligomers endcapped with maleimide as dienophiles on to poly(ethylene terephthalate-co-2,6-anthracenedicarboxylate),PET-co-A. Maleimide-capped poly(ethylene glycol) is grafted onto PET-co-A to improved its hydrophilicity. 2,6-Anthracenedicarboxylic acid is also incorporated into the known liquid crystalline polymer, LCP, poly(4-oxybenzoate-co-1,4-phenylene isophthalate), HIQ40. The resulting copolymer, poly(4-oxybenzoate-co-1,4-phenylene isophthalate-co-2,6-phenylene anthracenate), HIQ40-co-A, shows LCP behavior. These HIQ40-co-A copolymers are grafted with maleimide end-capped monomers and polymers andcrosslinked with bismaleimides through a Diels-Alder mechanism.

Embryonic stem cells (ESCs) are pluripotent cells derived from the inner cell mass of the blastocyst that can give rise to cells of the ectoderm, endoderm and mesoderm lineages. Once isolated from the blastocyst, ESCs can be cultured indefinitely in vitro in an undifferentiated state or can be induced to differentiate. In the case of mouse ESCs (mESCs), the cytokine leukemia inhibitory factor (LIF) is added to culture media to maintain pluripotency and is removed to induce differentiation. Although it is known that extracellular matrix (ECM) components influence stem cell maintenance, proliferation and differentiation, the precise effects of ECM environments on embryonic stem cell behavior have not been systematically studied. The main purpose of this thesis project was to investigate the behavior of undifferentiated mESCs cultured in different 3D hydrogel matrices and to determine whether viscoelastic and biochemical variations in the matrices differentially affect the ability of stem cells to self-renew; that is, retain their pluripotency or undifferentiated phenotype. Their behavior in 3D environments was compared to mESC behavior in traditional 2D culture. In addition, a new method of casting hydrogels in polydimethylsiloxane (PDMS) molds was developed in order to efficiently cast multiple hydrogels of varying sizes and shapes. The findings of this thesis project will benefit both the scientific and engineering community as it encourages researchers to re-evaluate the quality of standard 2D embryonic stem cell culture methods versus potentially novel and advantageous 3D hydrogel culture methods.

Transport of amorphous and semi-crystalline, oriented, annealed and non-annealed PET films has been studied using pure and mixed gas/vapor feeds to understand the influence of flavor molecules on the efficacy of the barrier material. Methanol has been used as the flavor molecule simulant, and pure methanol vapor sorption studies show swelling and relaxation effects in the polymer. Multi-component transport of O2/methanol and O2/CO¬2/methanol mixtures, performed at different activities of methanol, shows that vapor induced plasticization leads to increases in O2 and CO2 permeability. Annealed, semi-crystalline PET is shown to be most resistant to plasticization effects. It has been shown that the non-annealed film is less stable despite similar crystallinity as the annealed film due to the presence of orientation related stress in the material. Presence of crystals also restricts the chain motion, and helps suppress the plasticization effects. The results have been compared with the predictions of the dual mode model for multi-component mixtures. Plasticization effects at the high activities have been analyzed within the framework of the free volume theory. It has been proposed that only the densified domains of a glassy polymer be considered when evaluating fractional free volume change due to swelling in the polymer-penetrant system. The free volume parameter- BA has been evaluated for O2 and CO2 in PET and is found to be different from that for other high permeability polymers.

In this studing, application of the digital image correlation method (DIC) for determining the coefficient of thermal expansion (CTE) of Indium Tin Oxide/Polyethylene Terephthalate(ITO/PET) thin film/flexible substrate was proposed and the effects of thinkness variations of ITO and PET, respectively, on the CTE of the specimens was disscussed. The observation range of experimental temperature was chosen from room temperature to the glass transfer temperature of PET, 70¢J. A novel DIC experimental process for reducing the errors caused from the variations of the refractive index of the surrounding heated air was proposed. As a result, the experimental error of CTE measurement was reduced form 10~17% to less than 5%. The experimental results showed that the CTE of ITO/PET specimen is anisotropic. Futhermore, the CTE of an ITO/PET specimen will be increased by decreasing the thinkness of PET flexible substrate, and increased by increasing the thinkness of ITO film - which means decreasing the surface resistance of ITO film.