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Hospital-acquired infections are a significant contributor to clinically-related morbidity and mortality. The majority of these infections are associated with the use of invasive medical devices, where urinary catheters account for ~36% of cases. Current preventative strategies have shown short-term (<7 days) success, however their long-term (>28 days) efficacy is unclear. This thesis explores the use of solution-cast polyurethane nanocomposite (PUNC) materials for antimicrobial drug delivery in urinary applications. It is hypothesised that the enhanced barrier properties of PUNCs, afforded by the incorporation of well-dispersed nanoinclusions, would allow for the sustained release of an antimicrobial agent. The objectives of this research were to investigate the antibacterial, mechanical and barrier properties of PUNCs incorporating various silicates modified using antimicrobials, hypothesised to also act as dispersing agents. Organically modified silicates (OMS) were prepared at 110%, 200% and 300% cationic exchange capacity (CEC) using the biocide, chlorhexidine diacetate (CHX), which was hypothesised to perform the dual functions; dispersant and antibacterial agent. Resulting OMS were incorporated at 1wt% and 5wt% loadings into a PU matrix to produce PUNCs; PEU-CHX1.1MMT, PEU-CHX2.0MMT, and PEU-CHX3.0MMT, respectively. CHX performed well as a dispersant, producing intercalated to partially exfoliated PUNCS. Antibacterial activity was dependent on OMS type and loading. PEU-CHX1.1MMT materials had poor antibacterial properties, but the addition of free CHX into the materials significantly improved their efficacy, demonstrating long-term sterility in an in vitro urinary tract (UT) model. PEU-CHX2.0MMT and PEU-CHX3.0MMT at 5wt% OMS loadings had partially exfoliated structures and excellent antibacterial activity. Cytotoxicity was evident in all materials, although to a lesser extent in the latter. Overall, intermediate OMS loadings of CHX2.0MMT would be expected to produce PUNCs with favourable antibacterial activity and cytocompatibility. PUNC drug-release profiles demonstrated sustained release compared to pristine PU, indicative of enhanced barrier properties. Their ultimate tensile properties decreased with increased OMS loading or addition of free CHX.Higher cationic-exchanged OMS caused significant reductions in strain. Young's modulus increased in response to higher %CEC OMS and loading. PUNCs show promise as antibacterial biomaterials for long-term urinary applications, where antimicrobial release and mechanical properties can be modulated through organic modification and OMS loading.

Zugl.: Stuttgart, Univ., Diss., 2009

Exposure to high impact velocity is the principle limiting factor of material performance in ballistic applications for use in civilian and defense industries. Graphene has emerged as a material of scientific interest due to its exceptional mechanical and thermal properties. When incorporated appropriately in a polymer matrix, graphene can significantly improve properties of polymers at small loading, while preserving the integrity of the polymer. Graphene based polymer nanocomposites provide a novel approach for material design for ballistic applications. The reliability of graphene/polymer nanocomposites on end use applications depends on understanding the effect of structure-property relationship of nanocomposite. A first approach to engineering nanocomposite for ballistic applications requires thorough understanding of physical properties change with incorporation of nanofillers in polymer matrix. One significant class of properties tremendously affected by inclusion of nanofiller is thermodynamic properties. Therefore, a first investigative study, we explore non-linear elastic behavior of graphene using first principle method, specifically Density-Functional Theory (DFT), and atomistic simulation. Using DFT, we calculated the equation of state (EOS) and elastic constants of graphene. The results are in agreement with experimental and other theoretical studies using DFT. However, accuracy of atomistic simulations is limited by empirical potentials. Nevertheless, general anisotropic, non-linear mechanical behavior of graphene is evident on both approaches. Additionally we use molecular dynamics (MD) simulations to study effect of graphene nanofiller on thermo‑mechanical properties of polyurethane. We have calculated thermodynamic, structural and mechanical properties of the amorphous polyurethane and its graphene nanocomposite. Our results show significant enhancement of thermal-mechanical properties. The final part of this dissertation, we used non-equilibrium molecular dynamics (NEMD) simulations to investigate dynamic response behavior of polyurethane and its graphene nanocomposite. Calculation of Hugoniot states of polyurethane agrees with experimental studies. However, a phase change phenomenon observed in experimental work was not visible in the present work. This is due to bond breaking and formation, which is a clear characterization of phase changes. Graphene-polyurethane nanocomposites demonstrate similar shock wave propagation illustrating characteristics of impeding shock wave when subjected to different particle velocities. This is due to graphene inducing stress concentrations in the composite, which may increase yield strength.

The synthesis route for the preparation of polyurethane using 100% sustainable materials was proposed. Lignin, one of the most abundance biomass on Earth, was used as one raw material, while the other one used is soybean oil. The reaction occurs in 3 steps, and is done in 2 different pot reactions. Briefly, purchased epoxidized soybean oil is carbonated to synthesize carbonated soybean oil. Then carbonated soybean oil was reacted with coupling agent, 3-aminopropyltriethoxysilane to produce urethane monomers. Finally, prepared urethane monomers were polymerized with lignin to produce sustainable polyurethane. Molecular structures were intensively analyzed using Fourier-Transform Infrared Spectroscopy and Nuclear Magnetic Resonance Spectroscopy. In addition, mechanical properties of prepared polyurethane were analyzed in order to evaluate its performance and compare with the polyurethanes available commercially. Our results indicated that the highest tensile strength achieved was 1.4 MPa, which is slightly below the typical tensile strengths of processible polyurethane. Chemical properties of all the intermediates and products and implications for future research are discussed.

Hospital-acquired infections are a significant contributor to clinically-related morbidity and mortality. The majority of these infections are associated with the use of invasive medical devices, where urinary catheters account for ~36% of cases. Current preventative strategies have shown short-term (<7 days) success, however their long-term (>28 days) efficacy is unclear. This thesis explores the use of solution-cast polyurethane nanocomposite (PUNC) materials for antimicrobial drug delivery in urinary applications. It is hypothesised that the enhanced barrier properties of PUNCs, afforded by the incorporation of well-dispersed nanoinclusions, would allow for the sustained release of an antimicrobial agent. The objectives of this research were to investigate the antibacterial, mechanical and barrier properties of PUNCs incorporating various silicates modified using antimicrobials, hypothesised to also act as dispersing agents. Organically modified silicates (OMS) were prepared at 110%, 200% and 300% cationic exchange capacity (CEC) using the biocide, chlorhexidine diacetate (CHX), which was hypothesised to perform the dual functions; dispersant and antibacterial agent. Resulting OMS were incorporated at 1wt% and 5wt% loadings into a PU matrix to produce PUNCs; PEU-CHX1.1MMT, PEU-CHX2.0MMT, and PEU-CHX3.0MMT, respectively. CHX performed well as a dispersant, producing intercalated to partially exfoliated PUNCS. Antibacterial activity was dependent on OMS type and loading. PEU-CHX1.1MMT materials had poor antibacterial properties, but the addition of free CHX into the materials significantly improved their efficacy, demonstrating long-term sterility in an in vitro urinary tract (UT) model. PEU-CHX2.0MMT and PEU-CHX3.0MMT at 5wt% OMS loadings had partially exfoliated structures and excellent antibacterial activity. Cytotoxicity was evident in all materials, although to a lesser extent in the latter. Overall, intermediate OMS loadings of CHX2.0MMT would be expected to produce PUNCs with favourable antibacterial activity and cytocompatibility. PUNC drug-release profiles demonstrated sustained release compared to pristine PU, indicative of enhanced barrier properties. Their ultimate tensile properties decreased with increased OMS loading or addition of free CHX.Higher cationic-exchanged OMS caused significant reductions in strain. Young's modulus increased in response to higher %CEC OMS and loading. PUNCs show promise as antibacterial biomaterials for long-term urinary applications, where antimicrobial release and mechanical properties can be modulated through organic modification and OMS loading.

The use of polymer nanocomposites (NCs) in industrial applications has received growing attention over the past decade due to their improved mechanical properties. However, little work has been reported which analyses the efficacy of NCs in biological applications, including drug delivery systems and implantable materials. This thesis examines the effect of the chemistry of the organic modifier (OM) on the structure and biological performance of poly(ether)urethane NCs (PUNCs) and the influence of the method of drug incorporation on interactions between drug and NC. Organically modified silicates (OMS) were prepared using OMs varying in terminal functionality and alkyl chain length. PUNCs were solvent cast containing 1 and 3wt% OMS and particle dispersion analysed using X-ray diffraction and transmission electron microscopy. Findings revealed that use of an OM with methyl terminal, dodecylamine (12CH3), resulted in superior dispersion of OMS compared with a carboxyl terminated OM, aminododecanoic acid (12COOH), of equivalent alkyl chain length. This is believed to result from increased self interaction of 12COOH compared with 12CH3. Additionally, increased alkyl chain length was shown to improve NC dispersion with a chain length of sixteen units resulting in the optimum dispersion with a partially exfoliated NC structure. Analysis of cellular interactions with the PUNCs revealed a significant difference in both fibroblast and platelet adhesion to NCs incorporating 12CH3 compared with 12COOH. Surface analysis using ToF-SIMS demonstrated the presence of 12CH3 fragments on the NC surface supporting the hypothesis that surface expressed OMs alter cellular interactions with the NC. Altering the alkyl chain length also affected cellular interaction with an alkyl chain length of twelve units or greater, substantially reducing fibroblast adhesion without affecting cell growth inhibition or viability. Incorporation of a model drug, crystal violet, into the PUNCs demonstrated a lower degree of disruption to OMS dispersion when loaded post NC fabrication compared with pre fabrication. This is believed to result from interactions between the drug and NC constituents which also impacted on drug release from the NC system. Results show PUNC properties and biological interactions can be modulated through OM variation and fabrication method, thus showing potential for use in biomedical applications.

The use of polymer nanocomposites (NCs) in industrial applications has received growing attention over the past decade due to their improved mechanical properties. However, little work has been reported which analyses the efficacy of NCs in biological applications, including drug delivery systems and implantable materials. This thesis examines the effect of the chemistry of the organic modifier (OM) on the structure and biological performance of poly(ether)urethane NCs (PUNCs) and the influence of the method of drug incorporation on interactions between drug and NC. Organically modified silicates (OMS) were prepared using OMs varying in terminal functionality and alkyl chain length. PUNCs were solvent cast containing 1 and 3wt% OMS and particle dispersion analysed using X-ray diffraction and transmission electron microscopy. Findings revealed that use of an OM with methyl terminal, dodecylamine (12CH3), resulted in superior dispersion of OMS compared with a carboxyl terminated OM, aminododecanoic acid (12COOH), of equivalent alkyl chain length. This is believed to result from increased self interaction of 12COOH compared with 12CH3. Additionally, increased alkyl chain length was shown to improve NC dispersion with a chain length of sixteen units resulting in the optimum dispersion with a partially exfoliated NC structure. Analysis of cellular interactions with the PUNCs revealed a significant difference in both fibroblast and platelet adhesion to NCs incorporating 12CH3 compared with 12COOH. Surface analysis using ToF-SIMS demonstrated the presence of 12CH3 fragments on the NC surface supporting the hypothesis that surface expressed OMs alter cellular interactions with the NC. Altering the alkyl chain length also affected cellular interaction with an alkyl chain length of twelve units or greater, substantially reducing fibroblast adhesion without affecting cell growth inhibition or viability. Incorporation of a model drug, crystal violet, into the PUNCs demonstrated a lower degree of disruption to OMS dispersion when loaded post NC fabrication compared with pre fabrication. This is believed to result from interactions between the drug and NC constituents which also impacted on drug release from the NC system. Results show PUNC properties and biological interactions can be modulated through OM variation and fabrication method, thus showing potential for use in biomedical applications.

München, Techn. Universiẗat, Diss., 2001.

This research has been concerned with investigating stress cracking phenomena which occur when thermoplastic polyurethanes (TPU's) are immersed in seawater at low temperatures. The investigation was concerned with testing the following hypothesis: a) that cracking of TPU was due to environmental stress cracking (ESC) and/or b) due to structure and morphology changes which occur during the ageing period. The combined effects of polyurethane chemical backbone, domain structure and crystallinity on stress cracking in TPU were studied. Further, the investigation concerned itself with studying, on stress cracking, the effects of storage conditioning the TPU granules prior to processing, the processing conditions and various postcuring treatments of TPU. Characterisation and analytical techniques employed to study the structure of TPU's investigated consisted of thermal analysis and X-ray diffraction. Molecular weight distribution was studied by gel permeation chromatography and solution viscosity techniques. Processing'was evaluated by melt flow index (MFI), injection moulding and extrusion. A new accelerated ageing test for environmental stress cracking has been developed which uses high pressures. Also, a new type of ESC chemical class of reagent which relates the hydrogen bonding parameter of the ESC agent to that of the TPU's has been discovered and a theory developed. A test method has been designed to measure, in active environments, the existence of a critical strain for all the TPU examined whether commercial or laboratory synthesised materials. Results show that the stress cracking in TPU's is due to the following events: (a) a large reduction in molecular weight due to the processing, and (b) the combined effects of applied stresses and the hydrolysis of the polymer. Molecular weight reduction in TPU's and their resistance to ESe was also found dependent on the preconditioning history of unprocessed TPU granules, as well as any postcuring operations applied to the processed materials. It has been established that, the ESe resistance of TPU's can be improved by (i) optimising processing conditions, (ii) by insertion of slight crosslinking or by selecting certain types of diisocyanates, specifically p~phenylene diisocyanate, and trans 1,4-cyclohexane diisocyanate. A mechanism to explain ESe of TPU's inactive and mild environments is also proposed.