Investigation of the application of polylactic acid-calcium phosphate composite materials as novel periodontal barrier membranes

The ultimate aim of periodontal treatment is to regenerate the tissue lost during the disease process, thereby restoring the aesthetics and function of the periodontium. Guided tissue regeneration (GTR) is one technique that is used clinically to promote tissue regeneration. The technique employs a membrane to create space in the appropriate surgical site to produce periodontal regeneration. However there may be considerable potential to improve the outcomes of this technique by development of novel membrane materials. The aim of the studies described in this thesis was to investigate the potential of polylactic acid-calcium phosphate (PLA-Ca P) composite materials to be developed into a GTR membrane with increased potential for producing periodontal regeneration. Ca P materials included nano-hydroxyapatite (n-HA) and ß tri-calcium phosphate (ß-TCP). PLA-Ca P composite films were produced by the solvent casting method. The Ca P powders and the PLA-Ca P composite films were characterized. The degradation of PLA-Ca P composites was analysed in phosphate buffer saline (PBS). The bioactive potential of the composite films was determined in simulated body fluid (SBF). The growth and differentiation of PDL cells and osteoblasts were assessed on PLA-nHA composite films and the ability of these films to carry platelet derived growth factor (PDGF) and its effect on osteoblast growth was investigated. Further, fibre reinforced PLA-HA composite membranes were fabricated and their mechanical strength and kinetics of protein interactions were investigated. Finally mandibular alveolar bone profiles were analyzed to define the possible shapes required for manufacture of GTR membranes. Results showed that Ca P decreased the degradation and increased the bioactivity of the PLA-Ca P composite films. The cell proliferation on composite films containing 10 wt % nHA was high when compared to PLA films. However, cell proliferation decreased with increase in nHA concentration. The highest alkaline phosphate activity (ALP) was shown by cells on composite films containing 70 wt % nHA. The PDGF added to the PLA-nHA composite films retained its activity and increased the proliferation of osteoblasts. The flexural strength was high for the fibre reinforced PLA-HA composite membranes, containing maximum number of PLA fibres laid at 0°. The fibre reinforced membranes containing HA showed gradual and sustained protein release compared to fibre reinforced membranes without HA. The analysis of alveolar bone profiles of different patients showed marked similarities between each other, suggesting that only a few membrane shapes may be required to fit most patients in clinical use. These studies demonstrate the potential of fibre reinforced PLA-HA composite material to be used for the production of preshaped GTR membranes with favourable properties to increase periodontal regeneratio

Development Of A Multifunctional Catalyst For Combined Esterification And Transesterification Of Used Vegetable Oil

In this study, heterogeneous catalysts were used to catalyze the transesterification reaction. Two solid catalysts were prepared. Calcium on Zeolite Y and sulfated zarconia. Sulfated zarconia was prepared using the solvent free method in which zirconylcholride was mixed with ammonium sulfate

Gravitational Properties of the Proca Field

We study various properties of a Proca field coupled to gravity through minimal and quadrupole interactions, described by a two-parameter family of Lagrangians. St\"uckelberg decomposition of the effective theory spells out its model-dependent ultraviolet cutoff, parametrically larger than the Proca mass. We present pp-wave solutions that the model admits, consider linear fluctuations on such backgrounds, and thereby constrain the parameter space of the theory by requiring null-energy condition and the absence of negative time delays in high-energy scattering. We briefly discuss the positivity constraints$-$derived from unitarity and analyticity of scattering amplitudes$-$that become ineffective in this regard.Comment: 23 pages, revised positivity-bound analysis, references adde

Ergonomic Immobilization Frame for Radiotherapy

The primary purpose of this project is to demonstrate that patients can be safely immobilized using air in the general torso area so that radiation can be administered to that region. The primary target will be to treat tumors in the lungs and liver. By immobilizing patients during treatment it allows for the radiation to be consistent in targeting the desired region of the body, which would not be the case if the patient was moving. Air was chosen as the desired medium to immobilize the patient because of comfort and it provides an easy medium for radiation to travel through which does not interfere with the radiation. Through research the limiting factor of human body was the pulmonary cycle which was determined to be approximately 0.15 Psi. In order to use air for immobilization airbags were incorporated as a means to hold the air and once pressurized would be used as the restraint force on the patient. As a means to demonstrate that air in fact could be used to immobilize a patient a prototype of a radiation chamber was built to provide a proof of concept. The radiation chamber frame was built to completely encapsulate the patient 360 degrees. The two airbags were placed in the frame which provides complete immobilization of the patient from all angles. The patient had to be standing while the radiation was being administered in order to target certain areas which could not be included if the patient was sitting or lying down. A circular frame was the desired shape of the frame because it allows for radiation to enter and exit the chamber at the same angle regardless of where it is administered. The radiation chamber requires the use of radiation safe materials in any given area where the frame comes into contact with radiation, for this reason non-metallic materials were used. The chamber prototype was built using wood and plexiglass. Finite element analysis simulated an allowable applied pressure of 6.0 Psi applied to the shell. Prior to the given prototype, there was no means available to immobilize a patient while standing for radiotherapy. Experimental tests demonstrated that a person could be immobilized in the general torso area using air.https://scholarscompass.vcu.edu/capstone/1214/thumbnail.jp

A Possible Link between the Electroweak Phase Transition and the Dark Matter of the Universe

A possible connection between the dark matter and strong first order electroweak phase transition, which is an essential ingredient of the electroweak baryogenesis, has been explored in this thesis. It is shown that the extension of the Standard Model's minimal Higgs sector with an inert $SU(2)_L$ scalar doublet can provide light dark matter candidate and simultaneously induce a strong first order phase transition. There is however no symmetry reason to prevent the extension using scalars with higher $SU(2)_L$ representations. Therefore, by making random scans over the models' parameters, we show, in the light of electroweak physics constraints, strong first order electroweak phase transition and the possibility of having a sub-TeV cold dark matter candidate, that the higher representations are rather disfavored compared to the inert doublet. This is done by computing generic perturbativity behavior and impact on electroweak phase transitions of higher representations in comparison with the inert doublet model. Explicit phase transition and cold dark matter phenomenology within the context of the inert triplet and quartet representations are used for detailed illustrations

The factors driving continuance intention to online shopping (e-loyalty): behaviour differences in the case of Saudi Arabia

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University LondonThis study proposes a model of e-shopping continuance intentions that incorporate the revised technology acceptance model and expectation confirmation theory to measure continuance online shopping intentions within Saudi Arabia. Using structural equation modelling to confirm the model fit, and a 463-person sample, the author finds that perceived usefulness, enjoyment, and subjective norms determine online shopping continuance intentions, across male (30% of the sample) and female (70%) respondents. The structural weights are largely equivalent, yet the regression paths from site quality to perceived usefulness and perceived usefulness to continuation intentions are not invariant across the research sample. This research thus moves beyond consideration of online shopping intentions to include factors that may affect online shopping continuance. The research model is able to explain 61% of the variance in intentions to continue shopping online. Therefore, online strategies cannot ignore either direct or indirect differences in continuance intentions due to behaviour differences among shoppers in Saudi Arabia. With the high percentages of participants from the main populated regions in Saudi Arabia, the research model can be generalized across Saudi Arabia. Thus, the research has added to the limited literature on online repurchase intention or continuance intention by testing the proposed model in a context that has never before been tested. Furthermore, few prior studies use SEM as their methodological approach, and even fewer apply invariance analysis to verify behavioural differences based on gender, regional, education, e-shopping experience, and e-shopping spending with a sample obtained from Saudi Arabia. This study addresses these various knowledge gaps. Moreover, this thesis provides managers with useful and important information they can use to plan their Web sites and marketing strategies. The findings will help e-retailers to identify which web site attributes influence consumers’ e-shopping intentions, and thus improve the effectiveness of their e-shopping sites. A more thorough understanding of e-shopping continuance intention helps e-retailers to entice e-shoppers to shop online more, and entice non-online shoppers to shop online. Keywords: Internet shopping, e-shopping, technology acceptance, behavioural differences, continuance intentions, online shopping, Saudi Arabia.Government of Saudi Arabia represented by the Minister of Higher Educatio