2 resultados para Involuntary sterilization.
em Glasgow Theses Service
Resumo:
Poly(aryl-ether-ether-ketone) (PEEK) is a semi crystalline polymer which exhibits properties that make it an attractive choice for use as an implant material. It displays natural radiolucency, and MRI compatibility, as well as good chemical and sterilization resistance, both of which make it of particular interest in orthopaedic implants. However, PEEK has demonstrated poor cellular adhesion both in vitro and in vivo. This is problematic as implant surfaces that do not develop a layer of adhesive cells are at risk of undergoing fibrous encapsulation, which in turn leads to lack of a strong interface between the implant device and the patient tissue, which can in turn lead to failure of the implant and revision surgery . As incorporating nanotopography into a polymer surface has been demonstrated to be able to direct the differentiation behaviour of stem cells, a possible solution to PEEKs underlying issues with poor cellular response would be to incorporate specific nanoscale topography into the material surface through injection moulding, and then analysing if this is a viable method for addressing PEEKs issues with cellular response. In addition to nanoscale topography, the experimental PEEK surfaces were treated with oxygen plasma to address the underlying cytophobicity of the material. As this type of treatment has been documented to be capable of etching the PEEK surface, experiments were carried out to quantify the effect of this treatment, both on the ability of cells to adhere to the PEEK surface, as well as the effect it has upon the nanotopography present at the PEEK surface. The results demonstrated that there were a range of plasma treatments which would significantly improve the ability of cells to adhere to the PEEK surface without causing unacceptable damage to the nanotopography. Three different types of cells with osteogenic capacity were tested with the PEEK surfaces to gauge the ability of the topography to alter their behaviour: SAOS-2, osteoprogenitors and 271+ MSCs. Due to PEEKs material properties (it is non transparent, exhibits birefringence and is strongly autofluorescent) a number of histological techniques were used to investigate a number of different stages that take place in osteogenesis. The different cell types did display slightly different responses to the topographies. The SAOS-2 cells cultured on surfaces that had been plasma treated for 2 minutes at 200W had statistically significantly higher levels of von Kossa staining on the NSQ surface compared to the planar surface, and the same experiment employing alizarin red staining, showed a statistically significantly lower level of staining on the SQ surface compared to the planar surface. Using primary osteoprogenitor cells designed to look into if whether or not the presence of nanotopography effected the osteogenic response of these cells, we saw a lack of statistically significant difference produced by the surfaces investigated. By utilising HRP based immunostaining, we were able to investigate, in a quantitative fashion, the production of the two osteogenic markers osteopontin and osteocalcin by cells. When stained for osteocalcin, the SQ nanotopography had total percentage of the surface with stained material, average area and average perimeter all statistically significantly lower than the planar surface. For the cells that were stained for osteopontin, the SQ nanotopgraphy had a total percentage of the surface with stained material, average area and average perimeter all highly statistically significantly lower than those of the planar surface. Additionally, for this marker the NSQ nanotopography had average areas and average perimeters that were highly significantly higher than those of the planar surface. There were no significant differences for any of the values investigated for the 271+ MSC’s When plasma treatment was varied, the SAOS-2 cells demonstrated an overall trend i.e. increasing the energy of plasma treatment in turn leads to an increase in the overall percentage of staining. A similar experiment employing stem cells isolated from human bone marrow instead of SAOS-2 cells showed that for polycarbonate surfaces , used as a control, mineralization is statistically significantly higher on the NSQ nanopattern compared to the planar surface, whereas on the PEEK surfaces we observe the opposite trend i.e. the NSQ nanotopography having a statistically significantly lower amount of mineralization compared to the planar surface at the 200W 2min and 30W 1min plasma treatments. The standout trend from the PEEK results in this experiment was that the statistically significant differences on the PEEK substrates were clustered around the lower energy plasma treatments, which could suggest that the plasma treatment disrupted a function of the nanotopograhy which is why, as the energy increases, there are less statistically significant differences between the NSQ nanotopography and the Planar surface This thesis documents the response of a number of different types of cells to specific nanoscale topographies incorporated into the PEEK surface which had been treated with oxygen plasma. It outlines the development of a number of histological methods which measure different aspects of osteogenesis, and were selected to both work with PEEK, and produce quantitative results through the use of Cell Profiler. The methods that have been employed in this body of work would be of interest to other researchers working with this material, as well as those working with similarly autofluorescent materials.
Resumo:
Banks are often excluded in corporate finance research mainly because of the regulatory concerns. Compares to non-bank firms, banks are heavily regulated due to its special economic role of money and the uncertainty. Heavy regulation on banks could reduce the information asymmetry between the managers and investor by limiting the behaviour of banks at the time of the Seasoned Equity Offering (SEO), and by increasing the incentive for banks to avoid excessive risk-taking. Therefore, the market may be less likely to assume that bank issued securities signal information that the bank is overvalued compared to their non-bank counterparts. The objective of this thesis is therefore to examine commercial banks issued securities announcement effect. Three interrelated research questions are addressed in this thesis: 1) What is the difference in convertible bond announcement effect between banks and non-banks firm? 2) What is the difference in SEO announcement effect between banks and non-banks? 3) How do the stringency levels of bank regulation impact on the announcement effects of bank issued SEO? By using the U.S. convertible bond and SEO data from 1982 to 2012, I find that the bank issued a convertible bond and SEO announcement experience higher cumulative abnormal return than non-bank. This is consistent with the view that bank regulation reveals positive information about banks. Since banks are heavily regulated, the market is less likely to assume that the issuance of the convertible bond and SEO by banks signals information that is overvalued. These results are robust after controlling for a number of firm-, issue-, and market-specific characteristics. These results are robust by considering the different categories of non-bank industries by undertaking tests in relation to the differences in the CARS upon convertible bond/ SEO across industries, as well as the unbalanced sample between banks and non-banks by using the matched sample analysis. However, the relation between the stringency level of bank regulation and bank issued securities announcement effect may be nonlinear. As hypothesised, I find that bank regulation has an inverted U-shaped relation with the announcement effect of bank SEO by using the SEO data across 21 countries from 2001 to 2012. Under a less bank regulation environment, the market reacts more positively to the bank SEO announcement for an increase in the level of bank regulation. However, the bank SEO announcement effects become more negative if the bank regulation becomes too stringent. This inverted U-shaped relationship is robust after I use the exogenous cross-country, cross-year variation in the timing of the Basel II adoption as the instrument to assess the causal impact of bank regulation on SEO announcement effects. However, the stringency of regulation does not have a significant impact on the announcement effects of involuntary bank equity issuance.