Laser surface treatment of nylon 6,6 for the modification of wettability characteristics and subsequent enhancement of osteoblast cell response

The control of cell adhesion to synthetic polymers is a key factor in tissue engineering, resting on the ability to direct specific cell types to adhere and proliferate in order to stimulate tissue reconstruction. But often the surface properties are compromised for the sake of the bulk properties, leading to surfaces that do not support sufficiently the level of bioactivity required and accordingly the polymeric biomaterial will fail clinically. Laser treatment offers a unique means of enhancing the osteoblast cell response of the surface of a polymeric biomaterial, whilst keeping the already sufficient bulk properties intact. To this end, infra-red (IR) and ultraviolet (UV) lasers have been employed to modify the wettability characteristics of nylon 6,6, as wetting is often the primary factor dictating the adhesion and bonding potential of materials, as a route to enhancing the surface in terms of osteoblast cell response. What is more, modifying wettability characteristics in this way is a highly attractive means of estimating the biofunctionality of a polymer. IR (CO2) and UV (F2 and KrF excimer) lasers were employed to carry out two different processes: laser whole area irradiative processing and laser-induced patterning. With both CO2 and the excimer lasers changes in the wettability characteristics could be effected with subsequent enhancement of osteoblast cell response. This was also the case with both laser-induced patterning and laser whole area irradiative processing. Essentially, an approach has been established whereby the osteoblast cell response on the surfaces of laser treated nylon 6,6 can be predicted through the laser-induced wettability characteristics modification, particularly for the laser whole area irradiative processed nylon 6,6. This ultimately allows one to determine the osteoblast cell response of the laser surface treated nylon 6,6 surfaces directly from the laser operating parameters. In concurrence with established wetting theory the laser whole area irradiative processing of the nylon 6,6 surfaces caused increased surface roughness, increased surface oxygen content, increased polar component, γP , and increased total surface energy, γT ; thereby generating surfaces displaying reduced contact angle, θ, making the nylon 6,6 surfaces more hydrophilic. The laser-induced patterned samples differed from current theory insofar as the nylon 6,6 surfaces became less hydrophilic due to an increase in θ despite an increase in surface roughness, an increase in surface oxygen content, an increase in γP and an increase in γT . This phenomena can be explained by the transition in wetting regimes from a Wenzel regime to a mixed-state wetting regime. Nevertheless, collation of the wettability characteristics results revealed that θ was a strong correlative decreasing function of both γ P and γT , indicating that surface energy played a large role in determining the wetting nature of the nylon 6,6. It was found that for all laser whole area irradiative processed nylon 6,6 surfaces the osteoblast cell response was an increasing correlative and therefore predictive function of θ and was a decreasing function of γP . To an extent, the surface oxygen content and surface roughness could be used indirectly to foretell the osteoblast cell response of the nylon 6,6 surfaces. This is on account of the CO2 and KrF excimer laser whole area irradiative processing bringing about increased surface Abstract iii toxicity, which above a certain level hindered the osteoblast cell response. For the laser-induced patterned nylon 6,6 samples there did not appear to be any particular correlative trend between the modified surface parameters and osteoblast cell response. This can be accounted for by the transition in wetting regimes. Another important factor is that cell morphologies were modulated over all samples which suggests that varying surface parameters on account of laser surface treatment gave rise to variations in cell signaling. It was determined that θ, γP and γT all had very strong correlative relationships with the cytotoxicity. The cytotoxicity reduced upon an increase in θ until a minimum constant was achieved, whereas the cytotoxicity remained constant at low γP and γT until a point at which the cytotoxicity began to increase. These results are noteworthy as they allow one to deduce that, with constant cytotoxicity levels, the osteoblast cell response appeared to be modulated by the wettability characteristics. But once the cytotoxicity increased, the toxicity began to dominate and so negated the identified positive wettability characteristic correlations with osteoblast cell response. Practically, the surface roughness and surface oxygen content could be implemented indirectly to estimate the cytotoxicity. Increase in cytotoxicity was the result of the laser processing with higher fluences generating excessive melting. As a result of this, it is possible to deduce that there was a maximum threshold fluence, beyond which the toxicity of the nylon 6,6 began to dominate, giving rise to a less enhanced osteoblast cell response. On account of the correlative trends which have been identified between the laser surface treatment, wettability characteristics and osteoblast cell response of nylon 6,6 it is likely for one to have the ability to estimate the osteoblast cell response in vitro. This is significant as it indicates that laser surface modification of polymeric materials could have tremendous potential for application within the field of regenerative medicine

Primary schools at the crossroads : a study of primary schools abilities to implement educational change, with a particular focus on small primary schools

This thesis addresses the issue of primary schools' abilities to implement educational change and focuses, in particular, on small primary schools. A comparison is made between small and large primary schools, in order to determine whether there are differences between the ways in which each have adapted to and implemented changes.Whilst a series of educational changes since the Second World War have affected primary schools the thesis takes 1988 as a watershed date, since the Education Reform Act of that year made considerable statutory demands upon primary schools. The thesis examines, in particular, the ability of small schools to implement changes effectively, since this was questioned following the Act, and it seemed that this might precipitate closures and amalgamations at a faster rate than had previously been the case.The thesis is based upon research over an eight-year period, involving three postal surveys, a series of structured interviews, and a review of relevant literature. The focal point for much of the research is the headteacher, with all of the empirical work being focused on heads, since they have been central to the management of change in schools. Attention is also given, mainly through reviews of literature, to the role of the class eacher and the way in which this has changed in relation to that of the head.The thesis may be divided into two sections. In the first, the scene is set through an examination of the position of primary schools in general, and small primary schools in articular, before the Education Reform Act. This is followed by a review of published research and the author's empirical studies, in order to gain an understanding of the way n which schools have coped with the implementation of the Education Reform Act. The thesis ends with conclusions and recommendations which are based upon the research findings

The regulation and functions of ACSL3 and ACSL4 in the liver and hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a heterogeneous disease that often features dysregulated tumour lipid metabolism. ACSL3 and ACSL4 are two homologous long chain acyl-coenzyme A synthetases (ACSL) that preferentially catalyse the activation of monounsaturated and polyunsaturated fatty acids, respectively. Both enzymes are frequently overexpressed in HCC, and multiple reports have implicated ACSL4 in tumour progression. Increased expression of these isozymes in tumour cells can upregulate lipid metabolism through de novo lipogenesis, fatty acid β-oxidation and acyl chain remodelling of membrane phospholipids. We describe the subcellular functions of ACSL3 and ACSL4 in hepatocytes, and the transcriptional, epigenetic and post-translational mechanisms underpinning their regulation. We discuss the evidence that these enzymes can modulate hepatocarcinogenic signalling by oncoproteins, cell death by apoptosis or ferroptosis, and protein degradation through the ubiquitin-proteasome pathway. In addition, we survey how knowledge in this area may inform new approaches to the diagnosis and treatment of HCC and deepen our understanding of how lipid metabolic reprogramming can promote hepatic tumour growth

Dealing With Workplace Violence in Georgia’s Cities and Counties

Using the fears of workplace violence expressed by public employees as a reference point, this analysis examines the responses of city and county governments in the State of Georgia to the threat of external and internal violence. As a preliminary assessment of the responsiveness of city and county governments to the problem of workplace violence, officials in Georgia local governments with populations of 50,000 or higher were asked about both their perceptions of the threat and the specific actions taken by their governments to address it. While personal concerns and preparations were described, few officials indicated that their governments have formulated policies and implemented programs to address the problem. High percentages of officials, however, indicated that they expect more violence on a scale similar to the Murrah Federal Building bombing in Oklahoma City and that public employees are at greater risk than private sector employees

The Variable-Atmosphere Wave Tank

A facility was constructed for the study of water-entry, water-exit, and underwater trajectory behavior of small momentum-propelled missiles for varied trajectory launching angles, missile accelerations and velocities, wave fields and conditions of cavitation. A unique feature is the electromagnetic missile propulsion system. The facility is made principally of non-magnetic and electrically non-conducting materials to permit the determination of missile accelerating force from the reactive force on the launching coil

Magnetic Resonance

Contains reports on one research project