Magazine Articles
The articles below are from the Spring 2010 Issue of the AILU Magazine
Case study: a failing laser mark
When cutting or marking with lasers, it is tempting to think that the beam simply removes or oxidises a portion of the material in question. However, the effect that a laser beam has on a material can be quite complex, sometimes giving rise to unexpected deleterious long term effects. By using surface chemical analysis and depth profiling techniques, it is possible to determine the composition changes that the beam has caused, both at the surface and in regions hidden from sight beneath the surface and thereby avoid expensive reworking.
The example of surface analysis and depth profiling described in this paper relates to laser marking. It was carried out at Loughborough Surface Analysis Ltd for a customer in the aerospace industry.
The solution established was the opposite of what the customer had, in fact, been trying. When faced with a laser mark that would not adhere, they had turned up the power of the laser and increased the duration of exposure in an attempt to burn an adherent mark in the surface of the metal. The answer was to do the opposite, reduce the power of the laser, producing a slightly lesser contrasting laser mark, but one that remained adherent.
Mike Petty - Loughborough Surface Analysis Ltd.
IMAGE: The laser-marked “E” from a “CE” mark on a stainless steel product shows spalling. The square areas within the dark mark are where analysis was carried out. The irregular areas of bright contrast are where the laser mark has spalled off. Courtesy - Loughborough Surface Analysis Ltd
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The coronary stent: current requirements and future needs
Coronary Artery Disease (CAD), is the result of atherosclerosis, an age-related cardiovascular disorder in which fatty materials such as cholesterol builds up in the arterial wall. This eventually causes a blockage of the coronary artery that supplies blood to the heart causing angina or myocardial infarction (commonly known as a heart attack). As such, CAD is the leading cause of mortality in developed nations and accounts for over 100,000 deaths annually in the UK alone. Alongside medical therapy, coronary intervention in the form of a coronary stent implant in conjunction with balloon angioplasty, has become a less invasive and highly effective treatment for CAD.
The first line treatment of CAD is drug therapy. Should the drug therapy be insufficient to manage the condition, one of the next choices of treatments is to insert a catheter with a deflated balloon mounted at its tip; the balloon is inflated to open up the narrowed artery. The problem with this procedure is that when the balloon is later deflated and removed the blood vessel tends to recoil elastically, causing re-narrowing of the artery. It is primarily to overcome this problem that a coronary stent is used, as illustrated in the figure.
The long-term presence of a coronary stent will inevitably affect the constriction and dilation of blood vessels and for this reason biodegradable stents made from polymer or metal (such as iron or magnesium) that dissolve over time have been trialled. Modification of the surface of bare-metal stents in order to eliminate the need of any coatings is a promising economic approach for improving stent biocompatibility. Other promising developments include more specific and customised stents, such as diseasespecific stents for diabetic patients and lesion-specific stents for bifurcations. In situ customised stents that are designed so that the clinician to choose the ideal sized stent at the bedside depending on the result of the angiography have also been considered. Finally, stents can also be used as tools for drug delivery. It seems that the biocompatibility of coronary stents remains a fertile field for novel innovations.
Dr Tao Wang - School of Biomedicine, University of Manchester
IMAGE: The process of coronary stent insertion
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