Mechanical properties of stent-graft materials

An aneurysm is a localized blood-filled dilatation of an artery whose consequences can be deadly. One of its current treatments is endovascular aneurysm repair, a minimally invasive procedure in which an endoprosthesis, called a stent– graft, is placed transluminally to prevent wall rupture. Early stent–grafts were custom designed for the patient through the assembling of off-the-shelf components by the operating surgeon. However, nowadays, stent–grafts have become a commercial product. The existing endoprostheses differ in several aspects, such as shape design and materials, but they have in common a metallic scaffold with a polymeric covering membrane. This article aims to gather relevant information for those who wish to understand the principles of stent–grafts and even to develop new devices. Hence, a stent–graft classification based on different characteristics is presented and the desired features for an ideal device are pointed out. Additionally, the materials currently in use to fabricate this type of endoprosthesis are reviewed and new materials are suggested.Fundação para a Ciência e a Tecnologia (FCT

Stabilized biomass ash as a sustainable substitute for commercial P-fertilizers

The reuse of biomass ash as a fertilizer is generally recognized as good practice with several environmental benefits. However, the possible presence of leachable heavy metals in this ash limits the potential extent of its application and the implementation of an appropriate legal framework. For the first time, a method to stabilize wood ash based on the use of other by‐products (coal fly ash and rice husk ash) is presented. No commercial chemicals are employed in the procedure. The results show that despite the initial presence of leachable heavy metals in the ash, the final obtained material is stable. In addition, the lowering of pH (from 13.5 to approximately 7.5) due to carbonation reactions and the addition of Ca‐rich ash increases the phosphorous availability compared with the starting wood ash and makes the obtained material suitable for use in soil fertilization. The sustainability of the new proposed technology is quantitatively discussed with regard to the differences in embodied energy and CO2 footprint of phosphorous between raw materials and stabilized wood ash. This work shows that the prospects for energy saving and CO2 footprint reduction using stabilized wood ash as a substitute for inorganic commercial P‐fertilizers are significant and offer a new way to reach these objectives. The simplicity of the method and the general availability of the by‐products employed in the stabilization also render the procedure suitable for applications in developing countries