Development of biodegradable magnesium alloy stents with coating

Biodegradable stents are attracting the attention of many researchers in biomedical and materials research fields since they can absolve their specific function for the expected period of time and then gradually disappear. This feature allows avoiding the risk of long-term complications such as restenosis or mechanical instability of the device when the vessel grows in size in pediatric patients. Up to now biodegradable stents made of polymers or magnesium alloys have been proposed. However, both the solutions have limitations. The polymers have low mechanical properties, which lead to devices that cannot withstand the natural contraction of the blood vessel: the restenosis appears just after the implant, and can be ascribed to the compliance of the stent. The magnesium alloys have much higher mechanical properties, but they dissolve too fast in the human body. In this work we present some results of an ongoing study aiming to the development of biodegradable stents made of a magnesium alloy that is coated with a polymer having a high corrosion resistance. The mechanical action on the blood vessel is given by the magnesium stent for the desired period, being the stent protected against fast corrosion by the coating. The coating will dissolve in a longer term, thus delaying the exposition of the magnesium stent to the corrosive environment. We dealt with the problem exploiting the potentialities of a combined approach of experimental and computational methods (both standard and ad-hoc developed) for designing magnesium alloy, coating and scaffold geometry from different points of views. Our study required the following steps: i) selection of a Mg alloy suitable for stent production, having sufficient strength and elongation capability; ii) computational optimization of the stent geometry to minimize stress and strain after stent deployment, improve scaffolding ability and corrosion resistance; iii) development of a numerical model for studying stent degradation to support the selection of the best geometry; iv) optimization of the alloy microstructure and production of Mg alloy tubes for stent manufacturing; v) set up, in terms of laser cut and surface finishing, of the procedure to manufacture magnesium stents; vi) selection of a coating able to assure enough corrosion resistance and computational evaluation of the coating adhesion. In the paper the multi-disciplinary approach used to go through the steps above is summarized. The obtained results suggest that developed methodology is effective at designing innovative biomedical devices

Development of biodegradable magnesium alloy stents with coating

Biodegradable stents are attracting the attention of many researchers in biomedical and materials research fields since they can absolve their specific function for the expected period of time and then gradually disappear. This feature allows avoiding the risk of long-term complications such as restenosis or mechanicalinstability of the device when the vessel grows in size in pediatric patients. Up to now biodegradable stentsmade of polymers or magnesium alloys have been proposed. However, both the solutions have limitations. Thepolymers have low mechanical properties, which lead to devices that cannot withstand the natural contractionof the blood vessel: the restenosis appears just after the implant, and can be ascribed to the compliance of thestent. The magnesium alloys have much higher mechanical properties, but they dissolve too fast in the humanbody. In this work we present some results of an ongoing study aiming to the development of biodegradablestents made of a magnesium alloy that is coated with a polymer having a high corrosion resistance. Themechanical action on the blood vessel is given by the magnesium stent for the desired period, being the stentprotected against fast corrosion by the coating. The coating will dissolve in a longer term, thus delaying theexposition of the magnesium stent to the corrosive environment. We dealt with the problem exploiting thepotentialities of a combined approach of experimental and computational methods (both standard and ad-hocdeveloped) for designing magnesium alloy, coating and scaffold geometry from different points of views.Our study required the following steps: i) selection of a Mg alloy suitable for stent production, having sufficientstrength and elongation capability; ii) computational optimization of the stent geometry to minimize stress andstrain after stent deployment, improve scaffolding ability and corrosion resistance; iii) development of anumerical model for studying stent degradation to support the selection of the best geometry; iv) optimizationof the alloy microstructure and production of Mg alloy tubes for stent manufacturing; v) set up, in terms of lasercut and surface finishing, of the procedure to manufacture magnesium stents; vi) selection of a coating able toassure enough corrosion resistance and computational evaluation of the coating adhesion.In the paper the multi-disciplinary approach used to go through the steps above is summarized. The obtainedresults suggest that developed methodology is effective at designing innovative biomedical devices

Intercomparison of MODIS Albedo Retrievals and In Situ Measurements Across the Global FLUXNET Network

Surface albedo is a key parameter in the Earth's energy balance since it affects the amount of solar radiation directly absorbed at the planet surface. Its variability in time and space can be globally retrieved through the use of remote sensing products. To evaluate and improve the quality of satellite retrievals, careful intercomparisons with in situ measurements of surface albedo are crucial. For this purpose we compared MODIS albedo retrievals with surface measurements taken at 53 FLUXNET sites that met strict conditions of land cover homogeneity. A good agreement between mean yearly values of satellite retrievals and in situ measurements was found (R(exp 2)= 0.82). The mismatch is correlated to the spatial heterogeneity of surface albedo, stressing the relevance of land cover homogeneity when comparing point to pixel data. When the seasonal patterns of MODIS albedo is considered for different plant functional types, the match with surface observation is extremely good at all forest sites. On the contrary, in non-forest sites satellite retrievals underestimate in situ measurements across the seasonal cycle. The mismatch observed at grasslands and croplands sites is likely due to the extreme fragmentation of these landscapes, as confirmed by geostatistical attributes derived from high resolution scenes

Intercomparison of MODIS albedo retrievals and in situ measurements across the global FLUXNET network

Surface albedo is a key parameter in the Earth's energy balance since it affects the amount of solar radiation directly absorbed at the planet surface. Its variability in time and space can be globally retrieved through the use of remote sensing products. To evaluate and improve the quality of satellite retrievals, careful intercomparisons with in situ measurements of surface albedo are crucial. For this purpose we compared MODIS albedo retrievals with surface measurements taken at 53 FLUXNET sites that met strict conditions of land cover homogeneity. A good agreement between mean yearly values of satellite retrievals and in situ measurements was found (r² = 0.82). The mismatch is correlated with the spatial heterogeneity of surface albedo, stressing the relevance of land cover homogeneity when comparing point to pixel data. When the seasonal patterns of MODIS albedo are considered for different plant functional types, the match with surface observations is extremely good at all forest sites. On the contrary, satellite retrievals at non-forested sites (grasslands, savannas, croplands) underestimate in situ measurements across the seasonal cycle. The mismatch observed at grassland and cropland sites is likely due to the extreme fragmentation of these landscapes, as confirmed by geostatistical attributes derived from high resolution scenes.Keywords: FLUXNET, Remote sensing, Validation, Surface albedo, Plant functional types, MODIS, Terrestrial ecosystem

Interpreting canopy development and physiology using the EUROPhen camera network at flux sites

Peer reviewe

Key Messages ISGAN : Annex 6: Power Transmission & Distribution Systems

Power systems around the world are faced with a wide range of challenges in order to realize the objective to integrate an increased amount of renewable energy sources in the modern electricity grids. The consequences affect the daily operation and longterm planning of transmission and distribution systems, and the network owners and operator’s ability to ensure continuous, reliable and high quality of supply to the customers. The needs of each actor within the electrical supply chain provide drivers for revision of current practices and promotes future adaptions of functional components and systems, economic and regulatory areas. In this document, we describe the drivers for change regarding generation, demand, and grid, the resulting consequences this has on operation and planning of the power transmission and distribution systems, and finally the needs to ensure sustainability &amp; security of supply from the technology, market and policy perspectives.Emil Hillberg (RISE, Sweden) ISGAN Annex 6 Technical Lead, Focus Area Lead Technology Trends &amp; Deployment Gianluigi Migliavacca (RSE, Italy) Focus Area Lead Expansion Planning &amp; Market Analysis Kjetil Uhlen (NTNU, Norway) Focus Area Lead System Operation &amp; SecurityAntony Zegers &amp; Barbara Herndler (AIT, Austria) Focus Area Lead Transmission &amp; Distribution System Interaction </p

Key Messages ISGAN : Annex 6: Power Transmission &amp; Distribution Systems

Power systems around the world are faced with a wide range of challenges in order to realize the objective to integrate an increased amount of renewable energy sources in the modern electricity grids. The consequences affect the daily operation and longterm planning of transmission and distribution systems, and the network owners and operator’s ability to ensure continuous, reliable and high quality of supply to the customers. The needs of each actor within the electrical supply chain provide drivers for revision of current practices and promotes future adaptions of functional components and systems, economic and regulatory areas. In this document, we describe the drivers for change regarding generation, demand, and grid, the resulting consequences this has on operation and planning of the power transmission and distribution systems, and finally the needs to ensure sustainability &amp; security of supply from the technology, market and policy perspectives.Emil Hillberg (RISE, Sweden) ISGAN Annex 6 Technical Lead, Focus Area Lead Technology Trends &amp; Deployment Gianluigi Migliavacca (RSE, Italy) Focus Area Lead Expansion Planning &amp; Market Analysis Kjetil Uhlen (NTNU, Norway) Focus Area Lead System Operation &amp; SecurityAntony Zegers &amp; Barbara Herndler (AIT, Austria) Focus Area Lead Transmission &amp; Distribution System Interaction </p

Design and functional testing of a novel balloon-expandable cardiovascular stent in CoCr alloy produced by selective laser melting

Selective Laser Melting (SLM) is a promising technology for the manufacturing of patient-specific medical implants, due to the intrinsic potential in the realization of one of a kind parts with complex geometries. The present work analyses the production of balloon-expandable stents in cobalt-chromium alloy with a novel mesh which is realized using an industrial SLM system. The stent mesh optimized for the SLM process, was designed, produced, finished and functionally tested by balloon expansion. Electropolishing was used to clean the stent surface from sintered particles and to improve the surface finish. Roughness measurements were carried out on stents both in the as-built and the electropolished conditions, while mechanical properties were evaluated by tensile testing with dogbone specimens, produced with the same parameters of the stents and having comparable dimensions. Finally, the expansion behaviour of the CoCr stents, both in as-built and electropolished conditions, was assessed using a balloon catheter and measuring the diameter variation as a function of inflation pressure. The results confirm that SLM produced stents can be successfully balloon expanded without damaging their characteristic mesh

Selective laser melting of NiTi stents with open-cell and variable diameter

This work investigates the processing of NiTi open-cell peripheral stents with variable diameter by SLM and consecutive heat treatments. The production of open-cell designs via SLM requires dedicated processing strategies to avoid the use of support structures with comparable dimensions to the stent struts. Process parameters were studied using an SLM system operating with pulsed wave emission to assess the geometrical fidelity and the density of thin struts. The novel stent mesh was designed and produced employing gaps with unmelted powder between the consecutive cells along the build direction. Solution annealing and stress relieving treatments were assessed after SLM. The results show that regular struts with high density (&gt;99.5%) with an austenitic transformation finish below the room temperature can be achieved with SLM and dedicated heat treatment