Finite element and mechanobiological modelling of vascular devices

There are two main surgical treatments for vascular diseases, (i) percutaneous stent deployment and (ii) replacement of an atherosclerotic artery with a vascular graft or tissue engineered blood vessel. The aim of this thesis was to develop computational models that could assist in the design of vascular stents and tissue engineered vascular grafts and scaffolds. In this context, finite element (FE) models of stent expansion in idealised and patient specific models of atherosclerotic arteries were developed. Different modelling strategies were investigated and an optimal modelling approach was identified which minimised computational cost without compromising accuracy. Numerical models of thin and thick strut stents were developed using this modelling approach to replicate the ISAR-STEREO clinical trial and the models identified arterial stresses as a suitable measure of stent induced vascular injury. In terms of evaluating vascular graft performance, mechanical characterisation experiments can be conducted in order to develop constitutive models that can be used in FE models of vascular grafts to predict their mechanical behaviour in-situ. In this context, bacterial cellulose (BC), a novel biomaterial, was mechanically characterised and a constitutive model was developed to describe its mechanical response. In addition, the interaction of smooth muscle cells with BC was studied using cell culture experiments. The constitutive model developed for BC was used as an input for a novel multi-scale mechanobiological modelling framework. The mechanobiological model was developed by coupling an FE model of a vascular scaffold and a lattice free agent based model of cell growth dynamics and remodelling in vascular scaffolds. By comparison with published in-vivo and in-vitro works, the model was found to successfully capture the key characteristics of vascular remodelling. It can therefore be used as a predictive tool for the growth and remodelling of vascular scaffolds and graft

Evaluation of economy and compared energy efficiency on grape in west Azerbaijan province

A way of estimation agriculture development and product stability agricultural location is using of energy flow method. In this consideration, energy flow at agricultural ecosystems of Grape in two cities from west Azerbaijan province was compared. The related data of inputs and outputs for evaluation of energy efficiency in these gardens are become equivalent value of input and output energy efficiency. Energy value of used factors and input in grape gardens of uremia and sardasht were respectively 6417773 and 862570 k cal/ha and output (production) energy value of the gardens were 25632600 and 10123800 k cal/ha respectively. Energy efficiency values (output: input ration) were 3.99 and 11.7 respectively. Data showed in grape gardens of uremia the most use of energy were nitrogen fertilized usage and irrigation. In grape gardens of sardasht the most use of energy was nitrogen fertilized. In general, because of the climate conditions, topography, society culture in these regions, difference in energy efficiency of these gardens almost was reasonable. The number of inputs increases; effect increases any one of input decrease. Grape garden system of sardasht hasn’t any contamination and agricultural systems because of much Annual rainfall in this region are dry farming. There for, costs of irrigation and poisoning are deleted but inordinately poisoning of uremia gardens result in contamination and transformed these ecosystems

A novel small-caliber bacterial cellulose vascular prosthesis: production, characterization, and preliminary in vivo testing

Vascular grafts are used to bypass damaged or diseased blood vessels. Bacterial cellulose (BC) has been studied for use as an off-the-shelf graft. Herein, we present a novel, cost-effective, method for the production of small caliber BC grafts with minimal processing or requirements. The morphology of the graft wall produced a tensile strength above that of native vessels, performing similarly to the current commercial alternatives. As a result of the production method, the luminal surface of the graft presents similar topography to that of native vessels. We have also studied the in vivo behavior of these BC graft in order to further demonstrate their viability. In these preliminary studies, 1 month patency was achieved, with the presence of neo-vessels and endothelial cells on the luminal surface of the graft.This study was supported by the Portuguese Foundation for Science and Technology (FCT) and the European Community fund FEDER, through Program COMPETE, under the scope of the Projects FCOMP-01-0124-FEDER-007025 (PTDC/AMB/68393/2006), PEST-OE/EQB/LA0023/2013, PEST-C/FIS/UI607/2013, RECI/BBB-EBI/0179/2012 (FCOMP-01-0124-FEDER-027462) and the Projects "BioEnv-Biotechnology and Bioengineering for a sustainable world" and "Matepro-Optimizing Materials and Processes". NORTE-07-0124-FEDER-000048, co-funded by the Programa Operacional Regional do Norte (ON.2 - O Novo Norte), QREN, FEDER. The authors also acknowledge the fellowship awarded to Alexandre Felipe Leitao (SFRH/BD/66094/2009) funded by the Fundacao para a Ciencia e Tecnologia (FCT). The authors also thank support by FCT through the project BCGrafts, FCOMP-01-0124-FEDER-014773 (PTDC/EBB/EBI/112170/2009) and by the People Program (Marie Curie Actions) of the European Union's Seventh Framework Program FP7/2007-2013/under REA grant agreement n317512

Computational analysis of mechanical stress–strain interaction of a bioresorbable scaffold with blood vessel

This paper was accepted for publication in the journal Journal of Biomechanics and the definitive published version is available at http://dx.doi.org/10.1016/j.jbiomech.2016.05.035Crimping and deployment of bioresorbable polymeric scaffold, Absorb, were modelled using finite element method, in direct comparison with Co-Cr alloy drug eluting stent, Xience V. Absorb scaffold has an expansion rate lower than Xience V stent, with a less outer diameter achieved after balloon deflation. Due to the difference in design and material properties, Absorb also shows a higher recoiling than Xience V, which suggests that additional post-dilatation is required to achieve effective treatment for patients with calcified plaques and stiff vessels. However, Absorb scaffold induces significantly lower stresses on the artery-plaque system, which can be clinically beneficial. Eccentric plaque causes complications to stent deployment, especially non-uniform vessel expansion. Also the stress levels in the media and adventitia layers are considerably higher for the plaque with high eccentricity, for which the choice of stents, in terms of materials and designs, will be of paramount importance. Our results imply that the benefits of Absorb scaffolds are amplified in these cases

Sequential Structural and Fluid Dynamics Analysis of Balloon-Expandable Coronary Stents: A Multivariable Statistical Analysis

Several clinical studies have identified a strong correlation between neointimal hyperplasia following coronary stent deployment and both stent-induced arterial injury and altered vessel hemodynamics. As such, the sequential structural and fluid dynamics analysis of balloon-expandable stent deployment should provide a comprehensive indication of stent performance. Despite this observation, very few numerical studies of balloon-expandable coronary stents have considered both the mechanical and hemodynamic impact of stent deployment. Furthermore, in the few studies that have considered both phenomena, only a small number of stents have been considered. In this study, a sequential structural and fluid dynamics analysis methodology was employed to compare both the mechanical and hemodynamic impact of six balloon-expandable coronary stents. To investigate the relationship between stent design and performance, several common stent design properties were then identified and the dependence between these properties and both the mechanical and hemodynamic variables of interest was evaluated using statistical measures of correlation. Following the completion of the numerical analyses, stent strut thickness was identified as the only common design property that demonstrated a strong dependence with either the mean equivalent stress predicted in the artery wall or the mean relative residence time predicted on the luminal surface of the artery. These results corroborate the findings of the large-scale ISAR-STEREO clinical studies and highlight the crucial role of strut thickness in coronary stent design. The sequential structural and fluid dynamics analysis methodology and the multivariable statistical treatment of the results described in this study should prove useful in the design of future balloon-expandable coronary stents

Optimal Management of Vehicle-to-Grid and Grid-to-Vehicle Services Considering Reliability and Power Quality Constraints

Electric vehicles (EVs) are increasingly envisioned as a promising alternative for conventional transport systems because of their economic and environmental advantages and technological enhancements. However, the integration of EVs, the charging stations and other types of electric transport systems can result in a significant increase in the electric load demand in power grids. Moreover, because of the atypical aspects of the EVs and other types of electric vehicular systems, additional power quality issues can arise in the power grids. A thorough investigation is required to determine the optimal capacity of the electrical networks so that the high penetration of EVs in the distribution systems will not violate the grid codes and standards. Further, solutions need to be devised to facilitate the integration of EVs in distribution networks and suitable methods need to be developed to allow the EVs to support the power grids when connected. In this research project, a comprehensive study of the existing and potential impacts of EVs on power systems at medium voltage (MV) and low voltage (LV) levels are carried out using computer simulations and field measurements. Models, which can replicate the characteristics of the EVs when integrated into the distribution power systems and the analysis of the interaction between the EVs and the power systems components, are also developed. Most importantly, approaches for the effective participation and the optimal integration of EVs and demand management schemes are designed so that the codes and standards for power quality of the grids can be satisfactorily met. Accordingly, new control strategies are developed to effectively and efficiently operate the distribution systems under uncertainties, varying system conditions, and the types and applications of the EVs

A multiscale mechanobiological model using agent based models; Application to vascular tissue engineering

status: publishe