Biomechanics Research Center

Gaillimh, Ireland

Biomechanics Research Center

Gaillimh, Ireland
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McGrath D.J.,Biomechanics Research Center | Thiebes A.L.,RWTH Aachen | Cornelissen C.G.,RWTH Aachen | O'Shea M.B.,Biomechanics Research Center | And 4 more authors.
Biomechanics and Modeling in Mechanobiology | Year: 2017

Tracheobronchial stents are most commonly used to restore patency to airways stenosed by tumour growth. Currently all tracheobronchial stents are associated with complications such as stent migration, granulation tissue formation, mucous plugging and stent strut fracture. The present work develops a computational framework to evaluate tracheobronchial stent designs in vivo. Pressurised computed tomography is used to create a biomechanical lung model which takes into account the in vivo stress state, global lung deformation and local loading from pressure variation. Stent interaction with the airway is then evaluated for a number of loading conditions including normal breathing, coughing and ventilation. Results of the analysis indicate that three of the major complications associated with tracheobronchial stents can potentially be analysed with this framework, which can be readily applied to the human case. Airway deformation caused by lung motion is shown to have a significant effect on stent mechanical performance, including implications for stent migration, granulation formation and stent fracture. © 2017 Springer-Verlag Berlin Heidelberg


Bobel A.C.,Biomechanics Research Center | Petisco S.,University of the Basque Country | Sarasua J.R.,University of the Basque Country | Wang W.,University College Dublin | McHugh P.E.,Biomechanics Research Center
Cardiovascular Engineering and Technology | Year: 2015

Over the last decade, there has been a significant volume of research focussed on the utilization of biodegradable polymers such as poly-l-lactide-acid (PLLA) for applications associated with cardiovascular disease. More specifically, there has been an emphasis on upgrading current clinical shortfalls experienced with conventional bare metal stents and drug eluting stents. One such approach, the adaption of fully formed polymeric stents has led to a small number of products being commercialized. Unfortunately, these products are still in their market infancy, meaning there is a clear non-occurrence of long term data which can support their mechanical performance in vivo. Moreover, the load carry capacity and other mechanical properties essential to a fully optimized polymeric stent are difficult, timely and costly to establish. With the aim of compiling rapid and representative performance data for specific stent geometries, materials and designs, in addition to reducing experimental timeframes, Computational bench testing via finite element analysis (FEA) offers itself as a very powerful tool. On this basis, the research presented in this paper is concentrated on the finite element simulation of the mechanical performance of PLLA, which is a fully biodegradable polymer, in the stent application, using a non-linear viscous material model. Three physical stent geometries, typically used for fully polymeric stents, are selected, and a comparative study is performed in relation to their short-term mechanical performance, with the aid of experimental data. From the simulated output results, an informed understanding can be established in relation to radial strength, flexibility and longitudinal resistance, that can be compared with conventional permanent metal stent functionality, and the results show that it is indeed possible to generate a PLLA stent with comparable and sufficient mechanical performance. The paper also demonstrates the attractiveness of FEA as a tool for establishing fundamental mechanical characteristics of polymeric stent performance. © 2015, Biomedical Engineering Society.


PubMed | Biomechanics Research Center, University College Dublin and University of the Basque Country
Type: Journal Article | Journal: Cardiovascular engineering and technology | Year: 2015

Over the last decade, there has been a significant volume of research focussed on the utilization of biodegradable polymers such as poly-L-lactide-acid (PLLA) for applications associated with cardiovascular disease. More specifically, there has been an emphasis on upgrading current clinical shortfalls experienced with conventional bare metal stents and drug eluting stents. One such approach, the adaption of fully formed polymeric stents has led to a small number of products being commercialized. Unfortunately, these products are still in their market infancy, meaning there is a clear non-occurrence of long term data which can support their mechanical performance in vivo. Moreover, the load carry capacity and other mechanical properties essential to a fully optimized polymeric stent are difficult, timely and costly to establish. With the aim of compiling rapid and representative performance data for specific stent geometries, materials and designs, in addition to reducing experimental timeframes, Computational bench testing via finite element analysis (FEA) offers itself as a very powerful tool. On this basis, the research presented in this paper is concentrated on the finite element simulation of the mechanical performance of PLLA, which is a fully biodegradable polymer, in the stent application, using a non-linear viscous material model. Three physical stent geometries, typically used for fully polymeric stents, are selected, and a comparative study is performed in relation to their short-term mechanical performance, with the aid of experimental data. From the simulated output results, an informed understanding can be established in relation to radial strength, flexibility and longitudinal resistance, that can be compared with conventional permanent metal stent functionality, and the results show that it is indeed possible to generate a PLLA stent with comparable and sufficient mechanical performance. The paper also demonstrates the attractiveness of FEA as a tool for establishing fundamental mechanical characteristics of polymeric stent performance.


Dolan E.B.,Biomechanics Research Center | Dolan E.B.,National University of Ireland | Haugh M.G.,Biomechanics Research Center | Haugh M.G.,National University of Ireland | And 4 more authors.
Journal of the Royal Society Interface | Year: 2012

Severe heat-shock to bone cells caused during orthopaedic procedures can result in thermal damage, leading to cell death and initiating bone resorption. By contrast, mild heat-shock has been proposed to induce bone regeneration. In this study, bone cells are exposed to heat-shock for short durations occurring during surgical cutting. Cellular viability, necrosis and apoptosis are investigated immediately after heat-shock and following recovery of 12, 24 h and 4 days, in osteocyte-like MLO-Y4 and osteoblast-like MC3T3-E1 cells, using flow cytometry. The regeneration capacity of heat-shocked Balb/c mesenchymal stem cells (MSCs) and MC3T3-E1s has been investigated following 7 and 14 day's recovery, by quantifying proliferation, differentiation and mineralization. An immediate necrotic response to heat-shock was shown in cells exposed to elevated temperatures (45°C, 47°C and most severe at 60°C). A longer-term apoptotic response is induced in MLO-Y4s and, to a lesser extent, in MC3T3-E1s. Heat-shock-induced differentiation and mineralization by MSCs. These findings indicate that heat-shock is more likely to induce apoptosis in osteocytes than osteoblasts, which might reflect their role as sensors detecting and communicating damage within bone. Furthermore, it is shown for the first time that mild heat-shock (less than equal to 47°C) for durations occurring during surgical cutting can positively enhance osseointegration by osteoprogenitors. © 2012 The Royal Society.


Bobel A.C.,Biomechanics Research Center | Lohfeld S.,Biomechanics Research Center | Shirazi R.N.,Biomechanics Research Center | McHugh P.E.,Biomechanics Research Center
Polymer Testing | Year: 2016

Next-generation stents made from Biodegradable Polymers (BPs) aim to address the long-term risks (i.e. late restenosis and in-stent thrombosis) associated with both Bare Metal Stents and Drug Eluting Stents, whilst aiming to reduce the healthcare costs associated with secondary care. However, the true potential of BPs for cardiovascular load bearing applications does not appear to be fully realised. While the literature provides data on stiffness and strength of BPs, it is lacking pre-degradation experimental data on the recovery behaviour and temperature and strain rate dependency. In this paper, an experimental study is undertaken to address this knowledge gap using Poly (L-Lactide) (PLLA) samples, subjected to tensile testing. Stress-strain characteristics, recovery, relaxation and creep data at body temperature are reported and considered in the context of real-life stent deployment. The experimental data herein reveal a strong temperature and strain rate dependency, whilst demonstrating associated plasticity within the material. The work provides a physical evaluation of PLLA's pre-degradation behaviour, establishing key data points to allow the assessment of PLLA as a viable material in the wider context of stent deployment and load carrying capacity. © 2016 Elsevier Ltd


Grogan J.A.,Biomechanics Research Center | Leen S.B.,Biomechanics Research Center | McHugh P.E.,Biomechanics Research Center
Biomaterials | Year: 2013

Computer simulation is used extensively in the design of permanent stents. In order to address new challenges that arise in the design of absorbable metal stents (AMSs), such as corrosion and the limited mechanical properties of bioabsorbable alloys, new simulation and design techniques are needed. In this study a new method for simulating AMS corrosion is developed to study the effects of corrosion on the mechanical performance of a range of stent designs. The corrosion model is combined with an optimization strategy to identify AMS features that give optimal corrosion performance in the body. It is found that strut width is the predominant geometrical factor in determining long-term AMS scaffolding performance. An AMS with superior scaffolding performance to a commercial design is identified, based on deployment and corrosion simulations in stenosed vessels. These simulation and design techniques give new insights into in-vivo AMS performance and the role of device geometry in determining long-term scaffolding performance. © 2013 Elsevier Ltd.


Grogan J.A.,Biomechanics Research Center | Leen S.B.,Biomechanics Research Center | McHugh P.E.,Biomechanics Research Center
Journal of the Mechanical Behavior of Biomedical Materials | Year: 2013

The dimensions of coronary stent struts are similar to those of the metallic grains of their constituent alloys. This means that statistical size effects (SSEs), which are evident in polycrystals with few grains through their dimensions, can have detrimental effects on the mechanical performance of stent struts undergoing large plastic deformation. Current trends in coronary stent design are towards thinner struts, potentially increasing the influence of SSEs. In order to maintain adequate device performance with decreasing strut thickness, it is therefore important to assess the role of SSEs in the plastic deformation of stents. In this study, finite element modelling and crystal plasticity theory are used to investigate SSEs in the deformation of struts in tension and bending. The relationships between SSEs and microstructure morphology, alloy strain hardening behaviour and secondary phases are also investigated. It is predicted that reducing the number of grains through the strut cross section and increasing the number of grains along the strut length have detrimental effects on mechanical performance. The magnitudes of these effects are predicted to be independent of the uniformity of the studied microstructures, but dependent on alloy strain hardening behaviour. It is believed that model predictions will aid in identifying a lower bound on suitable strut thicknesses in coronary stents for a range of alloys and microstructures. © 2012 Elsevier Ltd.


PubMed | Biomechanics Research Center
Type: | Journal: Journal of the mechanical behavior of biomedical materials | Year: 2013

The dimensions of coronary stent struts are similar to those of the metallic grains of their constituent alloys. This means that statistical size effects (SSEs), which are evident in polycrystals with few grains through their dimensions, can have detrimental effects on the mechanical performance of stent struts undergoing large plastic deformation. Current trends in coronary stent design are towards thinner struts, potentially increasing the influence of SSEs. In order to maintain adequate device performance with decreasing strut thickness, it is therefore important to assess the role of SSEs in the plastic deformation of stents. In this study, finite element modelling and crystal plasticity theory are used to investigate SSEs in the deformation of struts in tension and bending. The relationships between SSEs and microstructure morphology, alloy strain hardening behaviour and secondary phases are also investigated. It is predicted that reducing the number of grains through the strut cross section and increasing the number of grains along the strut length have detrimental effects on mechanical performance. The magnitudes of these effects are predicted to be independent of the uniformity of the studied microstructures, but dependent on alloy strain hardening behaviour. It is believed that model predictions will aid in identifying a lower bound on suitable strut thicknesses in coronary stents for a range of alloys and microstructures.


PubMed | Biomechanics Research Center and RWTH Aachen
Type: | Journal: Journal of the mechanical behavior of biomedical materials | Year: 2016

Covered tracheobronchial stents are used to prevent tumour growth from reoccluding the airways. In the present work a combination of experimental and computational methods are used to present the mechanical effects that adhered covers can have on stent performance. A prototype tracheobronchial stent is characterised in bare and covered configurations using radial force, flat plate and a novel non-uniform radial force test, while computational modelling is performed in parallel to extensively inform the physical testing. Results of the study show that cover configuration can have a significant structural effect on stent performance, and that stent response (bare or covered) is especially loading specific, highlighting that the loading configuration that a stent is about to be subjected to should be considered before stent implantation.


PubMed | Biomechanics Research Center
Type: | Journal: Journal of the mechanical behavior of biomedical materials | Year: 2014

Nitinols superelastic properties permit self-expanding stents to be crimped without plastic deformation, but its nonlinear properties can contribute towards stent buckling. This study investigates the axial buckling of a prototype tracheobronchial nitinol stent design during crimping, with the objective of eliminating buckling from the design. To capture the stent buckling mechanism a computational model of a radial force test is simulated, where small geometric defects are introduced to remove symmetry and allow buckling to occur. With the buckling mechanism ascertained, a sensitivity study is carried out to examine the effect that the transitional plateau region of the nitinol loading curve has on stent stability. Results of this analysis are then used to redesign the stent and remove buckling. It is found that the transitional plateau region can have a significant effect on the stability of a stent during crimping, and by reducing the amount of transitional material within the stent hinges during loading the stability of a nitinol stent can be increased.

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