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Geith MA, Swidergal K, Hochholdinger B, Schratzenstaller TG, Wagner M, Holzapfel GA. On the importance of modeling balloon folding, pleating, and stent crimping: An FE study comparing experimental inflation tests. INTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN BIOMEDICAL ENGINEERING 2019; 35:e3249. [PMID: 31400057 PMCID: PMC9285761 DOI: 10.1002/cnm.3249] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 03/29/2019] [Revised: 07/23/2019] [Accepted: 08/03/2019] [Indexed: 06/10/2023]
Abstract
Finite element (FE)-based studies of preoperative processes such as folding, pleating, and stent crimping with a comparison with experimental inflation tests are not yet available. Therefore, a novel workflow is presented in which residual stresses of balloon folding and pleating, as well as stent crimping, and the geometries of all contact partners were ultimately implemented in an FE code to simulate stent expansion by using an implicit solver. The numerical results demonstrate that the incorporation of residual stresses and strains experienced during the production step significantly increased the accuracy of the subsequent simulations, especially of the stent expansion model. During the preoperative processes, stresses inside the membrane and the stent material also reached a rather high level. Hence, there can be no presumption that balloon catheters or stents are undamaged before the actual surgery. The implementation of the realistic geometry, in particular the balloon tapers, and the blades of the process devices improved the simulation of the expansion mechanisms, such as dogboning, concave bending, or overexpansion of stent cells. This study shows that implicit solvers are able to precisely simulate the mentioned preoperative processes and the stent expansion procedure without a preceding manipulation of the simulation time or physical mass.
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Affiliation(s)
- Markus A. Geith
- Institute of BiomechanicsGraz University of TechnologyGrazAustria
- Biomedical Engineering DepartmentKing's College LondonUnited Kingdom
- Faculty of Mechanical EngineeringOstbayerische Technische Hochschule RegensburgGermany
| | - Krzysztof Swidergal
- Faculty of Mechanical EngineeringOstbayerische Technische Hochschule RegensburgGermany
| | | | | | - Marcus Wagner
- Faculty of Mechanical EngineeringOstbayerische Technische Hochschule RegensburgGermany
| | - Gerhard A. Holzapfel
- Institute of BiomechanicsGraz University of TechnologyGrazAustria
- Department of Structural EngineeringNorwegian University of Science and TechnologyTrondheimNorway
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Obayi CS, Tolouei R, Mostavan A, Paternoster C, Turgeon S, Okorie BA, Obikwelu DO, Mantovani D. Effect of grain sizes on mechanical properties and biodegradation behavior of pure iron for cardiovascular stent application. BIOMATTER 2016; 6:e959874. [PMID: 25482336 PMCID: PMC5055204 DOI: 10.4161/21592527.2014.959874] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Pure iron has been demonstrated as a potential candidate for biodegradable metal stents due to its appropriate biocompatibility, suitable mechanical properties and uniform biodegradation behavior. The competing parameters that control the safety and the performance of BMS include proper strength-ductility combination, biocompatibility along with matching rate of corrosion with healing rate of arteries. Being a micrometre-scale biomedical device, the mentioned variables have been found to be governed by the average grain size of the bulk material. Thermo-mechanical processing techniques of the cold rolling and annealing were used to grain-refine the pure iron. Pure Fe samples were unidirectionally cold rolled and then isochronally annealed at different temperatures with the intention of inducing different ranges of grain size. The effect of thermo-mechanical treatment on mechanical properties and corrosion rates of the samples were investigated, correspondingly. Mechanical properties of pure Fe samples improved significantly with decrease in grain size while the corrosion rate decreased marginally with decrease in the average grain sizes. These findings could lead to the optimization of the properties to attain an adequate biodegradation-strength-ductility balance.
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Affiliation(s)
- Camillus Sunday Obayi
- a Department of Metallurgical & Materials Engineering , University of Nigeria , Nsukka , Nigeria.,b Laboratory for Biomaterials and Bioengineering (CRC-I), Department of Materials Engineering & CHU de Quebec Research Centre, Laval University , Quebec City , Canada
| | - Ranna Tolouei
- b Laboratory for Biomaterials and Bioengineering (CRC-I), Department of Materials Engineering & CHU de Quebec Research Centre, Laval University , Quebec City , Canada
| | - Afghany Mostavan
- b Laboratory for Biomaterials and Bioengineering (CRC-I), Department of Materials Engineering & CHU de Quebec Research Centre, Laval University , Quebec City , Canada
| | - Carlo Paternoster
- b Laboratory for Biomaterials and Bioengineering (CRC-I), Department of Materials Engineering & CHU de Quebec Research Centre, Laval University , Quebec City , Canada
| | - Stephane Turgeon
- b Laboratory for Biomaterials and Bioengineering (CRC-I), Department of Materials Engineering & CHU de Quebec Research Centre, Laval University , Quebec City , Canada
| | - Boniface Adeleh Okorie
- a Department of Metallurgical & Materials Engineering , University of Nigeria , Nsukka , Nigeria
| | - Daniel Oray Obikwelu
- a Department of Metallurgical & Materials Engineering , University of Nigeria , Nsukka , Nigeria
| | - Diego Mantovani
- b Laboratory for Biomaterials and Bioengineering (CRC-I), Department of Materials Engineering & CHU de Quebec Research Centre, Laval University , Quebec City , Canada
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A computational study of stent performance by considering vessel anisotropy and residual stresses. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2016; 62:307-16. [PMID: 26952428 DOI: 10.1016/j.msec.2016.01.064] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 01/11/2016] [Accepted: 01/24/2016] [Indexed: 11/23/2022]
Abstract
Finite element simulations of stent deployment were carried out by considering the intrinsic anisotropic behaviour, described by a Holzapfel-Gasser-Ogden (HGO) hyperelastic anisotropic model, of individual artery layers. The model parameters were calibrated against the experimental stress-stretch responses in both circumferential and longitudinal directions. The results showed that stent expansion, system recoiling and stresses in the artery layers were greatly affected by vessel anisotropy. Following deployment, deformation of the stent was also modelled by applying relevant biomechanical forces, i.e. in-plane bending and radial compression, to the stent-artery system, for which the residual stresses generated during deployment were particularly accounted for. Residual stresses were found to have a significant influence on the deformation of the system, resulting in a re-distribution of stresses and a change of the system flexibility. The results were also utilised to interpret the mechanical performance of stent after deployment.
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Kowalski W, Dammer M, Bakczewitz F, Schmitz KP, Grabow N, Kessler O. In-situ investigation of stress conditions during expansion of bare metal stents and PLLA-coated stents using the XRD sin(2)ψ-technique. J Mech Behav Biomed Mater 2015; 49:23-9. [PMID: 25974098 DOI: 10.1016/j.jmbbm.2015.04.020] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Revised: 04/14/2015] [Accepted: 04/17/2015] [Indexed: 11/27/2022]
Abstract
Drug eluting stents (DES) consist of platform, coating and drug. The platform often is a balloon-expandable bare metal stent made of the CoCr alloy L-605 or stainless steel 316 L. The function of the coating, typically a permanent polymer, is to hold and release the drug, which should improve therapeutic outcome. Before implantation, DES are compressed (crimped) to allow implantation in the human body. During implantation, DES are expanded by balloon inflation. Crimping, as well as expansion, causes high stresses and high strains locally in the DES struts, as well as in the polymer coating. These stresses and strains are important design criteria of DES. Usually, they are calculated numerically by finite element analysis (FEA), but experimental results for validation are hardly available. In this work, the X-ray diffraction (XRD) sin(2)ψ-technique is applied to in-situ determination of stress conditions of bare metal L-605 stents, and Poly-(L-lactide) (PLLA) coated stents. This provides a realistic characterization of the near-surface stress state and a validation option of the numerical FEA. XRD-results from terminal stent struts of the bare metal stent show an increasing compressive load stress in tangential direction with increasing stent expansion. These findings correlate with numerical FEA results. The PLLA-coating also bears increasing compressive load stress during expansion.
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Affiliation(s)
- Wolfgang Kowalski
- University of Rostock, Faculty of Mechanical Engineering and Marine Technology, Chair of Materials Science, 18051 Rostock, Germany.
| | | | | | - Klaus-Peter Schmitz
- University of Rostock, University Medicine, Institute for Biomechanical Engineering, 18119 Rostock-Warnemünde, Germany.
| | - Niels Grabow
- University of Rostock, University Medicine, Institute for Biomechanical Engineering, 18119 Rostock-Warnemünde, Germany.
| | - Olaf Kessler
- University of Rostock, Faculty of Mechanical Engineering and Marine Technology, Chair of Materials Science, 18051 Rostock, Germany.
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Schiavone A, Zhao L, Abdel-Wahab A. Effects of material, coating, design and plaque composition on stent deployment inside a stenotic artery—Finite element simulation. MATERIALS SCIENCE & ENGINEERING. C, MATERIALS FOR BIOLOGICAL APPLICATIONS 2014; 42:479-88. [DOI: 10.1016/j.msec.2014.05.057] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/19/2013] [Revised: 04/18/2014] [Accepted: 05/29/2014] [Indexed: 01/19/2023]
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Zhao S, Gu L, Froemming SR. On the Importance of Modeling Stent Procedure for Predicting Arterial Mechanics. J Biomech Eng 2012; 134:121005. [DOI: 10.1115/1.4023094] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The stent-artery interactions have been increasingly studied using the finite element method for better understanding of the biomechanical environment changes on the artery and its implications. However, the deployment of balloon-expandable stents was generally simplified without considering the balloon-stent interactions, the initial crimping process of the stent, its overexpansion routinely used in the clinical practice, or its recoil process. In this work, the stenting procedure was mimicked by incorporating all the above-mentioned simplifications. The impact of various simplifications on the stent-induced arterial stresses was systematically investigated. The plastic strain history of stent and its resulted geometrical variations, as well as arterial mechanics were quantified and compared. Results showed the model without considering the stent crimping process underestimating the minimum stent diameter by 17.2%, and overestimating the maximum radial recoil by 144%. It was also suggested that overexpansion resulted in a larger stent diameter, but a greater radial recoil ratio and larger intimal area with high stress were also obtained along with the increase in degree of overexpansion.
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Affiliation(s)
- Shijia Zhao
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0656
| | - Linxia Gu
- Department of Mechanical and Materials Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0656 Nebraska Center for Materials and Nanoscience, Lincoln, NE 68588-0656 e-mail:
| | - Stacey R. Froemming
- Hybrid Catheterization and Electrophysiology Laboratory, Children's Hospital and Medical Center, Omaha, NE 68114-4133
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Goldberg JB, Goodney PP, Kumbhani SR, Roth RM, Powell RJ, Likosky DS. Brain Injury After Carotid Revascularization: Outcomes, Mechanisms, and Opportunities for Improvement. Ann Vasc Surg 2011; 25:270-86. [DOI: 10.1016/j.avsg.2010.07.013] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2010] [Revised: 06/01/2010] [Accepted: 07/19/2010] [Indexed: 11/27/2022]
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Harewood FJ, McHugh PE. Modeling of Size Dependent Failure in Cardiovascular Stent Struts under Tension and Bending. Ann Biomed Eng 2007; 35:1539-53. [PMID: 17503185 DOI: 10.1007/s10439-007-9326-6] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2006] [Accepted: 05/02/2007] [Indexed: 11/25/2022]
Abstract
Cardiovascular stents are cylindrical mesh-like metallic structures that are used to treat atherosclerosis. The thickness of stent struts are typically in the range of 50-150 microm. At this microscopic size scale, the tensile failure strain has been shown to be size dependent. Micromechanically representative computational models have captured this size effect in tension. In this paper polycrystalline models incorporating material fracture are used to investigate size effects for realistic stent strut geometries and loading modes. The specific loading a stent undergoes during deployment is uniquely captured and the implications for stent design are considered. Fracture analysis is also performed, identifying trends in terms of strut thickness and loading type. The results show, in addition to the size effect in tension, further size effects in different loading conditions. The results of the loading analyses are combined to produce a tension and bending failure graph. This design safety diagram is presented as a tool to predict failure of stent struts. This study is particularly significant given the current interest in producing smaller stents.
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Affiliation(s)
- F J Harewood
- Department of Mechanical and Biomedical Engineering, National Centre for Biomedical Engineering Science, National University of Ireland, Galway, Ireland
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Murphy BP, Cuddy H, Harewood FJ, Connolley T, McHugh PE. The influence of grain size on the ductility of micro-scale stainless steel stent struts. JOURNAL OF MATERIALS SCIENCE. MATERIALS IN MEDICINE 2006; 17:1-6. [PMID: 16389466 DOI: 10.1007/s10856-006-6323-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2005] [Accepted: 05/24/2005] [Indexed: 05/06/2023]
Abstract
Vascular stents are used to restore blood flow in stenotic arteries, and at present the implantation of a stent is the preferred revascularisation method for treating coronary artery disease, as the introduction of drug eluting stents (DESs) has lead to a significant improvement in the clinical outcome of coronary stenting. However the mechanical limits of stents are being tested when they are deployed in severe cases. In this study we aimed to show (by a combination of experimental tests and crystal plasticity finite element models) that the ductility of stainless steel stent struts can be increased by optimising the grain structure within micro-scale stainless steel stent struts. The results of the study show that within the specimen size range 55 to 190 microm ductility was not dependent on the size of the stent strut when the grain size maximised. For values of the ratio of cross sectional area to characteristic grain length less than 1,000, ductility was at a minimum irrespective of specimen size. However, when the ratio of cross sectional area to characteristic grain length becomes greater than 1,000 an improvement in ductility occurs, reaching a plateau when the ratio approaches a value characteristic of bulk material properties. In conclusion the ductility of micro-scale stainless steel stent struts is sensitive to microstructure and can be improved by reducing the grain size.
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Affiliation(s)
- B P Murphy
- National Centre for Biomedical Engineering Science, National University of Ireland, Galway, Ireland.
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