@inproceedings{WeberRenkawitzBulstraetal., author = {Weber, Tim and Renkawitz, Tobias and Bulstra, Sjoerd K. and Grifka, Joachim and Verkerke, Gijsbertus Jacob and Dendorfer, Sebastian}, title = {Biomechanics of computer-assisted vs. conventional THR after one year follow up}, series = {XXV Congress of the International Society of Biomechanics, Glasgow, UK, 12th-16th July 2015}, booktitle = {XXV Congress of the International Society of Biomechanics, Glasgow, UK, 12th-16th July 2015}, language = {en} } @inproceedings{WeberRenkawitzGrifkaetal., author = {Weber, Tim and Renkawitz, Tobias and Grifka, Joachim and Bulstra, Sjoerd K. and Verkerke, Gijsbertus Jacob and Dendorfer, Sebastian}, title = {The musculoskeletal load scenario of computer-assisted Femur-First THR up to one year after surgery}, series = {VI International Conference on Computational Bioengineering, Barcelona, Sept. 2015}, booktitle = {VI International Conference on Computational Bioengineering, Barcelona, Sept. 2015}, language = {en} } @inproceedings{WeberStezowskiDullienetal., author = {Weber, Tim and Stezowski, P. and Dullien, Silvia and Dendorfer, Sebastian}, title = {Eine biomechanische Bewertung verschiedener Belastungsszenarios nach der Implantierung einer H{\"u}ft-Totalendoprothese}, series = {89. Jahrestagung der Vereinigung der Bayerischen Chirurgen e.V., 25. - 27. Juli 2012, Regensburg}, booktitle = {89. Jahrestagung der Vereinigung der Bayerischen Chirurgen e.V., 25. - 27. Juli 2012, Regensburg}, language = {de} } @inproceedings{WeberStezowskiDullienetal., author = {Weber, Tim and Stezowski, P. and Dullien, Silvia and Putzer, Michael and Dendorfer, Sebastian}, title = {Eine biomechanische Bewertung verschiedener Belastungsszenarien nach Implantierung einer H{\"u}ft-Totalendoprothese}, series = {GAMMA Workshop, Hannover, 2012}, booktitle = {GAMMA Workshop, Hannover, 2012}, language = {de} } @inproceedings{WeissGrossmannLeiboldetal., author = {Weiß, Roman and Großmann, Benjamin and Leibold, Marion and Schlegl, Thomas and Wollherr, Dirk and Weiss, Roman and Grossmann, Benjamin}, title = {Modeling and nonlinear control of antagonistically actuating pneumatic artificial muscles}, series = {2017 IEEE International Conference on Advanced Intelligent Mechatronics (AIM), 3-7 July 2017, Munich, Germany}, booktitle = {2017 IEEE International Conference on Advanced Intelligent Mechatronics (AIM), 3-7 July 2017, Munich, Germany}, publisher = {IEEE}, doi = {10.1109/AIM.2017.8014001}, pages = {94 -- 99}, abstract = {This paper discusses modeling and nonlinear control of a joint antagonistically actuated by two pneumatic, artificial muscles. A single model of the whole system is obtained by a combined physical and phenomenological modeling approach. The combined model for the joint, the muscles and the proportional valves results in a nonlinear, affine-in-control system description. The model is used to derive control laws for an input/output linearization approach to linearize the plant. Modeling and parametrization errors are covered via an outer control loop consisting of a state-feedback which is extended by an additional feedback of error integral. Extensive experimental results show the quality of the model and the performance of the respective control laws.}, language = {en} } @article{WesselyHausleiterMichaelisetal., author = {Wessely, Rainer and Hausleiter, J{\"o}rg and Michaelis, Cornelia and Jaschke, Birgit and Vogeser, Michael and Milz, Stefan and Behnisch, Boris and Schratzenstaller, Thomas and Renke-Gluszko, Magdalena and St{\"o}ver, Michael and Wintermantel, Erich and Kastrati, Adnan and Sch{\"o}mig, Albert}, title = {Inhibition of neointima formation by a novel drug-eluting stent system that allows for dose-adjustable, multiple, and on-site stent coating}, series = {Arteriosclerosis, Thrombosis, and Vascular Biology}, volume = {25}, journal = {Arteriosclerosis, Thrombosis, and Vascular Biology}, number = {4}, issn = {1524-4636}, doi = {10.1161/01.ATV.0000157579.52566.ee}, pages = {748 -- 753}, abstract = {Objective The risk of in-stent restenosis can be considerably reduced by stents eluting cytostatic compounds. We created a novel drug-eluting stent system that includes several new features in the rapidly evolving field of stent-based drug delivery. Methods and Results The aim of the present study was the preclinical evaluation of a stent-coating system permitting individual, on-site coating of stents with a unique microporous surface allowing for individualizable, dose-adjustable, and multiple coatings with identical or various compounds, designated ISAR (individualizable drug-eluting stent system to abrogate restenosis). Stents were coated with 0.75\% rapamycin solution, and high-performance liquid chromatography (HPLC)-based determination of drug release profile indicated drug release for >21 days. Rapamycin-eluting microporous (REMP) stents implanted in porcine coronary arteries were safe. To determine the efficacy of REMP stents, this novel drug-eluting stent platform was compared with the standard sirolimus-eluting stent. At 30 days, in-stent neointima formation in porcine coronary arteries was similar in both groups, yielding a significant decrease of neointimal area and injury-dependent neointimal thickness compared with bare-metal stents. Conclusion The ISAR drug-eluting stent platform as a novel concept for stent coating allows for a safe, effective, on-site stent coating process, thus justifying further clinical evaluation to decrease in-stent restenosis in humans. In-stent neointima formation can be successfully attenuated by drug-eluting stents. We introduce a novel conceptual approach for stent-coating that allows for dose-adjustable, on-site stent coating process if desired with multiple compounds. Microporous stents coated with rapamycin proved safe and effective for the limitation of neointima formation in a porcine coronary stent model.}, language = {en} } @inproceedings{WiesentGeithWagner, author = {Wiesent, Lisa and Geith, Markus A. and Wagner, Marcus}, title = {Simulation of Fluid-Structure Interaction between injection medium and balloon catheter using ICFD}, series = {11th European LS-DYNA Conference 2017, 9 - 11 May, Salzburg, Austria}, booktitle = {11th European LS-DYNA Conference 2017, 9 - 11 May, Salzburg, Austria}, isbn = {978-3981621549}, abstract = {Arteriosclerosis is a major health issue worldwide. While it is commonly treated by the implantation of an balloon-expandable stent, micro injuries may occur during stent deployment, and induce in-stent restenosis, whose consequence can be fatal. Studying this undesirable phenomenon is usually limited as experimental data is hard to obtain on ethical ground. Numerical simulation are performed to better understand this problem. To construct a more realistic simulation of a balloon-expandable stent, a partitioned strongly-coupled FSI simulation of the balloon deployment was set up using the ICFD solver of LS-DYNA, - a quite innovative approach. The complex balloon configuration as well as the interaction of the injection medium and the balloon structure was considered. The balloon structure consisting of shell elements was obtained from preliminary balloon folding and pleating simulations. The balloon consists of a flexible thin walled polyamide. The injection fluid is implemented using volume elements. Balloon deployment was initiated by a pressure boundary condition inducing a volume flow into the balloon. The initial feasibility analysis showed promising result including a continuous balloon deployment and a reasonable development of the fluid pressure and velocity field. However, applying this FSI approach to a more complex balloon structure led to a non convergent solution. The non-convergence could be mainly reduced to mechanical factors including the low wall thickness of the balloon (< 0.05 mm) and the flexibility of the polyamide. Further, the ICFD solver shows less accuracy concerning the FSI conditions when dealing with thin flexible structures as well as enclosed volumes. A shell thickness of 0.06 mm is believed to result in a convergent solution.}, subject = {Koronare Herzkrankheit}, language = {en} } @misc{WiesentHupkeBalketal., author = {Wiesent, Lisa and Hupke, Constantin and Balk, Christian and Schultheiss, Ulrich and Schratzenstaller, Thomas}, title = {Optimization of the cardiovascular stent design towards improved expansion behaviour and radial stiffness properties}, series = {Biomedizinische Technik}, volume = {63}, journal = {Biomedizinische Technik}, number = {s1}, doi = {10.1515/bmt-2018-6031}, abstract = {- Development of a FEA Tool for a realistic stent simulation - investigation on minor modification on the stent design on the expansion behaviour - analysis of three stent designs: classical stent design with pronounced dogbone effect, two modified stent design (non-dogbone-design)}, subject = {Kardiovaskul{\"a}res System}, language = {en} } @article{WiesentSchultheissSchmidetal., author = {Wiesent, Lisa and Schultheiss, Ulrich and Schmid, Christof and Schratzenstaller, Thomas and Nonn, Aida}, title = {Experimentally validated simulation of coronary stents considering different dogboning ratios and asymmetric stent positioning}, series = {PlOS One}, volume = {14}, journal = {PlOS One}, number = {10}, publisher = {PLOS}, doi = {10.1371/journal.pone.0224026}, pages = {1 -- 25}, abstract = {In-stent restenosis remains a major problem of arteriosclerosis treatment by stenting. Expansion-optimized stents could reduce this problem. With numerical simulations, stent designs/ expansion behaviours can be effectively analyzed. For reasons of efficiency, simplified models of balloon-expandable stents are often used, but their accuracy must be challenged due to insufficient experimental validation. In this work, a realistic stent life-cycle simulation has been performed including balloon folding, stent crimping and free expansion of the balloon-stent-system. The successful simulation and validation of two stent designs with homogenous and heterogeneous stent stiffness and an asymmetrically positioned stent on the balloon catheter confirm the universal applicability of the simulation approach. Dogboning ratio, as well as the final dimensions of the folded balloon, the crimped and expanded stent, correspond well to the experimental dimensions with only slight deviations. In contrast to the detailed stent life-cycle simulation, a displacement-controlled simulation can not predict the transient stent expansion, but is suitable to reproduce the final expanded stent shape and the associated stress states. The detailed stent life-cycle simulation is thus essential for stent expansion analysis/optimization, whereas for reasons of computational efficiency, the displacement-controlled approach can be considered in the context of pure stress analysis.}, subject = {Stent}, language = {en} } @article{WiesentSchultheissLullaetal., author = {Wiesent, Lisa and Schultheiß, Ulrich and Lulla, Philipp and Noster, Ulf and Schratzenstaller, Thomas and Schmid, Christof and Nonn, Aida and Spear, Ashley}, title = {Computational analysis of the effects of geometric irregularities and post-processing steps on the mechanical behavior of additively manufactured 316L stainless steel stents}, series = {PLoS ONE}, volume = {15}, journal = {PLoS ONE}, number = {12}, publisher = {PLOS}, doi = {10.1371/journal.pone.0244463}, pages = {1 -- 30}, abstract = {Advances in additive manufacturing enable the production of tailored lattice structures and thus, in principle, coronary stents. This study investigates the effects of process-related irregularities, heat and surface treatment on the morphology, mechanical response, and expansion behavior of 316L stainless steel stents produced by laser powder bed fusion and provides a methodological approach for their numerical evaluation. A combined experimental and computational framework is used, based on both actual and computationally reconstructed laser powder bed fused stents. Process-related morphological deviations between the as-designed and actual laser powder bed fused stents were observed, resulting in a diameter increase by a factor of 2-2.6 for the stents without surface treatment and 1.3-2 for the electropolished stent compared to the as-designed stent. Thus, due to the increased geometrically induced stiffness, the laser powder bed fused stents in the as-built (7.11 ± 0.63 N) or the heat treated condition (5.87 ± 0.49 N) showed increased radial forces when compressed between two plates. After electropolishing, the heat treated stents exhibited radial forces (2.38 ± 0.23 N) comparable to conventional metallic stents. The laser powder bed fused stents were further affected by the size effect, resulting in a reduced yield strength by 41\% in the as-built and by 59\% in the heat treated condition compared to the bulk material obtained from tensile tests. The presented numerical approach was successful in predicting the macroscopic mechanical response of the stents under compression. During deformation, increased stiffness and local stress concentration were observed within the laser powder bed fused stents. Subsequent numerical expansion analysis of the derived stent models within a previously verified numerical model of stent expansion showed that electropolished and heat treated laser powder bed fused stents can exhibit comparable expansion behavior to conventional stents. The findings from this work motivate future experimental/numerical studies to quantify threshold values of critical geometric irregularities, which could be used to establish design guidelines for laser powder bed fused stents/lattice structures.}, subject = {Koronarendoprothese}, language = {en} }