@article{BartschBehamGebhardtetal., author = {Bartsch, Alexander and Beham, Daniela and Gebhardt, Jakob and Ehrlich, Ingo and Schratzenstaller, Thomas and Monkman, Gareth J.}, title = {Mechanical Properties of NdPrFeB Based Magnetoactive Bisphenol-Free Boron-Silicate Polymers}, series = {Journal of Nanomedicine and Nanotechnology}, volume = {14}, journal = {Journal of Nanomedicine and Nanotechnology}, number = {6}, publisher = {Walsh Medical Media}, issn = {2157-7439}, doi = {10.35248/2157-7439.23.14.705}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:898-opus4-67425}, abstract = {Following a ban on many materials containing bisphenol-A, new bisphenol-free Boron silicates have been found as substitutes. The purpose of this study is to describe the mechanical properties of these bisphenol-free magnetoactive borosilicate polymers containing hard magnetic particles. Samples of 0\%, 33\% and 66\% by wt. were loaded for compression using a universal testing machine. The maximum forces occurring for different travel speeds were compared before and after post-magnetization treatments. The post-magnetization included 2 stages. In addition, the change in mechanical properties within 24 hours after the post-magnetization process was investigated. Furthermore, the influence of speed and particle content were investigated. In general, there is a correlation between the required compressive force and, the level of post-magnetization stress, the increase in travel speed and particle content in the boron silicate. Comparison of the non-post-magnetized and post-magnetized samples using two-tailed t-tests shows that the p-values for all weight fraction changes in NdPrFeB particles and travel speeds are less than 0.001. Also, a comparison between tests in which the traverse speed was varied also showed significant changes in the resulting compression forces. The same is valid for changes in the weight ratio of the NdPrFeB particles in the samples. For post-magnetized samples, no significant difference can be observed in the first 24 hours following magnetization. In summary, the material presents viscoelastic, plastic force-displacement behavior, which can be well recognized by its bi-linear curve shape. The investigation shows that borosilicate polymers based on NdPrFeB can have their mechanical behavior modified and controlled by post-magnetization processes. This opens new possibilities for many future applications.}, language = {en} } @article{BelliKreppelPetscheltetal., author = {Belli, Renan and Kreppel, Stefan and Petschelt, Anselm and Hornberger, Helga and Boccaccini, Aldo R. and Lohbauer, Ulrich}, title = {Strengthening of dental adhesives via particle reinforcement}, series = {Journal of the Mechanical Behavior of Biomedical Materials}, volume = {37}, journal = {Journal of the Mechanical Behavior of Biomedical Materials}, number = {9}, doi = {10.1016/j.jmbbm.2014.05.007}, pages = {100 -- 108}, abstract = {The bond between methacrylic polymer adhesives and dental restoratives is not perfect and may fail either in the short or in the long term. This study aims to evaluate the effects of particle incorporation in a self-etch model adhesive on mechanical and physical properties that are relevant during application and service. Filled adhesives containing 5, 10, 15 or 25 wt\% glass fillers were compared to their unfilled counterpart in terms of water sorption and solubility; viscosity and dynamic viscosity during polymerization were recorded using rheological measurements and compared to FTIR analysis of the real-time degree of cure. Elastic modulus and ultimate tensile strength measurements were performed in uniaxial tension; the energy to fracture was used to calculate the fracture toughness of the adhesives. Finally, the experimental adhesives were applied on dentin substrate to test the bond strength using the microtensile test. Results showed that the incorporation of 5-10 wt\% nanofiller to self-etching dental adhesives is efficient in accelerating the polymerization reaction and increasing the degree of cure without compromising the film viscosity for good wettability or water sorption and solubility. Fillers increased the elastic modulus, tensile strength and fracture toughness to a plateau between 5 and 15 wt\% filler concentration, and despite the tendency to form agglomerations, active crack pinning/deflection toughening mechanisms have been observed. The bond strength between resin composite and dentin was also improved when adhesives with up to 10 wt\% fillers were used, with no additional improvements with further packing. The use of fillers to reinforce dental adhesives may therefore be of great practical benefit by improving curing and mechanical properties.}, language = {en} } @article{BenditzAuerSpoerreretal., author = {Benditz, Achim and Auer, Simon and Sp{\"o}rrer, J.F. and Wolkerstorfer, S. and Grifka, Joachim and S{\"u}ß, Franz and Dendorfer, Sebastian}, title = {Regarding loads after spinal fusion, every level should be seen separately: a musculoskeletal analysis}, series = {European Spine Journal}, volume = {27}, journal = {European Spine Journal}, number = {8}, publisher = {Springer-Verlag}, doi = {10.1007/s00586-018-5476-5}, pages = {1905 -- 1910}, abstract = {The number of spinal fusion surgeries is steadily increasing and biomechanical consequences are still in debate. The aim of this study is to provide biomechanical insights into the sagittal balance of the spine and to compare spinal load before and after spinal fusion. METHOD: The joint reaction forces of 52 patients were analyzed in proximo-distal and antero-posterior direction from the levels T12-L1 to L5-S1 using musculoskeletal simulations. RESULTS: In 104 simulations, pre-surgical forces were equal to post-surgical. The levels L4-L5 and T12-L1, however, showed increased spinal forces compression forces with higher sagittal displacement. Improved restauration of sagittal balance was accompanied by lower spinal load. AP shear stress, interestingly decreased with sagittal imbalance. CONCLUSION: Imbalanced spines have a risk of increased compression forces at Th12-L1. L4-L5 always has increased spinal loads. These slides can be retrieved under Electronic Supplementary Material.}, subject = {Biomechanische Analyse}, language = {en} } @inproceedings{BillingGoetzWeberetal., author = {Billing, A. and G{\"o}tz, J. and Weber, Tim and Dendorfer, Sebastian}, title = {Positionsanalyse von winkelstabilen Plattenosteosynthesesystemen zur Versorgung von Metatarsalfrakturen mit Hilfe von patientenspezifischen biomechanischen Modellen}, series = {Vereinigung S{\"u}ddeutscher Orthop{\"a}den und Unfallchirurgen Jahrestagung 2015, Baden-Baden, Germany}, booktitle = {Vereinigung S{\"u}ddeutscher Orthop{\"a}den und Unfallchirurgen Jahrestagung 2015, Baden-Baden, Germany}, language = {de} } @misc{BirkenmaierDorniaLehleetal., author = {Birkenmaier, Clemens and Dornia, Christian and Lehle, Karla and Krenkel, Lars}, title = {Feasibility of detecting thrombotic deposits in membrane oxygenators using micro computed tomography}, series = {25th Congress of the European Society of Biomechanics, July 7-10, 2019, Vienna, Austria}, journal = {25th Congress of the European Society of Biomechanics, July 7-10, 2019, Vienna, Austria}, language = {en} } @article{BirkenmaierDorniaLehleetal., author = {Birkenmaier, Clemens and Dornia, Christian and Lehle, Karla and M{\"u}ller, Thomas and Gruber, Michael Andreas and Philipp, Alois and Krenkel, Lars}, title = {Analysis of Thrombotic Deposits in Extracorporeal Membrane Oxygenators by High-resolution Microcomputed Tomography: A Feasibility Study}, series = {ASAIO Journal / American Society for Artificial Internal Organs}, volume = {66}, journal = {ASAIO Journal / American Society for Artificial Internal Organs}, number = {8}, publisher = {Lippincott Williams \& Wilkins}, issn = {1538-943X}, doi = {10.1097/MAT.0000000000001089}, pages = {922 -- 928}, abstract = {Coagulative disorders, especially clotting during extracorporeal membrane oxygenation, are frequent complications. Direct visualization and analysis of deposits in membrane oxygenators using computed tomography (CT) may provide an insight into the underlying mechanisms causing thrombotic events. However, the already established multidetector CT1 (MDCT) method shows major limitations. Here, we demonstrate the feasibility of applying industrial micro-CT (μCT) to circumvent these restrictions. Three clinically used membrane oxygenators were investigated applying both MDCT and μCT. The scans were analyzed in terms of clot volume and local clot distribution. As validation, the clot volume was also determined from the fluid volume, which could be filled into the respective used oxygenator compared to a new device. In addition, cross-sectional CT images were compared with crosscut oxygenators. Based on the μCT findings, a morphological measure (sphericity) for assessing clot structures in membrane oxygenators is introduced. Furthermore, by comparing MDCT and μCT results, an augmentation of the MDCT method is proposed, which allows for improved clot volume determination in a clinical setting.}, language = {en} } @inproceedings{BirkenmaierKrenkel, author = {Birkenmaier, Clemens and Krenkel, Lars}, title = {Convolutional Neural Networks for Approximation of Blood Flow in Artificial Lungs}, series = {New Results in Numerical and Experimental Fluid Mechanics XIII: Contributions to the 22nd STAB/DGLR Symposium}, booktitle = {New Results in Numerical and Experimental Fluid Mechanics XIII: Contributions to the 22nd STAB/DGLR Symposium}, number = {1. Auflage}, editor = {Dillmann, Andreas and Heller, Gerd and Kr{\"a}mer, Ewald and Wagner, Claus}, publisher = {Springer International Publishing}, address = {Cham}, isbn = {978-3-030-79560-3}, doi = {10.1007/978-3-030-79561-0_43}, pages = {451 -- 460}, abstract = {Blood flow in channels of varying diameters <500μm exhibits strong non-linear effects. Multiphase finite volume approaches are feasible, but still computationally costly. Here, the feasibility of applying convolutional neural networks for blood flow prediction in artificial lungs is investigated. Training targets are precomputed using an Eulerian two-phase approach. To match with experimental data, the interphase drag and lift, as well as intraphase shear-thinning are adapted. A recursively branching regression network and convolution/deconvolution networks with plain skip connections and densely connected skips are investigated. A priori knowledge is incorporated in the loss functional to prevent the network from learning non-physical solutions. Inference from neural networks is approximately six orders of magnitude faster than the classical finite volume approach. Even if resulting in comparably coarse flow fields, the neural network predictions can be used as close to convergence initial solutions greatly accelerating classical flow computations.}, language = {en} } @misc{BirkenmaierKrenkel, author = {Birkenmaier, Clemens and Krenkel, Lars}, title = {Towards a realistic model of blood viscosity and coagulation in membrane oxygenators}, series = {6th European Conference on Computational Mechanics (Solids, Structures and Coupled Problems) - ECCM 6; 7th European Conference on Computational Fluid Dynamics - ECFD 7 : Glasgow, Scotland, UK, June 11-15, 2018}, journal = {6th European Conference on Computational Mechanics (Solids, Structures and Coupled Problems) - ECCM 6; 7th European Conference on Computational Fluid Dynamics - ECFD 7 : Glasgow, Scotland, UK, June 11-15, 2018}, abstract = {Modelling blood flow an shear induced coagulation in membraene oxygenators (MO) is challenging. The relevant geometry of oxygenator fibers (OF) and chaining threads is complex and spans several length scales. In relevant scales and regimes blood shows several significant non-Newtonian effects. Existing models are only capable of accounting for some, but not all relevant effects. Additionally, coagulation processes are influencing fluid properties and geometry significantly. Due to the enormous size of the discretised geometries highly detailed viscosity and coagulation properties of blodd flow in MOs. First step is to find a gemoetry dependent viscosity representation on basis of parametric micro channel experiments with anti-coagulated blood. Next step is a statistic coagulation model, based on micro channel experiments with human (re-calcified citrated) whole blood an evaluation of clinically used osygenators. Since shear rate dependent (i.e. viscosity dependet) coagulation in return influences the viscosity, a combined model with suitable implementation in a RANS framework is necessary. Towards this end, micro channel experiments with new and used single OFs triggering coagulation are performed. Structures of multimeric von Willebrand fibers (vWF), as indicator for shear induced coagulation, are compared to computed and measured flow conditions, using immunofluorescence microscopy, RANS-computations and µPIV, respectively. Preliminary examinations in clinically used MOs show good agreement between occurring structures of vWF, cell depositions and computed flow patterns (geometry form µCT-Scans). However, computed shear rates might be to low to actually trigger activation of vWF. The complex geometry of MOs results in huge meshes, which makes RANS with statistical modelling of viscosity and coagulation a reasonable approach. Towards this end, experimental data on micro channel level with evaluation on real application level is crucial. Especially regarding clotting processes, micro fluidic experiments are powerful research tool.}, language = {en} } @inproceedings{BirkenmaierKrenkel, author = {Birkenmaier, Clemens and Krenkel, Lars}, title = {Convolutional Neural Networks for Approximation of Internal Non-Newtonian Multiphase Flow Fields}, series = {14th World Congress on Computational Mechanics (WCCM), ECCOMAS Congress 2020: 19-24 July 2020, Paris, France}, booktitle = {14th World Congress on Computational Mechanics (WCCM), ECCOMAS Congress 2020: 19-24 July 2020, Paris, France}, editor = {Chinesta, F. and Abgrall, R. and Allix, O. and Kalistke, M}, publisher = {CIMNE}, doi = {10.23967/wccm-eccomas.2020.107}, abstract = {Neural networks (NNs) as an alternative method for universal approximation of differential equations have proven to be computationally efficient and still sufficiently accurate compared to established methods such as the finite volume method (FVM). Additionally, analysing weights and biases can give insights into the underlying physical laws. FVM and NNs are both based upon spacial discretisation. Since a Cartesian and equidistant grid is a raster graphics, image-to-image regression techniques can be used to predict phase velocity fields as well as particle and pressure distributions from simple mass flow boundary conditions. The impact of convolution layer depth and number of channels of a ConvolutionDeconvolution Regression Network (CDRN), on prediction performance of internal non-Newtownian multiphase flows is investigated. Parametric training data with 2055 sets is computed using FVM. To capture significant non-Newtownian effects of a particle-laden fluid (e.g. blood) flowing through small and non-straight channels, an Euler-Euler multiphase approach is used. The FVM results are normalized and mapped onto an equidistant grid as supervised learning target. The investigated NNs consist of n= {3, 5, 7} corresponding encoding/decoding blocks and different skip connections. Regardless of the convolution depth (i.e. number of blocks), the deepest spacial down-sampling via strided convolution is adjusted to result in a 1 × 1 × f · 2nfeature map, with f = {8, 16, 32}. The prediction performance expressed is as channel-averaged normalized root mean squared error (NRMSE). With a NRMSE of < 2 · 10-3, the best preforming NN has f = 32 initial feature maps, a kernel size of k = 4, n = 5 blocks and dense skip connections. Average inference time from this NN takes < 7 · 10-3s. Worst accuracy at NRMSE of approx 9 · 10-3is achieved without any skips, at k = 2, f = 16 and n = 3, but deployment takes only < 2 · 10-3s Given an adequate training, the prediction accuracy improves with convolution depth, where more features have higher impact on deeper NNs. Due to skip connections and batch normalisation, training is similarly efficient, regardless of the depth. This is further improved by blocks with dense connections, but at the price of a drastically larger model. Depending on geometrical complexity, spacial resolution is critical, as it increases the number of learnables and memory requirements massively.}, language = {en} } @misc{BirkenmaierKrenkelLehle, author = {Birkenmaier, Clemens and Krenkel, Lars and Lehle, Karla}, title = {Linking flow conditions in membrane oxygenators to arrangements of multimeric von-Willebrand-factor as indication for coagulation}, series = {World Congress of Biomechanics 2018, Convention Centre Dublin, 8.-12. Juli 2018}, journal = {World Congress of Biomechanics 2018, Convention Centre Dublin, 8.-12. Juli 2018}, abstract = {Introduction Shear induced multimerisation of von-Willebrand-factor (vWF) is supposed to play an important role in coagulation inside extracorporeal membrane oxygenators. However, there is no proof that links observed vWF structures to computed or measured flow conditions. Methods The structures of multimeric vWF fibers, observed in clinically used membrane oxygenators is examined using immunofluorescence microscopy (IFM) using Carstairs' staining method (positive ethics committee vote). The flow around the membrane fibres inside the oxygenator is investigated in terms of shear rate, wall shear velocity and streamlines by using CFD (RANS, Carreau-Yasuda viscosity, geometry remodelled after high-resolution µCT-scans). By interpreting the histological and numerical results in this common context, indications for shear induced coagulation mechanisms can be identified. Results The fibre structures of multimeric vWF build regular but not exactly symmetric formations around the contact face (CF) between the crosswise stacked oxygenator fibres (OF), see fig.1B, vWF marked red. Annular around the CF arranged, cells are likely to be found, see fig.1B, nuclei marked blue. The computed streamlines around the OF show attached flow around the circular fibres. However, the irregular arrangement of real OF produce considerable cross flow between the interconnected neighbouring channels, in contrast to previous 2D-simulations. Thus, the CF are washed around closely by blood, also from neighbouring channels. The wall shear velocity streamlines form regular, slightly asymmetric shapes around the contact faces. The occurring maximum shear rates are in the range of 1,000 1/s. Discussion The shapes of vWF structures found in clinically used oxygenators match the computational results in terms of wall shear velocity and streamlines well. The accumulation of cells close to the CF can also be explained by fluid mechanics, as there are small shear gradients and slow velocities. However, occurring shear rates between OFs are too low to trigger multimerisation of vWF. That raises the question where in the circuit the actual activation of vWF is started and how, at least partly chained, vWF multimeres are attracted towards the OF surface. A next step will be the investigation of the actual shear rate triggered (or mediated) multimerisation of vWF. Towards this end, microfluidic experiments with shear triggered coagulation will be performed. Also of big interest is the computation of the flow situation in the oxygenator in proximity to chaining threads, which have been ignored in computations so far. However, first a realistic representation of the effective viscosity in computations is needed, which is not available yet.}, language = {en} }