@article{49107,
abstract = {{The effect of plaque deposition (atherosclerosis) on blood flow behaviour is investigated via computational fluid dynamics and structural mechanics simulations. To mitigate the narrowing of coronary artery atherosclerosis (stenosis), the computational modelling of auxetic and non-auxetic stents was performed in this study to minimise or even avoid these deposition agents in the future. Computational modelling was performed in unrestricted (open) conditions and restricted (in an artery) conditions. Finally, stent designs were produced by additive manufacturing, and mechanical testing of the stents was undertaken. Auxetic stent 1 and auxetic stent 2 exhibit very little foreshortening and radial recoil in unrestricted deployment conditions compared to non-auxetic stent 3. However, stent 2 shows structural instability (strut failure) during unrestricted deployment conditions. For the restricted deployment condition, stent 1 shows a higher radial recoil compared to stent 3. In the tensile test simulations, short elongation for stent 1 due to strut failure is demonstrated, whereas no structural instability is noticed for stent 2 and stent 3 until 0.5 (mm/mm) strain. The as-built samples show a significant thickening of the struts of the stents resulting in short elongations during tensile testing compared to the simulations (stent 2 and stent 3). A modelling framework for the stent deployment system that enables the selection of appropriate stent designs before in vivo testing is required. This leads to the acceleration of the development process and a reduction in time, resulting in less material wastage. The modelling framework shall be useful for doctors designing patient-specific stents.}},
author = {{Pramanik, Sudipta and Milaege, Dennis and Hein, Maxwell and Hoyer, Kay-Peter and Schaper, Mirko}},
issn = {{2073-4352}},
journal = {{Crystals}},
keywords = {{Inorganic Chemistry, Condensed Matter Physics, General Materials Science, General Chemical Engineering}},
number = {{11}},
publisher = {{MDPI AG}},
title = {{{Additive Manufacturing and Mechanical Properties of Auxetic and Non-Auxetic Ti24Nb4Zr8Sn Biomedical Stents: A Combined Experimental and Computational Modelling Approach}}},
doi = {{10.3390/cryst13111592}},
volume = {{13}},
year = {{2023}},
}
@article{46507,
author = {{Pramanik, Sudipta and Milaege, Dennis and Hein, Maxwell and Andreiev, Anatolii and Schaper, Mirko and Hoyer, Kay-Peter}},
issn = {{1438-1656}},
journal = {{Advanced Engineering Materials}},
keywords = {{Condensed Matter Physics, General Materials Science}},
number = {{14}},
publisher = {{Wiley}},
title = {{{An Experimental and Computational Modeling Study on Additively Manufactured Micro‐Architectured Ti–24Nb–4Zr–8Sn Hollow‐Strut Lattice Structures}}},
doi = {{10.1002/adem.202201850}},
volume = {{25}},
year = {{2023}},
}
@article{29196,
abstract = {{In biomedical engineering, laser powder bed fusion is an advanced manufacturing technology, which enables, for example, the production of patient-customized implants with complex geometries. Ti-6Al-7Nb shows promising improvements, especially regarding biocompatibility, compared with other titanium alloys. The biocompatible features are investigated employing cytocompatibility and antibacterial examinations on Al2O3-blasted and untreated surfaces. The mechanical properties of additively manufactured Ti-6Al-7Nb are evaluated in as-built and heat-treated conditions. Recrystallization annealing (925 °C for 4 h), β annealing (1050 °C for 2 h), as well as stress relieving (600 °C for 4 h) are applied. For microstructural investigation, scanning and transmission electron microscopy are performed. The different microstructures and the mechanical properties are compared. Mechanical behavior is determined based on quasi-static tensile tests and strain-controlled low cycle fatigue tests with total strain amplitudes εA of 0.35%, 0.5%, and 0.8%. The as-built and stress-relieved conditions meet the mechanical demands for the tensile properties of the international standard ISO 5832-11. Based on the Coffin–Manson–Basquin relation, fatigue strength and ductility coefficients, as well as exponents, are determined to examine fatigue life for the different conditions. The stress-relieved condition exhibits, overall, the best properties regarding monotonic tensile and cyclic fatigue behavior.}},
author = {{Hein, Maxwell and Kokalj, David and Lopes Dias, Nelson Filipe and Stangier, Dominic and Oltmanns, Hilke and Pramanik, Sudipta and Kietzmann, Manfred and Hoyer, Kay-Peter and Meißner, Jessica and Tillmann, Wolfgang and Schaper, Mirko}},
issn = {{2075-4701}},
journal = {{Metals}},
keywords = {{General Materials Science, Metals and Alloys, laser powder bed fusion, Ti-6Al-7Nb, titanium alloy, biomedical engineering, low cycle fatigue, microstructure, nanostructure}},
number = {{1}},
publisher = {{MDPI AG}},
title = {{{Low Cycle Fatigue Performance of Additively Processed and Heat-Treated Ti-6Al-7Nb Alloy for Biomedical Applications}}},
doi = {{10.3390/met12010122}},
volume = {{12}},
year = {{2022}},
}
@article{31076,
author = {{Tillmann, Wolfgang and Lopes Dias, Nelson Filipe and Kokalj, David and Stangier, Dominic and Hein, Maxwell and Hoyer, Kay-Peter and Schaper, Mirko and Gödecke, Daria and Oltmanns, Hilke and Meißner, Jessica}},
issn = {{0167-577X}},
journal = {{Materials Letters}},
keywords = {{Mechanical Engineering, Mechanics of Materials, Condensed Matter Physics, General Materials Science}},
publisher = {{Elsevier BV}},
title = {{{Tribo-functional PVD thin films deposited onto additively manufactured Ti6Al7Nb for biomedical applications}}},
doi = {{10.1016/j.matlet.2022.132384}},
year = {{2022}},
}
@article{41496,
author = {{Hein, Maxwell and Lopes Dias, Nelson Filipe and Kokalj, David and Stangier, Dominic and Hoyer, Kay-Peter and Tillmann, Wolfgang and Schaper, Mirko}},
issn = {{0142-1123}},
journal = {{International Journal of Fatigue}},
keywords = {{Industrial and Manufacturing Engineering, Mechanical Engineering, Mechanics of Materials, General Materials Science, Modeling and Simulation}},
publisher = {{Elsevier BV}},
title = {{{On the influence of physical vapor deposited thin coatings on the low-cycle fatigue behavior of additively processed Ti-6Al-7Nb alloy}}},
doi = {{10.1016/j.ijfatigue.2022.107235}},
volume = {{166}},
year = {{2022}},
}
@article{41500,
abstract = {{Titanium alloys, especially β alloys, are favorable as implant materials due to their promising combination of low Young’s modulus, high strength, corrosion resistance, and biocompatibility. In particular, the low Young’s moduli reduce the risk of stress shielding and implant loosening. The processing of Ti-24Nb-4Zr-8Sn through laser powder bed fusion is presented. The specimens were heat-treated, and the microstructure was investigated using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. The mechanical properties were determined by hardness and tensile tests. The microstructures reveal a mainly β microstructure with α″ formation for high cooling rates and α precipitates after moderate cooling rates or aging. The as-built and α″ phase containing conditions exhibit a hardness around 225 HV5, yield strengths (YS) from 340 to 490 MPa, ultimate tensile strengths (UTS) around 706 MPa, fracture elongations around 20%, and Young’s moduli about 50 GPa. The α precipitates containing conditions reveal a hardness around 297 HV5, YS around 812 MPa, UTS from 871 to 931 MPa, fracture elongations around 12%, and Young’s moduli about 75 GPa. Ti-24Nb-4Zr-8Sn exhibits, depending on the heat treatment, promising properties regarding the material behavior and the opportunity to tailor the mechanical performance as a low modulus, high strength implant material.}},
author = {{Hein, Maxwell and Lopes Dias, Nelson Filipe and Pramanik, Sudipta and Stangier, Dominic and Hoyer, Kay-Peter and Tillmann, Wolfgang and Schaper, Mirko}},
issn = {{1996-1944}},
journal = {{Materials}},
keywords = {{General Materials Science}},
number = {{11}},
publisher = {{MDPI AG}},
title = {{{Heat Treatments of Metastable β Titanium Alloy Ti-24Nb-4Zr-8Sn Processed by Laser Powder Bed Fusion}}},
doi = {{10.3390/ma15113774}},
volume = {{15}},
year = {{2022}},
}
@article{41501,
author = {{Tillmann, Wolfgang and Lopes Dias, Nelson Filipe and Kokalj, David and Stangier, Dominic and Hein, Maxwell and Hoyer, Kay-Peter and Schaper, Mirko and Gödecke, Daria and Oltmanns, Hilke and Meißner, Jessica}},
issn = {{0167-577X}},
journal = {{Materials Letters}},
keywords = {{Mechanical Engineering, Mechanics of Materials, Condensed Matter Physics, General Materials Science}},
publisher = {{Elsevier BV}},
title = {{{Tribo-functional PVD thin films deposited onto additively manufactured Ti6Al7Nb for biomedical applications}}},
doi = {{10.1016/j.matlet.2022.132384}},
volume = {{321}},
year = {{2022}},
}
@article{33338,
author = {{Hein, Maxwell}},
journal = {{Crystals}},
publisher = {{MDPI}},
title = {{{Influence of Physical Vapor Deposition on High-Cycle Fatigue Performance of Additively Manufactured Ti-6Al-7Nb Alloy}}},
doi = {{10.3390/cryst12091190}},
year = {{2022}},
}
@article{33340,
author = {{Hein, Maxwell and Lopes Dias, Nelson Filipe and Pramanik, Sudipta and Stangier, Dominic and Hoyer, Kay-Peter and Tillmann, Wolfgang and Schaper, Mirko}},
journal = {{Materials}},
title = {{{Heat Treatments of Metastable β Titanium Alloy Ti-24Nb-4Zr-8Sn Processed by Laser Powder Bed Fusion}}},
year = {{2022}},
}
@article{41511,
author = {{Hein, Maxwell and Hoyer, Kay-Peter and Schaper, Mirko}},
issn = {{0933-5137}},
journal = {{Materialwissenschaft und Werkstofftechnik}},
keywords = {{Mechanical Engineering, Mechanics of Materials, Condensed Matter Physics, General Materials Science}},
number = {{7}},
pages = {{703--716}},
publisher = {{Wiley}},
title = {{{Additively processed TiAl6Nb7 alloy for biomedical applications}}},
doi = {{10.1002/mawe.202000288}},
volume = {{52}},
year = {{2021}},
}
@article{41516,
author = {{Tillmann, Wolfgang and Lopes Dias, Nelson Filipe and Franke, Carlo and Kokalj, David and Stangier, Dominic and Filor, Viviane and Mateus-Vargas, Rafael Hernán and Oltmanns, Hilke and Kietzmann, Manfred and Meißner, Jessica and Hein, Maxwell and Pramanik, Sudipta and Hoyer, Kay-Peter and Schaper, Mirko and Nienhaus, Alexander and Thomann, Carl Arne and Debus, Jörg}},
issn = {{0257-8972}},
journal = {{Surface and Coatings Technology}},
keywords = {{Materials Chemistry, Surfaces, Coatings and Films, Surfaces and Interfaces, Condensed Matter Physics, General Chemistry}},
publisher = {{Elsevier BV}},
title = {{{Tribo-mechanical properties and biocompatibility of Ag-containing amorphous carbon films deposited onto Ti6Al4V}}},
doi = {{10.1016/j.surfcoat.2021.127384}},
volume = {{421}},
year = {{2021}},
}
@article{24243,
abstract = {{The addition of Ag to amorphous carbon (a-C) films is highly effective in tailoring the tribo-mechanical properties and biocompatibility. For biomedical applications, Ag-containing a-C (a-C:Ag) represents a promising film material for improving the biofunctional surface properties of Ti-based alloys. In a sputtering process, a-C:Ag films, with Ag contents up to 7.5 at.%, were deposited with a chemically graded TixCy interlayer onto Ti6Al4V. The tribo-mechanical and biocompatible properties of a-C:Ag were evaluated. The influence of the Ag content on these properties was analyzed and compared to those of uncoated Ti6Al4V.
Raman spectroscopy reveals that the amount of incorporated Ag does not induce significant structural changes in the disordered network, only a reduced number of vacancies and sp3-coordinated C bonds within the sp2-dominant a-C network is assigned to the films with high Ag concentration. With increasing Ag content, stresses, hardness, and elastic modulus decrease from (2.02 ± 0.07) to (1.15 ± 0.03) GPa, from (17.4 ± 1.5) to (13.4 ± 0.9) GPa, and from (171.8 ± 8.1) to (138.5 ± 5.8) GPa, respectively. In tribometer tests, the friction behavior against Al2O3 in lubricated condition with a simulated-body-fluid-based lubricant is not affected by the Ag concentration, but the Al2O3 counterpart wear is reduced for all a-C:Ag films compared to a-C. The friction against ultra-high-molecular-weight polyethylene (UHMWPE) decreases continuously with increasing Ag concentration and the counterpart wear is lower at higher Ag contents. Compared to a-C:Ag, Ti6Al4V demonstrates lower friction against UHMWPE and higher friction against Al2O3. The a-C:Ag films are not exposed to abrasion by Al2O3 or pronounced material transfer of UHMWPE. The hardness difference and chemical affinity between the friction partners are decisive for the tribological behavior of a-C:Ag. Compared to Ti6Al4V, the a-C:Ag films show antibacterial activity against Staphylococcus aureus, while the proliferation of osteoblast-like cells is reduced by Ag.}},
author = {{Tillmann, Wolfgang and Lopes Dias, Nelson Filipe and Franke, Carlo and Kokalj, David and Stangier, Dominic and Filor, Viviane and Mateus-Vargas, Rafael Hernán and Oltmanns, Hilke and Kietzmann, Manfred and Meißner, Jessica and Hein, Maxwell and Pramanik, Sudipta and Hoyer, Kay-Peter and Schaper, Mirko and Nienhaus, Alexander and Thomann, Carl Arne and Debus, Jörg}},
issn = {{0257-8972}},
journal = {{Surface and Coatings Technology}},
title = {{{Tribo-mechanical properties and biocompatibility of Ag-containing amorphous carbon films deposited onto Ti6Al4V}}},
doi = {{10.1016/j.surfcoat.2021.127384}},
year = {{2021}},
}
@article{24086,
abstract = {{Laser beam melting (LBM) is an advanced manufacturing technology providing
special features and the possibility to produce complex and individual parts directly
from a CAD model. TiAl6V4 is the most common used titanium alloy particularly
in biomedical applications. TiAl6Nb7 shows promising improvements especially
regarding biocompatible properties due to the substitution of the hazardous
vanadium. This work focuses on the examination of laser beam melted TiAl6Nb7.
For microstructural investigation scanning electron microscopy including energydispersive
x-ray spectroscopy as well as electron backscatter diffraction are utilized.
The laser beam melted related acicular microstructure as well as the corresponding
mechanical properties, which are determined by hardness measurements
and tensile tests, are investigated. The laser beam melted alloy meets,
except of breaking elongation A, the mechanical demands like ultimate tensile
strength Rm, yield strength Rp0.2, Vickers hardness HV of international standard
ISO 5832-11. Next steps contain comparison between TiAl6Nb7 and TiAl6V4 in
different conditions. Further investigations aim at improving mechanical properties
of TiAl6Nb7 by heat treatments and assessment of their influence on the microstructure
as well as examination regarding the corrosive behavior in human bodylike
conditions.}},
author = {{Hein, Maxwell and Hoyer, Kay-Peter and Schaper, Mirko}},
issn = {{0933-5137}},
journal = {{Materialwissenschaft und Werkstofftechnik}},
keywords = {{Laser beam melting, titanium alloy, TiAl6Nb7, biomedical engineering, implants}},
pages = {{703--716}},
title = {{{Additively processed TiAl6Nb7 alloy for biomedical applications}}},
doi = {{10.1002/mawe.202000288}},
volume = {{52}},
year = {{2021}},
}