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Item type:Publication, Access status: with files , Three-dimensional distribution of Titanium hydrides after degradation of Magnesium/Titanium hybrid implant material - a study by X-ray diffraction contrast tomography(Multidisciplinary Digital Publishing Institute (MDPI), 2025-07-26); ; ; ; Hybrid implants composed of magnesium and titanium are a promising direction in orthopaedics, as these implants combine the stability of titanium with the biological activity of magnesium. These partly soluble implants require careful investigation, as the degradation of magnesium releases hydrogen, which can enter the Ti matrix and thus alter the mechanical properties. To investigate this scenario and quantify the hydrogen uptake along with its structural impacts, we employed inert gas fusion, scanning electron microscopy, X-ray diffraction, and a combination of synchrotron absorption and X-ray diffraction tomography. These techniques enabled us to investigate the concentration and distribution of hydrogen and the formation of hydrides in the samples. Titanium hydride formation was observed in a region approximately 120 µm away from the titanium surface and correlates with the amount of absorbed hydrogen. We speculate that the degradation of magnesium at the magnesium/titanium implant interface leads to the penetration of hydrogen due to a combination of electrochemical and gaseous charging.Publicationtype: Journal Article16 17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Regression models for the prediction of the influence of magnesium ions on primary endothelial cell (HUVEC) proliferation and migration(Elsevier, 2025-06-08); ; ; Angiogenesis is one of the first stages in fracture healing and bone repair. Therefore, numerous studies evaluating the effect of Mg as a promising degradable, metallic biomaterial on the proliferation and function of endothelial cells have been performed. However, these studies lack methodological homogeneity and therefore differ in fundamental conclusions. Here, Mg-concentration-, donor- and cell age- dependent relations to primary human umbilical cord vein endothelial cells (HUVEC) proliferation and migration were investigated systematically. The generated data were utilized to develop regression models in order to assess and predict the cell response on Mg exposition in a concentration range of 2–20 mM Mg in cell culture medium extract. A concentration of > 2 mM already induced a detrimental effect in the sensitive primary HUVECs. Molecular data quantifying angiogenesis markers supported this finding. An increased migration capacity has been observed at a concentration of 10 mM Mg. We compared linear regression, random forests, support vector machines, neural networks and large language models for the prediction of HUVEC proliferation for a number of scenarios. Using these machine learning methods, we were able to predict the proliferation of HUVECs for missing Mg concentrations and for missing passages with mean absolute errors below 10 % and as low as 8.5 %, respectively. Due to strong differences between the cell behaviour of different donors, information for missing donors can be predicted with mean absolute errors of 15.7 % only. Support vector machines with linear kernel performed best on the tested data, but large language models also showed promising results.Publicationtype: Journal Article6 5 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Introducing long-range particle interactions into phase-field models of sintering using continuum mechanics principles(Elsevier, 2025-04-10); ; ; ; This work presents a novel meso-scale phase-field model of solid-state sintering that couples the continuum thermodynamics and continuum mechanics governing the sintering process. The microstructure evolution is described by a system of equations consisting of one Cahn–Hilliard equation and a set of Allen–Cahn equations to distinguish neighboring particles. These equations are coupled with the balance of momentum of linear elasticity. The latter is defined by applying the Wang sintering forces as distributed body loads to compute advection velocities for the phase-field equations. This introduces long-range interaction mechanisms between particles. Our numerical implementation uses monolithic coupling and implicit time integration. It is based on the hpsint code, an efficient matrix-free finite element solver for phase-field simulations of many-particle sintering processes with advanced grain tracking capabilities and block preconditioning. With a simple academic test setup that analyzes a chain of identical particles we investigate in detail the problems of the original sintering model proposed by Wang around two decades ago and then clearly demonstrate how our new coupled approach resolves them. We then study a series of two- and three-dimensional benchmark problems to demonstrate the advantages of our novel model that clearly exhibits invariance of shrinkage regarding the model size (number of particles in the packing) and renders microstructures whose metrics agree well with estimates based on analytical and experimental studies.Publicationtype: Journal Article9 20 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Gene regulatory network analysis identifies MYL1, MDH2, GLS, and TRIM28 as the principal proteins in the response of mesenchymal stem cells to Mg²⁺ ions(Elsevier, 2024-12-01)28 101 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Strength and ductility loss of Magnesium-Gadolinium due to corrosion in physiological environment: Experiments and modeling(Elsevier, 2023-08-01); ; ; Luczak, MonikaWe propose a computational framework to study the effect of corrosion on the mechanical strength of magnesium (Mg) samples. Our work is motivated by the need to predict the residual strength of biomedical Mg implants after a given period of degradation in a physiological environment. To model corrosion, a mass-diffusion type model is used that accounts for localised corrosion using Weibull statistics. The overall mass loss is prescribed (e.g., based on experimental data). The mechanical behaviour of the Mg samples is modeled by a state-of-the-art Cazacu–Plunkett–Barlat plasticity model with a coupled damage model. This allowed us to study how Mg degradation in immersed samples reduces the mechanical strength over time. We performed a large number of in vitro corrosion experiments and mechanical tests to validate our computational framework. Our framework could predict both the experimentally observed loss of mechanical strength and the ductility due to corrosion for both tension and compression tests.Publicationtype: Journal ArticleScopus© Citations 2 42 104 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Utilizing computational modelling to bridge the gap between in vivo and in vitro degradation rates for Mg-xGd implants(Multidisciplinary Digital Publishing Institute (MDPI), 2023-06); ; ; Magnesium (Mg) and its alloys are promising materials for temporary bone implants due to their mechanical properties and biocompatibility. The most challenging aspect of Mg-based implants involves adapting the degradation rate to the human body, which requires extensive in vitro and in vivo testing. Given that in vivo tests are significantly more labour-intensive than in vitro and ethics prohibit direct experiments on animals or humans, attempts are commonly undertaken to infer conclusions on in vivo degradation behavior from in vitro experiments. However, there is a wide gap between these tests, and in vitro testing is often a poor predictor of in vivo outcomes. In the development of biodegradable Mg-based implants, considerable efforts are being made to reduce the overall time and cost of in vitro and in vivo testing. Finding a suitable alternative to predict the degradation of Mg alloys, however, remains challenging. We present computational modelling as a possible alternative to bridge the gap between in vitro and in vivo testing, thus reducing overall cost, duration and number of experiments. However, traditional modelling approaches for complex biodegradable systems are still rather time-consuming and require a clear definition of the relations between input parameters and the model result. In this study, Kriging surrogate models based on the peridynamic in vitro degradation model were developed to simulate the degradation behavior for two main alloys, Mg-5Gd and Mg-10Gd, for both in vitro and in vivo cases. Using Kriging surrogate models, the simulation parameters were calibrated to the volume loss data from in vitro and in vivo experiments. In vivo degradation of magnesium has one order of magnitude higher apparent diffusion coefficients than in vitro degradation, thus yielding the higher volume loss observed in vivo than in vitro. On the basis of the diffusivity of the Mg (Formula presented.) ions modeled under in vitro degradation, Kriging surrogate models were able to simulate the in vivo degradation behavior of Mg-xGd with a ratio between 0.46 and 0.5, indicating that the surrogate-modelling approach is able to bridge the gap between in vitro and in vivo degradation rates for Mg-xGd implants.Publicationtype: Journal ArticleScopus© Citations 1 16 122 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Exploring key ionic interactions for magnesium degradation in simulated body fluid – a data-driven approach(Elsevier, 2021-01-22); ; ; ; We have studied the degradation of pure magnesium wire in simulated body fluid and its subsets under physiological conditions to enable the prediction of the degradation rate based on the medium's ionic composition. To this end, micro-computed tomography and scanning electron microscopy with energy-dispersive X-ray spectroscopy were used, followed by a tree regression analysis. A non-linear relationship was found between degradation rate and the precipitation of calcium salts. The mean absolute error for predicting the degradation rate was 1.35 mm/yr. This comparatively high value indicates that ionic interactions were exceedingly complex or that an unknown parameter determining the degradation may exist.Publicationtype: Journal ArticleScopus© Citations 22 189 354 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Systematically Designed Periodic Electrophoretic Deposition for Decorating 3D Carbon-Based Scaffolds with Bioactive NanoparticlesThe coating of porous scaffolds with nanoparticles is crucial in many applications, for example to generate scaffolds for catalysis or to make scaffolds bioactive. A standard and well-established method for coating surfaces with charged nanoparticles is electrophoresis, but when used on porous scaffolds, this method often leads to a blockage of the pores so that only the outermost layers of the scaffolds are coated. In this study, the electrophoretic coating process is monitored in situ and the kinetics of nanoparticle deposition are investigated. This concept can be extended to design a periodic electrophoretic deposition (PEPD) strategy, thus avoiding the typical blockage of surface pores. In the present work we demonstrate successful and homogeneous electrophoretic deposition of hydroxyapatite nanoparticles (HAn, diameter ≤200 nm) on a fibrous graphitic 3D structure (ultralightweight aerographite) using the PEPD strategy. The microfilaments of the resulting scaffold are covered with HAn both internally and on the surface. Furthermore, protein adsorption assays and cell proliferation assays were carried out and revealed that the HAn-decorated aerographite scaffolds are biocompatible. The HAn decoration of the scaffolds also significantly increases the alkaline phosphatase activity of osteoblast cells, showing that the scaffolds are able to promote their osteoblastic activity.Publicationtype: Journal Article196 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Open porous dealloying-based biomaterials as a novel biomaterial platformThe close match of stiffness between implant material and bone is critically important to avoid stress-shielding effect and ensure a fast healing of injured tissues. Here, we introduce liquid metal dealloying method for synthesis of robust open porous biomaterials possessing low Young's modulus. The remarkable advantage of the liquid metal dealloying method is a large flexibility in selecting chemical composition of a desired porous biomaterial together with unique tunable microstructure. To demonstrate the versatility of the method, a number of open porous TixZr100-x alloys with different chemical compositions and microstructural characteristics was developed by dealloying precursor (TixZr100-x)yCu100-y alloys in liquid magnesium. The effects of the processing conditions and the precursors' chemical composition on the microstructure of the porous TixZr100-x as well as their mechanical behavior were discussed in detail. In particular, the porous TixZr100-x distinguish themselves due to a low and tunable stiffness ranging from 3.2 to 15.1 GPa and a rather high strength reaching up to 480 MPa. This unique combination of mechanical properties of the new open porous TixZr100-x alloys becomes even more interesting in view of preliminary biological tests highlighting their excellent cytocompatibility. Overall, the liquid metal dealloying provides an opportunity for designing a new biomaterials platform with flexible tunable functionality.Publicationtype: Journal Article176 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Corrosion of magnesium in static and dynamic (bioreactor) systems(European Society for Biomaterials, 2011); ; ; ; Publicationtype: Conference Paper19