| 1. |
- Moosmann, Julian, et al.
(författare)
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A load frame for in situ tomography at PETRA III
- 2019
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Ingår i: Developments in X-Ray Tomography XII. - : SPIE. - 0277-786X .- 1996-756X. - 9781510629196 ; 11113
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- A load frame for in situ mechanical testing is developed for the microtomography end stations at the imaging beamline P05 and the high-energy material science beamline P07 of PETRA III at DESY, both operated by the Helmholtz- Zentrum Geesthacht. The load frame is fully integrated into the beamline control system and can be controlled via a feedback loop. All relevant parameters (load, displacement, temperature, etc.) are continuously logged. It can be operated in compression or tensile mode applying forces of up to 1 kN and is compatible with all contrast modalities available at IBL and HEMS i.e. conventional attenuation contrast, propagation based phase contrast and differential phase contrast using a grating interferometer. The modularity and flexibility of the load frame allows conducting a wide range of experiments. E.g. compression tests to understand the failure mechanisms in biodegradable implants in rat bone or to investigate the mechanics and kinematics of the tessellated cartilage skeleton of sharks and rays, or tensile tests to illuminate the structure-property relationship in poplar tension wood or to visualize the 3D deformation of the tendonbone insertion. We present recent results from the experiments described including machine-learning driven volume segmentation and digital volume correlation of load tomography sequences.
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| 2. |
- Moosmann, Julian, et al.
(författare)
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Biodegradable magnesium-based implants in bone studied by synchrotron radiation microtomography
- 2017
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Ingår i: Developments in X-Ray Tomography XI. - : SPIE - International Society for Optical Engineering. ; 10391
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Konferensbidrag (refereegranskat)abstract
- Permanent implants made of titanium or its alloys are the gold standard in many orthopedic and traumatological applications due to their good biocompatibility and mechanical properties. However, a second surgical intervention is required for this kind of implants as they have to be removed in the case of children that are still growing or on patient's demand. Therefore, magnesium-based implants are considered for medical applications as they are degraded under physiological conditions. The major challenge is tailoring the degradation in a manner that is suitable for a biological environment and such that stabilization of the bone is provided for a controlled period. In order to understand failure mechanisms of magnesium-based implants in orthopedic applications and, further, to better understand the osseointegration, screw implants in bone are studied under mechanical load by means of a push-out device installed at the imaging beamline P05 of PETRA III at DESY. Conventional absorption contrast microtomography and phasecontrast techniques are applied in order to monitor the bone-to-implant interface under increasing load conditions. In this proof-of-concept study, first results from an in situ push-out experiment are presented.
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| 3. |
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| 4. |
- Raj, Akanksha, et al.
(författare)
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Lubrication synergy : Mixture of hyaluronan and dipalmitoylphosphatidylcholine (DPPC) vesicles
- 2017
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 488, s. 225-233
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Tidskriftsartikel (refereegranskat)abstract
- Phospholipids and hyaluronan have been implied to fulfil important roles in synovial joint lubrication. Since both components are present in synovial fluid, self-assembly structures formed by them should also be present. We demonstrate by small angle X-ray scattering that hyaluronan associates with the outer shell of dipalmitoylphophatidylcholine (DPPC) vesicles in bulk solution. Further, we follow adsorption to silica from mixed hyaluronan/DPPC vesicle solution by Quartz Crystal Microbalance with Dissipation measurements. Atomic Force Microscope imaging visualises the adsorbed layer structure consisting of non-homogeneous phospholipid bilayer with hyaluronan/DPPC aggregates on top. The presence of these aggregates generates a long-range repulsive surface force as two such surfaces are brought together. However, the aggregates are easily deformed, partly rearranged into multilayer structures and partly removed from between the surfaces under high loads. These layers offer very low friction coefficient (<0.01), high load bearing capacity (≈23 MPa), and self-healing ability. Surface bound DPPC/hyaluronan aggregates provide a means for accumulation of lubricating DPPC molecules on sliding surfaces.
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| 5. |
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| 6. |
- Wang, Min, et al.
(författare)
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The effect of temperature on supported dipalmitoylphosphatidylcholine (DPPC) bilayers : Structure and lubrication performance
- 2015
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 445, s. 84-92
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Tidskriftsartikel (refereegranskat)abstract
- Phospholipids fulfill an important role in joint lubrication. They, together with hyaluronan and glycoproteins, are the biolubricants that sustain low friction between cartilage surfaces bathed in synovial fluid. In this work we have investigated how the friction force and load bearing capacity of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) bilayers on silica surfaces are affected by temperature, covering the temperature range 25–52 °C. Friction forces have been determined utilizing the AFM colloidal probe technique, which showed that DPPC bilayers are able to provide low friction forces over the whole temperature interval. However, the load bearing capacity is improved at higher temperatures. We interpret this finding as being a consequence of lower rigidity and higher self-healing capacity of the DPPC bilayer in the liquid disordered state compared to the gel state. The corresponding structure of solid supported DPPC bilayers at the silica–liquid interface has been followed using X-ray reflectivity measurements, which suggests that the DPPC bilayer is in the gel phase at 25 °C and 39 °C and in the liquid disordered state at 55 °C. Well-defined bilayer structures were observed for both phases. The deposited DPPC bilayers were also imaged using AFM PeakForce Tapping mode, and these measurements indicated a less homogeneous layer at temperatures below 37 °C.
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| 7. |
- Wieland, D. C. Florian, et al.
(författare)
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Structure of DPPC-hyaluronan interfacial layers - effects of molecular weight and ion composition
- 2016
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Ingår i: Soft Matter. - : Royal Society of Chemistry. - 1744-683X .- 1744-6848. ; 12:3, s. 729-740
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Tidskriftsartikel (refereegranskat)abstract
- Hyaluronan and phospholipids play an important role in lubrication in articular joints and provide in combination with glycoproteins exceptionally low friction coefficients. We have investigated the structural organization of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) Langmuir layers at the solution-air interface at different length scales with respect to the adsorption of hyaluronan (HA). This allows us to assemble a comprehensive picture of the adsorption and the resulting structures, and how they are affected by the molecular weight of HA and the presence of calcium ions. Brewster angle microscopy and grazing incident diffraction were used to determine the lateral structure at the micro- and macro scale. The data reveals an influence of HA on both the macro and micro structure of the DPPC Langmuir layer, and that the strength of this effect increases with decreasing molecular weight of HA and in presence of calcium ions. Furthermore, from X-ray reflectivity measurements we conclude that HA adsorbs to the hydrophilic part of DPPC, but data also suggest that two types of interfacial structures are formed at the interface. We argue that hydrophobic forces and electrostatic interactions play important rules for the association between DPPC and HA. Surface pressure area isotherms were used to determine the influence of HA on the phase behavior of DPPC while electrophoretic mobility measurements were used to gain insight into the binding of calcium ions to DPPC vesicles and hyaluronan.
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| 8. |
- Wieland, D. C. Florian, et al.
(författare)
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Studying solutions at high shear rates : A dedicated microfluidics setup
- 2016
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Ingår i: Journal of Synchrotron Radiation. - : International Union of Crystallography. - 0909-0495 .- 1600-5775. ; 23:2, s. 480-486
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Tidskriftsartikel (refereegranskat)abstract
- The development of a dedicated small-angle X-ray scattering setup for the investigation of complex fluids at different controlled shear conditions is reported. The setup utilizes a microfluidics chip with a narrowing channel. As a consequence, a shear gradient is generated within the channel and the effect of shear rate on structure and interactions is mapped spatially. In a first experiment small-angle X-ray scattering is utilized to investigate highly concentrated protein solutions up to a shear rate of 300000 s-1. These data demonstrate that equilibrium clusters of lysozyme are destabilized at high shear rates.
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| 9. |
- Willumeit-Römer, Regine, et al.
(författare)
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Visualization of Implant Failure by Synchrotron Tomography
- 2018
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Ingår i: TMS 2018 147th Annual Meeting & Exhibition Supplemental Proceedings. - Cham : Springer. - 9783319725253 - 9783319725260 ; , s. 275-284
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Konferensbidrag (refereegranskat)abstract
- Magnesium (Mg) and its alloys degrade under physiological conditions. But how strong is the connection between the implant, the corrosion layer and the surrounding tissue, namely bone? Biomechanical tests like push-out tests have shown that a degraded Mg-pin is surprisingly well integrated with the bone “as reported by Castellani et al. (Acta Biomater 7(1):432–440, 2011) [1]”. High-resolution synchrotron tomography offers a deep look into the microstructure of the material as well as of the bone during deformation until fracture happens. Here we present first data from an in situ tomography experiment of a biodegradable Mg-based implant under compressive load showing how Mg implants are incorporated into bone.
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| 10. |
- Zander, Thomas, et al.
(författare)
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The influence of hyaluronan on the structure of a DPPC-bilayer under high pressures
- 2016
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Ingår i: Colloids and Surfaces B. - : Elsevier. - 0927-7765 .- 1873-4367. ; 142, s. 230-238
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Tidskriftsartikel (refereegranskat)abstract
- The superior lubrication properties of synovial joints have inspired many studies aiming at uncovering the molecular mechanisms which give rise to low friction and wear. However, the mechanisms are not fully understood yet, and, in particular, it has not been elucidated how the biolubricants present at the interface of cartilage respond to high pressures, which arise during high loads of joints. In this study we utilize a simple model system composed of two biomolecules that have been implied as being important for joint lubrication. It consists of a solid supported dipalmitoylphosphatidylcholin (DPPC) bilayer, which was formed via vesicles fusion on a flat Si wafer, and the anionic polysaccharide hyaluronan (HA). We first characterized the structure of the HA layer that adsorbed to the DPPC bilayers at ambient pressure and different temperatures using X-ray reflectivity (XRR) measurements. Next, XRR was utilized to evaluate the response of the system to high hydrostatic pressures, up to 2 kbar (200 MPa), at three different temperatures. By means of fluorescence microscopy images the distribution of DPPC and HA on the surface was visualized. Our data suggest that HA adsorbs to the headgroup region that is oriented towards the water side of the supported bilayer. Phase transitions of the bilayer in response to temperature and pressure changes were also observed in presence and absence of HA. Our results reveal a higher stability against high hydrostatic pressures for DPPC/HA composite layers compared to that of the DPPC bilayer in absence of HA.
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