| 1. |
- Björn, Linnea, 1994, et al.
(author)
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Scanning Small-Angle X-ray Scattering of Injection-Molded Polymers: Anisotropic Structure and Mechanical Properties of Low-Density Polyethylene
- 2023
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In: ACS Applied Polymer Materials. - 2637-6105. ; 5:8, s. 6429-6440
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Journal article (peer-reviewed)abstract
- Injection molding is known to create a layered anisotropicmorphologyacross the sample thickness due to varying shear and cooling ratesduring the manufacturing process. In this study, scanning small-angleX-ray scattering was used to visualize and quantify the distributionof hierarchical structures present in injection-molded parts of low-densitypolyethylene (LDPE) with varying viscosities. By combining scatteringdata with results from injection molding simulations and tensile testing,we find that oriented shish-kebab structures, as well as elongatedspherulite structures consisting of semicrystalline ellipsoids, contributeto high ultimate tensile strength along the flow direction. Furthermore,we show that a higher degree of orientation is found close to theinjection gate and in LDPE with higher viscosity, consequently fromelevated shear and cooling rates present during the injection moldingprocess.
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| 2. |
- Finnilä, Mikko A J, et al.
(author)
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Mineral Crystal Thickness in Calcified Cartilage and Subchondral Bone in Healthy and Osteoarthritic Human Knees
- 2022
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In: Journal of Bone and Mineral Research. - : Wiley. - 1523-4681 .- 0884-0431. ; 37:9, s. 1700-1710
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Journal article (peer-reviewed)abstract
- Osteoarthritis (OA) is the most common joint disease, where articular cartilage degradation is often accompanied with sclerosis of the subchondral bone. However, the association between OA and tissue mineralization at the nanostructural level is currently not understood. In particular, it is technically challenging to study calcified cartilage, where relevant but poorly understood pathological processes such as tidemark multiplication and advancement occur. Here, we used state-of-the-art microfocus small-angle X-ray scattering with a 5-μm spatial resolution to determine the size and organization of the mineral crystals at the nanostructural level in human subchondral bone and calcified cartilage. Specimens with a wide spectrum of OA severities were acquired from both medial and lateral compartments of medial compartment knee OA patients (n = 15) and cadaver knees (n = 10). Opposing the common notion, we found that calcified cartilage has thicker and more mutually aligned mineral crystals than adjoining bone. In addition, we, for the first time, identified a well-defined layer of calcified cartilage associated with pathological tidemark multiplication, containing 0.32 nm thicker crystals compared to the rest of calcified cartilage. Finally, we found 0.2 nm thicker mineral crystals in both tissues of the lateral compartment in OA compared with healthy knees, indicating a loading-related disease process because the lateral compartment is typically less loaded in medial compartment knee OA. In summary, we report novel changes in mineral crystal thickness during OA. Our data suggest that unloading in the knee might be involved with the growth of mineral crystals, which is especially evident in the calcified cartilage.
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| 3. |
- Gao, Zirui, et al.
(author)
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High-speed tensor tomography: iterative reconstruction tensor tomography (IRTT) algorithm
- 2019
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In: Acta Crystallographica Section A: Foundations and Advances. - 2053-2733. ; 75, s. 223-238
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Journal article (peer-reviewed)abstract
- The recent advent of tensor tomography techniques has enabled tomographic investigations of the 3D nanostructure organization of biological and material science samples. These techniques extended the concept of conventional X-ray tomography by reconstructing not only a scalar value such as the attenuation coefficient per voxel, but also a set of parameters that capture the local anisotropy of nanostructures within every voxel of the sample. Tensor tomography data sets are intrinsically large as each pixel of a conventional X-ray projection is substituted by a scattering pattern, and projections have to be recorded at different sample angular orientations with several tilts of the rotation axis with respect to the X-ray propagation direction. Currently available reconstruction approaches for such large data sets are computationally expensive. Here, a novel, fast reconstruction algorithm, named iterative reconstruction tensor tomography (IRTT), is presented to simplify and accelerate tensor tomography reconstructions. IRTT is based on a second-rank tensor model to describe the anisotropy of the nanostructure in every voxel and on an iterative error backpropagation reconstruction algorithm to achieve high convergence speed. The feasibility and accuracy of IRTT are demonstrated by reconstructing the nanostructure anisotropy of three samples: a carbon fiber knot, a human bone trabecula specimen and a fixed mouse brain. Results and reconstruction speed were compared with those obtained by the small-angle scattering tensor tomography (SASTT) reconstruction method introduced by Liebi et al. [Nature (2015), 527, 349–352]. The principal orientation of the nanostructure within each voxel revealed a high level of agreement between the two methods. Yet, for identical data sets and computer hardware used, IRTT was shown to be more than an order of magnitude faster. IRTT was found to yield robust results, it does not require prior knowledge of the sample for initializing parameters, and can be used in cases where simple anisotropy metrics are sufficient, i.e. the tensor approximation adequately captures the level of anisotropy and the dominant orientation within a voxel. In addition, by greatly accelerating the reconstruction, IRTT is particularly suitable for handling large tomographic data sets of samples with internal structure or as a real-time analysis tool during the experiment for online feedback during data acquisition. Alternatively, the IRTT results might be used as an initial guess for models capturing a higher complexity of structural anisotropy such as spherical harmonics based SASTT in Liebi et al. (2015), improving both overall convergence speed and robustness of the reconstruction.
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| 4. |
- Hanczyc, Piotr, et al.
(author)
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Photonics of Hydrothermally Treated ß-Lactoglobulin Amyloids
- 2024
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In: SMALL SCIENCE. - : WILEY. - 2688-4046.
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Journal article (peer-reviewed)abstract
- Increased temperature and high pressure are applied to beta-lactoglobulin fibrils in the autoclave, resulting in the acquisition of a composite material comprised of partially disassembled amyloid fibrils and carbon dots. Confirmation of the preservation of the beta-sheet motif attributed to amyloids in the hydrothermally treated fibrils is obtained through wide-angle X-ray scattering and ThT assay. Z-scan analysis reveals a two-photon absorption (2PA) enhancement in the low-lying transition band (La) of tyrosine, while quantum chemical calculations demonstrate a correlation between the yield of 2PA and the interspace distance between aromatic residues. Overall, the intrinsic optical properties of amyloid fibrils treated in a subcritical water environment are found to be linked with the pi-conjugation of tyrosine units and their through-space coupling. The resulting composite material is employed as a coating for a commercial ultraviolet light-emitting diode lamp, showcasing the potential utility of sustainable biomaterials with improved optical properties for photonics applications. By subjecting beta-lactoglobulin fibrils to elevated temperature and pressure in autoclave, partially disassembled fibrils are generated. The study reveals a correlation between fluorescence and two-photon absorption and the spacing of aromatic residues, shedding light on the mechanism behind the improved optical properties of amyloid fibrils. Furthermore, the hydrothermally treated beta-lactoglobulin fibrils are utilized to coat ultraviolet light-emitting diode lamps. image (c) 2024 WILEY-VCH GmbH
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| 5. |
- Kumar Rajasekharan, Anand, 1990, et al.
(author)
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Bioinspired Structural Hierarchy within Macroscopic Volumes of Synthetic Composites
- 2018
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In: Advanced healthcare materials. - : Wiley. - 2192-2640 .- 2192-2659. ; 7:18
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Journal article (peer-reviewed)abstract
- A key challenge in developing bioinspired composites is the fabrication of well-defined 3D hierarchical structures ranging from nano to the macroscale. Herein, the development of a synthetic polymer–apatite composite realized by integrating bottom-up self-assembly and additive manufacturing (AM) is described. The resulting composite exhibits a bioinspired hierarchical structure over its 3D macroscopic volume. The composite is assembled in a bottom-up manner, where periodic nanoscale assemblies of organic micellar fibrils and inorganic apatite nanocrystals are organized as bundles of mineralized microstructures. These microstructural bundles are preferentially oriented throughout the macroscopic volume of the material via extrusion based AM. The obtained structural hierarchy is investigated in 3D using electron microscopy and small angle X-ray scattering tensor tomography and correlated to the structural hierarchy and anisotropy observed in biological tissues such as bone and the bone–cartilage interface. This work demonstrates the possibility to form polymer–apatite composites with a well-defined hierarchical structure throughout its macroscopic volume, which is crucial for the development of mechanically optimized materials for applications such as bone and osteochondral implants.
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| 6. |
- Liebi, Marianne, 1984, et al.
(author)
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3D nanoscale analysis of bone healing around degrading Mg implants evaluated by X-ray scattering tensor tomography
- 2021
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In: Acta Biomaterialia. - : Elsevier BV. - 1878-7568 .- 1742-7061. ; 134, s. 804-817
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Journal article (peer-reviewed)abstract
- The nanostructural adaptation of bone is crucial for its biocompatibility with orthopedic implants. The bone nanostructure also determines its mechanical properties and performance. However, the bone's temporal and spatial nanoadaptation around degrading implants remains largely unknown. Here, we present insights into this important bone adaptation by applying scanning electron microscopy, elemental analysis, and small-angle X-ray scattering tensor tomography (SASTT). We extend the novel SASTT reconstruction method and provide a 3D scattering reciprocal space map per voxel of the sample's volume. From this reconstruction, parameters such as the thickness of the bone mineral particles are quantified, which provide additional information on nanostructural adaptation of bone during healing. We selected a rat femoral bone and a degrading ZX10 magnesium implant as model system, and investigated it over the course of 18 months, using a sham as control. We observe that the bone's nanostructural adaptation starts with an initially fast interfacial bone growth close to the implant, which spreads by a re-orientation of the nanostructure in the bone volume around the implant, and is consolidated in the later degradation stages. These observations reveal the complex bulk bone-implant interactions and enable future research on the related biomechanical bone responses. Statement of significance: Traumatic bone injuries are among the most frequent causes of surgical treatment, and often require the placement of an implant. The ideal implant supports and induces bone formation, while being mechanically and chemically adapted to the bone structure, ensuring a gradual load transfer. While magnesium implants fulfill these requirements, the nanostructural changes during bone healing and implant degradation remain not completely elucidated. Here, we unveil these processes in rat femoral bones with ZX10 magnesium implants and show different stages of bone healing in such a model system.
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| 7. |
- Rodriguez Palomo, Adrian, 1992, et al.
(author)
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In Situ Visualization of the Structural Evolution and Alignment of Lyotropic Liquid Crystals in Confined Flow
- 2021
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In: Small. - : Wiley. - 1613-6810 .- 1613-6829. ; 17:7
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Journal article (peer-reviewed)abstract
- Self‐assembled materials such as lyotropic liquid crystals offer a wide variety of structures and applications by tuning the composition. Understanding materials behavior under flow and the induced alignment is wanted in order to tailor structure related properties. A method to visualize the structure and anisotropy of ordered systems in situ under dynamic conditions is presented where flow‐induced nanostructural alignment in microfluidic channels is observed by scanning small angle X‐ray scattering in hexagonal and lamellar self‐assembled phases. In the hexagonal phase, the material in regions with high extensional flow exhibits orientation perpendicular to the flow and is oriented in the flow direction only in regions with a high enough shear rate. For the lamellar phase, a flow‐induced morphological transition occurs from aligned lamellae toward multilamellar vesicles. However, the vesicles do not withstand the mechanical forces and break in extended lamellae in regions with high shear rates. This evolution of nanostructure with different shear rates can be correlated with a shear thinning viscosity curve with different slopes. The results demonstrate new fundamental knowledge about the structuring of liquid crystals under flow. The methodology widens the quantitative investigation of complex structures and identifies important mechanisms of reorientation and structural changes.
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| 8. |
- Rodriguez Palomo, Adrian, 1992, et al.
(author)
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Nanostructure and anisotropy of 3D printed lyotropic liquid crystals studied by scattering and birefringence imaging
- 2021
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In: Additive Manufacturing. - : Elsevier BV. - 2214-8604. ; 47
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Journal article (peer-reviewed)abstract
- Extrusion-based 3D printing of hexagonal and lamellar lyotropic liquid crystals is a powerful technique to produce hierarchical materials with well-defined anisotropic structure. Tailoring the properties of 3D printed objects requires a precise control of the nanostructure; however, a sufficiently high degree of anisotropy is often not achieved. In this study, scanning small angle X-ray scattering was performed in situ at the exit of the needle during 3D printing. We study the induced anisotropy and nanostructure in hexagonal and lamellar lyotropic liquid crystals. Mapping of extruded filaments during printing revealed that narrower nozzle diameters (370 μm) resulted in less anisotropic structures with a wider distribution of orientation angles across the cross section, while larger nozzle diameters (550 μm) resulted in more anisotropic structures with an overall higher degree of orientation. The wall shear rate is higher for the narrower nozzle, which produces wall slip, resulting in a highly anisotropic shell, and a less aligned filament core. Further examination of the filaments revealed phase transitions due to solvent evaporation. The time scales were of 10 – 20 min of exposure to atmospheric conditions. Simultaneously, a loss in the macroscopic anisotropy of the hexagonal self-assembled structure was observed. These processes occur during and after extrusion-based 3D printing of liquid crystals and limit the fine control of the final structure. The variability of structures achieved for our different systems highlights the importance of structural characterization during and after extrusion to guarantee high anisotropy and well-defined structures.
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