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- Computed tomography (6)
- Osteoporotic vertebral fracture (3)
- Bone regeneration (2)
- Large animal model (2)
- Large animal model sheep (2)
- MMC (2)
- NDE (2)
- Sheep (2)
- Vertebroplasty (2)
- X-ray refraction (2)
Organisationseinheit der BAM
For the first time Metal Matrix Composites (MMC) have been investigated by 3D Computed Tomography combined with enhanced interface contrast due to X-ray refraction. X-ray refraction is a relatively new approach for the characterization of advanced materials. The related techniques of Refraction Topography and Refraction Computed Tomography have been developed and applied at our laboratory during the last decade to meet the actual demand for improved nondestructive characterization of high performance composites, ceramics and other low density materials and components. X-ray refraction occurs, when X-rays crosses interfaces of spherical or cylindrical shape (e.g. pores or fibres) in the same way as visible light is refracted by lenses. These X-ray optical effects can be observed at small scattering angles of few minutes of arc as the refractive index n of X-rays is nearly unity (n = 1 10-6). Due to the short X-ray wavelength of about 0.1 nm the technique determines the amount of inner surfaces and interfaces of nanometer dimensions. The technique is expected to solve many problems in understanding the meaning of micro and sub micro structures in materials science. With the results of the CT investigation, some questions could be clarified for a better understanding of fatigue failure mechanisms under cyclic loading conditions. The specimens for the test programme have been provided by MTU Aero Engines. They consist of a titanium matrix (Ti6242) reinforced by SiC fibres (SCS6). The investigations have been performed at the materials research station of BAM (BAMline) at the Synchrotron Facility BESSY in Berlin, Germany.
Erstmals wurden MMCs mit Hilfe der Interface-Kontrast verstärkenden Röntgen-Refraktions-Technik in Kombination mit der 3D-CT-Technik untersucht. Die Methode der Röntgen-Refraktions-Topography sowie der Röntgen-Refraktions-Tomography wurden in den letzten Jahren speziell für die zerstörungsfreie Charakterisierung von Leichtbau-Hochleistungs-Werkstoffen wie Verbund-Werkstoffen und Keramiken entwickelt. Die Technik basiert auf der Refraktion von Röntgenlicht an Grenzflächen zwischen Bereichen unterschiedlicher Elektronendichte wie z.B. Faser- und Matrix-Werkstoff. Auf Grund der kurzen Röntgen-Wellenlänge hat der Brechungsindex einen Wert dicht bei eins, sodass der Streuwinkel nur wenige Bogenminuten beträgt. Der Vorteil der kurzen Wellenlänge besteht jedoch darin, dass Poren und Risse detektiert werden können, deren Größe im Nanometerbereich liegen. Damit kann die Refraktions-Technik zum besseren Verständnis von Mikro- und Submikro-Strukturen in der Materialwissenschaft eingesetzt werden. Mit der hier vorgestellten Refraktions-CT wurden Ermüdungsmechanismen an MMCs, bestehend aus SiC-Faser verstärktem Titan (Ti6242) untersucht. Die Messungen wurden am Röntgen-Messplatz der BAM (BAMline) am Synchrotron-Speicherring-BESSY in Berlin Adlershof durchgeführt.
Biological erosion is a key process for the recycling of carbonate and the formation of calcareous sediments in the oceans. Experimental studies showed that bioerosion is subject to distinct temporal variability, but previous long-term studies were restricted to tropical waters. Here, we present results from a 14-year bioerosion experiment that was carried out along the rocky limestone coast of the island of Rhodes, Greece, in the Eastern Mediterranean Sea, in order to monitor the pace at which bioerosion affects carbonate substrate and the sequence of colonisation by bioeroding organisms. Internal macrobioerosion was visualised and quantified by micro-computed tomography and computer-algorithm-based segmentation procedures. Analysis of internal macrobioerosion traces revealed a dominance of bioeroding sponges producing eight types of characteristic Entobia cavity networks, which were matched to five different clionaid sponges by spicule identification in extracted tissue. The morphology of the entobians strongly varied depending on the species of the producing sponge, its ontogenetic stage, available space, and competition by other bioeroders. An early community developed during the first 5 years of exposure with initially very low macrobioerosion rates and was followed by an intermediate stage when sponges formed large and more diverse entobians and bioerosion rates in-creased. After 14 years, 30 % of the block volumes were occupied by boring sponges, yielding maximum bioerosion rates of 900 g m.
Blick in den Boden
(2016)
Vertebroplasty or kyphoplasty of osteoporotic vertebral fractures bears the risk of pulmonary cement embolism (3.5%–23%) caused by leakage of commonly applied acrylic polymethylmethacrylate (PMMA) cement to spongious bone marrow or outside of the vertebrae. Ultraviscous cement and specific augmentation systems have been developed to reduce such adverse effects. Rapidly setting, resorbable, physiological calcium phosphate cement (CPC) may also represent a suitable alternative.
PURPOSE: This study aimed to compare the intravertebral extrusion of CPC and PMMA cement in an ex vivo and in vivo study in sheep.
STUDY DESIGN/SETTING: A prospective experimental animal study was carried out. METHODS: Defects (diameter 5 mm; 15 mm depth) were created by a ventrolateral percutane-ous approach in lumbar vertebrae of female Merino sheep (2–4 years) either ex vivo (n = 17) or in vivo (n = 6), and injected with: (1) CPC (L3); (2) CPC reinforced with 10% poly(l-lactide-co-glycolide) (PLGA) fibers (L4); or (3) PMMA cement (L5; Kyphon HV-R). Controls were untouched (L1) or empty defects (L2). The effects of the cement injections were assessed in vivo by blood gas analysis and ex vivo by computed tomography (CT), micro-CT (voxel size: 67 µm), histology, and biomechanical testing.
Large animal models are highly recommended for meaningful preclinical studies, including the optimization of cement augmentation for vertebral body defects by vertebroplasty/kyphoplasty.
The aim of this study was to perform a systematic characterization of a strictly minimally invasive in vivo large animal model for lumbar ventrolateral vertebroplasty.
This is a prospective experimental animal study.
Lumbar defects (diameter 5 mm; depth approximately 14 mm) were created by a ventrolateral percutaneous approach in aged, osteopenic, female sheep (40 Merino sheep; 6–9 years; 68–110 kg). L1 remained untouched, L2 was left with an empty defect, and L3 carried a defect injected with a brushite-forming calcium phosphate cement (CPC). Trauma/functional impairment, surgical techniques (including drill sleeve and working canula with stop), reproducibility, bone defects, cement filling, and functional cement augmentation were documented by intraoperative incision-to-suture time and X-ray, postoperative trauma/impairment scores, and ex vivo osteodensitometry, microcomputed tomography (CT), histology, static/fluorescence histomorphometry, and biomechanical testing.
Minimally invasive vertebroplasty resulted in short operation times (28±2 minutes; mean±standard error of the mean) and X-ray exposure (1.59±0.12 minutes), very limited local trauma (score 0.00±0.00 at 24 hours), short postoperative recovery (2.95±0.29 hours), and rapid decrease of the postoperative impairment score to 0 (3.28±0.36 hours). Reproducible defect creation and cement filling were documented by intraoperative X-ray and ex vivo conventional/micro-CT. Vertebral cement augmentation and osteoconductivity of the CPC was verified by osteodensitometry (CPC>control), micro-CT (CPC>control and empty defect), histology/static histomorphometry (CPC>control and empty defect), fluorescence histomorphometry (CPC>control; all p<.05 for 3 and 9 months), and compressive strength measurements (CPC numerically higher than control; 102% for 3 months and 110% for 9 months).
This first-time systematic clinical assessment of a minimally invasive, ventrolateral, lumbar vertebroplasty model in aged, osteopenic sheep resulted in short operation times, rapid postoperative recovery, and high experimental reproducibility. This model represents an optimal basis for standardized evaluation of future studies on vertebral augmentation with resorbable and osteoconductive CPC.