Röntgenstrukturuntersuchungen an metallocenkatalysierten Polypropylenen

The subject of this thesis is the examination of the properties of polypropylene (PP) with different amount of isotacticity. The presented measurements show the large range of properties of polypropylene: lasting from plastic, semi-crystalline to highly elastic X-ray-amorphous. The lower the crystallinity, the higher the elasticity of the samples. Thus, the x-ray-amorphous sample achieves a complete resetting of the strain after the first drawing cycle. The stress-strain behavior of the sample was described by the Van der Waals model for polymers. By the dynamic-mechanical measurements the complex compliance was determined in dependence of the temperature, frequency and shear amplitude. Here the observed phase transitions could be correlated with the DSC measurements. Thereby, the amorphous X-ray sample turns out to have a great capability as rubber material; its rubber plateau extending over a temperature range of 150K. In order to decide which processes are responsible for these transitions, temperature dependent WAXS and SAXS measurements were performed. For this purpose, setups at the polymerbeamline in the HASYLAB at DESY were realized, which permitted efficient measurement periods with an accuracy comparable to Guiniertechnique. The high accuracy of +/-0.5 Grad in the scattering angle also allowed for a reflex analysis, by which the crystallite size was determined in dependence of the temperature and the crystal modifications. The results of these measurements led to an explanation of the reason for the calorimetry transitions. The investigation of the superstructure under uniaxial drawing revealed clearly the transition from a lamella structure to a fibrillae structure. Furthermore, the atomic structure and the superstructure as well as their orientation under uniaxial drawing were examined. Thereby, the change in crystallization became apparent and, in particular, a strain induced crystallization for the low crystalline samples could be observed

Adjacent vertebral failure after vertebroplasty: a biomechanical study of low-modulus PMMA cement

PMMA is the most common bone substitute used for vertebroplasty. An increased fracture rate of the adjacent vertebrae has been observed after vertebroplasty. Decreased failure strength has been noted in a laboratory study of augmented functional spine units (FSUs), where the adjacent, non-augmented vertebral body always failed. This may provide evidence that rigid cement augmentation may facilitate the subsequent collapse of the adjacent vertebrae. The purpose of this study was to evaluate whether the decrease in failure strength of augmented FSUs can be avoided using low-modulus PMMA bone cement. In cadaveric FSUs, overall stiffness, failure strength and stiffness of the two vertebral bodies were determined under compression for both the treated and untreated specimens. Augmentation was performed on the caudal vertebrae with either regular or low-modulus PMMA. Endplate and wedge-shaped fractures occurred in the cranial and caudal vertebrae in the ratios endplate:wedge (cranial:caudal): 3:8 (5:6), 4:7 (7:4) and 10:1 (10:1) for control, low-modulus and regular cement group, respectively. The mean failure strength was 3.3 ± 1 MPa with low-modulus cement, 2.9 ± 1.2 MPa with regular cement and 3.6 ± 1.3 MPa for the control group. Differences between the groups were not significant (p = 0.754 and p = 0.375, respectively, for low-modulus cement vs. control and regular cement vs. control). Overall FSU stiffness was not significantly affected by augmentation. Significant differences were observed for the stiffness differences of the cranial to the caudal vertebral body for the regular PMMA group to the other groups (p < 0.003). The individual vertebral stiffness values clearly showed the stiffening effect of the regular cement and the lesser alteration of the stiffness of the augmented vertebrae using the low-modulus PMMA compared to the control group (p = 0.999). In vitro biomechanical study and biomechanical evaluation of the hypothesis state that the failure strength of augmented functional spine units could be better preserved using low-modulus PMMA in comparison to regular PMMA cement

Bone cement allocation analysis in artificial cancellous bone structures.

Background One of the most serious adverse events potentially occurring during vertebroplasty is cement leakage. Associated risks for the patient could be reduced if cement filling is preoperatively planned. This requires a better understanding of cement flow behaviour. Therefore, the aim of the present study was to investigate bone cement distribution in artificial inhomogeneous cancellous bone structures during a simulated stepwise injection procedure. Methods Four differently coloured 1-mL cement portions were injected stepwise into six open-porous aluminum foam models with simulated leakage paths. Each model was subsequently cross-sectioned and high-resolution pictures were taken, followed by anatomical site allocation based on the assumption about a posterior insertion of the cannula. A radial grid consisting of 36 equidistant beams (0°-350°) was applied to evaluate the cement flow along each beam by measuring the radial length of each cement portion (total length) and of all four portions together (distance to border). Independently from the injection measurements, the viscosity of 20 cement portions was measured at time points corresponding to the start of the first and the end of the last injection. Results Despite some diffuse colour transitions at the borderlines, no interfusion between the differently coloured cement portions was observed. The two highest values for total length of each of the first three injected cement portions and for distance to border were indicated in directions anterior bilateral to the cannula along the 120°, 240° and 250° beams and posterolateral along the 60° beam. The two highest total lengths for the fourth cement portion were registered in the direction of the cannula along the 170° and 180° beams. Standard deviations of total length for each of the last three injected portions and for distance to border were with two highest values in directions anterior bilateral to the cannula along the 120°, 150°, 240° and 250° beams and opposite to the direction of the cannula along the 10° beam. The two highest values for the first cement portion were registered posterior bilateral to the cannula along the 70° and 350° beams. The values for averaged standard deviations of the total length of the fourth cement portion and the distance to border were significantly higher in comparison to the first cement portion (p ≤ 0.020). Dynamic viscosity at the start of the first injection was 343 ± 108 Pa∙s and increased to 659 ± 208 Pa∙s at the end of the fourth injection. Conclusion The simulated leakage path seemed to be the most important adverse injection factor influencing the uniformity of cement distribution. Another adverse factor causing dispersion of this distribution was represented by the simulated bone marrow. However, the rather uniform distribution of the totally injected cement amount, considered as one unit, could be ascribed to the medium viscosity of the used cement. Finally, with its short waiting time of 45 s, the stepwise injection procedure was shown to be ineffective in preventing cement leakage

Der Inklusion die Treue halten – Sieben Thesen zur Inklusion als Ereignis nach Badiou

Boger JM-A. Der Inklusion die Treue halten – Sieben Thesen zur Inklusion als Ereignis nach Badiou. In: Hinz A, Kinne T, Kruschel R, Winter S, eds. Von der Zukunft her denken – Inklusive Pädagogik im Diskurs. Bad Heilbrunn: Klinkhardt; 2016

Die Macht des Vorurteils: Menschenfeindliche Inklusionsvorstellungen

Zick A. Die Macht des Vorurteils: Menschenfeindliche Inklusionsvorstellungen. In: Lütje-Klose B, Boger M-A, Hopmann B, Neumann P, eds. Leistung inklusive? Inklusion in der Leistungsgesellschaft. Heilbrunn: Verlag Julius Klinkhardt; 2017: 26-38

The effect of standard and low-modulus cement augmentation on the stiffness, strength, and endplate pressure distribution in vertebroplasty

Vertebroplasty restores stiffness and strength of fractured vertebral bodies, but alters their stress transfer. This unwanted effect may be reduced by using more compliant cements. However, systematic experimental comparison of structural properties between standard and low-modulus augmentation needs to be done. This study investigated how standard and low-modulus cement augmentation affects apparent stiffness, strength, and endplate pressure distribution of vertebral body sections