[Phantom studies using a high-resolution CT for ex-vivo imaging of degradable magnesium implants and simulated peri-implant bone formation in rabbit tibiae]. / Phantomuntersuchungen an einem hochauflösenden CT zur Ex-vivo-Darstellung von degradierbaren Magnesiumimplantaten und simulierten periimplantären Knochenschichten in Kaninchentibiae.

PURPOSE: Evaluation of the suitability of the high-resolution CT XtremeCT for ex vivo imaging of degradable magnesium implants with simulated peri-implant bone formation in rabbit tibiae and development of a method for calibrating the mass concentration of a magnesium alloy in an implant volume. MATERIALS AND METHODS: Using specially designed phantoms, degradable magnesium implants of the alloys LAE442, ZEK100, AX30 and MgCa 0.8 %, without coating and with peri-implant bone formation simulated by a coating, as well as rabbit tibiae were scanned. CT numbers and the contrast-to-noise-ratio (CNR) of the studied materials were determined. The visual distinction between implant and coating was evaluated. To calibrate the implant density, exemplary LAE442 pins with different mass concentrations were scanned using a specially constructed phantom. Subsequently, CT numbers corresponding to the appropriate mass concentration were determined. RESULTS: The implants, coating and substantia corticalis showed a similar density. Visual distinction between coating and implant was strongly dependent on the respective magnesium alloy and chosen scan parameter. A CNR of at least 0.2 was required for a distinction between implant and coating. For the mass concentration, a high CT number linearity (R2=0.99) throughout the measuring range (1811-1273 mg/cm3 LAE442) was found. CONCLUSION: As expected, the XtremeCT is primarily suitable for the imaging of bone tissue and implants. Good visual distinction of peri-implant bone formation on magnesium implants in an ex vivo phantom model ranges from possible to difficult depending on the bone density and alloy composition.

Phototransformation studies of halo-substituted cinnamates by Raman spectrometry and quantum-chemical computations.

The comprehension of the cinnamic derivative phototransformation mechanisms is particularly important when these molecules are used as addressable photosensitive layers. In this work we show that the halo-substituted cinnamate sensitivity to the phototransformation is a function of the excitation wavelength and the substituent nature and position. With this intention, we underline the existence of various isomers and rotatomers by Raman spectroscopy and we assign the observed vibrational modes with the help of quantum-chemical calculations. These various aspects of our work clarify the relative roles of the steric, inductive and mesomeric effects according to the considered substitution.

Cholesteric liquid crystals with a helical pitch gradient: spatial distribution of the concentration of chiral groups by Raman mapping in relation with the optical response and the microstructure.

Cholesteric liquid crystals (CLC) selectively reflect light when the helical pitch is of the order of the wavelength of the incident beam propagating along the helix axis. The wavelength bandwidth, related to the optical anisotropy, is typically limited to a few tens of nanometers in the visible part of the spectrum, which is insufficient for applications such as white-or-black polarizer-free reflective displays and smart windows for the control of the solar light and heat. A way to make cholesteric films reflecting in a broad wavelength band consists in associating various cholesteric pitches in the same film. In this work, it is shown how a study by confocal micro Raman spectrometry mapping makes it possible to have access to information accounting for the local organization of CLCs in the case of graded pitch materials. These investigations will be correlated to the optical response and the transverse microstructure of the CLC material as investigated by transmission electron microscopy. An accurate analysis of the vibrational behavior evolution of the C==O can be correlated to the evolution of the populations of the chiral and achiral groups in the case of the interdiffusion of two CLC substances with various stoechiometries. Besides an easy measurement of the Raman spectrum gives the opportunity to quantify the relative ratio of the mesogenic species and thus to go up by a simple way to the pitch of the helical structure.

[Influence of different surface machining treatments of resorbable implants made from different magnesium-calcium alloys on their degradation--a pilot study in rabbit models]. / Einfluss der Oberflächenbearbeitung von resorbier- baren Implantaten aus verschiedenen Magnesium- Calciumlegierungen auf die Degradation - Erste Ergebnisse einer Pilotstudie am Kaninchenmodell.

To examine the influence of different surface machining treatments of resorbable implants 3x5 mm cylinders of magnesium-calcium-alloys with plane, rough or sand blasted surface and different concentrations of calcium (0.4 %, 0.8 %, 1.2 % und 2.0 %) were implanted into the distal femur condylus of 18 New Zealand White Rabbits. They were placed into the spongy-cortical passage. During six weeks the animals were examined daily and x-rayed weekly. After euthanasia the bone was explanted and scanned in a microcomputed tomograph. The implants were well tolerated by the rabbits, neither lameness nor signs of pain occured. Wound healing was mostly without complications. Eight of 36 implants (22 %) showed dehiscence of suture within first ten days, whereby implants made of 1,2 % MgCa were mainly affected (six of 12 cases, 50 %). At the place of insertion all implants induced obvious callus genesis which could be seen in MgCa 1,2-cylinders with plane surface and MgCa 0,8-cylinders with rough and sand blasted surface the most. Influence of different calcium concentrations on degradation behaviour could not be discovered. They showed different stages of resorption. Concerning the different surface machining treatments sand blasted implants showed the highest degree of degradation which could be seen by the totally loss of structure in micro-computed examinations. These implants also showed in six of 36 cases a clinical occurrence of gas production. Rough implants showed an irregular degradation with high degree of resorption of some implants and signs of degradation only in the border area of others. Cylindricity maintained in plane implants. They showed loss of structure only in border areas.

Theoretical and vibrational spectroscopic analysis of the CO stretching mode of cholesteryl alkanoates: the particular case of the cholesteryl acetate.

Structural and vibrational properties of the CO stretching bond of cholesteryl acetate and related steroids are investigated theoretically and by Micro-Raman spectroscopy. In this work, an analysis of the CO stretching mode for the cholesteryl acetate is presented. Experimental results in crystalline, isotropic liquid and liquid crystal phases are compared with quantum chemical calculations using semi empirical hamiltonians (AM1 and PM3) and the density functional theory. The calculations were performed on isolated molecules with different conformations as found on previous investigations giving strong evidence of their existence. Calculated frequencies are found to be very close to experiments and suggest the possible existence of the predicted conformers.