Quantitative three-dimensional (3D) imaging of angiogenesis during bone repair remains an experimental challenge. We developed a novel contrast agent containing 0.07-to 0.1-mm particles of zirconium dioxide (ZrCA) and established subtraction mCT using synchrotron radiation (sSRCT) for quantitative imaging of angiogenesis and bone repair. This method was applied to a rat model of tibial bone repair 3 days (DAY3; n ¼ 2), 5 days (DAY5; n ¼ 8), or 10 days (DAY10; n ¼ 8) after drill-hole injury. Using the same drill-hole defect model, its potential use was illustrated by comparison of bone repair between hindlimbs subjected to mechanical unloading (n ¼ 6) and normal weight bearing (n ¼ 6) for 10 days. Following vascular casting with ZrCA, the defect site was scanned with 17.9-and 18.1-keV X-rays. In the latter, image contrast between ZrCA-filled vasculature and bone was enhanced owing to the sharp absorption jump of zirconium dioxide at 18.0 keV (k-edge). The two scan data sets were reconstructed with 2.74-mm voxel resolution, registered by mutual information, and digitally subtracted to extract the contrast-enhanced vascular image. K 2 HPO 4 phantom solutions were scanned at 17.9 keV for quantitative evaluation of bone mineral. Angiogenesis had already started, but new bone formation was not found on DAY3. New bone emerged near the defect boundary on DAY5 and took the form of trabecular-like structure invaded by microvessels on DAY10. Vascular and bone volume fractions, blood vessel and bone thicknesses, and mineralization were higher on DAY10 than on DAY5. All these parameters were found to be decreased after 10 days of hindlimb unloading, indicating the possible involvement of angiogenesis in bone repair impairment caused by reduced mechanical stimuli. In conclusion, the combined technique of sSRCT and ZrCA vascular casting is suitable for quantitative 3D imaging of angiogenesis and its surrounding bone regeneration. This method will be useful for better understanding the linkage between angiogenesis and bone repair.

Low-intensity whole-body vibration (LIWBV) may stimulate bone healing, but the involvement of vascular ingrowth, which is essential for bone regeneration, has not been well examined. We thus investigated the LIWBV effect on vascularization during early-stage bone healing. Mice aged 13 weeks were subjected to cortical drilling on tibial bone. Two days after surgery (day 0), mice were exposed daily to sine-wave LIWBV at 30 Hz and 0.1 g peak-to-peak acceleration for 20 min/day (Vib) or were sham-treated (sham). Following vascular casting with a zirconium-based contrast agent on days 6, 9, or 12 and sacrifice, vascular and bone images were obtained by K-edge subtraction micro-CT using synchrotron lights. Bone regeneration advanced more in the Vib group from days 9 to 12. The vascular volume fraction decreased from days 6 to 9 in both groups; however, from days 9 to 12, it was increased in shams, while it stabilized in the Vib group. The vascular volume fraction tended to be or was smaller in the Vib group on days 6 and 12. The vessel number density was higher on day 9 but lower on day 12 in the Vib group. These results suggest that the LIWBV-promoted bone repair is associated with the modulation of vascularization, but additional studies are needed to determine the causality of this association.

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Abstract. The microstructures of oxide scales formed on MoSi 2 at medium-high temperatures in air were observed by TEM. Based on the observation, relationships between oxidation temperature and formation of MoO 3 and crystallization of amorphous SiO 2 scales were investigated. At 1273 K and 1373 K, the oxide scales had a structure consisting of amorphous SiO 2 with small amounts of fine MoO 3 particles. The oxide scales at 1573 K and 1773 K had a structure consisting of amorphous and crystalline SiO 2 . Growth rate of the oxide scale formed at 1773 K appreciably increased due to crystallization of amorphous SiO 2 . It was thought that the increase in the oxidation rate at 1773 K was caused by a change in the diffusion mechanism from O 2 diffusion to lattice diffusion of O 2-through SiO 2 . In addition, the diffusion coefficient of oxygen was estimated from the growth rate of SiO 2 scale.

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