A preliminary animal study of thermal rheology fluid as a new temperature-dependent liquid intravascular embolic material.

Purpose:Thermal rheology (TR) fluid, which comprises polyethylene (PE) particles, their dispersant, and solvent, is a material that increases in viscosity to various degrees depending on the type and ratio of these constituents when its temperature rises. The viscosity of type 1 (TRF-1) increases more than that of type 2 (TRF-2) near rabbit body temperature. This preliminary animal study aimed to determine the basic characteristics and embolic effect of TR fluid by comparing TRF-1 and TRF-2.Materials and methods:Twenty-four Japanese white rabbits underwent unilateral renal artery embolization using TRF-1 or TRF-2 and follow-up angiography at 7 or 28 days (4 subgroups, n = 6 each). Subsequently, the rabbits were euthanized, and the embolized kidneys were removed for pathological examination. The primary and final embolization rates were defined as the ratio of renal artery area not visible immediately after embolization and follow-up angiography, respectively, to visualized renal artery area before embolization. The final embolization rate and maximum vessel diameter filled with PE particles were compared between materials. Moreover, the embolic effect was determined to be persistent when a two-sided 95% confidence interval (CI) for the difference in means between the embolization rates was < 5%.Results:The final embolization rate was significantly higher for the TRF-1 than for the TRF-2 at both 7 (mean 80.7% [SD 18.7] vs. 28.4% [19.9], p = 0.001) and 28 days (94.0% [3.5] vs. 37.8% [15.5], p < 0.001). The maximum occluded vessel diameter was significantly larger for TRF-1 than for TRF-2 (870 µm [417] vs. 270 µm [163], p < 0.001). The embolic effect of TRF-1 was persistent until 28 days (difference between rates - 3.3 [95% CI - 10.0-3.4]).Conclusion:The embolic effect of TRF-1 was more persistent than that of TRF-2, and the persistency depended on the type and ratio of TR fluid constituents

In Situ X-Ray Diffraction Study of the Oxide Formed on Alloy 600 in Borated and Lithiated High-Temperature Water

In situ x-ray diffraction (XRD) measurements of the oxide film formed on Alloy 600 in borated and lithiated high-temperature water were conducted to demonstrate a capability to investigate rapid changes in oxide films during transient water chemistry conditions. In the presence of dissolved hydrogen (DH) = 30 cm3/kg [H2O] and dissolved oxygen (DO) < 0.06 ppm, only spinel oxides were detected and no significant NiO peak was found even after 1,220 h exposure. By contrast, once the DO was increased to 8 ppm, a NiO peak grew rapidly. Within 7 h, the amount of NiO became comparable to that of spinel oxide. However, when DO was decreased again below 0.3 ppm and DH was increased up to 30 cm3/kg [H2O], the ratio of NiO to spinel did not change during 10 h. Thus, the rate of dissolution of NiO in DH = 30 cm3/kg water seemed to be lower than the growth rate of NiO in high DO conditions. After these in situ XRD measurements, additional ex situ scanning electron microscope and energy dispersive spectrometry observations on cross sections of the oxide film were also conducted to check the validity of the results of the in situ XRD measurements. It was demonstrated that in situ XRD measurement is suitable for investigating time-dependent phenomena during formation of oxide films. The real time investigation of time-dependent phenomena is the benefit of in situ measurement. The details of the measurement method and the results are reported in this paper

Tensile deformation behavior of TRIP-aided bainitic ferrite steel in the post-necking strain region

Transformation induced plasticity (TRIP) steels present a remarkable balance of strength and ductility. However, their post-necking hardening behavior, which is required for press-forming and automobile crash simulation, is unreliable because of their stress-triaxiality dependency. Therefore, we analyzed the stress-triaxiality hardening in the post-necking strain regions of tensile loaded TRIP steel to accurately evaluate the stress and strain distribution. Tensile tests were accordingly conducted on small, round-bar specimens to evaluate the true stress vs. cross-sectional reduction ratio curves up to fracture. Additionally, the stress distribution inside each specimen was measured using synchrotron X-ray diffraction. Using these measurements, the hardening law for the TRIP steel was identified through a series of finite element (FE) simulations, in which a simplified phenomenological strain and stress-triaxiality hardening were found to agree well with the measurements in the post-necking strain region. As a result, the hardening rate of the TRIP steel showed a sudden decrease at the uniform elongation limit strain. The FE simulations including stress-triaxiality hardening successfully reproduced this hardening behavior up to the fracture, and the FE simulation including stress-triaxiality hardening and its saturation presented values closest to the XRD measurements. This simulation also agreed well with the measurements obtained in the tensile direction away from the neck center. A microstructural analysis of the retained austenite at the neck supported this result. The FE simulations revealed that a combination of the TRIP effect and its deactivation accelerates the localized deformation at the specimen neck under tensile loading