A flow diverter (FD) is a flexible, densely braided stent-mesh device placed endoluminally across an intracranial aneurysm to induce its thrombotic occlusion. FD treatment planning using computational virtual stenting and flow simulation requires accurate representation of the expanded FD geometry. We have recently developed a High Fidelity Virtual Stenting (HiFiVS) technique based on finite element analysis to simulate detailed FD deployment processes in patient-specific aneurysms (Ma et al. J. Biomech. 45: 2256–2263, 2012). This study tests if HiFiVS simulation can recapitulate real-life FD implantation. We deployed two identical FDs (Pipeline Embolization Device) into phantoms of a wide-necked segmental aneurysm using a clinical push-pull technique with different delivery wire advancements. We then simulated these deployment processes using HiFiVS and compared results against experimental recording. Stepwise comparison shows that the simulations precisely reproduced the FD deployment processes recorded in vitro. The local metal coverage rate and pore density quantifications demonstrated that simulations reproduced detailed FD mesh geometry. These results provide validation of the HiFiVS technique, highlighting its unique capability of accurately representing stent intervention in silico.

In vitro blood vessel biomodeling with realistic mechanical properties and geometrical structures is helpful for training in surgical procedures, especial those used in endovascular treatment. Poly (vinyl alcohol) hydrogel (PVA-H), which is made of Poly (vinyl alcohol) (PVA) and water, may be useful as a material for blood vessel biomodeling due to its low surface friction resistance and good transparency. In order to simulate the mechanical properties of blood vessels, measurements of mechanical properties of PVA-H were carried out with a dynamic mechanical analyzer, and the storage modulus (G') and loss modulus (G'') of PVA-H were obtained. PVA-Hs were prepared by the low-temperature crystallization method. They were made of PVA with various concentrations (C) and degrees of polymerization (DP), and made by blending two kinds of PVA having different DP or saponification values (SV). The G' and G'' of PVA-H increased, as the C or DP of PVA increased, or as the proportion of PVA with higher DP or SV increased. These results indicate that it is possible to obtain PVA-H with desirable dynamic viscoelasticity. Furthermore, it is suggested that PVA-H is stable in the temperature range of 0°C to 40°C, indicating that biomodeling made of PVA-H should be available at 37°C, the physiological temperature. The dynamic viscoelasticity of PVA-H obtained was similar to that of the dog blood vessel measured in previous reports. In conclusion, PVA-H is suggested to be useful as a material of blood vessel biomodeling.

To promote the functional restoration of the nervous system following injury, it is necessary to provide optimal extracellular signals that can induce neuronal regenerative activities, particularly neurite formation. This study aimed to examine the regulation of neuritogenesis by temperature-controlled repeated thermal stimulation (TRTS) in rat PC12 pheochromocytoma cells, which can be induced by neurotrophic factors to differentiate into neuron-like cells with elongated neurites. A heating plate was used to apply thermal stimulation, and the correlation of culture medium temperature with varying surface temperature of the heating plate was monitored. Plated PC12 cells were exposed to TRTS at two different temperatures via heating plate (preset surface temperature of the heating plate, 39.5°C or 42°C) in growth or differentiating medium for up to 18 h per day. We then measured the extent of growth, neuritogenesis, or acetylcholine esterase (AChE) activity (a neuronal marker). To analyze the mechanisms underlying the effects of TRTS on these cells, we examined changes in intracellular signaling using the following: tropomyosin-related kinase A inhibitor GW441756; p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580; and MAPK/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor U0126 with its inactive analog, U0124, as a control. While a TRTS of 39.5°C did not decrease the growth rate of cells in the cell growth assay, it did increase the number of neurite-bearing PC12 cells and AChE activity without the addition of other neuritogenesis inducers. Furthermore, U0126, and SB203580, but not U0124 and GW441756, considerably inhibited TRTS-induced neuritogenesis. These results suggest that TRTS can induce neuritogenesis and that participation of both the ERK1/2 and p38 MAPK signaling pathways is required for TRTS-dependent neuritogenesis in PC12 cells. Thus, TRTS may be an effective technique for regenerative neuromedicine.

In this study, the friction of eight kinds of poly(vinyl alcohol) hydrogel (PVA-H) samples has been studied under various load and velocity conditions to elucidate the effects of PVA factors such as the degree of polymerization (DP) and the saponification value (SV) on the tribological behavior of PVA-H. Results showed the variations of the friction properties due to the PVA factors in the two friction conditions found for the hydrogels: elastic friction and hydrodynamic lubrication. In the elastic friction, the larger frictions were induced by the higher values of DP and SV. In the hydrodynamic lubrication, on the other hand, PVA-Hs with lower SV showed larger friction. The results can then be used to adjust the parameters of PVA-H in order to get given friction properties, for instance for the friction between catheter or scalpel and PVA-H, which can be used as a biomodel material of artery or oral mucosa, for the training of surgeons.

No abstract

Materials composed of metals and plastic composites joined through adhesive bonding are being increasingly used. However, debonding of such materials may occur during manufacture or use. Nondestructive testing of adhesive bonding structures is required to evaluate their debonding. Herein, electromagnetic pulse-induced acoustic testing (EPAT) was used to detect debonding at the adhesive joint in plastic composite/metal specimens. EPAT uses a pulsed excitation current to generate guided waves in a specimen to detect debonding without contact, which makes it suitable for testing from the plastic composite side. Simulations were performed to analyze acrylic/aluminum (Al) and carbon fiber-reinforced plastic (CFRP)/Al specimens. The results showed that the Lorentz force in the z direction was the dominant mechanism in the generation of guided waves, and mainly the A0-mode Lamb wave was excited. The simulation and experimental results revealed that for specimens where the mechanical parameters of the plastic composite layer differed greatly from those of the metal, such as the acrylic/Al specimen, debonding

The experiments on initial stages of steam assisted gravity drainage(SAGD) process have been carried out using two-dimensional scaled reservoir models to investigate its production process and performance. Rising or growing process of the initial steam chamber, its shape and area, and temperature distributions have been visualized by using video and thermal-video pictures. As a drainage mechanism, the relationship between isothermal lines and chamber interface have been presented. The temperature on the interface, where the chamber was expanding, was maintained at almost constant temperature of 80 C. Furthermore, the effect of vertical well spacing between two horizontal wells on oil recovery has been investigated. For the case of usual SAGD, oil production rate increases with increasing vertical well spacing, however the leading time to start oil production by gravity drainage becomes longer. The results show that the well spacing may be a representative length for initial stage of the process. Based on these experimental results, a modified SAGD process by adding intermittent steam injection from the lower production well have been proposed. By applying the modified process, the time to generate near break-through condition between two wells was relatively shorten, and oil production was enhanced at the stage of rising chamber compared with that of usual SAGD process. Introduction There are vast heavy oil and oilsands reserves not fully exploited, because it is not easy to produce heavy oil efficiently and economically. However, steam-assisted gravity drainage (SAGD) process has been successfully applied to oilsands fields. The process has been developed by Butler and his co-workers. Their ideas was to overcome the problems associated with the highly viscous bitumen by gravity drainage in steam chambers generated by displacement of heavy oil. As shown in the reports on the UTF projects (phase A and B) in Canada, the SAGD process (see Fig. 1) has proven to be very superior process for the recovery of the bitumen due to its high recovery factor. Chung and Chung & Butler have reported experimental results for SAGD process with scaled and visual reservoir models. Furthermore, Chow & Butler have reported the numerical simulation results matching the Chung's experimental results with the STARSTM. Recently, Mukherjee have reported the successful forecast of the performance for the phase B of the UTF project. Butler gives an excellent review of the SAGD process. In this paper, the SAGD process operated by steam injection from upper well and production from lower well like that of UTF project, is hereinafter referred as "usual SAGD." A problem of the usual SAGD process for oilsands reservoirs is leading time to generate a steam chamber in near break-through condition between two horizontal-wells before production stage by rising and expanding chamber. The more economical SAGD production should be achieved by a modified process to shorten the period of initial stage and enhanced steam injection for effective usage of steam generation and production facilities. First, we have investigated characteristics of the usual SAGD process, especially expanding rate of steam chamber by gravity drainage and effects of vertical well spacing on it. It was found that by using shorter vertical spacing between two wells, leading time is reduced while production rate after break-through becomes lower. Based on experimental results, a modified process has been proposed to start oil production earlier and enhance oil production at higher rate after break-through. In this process, steam is injected from both of upper and lower wells. Then, the lower well has both functions of production and steam injection, which is similar to the single SAGD well developed and reported by Liderth. The steam is injected intermittently from the lower well, because steam injection holes and oil production holes at the well are quite close to prevent steam break-through. P. 467

Many patients with cerebrovascular diseases and the elderly have difficulty ingesting foods because of dysphagia. We hypothesized that repetitive contraction of the suprahyoid muscles via peripheral nerve magnetic stimulation could lead to recovery of swallowing function. The magnetic stimulation coils currently on the market are problematic because not all tissues around the suprahyoid muscles should be affected during magnetic stimulation, such as the alveolar nerve. The problem is due to the wide area covered by magnetic stimulation. With this factor in mind, we designed and fabricated a coil optimized to provide only a narrow range of stimulation. By adopting use of a magnetic core, we ensured that the coil distributes only a local eddy current during stimulation. We confirmed that the magnetic stimulation using this prototype coil could cause large contractions of the suprahyoid muscles without stimulating the alveolar nerve.