Development of a stereo dip-coating system for fabrication of tube-shaped blood vessel models.

Tube-shaped blood vessel models that mimic their geometries and mechanical properties can deliver reliable and realistic behavioral information such as deformation and rupture during procedures such as insertion of medical devices. Thickness of vessel walls is an important parameter for fabricating the blood vessel models owing to their strong influence on the model behavior, especially during deformation. The dip-coating method is used to fabricate blood vessel models; however, non-uniform wall thicknesses are observed using this method. This study aimed at finding the characteristics of stereo "angular control dip-coating" (ACDC) system to develop a dip-coating system that can produce tubular models with uniformed wall thickness. The system developed here enables an observation of the substrate behavior from two different views. The conditions of dip-coating used in this study produce 1.36-1.82 mm in the maximum and 0.188-0.435 mm in minimum wall thickness and the fabricated walls cover the realistic range of carotid arterial dimensions. The characteristics of the ACDC system indicate that ACDC is effective for fabricating the uniform wall thickness particularly in the strong curved parts.

Viscosity measurement of Xanthan-Poly(vinyl alcohol) mixture and its effect on the mechanical properties of the hydrogel for 3D modeling.

Biomodels made of poly(vinyl alcohol) (PVA) are demanded because they can represent the geometries and mechanical properties of human tissues realistically. Injecting and molding, commonly used in three-dimensional (3D) modeling, help to represent the blood vessels accurately. However, these techniques sometimes require higher pressures than the upper pressure limit of the dispensers for pouring in high viscosity materials; the material viscosity should therefore be lower. Moreover, the mechanical properties of the biomodels should be reproduced. This study proposes a PVA solution through the addition of xanthan gum (XG) for 3D modeling, which lowers liquid viscosity while maintaining the mechanical properties of biomodels. XG is known to facilitate the achievement of non-Newtonian fluidity; however, the effects of XG on a PVA solution and PVA hydrogel (PVA-H) are not confirmed. The viscosity measurement using 15 wt% PVA with XG solution (PVA/XG) shows that it will provide easier pouring than 17 wt% PVA solution. The tensile test using the PVA-H of PVA(15 wt%)/XG(0.2 wt%) reveals that the gel is comparable in Young's modulus to 17 wt% PVA-H. X-ray diffraction shows the crystalline structures of the PVA/XG gel and PVA-H are identical. Thus, this PVA/XG would be useful for fabricating biomodels using injection molding techniques.

Reproduction method for dried biomodels composed of poly (vinyl alcohol) hydrogels.

Models mimicking the realistic geometries and mechanical properties of human tissue are requiring ever-better materials. Biomodels made of poly (vinyl alcohol) are particularly in demand, as they can be used to realistically reproduce the characteristics of blood vessels. The reproducibility of biomodels can be altered due to dehydration that is observed after long periods of usage. In order to improve their usability, one should consider the method used to reproduce them; however, few studies have reported a method reproduce biomodels. This study proposes a novel reproduction method for biomodels that allows them to quickly and easily reproduce their geometric and mechanical properties. Specimens of the dried biomodels were reformed through immersion in temperature-controlled water. Our results show that water at 35 °C can be effective to reproduce both the geometric and mechanical properties of the specimens. X-ray diffraction (XRD) measurements revealed that water immersion can reform the crystal structure of the pre-dried specimens, and images obtained using micro-computed tomography acquisition show that the geometry of the specimens can be reformed by water immersion without introducing any defects. These results indicate that the proposed method can lead to high reproducibility of both the original geometric and mechanical properties of the dried biomodels.

Influence of plaque stiffness on deformation and blood flow patterns in models of stenosis.

BACKGROUND: Blood flow in stenotic vessels strongly influences the progression of vascular diseases. Plaques in stenotic blood vessels vary in stiffness, which influences plaque behavior and deformation by pressure and flow. Concurrent changes in plaque geometry can, in turn, affect blood flow conditions. Thus, simultaneous studies of blood flow and plaque deformation are needed to fully understand these interactions. OBJECTIVES: This study aims to identify the change of flow conditions attendant to plaque deformation in a model stenotic vessel. METHODS: Three plaques of differing stiffness were constructed on a vessel wall using poly (vinyl alcohol) hydrogels (PVA-H) with defined stiffness to facilitate simultaneous observations of blood flow and plaque deformation. Flow patterns were observed using particle image velocimetry (PIV). RESULTS: Decreases in Reynolds number (Re) with increased plaque deformation suggest that velocity decrease is more critical to establishment of the flow pattern than expansion of the model lumen. Upon exiting the stenosis, the location of the flow reattachment point, shifted further downstream in all models as plaque stiffness decreased and depended on the increase in upstream pressure. CONCLUSIONS: These results suggest that in addition to luminal area, plaque stiffness should be considered as a measure of the severity of the pathology.

Sumanenemonoone imines bridged by redox-active π-conjugated unit: synthesis, stepwise coordination to palladium(II), and laser-induced formation of nitrogen-doped graphitic carbon.

Sumanenemonoone imine compounds bridged by a redox-active π-conjugated unit on the basis of the conversion between 1,4-phenylenediamine and 1,4-benzoquinonediimine were synthesized and characterized. The stepwise coordination of the imino groups to Pd(II) in the sumanenemonoone imine compound bridged by 1,4-benzoquinonediimine was indicated by the titration experiment. Laser irradiation of a film of the metal-free quionediimine gave nitrogen-doped graphitic carbon, which was supported by an increase in conductivity and by Raman spectroscopy. The obtained graphitic carbon corresponds to carbonous compounds thermally treated at approximately 700-1000 °C. The ratio of nitrogen and carbon relative to that in the starting compound was nearly completely retained (5.4% decrease).

Flow observations in elastic stenosis biomodel with comparison to rigid-like model.

BACKGROUND: Plaques in blood vessels exhibit a wide range of stiffness depending on disease conditions: stiffness is an important factor in plaque behavior. The geometrical change in plaque based on its behavior can affect blood flow patterns. Thus, it is important to study both blood flow and deformation of plaques and blood vessels. OBJECTIVE: This study aims to identify the differences in flow conditions between in vitro models to discuss experimental materials for arterial wall and flow observation. METHODS: In order to observe the blood flow pattern and plaque deformation simultaneously, a PVA-H stenosis model was used. In addition, a silicone model was also used as a rigid-like model for comparison with the PVA-H model. PIV was employed to measure the flow velocity distribution and determine the flow levels in the models. RESULTS: PVA-H model exhibits expansion with an increase in upstream pressure and silicone model maintains the diameter. The expansion depends on their mechanical properties and influences flow conditions such as velocity changes and RAP in the parent artery. The balance between the expansion and change in flow conditions determines the final geometries of PVA-H model and flow pattern. CONCLUSIONS: The results suggest that the stiffness measurement for blood vessels and plaques such as ultrasound measurements would be important for accurate treatments.

Correlation between Reynolds number and eccentricity effect in stenosed artery models.

BACKGROUND: Flow recirculation and shear strain are physiological processes within coronary arteries which are associated with pathogenic biological pathways. Distinct Quite apart from coronary stenosis severity, lesion eccentricity can cause flow recirculation and affect shear strain levels within human coronary arteries. OBJECTIVE: The aim of this study is to analyse the effect of lesion eccentricity on the transient flow behaviour in a model of a coronary artery and also to investigate the correlation between Reynolds number (Re) and the eccentricity effect on flow behaviour. METHODS: A transient particle image velocimetry (PIV) experiment was implemented in two silicone based models with 70% diameter stenosis, one with eccentric stenosis and one with concentric stenosis. RESULTS: At different times throughout the flow cycle, the eccentric model was always associated with a greater recirculation zone length, maximum shear strain rate and maximum axial velocity; however, the highest and lowest impacts of eccentricity were on the recirculation zone length and maximum shear strain rate, respectively. Analysis of the results revealed a negative correlation between the Reynolds number (Re) and the eccentricity effect on maximum axial velocity, maximum shear strain rate and recirculation zone length. CONCLUSIONS: As Re number increases the eccentricity effect on the flow behavior becomes negligible.

Synthesis of oxosumanenes through benzylic oxidation.

Oxosumanenes were synthesized through benzylic oxidation. The electronic and redox properties were revealed to exhibit the expanded π-conjugation compared to sumanene. Single-crystal X-ray analysis of monooxosumanene showed columnar π-stacking in a concave-convex fashion. Stereoselective trimethylation of the trioxo derivative was performed via 1,2-addition to the carbonyl groups.