We are pleased to present the issue “Biomedical Flow Dynamics.” Biomedical engineering has been globally recognized as an engineering field for biomedical applications. From now, the combination of biomedical engineering with flow dynamics will unravel a new research field for engineering and science in biomedical applications. This transdisciplinary research that combines flow dynamics and biomedical engineering will enable the progress of research pertaining to cells and bodies under the emerging biological, computational simulations, and experimental engineering techniques. Therefore, this special issue tries to cover various research topics. We think that the papers are of great significance to all fields. Moreover, we believe that the researches will directly influence the quality of life. We sincerely appreciate the wonderful opportunity given to us by the JBSE's editorial board members. Furthermore, we would like to express our sincere gratitude to all the authors and reviewers for their excellent contributions and making this special issue fruitful. Finally, we are thankful to the JBSE editorial office for their technical assistance.

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If highly precise elucidation of the blood flow characteristics in a carotid bifurcation was possible, it would be widely applicable to diagnosis of circulatory diseases such as arteriosclerosis and cerebrovascular disease. This study was conducted to establish a new flow-dividing ratio estimation method applicable to an unsteady flow on a two-dimensional ultrasonic-measurement-integrated simulation of a carotid artery bifurcation for which it has been previously difficult to obtain a stable solution. In this new method, the flow-dividing ratio was directly adjusted by specifying the flow rate in a branch so that the difference of the Doppler velocities in the external carotid artery was decreased. The effectiveness of the proposed method was confirmed by a numerical experiment using the actual shape of a carotid artery bifurcation, and the superiority of the two-dimensional ultrasonic-measurement-integrated simulation over the ordinary simulation in terms of the reproducibility of the blood flow structure was clarified by analysis using clinical ultrasound data.

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The structural characteristic that O-glycan sugars prefer to bind to the regions forming β-strand structures is reported in this paper. While N-acetylglucosamine (GlcNAc) and mannose (Man) modification sites were contained in β-strand structures, fucose (Fuc) modification sites were found on β-strand and coil structures close to the β-strand structures. In particular, most Fuc modifications in EGF-like domains were identified on the edge of β-strand structures. Glycosyltransferases is thought to recognize motif residues in β-strand structures. The finding in this study that O-glycosylation preferred β-conformation and coil structures can be applied for the development of prediction methods and be useful to improve prediction accuracy.

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Lung sound is commonly analyzed when testing for lung abnormalities. However, the accuracy of this analysis is low and more information on sound generation and alteration is needed to improve the analysis quality. In the current study, an aeroacoustic investigation of sound generation in an airway model was performed experimentally to uncover the factors that change the sound characteristics due to bronchoconstriction. A T-branch configuration was used to represent an airway junction, and a constricted tube in the mother branch was used to represent a bronchoconstriction. Aeroacoustic sound was analyzed at several flow rates, representing different speed maneuvers. Constriction percentages of 25%, 50%, and 75% simulated different bronchoconstriction severities. The power spectral density of the produced sound increased over a wide frequency range as the flow rate and constriction level increased. The overall sound pressure level (OASPL) over several frequency bands was calculated and it was found to be related to the Reynolds number in the smallest cross-sectional area of the constriction. When constriction was less than 50%, the OASPL in the frequency range of 200-800 Hz increased as the Reynolds number increased. In the 75% constriction case, a smaller increase of OASPL was observed. In the frequency range of 150-10 000 Hz, all models demonstrated similar relationships between OASPL and Reynolds number. In the majority of frequency ranges, a Reynolds number of 4000 was required to generate 2 dB OASPL, and OASPL showed dramatic increases with higher Reynolds numbers. To find the source location based on Lighthill's sound analogy, turbulence strength measurements were performed 5 mm downstream from the constricted area. Small turbulence was observed, indicating that the sound sources were nearby. Our results show that the OASPL increase of the lung sound can be an indicator of the constriction presents in the airway.

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Cellular and animal experiments and computational fluid dynamics (CFD) have revealed that mechanisms of the initiation, growth and rupture of a cerebral aneurysm are related to hemodynamics. By direct observation of a cerebral aneurysm during craniotomy, thinning or thickening sites can be found on the aneurysmal wall. The thinning site of a cerebral aneurysm is considered to be at high risk of rupture. In addition, the thickening site of a cerebral aneurysm is not necessarily in a stable state since arteriosclerosis may have occurred. Hence, information on wall conditions, i.e., thinning and thickening, of a cerebral aneurysm is beneficial for clinical diagnosis and treatment. In this study, a hemodynamic parameter to effectively estimate the thinness or thickness of cerebral aneurysmal walls was investigated. CFD of hemodynamics in cerebral aneurysms developed at the anterior communicating artery (ACoA), a common site of cerebral aneurysms, was performed, and characteristic distributions of hemodynamic parameters were investigated by comparing the computational results with clinical images. As a result, a high value of the time-averaged wall shear stress (TAWSS) was found to be present at thinning sites, while a low TAWSS and a high relative residence time (RRT) of an indicator of blood retention were observed at thickening sites. Thinning and thickening sites each have their own characteristics distribution of hemodynamic parameters.

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The mechanical and oxidative performance of dl-α-tocopherol (vitamin E, VE) blended Ultrahigh Molecular Weight Polyethylene (UHMWPE) exposed to varying levels of electron-beam radiation was evaluated using hip simulator testing, FT-IR spectroscopy, gel-fraction analysis, differential scanning calorimetry, and tensile testing. Gel fraction values for the irradiated samples increased with the radiation dose, but decreased with higher concentrations of vitamin E. However, for higher doses of electron-beam radiation, the effect of vitamin E concentration was reduced, and increased gel fraction values were observed. The gel fraction values and hip simulator wear resistance values for a 0.3% (w/w) vitamin E blended UHMWPE sample irradiated with 300 kGy were equal to that for commercially available, highly-crosslinked UHMWPE. In addition, no significant changes in oxidation index, crystallinity, tensile strength or elongation-at-break were observed for the 300 kGy irradiated, 0.3% (w/w) vitamin E blended UHMWPE following oxidative ageing (ASTM F2003). Losses in elongation-at-break values were observed for samples receiving increased radiation doses, with higher vitamin E concentrations helping to attenuate these losses. However, for samples receiving 300 kGy of radiation, even the 1.0% vitamin E blended sample experienced a significant loss in elongation-at-break compared with its non-irradiated counterparts.

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