医学，生理学，医工学

Microbubbles can grow from nuclei and collapse violently under acoustic pressure. This phenomenon is called acoustic cavitation. The gas in the microbubbles is adiabatically compressed in the violent collapse, and its temperature can reach thousands of degrees. This is regarded as the primary mechanism of sonoluminescence and sonochemical reactions. Research undergoing on the use of acoustic cavitation for inducing therapeutic effects with ultrasound is described in this paper.

This paper expounds some important functional multiphase fluids which are related to biological and medical systems. Artificial blood or blood substitute, gel-dispersed fluid, micro capsule dispersed fluid for the intelligent drug delivery system, micelle of liquid crystal, liquid crystal dispersed fluid and thixotropic fluid are explained and their characteristics and applications are discussed.

Animals utilize flow for mass transport in the body, and for locomotion in water or through the air. In this paper, flow for oxygen transport is mainly discussed. Principally, the oxygen transport is divided into two parts: one is in a region from the atmosphere to the respiratory organ, and the other is from the respiratory organ to the tissue. The former is termed respiration system and the latter is circulation system. Circulation system, which usually consists of a heart and vessels, is required in any animals greater than 3 mm. Mostly in invertebrates, the blood is pumped out from the peristaltic heart, and flows freely between organs (open circulation system). A vertebrate heart is a chamber pump, and distribution of the blood is regulated to each organ in closed circulation system. Respiratory pigment is common in most animals which saves cost for the oxygen supply and the volume of circulating blood, though blood viscosity increases. Respiratory organs are categorized into three groups: gills, lungs and tracheae. The gill, which is an evaginated organ, is familiar among aquatic animals but not among territorial ones because it requires large surface and thin wall resulting poor rigidity in air. However, the gill has higher efficiency than a lung in general due to the counter current flow. For air breathing animals, a lung which reduces water loss during respiration is necessary especially in dry circumstances. Compact avian lungs work together with the thin-walled air sacs which make unidirectional ventilation flow through the lung. In human lungs, ventilation flow through the bronchus augments gas transport with steady streaming and Taylor dispersion. An insect respires with forced-ventilation or auto-ventilation: abdominal/thoracic pumping or muscle pumping, through the tracheal network, and both ventilation methods sustain aerobic metabolism during flight.

Mechanical properties of blood vessel walls are characterized by the terms like large deformation, strong nonlinearity, viscoelasticity, incompressibility, and anisotropy. The methods to study the mechanical properties of a material with such complicated characteristics is described first along with its structure. An example of stress/strain analysis of blood vessel wall considering residual stress/strain is introduced. Then, effects of smooth muscle contraction and relaxation on the mechanical properties of blood vessel wall are reviewed briefly with the methods to determine the smooth muscle contractility. Finally, a novel biomechanical role of vascular smooth muscle contraction and relaxation, i.e., control of intramural strain distribution, is proposed.

A computational fluid dynamics analysis of the On-X® bi-leaflet heart valve has been conducted. Unsteady blood flow in the hinge area was investigated using STORM/CFD2000. The Navier-Stokes equations were solved using a finite volume grid, and a PISO (pressure-implicit with splitting of operators) algorithm was employed to compute the pressure-velocity coupling. An alternating direction implicit(ADI) scheme was used to solve the set of linear algebraic equations. A moving grid methodology with a prescribed periodic motion was employed to simulate the opening and closing of the valve leaflet. Particular attention was paid to simulating the local flow inside the hinge socket of the On-X® valve where experimental measurements are very difficult or impossible. The results show that local flow patterns and pressure distributions in the hinge area of the valve induce full wash-out during the opening and closing phases.

The biological effects of radiation are of two types: stochastic (such as radiation‐induced cancer) and deterministic (such as erythema).The effective dose is used to assess the risk of stochastic effects, and the dose equivalent is used to assess the risk of deterministic effects. However, the effective dose and dose equivalent, body‐related protection quantities, are not measurable. Therefore, operational quantities (1‐cm dose equivalent and 70‐μm dose equivalent) are used to assess the effective dose and dose equivalent. Generally, the 1‐cm dose equivalent, determined using a monitoring badge, is used to assess effective dose, whereas the 70‐cm dose equivalent, determined using a monitoring badge, is used to assess dose equivalent. Furthermore, when using two monitoring badges, the 1‐cm dose equivalent of each badge is converted into the effective dose using calculation algorithms.

As seen in the blood flows containing a large number of red blood cells, many of the flows in the human body are multiphase flows and their multiphase characteristics are effectively used to sustain the life. However, as research topics in the field of multiphase flows, the bio-medical topics are relatively new compared with the classical application such as nuclear engineering, chemical engineering etc. In this review paper, we pick up mainly two topics. One is the blood flows with red blood cells. The other is the microbubbles for the medical application. That is, microbubbles as ultrasound contrast agents and their utilization for the ultrasound therapy as thermal energy converter and drag delivery agents.

Butterflies fly by combining wing flapping and gliding efficiently and have beautiful flight patterns. Moreover, the butterfly excels in rapid acceleration and turning. A number of studies on the mechanism of butterfly flight have been carried out in recent years. Moreover, a number of recent studies have examined the flow field around an insect wing. However, the dynamic behavior of the vortex formed on the insect wing and its growth process have not yet been clarified. The present authors conducted a flight observation experiment and clarified the behaviors of its wings in flight. Based on these results, we developed a flapping-wing robot without tail wings, which is similar to a real butterfly. The elastic deformation of the wings was found to be an important parameter for stable flight, and we focused on the flow field around the wings created by the flapping motion and its elastic deformation. The authors conducted a particle image velocimetry (PIV) measurement around the flapping butterfly wing of Idea leuconoe and investigated the vortex structure of the wing and its dynamic behavior. A vortex ring is formed over the butterfly wings when the wings flap downward to the bottom dead position. The vortex ring then passes over the butterfly completely and grows until reaching the wake at the bottom dead position. The vortex ring is formed over the wings regardless of the type of butterfly, although the scale of the vortex ring varies with the butterfly type.

This paper overviews how the author's group has been exploring on the decision-making process with social dilemma of individual vaccination, namely whether or not to be vaccinated, by means of the model of dynamics for epidemic spreading on a social network applied to evolutionary game theory. On underlying networks, both epidemic and information of agent's strategy are transferred, where the former is modeled by SIR and the latter is emulated as a spatial evolutionary game. Simulation results imply that both the vaccination acceptance fraction and final epidemic size are significantly affected by how strategy updating happens; namely whether he/ she copying from a neighbor or imitating a social trend, and underlying network topologies. The study poses one example of how the social physics helps to understand complex phenomenon taking place in a real world.

Recent progress in the applications of fine bubble technology to agriculture and marin is presented. Fine bubbles were examined in vitro to find whether antibacterial activities would be exhibited against Saccharomyces cerevisiae, Escherichia coli, Salumonella typhimulium, Staphylococcus aureus and Bacillus subtilis. Among them, Saccharomyces cerevisiae cells tended to grow well under both aerobic and anaerobic conditions by the action of microbubbles. Furthermore, the application of fine bubble technology has made it possible to give the high harvests of shrimps, seaweeds, strawberries, eggplants, tomatoes and pears. To clarify the underlying mechanism, interaction of microbubbles with a model protein, bovine serum albumin (BSA), was studied using fluorescence spectroscopy.

Ultrafine bubbles (UFB, Nanobubbles), which are fine bubbles with a bubble diameter of 1 μm or less, have been studied in many fields and become to be practically used. UFB suspended water can be applied for cleaning technology also. Urinary calculus, which is a kind of scale, is produced in pipe, heat exchanger and others, with decomposition of urea. It is a problem in toilets because it promotes the propagation of bacteria when it adheres, clogging water distribution pipes. In this research, the effect of UFB onto the adhesion (production) of urinary calculus is studied and its properties are investigated. It suggests that UFB existence would take the structure of urinary calculus to be brittle on the basis of urinary calculus adhesion during 3 month. Its effect would take scale adhered to be easily removal, while the inhibition of accumulation of urinary calculus could not observed by the existing of UFB.

Nanoparticles have been attracting much attention as a key material for new biomedical and pharmaceutical applications. For success in these applications, the nanoparticles are required to translocate across the cell membrane and to reach to inside of the cell. In this article, our computational studies regarding the permeation of nanoparticles across cell membrane were presented. Firstly, an all-atomistic molecular dynamics simulation study on the interaction of fullerenol C60(OH)n with the cell membrane was presented. Permeability of various C60(OH)n with different number of OH groups was investigated by a simple one-dimensional stochastic modeling based on a thermodynamic analysis derived from MD simulation. Secondly, permeation of cationic gold nanoparticle across a cell membrane under an external electric field was simulated by means of a coarse-grained molecular dynamics. We found a unique permeation pathway: when a weak electric field was applied the NP directly permeated across cell membrane without membrane disruption, suggesting that by controlling an external electric field NPs can be directly delivered into the cell with less cellular damage.

Numerical simulations of aerosol motion induced by sneezing and exhalation were carried out by CFD (Computational Fluid Dynamics) with modeled particles. For sneezing analysis, with and without covering by an elbow and wearing a face mask were modeled to clarify the effect of how to prevent scattering. Aerosol scattering from a talking passenger in a ventilated train was also analyzed to show a realistic situation that may cause infections of the virus. Those results have been published on the web through several SNSs to promote understanding the effect of infection prevention manner.

Inactivation of microorganism (bacteria, fungi, alga and plankton) using ultrasonic waves has attracted significant attention. However, the details of the inactivation mechanisms have not been cleared. This study aims to clarify the inactivation mechanisms of bacteria and fungi by acoustic cavitation. Escherichia coli (E. coli), Saccharomyces cerevisiae (S. cerevisiae) and Bacillus subtilis (B. subtilis) were used as the test microorganism. Inactivation was attempted by ultrasonic irradiation at frequencies of 20 kHz to 4.4 MHz and an acoustic power power of 10 W. Different frequency dependences of the inactivation were confirmed in E. coli, S. cerevisiae and B. subtilis. Based on these data, the mechanism of inactivation of microorganism is discussed with a focus on cell characteristics.

Extracorporeal membrane oxygenation (ECMO) is a respiratory or cardiac life support consisting of a vascular access cannula, a blood pump, and an artificial lung that removes carbon dioxide and adds oxygen. Venovenous ECMO is typically used for various forms of critical respiratory failure including severe pneumonia due to the new coronavirus, whereas venoarterial (VA) ECMO sees greater utilization in the patient with heart failure such as cardiac arrest or other clinical states in which cardiac dysfunction is a significant component of illness. The transference of gases occurs due to diffusion across the hollow fiber membranes packed in the module of the oxygenator. Emergence of microporous membrane tremendously enhanced gas diffusion, and currently microporous membrane with a dense layer on the blood-contacting surface is widely used for longer period of usage over weeks. As the usage period for respiratory failure is getting longer, development of more durable ECMO system is required in the future.

In this review, inactivation and activation of microorganisms using fine bubbles are introduced. In the first chapter, we introduce domestic and overseas research trends of sterilization methods using ozone and plasma. In the second chapter, we focus on researches such as cleaning of lipstick at cosmetic application, generation of plasma-activated microbubbles for sterilization of fresh foods and verification of underwater plasma characteristics under fine bubble dispersion for improvement of chemical activity of bubbles. The third chapter is an introduction of our activity through International Symposium on Application of High-voltage, Plasma & Micro/Nano Bubble to Agriculture (ISHPMNB).

We have developed a demonstration machine of a large-capacity air purification system that purifies a large amount of polluted air using a gas-liquid mixing nozzle and a multi-layer metal fiber filter.　A gas-liquid mixing nozzle, driven by the air blower, sucks and accelerates water to form a high-speed two-phase flow. In the centrifugal force field, all the fine particles and aerosols in the bubbles are transferred to the liquid phase water, and the hypochlorite water whose disinfecting effect has been confirmed by the Product Evaluation Technology Infrastructure Organization (NITE). The demo machine can remove fine particles and viruses in the air at 100 m3 per hour with a single nozzle. We have also developed a large-capacity air purification system that can purify 2400 m3 of air per hour with 24 nozzles. In the virus removal evaluation test conducted by The Japan Textile Products Quality and Technology Center (QTEC), the sterilization performance of 99.975% or more was confirmed. We aim to put this technology to practical use at an early stage to purify the air in hospitals, schools, office buildings, etc.