The calcaneus, the heel bone at the foot, is one of the most important bones for weight bearing. This bone supports almost the entire weight of the body when it contacts on the ground. Younger people suffer calcaneus fractures due to larger external forces such as a fall form a height or an accident while driving. However, calcaneus fracture in the elderly are often suffered by small external forces. Calcaneus fracture in the elderly have increased in recent years. For the proper treatment of calcaneus fractures, it is important to understand the fracture mechanism. The purpose of this study was to examine the risk of fracture of the calcaneus by performing FE analysis. A finite element (FE) model of the calcaneus was constructed based on CT images of the foot, and FE analysis was performed under three load conditions.

This study aims at analyzing the phase composition of Hydroxyapatite/TiO₂ coating fabricated by Suspension Plasm Spray (SPS). Hydroxyapatite[Ca₁₀(PO₄)₆(OH)₂, HAp] is a bio-ceramic material used as a plasma-sprayed coating to promote osseointegration of femoral stems. The HAp coatings are fabricated mostly by atmospheric plasma spraying (APS) process. But it provides coating with amorphous phase which is not suitable bio-integration. Suspension plasma Spray (SPS) is relatively new technique used to abstain coating from thermal decomposition. In this study SPS successfully deposited homogeneous, less porosity HAp coating onto the surface of titanium substrate. Furthermore, SPS firstly could deposit composite coating of HAp / Titania. This is oxygen-deficient types of composite coating, which can be functioned as visible-light responsive photocatalyst. Microstructure of titania coating is then characterized using XRD and Raman spectra to identify its crystal structure, and it contained oxygen-deficient phase of TiO₂. Details phase analysis of the phase composition was conducted by both Raman peak fitting analysis and XRD Rietveld analysis to validate the existence of Magneli phases which is important for antibacterial property of the biomaterial coating.

This research aims at developing a topological optimization method for fatigue and compressive strength of Polyurethane / Alumina composite considering pores distributions. The number of artificial hip joint surgery as well as the artificial hip joint itself have been increasing due to super-aging society. However, the service lives of the artificial hip joint are still shorter than expectation due to loosening. To prevent loosening, damage behavior of porous cancellous bone should be revealed. The effect of porosities on stress concentration behavior was firstly observed and the increased values of stress concentration factors were observed, which led to decreased compressive strength of porous components.

The number of artifical hip prostheses is increasing due to the super-aging society. Interfacial damages in HAp (Hydroxyapatite) coating on acetabular cup or damages in surrounding human bone can lead to release of mechanical fixation by surrounding cancellous bones, which is a major cause of loosening. However, the mechanism of loosening by such the damages was not sufficiently revealed yet. The aim of this study is to experimentally clarify the damage behavior of HAp coating on the surface of acetabular cup by cyclic loading using AE (Acoustic Emission) method and IR (Infrared thermography) method. The elastic wave at the time of coating damage near the edges was measured by AE method. Moreover, the temperature change due to friction and wear near the parietal surface was measured by IR method. The degree of coating damage was quantified by evaluating the temperature change caused by friction. It was clarified that delamination, friction and wear occurred step by step between simulated bone and acetabular cup. The mechanism of promoting loosening at the interface of simulated bone and acetabular cup was also discussed.

The purpose of this study is to clarify the creep deformation behaviors of a catheter made of nylon resin and stainless steel wires. In the previous studies, the creep deformation behaviors under step proportional loads have been investigated by changing the ratio of tension and torsion under hydrous conditions. Under hydrous conditions, it is considered that Young's modulus of the matrix will decrease and the braids made of the stainless steel wires will peel off. In addition, the loading histories for tension and torsion are closely related to the creep deformation behaviors. In this report, the experiments of creep deformation behaviors obtained under the three-step loading for tension and torsion are conducted under hydrous conditions, and these experimental results that the first stage is tensile load are compared with anhydrous conditions.

This study aims to reveal the mechanism of toxicity by experimentally evaluating the cytotoxicity of wear particles which was generated by fretting fatigue under cyclic loading. The super-aging society in Japan lead to the increase in the demand for artificial joints. Titanium alloy is usually used as the material of artificial joints and a hydroxyapatite (HAp) coating is applied to the prostheses surface to improve bone conductivity. However, fretting fatigue due to cyclic loading during walking causes damages such as wear, cracks, and peeling. The wear particles formed by damage can cause an inflammatory response in the body. However, the effect of generated wear particles on cells has not been clarified yet. Although the material used for the test specimens was not toxic, a marked decrease in cell number was observed during the fatigue test, suggesting that toxicity had occurred. The mechanism of promoting toxicity is considered to be the effect of mechanical load and wear particles. Wear particles generated by fretting fatigue caused toxicity to cells which lead to the decrease in cell numbers.

Currently, the population is ageing in Japan. Bone diseases are increasing with the ageing of the population. Porous bone filling material containing β-TCP has been widely used in clinical applications for this treatment. β-TCP porous material has high bioabsorbability. However, there are problems that β-TCP porous material has low compressive strength and cannot keep strength up to bone replacement. Therefore, we are tried to synthesize bone filling materials using the HHP method. By using the HHP method, it is expected that both strength and porosity can be achieved. We use this method to composite HA to β-TCP. As a result, we succeeded in synthesizing HA composite β-TCP bone filling material. However, the HA content was nearly 42%. The bioabsorbability is expected to decrease as the HA content increases. Therefore, it is necessary to suppress the HA content, so we tried to control the chemical reaction during HHP. The Ca/P ratio was changed for this purpose, and the mechanical properties were also investigated. As the result, the HA content was suppressed to less than 10%, and the β-TCP content was up to 80%. So, it was possible to synthesize bone filling material with a high bioabsorbability. The strength and porosity were respectively 59.0 MPa and 48.4%, and synthesized material had high strength than previous material.

Mild traumatic brain injuries (mTBI) occur in high-speed projectile sports due to collisions of the ball with the batter’s helmet. The purpose of this study was to examine a relationship between brain strain metrics and baseball ball impact locations. Baseball impacts simulations were carried out by using a finite element model of the head, baseball ball and helmet. From the results of the impact simulations, As the results, conventional brain strain metrics such as MPS and CSDM0.10 could not be evaluated for concussion risk during baseball impacts. On the other hand, since the cavitation pressure was reached in the baseball impact simulations, a new brain pressure metrics, Cumulative Pressure Damage Measure (CPDM) was newly defined. The results indicated that the CPDM was varied by the impact locations, indicating that this CPDM could be a new metrics of concussion risk in baseball impacts.

In this study, we measured ultrasound velocity in the calcaneus of 73 inpatients with traffic injuries using an ultrasound device. The results showed a significant gender difference with an average 1,559 [m/sec] of men and an average 1,532 [m/sec] of women. Because previous studies have reported that road injury is more likely to be severe at age 55 years, this study compared ultrasound velocities in patients 55 years and younger with those in patients 55 years and older and found a significant difference. These results suggest that bone strength varies with age and sex, resulting in a significant effect on injury severity.

Advanced automatic collision notification systems (AACN) enable early notification of road crashes as well as providing a prediction of occupant injury severity in road crashes. Occupant injury severity, when transmitted quickly and automatically, can be used by emergency medical services (EMS). This information allows EMS to respond quicker and be better informed and prepared when arriving at a road crash. Accurate injury prediction algorithms can improve survival rates of injured occupants. This is particularly important in Australia, as occupant injury severity in road crashes are higher than in Japan. In this study, the most appropriate injury risk factors that were found to influence occupant injury severity in South Australian road crashes were used. Combinations of the various risk factors produced around 33,000 injury prediction models. Each of these models was evaluated using Akaike's Information Criteria (AIC) to determine the optimal risk factor. The determined risk factor was used to construct a neural network injury prediction algorithm. The prediction accuracy of the algorithm was evaluated by 10-fold cross-validation. As a result of this study, an optimal injury prediction algorithm with high prediction accuracy according to AIC has been developed and is expected to be applied to AACN systems.

The crew safety at Launch Abort System (LAS) under the high impact load has been numerically investigated using the simplified Hybrid-III dummy model. We show that the simplified model has a good potential to reproduce the load reponse that matches with the experimental result by modifying the stress-strain curve that describes the deformation behavior in hip part.

In this study, we developed a finite element model considering the shape and mechanical properties of the cruciate ligament of the knee joint. The mechanical model of the ligament was identified by using MRI images of the knee joint set at flexion angles of 30, 60, and 90 deg. The three-dimensional surface geometries of the femur, tibia, anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) were segmented from the MRIs. The material properties of the ACL and PCL were obtained using the results from uniaxial tensile tests on actual ligament specimens. After inputting these conditions into a general-purpose finite element analysis software, we reproduced a drawer motion. When comparing the results obtained from this study to those of actual knee joint AP drawer tests, it was found that the attachment surface of the ligament and bone had a great influence on reproducing the bearing capacity. It was also found that precise identification of ligament anisotropy and attachment area is necessary to reproduce more accurate bearing capacity.

Chest injuries to vehicle occupants account for a large percentage of fatal car accidents. The development of brittle material dummies is necessary to visually determine the status of a fracture. In this study, a physical model was developed to reproduce a rib fracture of the lateral thoracic region of a passenger in a car using a brittle material with human bone characteristics. Poly Lactic Acid (PLA), a kind of plastic, was used as a brittle material, and specimens and physical models were created by a 3D printer to obtain physical properties. The physical model consists of six ribs from the fourth to the ninth thoracic vertebrae, and the ribs are designed to have the same width, length, and thickness as in humans. Physical models were produced for the elderly models in automotive safety performance tests.

A spinal cord injury (SCI) is recognized as one of the most devastating type of injuries in the world, and the development of a reliable computational prediction scheme of traumatic SCIs involved in traffic accidents and contact sports will be useful to elucidate its injury mechanism. In the present study, we built a micro-indentation tester to precisely characterize mechanical properties of the porcine spinal cord. A spherical indenter with a 0.5-mm diameter was slightly pressed into a transverse cross-section of the smoothly sliced samples at the rate of 30 and 150 μm/s, and its stress relaxation responses were recorded for 180 s. By applying Hertzian contact theory, we found that the instantaneous Young’s modulus of gray matter is significantly greater than that of white matter (P < 0.05) when intended at the higher loading rate (150 μm/s), while Young’s moduli of the gray and white matters are almost the same at the equilibrium state irrespective of a five-fold difference in the employed loading rates. We also found that the white matter is relatively insensitive to the loading rate compared to the gray matter, which may contribute to a mechanical protection of white matter even during the injurious deformation process. Although the specimen size is still limited, these results may enhance the capability of a computational prediction of traumatic SCIs in the future.

Recellularization is the process of the repopulation of organs with organ-specific cell types or stem cells through direct injection or continuous perfusion. However, vessel clogging is a serious problem reducing the efficiency of the seeding process. This process combines two complex phenomena, cell motion and fluid flow, into one challenging system where multiple parameters can influence the general outcome. Moreover, it is difficult to experimentally study the clogging phenomenon in the whole organ. Thus, in this study, we applied a resolved two-way CFD-DEM coupling approach to simulate the dynamic cell seeding under perfusion conditions. This work can provide some evaluations and predictions to enhance the efficiency of recellularization process.

This paper describes the results of performance comparison between the NDPAP device and the HNCPAP device. NDPAP device and HNCPAP device were separately attached to the neonatal spontaneous breathing simulator (PT-2), and the experiment was performed in a breathing mode (healthy lung, lung with increased airway resistance, lung with reduced compliance) that simulated breathing at a constant MAP of 500 Pa. In the experiment, diaphragm displacement, ventilation, alveolar pressure, flow, airway pressure, and CPAP pressure were measured. When the rise time from the minimum decompression value to MAP was investigated in the airway pressure waveform, it was about 0.1 second for the NDPAP device and about 0.025 second for the HNCPAP device. It was confirmed that the sensitivity of the NDPAP element was poor and that of the HNCPAP element was good. The CPAP pressure waveform at the time of inspiration in each respiratory mode of the HNCPAP element was a waveform in which the amplitude of the alveolar pressure was reduced. Therefore, it was found that respiratory monitoring is possible from the CPAP pressure waveform during inspiration.

Numerical analysis of cell membrane perforation in micro rectangular channels was performed to support the design of an on-chip droplet electroporation system. The computing software COMSOL Multiphysics 5.5 on Windows OS was used on the workstation HP Z8. The basic equations for the calculations were the current conservation equation and the asymptotic Smoluchowski equation for the calculation of cell membrane lysis, and the current conservation equation and the mobility equation were used for the calculation of electrophoresis. Under the above conditions, the numerical analysis by the finite element method was performed. When a cathode electrode and an anode electrode were arranged in the same plane, which is a low-cost electrode arrangement in a microreactor, it was found that two cell membrane lysis were formed at almost ideal positions.

In this research, the flow characteristics generated by a jellyfish type robot that collects suspended garbage were observed by flow visualization and PIV measurement. The jellyfish robot acts as a pump. The jellyfish type robot, which is driven by a DC servo motor, draws in a water mass inside by open motion of the bell. Then, the traped water mass is discharged downward by the closing motion of the bell, and garbage is collected by the trap net. As a result of PIV measurement, it was observed that the vortex structure developing from the tip of the bell was dominant flow structure. PIV detected flow structure shows not only the jet like flow generated by the closing bell motion, but also the induced flow from out side of the robot caused by the vortex ring. This induced flow improves the ability of the pump to transfer more water.

This paper reports on the visualization results of the phenomena of microbubble attachments to the burrs with the micro order in the tip of medical implant and of the interaction between the underwater explosion induced by the electrical discharge and the implant attached with microbubbles. The two attachments of microbubble were tested. One is that we attach the floating microbubble to the implant. The other is that flowing microbubble are continuously attached with the implant. The visualization results suggested that two or more microbubbles bound to the implant in the two attachments. The visualization images also indicated that not only the underwater shock but also the primary bubble induced by the explosion with the microbubbles, resulting in the motion of the microbubbles on the burrs of implant.

This paper reports numerical results underwater shock wave generation phenomena by an explosion in a closed space for establishment of shock wave pressure profile method related to the shock wave medical and biomedical application. In this study, a metal tube made of stainless steel were used as a closed space. A shock wave generated in a metal tube by detonating a micro-explosive (a 10 mg silver azide pellet). The process of underwater shock wave interaction with a metal tube and the generated shock wave propagation phenomena was simulated by using hydrocode ANSYS AUTODYN. The peak over pressure of shock wave generated form a metal tube was higher by different internal shape.

Amended Foodstuff Recycling Law promote to reduce food wastes by the recycle and reuse of wasted foods, and various strategies have been tried to reduce useless abandonment. The process grinding them into powder is generally included in the recycle process of wasted foods, and it is important to minimize total energy cost. Well dried foods are sometimes hard to crush into fine powders. More serious problem is that those foods are generally polluted with bacteria, then the feasibility of the food recycle process depends on the disinfection work as well as the grinding performance. The sterilizing effect was found in a shock impact crushing, and the relation between the shock pressure and the sterilizing effect has been studied. In this study dry powdered foods were crushed by successive impacting loads and the sterilizing effect was examined precisely. It was found that the sterilizing performance could be higher by making a metal layer on the plastic impactor with low shock impedance.

The purpose of this study is to develop a noninvasive method to obtain temperature distribution in tissues with ultrasonic CT system, using relation between sonic velocity and temperature. In this CT system, successive approximation method based on projection onto convex set method (POCS) and smooth processing is used to reconstruct sonic velocity distribution from projection data (sinogram) of wave propagation time through the tissue. In this study, CT reconstruction from sinogram obtained from the objects composed by multiple tissues was performed experimentally, and following results were obtained. (1) Reconstruction by AART with POCS and smooth processing showed better distributions compared with those by only AART. (2) Temperature distribution by AART with POCS and smooth processing was similar to that measured by thermocouples. (3) Error of shape information showed the adverse effect to reconstruct higher temperature near the center of tissue.

Cavitation is an unsteady motion which generates a lot of cavities to form a cloud and presents a repeating process called rebounding of its birth, growth, and collapse. In particular, it is considered that a strong shock wave of pressure is generated associated with the collapse of the cloud and it may cause serious problems such as erosion in fluid machinery. Many numerical studies have been conducted so far to clarify such unsteady behaviors of the cloud, however it is not well understood how the inception of the cavitation cloud may be occurred and how its unsteady behavior can be elucidated in the context of the multiphase flows. In this study, we make a two-dimensional numerical analysis of the multiphase flows for a submerged bubbly water jet injection into still water through a nozzle and then we investigate how the cloud cavitation can be made in this system. In this analysis, we employ the mixture model of liquids and gases to model the bubbly-water jet and we make a numerical analysis of the unsteady multiphase flows in Lagrangian description by utilizing the Smoothed Particle Hydrodynamics method. We finally illustrate a scenario of how the inception of the cloud is occurred and how its unsteady behaviors are made in the context of the multiphase flows.

In the gas turbine system, which is exposed to frequent variation of load, compressor operation needs to be monitored constantly. For the monitoring device, hot-wire probes or accelerometers are generally used, but those devices need measurement holes. Introducing the simple device that does not need measurement holes have been desired. So the adaptability of Acoustic Emission (AE) sensor to compressor monitoring was verified. AE sensor was installed on the surface of the casing of axial-flow compressor that was operated steadily. AE signal was acquired on 6 different operating points of the compressor. Frequency analysis of those AE signals showed that the lower flow coefficient φ became, the higher the voltage of AE signal became, in the band from 35kHz to 42kHz. So the AE signals were filtered from 35kHz to 42kHz and then root mean square (RMS) of the AE signals was calculated. As a result, the lower flow coefficient φ became, the higher RMS became. So the possibility of applying AE sensor to the compressor operation monitoring was suggested.

It is difficult to experimentally determine the waveform of the shock wave in nanometer scale that propagates and reflects in the solid. In present study, molecular dynamics (MD) simulation is perform to clarify this waveform in fcc crystalline Al and Ni. Simulated metal/metal collision system is similar to the equipment of the split Hopkinson pressure bar method, which is the high-speed deformation test method. Discrete physical quantity of atoms are converted to the one dimensional continuum quantity. The waveform of the incident and reflected shock waves are fitted to the complex function consisting of sine wave, exponential damping, Gaussian and sigmoid functions. The parameters of the complex function are obtained as a function of time. The fitted function well represents the nanometer level waveform of the shock wave.

Recently, importance of nanomaterials has been drastically increased in various fields such as environment, medicine, and industry. Demand for detection and identification of them is, therefore, inevitably increasing. In this study, we developed a flow cytometer to achieve a real-time single-particle detection of nanoparticles. The developed cytometer contains two beam paths (one for excitation of nanoparticles flowing in a PDMS microchannel, and the other for reference light, whose frequency is slightly shifted by two acousto-optic modulators) to cause heterodyne interference. The scattering light from the particles is overlapped with the reference light and recorded via a lock-in amplifier. An increase of the sensitivity by the combination of the flow cytometry with the heterodyne interferometry was confirmed by 2-μm particles. Furthermore, it was shown that the cytometer can detect individual 10-nm gold particles while the detection limit of conventional cytometers are hundreds of nanometers.

Although microphysiological systems have potential to culture cells closer to in vivo environment than conventional static culture, its complexity should be properly addressed for further development. In this study, we developed and evaluated electrothermal (ET) pumps which can contribute to the simplification of the systems by reducing the external mechanical pumps. Two different types of the ET pump installed in PDMS circular channel were examined. The pumps have either two-dimensional (2D) or three-dimensional (3D) electrode shape. The pump performance was compared with regard to the flow velocity and temperature rise by Joule heating. As a result, the flow velocity induced by the 3D electrode was larger than that induced by the 2D electrode. The temperature rise was found to be a function of the applied voltage and it showed almost no difference between the 2D and the 3D electrodes. From these results, Hela S3 cells were cultured using the 3D pump and a Peltier element that prevent an overheating of the cells. The cell growth in the culture chip with 3D ET pump showed similar growth rate as that in the static culture.

A wide variety of microfluidic devices have been developed for chemical reactions, medical research and PCR testing. Generally, microfluidic devices are made by joining one flat plate with microfluidic channels to another flat plate. Since the microfluidic devices are often used in combination with optical observation, it is necessary to use light-permeable materials to bond the microfluidic plates to minimize the amount of deformation without blocking the microfluidic channel while maintaining the light permeability. Currently, polydimethylsiloxane (PDMS), a type of silicone rubber, is used for research microfluidic devices. However, PDMS is not suitable for mass production because of its soft lithography and other manual processes. Also, since PDMS is gas-permeable, bubbles are generated from the flow channel walls of devices that undergo heating or chemical reactions, which can block the microfluidic channels. Therefore, it is required less expensive materials such as acrylic (PMMA) and polystyrene (PS) resins other than PDMS, but the bonding technology has not been established and mass production has not been achieved. In this study, we will establish a diffusion bonding technology for microfluidic devices, which unifies the bonding interface without melting the base material. This will contribute to the mass production of highly functional devices such as PCR chips and disposable medical devices made of less expensive acrylic resin.

Monitoring of cultivation is important for efficient industrial enzyme production by filamentous fungi. The purpose of this study is to clarify the relationship between morphology of filamentous fungi and enzyme production, and to provide novel monitoring method for filamentous fungus cultivation. we developed a microfluidic device to observe the complex hyphal morphology of filamentous fungi in real time, and observe a hyphal growth from spores wonder enzyme producing condition.

We proposed a quadrupole capillary dielectrophoretic (DEP) device, which was a new DEP device enabling invasive and effective cell-separation without contacting the cell suspension to metal electrodes. The device consisted of four brass rods and a glass capillary. The brass rods were glued around the glass capillary to facilitate cell separation by generating a non-uniform AC electric field in the entire cross-section of the glass capillary. Prior to the experiment, we numerically simulated distributions of the electric potential, electric field, and the gradient of electric field square in the cross-section of the glass capillary. Predictions demonstrated that the maximum of the gradient of electric field square were appeared near the internal wall of the glass capillary, implying that p-DEP and n-DEP cells would be separated effectively due to the steep slope of the gradient of electric field square created in the radial direction. The effectiveness of the quadrupole capillary dielectrophoretic device was verified by conducting cell-separation experiments using live and dead human breast epithelial cancer cells (MDA-MB-231).

Among human diseases, there are many muscle-related diseases such as ALS and muscular dystrophy. However, it is difficult to elucidate such diseases due to various body systems work in living organisms such as humans, animals, and plants. In order to remove the effects of complex interactions between organ periods, we focused on an in vitro experimental technique that used organoids to reproduce only specific organ functions. In this study, we have developed a device that allows time-lapse observation with an inverted microscope without removing skeletal muscle from the well plate. The mechanical approach is to quantitatively assess the deformation of the pillars due to skeletal muscle contraction from Young's modulus and the amount of deformation of the pillars. This method allows continuous experiments to be performed without removing skeletal muscle from the well plate. Biochemical studies have shown that artificial skeletal muscle continues to mature for 2 to 3 weeks after culture. The results of this experiment also showed a decrease in contractility at week 4, which is consistent with the previously reported biochemical maturation of the artificial skeletal muscle, confirming that the developed device was successful in continuously evaluating the maturity of the artificial skeletal muscle. In the future, they hope to incorporate neural organoids as a new element in the device and apply it as a neuromuscular model device.

In recent years, it has been revealed that physical exercise produces a variety of physiologically active substances called myokine, help to maintain healthy body functions A method of genetic analysis has been used to investigate myokines, however. Its clear assessment is difficult because of affection by other hormones. Therefore, in this research, we establish a simple experimental system for myokine research in vitro. In this experimental system, the artificial skeletal muscle is cultured with various extension patterns. Changes in skeletal muscle structure and culture medium allow us to investigate the effects of muscle movement patterns on myokine production. We have successfully fabricated a three-dimensional cultured skeletal muscle (artificial skeletal muscle) that can reproduce the contractile motion of a muscle by electrical stimulation (Figure 1). This artificial skeletal muscle can be removed from the culture dish with tweezers via the artificial tendons at both ends and relocated. One of the problems with this device is that the medium is electrolyzed and its pH is changed by the electric current during stimulation. In this study, a newly developed device was applied to provide mechanical stretching to the skeletal muscles. The device consists of an inexpensive (under $100) linear stage, which is used in 3D printers, and is controlled by an Arduino. Therefore, the conditions for mechanical shrinkage can be freely controlled.

In this study, we proposed a motor protein actuator in which actomyosin was reconstituted in a collagen gel. A collagen gel was used to achieve sufficient mechanical strength to be used as an actuator, whereas previous studies using motor proteins had low mechanical strength and could not be used as an actuator. The actuators were fabricated by just mixing actin, myosin, and collagen solutions and incubating them in a mold for 10 hours. This actuator is contracted by adding ATP and can be retracted multiple times by stretching. We performed three contractions and confirmed that we could obtain a stable contraction ratio of about 40%. These actuators can be made only from materials derived from living organisms and therefore have a low impact on the human body and the environment. The actuator is expected to be used in medical and micro-robotics and other fields in the future.

Larvae of water striders (Aquarius paludum paludum) has microtrichia and nanoscale tack shape structures. The form of tack shape structures is halfsphere (diameter: 250 nm, height: 125 nm). We hypothesized that the tack shape structures could prevent immersion their body from water surface by Cassie-Baxter’s condition when they locomote on water surface. The tack shape structures can remove microdroplets which enter between micro-hairs. In order to explain the water-repellency function of the tack shape structures, we proposed a water-repellency model. The model showed that the water-repellency function was sufficient to prevent touching of the water surface on the surface of water strider’s leg.