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This study developed a fibre-optic laser Doppler velocimetry sensor for use in opaque, high-temperature, and high-pressure fluid flows by inserting the fibre perpendicular to the main flow. The tip of the optical fibre was obliquely polished and chemically etched using a buffered hydrofluoric acid solution, and a reflective mirror was deposited on the surface of the oblique fibre tip. Based on the results of the verification test using the rotating annular open channel, the fabrication conditions of the fibre tip were optimized for measuring the lubricating oil flow. The flow velocity profiles in the engine’s oil flow of the lubrication system during engine bench testing were measured. These velocity profiles were influenced by variations in the measurement position, oil temperature, and engine speed. The measurement accuracy of this sensor was compared with the volumetric flow rate obtained by cross-sectional area integration of the flow velocity profile, as measured using a Coriolis flowmeter, and the difference was within 1%. By combining computational simulation for flow and optical attenuation and particle scattering in light transmission through a working fluid, this fibre-optic sensor achieved a measurement volume of 200 microns in length and 200 microns in width at a distance of 900–1000 microns from the sensor.

Autologous-engineered artificial tissues constitute an ideal alternative for radical surgery in terms of natural anticoagulation, self-repair, tissue regeneration, and the possibility of growth. Previously, we focused on the development and practical application of artificial tissues using “in-body tissue architecture (iBTA)”, a technique that uses living bodies as bioreactors. This study aimed to further develop iBTA by fabricating tissues with diverse shapes and evaluating their physical properties. Although the breaking strength increased with tissue thickness, the nominal breaking stress increased with thinner tissues. By carving narrow grooves on the outer periphery of an inner core with narrow grooves, we fabricated approximately 2.2 m long cord-shaped tissues and net-shaped tissues with various designs. By assembling the two inner cores inside the branched stainless-steel pipes, a large graft with branching was successfully fabricated, and its aortic arch replacement was conducted in a donor goat without causing damage. In conclusion, by applying iBTA technology, we have made it possible, for the first time, to create tissues of various shapes and designs that are difficult using existing tissue-engineering techniques. Thicker iBTA-induced tissues exhibited higher rupture strength; however, rupture stress was inversely proportional to thickness. These findings broaden the range of iBTA-induced tissue applications.

This study investigated six-month outcomes of first models of ascending aortic replacement. The molds used to produce the Biotube were implanted subcutaneously in goats. After 2–3 months, the molds were explanted to obtain the Biotubes (inner diameter, 12 mm; wall thickness, 1.5 mm). Next, we performed ascending aortic replacement using the Biotube in five allogenic goats. At 6 months, the animals underwent computed tomography (CT) and histologic evaluation. As a comparison, we performed similar surgeries using glutaraldehyde-fixed autologous pericardial rolls or pig-derived heterogenous Biotubes. At 6 months, CT revealed no aneurysmalization of the Biotube or pseudoaneurysm formation. The histologic evaluation showed development of endothelial cells, smooth muscle cells, and elastic fibers along the Biotube. In the autologous pericardium group, there was no evidence of new cell development, but there was calcification. The histologic changes observed in the heterologous Biotube group were similar to those in the allogenic Biotube group. However, there was inflammatory cell infiltration in some heterologous Biotubes. Based on the above, we could successfully create the world’s first Biotube-based ascending aortic replacement models. The present results indicate that the Biotube may serve as a scaffold for aortic tissue regeneration.

The thrombus formation process has yet to be fully simulated, which necessitates the design of a novel method for the quantitative assessment of device thrombogenicity that complements animal experiments/ex vivo experiments using animal blood and computational fluid dynamics analysis. This study aimed to develop a model blood capable of simulating the formation of red thrombus owing to stagnation of blood flow by applying the phenomenon of milk clot formation. To render the rheological properties of skim milk solution used as a model blood closer to those of human blood, the ratio of the amounts of casein in skim milk, calcium chloride, and rennet (constituents of the solution of the model blood) was varied and the rheological properties of the clot formation process of human blood and skim milk solution were measured using a cone-plate viscometer. Comparisons of the rheological properties of human blood and skim milk solutions during clotting revealed that during clot formation of human blood, four characteristic quantities of the time-series change in rheological properties were observed: the viscosity before clotting, coagulation start time, viscosity increase rate, and first yield viscosity. Further, hypercoagulable skim milk solutions with rheological properties similar to those of human blood were prepared by adjusting the solution composition ratio. When this model blood was circulated in a closed-loop circuit with a saccular aneurysm model, the growth rate of skim milk clot formation in the aneurysm model was significantly different in a flow diverter stent model and a micro-porous covered stent. The variation in porosity between these two stent models has a direct impact on the rate of embolisation. The proposed blood model can effectively replicate the formation of red thrombus, providing a valuable means to accurately and quantitatively assess the therapeutic efficacy of embolisation devices.

Biotubes are autologous tubular tissues developed within a patient’s body through in-body tissue architecture, and they demonstrate high potential for early clinical application as a vascular replacement. In this pilot study, we used large animals to perform implantation experiments in preparation for preclinical testing of Biotube. The biological response after Biotube implantation was histologically evaluated. The designed Biotubes (length: 50 cm, internal diameter: 4 mm, and wall thickness: 0.85 mm) were obtained by embedding molds on the backs of six goats for a predetermined period (1–5 months). The same goats underwent bypass surgery on the carotid arteries using Biotubes (average length: 12 cm). After implantation, echocardiography was used to periodically monitor patency and blood flow velocity. The maximum observation period was 6 months, and tissue analysis was conducted after graft removal, including the anastomosis. All molds generated Biotubes that exceeded the tensile strength of normal goat carotid arteries, and eight randomly selected Biotubes were implanted. Thrombotic occlusion occurred immediately postoperatively (1 tube) if anticoagulation was insufficient, and two tubes, with insufficient Biotube strength (2 months without aneurysm formation. The spots far from the anastomosis became stenosed within 3 months (3 tubes) when Biotubes had a wide intensity distribution, but the shape of the remaining two tubes remained unchanged for 6 months. The entire length of the bypass region was walled with an αSMA-positive cell layer, and an endothelial cell layer covered most of the lumen at 2 months. Complete endothelial laying of the luminal surface was obtained at 3 months after implantation, and a vascular wall structure similar to that of native blood vessels was formed, which was maintained even at 6 months. The stenosis was indicated to be caused by fibrin adhesion on the luminal surface, migration of repair macrophages, and granulation formation due to the overproliferation of αSMA-positive fibroblasts. We revealed the importance of Biotubes that are homogeneous, demonstrate a tensile strength > 5 N, and are implanted under appropriate antithrombotic conditions to achieve long-term patency of Biotube. Further, we clarified the Biotube regeneration process and the mechanism of stenosis. Finally, we obtained the necessary conditions for a confirmatory implant study planned shortly.

Objective: There is a need for small diameter vascular substitutes in the absence of available autologous material. A small diameter, long tissue engineered vascular graft was developed using a completely autologous approach called “in body tissue architecture technology (iBTA)”. The aim of this pilot study was to evaluate “Biotubes”, iBTA induced autologous collagenous tubes, for their potential use as small diameter vascular bypass conduits. Methods: Biotubes (internal diameter 4 mm, length 50 cm, wall thickness 0.85 mm) were prepared by subcutaneous embedding of plastic moulds (Biotube Maker) in three goats for approximately two months. Allogenic Biotubes (length 10 cm [n = 2], 15 cm [n = 2], 22 cm [n = 2]) were bypassed to both carotid arteries by end to side anastomosis with their ligation between the anastomoses in another three goats. Residual Biotubes were examined for their mechanical properties. After four weeks, the harvested Biotubes were evaluated histologically. Results: All Biotubes had sufficient pressure resistance, approximately 3000 mmHg. Although wall thickening occurred at two proximal anastomosis sites, all six grafts were patent without luminal thrombus formation, stenosis, or aneurysm deformation throughout the implantation period. Endothelial cells covered both anastomosis sites almost completely, with partial covering in the central portion of the grafts. Furthermore, α smooth muscle actin positive cells infiltrated the middle layer along almost the entire graft length. Conclusion: This preliminary study showed that small diameter, long, tissue engineered Biotubes could function properly as arterial bypass conduits in a large animal for one month without any abnormal change in vascular shape. Thus, small diameter, long Biotubes are potentially viable conduits, which are biocompatible and labour non-intensive, and therefore, suitable for clinical practice. Additionally, Biotubes can start the regeneration process in a short period of time.

The mosquito's wing is deforming during flapping stroke and the pitching angle is changed. The motion called “feathering motion” is considered that the wing is deformed passively by the aerodynamic force. But it is not established yet. In this paper, first, the bending stiffness of mosquito's wing for chord direction was measured with cantilever. Secondly, the flexible 10 times enlarged wing models which have same planar shape and wing area and different thickness were made with Polyphenylenesulfide resin films. Finally, the behavior of each enlarged wing models during flapping motion in the wind tunnel was measured and was compared with the motion of the real mosquito's wing. Then, both Reynold number and Strouhal number of model experiments were conformed to those of real mosquito. The results of measuring the bending stiffness of mosquito's wing for the chord direction showed the wide range values from 2 to 125 pNm2 and the averaged value of 53 pNm2. The results for the enlarged wing model showed that the amplitude of change of inclination angle during flapping motion decreased as the thickness of film increased. The enlarged wing model in which the bending stiffness was almost similar to that of real mosquito's wing showed the feathering motion like those of the real mosquito.

A new miniaturized fiber-optic laser Doppler velocimetry (LDV) sensor has been developed, which is capable of measuring the local velocity in various semi-opaque and opaque fluid flows, particularly whole blood velocity in vessels. The sensor has a convex lens-like fiber tip as a pickup and an improved optical transmission system with markedly decreased stray light. This paper describes methods for fabricating fiber tips like concave and convex lens and the characteristics of the optical sensor system equipped with the fabricated fiber tip. Conventional fiber-optic LDV sensors developed up to now have not been capable of measuring such opaque fluids because scattered light from scattering particles as erythrocytes has very low intensity, which makes signal-to-noise ratio of Doppler signal received by a sensor pickup significantly decreased. To overcome these problems, convex lens-like fiber tips have been fabricated by chemical etching, in which quartz fibers of multimode graded refractive index have been etched in aqueous solutions of hydrogen fluoride and ammonium fluoride under the appropriately controlled condition of the concentration of the solution, the etching duration time and the etchant temperature to obtain the desired curvature radius of the lens-like surface of the fiber tip. In this fiber-optic sensor, a laser beam emitted from the fiber tip can be focused at any position from about 0.1 to 0.5 mm distant from the fiber tip according to its curvature radius. The convex lens-like etched tip totally reduced the intensity of undesired reflecting light at the fiber end by 1/2 to 1/6 compared with normal cut fiber tip. Consequently, this fiber-optic LDV sensor system is capable of measuring the local flow velocity in semi-opaque and opaque fluids, whose turbidity was about five times higher than by any kinds of previous sensors.