Tsutomu Tajikawa

Development of a Completely Autologous Valved Conduit With the Sinus of Valsalva Using In-Body Tissue Architecture Technology A Pilot Study in Pulmonary Valve Replacement in a Beagle Model

Background— We developed autologous prosthetic implants by simple and safe in-body tissue architecture technology. We present the first report on the development of autologous valved conduit with the sinus of Valsalva (BIOVALVE) by using this unique technology and its subsequent implantation in the pulmonary valves in a beagle model. Methods and Results— A mold of BIOVALVE organization was assembled using 2 types of specially designed silicone rods with a small aperture in a trileaflet shape between them. The concave rods had 3 projections that resembled the protrusions of the sinus of Valsalva. The molds were placed in the dorsal subcutaneous spaces of beagle dogs for 4 weeks. The molds were covered with autologous connective tissues. BIOVALVEs with 3 leaflets in the inner side of the conduit with the sinus of Valsalva were obtained after removing the molds. These valves had adequate burst strength, similar to that of native valves. Tight valvular coaptation and sufficient open orifice area were observed in vitro. These BIOVALVEs were implanted to the main pulmonary arteries as allogenic conduit valves (n=3). Postoperative echocardiography demonstrated smooth movement of the leaflets with trivial regurgitation. Histological examination of specimens obtained at 84 days showed that the surface of the leaflet was covered by endothelial cells and neointima, including an elastin fiber network, and was formed at the anastomosis sides on the luminal surface of the conduit. Conclusion— We developed the first completely autologous BIOVALVE and successfully implanted these BIOVALVEs in a beagle model in a pilot study.

In-body tissue-engineered aortic valve (Biovalve type VII) architecture based on 3D printer molding

In-body tissue architecture--a novel and practical regeneration medicine technology--can be used to prepare a completely autologous heart valve, based on the shape of a mold. In this study, a three-dimensional (3D) printer was used to produce the molds. A 3D printer can easily reproduce the 3D-shape and size of native heart valves within several processing hours. For a tri-leaflet, valved conduit with a sinus of Valsalva (Biovalve type VII), the mold was assembled using two conduit parts and three sinus parts produced by the 3D printer. Biovalves were generated from completely autologous connective tissue, containing collagen and fibroblasts, within 2 months following the subcutaneous embedding of the molds (success rate, 27/30). In vitro evaluation, using a pulsatile circulation circuit, showed excellent valvular function with a durability of at least 10 days. Interposed between two expanded polytetrafluoroethylene grafts, the Biovalves (N = 3) were implanted in goats through an apico-aortic bypass procedure. Postoperative echocardiography showed smooth movement of the leaflets with minimal regurgitation under systemic circulation. After 1 month of implantation, smooth white leaflets were observed with minimal thrombus formation. Functional, autologous, 3D-shaped heart valves with clinical application potential were formed following in-body embedding of specially designed molds that were created within several hours by 3D printer.

Preparation of a completely autologous trileaflet valve-shaped construct by in-body tissue architecture technology

The aim of this study was to prepare completely autologous heart-valve-shaped constructs without using any artificial scaffold materials by in-body tissue architecture technology, which is a practical concept of regenerative medicine based on the biological defense mechanism against foreign bodies. Silicone rods were used as molds to achieve the tubular shape of the arteries, which were implanted in the subcutaneous spaces of rabbits. After 2 weeks of primary in-body tissue incubation, the silicone rods were completely encapsulated within a thin membranous connective tissue mainly consisting of collagen and having a thickness of approximately 100 microm. To achieve the trileaflet shape of the valve, the cylindrical tissues obtained were rolled up with polyurethane belts cut in the shape of three semi-ovals. The assembled tissues were reimplanted for 2 weeks for secondary incubation. The resulting tissues were over-encapsulated with the newly developed membranous connective tissue having a thickness of approximately 200-400 microm. The newly formed membranes were completely fused to the previously developed inner membrane. After the removal of the two artificial materials, tubular constructs with trileaflet-shaped internal surface were obtained. By controlling the formation of the encapsulating tissue in the two-step in-body tissue incubation process, we were able to develop completely autologous trileaflet valve-shaped constructs.

A completely autologous valved conduit prepared in the open form of trileaflets (type VI biovalve): Mold design and valve function in vitro†

In-body tissue, architecture technology represents a promising approach for the development of living heart valve replacements and preparation of a series of biovalves. To reduce the degree of regurgitation and increase the orifice ratio, we designed a novel mold for a type VI biovalve. The mold had an outer diameter of 14 mm for implantation in beagles, and it was prepared by assembling two silicone rods with a small aperture (1 mm) between them. One rod had three protrusions of the sinus of Valsalva, whereas the other was almost cylindrical. When the molds were embedded in the subcutaneous pouches of beagles for 1 month, the native connective tissues that subsequently developed covered the entire outer surface of the molds and migrated into the aperture between the rods. The mold from both sides of the harvested cylindrical implant was removed, and homogenous well-balanced trileaflets were found to be separately formed in the open form with a small aperture at the three commissure parts inside the developed conduit, which had a thick homogenous wall even in the sinus of Valsalva. Exposure of the obtained biovalves to physiological aortic valve flow in beagles revealed proper opening motion with a wide orifice area. The closure dynamics were suboptimal, probably due to the reduction in the size of the sinus of Valsalva. The mechanical behavior of this biovalve might allow its use as a living aortic valve replacement.

Development of Miniaturized Fiber-Optic Laser Doppler Velocimetry Sensor for Measuring Local Blood Velocity: Measurement of Whole Blood Velocity in Model Blood Vessel Using a Fiber-Optic Sensor with a Convex Lens-Like Tip

A miniaturized fiber-optic laser Doppler velocimetry sensor has been developed to measure the local blood velocity in vivo. The laser beam emitted from the sensor tip can be focused at any distance between 0.1 and 0.5 mm from the tip. Consequently, the sensor has a sufficiently high signal-to-noise ratio to measure the local velocity in almost any opaque fluid, including blood. The sensor head is inserted in an injection needle or a catheter tube. In the former case, it is inserted at an angle to the wall of a vessel and is scanned across the vessel to measure the velocity distribution. In the latter case, it is aligned parallel with the flow in a vessel. For all flows of whole human blood, whole caprine blood, and 69% hematocrit of bovine blood, the velocity distribution across the vessel could be measured very accurately. The insertion angle of the fiber into the flow significantly affects the measurement accuracy; an angle of about 50° is suitable when an injection needle is used. When a catheter is employed, an insertion direction opposite to the flow direction is better than parallel to the flow due to the generation of a wake behind the fiber.

Development of a Miniaturized Fiber-optic LDV Sensor for Local Blood Velocity Measurement

131 DOI: 10.5963/BER0203002 Development of a Miniaturized Fiber-optic LDV Sensor for Local Blood Velocity Measurement Local Velocity and Flow Profile Measurement of Pulsatile Blood Flow Modeled in Humans Shimpei Kohri, Tsutomu Tajikawa, Kenkichi Ohba Department of Medical Engineering, Aino University 4-5-4, Higashiohda, Ibaraki city, Osaka 567-0012 Japan Department of Mechanical Engineering, Kansai University, 3-3-35 Yamate-cho, Suita-shi, Osaka 564-8680 Japan s-kohri@me-u.aino.ac.jp

Oscillation Amplitude of a Collapsible Tube Near the Boundaries of Oscillatory Control-Space at Reynolds Numbers Characteristic of Larger Airways

The flow-induced oscillation of a collapsible tube is a model for the audible vibrations of various respiratory tract structures. Collapsible-tube oscillations can be mapped in a two-dimensional control space of operating points set by relative pressures. Within the oscillatory regions of that control space, frequency and amplitude vary with position. To determine the nature of the dynamical bifurcation at the boundary of oscillatory control space, it is important to know how oscillation amplitude varies near the boundary. We therefore investigated the control-space distribution of oscillation amplitude, in a region where oscillation occurred at the lowest possible Reynolds number. Control-space diagrams were obtained in the region 135<Re<350. It was found that the changes in amplitude when the operating point was varied across the control-space boundary from tube closed to tube oscillating were much milder than those seen when crossing from tube oscillating to tube open. Hysteresis of amplitude change was observed near both boundaries. The gradient of oscillation amplitude with change of flow-rate was especially steep when the tube oscillation was suppressed by increasing flow rate through the tube, i.e. the oscillation stopped quite suddenly. The amplitude changed more gradually after oscillation onset. The boundary between tube closed and oscillation shifted very little. But the tube-opening boundary was affected by both flow-rate and tube exterior pressure. So the oscillation amplitude was influenced by the direction of approach to the control-space boundaries, and the oscillatory region was wider when increasing flow-rate than when decreasing.

Influence of Valsalva Sinus on Flow Field around the Aortic Valve and the Valve Characteristics (Quantitative Evaluation by Experiments in vitro Using a Realistic Model)

One of the well known cures for the annuloaortic ectasia is a vascular grafting surgery using a composite graft as an artificial ascending aorta and an artificial valve. Although, almost all conventional grafts do not have Valsalva sinus at the aortic root, the influence of omitting the Valsalva sinus have not yet been clarified. In order to understand the effect of the Valsalva sinuses at aortic root on the valve characteristics and flow field around the valve and furthermore the coronary blood flow, the authors have fabricated some realistic models of aortic valve using three-dimensional modeling machine, and have investigated the effect of the sinus existence by particle image velocimetry (PIV). As the result, the fluctuation of flow rate at coronary artery in the case of the straight wall model was larger than the Valsalva sinus model. The valve leaflets were pulled to the left ventricle, which could cause a diastolic regurgitant flow from the aorta into the left ventricle. The leaflet suction in the Valsalva sinus model was weaker than the straight wall model. Flow visualization results showed that vortex flow occurred in the Valsalva sinus due to jet flow through the valve leaflets during systole. At early diastole, flow into coronary artery around the Valsalva sinus was smoothly than the straight wall model. Consequently it was concluded from a standpoint of flow and valve characteristics that the Valsalva sinus had an important role for the aortic valve and the inlet of the coronary circulation.

Development of New Method for Discriminating Embolus from Air Bubble in Pulsatile Blood Flow Using Ultrasound

Patients who have operation for artificial valve substitution frequently suffer from brain embolism. Micro air bubbles are generated with opening and closing of an artificial valve in such a patients blood. It is difficult to discriminate air bubbles from emboli by methods using ultrasonic wave. Hence, we tried to develop a new method for discriminating embolus from air bubble in pulsatile blood flow using ultrasound. We utilized the difference in motion of embolus and an air bubble when they are irradiated by ultrasound beam. It is considered that the difference in motion is caused from the difference in acoustic impedance and mass of them. As a result, we succeeded to discriminate emboli from micro air bubbles in pulsatile flows as well as in steady flow in the model experiments in vitro.

Influence of Valsalva sinus on flow field around the aortic valve and the valve characteristics

One of the well known cures for the aortic regurgitateon is a vascular grafting surgery using a composite graft as an artificial ascending aorta and an artificial valve. Although, almost all conventional grafts do not have Valsalva sinus at the aortic root, the influence of omitting the sinus have not yet been clarified. In order to understand the effect of the sinuses at aortic root on the valve characteristics and flow field around the valve and furthermore the coronary blood flow, the authors have fabricated some realistic models of aortic valve using 3D modeling machine, and have investigated the effect of the sinus existence by PIV. As the result, flow into coronary artery around the Valsalva sinus was smoothly than the straight wall model at early diastole. Consequently it was concluded from a standpoint of flow and valve characteristics that the sinus had an important role for the aortic valve and the inlet of the coronary circulation.