Biomedical subjects

A T Yokobori

Publications and source records attributed to A T Yokobori.

At least 19 recordsLinked to original sources

PubMed2004

The proposal of noninvasive quantitative diagnostic method of the atherosclerosis and the clarification of organ correlation of atherosclerosis and oxygen metabolism.

The proposal of noninvasive diagnostic method of mechanical degradation of vascular wall is clinically useful and it will be correlated with noninvasive diagnostic method of atherosclerosis. Supersonic Doppler effect sensor has been used to measure blood flow velocity as a noninvasive measuring method. However, it is remain problem whether the output from the Doppler effect sensor really detects the pure blood flow velocity. Theoretically, when the Doppler effect sensor is set perpendicular to the blood flow direction, that is, perpendicular to the blood vessel, the output will correspond to the expansion velocity of blood vessel wall, because it detect the frequency of Doppler shifted supersonic scattered from vascular wall. Previously, on the basis of this concept, using Doppler effect sensor, we showed this method can really detect the deformation velocity of blood vessel wall and it correlates the degradation of elastic property of blood vessel. Furthermore, using this proposed measuring method, atherosclerosis is found to progress correspondingly with the visco-elastic degradation of vascular wall. In this paper, on the basis of our proposed method, the quantitative noninvasive estimation method of the degradation of vascular wall and the progressive degree of atherosclerosis by unique parameter has been proposed. Using this method, the degradation of vascular wall is correlated to the oxygen metabolic function of blood vessel corresponding to the function of oxygen transportation and progression of atherosclerosis. Furthermore, the organ correlation on the atherosclerosis between lower limb and carotid is investigated by this proposed method.

Algorithms↗

PubMed1999

Use of porous hydroxyapatite graft containing recombinant human bone morphogenetic protein-2 for cervical fusion in a caprine model.

OBJECT: The efficacy of recombinant human bone morphogenetic protein-2 (rhBMP-2) for enhancing anterior cervical spine interbody fusion when added to a porous hydroxyapatite (HA) graft was investigated. METHODS: Fourteen mature goats underwent three-level anterior discectomies after induction of endotracheal anesthesia. Porous HA grafts that contained 0, 5, and 50 microg of rhBMP-2 were placed concurrently with anterior cervical spine plates to achieve interbody fusion. The fusion rate, radiological findings, biomechanical stiffness, and histological appearance were evaluated in 42 spinal units immediately and again at 4 and 12 weeks after graft and plate placement. At 12 weeks postsurgery, manual testing showed a 100% fusion rate in the spines with HA grafts containing high-dose rhBMP-2; however, only a 50% fusion rate was shown in spines with grafts that contained no or low-dose rhBMP-2. On radiographic and histological studies the process of solid fusion was seen to be more advanced in relation to the use of larger amounts of rhBMP-2. Biomechanical testing demonstrated significantly higher stiffness values for grafts that contained high-dose rhBMP-2 than those without rhBMP-2 in flexion at 4 weeks, as well as in flexion, extension, and lateral bending tests at 12 weeks. Histological analysis demonstrated that rhBMP-2 increased the amount of bone apposition on the surface of the implants and promoted bone formation in the porous structure without increasing the penetration distance. CONCLUSIONS: Through osteogenesis at the fusion site, the addition of rhBMP-2 to a porous HA ceramic graft enhances the rate of anterior cervical fusion.

Animals↗

PubMed1999

Osteogenic differentiation of cultured marrow stromal stem cells on surface of microporous hydroxyapatite based mica composite and macroporous synthetic hydroxyapatite.

In order to investigate the significance of hydroxyapatite based microporous composite (HA/mica composite) surfaces and a macroporous synthetic hydroxyapatite, rat marrow cell culture, which shows osteogenic differentiation, was carried out on six different culture substrata (two control culture dishes, two identical HA/mica composites, and two identical macroporous synthetic hydroxyapatites). A culture period of two weeks in the presence of beta-glycerophosphate (BGP), ascorbic acid, and dexamethasone resulted in abundant mineralized nodule formations that were positive for alkaline phosphatase (ALP) stain. The stain on the macroporous synthetic hydroxyapatite and the HA/mica composites were intense, the enzyme activity being about double that of control culture dishes. These data indicate that the synthetic macroporous hydroxyapatite surface and the HA/mica composite surface promotes osteoblastic differentiation.

Alkaline Phosphatase↗

PubMed1999

The effect of diameter ratio between vascular substitute and blood vessel on anastomosis.

It is necessary to maintain mechanical compatibility between a blood vessel and a vascular substitute to promote encapsulation around the anastomosed part. From this point of view, using linear elastic theory, we had previously performed stress analyses at the part anastomosed by tissue adhesion, in order to propose some methods of preventing stress concentration at this junction. In this study, based on the previous analyses, we have attempted to develop a concept that can be applied under the conditions of operation. That is, the initial diameter of a vascular substitute with high rigidity is chosen larger than that of a blood vessel. This will reduce the stress concentration around the anastomosed part, on average, during expansion of the blood vessel. We analysed the optimum diameter ratio between the vascular substitute and the blood vessel which causes the least stress concentration, on average, during this process, using linear elastic theory. Furthermore, numerical analyses of blood vessel deformation were performed using various nonlinear stress-strain laws. These results were compared to the analytical solution based on linear elastic theory.

Anastomosis, Surgical↗

PubMed1998

Osteogenesis mechanism based on kinetic theory.

In our earlier studies, we considered osteogenesis to be a nucleation mechanism accompanied by preliminary diffusion and showed the optimum mechanical conditions for promoting this ionic diffusion. In this study, we performed an analysis of the nucleation mechanism of hydroxyapatite (HA) in areas with a high concentration of transported Ca and PO4 ions in the pore region along the collagen alignment. We derived the equation of the HA nucleation rate as a function of hydrostatic tensile stress, sigma P and surface energy change (gamma-lambda), where gamma is the surface energy of the HA particle and lambda is the decreasing factor of gamma during HA nucleation. lambda is thus related to the effect of chemical and electric stimulations. Finally, we formulated a unified equation of the nucleation rate of HA, which consists of ionic diffusion and HA nucleation processes.

Algorithms↗

PubMed1998

Fracture toughness of hydroxyapatite/mica composite, packed hydroxyapatite, alumina ceramics, silicon nitride and -carbide.

By using the fracture toughness estimation method based on two-dimensional map, it was found that the ductility of the high porosity hydroxyapatite/mice composite was comparable with silicon carbide. It was measured to be higher than that of packed hydroxyapatite. Alumina ceramics with more than 96% aluminium oxide showed a higher fracture toughness than the composite material. When bending strength was compared, the strength of the composite was two or three times lower than that of packed hydroxyapatite and much lower than the other studied materials. The composite material showed high porosity, which in turn gives it a lower bending strength. However, the high porosity is more favourable for biocompatibility.

Aluminum↗

PubMed1997

Biomechanical evaluation of hydroxyapatite intervertebral graft and anterior cervical plating in a porcine cadaveric model.

The biomechanical properties of a porous hydroxyapatite (HA) intervertebral graft with or without anterior cervical plating were evaluated in cadaveric porcine cervical spine model using C3-4 discectomy and dissection of the posterior longitudinal ligament to cause instability. The experimental groups were intact (n = 11), instability (n = 11), autogenous bone implant (n = 6), HA graft implant (n = 5), autogenous bone with plating (n = 6), and HA graft with plating (n = 5). Porous HA with 40% porosity and scapular bone were used as grafts. The displacement rates of the cervical spine by compressive forces in the flexural, extensional, and lateral bending directions were evaluated using video-recording followed by computer-assisted analysis. The stiffness to compressive load was calculated from the load-displacement rate curve. The linear and non-linear coefficients of the Fung's equation were obtained based on the plot of Young's modulus against load. There were no statistical differences in the stiffness between the HA and autogenous bone graft in all directions. The two plating groups showed significantly increased stiffness in all directions. The non-linear coefficient value in Fung's equation was far larger in both HA and HA graft with plating groups than in the other groups in flexural compression. Porous HA graft has a compressive strength similar to autogenous graft in vitro, and anterior plating provides additional stiffness to the cervical spine. The larger non-linear coefficient value of the HA groups may represent the characteristic biomechanical brittleness of HA graft, but this is manifest only in flexural compression.

Animals↗

PubMed1997

Microscopical imaging of hydroxyapatite/mica composite and packed hydroxyapatite structure--an atomic force microscopy investigation.

A fine grained hydroxyapatite/mica composite material was studied by the atomic force microscopy method and the results were compared with results of atomic force microscopy studies of very five grained hydroxyapatite. In the investigation it was found that the fractal dimension diagram from the atomic force microscopy studies is a tool by which mechanical properties on the surface of the material can be predicted. The two investigated materials were found to show self-similarity properties, i.e., they are identical on the surface. The information given by the fractal dimension is important, and the fractal dimension analysis is an important tool in future designing and engineering of, especially, bioceramics and composites.

Aluminum Silicates↗

PubMed1995

Mechanical test method on the estimation of the lubricant performance by hyaluronic acid.

Cases with loss of articular cartilage or lowering of articular lubricant performance are frequent among patients afflicted by various gonarthropathies or those fitted with prosthetic joints. The management of such cases has necessitated evaluation studies on the clinical efficacy of using high molecular weight hyaluronic acid as an artificial synovial fluid with a view to improving articular lubricant performance. The proper implementation of such evaluation studies on lubrication performance requires testing methods capable of assessing basic lubricant performance not only with respect to articular cartilage alone but also with respect to various other combinations of materials, i.e., lubrication between articular bone and artificial joints, etc. In the present study, first, a simple standard lubricant performance test using several small readily procurable test specimens was devised. Then, this test was employed to evaluate the basic lubricant properties of hyaluronic acid intended for use as artificial synovial fluid.

Aged↗

PubMed1995

Theory of osteogenesis behavior based on calcium diffusion theory.

Osteogenesis is completed by the nucleation mechanism on crystal nuclei formation and growth after amorphous calcium phosphate accretion to collagen fibers. For nuclei formation, it is necessary to have preliminary ionic diffusion such as that of Ca2+ and PO4(3-) ions to this part. Therefore, promotion of ionic diffusion to this part is the first essential condition for osteogenesis. We have considered this phenomenon as the nucleation mechanism accompanied by preliminary diffusion behavior and shown the optimum mechanical condition on promoting this ionic diffusion. Furthermore, we noticed callus by callotasis as the typical example which fits this mechanical condition and investigated its histology. However, necking occurs at the site of callus sandwiched by cortical bones due to tensile stress, three axial tensile stress in radial and tangential directions, in addition to the tensile stress occurs at the netsection of the callus due to the constraint of cortical bones. Therefore, the size of pore along the collagen lamination and hole zone becomes large under this mechanical condition and ionic diffusion such as Ca2+, PO4(3-) is liable to occur at this part. By solving the partial differential equation of the stress-induced diffusion, diffusive particles are shown to concentrate at the high three axial tensile stress region. Therefore, a high concentrated region of Ca, PO4 is achieved and selective osteogenesis due to hydroxyapatite nucleation is considered to progress in this region. Histological investigation of the callus of rabbit showed that mineralization occurs at this site and supports the theory of stress-induced diffusion on osteogenesis behavior.

Animals↗

PubMed1994

Theoretical foundation on a noninvasive estimation for viscoelastic mechanical property of blood vessels by ultrasonic Doppler effect.

The method used in this paper is developed to estimate the degree of viscoelasticity of the blood vessel wall in a noninvasive mechanical method. In this proposed method, we can obtain an output waveform connected with mechanical behavior of blood vessels by using Ultrasonic Doppler Effect Sensory (UDES). Characterizing parameters on this waveform are established to estimate the mechanical properties of blood vessels. By analyzing the characteristics of these parameters, we attempt to estimate the viscoelastic property of blood vessels. Previously, it was found that these parameters are related to viscoelastic mechanical properties of materials. In this paper, we carried out computer analysis on the mechanical viscoelastic model and compared the theoretical behavior of blood vessels with the experimental output waveform by UDES. From these results, it was proved that values of these parameters connect with the change of the viscoelastic mechanical property of blood vessels. Therefore, the characterizing parameters of experimental output waveforms can be used to estimate the viscoelastic property of blood vessels in a noninvasive method.

Animals↗

PubMed1994

Algorithm of the noninvasive diagnosis method on the atherosclerosis by ultrasonic Doppler effect.

Previously we proposed Acoustical Imaging and Processing Method to measure the viscoelastic property of the blood vessels of a canine and the related materials using Ultrasonic Doppler Effect Measurement. Furthermore, its theoretical foundation was presented. In this paper, this method is applied to measure the viscoelastic mechanical property, that is, the mechanical degradation of human blood vessels by a percutaneous noninvasive method. Based on these results, we proposed the algorithm of the noninvasive estimation method on the viscoelastic mechanical property of the blood vessel by using Doppler Effect Sensor. This method makes it possible to discriminate the blood vessel with arteriosclerosis from a normal blood vessel. Clinical applications were successfully performed using our developed computer software based on our proposed algorithm.

Algorithms↗

PubMed1994

CAE software for the noninvasive diagnosis method on the atherosclerosis by ultrasonic Doppler effect.

Previously, we developed the noninvasive estimation method on the viscoelastic deterioration of the blood vessel and related materials by using Ultrasonic Doppler Effect Sensor and we presented its theoretical foundation. Furthermore, we applied this method to discriminate the human blood vessels with atherosclerosis from normal blood vessels, as the viscoelastic deterioration under in vitro condition and proposed the algorithm for its diagnosis. In the present paper, we propose the software for personal computer (AORTA) for clinical diagnosis on the atherosclerosis within a few minutes by using Ultrasonic Doppler Effect Sensor based on this algorithm. Using this software, we clinically applied this method to patients with atherosclerosis and normal people. It enables us to discriminate the atherosclerotic blood vessels from those of the normal blood vessel within several minutes. By using this system, it is found that the normal human blood vessel has elastic property. When the blood vessel becomes atherosclerotic, it deteriorates in elasticity and shows the viscoelastic property. This system evaluates noninvasively the viscoelastic property of the blood vessel and the degree of the atherosclerosis.

Arteriosclerosis↗

PubMed1994

The mechanical behavior and morphological structure of callus in experimental callotasis.

Experimental callotasis was made in rabbit femurs. In order to compare mechanical behaviors and morphological structure of callus in callotasis, mechanical tests and histological examination were performed. Twenty Japanese white male rabbits were used. The right femurs were osteotomized at the level of the midshaft with a rotary cutter and fixed with a mini-model external fixator. After a 5-day waiting period, bone lengthening was started at the rate of 0.25 mm two times a day. Animals were divided into four groups. Group 1 and Group 2 were continual distraction group, Group 3 and Group 4 discontinued distraction group. The viscoelastic property was demonstrated in continual distraction group irrespective of distraction period, we thought the central undifferentiated connective tissue in callus was mainly responsible for the mechanical behavior. On the other hand, in discontinued distraction group, viscoelastic property shifted to elastic property corresponding to the rest period, we thought this change of mechanical behavior was histologically owing to the replacement of undifferentiated connective tissue by cartilage and the partial union of bone in callus.

Animals↗

PubMed1994

Mechanical test methods for biomedical membranes.

It is important to estimate the mechanical characteristics and strength of biomedical membrane. For this purpose, previously we have proposed several mechanical test methods for biomedical membranes. To establish the safety design for biomedical membrane, such as cellophane membrane for hemodialysis, it is important to estimate the viscoelastic characteristics of these materials. On the other hand, artificial biomedical membrane such as tympanic membrane, are subjected to noncontact internal air pressure under the membranous state. To estimate mechanical characteristics of such membrane, it is necessary to develop a well-simulated test under the gaseous pressure and the other mechanical test under the membranous state. In this paper, several test methods for these purposes were shown. Furthermore, results obtained by these methods were shown and related to clinical problems. These proposed test methods are quite different from the axial tensile test. But they are also important to estimate the mechanical property of biomedical membrane. Each result obtained by these test methods has its own significance. By selection of the most suitable test method for each purpose and revealing these mutual relations, safety design of artificial organs can be performed from the viewpoint of the strength.

Cellophane↗

PubMed1993

Hybrid concept on the mechanical test method of small caliber blood vessel.

A mechanical test on small caliber blood vessel is difficult because the strength is very low and the dimension is very small. In the present paper a multifunctional axial test apparatus design is proposed. This has the characteristics such that the load cell and the environmental container for the specimen are built up in terms of cassette, respectively, and thus both are easy to equip and take off, that is, easy to replace. Also, the test methodology by internal pressure for small caliber blood vessels has been proposed. By using both of these methodologies, the characteristics of the mechanical behavior of small caliber blood vessels, such as compliance, stress relaxation, and viscoelastic property have been clarified. An attempt has been made on the application of this method to a clinical case.

Anastomosis, Surgical↗

PubMed1991

Acoustical imaging and processing of blood vessel and the related materials using ultrasound Doppler effect.

In the present paper a method is proposed to measure the degree of the degradation of the elasticity in natural blood vessel and the related materials by using ultrasound Doppler effect. It was found that the deformation rate and its acceleration in the radial direction of the blood vessel can be detected by acoustical imaging and processing using this method. These results were proven to correspond to the degree of the degradation of the elasticity, that is, the degree of viscoelasticity in the blood vessel from the wave versus time pattern detected and its simple analysis. This method was applied to predicting the arteriosclerosis of blood vessels of humans by acoustical imaging and processing uninvadedly, as the characteristics of viscoelasticity in blood vessels.

Algorithms↗

PubMed1991

Mechanical test methods of biomedical membranes such as used for otolaryngology.

Biomedical membranes, such as artificial tympanic membranes, are subject to noncontact internal air pressure. To estimate mechanical characteristics of such membranes, it is necessary to carry out the noncontact pressure test and membranous contact test, in addition to the usual monotonic tensile test, by using a rectangular specimen cut from the membranes. In this paper, these mechanical test methods and results on such biomedical membranes were studied. Some of the authors have already presented the mechanical test methods of cellophane membrane for hemodialysis under applied water pressure. Herein, we are concerned with the mechanical test methods of biomedical membranes such as tympanic membrane, in which gaseous pressure was applied.

Air Pressure↗