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Biomedical subjects

K Takakuda

Publications and source records attributed to K Takakuda.

At least 19 recordsLinked to original sources
PubMed2001

The biocompatibility and osteoconductive activity of a novel hydroxyapatite/collagen composite biomaterial, and its function as a carrier of rhBMP-2.

A hydroxyapatite/type I collagen (HAp/Col) composite, in which the hydroxyapatite nanocrystals align along the collagen molecules, has been prepared. The biocompatibility, osteoconductive activity, and efficacy as a carrier of recombinant human bone morphogenetic proteins (rhBMPs) of this novel biomaterial were examined. The composite material was implanted in the backs of Wistar rats, and specimens were collected for histological observations until week 24. In a second experiment, other samples of the composite material (5 x 5 x 10 mm3) were drilled and immersed in a solution of rhBMP-2 (0, 200, 400 microg/mL), and subsequently grafted in radii and ulnae in beagle dogs. As a control, three unfilled holes were left in one radius and ulna. X-ray images were prepared, and specimens collected for histological observation at weeks 8 and 12. Histological findings of the composites grafted in rats showed that the surface of the material was eroded as a result of macrophage infiltration. X-ray images and histological findings for the composites implanted in dogs support the idea that HAp/ Col has a high osteoconductive activity and is able to induce bone-remodeling units. In cases where the implants are grafted at weight bearing sites, treatment with rhBMP-2 at a dose of 400 microg/mL may be useful to shorten the time needed until bone union has occurred.

Animals↗
PubMed2001

Preparation and microstructure analysis of chitosan/hydroxyapatite nanocomposites.

Chitosan/hydroxyapatite (HAp) composites with a homogeneous nanostructure have been prepared by a co-precipitation method. According to TEM observations, HAp crystallites in the composites formed elliptic aggregations 230 nm in length and 50 nm in width. The typical length of the aggregations corresponded approximately to that of a chitosan molecule. The size of the constituent HAp crystallites was found to be predominantly 30 nm in length and 10 nm in width, and the c-axes were well aligned in parallel with the chitosan molecules in the respective aggregations. The growth of the HAp crystallites is considered to occur at nucleation sites, most probably forming the complexes with amino groups on chitosan with calcium ions. The compact composites obtained have been found to be mechanically flexible, and this flexibility has been improved further by heating at 120 degrees C for 20 min in an autoclave with saturated steam pressure.

Biocompatible Materials↗
PubMed2001

A study of induction of nerve regeneration using bioabsorbable tubes.

A silicone tube (S-tube) was packed with CPLA (copolymer of poly-L-lactide) fibers (S-tube+CPLA) or collagen fibers (S-tube+fiber). Two types of tube were prepared from a collagen sheet (Col-tube) and a bioabsorbable atelocollagen membrane for guided tissue regeneration (GTR-tube). They were packed with collagen fibers or films (Col-tube+fiber, GTR-tube+fiber and GTR-tube+film). Bridge grafting (15 mm in length) was performed with these tubes in a rat sciatic nerve model. Specimens were harvested after 8 weeks. Minifascicles were formed in the open space between the CPLA fibers in the S-tube+CPLA group. Regenerated axons were also formed in the degenerated collagen fibers in the S-tube+Col group. Immunocytochemistry evaluation revealed that Schwann cells invaded the space in the absorbing collagen fibers. Histologic analysis of the regenerated axons in the groups with Col-tubes or GTR-tubes revealed that both the Col-tube and the GTR-tube packed with collagen fibers were effective in providing a scaffold for regenerating nerve tissue.

Animals↗
PubMed2001

Development of an orthodontic simulator for measurement of orthodontic forces.

In this research we developed an orthodontic simulator for analysis of orthodontic forces distribution in the case of the continuous arch technique. In order to take into account vertical force, besides horizontal force and occlusogingival moment on instrumented artificial tooth, tooth root was designed as a ring load cell. Fixing each artificial tooth onto combined mechanical stages enabled variation of tooth anteroposterior position and inclination related to occlusal plane. Calibration of forces and moment of each instrumented artificial tooth showed linearity of outputs and provided the generalized inverse matrix for evaluation of forces and moments from measured strain data. A simulation to retract the anterior teeth was accomplished, and distribution of forces and moment acting at the bracket of each tooth were determined. The average accuracy was 82% and 97% in the horizontal and vertical direction, respectively, by comparing the applied forces and the evaluated ones.

Algorithms↗
PubMed2000

[Mechanical behavior of the cement layer of a cast crown--effect of the mechanical properties of casting alloy].

Experimental crowns with uniform thickness at their axial surfaces were made of dental casting gold-silver-palladium alloy (12% gold) and dental casting gold alloy (Type IV). They were cemented on model teeth for abutment and their deformations under applied loads were measured with strain gages. The effect of axial metal thickness on the crown's rigidity and the cement fracture strength were examined. Among the structures of cemented crowns and abutment teeth, that of the axial metal thickness of 0.3 mm had cement failure at the smallest loads. As the metal thickness was increased, the crown's deformation decreased and the cement failure load increased. For a thickness greater than 0.7 mm, however, the increase in failure load was not obvious. The difference of the casting alloy had no significant effect on the cement fracture. Accordingly, the rigidity of dental prostheses should be one of the most important design factors for preventing failure under occlusal load, and it is recommended that the thickness of the axial surface should be more than 0.7 mm.

Dental Alloys↗
PubMed1999

Cell culture test of TCP/CPLA composite.

Thermoplastic polymers filled with a ceramic powder (here described as a "composite") of beta-tricalcium phosphate (TCP) and copoly-L-lactide (CPLA) was prepared by a heat-kneading method. The TCP/CPLA composite obtained had a three-point bending strength of 51.26 +/- 634 MPa, a Young's modulus of 5.18 +/- 1.11 GPa, and a fracture strength of 52.64 +/- 2.975 MPa, which is sufficient for usage as an artificial bone implant material. According to cell culture tests using MC3T3-E1 cells, the TCP/CPLA composite showed no cytotoxicity and the cells were in close contact with the surfaces of the composite without any observable morphological change. These results suggest that a composite consisting of osteoconductive TCP and biodegradable CPLA is suitable as a bioactive artificial bone material.

Absorbable Implants↗
PubMed1999

Synthetic collagen fibers coated with a synthetic peptide containing the YIGSR sequence of laminin to promote peripheral nerve regeneration in vivo.

The usefulness of collagen fibers and the YIGSR sequence (Tyr-lle-Gly-Ser-Arg) of laminin for nerve regeneration were examined in vivo. Type I collagen gel (G-group), Type I collagen fibers (F-group), Type I collagen fibers coated with laminin (L-group) or the YIGSR sequence (Y-group) were packed into silicone tubes, 15 mm long, and transplanted to the sciatic nerves of Wistar rats. Empty silicone tubes were used as the control. The animals were sacrificed 8 weeks after transplantation. Bridging of the nerve was confirmed in the F-(7/12), Y-(7/10) and L-group (6/10), but no bridging was observed in any of the animals of the G- and control group. Nerve regeneration among the space of collagen fibers was observed, and it was suggested that fibroblasts infiltrated the gap in the substance of the degenerated collagen fibers were followed by Schwann cells on the basis of immunocytochemistry. The number of myelinated axons per regenerated tissue in the tube (density), and total area of myelinated axons per measured regenerated tissue in the tube (% axon area) in each the L- and Y-group were significantly higher than that in the F-group (P < 0.05). These results suggest the possibility of obtaining adequate nerve regeneration with new artificial materials only.

Journal Article↗
PubMed1997

A comparison of in vivo and in vitro strain with posterior fixed partial dentures.

PURPOSE: Deformation of fixed partial dentures during function has been related to clinical failures. However, such deformation has not been measured quantitatively, and the effect on deformation of the viscoelastic behavior of peridental structures is not well understood. The purpose of this study was to determine the strain distribution of fixed partial dentures during function and to compare the biomechanical behavior of fixed partial dentures in vivo and in vitro. MATERIAL AND METHODS: Three conventional posterior fixed partial dentures and two complete crowns were fabricated. Both in vivo and in vitro strain measurements of each of the five prostheses were recorded by a strain gauge method. A static load was produced through occlusal force in vivo and with a universal testing machine in vitro. RESULTS: The resulting difference between the strain distribution for the two crowns in vivo and in vitro was negligible, but the whole fixed partial denture demonstrated a substantial amount of strain in vivo. CONCLUSIONS: The results of this study suggest that serious problems with strain may occur in a long-span mandibular posterior fixed partial denture.

Adult↗
PubMed1996

Changes in lCBF, morphology and related parameters by fluid percussion injury.

We investigated the pathophysiological and morphological responses of anaesthetized rats to fluid percussion brain injury generated by an original midline fluid percussion injury device. Following different grades of trauma, lCBF was measured continuously in the right parietal cortex through a burr hole using laser Doppler flowmeter, and physiological parameters were monitored. Pathological changes also were evaluated microscopically. During the first 2 hours following trauma, we found four patterns of cerebral circulatory responses. Little measurable pathophysiological response occurred after percussion pulses of less than 1.33 atmospheres (atm). In animals subjected to pulses of greater than 4.30 atm, lCBF increased synchronously with blood pressure, and then both parameters decreased continuously until death. In animals subjected to pulses of 1.53 to 2.33 atm, trauma produced a transient increase in lCBF with no synchronous rise in blood pressure. In animals subjected to pulses of 2.70 to 3.87 atm, lCBF increased synchronously with blood pressure immediately following the injury, but had decreased markedly by 60 seconds and remained below the pre-injury baseline. Blood pressure recovered to baseline within 4 minutes of the injury. The transient increase in lCBF occurred within 5 seconds following percussion pulses of greater than 1.53 atm and appeared to be independent of the rise in systemic blood pressure. Apnoea occurred in animals subjected to pulses of greater than 1.53 atm, and the duration of apnoea and mortality rate correlated with the magnitude of the applied injury. A power decrease in the electroencephalogram post-injury and a delay in its recovery, both depended on the magnitude of the injury with few regional differences in the beta-2 band power. The distribution and extent of blood-brain barrier disruption and small haemorrhages also correlated with the magnitude of the injury. The number of neurons decreased significantly in both hippocampi by 2 weeks following moderate trauma. The four patterns of lCBF changes demonstrated in the present study, as well as the other responses to injury, may be useful for studying graded models of various diffuse brain injuries.

Animals↗
PubMed1996

Tensile behaviour of fibroblasts cultured in collagen gel.

An in vitro morphological study on the relation of the stress field and the orientation of cells with the use of the time lapse video recording system was carried out. Specimens of thin collagen gel membrane, within which cells are proliferating, were examined under various mechanical conditions. Cell stretching, cell orientation, cell migration, cell proliferation and generation of tensile stress in collagen gel were recorded. It was demonstrated that fibroblasts generate tension and change their orientation along the tensile direction. A hypothetical mechanism for such phenomena is proposed, that is, fibroblasts generate tension and make tense collagen fibres, then cells stretch themselves along the tense fibres and increase tension in this direction. Thus, this mechanism works as a positive feedback loop which enables cells to make tensile stresses and align along them in accordance with the mechanical environment.

Animals↗
PubMed1996

Magnetic resonance imaging and pathologic studies on lateral fluid percussion injury as a model of focal brain injury in rats.

In this study, morphologic changes in brain lesions initiated by moderate lateral fluid percussion injury in rats were investigated chronologically using high-resolution magnetic resonance imaging (MRI) and histopathologic methods. Rats were subjected to moderate fluid percussion injury (average 2.80 +/- 0.48 atmospheres) over the exposed dura overlying the right parietal cortex. MRI obtained in vivo were compared with corresponding pathologic findings at 1, 6, and 24 h and at 3, 6, 14 and 80 days after injury. T2-weighted images showed scattered low-signal intensity in the injured cortex within a few hours after injury, whereas histologic findings revealed intraparenchymal hemorrhages. T2-weighted images of the ipsilateral cerebral cortex and/or corpus callosum showed a high-signal-intensity area 4 h after injury. The high-signal-intensity area became largest in size between 6 and 24 h, then declined gradually, and almost disappeared 14 days after injury. Histologic examination revealed pyknosis, retraction of the cell body of neurons with vacuolated neuropil in the corresponding regions 6 and 24 h after injury, and cystic necrosis 14 days after injury. The location and extent of these pathologic changes were depicted accurately by MRI in vivo. In the hippocampus, pyknosis and retraction of the cell body of pyramidal neurons were observed on the injured side 24 h after injury, and the number of neurons in the CA1 and CA2-CA3 regions decreased significantly on the same side by 14 days after injury. It is concluded that morphologic changes in the brain following experimental traumatic brain injury in rats are detectable in vivo by high-resolution MRI, and that MRI may be useful for the evaluation of treatment effects in experimental brain injury.

Animals↗
PubMed1996

A cadaveric study on the stability of lumbar segment after partial laminotomy and facetectomy with intact posterior ligaments.

This study aimed to biomechanically investigate a change in the stability of decompressed segments in the degenerative lumbar spine. Cyclic loading tests to the cadaveric spinal unit were conducted in compressive and bending directions with a stepwise resection of the posterior elements such as wide fenestration (partial laminotomy), unilateral and bilateral facetectomy with the intact supra- and interspinous ligaments and spinous process. Flexion stability did not decrease significantly, and may reflect the fact that the aforementioned ligamentous structures were preserved throughout the resection process. After wide fenestration, the loss of compression stiffness amounted to only half that of bilateral facetectomy, and extension stiffness dropped to this same level. Lateral bending stiffness was maintained until unilateral facetectomy was performed. We recommend restricted decompression surgeries for a single-level central stenosis in the degenerative lumbar spine.

Aged↗
PubMed1995

An approach to computer aided porcelain forming system.

To examine a new concept for computerized production of dental prostheses, an experimental porcelain forming system was devised. Unlike other dental CAM systems, the system is intended to form porcelain much as human technicians do. The system builds up an object by alternately applying water and droplets of porcelain powder. Test specimens were made by forming porcelain powder into square plates under different forming conditions. Surface characteristics and shapes of formed porcelain were found to be affected by conditions such as quantity of water, forming area and forming thickness. The proper quantity of water for forming was influenced by evaporation. It was concluded that investigation into feedback control of the water supply in response to varying forming conditions is required.

Computer-Aided Design↗
PubMed1994

Fuzzy and conventional control of high-frequency ventilation.

A high-frequency ventilator was developed, consisting of a single-phase induction motor, an unbalanced mass and a mechanical vibration system. Intermittent positive pressure respiration was combined with high-frequency ventilation to measure end-tidal pCO2. Hysteresis was observed between the rotational frequency of the high-frequency ventilator and end-tidal pCO2. A fuzzy proportional plus integral control system, designed on the basis of the static characteristics of the controlled system and a knowledge of respiratory physiology, successfully regulated end-tidal pCO2. The characteristics of gas exchange under high-frequency ventilation was approximated by a first-order linear model. A conventional PI control system, designed on the basis of the approximated model, regulated end-tidal pCO2 with a performance similar to that of the fuzzy PI control system. The design of the fuzzy control system required less knowledge about the controlled system than that of the conventional control system.

Animals↗
PubMed1989

[Experimental HFV apparatus utilizing a mechanical vibration].

We make an experimental HFV apparatus in which the mass-spring system is utilized as the vibration actuator. When this apparatus is operated near the characteristic frequency of the mechanical vibration system, the efficiency is quite good and trivial motor is enough to realize the vibrating flow for the experimental ventilator. In this paper we first investigate the flow-frequency relations and found that above the characteristic frequency of the mechanical vibration system the oscillating volume of flow is nearly constant. Next we check the gas exchange between model-lung and atmosphere and obtain the relations among pressure vs. flow rate, pressure vs. rate of gas exchange.

High-Frequency Ventilation↗
PubMed1989

[Mechanical analysis of the denture bases using the photoelastic-coating method. 2. Upper complete denture bases under uniform bending moment load].

Deformation of the anterior teeth and palatal regions on upper complete dentures was investigated using the photoelastic coating method and strain gages. In this experiment, an uniform-moment bending load method was employed to simulate the occlusal situation, and the distribution of strain in epoxy resin, stainless swaged and Co-Cr alloy cast dentures were measured and analyzed. The 030-series reflection polariscope is compact and lightweight with its main components consisting of two polarizer/quarter-wave-plate assemblies attached to a common frame. The highest level of strain was seen in the anterior region of the palate and the low strain was observed in other regions. Differences in strain magnitude of the three dentures were not observed with test at the same point. But, when denture base materials with high flexural rigidity and bending strength were used on the palatal region of the denture base, strain was decreased in the anterior and other regions of the palate. Therefore, dentures using those materials could be effectively reinforced.

Dental Stress Analysis↗
PubMed1989

[Mechanical analysis of the denture bases, using the photoelastic-coating method. 1. Influence of the coating on mechanical properties of the test denture].

The anterior palatal area may be related with the flexural rigidity and bending strength of the upper complete dentures. Therefore, the deformation of this area should be measured widely and continuously when new materials were applied to the dentures. The influence of the photoelastic coating on the mechanical properties of the upper complete dentures was investigated, prior to the measurement of surface strains on the denture bases by the photoelastic coatings. In this experiment, the uniform-moment bending method was employed simulating the occlusal situation. The flexural rigidity of the denture bases depended on the palatal materials in spite of the presence of the coating. The strains concentrated on the anterior palatal area were slightly decreased when the coating was bonded to the polished surface of the palate. The reinforcing effect was significant when the resin dentures of low elastic modulus were coated. The photoelastic-coating method was suitable for the qualitative analysis of the strain distribution of the denture base and selecting the test points to make strain measurement accurate.

Dental Stress Analysis↗