OBJECTIVE Despite improvements in surgical techniques and instruments, high rates of rod fracture following a long spinal fusion in the treatment of adult spinal deformity (ASD) remain a concern. Thus, an improved understanding of rod fracture may be valuable for better surgical planning. The authors aimed to investigate mechanical stress on posterior rods in lumbopelvic fixation for the treatment of ASD. METHODS Synthetic lumbopelvic bone models were instrumented with intervertebral cages, pedicle screws, S2-alar-iliac screws, and rods. The construct was then placed in a testing device, and compressive loads were applied. Subsequently, the strain on the rods was measured using strain gauges on the dorsal aspect of each rod. RESULTS When the models were instrumented using titanium alloy rods at 30° lumbar lordosis and with lateral interbody fusion cages, posterior rod strain was highest at the lowest segment (L5–S1) and significantly higher than that at the upper segment (L2–3) (p = 0.002). Changing the rod contour from 30° to 50° caused a 36% increase in strain at L5–S1 (p = 0.009). Changing the rod material from titanium alloy to cobalt-chromium caused a 140% increase in strain at L2–3 (p = 0.009) and a 28% decrease in strain at L5–S1 (p = 0.016). The rod strain at L5–S1 using a flat bender for contouring was 23% less than that obtained using a French bender (p = 0.016). CONCLUSIONS In lumbopelvic fixation in which currently available surgical techniques for ASD are used, the posterior rod strain was highest at the lumbosacral junction, and depended on the contour and material of the rods.

Abstract Purpose Although it has been recognized that the medial meniscus extrusion (MME) leads to progressive cartilage loss and osteoarthritis (OA), about 20% of cases with MME had minor symptoms and poor progression of knee OA. However, it is still unclear which patients will have minimal symptoms or will not progress to degeneration. The purpose of this study is to compare the effect of the relationship between the MME and Joint line convergence angle (JLCA) on knee stress with the finite element (FE) analysis method. Methods The 65 year-old female was taken computer tomography (CT) from thigh to ankle. A 3-dimentional nonlinear FE model was constructed from the patient’s DICOM data. We made the six models, which was different from JLCA and MME. Contact stresses on the surfaces between femoral and tibial cartilages and both side of meniscus are analyzed. Results As the JLCA or MME increased, the stress load on the medial compartment increased. The effect of MME was stronger on the femoral side, while the effect of JLCA was stronger for the tibia and meniscus. If the JLCA was tilted valgus, the stress in the medial compartment did not increase even in the presence of MME. Conclusions This study revealed that the MME is associated with increased a stress loading on medial compartment structures. Furthermore, this change was enhanced by the varus tilt of the JLCA. In the case of valgus alignment, the contact pressure of the medial compartment did not increase so much even if with the MME. Level of evidence Level V

The surface of titanium (Ti) dental implants must be modified to improve their applicability, owing to the biological inertness of Ti. This study aims to use sandblasting as a pretreatment method and prepare a hydroxyapatite (HA) coating on Ti to improve its biocompatibility and induce bone bonding and osteogenesis. In this paper, sandblasted Ti discs were coated with α-tricalcium phosphate (α-TCP) via Er:YAG pulsed laser deposition (Er:YAG-PLD). An HA coating was then obtained via the hydrothermal treatment of the discs at 90 °C for 10 h. The surface characteristics of the samples were evaluated by SEM, SPM, XPS, XRD, FTIR, and tensile tests. Rat bone marrow mesenchymal stem cells were seeded on the HA-coated discs to determine cellular responses in vitro. The surface characterization results indicated the successful transformation of the HA coating with a nanorod-like morphology, and its surface roughness increased. In vitro experiments revealed increased cell attachment on the HA-coated discs, as did the cell morphology of fluorescence staining and SEM analysis; in contrast, there was no increase in cell proliferation. This study confirms that Er:YAG-PLD could be used as an implant surface-modification technique to prepare HA coatings with a nanorod-like morphology on Ti discs.

[This corrects the article DOI: 10.22603/ssrr.2021-0231.].

There are treatments available for enamel demineralization or acid erosion, but they have limitations. We aimed to manufacture a device that could directly form a hydroxyapatite (HAp) film coating on the enamel with a chairside erbium-doped yttrium aluminum garnet (Er:YAG) laser using the pulsed laser deposition (PLD) method for repairing enamel defects. We used decalcified bovine enamel specimens and compacted α-tricalcium phosphate (α-TCP) as targets of Er:YAG-PLD. With irradiation, an α-TCP coating layer was immediately deposited on the specimen surface. The morphological, mechanical, and chemical characteristics of the coatings were evaluated using scanning electron microscopy (SEM), scanning probe microscopy (SPM), X-ray diffractometry (XRD), and a micro-Vickers hardness tester. Wear resistance, cell attachment of the HAp coatings, and temperature changes during the Er:YAG-PLD procedure were also observed. SEM demonstrated that the α-TCP powder turned into microparticles by irradiation. XRD peaks revealed that the coatings were almost hydrolyzed into HAp within 2 days. Micro-Vickers hardness indicated that the hardness lost by decalcification was almost recovered by the coatings. The results suggest that the Er:YAG-PLD technique is useful for repairing enamel defects and has great potential for future clinical applications.

© 2020, International Federation for Medical and Biological Engineering. Joint dislocation is a critical problem of total hip replacement. We have newly proposed an artificial hip joint with a structure that prevents dislocation. The proposed joint has a simple form with a femoral head partially covered with an acetabular cup. In the present study, the effects of inset heights and slit configurations of the cup on the pull-out forces of the joint were evaluated using finite element analysis. Joint models with different inset heights and those with or without a slit in the cup were used for the analyses to estimate the pull-out forces of the joint. In the case without the slit, the maximum pull-out force of the joint with 1.0 and 1.5 mm of the inset height was approximately 12 and 40 N, respectively. In the case of 1.0-mm inset height, the maximum force of the joint with and without the slit was approximately 9 and 12 N, respectively. These results reveal that the maximum force is markedly changed by the inset height and is moderately affected by the slit. Thus, we can gain insights into a strategy to optimally design an artificial joint in which dislocation does not occur easily. [Figure not available: see fulltext.].

© 2020 Trans Tech Publications Ltd, Switzerland. Dental materials purely composed of calcium phosphate are ideal for dental medicine. We have been developing ultrathin amorphous calcium phosphate (ACP) sheets for enamel repair. In this study, long term stability of the ultrathin ACP sheets applied on enamel surfaces which kept in a simulated intraoral condition for 21 days was evaluated. Surface morphologies of the ACP sheets were observed by optical images. A boundary condition between the ACP sheet and the enamel was evaluated by cross-sectional SEM image. Durability of the ACP sheet was evaluated by a brushing test conducted after 21 days incubation. As a result of these evaluations, it was confirmed that the ACP sheets were stable even after long-term incubation under the simulated intraoral environment condition.

© 2020 Trans Tech Publications Ltd, Switzerland. Dental implants have been widely used to restore missing or damaged teeth. Peri-implantitis is one of the main causes of the implant loss. However, a consensus concerning clinically successful peri-implantitis treatment has not been reached at present. We have newly proposed a treatment method for the peri-implantitis by applying the intraoral laser ablation technique to induce a surface modification of dental implants. In the present study, we investigated the cell adhesion ability of α-tricalcium phosphate (α-TCP) films formed on titanium substrates by an Erbium-Doped:Yttrium, Aluminum, and Garnet (Er:YAG) laser deposition method. Cell adhesion was enhanced by the α-TCP films attached firmly to the substrates using the Er:YAG laser deposition method. This intraoral laser deposition technique can be used to recover the osteointegration ability which was lost by the treatment procedures for peri-implantitis.

Hydroxyapatite (HAp) is one of the main structural components in tooth. Therefore, the HAp is an ideal material to repair tooth substances. However, it has not yet been realized that tooth enamel and dentin are artificially repaired using the HAp in operative dentistry. We have proposed and developed a tooth restoration technique with intraoral laser ablation using an Er:YAG (Erbium: Yttrium-Aluminum-Garnet) laser in order to fabricate HAp films on tooth surfaces in the atmosphere at room temperature. Although HAp thin films were formed on dentin surfaces using the Er:YAG laser deposition method, it has still been unclear how is the mechanical durability of the HAp film on tooth substances. In the present study, we conducted brushing tests to evaluate the durability of adhesion between the HAp film and dentin. To form HAp layers on dentin surfaces, an ablation phenomenon was induced by the Er:YAG laser irradiated to the target of α-Tricalcium phosphate (α-TCP) under humid conditions. The deposited layers were hydrolyzed by dripping artificial saliva on the surface at 37 degrees Celsius for 24, 48, 72, 120, and 168 hours to create HAp films. The films hydrolyzed for more than 48 hours were attached on the dentin surface after the brushing tests. This result indicates that the α-TCP layer deposited on the dentin surface changes into a crystallized HAp material by the hydrolyzation for more than 48 hours. The crystallization of the film possibly contributes to the high adhesive durability of the HAp film deposited on the dentin.

In cosmetic dentistry, bleaching and laminate veneer methods are common treatments to improve the appearance of teeth. However, there are limitations to these treatments, as they damage the enamel which is not capable of recovering naturally. In this study, novel hydroxyapatite (HAp) sheets, which enable both enamel restoration and aesthetic treatments, were developed. Results indicated that the lower range of the sintering temperatures, of the pulsed laser deposition targets, produced lighter shades of amorphous calcium phosphate (ACP) sheets. Subsequently, the post-Annealing process of the sheets induced crystallization processes of the ACP sheets, to form HAp sheets, and improved the shade rank of the sheet. The shade rank of the developed sheet (6.8 ± 0.2) was almost comparable to the average shade rank of the teeth of Japanese people, within a range of 6.5 to 7.0.

Restoration and maintenance of tooth substance are primary concerns in operative dentistry. Intact tooth is mainly composed of hydroxyapatite (HAp). However, there are no practical HAp materials for the treatment of tooth decay and hypersensitivity. We have newly proposed and developed a tooth restoration technique with intraoral laser ablation using an Er:YAG laser in order to form the HAp thin film on tooth surface in the atmosphere at room temperature. However, the fabricated HAp film is not uniform for the present due to the unsettled water condition at the material surface during the laser ablation. In the present study, we tried to optimize the humid condition using a nebulizer for the fabrication of HAp layer with the Er:YAG laser deposition method. The HAp layers were fabricated on a titanium substrate while changing the flow rate of water mist in order to determine the relationship between the spraying amount and the HAp layer structure. It is revealed that there exists the optimal humid condition to fabricate the uniform hydroxyapatite coating film with the Er:YAG laser deposition method.

Potassium-substituted calcium phosphate free standing sheet for the treatment of dentin hypersensitivity was prepared and evaluated. The appropriate annealing condition for the target of pulsed laser deposition to prepare the potassium-substituted amorphous calcium phosphate (PS-ACP) sheet was investigated. The target annealed at 1000 �C was used to deposit the PS-ACP sheet. The annealing condition for the potassium-substituted hydroxyapatite (PS-HAp) sheet was evaluated by XRD and EDX. The potassium release rate from PS-ACP sheet in PBS, evaluated by ICP-MS, was 2.5 times larger than that of PS-HAp sheet. The robustness of the PS-ACP sheet was proved by the brushing test of the PS-ACP sheet affixed on a bovine dentin. The dentin tubules on the dentin surface was occluded by the PS-ACP sheet and which confirmed by SEM observations.

Tooth enamel cannot be naturally reconstructed once it is destroyed immoderately. Therefore, the restoration of enamel is important in dental treatment. Hydroxyapatite (HAp) can potentially be used for a novel dental biomaterial to repair the enamel. We have proposed a tooth restoration technique with intraoral laser ablation method. A thin layer of HAp was deposited on dentin surface in the atmosphere by ablation phenomenon using an Er:YAG (Erbium: Yttrium-Aluminum-Garnet) laser irradiated to the target of α-Tricalcium phosphate (α-TCP). Then, the deposited layer was hydrolyzed by dripping pure water on its surface in order to create HAp film. The adhesive strength between the HAp film and dentin was evaluated by quasi-static tensile tests. As a result of the mechanical evaluation, the adhesive strength was greater than approximately 3.8 MPa. It is clear that the HAp film created by the Er:YAG laser ablation method is attached tightly to the dentin.

Dentin hypersensitivity is induced by mechanical stimuli or heat stimuli applied via exposed dentin tubules. Resin coating and laser-irradiation are used for treatment but have some problems such as poor biocompatibility or difficulty for laser power setting. We have been developing a treatment that creates artificial tooth enamel by attaching flexible ultrathin calcium phosphate sheet to seal the dentin tubule orifice. In this study, the quantitative evaluation of dentinal permeability inhibition rate (DPIR) improved by attaching ultrathin amorphous calcium phosphate (APC) sheets on human dentin in vitro is presented. The obtained DPIR by overlaid APC sheets application was 81.1 ± 5.7 %.

Aims: To determine the prophylactic effects of an elastin peptide derived from the bulbus arteriosus of bonitos and prolylglycine (PG), a degradation product of elastin peptide, on vascular dysfunction in spontaneously hypertensive rats (SHRs). Main methods: Male 15-week-old SHR/Izm rats were fed without (control group) or with elastin peptide (1 g/kg body weight) for 5 weeks (EP group), or were infused via an osmotic mini-pump for 4 weeks with PG (PG group) or saline (control group). Using thoracic aortas, we assessed endothelial changes by scanning electron microscopy. Vascular reactivity (contraction and relaxation) and pressure-induced distension was compared. mRNA production levels of endothelial nitric oxide synthase (eNOS) and intercellular adhesion molecule-1 (ICAM-1) were investigated by real-time-polymerase chain reaction. Key findings: Aortas of the EP group displayed limited endothelial damage compared with that in the control group. Under treatment of SHRs with elastin peptide, the effect of phenylephrine returned closer to the normal level observed in normotensive Wistar-Kyoto (WKY/Izm) rats. mRNA production of eNOS (but not ICAM-1) was greater in the EP group than in the control group. Endothelial damage was suppressed and pressureinduced vascular distension was greater in the PG group than in the corresponding control group. Significance: These results suggest that elastin peptide from bonitos elicits prophylactic affects hypertensionassociated vascular dysfunction by targeting the eNOS signaling pathway. PG may be a key mediator of the beneficial effects of elastin peptide. (C) 2014 Elsevier Inc. All rights reserved.

Dentin hypersensitivity is induced by mechanical stimuli or heat stimuli applied via dentin tubules exposed by lost of dental enamel or gingival recession. Common treatments for dentin hypersensitivity are resin coating or laser irradiation. However, these treatments have some problems such as poor biocompatibility or insufficient durability. We have been developing a treatment that creates artificial tooth enamel by attaching flexible ultrathin calcium phosphate sheet having a crystal structure similar to that of tooth enamel to seal the dentin tubules. In this study, the quantitative evaluation of dentin tubule sealing rate improved by attaching ultrathin amorphous calcium phosphate (ACP) sheet on human dentin is presented. The obtained sealing-rate by APC sheet application was 70.9 ±4.8%.

It has been well known that bone has piezoelectric properties and these properties have been considered to be caused by the shift of the center of symmetry of the positive and negative electrical charge due to the strain of the collagen fibers included in the bone. Thus, it has long been considered that there were no piezoelectric effects in the hexagonal hydroxyapatite(HAp) which has center of symmetry of crystal. However, in recent years, the piezoelectric property of artificially synthesized HAp was reported. In the authors' previous report, a new result which showed the piezoelectricity of the hydroxyapatite(HAp) films fabricated by the pulsed laser deposition(PLD) method was reported. In this study, the effect of poling treatment on piezoelectric constant of pulsed laser deposited HAp films was investigated.

Ideal restoration of tooth substances requires hydroxyapatite (HAp), of which the tooth is composed. However, restoration treatment with HAp is not yet possible, as adherence to ceramics is very difficult. In the present study, we examined a tooth restoration technique using the intraoral laser ablation method. A thin layer of α-tricalcium phosphate (α-TCP) was deposited on the dentin surface by the ablation phenomenon using an Er:YAG laser, which has already been introduced into dental treatment, to irradiate the target α-TCP. The deposited layer was then hydrolyzed by dripping pure water on its surface in order to create a hydroxyapatite (HAp) coating. In this study, we developed a compact pulsed laser deposition (PLD) system using the Er:YAG laser. The interface structure between the HAp coating and the dentin surface was observed by scanning electron microscope (SEM). Electron micrographs showed that the HAp layer was formed on the dentin surface. Moreover, dentinal tubules were sealed with HAp particles. We evaluated the blockade effect of dentinal tubules using Pashle's method. The measured average value for the sealing rate of the dentinal tubules was 85.6±8.6%, which was greater than the value with resin coating treatment. The adhesive strength of HAp films deposited on dentin was evaluated by quasi-static tensile tests. On mechanical evaluation, the adhesive strength was greater than 3.8 MPa. The present results suggest that this technique will be useful for the repair of dentin and the treatment of hyperaesthesia.

Er:YAGレーザーによるパルスレーザーアブレーション(PLD)法のターゲットにハイドロキシアパタイト(HAp)の前駆体のリン酸カルシウム系材料(DCPD、α-TCP、β-TCP、CPP)を用い、レーザー光を2分間照射した。乾燥状態ではDCPDが強いPLDを示し、α-TCPは弱いPLD、β-TCP、CPPでPLDを認めなかった。純水滴下後では全てに強いPLDを認めた。純水滴下後10分照射でTi基板上に成膜し、37℃の恒温槽に3時間保持した膜のX線回折(XRD)パターンでHApのピークを示したのはα-TCPのみであり、ピークは時間経過とともに小さくなり、48時間でほぼ消滅してHAp膜となった。エナメル質にpH5.5の第一リン酸カルシウム溶液を塗布してα-TCPをレーザーで成膜し、恒温槽保持3時間後のXRDパターンでピークは認めず、HAp膜となっていた。レジン包埋後断面の走査型電子顕微鏡像で、エナメル質上に10〜20μm厚の緻密なHAp膜を認め、成膜速度は約1〜2μm/minであった。

The tendon is strong tissue that connects the muscle to the bone, and it is necessary to reveal the mechanism of the damage process in the tendon. This study aims to reveal the damage accumulation process of the tendinous tissue with AE Technique. Tensile tests were carried out, and AE signals were detected before the maximum stress. Therefore, the AE technique can find some fiber failure. With using Digital Image Correlation (DIC) technique, the some fiber failure on the surface of the tendon can be seen when the AE signals detected.

Tooth enamel cannot be reconstructed once it is destroyed immoderately. Hydroxyapatite (HAp) thin sheet can potentially be used for a novel dental biomaterial to repair the enamel. Using a pulsed laser deposition (PLD) method, we have successfully created a flexible HAp sheet of less than a few micrometers in thickness. Due to its flexibility, the HAp sheet is tightly adhered on curved surfaces at the target site. In the present study, we newly developed double-layered sheets composed of HAp film coated with tricalcium phosphate (TCP) thin layer. The HAp/TCP sheet was adhered to the extracted human teeth using a calcium phosphate solution for 3 days. The adhesive strength between the HAp/TCP sheet and tooth enamel was evaluated by quasi-static tensile tests. Moreover, the interface structure between them was observed by a scanning electron microscopy. As a result of the mechanical evaluation, the adhesive strength was greater than approximately 2.5 MPa. The electron microscopic observation revealed that the sheet was partially fused with the enamel. These findings suggest the possibility that enamel defects are repaired using the HAp/TCP sheet for a short duration.

Before a tooth erupts, the ameloblasts are lost, which means that the tooth enamel does not regenerate itself after tooth eruption. In the present study, we attempt to regenerate the tooth enamel artificially using a flexible hydroxyapatite (HAp) sheet. First, a HAp film was deposited on a soluble substrate by pulsed laser deposition (PLD) using an ArF excimer laser. Next, the HAp film was collected as a freestanding sheet by dissolving the substrate using a solvent. The HAp sheet was adhered to the extracted human teeth using a calcium phosphate solution. The variation of the crystal structure of the HAp sheet with time was investigated by X-ray diffraction analysis. Furthermore, the variation in the mechanical characteristics with time between the HAp sheet and dental enamel were evaluated using tensile and scratch tests. The results suggest that the HAp sheet became fused to the tooth enamel within approximately one week. © (2012) Trans Tech Publications.

Incomplete or subfailure injuries of tendons occur more frequently than their complete ruptures. However, the mechanical behavior of the incompletely injured tissues is poorly understood. In the present study, we quantified the mechanical properties, microstructure, and ultrastructure of rabbit patellar tendons subjected to non-destructive overloading. No significant changes in the mechanical properties were observed in the tendon specimens which were applied a subfailure stretch equivalent to 80% of the failure stress of the control tendons at a low strain rate (1.67 %/sec). There was a significant decrease not in the tensile strength but in the tangent modulus of the specimens when they were subjected to 90% of the control failure stress at the low rate. For the same level of overloading at a high strain rate (16.7 %/sec), both the modulus and strength of the overloaded specimens were significantly lower than those of the control ones. Microstructually, irrespective of the strain rate, crimped collagen fibers in the overloaded tendons were straightened by the 90% overloading. In contrast, adverse alterations in the ultrastructure were induced by the 90% overloading only at the high rate. These results indicate that tendinous tissues have potential capacities to maintain the original strength if a relatively high overload is monotonically applied at lower strain rates. However, it is possible that subfailure overloads delivered at higher strain rates produce more severe changes in the properties and structures of the tissues.

In vitro tissue culture experiments were performed to study the biornechanical response of collagen fascicles to restressing after exposure to non-loaded condition. Collagen fascicles of approximately 300 mu m in diameter were aseptically dissected from rabbit patellar tendons. They were cultured under no-load condition for I week, and then under a static stress of approximately 1.2 MPa for the subsequent I or 2 weeks. After culture, their mechanical properties were determined with a micro-tensile tester, and were compared to those of fascicles cultured under no-load condition and non-cultured, control fascicles. Tangent modulus and tensile strength of the nonloaded fascicles were significantly lower than those of the control fascicles at I week and gradually decreased thereafter. However, the modulus and strength were increased by restressing. After 2-week restressing, both parameters were significantly greater than those of the time-matched, non-loaded fascicles, although these values were still significantly lower than those of the control fascicles. That is, the application of stress after exposure to non-loaded condition suppressed the deterioration of the biomechanical properties of fascicles, although it did not improve. These results indicate that a short period of stressing is not sufficient for cultured collagen fascicles to completely recover their mechanical properties, if they are once exposed to no-stress condition even for a short period of time. These are similar to previous results observed in tendons and ligaments inside the body. (C)2006 Elsevier Ltd. All rights reserved.

Background After ligament reconstruction, mechanical deterioration of the grafted tendon is observed with revascularization and cellular infiltration. However, the effect of cellular infiltration on the mechanical properties of the tendon matrix has not been fully understood. Methods. Cultured fibroblasts derived from the rabbit patellar tendon were seeded around an acellular rabbit patellar tendon that had undergone freeze-thaw treatment. At time-0, 3, and 6 weeks after seeding the cells, we evaluated cellular distribution in the tendon using a confocal laser microscope and the mechanical evaluations of the tendon fascicles and the tendon bundles. Findings. The confocal laser microscopic analysis showed fibroblast infiltration ex vivo into the acellular tendon matrix. We could not find significant effects of the cellular infiltration on the tangent modulus of the tendon bundle, although the ex vivo cellular infiltration significantly reduced the modulus of the tendon fascicle. In addition, the tangent modulus of the incubated tendon without fibroblasts significantly decreased with time, particularly in the tendon bundle levels. Interpretation. The findings of this study suggested that the effects of ex vivo cellular infiltration on the mechanical properties of the tendon bundles are relatively small, compared with its striking effect on the tendon fascicles. (c) 2006 Elsevier Ltd. All rights reserved.

Development of irreversible residual strains in trabecular bone may be a mechanism by which age-related non-traumatic vertebral fractures occur. To investigate this concept, static and cyclic loading tests were conducted at low loading levels for cylindrical cores of cadaveric vertebral trabecular bone. Stresses were applied equivalent to elastic strains of either 750 or 1500 microstrain. Creep strains were measured during the tests, which lasted for 125,000 seconds (about 35 h), and for an additional 125,000 seconds after complete unloading. Emphasis was placed on the residual strains that developed, defined as the strain remaining at the end of the unloading phase. The results indicated that appreciable residual strains did develop, and were similar for static and cyclic loading. Irrespective of the applied load levels and loading modes, the residual strains that remained after the unloading phase were similar in magnitude to the originally applied elastic strain. Extrapolation of the observed residual strains to full recovery indicated that the time that would be required for full recovery was over 20 times longer than the duration of the applied loads. These results indicate that human vertebral trabecular bone does not creep in a linear viscoelastic fashion at low stress levels, and that creep mechanisms dominate the residual strains regardless of the loading mode. Taken together, these findings support the concept that non-traumatic vertebral fractures may be related to long-term creep effects because the trabecular bone does not have sufficient time to recover mechanically from creep deformations accumulated by prolonged static or cyclic loading. (c) 2005 Elsevier Ltd. All rights reserved.

The effects of frequency or duration of cyclic stress on the mechanical properties of collagen fascicles were studied by means of in vitro tissue culture experiments. Collagen fascicles of approximately 300 mu m in diameter were obtained from rabbit patellar tendons. During culture, cyclic stress having the peak stress of approximately 2 MPa was applied to the fascicles at 1 Hz for 1 hour/day (1 Hz-1 h group), at I Hz for 4 hours/day (1 Hz-4 h group), or at 4 Hz for 1 hour/day (4 Hz-1 h group). The frequency of 4 Hz and the duration of 1 hour/day are considered to be similar to those of the in vivo stress applied to fascicles in the intact rabbit patellar tendon. After culture for 1 or 2 weeks, the mechanical properties of the fascicles were determined using a microtensile tester and were compared to the properties of non-cultured, fresh fascicles (control group) and the fascicles cultured under no load condition (non-loaded group). The tangent modulus and tensile strength of fascicles in the 4 Hz-1 h group were similar to those in the control group; however, the fascicles of the 1 Hz-1 h and 1 Hz-4 h groups had significantly lower values than those of the control group. There was no significant difference in the tensile strength between the 1 Hz- 1 h and non-loaded groups, although the strength in the 1 Hz-4 It group was significantly higher than that of the non-loaded group. It was concluded that the frequency and duration of cyclic stress significantly affect the mechanical properties of cultured collagen fascicles. If we apply cyclic stress having the frequency and duration which are experienced in vivo, the biomechanical properties are maintained at control, normal level. Lower frequencies or less cycles of applied force induce adverse effects.

Growth-related changes in the mechanical properties of collagen fascicles (approximately 300 mum in diameter) were studied using patellar tendons obtained from skeletally immature 1 and 2 months old and matured 6 months old rabbits. Tensile properties were determined using a specially designed micro-tensile tester. In each age group, there were no significant differences in the properties among cross-sectional locations in the tendon. Tangent modulus and tensile strength significantly increased with age; the rates of their increases between 1 and 2 months were higher than those between 2 and 6 months. The tangent modulus and tensile strength were positively correlated with the body weight of animals. However, growth-related changes in the mechanical properties were different between collagen fascicles and bulk patellar tendons, which may be attributable to such non-collagenous components as ground substances and also to mechanical interactions between collagen fascicles.

Effects of cyclic stress on the mechanical properties of collagen fascicles were studied by in vitro tissue culture experiments. Collagen fascicles (approximately 300 mum in diameter) obtained from the rabbit patellar tendon were applied cyclic load at 4 Hz for one hour per day during culture period for one or two weeks, and then their mechanical properties were determined using a micro-tensile tester There was a statistically significant correlation between tensile strength and applied peak stress in the range of 0 to 5 MPa, and the relation was expressed by a quadratic function. The maximum strength (19.4 MPa) was obtained at the applied peak stress of 1.8 MPa. The tensile strength of fascicles were within a range of control values, if they were cultured under peak stresses between 1.1 and 2.6 MPa. Similar results were also observed in the tangent modulus, which was maintained at control level under applied peak stresses between 0.9 and 2.8 MPa. The stress of 0.9 to 1.1 MPa is equivalent to approximately 40% of the in vivo peak stress which is developed in the intact rabbit patellar tendon by running, whereas that of 2.6 to 2.8 MPa corresponds to approximately 120% of the in vivo peak stress. Therefore, the fascicles cultured under applied peak stresses of lower than 40% and higher than 120% of the in vivo peak stress do not keep the original strength and modulus. These results indicate that the mechanical properties of cultured collagen fascicles strongly depend upon the magnitude of the stress applied during culture, which are similar to our previous results observed in stress-shielded and overstressed patellar tendons in vivo.

Objective. To know the temporal changes of the mechanical properties of the regenerated and the residual tissues in the patellar tendon after removal of the central portion. Design. The regenerated and the residual tissues were compared to sham-operated tendons. Background. Although the structural properties of the whole patellar tendon after removal of the central portion have been investigated. no studies have distinguished between the regenerated and the residual tissues. Methods. For 52 skeletally mature rabbits, a full-thick, segmental defect was made at the central portion of the right patellar tendon, while a sham operation performed in the left tendon. At 3, 6, 12, and 24 weeks, we evaluated the mechanical properties and fibroblast density of the regenerated and the residual tissues as well as the blood flow and tissue dimensions of the patellar tendon. In addition, non-treated patellar tendons from six rabbits were served as the control for mechanical testing. Results. The tangent modulus and the tensile strength of the regenerated tissue progressively increased with time. On the other hand, these parameters of the residual tendinous portion decreased until 6 weeks, although they gradually increased thereafter. The tensile strength of the regenerated and the residual tissues at 24 weeks were approximately 80% and 75%, respectively, of the non-treated. control tendon. Abundant blood flow and cell proliferation were observed in the regenerative tissue until 6 weeks. Conclusion. The mechanical properties of the regenerated and the residual tissues after removal of the central portion in the patellar tendon are much different from those of the original tendon.

In-vitro tissue culture experiments were performed to study the effects of static stress on the mechanical properties of collagen fascicles obtained from the rabbit patellar tendon. After collagen fascicles having the diameter of approximately 300 mum were cultured for 1 and 2 wk under static stress between 0 and 3 MPa, their mechanical properties and cri. nip morphology were determined using a micro-tensile tester and a light microscope, respectively. The tensile strength and tangent modulus of the fascicles were significantly decreased by culture under no load compared to control fascicles. A statistically significant correlation, which was described by a quadratic curve, was observed between applied stress and tensile strength. The maximum tensile strength (16.7 MPa) was obtained at the applied stress of 1.2 MPa; the strength was within a range of control values. There was a similar correlation between applied stress and tangent modulus, and the modulus was maintained at control level under 1.3 MPa stress. The stress of 1.2 to 1.3 Alpa is equivalent to approximately 50 percent of the peak stress developed in the intact rabbit patellar tendon by running. Strain at failure of cultured collagen fascicles was negatively correlated with applied stress, and that at 1.2 to 1.3 MPa stress was almost the same as the control value. Crimp morphology in the fascicles cultured under about 1.2 MPa stress was similar to that in control fascicles. These results indicate that cultured collagen fascicles change the mechanical properties and structure in response to static tensile stress. In addition, their mechanical properties and structure are maintained at control level if the static stress of 50 percent of in-vivo peak stress is applied.

Objective. To know the effects of stress shielding on the biomechanical properties of collagen fascicles obtained from in situ frozen patellar tendons (an autograft model). Design. Collagen fascicles of approximately 300 mu m in diameter tt ere obtained from in situ frozen rabbit patellar tendons and also from in situ frozen and stress-shielded ones, and their mechanical properties and fibroblast density were determined. Background Stress shielding changes the mechanical properties of in situ frozen patellar tendons in which there exist no fibroblasts, The mechanisms of this phenomenon have not been studied well. Method. Patellar tendon of both in situ frozen group and in situ frozen and stress-shielded group were frozen in situ by liquid nitrogen to kill fibroblasts. Then, in the in situ frozen and stress-shielded group, no tension was applied to the tendons for 2, 3, and 6 weeks, while normal tension was applied to the tendons of the in situ frozen group. Tensile properties of the collagen fascicles obtained from these tendons were determined using a microtensile tester, and were compared to the collagen fascicles from nonfrozen, stress-shielded patellar tendons. Results. Tangent modulus and tensile strength of collagen fascicles from the in situ frozen and stress-shielded group progressively decreased with the time of stress shielding; however, these decreases were much smaller than those of the fascicles obtained from non-frozen, stress-shielded tendons. Although there were few fibroblasts in the patellar tendon of the in situ frozen and stress-shielded group at 2 weeks, the modulus and strength of the fascicles from the posterior portion were significantly lower than those in the in situ frozen group. In addition, the reduction of strength caused by stress shielding was much smaller in collagen fascicles than in bulk patellar tendons. Conclusion. The mechanical properties of collagen fascicles in in situ frozen tendons (an autograft model) are affected by stress shielding even under acellular condition.

With the aim of studying mechanisms of the remodeling of tendons and ligaments, the effects of stress shielding on the rabbit patellar tendon were studied by performing tensile and stress relaxation tests in the transverse direction. The tangent modulus, tensile strength, and strain at failure of non-treated, control patellar tendons in the transverse direction were 1272 kPa, 370 kPa, and 40.5 percent, respectively, whereas those of the tendons stress-shielded for 1 week were 299 kPa, 108 kPa, and 40.4 percent, respectively. Stress shielding markedly decreased tangent modulus and tensile strength in the transverse direction, and the decreases were larger than those in the longitudinal direction, which were determined in our previous study. For example, tensile strength in the transverse and longitudinal direction decreased to 29 and 50 percent of each control value, respectively, after 1 week stress shielding. In addition, the stress relaxation in the transverse direction of stress-shielded patellar tendons was much larger than that of non-treated, control ones. In contrast to longitudinal tensile tests for the behavior of collagen, transverse tests reflect the contributions of ground substances such as proteoglycans and mechanical interactions between collagen fibers. Ground substances provide lubrication and spacing between fibers, and also confer viscoelastic properties. Therefore, the results obtained from the present study suggest that ground substance matrix, and interfiber and fiber - matrix interactions have important roles in the remodeling response of tendons to stress.

Objective. To know the effects of stress shielding applied to the patellar tendon on the collagen fascicles. Design. The mechanical properties of collagen fascicles obtained from stress-shielded patellar tendons were compared to those of collagen fascicles from non-treated patellar tendons and those of stress-shielded bulk patellar tendons in the rabbit. Background. Effects of stress deprivation and stress enhancement on the mechanical properties of knee joint tendons and ligaments have been extensively studied in various animal models. However, the roles of such substructural components as collagen fascicles in the remodeling of tendons and ligaments have not been studied well. Method. Tensile and viscoelastic properties of collagen fascicles obtained from the rabbit patellar tendons which were completely stress-shielded for 1 to 3 weeks by a special method developed by the authors were determined using a micro tensile tester. Results. Stress shielding significantly decreased the tangent modulus, tensile strength, and strain at failure of collagen fascicles. However, these changes were much smaller than those observed in bulk tendons. The relaxation of stress-shielded collagen fascicles was greater than that of non-treated ones. Conclusions. Ground substance and mechanical interaction between collagen fascicles have important rules in the remodeling of tendons and ligaments.

Tensile tests of collagen fascicles cultured under cyclic stress conditions were performed. The relation between applied stress and mechanical properties was determined. Collagen fascicles cultured under stresses of less than 1 MPA lost the original strength. However, the strength was maintained at the original level by the application of stresses between 1 and 3 MPa.

Tensile and viscoelastic properties of collagen fascicles of approximately 300 pm in diameter, which were obtained from rabbit patellar tendons, were studied using a newly designed micro-tensile tester. Their cross-sectional areas were determined with a video dimension analyzer combined with a CCD camera and a low magnification microscope. There were no statistically significant differences in tensile properties among the fascicles obtained from six medial-to-lateral locations of the patellar tendon. Tangent modulus, tensile strength, and strain at failure of the fascicles determined at about 1.5 percent/s strain rate were 216 ± 68 MPa, 17.2 ± 4.1 MPa, and 10.9 ± 1.6percent (mean ± S.D.), respectively. These properties were much different from those of bulk patellar tendons for example, the tensile strength and strain at failure of these fascicles were 42 percent and 179 percent of those of bulk tendons, respectively. Tangent modulus and tensile strength of collagen fascicles determined at 1 percent/s strain rate were 35 percent larger than those at 0.01 percent/s. The strain at failure was independent of strain rate. Relaxation tests showed that the reduction of stress was approximately 25 percent at 300 seconds. These stress relaxation behavior and strain rate effects of collagen fascicles differed greatly from those of bulk tendons. The differences in tensile and viscoelastic properties between fascicles and bulk tendons may be attributable to ground substances, mechanical interaction between fascicles, and the difference of crimp structure of collagen fibrils. © 1999 by ASME.

A rabbit model was used to discover whether the effects of stress shielding on the mechanical properties of the patellar tendon depend on the degree of stress reduction. Ninety mature female Japanese White rabbits were divided into three groups: completely stress-shielded, partially stress-shielded, and sham-operation and contralateral controls. In the experimental groups, tension applied to the patellar tendon was 0%, approximately 30%. and 100% of the normal tension, respectively, with a polyester artificial ligament. Tensile tests were carried out on patella-patellar tendon-tibia complexes harvested 1, 2, 3, 6, or 12 weeks after surgery. The tensile strength decreased in comparison with the sham-operation group to 50.2, 13.5, 9.7, and 20.7% in the completely stress-shielded group and to 75.2, 57.6, 59.6, 57.3, and 72.9% in the partially stress-shielded group. The tensile strength in the completely stress-shielded group was significantly less than that in the partially stress-shielded group at 1, 2, 3, and 6 weeks. The cross-sectional area of the patellar tendon significantly increased to 132, 206, 237, and 136% in the completely stress-shielded group and to 136, 170, 175, 155, and 127% in the partially stress-shielded group, compared with the sham-operation group. The cross-sectional area of the completely stress-shielded tendon was significantly larger than that of the partially stress-shielded tendon at 1, 2, and 3 weeks. This study demonstrated that effects of stress shielding on the mechanical properties of the patellar tendon were dependent on the degree of stress shielding.

Tensile tests of the collagen fascicles obtained from stress-shielded patellar tendons (PTs) in the rabbit were conducted. The mechanical properties of these fascicles were compared to those of the collagen fascicles from non-treated, control PTs as well as those of the stress-shielded whole PTs. Generally, the results indicate that mechanical properties of stress-shielded collagen fascicles were significantly affected by the stress shielding. This observation indicate that the remodelling of tendons and ligaments depends on ground substance as well as interaction between collagen fascicles.

To assess the effects of stress shielding on the stress-strain behaviour of the in situ frozen tendon, which simulates an ideally oriented autogenous graft, patellar tendons (PT) of 26 Japanese white rabbits underwent in situ freezing with and without the stress shielding treatment. The patella-PT-tibia complexes excised at 3 and 6 weeks postoperatively were loaded between 0% and 3% strain. The material constants were computed by fitting the data to a constitutive equation. The material constants showed that the initial slope of the stress-strain curve of the group without stress shielding was significantly steeper than that of the group with stress shielding at 3 weeks, but not at 6 weeks. The increase in the slope of the stress-strain curve of the group without stress shielding was significantly more than that of the group with stress shielding at both 3 and 6 weeks.

【目的】高血圧の持続により動脈壁の肥厚・硬化が生じ、さらに高血圧の増悪が惹き起こされる。主たる病因は平滑筋細胞の肥大と弾性線維（エラスチン）の変性・崩壊であるが、降圧剤投与以外には防止する方法が知られていない。本研究では，動脈病変の予防・治療に関する基礎的研究として，カツオ動脈球から精製したエラスチンペプチドがSHRの動脈壁に及ぼす影響を検討した。 【方法】 生後15週齢雄性 SHR/Izm にエラスチンペプチド （3g/kg体重）を船橋SP飼料に混じ5週間自由摂取させた。実験期間終了後，門脈より採血し、prolyl glycine (PG) 濃度を測定した。内皮細胞の形態を，走査型電子顕微鏡を用いて観察するとともに、内皮細胞におけるendothelial nitric oxide synthase (eNOS) ならびにInter cellular adhesion molecule 1 （ICAM-1）の発現をRealtime-PCR法を用いて比較した。さらに、胸部大動脈における血管内圧ならびに血管反応性を調べるとともに，結合織関連因子（Lysyl oxidase, Elastin, type I collagen

動脈壁における弾性線維の変性・分解が高血圧や血管障害発症に関与することはよく知られている。本研究では、高血圧自然発症ラット(SHR/Izm)の血管形態および機能に対するカツオ動脈球由来エラスチンペプチドの影響を検討した。 実験1:エラスチン・ペプチドの影響 生後20週齢雄性SHRを2群に分け、うち1群にカツオ動脈球由来エラスチン・ペプチド(600mg/kg)を5週間経口投与した。血圧、体重、および大動脈における結合組織関連の発現に影響は認められなかったが、エラスチン投与群では、コントロール群に比べPHEに対する収縮反応が抑制された。 実験2: Proryl glysin(PG:エラスチンペプチドの分解産物)投与の影響 生後15週齢雄性SHRにPGを浸透ミニ・ポンプ(104 nmol/hr)を用いて4週間静脈内投与した。PG投与群の血管拡張能は、コントロールSHRより高かったが、WKYよりも低かった。電子顕微鏡の観察では、PG投与群の内皮の表面はコントロールに比べは滑らかで、WKYに近い状態であった。

骨のリモデリング現象をより詳細に理解するための基礎データとして，尾部懸垂や関節固定によって骨に作用する負荷を軽減させたラット脛骨に生じるひずみを計測した．これにより，負荷軽減手法の相違が骨の生体内ひずみに及ぼす影響について検討した．

骨の力学的適応メカニズムの解明や骨障害の予防・治療法の開発にとって不可欠な基礎データを取得するため，骨の生体内ひずみを長時間にわたり，動物の運動を拘束することなく計測することが可能な無線データ通信計測システムを用いた実験装置を作製した．そして，この作製した無線データ計測システムを用いて，家兎の大腿骨に生じる生体内ひずみの長時間実施して，通常状態において個体が曝される力学的環境を定量化した．さらに，膝関節固定を施した家兎大腿骨に生じる生体内ひずみ計測を行うことで，大腿骨に生じるひずみに及ぼす関節固定の影響について検討した．

遺伝子改変が腱の生体力学的特性に及ぼす影響について検討した。

家兎膝蓋腱を対象として非弾性的な単一の過負荷を作用させ，その後再負荷試験を実施した．これによって，過負荷が腱組織の応力－ひずみ関係に及ぼす影響について検討し，過負荷作用後の残存強度を定量化することを試みた．

ウシ大腿骨骨幹部から作製した皮質骨試料に対して，破壊まで至らないレベルの一定負荷を持続的に作用させた後，圧縮破壊試験を実施した．これにより，試料の接線係数や圧縮強度の変化を定量化することで，静的負荷が皮質骨の残存強度に及ぼす影響について検討した．

疲労骨折の発生要因に解明することを目的に，繰り返し負荷を作用させた後の皮質骨の残存強度を定量化するとともに，微小損傷観察の結果と比較検討した．

椎体骨折の発生メカニズムに関する知見を得るために，低荷重レベルの連続的または断続的なクリープ負荷によって生じる，ヒト椎体海綿骨の残存ひずみを定量的に解析した．

変形性関節症の発生メカニズムをより詳細に理解するとともに，その治療法の開発に貢献することを最終目標として，変形性関節症を人為的に発症させたラットの膝関節を対象に，脛骨ひずみの生体内計測，膝関節面の摩擦係数測定，および数学モデルを用いた関節荷重の解析などのバイオメカニクス的検討を行った．

通常の負荷レベルでの断続的な静的負荷が，海綿骨の残存ひずみにどのような影響を及ぼすのかを明らかにすることを目的として，ヒト椎体海綿骨に連続的もしくは断続的に静的一定荷重を作用させ，海綿骨に生じる時間依存性のクリープひずみの計測を行った．

ウシ脛骨骨幹部から作製した皮質骨試料の骨軸方向に，非破壊的な単一の過負荷を作用させた後，圧縮破壊試験を実施することで，試料の接線係数や圧縮強度の変化を定量化し，過負荷がその後の皮質骨の力学的挙動に及ぼす影響について検討した．

静的負荷や繰り返し負荷の大きさ，繰り返し負荷の周波数や作用時間，または除荷後の再負荷などの種々の力学的環境に対する，腱や靭帯を構成する微細構成要素であるコラーゲン線維束の生体力学的応答について検討した結果を報告した．

無線データ計測システムを用いて，関節固定を施した家兎の大腿骨に生じる生体内ひずみの長時間計測を行い，大腿骨に生じるひずみに及ぼす関節固定の影響について検討した．

明確な外傷を伴わない状況下における椎体骨折の発生メカニズムに関する知見を得るために，低荷重レベルの静的または繰り返し負荷によって生じる，ヒト椎体海綿骨のクリープひずみを定量的に解析した．

海綿骨に生じたクリープ変形の回復過程に注目し，除荷後に残存するひずみと負荷応力の関係や，残存ひずみに及ぼす負荷様式（静的負荷と繰り返し負荷）の影響について検討した．

ヒト椎体海綿骨に非弾性的かつ非破壊的な単一の負荷を作用させた後，生理的範囲内の大きさで繰り返し負荷を作用させる疲労試験を行い，単一の過負荷がその後の海綿骨の疲労挙動に及ぼす影響について検討した．

成長ホルモンのアンチセンス遺伝子を導入し、成長ホルモンの分泌を抑制させたトランスジェニックラットの皮質骨の力学的特性を測定した。

遺伝子改変が骨の微視的な力学的特性に及ぼす影響を明らかにするとともに、微視的特性と巨視的な骨の物理的性質との関係について検討した。

疲労骨折発生のメカニズムを解明するために、生体外で繰り返し負荷を作用させた骨組織の残存強度の変化を調べた。

無線データ計測システムを用いて、膝関節固定を施した家兎の大腿骨に生じる生体内ひずみの長期間計測を行った。

遺伝子改変が骨の生体力学的特性に及ぼす影響について検討した。

腱の中央部分を切除し、過大な負荷が作用する膝蓋腱損傷モデルを用いて、治癒再生組織並びに既存の腱組織の生体力学的特性に及ぼす過負荷の影響について検討した。（英文）

個体の運動を拘束することなく計測を行うことのできる無線データ通信計測システムを用いて、骨の生体内ひずみを長期間にわたり測定し、骨組織が生体内で曝される力学的環境の定量化を行った。（英文）

骨の生体内応力やひずみを長時間にわたり、 個体の運動を拘束することなく計測することが可能な無線データ通信計測システムの開発を行った。

膝蓋腱中央部に欠損を作成したモデルを用いて、 欠損部に形成される治癒再生組織、 既存の膝蓋腱両側部の力学的特性を調べた。

家兎脛骨上部の欠損部位に形成された仮骨の引張特性の経時的変化を調べるとともに、 X 線 uCT を用いて欠損部位の骨化の程度を調べ、 仮骨の力学的特性と CT 値との関連を明らかにした。

腱中央部の欠損部位に形成される治癒組織及びその周囲組織の力学的特性の変化を調べた｡

家兎大腿骨に繰り返し圧縮荷重を作用させた後､ Bulk stain 法による染色を行い､ 微小き裂を観察した｡

矩形欠損を作成した家兎膝蓋腱にストレスシールド術を施して､ 無負荷状態で形成される治癒組織の力学的特性を調べた｡

圧縮繰り返し負荷を作用させた家兎大腿骨の局所的な力学的特性を､ 原子間力顕微鏡を用いて測定した｡

エラスチンは，コラーゲンとともに皮膚，血管，靭帯などの生体軟組織を構成する線維状タンパク質である．エラスチンは高い不溶性のために抽出が難しく，精製が容易ではないこと，また高純度のエラスチンを大量に得ることができないために，エラスチンに対する応用研究だけでなく，基礎科学的研究もあまり進展していないのが現状である．そこで本研究では，生体高分子材料であるエラスチンのバイオマテリアル化技術の確立を最終目標とし，押込み試験によってエラスチン材料の弾性率を計測した．この際には，エラスチン材料の弾性率に及ぼす架橋剤濃度の影響について検討した．本実験では，魚類動脈球より精製したエラスチンを使用した．さらに，精製されたエラスチンの中から，分子量が比較的小さいβ―エラスチンを分離して実験に用いた．次に，β―エラスチン含有材料を作製するため，DMSO（ジメチルスルホキシド）に濃度100 mg/mlでエラスチンを溶解した．また，架橋剤には比較的高い細胞親和性を有するHMDI（ヘキサメチレンジイソシアネート）を用いた．エラスチン溶液に対して架橋剤濃度が20%と25%になるように添加してエラスチン材料を作製した．作製したエラスチン材料の力学的特性を押込み試験によって評価した．小型材料試験機を用いて，押込み速度1 mm/minでステンレス鋼製球状圧子（半径2.25 mm）を材料表面から0.5 mmの位置まで押し込んだ．その後，この押込み変位を300秒間維持し，その間の荷重緩和を計測した．得られた負荷時の押込み荷重－変位関係から，ヘルツの接触理論から導かれる式を用いてエラスチン材料の弾性率を算出した．その結果，架橋剤濃度によって変化するエラスチン材料の弾性率を押込み試験によって定量的に評価することが可能であり，高濃度の架橋剤を用いた条件で作製したエラスチン材料の弾性率が高値であることが示された．

骨固定用金属製インプラントの剛性は、骨修復中とその後とで適正値が異なり、骨修復中は高剛性、骨修復完了後は低剛性のほうが適切であることが実験的に示唆されている。さらに、この骨修復状況に依存した金属製インプラントの剛性の適正値の変化は力学的負荷方向に依存し、骨修復中は骨のねじり方向、骨修復後は軸方向の剛性が重要であると考えられる。そこで、本研究では、骨のねじり方向に高剛性であり、軸方向に低剛性となるように、意図的に大きな剛性異方性を付与した金属製インプラントの作製を試みる。この実現のため、材質と形状とを同時に制御することが可能な金属積層造形技術を用いる。初年度であった今年度は、金属積層造形に関する報告が既に多くなされている316Lステンレス鋼を供試材として用い、横方向には高ヤング率となり、縦方向には低ヤング率となるように、面内の直交する二方向の結晶方位を<110>/<100>および<111>/<110>に配向させることを意図したプレートを試作した。その結果、造形条件、造形方向および試験片切り出し方向に改善の余地を残したものの、プレートのヤング率を縦方向よりも横方向に高くすることに成功した。プレートの塑性変形挙動には、単結晶に類似した点も数多く認められた。ただし、造形体のミクロ組織はレーザー走査方向や積層方向に依存して不均質であったため、引張強さおよび伸びについては、結晶方位配向のみでは決まらず、力学的負荷方向と結晶粒形状との関係も影響することが示唆された。

Pure molecular solution of elastin is hardly extracted due to its insolubility. From this reason, many basic characteristics of elastin have not been fully elucidated not only in the area of biochemistry and molecular biology but also in that of biomechanics and biomaterial. Our overall goal was to determine whether the external medication using biomimetic materials which include elastin ingredients is effective for the maintenance and improvement of the extensibility of biological soft tissues such as tendons, ligaments, and skins during healing process. Specifically, in the present study, we developed elastin-based materials having the same elastic moduli as those of soft tissues. The tensile strength and failure strain of the elastin materials were approximately 58% and 50% of those of yellow ligaments, indicative of the incomplete mimicking of biological soft tissues. Further studies should be conducted to improve the strength and extensibility of the elastin materials.

In the metals with self-tunable elastic modulus developed by us, the elastic modulus is increased at the deformed part by the deformation-induced phase transformation, although low elastic modulus is maintained at the non-deformed part. In this project, as an application of the materials, the possibility of developing mechanical load responsive self-reinforced metallic implants was examined. When strain was systematically changed and applied to the materials, it was confirmed that the deformation-induced phase transformation occurred during elastic deformation. Further, when mechanical load was applied cyclically and then the change in elastic modulus was measured, an increase in the elastic modulus due to such the cyclic mechanical loading was obtained in a part of specimens. These experimental results indicate that the development of mechanical load responsive self-reinforced metallic implants is possible.

We focused on the fact that laser processing and film formation method with laser were inside and outside unification. That is, the cutting of the dentin and the removal of tartar with the Er:YAG laser were laser processing, and conversely, the laser irradiation of the bulk material (target) of hydroxyapatite (HAp) on the dentin in the oral cavity was laser deposition of HAp film. From this idea, we proposed the Er:YAG pulsed laser deposition (Er: YAG-PLD) method. In this study, first, a mist-supplying compact Er: YAG-PLD unit was fabricated. Subsequently, optimal forming conditions such as the type of laser contact tip and target, laser power and repetition rate, and the rate of water supply to the target for producing an HAp film that has excellent adhesion and can be applied to the treatment of dental hypersensitivity was established.

Collagen and Elastin are structural proteins of the dermis and are closely related to the tissue properties. It is known that ultraviolet rays decrease proteins such as elastin in the dermis. However, the biomechanical contribution of elastin to the skin properties remains unknown. The purpose of the present study was to determine whether the external medication of elastin ingredients is effective for the maintenance and improvement of the skin extensibility. Specifically, we studied the enhanced healing efficacy for ultraviolet damage by the application of an ointment involved elastin ingredients. The results obtained indicate that the stiffening or hardening of skin tissues due to the ultraviolet irradiation is presumably suppressed by the elastin application to skin tissues. Moreover, the elastin application possibly prevents the acanthosis of skin tissues due to the ultraviolet irradiation.

Osteoporotic model femur specimens were obtained from rats at 13 or 19 weeks after ovariectomization. In order to evaluate the bone mass and bone quality, the measurement of ultrasonic propagation characteristics, X-ray CT photography and dynamic mechanical analysis (DMA) were carried out. Furthermore, 4-point bending tests and static compression tests of control and osteoporotic model femur specimens were performed. During the tests, microdamage accumulation of rat femur was monitored by acoustic emission. Consequently, it was found that the influence of ovariectomization was more significant for proximal rather than diaphysis.

A functional fluoridated hydroxyapatite (FHAp) sheet that promotes dentin fastening and provides acid resistance was developed, and the technology for rapidly and strongly fixing the FHAp sheet onto dentin was established. First, the optimal conditions for fabricating FHAp thin films using pulsed laser deposition (PLD) were determined. Next, it was shown that a resist coating silicon substrate was useful as an isolation substrate for manufacturing FHAp sheets. The FHAp sheets were found to have five-fold greater acid resistance compared with HAp sheets. Furthermore, we established a pasting method that rapidly and strongly fixed the FHAp sheet onto the dentin.

Microdamage in load-bearing biological tissues is an important factor related to their homeostatic responses and diseases. However, there have been only a few reports on the microdamages not only in hard tissues such as bones but also in soft tissues such as blood vessels, tendons, and skins. In the present study, changes in the mechanical properties of osteoporotic bones, ultraviolet-irradiated skins, and hypertensive arteries were elucidated by means of compressive, tensile, or internal pressure tests. It was speculated that the decreases in the mechanical strength were linked to the microdamages in the tissues. We have an insight into the mechanisms of homeostatic responses and healing process in biological tissues.

The microdamage of rabbit patellar tendon under static tensile load was detected by AE technique. The damage process of intact and injured tendon was successfully monitored. It was found that the higher amplitude AE signals were detected before the maximum stress under the higher loading rate. It was then suggested that larger scale of microdamages, such as bundles of fibers, ruptured simultaneously under the higher loading rate. AE source location was corresponded with the area where the local strain increased. Consequently, the fundamental insights for the damage monitoring technique which are indispensable for the optimization of programs of sports training or rehabilitation are obtained.

Effects of elastin peptide from fish ductus arteriosus on vascular and cutaneous function was investigated using spontaneously hypertensive rats (SHR) or hairless rats. Chronic administration of elastin peptide to SHR resulted in ameriolation of endothelial injury and preservation of arterial elasticity. Prolyl glysin, a degradation product of elastin peptide, may be key sequence of elastin peptide, since continuous infusion of PG to SHR was effective to prevent endothelial injury. In cultured endothelial cells, expression of ICAM-1 and Caveoin was depressed by elastin peptide and PG. In rat model with ultraviolet irradiation, on the other hand, skin elasticity was higher in rats which administered elastin peptide to skin of rats rather than control rats. These results suggest that elastin peptide from fish arteriosus was effective for preservation of elasticity not only in artery but also in skin.

In the present study, our final goal was to obtain an insight into the mechanisms of adaptation to mechanical stresses in musculoskeletal tissues such as bones, tendons, and ligaments. Mechanical behavior after non-destructive overloading was measured for bone specimens as well as bone-tendon and bone-ligament complexes. Moreover, we studied the mechanical properties of bone-tendon complexes treated with enzymes. The results obtained show the possibility that the deformation behavior and failure modes of bones, tendons, ligaments, and the insertion site between bones and tendons.

日常生活の歩行や運動時に作用する低レベルの負荷であっても,生体内の骨組織に微小損傷が発生することが知られている.この微小損傷は,骨の新陳代謝プロセスを制御しており,常に形成と吸収を繰り返して新しい骨に生まれ変わりながら,骨の機能が維持されている.すなわち,力学的負荷の作用による微小損傷の発生は,骨の健全性を保つために必要な現象であるといえる.しかし,微小損傷発生と生体内で作用する力学的負荷との定量的な関係や,疲労損傷の発生機序は十分に理解されていない.本研究では,ウシ大腿骨骨幹部より作製した皮質骨試料の骨軸方向に,非破壊的な過負荷を作用させ,その後に発生した微小損傷を蛍光顕微鏡を用いて観察した.試料には単一負荷を作用させる条件だけではなく,生体内の実働負荷の環境である繰り返しや静的の過負荷を作用させることで負荷様式の相違が微小損傷の発生に及ぼす影響について検討した.また,3種類の蛍光色素を使用した蛍光顕微鏡観察を実施することで,継続的に作用させた過負荷のもとで発生する微小き裂の進展の様子を調べた.微小損傷の観察は,骨軸方向に対して平行もしくは垂直方向の断面内で実施し,過負荷下での微小損傷発生の状況に関する基礎的知見を得ることを試みた.蛍光顕微鏡観察では,負荷の作用に対応して段階的に染色された微小損傷が認められ,損傷が進展していく過程を示す画像が得られた.また,各染色領域のき裂長さの計測結果から,微小き裂の進展に過負荷様式の相違による影響が認められ,単一過負荷よりも,繰り返しの過負荷や静的過負荷の場合で損傷が顕著となる傾向がみられた.さらに,過負荷を作用させた試料では,線状の微小き裂だけではなく,拡散性の微小損傷を示す領域も確認された.このような微小損傷の蓄積が,骨の自己修復能力を超える場合に,最終的に骨折を生じさせるような大きなき裂へと進展していくことが示唆された.

The area fractions of collagen and elastin in the rat common carotid artery did not change between 8 and 64 weeks, whereas the elastic modulus of wall was significantly larger in 64 weeks old animals compared to younger ones. To know the reason, we have applied a hydromechanical isometric tension method to the analysis of cross-linking of collagen. In the method, a tissue specimen is stretched and heated to above collagen denaturation temperature, and kept at this temperature under constant strain condition. Stress relaxation observed thereafter indicates a measure of the amount of thermally stable, matured cross-linking ; stress reduction is a measure of cross-linking. First, we studies age-related changes of cross-linking in arterial wall using rat common carotid arteries aged 8, 16, 32, and 64 weeks. Small rectangular specimens were attached to a specially designed test apparatus, and immersed in distilled water in a thermostatic bath. While a tensile strain (in vivo strain) was applied to each specimen, specimen temperature was elevated to 100C. While the specimen was kept under this condition, force developed in the specimen was continuously monitored. Half-value period of load, i.e. the time elapsed for the reduction of load to a half, was used as a measure of cross-linking, and it was significantly longer in 64 weeks old animals than in younger ones. This result corresponds well to the results of the elastic modulus of wall, indicating that higher wall stiffness in older arteries is attributable to the larger amount of stable collagen cross-linking. Then, the HIT method was applied to common carotid arteries from DOCA-salt hypertensive rats, and the results were compared with those from the age-matched, normotensive animals. Relative amount of matured cross-links showed a tendency of increasing by hypertension, which explains higher elastic modulus in hypertensive arteries than in normotensive ones.

力学的環境要因による支配が顕著である骨の適応や疾患などの現象を完全に解明するためには,骨の力学的特性に及ぼす遺伝子情報と力学的環境要因との相互作用に関する研究が重要になるものとが考えられる.そこで本研究では,骨の性状を微視的に評価することの可能な微小硬さ試験ならびに骨の無機成分率計測を、成長ホルモンの分泌を遺伝的に抑制させたトランスジェニックラットの皮質骨に対して実施した.さらに,骨付着部付近の腱組織を摘出し,透過型電子顕微鏡による微細組織の観察を行った.成長の遺伝的抑制によって小型化したトランスジェニックラット(Transgenic群)および通常ラット(Control群)を実験に用いた.これらより大腿骨を摘出した後,長さ5mmの円筒状試料を切り出した.その後,試料断面を研磨し,マイクロビッカース硬さ試験機を用いて微小硬さを計測した.圧子に作用させる荷重を50gfとして硬さを算出した.また,試料の乾燥質量と試料を燃焼(600℃)させた後の骨灰質量の比から,骨の無機成分率を求めた.さらに,骨付着部付近の膝蓋腱から超薄横断切片を作製して,透過型電子顕微鏡によるコラーゲン線維構造の観察を実施した.Transgenic群の微小硬さおよび無機成分率に,Control群との間に有意な相違はみられなかった.従って,Transgenic群では骨形状は小さいが,骨の材料特性には成長ホルモンの抑制による変化がみられないことが示唆された.しかし,透過型電子顕微鏡による腱コラーゲン線維の観察では,Transgenic群の組織に占めるコラーゲン線維の含有割合に減少する傾向がみられた.線維の三次元的構造やクロスリンクなど,今回の横断面微細構造観察では調べることのできない分子レベルでの構造の違いがTransgenic群とControl群との間にあると考えられ,今後これらに関する検討が必要である.

繰り返し負荷が作用する期間中での骨強度の経時的変化は,疲労骨折の予測という観点からも重要であるにも関わらず明らかにされていない.そこで本研究では,家兎大腿骨皮質骨部からなる円筒状試料に,生体内で生じる程度の低いひずみ領域の負荷を生体外で繰り返し作用させ、骨の残存強度に及ぼす繰り返し負荷の影響を調べた.繰り返し数は,1×10^6と3×10^6回とし,ピーク圧縮応力5MPaの一定応力試験を行った.その後,繰り返し負荷を作用させた試料の残存強度を測定するために,圧縮破壊試験を行った.また,骨の微細構造の変化を調べるために,電子顕微鏡による観察を行うとともに,微小硬さを計測した.その結果,繰り返し負荷群の圧縮強度が有意に低下したのに対して,弾性係数には変化は生じておらず,繰り返し負荷は骨の破壊特性に大きな影響を及ぼすことが推察された.また,繰り返し負荷群の硬さ値が対照群よりも小さくなる傾向を示すとともに,微細構造の観察からは繰り返し負荷群の試料断面内に数多くの微小き裂が観察された.従って,繰り返し負荷が骨の微細構造に変化を引き起こし,負荷試験中の破断までは生じないものの,骨の残存強度を低下させることが示唆された.また,家兎の大腿骨,脛骨を用いて,原子間力顕微鏡の液中コンタクトモードで,ヘルツモデルを応用した局所弾性率の計測を行った.その結果,水平面での大腿骨(約15.3GPa)の局所弾性率は脛骨(約7.9GPa)よりも大きかった.さらに,大腿骨と脛骨ともに,水平面での局所弾性率が矢状面や前頭面よりも大きく,顕著な異方性がみられた.これらの結果から微小領域での力学的特性が生体組織が持つ合目的性によって,各組織や方向に依存して決定されている可能性が示唆され,今後繰り返し負荷を作用させた骨の局所弾性率を調べることで,骨疲労の機序に関する定量的な知見となり得ることが推察された.

骨組織に力学的負荷を作用させると,分極によって電荷が誘起される圧電現象を示すことが知られており,この現象が骨の形成・吸収に大きな影響を及ぼしているといわれている.しかしながら,骨に作用する力学的負荷と,それによって生じる圧電位との定量的な関係は調べられていない.そこで本研究では,力学的負荷が骨の圧電特性に及ぼす影響について定量的に検討した.成熟日本白色家兎の大腿骨に2本の電極を導電性接着剤を用いて固定した後,種々の条件の力学的負荷を骨に作用させ,発生する圧電位を測定した.まず,6N,40N,120Nの静的荷重を作用させると,それぞれ約4mV,10mV,10mVの圧電位が生じ,この結果より,低荷重領域では負荷の増大に伴い圧電位も増加するが,高荷重領域では負荷を増加させても圧電位に変化が生じないことが明らかになった.また,周波数4Hzの繰り返し負荷を,18N,44Nの2種類のピーク荷重で骨に作用させる実験を行い,その結果,繰り返し数1×10^2までならばピーク荷重時に生じる圧電位は常にほぼ一定であることが分かった.さらに,ピーク荷重34Nで,繰り返し周波数を0.1Hz,1Hz,5Hzの3種類に変化させて,圧電位の計測を行ったところ,繰り返し周波数の相違による圧電位の違いはみられなかったが,周波数の大きな繰り返し負荷を作用させた場合に,ピーク荷重が作用する前に圧電位がピークに達するという極めて興味深い現象が確認された.以上のような本研究の結果より,骨に生じる圧電位が最も有効に発生する負荷条件が存在する可能性が示唆された.今後は,より詳細な負荷条件を設定した実験を行うことで,負荷条件と圧電位の定量的な関係を完全に明らかにし,これにより骨の機能維持に最適な負荷条件を探求するための新しい知見が得られるものと推察される.