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Purpose: Subchondral insufficiency-type fracture is associated with rapidly progressive osteoarthritis of the hip, but are these fractures caused by a single load event such as an injury from a fall or by stress (fatigue) from repeated loading during the activities of daily life? Our biomechanical study applied repeated loading to a simulated osteoporotic bone model to investigate the relationship between an inverted acetabular labrum and the incidence of subchondral insufficiency-type fracture of the femoral head.Methods: We performed fatigue load testing on 15 osteoporotic composite femurs, applying 2000 N at 1 Hz, 1 million times or to failure, on 5 composite femurs without silicone rubber and 10 with 10x5 mm silicone rubber. Silicone rubber was inserted as a surrogate for inversion of the acetabular labrum between the acetabulum and femoral head.Results: No breakage was noted in the 5 specimens without silicone rubber, even after the application of 1 million individual loads at 1 Hz. Fractures appeared in the anterior femoral head in all 10 specimens with 10×5 mm silicone rubber, and mean number of loads to fracture was 6389. Conclusion: Our research selected an osteoporotic bone model to investigate the effects of loading tests that were designed to mimic typical repeated loads in daily activities, using silicone rubber as a surrogate for inversion of the acetabular labrum and resulting in the development of insufficiency-type stress fracture on the femoral head.Concept diagram or graphical abstract

Although studies suggest that subchondral insufficiency fracture of the femoral head may cause rapidly progressive osteoarthritis of the hip, the mechanism of that relationship remains unclear. Our biomechanical study aimed to provide more data in this area by quantifying pressure distribution on the femoral head for normal and inverted hips and by determining the effects of labral inversion on pressure distribution across the joint, focusing on types of fracture under load. We tested mid-sized fourth-generation composite femurs at 15° of adduction, and applied 1 mm/min of axial compressive force to the femoral heads until failure. Additionally, single loads (3000 N) were applied using Prescale film to investigate pressure distribution on the femoral head, with or without silicone rubber representing entrapment of an inverted acetabular labrum. In tests with an external load of 3000 N, the mean pressure for 10 × 5 mm of silicone rubber was 11.09 MPa, significantly greater (about 5.7-fold) than 1.94 MPa without silicone rubber. Different fracture patterns were observed with and without the 10 × 5 mm silicone rubber; when the 10 × 5 mm silicone rubber specimens were used, all eight cases showed fractures in the anterior femoral head. When silicone rubber representing an inverted acetabular labrum was placed between a hemispherical metallic platen and a composite bone model, the silicone rubber areas were subjected to extreme concentration of stress. The fractures that developed at the silicone rubber areas clearly represented subchondral fractures of the femoral head, rather than fractures of the femoral neck.

To increase the applicability of ultrasonic linear motors, we have developed a holding mechanism for the transducer using parallel leaf springs. The present mechanism is compact since the parallel leaf spring structure has functions for both holding and preloading at the same time. Also, a special design for the spring characteristics provides a non-linear load-displacement region with buckling phenomena. These results in a constant preload for some range of the displacement, then the motor performance does not alter even after abrasion of contact surfaces. In this report, the relationship between the dimension of the leaf spring and the force-displacement curves was investigated in order to obtain the design appropriate for constant preloading. Moreover, the effect of the vibration reduction by the holding mechanism was investigated theoretically and experimentally. The vibration reduction was as small as less than 10 % since the stiffness in terms of the vibration direction was relatively small. Finally, the dynamic responses of the motor with the holding mechanism were measured for a sinusoidal control signal. No prominent peak was observed in the motor's responses, however, the motor velocity change was distorted near the natural frequency of the holding mechanism.

Background and purpose Many clinical reports have indicated that polished hip stems show better clinical results than rough stems of the same geometry. It is still unknown, however, what the mechanical effects are of different surface finishes on the cement at the cement-bone interface. We compared mechanical effects in an in vitro cemented hip arthroplasty model. Methods Two sizes of double-taper polished stems and matt-processed polished stems (rough stems) were fixed into composite femurs. A 1-Hz dynamic load was applied to the stems for 1 million cycles. An 8-h no-load period was set after every 16 h of load. Stem subsidence within the cement, and compressive force and horizontal cement creep at the cement-bone interface, were measured. Results Compared to rough stems, stem subsidence, compressive force and cement creep for polished stems were a maximum of 4, 12, and 7-fold greater, respectively. There was a strong positive correlation between stem subsidence and compressive force for polished stems. In contrast, a strong negative correlation was found between stem subsidence and compressive force for rough stems. There was also a statistically significant relationship between compressive force on the cement and cement creep for the polished stems, but no significant relationship was found for rough stems. Interpretation This is the first evidence that different surface finishes of stems can have different mechanical effects on the cement at the cement-bone interface. Stem subsidence in polished stems resulted in compressive force on the cement and cement creep. The mechanical effects that polished taper stems impart on cement at the cement-bone interface probably contribute to their good long-term fixation and excellent clinical outcome.

In the hip replacing arthroplasty, to make the stem shape of an artificial hip joint fit to the morphology of proximal femoral canal is generally effective to the fixation in an initial stage. Furthermore, it contributes to reduce a stress shielding at the proximal femur. Therefore, this paper proposed the design method of the custom-made stem corresponding to each patient in order to improve the fill ratio of the stem to the proximal femoral canal. This modeling is mainly achieved by means of a Boolean operation (logical AND operation) of the cross sectional contours of the proximal femoral canal along the circular insert axis, which is decided by the bow of the femoral canal morphology with 3D X-ray CT images and a CAD system. As a result, the fill ratio of the stem to the proximal canal by the proposed method was higher than that by a method with the simple straight type as an insert axis. Also, the fill ratio and the spatial distributions of it in the femoral canals with this proposed method were so similar between the different femoral morphology. The result is important for a design of the custom-made model corresponding to variable femoral morphologies.

Milling tests were conducted in order to investigate the cutting performances of a binder-less PcBN tool in the machining of Ti-6Al-2Nb-1Ta (α-β type alloy) and Ti-15Mo-5Zr-3Al (β type alloy), which are used as surgical implant materials. In milling of the α-β type alloy, some micro chippings on the rake face of the tool were observed as a typical pattern of tool damage. In the case of the β type alloy, however, there were not only micro chippings on the rake face, but also many micro-flakes on the flank face. The occurrence of micro-flakes on the flank face influenced the structural strength of the cutting edge, and finally caused it to fail. Therefore, the rate of tool damage in milling of the β type alloy was higher than that in milling of the α-β type alloy. Measurement of cutting forces confirmed that in the case of the β type alloy the ratio of the principal cutting force to the thrust cutting force near the point of disengagement of the tool was much higher than that in the cutting process. The force of the principal direction near the point of disengagement was thought to be produced by strong adhesion to the flank face. Also, structure analysis using FEM revealed that the estimated shearing force of the adhesive was sufficient to break the flank face.

Using a binder-less PcBN tool, the influences of cutting speed on tool life and wear pattern in turning of Ti-6Al-2Nb-1Ta, which was a vanadium free titanium alloy for a surgical implant material, were investigated. In the condition of feed rate of 0.15mm/rev and depth of cut of 0.5mm with an application of a high pressure coolant, the tool life at cutting speed of 4.2m/s was the longest in the various cutting speeds. In conditions of cutting speed of below 4.2m/s the tool life was determined by chipping and flaking occurring on tool face, on the other hand, smooth wear on the tool face were observed in over 4.2m/s. And, it was confirmed that the smooth wear on the tool face in turning process appeared over 730°C of tool flank temperature , and the promotion of tool wear was so dependent on the cutting temperature. Also, in order to investigate this reaction in the cutting process, the experimental model reaction test between the tool material and the workpiece one by using the SPS equipment were conducted in addition to element analysis of the adhesive on the cutting edge using EDS and XRD. As a result, it was clarified that TiB2 was generated in the interface between the binder-less PcBN and the titanium alloy, and the reaction was sensitive to its temperature.

Using a binder-less PcBN tool, improvement of processing efficiency was tried in machining of a vanadium-free titanium alloy, Ti-6Al-2Nb-1Ta which was recently applied for a surgical implant material. The tool which is prepared through the direct conversion sintering of h-BN under both high pressure and temperature, exhibits an improved high thermal durability. It was confirmed that a binder-less PcBN tool exhibited lower flank wear and kept sharper cutting edge compared to the tools made of materials such as sintered carbide, conventional PcBN and polycrystalline diamond with Co-based binder, after turning in cutting speed of 4.2m/s, feed rate of 0.15mm/rev, depth of cut of 0.5mm under an application of a high pressure coolant. Also, milling tests were conducted with a radius end mill tool whose tip was made of the binder-less PcBN material. As a result, the possibility of high speed milling at cutting speed of 8.3m/s was found.

A new method of numerically controlled ultra fine polishing for brittle material is proposed. In this method, the offset of the polisher to the designed profile is controlled to be constant in non-contact, and the feed rate of polisher is fixed instead of polishing load. In this report, the surface polishing characteristics of this method and the influence of the viscosity of polishing compound are examined theoretically and experimentally. The following results are obtained : (1) When the clearance between the polisher and the work surface exceeds the definite value, the machining action does not occur. (2) The flow rate of polishing compound at the gap between the polisher and the work surface, and the stock removal rate are independent of the viscosity of polishing compound. (3) Observations of surface textures with roughness tester and AFM indicate that the surface roughness of polished surface is improved with the increase of the viscosity of polishing compound.

Efficient fine finishing of optical glass has been conducted by using a newly-developed setup which realizes the finishing of the non-contact type polishing with tin wheel floating by the effect of fluid lubrication. The polishing is made by using an electrophoresis phenomenon of fine grain in the water. when the electric power of DC voltage is supplied to the tin wheel rotating in the polishing compound, the grain concentrates on the wheel surface and causes the grinding action in a sense to the workpiece surface Experimental results show that the stock removal rate increases after first decreasing with the applied potential. It is found, however, that applied current intensity has little effect on the stock removal. The characteristics of polished surface have been exmined by AFM. The microtopography of the surface polished with fine abrasive grain indicates that the surface roughness of the order of nanometers is obtained even in the case that high voltage is supplied.

Thin diamond blade is widely used for the precision slicing of electronic parts such as magnetic head. It is well known experientially that some properties of blade have a great influence on the machining characteristics of workpiece, i.e. the work damage and the blade wear.ln order to understand the relation between the properties of blade and the machining characteristics, the mechanical properties of thin diamond blade are investigated in detail through the measurements of the tensile strength, the dynamic visco-elasticity and the wear resistance of bonding material. It is found from the experiments that there are notable differences in the mechanical properties of various blades.

The aim of this study was to evaluate the cytotoxicity of cubic boron nitride (cBN), a component of surgical cutting tools. The small quantities of cBN that typically remain on implants as a result of the manufacturing process may act as abrasives, injuring tissues surrounding the implant. To determine how cBN affects cells, we treated human neuroblastoma cells (NB-1) and human articular chondrocytes (nHAC-kn) with different concentrations of cBN powder and assessed cell growth and cell survival using the methyl-thiazol-tetrazolium (MTT) assay and a fluorescence probe assay. We also assessed the effects of tungsten carbide (WC) and cobalt (Co), two common components of joint implants, on cell growth and cell survival. Both cBN and WC moderately inhibited NB-1 and nHAC-kn cell growth. However, cBN and WC did not affect cell survival, even at high concentrations (40 microg/ml). By contrast, Co affected cell survival, inducing cell death in both cell types at increasing concentrations. These results suggest that cBN may be less toxic than WC alloys containing Co.

Ultrasonic motors are nonlinear in input–output characteristics, which causes problems for precise control. To obtain good controllability and realize low-cost fabrication, we proposed an ultrasonic linear motor using a multilayered transducer with independent electrode sets for the first longitudinal mode and the second bending mode. We can change the shape of the vibration locus at the friction head arbitrarily by independently controlling the amplitude and phase of each vibration component. Controllability in the proposed motor was investigated by changing the shape of the vibration locus. In the proposed motor, the nonlinear part of the input–output characteristics is suppressed to 1/20 of that in conventional ultrasonic motors. As a result, a good positioning resolution of 20 nm and a low-speed drive of 0.1 mm/s were obtained with a simple closed-loop control system.