The mechanical interaction between ultrahigh molecular weight polyethylene (UHMWPE) and a Co-28Cr-6Mo alloy in water was examined in order to clarify the wear resistance mechanism of vitamin E-containing UHMWPE in knee prostheses. The sample UHMWPE was pressed and rubbed against the surface of the Co-28Cr-6Mo alloy in water by using a computer-controlled pin-on-disk wear test apparatus. The formation of a UHMWPE transfer film on the surface of the Co-28Cr-6Mo alloy was reduced by the addition of vitamin E to UHMWPE. The pull-away force between UHMWPE and the Co-28Cr-6Mo alloy was also reduced by the addition of vitamin E. These results suggest that vitamin E reduces the attraction between UHMWPE and the surface of the Co-28Cr-6Mo alloy.

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Cartilage tissue was regenerated using fibroin sponge seeded with chondrocyte aggregates. The aggregates were formed on the sponge by micro-folding culture, where chondrocytes were cultured on a substrate containing an array of pits of 100 μm diameter. The aggregate-derived cartilage tissue showed higher safranin O staining intensity and was positive for collagen type II by immunostaining. However, its friction coefficient was higher than that of the cartilage tissue regenerated using individual cells. Moreover, the surface of this aggregate-derived cartilage tissue showed weak positive staining for collagen type I. Thus, regeneration of the aggregate-derived cartilage tissue has the possibility of forming larger amounts of extracellular matrix from a limited number of chondrocytes. However, such tissue showed relatively poor tribological function possibly because of its immature functional layer structure.

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This paper describes a prototype intelligent ankle-foot orthosis (iAFO) having an ankle joint with an adjustable viscous resistance torque. It was evaluated in a walking experiment involving a hemiplegic patient. The ankle joint was constructed with a magnetorheological (MR)-fluid damper having a changeable rotational viscosity. The iAFO consisted of an ankle joint, sensors for detecting walking, and a control box that comprised a circuit including Atmel AVR microprocessor and battery. Based on the difference in ankle joint function required in each stage of gait, walking was classified into three different phases in this study: the initial stance, mid-stance, and terminal stance/swing phases. A preliminary experiment was used to determine a method of detecting the shift from one phase to the next using the shank angle and foot contact information. The default resistance torque for each phase was configured. Using the prototype iAFO with the proposed control rules, a hemiplegic subject performed a walking experiment. While walking with the iAFO using suitable control rules, the ankle joint was maintained in dorsiflexion during the swing phase, and heel contact was achieved. In this respect, walking was better than unaided walking or walking using the iAFO with a resistance torque fixed at the highest level. The feasibility of the iAFO was confirmed.

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The purpose of the present study is to develop a direct and accurate method for measuring knee kinematics by using single-plane fluoroscopy. The study was carried out on a human cadaver femur. Computed tomography (CT) scan data of the femur was taken in order to construct 3D bone volume model of the femur. The femur was placed on an acrylic holder that was attached to a micromanipulator. The femur was rotated about in each orthogonal axis of the micromanipulator over a range of ±2°in 1°increments and then translated along each orthogonal axis over a range of ±2 mm in 1-mm increments. The 3-dimensional (3D) position of the femur (in other words, the 6 degree-of-freedom (DOF) parameters) was recovered by matching the digitally reconstructed radiographs (DRRs) generated from the 3D volume model of the femur and single-plane fluoroscopic images taken from the 25 positions generated by using the micromanipulator. The root-mean-square error (RMSE) of the overall rotation parameters was within 1.4°. For the translation parameters RMSE took its maximal value of 7.8 mm in the out-of-plane direction. This indicates that the present method has potential for clinical application.

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Physical exercise is a promising countermeasure for osteoporosis and strengthens skeletal muscle as well, resulting in a reduction of the risk of fall. However, physical exercise is not always safe and practicable, in particular, for osteoporotic patients with a decline in physical ability or under bed rest situation. We focused on electrically-elicited muscle contraction to prevent bone loss without any voluntary physical activities. To provide basic knowledge to determine effective stimulation patterns in this method, this study aimed to investigate the stimulation frequency and resting time dependencies of muscle contraction induced by electrical stimulation using rats, which is caused by muscle fatigue during the stimulation. A rat quadriceps was stimulated continuously or intermittently for 30 minutes by giving a repetition of 10-s electrical stimulation at 2, 5, 10, or 20 Hz, followed by 0-, 10-, or 20-s resting time. The change in muscle contraction force was monitored over the stimulation period, and average peak-to-peak force and accumulated peak-to-peak force for 30 min were analyzed as mechanical stimulus parameters. The data showed a larger decrease in the average peak-to-peak force at higher frequencies and with shorter resting times. The largest average peak-to-peak contraction force was observed in the 2-Hz stimulation with 20s-rests, which was larger 1.8, 3.7, and 8.1 fold than those in the 5-, 10-, and 20-Hz stimulation with 20s-rests, respectively. The 10s-rest did not show any increase in average peak-to-peak force when compared with the no-rest. On the other hand, the largest accumulated peak-to-peak contraction force was represented in the 10-Hz stimulation without resting time, larger 1.8, 1.2 and 4.2 fold than those in the 2-, 5-, and 20-Hz stimulation without resting time, respectively. Resting times did not contribute to increase in accumulated peak-to-peak force. These findings would contribute to basic researches on the prevention of osteoporosis using the electrically-stimulated muscle contraction, in particular, by providing useful information for the determination of stimulation pattern.

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Surface electromyography (sEMG) is commonly used to measure muscle activity because of easy application. Advantages of sEMG measurements include noninvasiveness and no pain. However, there are also problems with the sEMG technique when the activities of individual muscles are measured. The measurement of activity of individual muscles in the forearm with sEMG must be analyzed further because of superimposition of sEMG signals. In this work, a cylindrical phantom-forearm model filled with ground specimens of muscle was developed containing source and surface electrode pairs. A weak alternating current was applied to a source electrode pair immersed in the model, and the sEMG signals were measured with surface electrodes around the surface of the model. The attenuation characteristics of muscle action potential (MAP) were estimated from the measured sEMG, and the source position of the MAP was reverse-estimated. The reverse-estimated depth was accurate for less than 30mm of source depth. A 10% difference in the power exponent of attenuation caused errors in the reverse-estimation of less than 3mm.

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Precise assessment of therapeutic response in radiotherapy has been an important issue in the field of radiation oncology. This study proposed a methodology to evaluate therapeutic response based on tumor geometries. Three-dimensional (3D) tumor shapes were obtained from follow-up CT scans taken once a week throughout the treatment period. Tumor geometries were represented in two-dimensional (2D) surface geometry maps. These maps indicated the distances from the tumor center to surface at each azimuthal and horizontal angle by colors, in order to represent the characteristics of tumor morphologies. This method was applied to three clinical cases of head and neck cancer. The changes of tumor geometries could be represented visually and quantitatively using surface geometry maps. These maps provided valuable information about tumors for accurate diagnosis of tumor response to radiotherapy.

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Bone is often regarded as a composite material consisting of hydroxyapatite (HAp-like) mineral particles, organic matrix (mostly Type I collagen) and water phases in microscopic scale. The mechanical properties of bone at macroscopic scale depend on the structural organization and properties of constituents in the microscopic scale. In the attempts of understanding the effect of microscopic constituent on the mechanical properties of bone, the relationship between mechanical properties and mineral content of intact or completely demineralized samples have been studied. Even a slight alteration in the mineral content would have significant effect on the mechanical properties. In this work, the effect of degree of demineralization to the mechanical properties of bovine cortical bone was examined by gradually removing the mineral content and measuring constituents at every step till almost no traces of minerals were observed. Specimens were demineralized in 10% disodium EDTA solutions for 12, 24, 48, 72 hours and 14 days. The volume fraction of each structural constituent in the demineralized specimens was calculated from their X-ray absorption characteristics and quantifying transmitted X-ray intensity. Tensile tests were performed to measure the elastic modulus and ultimate strength of the demineralized specimens. This work shows the strong dependence of elastic modulus and ultimate strength of cortical bone to the mineral content as microscopic constituent. The degree of dependence with mineral loss has been demonstrated precisely so to provide the importance of mineral content and its role on the mechanical functioning of bone.

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The spinal cord is mainly composed of white matter and gray matter which consist of solid and liquid phases. When the tissue deforms, the liquid phase in the tissue flows out through between the solid phases. The interaction and frictional resistance between the two phases result in the macroscopic visco-elastic behavior. In addition, the solid phase in soft tissue contains a large amount of negatively-charged proteoglycan. This electro chemical behavior affects the visco-elastic properties of the tissue. This study investigated the electro-kinetic behavior of white matter and gray matter under a variety of compressive loadings. Column-shaped specimens, 5 mm diameter and 5 mm height, were made from white matter and gray matter of bovine cervical spinal cord, and the specimens were set in physiological saline. The streaming potential was measured under compressive loading, stress relaxation, and cyclic loading. The results showed the streaming potentials to have a linear relation to tissue stress in compression and relaxation. In cyclic loading tests, the streaming potential changes according to the stress change in the loading.

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In order to produce a biomimetic bearing made from a hydrated material, a polyvinyl formal (PVF) bearing that mimics articular cartilage has been proposed. PVF has material and tribological properties that reflect the different internal structures resulting from different parameters used in the PVF formation process. Reciprocating and multidirectional wear tests were performed, and plastic deformation attributed to pore deformation was observed; however, microscopic observations did not reveal any damage due to friction. PVF exhibited high wearresistance properties, and it is concluded that the proposed bearing overcomes the problem of low wear-resistance in bearing materials capable of developing hydration lubrication.

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This paper presents a method for quantifying tendon reflex dynamics addressing kinematical characteristics of the patellar tendon reflex. The method uses a limb-mounted three-dimensional motion sensor and an instrumented hammer to assess input-output relations of the patellar tendon reflex. A healthy adult male subject participated in our experiment. A simple rigid-body physical model was introduced to obtain viscoelastic and inertial responses of kinetic motion of the lower leg. This model is used to estimate knee extension torque by indicating the reflex responses of the muscle. A system identification method was then applied to describe the reflex responses to the hammer tapping by considering a second-order mathematical model with a delay term. Iterative prediction-error minimization was applied to the cascaded data for three tapping conditions: weak, medium, and strong. Good consistency was obtained between the analysis from the model and the measurement results. The results suggest that the proposed method was sufficiently feasible to characterize the reflex responses with a few characterized system parameters, which will be useful to provide additional quantitative assessment capability for neuromuscular diagnosis.

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Intracellular calcium ([Ca²⁺]_i) is a second messenger molecule critical for numerous intracellular signaling pathways in endothelial cells (ECs). Direct mechanical stimulation imposed on single ECs by a microprobe has been demonstrated to increase [Ca²⁺]_i levels in ECs. After an initial delay time, this Ca²⁺-signal propagates from the mechanically stimulated cell to its neighboring cells in the form of an intercellular Ca²⁺-wave, a process termed intercellular communication. Although intercellular communication is a fundamental property of many multicellular systems, it remains unclear as to whether intercellular communication following shear stress of ECs actually occurs, and if so, whether this communication occurs via gap junctions or the release of extracellular mediators including ATP. In the current study, we investigated ATP release from ECs during periods of shear stress and measured intercellular Ca²⁺-waves using adenosine 5'-triphosphate, P₃-(1-(2-nitrophenyl)ethyl)ester and disodium salt (NPE-caged ATP) stimulation. In addition, we investigated intercellular communication in ECs during shear stress using chemical inhibitors of both gap junctions and various components of the ATP paracrine signaling pathway. ECs subjected to shear stress loading released ATP. Using NPE-caged ATP, local increase of extracellular ATP induced a Ca²⁺-wave. Furthermore, [Ca²⁺]_i responses in ECs under shear stress loading was inhibited by the purinergic receptor blocker, ATPase, and several metabolic inhibitors including FCCP and rotenone. These results suggest that [Ca²⁺]_i communication mediated by ATP exists in ECs under shear stress loading in vitro.

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The effects of three-dimensional (3-D) culture and cyclic stretch stimulation on the expression of contractile proteins were investigated in freshly isolated rat aortic smooth muscle cells (FSMC). Primary cells were cultured statically on cell culture dishes (two-dimensional (2-D) culture) or in type I collagen gel matrix (3-D culture). Changes in their expression level of actin filaments (AFs) and smooth muscle myosin heavy chain (SM-MHC) were measured quantitatively using an accurately-calibrated fluorescent microscopy. The expression of AFs and SM-MHC decreased in both cultures in their early stages. Cell morphology was quite different between the two cultures: the cells had a flattened and irregular shape in the 2-D culture, while they had a fusiform shape with a well-defined long axis in the 3-D. Nineteen-day culture in the gel significantly increased the expression levels of AFs and SM-MHC while the expression levels remained low in the 2-D. Further and early increase in the expression levels was observed in the cells cultured in the gel with cyclic stretch of ∼8% amplitude and 1 Hz frequency. The cyclic stretch also induced alignment of FSMCs in the gel parallel to the stretch direction, and the cell alignment was observed earlier than the increase in their contractile proteins. These results indicate that the 3-D culture in collagen gel may increase the expression level of contractile proteins in FSMCs while maintaining their fusiform morphology, and cyclic stretch may efficiently increase the expression levels when the cells aligned in the stretch direction.

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The objective of this study is to analyze kinetics and kinematics of artificial knee joint at deep flexion, using a 2D geometric model. Our knee model was composed of the tibio-femoral and patello-femoral joints, including the patella tendon and the quadriceps muscles. Since the model was 2D, it neglected the rotation and the varus/valgus motion. In the model, such assumption was made that articulation surfaces were rigid and a point contact was made. Also it was assumed that the force and moment equilibrium conditions were always satisfied. The motion to be studied was decided as the motion from standing to deep squatting with heel-rising. From the simulation we found such results that the femur did not make a rollback and contact force at post-cam became pretty large in high and deep flexion, indicating the post-cam mechanism did not function well. Also patello-femoral contact forces reached larger than tibio-femoral contact forces. Our results demonstrated that how to design the post-cam and patello-femoral joint should be critical issues for developing a new prosthesis which can make deep flexion.

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