Masanobu Ujihira

Influence of loading duration on the start-up friction in synovial joints: measurements using a robotic system

OBJECTIVE: To determine how much and why static load influences friction in synovial joints. DESIGN: Start-up coefficient of friction in canine stifles was measured after different duration of static load. BACKGROUND: Previous investigators have shown that friction of cartilage on cartilage contact configurations sharply increases with stationary load duration. This phenomenon has not been confirmed in the entire synovial joint. METHODS:: A system to measure joint friction was designed using a robotic arm. Ten canine stifles from six animals were used. Start-up friction of the femoral condyle on the tibial plateau and femoral condyle on glass plate contact configurations was measured. The glass plate was chosen as a rigid surface where ploughing effect cannot occur. RESULTS: The mean value of the start-up frictional coefficient from femoral condyle on tibial plateau was 0.112 (SD 0.005) at 0 s stationary loading, and sharply increased with the stationary loading duration to 0.313 (SD 0.095) at 1800 s. Those from femoral condyles on glass plate were 0.005 (SD 0.003) at 0 s and 0.457 (SD 0.128) at 1800 s. CONCLUSIONS: Friction in synovial joints sharply increases with duration under static load. The ploughing effect on this increase is slight in friction in canine stifles. RELEVANCE: The lubrication mechanism is worth investigating to understand the pathology of joint diseases. Determining friction behaviour is necessary for the investigation of the lubrication mechanism.

Hydrogen Supplementation of Preservation Solution Improves Viability of Osteochondral Grafts

Allogenic osteochondral tissue (OCT) is used for the treatment of large cartilage defects. Typically, OCTs collected during the disease-screening period are preserved at 4°C; however, the gradual reduction in cell viability during cold preservation adversely affects transplantation outcomes. Therefore, improved storage methods that maintain the cell viability of OCTs are needed to increase the availability of high-quality OCTs and improve treatment outcomes. Here, we evaluated whether long-term hydrogen delivery to preservation solution improved the viability of rat OCTs during cold preservation. Hydrogen-supplemented Dulbeccos Modified Eagles Medium (DMEM) and University of Wisconsin (UW) solution both significantly improved the cell viability of OCTs during preservation at 4°C for 21 days compared to nonsupplemented media. However, the long-term cold preservation of OCTs in DMEM containing hydrogen was associated with the most optimal maintenance of chondrocytes with respect to viability and morphology. Our findings demonstrate that OCTs preserved in DMEM supplemented with hydrogen are a promising material for the repair of large cartilage defects in the clinical setting.

Pre-incubation with hyaluronan reduces cellular damage after cryopreservation in densely cultured cell monolayers.

Reduction of cellular damage in densely cultured cell monolayers after cryopreservation by pre-incubation with hyaluronan (HA) was investigated. Monolayers of human dermal fibroblasts were cultured for 24 h at a density of 0.5×104 or 5×104 cells/cm2. The following two experimental conditions were compared: cells incubated with or without 0.5% w/w HA solution for 6 h. Samples were frozen from 4 to -80°C at 0.3 or 3°C/min in a cryoprotectant solution containing 10% w/w dimethyl sulfoxide, cooled down below -185°C, and then thawed. Post-thaw cell viability was evaluated by the fluorescent double-staining technique using a fluorescence microscope, and cellular uptake of the fluorescein-isothiocyanate-labeled HA after pre-incubation was also observed. Cell viability decreased with increasing cell density at both cooling rates without preliminary HA incubation. However, cell viability did not decrease at either cooling rate with preliminary HA incubation. Cellular HA uptake was observed. Pre-incubation with HA reduces cellular damage in densely cultured cell monolayers.

Relationship between the conformity and the lubricating ability of synovial joints

OBJECTIVE: To relate conformity of sliding surfaces with the lubricating ability of synovial joints. DESIGN: Measurement of start-up friction in the stifles of various animals. Assessment of conformity by Hertzian contact area. BACKGROUND: Past studies showed that the start-up friction in synovial joints sharply increased with the loading duration. The reasons why the friction increased and why the increasing rate is different in different joints were, however, not found. METHODS: Nine stifle joints from various animals were used. A robotic arm was used to give the compressive force and the sliding motion to the joint. Start-up friction was measured by a universal force sensor. The principal curvatures of the sliding surfaces were directly measured by a radius-gauge. Hertzian contact area was calculated from the principal curvatures of the sliding surfaces. RESULTS: The duration until the frictional coefficient reached 0.1 was related to the Hertzian contact area. CONCLUSION: The conformity of sliding surfaces is related to the lubrication ability in synovial joints. The squeeze-film mechanism plays an important role in joint lubrication.

Gas Transport in Serpentine Microporous Tubes Under Steady and Pulsatile Blood Flow Conditions

A serpentine gas exchange unit was built with cylindrical tubular microporous membranes featuring periodic arcs with a fixed curvature ratio (ratio of tube radius to radius of curvature) of 1/14 and circular angles between 30 and 360 deg. Oxygen transfer was measured under steady and pulsatile blood flow conditions in vitro and ex vivo to assess the design features which most effectively augment gas transfer. Under steady blood flow conditions, oxygen transfer increased with circular angles beyond 70 deg. Under pulsatile conditions, a wide range of geometrical and fluid mechanical parameters could be combined to enhance gas transfer performance, which eventually depended upon the secondary Reynolds number and the Womersley parameter.

Influence of hooks and a lag screw on internal fixation plates for lateral malleolar fracture: a biomechanical and ergonomic study

BackgroundFor internal fixation of AO classification Type B lateral malleolar fracture, insertion of lag screws into the fracture plane and fixation with a one-third tubular plate as a neutralization plate are the standard treatment procedures. The one-third tubular plate is processed to a hook shape and hung on the distal end of the fibula. In this study, to compare the function of the hook and lag screws of a one-third tubular plate and LCP for osteosynthesis of lateral malleolar fracture, mechanical indices of internal fixation were compared among the one-third tubular plates with lag screws with and without the hook and a locking compression plate.MethodsAs mechanical tests, a compression test was performed in which compression in the bone axis direction produced by supporting the body weight was simulated, and a torsion test was performed in which external rotation of the bone axis caused by plantar flexion of the ankle joint was simulated. Muscle strength during walking and the force and torque acting on the ankle and knee joints were determined using inverse dynamic analysis. Finite element analysis was performed to analyze the function of hooks and lag screws. The joint reaction force determined by inverse dynamic analysis was adopted as the loading condition of finite element analysis.ResultsA stiffness equivalent to that of healthy bone could be achieved by all three internal fixations. It was clarified that the presence of the hook does not make a difference in stiffness. Displacement of the one-third tubular plate was small regardless of the presence or absence of the hook compared with those of locking compression plates.ConclusionsThe presence of the hook did not make any difference in stiffness, suggesting that active preparation of the hook is unnecessary. We also clarified that lag screws inhibit displacement.

STUDY ON FREEZING PROCESS OF KILLIFISH EGG: UTILIZING THE UNDERCOOLED STATE FOR CRYOPRESERVATION

The purpose of this study is to find the feasibility of preservation of large cell and tissue by maintaining the undercooled state in a freezing process, leading to avoiding the growth of ice crystals in the intracellular space, which causes destruction of cell and tissue. The fertilized killifish egg was employed to test biological tissue. The cooling system was equipped with Peltier devices and able to decrease the temperature of the test section to -50 degrees C. The cooling rate could be regulated by the electric current supplied to the Peltier devices. In the temperature range 0 to -40 degrees C, the morphology of fertilized killifish egg was observed under a microscope with a cooling rate from 0.1 to 10 degrees C/min. The damage rate to the egg in the intracellular undercooled state was evaluated by hatching rate. As a result, intracellular undercooled states were observed in the freezing process with the extracellular undercooling and the extracellular freezing. Extracellular undercooling proves to preserve the egg, and extracellular freezing frequently damages the egg. Thus the cryopreservation of biological material is achieved by maintaining the undercooled state until the temperature of -40 degrees C, then is instantly frozen by the liquid nitrogen to avoid the growth of ice crystals. The maintaining of the stable undercooled state of biological material is requisite for the initial phase in the freezing process. Therefore, dehydration or maintaining the extracellular stable undercooled state should be desirable to maintain the intracellular undercooled state for cryopreservation of biological material.

Measurement of effective thermophysical properties for Cryopreserved-State evaluation in frozen red blood cells suspension

The purpose of this study is to estimate the viability of frozen biological materials during cryopreservation with the thermophysical properties. Human red blood cells are selected as test biological material. Propylene glycol (0, 10 and 35%w/w) was selected as cryoprotectant. The test chamber was contacted with carbon heater on a copper block immersed in liquid nitrogen, and cooled from room temperature to -196°C at a cooling rate of 1 to 300°C/min. Temperature rise of 5°C was applied to the suspension at -190°C, the effective thermal diffusivity was determined with Laplace transform method. As a result, the effective thermal diffusivity decreased with decrease of intra-and extracellular ice formation fraction in their suspension, which affects their survival after thawing. Thus assessment of cryopreserved biological materials can be achieved with the thermophysical properties.

Viability evaluation using the effective thermal conductivity during extracellular freezing in killifish embryos

The purpose of this study is to evaluate the correlation between the viability of milliscale biological materials and their effective thermal conductivity during extracellular freezing in order to achieve successful cryopreservation. The killifish embryo (Oryzias latipes, orange-red variety, φ1.3mm sphere) was employed as a sample biological material and the viability was evaluated by the hatching rate. Dimethylsulfoxide-water was selected as the cryoprotectant. The thermal conductivity was measured using a self-heated thermistor technique developed by T. A. Balasubramaniam (1977). The thermistor (φ2.5mm sphere) was installed at the bottom of a test section 8×8×12mm, and exposed to biological material. The cooling system was equipped with Peltier devices and was capable of reducing the temperature of the test section to -30°C. Between 150 and 200 embryos were loaded in the test section with 5, 15 and 20% w/w Dimethylsulfoxide-water. The effective thermal conductivity during extracellular freezing was measured over the temperature range -20 to 6°C with a cooling rate of 0.1 to 10°C/min. The effective thermal conductivity increased from 0.5 to 1W/ (m·K) with decreasing temperature and increasing the cooling rate. The decrease in the hatching rate and the variation in the effective thermal conductivity were correlated. Thus the viability could be controlled using their effective thermal conductivity during the extracellular freezing.