Abstract:In this paper, brief review of the current studies on natural and artificial joint tribology at home and abroad has been made, including the origin and definition of tribologu,human biotribology, joint lubrication, wear life of MOP/MOM/COC artificial joints,natural cartilage tribology, the interface of artificial joints and host bones in terms of micro-tribology, artificial synovial fluid,etc. This paper especiallly demonstrated the achievements of Chinese researchers in the field of joint tribology.

Abstract:Objective: The modification and biotribology of the different artificial joint materials were investigated in this paper. The purpose of these studies focused on providing the reliable technological and theoretical basises for the new typical artificial joint designs. Method: Ti surface of Ti6Al4V alloy were modified by the surface carburizing, MAO and ion implantation. The aim was to increase the wear resistance. The filling modification technology was used to increase the loading capacity, creep resistance and wear resistance of UHMWPE. UHMWPE/BHA, UHMWPE/NC and UHMWPE/VE composites were prepared in this study. With polyvinyl alcohol (PVA) as matrix material and nano-hydroxyapatite (HA) as the enhancement, PVA/HA hydrogel composite was prepared. The biotribologies of these biomaterials were investigated in this paper. Results: (1) The surface modification of titanium alloy may obtain the ceramic layer with a combination of good performance, which can effectively improve the wear resistance of titanium alloy. (2) The filling modification of UHMWPE can get some good wear-resistant joint composites. The wear particles and biological reaction were reduced effectively.

Abstract:Objective For the research of relative motion and dynamic biomechanics of knee joint during squat. Providing the data of relative motion and biomechanics of knee joint for research of bio-tribology Methods Dynamic finite element (FE) model of knee and after total knee replacement (TKR), which include tibio-femoral, patello-femoral articulations and the surrounding soft tissues, were developed in this research, to simulate both the kinematics and the internal stresses during squat simulation. The kinematic simulating results and the contact stresses distribution of a full deformable contact analysis of knee and prosthetic knee joint during squat, were verified by comparing with the data from an unique experiment. Results The dynamic 3D relative movement data and the contact distribution and stress of both tibiofemoral and patellofemoral joint in dynamic deep flexion were obtained.The results showed that relatively higher contact stresses were distributed in three different areas: the interface of cam-post and the anterior tibia insert, medial-posterior tibia insert and posterior tibia trabecula. These were also main areas with high wear rate Conclusion The established dynamic FE models are capable of predicting the kinematics and the stresses during squat，and could be a efficient tool for the analysis of TKR, research of bio-tribology and knee prosthesis design.

Abstract:Objective Aims of this study were to investigate the mechanical properties of Ultra-high molecular weight polyethylene carrying Alendronate (UHMWPE-ALN) and to explore its potential application in clinic. Materials and Methods The UHMWPE-ALN samples and the control UHMWPE were prepared by hot-pressure. The tensile test, small punch test, micro hardness, the Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) were applied to measure the mechanical properties, the crystallinity and the phase of UHMWPE, respectively. Results ALN showed no effect on Young’s modulus, Yield strength and Hardness of UHMWPE. But Ultimate elongation, Ultimate strength and Work to failure of UHMWPE decreased significantly with adding ALN. DSC and XRD analyses showed that the crystallinity of UHMWPE-ALN decreased slight whereas no phase changes occurred in UHMWPE with added ALN. Conclusion It is feasible to fabricate UHMWPE-ALN with satisfied mechanical properties compared to the control UHMWPE when the content of ALN is lower than 0.25 wt%. The decreased crystallinity of UHMWPE-ALN is the major factor responsible for the decrease in mechanical properties.

Abstract:Objective tribological performance of the new bio-therapeutic lubricants is studied according to different composition concentration, including hyaluronic acid, albumin and alendronic acid sodium. Methods the bio-therapeutic lubricants were orthogonal experimental designed. Factors as friction coefficient, wear spot diameter and viscosity were investigated via a four-ball tribo-tester, viscosity meter and optical microscope. Results (1) hyaluronic acid has the most significant impact on the lubricant’s performance; (2) high albumin concentration will reduce friction, while increasing wear rate due to the possible tribocorrosion; (3) better lubricating performance is observed with higher alendronic acid sodium content. Conclusion bio-therapeutic lubricants partially recover the functions of synovial fluids and provide good lubricating property.

Abstract:Objective To study the effect of preparation parameters on structure and friction properties of PVA hydrogels, which provids an academic foundation for application potentials of PVA hydrogels for cartilage repair. Methods γ-Ray radiation crosslinked PVA hydrogels were prepared by freezing-thawing method combined with irradiation technique, microstructure and friction properties when sliding against nature articular cartilage were studied. Results (1) SEM observation illustrated that PVA hydrogels had a three-dimensional network structure and such structure became denser after irradiation. (2) Water content of PVA hydrogels increased with the increasing of irradiation dose and PVA concentration. (3) Friction properties of PVA hydrogels were performed on a reciprocating pin-on-plate machine sliding against nature articular cartilage. The results showed that at shorter loading times, a high proportion of the load was carried by fluid phase which resulted in a lower friction coefficient. As the time gone, more fluid was squeezed away from the contact zone, and the load was transferred to the solid phase of PVA hydrogels, which increased friction coefficient and reached a stable level. Lubrication mechanism transferred from biphasic lubrication to mixed lubrication. Friction coefficients of PVA hydrogels increased with the increasing of irradiation dose and PVA concentration.

Abstract:Objective The effective lubrication performance of the metal-on-metal hip implants only requires the optimum conformity within the main loaded area, while it is advantageous to increase the clearance in the equatorial region. Such a varying clearance can be achieved by changing the radius of the curvature of the surfaces of the components. Alpharabola is one specific example of such surfaces. The aim of this study was to investigate the EHL performance of a novel prosthesis employing Alpharabola cup under realistic walking conditions. Method A transient elastohydrodynamic lubrication model was created for this novel hip prosthesis. A normal walking gait was represented by the ISO specified dynamic operation conditions. Complete numerical solutions were obtained by solving the Reynolds equation in spherical coordinates, the film thickness equation and the load balance equations using Multi-grid technologies. Results Detailed variations in film profile and pressure distribution during one convergent walking cycle were analyzed. The effect of parameter ? on quasi-static and transient solutions of the central and minimum film thicknesses and maximum pressures was investigated. The transient and quasi-static solutions for the same parameter ? were compared. The lubrication performance of Alpharabola hip prostheses and that of a spherical hip prosthesis were compared under both transient and quasi-static conditions. Conclusion It was found that both the squeeze film action and the non-spherical acetabular surface can significantly improve lubrication performance under realistic walking conditions, in increasing the predicted lubricant film thickness and decreasing the maximum hydrodynamic pressure. The metal-on-metal Alpharabola hip prosthesis was shown to benefit from fluid film lubrication significantly more than spherical hip prostheses.

Abstract:BIOLOX?delta is a new high performance ceramic composite material with outstanding material properties which are based on complex reinforcing mechanisms. In particular, the fracture toughness is increased by 2 reinforcing ingredients, i.e. zirconia and oxide platelets. It is shown that the improved material properties in comparison to pure alumina leads to significant higher reliability of the components for surgery. For materials containing zirconia as a reinforcing element the issue of stability in hydrothermal environment is of particular interest. For this purpose an extreme test setup has been chosen where severe hydrothermal treatment in water vapour at 134°C and cyclic mechanical loading at a very high stress level are combined. All specimens survived these test conditions which simulate a multiple of the expected in-vivo loading. An analysis of the phase composition shows that the reinforcing mechanisms have been thoroughly activated regardless of environmental conditions. From this outstanding result it is concluded that BIOLOX?delta provides highest probability of long term durability in well designed artificial joint systems.

Abstract:Objective Partial Foot Amputation (PFA) is the most commonly employed amputation in clinic. Analysis of gait changes induced by three typical amputation levels of PFA (Metatarsophalangeal joints, transmetatarsal, Lisfrane joints) will contribute to design suitable aid devices, such as orthopedic shoes, partial foot prosthesis, and so on. Method Measure the walk speed, step length, step frequency, peak plantar pressure, impulse, contact time and contact area with Footscan plantar pressure measure system and OPTOTRAK motion analysis system, and then compare these parameters among three amputation levels. Results The gaits are obvious different among these three different levels of foot amputation: the shorter the residual foot, the shorter the step and the more obvious the biped loading time difference; peak force occurs mainly at the metatarsal and the heel area for the MTP, while occurs at the midfoot and heel area for the TMA and Lisfrane amputation. Conclusions It is maybe important to take into account of amputation level when aid device is designed for PFA patient to improve the gait.

Abstract:Objective To elucidate if IL-8-induced L-selectin shedding is associated with the changes in microtopology and stiffness of cell membrane, which in turn regulates the kinetics of L-selectin binding to its ligands. Method Intact Jurkat cells constitutively expressing L-selectin (Case I) were incubated by IL-8 (Case II), pre-incubated by TAPI-0 following by incubating with IL-8 (Case III), or treated by TAPI-0 alone (Case IV). The microtopology and stiffness of cell membrane were measured using electron scanning microscopy and micropipette aspiration assay, respectively. Results The presentation of microvilli on the surface was reduced and cell membrane became smooth in Cases II and III but not in Case IV, as compared to that in Case I. No significant difference in membrane stiffness was found for all four cases. Conclusion Surface microtopology of a Jurkat cell was modified by IL-8 treatment, which would affect the binding kinetics of L-selectin to its ligands, whereas membrane stiffness retained the same as that for an intact cell, which would not contribute to the kinetics.

Abstract:Objectives To investigate the long-term changes of fixation strength of pedicle screw augmented with calcium phosphate cement in vivo. Methods Twelve pedicle screws were bilaterally planted in to six lumbar vertebrae of each sheep, including 4 non-augmented as control, 4 augmented with calcium phosphate cement (CPC) and 4 augmented with polymethylmethacrylate (PMMA). A total of twelve female adult sheep were operated, and they were randomized into four study periods of 1 day, 4 weeks, 12 weeks and 24 weeks after operation. At the end of every assigned study period, the animals were killed and lumbar vertebrae were harvested. Then axial pull-out tests conducted on the pedicle screws of the isolated vertebrae. The maximum pull-out force (Fmax) and energy absorption value (EAV) of the different screw planting methods at the same time and those of the same screw planting method but at the different study periods were compared by twos, respectively. Results The mean BMD was 0.923±0.082g/cm2 in the group of one day after surgery, 0.910±0.098 g/cm2 group at 4 w, 0.952±0.123 g/cm2 group at 12w and 0.912±0.126 g/cm2 group at 24w. There was no significant difference in the bone mineral density (BMD) of the animals between every two group (p﹥0.05). The mean maximum pull-out force in the CPC group was 893.13±63.91N 24 hours after operation，916.50±109.88N at 4w，1022.04±73.85N at 12w and 1104.91±112.33N at 24w. A positive correlation existed between Fmax and EAV (P﹤0.001). No significant difference in Fmax and EAV was found among the 1-day, 4-week, 12-week and 24- week control group, so were CPC group and PMMA group (P﹥0.28). At the end of every study period, the Fmax and EAV of CPC group were unanimously greater than those of control group (P﹤0.001). And the Fmax and EAV of PMMA group were statistically greater than those of CPC group (P﹤0.003) but an exception, the 24-week EAV (P﹥0.18). Conclusions Results of this research demonstrated that the fixation strength of pedicle screw can be significantly improved by augmentation using the injectable calcium phosphate cement, and the augmentation is not only immediate but maintainable in vivo for quite a long time. CPC may be a favorable substitute of PMMA for the augmentation of pedicle screw.

Abstract:In order to avoid the adjacent segment disease resulted from spine fusion, the concept of non-fusion technology arose and is becoming popular. The posterior non-fusion devices in lumbar spine have used clinically, but no long-term follow-up data about these devices is reported, and the basic study is not enough. We reviewed the biomechanical evaluation about posterior non-fusion technologies in lumbar spine, including range of motion, intradiscal pressure, facet joints and the biomechanical methods. We found these non-fusion technologies have advantages in treating lumbar degenerative diseases, but more deep study needs to be done.