Abstract:This paper expounds the statistical work on artificial joint failure and their primary results in China and abroad. From the view of clinical demand, biomechanics and engineering, the paper proposes that it is the basic technology, manufacturing techniques and clinical conditions that lead to artificial joint failure. The paper also elaborates the demand on further improving the clinical medicine of artificial joint and prosthesis technology, and presents some suggestions to promote the domestic statistics work on artificial joint failure.

Abstract:Arteries in vivo are subjected to lumen pressure, shear flow and axial tension due to surrounding tissue tethering. The axial stress affects arterial function including its response to pressure and flow. While the effects of blood pressure and shear flow are well documented, the effects of axial tension on vascular remodeling have just gradually gained attention recently. This review summarizes the results on the observation of the axial tension in arteries and responses of arteries to elevation and reduction of the axial stress. It is concluded that the axial tension in arteries plays an important role in regulating normal arterial function and tissue remodeling and adaptation and disease development. Research on vascular remodeling under axial tension shall strengthen the understanding of normal physiological functions and pathological changes of the arteries.

Abstract:Objective To propose a detailed method on the diagnosis of dislocation failure by studying the mechanism of mechanical failure and causes of dislocation occurrence after the total hip arthroplasty (THA). Methods The correlation between dislocation failure and clinical situation, product design and patients was analyzed by establishing the dislocation model to study the biomechanical mechanism of dislocation procedure. Results The reasoning route for dislocation analysis after THA was proposed and the visual hip prosthesis motion analysis software was developed and validated. Conclusions Case study on dislocation failure after THA shows that the proposed method and developed software can judge the cause of dislocation incidence in detail, and determine the relationship between implanting position for the hip prosthesis and dislocation incidence. Meanwhile, it can find the best implanting position before operation and analyze the risk of dislocation incidence, which will be helpful for the prosthesis design.

Abstract:Objective To develop a novel measurement system composed of micro-CT, mechanical loading device and digital volume correlation (DVC) technique, so as to measure the three-dimensional microstructural deformation field in bone tissue. Methods Uniaxial compression was applied on the specimen with the micromechanical loading device, and CT scans were also conducted while maintaining the same loads; then sequential CT images were matched and searched accordingly by DVC method to calculate the micro-displacement in the specimen along three directions before and after loading; repeated scanning of zero-displacement and rigid body translation were used to evaluate the accuracy and precision of the system. The three-dimensional distribution of displacement field in bovine cancellous bone was measured by the system. Results The result from repeated scanning of zero-displacement showed that the highest accuracy of measurement was performed in the loading direction and the precision was less than tenth of the CT resolution. The result of rigid body translation showed that the standard deviation was 0.001~0.002 μm. For cancellous bone specimen under the load of 600 N, the range of micro-displacement was 100.35~110.25 μm, with multilayer field distribution. Conclusions The accuracy and precision of this measurement system can meet the requirement of DVC method. It is proved that this system can be used for measuring the three-dimensional micro-deformation field in the cancellous bone and as a measurement platform for investigating the relationship between deformation distribution and structural response in bone tissue for the future research.

Abstract:Objective To obtain an optimized method of providing hyperelastic parameters of soft tissue, and to promote the simulation accuracy in explicit solution of finite element analysis (FEA) on soft tissue impact test. Methods Compressive properties of soft tissue from six fresh planta were measured. The experimental data were used to calculate the FEA material properties, which were then optimized by Poisson’s ratio. With the same loading and boundary conditions as the experiment, the FEA model was conducted for simulation. The simulation results were verified by both the experimental data and literature data. Results The force-displacement curve of soft tissue presented an exponential growth trend in the in vitro biomechanical experiment. When the compression ratio was under 45%, the FEA simulation result was consistent with the experimental data. When the compression ratio was above 45%, the closer the Poisson’s ratio up to 0.5, the higher the accuracy of FEA simulation result. However, there was a strong linear correlation between the FEA simulation results and experimental data (R2=0.9923) when the Poisson’s ratio was 0.497. Conclusions The simulation result of material parameters in FEA model is preferable in this study. With a lower compression ratio, the simulation results from FEA model are in consistency with the experimental data. Increasing the Poisson’s ratio can promote the simulation accuracy of the FEA model when the compression ratio is high.

Abstract:Objective To investigate the effect of hip protector on biomechanical response of the human pelvis-femur complex under lateral pelvic impacts during sideways falls using three dimensional (3D) finite element (FE) method. Methods Based on the model database of China Mechanical Virtual Human, a 3D FE model of the pelvis-femur-soft tissue complex including cortical bone, cancellous bone and soft tissue capsule and the pelvis-femur-soft tissue complex with a two layer hip protector were created, respectively. The rigid plane model was also constructed in the two models for ground simulation and constrained in all freedoms. The average hip lateral impact velocity of 2 m/s was applied to the two models, and the time for simulation analysis was set at 20 ms. The stress and strain distribution on the two models under lateral impacts could be obtained by the 3D FE calculation. The comparative analysis was performed to study the effect of the hip protector on biomechanical response of the pelvis-femur complex. Results The hip protector made the peak Von Mises stress appeared 4 ms more earlier in the pelvis-femur complex with a significant decrease in the stress and strain level. The average Von Mises stress peak was decreased by 67.88% and 69.34% in the cortical bone and in the cancellous bone, respectively, and the compressive principal strain peak was decreased by 63%. Conclusions Under lateral pelvic impacts, the two-layer hip protector could act as safeguard for pelvis-femur complex, thus effectively prevent the occurrence or reduce the risk of bone fracture.

Abstract:Objective To study the role of medial collateral ligament (MCL) in maintaining the stability of the knee joint by constructing the three-dimensional (3D) finite element model of the knee joint. Method sCT scans were performed after the MCL was marked by steel wires and the end point was marked by the dill hole. Then the 3D finite element model of the knee joint including ligaments was constructed with Mimics, Geomagic and Ansys software to simulate the anterior-posterior translation, valgus and internal-external rotation of the knee joint at different flexion angles. Results With the knee at 0, 30, 60, 90 and 120 degree of flexion，the initial stresses of MCL were 4.84, 3.55, 2.17, 1.26 and 0 MPa, respectively. When the knee joint was subjected to anterior translation loading, the stresses were 7.22, 5.78, 4.07, 2.84 and 1.4 MPa, respectively. When the knee joint was subjected to posterior translation loading, the stresses were 8.14, 6.45, 4.19, 2.92 and 1.6 MPa, respectively. When the knee joint was subjected to internal rotation loading, the stresses were 6.81, 5.23, 3.29, 2.25 and 0.97 MPa, respectively. When the knee joint was subjected to external rotation loading, the stresses were 6.28, 5.00, 3.34, 2.21 and 0.82 MPa, respectively. When the knee joint was subjected to valgus loading, the stresses were 11.00, 9.55, 7.25, 5.94 and 3.11MPa, respectively. Conclusions The biomechanical function of MCL can be effectively analyzed by establishing the 3D finite element model of the knee joint to simulate the anterior-posterior translation, valgus and internal-external rotation of the knee joint.

Abstract:Objective To construct a system for studying the ultrastructure and mechanical properties of insect flight muscle fiber in different activated states so as to carry out cardiac biomechanics study in physiological environment, and further promote understanding of the relationship between cardiac structure, mechanical properties and physiological function, and provide more clues for the basic and clinical research on cardiac diseases. Methods The ultrastructure of insect flight muscle fibrils in rigor, relaxed and activated state was investigated using the tapping mode of atomic force microscopy (AFM), and the elasticity of muscle fibers in different physiological states was studied using the nanoindentation. Results Sarcomere lengths of insect flight muscle fiber in rigor, relaxed and activated state were (2.10±0.05), (3.10±0.10), (2.50±0.15) μm (2 mmol/L Ca2+), (2.60±0.25) μm (5 mmol/L Ca2+) and (2.55±0.15) μm (10 mmol/L Ca2+), respectively, while the A-band length maintained at 1.50 μm and I-band changed from 0.7~1.6 μm. Mechanical test found that the elasticity of different bands or lines in the same physiological state varied in the order of Z-line>M-line>overlap>I-band. Conclusions Critical Ca2+ concentration for muscle fiber activation was 5 mmol/L, and sarcomere length distributions were in line with the relative slip theory and structure model, and AFM was the potential tool for the high resolution study on ultrastructure and mechanical properties of the muscle fibers.

Abstract:Objective To investigate the gait stability of healthy old and young adult volunteers during walking using the nonlinear time series analysis method so as to comprehensively assess the dynamic balance of human and provide important references for the prediction of fall risk. Methods The Vicon motion capture system was used to collect three-dimensional kinematic data of healthy volunteers (seven old subjects and ten young subjects) at different walking speed (80%, 100%, 120% of the natural walking speed). The anterior-posterior and medio-lateral motions of the seventh cervical and tenth thoracic vertebrae, as well as the flexion-extension and abduction-adduction angles of the lower extremity joints, were obtained from 30 consecutive gait cycles to calculate the largest Lyapunov exponents and analyze the difference of gait stability between the old and young group and the influence of walking speed on gait stability. Results The gait stability in the young group was better than that in the old group, and there were significant differences in certain motion segments (P＜0.01). The gait stability in both groups were reduced with the increase of speed (P＜0.05). Conclusions The largest Lyapunov exponent based on nonlinear time series analysis method can be used to effectively and quantitatively analyze the gait stability of each motion segment in human during walking.

Abstract:Objective To study the postoperative effects on hearing restoration after different types of ossicular reconstruction with partial ossicular replacement prosthesis (PORP). Methods CT data of the right ear from a healthy volunteer were digitalized and imported into PATRAN software to reconstruct the 3D finite element model of the ear by a self compiling program. Dynamic analysis was conducted on the sound transmission to make comparison between the calculated results and experimental data. Results Results of the dynamic analysis for normal human ear were in good agreement with the experiment data, which confirmed the validity of the FE model. At the frequency between 0.1~10 kHz, hearing restoration with partial retaining the handle of malleus was better than that without retention after the replacement of PORP, and the value of hearing restoration was between 11.56~28.91 dB. The maximum stress of tympanic membrane with partial retaining the handle of malleus was less than that without retaining. At the frequency between 0.1~0.6 kHz as well as between 2~10 kHz, better hearing restoration was obtained when the thickness of the cartilage slice was 2.0 mm. At the frequency between 0.6~2 kHz, better hearing restoration was obtained when the thickness of the cartilage slice was 0.1 mm. Conclusions For ossicular reconstruction with PORP, the effect of retaining the handle of malleus was much better than that without retaining. The effect of hearing restoration was better when the thickness of the cartilage placed between the tympanic membrane and the contact surface of the PORP was within the range of 0.1~2.0 mm.

Abstract:Objective To identify the differentially expressed genes of osteoblasts under the stimulation of mechano growth factor E peptide( MGF-Ct24E) and mechanical stress by microarray analysis. Methods Primary osteoblasts were cultured in vitro, which were subjected to mechanical stimulation(with the mechanical strain of 12% and frequency of 0.5 Hz) and MGF-Ct24E treatment(50 mg/L), respectively. The gene expression profiles were analysed by cDNA microarrys and quantitative PCR was used to validate the microarray data. ResultsCompared with the control group, 1 866 genes were found to have differentially expressed in the mechanical loading group, in which 1 113 genes were up-regulated, while 753 genes were down-regulated. 1 178 genes were found to have differentially expressed in the MGF-Ct24E group, in which 796 genes were up-regulated and 382 genes were down-regulated. GO analysis suggested that the gene expression profile of MGF-Ct24E group was consistent with that of the mechanical loading group and differentially expressed genes were mainly involved in cell proliferation and differentiation, response to mechanical stress and mechaotransduction. ConclusionsThe microarray analysis showed that MGF-Ct24E treatment had similar effects with the mechanical loading on the gene expression of osteoblasts, which might provide a novel approach to study the usage of MGF-Ct24E for treating bone repair in the absence of mechanical stimulation.

Abstract:Objective To investigate the effect of different mechanical environment ( in vivo and in vitro) on expression of basic fibroblast growth factor (bFGF) and explore the role of mechanical stimulation in corneal tissue repair after laser assisted in situ keratomileusis (LASIK) surgery. Methods Animal models by LASIK surgery were established to keep the corneas under different mechanical environment. The experimental animals were killed at the first week or the first month after LASIK surgery to obtain the corneas. In addition, the primary corneal fibroblasts were subjected to cyclic mechanical stretch (0.1 Hz; 5%, 10%, 15% stretch; 6 h or 24 h) using Flexcell 4 000 tension system. Expression of bFGF was determined by ELISA method. Results At the first week after LASIK surgery, expression of bFGF was increased significantly in 30% group (residual stroma bed accounting for 30% of the whole cornea), as compared with the control group (P<0.05), and then it was decreased to the normal level in all groups at the first month after LASIK surgery. Analysis on the same surgery method at different time showed that there were significant differences only in 30% group at the first week and month (P<0.05). Cyclic stretch experiment in vitro indicated that bFGF expression in 15% stretch group was significantly increased after 6 h than that in the control group (P<0.05), with a significant decrease after 24 h (P<0.05). Conclusions Mechanical stimulation can regulate bFGF expression of corneal tissues and corneal frbroblasts, and bFGF plays a positive role in the early corneal tissue repair after LASIK surgery.

Abstract:Objective To establish the cutting force model of biopsy needle from the aspect of cutting mechanics and to reveal the relationship between cutting force of the needle and geometry of the needle tip. Methods Based on the traditional theory of metal cutting, a mathematical model of biopsy needle geometry was established. The needle cutting edge was divided into a series of elementary cutting tools (ECTs) with varying inclination and normal rake angles. The oblique cutting experiment was performed on the soft tissue cutting setup and a functional cutting force model was developed based on these ECTs. Results The force model could predict the cutting force of biopsy needle well. When the bevel angle ξwas 30°, 45° and 60°, the experimental forces of 18 G biopsy needle were 1.33, 1.38, and 1.56 N, respectively, while the predicted values were 1.29, 1.43, and 1.52 N, respectively. The relative error was less than 5%. Conclusions This cutting force model of biopsy needle quantitatively describes the relationship between the cutting force and geometry of the needle tip. The results can be used for the design and evaluation of new needle, and preoperative planning of needle insertion trajectory.

Abstract:Objective An arterial blood pressure fitting method, based on pulse wave signal and vessel elastic chamber model, was researched and implemented to meet the requirement of continuous blood pressure (BP) measurement in health care. Methods Photoplethysmography (PPG) signal, electrocardiograph (ECG) signal and BP data of the subjects were collected by a self developed wearable physiological monitoring system. In accordance with the temporal relation between ECG and PPG signals, the equation of regression analysis on systolic BP value and pulse wave transient time (PWTT) was deduced, and the diastolic BP measurement was achieved by coefficients analysis on PPG wave and parameter calculation on blood vessel single elastic chamber model. Results The experiment results showed that the mean difference and the standard deviation of the method were （0.51±0.74) kPa［(384±5.54) mmHg］, reaching the standard (0.665±1.064) kPa［(5±8) mmHg］ proposed by Association for the Advancement of Medical Instrumentation (AAMI). Conclusions Human blood pressure can be estimated by the pulse wave signal and elastic chamber model, which provides a new method for the continuous blood pressure measurement.

Abstract:Objective To study the rule of aerosol deposition in human upper respiratory tract and analyze the impact of respiratory pattern on aerosol deposition. Methods A computer model of human upper respiratory tract was established first. CFD (computational fluid dynamics) method was then used to numerically simulate the aerosol deposition within the human upper respiratory tract and the rule of aerosol deposition was analyzed. Results The efficiency of aerosol deposition in human upper respiratory tract was improved with the increase of inertial parameter. The breathing intensity and aerosol property had little impact on the pattern of aerosol deposition, which was at most in larynx due to the inertial impact and turbulent dispersion. Under the mode of cyclic inhalation, the aerosol deposition efficiency was higher at unsteady respiratory than that at steady respiratory, at cyclic inhalation than at cyclic exhalation. Conclusions Inertial impact is the main key deposition mechanism for micro aerosol, while turbulent dispersion, secondary flow and recirculation flow have an equally important impact on aerosol deposition in human respiratory tract.

Abstract:Objective To establish a numerical calculation and analysis model of lumbar disc herniation so as to provide a method of detecting and assessing the mechanical mechanism of lumbar disc herniation. Methods Based on CT of a healthy adult, the vertebra and intervertebral disc of lumbar 4~5 segment were reconstructed by Mimics 10.01 software and Geomagic 10.0 software, respectively. By adding the lumbar attaching ligaments and transforming the corresponding material properties of the extruded disc in Ansys software, the finite element model of L4~5 was established to create the intact disc and extruded disc model. The finite element method was employed to simulate the biomechanical properties of the two models under the loads of axial compression, flexion, lateral bending, extension and rotation. Results After the lumbar disc was extruded, the stress distribution on the disc and the ability of load transfer were changed. The stress was concentrated at the posterior lateral of annulus fibrous. Under the same loads, the maximum deformation of the extruded disc was larger than that of the intact disc. The contact forces of the facet joints in the extruded disc model were larger than that in the intact disc model. Conclusions After the lumbar disc was extruded, the load-bearing capacity was decreased and the stress level of the articular process was increased, and the loads on the facet joints were also enhanced, leading to the decline of stability in the lumbar vertebrae.

Abstract:Objective To discuss the method for defining personalized materials properties of the fresh human long bone with alcohol treatment and the effect from the number of bone materials on finite element results. Methods Based on images from CT scans, a three dimensional solid model of the long bone was established in Mimics, which was then classified into the cortical bone, cancellous bone and marrow in Hypermesh. Based on relevant empirical formulas, material parameters of the cortical bone and cancellous bone were given, respectively, and 5 finite element analysis (FEA) models with different numbers of materials were set up. The simulation for linear elasticity of the compression was carried out in Abaqus and the results were validated by in vitro verification test. Results Under the end displacement ranging from 0 to 1 mm, the average relative error between the simulation results and the experimental data for holistic force-displacement was about 10%, when the materials number was defined as 1 kind of the cancellous bone and over 10 kinds of the cortical bone. And the average relative error between the simulation results and the experimental data for the deformation of the measurement points was 14.6%. The error of holistic force displacement for 1 kind of the cortical bone was 2.83% when the end displacement ranged from 0 to 0.5 mm. Conclusions (1) Using the gray value of CT scans, materials properties of the main component of the bone could be defined accurately. (2) The simulation result was greatly affected by the material number of the cortical bone, and defining 10 kinds of the cortical bone could satisfy the FEA need. (3) The FEA model with 1 kind of the cortical bone also could satisfy the need of analysis under small deformation.

Abstract:Adult-acquired flatfoot deformity (AAFD), which is mainly caused by posterior tibial tendon dysfunction (PTTD), is a common foot and ankle disease, and most of the deformities are flexible. How to explain the pathogenesis of AAFD and choose proper surgical treatment for the deformity has become a hot research focus nowadays. With the development of in vitro modeling technique for flatfoot, the accuracy and repeatability of the biomechanical tests have been gradually recognized, and the research results have also provided important theoretical basis for the clinical treatment of flatfoot deformity. In this article, the biomechanical mechanism of AAFD caused by PTTD, and the various modeling methods of flatfoot based on cadaver or finite element model were veviewed. The biomechanical characteristics of different reconstruction procedures in relative basic researches on flatfoot deformity were also analyzed and compared. The author believes that on the basis of simulating the dynamic stability of foot by tendon loading, the in vitro model of flexible flatfoot established by selective ligaments section is more reliable, and the reconstruction procedure adopted by various flatfoot models has different biomechanical characteristics. The soft tissue reconstruction and the bony procedures should be performed at the same time, and individual bony procedures should be chosen based on the degree and feature of the deformity.