Abstract:Objective To propose some detailed methods for diagnosis of aseptic loosening failure in clinic by studying the mechanical mechanism and the specific causes of aseptic loosening failure after the total hip arthroplasty (THA). Methods The causes of aseptic loosening were investigated from the view of biomechanics, such as strength of the bone cement layer, interface fretting, stress shielding, wear and osteolysis; the relationships between aseptic loosening failure and products, clinical and patient factors were analyzed; the method to detect loosening before the revision surgery was also studied. Results The reasoning route for aseptic loosening failure analysis after THA was proposed, and detection of aseptic loosening with fluoroscopic analysis (FSA) technique before the revision surgery was conducted successfully. Conclusions The reasoning route for aseptic loosening failure analysis can help to discover reasons of failure occurrence. Loosening can be detected and confirmed in vivo by FSA method, which can also assist the clinician for diagnosis and treatment of aseptic loosening after the THA.

Abstract:Objective To investigate effects of aging on the fracture mechanical behavior of human dentin with finite element numerical method. Methods The finite element model was established according to the typical compact tension specimen in the experiment. The stable crack growth in human dentin was simulated with the cohesive zone model to compare the crack extensions of the young and aged dentin. Results The growth toughness and plateau toughness of the aged dentin were 0.51 and 1.19 MPa?m1/2, respectively, which were significantly lower than those of the young dentin (7.48, 1.71 MPa?m1/2). However, the initiation toughness of the young and aged dentin showed no significant difference with 0.51 and 0.38 MPa?m1/2, respectively. Conclusions The crack growth resistance of human dentin is decreased significantly with aging. Based on the cohesive zone model, the crack growth behavior of biological hard tissue, whose mechanical properties are related with age (such as the human dentin), can be well predicted by using numerical methods.

Abstract:Objective To investigate the influence of acetabular morphology on contact mechanics of the human hip joint. Methods One anatomical finite element (FE) model of natural hip joint and three simplified FE models with different acetabular geometry were established to study the contact mechanics of hip joint under gait loads. Results (1) Contact predicted by the anatomical model was mainly distributed in the acetabular medial-superior area, from anterior to posterior, with the peak contact pressure occurred in the anterior-superior area; (2) Compared with the anatomical model, the rotational ellipsoid produced similar contact behavior, while the sphere and the rotational conchoids predicted that contact was distributed in the medial-lateral direction; (3) The rotational ellipsoid predicted the largest contact area and the lowest peak contact pressure and Von-Mises stress; (4) The sphere and rotational conchoids had similar contact mechanical behavior. Conclusions Compared with the sphere and rotational conchoids, the rotational ellipsoid could be more preferable to represent the anatomical morphology of the acetabulum and its contact mechanics.

Abstract:ObjectiveTo develop a finite element computational model of the torso for the numerical simulation of mechanical responses of human torso to non-penetrating ballistic impact. MethodsBased on the CT data of a Chinese adult man, the finite element model of human torso was created by using the medical image processing software Mimics and the finite element pre-processing software HyperMesh. The pressure and acceleration response of the human torso outfitted with soft body armor to the ballistic impact from 9 mm ammunition at a velocity of 360 m/s was calculated numerically by the explicit finite element code LS-DYNA. ResultsThe finite element model of human torso including thoracic skeletal structure, organs, mediastinum and muscle/skin was established. The pressure response of heart, lung, liver and stomach, as well as the acceleration response of sternum were obtained by numerical calculation. It was found that the peak pressure and its time phase were dependent on the distance between the impact point and the measured point wherever in various organs or different position of an organ. Conclusions The finite element computational model of human torso outfitted with soft body armor is available for the simulation of human response to non-penetrating ballistic impact, and the simulated response can be used as evidence for the investigation on mechanism and protection of behind armor blunt frauma.

Abstract:Objective To obtain the axial elastic modulus of rabbit articular cartilage based on the ultrasound swelling observation technique and the triphasic theory, and to explore the triphasic mechanical properties of the osteoarthritis cartilage with different pathological grades. Methods The articular cartilage samples from rabbit knees were assessed according to the different pathological grades. The swelling strains were recorded based on the high frequency transient ultrasound measurement technique. The axial elastic modulus of the cartilage samples was extracted based on the fixed charge density, the water volume fraction and the triphasic model. Correlation analysis was also made. Results There were both significant differences in axial elastic modulus between the normal cartilages and among the osteoarthritis cartilage with different pathological grades (P<0.05). The value of axial elastic modulus decreased with the increase of osteoarthritis grades. For normal cartilage samples, the average axial elastic modulus was (15.87±6.30) MPa. For osteoarthritis cartilages of grade 1, 2 and 3, the value of axial elastic modulus were (11.33±5.21), (9.15±5.68) and (6.05±4.99) MPa, respectively. Conclusions This study showed there are significant differences in triphasic mechanical properties of the articular cartilage with different osteoarthritis grades, which may provide some new thought for the quantitative assessment of osteoarthritis grade based on mechanical properties of cartilage.

Abstract:Objective To simulate the supination-external rotation ankle injury and establish a 3D finite element model of the ankle. Methods Based on CT images of the normal human ankle joint, the 3D model of the ankle with ligaments was established. The supination-external rotation ankle injuries with four different degrees of Lauge-Hanson were analyzed by finite element method. Distributions of the ankle joint stress and tibial articular surface pressure were obtained. Results The maximum stress was at the anterior tibiofibular ligament attachment point of the tibial under supination-external rotation loading. When the anterior tibiofibular ligament was ruptured, the maximum stress was at the interosseous membrane. After the interosseous membrane was ruptured, the high stress was at the posterior ligament of the ankle. When the posterior tibiofibular ligament was ruptured, the high stress was at the deltoid ligament. The high pressure was at the distal fibula or the rear of tibial articular surface. Conclusions The established ankle-foot 3D numerical model can be used for the mechanical analysis of supination-externalrotation ankle injury. The calculated distributions of the ankle stress and the tibial articular surface pressure were in agreement with the description of Lauge-Hanson classification.

Abstract:Objective To explore the effect of avascular necrosis cystic degeneration on distribution of bone density. Methods Based on the bone reconstruction model of Weinans and Huiskes, bone density distribution in normal femoral head and in femoral head with avascular necrosis cystic degeneration were calculated by finite element analysis. Results (1) The medial system of lamellae, lateral system of lamellae, intertrochanteric arch and Ward's triangle were generated on the normal proximal femur under simulation. (2) If a primary cystic degeneration occurred, a secondary cystic area would appear below the primary one and its bone density would decrease dramatically with the primary cystic area increased. Cystic degeneration would also change the femoral bearing truss system. Conclusions (1) Wolff’s law on bone remodeling is consistent with modern topology optimization theory. (2) If cystic degeneration appeared due to avascular necrosis of the femoral head, it should be treated timely to prevent the secondary cystic degeneration and collapse of the femoral head.

Abstract:Objective To optimize the baseline on the trapezoidal cross section of stent wires, so as to reduce the risk of intracranial saccular aneurysm rupture after the implantation of such stents. Methods Thirty-eight trapezoidal cross-section wire stents with different baselines were constructed to establish the finite element models. Numerical simulation by fluid-solid interaction method was conducted to calculate 38 maximum pressure gradients on the aneurysm wall. GRNN (general regression neural network) and GA (genetic algorithm) were used to optimize the baseline on the cross-section of stents with trapezoidal cross-section wire so as to minimize the maximal pressure gradient on the aneurysm wall. Results Compared with the traditional stent with rectangular cross-section wire, the maximal pressure gradient on the a neurysm wall was reduced by 7.86% after the implantation with the optimized stent with trapezoidal cross-section wire. Conclusions The combination of GRNN and GA is an effective approach for stent optimization.

Abstract:Objective To investigate the effect of mechanical loading with different magnitudes on the proliferation, differentiation and activity of preosteoclasts and osteoclasts. Methods One group of RAW264.7 preosteoclastic cells cultured in osteoclast inductive medium were subjected to the cyclic tensile strain for three days, and then cultured for four days; the other group of RAW264.7 cells were induced in osteoclast inductive medium for four days to be osteoclasts, then subjected to the cyclic tensile strain for three days. Results Under the tensile strain at different magnitudes, the proliferation variations in two groups of RAW264.7 cells were approximately identical, but changes in the activities of tartrate-resistant acid phosphatage (TRAP) and numbers of TRAP-positive multinucleated cells (osteoclasts) in the two groups were significantly different. Under the moderate tensile strain (2 500 με), the reduction of TRAP activity and osteoclasts number were both the highest in the first group, and both the lowest in the second group. Conclusions The influence of different tensile strain on osteoclast differentiation and osteoclastic activity of preosteoclasts in early differentiation is different to that of the preosteoclasts already differentiated into osteoclasts.

Abstract:Objective To investigate the effects of substrate stiffness on the adhesion, spreading and migration of hepatocellular carcinoma cells as well as the regulation of cytoskeleton assembly and integrinβ1 expression, and to explore the role of substrate mechanical properties in the metastasis of hepatocellular carcinoma cells. Methods The polyarcylamide gel with different stiffness was achieved by varying the relative ratio of acrylamide to bis acrylamide. The substrate surface was cross linked with extracellular matrix molecules for cell adhesion. The adhesion, spreading and migration of hepatocellular carcinoma cells on substrates with different stiffness were recorded by phase contrast microscope and made quantitative analysis by Image J software. The cytoskeleton assembly on substrates with different stiffness was detected by immunofluorences assay, and the expression of integrinβ1on different substrates was measured by flow cytometer. Results The rigid substrate enhanced the adhesion and spreading of hepatocellular carcinoma cells in shortened time. Neither the soft (1.1 kPa) nor over rigid (glass) substrate facilitated the migration of hepatocellular carcinoma cells, and the maximum migration velocity was found on the substrate with moderate stiffness（10.7 kPa）. The rigid substrate could promote cytoskeleton assembly and integrinβ1 expression. Conclusions The effects of substrate stiffness on adhesion, spreading and migration of hepatocellular carcinoma cells are regulated by the cytoskeleton assembly and integrin expression.

Abstract:Objective To develop a batch process method for kinematics data of mass population based on MATLAB. Methods Based on MATLAB, the original coordinate data of markers from motion capture system were first batch-read with interpolation processing for eliminating the error points. The body-fixed base of contiguous rigid body attached on human body was then constructed as the reference base and body-fixed base of relative joint kinematics computing. The flexion/extension, abduction/adduction, internal and external rotation angular displacement, angular velocity and angular acceleration of joints were obtained based on the rigid body kinematics, the basic description of rigid body posture and the direction cosine matrix. Results Taking climbing upstairs and squatting as samples, the joint kinematics of lower extremity were analyzed and calculated by the batch process method for kinematics data of mass population based on MATLAB to prove the effectiveness and accuracy of the method. Conclusions The batch process method for kinematics data of mass population based on MATLAB was proved to be effective and accurate, and can be provided as a statistical analysis tool for anthropometry, human engineering, etc.

Abstract:Objective To explore the influence of basketball shoes on impact force and corresponding muscle activation in the lower limb during the active and passive landing. Methods Twelve male ball players wearing two types of shoes (basketball shoes with cushioning insole vs. control shoes) performed the jump drop and passive landing from three different height on the tiltable platform. The dynamometric platform and electromyography (EMG) measurement system were used to collect the impact forces and EMG data from 5 major muscles in the lower limb simultaneously. Results As for the active drop jump, wearing basketball shoes didn’t have any effect on the amplitude/frequency of impact forces and muscle activation in the lower limb. However, during the passive landing, wearing basketball shoes could significantly decrease the amplitude of impact forces, the peak loading rate and the input frequency (P<0.05), and the post-activation of major muscles in the lower limb were also significantly decreased (P<0.05). Conclusions During the active landing, the intervention of footwear shows no significantly influence on characteristics of impact forces and muscle activation. However, when the human body does not under the full control of landing, wearing basketball shoes can change the input frequency, decrease the muscle post-activation, and play a positive role in preventing the sports injuries and enhancing the metabolic efficiency during the landing.

Abstract:Objective To investigate the effect from local vibration stimulus on the total hemoglobin and oxygen hemoglobin change of biceps muscles. Methods Arm Vibration Massage Band was used by twelve volunteers(female college students) to receive the local vibration stimulus. By using the Near Infrared Spectroscopy, the total hemoglobin and oxygen hemoglobin of biceps muscles were measured at 10th minute before vibration, 10th minute during vibration and at 15th minute after vibration, respectively, to get the variation tendency at each minute. Repeated measured one-way ANOVA was used to compare the differences in the test Results. Results The total hemoglobin of biceps muscles was significantly increased at 15th minute after vibration (P<0.05), and the total oxygen hemoglobin of biceps muscles was significantly increased at 10th minute during vibration and 15th minute after vibration (P<0.05). The maximum value of the total hemoglobin and oxygen hemoglobin occurred at 5th minute during 10-minute vibration stimulus, and compared with 10th minute before vibration, the total hemoglobin and oxygen hemoglobin could continue to be higher at 15th minute after vibration with a stable tendency. Conclusions The local vibration stimulus can acutely increase the total hemoglobin and oxygen hemoglobin of biceps muscles, which can reach the maximum value with sustained vibration stimulus for at least 5 minutes.

Abstract:Objective To investigate changes in plantar pressure distributions on forefoot and hindfoot region during the support phase under different Achilles tensile loads. Methods Six fresh frozen human below-knee specimens were used and placed on the material testing machine. The ankles were kept in neutral position and the axial load of 350 N was applied on the specimens. Achilles tensile loads varied from 0 kg to 80 kg (0, 100, 200, 300, 400, 500, 600, 700, 800 N）were applied by weights. Two scales were placed under the forefoot and hindfoot region of the specimen, respectively, to record the pressure under the Achilles tensile loads. Results With the Increasing Achilles tensile force, the pressure on forefoot region was increasing, while the pressure on the hindfoot was decreasing. The percentage of average plantar pressure in forefoot and hindfoot region over the total plantar pressures presented a linear relationship with the Achilles tensile force (P<0.01, R2=0.996). Conclusions The support phase of foot in vitro was simulated and the plantar pressure distributions on forefoot and hindfoot region was investigated in this paper. The result can provide theoretical evidences for some diseases (such as diabetic foot ulcers, metatarsalgia) caused by plantar pressure changes due to Achilles tensile contracture in clinic.

Abstract:Objective To compare the biomechanical behavior of a triple Endobutton technique for anatomic reconstruction of coracoclavicular ligament and with a modified Weaver-Dunn procedure. Methods Twelve fresh frozen cadaveric shoulders were applied with 70 N in superior, anterior and posterior direction, respectively, to measure displacement of the acromioclavicular joint. The failure test with the load at the rate of 25 mm/min was conducted to record the failure load and failure mode. The specimens were then randomly assigned to 2 groups: the triple Endobutton technique group and the modified Weaver-Dunn procedure group for reconstruction and to conduct displacement test and failure test again. The stability and mechanical strength of acromioclavicular joints after reconstruction under different states were then compared. Results The triple Endobutton technique group had significantly less anterior ((8.72±1.41) mm vs (37.03±5.05) mm) and posterior ((8.03±3.68) mm vs (14.85±1.89) mm) displacement than that in the modified Weaver-Dunn procedure group after reconstruction (P<0.05), and the former had similar displacement ((7.81±2.22) mm anterior and (7.16±1.95) mm posterior) as compared to the intact state. There were no significant differences in superior displacement among the groups. The modified Weaver-Dunn procedure group had significantly smaller failure loads ((172±9) N) than that in the triple Endobutton technique group ((687±115) N) and the intact ligament group ((685±234) N) (P<0.05). Conclusions The triple Endobutton technique has less anterior and posterior displacement and its stability is more closely approximate to the intact ligament; meanwhile, it has similar strength as coracoclavicular ligaments, which can better restore the function of coracoclavicular ligaments.

Abstract:Objective To investigate the feasibility of a novel Ni-Ti shape memory alloy vertebral reduction fixator for treating vertebral compression fractures. Methods The experimental thoracic-lumbar fracture units made from adult fresh-frozen cadaver vertebral specimens were randomly assigned to 3 groups for testing: control group, percutaneous kyphoplasty group (PKP group) and percutaneous vertebral body reduction fixator group (Ni-Ti fixator group). The vertebral height and peak load on the specimens were measured before and after the two kinds of operations, respectively, to compare the restoration of compression fractures. Results Compared with the control group, both the PKP and Ni-Ti fixator groups could significantly restore the collapse of the vertebral endplate. The vertebral height of the PKP group and Ni-Ti fixator group was raised from (2.01±0.21) and (2.00±0.18)cm before the operation to (2.27±0.18) and (2.31±0.17) cm after the operation, respectively. The peak loads on the vertebrae for the PKP and Ni-Ti fixator group were (2 880.75±126.17) and (2 888.00±144.69) N, respectively, with no statistical differences found in between, while those for the control group were (2 017.17±163.71) N. Conclusions The Ni-Ti shape memory alloy vertebral reduction fixator can effectively restore the collapse of the vertebral endplate, maintaining the immediate biomechanical stability of the vertebrae, and reducing the adverse reactions due to the injection of polymethyl methacrylate (PMMA) cement during percutaneous kyphoplasty.

Abstract:Objective To study the effect from the content change in hydroxyapatite (HA) on mechanical properties of polyvinyl alcohol/hydroxyapatite(PVA/HA)composite hydrogel and its load bearing characteristics based on experiment and finite element simulation. Methods The compression and stress relaxation tests of PVA/HA composite hydrogel were performed on the UMT test machine. Through the simulation and experimental results, the load-bearing characteristics of PVA/HA composite hydrogel and the effect of HA on PVA/HA composite hydrogel performance were investigated. Results With HA content increasing, the compression modulus of PVA/HA composite hydrogel was first increased and then decreased, while its permeability coefficient was first decreased and then increased. When the HA content was 3%，the compression modulus of PVA/HA composite hy drogel reached maximum (1.25 MPa)and its permeability coefficient reached minimum(1.59×10-3 mm4?N-1?s-1). The fluid bearing proportion of PVA/HA composite hydrogel was first increased and then decreased with the loading time increasing, which presented a nonlinear change. The proportion of the fluid bearing was significantly increased after HA added into PVA / HA composite hydrogel. The stress relaxation rate was first increased and then decreased with HA content increasing. Under the same loaded displacement, PVA / HA composite hydrogel with 3% HA content could disperse more contact stress. Conclusions The internal bearing characteristics of PVA / HA composite hydrogel have a great impact on its mechanical properties. When the HA content is 3%, the PVA / HA composite hydrogel has the best mechanical properties, which are closer to those of the natural articular cartilage.

Abstract:Objective To report the method used to treat knee joint contracture by static progressive stretch and evaluate its curative effect. Methods Sixteen patients with knee joint contracture after the orthopedic surgery were selected，including 2 femoral shaft fractures, 5 distal femur fracturs, 4 patellar fractures, 5 tibial plateau fractures. The average course of postoperative treatment was 13.7 weeks. Static progressive stretch (SPS) was applied by isokinetic dynamometer, with 5 sets of stretch in one direction for one treatment, each set lasts 5 minutes with 1 minute interval for rest, and the degree of joint position was increased progressively for the next set. Patients received SPS 2 times per day, 30 minutes per time, 5 days per week, and the course of treatment lasted 2 months. The knee flexion degree (F), extension degree (E) and range of motion (R) were measured by goniometer before treatment, after treatment, 6 months after treatment, respectively. Results E, F and R of the knee joint were improved significantly both after treatment and 6 months after treatment as compared with those before treatment. Conclusions Application of isokinetic dynamometer by static progressive stretch can be used to treat knee joint contracture effectively.

Abstract:To be the representative fruition resulted from the rapid development in micro-nano theory and technology, atomic force microscopy (AFM) has greatly promoted the expansion of biological research in micro-nano scale, and facilitated the birth and development of micro-nano biology as an important technique in its 25-year evolutional progress. Based on the fundamental principles and detection modes of AFM, as well as the author’s research findings and work experience in this field, the paper reviews the application of AFM in the study on ultrastructure and biomechanical properties of cells and biomacromolecules in the aspects of biological structure and morphology, surface physicochemical characterization and mechanical manipulation of biological macromolecules, and focus on some important scientific and technical problems on AFM in micro-nano biomedical research needed to be improved and solved urgently, with exploratory insights and recommendations for potential users in ultrastructure and biomechanics of cells and biomacromolecules.