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Abstract:Objective To explore the effects of dynamic axial compressive strain on the mRNA expression of bone formation related-genes in osteoblasts seeded in 3D silk fibroin scaffolds. Methods In the experimental group, MC3T3-E1 cells were seeded in 3D scaffolds and then subjected to dynamic axial compressive strain (at amplitude of 5% and frequency of 1 Hz, 30 min/day for 20 days), while in the control group, MC3T3-E1 cells were cultured statically without any mechanical stimulation. The gene expression of alkaline phosphatase (ALP), collagenⅠ(COL-Ⅰ), runt-related transcription factor 2 (Runx2), osterix (Osx), osteocalcin (OCN) was detected by real-time PCR. Results Under cyclic axial compressive strain, the Runx2, Osx and COLⅠmRNA levels increased by 280%, 68.9% and 79.6%, respectively, while the ALP and OC mRNA levels also up-regulated by 10.7% and 26.9%, respectively. There were significant differences in mRNA expression of osteogenesis-related genes between the experimental group and control group (P＜0.05). Conclusions Under the stimulation of cyclic axial compressive strain, the osteogenic differentiation of osteoblasts seeded in the silk fibroin scaffolds is promoted, with a significant up-regulation in the mRNA expression of COLⅠ, Runx2, Osx and OCN, which suggests that the stimulation of compressive stress at physiologic magnitude could be one of important mechanisms in promoting fracture healing. This research finding will be important for the clinic application of mechanical stimuli-mediated cell therapy for bone defection.

Abstract:Objective To compare contact mechanics of cartilage in normal hip and that in hip with Cam-type femoroacetabular impingement (FAI) using finite element method. Methods The 3D finite element models of normal hip and Cam-type FAI hip joints with varied Alpha angles were constructed. The contact pressures and stresses of intra-articular cartilages during routine daily activities, such as walking, sitting and standing, were calculated. Results During the whole gait cycle, the distribution of cartilage contact pressures on Cam-type FAI hip models with varied Alpha angles was similar to that in normal hip model, and no concentrated areas of high contact pressures and Von Mises stresses appeared. While during the motion of sitting and standing, the cartilage contact pressure on Cam-type FAI hip models was higher than that in normal hip model and increased with the Alpha angle increasing, and the contact area was mainly located at anterosuperior region of acetabular rim, where a concentration of high contact pressures and Von Mises stresses appeared. Conclusions Mode of motion is the key factor which causes changes of cartilage contact mechanics in Cam type FAI joints. Abnormally high cartilage contact pressures and Von Mises stresses might be the inducement to cartilage degeneration and eventually lead to osteoarthritis.

Abstract:Objective To analyze the contact failure of monolithic lithium disilicate CAD/CAM crowns by experiment and numerical simulation, and explore the influences of adhesives aging in water on load-bearing capacity of the crowns. Methods The specimens of sectioned monolithic lithium disilicate crowns were designed and manufactured, and evenly divided into two groups and stored in the air and in the distilled water for 30 days, respectively. The specimens were then subjected to monotonic contact loads to compare and analyze their load-bearing capacity. The fractured surfaces and adhesive interfaces of the specimens were observed by scanning electronic microscope. Meanwhile, the stress distribution on the crowns was calculated by numerical simulation to analyze the adhesives aging influence on load-bearing capacity of the crowns. Results The fracture loads on crowns stored in the air and in the water were (561.51 ± 65.66) N and (398.09 ± 90.20) N, respectively, indicating a significant difference. The tensile stress increased considerably at lower surface of the ceramic crown due to the reduction of adhesive strength at the interface of ceramic crown and substrate, which could increase the propensity of contact failure. Conclusions The adhesives aging in water reduces the bonding strength, and accordingly changes the tensile stress distributions, which can lower the load bearing capacity of the lithium disilicate crowns. The research finding provides references for the design and manufacturing of all-ceramic CAD/CAM restored crowns in clinic.

Abstract:Objective To study the anisotropic mechanical properties of the thoracic aorta in porcine. Methods Twenty-one porcine thoracic aortas were collected and categorized into three groups. The aortas were then cut through in their axial directions and expanded into two dimensional planes. Then, by setting the length direction of the planar aortas (i.e., axial directions of the aortas) as 0°, each planar aorta was counterclockwisely cut into 8 samples with orientation of 30°, 45°, 60°, 90°, 120°, 135°, 150° and 180°, respectively. Finally, the uniaxial tensile tests were applied on three groups of samples at the loading rates of 1, 5 and 10 mm/min, respectively, to obtain the elastic modulus and ultimate stress of the aorta in different directions and at different loading rates. Results The stress-strain curves exhibited different viscoelastic behaviors. With the increase of sample orientations, the elastic modulus gradually increased from 30°, reached the maximum value at 90°, and then gradually decreased till 180°. The variation trend of ultimate stress was similar to that of elastic modulus. Moreover, different loading rates showed a significant influence on the results of elastic modulus and ultimate stress, but a weak influence on the anisotropic degree. Conclusions The porcine thoracic aorta is highly anisotropic. This research finding provides parameter references for assignment of material properties in finite element modeling, and is significant for understanding biomechanical properties of the arteries.

Abstract:Objective To establish 3D finite element of human cervicothoracic spine C5-T2 based on CT images, and explore effects on stability of the cervicothoracic spine after total spondylectomy (TS) by using various combinations of internal fixation devices (pedicle screw, titanium mesh, steel plate), including the stress distributions on these internal fixation devices. Methods The intact finite element model of cervicothoracic spine C5-T2 was established and validated by comparing the model’s range of motion (ROM) with that of other in vitro experiments. Then four reconstruction models after TS of cervical spine segment C7 were established: TM+AP+DPS model (titanium mesh + anterior plate + posterior double-segmental pedicle screw), TM+AP+SPS model (titanium mesh + anterior plate + posterior single-segmental pedicle screw), TM+DPS model (titanium mesh + posterior double-segmental pedicle screw), AP+DPS model (anterior plate + posterior double-segmental pedicle screw). ROM of each reconstruction model under flexion, extension, lateral bending and rotation and stress distributions on these internal fixation devices were then analyzed. Results ROM of the reconstruction segments was greatly reduced by over 93% as compare to that of the intact model. Stress concentration phenomenon appeared on the titanium mesh in the TM+AP+SPS model. Conclusions The fixation effects of four reconstruction models are similar. Stresses on 3 DPS fixed-models are more evenly distributed, indicating that the overall stability of DPS fixed-model is superior to that of SPS fixed-model.

Abstract:Objective To develop a double-gasbag weight loss equipment based on body weight support treadmill training (BWSTT)，and analyze the reasonability of the structure design. Methods The mathematical model of double gasbags in the process of air inflation was established, and the 3D model of double gasbags was established and meshed using Gambit; the analog computation for gas flow of the gasbag was conducted using Fluent; normal subjects with body weight below 80 kg were selected for clinical experiments based on designing and roughing of the prototype. Results The inflation time of double gasbags was 16.9 s and the maximum weight loss percentage was 90%; the pressure inside double gasbags was 2 kPa, and the relationship between the weight loss percentage and inside pressure of the gasbag was obtained by clinical experiments, which verified the reasonability of the gasbag structure. Conclusions The double-gasbag structure can meet the requirements of weigh loss training, which provides an effective weight loss support method and a feasible structural design for patients with lower limb dysfunction during rehabilitation training.

Abstract:Objective To investigate the influence from compressing manipulation by flexing hip and knee in supine position on stress distributions in the pelvis and strain distributions in the sacroiliac joints by 3D finite element method, and discuss the possibility of moving the whole sacroiliac joints under such manipulation. Methods A 3D finite element model of the normal pelvis was constructed based on CT images. According to the manipulation principle, the compressing force in flexing hip and knee was decomposed in two directions, and loaded on the 3D finite element model to calculate stress of the pelvis and strain of the sacroiliac joints. Results Under the loading of simulative manipulation, stress of the pelvis was mainly located at 1/3 part of the anterior inferior of the sacroiliac joints, the greater sciatic notch, and the middle 1/3 part of the inferior and anterior of gluteal lines. The maximum strain of the sacroiliac joints was mainly located in the posterior superior, posterior inferior and central 1/2 part of the sacroiliac joints. Conclusions The compressing manipulation by flexing hip and knee can only move 1/3 part of the interior of the sacroiliac joints, rather than the whole of the sacroiliac joints.

Abstract:Objective To study effects of the bacterial biofilm at different growth stages on dynamic behavior of the titanium partial ossicular replacement prosthesis (PORP), so as to provide theoretical references for clinical treatment of diseases such as secretory otitis media. Methods Based on the CT scan images of normal human right ear and combined with the self compiling program, a 3D finite element model of the ear was reconstructed for dynamic analysis on sound conduction, and compared with the experimental data. The model was computed by harmonic response analysis method, and the sound conduction effect of bacterial biofilm grown on PORP at different growth stages was analyzed. Results The simulated amplitude of umbo and stapes footplate was in accordance with experimental measurements, which confirmed the validity of this numerical model. The existence of biofilm would cause 0-1.6 dB hearing loss at low frequencies. The growth of biofilm in the radial direction of PORP would cause 0-12 dB hearing loss at intermediate and high frequencies, especially at 8 kHz, and the hearing loss could be as high as 11.2 dB. Conclusions The bacterial biofilm has an impact on hearing by reducing the hearing at low frequencies while raising a little at high frequencies. The biofilm grown in the radial direction of PORP will reduce hearing, and affect the working efficiency of PORP on hearing restoration.

Abstract:Objective To numerically simulate the motion characteristics of red cells in shear flow, so as to provide theoretical references for exploring pathogenesis of cardiovascular diseases and conducting experimental studies of blood circulation. Methods The hyper-elastic model of red cells with membrane thickness was established. Based on feedback force method and finite element immersed boundary method, the deformation and motion of red cells in shear flow were simulated. The solid was defined as being hyper-elastic and solved by finite element method, while the fluid was defined as incompressible Newton fluid and solved by finite difference method. Results The tank tread-like motion characteristics of red cells in shear flow were gained by numerical simulation. The simulation results in the study were consistent with the results in the literature, which validated the reliability of the proposed method in the study. Conclusions The immersed boundary method adopted in the study shows obvious advantage in solving the large deformation problem by preferably demonstrating the whole process of red cell deformation in shear flow.

Abstract:Objective To analyze the influence of microporous parameters on mechanical behavior of bone tissue engineered-scaffolds, and provide references for optimizing the microporous structure design. Methods The finite element models of scaffolds with microporous structures were established by using ANYSYS software. The relationships between porosity and maximum equivalent stress as well as maximum total deformation were calculated. The effects of microporous spacing and diameter on maximum equivalent stress, maximum total deformation and internal strain were compared and analyzed. Results The influence rule of microporous spacing in x and y direction was consistent. With the increase of microporous spacing from 0.6 mm to 2.0 mm, the maximum equivalent stress reduced from 63.1 MPa to 46.3 MPa, the maximum total deformation reduced from 23.8 μm to 21.8 μm, and the proportion of the best strain range increased from 80% to 84%. However, with the increase of microporous spacing in z direction, the maximum equivalent stress increased from 38.3 MPa to 47.8 MPa, the maximum total deformation increased from 20. 8 μm to 22.8 μm, and the proportion of the best strain range fluctuated within the range of 82%-85%. With the increase of microporous diameter in x and y direction from 0.1 mm to 1.0 mm, the maximum equivalent stress increased from 32.4 MPa to 78.4 MPa, the maximum total deformation increased from 19.9 μm to 38.2 μm, and the proportion of the best strain range reduced from 90% to 53%. With the increase of microporous diameter in z direction, the maximum equivalent stress reduced from 58.8 MPa to 37.9 MPa, the maximum total deformation increased from 23.3 μm to 25.9 μm, and the proportion of the best strain range increased from 82% to 87%. Conclusions The greater the porosity and the proportion of the best strain range, the smaller maximum equivalent stress and maximum total deformation would be, the scaffolds would have the better biological and mechanical properties. These results have reference values for design and optimization of scaffold structure.

Abstract:Objective To investigate the effects of heel heights on gait of young women when going downstairs, and analyze the injury risk of women wearing high-heeled shoes during stair descent. Methods The gait from 17 young women wearing shoes with 4 different heel heights during their stair descent was measured by infrared high-speed motion capture system. The subjects’temporal parameters of gait and 3D joint angles of lower extremity were calculated and analyzed. Results Compared with flat shoes, the gait cycle increased when wearing 3 cm, 5 cm, 7 cm high-heeled shoes during stair descent, and the stance phase proportion and double-support stance phase proportion decreased, while the step width also decreased evidently. For 5 cm, 7 cm high-heeled shoes, the ankle range of motion (ROM) in the sagittal plane would reduce significantly, and for all the 3 cm, 5 cm, 7 cm high-heeled shoes, the ankle ROM in transverse plane would increase during stair descent. Wearing 3 cm, 5 cm high-heeled shoes could make the knee ROM in the sagittal plane significantly reduce, while wearing 3 cm, 5 cm, 7 cm high-heeled shoes, the knee ROM in the transverse plane would increase evidently. Wearing 5 cm, 7 cm high-heeled shoes, the maximum hip flexion angle was greater than that of wearing flat shoes, and the minimum hip flexion angle would be also greater when wearing 3 cm, 5 cm, 7 cm high-heeled shoes. Conclusions During stair descent, with the increase of heel heights, the gait cycle and swing phase proportion increase, while the stance phase proportion, double-support stance phase proportion and step width decrease, which will raise the risk of falling. Meanwhile, the knee and ankle ROMs in sagittal plane decrease gradually, while those in transverse plane come to increase. The research findings can help to further understand the influence of heel heights on gait characteristics and patterns during stair descent and provide reference for possible injury risk analysis.

Abstract:Objective To compare biomechanical characteristics of the knee joint during forward walking and backward walking. Methods Temporal-spatial, kinematics, kinetics parameters of 13 healthy young male volunteers were collected and compared by 3D motion capture system Vicon T40 and force platforms AMTI OR6-7. Results Compared with forward walking, the speed, cadence and stride length significantly decreased, while the gait cycle and stance phase percentage in gait cycle significantly increased during backward walking. In the sagittal plane, the range of motion (ROM), the maximum flexion/extension moment of the knee were smaller during backward walking. In the frontal plane, the ROM of knee varus/valgus during backward walking decreased, and the peak value of knee adduction moment significantly reduced in the early stance phase while significantly increased in the late stance phase of backward walking. The peak value of ground reaction force (GRF) was significantly larger in the early stance phase while smaller in the late stance phase during backward walking than that during forward walking. Conclusions The biomechanical characteristics of the knee joint during forward walking and backward walking are significantly different. Compared with forward walking, backward walking is helpful to reduce the medial compartment load in the early stance phase. Further study will be needed to investigate the effects of backward walking on knee joint loading in the late stance phase.

Abstract:Objective To investigate the possible effect of fully knee extension in sitting position with or without hip adduction on quadriceps imbalance in patients with patellofemoral pain syndrome (PFPS) by using surface electromyography (sEMG). Methods sEMG signals of vastus lateralis (VL) and vastus medialis oblique (VMO) muscles from 30 patients with PFPS as PFPS group and 30 healthy subjects as control group were collected, during their fully knee extension in sitting position with or without hip adduction. All the EMG data were then analyzed by extracting time domain indexes, namely, the root mean square (RMS) and integrated EMG (IEMG), to compare the balanced relationship between VL and VMO muscles. Results In PFPS group, there were no significant differences in VL time domain indexes during knee extension in sitting position with or without hip adduction, while statistical differences were found in VMO time domain indexes, and values of RMS and IEMG of VMO were higher under hip adduction, which indicated that the VMO muscle recruitment was strengthened. Conclusions Fully knee extension in sitting position with hip adduction can promote EMG activities of VMO muscles in patients with PFPS, which will help to balance the VL and VMO muscles.

Abstract:Objective To compare the biomechanical stability of distal femoral fracture with metaphyseal comminution fixed by unilateral or bilateral locking plates. Methods Distal femoral fracture with metaphyseal comminution (AO type C2.3 fracture) models were established in 22 artificial femoral specimens, and randomly divided into single plate group (group A, n=11) and double-plate group (group B, n=11). In group A, the fractures were fixed by lateral anatomic locking plates, and in group B, the fractures were fixed by lateral anatomical locking plates at lateral side and straight locking plates medially, respectively. In each group, 5 specimens were applied with axial compression and 3 specimens were applied with cyclic axial loading to measure medial subsidence, and the remaining 3 specimens were applied with failure loading to record the maximum load to failure. Results For axial compression, the mean medial subsidence of group A and group B were (2.61±0.28) mm and (0.46±0.08) mm, respectively. For cyclic axial loading, the mean medial subsidence of group A and group B were (1.56±0.12) mm and (0.43±0.05) mm, respectively. For failure loading, the maximum loads to failure of group A and group B were (5 567±338) N and (9 147±186) N, respectively, which all showed significant differences in two groups (P＜0.05). Conclusions For fixing distal femoral fracture with metaphyseal comminution, bilateral locking plates show stronger resistance to medial compression than unilateral locking plates and thus increase the stability of medial column of distal femur, which contributes to patient rehabilitation at early stage.

Abstract:开展漏斗胸微创矫形手术的生物力学研究以及阐述矫形机制对于提高矫形手术水平、开展个性化手术治疗、发展新的矫形手术方法和扩展微创矫形手术的应用范围具有重要意义。漏斗胸微创矫形手术已经成功用于儿童的漏斗胸矫形，但是成人漏斗胸矫形手术的应用还未普及。面对漏斗胸矫形可能会加重脊柱侧弯的风险，医生被迫放弃手术，致使部分漏斗胸合并脊柱侧弯的患者终生不能得到治疗。总结漏斗胸微创矫形手术的生物力学研究进展，包括胸廓模型的三维重建、矫形模型的应用、矫形过程的数值模拟以及数值模拟结果在临床的应用。结合成人漏斗胸矫形数值模拟的特点提出解决方法，并针对漏斗胸的生物力学研究现状提出需要解决的问题，如计算模型需要考虑主要肌肉、椎间盘、前后纵韧带、椎体横凸棘间韧带和棘上韧带，验证数值计算结果的实验研究方法等。

Abstract:Obstructive sleep apnea hypopnea syndrome (OSAHS) is a kind of disease characterized by repetitive pharyngeal collapse during sleep, and its pathogenesis involves multiple aspects. In this paper, from the aspect of biomechanics, various factors that might induce sleep apnea were studied based on anatomic and physiological characteristics of human upper respiratory system, and biomechanical models of OSAHS reported in recent years as well as potential mechanical pathogenesis of OSAHS were then analyzed. Finally, the prospects of future researches on OSAHS biomechanics were discussed. Establishing the biomechanical model of upper airways is an effective method not only important for studying pathogenesis of OSAHS, but also helpful for preoperative assessment and postoperative predictions for OSAHS treatment in clinic.