Abstract:

Abstract:

Abstract:Objective To compare the differences of neck injury risks for different mummies during arrested landing on naval vessels. Methods Based on the established dynamic model of dummy-belt-seat systems and mechanical model of head-neck, with the acceleration curve at seat base during typical arrested landing reported in the literature as the input, numerical simulation was conducted to test the validity of the model, and the axial force, shear force， bending moment of typical joints in dummy neck during arrested landing were obtained. Results The injury index Nkm of 95 percentile dummy was higher than that of 5 percentile dummy. The injury index Nij of the dummy’s upper and lower cervical spine was smaller than 0.2, meanwhile the Nkm was around 0.65. Conclusions During arrested landing, human neck was much easier to get hurt due to the shear force. The research findings can provide data support for evaluating neck injury risks of pilots with different sizes during typical arrested landing process.

Abstract:Objective To compare and analyze the effect of membrane element and spring element on biomechanical responses of cervical ligaments. Methods Based on the existing 6-year-old pediatric neck finite element model, the ligaments were simulated by membrane element and spring element, respectively. Then dynamic tensile test of C4-5 vertebrae and tensile test of full cervical spine were conducted. The membrane element model was also used to simulate the bending test, and the simulation results were analyzed. Results In dynamic tensile test of C4-5 vertebral segment, the final failure force of membrane element simulation test and spring element simulation test was 1 207 N and 842 N, respectively, and their difference from the cadaver experiment was 0.6% and 30.6%, respectively. In full cervical tensile test, the difference of peak force from membrane element simulation test and cadaver experiment was 1.8%. The peak force of spring element simulation test was 484 N, and the difference from simulation test and cadaver experiment was large. The simulation result of membrane element bending test was good. Conclusions The spring element had some limitations in force simulation. The membrane element had higher biofidelity and could reflect the biomechanical response of the ligaments.

Abstract:Objective To investigate the relationship between microstructure characteristics and its mechanical behavior. Methods The compression experiments on longitudinal and transverse specimens of the cortical bone from bovine femoral bone were conducted. The fracture routes of longitudinal and transverse specimens and microstructural features of fractured surfaces were observed. The effects of osteon orientation on elastic modulus and ultimate fracture strength of the bone were analyzed based on the theory of composite micromechanics. Results The compressive elastic modulus and ultimate fracture strength of longitudinal specimens were significantly greater than those of transverse specimens. The fracture routes of longitudinal specimens were along their loading direction (0°) and relatively flat, while the fracture routes of transverse specimens were relatively zigzagging, being approximately 45° with their loading direction. There were many striped structures on fractured surfaces of longitudinal specimens and the fractured surfaces were relatively smooth, while there were many annular concave and convex structures on fractured surfaces of transverse specimens and the fractured surfaces were relatively rough. Conclusions The bovine femoral bone had anisotropic mechanical properties, and its anisotropic mechanical properties were closely related to the orientation of osteons.

Abstract:Objective Based on structure of animal trabecular bone, implants with porous structure were designed to describe mechanical properties of trabecular structure and explain significance of bionic trabecular porous implants in clinical treatment. Methods Based on anisotropic mechanical properties of animal trabecular bone, a porous structure was designed using the topology optimization method. The principles of partition and block reconstruction were first proposed according to bone function theory. The trabecular structure was then reconstructed based on micro-CT images. The boundary constraint and external load were applied on this model according to the respective-volume-element (RVE) method. Taking the solved mechanical properties as objective functions of optimization, the porous structure design and optimization were conducted using the variable density method and the homogenization method. Results The trabecular bone possessed the anisotropic mechanical properties. It was found that the volume fraction showed an increasing trend from the edge to the middle across the same section of trabecular bone. But there was no obvious regular pattern in Poisson’s ratio, which was evenly distributed in the range between 0.17 and 0.30. As to the values of elastic modulus and shear modulus, they were both significantly higher in the main pressure position compared with those in the other positions. After topography optimization based on these mechanical properties, the Poisson’s ratio of the optimized model was in the same range as the animal trabecular bone. The elastic modulus error was less than 14%， with the minimum being only 3%. In addition, the shear modulus error was below 8%， which ultimately complied with criteria of the original goal. Conclusions The designed porous structure based on topology optimization had the same anisotropic characteristics as animal trabecular bone, while reducing the stress concentration phenomenon, which could achieve the specific design for porous structure, thus providing a reasonable and effective method for clinical porous implants.

Abstract:Objective To study the morphology and fractal characterization of UHMWPE wear particles by simulation experiment on knee joint, analyze the classification characteristics of wear particles and discuss the correlation between fractal dimension and wear state. Methods The knee joint simulator was used to realize the knee joint wear motion. The forged CoCrMo alloy and UHMWPE were selected as artificial joint prosthesis materials. The wear particle extraction was based on ISO 17853. The automatic extraction and fractal identification system of wear particles were used to investigate fractal characteristics of wear particles. Three kinds of models were established to classify and recognize wear particles, by using the meshing method, cluster analysis and genetic simulated annealing algorithm, respectively. Results The fractal characteristics of UHMWPE single wear particles was very obvious. The fractal dimension calculated by radar fractal method decreased, during the transition from the larger size of strip debris to the smaller size of roundness debris, and the fractal dimension D of spherical debris was close to zero. The weighted sum of squared error values of fractal dimension for wear particle population classification was the smallest by the model of genetic simulated annealing algorithm, and the clustering feature was very obvious. When the wear cycles were low, the large fractal dimension of strip, needle and fibrous abrasive debris with larger fractal dimension had the largest proportion, and the main abrasion modes were the ploughing and spalling wears. With the extension of wear period, the proportion of wear particles with large fractal dimension decreased, and the proportion of flaky, blocky and near-spherical wear particles with low fractal dimension increased clearly. The wear mechanism changed to the fatigue and adhesive wear, and the wear state transited to the composite wear period. During the stable wear period, the proportion of all kinds of abrasive grains changed little. Due to the increase in the number of small particles, the fractal dimension decreased in stable wear state. Conclusions Based on the improved radar graph method, the fractal dimension of wear particles with different profiles could be obtained by automatic extraction and fractal identification system of wear particles. The research findings can be used in shape extraction, fractal dimension calculation and parameter statistics, as well as providing a new digital analysis tool for identification and diagnosis for wear particles of artificial prosthesis.

Abstract:Objective To study the effects of mechanical load on in vivo degradation performance of high-purity magnesium (HP Mg, 99.99 wt.%) quantitatively. Methods Cylindrical Mg specimens, with a 2 mm diameter and a 14 mm length, were mounted in polyetheretherketone (PEEK) rings to bear compressive stresses ［（6.2±0.6） MPa］, tensile stresses ［（4.6±0.1） MPa］ or no stress (as control). The specimens under different stress states were implanted subcutaneously in dorsal abdominal regions of SD rats for 4 weeks. The mass loss, residual volume and surface morphology of the specimens and staining of surrounding soft tissues were used to analyze the degradation rate of HP Mg. Results Specimens and rings were completely encapsulated by membranous tissues after implantation for 4 weeks. No significant differences in the degradation rates were noted between specimens bearing stress and the control. The corrosion layers of specimens under each stress state were uniform. Conclusions The compressive and tensile stresses (4-6 MPa) could not affect significantly HP Mg degradation performance in vivo. The research findings provide theoretical references for the design and clinical application of Mg-based degradable implants.

Abstract:Objective To compare the biomechanical stability of different fixation methods for unstable pelvic fractures, so as to provide references for clinical treatment. Methods An unstable pelvic fracture model (Tile C) with the sacroiliac joint dislocation at one side and the pubic rami fracture was constructed via three-dimensional finite element method. In the front of the pelvis, the fracture models were fixed with anterior pelvic Stoppa approach (ASA),subcutaneous anterior pelvic approach (APA), anterior pelvic ilioinguinal approach (AIA) and anterior pelvic external fixation (AEF),and the rear was fixed with sacroiliac joint screw (SIJS）and posterior tension-band plate (PTP). The Von Mises stress and strain distributions of fracture models fixed by different combinations of fixation approaches were analyzed under simulated standing conditions. Results After the models were applied with 500 N vertical load, the maximum stresses at the fracture sites were all reduced, which were smaller than 10 MPa in the front of the pelvis. The maximum stress at the anterior and posterior part of implants in sequence was ASA＜AIA＜AEF＜APA, and the average displacement under the same stress in sequence was ASA＜AIA＜AEF＜APA. Meanwhile, the maximum stresses at the sacroiliac joint and the posterior part of implants in PTP group were significant smaller than those in SIJS group, and the maximum total displacement and vertical displacement in PTP group were also smaller than those in SIJS group. Conclusions Unstable pelvic fractures could be significantly improved when the fracture was fixed by implants in eight combined methods. However, the overall biomechanical properties of the AIA groups were superior to those of the AEF groups and the APA groups. The stability of PTP groups in the treatment of posterior injury was better than that of SIJS groups.

Abstract:Objective In view of the problems existing in traditional external fixator, to invent a novel single shoulder airbag external fixator, and evaluate the reductional stretch force produced by it. Methods The three-dimensional finite element model of human clavicle was established. The loading conditions of the single shoulder airbag external fixator and the reductional stretch force produced by the external fixator were analyzed comprehensively and systematically. The actual loading conditions of the single shoulder airbag external fixator and the traditional eight-figure bandage external fixator were compared and analyzed by experiment. Results Reductional stretch force produced by the single shoulder airbag external fixator was more uniform and larger than that produced by traditional external fixator, and could be adjusted by the patient himself. Conclusions The force and the loading method of the single shoulder airbag external fixator on the shoulder were more favorable for the stretched reduction of clavicle fractures and maintaining the position of clavicle fractures, and it could make the patients with clavicle fractures more comfortable.

Abstract:Objective To explore the effects of screw configurations on bone healing, so as to provide the basis for related fracture treatment. Methods The process of bone healing under different screw configurations was studied by finite element method, and the change in the process of callus growth during healing periods was simulated by interfragmentary strain theory (IFS). The iterative process for renewing callus modulus in every finite element was conducted by the second-developed ABAQUS based on Python scripting language, thus the process of fracture healing was simulated. Results The effect from different numbers of screws on bone healing was smaller than that from different working length of bone plates. On the premise of stable fixation, given the certain working length of bone plates, the effect from different screw numbers on stress distributions in plates or screws was relatively small, while the effect from different working length on stress distributions in plates or screws was relatively large, and the stress distribution in plates was larger than that in screws at different working length. Conclusions It is necessary to take more consideration on working length of bone plates than the number of screws when they are under a stable fixed situation, and it is a wise choice to reduce the screw numbers and choose a suitable working length for bone healing process.

Abstract:Objective To analyze the relationship between fatigue strength and connector length of intracranial artery stents, so as to investigate the exact location of fatigue fracture for the stent. Methods The fatigue life for 3 kinds of artery stents were analyzed by finite element analysis method of fatigue fracture, and distribution map of dangerous points was drawn by means of Goodman curve. Based on F2477-07 standard from American Society for Testing and Materials (ASTM), the fatigue life for 3 kinds of stents was tested. Results If the length of the support connector was longer, the maximum equivalent stress and the average stress in dangerous points of the stent would be larger. If the distribution of dangerous points was more close to the curve of fatigue limit, and fatigue fracture was more likely to occur in the stent. Goodman curves indicated that 3 kinds of stents was safe to be used in the body for ten years. Finite element analysis and experimental result showed that fatigue life near the stent junction was relatively lower, and dangerous points of the stent was located at the arc junction. Conclusions It is reasonable to study stents by finite element analysis, whose results are basically coincided with the experimental data. Fatigue life can be extended by reducing connector’s length for the design of stent structure.

Abstract:Objective To analyze the influence of round window lesion on dynamic responses from the middle ear. Methods Based on CT scan images of healthy human ear, the three-dimensional finite element model of human ear was rebuilt by PATRAN software, then NASTRAN software was applied to conduct coupled solid-fluid frequency response analysis. The feedback of round window lesion on dynamic response of the middle ear was investigated by numerical simulation. Results Round window closure caused by sclerosis led to more decline in amplitude of stapes than congenital round window closed, maximally can reach 30.2 dB, and the latter had no obvious influence on velocity of stapes. In term of phase angle, on condition of sclerosis, change of phase for stapes and round window reached 90° at most and kept a difference value of 180°. In contrast, on condition of congenital round window closed, change of phase for stapes reached 270° at most，meanwhile change of phase for round window disappeared. Conclusions The dynamic response of the middle ear showed different feedback to congenital and otosclerotic round window fixation based on amplitude, velocity and phase. The research findings provide the theoretical basis for diagnosing and fixing round window lesion in future.

Abstract:Objective To investigate the effect of the different rehabilitation training method on the first ray of postoperative hallux valgus (HV). Methods Based on medical images of HV patient, a comprehensive three-dimensional finite element model of HV foot was established, including bones, sesamoid, cartilage, ligaments, soft tissues, Achilles tendon. The passive/active plantar flexion and dorsal flexion as well as standing were simulated to investigate the biomechanical behavior of distal osteotomy fragment of the postoperative HV. Results The stress distribution on distal osteotomy fragment during passive training was more uniform, and the peak stress (7.78 MPa) was greater than that during stance phase and active training. The distal osteotomy fragment displacement during passive training (0.98 mm) in anterior-posterior direction was greater than that during stance phase (0.69 mm) and active training (0.38 mm). Conclusions The passive training could promote the contact of osteotomy surface and reduce the healing time of osteotomy, which would be beneficial for rehabilitation of postoperative HV.

Abstract:Objective To analyze kinematic characteristics of children with spastic cerebral palsy during walking based on the method of gait analysis. Methods The gait of 14 children with spastic cerebral palsy and 16 healthy children, who were required to walk back and forth on level ground at normal speed, was tested using portable gait analyzer. The gait differences between diseased side and healthy side of lower limbs for children with spastic cerebral palsy, as well as the gait differences between children with spastic cerebral palsy children and healthy children were compared. Results For children with spastic cerebral palsy, single step time, swing time and toe-off time of diseased side were significantly longer than those of healthy side (P＜0.05), while step frequency, velocity and terminal stance were significantly shorter than those of healthy side (P＜0.05). Compared with healthy children, gait cycle time, single step time, stance time, swing time, percentage of stance phase, mid stance phase, pre-swing stage and toe-off time for diseased side of children with spastic cerebral palsy were significantly longer (P＜0.05). Stride, velocity, step frequency and terminal stance of the children with spastic cerebral palsy were significantly lower than those of healthy children (P＜0.05). Pulling acceleration for children with spastic cerebral palsy also decreased compared with healthy children (P=0.05). Conclusions The stability of children with spastic cerebral palsy decreased during walking, and their single step time, swing time, toe-off time and pulling acceleration might be considered as the sensitive indicators.

Abstract:Aiming at the background and significance of biomechanical researches on lumbar interbody fusion, the research progress of interbody cage and interbody fusion was reviewed and its prospect was forecasted. The related work was summarized, including research method of lumbar biomechanics, biomechanics of interbody cage, and biomechanics of lumbar interbody fusion. The main research directions on biomechanical study of lumbar interbody fusion were: modeling refinement of finite element method， geometrical optimization of traditional fusion device, clinical application of new porous fusion device, and diversification of the supplemented fixation method. Finally, the prospect of biomechanics of lumbar interbody fusion was discussed. The review and prospect on biomechanics of lumbar interbody fusion will provide references for clinical treatment of lumbar spine diseases.

Abstract:In the process of central nervous system (CNS) development and maturation, the biomechanical factors have not been highly valued for a long time. In recent years, a large number of studies have shown that mechanical environment strongly affects the migration, differentiation and maturation of nerve cells, as well as the cell-cell interactions. Mechanical factors play an important role in realization of the structure and function of the brain and spinal cord. This review briefly summarized the role of biomechanics in CNS perception, path-finding, regulation and network shaping during CNS development. The effects of static and dynamic mechanics on mechanobiological response of nerve cells were also introduced, hoping to provide some ideas for CNS reconstruction and repair in future.