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Abstract:Objective To study the polarization and arrangement of epithelial cells in the embryonic development of drosophila. Methods A finite element model was established to simulate the development of drosophila egg, and an ABAQUS UMAT user subroutine that describes the growth of materials was developed. The developmental process of the stages 8 (S8) to the initial state of the stage 10 (S10) was simulated， and the direction of principal stress and the distribution of the in-plane maximum shear stress (MSS) in the epithelial cell layer was analyzed, in order to predict the polarization and arrangement of the epithelial cells. Results The orientation of the epithelial cells was consistent with the direction of the maximum principal stress, and the aspect ratio of cells was proportional to the magnitude of the MSS. Conclusions The polarization and arrangement of the epithelial cells are controlled by the stress state in the tissues.

Abstract:Objective To study the vibration characteristics of a normal C2-7 cervical spine finite element model and vibration changes of a cervical facet joint with different degrees of impairment or that is resected. Methods The finite element model of a normal C2-7 cervical spine based on computed tomography (CT) scan images was established and validated. Next, the normal frequency and first ten modes of the normal cervical spine model were extracted. A facet joint was considered without or with joint constraints with a friction coefficient of 0.01, 0.1 and 0.2 to simulate a resected facet joint or a facet joint with mild, moderate, and severe damage, respectively. Thus, the effects of different types of damage to the cervical spine on their natural frequencies could be studied. Results The minimum natural frequency of the normal model occurred in the extension and lateral bending modes and it was approximately 12 Hz. A large displacement in the model occurred mainly in the atlas. The frequency of the model with the constrained joint was higher than that without joint constraints; however, the natural frequencies of the facet joints with different friction coefficients remained almost unchanged. Conclusions The study of the natural frequency, mode shape, and amplitude of the cervical spine provided the basis for further studying its dynamic characteristics, which is of tremendous significance in the nursing and treatment of cervical vertebrae. A vibration environment of 12 Hz should be avoided in daily activities and cervical treatment to prevent severe damage to the cervical spine.

Abstract:Objective The functional relation between the correction angle and orthopedic force of scoliosis can be derived based on the force principle of scoliosis correction. The position and size of the orthopedic force with the best effect of spinal correction can be calculated to provide a theoretical calculation method for the application of orthopedic forces on scoliosis. Methods The coordinates of the scoliosis central axis were collected based on the computed tomography (CT) data of scoliosis. The spline curve of scoliosis was fitted using the MATLAB software. The scoliosis constitutive polynomial was obtained, and then, the scoliosis Cobb angle was calculated by programming. Based on the clinical medicine and experimental data of spinal biomechanics, a curved beam model was used for the correction calculation and analysis of scoliosis. Results The function relation between the orthopedic force and angle at any positions was derived at different orthopedic forces. The comprehensive elastic modulus of the spine was 0.29 MPa, as calculated by the function relation. Conclusions The calculation and analysis provided a reliable theoretical basis for the relationship between the loading position, size, and restoration angle of the orthopedic forces during scoliosis correction. For patients with different types of scoliosis, the function relation between the orthopedic angle and orthopedic force could be optimized to obtain the optimal orthopedic force and loading position.

Abstract:Objective To establish the three-dimensional (3D) finite element (FE) model of thoracolumbosacral T1-S spine based on the computed tomography (CT) images of patients with scoliosis and study its dynamic characteristics. Methods The established scoliotic model was validated by axial compression and shear loading, and the predicted responses were in good agreement with the experimental data. The modal and harmonic analyses were performed using the ABAQUS software, and during the harmonic analysis, the dynamic response of the model was collected at frequencies 5 Hz and 10 Hz. Results From the modal analysis, the first fourth-order modal was extracted. The first- and second-order resonant frequencies of the model were 1.097 Hz and 1.384 Hz, respectively, and the vibration mode was longitudinal bending and lateral bending, respectively. The distribution of the second- and third-order modal resonant frequencies were 5.688 Hz and 28.090 Hz, and the vibration mode was vertical vibration and twisting around the long axis, respectively. The peak amplitude in the harmonic analysis appeared near the modal frequencies, and the average amplitude of vertebral body of the lateral convex segment was larger than that of other segments of the scoliotic spine. Under the vibration frequencies of 5 Hz and 10 Hz, the stress inhomogeneously concentrated on the concave and convex sides of the segments of the vertebral deformity as well as on the intervertebral disc. Conclusions The segments of the spinal deformity in patients with scoliosis were the weak links of their spines and more vulnerable to damage in a vibrating environment. Patients with scoliosis should avoid a vibrating environment, particularly in a sensitive frequency range. The research outcomes provide methodological assistance and mechanical analysis references for the protection, rehabilitation treatment, and clinical pathological studies of patients with scoliosis.

Abstract:Objective To study the effect of vibration environments on patients with posterior lumbar interbody fusion in daily life. Methods Finite element models of an intact lumbar spine and a postoperative model with fixed L4-5 segments were established. Subsequently, a 40-kg mass point was applied to the upper end plate of the L1 segment to perform a modal analysis. Results In comparison with an intact lumbar spine, the resonance frequency for each order of the whole lumbar spine was reduced after posterior lumbar interbody fusion, and the primary movement of the corresponding modes were also changed. The first two inherent frequencies of the modal in the fusion model were 2.94 Hz and 3.81 Hz, which were close to the vibration frequencies in daily life. In the first three order vibrations, the mode amplitudes of the posterior elements for the L2 and L3 segments increased in the fusion model, which could increase the risk of postoperative degeneration at such locations. In addition, the vibration amplitude of the intervertebral disc of the L3-4 segments clearly increased, particularly at the part of the disc near the L3 vertebral body, which could lead to increased stress and strain and further accelerate its degeneration. Conclusion sBased on the modal analysis of a lumbar spine after posterior lumbar interbody fusion, the investigation of the vibration characteristics of the postoperative lumbar spine will provide some theoretical guidance for the recovery and healthy life of the patients after the corresponding surgery.

Abstract:Objective To study the process of stent graft implantation into the aortic dissection model by finite element simulation, calculate the stress distribution at different locations of the aorta after the implantation, and analyze the biomechanical mechanism of new lesions for implantation of stent grafts. Methods Based on the computed tomography angiography (CTA) image data of the aorta, a three-dimensional geometric model of patient-specific aortic dissection was established with image segmentation and reconstruction. The wall thickness and material properties of the aortic dissection of the computational models were set according to the literature data. Stent grafting rings with different geometric parameters were designed in a computer-aided design (CAD) software, and the procedure of stent graft implantation was simulated by a finite element analysis software. Results When the implanted stent graft reached a steady-state, the maximum Von Mises stress of the aorta was markedly related to the position of the stent graft and located at the bare stent or small nickel-titanium alloy ring. In the long-term, this force might cause a new tear to appear at the treated aorta. Conclusions The position of the stent graft had a weak effect on the distribution of the maximum Von Mises stress of the aorta, but there was an obvious effect on the Von Mises stress of the aorta. These research outcomes may provide significant guidance for selecting the position of the stent graft.

Abstract:Objective To study the effects of PVA-H coating thickness and tip angle on the tissue injury caused by the implantation of neural electrodes. Methods Simulated implantation experiments were conducted based on a tissue injury evaluation system to evaluate the tissue injury caused by electrode implantation. The coating thicknesses were controlled by the number of dip coating times (0, 1, 2, and 3), whereas the tip angles were set as 30°, 40°, and 50°. The maximum tissue strain and insertion force were selected as the measurement of the tissue injury. Results thicker hydrogel coating and larger tip angle would cause more serious tissue injury. Simultaneously, reducing the tip angle of the neural electrode could reduce the degree of the hydrogel coating effect on the tissue injury. When the tip angle was 30°, the maximum strain and the peak insertion force increased by 3.4% and 3.8%, respectively, whereas when the wedge angle was 60°, the maximum strain and maximum insertion force increased by 11.3% and 18.1%, respectively. Conclusions The hydrogel coating of the neural electrode increased the injury of biological tissues caused by the implantation of the neural electrode. However, the method of decreasing the tip angle of the electrode could reduce the degree of the negative effects of the hydrogel coating thickness on the implantation injury.

Abstract:Objective To study the tooth and periodontal stress distribution and tooth displacement after apical root resection, so as to provide data support for clinicians to perform apical root surgery and improve the cure rate of apical root surgery. Methods Three-dimensional (3D) finite element model of normal maxillary central incisor with its periodontal tissues was established based on Micro CT image data. Then periapical periodontitis and apical root resection surgery were simulated. The model of periapical periodontitis and maxillary central incisor with different apical root resection length (3, 4, 5, 6, 7, 8 mm) and their supporting tissues were established. With the occlusal force applied, the biomechanical behavior of postoperative healing teeth was studied by 3D finite element analysis. The optimal apical resection length was obtained by comparing biomechanical effects of surgical restoration. Results The completely healed model reduced the stress (by 26.8%) and displacement (by 7.3%) compared with the apical periodontitis model. With the increase of apical root resection length, the stress of the teeth neck and periodontal ligament increased by 11.14% and 29.27%, respectively, when the root resection was 8 mm. The stress of the alveolar bone increased by 83.11%. The stress of new apical root at the section increased on the whole compared with the same part of normal tooth. The displacement of the tooth along the long axis also increased. The displacement significantly increased by 18.39% when the resection length was over 5 mm. Conclusions Apical root resection significantly improves the biomechanical properties of refractory apical periodontitis tooth. The recommended resection length was 3-5 mm and the crown-to-root ratio (CRR) should be larger than 0.84.

Abstract:Objective To conduct a comparative study of the biomechanical characteristics of anatomical and vertical reconstruction for the coracoclavicular ligament. Methods Thirty fresh adult cadaveric specimens of the shoulder joint were dissected, whereas other soft tissues of the shoulder joint were resected, and only the clavicle-coracoclavicular ligament-scapula structures were retained. All the specimens were randomly divided into three groups, with ten specimens in each group. In Group 1, the coracoclavicular ligament was retained; in Group 2, the cone ligament was reconstructed vertically based on the classical Steven technique; and in Group 3, the conical ligament was reconstructed anatomically based on the central site of the original ligament. Biomechanical tests under vertical tensile resistances were conducted separately on the three groups, and the tensile forces that caused the rupture of the coracoclavicular ligament or reconstruction failure were recorded. Results In Group 1, clavicle and coracoid fractures were not found, and the tensile force that caused the coracoclavicular ligament rupture was (650.41 + 35.88) N. In Group 2, clavicle fracture (two cases), endobutton pull-out from the clavicle (two cases) or coracoid (five cases), and coracoid fracture (one case) occurred, and the tensile force that caused the failure of the coracoclavicular reconstruction was (725.68 + 35.37) N. In Group 3, clavicle fracture (three cases ), endobutton pull-out from the clavicle (one case) or coracoid (five cases), and coracoid fracture (one case) occurred, and the tensile force that caused the failure of the coracoclavicular reconstruction was (765.15+13.68) N. Conclusions The tensile forces in the anatomical and vertical reconstruction of the coracoclavicular ligament were both superior to those of the primary ligament, with the anatomical reconstruction being superior to vertical reconstruction under a tensile effect.

Abstract:Objective To investigate the influence of the microscale attractive interaction on the elastic properties of DNA film in multivalent ion solutions. Methods Kornyshev's electrostatic zipper model was employed to describe the interaction energy between the DNA strands. The thought experiment method and macroscopic continuum bar model were combined to predict the stress-strain relationship, prestress, and elastic modulus of the DNA biofilm.Results Given the packing conditions, the DNA film exhibited a tensile prestress and negative elastic modulus. The prestress of the DNA biofilm ranged from -1.52 MPa to 1.17 MPa, and its elastic modulus ranged from -4.2 MPa to 64 MPa. Conclusions In contrast with monovalent solutions, the microscopic attractive interactions in multivalent solutions caused the elastic properties of the DNA film to exhibit a non-monotonous relationship with the variation in the packing density and salt concentration. The tensile elastic properties were significantly different from the compressive ones, and the tensile/compressive prestress as well as the positive/negative elastic modulus transformed each other. These results can contribute to understanding the mechanism of viral replication and provide references for gene detection and gene therapy.

Abstract:Objective To study the stress on elastic substrate of an in vitro endothelial cell dynamic culture device, whose hemodynamic environment is designed to simulate the human body, and to test and observe the shear stress changes in elastic substrate of parallel plate flow chamber under different tensile stresses. Methods A series of static tensile tests were adopted to fit the condition of dynamic stretching. Namely, the silicone sheet with 2 different thicknesses were put into the device, and then applied with static stretch at the interval of 10% tensile rate (0%, 10%, 20%, 30%), and under the condition of maintaining its tensile rate, the chamber height after the stretch of silicon sheet was calculated. Based on the calculation of shear stress, shear stress curves at different tensile rates were obtained, to make comparative analysis on variation of the shear stress with the thickness of silicon sheet. Results The experimental result was consistent with the theoretical analysis. When the tensile rate was 30%, silicon sheet with 0.5 mm thickness would produce certain influence on shear stress of parallel plate flow chamber along with the change of tensile rate (the height of chamber), and the average and maximum shear stress were reduced by 10.1% and 10.4%, respectively. Conclusions The influence factors caused by the change of elastic substrate thickness after the introduction of tensile stress must be taken into account for the calculation of shear stress in parallel plate flow chamber. The result can provide experimental technology for the culture of endothelial cells in vitro and the design and development of novel parallel plate flow chamber.

Abstract:Objective To evaluate the influence of different load carriages during military walking on the gait of lower limbs. Methods In a randomized cross-over design, 15 healthy young males were asked to perform self-paced walking with a normal uniform under a load carriage of 0 kg, 7.5 kg, 27 kg, and 50 kg for four times. The kinematics parameters of the pelvis, knee, and ankle were evaluated by the Vicon motion capture system and AMTI force plates. Results With increasing load carriage, the stride frequency relatively improved, whereas the stride reduced and the speed was maintained on the whole. The peak left/right hip flexion and extension angle and peak knee adduction angle were obviously affected by the load carriage, whereas the movement magnitudes could be maintained. The peak varus angle of the left ankle and peak valgus angle of the right ankle were also affected. The peak force and moment of the left/right knee and ankle increased. Conclusions With increasing load carriage, overall, the movement magnitudes of lower limb joints were maintained under the given loads, whereas the lower limb loads were increased, which could increase the potential risk of lower limb injuries.

Abstract:Mock circulatory system (MCS) is an experimental platform for simulating hemodynamic performance of human circulatory system, and has been widely used in in-vitro hemodynamic performance evaluation of passive devices such as ventricular assist devices (VADs), artificial valves, as well as hemodynamic responses of mock circulation loop. MCSs are capable of simulating various physiological conditions, including health, exercise, and heart failure, by adjusting drive element of heart simulator and lumped-parameter element of vasculature components. Since 1 960 s, the research and development target of MSCs has evolved from meeting the basic performance evaluation requirement of VADs and mechanical valve to mimicking local hemodynamic characteristics in vital organs. This review summarizes the design principles, system construction of MCSs as well as its research progress and future prospects.

Abstract:Tai Chi, developed from a kind of martial arts into a new form of exercise therapy, has received wide attention. Studies on the rehabilitation effects of Tai Chi and its mechanism have been conducted by researches in both China and other countries, and most of these studies are concerned with Tai Chi’s role in balance improvement. According to the purpose of the study and the evaluation index, the rehabilitation function and biomechanical characteristics of Tai Chi exercising were reviewed. The biomechanical mechanism of rehabilitation function was discussed by comparing the differences between the research method and the conclusion. Due to the lack of a unified specification for the standard and duration of Tai Chi exercising, some study result are inconsistent. Enhancing biomechanical researches on Tai Chi and setting different practicing standards for people with various health conditions will be a main direction for Tai Chi study in the future.

Abstract:Cells are exposed to mechanical stress, such as fluid shear stress (FSS), mechanical strain, hydrostatic pressure in vivo. FSS is considered to be the most important stress during bone homeostasis and remodeling. At present, most studies are mainly about the FSS effect on osteocytes and osteoblasts. However, the effects of FSS on bone mesenchymal stem cell (BMSCs) are not fully understood. BMSCs are of great significance in bone reconstruction and clinical treatment, so researchers increasingly focus on the response of BMSCs to FSS. The response of BMSCs to FSS depends on the alteration of cytoskeleton, matrix stiffness and elasticity, osteogenic signaling pathways and so on. In this review paper, the recent researches about the mechanotransduction mechanism of FSS, and its effect on differentiation and function of BMSCs are summarized, so as to provide new insights for studying construction of tissue engineered bone and treatment of bone diseases.