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Abstract:Rehabilitation technical aids have great significance in improving life quality of people with disability and reducing burdens of care for family and society. Nowadays, the policy, research funding and industrial environment in China all provide a good chance for rehabilitation technical aids research, which has already made great progress. Biomechanics plays an important role in design of rehabilitation technical aids. On the one hand, biomechanics can provide important references for measurement and evaluation on biomechanical characteristics of physical disabilities, so the design of rehabilitation technical aids can meet the requirements of maintaining or improving biomechanical functional capabilities of individuals with disabilities. On the other hand, the biomechanical interaction between human body and rehabilitation technical aids should also be considered carefully during the optimization of design. As an introduction to this special issue on rehabilitation, this paper will briefly review the progress of rehabilitation technical aids research in recent years in China, and then introduce some biomechanical researches in development of rehabilitation technical aids.

Abstract:Objective To study the effect of passive motion from lower extremity on electromyography (EMG) activity of major muscles when the back under headdown tilting state. Methods Thirty healthy subjects were selected. The EMGs of erector spinal and trapezius muscles were recorded and analyzed when human body was under head-down tilting at angel of 0°, 10°, 20° and 27° in static mode, respectively, in sway mode (along the axis of Z with frequencies of 120 and 140/min， respectively) and in vibration mode (along the axis of Y with frequency of 680/min) with the help of multifunctional test bed. Results In the static mode, the median frequency (MF) decreased with the increase of head-down titling angle; in the sway mode, the MF at each of 4 head-down tilting angles was smaller than that in the static mode. When the frequency was 120/min, the MF decreased with head-down tilting angle increasing, but when the frequency reached 140/min, the variation of MF became irregular. In the vibration mode, the MF increased with the increase of head-down tilting angle and was larger than that in the static mode. Conclusions In the static mode, the muscle fatigue increased with the headdown tilting angle increasing; in the vibration mode, smaller head-down tilting angle should be selected to achieve better treatment effect; but in the sway mode, larger head-down tilting angle would be better, and the sway frequency should be set lower than 120/min to avoid potential damage due to excessive muscle fatigue.

Abstract:Objective To assess the injury risks and affecting factors of spinal loads at L5/S1 joint for caregivers during manual patient-handling tasks, so as to find a suitable handling way to effectively reduce such risks. Methods Kinetic data were collected from nine female caregivers performing six patient handling tasks on three agent ‘patients’ with different weight. Peak L5/S1 force was calculated based on a multi-segment three-dimensional model to investigate the characteristics of injury risks, and the correlations between the peak L5/S1 force and six affecting factors were specifically analyzed. Results Peak compression of the tasks all exceeded the safe thresholds of 3.4 kN; Peak anterior-posterior force for those repositioning tasks were above the threshold of 0.5 kN. Different tasks showed different biomechanical characteristics for risk of injury and affecting factors, and there was a significant correlation between the L5/S1 loads and the moving distance of center of gravity, and the ground reaction force as well (P<0.01). Conclusions Manual patient handling tasks could cause different injury risks by high loads on spinal low back. Decreasing the range of motion of the whole body and avoiding jerk movement during the patient handling tasks would help caregiver to reduce the injury risks.

Abstract:Objective To understand kinetics characteristics of gait termination for children with backpacks， and compare the difference between planned gait termination (PGT) and unplanned gait termination (UPGT) as well as effects of backpack carrying by children at the moment of gait termination. Methods Twelve boys (age (9.85±1.34) years old, height (140.89±11.57) cm, weight (34.96±9.62) kg) were recruited in this study. The gait termination scene in real life was simulated in the lab by the subjects who were required to carry different backpacks, while the parameters of ground reaction force and center of pressure (COP) during PGT and UPGT were recorded by two 3D force plates. Results There were significant differences in the peak ground reaction force curve between gait termination and normal walking. Meanwhile the peak ground reaction force and COP shifting during PGT and UPGT were both significantly larger than those during normal walking， and the values were increased with the increase of backpack load. The maximum ground reaction force and COP shifting were found during UPGT while the subject was carrying backpack equal to 15% of the body weight (15% BW). Conclusions The change of ground reaction force was useful for gait termination，but children will suffer much more impact force during both PGT and UPGT, and make the control on postural balance more difficult, which could be dangerous with the increase of backpack load. It is advised that children should lighten their backpack loads, which will be helpful to prevent accidental injuries during suddenly external disturbance.

Abstract:Objective To evaluate effects of soles with different hardness on kinematic parameters of human lower extremity during walking by conducting kinematic analysis on subjects walking with soles of different hardness. Methods Subjects were required to wear 3 kinds of shoes with soles of different hardness and walk on the treadmill at the speed of 6 km/h. Vicon infrared camera system was used to capture the motions of subjects during walking, and kinematic parameters such as heel height, toe height, knee angle and ankle angle were collected for experimental analysis. Results Compared with the other shoes, the gait cycle was increased when subjects wearing soft-soled shoes, with the smallest angel of the forward pendulum of crus. The forward pendulum of thigh was the smallest and the back pendulum was the largest when subjects wearing medium-hardness shoes. The forward pendulum of thigh was the largest and the back pendulum was the smallest when subjects wearing hard-soled shoes. The time of swing phase was relatively stable. Conclusions Soft-soled shoes are more suitable for slow walking during a short period, while medium-hardness shoes have the smallest impact on lower extremity kinematics during walking for a long period, and hard-soled shoes are suitable for fast walking during a short period.

Abstract:Objective To investigate biomechanical properties of the contact interface between residual limb and prosthetic socket of the transfemoral amputee during walking by using threedimensional (3D) finite element analysis method, so as to provide references for establishing the complete system of measurement, design and evaluation on prosthetic socket. Methods Based on CT images, two 3D geometric models of a trans-femoral amputee including the femur, soft tissues and transfemoral socket was established, with soft tissues defined as non-linear hyper-elastic and linear elastic material, respectively. The behaviors of the interface between trans-femoral residual limb and prosthetic socket were defined as nonlinear contact. Dynamic loads on the knee joint were applied on distal ends of both the hyper-elastic model and linear elastic model to simulate loading on residual limb-prosthetic socket system during heel strike, mid-stance and toe off phase in a gait cycle, respectively. The stress distributions on interface between trans-femoral residual limb and prosthetic socket were calculated to compare and analyze the effects of different mechanical properties (i.e. hyper-elasticity and linear elasticity) of the femur soft tissue on biomechanical behaviors of the interface. Results For both the hyper-elastic model and linear elastic model, the peak contact pressures were all located on the distal end of the residual femur during different gait phases. The peak contact pressure on the interface of the hyper-elastic model during heel strike, mid-stance and toe off phase was 55.80, 47.63 and 50.44 kPa, respectively, while that on linear elastic model was increased by two times, being 149.86, 118.55 and 139.68 kPa, respectively. Simulation on longitudinal and circumferential shear stress distributions at the limb-socket interface showed that stress on the interface was higher at the distal end of soft tissue during different gait phases. From heel strike to toe off phase, some pressures were transferred from the rear edge to the front edge of the socket. Conclusions The pressure and shear stress distributions on the contact interface between transfemoral residual limb and prosthetic socket were different during different gait phases, thus the relative mechanical properties should be considered in the socket design.

Abstract:Objective Try to design a novel axillary crutch with the feature of simple structure, nice appearance, and strong practicality, so as to overcome shortcomings for the past crutches. Methods Based on the methods of modular design and flexible design, an innovative design for axillary crutches was proposed from the aspect of human biomechanics, ergonomics, and industrial design as well. Results The feasibility and clinical applicability of the design were verified by mechanical analysis, finite element analysis, quality inspection of the prototype and preliminary clinical use. Conclusions The novel axillary crutch as the result of the research and design in this study is of great clinical significance. It can effectively reduce the force of wrist and axillary for users, and cut down the occurrence of the secondary damage. Also this study can provide a useful reference for design of other similar crutches.

Abstract:Objective To observe electromyography (EMG) activity and kinematic characteristics of the dorsal and ventral muscles during extension-flexion of the trunk． Methods Ten healthy male subjects stood on a test platform, performing the front and back lifting and lowering. The EMG activity of 10 muscles (rectus abdominus, external oblique, gluteus medius, erector spinae, multifidus), the angular movement, the plantar center of pressure (COP) were recorded at the same time. The average amplitude of EMG, contribution ratio of muscles, and COP displacement were calculated, and statistical analyses of all the data were conducted． Results During front lifting and lowering, the activity of dorsal muscles was greater than that of ventral muscles under both loading and unloading, and the contribution ratio of dorsal muscles was increasing with loading. During back lifting and lowering, the activity of ventral muscles was slightly greater, but the contribution ratio of both dorsal and ventral muscles was very close. The contribution ratio of ventral muscles was increasing with loading, while the activity of dorsal muscles decreased. The activity of gluteus medius was increasing with loading, but the contribution ratio was basically consistent under both loading and unloading. Conclusions During extension-flexion of the trunk, muscle activation varies with the load size and trunk position. Under loading at front, dorsal muscles are working as an agonist, while ventral muscles as antagonist; under loading at back, ventral muscles become an agonist and dorsal muscles as a co-activator. The activity of gluteus medius might play a role of stabilization during front and back lifting and lowering.

Abstract:Objective To investigate acute effects of anaerobic exercises by a bicycle ergometer on arterial elastic modulus and local hemodynamics in human common carotid arteries with different genders. Methods Nine male and eight female healthy young volunteers at the age of 20-30 year-old successively underwent four groups of exercise trainings with the same workload by an anaerobic bicycle ergometer. The waveforms of arterial diameter and center-line blood velocity were measured in the right common carotid artery using a color Ultrasonic Doppler for each group when at rest and right after exercise training. The heart rate, systolic and diastolic blood pressures were simultaneously measured in brachial artery using an automatic electronic sphygmomanometer. All the measured data were analyzed based upon the principle of classic hemodynamics. The arterial elastic modulus and local hemodynamic parameters, including pressure-strain elastic modulus, flow rate, circumferential strain, wall shear stress and oscillatory shear index (OSI), were then calculated. Results The heart rate and arterial elastic modulus increased after exercises; with the accumulative exercises, in one cardiac cycle, the maximum and mean center-line velocity and flow rate increased while the minimum velocity and flow rate decreased; the systolic and mean blood pressure increased while diastolic blood pressure exhibited no significant change; no significant change could be found in the circumferential strain; the maximum and mean shear stress increased significantly while the minimum shear stress reduced; the oscillatory shear index also increased. Conclusions The anaerobic exercises by a bicycle ergometer may increase the arterial elastic modulus and induce significant effects on local hemodynamic parameters in common carotid arteries for young volunteers with different genders at the age of 2030 yearold. The results in this study could provide useful hemodynamic information for regulation of cerebrovascular function by anaerobic exercises.

Abstract:Objective Based on the finite element method, both sacroiliac fusion and sacroiliac contact models were built to compare the biomechanical differences between the two models and to explore the biomechanical mechanism in the treatment of low back pain by sacroiliac fusion. Methods Two pelvic finite element models were constructed, including the pelvic ring, sacrum, part of the femur, ligaments, cartilage and joint contact. The sacroiliac joints were set to be contact in one model and fusion in the other, respectively. Differences in mechanical conduction on the pelvic ring and the stress on the sacroiliac cartilage under 500 N load between the two models were explored. Results For the fusion model, stresses and displacement on the sacroiliac joint were significantly lower than that of the contact model, especially on the sacroiliac cartilage, where the displacement was reduced by 261% from 0.83 mm to 0.23 mm, and the stresses reduced by 32% from 6.6 MPa to 5.0 MPa. However, the transfer of stress on the pelvic ring was relatively more concentrated in the fusion model. Conclusions Sacroiliac fusion may provide better therapeutic effects on the treatment of low back pain, but the risk of disc herniation and femoral head necrosis must be assessed seriously in advance.

Abstract:Objective To study the influence from different assigned gradients of material attributes on mechanical properties of the vertebral finite element model. Methods An adult human spine (T12-L5) was CT scanned, and the 3D models of each vertebra were reconstructed in MIMICS, which were then modified in Geomagic and imported into ANSYS for meshing. The element models were imported back to MIMICS and assigned with material properties by separating into 8 kinds of gradients (2, 4, 8, 10, 50, 100, 200, 400 divisions). These models were then imported to ANSYS again for finite element analysis under the same loading condition. Results Significant differences were found in stresses from models with 2, 4, 400 gradients, but the deviations between 8, 10, 50, 100, 200 gradients were not obvious. Conclusions The material attributes of finite element model should be appropriate, and the assigned gradient of 10 divisions could be better guarantee the accuracy of calculation and enhance the calculation speed as well, which is suitable for personalized rapid finite element modeling in clinic.

Abstract:Objective To establish the biomechanical model of the upper airway, trachea and part of bronchus, and study the influences of different breathing modes on flow characteristics and airway resistance. Methods Based on data of CT scans, three-dimensional finite element model of an anatomically accurate upper airway was established, including the nasal cavity, oral cavity, pharynx, larynx, trachea and part of bronchus. According to several typical cases in reality, numerical simulations were performed on airflow characteristics in upper airway with different proportion of oral airflow and nasal airflow. Results When only a small amount of airflow was inhaled from the mouth, the distribution of airflow characteristics and the airway resistance were similar to the case of nasal inhalation. When a large amount of airflow was inhaled or exhaled through the mouth, the distribution of airflow, pressure and shear stress changed significantly in the respiratory tract. The main differences were observed in the nasal cavity and the oral cavity. Conclusions Establishing the biomechanical model of the upper airway, trachea and part of bronchus is helpful to understand airflow distributions in the entire upper airway and part of bronchus during respiration and to build the platform of numerical research on pathogenesis of upper airway structure-related diseases.

Abstract:Objective To analyze the stress distribution and peak stress on midshaft clavicular fractures fixed by titanium elastic nail (TEN) or reconstruction plate, respectively. Methods CT data of the clavicle was adopted to reconstruct the intact clavicle model and the midshaft clavicular fracture models with the TEN and reconstruction plate fixation by using Mimics software. All the threedimensional finite element models were analyzed using Abaqus 6.9 software. The distal displacement, the peak stress and stress distribution on the distal clavicle under the axial load (250 N) and vertical load (250 N) were calculated for the three models. Results The axial displacement of the distal clavicle under the axial load showed TEN (0.23 mm)>intact clavicle (0.14 mm)>reconstruction plate (0.11 mm), respectively. While the vertical displacement of the distal clavicle under the vertical load was 5.12 mm for TEN, 3.71 mm for intact clavicle and 2.25 mm for reconstruction plate, respectively. But the peak stress of the clavicle under the axial load was 33.1 MPa for TEN, 18.7 MPa for reconstruction plate, and 15.5 MPa for intact clavicle model, respectively. And the peak stress under the vertical load was 146.3, 64.1, 56.1 MPa in the TEN, intact clavicle model, and reconstruction plate model, respectively. The stress distribution in TEN model under both kinds of loads was similar to that in intact clavicle model, while under the vertical load, the stress distribution in reconstruction plate model was clearly different with that in intact clavicle model. For the implants under the axial load, the peak stresses were 191.5, 52.3 MPa in the TEN model and reconstruction plate model, respectively, and the peak stress on implants under the vertical load was 1 248.0, 421.7 MPa in the TEN model and reconstruction plate model, respectively. Conclusions The TEN for treating midshaft clavicular fractures showed a stress distribution similar to the intact clavicle, with a higher peak stress and a higher peak implant stress at the fracture site. The reconstruction plate fixation for midshaft clavicular fractures was shown to be more stable, but with obvious stress shielding. Therefore, TEN is generally preferable for treating the simple displaced fractures of midshaft clavicle. However, the ipsilateral shoulder should avoid excessive exercise and weight bearing in the early postoperative period.

Abstract:Objective To investigate effects of different de-cellularization methods on biomechanical properties and histological structure of annulus fibrosus in pigtails and provide experimental evidence for the construction of tissue engineering annulus fibrosus. Methods Sixty Fresh annulus fibrosus were dissected from caudal disks of pigs and randomly assigned to 4 groups with 15 in each group. Triton X-100 group(Group A): annulus fibrosus were treated with hypotonic Tris-HCl buffer for 48 hours and de-cellularized with Triton X-100, DNase Ⅰ and RNase A. SDS group (Group B): annulus fibrosus were subjected to 3 cycles of freeze-thaw and subsequently de-cellularized with SDS, DNaseⅠ and RNase A. Trypsin group (Group C): annulus fibrosus were de-cellularized with Tris buffer containing trypsin, DNase Ⅰ and RNase A. Control group: fresh annulus fibrosus underwent no treatment. After the de-cellularization process was completed, hematoxylin-eosin (HE) staining was carried out to examine the efficacy on cell removal, and the ultrastructure of annulus fibrosus were observed by scanning electron microscopy. The collagen content, glycosaminoglycan (GAG) content and biomechanical parameters in each group were also detected. Results HE staining and scanning electron microscopy showed that no residual cells were found in Group A, B and C. The structure of annulus fibrosus in Group A was not disturbed, while that in Group B and C was damaged severely and slightly, respectively. There was no statistical difference in collagen content among Group A, B and C, as compared to the control group (P>0.05). But the GAG content was significantly more lower in Group A, B and C than in the control group (P<0.05). There was no statistical difference in ultimate load, ultimate stress, toughness, elastic modulus and mechanical work to fracture between Group A, C and control group (P>0.05), while these parameters of Group B were lower than those in the control group (P<0.05). Conclusions The Triton X-100-treated annulus fibrosus retained the major extracellular matrix composition after cell removal and preserved the major structure and mechanical strength, which is preferable for the construction of tissue engineering annulus fibrosus.

Abstract:Objective To study the morphology and biomechanical properties of the improved acellularized nerve scaffold using the technique of hypotonic buffer combined with freeze-drying. Methods The traditional acellularized nerve scaffold (traditional group) was made to be improved with the technique of hypotonic buffer combined with freeze-drying (improved group). After the acellularization process was completed, the histological structure of nerves in each group was observed by HE staining and scanning electron microscope. The interval porosity and void diameter in each group were measured by Mimics software. The biomechanical properties of nerves in each group were tested by mechanical apparatus (Endura TEC ELF3200). Results The acellularization effect of the improved chemical method with the technique of hypotonic buffer combined with freeze-drying was similar to that of the traditional Hudson method, but the histological structure was more porous in improved group than that in traditional group. The interval porosity of traditional group and improved group were 34.5% and 49.3%, respectively; the void diameter of traditional group and improved group were 11.96 and 17.61 μm, respectively. Biomechanical testing results showed that there was no statistical difference in ultimate load, ultimate stress, ultimate strain and mechanical work to fracture in each group (P>0.05). Conclusions The acellularized nerve prepared by hypotonic buffer combined with freeze-drying can be used as a new kind of nerve scaffold material to make better contribution to cell combination.

Abstract:Objective To evaluate and compare the differences in COSMOL articular cartilage (AC) simulation due to the application of collagen fibril reinforcement property. Methods Collagen fiber stress was modeled independently according to its orientation in AC and written into the original poro-elastic AC model. Function call was used to avoid quadric strain term. The iteration of solver was increased for better convergence. Results The initial superficial Y displacement of the reinforced model was 15 μm, which was 17.6% of the non-reinforced model. X normal strain of the reinforced model was 10% of that in the non-reinforced model, but the superficial X normal stress of the reinforced model was 10 times higher than that of the non-reinforced model. Conclusions The application of collagen fibril reinforcement property in COMSOL AC simulation is achieved, which provided the computational model and theoretical analysis for collagen fibril lesion. Lateral reinforcement of collagen fiber can constrain the vertical strain, by which enlarge AC load capacity and improve AC mechanical properties.

Abstract:Objective To test and evaluate the effect of neck muscular strength training for military pilots at different time durations based on a self-developed pilot neck muscle training device. Methods The neck muscular strength training device, CME-1, was used to train the military pilots and military smithery members for 2, 3 and 6 weeks, respectively. The isometric and changeable velocity and resistant (CVR) modes were performed and the neck muscular strength at those different time durations was measured to evaluate the training effect. Results For all 60 military pilots trained at different time durations, the average neck muscular strength and the mean value of peak impulse in 10 seconds in anteflexion, retroflexion, right/left lateroflexion were significantly improved after training (P<0.05). After 3 weeks’ training, the average neck muscular strength of the four flexion was increased by 47.3％, 44.8％, 70.5％ and 59.6％, respectively, while the mean value of peak impulse in 10 seconds were increased by 49.3％, 41.3％, 65.0％ and 55.5％, respectively. The mean value of the peak impulse in 10 seconds of the retroflexion muscles after 3 weeks’ training was increased in comparison with 2 weeks’ training, but not significant (P>0.05). For 11 military smithery members after 6 weeks’ training, both the average muscular strength and the mean value of peak impulse in 10 seconds in all directions were significantly enhanced (P<0.001), with the average muscular strength increased by 71.1％, 83.7％, 78.6％ and 75.2％ respectively, while the mean value of peak impulse in 10 seconds was increased by 136.9％, 138.5％, 114.1％ and 114.4％, respectively. Conclusions This study provides the physiological basis for establishing the military standards of neck muscular strength training for different fighter pilots, the proper method for training those pilots with low neck muscular strength, as well as the reference of neck muscular training duration and strength target for high performance aircrafts and carrier aircrafts.

Abstract:With the regulation of mechanical microenvironment being realized as an important role playing in the differentiation of bone marrow mesenchymal stem cells (BMSCs), the systematic researches on stem cells are gradually deepened into the extended cellular biomechanical field, which lead to a hot research focus on cellular biomechanical properties, basic mechanical structure units and network-like mechanical architecture among cells. In this paper the analysis on mechanical properties of BMSCs and mechanical molecular basic research on integrins and cadherins are reviewed, and the main frame of network like mechanical regulation is speculated and constructed, combined with the internal bony structure and mechanical geometric properties of the tunneling nanotubes (TNTs). The possibility of synergistic effect among the above important mechanical structures in the network-like mechanical microenvironment is also investigated.