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Abstract:Objective To explore the feasibility of applying fractional flow reserve (FFR) into the assessment of carotid stenosis, and analyze the effects from elastic modulus of vessel wall on hemodynamic parameters of carotid artery stenosis model and FFR calculation results. Methods The standard models of carotid bifurcation and stenosis models with different stenosis rates were established by computer-aided design software. Assuming that the vessel wall was linear elastic material and the blood was incompressible Newtonian fluid, the fluid-structure coupling simulation of blood flow in carotid artery stenosis model under the pulsating flow was carried out by finite element analysis, and the relevant hemodynamic parameters were obtained, and the corresponding FFR was calculated. Results When the elastic modulus was fixed, the FFR for narrow part of the model decreased gradually with the increase of the stenosis rate, and the relative difference between the FFR of elastic wall and rigid wall increased with the increase of the stenosis rate; when the stenosis rate was fixed at 70%, the FFR decreased gradually with the increase of elastic modulus. Conclusions The effect of vascular wall elasticity should be considered in the process of functional assessment on carotid stenosis with FFR; the larger stenosis rate will lead to the greater influence from elastic modulus of vessel wall on FFR.

Abstract:Objective To comprehensively consider the effect of low diverter (FD) implantation on aneurysmal sac and its branches, so as to provide references for making a more reasonable surgical strategy for intracranial aneurysm embolization in clinical practice. Methods Based on computational fluid dynamics (CFD) method, the FD implantation procedure was simulated by using porous media model innovatively. Changes in hemodynamic parameters of aneurysmal sac and side branch with different diameters before and after FD implantation were compared and analyzed, such as blood flow field, velocity, wall pressure and wall shear stress (WSS). Results FD changed the hemodynamic characteristics of aneurysms. The blood flow velocity decreased significantly. The WSS on aneurysmal neck increased, while the difference of WSS between proximal and distal cervical area reduced conversely. Different side branch diameters of vessels had different effects on hemodynamic characteristic changes. The larger diameter would cause the greater blood flow reduction in side branch after FD implantation, but the decrease in velocity of aneurysmal sac and pressure on aneurysmal roof became smaller simultaneously. Meanwhile, the increase of WSS on aneurysmal neck was inversely proportional to the diameter of side branch. Conclusions The larger branch diameter of vessels would cause the worse effect of FD embolization therapy for intracranial aneurysm, worse atherosclerosis improvements and greater possibilities of branch occlusion or other ischemic complications. Doctors should pay more attention to such cases in FD interventional intravascular embolization in clinic.

Abstract:Objective To study the influence of different support heights, support numbers and cross-sectional dimensions on support performance of NiTi thoracic aortic stents. Methods Twenty-seven scaffold models with different parameters were established by using AutoCAD 2016 and SoildWorks 2014 software. HyperMesh 14.0 was used for tetrahedral mesh division, and ABAQUS 2017 was used for support performance simulation analysis. Results With the decrease of support height, the support stiffness would increase; a larger cross-section size would lead to a larger support stiffness; with the increase of support numbers, the support stiffness would increase. Among the influencing factors of support performance, the order of influence degree was support height＞section size＞support numbers. Conclusions The research findings have certain guiding significance for the development and research of thoracic aortic stents, and provide theoretical basis for the selection and optimization of clinical stents.

Abstract:Objective To evaluate the harmfulness of micro-miniature unmanned aerial vehicles (UAV) to human body, especially to head caused by accidental uncontrolled crash. Methods The dynamic numerical simulation analysis was carried out by using ABAQUS software. The free-falling UAV was simplified in different geometric shapes to impact human head and the damage degree of human head caused by the impact was analyzed. Based on the biological tissue performance parameters, human head and neck was simplified as a mass-spring system and the head was modeled with actual skin texture. Results When the UAV fell from 10 m with weight of 0.5 kg, the abbreviated injury scale (AIS) of the disc-shaped UAV was 1.04, and the AIS of the corn-shaped and sphere-shaped UVA were 1.95 and 2.48. For the UAV with the same geometric shape, as the mass and the falling height increased, both impact acceleration of the head and the AIS increased. When the UAV impacted human head at different angles, the disc-shaped UAV exhibited the smallest impact acceleration, AIS and damage degree. The corn-shaped and sphere-shaped UVAs had small differences in impact acceleration and AIS, but their damage degrees were large. Conclusions When the uncontrolled micro-miniature UAV impacts human head, the mass, height or contact shape of the UAV have a significant influence on the damage degree of human head.

Abstract:Objective To explore the dynamic characteristics of the thoracolumbar osteoporotic vertebral bodies under free state. Methods Based on CT data from the thoracic and lumbar vertebral body of a healthy female volunteer, model materialization and intervertebral disc tissue reconstruction were realized by using the computerized processing software. The finite element models of normal thoracolumbar vertebral body and thoracolumbar osteoporotic vertebral body were established in ABAQUS 6.14 to perform modal analysis. Results Compared with the normal model, the osteoporosis model had a lower natural frequency and a lager amplitude. As the vibration frequency increased, the model vibration type changed from uniaxial and unidirectional motion to multiaxial and multidirectional motion, and the responsible vertebral body for the maximum amplitude moved down gradually. Conclusions Modal analysis can better analyze dynamic characteristics of the thoracolumbar osteoporotic vertebral body. Patients with osteoporosis should try to avoid the specific vibration environment, so as to decrease the risk of intervertebral disc tissue degeneration, strain of thoracolumbar soft tissues and lesion in posterior structures of the vertebral body.

Abstract:Objective To study the effects of prosthetic alignment on internal contact mechanical characteristics of intact knee joint for transfemoral amputees. Methods The gait experiment of transfemoral amputees was performed under different alignment conditions, and the differences of lower limb motion and ground reaction force (GRF) were analyzed and compared with those of the non-amputees. The three-dimensional （30） finite element model of knee joint was build and used to analyze the effect of alignments of socket adduction and abduction on internal contact mechanical characteristics between femur cartilage, tibia cartilage and meniscus. Results For knee joint of the non-amputees, contact force was mainly concentrated on the medial sides at the moment of the first GRF peak, while contact force was mainly concentrated on the lateral sides at the moment of the second GRF peak. However, for intact knee joint of the transfemoral amputees, contact force was mainly concentrated on the medial side at the moment of two GRF peaks. The stress of the medial meniscus, contact force and contact area between the medial meniscus and cartilage all obviously increased under the alignment of 6° socket adduction. Conclusions Compared with non-amputees, the incidence of knee osteoarthritis (OA) in amputees was higher, which was related to the long-term overload of the medial knee joint. The alignment of socket adduction may increase the risk of knee OA in the intact side of transfemoral amputees. In clinic, excessive adduction of the socket should be avoided during prosthetic alignment.

Abstract:Objective To analyze the influence of bone graft and prosthesis on stress distributions in internal structure and surrounding bone tissues of implant prosthesis. Methods Two models of maxillary central incisor implants supported by two kinds of labial alveolar bone models were established, which were restored by porcelain fused metal (PFM) crown and zirconia all-ceramic crown, respectively. The mechanical loads were applied to analyze the influence of bone graft and two different prostheses on stress distributions of internal structure of the implant and interface between the implant and bone. Results In bone graft group, the stress in labial part of the retaining screw and labial bone tissues of the implant was much lower than that in non-bone graft group, but the stress of the implant neck was higher in bone graft group than that in non-bone graft group. Under the same bone condition, the stress of zirconia all-ceramic crown group on lip side of the retaining screw was greater than that of PFM crown group. Conclusions Prosthesis have little effect on stress distributions of internal structure and surrounding bone tissues of implant prosthesis, but the difference of labial bone affected by bone grafts can affect stress concentrations of the retaining screw and the implant-bone interface.

Abstract:Objective To analyze mechanical characteristics for stress accumulation of the maxillary complex during expansion until complete fracture of the mid-palatal suture by using the three-dimensional (3D) finite element method, and verify validity of the model. Methods The finite element maxillary complex model containing the microimplants was established. The yield strength of the mid-palatal suture was set, and the transverse displacement of 0.25 mm was loaded every 5 ms as the load until the suture was completely fractured. The CT images of one clinical patient before and after expansion were compared and verified. Results During 0-17 ms, the stress was mainly concentrated around the microimplants, the middle of the mid-palatal suture and the zygomatico-maxillary sutures. During 18-60 ms, cracks began to occur in the mid-palatal suture, and expanded forward and backward. During 61-71 ms, the rupture path was followed by posterior part of the mid, palatal suture-the front part and the back part. Conclusions The 3D finite element model of microimplant-assisted expansion based on fracture mechanics was effective and the calculated fracture process result were more consistent with clinical practice. The research findings provide the mechanical reference model for more effective research on microimplant-assisted palatal expansion in the future.

Abstract:Objective To investigate the high-fat diet effect on morphology and stiffness of endothelial cells. Methods SD rats were randomly divided into high-fat diet group (AS group, n=3) and control group (CON group, n=3). Rat aortic endothelial cells were obtained from rat thoracic aorta by explant method. Cell morphology was observed under inverted microscopy. The mean fluorescent intensity of F-actin in two groups was calculated by immunofluorescence staining. Cell stiffness was measured by atomic force microscopy (AFM). Results The endothelial cells migrated from tissue plant on the 7th day and formed confluence after cultivation for 14 days. Endothelial cells were identified by factor Ⅷ immunofluorescence staining. Cells in AS group showed enhanced perimeter (P＜0.01), aspect ratio (P＜0.01), and area (P＞0.05), while less circularity (P＜0.01) compared with the cells in control group. The mean fluorescence intensity of F-actin in AS group was significantly higher than that in control group (P＜0.01). AFM showed that the cell stiffness of AS group was significantly higher than that of control group (P＜0.01). Conclusions High-fat diet would change the morphology and stiffness of endothelial cells, which might subsequently affect their normal function and become an important incentive to AS.

Abstract:Objective To make biomechanical evaluation on ultimate pullout strength of the suture anchors based on the angle of suture anchor (SA) implanted into the humerus during arthroscopic rotator cuff repair (RCR) surgery. Methods Polyurethane materials with densities of 0.16 g/cm3 and 0.32 g/cm3 were used to simulate osteoporosis and normal cancellous bone, and polyurethane materials with densities of 0.64 g/cm3 and 3 mm thickness were used to simulate human cortical bone. The two kinds of cancellous bone models were respectively adhered together with cortical bone model to construct human humerus model. Titanium metal suture anchors were inserted into humerus models at 45°, 60°, 75° and 90° angle, then the continuous tensile experiments were performed, and 45° pulling direction between the humerus model surface and suture anchor was used to simulate the supraspinatus physiological traction direction, and each group was continuously tested 8 times, recording the pullout strength and failure modes. ResultsThe pullout force of high-density bone models was significantly higher than that of low-density bone models (P＜0.001), and at the same density, compared with 45°, 60° and 75°, the implant angle of 90° has a larger pullout force (P＜0.01). Conclusions In the model of humerus, the 90° implantation of suture anchor showed better biomechanical properties, and the vertical implantation of anchor in the repair of rotator cuff was beneficial to the knotting during operation and postoperative recovery of the supraspinatus.

Abstract:Objective To investigate gait characteristics of both lower limbs in female patients before and after unilateral total knee arthroplasty (TKA). Methods Based on three-dimensional (3D) motion capture system and independent-sample t test, gait parameters of 10 female patients were compared in both lower limbs and compared with those of 10 healthy subjects before and after TKA. Results The preoperative stance phase, peak adduction angle, adduction-abduction range of motion (ROM) and peak flexion moment of the unoperated knee were significantly higher than those of the operated knee (P<0.05), while postoperative gait parameters were similar in both sides. Compared with the control group, the patients had significantly lower speed and stride length, longer double support time before TKA (P<0.05). Moreover, the operated knee demonstrated significantly lower peak extension and adduction angles, adduction-abduction ROM, peak flexion and abduction moments, higher peak adduction moment, and the unoperated knee revealed significantly lower peak extension angle, higher peak flexion and adduction moments than the control group before TKA (P<0.05). The greater differences of peak knee extension angles and adduction moments of both sides still existed in the two groups after TKA (P<0.05). Conclusions Unilateral TKA could ease pain and reduce gait deviations in both lower limbs of patients. However, there were still gait differences compared with the control group. Patients still suffered deficits in joint function, such as muscle strength and proprioception, and revealed pathological gait and posture. It’s advised that patients should enhance muscle strength of the operated limb, and take gait correction exercises. Female patients should also control walking speed to avoid increasing pressure on the knee after TKA.

Abstract:Objective To observe the effects of electro-acupuncture on loading of lower limb joints in patients with knee osteoarthritis (KOA) during stair climbing and explore the related biomechanical mechanism. Methods Forty patients with KOA were randomly assigned, with 20 patients in observation group (electro-acupuncture group, EA group) and 20 patients in control group (superficial acupuncture group, SA group). Finally 18 patients in each group completed the study. In observation group, seven knee acupuncture points were chosen and patients were connected with electro-acupuncture instrument; while in control group, the electro-acupuncture instrument was connected but not electrified after superficial acupuncture at non-acupoint points. The three-dimensional gait analysis system was used to assess the biomechanical characteristics during stair climbing before and after treatment, including peak vertical force (PFz), vertical impulse (IFz) and symmetry index (SI%). Results After 3 weeks of treatment in EA group, PFz of the right foot during stair ascent and PFz of the left foot during stair descent increased (P＜0.05); IFz of both feet during stair ascent and IFz of the right foot during stairs descent significantly decreased (P＜0.05); no significant differences were found in SI% of peak and impulse (P＞0.05). In SA group, only SI of impulse during stairs ascent increased (P＜0.05). There was no significant difference between two groups before and after treatment (P＞0.05). Conclusions Electro-acupuncture can effectively improve the joint load capacity and reduce the dynamic cumulative load of patients w

Abstract:Objective To explore the characteristics of plantar pressure of ankle joints at different limb laterality and different stress positions. Methods Twenty-three healthy subjects were recruited to perform walking trails. Each subject was tested for plantar pressure in ankle neutral position, ankle inversion and ankle eversion through simple custom-designed walkways and plantar pressure plate. The evaluation indices were peak pressure, contact area, contact time percentage, M/L (ratio of sum of medial plantar peak pressure to sum of lateral peak pressure), A/P (ratio of sum of toe peak pressure to heel peak pressure). Results The peak pressure of the first metatarsus bone in the dominant foot was significantly larger than that in the non-dominant foot, and the peak pressure of the fifth metatarsus bone was significantly smaller than that on the non-dominant foot. The M/L of dominant side was significantly larger than that of the non-dominant side. Except for the peak pressures of the mid-foot and the first toe, there were significant differences in other regions among the three ankle positions. The percentage of contact time in each area during inversion was greater than that in neutral position, and the percentage of contact time of plantar regions during eversion was longer than that in neutral position except the second toe. The M/L in inversion, neutral and eversion position were 1.24±0.46, 1.06±0.26, 0.88±0.25. The M/L of dominant foot was greater than that of the non-dominant foot, and the A/P during inversion and eversion was greater than that in neutral positions. Conclusions The stability of the dominant foot was better than that of the non-dominant foot. The standing stability decreased during inversion and eversion. During inversion, the body shifted inward and forward to maintain the stability. During eversion, the center of gravity shifted outward and forward to maintain the stability.

Abstract:Objective To build a method for calculating the optimal length of hamstring muscles in vivo, and make comparison with other indirect parameters which represent the optimal length. Methods By synchronously recording knee flexion torque and kinematic data, the musculoskeletal model of lower limbs was built to obtain hamstring strength and muscle length, and to further calculate the optimal length of hamstring muscles. Results Flexion angle at peak knee flexion torque was significantly greater than that at peak hamstring strength and their correlation coefficient was 0.741. The optimal lengths of each bi-articulated hamstring muscles were significantly greater than the corresponding muscle lengths during standing and their correlation coefficients was low. Conclusions The established estimating method for optimal length of hamstring muscles provided references for future studies on injury mechanism and risk factors. Flexion angle at peak knee flexion torque could partly represent the optimal length of hamstring. It is not suggested that hamstring muscle length during standing should be used as an approximation of hamstring optimal length.

Abstract:Objective To construct an early warning model of fall risk for the elderly based on six kinds gait parameters. Methods A digital field was used to collect parameters from six kinds of gait for the elderly with or without the history of falls, and the binomial logistic regression analysis was used to establish a regression equation for predicting the fall risks in the elderly, and an early warning model was constructed. Results The regression equations constructed according to the parameters from six kinds of gait were statistically significant. The overall correct rate was predicted from high to low: walking forward with closed eyes (97.1%), walking backward with open eyes (92.9%), walking backward with closed eyes (88.6%), walking forward with open eyes (87.1%), turning head up and down with open eyes (85.7%), turning head left and right with open eyes(82.9%). The constructed early warning model for fall risk of the elderly mainly included five steps, namely, judgment, test, extraction, calculation and early warning, which was suitable for gait testing and evaluation of the elderly in the laboratory. Conclusions Parameters from six kinds of gait could predict the fall risk of the elderly. Among them, walking forward with closed eyes was best to predict the fall risk in the elderly. The established early warning model of fall risk for the elderly could be used to predict the fall risk of 65-75 year old people within one year, which could provide early warning based on the probability of falling, playing a positive effect on preventing falls in the elderly.

Abstract:Objective To investigate the correlation between mechanical properties and hemostatic ability of the sealing hydrogels. Methods The gelation time, elastic modulus, viscous modulus, bursting strength and hemostatic ability of the hyaluronic acid/gelatin hydrogels were measured. Compared with fibrin sealant, gelation time and mechanical parameters were proposed to judge the feasibility of sealing hydrogels to be used for hemostasis in clinic. Results Hydrogels with a long gelation time, low elastic modulus, low viscous modulus and small bursting strength were merely suitable for hemostasis in minor bleeding. The hydrogels with short gelation time, high elastic and viscous modulus and large bursting strength could effectively reduce the blood loss in the cases of massive bleeding. Conclusions The hemostatic ability of a hydrogel was correlated to its gelation time, elastic modulus, viscous modulus and bursting strength. To achieve hemostasis as effective as fibrin sealant, the gelation time of a sealing hydrogel should be less than 120 s, its elastic and viscous modulus should exceed 600 Pa and 120 Pa, respectively. For the damage with diameter of 2 mm in the tissue model, the burst strength should exceed 10.7 kPa and preferably be larger than 16.0 kPa.

Abstract:The elastic stress and viscous shear stress experienced by the vessel wall under pulse blood pressure and blood flow and the mechanical properties of the substrate constitute the in vivo mechanical niches of vascular cells, and these mechanical stimuli are involved in regulating the biological responses of vascular cells and inducing the remodeling and pathological changes of vascular tissues. Although many experimental studies on vascular mechanobiology have been reported, the quantitative correlation between the mechanical stimuli of in vitro experiments and the physiological and pathological conditions of blood vessels remains to be elucidated. This paper summarized the quantitative evaluation method of in vivo mechanical niches of vascular cells from the viewpoint of biomechanics, and then focused on effects of the physiological locations and aging on mechanical behaviors of the vessel wall. This paper also explored the physiological and pathological characteristics of the cellular mechanical niches and their implications for current vascular mechanobiological studies.

Abstract:The aerodynamic characteristics of bobsleigh play a very important role in the result of the race. In order to improve the performance, it is necessary to optimize the bobsleigh aerodynamics and reduce its aerodynamic drag as much as possible. Foreign scholars has mainly used computational fluid dynamics (CFD) numerical simulation, wind tunnel experiments and other methods to study the aerodynamic characteristics and optimize drag reduction method, but the relevant research has not yet been carried out in China. In order to have a clear understanding of the technical requirements of bobsleigh aerodynamic optimization and drag reduction, the research result of bobsleigh aerodynamics in recent 20 years have been systematically combed, mainly including numerical simulations and wind tunnel experiments of aerodynamic optimization of bobsleigh body shape and athletes’ positions and attitudes in the bobsleigh, and the possible future development direction of bobsleigh aerodynamics research has been put forward: the systematic study of bobsleigh aerodynamics optimization and comprehensive assessment of bobsleigh aerodynamic drag reduction effects; the study on the interaction between athlete glide control and bobsleigh aerodynamics. These studies will provide an important scientific guidance for the optimization and improvement of bobsleigh sports equipment and the daily training of athletes.

Abstract:Osteoarthritis (OA) is a chronic degenerative joint disease characterized by joint pain and stiffness, which predisposes to the elderly. The onset of OA is slow, the course of disease is long, and the early clinical manifestations and histological changes are not obvious, which limits the early diagnosis and treatment of the disease. The micro-structure of articular cartilage determines the macro-mechanical properties of cartilage. The micro-structure of articular cartilage changes in a depth-dependent manner, which makes the mechanical properties of cartilage also depth-dependent. From superficial to deep areas of cartilage, the anti-load and anti-deformation ability of cartilage increases gradually. However, with development of the disease, the change of cartilage micro-structure leads to the decrease in load resistance and deformation resistance of OA cartilage. Therefore, the mechanical properties of articular cartilage can be inferred by detecting the micro-structure of articular cartilage. On the other hand, the mechanical properties of articular cartilage can be used to understand the micro-changes of cartilage, which is helpful to understand OA development and facilitate early diagnosis of the disease. This paper reviewed the recent research literatures on mechanical properties of articular cartilage under normal and acute or chronic injuries, and elaborated the relationship between the structure and mechanical properties of articular cartilage, which further provided the theoretical basis for the OA development, early diagnosis and treatment.