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Abstract:Biomechanics has become one of the most active research fields in biomedical engineering. In recent years, remarkable progresses in biomechanics have been made in exploring the mechanism from cellular and molecular level, and developing new therapeutic or diagnostic concepts and technologies based on biomechanical theory and methods, which effectively promote the development of basic biomedical science and clinic, and relevant research fields related to human health and diseases. In this review, the advances in biomechanics of vascular, musculoskeletal system, organ, cellular and molecular research fields, etc. in China during the year 2016-2018 were mainly introduced.

Abstract:Objective To investigate the influence of straightening phenomenon caused by stent implantation on biomechanical environment changes in vascular lesions, so as to explore biomechanical mechanism of restenosis and stent optimization. Methods Based on the computed tomography (CT) images of a patient, the balloon model, the left anterior descending coronary(LAD) artery model and two stent models (idealized stent and straightened stent) were reconstructed by Mimics, Geomagic and Pro/E software. The balloon-stent-LAD artery mechanical models were then established with the ABAQUS software. Based on the numerical simulation results, the influence of straightening phenomenon on mechanical environment at vascular lesions was analyzed. Results When the stents were expanded under the same inflation pressures (1.013 MPa), the Von Mises stress increased on vascular wall of the straightened stent model compared with the idealized stent model, and stress concentration occurred especially at the proximal and distal area of the stented regions and on the myocardial surface. The average and the maximum Von Mises stress on vascular wall of the idealized stent model were 0.39 MPa and 5.12 MPa, respectively. The average and the maximum Von Mises stress on vascular wall of the straightened stent model were 0.45 MPa and 7.43 MPa, respectively. Conclusions The straightening phenomenon caused by stent implantation would change the distribution of Von Mises stress and induce stress concentration. This kind of mechanical environment would cause greater damage to vascular wall, then might cause mechanical injury and vascular remodeling, leading to a higher risk of neointimal hyperplasia and subsequent restenosis. The research findings will be helpful for explaining the mechanism of in-stent restenosis, and may provide clinical guidance for the interventional surgery and optimization of stent design.

Abstract:Objective To analyze the hemodynamic parameters of Stanford type B aortic dissection based on computational fluid dynamics (CFD), so as to make a thorough evaluation of the disease. Methods Based on CTA images of a patient with complex Stanford type B aortic dissection, the three-dimensional model and hemodynamic numerical simulation were carried out to analyze the velocity distribution of flow field and intersecting fracture profile, as well as the wall shear stress. Results The maximum velocity of blood flow at the entry tear and re-entry tear could reach 1.2 m/s and 2 m/s, respectively, providing references for further evaluation on aortic rupture position and prediction of aortic rupture risk. An obvious low wall shear stress zone was formed on false lumen wall near the entry tear, which was consistent with the thrombus position in the patient. Conclusions CFD could effectively analyze the hemodynamic characteristics of complex aortic dissection, obtain the correlation between aortic dissection and wall shear stress at aorta arch and descending aorta, which contributed to guiding clinical assessment of aortic function for preventing the diseases.

Abstract:Objective To study the hemodynamic effect of the convertible vena cava filters on treating pulmonary embolism with different thrombus diameters and contents. Methods Three kinds of simulated filter models with the same diameter but different filtering structures (L-style, S-style and W-style) were built and then the hemodynamics of the filter after its implantation into the vessels was analyzed by using computational fluid dynamic (CFD) method. Results Without thrombus in the vessels, three kinds of filters in blood had some obstructive effects and increased the average outlet velocity. While the L-style filter caused the maximum average outlet velocity, the S-style filter was in the middle, and the W-style filter was the lowest. Under the condition of thrombus, the structures of the filter rods had no obvious effect on the average outlet velocity of blood flow and thrombus, and differential pressure of blood flow and thrombus between inlet and outlet. With the increase of thrombus’s diameter and content, the hemodynamic factors showed varying degrees of decreasing tendency. The wall shear stresses (WSS) on three kinds of filter rods caused by blood flow were in normal ranges, and WSS on the lower end of filter supports, the joints of supports and filter rods were below the minimum value, where thrombosis was easy to occur. Conclusions The hemodynamic effect of three kinds of convertible vena cava filters with different filtering structures, different thrombus diameters and contents in vessels were analyzed by using CFD method, which would provide theoretical references for the design and development of novel filters.

Abstract:Objective To study the changes of nitric oxide (NO) concentration in arterial-capillary-venous vessels and the dynamic regulation mechanism of NO on the vessels during ventilation changes. Method The pulmonary vascular network model was established by using the COMSOL Multiphysics software, the dynamic regulation of NO on blood vessels was introduced, the flow-multiphysics coupling simulation was conducted to explore the effect of oxygen and blood flow on NO concentration and its distribution in pulmonary vascular network, and the dynamic regulation of NO on pulmonary vascular function in the case of ventilation lacking. Results Oxygen concentration and blood flow would jointly affect the NO distribution in the pulmonary vascular network. When lung ventilation was insufficient, the amount of oxygen entering the pulmonary capillaries decreased, and the NO concentration in pulmonary vein walls under static conditions was significantly reduced. The reduction of NO concentration under dynamic conditions led to vasoconstriction and decrease of blood vessel radius, resulting a dynamic compensation. Regulation of vascular tension regulation coefficient α would directly affect the regulation of NO. When α worked within a certain range, a higher value of α meant a larger change in vascular radius and a smaller change in NO concentration, and its effective value was greater than 1. Conclusions The research findings revealed the change of NO concentration in arterial-capillary-venous vessels due to the change of ventilation as well as the dynamic regulation mechanism of NO in blood vessels, and predicted the effective value range of α，thus providing theoretical basis for further research on the mechanism of blood flow, ventilation perfusion ratio affected by vasoconstriction and vascular resistance changes due to ventilation insufficiency.

Abstract:Objective To study the effect and mechanism of capillary microcirculation disturbance on intracerebral hemorrhage. Methods The loading effect of capillaries was replaced by the introduction of porous media. A microcirculation model from the capillaries to the veins was established. The appropriate mechanical boundary conditions were set up for the model by referring to various physiological conditions of human body, and the changes in blood pressure and stress of vascular wall under various conditions were simulated. Results Under normal circumstances, the whole blood pressure of the LSA was relatively low, and the pressure difference between the beginning and the end of the LSA was more obvious, and the stress of all parts of the vascular wall was at the same level. In the case of microcirculation disorder, the whole blood pressure of the LSA increased and the pressure difference between the beginning and the end of the LSA significantly decreased. The stress for each part of the vessel increased and the stress at the end of the LSA increased most significantly. Conclusions The influence of microcirculation disturbance on hemodynamics of the LSA was particularly significant. It was an important factor leading to hemorrhage of the LSA rupture. The research findings are of important theoretical and practical significance for understanding the mechanism of cerebral vascular rupture and preventing the occurrence of cerebral hemorrhage in the case of microcirculation disturbance.

Abstract:Objective To investigate the mechanism of occurrence and rehabilitation of heel pain, so as to provide a theoretical basis for the effectiveness of heel pain treatment. Methods The CT and MRI data acquired from feet and knees of patients with heel pain were reconstructed to establish the bone-muscle composite finite element model. Based on the established model, the effect of calf muscle contracture on biomechanical properties of the foot and ankle was simulated by using the finite element method . Results When the calf muscles produce upward lifting power, plantar pressure was transferred from the heel area to the forefoot area, and there was no significant difference in pressure distribution by different combination schemes of muscle forces. The strain of the plantar fascia was increased, with stress concentration on the calcaneus surface. Under 240 N force, the peak stress at the Achilles tendon attachment position and the calcaneus nodules was up to 10.82 MPa and 11.2 MPa, respectively. Conclusions The stress concentration in calf muscles and Achilles led to the changes in biomechanics of the ankle, which resulted in heel pain. The method of improving the overall biomechanical environment by releasing concentrated stress to restore the position of the bones and joints of the ankle joint is the mechanism for rehabilitation of heel pain.

Abstract:Objective To investigate the feasibility of manual reduction with inverse shift for pronation-extorsion trimalleolar fracture by applying the finite element method combined with clinical experience. Methods Based on CT images and anatomical features of bone, ligaments and other tissues as well as material parameters, a normal ankle model with completed muscles and bones for a Chinese young male was established. According to the related characteristics of the pronation-extorsion trimalleolar fractures, fracture was simulated in the proper position to make osteotomy model. The finite element model of pronation-extorsion trimalleolar fractures was thus established and then applied with mechanical loading to simulate manual reduction with inverse shift. Results The established finite element model of pronation-extorsion trimalleolar fractures was effectively restored by the displacement loading. Conclusions The finite element analysis on pronation-extorsion trimalleolar fractures by inverse shift maneuver could further prove the feasibility, effectiveness and scientificity of manual reduction with inverse shift based on clinical experience.

Abstract:Objective To compare the biomechanical effects of n-HA/PA66 vertebral body cage and percutaneous vertebroplasty for treating osteoporotic vertebral fracture, so as to provide theoretical foundations for clinically choosing operative approach and numbers of n-HA/PA66 cage. Methods Based on finite element models of normal vertebral T11-L3, four finite element models of vertebral T11-L3 with n-HA/PA66 cage implanted by different approaches (transversus approach A, B and psoas major muscle approach A, B) were established. Two controlled models without intertransverse ligaments were also built. Besides, two finite element models of osteoporotic vertebral T11-L3 with injection of 1.8 mL or 3.6 mL bone cement were built, respectively. The loads of 500 N and force torque of 7 N·m from different directions were applied on nine models, to calculate and analyze the displacement and stress of the osteoporotic vertebrae during standing, extension, anteflexion, lateral bending, and rotation, and to investigate the biomechanical effects from two kinds of osteoporotic vertebral fracture treatment on vertebral body. Results Under the same loading, bone cement could lead to a larger stress increase while a smaller displacement decrease in vertebral body compared with n-HA/PA66 cage. The model with n-HA/PA66 cage implanted by psoas major muscle approach A (namely, a cage was implanted through psoas major muscle) had the minimal increase in vertebral stress while the maximum decrease in displacement. Conclusions In order to reduce the risk of the additional fracture due to stress increment and recover the stiffness of osteoporotic vertebrae, clinicians are suggested to implant one n-HA/PA66 cage through psoas major to treat the osteoporotic vertebral fractures.

Abstract:Objective To investigate the gene expression of Piezo1 in four types of bone cells at different stages of osteogenic differentiation under fluid shear stress (FSS). Methods The mouse-derived mesenchymal stem cells (MSC), osteoblast-like cells MC3T3-E1, post-osteoblasts MLO-A5 and osteocytes MLO-Y4 were exposed to FSS at different magnitude (0.1, 1.1 Pa) with a custom-made cone-plate flow chamber for 0.5, 1, 3, 6, 12 h, respectively. The expression of Piezo1 mRNA was assessed by quantitative real-time polymerase chain reaction. Results Both Piezo1 and Piezo2 were expressed in four types of bone cells. The expression of Piezo1 was significantly up-regulated in all cells under FSS stimulation, and the expression level under 1.1 Pa FSS was significantly higher than that under 0.1 Pa FSS. In addition, the expression of Piezo1 in MSC, MC3T3-E1 and MLO-A5 cells increased to the highest level at 1 h under FSS stimulation. The expression of Piezo1 in MC3T3-E1 cells was much higher than that in the other three types of cells. Conclusions The expression of Piezo1 was related to the process of osteogenic differentiation, FSS level and loading time, and this research finding is of great significance to reveal the mechanism of mechanotransduction in bone tissues and to establish clinical treatment for bone diseases.

Abstract:Objective To study the mechanical properties of porcine descending aorta. Methods The porcine descending aortas were divided into 5 groups by the distance from the heart, and tissues in each group were subdivided into ventral-quadrant part and lateral-quadrant part. Stress-stretch curves were obtained by using uniaxial tension test. The moduli of elastic and collagen fiber and collagen fiber recruitment parameter of tissues in 5 groups (Position 1-5) were first analyzed by a classical mathematical model. Then the mechanical differences between tissues of ventral quadrant and lateral quadrant were compared. Results The modulus of circumferential collagen fibers increased gradually away from the heart. The modulus of circumferential elastic fibers had the same trend except for tissues at Position 5 (the most distal one). The elastic fibers modulus of tissues decreased at Position 5. At the most distal position, the circumferential and axial elastic fiber modulus of the lateral quadrant was lower than that of ventral quadrant by 19% and 33%, respectively. The axial and the elastic fiber modulus of the ventral quadrant was similar with that of tissues at Position 4 and 5. For the whole descending aorta, the circumferential collagen fiber modulus of the lateral quadrant was higher than that of ventral quadrant by 26% and the circumferential elastic fiber modulus of the lateral quadrant was higher than that of ventral quadrant by 16% at the proximal 4 positions. Conclusions The circumferential mechanical properties of porcine descending aorta were related with regions. The ventral quadrant of the most distal aorta showed abnormally soft trend. The research findings can be used to better understand the mechanism of aorta and improve the spatial accuracy of computer models.

Abstract:Objective To evaluate the characteristics of spatial distribution and time accumulation of impact acceleration at different parts of human body during backward falling process. Methods Four healthy men and four healthy women (20-20 years old) were enrolled. The tri-axial acceleration on head, chest, left/right arm/hand/foot, left/right front/back hip, left/right femur head, sacrum and coccyx throughout the backward falling were measured by ADXL335 tri-axial acceleration sensor. Systemic acceleration distribution of backward falling was polynomial fitted by signal magnitude vector (SMV) of its first peak. Besides, parameters of impulse mechanics such as zero-g time, total falling time, peak SMV, relative pressure impulse of the vulnerable sites (head, hip and its related sites) were also calculated. Results Compared with the other parts of the body, the peak SMV and relative impulses of left/right back hip and head were significantly higher (P＜0.05). Acceleration that paralleled to the ground in left/right back hip was also relatively large. The rotational transform angles of left/right back hip, left/right femur head, sacrum and coccyx were significantly larger (P＜0.05). In addition, during the process of falling backward to the ground, a sliding tendency toward the sagittal plane 53.58°±6.75° occurred at all testing sites. Conclusions Head and hips are vulnerable during backward falling, and their zero-g time (0.26±0.05) s can be used as the longest starting time of falling protection devices. The large change angle of left/right hip, left/right femoral head, sacrum and coccyx may be the important cause of the sprain during backward falling.

Abstract:Objective To explore the correlation between gait parameters at 14 days and knee function and quality of life at 3 months after total knee arthroplasty (TKA). Methods Eighteen patients who underwent TKA were analyzed by using three-dimensional gait analysis system to observe their gait parameters. Knee joint function and life quality of the patients at 3 months after TKA were evaluated with WOMAC (Western Ontario and McMaster Universities Arthritis Index) and SF-36 (short form 36-item health survey scores) assessment scale and their correlations were analyzed simultaneously. Results At 14 days after TKA, single support time (SST) and peak knee flexion at swing (PKF) of the operated side of the leg were significantly smaller than those of the healthy side of the leg. The knee flexion angle at mid-stance (MKF) and knee valgus angle at mid-stance (MKV) of the operated side of the leg were significantly larger than those of the healthy side of the leg. There was a moderate negative correlation between the spatiotemporal parameters of the operated side of the leg and the WOMAC score during gait, while a high correlation between the WOMAC score and peak knee flexion at swing (PKF), MKF and MKV. Except for the step length and forward velocity, the other gait parameters were significantly correlated with SF-36 life quality score. The single support time (SST) and PKF had a highly positive correlation, while the MKF and MKV had a moderate negative correlation with SF-36 life quality score. Conclusions The SST, MKF, MKV and PKF in postoperative early gait analysis (14 days) results can be used as the effective indicators to judge postoperative knee function and rehabilitation efficacy of life quality after TKA surgery.

Abstract:Objective To study the biomechanical influence of posterior laminectomy with varying extent on adjacent segment after lumbar interbody fusion. Methods Three finite element models of lumbar posterior fusion were developed based on the validated intact lumbar model. These models were: posterior fusion with bi-lateral incision of facet joint (Bi-TLIF），inferior partly incision of laminar (PLIF)，total laminectomy (LAM-PLIF). The range of motion (ROM), intradiscal pressure (IDP), facet joint contact force (FJF) of adjacent segment of fusion models under various loading were compared with the intact model. The follower load of 400 N under 7.5 N·m torque was exerted on superior endplate of L1 segment. The 6-DOF (degree of freedom) of sacroiliac joint surface was constrained during loading. ResultsDuring flexion, obvious biomechanical changes of superior adjacent segment (L3-4) were found in Bi-TLIF, PLIF, LAM-PLIF surgery groups. Compared with the intact model, the ROM in Bi-TLIF, PLIF, LAM-PLIF group increased by 1.0%, 9.3%, 24.5%, respectively, while IDP in the above fusion groups increased by 1.4%, 4.3%, 10.0%，respectively. These changes were not obvious in other postures. For FJF, the Bi-TLIF and PLIF group showed obvious increasing effect on L3-4 segment, while almost had no effect on L5-S1 segment. Conclusions Laminectomy increased ROM, IDP and FJF of adjacent segment (especially superior adjacent segment) after posterior lumbar fusion, which might increase the risk of adjacent segment degeneration. This biomechanical effect was more obvious with the increase in incision range of laminar. Therefore, preserving more posterior complex during decompression has a positive effect on preventing adjacent segment degeneration (ASD) following lumbar fusion surgeries.

Abstract:Bone remodeling can keep the biomechanical properties, which is of great significance to maintain bone strength. Normal skeletal development requires tight coordination of transcriptional networks, signaling pathways and biomechanical cues, and many of these pathways are dysregulated in pathological conditions affecting bone. lncRNA is a group of RNAs with broad biogenesis, which are longer than 200 nt and highly conserved in their secondary and tertiary structures. Studies show that many lncRNAs are involved in normal development or balance of the skeletal system, the regulation of osteoblast differentiation, and the pathogenesis of osteosarcoma. Dysregulation of lncRNA expression is closely related to many bone diseases and it is expected to be a biomarker for predicting bone diseases. In this review, the characteristics and mechanisms of lncRNA involved in bone remodeling and its possible role were summarized, and the likely utility of IncRNAs as biomarkers and therapeutic targets for diseases of the skeletal system was discussed, including osteoarthritis, osteoporosis, and cancers of the skeletal system, so as to provide references for the better understanding and study on lncRNA biological function in organisms.

Abstract:Risk factors for running injuries can be clustered into intrinsic factors and extrinsic factors. Intrinsic factors include human anatomy, history of previous injuries, sports biomechanics and human neuromuscular control, etc. Extrinsic factors include training method , running shoes and running surfaces, etc. Running surface is considered as one of the most potential risk factors for running injuries. This review summarized the findings on kinematics, kinetics, neuromuscular control and running injuries of lower extremity during running on different surfaces. In general, neuromuscular adjustment may contribute to kinematic adaption during running on different surfaces, and runners can adapt their kinetics and stiffness of lower extremity to achieve similar impact force. However, studies on biomechanical changes during running on different surfaces mainly focus on only one aspect of kinematics, kinetics and neuromuscular regulation. Further studies should focus on three-dimensional biomechanical analysis during running on different surfaces, as well as specific mechanisms of neuromuscular regulation for these biomechanical adjustments.

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