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Abstract:The critically ill coronavirus disease 2019 (Covid-19) patients usually present acute respiratory distress syndrome (ARDS), or even acute respiratory failure, and require mechanical ventilation (MV) to provide support for breathing. However, clinical studies have found an extraordinarily high mortality rate (>50%) for those Covid-19 patients who underwent MV. Considering the mechanical nature of MV, the high mortality rate is highly possible to be associated with mechanical stretch-induced lung injury during MV. Thus, it is imperative to understand the MV-induced pathological alterations in the respiratory system and corresponding mitigation measures in order to improve the therapy of critically ill Covid-19 patients. Ventilator-induced lung injury in therapy of critically ill Covid-19 patients involves several biomechanical factors and mechanisms, including changes in respiratory parameters, inflammatory cytokines storm, ciliary-mucus system, airway smooth muscle cells, lung fibrosis, and stretch-activated cell signaling. It is hoped that these biomechanical issues can be diligently investigated, so as to provide insights for optimizing the therapy for Covid-19 as well as other respiratory diseases.

Abstract:Objective To investigate the pathogenesis of type-B aortic dissection by using morphological analysis and computational fluid dynamics (CFD) method, so as to provide evidence for the effective prediction of type-B aortic dissection. Methods Six primary type-B dissection cases scanned by CT (dissection group) and six normal cases applied to black-blood MRI (control group) were included in this study and patient-specific three-dimensional (3D) models of aorta were established through image segmentation and 3D reconstruction. The pre-type-B dissection aortas were constructed by applying the scaling algorithm to shrink the dissection and then compared with subjects in control group. The differences between morphological parameters and hemodynamic parameters of the two groups were compared. Results Compared with the normal cases, the area of the descending aorta increased dramatically in dissection group ［(892.03±263.78) mm2 vs (523.67±64.10) mm2, P=0.036］. A significant decrease in angle of the left subclavian artery occurred (66.62°±20.11° vs 100.40°±15.35°, P=0.036). The tortuosity of the aorta also had an obvious increase (0.37°±0.07° vs 0.21°±0.51°, P=0.011). The time-averaged wall shear stress (TAWSS) in dissection group was obviously higher than that in control group; the flow in the dissection region was vortex flow at low speed and the oscillating shear index (OSI) was higher. Conclusions The results of this study can be used to provide guidance for the early diagnosis and treatment of type-B aortic dissection.

Abstract:Objective Hemodynamic disorder of the pulmonary artery (PA) is the main cause of pulmonary arterial hypertension related to congenital heart disease (PAH-CHD). To study the hemodynamic characteristics of PA, so as to understand biomechanical factors in the occurrence and development of PAH-CHD. Methods Clinical and imaging data were collected in five PAH-CHD patients and five matched controls (Non-PAH) to reconstruct subject-specific three-dimensional (3D) PA models. Computational fluid dynamics (CFD) was performed to compare the hemodynamic difference of flow patterns, wall shear stress (WSS) and normalized energy loss (E·) in the two groups. Results Hemodynamics-related parameters showed that the velocity and WSS were higher in the left and right PA branches of PAH-CHD patients, with significantly lower WSS in the main PA. The E· significantly increased in PAH-CHD patients and positively correlated with normalized PA diameter and inflow. Conclusions Compared with Non-PAH subjects, PAH-CHD patients have obviously higher velocity and WSS in PA branches, lower WSS in main PA and greater E·, indicating these hemodynamic parameters are related with the PAH-CHD, which can be used as potential biomechanical factors for the clinical evaluation of PAH-CHD.

Abstract:Objective To analyze the hemodynamic parameters of anomalous origin of the right coronary artery from the left coronary artery sinus (AORL) based on computational fluid dynamics (CFD), so as to make an evaluation of the disease. Methods A normal right coronary artery (RCA) case and an AORL case were selected. Two models were reconstructed in Mimics software and imported into ANSYS CFX software for hemodynamics simulation. The hemodynamics of normal RCA model and AORL model were compared. Results AORL model had a smaller volume flow (9.35 cm3/s), which might lead to insufficient blood supply downstream of the RCA; the pressure at the acute corner of AORL model (13.78 kPa) was lower than normal RCA model (14.9 kPa); the wall shear stress (WSS) of AORL model (12.83 Pa) was larger than that of normal RCA model (9.74 Pa); the total deformation of AORL model was relatively large. Conclusions The entrance velocity and pressure of AORL were lower than those of normal RCA, which might lead to ischemic symptoms. The research findings are of theoretical significance for the effective evaluation of ischemia and other diseases in clinic.

Abstract:Objective To establish a comprehensive method combining physical model experiment and numerical simulation for studying airflow state of upper respiratory tract. Methods Based on CT medical images published online, a three-dimensional (3D) model of human upper respiratory tract was reconstructed. Based on 3D printing technology, an experimental model of the upper respiratory tract was established and the flow process of respiration was measured. A numerical simulation model was created based on the meshing of upper respiratory tract model and the turbulent Realizable k-ε model. Results Firstly, the result of numerical simulation was compared with the experimental conditions, and good agreement was achieved. The numerical simulation results showed that the airflow in respiratory process was in a parabolic shape; the distribution of flow field, pressure on wall and vortex structure were different between inspiratory and expiratory phases; there were air residues in the upper and lower nasal passages during the respiratory exchange process. In addition, the effects of airflow on physiological environment of the upper respiratory tract were preliminarily analyzed through the steak line, pressure field and vortex structure distribution. Conclusions The method proposed in this paper has the characteristics of pertinence, rapidity and accuracy, which gives full play to the advantages of reliable physical experiments and fine numerical simulation, and is applicable for studying different problems of the upper respiratory tract in different cases, with a high value for personalized diagnosis and treatment in clinic.

Abstract:Objective The flow field of electromagnetically driven pulsating perfusion blood pump was simulated by computational fluid dynamics (CFD) method, and the flow state of blood in blood pump was improved by modifying the structure of pump head, so as to improve its anti-hemolytic performance. Methods The influences of changes in pump head structure on flow field in the pump were analyzed by using Fluent 17.0. Four simulation experiments were carried out to analyze streamline distributions of the internal liquid, the turbulent flow energy distribution on axis of the model, pressure loss of blood flowing through the pump head and shear stress on surface of the model. Results In the four experiments, when the angle between the inlet and outlet of the pump head was symmetrical and the angle between the pump head and the symmetrical axis (α) was 30°, there was no obvious disturbance in the flow line and the turbulence degree was low. In Experiment 1, the pressure loss was 376.8 Pa, with the minimum value. The maximum shear stress in Experiment 2 and 3 was 258.6 Pa and 302.8 Pa, respectively, which met the biomechanical requirements of blood pump such as pressure loss and hemolysis. The model with α=30° was selected as pump head structure of the pulsating blood pump driven by electromagnetic force, and was fabricated by 3D printing technology. Conclusions By optimization of the pump head, the hemolysis performance of the blood pump was improved. The research results can be applied to the design and experiment of a new electromagnetic drive pulse perfusion blood pump.

Abstract:Objective To study the changes in biomechanical properties of human cornea after laser in situ keratomileusis (LASIK) and predict corneal stiffness after the LASIK surgery. Methods According to the measurement results from corneal visualization scheimpflug technology (Corvis ST), the corneal tangent stiffness coefficient (STSC) and energy absorbed area (Aabsorbed) were calculated. The change patterns of corneal stiffness and viscosity after refractive surgery were analyzed. Results The difference of corneal STSC and Aabsorbed before and after LASIK had a statistical significance (P<0.05). The obtained formula for predicting corneal stiffness after refractive surgery was: Sbefore surgery =1.055bIOPbefore surgery + 0.015CCTbefore surgery，Safter surgery =0.937Sbefore surgery +0.019CCTafter surgery. Conclusions LASIK surgery not only changes corneal thickness, but also reduces corneal stiffness and viscosity. Prediction of corneal stiffness after surgery can provide guidance for the design of clinical surgery and improve the safety of surgery.

Abstract:Objective To design and develop an in vitro simulation device for circumferential stress of mural coronary artery, so as to achieve the in vitro loading of mural circumferential stress under coronary myocardial bridge oppression with different degrees. MethodsUsing the in vitro simulation device for myocardial bridge coronary artery hemodynamics, the in vitro measurement of mural circumferential stress was achieved. Based on the experimental data, the in vitro loading of mural circumferential stress under coronary myocardial bridge oppression with different degrees was achieved. Results The in vitro measurement experiment showed that the maximum, average and fluctuation of circumferential stress at proximal end of mural coronary artery would increase significantly with the increase in the degree of myocardial bridge oppression. The in vitro loading experiment of mural circumferential stress verified that the loading waveform coincided basically with the experimental waveform from in vitro measurement. Conclusions The device could realize the in vitro loading of mural circumferential stress, which provided an in vitro simulation platform which was as close as possible to the in vivo environment, so as to explore the influence from hemodynamic abnormality of proximal mural coronary artery on the occurrence of atherosclerosis and plaque rupture.

Abstract:Objective To realize the extra-oral measurement of initial recovery force produced by orthodontic wire using simulated dental model. Methods A clinical patient was selected as the study objective, and maxillary dental models, which were in accordance with the real dentition of patient, were fabricated by three-dimensional printing. An orthodontic force measuring system was constructed using Nano17 F/T mechanical sensors to measure the initial recovery forces on two maxillary central incisors, which were produced by a standard circle Ni-Ti wire with the diameter of 355.6 μm after the archwire was assembled on the dental model. Results Central incisor 21 suffered a lager initial orthodontic force compared with incisor 11, and the force systems on two incisors were both adverse to tooth ideal movement, therefore, an assistive device was necessary to improve force status of the teeth. When the orthodontic treatment plan was optimized, a satisfactory result was obtained after 18 months of treatment. Conclusions Force systems caused by orthodontic wire and exerted on the teeth could be accurately measured using the simulated dental model of patient, so as to predict the teeth moving type, and improve teeth treatment plan on this basis. The extra-oral measuring technique of orthodontic force provides an important reference for clinical orthodontic treatment, and creates a novel idea for the optimal design of orthodontic plan.

Abstract:Objective To investigate the pathological mechanism of spinal injury by axial compression experiment on animal spine, so as to provide references for the treatment, prevention and research of spinal injury. Methods The biomechanical study of rabbit spine segments was performed by axial segment compression experiment. The compression process was recorded and strain analysis was performed by digital image correlation (DIC) technology. Results From the top to the bottom of the spine, the ultimate load and bearing capacity of the segment increased continuously; the average limit load of the corresponding single vertebral body was significantly larger than the segment; the strain of the intervertebral disc in the horizontal and vertical directions was significantly larger than that of the upper and lower vertebral bodies. Conclusions In the process of spine compression, the bearing capacity of the intervertebral disc should be taken into account and the injury of spinal segments is mainly manifested as abnormality of the intervertebral disc. The research findings contribute to the prevention and treatment of spinal compression fractures, as well as the design of related therapeutic instruments and assistive devices.

Abstract:Objective To investigate the mechanism of mechano-chemical coregulation in chemokine-induced calcium response of Jurkat T cells under fluid shear stress (FSS). Methods By using parallel-plate flow chamber combined with fluorescence microscope, the calcium response of Jurkat T cells on CXCL12 was observed to extract the corresponding characteristic parameters under static or flow state, with or without extracellular Ca2+, respectively. Results Immobilized CXCL12 could induce firm adhesion of the circulating Jurkat T cells, and the arrested cells increased with the increase of CXCL12 concentration. Force could trigger the calcium response of Jurkat T cells and sharply raised the activation ratio from 4% up to 75% when the FSS increased from 0 to 20 mPa. Under 20 mPa FSS, extracellular Ca2+ could stimulate quickly the calcium response by shortening the delay time (about 23 s), and enhance calcium intensity by prolonging the climbing time (about 7 s) and half time (about 20 s). Conclusions The cooperation between FSS and extracellular Ca2+ would accelerate and enhance CXCL12-mediated-calcium response of Jurkat T cells, which indicated a fast mechanosensitive pathway through ‘extracellular calcium influx-intracellular calcium store release’. The research results would contribute to understanding the process of T cells activation and providing the clue for relevant pathological and drug research.

Abstract:Objective To investigate the changes of plantar pressure distributions and risk of falling before and after the occurrence of neurogenic intermittent claudication (NIC) in patients with central lumbar spinal stenosis (LSS), so as to provide theoretical and data references for the application of plantar pressure analysis in judgment of walking abilities for LSS patients. Methods Twelve patients with LSS at the L4-5 segment were selected as the LSS group, while twelve healthy adults at the same age were selected as the control group. Footscansystem was used to measure plantar pressure of these subjects during walking. Contact area percentage of the total foot contact area (CA%), pressure-time integral (PTI), foot progression angle (FPA), contact time percentage of the stance time (CT%) and total stance time (CT) in both LSS group and control group were compared to evaluate changes of plantar pressures during walking．Results Before the occurrence of NIC, compared with the control group, the LSS group had lower CT% during the forefoot push-off phase (FFPOP) and higher CT% during the initial contact phase (ICP), the total CT and FPA also increased, and the PTI of the 1st-3rd metatarsals and the CA% of the 2nd and 3rd metatarsals were higher. After the NIC occurred, for LSS group, CT% during ICP and forefoot contact phase (FFCP) decreased, CT% during the foot flat phase (FFP) and FFPOP as well as total CT and FPA increased, the PTI and CA% increased in 1st-4th metatarsals. Moreover, the CA% also increased in toe zone, both the PTI and CA% decreased in heel zone. Conclusions In patients with central LSS during walking, the distribution of plantar pressure shifts forward, with abnormal phase of the stance time occurring. Such abnormality will be further aggravated by NIC, indicating a higher risk of falling.

Abstract:Objective To compare and analyze the lower limb muscle activity and knee joint force during the stance periods of gait cycle in patients with osteoarthritis before and after total knee arthroplasty (TKA). Methods Based on the OpenSim platform, lower extremity musculoskeletal models of one healthy subject and three patients with osteoarthritis before and after TKA were established. A three-dimensional （3D） motion capture system and a force platform were used to collect the lower limb kinematic data and the ground reaction force during walking, which were used as input parameters to simulate the lower limb muscle activation and knee joint forces. Results The results from the musculoskeletal model were consistent with the results by inverse dynamics based on the 3D motion capture system. The patient's rectus femoris was activated in the loading response and mid stance phases, which was different from that of healthy subject. The activation timing and amplitude of the quadriceps muscle in 3 patients were significantly different before and after TKA. The peak joint forces of 3 patients before TKA were 2.95, 3.15 and 3.43 times of body weight (BW) with the constant load of more than 2 times of BW during stand phase. The peak joint force after TKA were 2.09, 2.48 and 3.96 times of BW respectively. The joint force was not improved and the knee function did not reach the normal level six months after TKA. Conclusions The results of the established musculoskeletal model have certain reliability, and this model can provide a biomechanical auxiliary method for TKA surgery in the future.

Abstract:Objective To examine the effects of shoe cushioning on impact characteristics, kinematics and dynamics of lower extremities before and after neuromuscular fatigue during drop landing. Methods Fifteen trained male athletes were required to execute three successful trials of drop landing from a 60-cm platform before and after fatigue protocol. The impact force, loading rate, lower extremity kinematics, joint moment, joint stiffness were compared. Results Before fatigue, highly-cushioned shoes reduced the loading rate at heel before fatigue, and the time to peak loading rate of heel was significantly shorter than that of control shoes. After fatigue, highly-cushioned shoes significantly reduced the peak impact force and loading rate at heel, loading rate at forefoot. Meanwhile the time to peak impact force and peak loading rate at heel were significantly longer, and the contact and minimum angle of ankle were significantly greater. No significant changes were found in lower extremity stiffness, peak moment and joint stiffness of ankle. Conclusions In the situation where neuromuscular activity is reduced, highly-cushioned shoes can effectively attenuate the impact, thereby helping to avoid or reduce the potential impact damage after fatigue.

Abstract:Objective To study the relationship of the tibial plateau subchondral trabecular bone (STB) microstructure and the cartilage degeneration with the lower limb alignment based on individual trabecula segmentation (ITS) and histology analysis in knee osteoarthritis (OA). Methods Hip-knee-ankle (HKA) angles were measured on the full-length lower extremity films of patients before total knee arthroplasty (TKA). The tibial plateau excised from the TKA were collected for micro-CT scanning and ITS analysis. The cartilage degeneration was evaluated by histology. The relationship between the HKA angle and the changes in microstructural parameters of STB and cartilage degeneration were analyzed. ResultsThe plate, rod and axial bone trabecular volume fraction (BV/TV, pBV/TV, pBV/TV), ratio of trabecular plate versus rod (P/R), plate trabecular number density (pTb.N), plate trabecular thickness (pTb.Th), trabecular plate surface area (pTb.S), trabecular rod length (rTb.L), and plate-plate and plate-rod junction density (P-P Junc.D, P-R Junc.D) of the subchondral bone of the tibial plateau were significantly related to the cartilage degeneration OARSI score and the HKA angle. The greater the deviation of the lower limb alignment, the greater the number of subchondral trabeculae, the thicker the trabeculae, the greater the bone mass, the stronger the connectivity, especially the plate trabeculae on the affected side of tibial plateau, and the higher the OARSI score of cartilage degeneration. Conclusions Abnormal lower limb alignment may cause abnormal microstructure of the plate and rod STB of the tibial plateau by changing the stress distribution of the knee, especially the significant increase and thickening of the plate trabecular and axial trabecular bone, which may be an important risk factor that further aggravates the degeneration of articular cartilage and the progress of OA. Therefore, lower limb alignment correction with surgical intervention and improving STB with bone metabolism agents may efficiently contribute to preventing cartilage damage and mitigate OA progression.

Abstract:Objective To evaluate the effects of oral undenatured collagen type Ⅱ on rehabilitation of knee osteoarthritis. Methods Sixteen patients with levelⅠand Ⅱ knee osteoarthritis (KOA) were recruited in this study. The WOMAC questionnaire was used to measure the symptoms of knee joint in patients. The KneeKG 3D evaluation system was used to measure the kinematics characteristics of the knee joints. The pair t-test was applied to analyze the differences in knee kinematics after taking undenatured collagen type Ⅱ for 3 months. Results After taking undenatured collagen type Ⅱ, the patient’s feeling of knee joint pain, stiffness, and the difficulty of daily life was reduced. In addition, the knee flexion angle increased from 51.8°±15.2° to 58.4°±10.7° (P<0.05), and the knee varus angle decreased to 2.1°±4.8°. The improvement rate of knee varus was 82%. Conclusions Taking undenatured collagen type Ⅱ for 3 months could play a role in rehabilitation for patients with early KOA. The knee range of motion was close to the level of healthy elderly people, thus improving the symptoms of knee varus.

Abstract:Pulmonary fluid refers to a thin and continuous liquid layer mainly consisting of airway mucus and lining liquid on the inner surface of alveoli, which is essential for maintaining a healthy lung. The clinical significance of rheological properties of pulmonary fluid in airway stability, pulmonary barrier and clearance functions, ventilator induced lung injury and surfactant replacement therapy in infant respiratory distress syndrome was introduced in this paper. Furthermore, a variety of classical methods for measuring surface tension and liquid viscosity, such as Langmuir-Wilhelmy balance, captive bubble method, glass capillary viscometer and rotational viscometer, and emerging techniques (e.g. particle tracking microrheometer and axisymmetric drop shape analysis) were reviewed, and their advantages and drawbacks were also compared, in order to provide an important reference for the assisted diagnosis and treatment of lung diseases in clinical practice.

Abstract:As the most important tissues of the motor system, skeleton and skeletal muscles are closely related to each other. The concept of bone-muscle units has been proposed for a long time, and they are linked closely by mechanical loading generated by exercise. Skeleton provides mechanical support attachments for skeletal muscle force, and contraction of skeletal muscle drives body movement. During the process of body movement, acting as an intermediate medium between the mechanical load and bone, skeletal muscles regulate metabolic activity of the bone through endocrine factors and mechanical stimulation, which is closely related to continuous bone remodeling and maintains good structure and function of the bone. This review focuses on recent research progress of skeletal muscle affecting bone remodeling by applying mechanical stimulation to the bone, which will provide some new ideas for prevention and treatment of bone metabolism diseases.

Abstract:The influence of angled abutments on stress of peri-implant bone is a controversial issue. It is widely accepted that the use of angled abutments will increase adverse stress distributions on implants and surrounding bones. However, comparisons of clinical success rates of implants restored with angled and straight abutments indicate no significant differences. This review summarized the clinical application and biomechanical research associated with angled abutments. The use of angled abutments did not detrimentally affect the retention of dental implants, and tt was possible that the magnitude of stress within peri-implant bone increased or decreased under different conditions. Therefore, further researches should be conducted to confirm that favorable peri-implant stress levels may be induced if suitable angulation of abutments is selected.