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Abstract:Corona virus disease 2019 (COVID-19) has been the focus of global attention since its outbreak. With the rapid spreading of COVID-19, serious challenges including medical management system, medical resources, emergency response, medical devices and instruments gradually occur, revealing many shortcomings among these aspects. Herein, through the principles, viewpoints and methods of biomechanics, this article recognizes and analyzes the existing problems that are urgently needed to be solved, such as the study of in-vitro viability of the virus, the biomechanics of aerosol, the fluid mechanics in public transportation and places, the relationship between respiratory diseases and cardiovascular diseases, the improvement of medical devices, with an objective of taking advantages of biomechanics in epidemic prevention and control, so as to promote the development of biomechanics.

Abstract:Objective To explore the effect of restraint system misuse on head-neck injuries for rear occupant of 6-year-old children in frontal impact crashes. Methods Based on the previously validated 6-year-old child occupant finite element model, in terms of ECE R44 testing regulations, the impact crash under right and wrong use of restraint system was simulated in Pam-Crash software. Results The force and moment of the neck were the minimum by merely using booster seat, but the maximum intracranial pressure, the maximum stress and the maximum principal strain were larger than their damage threshold and would cause fatal brain damage in child head. The only use of adult safety belt would cause more serious damage in child neck with larger force and moment. Conclusions Two ways of misusing the restraint system would aggravate head-neck injuries of the 6-year-old child. The proper use of the restraint system can provide the best protective effect for head and neck of the 6-year-old child occupant.

Abstract:Objective A three-dimensional （3D） printing precise pressure device was designed specifically targeted at cambered limbs according to the requirement of postoperative rehabilitation of total knee replacement(TKR), and its effectiveness and safety was verified by finite element analysis. Methods Based on gastrocnemius muscle of lower limbs as the pressurized objects, the precise pressure device was designed, which contained an air pressure generating module, an inflatable airbag and a 3D printing brace. Through the closed loop control algorithm, the device stably supplied different pressures in the airbag. Distributed pressure data of the airbag-skin within contact surface were collected under different experimental conditions and imported into biomechanical simulation software which combined CT images to reconstruct 3D model of the lower limb mechanics. Finally, the effective compression area fraction and the joint micro-motion angle under each condition were obtained, to verify the effectiveness and safety of the system. Results Using generally preferred 4 cm-size offset and 4-barrel airbag configurations, under different intracapsular pressure of 5.32，6.65，7.98，9.31，10.64 kPa, the simulated knee joint micro-motion angles were 5.3°, 6.1°, 7.2°, 9.5°, 10.6°， respectively, and the effective compression area fraction could be up to 90-8%-95-2%. Conclusions For the optimized scheme, the dynamic range of joint micro-motion angle and the effective compression area fraction caused by different airbag pressure values were the best and met the design requirements of effectiveness and safety. The research findings can contribute to analyzing the influence of compression system on limb biomechanics, which are of great significance for effective and safe rehabilitation training after TKR.

Abstract:Objective To establish the model of rabbit vena arterialization, so as to investigate the difference of mechanical parameters between arteries and veins as well as before and after arterialization. Methods Twenty-four rabbits were randomly divided into experimental group (n=12) and control group (n=12). By establishing the rabbit vena arterialization model for experimental group, the arterial blood could flow into the veins. After model creation, the vein would be removed 4 weeks after surgery. In the meantime, the external jugular veins and cephalic arteries extracted from control group were acquired. Compressive pressurizing and stretching tests on all vessels were conducted at the same time(including arteries, veins and arterialized veins). Observation was supported by HE staining and immune tissue chemical techniques. Results There were no deaths among the 24 rabbits, with unobstructed blood flow in veins. With the increase of intravascular pressure, the outer diameter of veins changed at first and then stabilized at a fixed value. The elasticity of veins was worse than that of arteries. The external diameter of veins increased rapidly with internal pressure of veins increasing and reached its extreme elasticity. Comparatively, the elasticity of arteries increased slowly. HE staining results showed that thickness of the vascular wall was thinner, while it became thicker after vena arterialization. After vena arterialization, proliferating cell nuclear antigen（PCNA） and α-actin showed positive results. It further proved that proliferation existed among smooth muscle cells, and veins showed the tendency of restenosis again. The elasticity of veins after transplantation into the arterial system was improved compared with that before transplantation. Conclusions Accompanied by the increasing pressure, the vein could reach its elasticity extremity faster than the artery. Under such a long-term high pressure, vein intima was vulnerable. After vena arterialization, with the gradual thickening of vein intima, the tendency of vessel restenosis was obvious, and the elasticity of veins has been improved after transplantation.

Abstract:Objective To analyze the effects of anesthesia-induced thermoregulatory system impairment and low temperature environment of the operating room on the perioperative thermoregulation of individualized patients by constructing a computer simulation model. Methods A simple anesthesia model was proposed and then incorporated into the self-developed individualized thermoregulatory model, in which human body was represented as a cylinder with two layers of the core and the skin. The integrated model could be used to assess the effects of individualized characteristics such as age, obesity, and cardiovascular diseases on thermoregulation by modifying different physiological parameters involving sweating, shivering and cutaneous vasomotion. Simulation of the general anesthesia effects on human thermoregulation could be achieved by reducing basal metabolic rate and thresholds for vasoconstriction and shivering. Results The elderly people showed lower core temperature but higher skin temperature, compared with the young people. In a low temperature environment, an increase in fat thickness or an increase in severity degree of the left ventricular failure (LVF) might alleviate the decrease in core temperature, while an increase in wind speed or relative humidity could result in a decrease in core temperature. When the threshold setting of vasoconstriction was reduced by 0-5-3 ℃, the core temperature showed a significant decrease. Conclusions By comparing model simulations with experimental measurements, the reliability and validity of the model in predicting human transient thermal responses during varying external thermal environment was verified. The individualized characteristics of human body had an important influence on human body temperature in a low temperature environment. Moreover, the combination of individualized characteristics of human body and general anesthesia further complicated the body′s thermoregulation and posed significant challenges for clinicians.

Abstract:Objective To deduce analytic solution of the displacement and stress distributions for the coronary stent based on reasonable assumptions, and to investigate the influence from the wave number of support bars on stress distributions by combining the results of finite element analysis. Methods A local cylindrical coordinate system was established to deduce analytical solution of the displacement and stress components of the periodic support bar of the rectangular-wave type vascular stent under vascular systolic pressure. The support bar model was established by using ANSYS, to calculate the numerical results of stress analysis. By analyzing the consistency of stress curves obtained from the two methods, the accuracy and applicability of analytical solutions were verified. The influence from the number of wave crests for support bars on the stress under systolic pressure was investigated by analytic solution. Results The analytical stress curves were basically in conformity with those from the ANSYS results. When the number of wave crests was 6, there were both tensile and compressive stresses in circumferential direction of the cross bar. Conclusions When the number of wave crests was 6, such stents could effectively prevent restenosis in blood vessels during working. The derived analytical solution could be used to analyze mechanical properties of one-cycle support bars of rectangular-wave type stent, and the research findings provided a new idea to further recognize and study the stress distributions on coronary stent to reduce the restenosis rate of interventional therapy.

Abstract:Objective To investigate the differences in mechanical properties of the sclera in different regions. Methods The sclera of sus scrofa was divided into 3 regions, namely, anterior, equatorial and posterior area. Local indentation was performed on different areas of the whole sclera. Strip specimens of different regions were circumcised along the equatorial direction, and subjected to uniaxial stretching by INSTRON 5544. Results Within the normal physiological stress range, the stiffness at anterior, equatorial, and posterior area of the sclera measured by local indentation was (0.91±0.21), (0.6±0.16), (0.39±0.13) MPa, respectively. The elastic modulus at anterior, equatorial, and posterior area of the sclera measured by uniaxial stretching was (1-28±0.37), (0.95±0.31), (0.72±0.28) MPa, respectively. Conclusions The local indentation could reflect regional mechanical properties of the sclera. The anterior sclera performed a higher stiffness than the equatorial and posterior areas. The results provide references for further study on the pathogenesis of ocular diseases including myopia.

Abstract:Objective To explore the effects of facial asymmetry on stress distributions in temporomandibular joints (TMJs) for patients with mandibular prognathism. Methods Eight 3D maxillofacial models were established in MIMICS based on cone-beam CT of 4 mandibular prognathism patients with asymmetry and 4 mandibular prognathism patients without asymmetry. Muscle forces and boundary conditions corresponding to the unilateral occlusion (unilateral molar chewing) were applied on the models in ABAQUS. The maximum and the minimum principal stresses of TMJ were chosen for analysis. Results There were significant differences in the maximum and minimum principal stresses at the condyles between the mandibular prognathism patients with and without facial asymmetry under unilateral occlusions (P<0-05). Compared with patients without facial asymmetry, the stresses on the condyle in patients with asymmetry increased by 2-3 times, and the stresses on articular fossa increased by 5-7 times. Among the mandibular prognathism patients with asymmetry, the stresses of the ipsilateral TMJ in patients with temporomandibular disorder (TMD) were significantly higher than those in patients without TMD. Conclusions Facial asymmetry increased the stresses of the articular fossa and condyle in patients with mandibular prognathism. TMD would cause greater stresses in ipsilateral TMJ of the mandibular prognathism patient with asymmetry. Therefore, different treatment strategies should be considered for mandibular prognathism with facial asymmetry.

Abstract:Objective To explore the effect of concave and convex interface on in vitro culture of mouse embryonic stem cells. Methods Mouse embryonic stem cells were cultured on substrate with concave and convex interface. The biological morphology of cell colony was observed. The pluripotency of embryonic stem cells was detected by immunofluorescence and alkaline phosphatase (ALP) staining. Results Embryonic stem cells on concave substrates and convex substrates had higher stereo degree and circularity than those on flat substrates, but it was more obvious on concave substrates. Besides, the expression level of Oct4-GFP and the staining intensity of ALP in embryonic stem cells which were cultured on concave substrates and convex substrates were significantly higher than those on flat basement, especially on concave substrates. Conclusion sCompared with flat substrates, concave substrates and convex substrates had positive effects on the pluripotency maintenance of embryonic stem cells, which could help to maintain pluripotency, but concave substrates had better effects. Changing the substrate curvature could help to maintain pluripotency of embryonic stem cells cultured in vitro. The research findings are of great significance to the study and clinical application of embryonic stem cells.

Abstract:Objective To investigate the interaction between von Willebrand factor (vWF) A1 and A3 domain, and type 2 M mutant W1745C-A3 effect on thermal stability and mechanical stability of A3/A1. Methods The crystal structures of A1 and A3 were downloaded from Protein Data Base (PDB). The wild-type (WT) A3/A1 structure was obtained by using SwarmDock Server, then W1745C-A3/A1 mutant was constructed by replacing the Trp1745 with Cys1745 in A3/A1. Through steered molecular dynamics simulation, formation and evolution of hydrogen bond and salt bridge between A1 and A3 interfaces were observed, and the differences in conformation, disrupted force and dissociation time between WT-A3/A1 and W1745C-A3/A1 were compared. Results There were 5 pairs of hydrogen bonds with survival rate > 0-2 and 1 pair of salt bridge with survival rate > 0-5 between A1 and A2. The W1745C-A3/A1 complex could withstand greater disrupted force and longer dissociation time compared with WT-A3/A1, by improving the stability of hydrogen bonds and increasing 1 pair of stable salt bridge. Conclusions The interaction between A1 and A3 would hinder the binding sites of A1 to GPIbα, and the W1745C-A3 mutation would further reduce the affinity of A1 to platelets. These results provide references for revealing the molecular mechanism of von Willebrand diseases in the clinic and developing the corresponding drugs targeted to hemostasis disorders.

Abstract:Objective To explore the effects of osmotic pressure on biomechanical properties and immune function of immature dendritic cells (imDCs) from mechanobiological viewpoint. Methods After treated with different osmotic pressures, the cell viability of imDCs was detected using cell counting kit-8 (CCK-8). The changes in morphology of imDCs were observed under laser scanning confocal microscope. Cell electrophoresis was applied to detect the changes in cell electrophoresis mobility. The membrane fluidity of the cells was detected by fluorescence polarization method, and the expression changes of immune-related molecules were detected by real-time fluorescent quantitative PCR (qPCR). The phagocytic ability of the cell was detected by flow cytometry. ResultsBoth hyperosmosis and hypoosmosis could remodel the cyoskeletonof cells, even induce apoptosis. The electrophoresis mobility of the hypoosmosis group was significantly higher than that of the normal osmolarity group, while that of the hyperosmosis group was lower than that of the normal osmolarity group (P<0-05). Fluorescence polarization results showed that both hyperosmosis and hypoosmosis could significantly decrease the membrane fluidity of cells (P<0-05). The results of qPCR detection showed that both hyperosmosis and hypoosmosis could significantly increase the expression of CCR7, CD40, CD205, CD11a, CD11c on the surface of DCs, and the phagocytosis of cell was increased (P<0-05). Conclusions Hypertonic and hypotonic stress can influence biomechanical properties of imDCs and expression of immune-related molecules. The research findings are important for further understanding the immune regulation function of DCs.

Abstract:Objective To investigate the conduction behavior of fluid flow induced by physiological loads at different scales of bone. Method sThe multiscale bone models were established by using the COMSOL Multiphysics software, and the fluid behaviors were investigated at macro-, meso- and micro-scale. Results At macro-meso scale，the distribution of pore pressure and fluid velocity of osteon near the periosteum and endoosteum were different from that in other parts. Due to the different structure and material parameters at different layers, the loading and fluid pressure caused different biomechanical responses in the process of transferring from macro-scale to micro-scale. Conclusions The multi-scale layered modeling of bone structure-osteon-lacunae-bone canaliculi was established, which provided the theoretical reference for deeper understanding of fluid stimulation and mechanotransduction.

Abstract:Objective To study the influence of hollow screws with five kinds of spatial distributions on the fixation effect of femoral neck fracture. Methods Geometric models of femoral neck fracture with Pauwels type I, II and III were built by reverse engineering according to CT images of the femur. Based on the finite element analysis software ANSYS, the stress distributions of internal fixation, head side and stem side of femoral neck and the displacement distributions of the model fixed by different methods were obtained. Results For femoral neck fracture with Pauwels type I, II and III, the maximum stresses at head side of femoral neck were the inverted triangle fixation method, two-screw parallel fixation method, two-screw parallel fixation method, respectively. The maximum stresses at stem side of femoral neck were the inverted triangle fixation method, inverted triangle fixation method and two-screw parallel fixation method, respectively. The minimum stresses on the screws were the cross fixation method, and the minimum displacements of the model were double-supported fixation method. Conclusions The probability of screw deformation and fracture is the smallest for cross fixation method. Inverted triangle fixation method can provide a good mechanical environment for fracture site. For femoral neck fracture with Pauwels typeⅠ and Ⅲ, double-supported fixation method has the strongest ability to prevent femoral neck shortening. While for femoral neck fracture with Pauwels typeⅡ, cross fixation method has the strongest ability to prevent femoral neck shortening.

Abstract:Objective To investigate the effects from head angle and locking times of locking screws on mechanical properties of the screw-plate system, so as to provide a theoretical basis for doctors to select appropriate locking screws and master the locking times in clinical surgical procedure. Methods Locking screws with different head angles were selected to match with locking compression plates in the case of different locking times, and cantilever bending method was used to compare the differences of mechanical properties in each group. Results There were significant differences in failure load and bending stiffness between locking compression plate and locking screw with different head angles (P<0-05). The mechanical properties of the screw-plate system with the best locking degree were optimum. There was no significant difference between 3 time-locking and 1 time-locking (P>0-05). The failure modes of locking screw with different head angles and different locking times were different, and the failure mode of locking screw had a positive correlation with its head angle and locking times. Conclusions The differences in mechanical properties between locking screw with different head angles and locking compression plate cannot be neglected. It is suggested that doctors should choose locking screw and locking compression plate with the best locking degree in clinical procedure, and choose the right torque wrench to lock in multiple times if necessary, thus to prevent screw loosening from affecting recovery of the patients.

Abstract:Objective To study the effect of the reinforcing and reducing method of acupuncture reported in first Chapter the Nine Needles and Twelve Yuan of the Miraculous Pivot on interstitial fluid pressure (IFP) in subcutaneous tissue of minipig, and to investigate its biomechanical mechanism of regulating the interstitial fluid. Methods Nine healthy minipigs were randomly selected for reinforcing method (pull or press) and reducing method (wave a big pinhole), and tested on soft skin tissues of the abdomen. The IFP in the normal state (NS), the low volume (LV) state (by extracting interstitial fluid) and the high volume (HV) state (by injecting saline solution) was measured before and after acupuncture. Results In the normal state, pulling and pressing the needle could obviously increase IFP, while reducing method could significantly decrease IFP, leading to a rapid decrease in 5 min after acupuncture. In the LV state, pulling and pressing the needle could increase IFP. However, in 10 min after acupuncture, the descend rates of IFP were relatively slower. In the HV state, the reducing method could significantly decrease IFP, and the changing trend in 5 min after acupuncture was different from that of the control group. Conclusions The reinforcing and reducing method of acupuncture could increase or decrease IFP, which proved that the acupuncture method could regulate IFP in the opposite direction. The research findings provide a new scientific basis for using reinforcing and reducing method of acupuncture in clinic.

Abstract:Objective To study the internal relationship between resting tremor and slow response in patients with Parkinson’s disease. Methods The movement characteristics of wrist joints in valgus direction was studied by dynamic modeling on wrist joints of the upper limbs. The system delay concept was introduced with human autonomous control and the sensory delay characteristics of Parkinson’s patients was simulated, to make stability analysis and dynamic response of the involuntary wrist movement. Results The stability analysis and numerical solution of this time-delayed control system showed that when the sensation was delayed to a certain extent, involuntary tremor of wrist joints in patients with Parkinson’s disease would happen, which conformed to resting tremor from Parkinson’s disease. Conclusions Resting tremor from Parkinson’s disease is caused by sensation and movement delay.

Abstract:Anterior cruciate ligament (ACL) deficiency is a common clinical injury that seriously affects the function of the knee. Although ACL reconstruction (ACLR) can rebuild the structure of the ACL, it does not restore the normal kinematics and dynamics of the knee. In recent years, motion analysis has been widely applied in sports science and rehabilitation. In clinics, motion analysis is mainly applied to the evaluation of clinical outcomes of the ACLR knee. It is also a scientific objective tool to assess the potential risk factors of secondary injury and early onset of osteoarthritis after ACLR. In-depth understanding of the knee functional kinematics and kinetics after ACLR will significantly improve the efficacy of current ACL deficiency treatment and rehabilitation regime. This paper reviewed studies of the knee joint motion analysis after ACLR in the past decade. The current knowledge of the ACLR knee motion from studies using optical motion capture and biplanar fluoroscopic imaging system based tracking technique was synthesized. Clinical studies have reported that regardless of the type of graft and surgical technique of the ACLR, the postoperative knee still exhibits abnormal kinematics in functional tasks, but the relationship between early-onset OA and the biomechanical changes in the ACLR knee remains unknown. Restoring the rotational stability of the knee is still one of the biggest challenges in clinical ACLR surgery. Future studies should explore the impact of ACLR on the biomechanical mechanisms of the knee joint through an appropriate research design and long-term follow-up, and help clinicians and physiotherapists to develop more effective interventions.

Abstract:The controllability of hardness and its control method, the corresponding direction of differentiation of mesenchymal stem cells (MSCs) regulated by different hardness, and the role of integrin in the signaling pathway through which hardness regulates MSCs differentiation were briefly described in this paper. Among them, the role of integrin in the signaling pathway of hardness regulation of MSCs differentiation was highlighted. Signal pathways in which hardness regulates MSCs differentiation include Rho/ROCK signal pathway, integrin/FAK signal pathway, ERK signal pathway, JNK signal pathway, Wnt-catenin signal pathway and PI3K/Akt signal pathway, etc. Integrin, as a transmembrane heterodimer glycoprotein, participates in part of the signal pathway to transmit mechanical signals to MSCs. Different integrin families participate in different signaling pathways to regulate the differentiation of MSCs in different directions, and there are certain mutual influences among these signaling pathways. The research findings provide a theoretical basis for the application of tissue repair, organ reconstruction and regenerative medicine.

Abstract:Aging is a major risk factor for diseases such as osteoarthritis (OA) and osteoporosis. However, they are not necessarily the results of aging, and the relationship between changes in bone and cartilage associated with aging and disease progression is still unclear. Studies have shown that the development and progression of OA is not a simple cartilage wear process, while its occurrence involves complex biological, chemical and mechanical changes in the tissues of the entire joint, especially the interaction of mechanics and biochemistry between cartilage and subchondral bone. Aging contributes to the occurrence and development of OA, but it is not the cause of OA. Changes associated with aging provide a foundation for OA to start, making joints more susceptible to other factors such as abnormal biomechanics and biochemistry, thereby promoting the development of OA. Therefore, understanding the basic mechanisms by which aging affects joint tissue may provide new targets for slowing or preventing the development of OA. In this paper, the related research progresses are reviewed from three aspects, i.e. age-related changes in cartilage and subchondral bone, mechanical conduction and angiogenesis.

Abstract:OpenSim musculoskeletal modelling has developed rapidly and been widely utilized due to its open-source. Apart from calculation of the basic kinematic and kinetic data, subject-specific OpenSim model could reveal information of neuromuscular control, muscle forces and geometry, and contact forces. Image-based model-ling of the neuromuscular control in pathological gait and ergonomic evaluation of the prostheses confirmed the reliability and feasibility, but limitations in time-consumption and foot-ankle modelling also existed. The subject-specific modelling of pathological gait could improve the accuracy and diversity of clinical biomechanics and medical engineering research. It could also reveal the pathological features, and provide scientific evidence to design specific and accurate protocols of motor function diagnosis and rehabilitation, health monitoring and evaluation, and ergonomic customization and assessment of devices, as well as future directions and implications in the research field.