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.

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.

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.

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.

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.

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.

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.

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.

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.