Abstract:Objective To construct a three-dimensional (3D) dynamic head-neck finite element model which accords with the anatomical structure, and study its dynamic responses under the external force. Methods By using the neck CT images of a Chinese adult male volunteer and obtaining the 3D cervical point cloud data, the finite element model of cervical spine was established using ICEM-CFD and HyperMesh software. This model, including vertebrae, intervertebral discs, facet joints, ligaments and cartilage tissues, and combining with the established and verified head finite element model, was assembled as human head-neck finite element model with detailed anatomical structures. Results The model was validated by data of head-neck axial impact experiments reported in previously published literature. The simulation results showed that the neck deformation, head acceleration, head force and injury positions were preferably consistent with the experimental data. Conclusions The established 3D dynamic finite element model can be used to study head-neck dynamic responses and damage mechanism in the fields of traffic safety and impact injuries.
Abstract:Objective To explore the regularity of time-dependent changes in morphology and biomechanical properties of brain tissues in pigs, and value the feasibility of deducing the postmortem interval (PMI). Methods Brain tissues were taken from 42 pigs and kept in an artificial climate chamber with the temperature of 25 ℃ and humidity of 75%. The samples were collected from telencephalon at sequential time intervals (0, 12, 24, 36, 48, 60 h；n=6) according to the principle of predefined time, position, direction, ratio, quantity and shape. The samples fixed with formaldehyde were then immediately tested by mechanical testing machine to obtain their biomechanical parameters and the histological sections were prepared. Results With the extension of PMI (0-60 h), brain tissues gradually became discolored, weak, mudding and liquefied under the influence of autolysis and putrefaction. Both clearance area of the white matter and its integrated optical density (IOD) significantly increased during 0-48 h. Biomechanical properties of brain tissues including the limit load, average force, elastic modulus and fracture energy all presented a declining tendency at the interval of 12-60 h. The limit load was considered highly statistically significant, and statistical differences were found in average force, elastic modulus and fracture energy. Conclusions There exists a significantly negative structure-activity relationship between the morphology of brain tissues and biomechanical properties. The limit load of postmortem brain tissues in 60 h is the optimum in the window period, which can be used as a new method for estimating PMI.
Abstract:Objective To design a novel double-leaf proximal humeral locking plate for fixing greater and lesser tuberosities in complex proximal humeral fractures, and evaluate its fixing stability by biomechanical tests. Methods Twelve fresh-frozen humerus specimens with intact rotator cuff were randomly divided into two groups (Group A and Group B) to establish the same greater and lesser tuberosities fracture models. Specimens in Group A were fixed with the double-leaf proximal humeral locking plate, while specimens in Group B were fixed with the proximal humeral internal locking system (PHILOS) and tension band suture, and a 3.5-mm cannulated screw was added to stabilize the lesser tuberosity. The tensile test on subscapularis, infraspinatus and teres, supraspinatus as well as the load-to-failure test on greater and lesser tuberosities were performed on specimens in two groups. Results For subscapularis tensile tests, displacements under 150 N tensile stretch and after fatigue test in Group A were both significantly smaller than those in Group B (P<0.05). For infraspinatus and teres tensile tests, there were no statistical differences between Group A and B in displacements under 150 N tensile stretch and after fatigue test (P>0.05). For supraspinatus tensile tests, there were no statistical differences between Group A and B in displacements under 90 N tensile stretch and after fatigue test (P>0.05). For load-to-failure tests on lesser tuberosity, the failure load in Group A was significantly greater than that in Group B (P<0.05), and the failure displacement in Group A was significantly smaller than that in Group B (P<0.05). For load-to-failure tests on greater tuberosity, there were no statistical differences between Group A and B in both the failure load and failure displacement (P>0.05). Conclusions Compared with the ordinary tension band suture plus cannulated screw for fixing lesser tuberosity, the novel double-leaf proximal humeral locking plate shows more obvious biomechanical stability, with the advantage of simultaneously fixing greater and lesser tuberosities. The research findings provide a new choice for the clinical treatment of complex proximal humeral fractures.
Abstract:Objective To compare biomechanical properties of pedicle screw with different axial angles and interbody cage with different positions for unilateral transforaminal lumbar interbody fusion (TLIF) surgery. Methods The normal L3-5 finite element (FE) model was established and validated. Then one bilateral TILF reconstruction FE model and four unilateral TILF reconstruction FE models with different pedicle screw-cage combination types at L4-5 level were constructed, respectively. Namely, Model A (a small axial angle-implanted screw and an ipsilaterally-placed cage), Model B (a small axial angle-implanted screw and a contralaterally-placed cage), Model C (a large axial angle-implanted screw and an ipsilaterally-placed cage), Model D (a large axial angle-implanted screw and a contralaterally-placed cage). The range of motion (ROM) of 4 reconstruction models under various physiological stresses as well as the maximum Von Mises stresses on pedicle screw, cage-L4 inferior endplate were compared. Results The ROMs at fusion segment (L4-5) in 4 unilateral TLIF reconstruction models were significantly decreased compared with the normal model, but they were still larger than bilateral TLIF reconstruction model. For 4 unilateral TLIF reconstruction models, Model C showed the largest decrease in stability, and the ROM of Model C was 50.7%, 89.9%, 90.3% of the normal model in flexion-extension, lateral bending, axial rotation, respectively. When comparing the maximum Von Mises stress of posterior pedicle screw and cage-L4 inferior endplate in 4 unilateral TLIF reconstruction models, Model C could bear relatively smaller stress under most loading modes, except in ipsilateral lateral bending and axial rotation. Conclusions The unilateral TLIF reconstruction model with a large axial angle-implanted screw and an ipsilaterally placed-cage can achieve the optimal stability. By narrowing the difference in stability with the bilateral TILF model, the unilateral TLIF reconstruction model can reduce the risk of screw failure and cage subsidence, which is worth of clinical application.
Abstract:Objective To investigate the effect of cervical spinous process fracture with posterior ligamentous complex (PLC) injury on biomechanical stability of the goat cervical spine specimen in vitro, and evaluate the role of posterior structure in maintaining the stability of cervical spine. Methods Twenty-four fresh goat cervical spine C3-6 specimens were randomly and evenly divided into 3 groups: control group (group A), simple cervical spinous process fracture group (group B) and cervical spinous process fracture with PLC injury group (group C). Under loading of 1.5 N·m torque, the range of motion (ROM) in each group was respectively measured under 6 working conditions: flexion, extension, lateral bending and axial rotation, and the ROM differences among 3 groups were compared by using one-way ANOVA analysis. Results Simple cervical spinous process fracture had little effect on the stability of cervical spine and there was no significant difference in ROM between group B and control group (P>0.05) under all working conditions. Compared with control group, the ROM in flexion, extension and axial rotation significantly increased in group C (P<0.05), and no significant ROM difference was found in lateral bending between control group and group C (P>0.05). Conclusions Simple cervical spinous process fracture does not affect the overall stability of cervical spine. Cervical spinous process fracture with PLC injury is more likely to cause cervical instability than simple cervical spinous process fracture, and surgical intervention is required in cervical spinous process fracture with PLC injury.
Abstract:Objective To compare the influence of two fatigue protocols on kinematics of lower extremities as well as time/frequency-domain characteristics of impact force during human landing. Methods A total of 15 trained male athletes (sprint/jumping events) were selected and their kinematics in sagittal/frontal plane and time/frequency-domain characteristics of ground reaction force (GRF) under pre- and post-fatigue conditions with two fatigue protocols (constant speed running, shuttle running + vertical jumping) were collected by the Vicon motion capture system and Kistler 3D force plates. Results (1) Both fatigue protocols showed a significant decrease in the angle of hip and knee joints on the sagittal plane, and an increase in the flexion range of motion (ROM). The running + jumping fatigue protocol showed a significant increase in the flexion ROM of ankle joint, the maximum flexion angular velocity of knee joint (P<0.05), the abduction ROM of hip joint and the maximum abduction angular velocity of hip and knee joints (P<0.05). (2) No significant differences were found in time/frequency-domain characteristics of impact force between pre- and post-tests for both fatigue protocols. The running and running + jumping fatigue protocols showed lower amplitude spectra of the GRF in the frequency domain at 3.51, 8.20 Hz and 1.17, 3.51, 7.03 Hz, respectively (P<0.05). Conclusions Both fatigue protocols can induce a more flexed landing posture of lower extremities under the impact of landing, and the running + jumping fatigue protocol shows a better effect with shorter intervention time, which indicates such fatigue protocol has more advantages from the perspective of experimental methodology. The research findings can provide further references for studying force characteristics after fatigue.
Abstract:Objective To investigate the effects of insole parameter changes on biomechanical mechanism of heel pain by finite element methods. Methods The 3D finite element model of foot, crus bones, gastrocnemius muscle and knee joint was reconstructed based on CT images. The plantar pressure distribution and peak pressure were calculated by changing the shape, thickness and hardness of the insole. Results The distribution of plantar pressure calculated by the finite element model was generally consistent with that measured by the pressure plate, and the values were very close. Compared with the barefoot standing, the peak pressure of the heel was decreased by 20.5%, 59.2% and 38.4%, and that of the metatarsal head was decreased by 9.9%, 18.1% and 46.7%, with flat insole, half-contact insole and full-contact insole, respectively. For patients with heel pain, the pressure peak of the heel and the metatarsal head at plantar surface decreased with the conventional thickness of insole increasing and the hardness of insole decreasing. Conclusions The changes in insole parameters have a significant influence on the plantar pressure distribution. Finite element analysis can contribute to discovering the etiology and pathology of heel pain, so as to provide the theoretical basis for clinical treatment.
Abstract:Objective To study high-quality and high efficient meshing methods for skeleton. Methods Based on characteristics of bone structure, the mesh generation technology of computational fluid dynamics (CFD) was applied in mesh generation for bone biomechanics. Hexahedron elements and tetrahedron elements were used to simulate cortical bone and cancellous bone, respectively. Results By using CFD mesh generation technology, high-quality hexahedral elements could be obtained, the structure characteristics of skeleton could be preferably simulated, and computer automatic meshing could be implemented. The amount of time for meshing bones by the new method was only about 1/5 of that by the traditional method, and the calculation results obtained from the finite element model were basically consistent with the results from the cadaver experiment. Conclusions The CFD mesh generation technology can be applied in the field of bone biomechanics, which provides an effective approach to reconstruct complex human skeleton.
Abstract:Objective To investigate the mechanical properties of human enamel based on resonant ultrasound spectroscopy (RUS). Methods The rectangular parallelepiped specimens of human enamel were processed. The theoretical resonant frequencies of specimens were estimated and paired with the experimental resonant frequencies measured from RUS experiments. An iterative procedure was used to adjust elastic constants of enamel until the theoretical frequencies corresponded to the experimental frequencies based on minimum mean-squared error criterion. In addition, elastic modulus, shear modulus and Poisson’s ratio were calculated respectively. Results The elastic modulus, shear modulus and Poisson’s ratio ranged from 61.52 to 80.46 GPa, 21.51 to 51.86 GPa and 0.18 to 0.43, respectively. Eliminating the effect of large specimen variances, the average of elastic modulus, shear modulus and Poisson’s ratio was 72.84 GPa, 31.94 GPa and 0.27, respectively. Conclusions RUS performs a feasibility of measuring the mechanical properties of human enamel with repeatable and nondestructive advantages. All the elastic constants and mechanical parameters can be estimated through a signal experiment. The results provide references for the development of biomimetic dental restoration materials.
Abstract:Objective To provide references for the clinical treatment of patients with periodontal diseases by modeling and analysis based on four software and obtaining stress distributions of the patient’s teeth, according to CT data and plaster model of the patient’s teeth. Methods The CT data were preliminary processed by using Mimics software to establish three-dimensional (3D) cloud model. The 3D surface model of the teeth was then constructed by using Geomagic software to make parameter modeling and reverse engineering. The 3D surface model was imported into SolidWorks to obtain the 3D entity model by entity conversions. Finally, the 3D entity model was imported to ANSYS for analysis. Results The stress distributions on the upper teeth were obtained, and the location of stress concentration points was determined. The stress concentration points of the teeth were analyzed separately, and the maximum stress was 1 774.8 MPa. The occlusal relationship was adjusted based on stress distributions, and the maximum stress after adjustment was reduced to 1 529 MPa. Conclusions This dental modeling and analysis method can simulate various occlusal relationships and calculate tooth stress distribution after amendment, which provides the theoretical basis for clinical treatment of periodontal diseases.
Abstract:Objective By analyzing mitochondrial function, reactive oxygen species (ROS) and adenosine triphosphate (ATP) production under different levels of RalA and caveolin-1 (Cav-1) expression, to investigate the regulation role of RalA played in cancer metabolism and explore the possibility of its regulation role involved in Cav-1 and caveolae motility. Methods Firstly, RalA and Cav-1 expression were inhibited by siRNA in breast cancer cell line MDA-MB-231, and then the changes of mitochondrial membrane potential (MMP), ROS production, ATP generation and L-lactate level before and after inhibition were assessed by Western blotting, confocal microscope and fluorescence quantification. Results (1) The decreased RalA and Cav-1 expression led to a significant reduction of MMP directly. (2) Low RalA and Cav-1 expression resulted in an inhibition of ATP production and an increase of H2O2 generation. With the reduction of MMP, mitochondrial malfunction was observed. (3) With mitochondrial function suppression, an elevated level of glycolysis metabolite L-lactate was also detected in RalA and Cav-1 deprived cells. Conclusions RalA and Cav-1 mediate cellular metabolic switch by inhibiting mitochondrial function and simultaneously boosting glycolysis. This regulation role of RalA depends on its association with Cav-1, and possibly is related to the endocytosis and motility of caveolae. The research findings enrich the cancer metabolic studies, and provide a novel approach for cancer therapeutic strategy targeted to cellular metabolism.
Abstract:Objective To investigate the effect of frequency on osteoblast apoptosis induced by tensile strain. Methods MC3T3-E1 cells were applied with 1% biaxial tensile strain at the frequency of 1, 2, 3, 4, 5 Hz, respectively for 1 hour per day in 8 days. The survival rate of the cells was determined by activity of lactate dehydrogenase (LDH). Annexin V-FITC/ PI Flow cytometry was used to test cell apoptosis. Real-time RT-PCR was used to detect the gene level of apoptosis markers caspase-3, -9 as well as Bcl-2 and Bax, and Western blotting was used to test protein expressions of caspase-3, -9. Results Different loading frequencies had no effect on osteoblast activity of LDH. There was no significant difference in the total apoptosis rate of flow cytometry at different frequencies. However, the frequency of 2 Hz could induce early osteoblast apoptosis. Tensile strain at the frequency of 2 Hz could significantly increase the expression of caspase-3, -9 gene and protein, and induce cell apoptosis with the up-regulation of the Bax/Bcl-2. Conclusions Osteoblast apoptosis and death cannot be induced by 1% biaxial tensile strain at the frequency of 1-5 Hz, but the frequency of 2 Hz can induce the early apoptosis of osteoblasts by up-regulating the expression of Bax/BCl-2.
Abstract:Objective To study the characteristics of mouse-desktop and wrist-desktop contact pressure distributions during different mouse operations, and investigate the influence of desktop on the mouse and wrist during mouse operations, so as to obtain biomechanical references for musculoskeletal disorders of the hand and wrist. Methods The laser scanner and TekScan pressure measurement system were employed to measure contact area and contact pressure of the mouse and wrist during different mouse operations. Results The contact pressure, contact area, and contact force varied with time, and the peak contact pressure of the mouse and wrist with desktop were obtained. The peak contact pressure of the mouse in single clicking of left, right key and scrolling of middle key was 62.87, 33.83, 74.66 kPa, respectively, and for the wrist, the minimum contact pressure appeared in key clicking, being 23.25, 11.02, 16.26 kPa, respectively. Conclusions During mouse operations, the thenar, hypothenar as well as the ulnar and radial sides of the wrist are persistently subjected to the continuous pressure, therefore, repetitive and continuous mouse operation can lead to the development of carpal tunnel syndrome of wrist or other MSDs.
Abstract:Mechanical forces can induce aseptic inflammatory reactions in human tissues including periodontium, and promote the pyroptosis of immune cells and some non-immune cells such as periodontal ligament cells. Recent studies have revealed that Gasdermin-D (GSDMD) plays an indispensable role in inflammation as well as pyroptosis, while it remains unknown whether GSDMD participates in the mechanical force-induced inflammatory reaction and pyroptosis. The current progress in researches about the mechanical force-induced inflammatory reaction and the signaling pathways of pyroptosis in human tissues is reviewed.
Abstract:Interventional stents are emerging medical apparatus and instruments which can be implanted into the lesion location to reopen and scaffold the blocked cavities. The ideal stents must have reliable mechanical properties, and the current research methods on mechanical properties of the stents are mainly based on theoretical analysis, numerical analysis and experimental test. In this article, all kinds of analytic methods on testing mechanical properties of the stents and their limitations are discussed and summarized in detail, and further research on the stents is prospected as well.