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Abstract:Objective To evaluate mechanical comprehensive performance of the flexible neural electrode with coating modification, so as to provide references for optimal design of the electrode and coating parameters. Methods Simplified mechanical models were established for the contact phase, implantation phase and micromotion phase. The electrode material was polyimide, the coating material was PEG, and PDMS mold injection method was selected as the coating method. The coating thickness gradients were set as 40, 80, 120, 160 and 200 μm, respectively, and the three factors (the critical load, the maximum total deformation and the maximum strain of brain tissues) were comprehensively evaluated. Results As the thickness increased, the critical load increased, the maximum total deformation and the maximum strain of brain tissues decreased, but meanwhile, the strain area of brain tissues increased. For consideration of equilibrium for three factors, 200 μm was chosen as optimal thickness of the coating. At this thickness, the critical load was 17.9 mN, the maximum total deformation was 10.1 μm, and the maximum strain of brain tissues was 0.011 4. Conclusions The coating thickness had a great influence on mechanical properties of the neural electrode. The optimal parameters could be selected by setting influencing factors from the mechanical performance factors under specific case. The optimal parameter selection of coating can improve the electrode performance, which is of great significance for clinical application of the neural electrode.

Abstract:Objective To make drilling mechanical and thermal analysis of bones with different drill bits and drilling parameters, so as to reduce the drilling force and drilling temperature in drilling process and decrease the damage to surrounding bone tissues. Methods The bone drilling model was established by finite element simulation software AdvantEdge. By comparison with the pig femur drilling experiment, the simulated and experimental results of standard twist driII and three standard multi-facet drills at different speeds and feed rates were analyzed. Results The simulation and experiment comparison showed that the influences of driII bit structure, drilling speed, feed rate on drilling force and drilling temperature were consistent, and the established simulation model was credible. Conclusions Under the same drilling conditions, the multi-facet driII for drilling rubber had lower drilling force and drilling temperature than the standard twist drill. The research findings provide theoretical basis for the application of multi-facet driII in fracture surgery.

Abstract:Objective To study the stress distribution and biomechanical stability of the long-type composite locking plate already used in clinic practice and the novel short-type composite locking plate for treating Sanders type IIa, IIb and IIIab calcaneal fractures. Methods The three-dimensional (3D) models of Sanders type IIa, IIb and IIIab calcaneal fractures were established, and the force conditions of calcaneus in neutral standing position and under 20°dorsal extension were simulated. By referring to the physical form of human specimens, 500 N vertical axial load was applied, so as to study the displacement and relative displacement of the fracture block under the force, and the force conditions of bone tissues and internal fixation were analyzed. Results For Sanders type IIa, IIb calcaneal fractures treated with long-type and short-type composite locking plates, the stress concentration positions of the plates and calcaneal fractures were basically the same. The maximum stress difference of the two plates for fixing calcaneal fractures with the same type was smaller than 5 MPa, and there was no significant difference in the maximum displacement of the fracture models. For Sanders type IIIab calcaneal fractures treated with long-type and short-type composite locking plates, the maximum stress concentration occurred in the forearm of plate screws, indicating the risk of metal fatigue. The maximum stress difference was up to 12 MPa, and the maximum calcaneal displacement was up to 9 μm. Conclusions The long-type and short-type composite locking plates showed no significant differences in treating Sanders type IIa, IIb calcaneal fractures. For fixing Sanders type IIIab calcaneal fractures, the long-type composite locking plate was superior to the short-type composite locking plate.

Abstract:Objective To investigate the effect of medial collateral ligament (MCL) repair and coronoid process fracture fixation on stability of the Terrible Triad of the elbow. Methods CT and MRI scan images of elbow joints from one healthy 28-year-old male volunteer were used to establish three elbow models. Model A: normal model. Model B: repair of coronoid process fractures, without MCL repair. Model C: repair of MCL, without repair of ulnar coronoid processes. Longitudinal loads were applied on the three models to analyze the displacement and stress distributions of the elbow joint under different working conditions and compare the stability of the elbow joint. Results The displacement and stress distributions of the three models were similar. The maximum displacement and maximum stress of the articular surface were located at the ulna pulley notch, while the minimum displacement was located at the coronoid process and its medial side. The minimum stress was located at the lower lateral side of the coronoid process. There were no statistical differences in the maximum displacement and stress among the three models (P>0.05). Conclusions When the lateral column is stable, the effect of repairing the MCL and fixing the fracture block of ulnar coronoid process is similar.

Abstract:Objective To quantitatively explore the influence of knife sharpness on forearm wounds in knife slash cases. Methods The finite element models of the upper limb and knives with 3 degrees of sharpness (with sharp blade, blunt blade, wide blade) were developed based on human CT images and prototype of slash knife. The slash by 3 kinds of knives on the forearm at velocity of 4 m/s and duration of 10 ms was simulated, so as to analyze changes in contact forces, wound dimensions and energy. Results During the slash by knives with sharp, blunt, wide blade, the blades reached the ulna at about 65, 85, 95 ms, respectively. The corresponding slash forces were 846, 1 064 and 1 865 N; the wound lengths were 135.64, 105.47 and 99.23 mm; the wound depths were 38.77, 27.81 and 18.74 mm. With the sharpness of blade decreasing, the wound formation was slowed, the length and depth decreased and the slash force increased. The model system for slash knife with sharp blade had obviously greater total energy and inner energy, but smaller kinetic energy, compared with slash knife with blunt blade and wide blade. Conclusions The method for quantitatively assessing wound formation in knife slash upon the forearm was developed. The research findings deepen the understanding of biomechanical mechanism of wound formation by knife slash, and provide new scientific means for forensic investigation and court trial of knife slash cases.

Abstract:Objective To investigate the transport and deposition behaviors of lowdensity lipoproteins (LDL) in the carotid artery and explore their associations with hemodynamic and morphological factors, so as to provide theoretical references for assessing the risk and predisposing regions of atherosclerosis based on the characteristics and associated factors of LDL deposition at the carotid artery wall. Methods Subject-specific computational models of the carotid artery based on medical images from six healthy volunteers were built, and the transport and wall deposition of LDL under pulsatile flow conditions were simulated, and finally the correlations of wall LDL concentration and total area of regions with LDL concentration polarization with flow velocity and morphological parameters of the carotid artery were quantitatively analyzed. Results Regions with significant LDL deposition often appeared in carotid sinus near distal end of the common carotid artery, with the degree and spatial distribution of deposition differing considerably among subjects. The degree of LDL deposition was determined mainly by flow velocity, i.e., the lower the flow velocity was, the higher the degree of LDL deposition and accordingly the larger the area of wall regions with LDL concentration polarization was; whereas the spatial distribution of LDL deposition was significantly affected by morphological characteristics (especially bifurcation eccentricity ratio) of the carotid artery, for example, the distribution patterns could be divided into two typical types (i.e., circular distribution, unilateral distribution) according to bifurcation eccentricity ratio. Conclusions Flow velocity and morphological characteristics of the carotid artery are major factors determining respectively the degree and spatial distribution of LDL deposition, and therefore subject-specifically measuring these parameters will provide useful information for screening individuals at high risk of atherosclerosis or identifying atheroprone regions.

Abstract:Objective To establish a method for non-invasive calculation of fractional flow reserve (FFRCT) with the shape resistance of coronary artery stenosis as boundary condition, and to verify the accuracy of this method. Methods CT angiography images of 16 patients with coronary artery disease were reconstructed; the mathematical model of shape resistance was established by considering the minimum cross-sectional area and the length of stenosis of coronary artery stenosis, the induced pressure difference as the boundary condition was applied to calculate FFRCT (named as shape resistance method ). The values of clinical FFR were taken as the gold standard, previous diameter method and volume method were taken as control method, and accuracy of shape resistance method was investigated from the aspects of mean error rate, accuracy rate, sensitivity rate, positive prediction rate and negative prediction rate. Results The mean error rate of calculated FFRCT by the diameter method, volume method and shape resistance method were 11.76%, 10.46%, 4.82%, the accuracy rates were 85%, 65%, 90%, the sensitivity rates were 87.5%, 66.7%, 87.5%, the positive prediction rate were 75%, 25%, 87.5%, respectively, while the negative prediction rates were all 91.6%. Conclusions The established shape resistance method is better than the diameter method and volume method from the aspects of mean error rate, accuracy rate, sensitivity rate and positive prediction rate; the FFRCT based on the shape resistance method and clinical FFR have good consistency, and this work may provide a new way for the calculation and application of FFRCT.

Abstract:Objective To design a novel strain loading device for studying the mechanical biology of adherent cells. Methods Based on the technology of substrate deformation loading, the device adopted controllable stepper to cause deformation of the silastic chamber, so as to realize cell loading with multiple units and large strain. The device was developed to test its loading functions. The three-dimensional (3D) models of the silastic chamber were established to simulate the loaded chamber by the finite element technology, and uniformity of the strain field was analyzed. The device applied 5% strain to bone marrow stromal cells (BMSCs) with 0.5 Hz stretch frequency at 2 hours per day for 5 days, and an inverted phase contrast microscope was used to observe the morphology of BMSCs. Results The developed strain loading device for adherent cells in vitro could provide mechanical unidirectional strain up to 50% with three groups of cell loading substrates; within the 10% stain range, the area of uniform strain filed on the silastic chamber remained above 50%, which ensured that the cells were loaded evenly; the morphology of BMSCs was obviously altered, and the direction of arrangement tended to be perpendicular to the loading direction of principal strain. Conclusions The device shows the advantages of reliable operation, wide strain range, adjustable frequency and convenient operation. It can be used to load multiple cell culture substrates at the same time, which provides convenient conditions for the study of cell mechanobiology.

Abstract:Objective To develop a new type of electric stapler, so as to solve the problems of insufficient rotation angle, inconvenient operation and difficulty in controlling the pressing strength of existing products. Methods An electric stapler was designed and manufactured. The motion trajectory curve of the prototype was measured by using the three-coordinate imaging instrument to build functional test platform of the prototype, and the goodness of fit was used to evaluate consistency between the theoretical curve and the measured curve. The small intestine tissues of fresh pig were anastomosed at different bending angles of the front end, and the forming rate of the anastomotic stoma was measured. Results The goodness of fit between the test curve and the theoretical curve for both turning motion and shooting motion was ideal, while the goodness of fit between the test curve and the theoretical curve for pressing motion was not ideal when the turning joint was bent at 0°-30°, and was ideal when it was bent at 45°-60°. In performance test, the deformity rate of the nail was smaller than 1.14%, indicating that the bending angle had no significant impacts on the anastomotic effect. Conclusions The kinematics curves of shooting motion and turning motion are consistent with the theoretical curves. The pressing motion curves fluctuate at different bending angles, which will not affect the anastomotic effect, and the effect of the electric stapler meets the clinical requirements.

Abstract:Objective To study the influence of different moment-to-force ratios (M/F) and forces on canine displacement and periodontal ligament (PDL) stress. Methods A three-dimensional (3D) mandibular model was established based on CT images. The orthodontic force systems without a moment and with various M/F were applied to the canine for numerical calculation of its translation. An optimum force system to realize canine translation was validated by analyzing translation displacement of the canine in each case. Results The PDL stress increased with an increase in force magnitude in all cases. The PDL stress first decreased with an increase in the M/F before the M/F reached the optimum value (M/F=10.1 mm), and then increased with an increase in the M/F. The initial displacement of the canine was inclined movement, which was most close to translation when the precise optimum M/F was applied. Conclusions The canine movement requires an appropriate force to prevent root absorption, whereas the translation movement requires an optimal M/F value which is within the physiological range. Understanding the influence of force and moment on tooth translation can help to apply more reasonable orthodontic force system and design more reasonable orthodontic device.

Abstract:Objective To establish a refined model of trunk composed of different lumbar segments, lumped thoracic spine and pelvis, analyze the kinematic differences between patients with lumbar disc herniation (LDH) and healthy people during three daily activities, and to compare the refined trunk model with the simplified trunk model adopting the whole lumbar segment, and discuss the necessity of using the refined trunk model for kinematic analysis of LDH patients. Methods Motion capture system NDI was used to collect kinematic parameters of each segment from 15 healthy people and 7 male LDH patients during level walking, trunk flexion and contralateral pickup, then the kinematic differences between patients and healthy people by the two models were compared respectively. Results During level walking, the rotation of the thoracic segment and pelvis for LDH patients increased, while no significant change was found in motion angle of the whole lumbar segment, and the rotation angle of L4-5 segment significantly reduced. During trunk flexion, the flexion angles of all lumbar segments for LDH patients were reduced by varying degrees, and the flexion angle of L3-4 segment was significantly different from that of healthy people. During contralateral pickup, the performance on the sagittal plane was similar to that during flexion. However, the lateral bending angles of L3-4 segment and L4-5 segment for LDH patients were significantly lower than those for healthy people. ConclusionsLDH patients mainly restrict the motion of injured lumbar segments in daily activities. During some motions, only refined model can discover the abnormal motion of injured lumbar segments. Therefore, it is necessary to subdivide the lumbar spine into 5 independent segments for analyzing the kinematic characteristics of LDH patients.

Abstract:Objective To conduct dynamic impact failure test of rabbit single vertebra, and make comparison with the static compression experiment, so as to study damage mechanism of the vertebral body under the axial impact. Methods The voltage waveform diagram of the force sensor and the detailed process of the vertebral impact were obtained by the oscilloscope and high-speed photography through the drop hammer dynamic impact experimental device. Results The average static load of the thoracic and lumbar vertebra were 910 N and 947 N, respectively; the average dynamic load of the thoracic and lumbar vertebra were 1 196 N and 1 026 N, respectively; the average thoracic and lumbar dynamic load coefficients were 1.37 and 1.08; under static load, the average stress of the thoracic and lumbar vertebra was 15.28 MPa and 12.51 MPa, respectively; under dynamic load, the average stress of the thoracic and lumbar vertebra was 20.03 MPa and 13.56 MPa; during dynamic impact, the mean longitudinal strain and transverse strain was -0.3 and -0.005 (compression); under dynamic conditions, the destruction energy of vertebrae increased from 0 J to 4.4 J. Conclusions Under dynamic and static experimental conditions, the dynamic load of the same vertebral body was greater than that of the static load; the average dynamic load coefficient of the thoracic vertebra was larger than that of the lumbar vertebra; the equivalent stress of the thoracic vertebra was greater than that of the lumbar vertebra; the axial strain of vertebra under impact was greater than the transverse strain; energy growth of the vertebral body presented a slow at first and then a rapid changing process. The research findings can provide some guidance for prevention and rehabilitation of human vertebral body injury in clinic.

Abstract:Objective To analyze the efficacy and biomechanical properties of locking proximal femoral plate (LPFP) and proximal femoral nail anti-rotation (PFNA) for treating intertrochanteric fracture in elderly patients. Methods One hundred and six elderly patients with intertrochanteric fracture of femur were randomly divided into LPFP group (53 cases) and PFNA group (53 cases). After treatment intervention, the operation time, intraoperative bleeding volume, weight-bearing time, fracture healing time and Harris hip function score of 9 months after operation in two groups were recorded. The complications after operation in two groups were analyzed. Ten elderly fresh femoral specimens were selected to prepare the model of intertrochanteric femoral fracture in the elderly. They were randomly divided into PFNA group and LPFP group with 5 models in each group. After treatment and intervention, axial compression test, destructive load test and torsional stiffness test were conducted by mechanical testing machine, and biomechanical properties were recorded. Results The average operation time, weight-bearing time and fracture healing time in PFNA group were shorter than those in LPFP group (P<0.05), and the average intraoperative bleeding volume in PFNA group was less than that in LPFP group (P<0.05), and the average Harris score was higher than that in LPFP group (P<0.05). The total incidence of postoperative complications in PFNA group and LPFP group was 7.56% and 18.87%, respectively, indicating a significant difference between the two groups (P<0.05). After intervention treatment, the average axial compression, damage load and torsional stiffness in PFNA group were higher than those in LPFP group (P<0.05). ConclusionsPFNA caused minimal trauma for treating intertrochanteric femoral fractures in the elderly. With its good biomechanical properties, PFNA could effectively promote fracture healing and hip function recovery, and significantly reduce the incidence of hip varus, screw loosening and cutting complications.

Abstract:Objective To observe biomechanical characteristics and advantages of the self-developed anatomical locking plate of sternoclavicular joint by comparison with the radial distal oblique T-shaped locking plate and sternoclavicular hook plate. Methods Nine embalming and moistening adult corpses were selected, including 6 males and 3 females. Model of complete dislocation of the sternoclavicular joint caused by complete removal of the sternoclavicular joint specimen. The bilateral sternoclavicular joints of 9 specimen models were randomly numbered, matched and divided into Group A(experimental group, sternoclavicular joint anatomical locking plate), Group B(control group 1, the radial distal oblique T-shaped locking plate) and Group C(control group 2, sternoclavicular hook plate), with 6 sternoclavicular joints in each group. All specimens were placed with steel plates on both sides and fixed on the universal mechanical test machine. Three biomechanical experiments were carried out, including loading of distal clavicle, torsion of distal clavicle and anti-pull out of sternum handle screw. Results Distal clavicle loading test: the load-displacement of specimens in three groups showed a linear relationship. The compressive deformation resistance in experimental group was stronger than that in two control groups. Distal clavicle torsion test: the relationship between torque and torsion angle was linear. The torsional deformation resistance in experimental group was stronger than that in two control groups. Anti-pullout test of sternum handle screw: there was a significant difference in the maximum anti-pullout force of sternum handle screw among the three groups (P＜0.05). The anti-pullout performance of the sternum handle screw in the experimental group was better than that in the two control groups. Conclusions The self-developed sternoclavicular joint anatomical locking plate is superior to the oblique T-shaped locking plate of distal radius and the plate of sternoclavicular hook in terms of anti-compression, anti-torsion and anti-pullout of sternoclavicular screw, so as to provide an ideal internal fixation device for the treatment of fracture and dislocation of sternoclavicular joint.

Abstract:Objective To study the factors leading to the increased risk of falls when the elderly cross obstacles with different load distributions in their hands, and to explore the gait strategies to prevent falls for elderly people with different load distributions during obstacle crossing. Methods Twelve young healthy (control group) and 12 elderly healthy participants performed walking tasks with or without obstacle crossing at their daily speed under different load distributions. Surface electromyography (sEMG) signals were collected from both sides of the lateral femoris, rectus femoris and medial femoris. Then the average sEMG was analyzed and compared. The numbers of contact incident during obstacle touching were also recorded. Results Age, weight carrying and obstacle all had significant influences on the activity level of lower limb muscles in elderly people. A total of 9 contact incidents occurred in 1 152 obstacle crossing tests. In addition, the contribution of right vastus medialis muscle was the greatest in the elderly and young adults when they completed the weight carrying and obstacle crossing tasks. Conclusions The elderly people had the lowest risk of falling down by taking advantage of the dominant side of the leg to take the lead in obstacle crossing under the uniform distributions of load. The research findings provide references for systematic assessment of fall risk in the elderly and have certain guiding significance for lower limb exercise or rehabilitation training in the elderly.

Abstract:Objective To investigate the translation and rotation of healthy elbow joints during active flexion and extension, so as to provide references for the treatment of elbow instability and injuries. Methods Ten healthy subjects with no history of upper extremity trauma were recruited. Dual fluoroscopic imaging system (DFIS) was applied to quantify six-degree-of-freedom (6-DOF) kinematics of humeroulnar and humeroradial joint from full extension to maximum flexion in supination position. Correlation analysis was used to evaluate the relationship between the 6-DOF kinematics of the elbow joint. Results Valgus angle of humeroulnar joint gradually decreased from 15.2°±3.1° to 5.3°±2.3° with the flexion increasing. Valgus angle of humeroradical joint gradually decreased from 19.7°±4.2° to 8.2°±2.4° from full extension to maximum flexion. The valgus angle of humeroulnar and humeroradial joint was linearly related to the flexion angle during flexion and extension. The internal rotation of humeroulnar joint was quadratic nonlinearly related to the flexion angle during motion. The maximum internal rotation of the ulnar was 4.0°±4.9° at 110° flexion, and the maximum external rotation was 5.1°±4.2°. The internal rotation of humeroulnar joint gradually increased from 3.2°±16.0° to 27.2°±18.0°. Conclusions During normal flexion and extension of the elbow, the valgus angle of humeroulnar joint decreased linearly, while the internal and external rotation angle showed a nonlinear change, which first rotated internally and then rotated externally. The valgus angle of humeroradial joint decreased linearly and the internal rotation angle increased linearly. Therefore, humeroulnar joint is not a hinge joint during elbow flexion and extension. There is a kinematic difference between humeroulnar joint and humeroracial joint. For clinical treatment of complex elbow injuries, elbow instability and elbow replacement, different motion characteristics in joints should be considered to improve the outcome after surgery.

Abstract:Pulmonary hypertension (PH) is a devastating disease caused by different etiology and characterized by the progressive elevation of pulmonary vascular resistance and pulmonary artery pressure. As a new method that applied to clinical studies, computational fluid dynamics (CFD) gradually becomes a powerful tool for in-depth understanding of the disease progression. It can noninvasively obtain the patient-specific hemodynamic parameters at any point of the vessel and present them through the visualization technology. In this paper, an overall review of CFD with the focus on PH, including the numerical simulation method, boundary conditions, blood characteristics and relevant hemodynamic parameters was presented.

Abstract:With the development of the 3rd-generation high-throughput sequencing technology and tissue engineering, recent studies show that many long-chain non-coding RNAs (LncRNAs) have played an important role in osteogenic differentiation of mesenchymal stem cells (MSCs). LncRNAs, which are involved in the regulation of mechanical regulation, further regulate bone-related cell functions and play a regulatory role at multiple levels, including transcription, post-transcriptional and epigenetic. LncRNAs may be involved in the osteogenic differentiation and bone remodeling of MSCs, the regulation of bone-related cell functions as a mechanical response molecule, as well as the pathological process of skeletal diseases.

Abstract:In recent years, with the growth of social development, the incidence of lumbar vertebrae diseases has increased year by year, and many surgical methods have been developed. These treatment methods mark the accumulation of surgical experience and the development of medical technology. However, a new issue appears, i.e. how to evaluate the degree of lumbar disease and postoperative rehabilitation. There is an urgent need to establish a quantitative index of preoperative examination and postoperative rehabilitation criteria for lumbar disease from both doctors’ and patients’ perspectives. The current studies show that the measurement of the center of rotation (COR) for lumbar vertebrae and surface electromyography (sEMG) can reduce the error in the evaluation of clinical curative effect for treating lumbar disease and can be applied widely. This review summarizes the relationship between COR and lumbar disease, as well as the role of COR and sEMG joint evaluation in clinical operation and postoperative rehabilitation.