Abstract:Objective To establish a valid human head-neck model and ballistic helmet model, and analyze biomechanical responses of the cervical spine under bullet impacts on ballistic helmet with different weights. Methods A uniformly distributed weight of 2 kg was applied on the helmet (1.24 kg), and bullet impacts from frontal, lateral and crown directions at the speed of 450 m/s were considered to obtain the mechanical response of human vertebrae. Results The stress of the cervical spine was significantly higher than that of the skull under bullet impacts, and the stress of C3 segment was the largest, indicating that the cervical spine was more vulnerable than the head during bullet impacts under the protection of ballistic helmet. When the weight of helmet attachment was not considered, the maximum stress of the cervical spine under lateral impact was 2.58% higher than that under frontal and crown impacts. The frontal impact led to the greatest damage to the head, with an increase of 59.4% in head stress. When the weight of helmet attachment was considered, a lager helmet weight would cause a more serious spine injure. When the helmet weight was increased from 1.24 kg to 3.24 kg, the crown impact led to the greatest damage to the cervical spine, with an increase of 12.98% in cervical stress compared with impacts from other directions. Conclusions Lightweight should be considered in the design of ballistic helmet, and the research findings provide scientific references for the design of ballistic helmet.
Abstract:Objective Based on the principle of uncemented stem design, the femoral anteversion in different CT planes before total hip arthroplasty (THA) and stem anteversion after THA was compared, so as to find out the preoperative measurement to estimate stem anteversion in patients with developmental dysplasia of the hip(DDH) after THA. Methods Twenty-one primary THA patients (28 hips) who were diagnosed with DDH between September 2007 and May 2013 in Shanghai Ninth People’s Hospital Affiliated to Shanghai Jiao Tong University School of Medicine were selected. Preoperative and postoperative CT scans were performed on all patients. The femoral anteversion angle was defined as the angle between the midcortical line between the anterior and posterior cortical line in five CT slices and the posterior condylar axis. The slice levels for the 4 femoral sites were selected，including the area just distal to the femoral head, the center of the lesser trochanter，1 cm height above center of the lesser trochanter, 2 cm height above center of the lesser trochanter (marked as femoral anteversion 1-4). Femoral anteversion 5 was defined as the midcortical line of the anterior cortical line in the slice of 2 cm height above center of the lesser trochanter and the posterior cortical line in the slice of 50% of the distance from the top of greater trochanter to the center of the lesser trochanter above the center of the lesser trochanter. The stem anteversion angle was defined as the angle formed by the stem neck major axis and the posterior aspect of the femoral condylar line. The cup version and stem alignment were also calculated. The difference value and correlation coefficients of femoral anteversion 1-5 and stem anteversion were compared. Results Femoral anteversion 1-5 was 17.70°±10.54°, 35.59°±7.21°, 31.09°±7.98°, 24.71°±9.11°, 21.94°±10.10°, respectively。Stem anteversion was 20.52°±10.90°. The difference value between stem anteversion and femoral anteversion 1-5 was 2.82°±6.27°, -15.08°±7.99°, -13.80°±15.68°, -4.19°±5.69°, -1.42°±4.07°, respectively. Cup anteversion was 25.60°±11.65°, and combined antevertion was 46.11°±13.28°，sagittal stem tilt was 1.13°±1.53°. There were statistically significant differences between femoral anteversion 1-4 and stem anteversion (P＜0.05), and no statistical difference was found between femoral anteversion 5 and stem anteversion. The correlation coefficients of femoral anteversion 1-5 and stem anteversion were 0.829, 0.681, 0.689, 0.853, 0.928, respectively. Conclusions Femoral anteversion 5 had a highly positive correlation with stem anteversion, which was an effective a substitute of stem anteversion before THA.
Abstract:Objective To calibrate contact parameters of liver tissue discrete element model. Methods Based on MATLAB image processing technology, the accumulation angle of liver tissues was measured. The ‘Hertz-Mindlin with JKR’ contact model was used to simulate the accumulation angle of liver tissues. The orthogonal experiment was designed with the coefficient of rolling friction and the energy of JKR surface as factors. The parameters of the contact model were calibrated by batch processing, and the optimal parameter combination was verified by secondary simulation calibration. Results The accumulation angle obtained by the physical test was 11.2°±0.86°. In the orthogonal experiment, the accumulation angle of the 6th set of parameter combinations was 11.8°, and the relative error was 5.1%. The simulation test and the physical test had a high similarity in accumulation angle and shape. The sequence of factors affecting the accumulation angle was the JKR surface energy between the tissue particles and the stainless steel plate > the rolling friction coefficient between the tissue particles and the stainless steel plate > the JKR surface energy between the tissue particles and the tissue particles=the rolling friction coefficient between the tissue particles and the tissue particles. Conclusions The optimization parameter could be used to further conduct the discrete element simulation between the tissue particles and the pulverizer, so as to reveal the accumulation and flow state of the tissue particles under the action of myoma pulverizer.
Abstract:Objective In order to make up for the deficiency in the existing photoplethysmography feature point recognition algorithms which need manually setting the selecting threshold and have poor adaptability to complex waveforms, an automatic reognition algorithm for feature points based on monotonic increase in geometrical characteristics of pulse wave ascending branch was proposed. Methods A ‘reference point’ was determined in each pulse period by zero crossing detection after two Hilbert transformation. The nearest concave and convex inflection points that searched around the ‘reference points’ were the notchs and systolic peaks. Results By using the 18 sets of data in the MIT-BIH standard database for verification, the average sensitivity, precision and detection accuracy reached 99.94%, 99.72% and 99.68%, respectively. Compared with the existing four algorithms, there was a significant improvement in the precision. Feature points could still be accurately identified for complex waveforms. Conclusions The proposed algorithm achieved a higher detection accuracy in the process of searching and determining the position of the pulse wave notchs and systolic peaks, and exhibited a stronger adaptability to the waveform change. The research results provide a good foundation for physiological and pathological analysis through pulse wave features extraction in clinic.
Abstract:Objective To explore the effects of the interfacial debonding caused by water environment in the mouth and the interfacial defects between the crown and cement on stress distributions in all-ceramic crowns. Methods The three-dimensional solid model of lithium disilicate CAD/CAM crowns for the first mandibular molar was established. Seven debonding states between inferior surface of the crown and top surface of the cement (Stage 1-7) as well as two interfacial defects (Case I and II) were defined in finite element software ABAQUS. The bottom of nine models was completely constrained. For stress calculation, the 600 N vertical load was applied at occlusal surface via an analytical rigid hemisphere with the diameter of 5 mm. Results Under occlusal vertical load, the stress on interior of the crown and top surface of the cement was mainly distributed at the boundary of the debonding areas and margin of the defects. The first principle stress on interior of the crown did not exceed its ultimate tensile strength, but the maximum tensile stress of the cement exceeded its ultimate tensile strength, leading to cohesive failure in the cement. Conclusions The axial wall played a critical role in maintaining the principal tensile stress of the crown at a lower level. The defects at bonding interface between the crown and cement had a more significantly impact on load capacity of the crown than the increase in debonding areas. In order to improve load bearing capacities of all-ceramic crowns, attention should be paid to avoid defects in clinical prosthodontic practices.
Abstract:Objective To study the blood flow in aneurysm and its influence on mechanical properties of vascular walls for two kinds of common aneurysms, so as to improve the diagnosis and treatment of aneurysms and the prognosis of patients. Methods The interaction between the aneurysm-carrying vessels and blood of two common aneurysms was studied by fluid-structure interaction method. The blood flow velocity, wall deformation, stress distribution and damage form of aneurysm-carrying vessels were analyzed. Results The blood flow in both aneurysms were slow and stable, which resulted in better deposition and adhesion conditions. The junction between the aneurysm and the downstream of the blood vessel was a dangerous place for damage. The spindle aneurysm would undergo shear failure on outer wall of the aneurysm, while the cystic aneurysm would undergo stretching failure on inner wall. Under the effect of the same blood flow, a larger stress appeared on the cystic aneurysm, which was more prone to damage, and the tensile failure would lead to a more serious consequences. Conclusions The junction at the aneurysm and blood vessel is prone to damage, and the cystic aneurysm is more dangerous and harmful.
Abstract:Objective To study the effect of sand therapy on the hemodynamics of flexural femoral artery, and further reveal the therapeutic mechanism of sand therapy from the perspective of hemodynamics. Methods The three-dimensional finite element model of the curved femoral artery was established based on CT images of human aorta, and the data of heart rate, peak blood flow velocity and inner diameter of femoral artery measured by the experiment were used as initial conditions and boundary conditions to carry out finite element numerical simulation. The blood flow velocity, pressure and wall shear stress before and after sand therapy were analyzed and compared under fluid-solid coupling condition. Results Compared with treatment before sand therapy, the longitudinal velocity of the flexural segment of blood vessel increased significantly, with an increase of 22.76%. The secondary reflux velocity decreased significantly, with a relative decrease of 18.26%. The wall shear stress decreased by 2.01% after sand therapy. Conclusions Sand therapy had a significant effect on blood fluidity, by improving blood flow of femoral arteries, and preventing deposition of arterial platelets. The transverse flow phenomenon was obviously weakened after sand therapy, which could avoid the deposition of substances in blood and had a positive effect on the prevention of atherosclerosis, thrombosis and other vascular diseases.
Abstract:Objective To study the changes of transcriptome levels in a Bama minipig model of hypertrophic scar during wound healing and pressure therapy by using RNA sequencing (RNA-seq) technique. Methods The Bama minipig model was established by skin wounds from the back and pressure (3.4 kPa) was initiated at 60 days after skin injury. Total RNA was extracted from scar tissues at 0, 14, 30, 60, and 90 days after skin injury and then sequenced. The resulting sequences were mapped to porcine reference genomes and transcriptomes were reconstructed to search for differentially expressed genes (DEGs). The DEGs were further subjected to GO and KEGG analysis using bioinformatics method, while part of the genes were selected for verification using qRT-PCR. Results After preprocessing, more than 78% reads in each group were accurately aligned to the reference sequence. The DEGs identification result showed that 568 genes were differentially expressed after pressure treatment, with 289 up-regulated and 279 down-regulated. GO enrichment analysis revealed that DEGs in each group were mainly associated with extracellular matrix, tissue development and skin development. KEGG analysis showed that the DEGs in each group during wound healing were mainly enriched in extracellular matrix-receptor interactions, focal adhesion and apoptosis pathways; while the DEGs after pressure treatment were mainly enriched in PI3K-Akt and MAPK signaling pathway except the pathways mentioned. qRT-PCR showed that the expression patterns of 6 DEGs were consistent with RNA-seq analysis, confirming the reliability of RNA-seq result. Conclusions RNA-Seq analysis identified differentially expressed genes in animal model of scars during wound healing and pressure therapy, which provided experimental evidence for clinical scar treatment.
Abstract:Objective To study the effects of abnormal blood flow on the secretion of ET-1/NO and the expression of the mRNA and the protein of ET-1, eNOS, VCAM-1, ICAM-1 and MCP-1 in human umbilical vein endothelial cells (HUVECs), so as to explore the mechanism of atherosclerosis （AS） caused by abnormal hemodynamics. MethodsThe HUVECs were divided into stress group, wall pressure group and normal group according to the different stress. The HUVECs were cultured under the corresponding stress for 24 hours and then collected. The secretion levels of NO and ET-1 were detected by enzyme method and radioimmunoassay method. The mRNA expression levels of eNOS and ET-1 were detected by qPCR. The expression levels of the mRNA and the protein of VCAM-1, ICAM-1, MCP-1 were detected by qPCR and Western blot. Results Compared with normal group, the secretion level and the mRNA expression level of ET-1 in wall pressure group increased significantly (P＜0.01), and the secretion level of NO and the mRNA expression level of eNOS in stress group also increased significantly (P＜0.01), The expressions level of the mRNA and the protein of VCAM-1, ICAM-1 and MCP-1 obviously increased in stress group and wall pressure group (P＜0.01). Conclusions Stress or wall pressure acting on HUVECs alone could lead to its dysfunction of the secretion and the expression of gene and protein. The mechanism of AS caused by abnormal blood flow was related to these dysfunction of HUVEC.
Abstract:Objective To design and implement a control algorithm in a 6 degree of freedom (DOF) robotic manipulator, so as to simulate the spinal motion and provide stable and efficient testing plan for biomechanical tests on spinal implants. Methods The recognition method of stiffness matrix for L2-5 spinal system was firstly studied for decoupling purpose. Secondly, the direct force control system under each axial motion was established by combining the 6-axis manipulator control system with the incremental proportion integration differentiation (PID) control algorithm. By using the 6-axis direct force control system, pure moment of 7.5 N·m was applied in the direction of main motion axis to simulate flexion-extension (FE), lateral bending (LB) and axial rotation (AR) motion of L2-5 spinal segment. Results The range of motion (ROM) of L2-5 segment in FE, LB and AR direction was 23.01°,27.92°,9.81°, respectively. A 7.5 N·m pure moment could be achieved in the main motion axis, while maintaining zero force/moment in the unconstrained axis with root mean square (RMS) errors being less than 3 N and 0.1 N·m, respectively. Conclusions The proposed algorithm of direct force control using PID controller with predetermined stiffness decoupling matrix was capable of applying pure moment to the spine under FE, LB, AR motion. The research findings have a relatively high value of engineering application for various biomechanical testing of lumbar vertebrae.
Abstract:Objective To study the method of estimating noninvasive dynamic respiratory mechanics parameters for patients with chronic obstructive pulmonary disease (COPD). Methods By simplifying the human respiratory system into a first order single compartment model and setting constraints based on optimization method, the respiratory system resistance and compliance of COPD patients were estimated. Results By using the model and setting the constraint conditions in the simulation experiment, the respiratory system resistance and compliance of COPD patients with spontaneous breathing could be estimated, and the results were relatively accurate (within 5% error). The estimated result could be obtained by data of one respiratory cycle within three respiratory cycles, which could meet the requirements of dynamic monitoring data. Conclusions Based on optimization method, the noninvasive dynamic evaluation on respiratory resistance and compliance of COPD patients were carried out in simulation experiments and proved to be feasible for further clinical trials. The research findings could help doctors to monitor the resistance and compliance changes of COPD patients in real time after clinical trial, and provided references for diagnosis and treatment of COPD.
Abstract:Objective To analyze the differences in mechanical properties of arterial vessels at different sites and the effects of different test methods on the experimental results. Methods A unique fixtures based on characteristics of artery shape was designed. The porcine thoracic aorta and common carotid arteries were applied with uniaxial tensile tests under 4 different states (tubular vessels in axial and radial direction and sheets in axial and circumferential direction), and data fitting analysis was conducted on their nonlinearity. Results The mechanical properties of aorta vessels under tubular state were stronger than those under sheet state, and the difference in such numerical results became more significant with the diameter of the tube decreasing. Conclusions The experiment results, provide more comprehensive and reliable vascular mechanical parameters to provide data support for constructing finite element model and constitutive relationship of blood vessels, and guide design and manufacture of tissue engineered vascular grafts. At the same time, it is also beneficial to study and analyze the potential pathophysiology of certain vascular diseases, which will help doctors to present better therapeutic effects in clinical treatment.
Abstract:Objective To measure and investigate the anatomical characteristics of the proximal femur canal curves in patients with developmental dysplasia of the hip (DDH), and to provide references for the design of femoral stem of DDH patients. Methods Three-dimensional reconstructions of the proximal femur were conducted from the CT data, and the anatomical morphology characteristics were obtained from 64 patients with DDH (74 hips, 12 males, 52 females, average age of 45.3 years) and 30 healthy controls (30 hips, 21 males, 9 females, average age of 29.4 years). Multiple anteroposterior diameter and mediolateral diameter around the lesser trochanter at different heights and the fitting curves of different groups were obtained. Results The femoral neck anteversion angle, neck-shaft angle, height of the isthmus, canal flare index (CFI), femoral head diameter and femoral offset of DDH patients and healthy controls were 26.39°±14.74° and 15.68°±7.95°, 125.65°±5.73° and 129.19°±5.80°, (99.14±14.62) mm and (110.13±11.73) mm, 3.63±0.77 and 4.45±0.79, (44.01±5.75) mm and (47.26±3.94) mm, (31.80±3.82) mm and (36.42±4.84) mm, respectively. DDH group had the significantly greater femoral neck anteversion angle, and other anatomical morphology characteristics were significantly smaller than the control group. The obtained anteroposterior diameter, mediolateral diameter and the fitting curves showed that DDH group had narrow medullary cavity and forward shifting anteroposterior diameter. In addition, there was a statistical significance between the Crowe Ⅳ DDH and other types of DDH, and deformation degree of the femur increased with the increase of DDH type. Conclusions The proximal femur of DDH patients was significantly different from the healthy controls. Moreover, there were significantly morphological differences between different types of DDH. The research findings can be used as quantitative references for understanding the morphological feature of DDH patients and the corresponding design of femoral stem for DDH patients.
Abstract:Objective To identify the effect of the repeatability of muscle activations on extraction of consistent motor modules across trials. Methods The activities of sixteen muscles in twelve subjects who consistently walked at a self-selected speed were recorded. The intraclass correlation coefficient (ICC) was used to identify inter-stride repeatability of muscle activities and motor modules. Based on the repeatability of muscle activation, three types of muscle sets were organized. Results The reliable set containing the muscles showed high ICC (>0.4), but the whole-body and mixed sets containing the muscles showed poor ICC (＜0.4). When motor modules were extracted from each set, the reliable set showed the highest repeatability of motor module extraction, but the whole-body and mixed sets presented significantly lower repeatability. Conclusions Greater repeatability of muscle activations result ed in consistent motor modules. Extraction of consistent motor modules was a critical issue, especially in real-time motion recognition based on muscle patterns.
Abstract:As the main organ of the body, the load-bearing ability of bone is closely connected to its biomechanical properties. Bone is a complex hierarchical biomaterial, whose biomechanical properties are determined by its own structure and biological characteristics. Because of its mechanical adaptability, bone tissues represent different biomechanical properties under different mechanical loading. To quantify the complicated properties of bone and provide an accurate theoretical basis for clinical research, it is necessary to give insight into the biomechanical properties of bone at different levels and the constitutive relationships of bone tissues. In this review, relative researches on constitutive relationships in recent years were summarized based on its hierarchical biomechanical properties.
Abstract:Vibration represents a micro reciprocating motion of a particle or object along a line or arc relative to a reference position, while the effect of low-magnitude high-frequency vibration (LMHFV) on skeletal system cells is similar to the mechanical stimulation of muscle movement. Bone mesenchymal stem cells (BMSCs), which have been identified as force-sensitive cells, exist in the bone marrows and have the potential of multi-lineage differentiation. Their biological characteristics can change functionally according to the appropriate stimulation in vitro, in order to reach the optimal demand of the stimulation. LMHFV can promote the osteogenic differentiation of BMSCs, therefore, the research on its mechanism can contribute to the application of vibration in the treatment of diseases such as osteoporosis, fracture, osteogenesis imperfecta, obesity as well as the promotion of orthodontic tooth movement. This paper summarizes the recent progress about the effects of vibration on BMSCs stem cells in osteogenesis and the possible mechanisms, so as to provide research ideas and methods for studying the mechanical as well as biological changes of BMSCs under vibration stimulation.
Abstract:The high elastic modulus of scaffolds or implants will result in stress shielding effect, which may lead to bone resorption and scaffold or implant loosening in the late stage. Porous scaffolds and implants can adjust their porosity and elastic modulus according to the mechanical environment, thereby reducing stress shielding; meanwhile, porous structures are beneficial to bone tissue growth, which is conducive to osseointegration. Three kinds of basic structure for porous scaffolds and implants by 3D printing were summarized, namely, uniform porous structure, bone-like trabecular structure and functionally graded structure. The design methods of these structures were introduced respectively, including computer-aided design (CAD)-based, implicit surface-based, image-based and topology optimization-based design method, so as to provide references for solving the stress shielding problem, as well as designing porous scaffolds and implants.