Search

Irreversible osteoporosis may occur in astronauts during long-term space flight. The flow field of tissue fluid in the lacunar-canalicular system (LCS) of osteon and the mechanical response of osteocytes to the flow field under different gravity fields were studied by numerical simulation. This study is expected to explain how the decrease in liquid transmission within microgravity can be a cause of osteoporosis in astronauts from the perspective of biomechanics using a fundamental research approach. A 3D axisymmetric fluid-solid coupling finite element model of an osteon with a two-stage pore structure (Haversian canals and lacunar-canalicular network) and osteocytes was established. The model compared the influence of differences in pulsating pressure of arterioles in Haversian canal, from 33 mmHg to 45 mmHg within a microgravity field (0 g), Earth's gravity field (1 g), and a high G gravitational fields (2-8 g). The liquid flow velocity in the LCS within a microgravity field was less than that within a normal gravitational field, and the flow velocity increased with gravitational acceleration. There was a significant liquid pressure gradient in the osteocytes within a normal and higher gravitational field compared with in microgravity. A reduction in the fluid flow velocity and fluid shear stress on osteocytes in different zones in microgravity compared with Earth's gravitational field. For these reasons, possibly causing a decrease in mechanical conduction and biochemical function, even cell death, leads to increased osteoclast activity, eventually causing the loss of a large quantity of bone. Graphical abstract A 3D axisymmetric fluid-solid coupling finite element model of an osteon with a two-stage pore structure was established. The model compared the influence of magnitudes of gravity on liquid transmission in LCS and mechanical response of osteocytes. The mean flow velocity of liquid in various layers (shallow, middle, and deep) increased linearly as acceleration due to gravity increased, and there was a significant liquid pressure gradient in osteocytes within a normal gravitational field compared with in microgravity. In microgravity environment, the osteocytes were unable to experience the pressure difference compared to that of Earth, possibly causing a decrease in mechanical conduction and biochemical function, even cell death, leading to increased osteoclast activity, eventually causing the loss of a large quantity of bone. [ABSTRACT FROM AUTHOR]

BACKGROUND: Once the articular cartilage has a crack defect, its mechanical properties will change. In previous studies, the investigation of damaged articular cartilage mostly focused on compression, and there were few studies on tensile properties. OBJECTIVE: To measure the uniaxial quasi-static tensile properties by preparing crack defects on the cartilage layer samples. METHODS: The articular cartilage of the fresh adult pig knee joint was selected to prepare a cartilage specimen containing a crack defect. The tensile properties were tested at different stress rates (0.001, 0.01 and 0.1 MPa/s) and the creep properties were tested under different constant stresses (1, 2 and 3 MPa). RESULTS AND CONCLUSION: (1) In the tensile test at different stress rates, as the stress rate increases, the stress required to reach the same strain increased gradually, and the Young's modulus of the test piece increases with the increase of the stress rate. (2) The tensile stress-strain curves of the articular cartilage with cracks at different stress rates did not coincide, indicating that the tensile properties of the articular cartilage with crack defects are rate-dependent. (3) In the creep experiment under different constant tensile stress levels, the creep strain increased with the increase of the tensile stress level, the creep compliance decreased with the increase of the tensile stress level, and with the creep time. The creep strain increased rapidly and then increased slowly. (4) To conclude, different stress rates and different constant stresses have great influence on the tensile mechanical properties of articular cartilage with crack defects. The experimental results provide a mechanical reference for the repair of defective articular cartilage. [ABSTRACT FROM AUTHOR]

Background. There is high risk in the correction surgery of pectus excavatum with scoliosis because of the lack of the correction mechanism of pectus excavatum with scoliosis. This study performed a comprehensive analysis about the impact that pectus excavatum had on scoliosis and elaborated its biomechanical mechanism in pectus excavatum patients with scoliosis. Methods. 37 pectus excavatum patients were selected. According to age, Haller index of pectus excavatum, offset coefficient, vertical position, sternal torsion angle, and asymmetric index, 37 patients were, respectively, divided into 2 compared groups. The result was statistically calculated. Results. The scoliosis incidence and severity did not correlate with Haller index, offset coefficient, vertical position, sternal torsion angle, and asymmetric index of pectus excavatum, and there was no statistical significance between the two compared groups. Conclusions. The incidence and severity of scoliosis in PE patients with scoliosis have nothing to do with the geometric parameters of pectus excavatum but correlate with age. The scoliosis will aggravate with the increase of age. The heart may provide an asymmetric horizontal force to push the spines to the right. The mechanism of how the biomechanical factors exert influences on spines needs to be further investigated to keep the spine stable. [ABSTRACT FROM AUTHOR]

The method of numerical simulation has been used in the research setting for purposes related to the correction process of the pectus excavatum with scoliosis. Although a convenient method, the validity and accuracy of this technique need to be tested. Further complicating the validity of this technique is that we are unable to confirm results of numerical simulation via electrical measurement experiments in humans because of ethical considerations, nor are we able to attain cadavers of pectus excavatum with scoliosis to perform electrical measurement experiments on. Both animal thorax and artificial thorax models can be used for thoracic deformation experiments, but the translation of these models to humans is unclear due to contrasting anatomical arrangements of chest cavities. This paper attempts to solve this problem by making a PVC thorax model and carrying out electrical measurement experiments to assess strain-displacement under physiological loading conditions. We present data showing biomechanical responses of the thoracic skeleton to compressive loading, which may be used to guide the development of computational models of the thoracic skeleton and ultimately improve the treatment strategy of pectus excavatum. [ABSTRACT FROM AUTHOR]

Background: Facet joints play a significant role in providing stability to the spine and they have been associated with low back pain symptoms and other spinal disorders. The influence of a follower load on biomechanics of facet joints is unknown. A comprehensive research on the biomechanical role of facets may provide insight into facet joint instability and degeneration.Method: A nonlinear finite element (FE) model of lumbar spine (L1-S1) was developed and validated to study the biomechanical response of facets, with different values of follower preload (0 N,500 N,800 N,1200 N), under loadings in the three anatomic planes. In this model, special attention was paid to the modeling of facet joints, including cartilage layer. The asymmetry in the biomechanical response of facets was also discussed. A rate of change (ROC) and an average asymmetry factor (AAF) were introduced to explore and evaluate the preload effect on these facet contact parameters and on the asymmetry under different loading conditions.Results: The biomechanical response of facets changed according to the loading condition. The preload amplified the facet force, contact area and contact pressure in flexion-extension; the same effect was observed on the ipsilateral facet while an opposite effect could be seen on the contralateral facet during lateral bending. For torsion loading, the preload increased contact area, decreased the mean contact pressure, but had almost no effect on facet force. However, all the effects of follower load on facet response became weaker with the increase of preload. The greatest asymmetry of facet response could be found on the ipsilateral side during lateral bending, followed by flexion, bending (contralateral side), extension and torsion. This asymmetry could be amplified by preload in the bending (ipsilateral), torsion loading group, while being reduced in the flexion group.Conclusions: An analysis combining patterns of contact pressure distribution, facet load, contact area and contact pressure can provide more insight into the biomechanical role of facets under various moment loadings and follower loads. The effect of asymmetry on facet joint response should be fully considered in biomechanical studies of lumbar spine, especially in post structures subjected to physiological loadings. [ABSTRACT FROM AUTHOR]

Summary: Bioreactor, which is used for in vitro construction of tissue-engineered cartilage, has been extensively studied by researchers. The growth and development of articular cartilage tissue are affected by biomechanical and biochemical factors, especially mechanical condition. Kinds of mechanical conditions including compressive and shear force, fluid flow, hydrostatic pressure, and tissue deformation, were developed in the past years. However, most mechanical conditions of improved bioreactor involve only one or two external force, which is merely partial for engineering cartilage tissue. No bioreactor which can simulate a normal articular cartilage in terms of structure and function has been reported. Consequently, simulation of bionic mechanical environment of a normal articular cartilage is considered to be the optimal environment for culturing the functional articular cartilage in vitro. Based upon this purpose, we designed a rolling-compression loading bioreactor. It could provide cultures with multi-mechanical stimulations and sufficiently mimic the complex mechanical environment of a normal articular cartilage. We propose that this comprehensive rolling-compression loading bioreactor can enhance the cultivation of functional cartilage constructs in vitro. [ABSTRACT FROM AUTHOR]

• Elastic modulus, Poisson's ratio, temperature of the periodontal ligament affected the biomimetic degree of finite element simulation. • Established Prony series viscoelastic finite element model based on the relaxation experiment. • Proposed a method: response surface method and finite element inverse analysis method. • Identify the material parameters of the periodontal ligament by Box–Behnken design. The orthodontic treatment can be guided by the finite element (FE) simulation of periodontal ligament (PDL) mechanical properties, and the biomimetic degree of FE simulation can be primarily affected by the material properties of the PDL. According to the principle of parameter inverse, a method: response surface (RS) method and FE inverse method were proposed to identify the material parameters of PDL. The Prony series viscoelastic FE model was established based on the relaxation experiment. With root mean square error of simulation results and experimental results as the objective function, the optimal parameter combination was obtained by RS method, and the FE simulation result were compared with the experimental result. The result showed that the optimal parameters of the PDL were elastic modulus: 3.791 MPa, Poisson's ratio: 0.42, temperature: 29.294°C separately, and the simulation result of optimal combination maintained consistency with experiment with the correlation coefficient of 0.97258, indicating that the method proposed in this paper could well identify of PDL material parameters. The parameter identification method used in this paper can significantly improve the calculation efficiency, and reduce the parameter identification error compared with the simple FE inverse method, which has scientific significance and theoretical value. [ABSTRACT FROM AUTHOR]