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Abstract:Objective As the photostability of calcium ions (Ca2+) indicators is an important property for indicating the temporal features of cytosolic Ca2+ in cells, this study aims to quantitatively measure the light-induced fluorescence enhancement in cells stained with Ca2+ indicators. Methods Five cell lines, MC3T3-E1, RAW264.7, MLO-Y4, MEF3T3 and HEK293, were exposed to the light with five levels of optical power, respectively, so as to investigate the light induced responses of two commonly-used Ca2+ indicators, Fluo-4 AM and Oregon green. The light-induced fluorescence enhancement, the succeeding photobleaching and the thapsigargin (TG)-induced responsive peak followed by were observed. The characteristic parameters of responsive peaks were further analyzed. Results Light with higher power level would induce the fluorescence enhancement for both Fluo-4 AM or Oregon green, while the responsive percentage as well as the magnitude and time span of light-induced peak of Oregon green-stained cells were significantly lower than those of Fluo-4 AM-stained cells. Conclusions The use of Oregon green with low power level light shows better photostability to indicate the intracellular Ca2+.

Abstract:Objective To study the effect of three different kinds of mechanical stimuli (i.e. strain energy density, equivalent stress and equivalent strain) on numerical simulation of bone remodeling. Methods A two-dimensional finite element model of the proximal femur was constructed. Based on the mechanostat theory and finite element method, the inner structure of the proximal femur and its density distributions under the three different stimuli were predicted. Then the simulation results were compared quantitatively with calculation results obtained from CT images. ResultsThe predicted density distributions on the proximal femur under different stimuli were all well matched with the real structure of the proximal femur. By comparing the values and shapes of the calculated bone density curves, the predictions from the model using equivalent stress as mechanical stimuli were mostly consistent with the CT images. ConclusionsThe equivalent stress might play a leading role in mechano-regulation algorithms of bone remodeling. The accurate prediction of bone remodeling process will provide a theoretical basis for clinical practices such as orthopedic surgery, treatment of bone diseases and personalized design and optimization of prosthesis.

Abstract:Objective To investigate the interaction between vessel and vena cava filter (VCF) with different numbers of support poles and the influence on blood flow during its implantation by using finite element method and computational fluid dynamics method, so as to provide more scientific guidance for intervention treatment and design & development of the filter. Methods Three kinds of VCF models with 4, 6, 8 support poles were established by using Solidworks, respectively. The stress distribution and radial support stiffness of the vessel and filter under working condition were then simulated and analyzed by using ABAQUS. The distributions of blood flow velocity, pressure and shear stress after VCF implantation were simulated by using Fluent. Results All the mechanical and fluid properties of the three kinds of VCFs were within the scope of security. The comprehensive mechanical performance of the 6-pole filter was better, while for the 8 pole-filter, it showed larger stress under working condition, larger support intensity, higher exit velocity, larger shear stress on the filter mesh, and the trail of the flow was changed from laminar to transition flow, which might cause some damage to the vessel wall. The 4 pole-filter under working condition had a larger stress on the vessel, while its exit velocity was lower, which could be likely to cause local damage on the vessel wall, and disadvantageous to accurately positioning the filter in diseased region of the vessel. Conclusions The 6 pole-filter has a superior hemodynamic effect and comprehensive mechanical properties, which reduces the potential possibility of damage to the vessel wall caused by implantation of the filter. The simulation analysis on VCF provides a good reference for design of the filter and its intervention treatment in clinic.

Abstract:Objective To study the effects of radiation sensitivity coefficient, frequency of treatment and mature age of tumor cells on therapeutic efficacy by numerical simulation. Methods A hybrid mathematical model for the growth of solid tumor under radiotherapy was established, with considering the influence of both tumor microenvironment (including oxygen, extracellular matrix and matrix-degrading enzymes) and tumor activities (including proliferation, apoptosis and adhesion) on tumor growth. The linear quadratic model was also introduced to depict tumor response to radiotherapy. The progresses of tumor growth under different conditions were simulated to assess the therapeutic efficacy. Results The therapeutic efficacy was better when the radiation sensitivity coefficient and mature age of tumor cells increased. When the total amount of the radiation dose was the same, the effects of treatments seemed no difference either with high frequency or low frequency. Conclusions The simulation results are consistent with the clinical results, which can provide a new method for the theoretical and clinical research on tumor radiotherapy.

Abstract:Objective To analyze different biomechanical properties between Coflex and X-STOP device in the treatment of lumbar spinal stenosis (LSS), and provide references for design improvement of interspinous process spacer. MethodsFour finite element models, i.e., the L2-5 healthy segment model, the mild degenerated L4/5 segment model, the X-STOP-fixed L4/5 segment model, the Coflex-fixed L4/5 segment model, were constructed based on the normal lumbar CT images of a volunteer, and the models under flexion, extension, lateral bending and axial rotation were simulated to compare range of motion (ROM) changes and stress distributions on the spinous process and interspinous process spacer. ResultsX-STOP and Coflex decreased extension ROM by -48.12% and -75.35%, respectively, and released disc pressure by -58.03% and -80.75%, respectively. Coflex even restricted flexion ROM by -59.58% and reduced flexion disc pressure by -52.84%. No distinct changes appeared in lateral bending and axial rotation ROMs and disc pressure. The largest Von Mises stress appeared at the U-shape place during flexion in Coflex and at connection between left wing and screw during torsion in X-STOP, respectively. The largest contact pressure between Coflex and spinous process was 31.38 MPa during bending, and that between X-STOP and spinous process was 46.86 MPa during torsion. Conclusions Both X-STOP and Coflex are an effective treatment for LSS, and can effectively restrict the ROM of extension and reduce the disc pressure, without affecting the adjacent segments.

Abstract:Objective To evaluate biomechanical differences between anterior titanium plate internal fixation and posterior pedicle screw internal fixation for treating type Ⅱ unstable Hangman’s fracture by finite element analysis. Methods An intact finite element model of the upper cervical spine (C0-3) was established and validated, and an unstable model was also established. Two different internal fixation models, i.e. anterior titanium plate+Cage with bone graft (Plate+Cage) and C2 pedicle screws+C3 lateral mass screws (C2PS+C3LMS) were established, respectively, based on the unstable model. The vertical load of 40 N was applied on the occiput to simulate head weight and 1.5 N?m torque was applied on the occiput to simulate loading conditions of flexion, extension, lateral bending and rotation. Range of motion (ROM) of C2-3, force pathway and strain at the fractured line were calculated and analyzed. ResultsCompared with the unstable model, the Plate+Cage model could decrease the ROM by 92.4%, 97.1%, 96.5% and 90.0%, while the C2PS+C3LMS model could decrease the ROM by 88.6%, 90.2%, 95.7% and 90.3%, in flexion, extension, lateral bending and axial rotation, respectively. The maximum stress of the Plate+Cage model was smaller than that of the C2PS+C3LMS model under 4 loading conditions. Conclusions The anterior Plate+Cage fixation possesses better stability than the posterior C2PS+C3LMS fixation in flexion and extension, while both fixation methods show similar stability in lateral bending and axial rotation. The anterior Plate+Cage fixation is more reasonable in structure and stress distributions, and can achieve reduction, decompression, fixation and fusion in one step, thus it is an effective operative procedure for treating typeⅡ Hangman’s fracture.

Abstract:Objective To investigate the changes of plantar pressure distributions in children with the unilateral developmental dysplasia of the hip (DDH) who underwent the Pemberton’s pericapsular osteotomy (PPO) at early age, so as to provide valuable references for clinical therapy and rehabilitation of such patients. Methods Eighteen child patients who underwent PPO before 4 year old were selected as the PPO group, while 18 healthy children at the same age with normal feet were selected as the control group. Footscan system was used to measure the plantar pressure of these subjects during walking. The parameters, i.e. contact area percentage of the total foot contact area (CA%), pressure-time integral (PTI) and contact time percentage of the stance time (CT%) in both PPO group and control group were compared to evaluate changes of the plantar pressures during walking. Results Compared with the sound limb in control group and the unaffected limb in PPO group, the affected limb in PPO group showed higher PTI in the 2nd to 5th toe zone and lower PTI in the medial heel zone. The affected limb in PPO group had a higher CA% in the 4th and 5th metatarsals than the unaffected limb in PPO group and the sound limb in control group, and a lower CA% in the 1st and 2nd metatarsals than the unaffected limb. Compared with the unaffected limb in PPO group and the sound limb in control group, CT% of the affected limb in PPO group increased in the forefoot push-off phase and decreased in the initial contact phase, and the total contact time of the affected limb was shorter than that of the unaffected limb in PPO group and the sound limb in control group. Conclusions There exist residual plantar pressure deviations during walking in DDH patients following PPO at early age, thus a longer period of intensive rehabilitation may be required to change the residual abnormality.

Abstract:Objective To investigate the role of microRNA-34a (miR-34a) in the proliferation of vascular smooth muscle cells (VSMCs) induced by low shear stress (LowSS). Methods Using co-culture parallel plate flow chamber system, endothelial cells (ECs) and VSMCs were co-cultured and applied with normal shear stress (1.5 Pa) and LowSS (0.5 Pa) for 12 h. The expression of proliferating cell nuclear antigen (PCNA) in the co-cultured VSMCs was detected by Western blotting to determine the proliferation capacity of VSMCs. Real-time PCR was used to examine the miR levels of miR-34a in the co-cultured VSMCs. The target proteins of miR-34a were predicted by TargetScan, miRWalk and some other websites. Western blotting was used to detect expression of Forkhead box j2 (Foxj2) in the co-cultured VSMCs. Mimics and inhibitor were used to up-regulate or inhibit the expression of miR-34a, and then the expression of Foxj2 and PCNA was detected by Western blotting to verify the regulation relationship between miR 34a and Foxj2. Results Compared with NSS, LowSS promoted the PCNA expression and significantly up-regulated the miR-34a expression in the co-cultured VSMCs. Foxj2 was predicted to be the downstream target protein of miR-34a by TargetScan, miRWalk and some other websites. Foxj2 expression decreased significantly in the co-cultured VSMCs under LowSS application. Under static condition, the expression of Foxj2 obviously decreased and the expression of PCNA obviously increased by up-regulating miR-34a expression in VSMCs. While inhibiting the expression of miR-34a in VSMCs would result in a significant increase in the expression of Foxj2 and a significant decrease in the expression of PCNA. Conclusions LowSS can promote the proliferation of VSMCs by regulating miR-34a and target protein Foxj2 in the co-cultured VSMCs. This research finding will provide new mechanobiological experimental reference for further illustrating the pathogenesis of atherosclerosis and finding the therapeutic targets for drugs.

Abstract:Objective To discuss the mechanostat of bone remodeling under dynamic loads. Methods By analysis on mechanostat of bone remodeling and absorption from the idea of mechanical fatigue strength theory, the mechanostat of bone remodeling under dynamic loads was developed. Damage was selected as the mechanical stimulus under dynamic loads and the model of bone remodeling under dynamic loads was proposed. Physical exercise for prevention and treatment of osteoporosis was simulated to analyze the biomechanical phenomenon why the osteogenesis effect under dynamic loads seems better than that under static loads. Results The biomechanical phenomenon as mentioned above was reasonably explained. An increase of 10%-30% in physical exercise could cause an increase of 3.13% 8.61% in bone mineral density. Conclusions The mechanostat of bone remodeling under dynamic loads will provide theoretical guidance for using mechanical vibration to treat or prevent diseases related to bone metabolism, which is the supplement and improvement for mechanostat of bone remodeling.

Abstract:Objective To design and fabricate novel mesoporous calcium silicate/calcium phosphate cement (MCS/CPC) scaffolds for bone repair and investigate their in vitro biomechanical properties under different external forces. Methods MCS and CPC in certain proportion were mixed to form plotting material, and the composite MCS/CPC scaffolds with pore size of 350 μm and 500 μm were fabricated by 3D bioplotting technique, respectively. Surface topographies of the scaffolds were observed by scanning electron microscope (SEM). The compressive strength and mechanical properties of the scaffolds under dynamic cyclic loads at different frequencies were studied through universal mechanical testing machine and dynamic mechanical analysis instrument. Results MCS/CPC scaffolds with controllable macroporous structures could be fabricated by 3D bioplotting technique. Scaffolds with pore size of 350 μm had higher compressive strength ［(9.8±0.39) MPa］ and compressive modulus ［(132.5±4.3) MPa］. In addition, at the loading frequency of 1-100 Hz, scaffolds with pore size of 350 μm had a higher storage modulus. ConclusionsMCS/CPC scaffolds with pore size of 350 μm fabricated by 3D bioplotting technique possess not only regular pore connectivity and high compressive strength, but also structural stability under dynamic loads, which are promising as novel biomaterials for bone repair.

Abstract:Objective To study the relationship between on-line correction and stiffness of the upper limb during human movements, so as to improve the measurement accuracy of stiffness and to assess the on-line correction capability. Methods Five kinds of upper limb goal-directed movements in a horizontal plane were designed. The stiffness values at 5 different positions, i.e. in the early period, early to mid period, mid period, mid to late period and late period separately during the movements with sudden perturbation were measured to investigate the regular pattern of human hand stiffness influenced by such on-line correction, as well as the relationship between the movement accuracy and hand stiffness. Results The stiffness was always varying during the movements, and the variation of the stiffness would influence the movement error. On-line correction during the movements could induce an increase in the value of stiffness amplitude, especially at the position in late period of the movement. However, no significant linkage was found between the change of stiffness and the occurrence time or content of on-line correction. Conclusions On-line correction plays an important role in goal-directed movements. Considering that on-line correction may cause a change in the amplitude of the stiffness, the on-line correction function of patients can be more accurately assessed by measuring stiffness value in specific experiments, combined with other medical diagnosis methods in clinic.

Abstract:Objective To assess the surgical and rehabilitation effects of total hip arthroplasty (THA) through comparing changes of gait parameters in patients before and after THA.MethodsThe gaits of 7 THA patients during their natural walking before THA and in the 25th week after THA were tested by using a portable gait analyzer (IDEEA, MiniSun, USA). The gait parameters including single limb support (SLS) time, double-limb support (DLS) time, SLS/DLS, stride length, foot fall strength were collected for statistic analysis by SPSS 16.0 and Excel 2010. Results The SLS of the healthy leg after THA significantly decreased (P<0.05); for the majority of THA patients, the SLS of the diseased leg decreased, the DLS and SLS/DLS of the healthy leg also decreased obviously, while the foot fall strength of the diseased leg increased after THA. Conclusions The SLS of the healthy leg can be used as a sensitive parameter to evaluate the operation effect of THA. The portable gait analysis system can quantitatively reflect the subject’s gait, thus it is a non-invasive and convenient method of evaluating the operation effect in clinic.

Abstract:Objective To propose a design method of isothermal chamber for tidal volume testing equipment. Methods According to the State Equation of Ideal Gas, the gas volume was accurately calculated and injected into an airtight chamber, and then the pressure and temperature changes in the chamber were measured. To keep constant temperature, the fine copper wire was padded into the chamber to absorb the heat produced by the gas compressed during the injection. Results For the chamber of 1L, 300 g/L copper should be filled at least and with not more than 100 mL gas to keep the temperature inside the chamber isothermal. The experiment system was then connected with ventilator to compare the measured tidal volume and given tidal volume. The results showed that the experimental error was within 2%, which proved the accuracy of this testing equipment. Conclusions The establishment of the physical model of isothermal chambers can accurately detect the tidal volume of ventilator, which provides a theoretical basis and data support for factory inspection and supply more choices for ventilator maintenance in clinic.

Abstract:The current experimental methods, such as the motion capture system, high-speed video, plane photography and surface EMG, cannot show the details of the muscle strength, or explain the nerve-muscle coordination mechanism during human motion. Thus, computer modeling and simulation are developed and become a new method for researchers in China to study human motion, and the software LifeMOD, AnyBody, ANSYS are mainly used even if these softwares have some limitations such as less precise muscle control and relatively higher prices. Developed by Stanford University, OpenSim is an open-source platform for muscle model development, simulation and analysis of neuromuscular system based on C++ and Java. In this paper, on the basis of computer modeling and mathematics theoretical derivation, the OpenSim modeling theory and simulation steps were introduced in detail to provide some theoretical references for researches on sport biomechanics. The future research directions by using OpenSim modeling simulation to study neuromuscular mechanism of the hemiplegic gait and Parkinson gait, and to improve and perfect the rehabilitation ways of the abnormal gait were also discussed.

Abstract:Clinically, abdominal aortic aneurysm (AAA) may continue to expand or even rupture after endovascular aneurysm repair (EVAR) due to endoleak or endotension. The existence of endoleak and endotension can significantly affect the mechanical/hemodynamic environment in AAAs, thus changing the strain and stresses on aneurysm wall, further influencing the transportation of low density lipoprotein (LDL), oxygen and nitric oxide (NO) in AAAs and aneurysm wall, which might eventually alter the biochemical environment and physiological property of aneurysm wall. This review focused on biomechanical mechanism of AAA enlargement after EVAR and its recent research progress, which indicated that reduction of the aneurysm wall strength due to deterioration of biomechanical environment (such as increase of tensile stress on aneurysm wall) and abnormity of biochemical environment (such as increase of LDL deposition, change of oxygen concentration) might be the source leading to AAA enlargement after EVAR. Based on previous studies, the authors propose that comprehensive investigations on AAA enlargement after EVAR from the perspective of biomechanics and mechanobiology have great research values and clinical significance, which will help clarify the mechanism of AAA enlargement after EVAR, as well as optimize the strategies of aneurysm repair surgery and designs of interventional medical devices.