Abstract:The overview of current progress in cellular and molecular biomechanics was presented. Relevant scientific issues, methodological approaches, and potential applications were discussed.

Abstract:Objective Cell adhesion is an essential process for cell migration. The influence of shear stress on the adhesion of VSMCs was elucidated in a co-culture system and to provide some experimental evident in molecular mechanisms of shear stress-induced cell migration in vascular wall. Methods Using a parallel-plate co-culture flow chamber system, human VSMCs co-cultured with human ECs were exposed to static or laminar shear stress, 15dynes/cm2, conditions for 12 hours, with VSMCs cultured alone at static condition as a control. The adhesion of VSMCs was then assessed with cell adhesion assays. The activation of Phosphatidylinositol-3 kinase (PI3K/Akt) pathway in VSMCs was assessed by western blotting. Results It demonstrated that VSMCs co-cultured with ECs under static condition induced VSMC adhesion, whereas the shear stress applied to EC side for 12h significantly inhibited this process. Western blotting showed that there was a consistent correlation between the level of Akt phosphorylation and the efficacy of shear stress-induced EC regulation VSMC adhesion. Conclusions Our findings indicate that shear stress protect against EC-induced VSMC adhesion. Akt is a major downstream factor of PI3K involved in the process.

Abstract:Objective To investigate the possible signal transduction pathways involved in the low shear stress-induced up-regulation of IL-8 mRNA expression in cultured human umbilical vein endothelial cells (HUVECs). Methods LightCyclerTM system was employed to assay the expression of IL-8 mRNA of HUVECs. The results were compared with each among the groups stimulated by low shear stress (4.20 dyne/cm^2) with/without kinds of inhibitors. Results (1)HUVECs pre-treated with cAMP-dependent protein kinase inhibitor (KT5720), or phospholipase C inhibitor (neomycin), or tyrosine protein kinase inhibitor (tyrphostin-25) partially inhibited the low shear stress-induced up-regulation of IL-8 mRNA expression; (2) EGTA or the intracellular Ca(superscript 2+) chelator BATPA/AM or verapamil, a Ca(superscript 2+) channel blocker, also partially suppressed up-regulation of IL-8 gene induced by low shear stress; (3) G protein was involved in the low shear stressinduced IL-8 mRNA expression; (4) HUVECs pre-treated with cGMP-dependent protein kinase inhibitor (KT5823) had no effect on such gene expression. Conclusions (1) There are several signal molecules, for example, the protein kinase C, Ca(superscript 2+), and so on involved in up-regulation of IL-8 mRNA expression induced by low shear stress. (2) Activation of G protein is necessary.

Abstract:Objective To investigate the regulation of proliferation of rat marrow mesenchymal stem cells (rMSCs) by mechanical stretch. Methods rMSCs were isolated and purified by density gradient centrifugation, expression of relative surface antigens was detected by immunochemistry staining, and distribution of cell cycle was analyzed with flow cytometry. rMSCs were exposed to stretch with different time and magnitude, MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrasodium bromide) was used for proliferation assay and expression of c-fos gene was examined by RTPCR. Results rMSCs could be perfectly achieved by the combination of density gradient centrifugation and adhesion difference, and cultured stably in DMEM medium containing 15% fetal bovine serum (FBS). The cells exhibited an elongated fusiform shape and CD44 and Fibronectin positive while CD34 negative. Flow cytometry revealed that G0/G1 phase cells amount to 90%. MTT assay showed that O.D values of rMSCs increased after exposure to stretch, and revealed a time-and strain-dependence manner within all time and stretch ranges studied. In contrast to control group, expression of c-fos gene in rMSCs showed a significantly increase after exposure to 1Hz, 8% strain for 60 minutes. Conclusion mechanical stimulation is crucial to regulating the cell growth and proliferation. The appropriate mechanical stretch could be an accelerant for proliferating capacity of rMSCs in vitro.

Abstract:Objective To find the mechanism for excitation-contraction (E-C) coupling modes in embryonic cardiomyocytes; Method The membrane potential and intracellular Calcium were respectively measured with whole cell patch clamp and Calcium imaging methods; Results There exist two kinds of E-C coupling modes. One is similar to the E-C coupling mode of mature cardio-myocytes and its membrane potential was related to Sodium Channel and L-Calcium channel. The other mode is more basic for embryonic cardio-myocytes, which is controlled by intracellular Calcium oscillationto cause the slight change of membrane potential through Na(superscript +)-Ca(superscript 2+) exchanger. Compared to the second one, the first mode is more regular. Conclusion Two kinds of E-C coupling modes exist for embryonic cardiomyocytes.

Abstract:Objective Using a lens-induced method to establish myopia model in guinea pig to study the changes of viscoelastic properties of sclerotic fibroblasts in the experimental eye model. Methods 10 two-week-old guinea pigs were lens-induced monocular. A spherical lenses of -10.00D were wear to the unilateral eye with the other eye treated as self-control. 10 two-week-old guinea pigs were randomly chosen as normal-control. The sclerotic fibroblasts of each group were cultured and passed for 1 generations in vitro. All this were studied by light microscope and pathology. This study utilized the micropipette aspiration technique with a viscoelastic solid model to investigate the viscoelastic properties of scleral fibroblasts from normal and myopia guinea pigs sclera. Results Eyes became myopic (-9.08±0.21) D and elongated (1.91±0.07) mm 45 days after insertion of the lenses (p<0.05). Experimental studies have shown that the viscoelastic properties of the scleral fibroblasts in LIM group exhibited a significantly higher equilibrium modulus E(subscript ∞), instantaneous modulus E0, and apparent viscosity μ (E(subscript ∞)=0.43555±0.13043kPa, E0=0.76691±0.21674kPa, μ=4.17255±1.59239kPa?s, n=58) compared with normal-control group (E(subscript ∞)=0.30055± 0.07713kPa, E0=0.52553±0.14053kPa, μ=1.94124±1.03281kPa?s, n=52, p<0.05) and self-control group (E(subscript ∞)=0.34792±0.09709kPa, E0= 0.59722±0.18118kPa, μ=2.17855±1.22801kPa?s, n=49, p<0.05). Conclusions Lenses can induce axial growth and lead to myopia in young guinea pigs. The results suggest that the scleral fibroblasts become stiffer with the development of myopia.

Abstract:Objective For understanding the biophysical process of T-cell immune response, to reveal the diffusive features of the adhesion molecules in the complicated topographic cell contact area, and develop a method to estimate the diffusive coefficient. Method In this paper, by taking an account of the crowding effect of the adhesion molecules, we present a porous structural model of the cell contact area, and derived the diffusion equation of the free ligand molecules on the cell contact area. In the cases of the cell contact area being the isotropy porous structure, the diffusive damping factor γ is related with the obstruct density σ by an analytical expression, and in the case of axial-symmetry, the logarithmic distribution character of γ is obtained too. Results The retardation of the free ligand diffusion will be strengthened as increasing of the diffusive damping factor γ and decreasing of the obstruct density σ in the contact area, and using FRAP experiment data, the parameter α, γ and ξ have been estimated as 0.2~0.4, 0.40~0.56 and 0.73~0.75 for the adhesion system of CD2/CD58 and CD28-CD80, respectively. Conclusion A new method to estimate the diffusive retardation coefficient ξ of the adhesion molecules by measuring the fluorescence recovery level on the photobleaching region of the contact area is proposed.

Abstract:Objective Quantifying the contribution of the non-specific interactions to the specific selection-ligand bidings. Methods We used optical tweezers to quantify the non-specific interaction dependence of bond rupture forces on loading rates and of bond lifetimes on applied forces by measuring the adhesions between two BSA (Bovine serum albumin)-coated glass beads. Results The results indicated that the rupture force dependence for non-specific interactions under lower loading rates presented from the similar transition phase as that for specific selectin-ligand bindings. While the differences in rupture force between non-specific and specific interactions became more and more evident with increase of loading rates, the increase rate of rupture force for non-specific interactions was much lower than that for selectin-ligand bindings. Under the same external force, the mean lifetime for non-specific interactions was lower than that for specific bindings. Lifetime for non-specific interactions decreased slightly with increase of applied forces, and no transition phases between slip and catch bonds were found. Conclusion This work provides the bases for quantitatively evaluating the effect of non-specific interactions in measuring selectin-ligand bindings.

Abstract:Objective To study the collapse of biomolecules, focusing on the effect of the composition of chain, temperature and stiffness on the chains self-assembly. Method A coarse grained molecular dynamics method is adopted to simulate the collapse of the biomolecules with two kinds of sequence composition. Results We find that the inhomogeneity can induce network-like microstructures in the equilibrium structure of chain. And the stiffness of chain determines the global structure of chains. When the chain is soft, both homogeneous and inhomogeneous chains collapse to globular structure; however, when the chain is stiff, the chains evolve to rod-like or toroidal structure. We also find that the inhomogeneous chain is more sensitive to temperature change in comparison with the homogeneous chain. Conclusions This study will help understand the mechanisms of self-assembly and relationship between function and structure of biomolecules.

Abstract:Objective To generate 2-dimensional (2D) vascular networks by numerical simulation of tumor angiogenesis moving along random directionin order to provide more realistic microvascular networks for the study of hemodynamics, drug delivery and anti-angiogenesis in solid tumors. Methods To extend the migration of endothelial cells on sprouts from four directions-moving up, down, left or right-in previous models to random direction in the present model, and develop a relevant 2D discrete model to simulate the process of tumor angiogenesis and compare the simulation results with some corresponding experimental data. Results Contrast with the unimproved or some previous models, the features of tumor microvascular networks generated from our model by simulating the angiogenesis in caecum tumor, such as vascular tortuosity, branching and anastomosis, are closer to the physiological facts and more resemble the experimental observations. Conclusions The present model could simulate the process of tumor angiogenesis numerically, and provide a relatively more actual network structure of tumor microvasculature for the research about microcirculation, drug delivery and anti-angiogenesis in solid tumors.

Abstract:Objective To study the effect of external counterpulsation on cerebral blood flow. Methods Cerebral blood flows were simulated on hemodynamics models of cerebral blood on condition of normal and stroke with practical measured normal carotid blood pressure pre-ECP and during ECP. Results stroke and ECP may bring change of blood perfusion flow of brain. Conclusion the blood perfusion of brain was improved and the time-dependent pattern of timedependent cerebral arterial blood was changed with ECP.

Abstract:Objective To study N-methyl-D-aspartate activated single-channel kinetics behavior based on 3- and 4- state model. Methods The distribution of single-channel parameters were calculated in the different Mg ion concentration and holding potential based on 3- and 4-state model and compared it with data from experiment. Result The block rate depends linearly on Mg ion concentration when Mg ion concentration was greater than 20 μmol/L, however, when Mg ion concentration was less than 20 μmol/L, it is independent of Mg ion concentration. Conclusion There is a second blocking mechanism in addition to the Mg block at very low Mg ion concentrations. It may be because of the result of a voltage-dependent conformational change.

Abstract:Objective To make the research on the biomechanical properties and viscoelasticity with fresh adult corpse to provide the biomechanics parameters for clinic. Method The stress relaxation and creep tests were made. Result The reduced stress relaxation function and creep function were obtained by making the experimental data normalization and then using regression analysis to obtaine the coefficient and fitting curve. Conclusion The quantities of stress relaxation and creep of MCL are lower than that of ACL in 7200s. The experimental results were analyzed and discussed.

Abstract:Objective To study the change of hemorrheological index during the steroid-induced necrosis of the femoral head. Methods 20 rabbits were randomly divided into 2 groups. In group A, 10 rabbits were given 40μg?kg^(-1) of LPS intravenously 2 times at an interval of 24 hours, and immediately injected intravenously with 20mg?kg^(-1) of prednisoloni acetates once time. In group B, 10 rabbits were used as control. At the 24th, 3rd, 7th, 14th, 21st day after the injection, hemorrheological index, blood-lipid levels and the blood platelet levels were measured, and then after the last measure the rabbit's femoral head and liver were undertaken light microscopic examination. Results The 24th hour after the injection of group A, hemorrheological index and blood-lipid levels increased (P<0.01), the blood platelet levels decreased (P<0.01). At the 3, 7, 14 and 21 day, abnormal indexes lasted during the whole observation. Histologically, the 21st day after the injection, In group A the degeneration and necrosis of the hepatocytes and osteocytes were found. In group B, the hepatocytes and osteocytes were normal as usual. Conclusion Abnormality in hemorrheological index might potentiate the prethrombotic status and induce the thrombus formation in steroid-induced necrosis of the femoral head.

Abstract:Objective We produced a model by given alcohol orally in order to study the effects of little ethanol on bone biomechanics property of growing mice. Methods Thirty six-week-old KM mice, clean grade, half male and half female, initially weighing 25~35g, were randomly divided into 3 groups. These groups were basal control which were killed at the beginning of the experiment; intact control that were given distilled water with 10 ml?kg^(-1)?d^(-1), 50%(V/V) ethanol group (Model) according to the dosage of 4g?kg^(-1)?d^(-1) for 60 days. All mice were killed by taken out their eyeball to collect the forth lumbar vertebra and right femur for testing biomechanical properties including Indentation Test of vertebra and fall-loading test of proximal femoral neck. Result Maximal resistibility of lumbar vertebra decreased 63.6% significantly (P<0.01) and structural mechanical strenth of right proximal femoral neck declined (-29.4%, P<0.01) in Model group, Conclusion Little ethanol had badly affected biomechanical properties including vertebra and proximal femoral neck in growing mice.

Abstract:Objective As a new graft biomaterial for tissue engineering, small-intestinal submucosa (SIS) has an excellent biomechanical property. This study aims to investigate an ideal method for crosslinking porcine small-intestinal submucosa. Methods Stabilizing porcine SIS by Glutaraldehyde(GA) and photofixing samples from the same animal with methylene blue, then testing them together with original samples by material test machine. Data were obtained and analyzed, including ultimate tensile stress (σ(subscript max)), breaking strain (ε(subscript m)), and modulus of elasticity(E) under 0.3MPa stress. Results The ultimate tensile stress of three groups are respectively 6.01±1.43、6.96±0.93 and 12.94±2.03MPa. Samples following GA treatment improve correspondingly, but stiffness of the tissue is increased. Intensity of samples following photofixing with methylene blue improve slightly, and flexility improve. Conclusion This study stabilized porcine SIS by GA and methylene blue for the first time, and through comparing their biomechanical properties of uniaxial tensility, it was testified that the method of photooxidation shall be developed as a valid treatment to crosslink SIS.

Abstract:Objective To investigate the effect of abductor load to the femoral head in the Chiari pelvic osteotomy by biomechanics. Methods The three-dimensional finite element hip models of Chiari pelvic osteotomy was constituted to observe the regularity of stress distribution according different abductor loads using the nonlinear contact analysis. Results It was found that the contact pressure and the peak stress after Chiari pelvic osteotomy decreased remarkably, but the contact area increased clearly. With the decreasing of the abductor loads, contact pressure and peak stress decreased correspondingly. And the contact pressure distribution transferred from the original acetabular area (pressure turning into low) to the new acetabular area (pressure turning into high) gradually. But the changes of the contact area were not significant after Chiari pelvic osteotomy corresponding to different abductor loads. Conclusion The biomechanics changes owing to abductor load plays an important role in Chiari pelvic osteotomy.

Abstract:Objective To evaluation the biomechanical changes on the vertebral body、annuli fibrosis and faced joint of the adjacent segments on the condition of anterior cervical discectomy and plant fixation. Method To measure five cervical spine specimens scope of dimensional and variety of stress on 3 conditions: normal, single segment plant fixation and double segment plant fixation. Each group was measured under the loading of states of vertical compression, flexion, extension and lateral bending. Result After anterior cervical discectomy and plant fixation, at the adjacent segment, the stress、displacement increased significantly except the state of flexion (P<0.05). When the double segment plant fixation compared with the single segment, there was no statistical differences. Conclusion Anterior cervical discectomy and plant fixation can improve the stress and displacement significantly at the adjacent segments, maximum at the state of extension. But there was no statistical differences of the segment selection.

Abstract:Objective To compare the anatomy and biomechanical test difference between atlas pedicle screw and atlas lateral mass screw, and provide theoretical basis for reasonable clinical choice of the posterior atlas screw fixation technique. Methods The relative parameters of sixteen sets of fresh Chinese adults' atlas specimens were measured with an digital caliper and a goniometer, including The mean maximum length of C1 lateral mass screw (L1)、the distance from its entry point to posterio redge of C1 posterior arch (L2)、in the lateral mass of C1 (L3)、in the posterior arch (L4) and the averaged maximum length of C1 pedicle screw (L3+L4) and so on. The extraversion and upslope angle of atlas pedicle screw and atlas lateral mass screw. The unicortical and bicortical lateral mass screw or pedicle screw were placed on atlas in sixteen fresh spine specimens separately. The length and the pull-out strength of the screw were measured and tested. Results The mean maximum length of C1 lateral mass screw (L1) was 25.01±0.23mm, the distance from its entry point to posterio redge of C1 posterior arch was (L2) 9.85±1.31mm. The averaged maximum length of C1 pedicle screw (L3+L4)was 29.8±1.27mm, 10.47±1.51mm was in the posterior arch (L4), 19.58±1.63mm was in the lateral mass of C1 (L3). The extraversion and upslope angle of atlas pedicle screw and atlas lateral mass screw was respectively 10o, 5o and 15o, 20o. Atlas bicortical pedicle screw was the strongest fixation method. Its pull-out strength averaged (1686.0±425.3) N. No statistically significant difference was observed between atlas unicortical pedicle screw (1082.5±292.7)N and atlas bicortical lateral mass screw (1127.2±367.1)N. atlas unicortical lateral mass screw (785.2±402.7)N was the weakest fixation technique. Conclusion Because of difference entry point between atlas pedicle screw and atlas lateral mass screw, atlas pedicle screw was longer than atlas lateral mass screw. Due to the extraversion and upslope angle of atlas lateral mass screw was bigger than atlas pedicle screw, length of atlas lateral mass screw was longer than in the lateral mass of atlas pedicle screw. In a giving patient, it would be better to choose C1 pedicle screw than C1 lateral mass screw, if he or she is suitable for both techniques.

Abstract:Objective To explore the biomechanical properties of locking compression plate for treating unstable sacral fractures and therefore to provide scientific foundation for clinic application.Methods 3-dimension finite element models were used to simulate normal pelvis and the unstable pelvis sufferedⅠsection ,Ⅱsection orⅢsection sacral fracture respectively and the fractures of pubis limbs.The unstable pelvises fixed with one screw for the fracture superior pubis limb and sacral screws,sacral bars or locking compression plate for the fracture of sacrum respectively were simulated.The mobility of the sacrum and pubis were calculated after giving 500N axial load on 5thlumbar vertebra and the bone stress distribution of the fixed unstable pelvis under axial load were compared with that of normal pelvis. Results Among the three fixing methods,the fixative effects of sacral screws are excellent and the effects of sacral bars and locking compression plate were similar.When the pelvis was under axial load ,the bone stress distribution of the unstable pelvis fixed with one of three methods were similar as that of normal pelvis.Conclusion It was a practical methods for treatment of the unstable sacral fractures fixed with locking compression plate,especially for the treatment of unstable sacral fractures,concomitant fracture of lilac ala or comminutedⅡsection orⅢsection sacral fracture.

Abstract:Objective To set up an obstructive sleep apnea hypopnea syndrome (OSAHS) animal model and investigate the effect of the mechanical environment change in pharyngeal cavity on mechanical property of trachea. Method An OSAHS animal model was obtained by culturing Guizhou mini-type pigs in low pressure chamber; the in situ longitudinal stretch ratio, the morphologies of no-load state and zero-stress stateas well as the pressure (p)-volume (V) relationship under different longitudinal stretch ratios of trachea were measured; The zero-pressure compliance describing the mechanical property of trachea was calculated based on the p-V relationship; Compared the obtained data in model pigs with those in control group. Results The OSAHS symptom appeared in the model pigs. Compared with control group, the geometrical sizes of no-load state and zero-stress state in model pigs increases, as same as the zero-pressure compliance under different longitudinal stretch ratios. The ultrastructure of trachea's mucosa of the model pig was significantly remodeled. Conclusion The method to establish the OSAHS animal model is reasonable. The geometrical structure and morphology as well as the mechanical property of trachea remodeled have all changed in this mechanical environment of trachea.

Abstract:Tissues and cells in the body are continuously exposed to a complex mechanical environment. Mechanical stimulations are critical to morphological, developmental and functional states of living cells. The fashion of the mechanical stimuli applied to the cells is supposed to be extremely important for the induced cell response and function. Proliferation and differentiation of bone marrow mesenchymal stem cells would be affected by mechanical stimulation. Meanwhile, the mechanical regime is extremely important, different regime may induce totally different effect. This paper focused on review in progress of the differentiation of bone mesenchymal stem cells induced by mechanical stimulation.

Abstract:Mechanical stress plays an important role in bone growth and bone remodeling. It causes stretch stress and fluid flow shear stress, which can be sensed by mechano-sensory cells, e.g. osteocyte and osteoblast, and induces changes of gene expression in those cells. The fluid flow shear stress is thought to be the main stimulin in this process. However, up to now, it is still not clear for what signals are triggered in mechano-sensory cells and how the flow shear stress exactly affects the expression of specific proteins. Evidences have shown that the stress-sensitive cation channels, the integrin-cytoskeleton complexes and the gap junction/CX43 hemi-channels may be key players in transducing mechanical signals, presumably via mitogen-activated protein kinase pathway, PKA/PKC pathway, NFκB pathway, RhoA/ROCK pathway and Ca(superscript 2+) signaling pathway. At the far end of the response, there is evidence for regulation at the level of gene transcription. For example, the production of cell growth factors, transcription factors and osteogenic proteins is enhanced significantly in osteocytes and osteoblasts after FSS stimulation. The precise mechanism involved in mechano-transduction and signal transduction remains to be elucidated.