Abstract:Articular cartilage is a layer of low-friction, load-bearing soft hydrated tissue covering articulating bony ends in diarthrodial joint. The vital mechanical function is maintained by the metabolism of chondrocytes, which is largely controlled by the physical factors such as joint loading. In this paper, studies on mechanical behaviors and theoretical modeling of articular cartilage and chondrocytes are reviewed with the particular emphasis on physical regulation of chondrocytes biosynthetic activities toward tissue maintenance, and its application in functional tissue engineering for cartilage repair and regenerative medicine. In this review article, first, the molecular composition and ultrastructure of articular cartilage and its tensile, compressive, and shear properties will be described, with their interrelationships emphasized. Then, the widely-used constitutive models, i.e., the biphasic and triphasic mixture theories, will be introduced to describe the tissues’ mechano-electrochemical behaviors, and with special emphasis on the recent advances toward the simplification of the complex triphasic theory described. Finally, mechanical properties, and theoretical modeling of chondrocytes and chondrons, are reviewed to enhance understanding of mechano-electrochemical signals around and in chondrocytes embedded within the extracellular matrix. In light of the mixture theories, the flow-dependent and flow- independent viscoelastic behaviors, swelling behaviors, and electrokinetic behaviors of articular cartilage have been successfully and theoretically described. The extension of mixture description to the chondrocytes and the surrounding pericellular matrix in the literature has also provided new insights in the physical regulatory mechanisms that influence cell behaviors in situ. In conclusion, with the powerful mixture theories, and new experimental techniques, novel and invariant approaches to investigate the chondrocyte-matrix interactions have been developed, with possible beneficial approaches toward successful engineering of artificial cartilage.

Abstract:The Virtual Physiological Human is an initiative that is strongly supported by the European Commission for the development of an integrated model of human physiology at multiple scales from the whole body through the organ, tissue, cell and molecular levels to the genomic level. Its development was considerably advanced by the activities of the STEP project, a Coordinated Action funded by the EC, which began in early 2006. This paper provides an overview of the VPH and the developments it has engendered in the rapidly expanding world-wide activities associated with the physiome. It then focuses on one particular project, the Living Human Project, to illustrate the type of advances that are taking place to further the aims of the VPH and similar initiatives worldwide.

Abstract:Objective The finite element method (FEM) is gaining an increasing impact in dental biomechanics. This work introduces two FEM case studies focusing on the periodontal ligament(PDL). This knowledge is highly desirable, especially considering movement of teeth to their correct position by e.g. braces. The entire simulation chain covers multimodal 3D image processing, highly detailed segmentation of the dental structures, automatic mesh generation, implementation of typical orthodontic load cases, and finally the numerical computation. Methods The first model was generated by means of resampling standard computed tomography (CT) data of a human premolar whereas the 2(superscript nd) model was based on cone beam computed tomography (CBCT) data of a human incisor as a new imaging modality with resolution of 0.125 mm in x, y, and z-direction. After segmentation, FEM meshes were generated with focus on preserving volume and topology of the PDL. Both models were tested by intruding the tooth with a continuous load of 0.5 N. Results In spite of artefacts in the CBCT data, both FEM-models were suitable for FEM simulation. Increased hydrostatic pressure was observed at the apical part of the PDL of the incisor as well as of the premolar. Conclusion Both modelling strategies produced feasible FEM models. Volume and topology preserving meshing algorithms were used for generation of these models. Intrusion of an incisor leads to increased hydrostatic pressure near the apex and on some locations at the medium level between gingiva and apex.

Abstract:Objective Computational simulation technology has become an indispensable tool for researchers across the biomechanics discipline. Crucial to the effectiveness of such a tool is its ability to efficiently simulate patient-specific problems. This paper will present a unique and exceptionally efficient approach that converts 3D digital images (provided typically by CT, Ultrasound or MRI scanners)directly into highly accurate computational models. Method The majority of approaches adopted have involved generating a surface model (either in a discretized or continuous format) from the scan data, which is then exported to a commercial mesher-a process which is time consuming, not very robust and virtually intractable for the complex topologies typical of image data. A more direct approach' is to combine the geometric detection and mesh creation stages in one process. This approach involves identifying volumes of interest (segmentation of 3D image) and then directly generating the volumetric mesh based on an orthotropic grid intersected by interfaces defining the boundaries. This methodology is used that generates 3D hexahedral or tetrahedral elements throughout the volume of the domain, thus creating the mesh directly. Results Treating the problem using an image-based meshing approach is remarkably straightforward, robust, accurate and efficient. Indeed meshes can be generated automatically which is of image-based accuracy with domain boundaries of the finite element model lying exactly on the iso-surfaces thereby taking into account partial volume effects and providing sub-voxel accuracy. Conclusion Meshing from image data presents a number of challenges but also unique opportunities so that a conceptually different approach can provide, in many instances, better results thantraditional approaches. The ease and accuracy with which models can be generated opens up a wide range of previously difficult or intractable problems to numerical analysis, including blood flow, and patient-specific implant design.

Abstract:Objective To explore a easier and more precise method of establishing the finite element model of the reconstruction following resection of peri-acetabular tumors, and the internal fixation system Method Using the CT images scanning from L3 to middle-femur to process and generate the STL model of the pelvis and the internal fixation system by Simplewares, after visual assembling, the whole solid model including the internal fixations were to be set up after repair and optimization by Geomagic, afterwards, the error analysis will be introduced. Eventually following the preprocessing of finite Element Models by Abaqus the final finite element model is established and calculated. Result the finite element model with ligament of the reconstruction following resection of peri-acetabular tumors holds high geometry comparability and precise mechanical similarity. Conclusion The compensation using reconstruction by pedicle screws and rods makes the pathway of mechanical force signal transduction more complete. The structure of the postoperative pelvis is integrity and holds stable mechanical response; the visual assembly simplify the modeling procedure with complicated internal fixation e and the high-precison software of reverse engineering guarantees the accuracy of the model.

Abstract:Objective To establish a three-dimensional (3D) geometrical and gridding model of human heart, and carry out the finite element (FE) simulation. Method With visible data of digital human heart, a 3D structures of the heart s configurations and interior structures are constructed by software 3D-DOCTOR and SOLIDWORKS. The model has been imported into FE software ABAQUS by format STEP. The natural frequency and the stresses of the model are analyzed under the blood pressure. Result The digital model of the human heart has been developed, which could provide the 3D configurations and interior structures as well as the volume of the heart. The different mechanics behaviors in different regions within the heart has been demonstrated. The frequency and the stresses of the heart from 3 different regions have been obtained under blood pressure. Conclusions A 3D visualization geometrical and gridding model of the heart is developed by digital human data, which can show the configurations and internal structures of the heart. By using FE method, the model can be used to provide a visualization numerical simulation platform for biomechanics analysis of the heart.

Abstract:Objective To investigate the biomechanics changes of the reconstructed pelvis after sacrectomy. Methods Three three-dimensional finite element pelvic models were established: (1)a normal pelvic model, (2)a defective pelvic model on which sacrectomy was operated between S1 and S2 sacral vertebrae, and(3)a reconstructed pelvic model. Sitting posture was stimulated under the load of body weight, and the stress and displacement distributions of these models were calculated and compared. Results The displacement of anchor point on the sacral promontory, the stress distributions of the pelvis and the reconstruction instruments of the three models were all obtained. Conclusion Sacroiliac joint reconstruction can increase the stiffness of the defective pelvic and decrease the maximum stress around the sacroiliac joint, thus reducing the breakdown risk of the defective pelvis. Part of titanium sticks between L5 pedicle screw and iliac screw is the weakest region in the instrument. It is suggested that the bending of titanium sticks should be conducted carefully without forming acute angle and significant stress concentration on the titanium sticks so as to reduce the risk of sticks breakdown.

Abstract:Objective To analyze the relationship between the cell proliferation and flow fields inside theβ-tricalcium phosphate(β-TCP)scaffold with the computational fluid dynamics. Methods Theβ-TCP scaffolds combined with mesenchymal stem cells were perfused dynamically with a bioreactor for several weeks. The histological and morphometric studies were performed. The CFD modeling was established to reveal the relationship between the cell proliferation and the flow field. Results Histological study showed that the cells proliferated through the whole scaffold along with the time. The cells formed a continuous monolayer in the first week. Some pores were fully filled with cells after 2 weeks' culture. Most of pores were fully filled after 4 weeks' culture, while in some areas the cell coverage decreased. The CFD modeling showed that the optimal fluid velocity and shear stress for the cell proliferation were 0.14~0.64 mm/s and 0.0029~0.017 Pa respectively. Conclusion The microenvironment including the fluid velocity and shear stress had the effect on the cell proliferation inside the scaffold. The size of the interconnecting passages of the pores inside the scaffold changed during the cell proliferation. So did the microenvironment. These factors should be taken into account during the design of scaffold for bone tissue engineering.

Abstract:Objective To compare the effects on biomechanics (?) hemodynamics and plasma levels of brain natriuretic peptide (BNP) when pacing in right ventricular septum and in right ventricular apex. Method Sixty-eight patients performed with DDD pacing, of whom forty-eight with sick sinous syndrome(SSS)and twenty with completely atrioventricularblock, were grouped randomly into two terms according to the site where the ventricular pacing lead fixed. Group one received right ventricular septum(RVS)pacing while the other group received right ventricular apex (RVA) pacing. The QRS waves of the ECG, the left ventricular ejection fraction (LVEF), the cardiac index (CI), the stroke volume (SV) and plasma levels of brain natriuretic peptide (BNP) were compared before and after operations. Patients with SSS in the two groups were programmed and modified three months after operation. Their hemodynamics parameters and plasma levels of BNP were recorded and analyzed in the next three months. Result The QRS duration of lead II of RVA group was longer than RVS group dramatically (P<0.05).There were no obvious differences on LVEF, CI, SV and plasma levels of BNP among the two groups before operation. Compared the hemodynamics and plasma levels of BNP with those in RVS group, the LVEF, CI and SV in RVA group all decreased significantly (P<0.05) three months after operation, but the plasma levels of BNP increased notably (P<0.01). To compare the same parameters for patients with SSS in RVA groups, the LVEF, Cl and SV three months after programming and optimization also increased remarkably(P<0.05), while the plasma levels of BNP decreased obviously (P<0.01), but still higher than those of preoperation evidently (P<0.05). To those patients with SSS in RVS group, there were no difference on LVEF, CI and SV three months after programming and optimization (0.05), however, the plasma levels of BNP decreased remarkably (P<0.05), but there were no difference when compared with those before preoperation (P>0.05). Conclusion The IRVA pacing disturbs the biventricular electrical synchrony and results in the deterioration of the hemodynamics, while the RVS pacing could farthest keep the normal sequence of electrical activity and the synchronous contraction and has no negative effect on the hemodynamics. The RVS pacing shows more physiological better than the RVA pacing.

Abstract:Objective To reveal the morphological changes, zero-stress state, apoptosis and dedifferentiation of vascular smooth muscle cell(VSMC)of the arterial wall during vascular remodeling induced by alterations of flow shear stress. Methods The ligation on some distal branches of left carotid was clone in the one and same rat to induce low shear stress state in the left common carotid artery(LCA)and high shear stress state in the right common carotid artery (RCA), while the rats with sham-operation without ligation were used as the normal control. The arterial morphology was examined by light microscopy and Transmission Electronic Microscope (TEM). Open angle was measured under the zero stress state. The apoptotic cells were detected by TdT-mediated dUTP-biotin nick end labeling (TUNNEL) staining. The expression of h1-calponin, which is a marker for the differentiated state of VSMC, was inspected with Western blotting. Results At 7(superscript th) day after operation of the LCA, the inner diameter was decreased about 13%, the ratio of wall thickness to inner diameter was increased significantly and the open angle was reduced. Otherwise, the thickness of sub-endothelial and VSMC apoptotic were significantly increased while the h1-calponin decreased significantly. Conclusion The significantly decreased shear stress could induce the vascular remodeling in a short time. The apoptosis and dedifferentiation of VSMC might be one of early events during the vascular remodeling induced by low flow or low shear stress.

Abstract:Objective To observe the three dimensional micro-architecture of osteoporosis and non-osteoporosis cancellous bone and its effect on bone strength. Methods 16 adult female sheep were randomly divided into 2 groups: sham-operate group with only ovary-reveal (8 sheep) and OVX group with ovarietomy (8 sheep). During the operation, all sheep underwent dual energy x-ray absorptiometry (DEXA) for the lumbar vertebrae. 12 months after operation, all sheep were sacrificed and underwent DEXA scan for lumbar spine. The cylindrical trabecular bone of vertebral body was harvested by trepan and reconstructed by micro-CT. In biomechanical evaluation, the axial compressing tests were accomplished on the cylindrical bone. Result The BMD in OVX group decreased significantly than that in Sham group (P<0.01). In micro-architecture analysis, the BS/BV, Tb. Th and Tb. N in OVX group also decreased significantly, while the Tb. N and BVF increased (P<0.01). In biomechanical testing, the maximum compressing strength of trabecular bone in OVX group was lower than that in sham group. The Tb. Th was highly correlated with maximum compressing strength of trabecular bone (r=0.945, R^2=0.886). The BVITV (r=0.783, R^2=0.586) and BSITV (r=0.643, R^2=0.372) were correlated with the maximum compressing strength. Conclusion The altering micro-architecture of trabecular bone has effect on its mechanical properties. There is some correlation between micro-structure parameters and bone strength.

Abstract:Objective To establish a biomechanical model of stress and bone growing which can be quantificated quantified numerically. Methods Animal experiments, parameter inversion identification of bone growth equation and computer techniques were integrated used. Weto studied study the effects of stress environments on bone growth and remodeling in rapid growing rats. According to the changes of bone mineral density(BMD)of the proximal femur and its loading stimulus, we inversed the unknown parameters (B and K) of bone growth and remodeling equation. Results The model established in this paper study was able could not only numerically to simulate the relationship between outer stimulus and the femur BMD variation of the rapid growing rats, but also to predict the growth trend of rat femur under different stress conditions in a certain periods within its lifecycle. The idea and method used in the model creating in this paper provide some useful clue and reference for establishing human model of bone growth and remodeling.

Abstract:Objective To reveal the influence of different type lumbar disc disorders(T11-S1)to lumbar curvatureby analyzing of the cases suffering lumbar curvature straightening. Method Retrospective analysis of lumbar disc disorder including degeneration, protrusion and intervertebral space narrowing in T11-S1 were made in curvature straighten group(69 cases)and control group(the same age with normal lumbar curvature,41 cases),respectively. The statistical analysis was given to the different incidence of some parts of disc disorder between two group. Result The incidences of disc disorder in T11-L2 including degeneration, protrusion and intervertebral space narrowing are very low both in curvature straighten group and control group, however, the incidence occurred in L2-S1 increase obviously, especially in curvature straighten group. In segment of L2-S1, the incidence of disc degeneration, protrusion and intervertebral space narrowing in lumbar curvature straighten group is higher than that of control group (P<0.05或P<0.001) except the disc degeneration and protrusion of L2-3 (P>0.05). Conclusion The incidence of lumbar disc affection in L2-S1 increase obviously among the patients suffering with lumbar curvature straighten and, shows that the disc disorder as the local factor may be the motivation led to lumbar curvature straighten.

Abstract:Over the last decade, advances in computational performance have led to the development of new methods for generating finite element models of spinal vertebrae from image data. This paper reviews the methods used and assesses the likely accuracy of the models generated. The model predictions will be influenced by the mesh density and generation method, the material property assignation and the applied boundary conditions. Each of these factors is considered and their relative contribution to the model errors are discussed.

Abstract:Trophoblast cell (TC) invasion of the uterine endometrium is an essential process in the remodeling of the uterine vasculature. TCs enter endometriurn firstly, then invade the endometrial capillaries, migrating within the uterine vasculature, and eventually reside in the spiral arteries of the uterus. After that, those intravascular TCs remodel the spiral arteries to ensure enough blood supplies to the fetal. The direction of blood flow is from the spiral arteries to the microvessels, which suggests that the migration of trophoblast cells is against the stream of blood flow. This paper has summarized recent studies on the unique migratory phenomenon of TCs mainly in the terms of methodology including the cell model employed and the research methods involved, in addition to the factors regulating the migration of TCs, with a view to providing theoretical basis and reference on this field.

Abstract:The normal mechanical properties of the chondrocytes and the pericellular matrix(PCM)is significant for maintaining the healthy articular cartilage. In the compressive stress environment, the chondrocytes exhibit viscoelastic solid material properties with anisotropic and inhomogeneous compressive mechanical characteristics. The PCM plays a definite mechanical protective role for the chondrocytes. The compressive stress may have an important influence on the metabolic activity of the chondrocytes. In spite of these, the biomechanical properties of the chondrocytes and the PCM are not fully understood, and still need further more study.