Abstract:All tissues in the body are subjected to biomechanical force originating either from tension, created by cells themselves, or from the environment. Biomechanical force not only can induce cell proliferation, but also induce cell death. While biomechanical force at physiological levels is essential to develop and maintain organic structure and function, elevated mechanical stress may result in cell death leading to pathological conditions. In eukaryotic cells, the nucleus contains the genome and is the site of transcriptional regulation. The nucleus is the largest and stiffest organelle and is exposed to mechanical forces transmitted through the cytoskeleton from outside the cell and from force generation within the cell. Here, we discuss the effect of intra- and extracellular forces on nuclear shape and structure and how these force-induced changes could be implicated in nuclear mechanotransduction, ie, force-induced changes in cell signaling and gene transcription. We review mechanical studies of the nucleus and nuclear structural proteins, such as lamins. Dramatic changes in nuclear shape, organization, and stiffness are seen in cells where lamin proteins are mutated or absent, as in genetically engineered mice, RNA interference studies, or human disease.. We also highlight studies that link changes in nuclear shape with cell function during developmental, physiological, and pathological modifications. Together, these studies suggest that the nucleus itself may play an important role in the response of the cell to force. Therefore, mechanical stimuli must be sensed by cells and transmitted through intracellular signal transduction pathways to the nucleus. Changes in the shape and structural organization of the cell nucleus occur during many fundamental processes including development, differentiation , mature and aging. In many of these processes, the cell responds to biomechanical force by altering gene expression within the nucleus. However, how the nucleus itself senses and responds to such mechanical cues is not well understood. In addition to these external forces, epigenetic modifications of chromatin structure inside the nucleus could also alter its physical properties. Here we review our current literatures in related to the structure and mechanobiology of cellular nucleus. To achieve a better understanding the relationship between the mechanobiology of cell nucleus and the nuclear material properties, we need to do more research ranging from molecule to tissue.

Abstract:Bioreactors could be used to simulate the growth conditions of cells and tissues in vivo which have benefits for the proliferation and differentiation of seeding cells and the tissue construction in vitro. Some papers in this issue were introduced and the application of bioreactors in tissue engineering were summarized. It was suggested to use the multidisplinary approach including the biomochanical methods to develop the bioreactors and to investigate the key parameters of the cells growth and tissue construction for the functional tissue engineering.

Abstract:Objective To study the relationship between the construction of large engineered bone and flow shear stress inside the β-tricalcium phosphate (β-TCP) scaffold in perfusion bioreactor with the flow model. Method The scaffolds seeded with human bone marrow-derived mesenchymal stem cells were cultured in perfusion bioreactor. The viscosity of the media was 1.12 mPa?s, 223 mPa?s, and 3.35 mPa?s respectively The construction of the tissue-engineered bone was assessed through the proliferation and osteogenic differentiation of cells and histological assay of the constructs. The flow model was established to calculate the flow shear stress inside the β-TCP scaffold. Result The cell viabilitywas highest in the group with the viscosity of 223 mPa?s. The alkaline phosphatase activity at day 28 and the osteocalcin secretion after 7 days were higher in the two groups with the viscosities of 223 mPa?s and 3.35 mPa?s than in the group with the viscosity of 1.12 mPa?s. Increasing the viscosity of the medium resulted in an earlier emergence of secretion peak of osteopontin. After 28 days of culture, the mineralized extracellular matrix formed inside the scaffold was most in the group with the viscosity of 3.35 mPa?s. The averaged flow shear stress in the scaffold was 5 mPa, 11 mPa, and 15 Pa accordingly when the viscosity of the media was 1.12 mPa?s, 223 mPa?s, and 335 mPa?s respectiwly. Conclusions In this study, a 15 mPa of flow shear stress was optimal in the construction of a large-scale tissue-engineered bone using the β-TCP scaffold combined with human bone marrow-derived mesenchymal stem cells in a perfusion bioreactor.

Abstract:Objective To develop a steady-state mathematical model for oxygen concentration profile in perfusion bioreactor and a cardiac tissue construct as a function of flow rate and cell density. Method The cardiac tissue construct was cultured in perfusion bioreactor using scaffold with parallel channel array. The mathematical model was solved by computational fluid dynamics (CFD) commercial software to investigate the effects of cell densities and flow rate on oxygen concentration profiles in the construct. Result The simulation results indicated that the parallel channel array could mimic the role of the capillary network to enhance mass transport and improve the oxygen distribution partially in the scaffold. Oxygen concentration could increase with the medium flow rate, which was enough for low cell density in construct. However, this method couldn't provide enough oxygen for high cell density due to the less number and simple formation of the channel. Conclusions The mathematical model could be used to optimize scaffold geometry and flow condition for constructing cardiac tissue in perfusion bioreactor.

Abstract:Objective To simulate the flow field within large scale porous β-TCP scaffold in perfusion bioreactor. Method The computational fluid dynamics (CFD) method was used to simulate the flow conditions within large scale porous β-TCP scaffold in our newly designed perfusion bioreactor. The velocity field and the flow shear stresses within the scaffold at different perfusion flow rates were estimated by our simulation model. Result The velocity field and the flow shear stress throughout the scaffold could be well simulated with this method. The corresponding flow velocities in the scaffold pores at flow rate of 3 ml/min, 6 ml/min and 9 ml/min were (0227±0.062) mm/s, (0.459±0.125) mm/s and (0.701±0.193) mm/s. The flow shear stresses within the scaffold at flow rate of 3 ml/min, 6 ml/m in and 9 ml/min were 52±1.5 mPa, 1.06±3 mPa and 162±4.6 mPa respectively. Conclusions This simulation modeling could be used to compare results obtained from different perfusion bioreactor systems or different scaffold microarchitectures. It could allow specific shear stresses to be determined that optimize the distribution, proliferation or differentiation of seeded cells and the microarchitectures of the scaffold.

Abstract:Objective To examine the feasibility of expanding MSCs from the isolated bone marrow mononuclear cells using a rotary bioreactor system. Methods The cells were cultured in a rotary bioreactor with Myelocult? medium with addtion of supplementary factors such as stem cell factor (SCF), interleukin 3 and 6 (IL-3, IL-6). The MSCs were measured and compared the changed of its apparent, hyperplasia and differentiation before and after treated by the bioreactor. Resules After 8 days of culture, total cell numbers, Stro-1(superscript +) CD44(superscript +) CD34(superscript +)MSCs and CD34(superscript +) CD44(superscript +)Stro-1(superscript -) HSCs were increased 9, 29, and 8 folds respectively. The bioreactor-expanded MSCs showed expression of primitive MSCs markers endoglin (SH2) and vimentin, whereas markers associated with lineage differentiation including osteocalcin (osteogenesis), Type Ⅱ collagen (chondrogenesis) and C/EBPa (adipogenesis) were not detected. Colony forming efficiency-fibroblast per day (CFE-F/day) of the bioreactor-treated cells was 1.44-fold higher than that of the cells without bioreactor treatment. Upon induction, the bioreactor-expanded MSCs were able to differentiate into osteoblasts, chondrocyles and adipocyles, which showed no difference with that of MSCs without treating by Bioreactor. Conclusion It could conclude that the rotary bioreactor with the modified Myelocult? medium reported in this study could be used to rapidly expand MSCs.

Abstract:Objective The bioreactor is an important facility for tissue engineering research. A research platform of bioreactor system for blood vessel on the virtual instrument was built. Method Slider-crank mechanism was used in this system to strain the bellows so as to simulate pulse flow of human blood vessels. This system can measure and control such parameters as pressure by using LabVIEW platform, and by connected with PC, the remote watch and control could be realized, which primarily achieved step-control and automatization. Result Experiments show that the bioreactor was able to exert appropriate biomechanical stimulation to cells, and detect various parameters accurately. Conclusions This bioreactor system for bloodvessel on the virtual instrument was valuable in practical application.

Abstract:Objective To research on cell seeding for large-area tissue construction in a bag bioreactor. Method A tissue engineered 3-D model system was developed by using human fibroblasts and porous polyethylene terephthalate (PET) polymer scaffolds. The effects of shaking speed and initial cell concentration in suspension on cell seeding kinetic, cell seeding efficiency, initial seeding density and cell distribution within the scaffolds were studied. Result Under the experimental conditions, the process of human fibroblasts seeding to large-area PET generally followed the first order reaction kinetics. And at low initial cell concentration, the seeding efficiency and initial seeding density decreased with the increasing shaking speed, while at high initial cell concentration the results were reverse. The cell distributing uniformity all decreased with shaking speed increased for all different cell concentrations, but there was no significant difference in uniformity between different initial cell concentrations under the same shaking intenslty. Conclusions The horizontal shake seeding method used in a bag bioreactor for large-area scaffold was approved feasible, which provides basic foundation for further optimizing cell seeding method for such large-area tissue construction.

Abstract:Objective To analyze the possible causes of complication in vertebroplasty (PVP) operation from the view of biomechanics and provide some preventive suggestions accordingly. Method The 16 lunbar spinal vertebrae with osteoprotic compression fracture from the 14 elderly corpses (the vertebral bone mineral density T<-2.5) were selected and monitored to meet the demands of clinical assessment of PVP under C-arm. With the adoption of micro pressure unisensor (5mv/bar) and carrier frequency amplifier as well as its Signai-Soft6000 (PICAS & SIGNALOG 6000) produced by AG company and Peekel Instrument GmbH respectively, the dynamic changes with pressure in each vertebrae vertebroplasty were assessed by using statistical description and analysis through descriptive statistics and nonparametric statistical approach; the possibility of complication was also clinically examined. Result Each vertebra of vertebroplasty met the clinical evaluation requirements. Each time after putting to (the instrument with the set of Yamshidi-Nadel provided by Kypho of America for injection of bone cement into the vertebrae; each putting could contain about 1.5 mL bone cement) inject bone cement into the vertebrae, the pressure P(subscript max) was not very high, with 500 kPa bar below for majority and the effect caused showed a significant statistical difference (P<0.01). Whereas, the pressure within the area of the vertebral P(subscript area) value was not high either, the majority was 10.00 Unit lower, which also led to the effects of significant difference (P<0.01). Both two states showed partial distribution. After making the statistical analysis to the casual two puttings between the first, second, third and fourth putting of each vertebrae, there existed the general differences. The differences were also found between other puttings (a<0.0083) on the statistics basis apart from between the first and second and between the third and fourth. Conclusions For osteoporosis of lumbar vertebral compression fractures vertebroplasty (PVP), its bone cement injected into the vertebrae could achieve clinical evaluation requirements with three putts enough (about 4.5 ml of bone cement), and no need to have fourth-bone cement injection, which not only could avoid frivolous behavior, but also reduce the risk of surgical complications.

Abstract:Objective To measure and compare maximum resist compressive strength and torsional strength of newly-designed expansion cancellous screw with that of cannulated compression screw in fixation of femoral neck fracture, and to evaluate the effects of ECS screws. Methods Eighteen pairs (thirty six specimens) of cadaveric human proximal femurs were randomly divided into three groups, i.e. each group with six pairs (twelve specimens). Simulate uniped standing and compare the maximum femoral neck strength and torsional strength with using screws in different types and numbers, i.e. two ECS and two CCS, two ECS and three CCS, three ECS and three CCS. Result The maximum femoral neck strength and torsional strength from fixation with ECS was significantly greater than that of CCS with the same types and numbers; the fixations with two ECS and with three CCS showed no significant difference. Conclusions The results suggested that as compared with CCS, the expansion cancellous screws might have better effect in femoral neck fracture. The fixation effect with two ECS sometimes could have the same virtue as that with three CCS.

Abstract:Objective Study the methods of establishing 3D photo-elastic model for unilateral maxillary defects. Method Unilateral maxillary defects epoxy model was made according to the silicone impression model of unilateral maxillary defects made by using standard tooth and maxillary model. Result Epoxy unilateral mandibular defects model was developed. The ratio of epoxy resin teeth, alveolar bone and silicone rubber (PDL) elastic modulus was 13.3:1:0.001, which is close to the clinical condition. Conclusions This epoxy-optical model of unilateral maxillary defects with high sensitivity and visual acuity could well meet the demand of the photoelastic experiments.

Abstract:Objective To investigate the mechanical property and tooth canal structure changes after RCT. Method Three-Dimensional Finite Element model of tooth and centerline of tooth canal were constructed to research into the mechanical property and tooth canal structure, respectively. Result Three-dimensional finite element model and centerline model were separately constructed and made the comparison for the changes of mechanical property and tooth canal before and after RCT. Conclusions The method could be used to fast set up three-dimensional finite element model of tooth and centerline model and used for all kind of tooth to analyse their biomechanics properties.

Abstract:Objective Study the changes of hemodynamics after stent intervention to sinuous aneurysms. Method Geometrically idealized model of three-dimensional sinuous aneurysms and curved stent was constructed using CAD software. Numerical simulations of stented and nonstented models were performed respectively in steady flow according to CFD method using finite element software. Hemodynamics data in the two models were compared in terms of flow field, pressure and the distribution of Wall Shear Stress (WSS). Result Velocity of blood flow in stented model is greatly weaken than the nonstented, and the local high pressure is markedly decreased at the proximal aneurismal dome, and the pressure along the wall of the distal aneurysm is also decreased and more uniform. The local elevated WSS at the proximal lip of the distal aneurysm disappeared after stent intervention, instead small and uniform WSSs distribute along a majority of the aneurismal wall. Conclusions Velocity of flow is obviously depressed after stent intervention, and the counterpoised pressure distribution of the stented model is more uniform with the weakened flow velocity in the aneurysm cavity, which are beneficial to the thrombus formation in the aneurismal cavity.

Abstract:Abstract: Biomechanical properties of bone provide important and direct reference for osteoporosis prediction and assessment. However, it remains difficult to achieve non-invasive assessment of biomechanical properties of osteoporosis patient in clinic. Thus, developing indirect method to predict the biomechanics of bone is profound and valuable both in osteoporosis research and in clinic application. In this paper, current studies on prediction of biomechanical properties of osteoporosis bone are reviewed, and its future advances are also in prospect.

Abstract:Posterior cruciate ligament is crucial to the stability of knee joint. PCL, located in the central part of knee joint, plays a critical role as the axis of rotation and extension-flexion motion of knee joint. Compared with anterior cruciate ligament, it is deeper located, less susceptible to injury and less symptomatic when injured, therefore related research on PCL has long been neglected. Since 1990s, as studies on PCL especially on its anatomic and biomechanical properties has deeply progressed, these properties of PCL have become more and more important as the guidance of clinical practice of PCL reconstruction. Based on this, the latest progresses in researches on anatomic and biomechanical properties of PCL were reviewed in this article.