Abstract:The intracellular calcium signaling, which is modulated by the microenvironment of cells, is closely related to the cell's self renewal, differentiation, proliferation, and its apoptosis. The study on the quantitative modulation of the intracellular calcium signals could not only help to understand the dynamic behavior of such kind of signaling, but also play a significant role in the control of cell fate, simulation of cell behavior and bionics of cellular biological systems. This paper briefly reviewed the progress on the quantitative modulation of intracellular calcium signals induced by shear flow, including (1) experimental phenomena and the associated mechanisms of shear flow activated intracellular calcium response; (2) mathematical modeling and simulation of the intracellular calcium response induced by shear flow; (3) feedback control of the intracellular calcium signals by shear flow.

Abstract:As a rapidly developing area in biomechanics, mechanics of biological materials aims to investigate the fundamental relationship between functions, properties, structures, and compositions of various natural biological materials at different length scales and the underlying physical mechanisms through experimental research and theoretical analysis, and to provide inspirations from the splendid living world for the biomimetic design of new materials. In this paper, some recent achievements, mainly made by Chinese scholars in this field, are briefly reviewed, including the stiffening and toughening mechanisms of such biological composites as nacres and horns, the relation between the surface wetting behavior and the micro/nanostructures, and some relevant biomimetic applications as well. The contents of seven invited papers published in this special issue are also introduced.

Abstract:Objective To investigate the specific roles of gap junction and ATP in mechanical stimulation induced calcium transfer in osteoblasts. Methods The isolated osteoblastic pattern without gap junctions was established by using the micropatterning method. Then fluid shear stress was applied on cells using the flow chamber to observe and analyze the characteristic parameters of calcium response. Results Multiple calcium response still occurred in osteoblastic pattern without gap junction, but the response time to the first responsive peak was much longer than that with gap junction. When the intracellular and extracellular calcium ions were removed, only 40% cells responded to the mechanical stimulation, with single peak and multiple peaks accounting for 50%, respectively. If ATP pathway was blocked, only 20% cells responded, most of which showed single peak. Conclusions ATP was the major pathway mediating intercellular calcium transfer, while the gap junction was not the necessary one.

Abstract:Objective To study mechanical properties of the microstructure of the articular cartilage with biological activity by nanoindentation tests under the condition of keeping the articular cartilage in water. Methods The different abilities to keep in situ mechanical properties of the articular cartilage with cold mosaic method or with moisturizing method were evaluated by experiments, and the mechanical properties of the microstructure of the articular cartilage in different kinds of solution used in moisturizing method were also obtained. Results The experiment showed that the elastic modulus on the cartilage surface layer with cold mosaic method was much higher than that with moisturizing method, and the elastic modulus on the cartilage surface and deep layer in chitosan and saline were much lower than that in distilled water. Conclusions The moisturizing method is better at preserving in situ mechanical properties and biological activity of the biological materials, and chitosan and saline are proved to have the effect of keeping mechanical properties of the cartilage used in moisturizing method.

Abstract:Objective To study the effects of mineral-collagen interfacial behavior on the microdamage progression within bone tissue. Methods Based on the finite element model, cohesive elements were introduced and the traction-separation law was used to simulate the role of ionic interactions, hydrogen bonds and van der waals forces. The effects of aforementioned interactions on the microdamage progression within bone were studied by the random field theory and probabilistic failure analysis. Results Strong interfaces (ionic interactions in both opening and sliding modes) between the mineral and collagen phases might encourage the formation of linear cracks in bone, whereas weak interfaces (van der Waals in opening mode and viscous shear in sliding mode) might facilitate the formation of diffuse damages. In addition, there existed a transitional interfacial bonding strength (hydrogen/van der Waals bonds) that governed the transition of microdamage accumulation from linear microcrack to diffuse damage.Conclusions The results from this study will help to understand the effects of mineral collagen interfacial behavior on microdamage accumulation in bone and further investigate the underlying mechanism of bone fracture due to osteoporosis or ageing.

Abstract:Objective To Investigate the toughness mechanism of the hierarchical and eximious micro-nanostructures from shankbone biocomposite. Methods The hierarchical micro-nanostructures of a mature shankbone were observed with a scanning electronic microscope and then to explore the toughness mechanism of this shankbone by the analyses on the models with hierarchical micro-nanostructures. Results The shankbone was made from a kind of biocomposite with hierarchical micro-nanostructures, consisting of hydroxyapatite and collagen protein matters. The micro-nanostructural model analyses at different scales indicated that the multilayer microstructure of the bone increased its fracture energy and the crossed microstructure of the hydroxyapatite fiber sheets as well as its long and thin shape size enhanced the maximum pullout energy of the fiber sheets. Conclusions The hierarchical and eximious micro-nanostructures in the bone endow the shankbone with high fracture toughness, and can be applied to the design of biomimetic composites.

Abstract:Objective To report a self-developed cell carrier made of silicone rubber membrane, and to calculate the strain distributions on the membrane and analyze biocompatibility of the silicone rubber by three dimensional (3D) finite element method (FEM) so as to make a comprehensive evaluation on this silicon rubber membrane and provide theoretical basis for cellular research under stress stimulation. Methods The silicon rubber was made into a membrane with the thickness of 0.1 cm. Based on elastic modulus and Poisson’s ratio of the silicone rubber membrane, 3D FEM was used to simulate the deformation of the membrane induced by the stretch stress. MTT method was used to compare the growing situation of cells cultured on the silicone membranes and in standard plastic plates, respectively. Embedding experiment was also conducted to find out whether the material had biological toxicity or not. ResultsUnder the loading of 0.5%~20% strain, the area with effective strain was in the center of the membrane, accounting for 90% of the total area. There still existed some differences in biocompatibility between the silicon rubber membrane and standard plastic plate, but the material itself showed no toxicity. Conclusions Stress distributions on the surface of this self-developed silicon rubber membrane and its biocompatibility were generally acceptable for cell culture, but its surface should be further improved to fit for cell stress experiment.

Abstract:Objective To analyze the compressive strength and fracture mode between four kinds of dental zirconia CAD/CAM ceramic materials by Hertzian contact test. Methods Four CAD/CAM ceramic materials including Cercon smart, Lava, Porcera, and CEREC 3 were selected. Six zirconia sectioned flat specimens were prepared in each group. The critical load and fracture load as well as the fracture mode for each specimen were analyzed with digital image correlation (DIC) technique. Results It was found that cracks were initiated at the middle level of the veneer below the contact zone and propagating along an arc curve into the core/veneer interface, which eventually caused the debonding of the core/veneer layers. For the four ceramic systems, there were no significant differences in the critical load（P＞0.05）, while there were significant differences in the fracture load（P＜0.05）. Conclusions The compressive strength of the four zirconia CAD/CAM ceramic materials could substantially meet the clinic requirement for oral functions regarding the maximum occlusal load. Crack initiation and complete fracture only occurred in the veneer, which indicated that the strength of the veneer should be further reinforced.

Abstract:Objective To study the variation of rupture distance of liquid bridge with different liquid volume, spherical radius and solid-liquid contact angle. Methods The process of stretching and rupture of liquid bridge between a sphere and a plane was simulated by Surface Evolver program. The rupture distance of liquid bridge which depended on the liquid volume, radius of sphere and wetting property of surface was calculated from the simulation. Results The theoretical formula of rupture distance which was related to the liquid volume, spherical radius and contact angle was derived based on the formula given by Lian and Willett, et al. The simulation result was in agreement with the theoretical result when the solid surface was hydrophilic (error <4.3%); when the solid surface was hydrophobic, the error between the simulation and theoretical results showed to be greater with the hydrophobicity enhanced. Conclusions The quasi-static process of stretching and rupture of liquid bridge can be well simulated by Surface Evolver program and the rupture distance can be given accurately from the simulation result. The error between the simulation and theoretical results in rupture distance on the hydrophobic surface appeared significantly increasing, because the formula given by Lian and Willett, et al was derived from data based on the hydrophilic surface.

Abstract:Objective To design and build a new dynamic load and circulating perfusion bioreactor system and test its performance. Methods The design principle of the bioreactor system was specified and the dynamic strain loading system and 3D perfusion culture system were designed and built accordingly. A special culture chamber for 3D perfusion and compressive loading was also developed. The sterility of the culture chamber and the accuracy and stability of the strain loading were measured, and the result from the culture of tissue engineering bone was preliminarily observed. Results This bioreactor system could provide compressive strains with different magnitudes and frequencies, as well as perfusions under different flow conditions. It could be controlled accurately and operated easily with a steady performance. No germs were grown in the culture medium after 5 days’ running. The preliminary results showed that after the tissue engineering bones were cultured in the bioreactor for 10 days, cell proliferation and ALP activity in this perfusion culture and loading group were significantly higher than those in the static culture group and the simple perfusion culture group. Conclusions The bioreactor could be an ideal dynamic culture and loading device for biomechanical study of tissue engineering bone.

Abstract:Objective To develop a wear prediction model for hard-on-hard hip joint replacement under the condition of complex dynamic loading and time-dependent motion, and to apply it to the study on wear prediction of the typical metal-on-metal hip joint replacement in the complicated three-dimensional (3D) physiological motion condition. Methods The finite element model for contact mechanics was established and the fixed-tracked method was adopted to make the dynamic wear reappear on the bearing surface of artificial hip joint with 3D Euler transformation, and the data communication about the corresponding contact and wear for simulation was also made. Results The wear prediction test showed that the spherical bearing geometry of the artificial hip joint gradually became the non-spherical form due to the wear with time; meanwhile, the corresponding contact area was increased, the distribution of the contact pressure tended to be flattened, and the maximum contact pressure was decreased. Conclusions The wear prediction model developed here for metal-on-metal hip joint replacements with bilateral bearing surfaces under the condition of complex dynamic loading and motion could be used to carry out simulation test for the wear prediction of metal-on-metal artificial joint, which provides a new method to understand the wear mechanism of hip joint replacement.

Abstract:Objective To develop a set of loading device that can simulate the spinal movement in vitro so as to carry out the biomechanical experiment on human spine. Methods Based on the principle of bearing, the rotary locking device was designed and fixed on the loading plate, which was rotated to the position for testing and then locked by the bolt before loading. And then, with the auto-loading power provided by the universal testing machine, the pure moment of flexion/extension, left/right bending and left/right axial rotation were applied on the spine specimen to simulate the spinal movement in vivo. Finally, the position of the spine specimen before/after loading was measured by the 3D scanner. With the loading device, the range of motion under these six loading conditions for six fresh (one-year age) porcine cervical spines (C2-C6) was tested, and precision of the loading device as well as error analysis were testified by experiments. Results A set of experimental device for the three-dimensional movement measuring for human spine was developed. Data of neutral zone and range of motion for the porcine cervical spine in six directions were acquired with the total measurement error being less than 3.5％. Conclusions The delicate design of this loading device could simulate the spinal motion in vitro and thus achieve the rapid loading of the human spine. This is an inexpensive, simple and practical device, which can significantly increase the test efficiency and has great application value in loading on the spine in vitro.

Abstract:Objective To obtain the statistical data from the range of motion in lower limb of the Chinese people during their stair ascent so as to provide references for the design of artificial joints with large range flexion. Methods Common staircase as an experimental device was designed, and motion capture system（Optotrak Certus, NDI）and 3D force plate（AMTI, Bertec）were used to establish a systematic method to measure the lower limb motion from 40 subjects during stair ascent. Results The variation of joint angle and range of motion in hip, knee and ankle joints for the 40 subjects in different directions within one cycle were obtained and calculated. The range of motion in hip, knee and ankle joints at the sagittal plane were -1.6°~66.7°, 0°~91.4°,-20.8°~22.4°, respectively. Conclusions During the movement of stair ascent, the range of motion at the sagittal plane in hip, knee and ankle joints reached the maximum, with the most flexion in hip and knee. Compared with the movement during walking and jogging on flat road, the range of motion in joints both in hip and knee at the sagittal plane were larger during stair ascent.

Abstract:Objective To study different ambient temperatures effected on hemorheological characteristics of rats. Methods 70 rats were divided into 7 groups evenly and raised at the ambient temperature of 7, 12, 16, 22, 28, 32 and 35 ℃, respectively, for 7 days. 5 mL blood was collected by heart puncture technique from each rat to test their hemorheological parameters within 2 hours. Results When the ambient temperature was at 7, 12, 32 or 35 ℃, the hemorheological parameters were abnormal, the variability of erythrocytes was reduced, the resistance of capillaries was increased and the erythrocytes was assembled easily, thus preventing the normal blood circulation, slowing the local blood stream, causing the hypoxia and affecting the organic metabolism and function. Conclusions The hemorheological parameters were optimal within the ambient temperature range of 16~28 ℃, with the resistance of blood flow being smaller and the rheological properties of red blood cells being better. As for keeping the good microcirculation of the organism, it seems that the lowest and highest ambient temperature should be around 7 ℃ and 32 ℃, respectively.

Abstract:Objective To investigate the changes of bone mineral density (BMD) and biomechanical properties of the femur after ipsilateral tibia fracture in rats, and its relationship with the tibia fracture union. Methods Forty 3-month-old female SD rats were divided into 2 groups randomly and evenly: the surgery group and the control group. The surgery group received middle shaft fracture and fixation surgery on the right tibia. BMD of the right femur was measured both before the surgery and at 2nd, 4th, 6th, 8th, 10th, 12th week after the surgery, respectively. Ten rats in the surgery group and ten rats in the control group were executed at 6th and 12th week after the surgery, respectively, to test the biomechanical properties of their right tibia and femur. Results The radiological union rate and mechanical union rate of the tibia were 50% and 70%, respectively, at 6th week after the surgery, and those at 12th week after the surgery were both 100%. At 2nd, 4th, 6th, 8th week after the surgery, BMD of the right femur in the surgery group was significantly lower than that in the control group (P<0.05). Compared with the control group, there was no statistical difference in BMD of the right femur at 10th, 12th week after the surgery. Biomechanical properties of the right tibia and femur at 6th week after the surgery showed obviously worse than those at 12th week after the surgery (P<0.05). Analysis showed that the fracture union was highly related with mechanical properties of the tibia (P<0.01), which was also highly related with BMD and mechanical properties of the femur (P<0.001). Conclusions In the early stage of tibia fracture, disuse osteoporosis might occur due to the decrease of BMD and worse mechanical properties in the ipsilateral femur, but as the tibia fracture united, BMD and biomechanical properties of the femur became normal again.

Abstract:Objective To study the correlation between the amount of reduction loss and the length of fixator moment arm after treating acrmioclavicular（AC）joint dislocation with the endobutton technique as viewed from mechanics. Methods 24 patients with acute AC joint dislocation were treated with the endobutton technique and made the follow-up from Mar. 2009 to Dec. 2010 in Shanghai Ninth People’s Hospital. The loss of reduction was observed by evaluating the change of distance between the coracoid and clavicle three days and six months after the operation, respectively. Meanwhile, the length from the upper endnobutton midpoint to the proximal end of clavicle (L1) and the whole length of clavicle (L) were measured and the ratio of L1/L as the moment arm of the fixator was calculated to study the correlation between reduction loss and moment arm. Results All the 24 patients received good reduction after the operation, and the distance between the coracoid and clavicle returned to normal. The average distance between the coracoid and clavicle three days and six months after the operation was (28.2±3.9) and (29.5±4.1) mm, respectively. The amount of average reduction loss was (1.3±1.2) mm. The average moment arm was 0.79±0.03. There was a significant negative correlation between the reduction loss and moment arm with the correlation coefficient -0.498(P＜0.05). Conclusions For the treatment of AC joint dislocation using endobutton technique, the position of the endobutton is closely related with the loss of reduction postoperatively. The shorter the moment arm, the greater the loss of reduction would be. The proper moment arm should be around 0.80.

Abstract:Mesenchymal stem cells (MSCs) is an ideal cell type extensively used in cartilage multipotency to differentiate into cartilage and can be isolated from a wide variety of tissue sources with strong in vitro expansion. Since cartilage has the important mechanical properties, it is necessary to highlight and evaluate the mechanobiological properties of MSC-based tissue engineered cartilage. To better understand the relationship between inducing factor of cartilage repair, signal pathway and mechanical properties, this paper reviews the advances made on research of mechanobiology in MSC-based tissue engineering cartilage, discusses the existing problems in this field, and try to point out some new approaches or directions worthy of such investigation.