Abstract:The cytoskeleton of the adherent cell is probably the most complex soft matter in nature. It is composed of hundreds of different proteins that not only interact with each other but also polymerize into long chains and ultimately form a dense network structure. To understand the dynamics of such a complex structure is obviously a great challenge, requiring the joint efforts of multiple disciplines including but not limited to biology, chemistry, physics and physiology. Recently, some important features of the cytoskeleton dynamics have been revealed. For example, the cytoskeleton is far from thermodynamic equilibrium, markedly prestressed, rheologically scale free, and fluidizes in response to a transient stretch. These dynamics behaviors of the cytoskeleton may play important or even determinant roles in many important cell functions such as adhesion, migration and differentiation, and thus further participate in the pathophysiological processes. In this review, we will briefly introduce these dynamics behaviors, describe the results from corresponding studies, and discuss their important implications.

Abstract:As the frontier of biomechanics research, cellular and molecular biomechanics is an interdisciplinary research field at the cutting edge of applied mechanics and life science and biology, which brings us many challenging problems to the current theories and techniques in biomechanics due to its importance and complexity. This paper will give a brief review on several of these challenging problems and make some comments on the papers included in this special issue, such as the mechanical properties and modeling methods of cell, the modeling of mechanochemical couplig and multiscale modeling methods in cell mechanics, so as to stimulate the common interest within not only the biomechanics but also the applied mechanics community.

Abstract:Objective To elucidate the spreading dynamics of β2 integrin expressed human neutrophils (PMNs) on ICAM-1-immobilized substrate. Methods The fraction of PMN spreading on the substrate pre coated by 10, 20, or 100 μg/mL intercellular adhesive molecule-1 (ICAM-1) was quantified when that on 2% human serum albumin (HSA) immobilized or that on blank substrate was served as control. The site density of β2 integrin expressing on PMNs was determined using flow cytometry and the regulation of β2 integrin subunits was defined using the fraction of PMN spreading on 100 μg/mL ICAM-1 substrate by blocking CD11a or CD11b subunit of β2 integrin. Results PMN spreading was presented on ICAM-1-immobilized substrate but absent on 2% HSA-immobilized substrate, supporting the specificity of β2 integrin induced spreading. Time course of neutrophil spreading on ICAM-1 substrate was density dependent of both ICAM-1 and β2 integrin molecules. The fraction of PMN spreading was reduced significantly when the expression of CD11b subunit was blocked. Conclusions PMN spreading was mediated specifically by β2 integrin-ICAM-1 interactions and determined by the expression of β2 integrin and ICAM-1, in which CD11b subunit played a dominate role.

Abstract:Objective To investigate the effect of shear stress combined with lysate of myocardial cells on cardiomyogenic differentiation of bone marrow mesenchymal stem cells (BMSCs). Methods Myocardial cells isolated from neonatal rats were lysed by repeated freezing and defrosting. BMSCs isolated from the marrow of adult rat tibia and femur were randomly assigned to four groups: Group A was BMSCs cultured in complete medium under static state as the control; Group B was BMSCs subjected to laminar shear stress with a parallel plate type device; Group C was BMSCs induced by lysate of myocardial cells; Group D was BMSCs subjected to shear stress combined with lysate of myocardial cells. The cardiomyogenic differentiation of BMSCs was analyzed by RT-PCR, immunocytochemistry and Western blotting. Results Shear stress or/and lysate of myocardial cells treatment induced the expression of cardiomyocyte related markers at both mRNA and protein levels. A combination of shear stress and lysate of myocardial cells had a stronger effect on the expression of cardiomyocyte related markers than either treatment alone. Conclusions Shear stress combined with lysate of myocardial cells treatment could induce BMSC differentiation into cardiomyocytes, which provided an approach to obtain more committed differentiated cells for research or for clinic, and as reference for the design of appropriate biological reactor.

Abstract:Objective To investigate effects of the cyclic stretch on rat bone marrow mesenchymal stem cells (rBMSCs) proliferation and the related signal molecules. Methods The cyclic mechanical stretching apparatus was used to study the effects of the cyclic stretch on the growth of rBMSCs with different parameters. The expression of c fos was measured by RT PCR at mRNA level and the levels of phosphorylated extracellular signal regulated kinase 1/2 (p-ERK1/2), total ERK1/2 (t-ERK1/2) and c-fos proteins were detected by Western blotting. Results The proliferation of rBMSCs could be stimulated by the cyclic stretch, and the number of cells was increased to 1.4 times compared with that of the control group at 1 Hz, 10% strain for 15 min and then being static for 6 h. Moreover, the expressions of c-fos mRNA and protein levels were increased significantly after the stimulation of the stretch. On the other hand, it was found that the cyclic stretch could remarkably enhance the phosphorylation of ERK1/2, but did not influence the level of t-ERK1/2. After treated with PD98059, the proliferation of rBMSCs stimulated by the cyclic stretch was inhibited prominently in a dose dependent manner and the expressions of p-ERK1/2, as well as c-fos at gene and protein levels were sharply down regulated. Conclusions ERK1/2 signal molecules play an important role in regulating the cyclic stretch on the proliferation of rBMSCs and transcription factors may take part in the regulations during this progress.

Abstract:Objective To develop a new set of algorithms for high-resolution cellular traction force recovery based on two-dimensional Fourier domain by addressing the ill-posed nature of classic cellular force traction recovery. Methods By exploring the inherent characteristics and rules of displacement data on the substrates and Green’s function in the Fourier domain, the phenomenon of ill-posed deconvolution arising in cellular force traction recovery was investigated and a set of self-adaptive filtering algorithms was consequently developed to remarkably restrain the high frequency noise amplification. Results The ill-posed nature of classical Fourier transform traction cytometry (FTTC) made cellular traction force recovery extremely unstable, especially for relatively dense displacement data sampling. In contrast, the proposed self-adaptive filtering algorithms based on FTTC could make cellular traction force distribution more stable and reliable, as the effect of high frequency noise in displacement field on recovery results was weakened significantly. Conclusions This new technique for cellular traction force recovery can effectively suppress the noise and therefore improve the stability of force recovery procedure and spatial resolution, which is expected to find wider application in the study of cell substrate interactions.

Abstract:Objective To investigate the effect from different pore sizes of co culture inserts on the permeability of biomacromolecules through polyethylene terephthalate (PET) membrane so as to solve the key technology problem in mechanobiology experiment on vascular cells. Methods Inserts with 0.4 μm and 1.0 μm pores on the PET membrane were studied using flow chamber system. Low shear stress was subjected to the co-cultured system of endothelial cell (EC)/vascular smooth muscle cell (VSMC) and the concentration of platelet-derived growth factor BB (PDGF-BB) was detected by ELISA. Under the static condition, vascular cells were cultured on the plate (with no cell on PET membrane), on the outer side of PET membrane, and on the both sides of PET membrane, respectively. Then the recombinants PDGF-BB (rPDGF-BB) were added on the different sides of PET membrane. Western blotting was used to detect the change in expressions of p-ERK1/2, p-Akt and Lamin after cells were stimulated by rPGDF BB. Results After low shear stress subjection for 12 h, the concentration of PDGF-BB in the medium from VSMC side was significantly higher than that from EC-side. rPDGF-BB passed through 0.4 μm and 1.0 μm pores on the PET membrane and modulated expressions of p-ERK1/2, p-Akt and Lamin A in cells cultured on the opposite side of PET membrane and cells cultured on the plate separately. When cells were cultured on the both sides of PET membrane, rPDGF-BB only stimulated cells cultured on the same side of 0.4 μm pores on PET membrane, but had no specific effect on cells cultured on the opposite side. Conclusions PET membrane with both 0.4 μm and 1.0 μm pores was permeable to PDGF-BB, and cells cultured on the membrane could affect the permeability. The efficiency of PDGF BB passing through 0.4 μm pores was significantly repressed with cells cultured on the both sides, which was more similar to that in vivo.

Abstract:Objective To compare the method based on computational fluid dynamics (CFD) and fluid structure interaction (FSI) with the traditional Reynolds equation method in the study of an artificial hip joint lubrication system. Methods Using business software Adina as a computing platform, the metal-on-metal total hip replacement (MOM THR) model was developed as the subject to establish the rigid and elastic CFD model, respectively. Results The film- thickness curve obtained by the CFD&FSI method had a significant depression in the center, which was more reasonable than that obtained by the traditional Reynolds equation method. The model with elastic surface under the given load showed a significant deformation at the FSI surface of the acetabular cup femoral head, and the deformation was consistent with the pressure and film thickness distribution in fluid field. Conclusions The CFD&FSI method used here was more reasonable than the traditional method when computing the elasto-hydrodynamic lubrication of an artificial hip joint system.

Abstract:Objective To design a novel device with dynamic occlusal loads so as to investigate the influence of occlusal force on Ni release from Ni-Cr PFM alloys. Methods Based on the average force(45 N) and rate(80 cycles/min) of human mastication, a novel device with dynamic occlusal loads was designed to study the Ni release from three commonly used Ni-Cr PFM alloys (Shangchi, Stellite, BEGO) in the artificial saliva with pH 2.3 and pH 7.4, respectively. Results This novel device with dynamic occlusal loads worked well to simulate the average force and chewing cyclye. In the artificial saliva with pH 2.3, the amount of Ni release in Shangchi, Stellite and BEGO was 6.9(2.07) μg/cm2, 3.7(0.662) μg/cm2 and 5.88(1.57) μg/cm2, respectively; while in the artificial saliva with pH 7.0, the amount of Ni release in Shangchi, Stellite and BEGO was 0.272(0.059) μg/cm2, 0.144(0.014) μg/cm2 and 0.435(0.053) μg/cm2, respectively. For the same Ni-Cr PMF alloys, the amount of Ni release in the artificial saliva with pH 2.3 was much higher than that with pH 7.0 (P<0.01), showing statistical differences. Conclusions The device with dynamic occlusal loads could be used effectively to evaluate the influence of occlusal force on Ni release from Ni-Cr PFM alloys in vitro. The acid environment could obviously accelerate the Ni release from Ni-Cr PFM alloys. This study showed the amount of Ni release in Stellite was relatively lower than that in the other two alloys.

Abstract:Objective To study the repairing mechanism of mechanical microdamage around implants in the cortical bone of rats. Methods Thirty rats were divided into the ovariectomy group (OVX) and the sham group. At three months after the ovariectomy, a hole was drilled in the right tibial diaphysis by a metal pin. The rats were executed at 1, 2 and 4 weeks, respectively, after the hole drilling. The tetracycline and calcein labeling were performed before the execution. Bone segments containing the hole were stained with the basic fuchsin, embedded in the methylmethacrylate and cut into sections with thickness of 50 μm. Histomorphometric measurement was conducted on bone sections using Bioquant image analysis system. Results Bone resporpion cavities related to the microdamage occurred in both the OVX rats and the sham operated rats. The bone porosity and the number of bone resorption cavities were both greater in the OVX rats than that in the sham operated rats (P<0.05). In addition, the number of bone resorption cavities significantly increased with time after the surgery (P<0.05). Conclusions Increased bone porosity and resorption cavities in OVX rats may be related to the crack formation and the estrogen deficiency, which made the bone remodeling in the cortical bone of OVX rats more active. However, remarkably increased resorption cavities would reduce the bone strength and increase the risk of bone fracture.

Abstract:Objective To test the mechanical properties of a self-developed novel anterior mid-distal humerus anatomic locking plate (hereinafter referred to as the new plate) and to improve its design to provide theoretical support for its clinical application. Methods Twenty intact humerus from embalmed human cadavers were obtained and used for the biomechanical test on mid-distal humeral shaft fracture models by using the new plate (group A) and 4.5 mm LC DCP（limited contact dynamic compression plate）(group B), respectively. Both groups were compared under axial compression, medial-lateral bending, medial-lateral three-point bending and external rotation torque. Results The stiffness, strength and stress shielding of the new plate for mid-distal humeral shaft fractures under four different loads were superior to those of 4.5 mm LC-DCP, and the differences were statistically significant(P<0.05). Conclusions The new plate can satisfy the requirements of physical training at early stage for fixed mid-distal humeral shaft fractures, which gives great clinical values.

Abstract:Objective The research on vortex structure and vortex evolution in human upper respiratory tract can help to deepen the understanding of the characteristics of the airflow in human upper respiratory tract, which could give some very important assist in analyzing the diffusion, transition and deposition patterns of aerosol in human upper respiratory tract. Methods Large eddy simulation was used to simulate the vortex structure and vortex movement in human upper respiratory tract under the condition of low intensive respiratory patterns, and the vortex structure and vortex evolution in mouth throat model and in trachea triple bifurcation were discussed. Results Jet formations from airflow in pharynx and laryngeal led to two vorticity growth regions; flat vortex appeared in the throat; a curved vortex like the trachea wall appeared in the anterior wall of trachea, and nearly symmetric reverse vortex pairs appeared in the trachea; the vorticity in the G0 trachea end extended from the trachea wall to the center of the trachea, and moved to the G1 bronchial; the vorticity in bronchial of every class presented an asymmetric distribution. Conclusions The vortex structure and vortex evolution are the remarkable characteristics of the airflow in human upper respiratory tract, and the geometric airway characteristics is the main factor that results in the transformation of variable sizes of vortex structures.

Abstract:Objective To develop a microscopic 3D morphology testing system used for measuring the natural texture of human incisor, and provide practical data for the individualized technique used in dental restoration. Methods Based on microscope and digital image correlation (DIC), a microscopic 3D morphology testing system with its software was developed. The precision of this system was then evaluated, and the characterization of the 3D surface morphology for human incisor was measured by the system. Results Within the field of view (FOV) of 17 mm×12 mm, the accuracy of in plane displacement was estimated as 0.6 μm, while that of out of plane displacement was 5.4 μm. The dimension of horizontal grooves on the labial surface of incisor was determined, where the depth and length for the long groove were 83 μm and 5.28 mm, respectively; the depth and length for the short groove were 40 μm and 4.24 mm, respectively, and the space between the two grooves was 2.85 mm. Conclusions The microscopic 3D morphology testing system is an effective instrument for measuring the surface morphology of human incisors accurately.

Abstract:Objective To study the law of shape changes of mandiblular distraction osteogenesis in the patient with hemifacial microsomia(HFM) and compare the results with the real effect on the patient by establishing the models of mandibular and masticatory muscles, and to put forward some good suggestions on procedures of treating patients diagnosed as HFM and related cases. Methods Based on the original data of the patient with HFM, combined with the MIMICS software (medical image control system software), the model of the patient’s mandibular and masticatory muscles was constructed by applying the technique of three dimensional (3D) reconstruction, and then put the entity structure into the ANSYS software to simulate the effect of the surgery. Results The established preoperative and postoperative finite element analytic model could present the characteristics such as digitalization and individuation. Conclusions Compared with the effects of the real surgery for the same patient, the result of numerical simulation showed to be good matching and could provide personalized guidance for different patients before their operation.

Abstract:Objective To design a global sliding mode control algorithm for the purpose of eliminating the chattering effect in conventional sliding mode control algorithm on both the controller and controlled plant from the conventional sliding mode control algorithm and regulating the intra aorta pump in response to the demand of blood circulation system in human. Methods A dynamic disturbance compensator was used to estimate the uncertainty of the intra aorta pump control system. Computer simulations and in vitro experiments were also conducted to verify the dynamic characteristics and robustness of the controller. Results As the dynamic disturbance compensator was used to estimate the uncertainty of system, the chattering effect in sliding mode control algorithm was eliminated. When the reference flow rate was set at 5 L/min, the response time was 80 ms without any overshot and static error. When the load torque of the controller was increased to 0.4 N·m, the response time was 25 ms. When the pulsatile signal was input as the reference flow rate, the dynamic response time was 80 ms with the maximum error of flow rate being 0.03 L/min. In the in vitro experiments, as the feedback frequency of flow rate signal and pump speed signal were lower than that in the ideal condition, the controller performance was deteriorative compared with computer simulation. The experimental results demonstrated that when the reference flow rate was set at 5 L/min, the response time was 0.26 s with the error of flow rate being 0.1 L/min. Conclusions The controller provided in this paper can accurately regulate the intra aorta pump according to the reference flow rate. Furthermore, it has a strong robustness for the uncertainty and disturbance of the control system. Due to the use of dynamic disturbance compensator, the chattering effect of the algorithm has been eliminated.

Abstract:Objective To provide theoretical reference for the research on lateral postural control in older people by using the electromyography （EMG）technique to compare the neuromuscular reaction between the young and older people during lateral perturbation. Methods Postural reactions of 14 young people and 14 older people as subjects were evoked by sudden unpredictable medio lateral translation platform. The surface EMG data were collected from peroneus longus, anterior tibialis, gluteus medius and erector spinae of the left side of the body. Results The latencies in anterior tibialis, gluteus medius and erector spinae were obviously delayed in older people, and the duration of time to peak in peroneus longus, anterior tibialis and gluteus medius of older people was much longer than that of young people. Conclusions The delayed response of ankle, hip and trunk muscle and the low efficacy of contraction rate in ankle and hip muscles to the unexpected perturbation might be the primary reason for the decrease of lateral postural control in older people.