Abstract:Cellular and molecular biomechanics is one of major fields in biomechanics, and much progresses in mechanobiological and/or mechanochemical coupling have been made in the past three decades. As the most active field in biomechanics and biomedical engineering, it makes great impacts in biology, medicine, as well as agriculture. Here the conceptual framework, scientific issues, and methodological approaches in the field were reviewed, and some of open issues were discussed.

Abstract:Digital image correlation (DIC) is a non-contact optical method, which can be widely applied to characterization of mechanical behavior of biological materials. This paper described the basic processes of this method in determining the displacement and strain components. Three applications were presented to illustrate how this technique was applied. The first application was to evaluate the mechanical behavior of the bovine artery (soft tissue). The second was to identify the fracture toughness of human dentin (hard tissue). The last was an example to measure shrinkage strain of human dentin at microscopic scale.

Abstract:Objective A novel technology of microcantilever sensor platform for label-free detection of clenbuterol antigen-antibody specificity binding is reported. Methods Thiolated clenbuterol antibody was immobilized on the gold-coated side of the microcantilever by self-assembled monolayer technique. Consequently the deflections of the microcantilever corresponding to the process of injecting different concentration of clenbuterol antigen were real-time monitored by optical lever technique. The activity of thiolated clenbuterol antibody and the clenbuterol antigen-antibody binding on the gold-coated side of the microcantilever were confirmed by an Enzyme-Linked Immunosorbent Assay (ELISA). Results The sensitivity of detecting clenbuterol is better than 1ng/ml. Microcantilevers functionalized with thiolated clenbuterol antibodies were exposed to 1 μg /ml of Chloramphenicol (CAP), and no significant response was detected, which confirmed the specificity of the immobilization method. In addition, clenbuterol antigen-antibody binding on the microcantilever generates a compressive surface stress and the surface stress is linear to logarithm of clenbuterol concentration over a range of concentration from 1ng/ml to 1μg/ml. Conclusions It is possible for detection of clenbuterol by microcantilever sensor platform.

Abstract:Objective To study the effect of different carotid artery flow waveform on the wall shear stress of carotid artery bifurcation. Methods Special software is used to construct the carotid bifurcation TF-AHCB numerical model. Womersley method is used to compute Bloch and Holdsworth that two classic blood flow velocity profiles, and this two velocity profiles were inputted separately into CFD software as inlet conditions to compute the flow field and wall shear stress distribution of carotid artery bifurcation. Results Low wall shear stress zones of carotid artery bifurcation outboard root produced by different flow waveform are similar, but Holdsworth waveform makes oscillatory shear index increased significantly because of its lower dicrotic notch. Oscillatory shear index produced by Holdsworth waveform is the Bloch waveform’s 1.75 times and in some areas high up 0.49. Conclusion In the carotid artery bifurcation hemodynamics numerical experiments or simulant experiments, correctly inlet flow waveform and velocity profile conditions are important.

Abstract:Objective To analyse the influence from the change of blood flow at T-bifurcation vessel on thrombus formation from hydrodynamics perspectives, which mainly considers blood velocities, branch vessel diameters, T-bifurcation angles and blood viscosities. Combined with pertinent medical cases, the hypothesis in medicine about thrombus formation here is studied and validated from multidisciplinary angle. Method The geometry model of T-bifurcation artery is created to numerically analyse the flow field in vessel and the influence of different kinds of blood flow on thrombus formation. Results There are two "larger-regional" vortexes in the main and branch vessel near bifurcation. In addition, downstream the bifurcation joint there is also a smaller region, where local velocity is low and shearing stress appears to abruptly increase. This is in favor of thrombus, so to be "location apt to thrombus". Conclusions Thrombus formation in "location apt to thrombus" also has close relationship with branch vessel diameter, blood velocity, bifurcation angle and blood viscosity.

Abstract:Objective To simulate the instantaneous central trajectory of four-bar artificial knee joint and to analyze the stability of the prosthetic system. Methods By establishing a model for the instantaneous center trajectory and the stability of four-bar artificial limb knee, a simulation software package was developed based on LabView programming platform. Results The dynamic trajectory of the instantaneous center of four-bar artificial knee joint was simulated in the developed software system, showed in animation, and calculated the value of x/y – the value of the hip torque needed to maintain the body’s stability, and saved the relevant data. Compared to actual data, the software could accurately describe the instantaneous center of four-bar artificial knee joint. Conclusion Preliminary test results showed that the developed software system was able to provide both visual display and numerical results of the instantaneous central trajectory of four-bar artificial knee joint and its stability. These would help engineers and clinicians in the design and optimization of four-bar artificial knee joint mechanisms.

Abstract:A review of cell traction forces (CTFs) measurement based on Biological Micro Electromechanical Systems (BioMEMS) microposts matrix is presented. CTFs are exerted by cells and transmitted to the underlying substrate through focal adhesions and close contacts, which is essential for cells movement. Cells probe the mechanical compliance of the extracellular matrix (ECM) in part by locally deforming it with nanonewton-scale traction forces. Precision measurement of CTFs is significant for many researches such as cell biology and tissue engineering and so on. Enabled by the advancement in BioMEMS technology, surface treated high aspect ratio Polydimethylsiloxane (PDMS) microposts matrix devices, which serve as BioMEMS sensors for detecting cellular nanoforces and studying in vitro cell mechanics, have been developed. Closely spaced vertical microposts matrixes were designed to encourage cells to attach and spread across multiple microposts, and to bend the microposts like vertical cantilevers as the cells locomote on the surface. Using this dense and discrete matrix of microposts rather than a conventional continuous substrate, CTFs can be directly measured and quantified by processing the microscopy images of the deformations of microposts. The resolution of the force was in tens of nN/?m scale. At first, the conventional CTFs measurement methods were concisely summarized. Then BioMEMS microposts matrix method was described in detail, including principle and fabrication process, surface treatment and cell experiment results. Furthermore, high aspect ratio structure collapse problem was investigated.

Abstract:Objective To investigate the effect of the cirrhosis and detachment of the ligaments, tendons and stapes replacement prosthesis on the sound transmission of the human ear. Method Based on the CT data, the geometrical model of human ear is established by a C++ program developed by the authors. Then numerical model is built up through the finite element software PATRAN where the geometrical model is imported and the material properties, interface of the joints and boundary conditions is defined. Result Amplitude variation laws of the stapes footplate and umbo are obtained by comparing the frequency response analytic results between the normal ear and pathological ear, Moreover, the sheath shaped stapes replacement prosthesis is constructed based on the analysis of the numerical model developed by the authors. Conclusion The accuracy of the model in this paper has been validated by the well matched computational and experimental results in normal ear, and it can be used to simulate the human transmission. The computational results of pathological ear can explain the effect of lesion for sound conduction from the mechanical view, and provide a reference for the treatment of ear illness. Comparing with the effect of the ring shaped stapes prosthesis which is commonly used in our country, the sheath shaped stapes replacement prosthesis is more suitable for the physiological function of the human ear and the hearing recovering effect will be better.

Abstract:Objective To determine the biomechanical behavior of porcine cornea by establishing the relationship between the young’s modulus and intraocular pressure (IOP). Methods Eleven fresh porcine corneal specimens were examined under inflation conditions to determine the constitutive relationships of the material through static loading conditions (pressure range: 25mmH2O~1000mmH2O). The forward deflection of porcine anterior corneal apex was measured by the laser displacement sensor. The pressure-deformation results were analyzed on the basis of shell theory to estimate elastic modulus of the cornea and derive its relationship with IOP. Results The porcine corneas showed a nonlinear corneal forward displacement/IOP and stress/strain relationship with an initial low stiffness stage and a later high stiffness stage. In spite of the nonlinearity between the internal pressure and apex forward deflection, the relationship between the young’s modulus and the IOP was almost linear. Conclusions The inflation configuration can be used to estimate the mechanical property of corneas, and the resulted material parameters could be applied to numerical simulations of refractive surgery procedures, contact lens fitting, artificial cornea design and other applications.

Abstract:Objective The affecting factors of bond strength between metallic orthodontic bracket and tooth surface were studied. Methods The bond strength of two samples were tested，observing the picture of bracket base structure. Micro-hardness was tested by hardness tester. The elemental composition of two samples was studied by using energy dispersive X-ray spectroscopy (EDX). Results (1)The bond strength of two samples were different;(2)The base structure of samples were obvious difference;(3)The Vickers Hardness of two samples was comparable; (4)The elemental composition of two samples was similar. Conclusions The base structure of bracket has significant influence on bracket’s bond strength.

Abstract:Objective This rotated-compression experiment of adult pelvis of wrist cartilage was to provide some relevant evidences to the injury and chronic strain of this configuration, and to prevention and cure of it. Method Histological experiments of pelvis of wrist cartilage of normal adults. Result Regular pelvis of wrist cartilage is fibro cartilage, and the fiber array of all parts in it are different according to various structure functions; also vascular is rich, but no nerve visible. After durative and rotated pressure experiments, tissue cells in pelvis of wrist cartilage were deformed, cartilage lacuna was nearly disappeared, and vascular was injured. Conclusions The histological structure of pelvis of wrist cartilage has functionally adaptation, and ample vascular to provide nutrition. However, excessive load can make histology structure changed, which loses supply of nutrition, and is fatigue injured.

Abstract:Objective To evaluate the effects of Wnt/β－catenin signals on the callus modelling and the biomechanical properties of the fractured tibia in mice. Methods Col2al-ICAT transgenic mice were used and ICAT transgene could specifically expressed in chondrocytes and served as a competitive inhibitor to block Wnt/β－catenin signals. 8-week-old Col2al-ICAT mice and WT littermates were used in each group and a transverse osteotomy was performed at the middle of the tibia. Fractured bones were stabilized by inserting the inner pin in the cavity. Roentgenography, histology observation and four point bending test were used to compare the callus modelling and biomechanical properties of fractured tibia between two groups 5 weeks after surgery. Results The roentgenograph revealed that the fracture repair were completed in the WT mice while the fracture line was still visible in the Col2al-ICAT mice. Histology sections showed that there were thicker cortical bone and less woven bone in WT mice than in Col2al-ICAT transgenic mice. Four-point bending test showed that the maximum breaking load of fractured tibia in WT mice was significantly higher than in Col2al-ICAT transgenic mice. Conclusion The block of Wnt/β－catenin signals could delayed the callus modelling and then the recovery of the biomechanic properties of fractured bone.

Abstract:Objective To study the geometric features of proximal femur for the Chinese AVN population so as to provide anatomical references for hip prosthesis selection and design. Methods From January 2004 to August 2008, we collected 186 patients which 281 hips undertaken total hip arthroplasty for AVN. All the standard anteroposterior(AP) and mediolateral (ML)X-ray films were obtained and measured to observe the proximal canal geometry by curve fitting technique. All cases with completed data were analysed respectively according to gender and age. Results 59 cases couldn’t obtain completed data and were excluded for unclear cortical margin and severe collapsed femoral head. The completed data from 127 cases were studied and successfully established medial, lateral, anterior and posterior curves to observe the proximal canal geometry. According to age, the medial part of the distal femur had statistical difference, while according to gender, there was no statistical difference. However, compared with data of normal Chinese population, there was difference at the proximal part of lesser trochanter. Conclusion We gained a large series data of AVN proximal femur and fitted 4 curves for describing the canal of AVN population. The results not only provide useful information of AVN, but also indicate that AVN, as a kind of disease, has the potential of an independent factor affecting the geometric features of proximal femur.

Abstract:Objective To investigate how to treat distal femur fractures by using unicortical or bicortical screws in the proximal end of the less invasive stabilization system, LISS. Methods We took 115 Caprine right femurs, and all of them were created to simulate an AO/33-A3 fracture. All fracture models were fixed by a right 5 hole LISS Plate. They were treated differently by using unicortical or bicortical screws in the proximal end of the LISS plate, and at the same time, they were tested by withdrawal force and torsional force. Results When we using bicortical locked screws in the first and third hole of the proximal end of LISS, it reached the best balance with the distal end, and it created the biggest force to resist torsional force. Conclusion In this test, we can conclude，that using bicortical screws in the first and third hole of the proximal end of the LISS is the best way when we treat distal femur fractures AO/33-A3, it can reach the best balance with the distal end, and it created the biggest force to resist torsional force, and it can decrease the shearing force, torsional force, and then it can prevent hardware failure.

Abstract:Finite element analysis is able to calculate the stress and strain changes of modeled structures. It has unique advantages in the biomechanical research on foot and ankle.It is also important in the clinical researches on etiologies, pathologies and treatments of foot and ankle. Current researches in foot and ankle finite element analysis include tendon and muscle mechanics, bone stress/strain distribution in pathological condition, internal fixation stabilities. In addition, orthosis and footwear design.It also combines plantar pressure analysis for etiological and therapeutic research.

Abstract:Foot arch includes medial, lateral longitudinal arch and transverse arch. Deep research has been performed on its construction, biomechanics and clinical significance of longitudinal arch. However, the study of transverse arch is deficient. There are some different opinions on the construction and biomechanics of transverse arch, which becomes one of the hot issues. This paper focuses on reviews of the progress of foot transverse arch researches in recent years.