Abstract:Objective To study the influence of intracapillary-transcapillary-interstitial unsteady coupling flow on the whole flow field and drug delivery in solid tumor. Methods Develop coupled fluid flow model. Intracapillary flow is governed by Navier-Stokes equations, transcapillary and interstitial fluid flow are described by Starling's law and Darcy's law respectively. Simulate the unsteady flow caused by step increase of capillary pressure and pulsating analytically and numerically. Results Relative to intracapillary, transport of pressure in the interstitium has hysteresis effect. The change of intracapillary flow will arise transient redistribution of interstitial fluid, and as a result, transcapillary pressure and interstitial pressure gradient will be increased. Conclusion Unsteady flow could increase transmural transport of drug and convective diffusion in tumor tissues as well.

Abstract:Objective To investigate how fluid shear stress regulates the expression of tissue factor (TF) in Endothelial cells. Methods The endothelial cells were subjected to fluid shear stress of 12 dyn/cm2(1 dyn/cm2=0.1 Pa) for 20 min in the flow chamber, and then the expression of Egr-1 and Sp1 during the expression of TF gene were detected by elector-phoretic mobility shift analysis (EMSA) and Western Blot (WB). Results (1) Only the expression of Spl was detected in static group and no Egr-1 expression was found; (2) Shear stress caused the level of phosphorylated Sp1 and the expression of Egr-1 increasing; (3) EMSA showed that Egr-1 had more competence than Sp1 in binding sites of the Sp1/Egr-1. Conclusion The nuclear transcription factors could play different roles in the process of the expression of TF gene: Spl is crucial to the basal expression of TF gene in the static condition, the displacement of Sp1 by Egr-1 and phosphorylated Sp1 may be involved in the expression of TF gene induced by fluid shear stress.

Abstract:Objective The three-dimensional knee model has been developed to compute the kinetics of patella-femoral joint. Methods The three-dimensional skeletal model, including superior end of tibia, inferior end of femur and patella, has been developed based on CT image processing and CAD technology. In addition, quadriceps has been defined as straight-line model with ligaments and other soft tissues defined as non-linear elastic fiber model. Quadriceps forces were used as input control variable. Results Such an effective model has been built up successfully in this way. Conclusion It is useful for some kinetic parameters in gait of patella-femoral joint to be computed based on this model.

Abstract:Objective To simulate the growth of axons in the developing nervous system numerically. Methods A set of mixed parabolic-gradient nonlinear equations was established based upon the principles of the developing neural biology, which was computed by the ADI scheme and the modified Euler' s method. Results (1) In the first case that one target was uniformly surrounded by ten axons in a square area, the pathway of the growing axons we simulated coincided with those obtained by the formers; (2) in the second case that a group of two-by-two-placed targets was surrounded by the same axons as in (1), the results correctly reflected the chemotaxis of the growing axons; (3) in the final case that a stream of targets lined near the upper edge of the square area and a stream of axons lined near the lower edge, the results approximately displayed the bundling and debonding courses of the growing axons. Conclusion The mathematical model and the numerical method presented in this paper can simulate the main phenomenon observed in the related experiments.

Abstract:Objective To provide theoretical basic for clinical judge of bone healing and to determine the removing time of the outer fixator by comparing the healing speed of transverse fracture with that of oblique fracture in the same locality under the same condition. Method Using three-dimensional limited elementary analytic method to analyze the maximum stress values, the maximum shifting quantity and the maximum quantity between the two far endings of extremities in the middle of the skeleton under the same condition as the callus with the same mechanical function filling up the both endings when placing the same loads on the perpendicular axis, transverse axis and the sagittal axis, and to compare the differences between the two kinds of fractures-transverse fracture and oblique fracture. Result At the far ends of the extremities under various kinds of loans, the stress and shifting shows little difference in the same surface for the transverse fracture. To make it broken, the loads need to reach fairly high value. For the oblique fracture, the stress and shifting appeared on them are rather distinctive because the two endings of the fracture were not in the same surface. The near end received more power and appeared less shifting while the far end received less power but larger shifting. Only bythe less loads could make it broken .The near end would become broken first, and affected the whole fracture line because of the dense of stress, then caused afresh fracture. Pressure or extension placed upon the perpendicular axis induced less shifting on the far end of the extremities while pressure placed upon the horizontal axis and the sagittal axis could cause larger shifting even though with the less pressure. Conclusion In the same locality and under the same condition of mechanical function, the transverse fracture could be concrescence faster than that of the oblique fracture.

Abstract:Objective To study three-dimensional finite element model of pelvis and make its stress analysis after-sacrum tumar excision. Methods By using theanalysis software-"ansys", we have established two models: the whole pelvic model and the model after- sacrum tumar excision, and compare the stresses getting from the models. Results After establishing the two models and loading on them respectively, the results were got as following:(1) In the whole pelvic model, the forcestransmittedalong theroute: lumbar→sacrum→sacroiliac joint→ilium→ischial. For each of the node, the force distribution is symmetrical with limited intensity of pressure . While in the model with sacrum tumar excision, the transmission is affected. (2) In the SF model, the forces of nodes in the sacroiliac joint and ischium are larger than that in the same nodes in the whole pelvic model,which may cause the stability of pelvic is descend and the opportunity of loss of pelvic integrality is ascend. Conclusion By establishment of pelvic three-dimensional finite element model after- excision of sacrum tumar and its stress analysis comparing with the whole pelvic model, it is proved that its stability has been changed.

Abstract:Objective To evaluate the biomechanical properties of the callus during osteoporotic fracture healing with the treatment of low-intensity pulsed ultrasound (LIPUS) in rats. Methods Forty-two female SD rats of 4.5-month-old were involved in the study ,36 of which underwent bilateral ovariectomy. Ten weeks later when the osteoporosis was confirmed, the 36 rats had their bilateral femoral shaft closely fractured. After serious selection only 26 rats finally entered the experiment. On the day after fracture, a hind limb was chosen randomly to receive LIPUS as treatment withthe other limb as control. The LIPUS was done 20 minutes daily with a 200μsec burst of 1.5MHz sine waves repeated at 1kHz and an average intensity of 50mW/cm2. The rats were sacrificed on 4, 6, 8, 12 weeks after treatment, respectively, and their bilateral femurs were taken for biomechanical analysis with three point bending test. Results When compared with the control side on 4, 6, 8, 12 weeks after LIPUS treatment, respectively, the peak load of the callus in treated side was higher about 58.75%, 76.53%, 37.04%, 22.14%, the peak stress was higher about 29.21%, 66.43%, 29.08%, 16.90%, and the elastic modulus was higher about 34.01%, 61.04%, 46.15%, 31.77%. Except for the peak stress in 4 weeks and the elastic modulus in both 4 and 6 weeks, all the differences were significant (P<0.05), especially for the peak load in 6 weeks and the peak stress in 8 weeks (P<0.01). Conclusions LIPUS can improve the biomechanical properties of the callus during the osteoporotic fracture healing in rats, thus providing a new way to treat osteoporotic fractures clinically.

Abstract:Objective To describe the characteristics of cerebral vascular hemodynamic indexes (CVHI) in a rural population over 40 years. Methods Participants over 40 years were selected from a rural area by cluster sampling. General information, common risk factors of stroke were investigated and CVHIs were checked. All participants being enlisted in the study were grouped by age, gender, left and right carotid checking position. Differences of CVHIs between groups were compared and overall distributional characteristics were described. Results CVHIs, such as Vmax, Vmin, Vmean, Qmean and Dp in the population, were decreased along with ageing, while Wv, Zcv, Rv, DR and Cp were increased with ageing. There were differences of the indexes between left or right carotid, as well as male or female, but no obvious trends. Conclusions There is significant relationship between the change of CVHIs and ageing.

Abstract:Objective A 3-D solid model of a human maxillary first molar was constructed and exported into a 3D-finite element model with analysis of the stress distribution of the tooth. Methods Using the CT scanning of a normal adult, with the help of the computer program and software, a 3D finite element model was established. Three different loading conditions were simulated: vertical, lateral occlusal loading and both of them. Result Stress concentration were found on the surface where the load was applied, and at the lingual cervical part of the crown when the stresses arising from sideways and combination. Conclusion The method of this study can construct a relatively accurate model of the tooth, and provides a reasonably simple and effective model for biomechanical analysis of the molar applications.

Abstract:Computer-Aided Tissue Engineering (CATE) enables many novel approaches in modeling, design, and fabrication of complex tissue substitutes with enhanced functionality and improved cell-matrix interactions. Central to CATE is its bio-tissue informatics model that represents tissue biological, biomechanical, and biochemical information that serves as a central repository to interface design, simulation and tissue fabrication. This paper presents a study of applying CATE approach for the biomimetic design of bone tissue scaffold. A general CATE-based process for biomimetic modeling, anatomic reconstruction, CAD model based tissue scaffold design, quantitative computed tomography characterization, finite element analysis and freeform extruding deposition for fabrication of scaffold is presented.

Abstract:Shear-induced platelet aggregation (SIPA) plays a key role in arterial thrombogenesis. High shear stress triggers von Willebrand factor (vWF) binding to platelet membrane glycoprotein Ⅰ b and subsequent platelet activation, such as adhesion and aggregation. On the contrary, no SIPA phenomenons were found under low shear flow. So, SIPA is a coupled reaction in the mechanism of biochemistry and mechanics. These investigations based on the clue of proteins contribute to explore the complex molecular mechanism of SIPA.

Abstract:Tissue engineering is a kind of interdisciplinary study based on applying the principles of both engineering and life sciences for the development of biological substitutes and try to restore, maintain or improve the tissue function. Bioreactors are used in tissue engineering study as very important devices. Currently, the research on the improvement of bioreactors are mainly stressed on the biomechanics, three-dimensional culture, mass transport, the culture environment condition (pH, the oxygen tension, etc.) and physics factors such as electric filed, magnetic field, stress field,etc. The discussion about bioreactors in this paper mainly probe into the biomechanics problems of Bioreactors in tissue engineering.