Objective The influencing parameters of solid and fluid computing fields for the scaffolds models with regular square holes were discussed by nonlinear fluid-solid-coupling approaches.The numerical computational resuits of which the models were regarded as both rigid body and non-linear elasticity were compared as well.Method One direct fluid-solid-coupling approach and two indirect fluid-solid-coupling approaches were adopted,and the calculating reliability of three kinds of fluid-solid coupling methods was verified.Rasults The solid-fluidcoupling computational results are obtained in light of 12 kinds of scaffolds models which are constructed by 3 groups of square side length(50,100 and 150 μm)and 4 groups of porosity(61%,65%,77%and 84%).The field parameters of those solid models including stress,strain and displacement and those fluid models including static pressure,velocity,wall shear stress and strain rate are achieved and compared.Conclusion There appear some difference between the results of porous scaffold models as a rigid body and as non-linear elasticity.The different porosity with the same pore radius or the different pore radius with the same porosity would affect the field parameters of solid models and fluid models in varying degrees.

Objective To explore the isometry of grafts in PCL(posterior cruciate ligament)double-bundle re-construction under femoral tunnel shifting condition.Method Knee specimens from ten fresh frozen cadavers were used.PCL were divided into anterolateral bundles(ALB)and posteromedial bundles(PMB)to the inser-tion footorint.The anterior,postedor,proximal,distal and central points of the two bundles'femoral attachment site were respectivelyanchored to the middle of the PCL's tibial attachment site by the trial wires.Changes in length of the intra-articular part of the wires were recorded while the knee was flexed from 0°to 120°.Result The length changes in every point were compared.All of the maximal length changes of ALB's proximal,pos-todor points and PMB's proximal points were not greater than 2mm.No significant difference between the length changes of ALB's proximal point and posterior(P=0.864>0.05)was found.Conclusions The femo-ral tunnel for the PCL double-bundle reconstruction should be located as follows:ALB should be at the middle point of upper edge of femoral attachment site(proximal point),while PIVIB at the middle point of femoral attachment site(proximal point).

Objective Prepare biomimetic muitilayered scaffold which has similar structure of natural cartilage.Method By lyophilizing the scaffolds which were prefrozen at-20℃ and in liquid nitrogen successively,we prepared double-layered spongy scaffolds.By partially thawing the prefrozen samples and refreezing them in liquid nitrogen before the final liyophilization,we prepared biomimetic multilayered scaffolds with about 2mm thickness.XRD and FT-IR were used to confirm the interaction between collagen and chitosan.SEM was used to observe the morphologies of the scaffolds.The mechanical properties of pure chitosan scaffolds,pure collagen scaffolds,composite single-layered scaffolds and biomimetic multilayered scaffolds were compared both in dry and wet conditions.Results There was chemical interaction between collagen and chitosan.Composite materials will form better pore structure.The biomimetic multilayered scaffolds have upright pores,round pores and a dense layer from bottom to top of the scaffolds.The scaffolds have quite different mechanical properties between dry and wet state.Under wet state,the different layers of the biomimetic muitilayered scaffold have different mechanical properties.Results The biomimetic structure of the multilayered scaffold is very close to that of the natural articular cartilage,and the different layers of the biomimetic muitilayered scaffold had different mechanical properties under wet state.These are hopefully beneficial to help maintain the phenotypes of chondrocytes and promote the repairing effect of cartilage defects.

Objective To adopt a three-dimensional limited element analytic method to research into the cause and mechanism of the complications taking place after resection of head radius.Method To adopt a three-dimensional limited element analytic method to research into the stress transmission action of the head radi-us and the distribution alteration of the stress transmission after resection of head radius impacting on the stability of elbow and wrist.Result In normal cases,the stress value transmitted via head of radius takes 58% of the stress placed,36.85% via humeroulnar joint.The head of radius places a leading role in the stress transmission of the elbow joint.After rasection of the head of radius,the lateral of humeroulnar joint bears about 43% of the stress placed while the medial part bears about 21.6% of the stress.To compare with that before the resection of the head of radius the stress on the lateral is obviously increased more than the medial part.Conclusions The head of radius places a leading role in the stress transm ission of the el-bow joint.The resection of the head radius breaks the normal distribution of the stress on the elbow joint and produces great effect on the stability of the elbow joint and wrist joint.Therefore,in clinics we should pay great attention to the indication of rasection of the head of radius.

Objective In order to avoid potential injuries imposed to human body,it could be feasible to use the musculoskeletal models which can be reconstructed from the cadaver color cryosection(CCC)images,computerized tomography(CT)images,magnetic resonance(MR)images or other images to analyze the dynamic properties of muscles in vivo during human movement.Mothod We reconstruct the lower limb musculoskeletal model and define the uniform ioint coordinate system(JCS)on the model and the subject.The coordinate transformation of the muscle attachment points both on the model and the subject is described in detail.Results The length and the moment arm of the biceps femoris(short head)during knee flexion are calculated and analyzed.Conclusion This method plays an important role in improving the kinematics and dynamic simulation and the muscle force estimation.

Objective To evaluate the biomechanical effects of using a new injectable calcium phosphate cement to consolidate the fixation of osteoporotic intertrochanteric fracture.Method Five matchod pairs of human cadaver femora were used to produce the model of intertrochanteric fracture.All fractures were fixed with dynamic hip screws(DHS),and divided into two groups.In the CPC consolidation group of each pair,CPC was used to grout the hip screw and to fill the posteromedial defect.All femora were subjected to biomechanical test.Results Under the loading of 500 N,in the CPC consolidation group,the mean axial stiffness is(691.93±18.90)N/mm and the horizontal shear stiffness is(5553.84±27.47)N/mm.The mean lateral and medial strength is(5.15±0.35)MPa and(4.13±0.24)MPa.The torsion stiffness was 0.41 and the ultimate loading is(3580±286)N.In the control group,the mean axiak stiffness is(453.45±19.75)N/mm,the horizontal shear stiffness is(3848.87±22.63)N/mm,the mean lateral and medial strength is(3.12±0.37)MPa and(1.80±0.21)MPa,and,the torsion stiffness is 0.35 and the ultimate loading is(2512±189)N.Consolidation fixation with CPC increased each of the biomechanical efficiency(P＜0.05).Conclusions CPC consolidation of osteoprotic femoral head and the medial defect of intertrochanteric fracture can significantly improve the overall stability and decrease the rate of postoperative complication.

Objective To study the stability of micro-implant orthodontic anchorage(MA)with different pitch in the case of immediate loading.Method Employing 3D finite element analysis method,the stress and dis-placement distribution on the bone interface of MIA with different pitch(0.3 mm、0.5 mm、0.7 mm and 1.0 mm,respectively),which was 1.47 N loaded vertically in the major axis direction,were analyzed.Result The pitch affected the stress distribution significantly,because the maximum stress increased with the pitch decreasing and the impact of pitch on stress distribution on neck and central locations of MIA were different;to decrease the pitch could reduce the max displacement of the jaw,but the impact of pitch on displacement distribution of MIA was not significant.Condusions In the case of immediate loading.MIA with pitch 0.5 mm-0.7 mm is suggested to be selected as orthodontic anchorage in the clinic.

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 ansmitted to the underly-ing substrate through focal adhesions and close contacts.which is essential for cells movement.Cells probe the mechanicaI compliance of the exlracellular mabix (ECM) in part by locally deforming it with nanonewton-scale traction forces.Precision measurement of CTFs is significant for many researches such as call biology and tissue engineering and so on.Enabled by the advancement in BioMEMS technology,surface treated high aspeect ratio Polydimethyisiloxane(PDMS)micropos matrix devices,which serve as BioMEMS sensom for de-tecting cellular nanoforces and studying in vitro cell mechanics,have been developed.Closely spaced vartical 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 dis-crete matrix of microposts rather than a convanfional 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/μm scale.At first,the conventional CTFs measurement methods were concisely summa-rized.Then BioMEMS microposts matrix method was described in detail,including principle and fabfication process,Surface treatment and cell expedment results.Furthermore,high aspect ratio structure collapse prob-lem was investigated.

Objective To improve the long-term biocompatibility and mechanical stability of Titanium alloy implants.Method Micro-nano patterned TiO_2 thin films have been prepared on TC4 substrates via a sol-gel dipcoating method with Ti(OC_4H_9)_4(TEOT)as precursor and polyethylene glycol(PEG)as organic template.The Influence of PEG concentration upon the morphology of the target films has been studied by using AFM.The wettability and tribological properties of the target films have been studied by means of optical contact angle measuring instrument and UMT-2.Results When increasing the PEG concentration to 3.5 g/100 mL,a parallel arranged groove structure can be obtained on the surface of the sample;compared with TiO_2 sol-gel film without adding organic template,the wear resistance of the patterned film is better.Conclusions The feature of the patterned TiO_2 films can be controlled by adding different amount of Organic template;and it has been proved that a certain kind of patterned structure can imeprove the wear resistance of the film.

Tissue engineering is one of the most promising subjects,which has broad application prospects in the fields of regenerative medicine and human health care.According to the papers published in this current issue about scaffold material preparation and mechanical environment affection to cells during the construction process of tissue engineering,this paper describes the current status and progress of tissue engineering research at home and abroad,indicating that tissue engineering research is developing to a deeper and wider field.