Long-Term Mechanical Property Prediction of the Proximal Tibia after Knee Arthroplasty / 医用生物力学

Objective To study the short-term variation patterns of graft viscosity after anterior cruciate ligament reconstruction (ACLR) surgery. Methods Six male New Zealand rabbits were selected. The ACLR animal model of unilateral knee was made with Achilles tendon as the graft. The experimental rabbits were euthanized 15 days after ACLR surgery, with removal of the graft, healthy anterior cruciate ligament (ACL) and Achilles tendon. The cross-sectional area and viscosity coefficient of the graft were measured, and the creep experiments were carried out under equilibrium conditions of 0.1 MPa and 1 MPa, respectively. The viscosity coefficent was calculated. Variation patterns of graft viscosity were summarize. The grafts were compared with healthy ACL. Results The cross-sectional area of the graft increased slowly within 15 days after ACLR surgery. The viscosity of ACL and graft changed nonlinearly. The viscosity coefficient was quite different under different stresses. The viscosity coefficient of the graft decreased with the time after ACLR surgery, which was more obviously under the condition of low stress. Conclusions The results are helpful to guide the implementation of early postoperative rehabilitation plan after ACLR surgery .

Stress Relaxation Behavior of Collagen Type II- Silk Fibroin Composite Cartilage Scaffold under Different Degradation Cycles / 医用生物力学

Objective To study stress relaxation behaviors of cartilage scaffolds under different degradation cycles by using finite element analysis combined with theoretical models. Methods Based on the established degradation theoretical model, the elastic modulus of the scaffold was calculated under different degradation cycles. The finite element model of cartilage scaffolds was established and stress relaxation simulation was performed to analyze the variation of scaffold relaxation stress with time. The stress relaxation constitutive model was established to predict mechanical properties of the scaffold. Results The elastic modulus of cartilage scaffolds at 14 th, 28th, 42nd, 56th day after degradation was 32. 35, 31. 12, 29. 91, 28. 74 kPa, respectively. The upper layer for cartilage scaffolds was the largest. The overall relaxation stress of the scaffold decreased rapidly with time and then tended to be stable. At 8th week after degradation, the stress which the scaffold couldwithstand was still within the physiological load range of the cartilage. The predicted results of the stress relaxation constitutive model were in good agreement with the finite element simulation results. Conclusions The elastic modulus of the scaffold gradually decreases with the increase of degradation time. The longer the degradation period is, the less stress the scaffold can withstand. At the same degradation period, the larger the applied compressive strain, the larger the stress on the scaffold. Both the finite element simulation and stress relaxation constitutive model can effectively predict stress variations of cartilage scaffolds under degradation

Research Progress on Biomechanics and Mechanobiology of Articular Cartilage in 2022 / 医用生物力学

As a kind of elastic load-bearing connective tissues on bone surface in dynamic joints, articular cartilage can provide low wear lubrication, shock absorption, load transfer and other supporting functions, and has hierarchical fiber composite structures and excellent mechanical properties. As an avascular and aneural tissue,the degenerated articular cartilage lacks the capability of self-healing after damage. The high incidence of arthritisis still a hot spot in basic and clinical researches. Articular cartilage is a mechanical sensitive tissue, andmechanical environment will affect the development of tissues in different directions. Extensive researches onbiomechanics and mechanobiology of articular cartilage were conducted in 2022. Many studies on morphology, function and mechanical state of cartilage,as well as mechanical state of cartilage under different conditions were reported. Some cartilage-related loading devices were designed at animal, tissue and cell levels. Researches onthe repair of cartilage degeneration and injury under mechanical loads were carried out in vitro and in vivo, andsome important repair method and means were obtained. The biomechanical and mechanobiology research on articular cartilage is the basis of arthritis, cartilage defect and repair. The influence of quantitative mechanical under 4 conditions on the repair of articular cartilage injury needs further study in vivo and in vitro

Numerical Analysis on Micro-Element Streaming Potential of Articular Cartilage / 医用生物力学

Objective To investigate the distribution of streaming potential generated by interstitial fluid flow in articular cartilage and obtain electrical characteristics of articular cartilage. Methods The governing equation of fluid and electrostatic theory were combined to establish a two-dimensional (2D) micro-element model of cartilage, and the steady streaming potential generated in microelement under certain pressure was calculated by finite element method. Results The streaming potential in micro-pore model of articular cartilage with the length of 5 μm was about 38.4 μV. The effect of external pressure and Zeta potential on streaming potential of articular cartilage model was significant and showed a linear increase relationship. The streaming potential decreased with the increase of ion number concentration, but the concentration had different effects on streaming potential of articular cartilage. When the ion number concentration was low, streaming potential was more dependent on ion number concentration. When ion number concentration was high, the effect of ion number concentration on streaming potential was very small. Conclusions The results of this study provide important theoretical basis for differentiation and proliferation of chondrocytes, prevention and treatment of articular cartilage diseases, development of tissue-engineered cartilage and repair of articular cartilage injury by means of electric current, electric field and electromagnetic field stimulation.

Experimental study of the response of articular cartilage surface roughness to load / 生物医学工程学杂志

Cartilage surface fibrosis is an early sign of osteoarthritis and cartilage surface damage is closely related to load. The purpose of this study was to study the relationship between cartilage surface roughness and load. By applying impact, compression and fatigue loads on fresh porcine articular cartilage, the rough value of cartilage surface was measured at an interval of 10 min each time and the change rule of roughness before and after loading was obtained. It was found that the load increased the roughness of cartilage surface and the increased value was related to the load size. The time of roughness returning to the initial condition was related to the load type and the load size. The impact load had the greatest influence on the roughness of cartilage surface, followed by the severe fatigue load, compression load and mild fatigue load. This article provides reference data for revealing the pathogenesis of early osteoarthritis and preventing and treating articular cartilage diseases.

Numerical Analysis on Degradation of Cartilage Scaffold under Perfusion Loading / 医用生物力学

Objective To study the effect of irrigation mechanical stimulation on scaffold degradation by numerical simulation, so as to predict its degradation degree. MethodsBased on perfusion experimental data, the fluid-solid coupling model was established by Comsol. The finite element model of scaffold was established by ABAQUS. Based on the models, the degradation performance of scaffold was simulated and predicted. Results The fluid-solid coupling simulation showed that the initial pressure at the speed of 15.79 mL/min was two-fold of that at 7.89 mL/min. Along the thickness of scaffold from the surface to the bottom, the pressures between the two velocities were decreased and gradually close to each other. The degradation of scaffold structure could be simulated dynamically by combining the degradation constitutive model with the finite element model. The obtained degradation data were consistent with the experimental data, and the residual molecular weight reached 0.643 on the 56th day. Compared with the experimental data, the simulation accuracy was higher than 98%. Conclusions The larger the perfusion velocity is, the greater the pressure on scaffold will be. Under the same perfusion velocity, the maximum force occurs on the surface of scaffold. The degradation pattern of scaffold can be predicted by applying the degradation constitutive model and the finite element model.

Study on transport of small molecule rhodamine B within different layers of cartilage / 生物医学工程学杂志

The small molecule nutrients and cell growth factors required for the normal metabolism of chondrocyte mainly transport into the cartilage through free diffusion. However, the specific mass transfer law in the cartilage remains to be studied. In this study, using small molecule rhodamine B as tracer, the mass transfer models of cartilage were built under different pathways including surface pathway, lateral pathway and composite pathway. Sections of cartilage at different mass transfer times were observed by using laser confocal microscopy and the transport law of small molecules within different layers of cartilage was studied. The results showed that rhodamine B diffused into the whole cartilage layer through surface pathway within 2 h. The fluorescence intensity in the whole cartilage layer increased with the increase of mass transfer time. Compared to mass transfer of 2 h, the mean fluorescence intensity in the superficial, middle, and deep layers of cartilage increased by 1.83, 1.95, and 3.64 times, respectively, after 24 h of mass transfer. Under lateral path condition, rhodamine B was transported along the cartilage width, and the molecular transport distance increased with increasing mass transfer time. It is noted that rhodamine B could be transported to 2 mm away from cartilage side after 24 h of mass transfer. The effect of mass transfer under the composite path was better than those under the surface path and the lateral path, and especially the mass transfer in the deep layer of cartilage was improved. This study may provide a reference for the treatment and repair of cartilage injury.

Enzyme-instructed and mitochondria-targeting peptide self-assembly to efficiently induce immunogenic cell death

Immunogenic cell death (ICD) plays a major role in cancer immunotherapy by stimulating specific T cell responses and restoring the antitumor immune system. However, effective type II ICD inducers without biotoxicity are still very limited. Herein, a tentative drug- or photosensitizer-free strategy was developed by employing enzymatic self-assembly of the peptide F-pY-T to induce mitochondrial oxidative stress in cancer cells. Upon dephosphorylation catalyzed by alkaline phosphatase overexpressed on cancer cells, the peptide F-pY-T self-assembled to form nanoparticles, which were subsequently internalized. These affected the morphology of mitochondria and induced serious reactive oxygen species production, causing the ICD characterized by the release of danger-associated molecular patterns (DAMPs). DAMPs enhanced specific immune responses by promoting the maturation of DCs and the intratumoral infiltration of tumor-specific T cells to eradicate tumor cells. The dramatic immunotherapeutic capacity could be enhanced further by combination therapy of F-pY-T and anti-PD-L1 agents without visible biotoxicity in the main organs. Thus, our results revealed an alternative strategy to induce efficient ICD by physically promoting mitochondrial oxidative stress.

Development of Strain Loading Device for Adherent Cells in vitro / 医用生物力学

Objective To design a novel strain loading device for studying the mechanical biology of adherent cells. Methods Based on the technology of substrate deformation loading, the device adopted controllable stepper to cause deformation of the silastic chamber, so as to realize cell loading with multiple units and large strain. The device was developed to test its loading functions. The three-dimensional (3D) models of the silastic chamber were established to simulate the loaded chamber by the finite element technology, and uniformity of the strain field was analyzed. The device applied 5% strain to bone marrow stromal cells (BMSCs) with 0.5 Hz stretch frequency at 2 hours per day for 5 days, and an inverted phase contrast microscope was used to observe the morphology of BMSCs. Results The developed strain loading device for adherent cells in vitro could provide mechanical unidirectional strain up to 50% with three groups of cell loading substrates; within the 10% stain range, the area of uniform strain filed on the silastic chamber remained above 50%, which ensured that the cells were loaded evenly; the morphology of BMSCs was obviously altered, and the direction of arrangement tended to be perpendicular to the loading direction of principal strain. Conclusions The device shows the advantages of reliable operation, wide strain range, adjustable frequency and convenient operation. It can be used to load multiple cell culture substrates at the same time, which provides convenient conditions for the study of cell mechanobiology.

Effects of Collagen Fiber Bundle on Mechanical Properties of Articular Cartilage / 医用生物力学

Objective To study the effects of collagen fiber bundle on mechanical properties of articular cartilage, so as to provide references for clinicians to guide the rehabilitation of patients with early cartilage injury. Methods The two-dimensional (2D) numerical model of fiber-reinforced porous viscoelasticity was established, with consideration of the relationship of fiber distribution, elastic modulus, porosity and permeability with cartilage depth. The influences from local fracture of the fiber bundle, the progressive fracture from the surface and the fiber bundle size on mechanical properties of the cartilage were studied, and the maximum principle strain of cartilage matrix was obtained. Results The maximum principal strain of the matrix occurred at a position in middle layer of the cartilage, about upper 1/3 of the cartilage, which was not affected by fiber breakage mode and fiber bundle size. The strain of the cartilage with thicker fiber bundles decreased. Conclusions The middle layer of the cartilage was prone to mechanical damage. The thicker fiber bundle could reduce the maximum principal strain of the matrix. Once the fiber bundle broke, the maximum principal strain of the cartilage matrix with thicker fiber bundle became larger, leading to an easier evolution of the cartilage damage.

Experimental Study on Ratcheting Behavior of Defective Cartilage under Cyclic Compressive Loading / 医用生物力学

Objective To study the ratcheting behavior of defective cartilage under cyclic compressive loading, so as to explore the pattern of damage evolution for defective articular cartilage. Methods Fresh articular cartilage was obtained from the distal femur of adult porcine, and the cartilage samples with different depth of defect were applied under triangular wave cyclic loading with different parameters. Combined with non-contact digital image technology, the ratcheting strain at different layers of cartilage was obtained. Results With the increase of loading cycles numbers, the ratcheting strain at each layer of cartilage increased sharply at first, then increased slowly and tended to be stable, and the ratcheting strain decreased gradually from shallow layer to deep layer. The response of each layer to cycle number was different. The strain in shallow layer increased rapidly within 50 cycles, while the strain in middle layer increased rapidly within 100 cycles and the strain in deep layer increased rapidly within 75 cycles. The ratcheting strain in shallow and deep layers was positively correlated with the stress amplitude and defect depth, and negatively correlated with the loading rate, while hysteresis response occurreds in middle layer. Conclusions The ratcheting behavior of cartilage was affected by special structure of the cartilage. The defect caused the strain increasing in each layer of cartilage, which could easily result in the aggravation of damage. The experiment results provide references for the construction of tissue-engineered cartilage.

Experiments study on mechanical behavior of porcine lumbar intervertebral disc after nucleotomy under compression / 生物医学工程学杂志

In order to study the mechanical behavior of degeneration and nucleotomy of lumbar intervertebral disc, compression experiments with porcine lumbar intervertebral discs were carried out. The lumbar intervertebral discs with trypsin-treated and nucleus nucleotomy served as the experimental group and the normal discs as the control group. Considering the effects of load magnitude and loading rate, the relationship between stress and strain, instantaneous elastic modulus and creep property of intervertebral disc were obtained. The creep constitutive model was established. The results show that the strain and creep strain of the experimental group increase significantly with the increase of compression load and loading rate, whereas the instantaneous elastic modulus decreases obviously, compared with the control group. It indicates that the effect of load magnitude and loading rate on load-bearing capacity of intervertebral disc after nucleotomy is larger obviously than that of normal disc. The creep behavior of the experimental group can be still predicted by the Kelvin three-parameter solid model. The results will provide theoretical foundation for clinical treatment and postoperative rehabilitation of intervertebral disc disease.

Early results of thoracic remodeling for patients with bar removal after pectus excavatum correction in minimal-procedure / 中华胸心血管外科杂志

Objective To study thoracic re-remodeling and therapeutic effect after the bar removal for pectus excavatum corrected by minimal-invasive technique.Methods 145 cases with pectus excavatum,male 115,femal 30;adults in 59,children 86;corrected by minimal-invasive technique improved and performed by the same group surgeon.Bar removed 12-82 months after the procedure,appraising index of curative effects include in chest appearance,thoracic index,thoracic computer tomography(CT) and the distance between the behind of sternum to the anterior border of thoracic spine in the sagittal view.Results The chest shape was good.Thoracic index:before bar removal 2.36 ± 0.32 in children,2.60 ± 0.45 in adults;after that,2.77 ± 0.44 in children,3.04 ± 0.56 in adults.There was all subsidence on the each point of the sternum,descent the maximum at the inferior end of the midsternum,(15.18 ±7.95)mm in children,(14.93 ± 8.81) mm in adults,comparing with bar removal before and after.There was statistical significance.Not the signs of compressing the heart on the CT view.The time interval of the bar removed 3-year in children,5-year in adults without affecting the development of the patients' thorax.Conclusion The sternum descended slightly after bar removal when pectus excavatum corrected to expecting effects.After that,thoracic remodeling again,the chest shape well.

Three-dimensional culture of chondrocytes/3D-printed composite scaffolds under compression loading / 中国组织工程研究

BACKGROUND: The silk fibroin/type II collagen composite scaffold has been prepared by low-temperature bio-3D printing technology in the previous study and the scaffold has good mechanical properties. Studies have shown that mechanical stimulation is beneficial to bone remodeling, and gradient loading strain is beneficial to the activation of osteoblasts and osteoclasts. OBJECTIVE: To co-culture silk fibroin/type II collagen composite scaffolds with chondrocytes under compression loading, to observe the proliferation of cells, and to observe the preliminary repair effect of silk fibroin/type II collagen composite scaffold on cartilage defects. METHODS: The silk fibroin/type II collagen composite scaffold was prepared by low-temperature 3D printing to detect the porosity of the scaffold. The passage 3 mouse chondrocytes ADTC-5 were inoculated on the silk fibroin/type II collagen composite scaffold and cultured under static culture and mechanical load respectively. (1) Static culture: blank scaffold was set as control, and cell proliferation was detected by MTT assay at 1, 3, 5, 7, 10, 14 days of inoculation. (2) Culture under mechanical load: blank scaffold was set as control. At 1 day after inoculation, 0％, 1％, 5％, 10％, 15％, 20％ compressive strains were applied to the cell-scaffold complex, and continued to load for 3 days. Cell proliferation was detected by MTT assay, and the distribution, adhesion and morphology of the cells on the scaffold were observed by scanning electron microscopy and hematoxylin-eosin staining. A cartilage defect of 3.5 mm in diameter was made in the bilateral knee joint of New Zealand rabbits. The silk fibroin/type II collagen composite scaffold was implanted onto the left side, and no material was implanted onto the right side. The repair site was observed at 8 weeks after surgery. RESULTS AND CONCLUSION: (1) The porosity of the scaffold was (89.3±3.26)％, which was conducive to cell attachment. (2) After 5 days of static culture, the chondrocytes proliferated well on the surface of the composite scaffold. Under 0％, 1％, 5％, 10％, 15％, 20％ compressive strains, the cell proliferation on the scaffold first increased and then decreased, wherein the cell proliferation was highest under 10％ compressive strain, and lowest under 20％ compressive strain. (4) Under the scanning electron microscopy, the chondrocytes in the 0％ load group were distributed in the surface of the scaffold with irregularities, the cell morphology was obvious, and the cell protrusions were fully extended. There were few or no chondrocytes on the contact surface of the 10％ load group, and more cells distributed on the lateral and internal surfaces of the first layer, but the cell morphology was flat with obvious protrusions. (5) Hematoxylin-eosin staining showed that the chondrocytes in the 0％ load group were concentrated on the surface of the scaffold, and there were almost no cells in the pores, while the chondrocytes in the 10％ load group were distributed in the scaffold pores. (6) There was still a circular defect model with no scaffold implantation, and no obvious repair appeared; similar hyaline cartilage appeared in the defect after scaffold implantation, but there was no adhesion to the surrounding defected cartilage, and the new hyaline cartilage was independent. Overall, the adsorption, proliferation and growth of chondrocytes on the silk fibroin-type II collagen scaffolds is better when the compressive strain is 10％, and the composite scaffold can be used as a repair material for cartilage defects.

Influence of dynamic mechanical stimulation on tissue engineering annulus fibrosus / 中华骨科杂志

Objective To investigate the influence of dynamic mechanical stimulation on the annulus fibrosus (AF) cells seeded on silk scaffolds.Methods AF cells were isolated from rabbits and were seeded on the scaffold,then cultured for 3,7,14 days with different range of dynamic compression.Stereomicroscope and scanning electron microscope (SEM) was used to observe the surface morphology of tissue engineering annulus fibrosus cells (TE-AFs).After fixation,samples were harvested for histological staining.AF cells related extracellular matrix (ECM) was evaluated by the quantitative analysis of total DNA,proteoglycan and collagen I.The mechanical properties were compared within different groups.Results Stereomicroscope and SEM results showed that the colors of TE-AFs in all groups were deepening with time going.SEM showed cell adhesion on the scaffold and the secretion of extracellular matrix.Histological,immunohistochemical staining,biochemical quantitative analysis and total DNA content showed that the AF cells inside scaffolds could support AF cell attachment,proliferation and secretion.As a result,the compressive properties were enhanced with increasing culture time.Stereomicroscope showed that the colors of TE-AFs in all groups were deepening with time going after dynamic compression.HE staining,Safranin O staining and Type Ⅰ collagen staining showed that cell proliferation and secretion,GAG secretion and collagen secretion were increased with time going within different groups.Quantitation of GAG achieved maximum in 15％ strain group,and quantitation of collagen achieved maximum in 10％ strain group.The total DNA content achieved maximum in 5％ strain group,and compression elastic modulus achieved maximum in 15％strain goup.The height of TE-AFs did not change after mechanical stimulation for 14 days.Conclusion Suitable mechanical stimulation is a positive factor for new AF tissue engineering that will tend to the nature tissue.Excessive compression can accelerate the progress of cell apoptosis.

Analysis of the stress state in articular cartilage defect repairing area / 生物医学工程学杂志

Based on transversely isotropic theory, a finite element model for three-dimensional solid-liquid coupling defect repair of articular cartilage was established. By studying stress state of host cartilage near the restoration interface, we identified deformation type of cartilage and discussed the cause of restoration interface cracking. The results showed that the host cartilage surface node near the restoration interface underwent compression deformation in the condition of surface layer defect repair. When the middle layer, deep layer or full-thickness defect were repaired, the node underwent tensile deformation. At this point, the radial dimension of cartilage increased, which might cause restoration interface cracking. If elastic modulus of the tissue engineered cartilage (TEC) was lower (0.1 MPa, 0.3 MPa), the host cartilage surface layer and middle layer mainly underwent tensile deformation. While elastic modulus of TEC was higher (0.6 MPa, 0.9 MPa), each layer of host cartilage underwent compression deformation. Therefore, the elastic modulus of TEC could be increased properly for full-thickness defect repair. This article provides a new idea for evaluating the effect of cartilage tissue engineering repair, and has a certain guiding significance for clinical practice.

Ratcheting strain and theoretical prediction of articular cartilage under cyclic loading / 医用生物力学

Objective To obtain the ratcheting strain of articular cartilage under different loading conditions,and construct the theoretical model so as to predict the ratcheting strain of cartilage.Methods The fresh articular cartilage obtained from the trochlear of distal femur was used as experimental subject.The ratcheting strain of articular cartilage was tested under cyclic compressive loads by applying the non-contact digital image correlation technique.The theoretical model was constructed to predict the ratcheting strain of articular cartilage with different stress amplitudes and stress rates.The results from predictions were compared with the experimental results.Results The ratcheting strain of cartilage increased rapidly at initial stage and then showed the slower increase with cycles increasing.The ratcheting strain increased with stress amplitude increasing when the stress rate was constant.However,the ratcheting strain decreased with stress rate increasing when the stress amplitude was constant.When the stress rate increased,the ratcheting stain decreased.The prediction results of the established theoretical model were in good agreement with experimental results.Conclusions The ratcheting strain of articular cartilage is proportional to the stress amplitude,and inversely proportional to the stress rate.The established theoretical model can predict the ratcheting strain of articular cartilage and provide guidance for the construction of tissue engineered artificial cartilage.

Micromechanical properties of articular cartilage resilience under different compression conditions / 中国组织工程研究

BACKGROUND: It is of great significance to study the resilience of articular cartilage for human daily routine and their match quality. OBJECTIVE: To analyze the micromechanical properties of articular cartilage resilience under different loads and at time points. METHODS: The swine cartilage samples coated with tracers were compressed using the MTF-100 tensile machine, and the cartilage compression and resilience were recorded by CCD. Images were processed using digital image correlation technology.RESULTS AND CONCLUSION: During resilience, the strain value on the superficial surface of the cartilage was decreased most, successively followed by the middle layer and the deep layer, while the time of a decrease from 20%, 10% and 6% to 3% was similar. The longer the resilience time was, the more slowly the strain changed in different layers of the cartilage, but the ultimate strain was less than 1%. On the same layer under different compressive stress, the larger load caused faster strain change firstly, and then the smaller load brought about faster strain change. The effect of different continuous compressive time on the same layer of cartilage was similar with the load. These results showed that 90% resilience of the articular cartilage occurred within the first 15 minutes. The mechanical resilience of different layers of the articular cartilage has a close relationship with the loading and the loading time, and both compressive time and loading do harm to the resilience of articular cartilage. Besides, the cartilage will rebound to the state before compression.

The mechanical and biological responses of MC3T3-E1 cells under hypergravity / 医用生物力学

Objective To explore the effect of hypergravity on morphology and osteogenesis function of preosteoblast MC3T3-E1 ceils.Methods The cultured MC3T3-E1 cells under hypergravity by different loading forces were divided into five groups,including control group,5 g group,10 g group,15 g group and 20 g group.The experimental groups were loaded for 30 min each time in 3 successive days,and the control group with no g-value was synchronously exposed to the same surrounding.The morphology of cytoskeletal protein was observed by phalIoidin staining,The alkaline phosphatase (ALP) content was examined by ALP activity assay kit,the gene expression of ALP,collagen Ⅰ (Col Ⅰ),osteocalcin (OC),runt-related transcription factors (Runx2) was measured by real-time quantitative PCR,and the protein expression of Col Ⅰ and OC was tested by Western blotting.Results Under the condition of hypergravity,cell body of osteoblast became thinner,but its surface area increased significantly;with the structure of skeletal arrangement becoming loose,actin microfilament structure reduced so that the orderly arrangement of actin-like dispersion lowered.The gene expressions of related indicators of osteogenic differentiation including ALP,Col][,OC,Runx2 were significantly up-regulated,which was the same as Col Ⅰ protein and OC protein after hypergravity loading.A very minute quantity of small red-orange nodules was found in the control group,while the cells in experimental groups after hypergravity loading obviously formed various sizes of red-orange nodules.Conclusions Under hypergravity,changes in osteoblast morphology can be triggered by rearrangements of skeletal structure.Furthermore,osteoblast maturation and differentiation can be stimulated effectively by up-regulating differentiation-related gene and protein expressions.

Numerical analysis on damage evolution of rectangular articular cartilage with micro-defect under compressive loads / 医用生物力学

Objective To study the damage propagation and evolution mechanism of cartilage under compressive loads.Methods The fiber-reinforced porous elastic model of cartilage with micro-defect was established by using finite element method,and the process of damage evolution under compressive loads was simulated and analyzed with parameters.The patterns of stress and strain distributions on cartilage matrix and collagen fiber at different damage extension stages were obtained.Results The strain in the surface and forefront of cartilage damage increased significantly with the increase of compression displacement,and they were obviously in positive correlation;in the process of damage evolution,there was a trend that cartilage extended to the deep and both sides simultaneously;cracks and damage in cartilage extended preferentially along the fiber tangent direction.With the aggravation of cartilage damage,the lateral extension speed was significantly faster than the longitudinal extension speed.Conclusions The process of cartilage damage extension has a close relationship with the distribution of fibers.The damages in matrix and fiber promote each other.The evolution speed and degree of cartilage vary constantly in different layers and at different stages.These results can provide the qualitative reference for prediction and repair of cartilage damage,as well as the theoretical basis for explaining pathological phenomena of damage degeneration and its clinic treatment.