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.
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.
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.
Based on the current study of the influence of mechanical factors on cell behavior which relies heavily on experiments in vivo, a culture chamber with a large uniform strain area containing a linear motor-powered, up-to-20-Hz cell stretch loading device was developed to exert mechanical effects on cells. In this paper, using the strain uniformity as the target and the substrate thickness as the variable, the substrate bottom of the conventional incubation chamber is optimized by using finite element technique, and finally a new three-dimensional model of the incubation chamber with “M” type structure in the section is constructed, and the distribution of strain and displacement fields are detected by 3D-DIC to verify the numerical simulation results. The experimental results showed that the new cell culture chamber increased the accuracy and homogeneous area of strain loading by 49.13% to 52.45% compared with that before optimization. In addition, the morphological changes of tongue squamous carcinoma cells under the same strain and different loading times were initially studied using this novel culture chamber. In conclusion, the novel cell culture chamber constructed in this paper combines the advantages of previous techniques to deliver uniform and accurate strains for a wide range of cell mechanobiology studies.
Triply periodic minimal surface (TPMS) is widely used because it can be used to control the shape of porous scaffolds precisely by formula. In this paper, an I-wrapped package (I-WP) type porous scaffolds were constructed. The finite element method was used to study the relationship between the wall thickness and period, the morphology and mechanical properties of the scaffolds, as well as to study the compression and fluid properties. It was found that the porosity of I-WP type scaffolds with different wall thicknesses (0.1 ~ 0.2 mm) and periods (I-WP 1 ~ I-WP 5) ranged from 68.01% ~ 96.48%, and the equivalent elastic modulus ranged from 0.655 ~ 18.602 GPa; the stress distribution of the scaffolds tended to be uniform with the increase of periods and wall thicknesses; the equivalent elastic modulus of the I-WP type scaffolds was basically unchanged after the topology optimization, and the permeability was improved by 52.3%. In conclusion, for the I-WP type scaffolds, the period parameter can be adjusted first, then the wall thickness parameter can be controlled. Topology optimization can be combined to meet the design requirements. The I-WP scaffolds constructed in this paper have good mechanical properties and meet the requirements of repairing human bone tissue, which may provide a new choice for the design of artificial bone trabecular scaffolds.
A solid-liquid two-phase finite element model of articular cartilage and a microscopic finite element model of chondrocytes were established using the finite element software COMSOL in this study. The purpose of the study is to investigate the mechanics environment and the liquid flow field of the host cartilage chondrocytes in each layer by multi-scale method, under physiological load, with the different elastic modulus of artificial cartilage to repair cartilage defect. The simulation results showed that the uniform elastic modulus of artificial cartilage had different influences on the microenvironment of different layer chondrocytes. With the increase of the elastic modulus of artificial cartilage, the stress of the shallow surface layer and the intermediate layer chondrocytes increased and the stress of deep layer chondrocytes decreased. The flow field direction of the middle layer and the bottom layer of cartilage can also be changed by artificial cartilage implantation, as well as the ways of nourishment supply of the middle layer and underlying chondrocytes change. A barrier to underlying chondrocytes nutrition supply may be caused by this, thus resulting in the uncertainty of the repair results. With cross-scale finite element model simulation analysis of chondrocytes, we can quantitatively evaluate the mechanical environment of chondrocytes in each layer of the host cartilage. It is helpful to assess the clinical effect of cartilage defect reparation more accurately.
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.
Superficial cartilage defect is an important factor that causes osteoarthritis. Therefore, it is very important to investigate the influence of superficial cartilage defects on its surface morphology and mechanical properties. In this study, the knee joint cartilage samples of adult pig were prepared, which were treated by enzymolysis with chymotrypsin and physical removal with electric friction pen, respectively. Normal cartilage and surface treated cartilage were divided into five groups: control group (normal cartilage group), chymotrypsin immersion group, chymotrypsin wiping group, removal 10% group with electric friction pen, and removal 20% group with electric friction pen. The surface morphology and structure of five groups of samples were characterized by laser spectrum confocal microscopy and environmental field scanning electron microscopy, and the mechanical properties of each group of samples were evaluated by tensile tests. The results show that the surface arithmetic mean height and fracture strength of the control group were the smallest, and the fracture strain was the largest. The surface arithmetic mean height and fracture strength of the removal 20% group with electric friction pen were the largest, and the fracture strain was the smallest. The surface arithmetic mean height, fracture strength and fracture strain values of the other three groups were all between the above two groups, but the surface arithmetic mean height and fracture strength of the removal 10% group with electric friction pen, the chymotrypsin wiping group and the chymotrypsin soaking group decreased successively, and the fracture strain increased successively. In addition, we carried out a study on the elastic modulus of different groups, and the results showed that the elastic modulus of the control group was the smallest, and the elastic modulus of the removal 20% group with electric friction pen was the largest. The above study revealed that the defect of the superficial area of cartilage changed its surface morphology and structure, and reduced its mechanical properties. The research results are of great significance for the prevention and repair of cartilage injury.
Objective To fabricate a novel composite scaffold with acellular demineralized bone matrix/acellular nucleus pulposus matrix and to verify the feasibility of using it as a scaffold for intervertebral disc tissue engineering through detecting physical and chemical properties. Methods Pig proximal femoral cancellous bone rings (10 mm in external diameter, 5 mm in internal diameter, and 3 mm in thickness) were fabricated, and were dealed with degreasing, decalcification, and decellularization to prepare the annulus fibrosus phase of scaffold. Nucleus pulposus was taken from pig tails, decellularized with Triton X-100 and deoxycholic acid, crushed and centrifugalized to prepare nucleus pulposus extracellular mtrtix which was injected into the center of annulus fibrosus phase. Then the composite scaffold was freeze-dryed, cross-linked with ultraviolet radiation/carbodiimide and disinfected for use. The scaffold was investigated by general observation, HE staining, and scanning electron microscopy, as well as porosity measurement, water absorption rate, and compressive elastic modulus. Adipose-derived stem cells (ADSCs) were cultured with different concentrations of scaffold extract (25%, 50%, and 100%) to assess cytotoxicity of the scaffold. The cell viability of ADSCs seeded on the scaffold was detected by Live/Dead staining. Results The scaffold was white by general observation. The HE staining revealed that there was no cell fragments on the scaffold, and the dye homogeneously distributed. The scanning electron microscopy showed that the pore of the annulus fibrosus phase interconnected and the pore size was uniform; acellular nucleus pulposus matrix microfilament interconnected forming a uniform network structure, and the junction of the scaffold was closely connected. The novel porous scaffold had a good pore interconnectivity with (343.00 ± 88.25) µm pore diameter of the annulus fibrosus phase, 82.98% ± 7.02% porosity and 621.53% ± 53.31% water absorption rate. The biomechanical test showed that the compressive modulus of elasticity was (89.07 ± 8.73) kPa. The MTT test indicated that scaffold extract had no influence on cell proliferation. Live/Dead staining showed that ADSCs had a good proliferation on the scaffold and there was no dead cell. Conclusion Novel composite scaffold made of acellular demineralized bone matrix/acellular nucleus pulposus matrix has good pore diameter and porosity, biomechanical properties close to natural intervertebral disc, non-toxicity, and good biocompatibility, so it is a suitable scaffold for intervertebral disc tissue engineering.
Objective To evaluate the influence of PKH26 labeling on the biological function of the goat nucleus pulposus cells and the biological function of seeded cells in nude mice by in vivo imaging techonology. Methods Primary nucleus pulposus cells were isolated by enzymatic digestion from the nucleus pulposus tissue of the 1-year-old goat disc. The nucleus pulposus cells at passage 1 were labeled with PKH26 and the fluorescent intensity was observed under the fluorescence microscopy. The labeled cells were stained with toluidine blue and collagen type II immunocytochemistry. The cells viability and proliferation characteristics were assessed by trypan blue staining and MTT assay, respectively. Real-time fluorescent quantitative PCR was used to detect the gene expressions of collagen types I and II, and aggrecan. The fluorescent intensity and scope of the nucleus pulposus cells-scaffold composite in vivo for 6 weeks after implanting into 5 6-week-old male nude mice were measured by in vivo imaging technology. Results Primary nucleus pulposus cells were ovoid in cell shape, showing cluster growth, and the cells at passage 1 showed chondrocyte-like morphology under the inverted phase contrast microscope. The results of toluidine blue and collagen type II immunocytochemistry staining for nucleus pulposus cells at passage 1 were positive. The fluorescent intensity was even after labeling, and the cell viability was more than 95% before and after PKH26 labeling. There was no significant difference in cell growth curve between before and after labeling (P gt; 0.05). The real-time fluorescent quantitative PCR showed that there was no significant difference in gene expressions of collagen types I and II, and aggrecan between before and after labeling (P gt; 0.05). Strong fluorescence in nucleus pulposus cells-scaffold composite was detected and by in vivo imaging technology. Conclusion The PKH26 labeling has no effect on the activity, proliferation, and cell phenotype gene expression of the nucleus pulposus cells. A combination of PKH26 labeling and in vivo imaging technology can track the biological behavior of the cells in vivo.