Xizheng Zhang

Mechanical strain promotes osteoblast ECM formation and improves its osteoinductive potential

BackgroundThe extracellular matrix (ECM) provides a supportive microenvironment for cells, which is suitable as a tissue engineering scaffold. Mechanical stimulus plays a significant role in the fate of osteoblast, suggesting that it regulates ECM formation. Therefore, we investigated the influence of mechanical stimulus on ECM formation and bioactivity.MethodsMouse osteoblastic MC3T3-E1 cells were cultured in cell culture dishes and stimulated with mechanical tensile strain. After removing the cells, the ECMs coated on dishes were prepared. The ECM protein and calcium were assayed and MC3T3-E1 cells were re-seeded on the ECM-coated dishes to assess osteoinductive potential of the ECM.ResultsThe cyclic tensile strain increased collagen, bone morphogenetic protein 2 (BMP-2), BMP-4, and calcium levels in the ECM. Compared with the ECM produced by unstrained osteoblasts, those of mechanically stimulated osteoblasts promoted alkaline phosphatase activity, elevated BMP-2 and osteopontin levels and mRNA levels of runt-related transcriptional factor 2 (Runx2) and osteocalcin (OCN), and increased secreted calcium of the re-seeded MC3T3-E1 cells.ConclusionMechanical strain promoted ECM production of osteoblasts in vitro, increased BMP-2/4 levels, and improved osteoinductive potential of the ECM. This study provided a novel method to enhance bioactivity of bone ECM in vitro via mechanical strain to osteoblasts.

An adaptation model for trabecular bone at different mechanical levels.

BackgroundBone has the ability to adapt to mechanical usage or other biophysical stimuli in terms of its mass and architecture, indicating that a certain mechanism exists for monitoring mechanical usage and controlling the bones adaptation behaviors. There are four zones describing different bone adaptation behaviors: the disuse, adaptation, overload, and pathologic overload zones. In different zones, the changes of bone mass, as calculated by the difference between the amount of bone formed and what is resorbed, should be different.MethodsAn adaptation model for the trabecular bone at different mechanical levels was presented in this study based on a number of experimental observations and numerical algorithms in the literature. In the proposed model, the amount of bone formation and the probability of bone remodeling activation were proposed in accordance with the mechanical levels. Seven numerical simulation cases under different mechanical conditions were analyzed as examples by incorporating the adaptation model presented in this paper with the finite element method.ResultsThe proposed bone adaptation model describes the well-known bone adaptation behaviors in different zones. The bone mass and architecture of the bone tissue within the adaptation zone almost remained unchanged. Although the probability of osteoclastic activation is enhanced in the overload zone, the potential of osteoblasts to form bones compensate for the osteoclastic resorption, eventually strengthening the bones. In the disuse zone, the disuse-mode remodeling removes bone tissue in disuse zone.ConclusionsThe study seeks to provide better understanding of the relationships between bone morphology and the mechanical, as well as biological environments. Furthermore, this paper provides a computational model and methodology for the numerical simulation of changes of bone structural morphology that are caused by changes of mechanical and biological environments.

High-frequency and low-magnitude whole body vibration with rest days is more effective in improving skeletal micro-morphology and biomechanical properties in ovariectomised rodents.

We explored the optimal regime in preventing or treating bone loss, using ovariectomised rodents loaded by mechanical stimuli with rest days during the loading cycle. Eighty-four Sprague-Dawley rats, aged 6 months, were randomly divided into 7 groups after bilateral ovariectomy. Mechanical vibration with 1-day rest (ML1R), with 3-day rest (ML3R), with 5-day rest (ML5R), with 7-day rest (ML7R), daily loading (DL), comparing the ovariectomised group (OVX) with baseline (BCL) measurements. After a recovery of one week, all the rodents were loaded daily by whole body vibration at 35 Hz and 0.25 g for 15 minutes. Eight weeks later, a three-point bending test of the radius and micro-CT scanning of the femoral head were performed after animal sacrifice. Large improvements in biomechanical properties occurred in all the experimental groups for failure load, elastic modulus and deflection, while a significantly enhanced efficacy was detected in ML7R compared with daily loading (p<0.05). In micro-CT scanning, bone volume fraction, trabecular thickness, number and separation were improved by the regime in all experimental groups, while ML7R showed a significant improvement over daily loading (p<0.05). Early bone loss in human subjects may be improved by high-frequency and low-magnitude whole body vibration with rest days or daily stimuli. Mechanical stimulus with a 7-day rest was more effective in improving biomechanical properties and micro-morphology compared with daily loading. This may have clinical implications in relation to the prevention and treatment of hip fractures, and in postoperative management following hip arthroplasty.

A comparative study of mechanical strain, icariin and combination stimulations on improving osteoinductive potential via NF-kappaB activation in osteoblast-like cells

BackgroundThe combination of drugs and exercise was the effective treatment in bone injure and rebuilding in clinic. As mechanical strain has potential in inducing the differentiation of osteoblasts in our previous study, the further research to investigate the combination of mechanical strain and icariin stimulation on inducing osteoblast proliferation, differentiation and the possible mechanism in MC3T3-E1 cell line.MethodsA whole cell enzyme-linked immunosorbent assay that detects the bromodeoxyuridine incorporation during DNA synthesis was applied to evaluate the proliferation. The mRNA expression of alkaline phosphatase (ALP), osteocalcin (OCN), type I collagen (Col I), bone morphogenetic protein-2 (BMP-2) and BMP-4 was detected by real-time reverse-transcription polymerase chain reaction. The activity of ALP was analyzed by ELISA and the protein expression of OCN, Col I and BMP-2 was assessed by western blot. Moreover, the activity of nuclear transcription factor kappa-B (NF-κB) signaling pathway was investigated with the expression of inhibitor of κB (IκB) α, phosphorylation of IκB-α (P-IκB-α), p65, P-p65 by western blot.ResultsWe observed that compared to single mechanical strain or icariin stimulation, the mRNA and protein expressions of ALP (Pxa0<xa00.05 or Pxa0<xa00.01), OCN (Pxa0<xa00.01) and Col I (Pxa0<xa00.05 or Pxa0<xa00.01) were increased significantly by the combination of mechanical strain and icariin stimulation. Moreover, the combination of mechanical strain and icariin stimulation could up-regulate the expression of BMP-2 (Pxa0<xa00.01) and BMP-4 compared to single mechanical strain or icariin stimulation. The combination of mechanical strain and icariin stimulation could activate NF-κB signaling pathway by increasing the expression of IκB α, P-IκB-α, p65, P-p65 (Pxa0<xa00.01).ConclusionThe combination of mechanical strain and icariin stimulation could activate the NF-κB pathway to improve the proliferation, differentiation of osteoblast-like cells.

A non-linear finite element model of human L4-L5 lumbar spinal segment with three-dimensional solid element ligaments

This paper establishes a non-linear finite element model (NFEM) of L4-L5 lumbar spinal segment with accurate three-dimensional solid ligaments and intervertebral disc. For the purpose, the intervertebral disc and surrounding ligaments are modeled with four-nodal three-dimensional tetrahedral elements with hyper-elastic material properties. Pure moment of 10 N·m without preload is applied to the upper vertebral body under the loading conditions of lateral bending, backward extension, torsion, and forward flexion, respectively. The simulate relationship curves between generalized forces and generalized displacement of the NFEM are compared with the in vitro experimental result curves to verify NFEM. The verified results show that: (1) The range of simulated motion is a good agreement with the in vitro experimental data; (2) The NFEM can more effectively reflect the actual mechanical properties than the FE model using cable and spring elements ligaments; (3) The NFEM can be used as the basis for further research on lumbar degenerative diseases.

Establishment and verification of a non-linear finite element model for human L4–L5 lumbar segment

Object: To establish a non-linear finite element (FE) model for human L4–L5 lumbar segment and verify its reliability. Method: A FE model of human L4–L5 lumbar segment was established. Some empirical expressions were used to simulate the mechanical properties of vertebral body. The annulus fibrosus and nucleus were assigned hyper-elastic material. The surrounding ligaments were assigned be unsymmetric spring elements. The FE model was developed in ABAQUS software under the loading conditions of axial compression, lateral bending, extension, torsion, and flexion. Result: The result curves of different loading conditions all represent a similar nonlinear curve. The axial force and displacement curve of L4–L5 FE model was closely correlated with the published results of in vitro experimental study. The relationship between moment and degrees also showed a good agreement with the experimentally determined in vitro data during the loading condition of lateral bending, extension, torsion, and flexion. Conclusion: The FE model established in this paper can effectively reflect the actual mechanical properties of human L4–L5 lumbar spine. It can be used as the basis for further research on lumbar degenerative diseases and related treatments.

Morphometry in the ovariectomized rat model of osteoporosis after continuous and intermittent vibration

To research the change of bone structure in the osteoporotic rats after high frequency and low magnitude vibration with different intervals by histomorphometry. Forty-two wistar rats aged six months were divided into six groups, which were CG (control group), OCG (ovariectomized control group), CVG (continuous vibration group), IVGIO (intermittent vibration groups with interval of one week), IVGIT (intermittent vibration groups with interval of two weeks) and IVGIF (intermittent vibration groups with interval of four weeks). All the rats were executed by manual cervical dislocation after eight weeks. The bone trabecula structure, mineralization rate and other indicators of the rats tibias were compared after resin embedded undecalcified section. It was shown that the high frequency and low magnitude stimuli would prevent osteoporosis and the best effect was obtained in the IVGIO

Relationships between the three-dimension morphologic parameters of proximal femurs

To measure the three-dimensional morphologic parameters of proximal femurs and analyze the correlations between these parameters, as well as differences with the aging, which can provide the basic data and reference for the prediction of proximal femoral strength. 20 healthy males with no history of hip disease were selected, whose range of ages was 61-80. The proximal femur of each subject was scanned using clinical QCT (GE Medical System/LightSpeed16). All right proximal femurs of subjects were selected to do 3D reconstruction. Three-dimensional morphologic parameters of proximal femurs were measured and an auxiliary line was drawn according to these obtained data using our self-designed algorithm. Thus, three-dimensional morphologic parameters of proximal femurs can be measured accurately. There are 8 parameters measured and calculated including diameter of femoral head (HD), height of femoral head (HH), distance of head center from shaft axis (OFF), neck shaft angle measured as angle between neck and shaft axis (NSA), height of the top of the greater trochanter above a line perpendicular to the shaft axis and passing through the head center (TRH), thickness of the femur 25mm below the lower edge of the lesser trochanter (TOF), diameter of the most narrow end of neck(ND), length of neck(NL). The 20 samples were divided into two independent age groups. A group of subjects were 61-70 years old and B group of subjects were 71–80 years old. These two groups of samples were performed Two-Independent-Samples Non-parametric Tests (Mann-Whitney U Tests) to determine the differences between the 3D morphologic parameters. The 20 samples were performed correlation analysis between each two parameters. There are no significant differences between two groups in all parameters except ND. There are significant correlations between most parameters at the significant level of 0.01 and 0.05 when performed correlation analysis. Three-dimensional morphologic parameters of proximal femur can be measured more accurately by using the self-defined measurement rules and self-developed algorithms. From the analysis results we can find out that three-dimensional morphologic parameters of proximal femurs in different age groups are of differences. Meanwhile there are significant correlations between some of the parameters. This can provide data references of geometry factors affecting strength of proximal femur for the future analysis.

Computational Model for the Underlying Mechanisms Regulating Bone Loss by Mechanical Unloading and Estrogen Deficiency

Abstract The objective of this paper is to investigate the different effects of disuse and estrogen deficiency on bone loss and the underlying mechanisms. A mechanical-biological factors coupled computational model was built to simulate different patterns of bone loss induced in female rats by hind limb unloading, ovariectomy, or both in an animal study. A remodeling analysis was performed on a representative cross section of 6 mm 2 of cancellous bone in the distal femoral metaphysis of the rats. The BMU activation frequency, the refilling rate, and the principal compressive strain in the state of mechanical unloading and estrogen deficiency were simulated to interpret the underlying mechanisms. Simulated bone loss patterns due to mechanical unloading, estrogen deficiency, or both all corresponded with the experimental observations. The results show that mechanical unloading and estrogen deficiency cause different bone loss patterns; moreover, mechanical unloading induces a greater degree of bone loss than estrogen deficiency, which can lead to improved treatment and prevention strategies for osteoporosis.

Mechanical properties in the ovariectomized rat model of osteoporosis after continuous and intermittent vibration

High frequency and low magnitude mechanical signal is endorsed as a new approach in preventing osteoporosis. The model of osteoporosis was established by forty-two wistar ovariectomized rats aged six months. Following a eight-week protocal composed of continuous and intermittent vibration, all the rats were executed by manual cervical dislocation. Biomechanical properties were determined by three point bending test of left ulnas and compression test of left tibial compact and cancellous bone. It was shown that the high frequency and low magnitude stimuli would prevent osteoporosis and the best effect was obtained in the IVGIO.