Jiazi Gao

Seven Day Insertion Rest in Whole Body Vibration Improves Multi-Level Bone Quality in Tail Suspension Rats

Objective This study aimed to investigate the effects of low-magnitude, high-frequency vibration with rest days on bone quality at multiple levels. Methods Forty-nine three-month-old male Wistar rats were randomly divided into seven groups, namely, vibrational loading for X day followed by X day rest (VLXR, X = 1, 3, 5, 7), vibrational loading every day (VLNR), tail suspension (SPD), and baseline control (BCL). One week after tail suspension, rats were loaded by vibrational loading (35 Hz, 0.25 g, 15 min/day) except SPD and BCL. Fluorescence markers were used in all rats. Eight weeks later, femora were harvested to investigate macromechanical properties, and micro-computed tomography scanning and fluorescence test were used to evaluate microarchitecture and bone growth rate. Atomic force microscopy analyses and nanoindentation test were used to analyze the nanostructure and mechanical properties of bone material, respectively. Inductively coupled plasma optical emission spectroscopy was used for quantitative chemical analyses. Results Microarchitecture, mineral apposition rate and bone formation rate and macromechanical properties were improved in VL7R. Grain size and roughness were significantly different among all groups. No statistical difference was found for the mechanical properties of the bone material, and the chemical composition of all groups was almost similar. Conclusions Low-magnitude, high-frequency vibration with rest days altered bone microarchitecture and macro-biomechanical properties, and VL7R was more efficacious in improving bone loss caused by mechanical disuse, which provided theoretical basis and explored the mechanisms of vibration for improving bone quality in clinics.

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.

Relationship between microstructure, material distribution, and mechanical properties of sheep tibia during fracture healing process.

The aim of this study was to investigate the relationship between microstructural parameters, material distribution, and mechanical properties of sheep tibia at the apparent and tissue levels during the fracture healing process. Eighteen sheep underwent tibial osteotomy and were sacrificed at 4, 8, and 12 weeks. Radiographs and micro-computed tomography (micro-CT) scanning were taken for microstructural assessment, material distribution evaluation, and micro-finite element analysis. A displacement of 5% compressive strain on the longitudinal direction was applied to the micro-finite element model, and apparent and tissue-level mechanical properties were calculated. Principle component analysis and linear regression were used to establish the relationship between principle components (PCs) and mechanical parameters. Visible bony callus formation was observed throughout the healing process from radiographic assessment. Apparent mechanical property increased at 8 weeks, but tissue-level mechanical property did not increase significantly until 12 weeks. Three PCs were extracted from microstructural parameters and material distribution, which accounted for 87.592% of the total variation. The regression results showed a significant relationship between PCs and mechanical parameters (R>0.8, P<0.05). Results of this study show that microstructure and material distribution based on micro-CT imaging could efficiently predict bone strength and reflect the bone remodeling process during fracture healing, which provides a basis for exploring the fracture healing mechanism and may be used as an approach for fractured bone strength assessment.

Age-related regional deterioration patterns and changes in nanoscale characterizations of trabeculae in the femoral head.

This study aimed to investigate the mechanical properties and features of bone materials at the nanoscale level in different regions of the femoral head in elderly patients with femoral neck fracture. Ten femoral heads from female patients with femoral neck fractures were extracted during surgery (five for the Aged group, aged 65-66 years; five for the Advanced aged group, aged 85-95 years). The femoral head was divided into three equal layers (anterior, central, and posterior) in the coronal view, and each layer was segmented into five regions (superior, central, inferior, medial, and lateral). Nanoindentation testing and atomic force microscopy imaging were used to study the mechanical properties and surface morphology of the specimens. No statistical differences in grain size were found between age groups, which suggested that the nanostructure of trabeculae in the femoral heads of postmenopausal women cannot be used to predict age-related bone loss and fracture risk. Mechanical properties in the longitudinal direction deteriorated more quickly than those in the transverse direction for the whole femoral head. Comparisons between layers showed a higher deterioration rate with aging in the anterior layer than in other layers. In different regions, mechanical properties of the medial and lateral regions deteriorated more quickly than those in the three other regions, and deterioration in the longitudinal direction was more serious than that in the transverse direction. The regional deterioration patterns and material properties with aging observed in this study contribute to an understanding of the age-related fracture mechanism and provide a basis for predicting age-related fracture risk and decreasing early fixation failure in the proximal femur.

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.

Quantification of Age-Related Tissue-Level Failure Strains of Rat Femoral Cortical Bones Using an Approach Combining Macrocompressive Test and Microfinite Element Analysis

Bone mechanical properties vary with age; meanwhile, a close relationship exists among bone mechanical properties at different levels. Therefore, conducting multilevel analyses for bone structures with different ages are necessary to elucidate the effects of aging on bone mechanical properties at different levels. In this study, an approach that combined microfinite element (micro-FE) analysis and macrocompressive test was established to simulate the failure of male rat femoral cortical bone. Micro-FE analyses were primarily performed for rat cortical bones with different ages to simulate their failure processes under compressive load. Tissue-level failure strains in tension and compression of these cortical bones were then back-calculated by fitting the experimental stress-strain curves. Thus, tissue-level failure strains of rat femoral cortical bones with different ages were quantified. The tissue-level failure strain exhibited a biphasic behavior with age: in the period of skeletal maturity (1-7 months of age), the failure strain gradually increased; when the rat exceeded 7 months of age, the failure strain sharply decreased. In the period of skeletal maturity, both the macro- and tissue-levels mechanical properties showed a large promotion. In the period of skeletal aging (9-15 months of age), the tissue-level mechanical properties sharply deteriorated; however, the macromechanical properties only slightly deteriorated. The age-related changes in tissue-level failure strain were revealed through the analysis of male rat femoral cortical bones with different ages, which provided a theoretical basis to understand the relationship between rat cortical bone mechanical properties at macro- and tissue-levels and decrease of bone strength with age.

Morphological and Microstructural Alterations of the Articular Cartilage and Bones during Treadmill Exercises with Different Additional Weight-Bearing Levels

The aim of this study was to investigate the morphological and microstructural alterations of the articular cartilage and bones during treadmill exercises with different exercise intensities. Sixty 5-week-old female rats were randomly divided into 10 groups: five additional weight-bearing groups (WBx) and five additional weight-bearing with treadmill exercise groups (EBx), which were subjected to additional weight bearing of x% (x = 0, 5, 12, 19, and 26) of the corresponding body weight of each rat for 15 min/day. After 8 weeks of experiment, the rats were humanely sacrificed and their bilateral intact knee joints were harvested. Morphological analysis of the cartilages and microcomputed tomography evaluation of bones were subsequently performed. Results showed that increased additional weight bearing may lead to cartilage damage. No significant difference was observed among the subchondral cortical thicknesses of the groups. The microstructure of subchondral trabecular bone of 12% and 19% additional weight-bearing groups was significantly improved; however, the WB26 and EB26 groups showed low bone mineral density and bone volume fraction as well as high structure model index. In conclusion, effects of treadmill exercise on joints may be associated with different additional weight-bearing levels, and exercise intensities during joint growth and maturation should be selected reasonably.

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.

Whole body vibration with rest days could improve bone quality of distal femoral metaphysis by regulating trabecular arrangement

Low-magnitude, high-frequency vibration (LMHFV) with rest days (particularly seven rest days) was considerably effective in improving the morphological and mechanical properties of rat proximal femur. However, current knowledge is limited regarding the possible benefit of this mechanical regimen to other bone sites and whether the optimal rest days are the same. This study followed our previous experiment on LMHFV loading with rest days for three-month-old male Wistar rats. The experiment involved seven groups, namely, vibrational loading for X day followed with X day rest (X=1, 3, 5, 7), daily vibrational loading, tail suspension and baseline control. Micro-computed tomography (micro-CT) scanning was used to evaluate the microarchitecture of the distal femoral trabecular bone. Micro-CT image-based microfinite element analysis was performed for each distal femoral metaphysis. LMHFV with rest days substantially changed the trabecular arrangement from remarkably plate-like to rod-like. Vibrational loading with 1 day rest was substantially effective in improving the architecture and apparent- and tissuelevel mechanical properties of the rat distal femoral metaphysis. This study may provide an improved understanding of the sitespecific responses of bone tissue to LMHFV with rest days for a substantially effective therapy of a targeted bone site.

Effects of Scan Resolutions and Element Sizes on Bovine Vertebral Mechanical Parameters from Quantitative Computed Tomography-Based Finite Element Analysis

Quantitative computed tomography-based finite element analysis (QCT/FEA) has been developed to predict vertebral strength. However, QCT/FEA models may be different with scan resolutions and element sizes. The aim of this study was to explore the effects of scan resolutions and element sizes on QCT/FEA outcomes. Nine bovine vertebral bodies were scanned using the clinical CT scanner and reconstructed from datasets with the two-slice thickness, that is, 0.6 mm (PA resolution) and 1 mm (PB resolution). There were significantly linear correlations between the predicted and measured principal strains (R2 > 0.7, P < 0.0001), and the predicted vertebral strength and stiffness were modestly correlated with the experimental values (R2 > 0.6, P < 0.05). Two different resolutions and six different element sizes were combined in pairs, and finite element (FE) models of bovine vertebral cancellous bones in the 12 cases were obtained. It showed that the mechanical parameters of FE models with the PB resolution were similar to those with the PA resolution. The computational accuracy of FE models with the element sizes of 0.41 × 0.41 × 0.6 mm3 and 0.41 × 0.41 × 1 mm3 was higher by comparing the apparent elastic modulus and yield strength. Therefore, scan resolution and element size should be chosen optimally to improve the accuracy of QCT/FEA.