Multiscale investigation on the effects of additional weight bearing in combination with low-magnitude high-frequency vibration on bone quality of growing female rats

Effects of different running intensities on the micro-level failure strain of rat femoral cortical bone structures: a finite element investigation

BACKGROUND

Running with the appropriate intensity may produce a positive influence on the mechanical properties of cortical bone structure. However, few studies have discussed the effects of different running intensities on the mechanical properties at different levels, especially at the micro-level, because the micromechanical parameters are difficult to measure experimentally.

METHODS

An approach that combines finite element analysis and experimental data was proposed to predict a micromechanical parameter in the rat femoral cortical bone structure, namely, the micro-level failure strain. Based on the previous three-point bending experimental information, fracture simulations were performed on the femur finite element models to predict their failure process under the same bending load, and the micro-level failure strains in tension and compression of these models were back-calculated by fitting the experimental load-displacement curves. Then, the effects of different running intensities on the micro-level failure strain of rat femoral cortical bone structure were investigated.

RESULTS

The micro-level failure strains of the cortical bone structures expressed statistical variations under different running intensities, which indicated that different mechanical stimuli of running had significant influences on the micromechanical properties. The greatest failure strain occurred in the cortical bone structure under low-intensity running, and the lowest failure strain occurred in the structure under high-intensity running.

CONCLUSIONS

Moderate and low-intensity running were effective in enhancing the micromechanical properties, whereas high-intensity running led to the weakening of the micromechanical properties of cortical bone. Based on these, the changing trends in the micromechanical properties were exhibited, and the effects of different running intensities on the fracture performance of rat cortical bone structures could be discussed in combination with the known mechanical parameters at the macro- and nano-levels, which provided the theoretical basis for reducing fracture incidence through running exercise.

Investigation on the Differences in the Failure Processes of the Cortical Bone under Different Loading Conditions

Cortical bone is a transversely isotropic material, and the mechanical properties may be related to the loading direction on the osteon. Therefore, analyzing the differences in the failure processes of cortical bone under different loading conditions is necessary to explore the measures for reducing the incidence of fracture. In this study, to investigate the effects of different loading directions on the fracture performance in the cortical bone, a numerical method that could simultaneously simulate the failure processes in the cortical bone structure under compression and bending loads was established based on continuum damage mechanics theory. The prediction accuracy and feasibility of the numerical method were first verified by comparing with the corresponding experimental results. Then, the differences in the failure process and fracture performance of the same cortical bone structure under compression and bending loads were investigated. The simulation results indicated that for the same structure, the slip-open failure mode appeared under compression load, and the crack propagated along a certain angle to the loading direction; the tension-open failure mode appeared under bending load, and the crack propagated along the direction perpendicular to the loading direction. Meanwhile, the fracture load was greater and the fracture time was later in the compression than in the bending condition. These phenomena stated that discrepant failure processes and fracture patterns occurred in the same cortical bone structure under different loading conditions. The main reason may be related to the tension–compression asymmetry and transversely isotropic characteristics in the cortical bone material. The fracture simulations in the cortical bone under different loading conditions could improve the prediction accuracy in bone biomechanics and provide the prevention method for cortical bone damage and fracture.

Effects of Titanium Implant Combined with Nano-Indentation in the Vertical Control of Physiological Anchorage Spee’s Wire System Corrective Technology

In the current research, there was, in the vertical control of physiological anchorage spee’s wire system (PASS) technology, an investigation on the role of titanium implant technology in combination with nano-indentation experiment the present research. The human jaw was selected as the sample to be cut vertically, by doing do, to obtain a test slice of about 2 mm through a cutting machine following the nano-indentation test. The slice was frozen and preserved in normal saline and taken out during the test. 40 outpatients who underwent orthodontic therapy were chosen as the research objects and rolled in a random manner into a control category and an category of observation. Then, mechanical biological therapy (MBT) correction was conducted for the outpatients from the control category and PASS correction therapy based on the nano-indentation experiment was for outpatients from the category of observation. Following therapy, the therapy conditions of these two categories were compared, showing that the load was a fixed value and the depth of the indentation was increasing. Under the action of external force, the periodontal ligament might undergo elastic deformation, changing with duration. Dentition alignment duration, ligation duration, and deligation duration were less for participants in the observation group compared to those in the control category (P less than 0.05). The inclination between the longitudinal plane of the top central incisor and the sella juncture root point plane (UI-SN angle), the spacing between both the top mandibular teeth margin and the nasal root juncture molar seat point (UI-NA distance), and the angle between the upper and lower central incisor tooth axis and the NA connection (UI-NA angle) were all significantly less pronounced in the category of observation than in the control category (P less than 0.05). However, the angle of upper and lower central incisor long axis (UI-LI angle) from the category of observation was hugely greater than that of the control category (P less than 0.05). The value of dental arch width in the category of observation was smaller significantly than the value of the control category (P less than 0.05), and the changes in dental arch width were larger than those in the control category (P less than 0.05). Besides, the measured values of X-ray projections of outpatients from the category of observation were higher at of the control category (P less than 0.05). In conclusion, nano-indentation experiment can accurately match the equipment required in the therapy. The application of titanium materials combined with the vertical control of PASS correction technology can effectively alleviate the clinical symptoms of outpatients so as to improve the therapy effect.

Exercise and Diet: Uncovering Prospective Mediators of Skeletal Fragility in Bone and Marrow Adipose Tissue

PURPOSE OF REVIEW

To highlight recent basic, translational, and clinical works demonstrating exercise and diet regulation of marrow adipose tissue (MAT) and bone and how this informs current understanding of the relationship between marrow adiposity and musculoskeletal health.

RECENT FINDINGS

Marrow adipocytes accumulate in the bone in the setting of not only hypercaloric intake (calorie excess; e.g., diet-induced obesity) but also with hypocaloric intake (calorie restriction; e.g., anorexia), despite the fact that these states affect bone differently. With hypercaloric intake, bone quantity is largely unaffected, whereas with hypocaloric intake, bone quantity and quality are greatly diminished. Voluntary running exercise in rodents was found to lower MAT and promote bone in eucaloric and hypercaloric states, while degrading bone in hypocaloric states, suggesting differential modulation of MAT and bone, dependent upon whole-body energy status. Energy status alters bone metabolism and bioenergetics via substrate availability or excess, which plays a key role in the response of bone and MAT to mechanical stimuli. Marrow adipose tissue (MAT) is a fat depot with a potential role in-as well as responsivity to-whole-body energy metabolism. Understanding the localized function of this depot in bone cell bioenergetics and substrate storage, principally in the exercised state, will aid to uncover putative therapeutic targets for skeletal fragility.

Possible effects of whole body vibration on bone properties in growing rats

Objectives

To examine the effects of whole body vibration (WBV) on bone properties in growing rats, and to explore the optimal conditions for enhancing bone properties.

Methods

Thirty-six 4-week-old male rats were divided into 1 control and 5 experimental groups. Each experimental group underwent WBV at 15, 30, 45, 60, and 90 Hz (0.5 g, 15 min/d, 5 d/wk) for 8 weeks. We measured bone size, muscle weight and bone mechanical strength of the right tibia. Trabecular bone mass and trabecular bone microstructure (TBMS) of the left tibia were analyzed by micro-computed tomography. Serum levels of bone formation/resorption markers were also measured.

Results

WBV at 45 Hz and 60 Hz tended to enhance trabecular bone mass and TBMS parameters. However, there was no difference in maximum load of tibias among all groups. Serum levels of bone resorption marker were significantly higher in the 45-Hz WBV group than in the control group.

Conclusions

WBV at 45–60 Hz may offer a potent modality for increasing bone mass during the period of rapid growth. Further studies are needed to explore the optimal WBV conditions for increasing peak bone mass and TBMS parameters. WBV modality may be a potent strategy for primary prevention against osteoporosis.