Abstract:The physical mechanism by which cells sense high-frequency mechanical signals of small magnitude is unknown. During exposure to vibrations, cell populations within a bone are subjected not only to acceleratory motions but also to fluid shear as a result of fluid-cell interactions. We explored displacements of the cell nucleus during exposure to vibrations with a finite element (FE) model and tested in vitro whether vibrations can affect osteocyte communication independent of fluid shear. Osteocyte like MLO-Y4 … Show more
“…The density ratio 0.4 : 1 : 1.2 (600 kg/m 3 : 1500 kg/m 3 : 1800 kg/m 3 ) of membrane, cytoplasm, and nucleus was assumed [26]. Young's modulus of membrane, cytoplasm, and nucleus was chosen at 1 kPa, 1.5 kPa, and 6 kPa, respectively, and Poisson's ratio was 0.3, 0.37, and 0.37 for membrane, cytoplasm, and nucleus, respectively.…”
Section: Methodsmentioning
confidence: 99%
“…Previously, Young's modulus of 6.5 kPa and Poisson's ratio of 0.5 were assigned to the cytoplasm of an osteoblastic cell [22]. Elastic modulus of cytoplasm of osteocyte-like MLO-Y4 cell was set at 1.5 kPa [26]. Similarly, based on the measurements by atomic force microscopy, Young's modulus of 6 kPa was assigned to the osteoblast nucleus [30].…”
Section: Methodsmentioning
confidence: 99%
“…Similarly, based on the measurements by atomic force microscopy, Young's modulus of 6 kPa was assigned to the osteoblast nucleus [30]. The elastic modulus of 1 kPa and Poisson's ratio of 0.3 were selected for the membrane of the adherent eukaryotic cell [16, 26]. …”
Bone cells are deformed according to mechanical stimulation they receive and their mechanical characteristics. However, how osteoblasts are affected by mechanical vibration frequency and acceleration amplitude remains unclear. By developing 3D osteoblast finite element (FE) models, this study investigated the effect of cell shapes on vibration characteristics and effect of acceleration (vibration intensity) on vibrational responses of cultured osteoblasts. Firstly, the developed FE models predicted natural frequencies of osteoblasts within 6.85–48.69 Hz. Then, three different levels of acceleration of base excitation were selected (0.5, 1, and 2 g) to simulate vibrational responses, and acceleration of base excitation was found to have no influence on natural frequencies of osteoblasts. However, vibration response values of displacement, stress, and strain increased with the increase of acceleration. Finally, stress and stress distributions of osteoblast models under 0.5 g acceleration in Z-direction were investigated further. It was revealed that resonance frequencies can be a monotonic function of cell height or bottom area when cell volumes and material properties were assumed as constants. These findings will be useful in understanding how forces are transferred and influence osteoblast mechanical responses during vibrations and in providing guidance for cell culture and external vibration loading in experimental and clinical osteogenesis studies.
“…The density ratio 0.4 : 1 : 1.2 (600 kg/m 3 : 1500 kg/m 3 : 1800 kg/m 3 ) of membrane, cytoplasm, and nucleus was assumed [26]. Young's modulus of membrane, cytoplasm, and nucleus was chosen at 1 kPa, 1.5 kPa, and 6 kPa, respectively, and Poisson's ratio was 0.3, 0.37, and 0.37 for membrane, cytoplasm, and nucleus, respectively.…”
Section: Methodsmentioning
confidence: 99%
“…Previously, Young's modulus of 6.5 kPa and Poisson's ratio of 0.5 were assigned to the cytoplasm of an osteoblastic cell [22]. Elastic modulus of cytoplasm of osteocyte-like MLO-Y4 cell was set at 1.5 kPa [26]. Similarly, based on the measurements by atomic force microscopy, Young's modulus of 6 kPa was assigned to the osteoblast nucleus [30].…”
Section: Methodsmentioning
confidence: 99%
“…Similarly, based on the measurements by atomic force microscopy, Young's modulus of 6 kPa was assigned to the osteoblast nucleus [30]. The elastic modulus of 1 kPa and Poisson's ratio of 0.3 were selected for the membrane of the adherent eukaryotic cell [16, 26]. …”
Bone cells are deformed according to mechanical stimulation they receive and their mechanical characteristics. However, how osteoblasts are affected by mechanical vibration frequency and acceleration amplitude remains unclear. By developing 3D osteoblast finite element (FE) models, this study investigated the effect of cell shapes on vibration characteristics and effect of acceleration (vibration intensity) on vibrational responses of cultured osteoblasts. Firstly, the developed FE models predicted natural frequencies of osteoblasts within 6.85–48.69 Hz. Then, three different levels of acceleration of base excitation were selected (0.5, 1, and 2 g) to simulate vibrational responses, and acceleration of base excitation was found to have no influence on natural frequencies of osteoblasts. However, vibration response values of displacement, stress, and strain increased with the increase of acceleration. Finally, stress and stress distributions of osteoblast models under 0.5 g acceleration in Z-direction were investigated further. It was revealed that resonance frequencies can be a monotonic function of cell height or bottom area when cell volumes and material properties were assumed as constants. These findings will be useful in understanding how forces are transferred and influence osteoblast mechanical responses during vibrations and in providing guidance for cell culture and external vibration loading in experimental and clinical osteogenesis studies.
“…Vibration promotes osteogenic differentiation 64 , cell communication 65 , while reduces osteoclast formation 66 and expression of osteoclastforming RANKL in osteocytes 67 , which is increased during unloading 68 . Table 2.…”
SummaryBackground: Vibration therapy (VT) has been proposed as an option to improve physical performance and reduce the negative effects of ageing on bone, muscles and tendons. Several discrepancies exist on the type of applications, frequency and magnitude. These differences reflex on the contradictory clinical results in literature. Aim of the present study is to carry on an exhaustive review to focus on technical options on the market, clinical applications in orthopaedic practice and expected outcomes. Methods: a literature review using the key words "vibration therapy" and "whole-body vibration" and "orthopaedics" was performed. After checking the available abstracts 71 full text articles were evaluated. Results: fifty-one articles focused on the effects of VT on muscles and tendons reporting ways of action and clinical outcomes. In a similar way 20 studies focused on the influence of VT on bone tissue with regard on ways of action and clinical trials. Conclusions: VT provides anabolic mechanical signals to bone and musculo-tendinous system. The best effects seem to be achieved with devices that deliver low-intensity stimuli at high frequencies providing linear horizontal displacement.
“…Another hypothesis is that mechanical stimulation signals are amplified within the bone tissue by stress-generated increase in fluid flow resulting from direct bone stimulation, thereby activating osteocytes, which act as mechanosensors to mediate the skeleton’s response (26,27). However, there is also considerable evidence that suggests the vibrations cause larger displacements in cell nuclei than fluid shear, indicating the mechanism of action is more likely due to the mechanical coupling between these oscillating cell nuclei and the cytoskeleton, which ultimately induces actin remodeling and reduces bone resorption (6,28,29). …”
Rational and Objectives
Low intensity vibration (LIV) may represent a nondrug strategy to mitigate bone deficits in patients with end-stage renal disease.
Materials and Methods
Thirty end-stage renal patients on maintenance hemodialysis were randomized to stand for 20 minutes each day on either an active or placebo LIV device. Analysis at baseline and completion of 6-month intervention included magnetic resonance imaging (tibia and fibula stiffness; trabecular thickness, number, separation, bone volume fraction, plate-to-rod ratio; and cortical bone porosity), dual-energy X-ray absorptiometry (hip and spine bone mineral density [BMD]), and peripheral quantitative computed tomography (tibia trabecular and cortical BMD; calf muscle cross-sectional area).
Results
Intention-to-treat analysis did not show any significant changes in outcomes associated with LIV. Subjects using the active device and with greater than the median adherence (70%) demonstrated an increase in distal tibia stiffness (5.3%), trabecular number (1.7%), BMD (2.3%), and plate-to-rod ratio (6.5%), and a decrease in trabecular separation (−1.8%). Changes in calf muscle cross-sectional area were associated with changes in distal tibia stiffness (R = 0.85), trabecular bone volume/total volume (R = 0.91), number (R = 0.92), and separation (R = −0.94) in the active group but not in the placebo group. Baseline parathyroid hormone levels were positively associated with increased cortical bone porosity over the 6-month study period in the placebo group (R = 0.55) but not in the active group (R = 0.01). No changes were observed in the nondistal tibia locations for either group except a decrease in hip BMD in the placebo group (−1.7%).
Conclusion
Outcomes and adherence thresholds identified from this pilot study could guide future longitudinal studies involving vibration therapy.
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