Bone metabolism is regulated by mechanical stimuli such as gravity and exercise. If bone formation can be promoted by artificial mechanical stimulation, the quality of life of the aging society can be improved, such as by reducing the progression of osteoporosis and preventing patients from being bedridden. Micro-vibration stimulation with frequencies of 15 Hz to 90 Hz and acceleration amplitudes of 0.1 g to 0.3 g is effectively promotes bone formation in animal models. However, the mechanism of how these weak vibrations are sensed by bone cells and are used to regulate bone metabolism is unknown. In this study, we developed a device to apply micro-vibration stimuli to osteoblasts cultured on a glass bottom dish and observed the cell response to the stimuli using a confocal laser scanning fluorescence microscope. The device performance was confirmed using driving tests, and the calcium signaling response of osteoblasts to micro-vibration stimuli was observed in real time and in situ. The calcium signaling response characteristics of the cells differed when the cells were subjected to 45 Hz and 90 Hz micro-vibration stimuli, even under a constant acceleration amplitude of 0.2 g.
Patients recovering from bone disruption due to trauma or surgery need to limit movement to minimize shear force, thereby protecting callus formation and osteogenesis. Patients often use their arms to assist with functional activities, but pushing is frequently limited to < 4.5 kg when upper body bone fracture has occurred. With only verbal instructions, patients’ ability to limit weight bearing (WB) accurately is poor. A therapeutic intervention to improve patient adherence with upper extremity (UE) WB guidelines during functional mobility using an instrumented walker could be beneficial. Therefore, the purpose this article is to describe a feedback training protocol to improve ability to modulate UE WB in older adults and then provide an overview of the efficacy of this protocol and subsequent development of a Clinical Force Measuring Walker. An instrumented walker was used to measure UE WB during functional mobility in healthy older subjects (n = 30) before, during, and after (immediately and 2 hours) practice with visual and auditory concurrent feedback training. During feedback training, force was significantly reduced after all 3 sessions as compared to baseline. When using the front wheeled walker, UE WB force during the second and third feedback training sessions went down compared to the first session. Force during the third feedback training session was greater than the two previous sessions while transferring sit-to-stand and stand-to-sit. After completion of practice with feedback, UE WB force was significantly reduced and remained so 2 hours later. These findings suggest that feedback training is effective for helping patients to modulate UE WB. Use of an instrumented walker and feedback training would be beneficial in clinical practice, especially with older patients. More intensive feedback training with additional sessions and or simultaneous visual and auditory cues during whole practice may be needed to get UE WB force below a 4.5 kg (44.5 N) threshold.
Modeling of the human spine is important for establishing quantitative assessment methods of low back pain (LBP) caused by manual material handling (MMH). This study developed mathematical models of the lumbar and thoracic spine based on the elastic beam theory. Two types of models, uniform and non-uniform, were derived. First, to simplify the Bernoulli-Euler beam theory, three assumptions were introduced for the uniform beam model: (i) the vertebrae and intervertebral disc were considered as a composite material, (ii) constant cross-sectional area, and (iii) conversion of muscular strength to bending moment. However, on fitting to the actual spine position data from the literature, the uniform beam model was found to be unable to reproduce the spine shape, particularly in the lumbar region. Therefore, the non-uniform beam model was derived by removing assumption (ii), which does not agree with the actual human spine profile. Consequently, the spine was modeled as a trapezoid from around S1 to C7 in the sagittal plane, by adjusting the proportionality factor of trapezoid via tapering or widening, and the non-uniform beam model was found to better reproduce the spine shape, including the lumbar region. The model has practicability, such as estimation of spine shape; however, the proportionality factor that was used to reproduce the spine shape did not agree with the actual human spine profile; further theoretical development has been left as future work.
Bone tissue is a composite material consisting of hydroxyapatite and collagen. It is known that bone tissue becomes brittle with age not only because of decreased bone density but also because of excessive apatite deposition in the tissue. Demineralization provides a means for changing the mechanical properties of bone. Although demineralization decreases the elastic modulus of bone tissue, it also increases the flexible deformation compliance of the tissue. Previous studies have shown that localized demineralization around the areas of stress concentration in cortical bone specimens can improve impact fracture toughness despite reducing the stiffness. Demineralization is usually performed via chemical reactions in solution. This method is not suitable for limited demineralization at specific areas because of the infiltration and outflow of the solution. In this study, we focus on reactions induced by electric stimulation and investigate the possibility of demineralization by applying voltage. X-ray diffraction was used to verify the demineralization progression. The absence of apatite peaks in the X-ray diffraction pattern of the bone specimen after voltage application shows that demineralization has occurred after this treatment. To investigate the relationship between the electrode shape and the demineralized area, the hardness distribution on the surface of specimen was measured via multiple-point micro-indentation tests. The impact fracture characteristics in the limited areas demineralized by voltage application were measured through Charpy loading tests. As a result, it was found that the demineralization was accelerated at the contact area of the electrode to specimen surface during the voltage application. And it was suggested that the limited demineralization may improve the fracture strength of the bone tissue.
Although cardiac strain has been used as a practical mechanical indicator to estimate cardiac functions, measurement of strain is still difficult due to the need for operator proficiency and special equipment to perform echocardiography and magnetic resonance imaging (MRI). Hence, a modified indicator that can be calculated more easily at the bedside is needed to assess cardiac function based on cardiac morphology. The circumferential strain of the left ventricular (LV) wall and the contraction potential energy were numerically investigated in this study using a thick-walled cylindrical model under different myocardial thicknesses, stiffnesses, and diastolic pressures for given specific ejection fractions (EFs) or end-diastolic volumes. The LV wall was modeled as a visco-hyperelastic, continuous material. We proposed the modified ejection fraction (mEF), which is the product of EF and the contractility percentage of the internal volume within the epicardium, as an indicator of circumferential strain. Calculated peak circumferential strain was better estimated by mEF than EF. Furthermore, the contraction potential energy correlated well with circumferential strain and mEF. Our results regarding mEF are consistent with those obtained in 7 previous clinical studies. mEF may be a useful and practical indicator of the reduced contraction potential energy of the local myocardium and of heart failure, regardless of imaging modalities and vendors.