Bone is subjected in vivo to both high amplitude, low frequency strain, incurred by locomotion, and to low amplitude, broad frequency strain. The biological effects of low amplitude, broad frequency strain are poorly understood. To evaluate the effects of low amplitude strains ranging in frequency from 0 to 50Hz on osteoblastic function, we seeded MC3T3-E1 cells into collagen gels and applied the following loading protocols for 3min per day for either 3 or 7 days: (1) sinusoidal strain at 3Hz, with 0-3000μstrain peak-to-peak followed by 0.33s resting time, (2) "broad frequency vibration" of low amplitude strain (standard deviation of 300μstrain) including frequency components from 0 to 50Hz, and (3) sinusoidal strain combined with broad frequency vibration (S+V). The cells were harvested on day 4 or 8. We found that the S+V stimulation significantly repressed cell proliferation by day 8. Osteocalcin mRNA was up-regulated 2.6-fold after 7 days of S+V stimulation, and MMP-9 mRNA was elevated 1.3-fold after 3 days of vibration alone. Sinusoidal stimulation alone did not affect the cell responses. No differences due to loading were observed in alkaline phosphatase activity and in mRNA levels of type I collagen, osteopontin, connexin 43, MMPs-1A, -3, -13. These results suggest that osteoblasts are more sensitive to low amplitude, broad frequency strain, and this kind of strain could sensitize osteoblasts to high amplitude, low frequency strain. This suggestion implies a potential contribution of stochastic resonance to the mechanical sensitivity of osteoblasts.
- Mechanical vibration
ASJC Scopus subject areas
- Orthopedics and Sports Medicine