Continuous cyclic stretch induces osteoblast alignment and formation of anisotropic collagen fiber matrix

Bone tissue geometry shows a highly anisotropic architecture, which is derived from its genetic regulation and mechanical environment. Osteoblasts are responsible not only for bone formation, through the secretion of collagen type I, but also for sensing the mechanical stimuli due to bone surface strain. Mechanotransduction by osteoblasts is therefore considered one of the regulators of anisotropic bone tissue morphogenesis. The orientation of osteoblasts and the secreted collagen matrix was successfully regulated by applying a continuous mechanical stress on osteoblasts for a long period. Under a continuous cyclic stretch of 4% magnitude at a rate of 2 cycles min−1, osteoblasts reoriented their actin stress fibers in the direction that minimizes the strain applied to them. Extended culture of up to 2 weeks resulted in the formation of collagen fibers in the extracellular spaces, and the preferred orientation of these fibers was parallel to the direction of cell elongation. To the best of our knowledge, this is the first report to establish anisotropic bone matrix architecture following the alignment of osteoblasts under mechanical stimuli for long-term cultivation.