Mechanical loading promotes calcification of tissue-engineered bone in vitro

Cyclic mechanical loading can stimulate bone cells in vivo, resulting in the mechano-adaptive osteogenic response of bone. The objective of this study was to investigate the capability of mechanical loading to promote three-dimensional osteoblastic calcification in vitro. A bone-like construct was made by seeding osteoblasts that were obtained from mesenchymal stem cells of rat bone marrow into a type I collagen sponge scaffold. A sinusoidal compressive mechanical load with a peak of 0.2% deformation was applied to the construct at 0.8 Hz for 3 min per day for 35 consecutive days using a piezoelectric mechanical stimulator. This mechanical loading applies not only substrate strain, but also oscillatory fluid flow strain to the cells in the sponge. The degree of osteoblastic calcification was monitored non-destructively once a day utilizing a near-infrared light. The degree of calcification was evaluated as bulk density or calcium content (mg/cm3) based on the optical data. In constructs stimulated by mechanical loading, the degree of calcification started to increase after day 10 and ultimately reached a bulk density of about 44 mg/cm3 and a calcium content of about 4 mg/cm3. In contrast, controls without stimulation did not display a noticeable increase in calcification. Microscopic observation of cross-sectioned samples revealed a heterogeneous distribution of calcification, where a rich calcified matrix was observed in the upper region of the construct, which also had a higher cell density. In conclusion, mechanical loading could enhance osteogenesis in vitro, suggesting its applicability to bone tissue engineering. © 2010 by JSME.