Apparent elastic modulus of ex vivo trabecular bovine bone increases with dynamic loading

Although it is widely known that bone tissue responds to mechanical stimuli, the underlying biological control is still not completely understood. The purpose of this study was to validate required methods necessary to maintain active osteocytes and minimize bone tissue injury in an ex vivo three-dimensional model that could mimic in vivo cellular function. The response of 22 bovine trabecular bone cores to uniaxial compressive load was investigated by using the ZETOS bone loading and bioreactor system while perfused with culture medium for 21 days. Two groups were formed, the "treatment" group (n = 12) was stimulated with a physiological compressive strain (4000με) in the form of a "jump" wave, while the "control" group (n = 10) was loaded only during three measurements for apparent elastic modulus on days 3, 10, and 21. At the end of the experiment, apoptosis and active osteocytes were quantified with histological analysis, and bone formation was identified by means of the calcium-binding dye, calcein. It was demonstrated that the treatment group increased the elastic modulus by 61%, whereas the control group increased by 28% (p<0.05). Of the total osteocytes observed at the end of 21 days, 1.7% (±0.3%) stained positive for apoptosis in the loaded group, whereas 2.7% (±0.4%) stained positive in the control group. Apoptosis in the center of the bone cores of both groups at the end of 21 days was similar to that observed in vivo. Therefore, the three-dimensional model used in this research permitted the investigation of physiological responses to mechanical loads on morphology adaptation of trabecular bone in a controlled defined load and chemical environment.