A device for long term, in vitro loading of three-dimensional natural and engineered tissues

In vitro studies of mechanical loads applied to three-dimensional tissue constructs are important to the design and production of functional, engineered bone tissue. This study reports the development and characterization of a mechanical device capable of subjecting a three-dimensional section of natural or engineered tissue to precise, reproducible four-point bending deformations over a range of programmable magnitudes and frequencies. To test the biological and mechanical capabilities of the system, a low-cycle (360 cycles/day), medium-range strain (2500 microstrain), long-term (16 day) loading regime was applied to rat bone marrow stromal cells cultured in porous DL-polylactic acid scaffolds. Cells proliferated in culture throughout the experiment, and with time showed an increase in alkaline phosphatase expression per cell. Calcium and phosphorus mineral deposition by the unloaded group was significantly greater (p<0.05) than that deposited by the loaded group. The molar ratio of calcium to phosphorus in the unloaded group (0.94:1) was significantly greater (p<0.05) than that of the loaded group (0.41:1). The loading device presented here is a tool which can be used to help elucidate contributions of mechanical loading/fatigue on biodegradable materials, as well as study the effects of mechanical loading on natural or engineered tissues in vitro.