QUANTITATIVE STRUCTURAL ASSESSMENT OF RAT TIBIAL EPIPHYSEAL EXPLANTS KEPT IN MICROGRAVITY CONDITIONS

It is well verified that protracted exposure to microgravity conditions leads to physiological modifications in humans. During spaceflight, the most important variations concern the skeletal system. In fact, a decrease in gravitational loading induces significant bone changes in man and experimental animals in terms of bone loss and mechanical properties decay. Although several hypotheses have been formulated, the mechanisms of spaceflight-induced bone modifications are still mostly unknown. Instead, it is widely accepted that the mechanical properties of cancellous bone are related not only to mineral content, but also to trabecular micro-architecture arrangement. This work aims to investigating the long-term effects of weightlessness conditions on the structural and mechanical properties of cancellous bone samples kept, in vitro, in simulated microgravity conditions. To simulate microgravity conditions, a particular in vitro 3D organ culture model, based on the Rotatory Cell Culture System (RCCSTM) bioreactor, was applied to rat tibial bone fragments (proximal epiphysis). The RCCSTM represents the unique existing bioreactor operating on the Earth\u2019s surface capable to reproduce, in vitro, optimal conditions to simulate microgravity. A quantitative evaluation of the changes in the bone mechanical properties was possible by using a 3D numerical model based on the Cell Method, which allows to estimate, and, subsequently, compare the trabecular structures of bones kept in different conditions