The deterioration of the musculoskeletal system is a serious health concern for long term space missions. The accumulated information over the past decades of space flights showed that microgravity impacts significantly the musculoskeletal system with muscle atrophy and bone loss. Until now, it has been difficult to make reasonable predictions of the bone loss for prolonged space missions due to the lack of in-space experimental data and weak understanding of the mechanobiological bone mechanisms. On earth, the healthy musculoskeletal degradation is mainly age related with osteoporosis and delayed fracture healing. A better understanding of the bone mechanobiological functions could help us improve our model predictions of the musculoskeletal health system during long term space missions.We develop a numerical model able to predict the bone loss at the mesoscopic scale (bone trabecula) in microgravity. The model is able to correlate the calculated bone degradation mechanism with data available in the literature showing the effective bone density loss measured experimentally. An optimization algorithm is used for an average bone microstructure distribution and long-term prediction. Extrapolation is made to link the local bone loss at the structural scale with the corresponding effective bone strength. The first part of the paper details the extraction of the bone microstructure using micro-CT images and numerical model development. Next, the degradation and optimization schemes are detailed. Finally, some results are presented for long term degradation.

The review focuses on the current studies of the deformation response and accompanying structural transformations of thermoplastic semicrystalline polymers subjected to uniaxial tension prior to the yield point. The mechanisms of strain-induced cavitation of amorphous layers and damages of crystalline lamellae are analyzed in line with novel results on the deformation behavior of solid polymers at temperatures exceeding the glass transition point. The coupling of viscoelastic and plastic deformation mechanisms with the small-strain structural transformations is critically discussed on the basis of the advanced theoretical modeling of mechanical properties of semicrystalline polymers.

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