Research on solute transport behaviors in the lacunar-canalicular system using numerical simulation in microgravity

The lack of mass transfer in microgravity might be the underlying cause of disuse osteoporosis in astronauts after long-term space flights. The osteons are cylindrical structures and are the main structural units of the diaphysis in long bones.

A multi-scale 3D fluid-solid coupled finite element model of osteon with a two-stage pore structure was developed using COMSOL software in order to investigate solute transport behaviors in the lacunar-canalicular system (LCS) induced by physiological strain loading. Certain small molecules that are necessary as solutes in tissue fluid for osteocyte metabolism were simplified to micro-particles. A comparative analysis of solute transport behaviors in the LCS induced by physiological strain loading was conducted with a frequency of 0.2-2.5 Hz in microgravity and the Earth's gravitational fields.

The average velocity of solute transport in lacunae in microgravity was 2-3 orders of magnitude lower than in Earth's gravitational field. The number of particles that represented solute transport quantity in the middle and deep lacunae increased steadily with a load frequency within the Earth's gravitational field. However, it differed based on the load frequency in microgravity, with the number of particles increasing with frequencies in the range of 0.2-0.5 Hz and 0.8-2 Hz, and decreasing with frequencies in the range of 0.5-0.8 Hz.

A moving load with appropriate frequency could promote solute transport to the middle and deep lacunae, effectively preventing apoptosis of deep osteocytes due to a lack of nutrients. The results of this study provided theoretical guidance for preventing bone loss in astronauts during long-term space flights.