Simulation Study On Biomechanical Mechanism Of Fighting Osteoporosis In Microgravity

Aviation medicine shows that long-term space flight will cause a series of adaptive changes in the body of astronauts,and these changes will cause many symptoms similar to human aging or diseases.Among them,disuse osteoporosis caused by a large number of continuous bone loss is one of the main reasons that hinder human long-term space stay.Bone is a dynamically renewed tissue.It senses the mechanical microenvironment through the osteocytes in the bone and dynamically adjusts the bone mass to adapt to the external mechanical environment.Osteon is the basic unit of nutrition and function in bone.The lack of gravity may lead to insufficient mechanical stimulation of osteocytes.This paper takes the femoral osteon with the most serious bone loss in astronauts as the research object,in order to explore the deep-seated causes of disuse osteoporosis in astronauts from the perspective of biomechanics.A three-dimensional fluid solid coupling finite element model of Osteon with second-order pore structure(Haversian canal,bone lacuna bone tubular system)is established.The effects of different gravity environment and motion state on human arterial pressure and Osteon strain load are considered.The changes of Mises stress of solid matrix of Osteon and mechanical microenvironment of osteocyte(FSS and liquid pressure)under negative gravity environment(-1 g),microgravity environment(0 g),earth gravity environment(1 g)and high G environment(2.5 g and 3.7g)were studied by numerical simulation.The simulation results show that:(1)in the microgravity environment,the FSS and liquid pressure of osteocytes are lower than those in the earth’s gravity field,and increase with the increase of G.Under static load,even if 3.7 g gravity field is applied,the fluid shear stress of a small number of osteocytes fails to reach the threshold of biological reaction of osteocytes(0.8 Pa),indicating that moderate exercise plays an important role in maintaining bone mass.(2)Under the earth gravity field(1 g)and microgravity environment(0 g),the human body carries out high load training(bone strain 3000 με)at different frequencies(0 Hz,0.125 Hz,0.5 Hz,2 Hz,8 Hz),The liquid velocity and pressure on the surface of osteocytes change periodically with the cyclic load,which is higher than that in the resting state of human body(0 g,0 με)The flow velocity and fluid pressure on the surface of osteocytes were 2～4 orders of magnitude higher.The absolute value of liquid pressure on the surface of osteocytes increases linearly with the load frequency.(3)Compare the mechanical microenvironment of bone matrix and osteocytes in the earth’s gravity field(1g),microgravity environment(0 g)and three kinds of artificial gravity devices(centrifuge with arm length of 7.6 m and 2.4 m,lower body negative pressure chamber)in microgravity environment,the results show that the artificial gravity provided by the long arm centrifuge in the microgravity environment makes the mechanical microenvironment of osteocytes closer to the gravity field of the earth;The short arm centrifuge did not significantly improve the mechanical stimulation of osteocytes,but it had great advantages over the long arm centrifuge in space;The lower body negative pressure chamber can effectively improve the hydrodynamic microenvironment of osteocytes.In microgravity environment,astronauts’ resistance training can effectively resist the continuous loss of bone mass;The loss of mechanical stimulation may only be one of the reasons for the continuous loss of bone in astronauts,while the decrease of interstitial fluid volume and vascular pressure in legs may be another important reason;When astronauts carry out confrontation training,properly adjusting the movement resistance and frequency according to individual differences can make up for the lack of mechanical stimulation of osteocytes caused by gravity loss to a certain extent;Compared with the centrifuge,the lower body negative pressure chamber has good expansibility.This study provides theoretical guidance for astronauts to fight osteoporosis from the perspective of biomechanics.