| With the continuous exploration of space,people pay attention to the osteoporosis and other symptoms of astronauts,and humans on the earth will have similar symptoms as they grow older.We speculate that bone loss caused by changes in bone structure caused by microgravity and aging is an important reason for osteoporosis.In this paper,the axisymmetric fluid solid coupling finite element model of bone lacunae and canaliculi system in bone tissue is established by COMSOL Multiphysics software.To compare the transport of tissue fluid in the bone lacuna canaliculus system under static load in various gravity fields(0-8g);The mass transfer behavior of the lacunar canalicular system under different working conditions was compared and analyzed after applying cyclic load(1Hz,1.5Hz,2Hz);Simulate the distribution of sound field and thermal field when low-intensity pulsed ultrasound irradiates the bone lacuna bone tubule system,and combine with the particle tracking function of the software,simplify the small molecular substances such as nutrients metabolized by bone cells in the bone lacuna bone tubule system into particles.The specific research contents are as follows:The first part is to establish a two-dimensional axisymmetric fluid-structure coupling finite element model of the lacunar bone canaliculus system based on the real human bone tissue structure.The results showed that the fluid pressure and velocity in the bone lacunae increased with the increase of gravity acceleration,and the tissue fluid flowed in from the upper end of Haversian tube and flowed out from the lower end of Haversian tube,forming a loop.In addition,the pressure and flow rate in the shallow bone lacunae are the largest,the middle level is the smallest,and the deep level is the smallest,indicating that the mass transfer in the deep bone lacunae is the most difficult,which is easy to cause the death of the deep bone cells.However,the decrease of the volume of bone cells will reduce the flow velocity and pressure in the bone lacunae,and the maximum flow velocity and pressure under the influence of the shape of bone cells will increase by 520% and 31.36%,respectively,compared with the minimum;The maximum flow rate and pressure under the influence of osteocyte angle increased by 60.14% and 12.05% compared with the minimum,respectively,indicating that different shapes and directions of osteocytes will also bring different mechanical stimuli to osteocytes,affecting the process of bone reconstruction.However,the fluid shear stress on the surface of other bone cells will be reduced by 33.8% due to the lacuna vacancy caused by aging.The crisscross of bone tubules in the bone lacunar bone tubule system will increase the complexity of the bone lacunar bone tubule system,and the fluid pressure,flow rate and fluid shear force on the surface of bone cells in the bone lacunar will increase by 5.65%,24.86% and 26.87% at most.The second part is to establish a three-dimensional axisymmetric fluid structure coupling finite element model including human bone lacunae and canaliculi system.The results showed that under cyclic displacement load,the fluid velocity,pressure and fluid shear stress on the surface of bone cells in the canaliculus increased linearly with the frequency load.In the microgravity field(0g),the liquid in the bone lacunae is evenly distributed,while in the earth gravity field(1g)and high G(5g)gravity field,the liquid pressure gradient in the bone lacunae is obvious.The symmetrical plane applied displacement load makes the mechanical properties of each bone lacuna and each bone cell more similar,while the asymmetrical plane applied load makes the mechanical properties of each bone lacuna and each bone cell more different,and the flow rate in the bone tubule is about 2 orders of magnitude higher than that in the bone lacuna.The number of bone tubules will decrease with age,which makes the structure of bone lacunae and bone tubules system degenerate.The simulation results show that the number of bone tubules connected by bone lacunae decreases,leading to the reduction of the extreme value and the extreme value difference of the mechanical response of bone cells.This shows that when the number of bone tubules is large,bone cells can feel stronger mechanical stimulation and promote bone reconstruction.The third part is to irradiate the three-dimensional model of bone lacunae and canaliculi system with low intensity pulsed ultrasound.The results showed that ultrasound irradiation reduced the total number of particles in the bone lacunae when the total number of particles released was unchanged,which indirectly indicated that ultrasound irradiation accelerated the material transport in the bone lacunae bone canaliculus system,and the number of particles in the bone lacunae decreased with the increase of the ultrasonic frequency within the range of 1-1.5MHz.The closer to the ultrasonic incident surface,the greater the sound pressure in the sound field.The maximum sound pressure at 5 μm from the top of the model is 62.14% and 168.48%higher than the maximum sound pressure at 15 μm and 25 μm.The sound pressure inside the model will increase with the increase of the excitation sound pressure.At the same time,the closer to the ultrasonic focus area,the denser the thermal field temperature contours.In microgravity environment,the mass transfer in the bone lacuna bone tubule system slows down,and the bone cells cannot obtain enough nutrients,nor can they feel the due mechanical stimulation,which is easy to cause the death of bone cells,thus causing bone loss.However,the bone lacuna vacancy and the decrease of the number of bone tubules caused by aging will damage the internal structure of the bone lacuna bone tubule system,which is also not conducive to the mechanical response of bone cells.Proper exercise and ultrasonic irradiation can improve this situation.This paper provides a theoretical reference for astronauts and the elderly to fight against osteoporosis through numerical simulation. |
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