Biomechanical Experimental Study On The Effects Of High-G Extreme Environment On Bone Tissue

Gravity is the basis for maintaining human physiology.In general,the human body is only subjected to the gravity of 1G.However,as the external environment or the form of movement changes,the human body will take on additional inertial forces.If the vector sum of inertial force and gravity is greater than 1G,it is called high-G.In recent years,the launch and return of spacecraft and the take-off and landing of aircraft have all faced high-G extreme environments,which have given high-G mechanical action to pilots and astronauts.The skeletal system is important for maintaining human life.Under the high-G extreme environment,changes in the morphological structure and mechanical properties of bones,changes in the mineral content of bone,the damage of the bone tissue and the mechanism of reconstruction of the skeletal system are the urgent problems in the mechanical biology.In this experiment,we established an animal experiment model to study the effects of different intensities of high-G mechanical loads on the bone tissue and its possible mechanism of action by means of biomechanics,so as to lay a theoretical foundation for the study of bone tissue damage against the extreme mechanical environment.Forty-eight 280-320 g healthy rats were selected and randomly divided into 5 groups,control group,the 2G group,the 4G group,the 6G group and the 8G group.Rats in the high-G group were exposed to high-G load 3 times a day,each time for a continuous duration of 3 minutes,interval 40 minutes,5 days per week for a total of 4 weeks.The control group received no exposure and was fed normally for 4 weeks.After the end of the experiment,both sides of the rat's femur were obtained and the three point bending test of macroscopic mechanics was carried out.The microstructural parameters of the Micro-CT and the quantitative analysis of the chemical components of the femur diaphysis were measured.The experimental results showed that the high-G extreme environment obviously inhibited the growth of rats.The weight of rats in the control group increased significantly,and there was a significant difference between the control group and the high-G group from the second week.The body weight of the 2G group was maintained at about 320 g and the body weight of the 4G group,the 6G group,and the 8G group was about 310 g in the 3rd week.However,the body weight of the control group continued to increase substantially.In terms of macroscopic mechanical properties,the ultimate load of 2G,4G,6G and 8G groups decreased by 18.6%,12.8%,19.3% and 8.3% respectively,and the limit deflection also decreased by 16.1%,8.2%,11.5% and 18% respectively,compared to the control group.But there was no significant difference between the highG groups(P>0.05),and there was no significant difference between the modulus of elasticity(P>0.05).In terms of microstructure,there was no significant change in bone mineral density of cancellous bone and cortical bone in femur(P>0.05).The trabecular separation degree of cancellous bone in high-G group increased compared to the control group,and the porosity of cortical bone increased with the increase of G value,and there is no obvious change in other bone structure parameters.In quantitative analysis of chemical composition,the control group had the highest calcium content and the lowest phosphorus content.With the increase of G value,calcium content decreased significantly,phosphorus content increased significantly(P<0.05),but there was no significant change in magnesium,potassium and sodium content(P>0.05).According to experimental data,the extreme high-G environment leads to significant bone damage.High-G environment will inhibit the growth of rats,significantly reduce body weight while reducing calcium content,increasing phosphorus content,and increase the degree of separation of trabecular bone and the porosity of cortical bone,so as to make the bone structure loose,resulting in decreased mechanical properties of the femur,the ultimate load,ultimate deflection decreases,brittleness increases,but the mineral density of the femur have no obvious change.According to the change of body weight,porosity of cortical bone and calcium and phosphorus content in rats,it can be inferred that the damage is more serious with the increase of G value.