| There are many factors affecting the mechanical response of brain tissue.Sample temperature and Sample geometry are considered to be two important aspects.Temperature involves the preservation temperature of the sample,the temperature of the sample itself and the temperature of the test environment.Different sample temperatures may have different effects on the mechanical properties of brain tissue.Therefore,it is necessary to study the effect of sample temperature on the mechanical properties of brain tissue.The material properties of the soft and easy deformation of brain tissue lead to the failure to obtain the normal brain tissue samples.This is the reason why most researchers use ideal geometric models to replace the actual geometry in the finite element modeling of the brain tissue samples.However,replacing the actual geometry with the ideal model may cause greater error in the study of brain tissue.So,it is necessary to study the effect of sample geometry on the mechanical properties of brain tissue in order to get more accurate brain tissue material parameters.For studying the effect of temperature on the mechanical properties of brain tissue,the specimens of this study were cut from the fresh brain tissue,each with dimensions of Ф9 mm×6 mm.The force-displacement curves of each specimen under four temperatures(13℃,20℃,27℃ and 37℃)were obtained by unconstrained uniaxial compression tests with loading rates of 0.05 mm/s and 5 mm/s respectively.The compression engineering stress-engineering strain curves of each specimen were obtained by the definition formula of engineering stress.The one-way ANOVA or Kruskal-Wallis test was used to study whether different temperatures can significantly alter mechanical properties of brain tissue.The Tukey method was used to study difference of engineering stresses between various temperature.The results showed that under high speed or low speed,there was no significant difference in the engineering stress of brain tissue at the temperature of 20-37 degrees.When the sample temperature is 13 degrees,the engineering stres s increases significantly under high strain rate.For studying the effect of sample geometry on the mechanical properties of brain tissue,the specimens of this study were cut from the fresh brain tissue,each with dimensions of Ф14 mm×10 mm.The actual geometry of the specimen of brain tissue was obtained by reverse engineering,and the force-displacement curve of each specimen was obtained by the dynamic unconstrained uniaxial compression test with the loading rate of 5 mm/s.Based on the finite element modeling of specific samples,the simulation and test force-displacement curves are fitted by optimizing the material parameters.The optimized parameters are replaced by regular cylindrical geometry models,and the force-displacement curves are calculated.The results show that there is a significant difference between biomechanical response obtained by the ideal geometric model and the actual geometric specimen.In conclusion,different sample temperatures will affect the compressive properties of brain tissue,and the effect will be significant at low temperature.Therefore,the temperature of the brain specimen should be ensured to be in accordance with the living subject when studying the biomechanical response of living tissue.Finite element analysis with ideal model instead of the actual geometric model of specimen will affect the material parameters of brain tissue.Therefore,in the analysis of the material properties of the brain tissue,it is suggested that the actual geometry be used for studying. |
