Research On The Viscoelastic Mechanical Behavior Of Brain Tissue

Human brain,the most complex information processing and decision making system in nature,is the control center of the various functions of the body.Nearly 80% of the brain consists of water,which makes our brain the most vulnerable part of our body.Brain damage has become one of the major diseases that threaten human health.The understanding of the mechanical properties and damage mechanism of brain tissue is still limited,which restricts the effective prevention of brain injury,precise diagnosis and treatment of brain diseases.The study of the mechanical behavior of brain tissue is of great significance for the development of brain safety devices and the exploration of new methods for brain injury and brain disease treatment.The tensile strength of brain tissue is less than 10 kPa.This means the cutting process can readily incur damage to brain tissue.To achieve the accurate characterization of mechanical properties,the minor invasive cutting of brain tissue specimen is the prerequisite.Mold and scalpel are often used to cut the specimen.Inspired by the ability of mosquitoes to insert their proboscises into human skin with astonishing tiny forces,in this study,the metal wire with a high density of micro/nano saw teeth is used as sawblade in conjunction with reciprocating action to cut the brain tissue,regular specimen with less damaged are obtained.The surface of the micro/nano structured metal wire is hydrophobic,effectively reducing its adhesion to brain tissue.The compression responses of the brainstem at different strain rates(0.005 /s,0.05 /s,0.15 /s)exhibit typical viscoelastic properties.Fourier transform infrared spectroscopy(FT-IR)indicates the presence of polar groups such as CO-NH2,COO? and PO2? in the brainstem,promoting the interaction between biomolecules and water molecules.Differential scanning calorimetry(DSC)suggests that the changes in the configuration,and/or rearrangement of the biomolecule chain during loading will cause energy dissipation.This explains why brainstem exhibits viscous behavior at macro level.In addition,Ogden,Fung and Gent models were used to fit the brainstem compression test data,and it was found that the Ogden model was more suitable to demonstrate the hardening of brainstem at low strain rate.In the tensile experiments of white matter and brain grey matter with different strain rates(0.005 /s,0.025 /s,0.15 /s,0.25 /s),white matter is stiffer than grey matter.At higher strain rates(> 0.005 /s),white matter absorbs more energy than grey matter,whereas at low strain rate(0.005 /s)the reverse trend is observed.In order to understand the difference of viscoelasticity between white matter and grey matter,the grey and white matters were analyzed using DSC and FT-IR.The results show that the presence of strong polar groups and hydrogen bonds in white matter enhances the interaction between biomolecules,which decreases the flexibility of biomolecules and results in relatively low energy dissipation in the variation of biomolecule configuration.Based on the above study on the viscoelastic mechanical behavior and the discussion of mechanism at micro/nano level,hydrogels with similar mechanical properties were prepared and used in the treatment of brain tissue injury and brain tumor.The hydrogel consists of chitosan,sodium hyaluronate and sodium glycerophosphate,which is liquid at low temperature(4°C)and forms gels when temperature is increased to body temperature(37°C).These hydrogels are biocompatible and biodegradable.The in vitro drug release experiments indicate that the hydrogel is injectable,pH sensitive and owes a sustained and effective drug release characteristic.