Effect Of In Vitro Preservation On Mechanical Properties Of Brain Tissue

The ever rising concerns on traumatic brain injuries caused by impact loading conditions such as car accidents,blasts,sports or even daily falls have stimulated intensively studies on the mechanical property of brain tissue.The research results can find applications in robot aided surgery,surgeon training and development of protective facilities.There is no doubt that accurate assessment of brain tissue mechanical properties is a prerequisite for this study.A large number of data have been documented with respect to the in vitro properties of brain tissue.Although it is well agreed that the brain tissue demonstrates typically viscoelastic behavior,the data reported in literature show large discrepancies.The preservation duration and temperature after dissection have demonstrated their effects on the mechanical response of brain tissue.Owing to the lack of consistence of reputed data and the relevant analyses of the underlying reasons,diverse storage temperatures and durations have been used.The most popular preservation method is to store the brain tissue at 1-4? for a few hours up to few days.To now,however,little is known on whether the storage duration at this temperature will influence the mechanical properties of brain tissues and what the biological mechanism is,if any effect exists.In this thesis,differential scanning calorimetry(DSC)measurements and uniaxial compression mechanical experiments are performed to investigate this issue at molecular and macro levels.DSC mainly measures the denaturation temperature and enthalpy.The denaturation temperature refers to the temperature at which the conformation change occurs.The enthalpy is the change of the energy at the phase transition.The results indicate,for the brain tissue stored at 1? without any liquid medium,the longer the storage time,the lower the denaturation temperature,and the lower the endothermic enthalpy.The denaturation temperature is related to the mechanical strength of the tissue,the lower the denaturation temperature,the worse the mechanical strength.The enthalpy becomes smaller,indicating that the energy absorbed by the biological tissue is also less and the structural damage is more serious.The uniaxial compression experiment also confirms that the tissue performance deteriorated with the prolonged preservation duration.DSC analyses rules out the possibility of damaging effect incurred by the formation of ice.Light and transmission electron microscopy reveals the biological mechanisms.Light microscopic analysis shows that with the increase of preservation time(0-14 h),the nucleus shrinks and dissolves.Transmission electron microscopy shows the degeneration of myelin sheaths and the vacuolization of cristae.The results of this study provide some reference data for the in vitro preservation of brain tissue.