Application Of Bionic Micro/Nano Saw Toothed Wire In Cutting Super Soft Brain Tissue

The study of the mechanical properties of brain tissue has guiding roles in the development of protective facilities and medical diagnosis because of its super soft property. The non-destructive cutting of brain tissue specimen is the prerequisite for the accurate characterization of mechanical properties of brain. Currently, the commercial medical surgical scalpel and house-made cutting mode are commonly used to prepare the specimens. The cut specimens may readily experience large damage during the cutting process due to the super soft nature of brain tissue, which in turn influences the measure of the real mechanical property of the brain tissue.The mosquito’s micro/nano structured fascicle of the proboscises and its amazing oscillation inserting skill make the proboscises penetrate easily into human skin with an astonishing low force. Inspired by the mechanical principle of the mosquito penetrating, by means of SEM and XRD, this thesis is designed to explore a feasible preparation method that metal oxide particles are successfully implanted onto molybdenum wire surface to form the biomimetic sawblade with a high density of micro/nano saw teeth:The original Mo wire is polished with sand paper and then treated with acids to introduce active anchoring sites onto the wire surface. After dip coating of iron precursor, a metal salt shell forms on Mo wire. Finally, this wire is calcined in high temperature to implant the saw teeth.In order to study the cutting effect of saw teeth wire, using a sawblade in conjunction with reciprocating action to carry out the cutting experiments, the cutting effect of saw toothed wire was investigated. The results indicate the reduction of the cutting force is remarkable, which results from a combined function of the micro/nano sharp saw teeth and the reciprocating cutting. Subsequently cutting speed and reciprocating frequency on the cutting force are studied in detail. The results indicate when no reciprocating action gets involved, the cut-in force and displacement decrease with increasing cutting speed. By contrast, if the reciprocating action is introduced, the cut-in force increases, albeit quite small, as the increase of cutting speed. It is observed that the effect of frequency of the reciprocating action on the cut-in force in the range of investigation is not substantial. On the contrary, the cut-in force is more sensitive to cutting speed with respect to the frequency of reciprocating action.Finally, the quasi-static tensile and stress relaxation tests of dog brain tissue are tested, and the stiffening effect of brain tissue in tensile loading with strain rates demonstrates a strong strain rate dependency. The constitutive model is built up based on the experimental data, then the five-parameter viscoelasticity property and the failure criterion of equivalent Mises stress are then imbedded into the ABAQUS software to implement the numerical simulation of the cutting process of viscoelastic brain tissue. The result of cutting simulation shows that both the cut-in force and cut-in displacement decrease with the increase of the radius of Mo wire.The obtained results can provide referential information for the non-destructive cutting of soft tissue and the cutting mechanism of viscoelastic materials.